FreeBSD/Linux Kernel Cross Reference
sys/vm/vm_page.c

     /*-
      * SPDX-License-Identifier: (BSD-3-Clause AND MIT-CMU)
      *
      * Copyright (c) 1991 Regents of the University of California.
      * All rights reserved.
      * Copyright (c) 1998 Matthew Dillon.  All Rights Reserved.
      *
      * This code is derived from software contributed to Berkeley by
      * The Mach Operating System project at Carnegie-Mellon University.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      from: @(#)vm_page.c     7.4 (Berkeley) 5/7/91
     */
    
    /*-
     * Copyright (c) 1987, 1990 Carnegie-Mellon University.
     * All rights reserved.
     *
     * Authors: Avadis Tevanian, Jr., Michael Wayne Young
     *
     * Permission to use, copy, modify and distribute this software and
     * its documentation is hereby granted, provided that both the copyright
     * notice and this permission notice appear in all copies of the
     * software, derivative works or modified versions, and any portions
     * thereof, and that both notices appear in supporting documentation.
     *
     * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
     * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
     * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
     *
     * Carnegie Mellon requests users of this software to return to
     *
     *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
     *  School of Computer Science
     *  Carnegie Mellon University
     *  Pittsburgh PA 15213-3890
     *
     * any improvements or extensions that they make and grant Carnegie the
     * rights to redistribute these changes.
     */
    
    /*
     *      Resident memory management module.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include "opt_vm.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/counter.h>
    #include <sys/domainset.h>
    #include <sys/kernel.h>
    #include <sys/limits.h>
    #include <sys/linker.h>
    #include <sys/lock.h>
    #include <sys/malloc.h>
    #include <sys/mman.h>
    #include <sys/msgbuf.h>
    #include <sys/mutex.h>
    #include <sys/proc.h>
    #include <sys/rwlock.h>
    #include <sys/sleepqueue.h>
    #include <sys/sbuf.h>
    #include <sys/sched.h>
    #include <sys/smp.h>
    #include <sys/sysctl.h>
    #include <sys/vmmeter.h>
    #include <sys/vnode.h>
    
    #include <vm/vm.h>
    #include <vm/pmap.h>
    #include <vm/vm_param.h>
    #include <vm/vm_domainset.h>
   #include <vm/vm_kern.h>
   #include <vm/vm_map.h>
   #include <vm/vm_object.h>
   #include <vm/vm_page.h>
   #include <vm/vm_pageout.h>
   #include <vm/vm_phys.h>
   #include <vm/vm_pagequeue.h>
   #include <vm/vm_pager.h>
   #include <vm/vm_radix.h>
   #include <vm/vm_reserv.h>
   #include <vm/vm_extern.h>
   #include <vm/vm_dumpset.h>
   #include <vm/uma.h>
   #include <vm/uma_int.h>
   
   #include <machine/md_var.h>
   
   struct vm_domain vm_dom[MAXMEMDOM];
   
   DPCPU_DEFINE_STATIC(struct vm_batchqueue, pqbatch[MAXMEMDOM][PQ_COUNT]);
   
   struct mtx_padalign __exclusive_cache_line pa_lock[PA_LOCK_COUNT];
   
   struct mtx_padalign __exclusive_cache_line vm_domainset_lock;
   /* The following fields are protected by the domainset lock. */
   domainset_t __exclusive_cache_line vm_min_domains;
   domainset_t __exclusive_cache_line vm_severe_domains;
   static int vm_min_waiters;
   static int vm_severe_waiters;
   static int vm_pageproc_waiters;
   
   static SYSCTL_NODE(_vm_stats, OID_AUTO, page, CTLFLAG_RD | CTLFLAG_MPSAFE, 0,
       "VM page statistics");
   
   static COUNTER_U64_DEFINE_EARLY(pqstate_commit_retries);
   SYSCTL_COUNTER_U64(_vm_stats_page, OID_AUTO, pqstate_commit_retries,
       CTLFLAG_RD, &pqstate_commit_retries,
       "Number of failed per-page atomic queue state updates");
   
   static COUNTER_U64_DEFINE_EARLY(queue_ops);
   SYSCTL_COUNTER_U64(_vm_stats_page, OID_AUTO, queue_ops,
       CTLFLAG_RD, &queue_ops,
       "Number of batched queue operations");
   
   static COUNTER_U64_DEFINE_EARLY(queue_nops);
   SYSCTL_COUNTER_U64(_vm_stats_page, OID_AUTO, queue_nops,
       CTLFLAG_RD, &queue_nops,
       "Number of batched queue operations with no effects");
   
   /*
    * bogus page -- for I/O to/from partially complete buffers,
    * or for paging into sparsely invalid regions.
    */
   vm_page_t bogus_page;
   
   vm_page_t vm_page_array;
   long vm_page_array_size;
   long first_page;
   
   struct bitset *vm_page_dump;
   long vm_page_dump_pages;
   
   static TAILQ_HEAD(, vm_page) blacklist_head;
   static int sysctl_vm_page_blacklist(SYSCTL_HANDLER_ARGS);
   SYSCTL_PROC(_vm, OID_AUTO, page_blacklist, CTLTYPE_STRING | CTLFLAG_RD |
       CTLFLAG_MPSAFE, NULL, 0, sysctl_vm_page_blacklist, "A", "Blacklist pages");
   
   static uma_zone_t fakepg_zone;
   
   static void vm_page_alloc_check(vm_page_t m);
   static bool _vm_page_busy_sleep(vm_object_t obj, vm_page_t m,
       vm_pindex_t pindex, const char *wmesg, int allocflags, bool locked);
   static void vm_page_clear_dirty_mask(vm_page_t m, vm_page_bits_t pagebits);
   static void vm_page_enqueue(vm_page_t m, uint8_t queue);
   static bool vm_page_free_prep(vm_page_t m);
   static void vm_page_free_toq(vm_page_t m);
   static void vm_page_init(void *dummy);
   static int vm_page_insert_after(vm_page_t m, vm_object_t object,
       vm_pindex_t pindex, vm_page_t mpred);
   static void vm_page_insert_radixdone(vm_page_t m, vm_object_t object,
       vm_page_t mpred);
   static void vm_page_mvqueue(vm_page_t m, const uint8_t queue,
       const uint16_t nflag);
   static int vm_page_reclaim_run(int req_class, int domain, u_long npages,
       vm_page_t m_run, vm_paddr_t high);
   static void vm_page_release_toq(vm_page_t m, uint8_t nqueue, bool noreuse);
   static int vm_domain_alloc_fail(struct vm_domain *vmd, vm_object_t object,
       int req);
   static int vm_page_zone_import(void *arg, void **store, int cnt, int domain,
       int flags);
   static void vm_page_zone_release(void *arg, void **store, int cnt);
   
   SYSINIT(vm_page, SI_SUB_VM, SI_ORDER_SECOND, vm_page_init, NULL);
   
   static void
   vm_page_init(void *dummy)
   {
   
           fakepg_zone = uma_zcreate("fakepg", sizeof(struct vm_page), NULL, NULL,
               NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
           bogus_page = vm_page_alloc(NULL, 0, VM_ALLOC_NOOBJ |
               VM_ALLOC_NORMAL | VM_ALLOC_WIRED);
   }
   
   /*
    * The cache page zone is initialized later since we need to be able to allocate
    * pages before UMA is fully initialized.
    */
   static void
   vm_page_init_cache_zones(void *dummy __unused)
   {
           struct vm_domain *vmd;
           struct vm_pgcache *pgcache;
           int cache, domain, maxcache, pool;
   
           maxcache = 0;
           TUNABLE_INT_FETCH("vm.pgcache_zone_max_pcpu", &maxcache);
           maxcache *= mp_ncpus;
           for (domain = 0; domain < vm_ndomains; domain++) {
                   vmd = VM_DOMAIN(domain);
                   for (pool = 0; pool < VM_NFREEPOOL; pool++) {
                           pgcache = &vmd->vmd_pgcache[pool];
                           pgcache->domain = domain;
                           pgcache->pool = pool;
                           pgcache->zone = uma_zcache_create("vm pgcache",
                               PAGE_SIZE, NULL, NULL, NULL, NULL,
                               vm_page_zone_import, vm_page_zone_release, pgcache,
                               UMA_ZONE_VM);
   
                           /*
                            * Limit each pool's zone to 0.1% of the pages in the
                            * domain.
                            */
                           cache = maxcache != 0 ? maxcache :
                               vmd->vmd_page_count / 1000;
                           uma_zone_set_maxcache(pgcache->zone, cache);
                   }
           }
   }
   SYSINIT(vm_page2, SI_SUB_VM_CONF, SI_ORDER_ANY, vm_page_init_cache_zones, NULL);
   
   /* Make sure that u_long is at least 64 bits when PAGE_SIZE is 32K. */
   #if PAGE_SIZE == 32768
   #ifdef CTASSERT
   CTASSERT(sizeof(u_long) >= 8);
   #endif
   #endif
   
   /*
    *      vm_set_page_size:
    *
    *      Sets the page size, perhaps based upon the memory
    *      size.  Must be called before any use of page-size
    *      dependent functions.
    */
   void
   vm_set_page_size(void)
   {
           if (vm_cnt.v_page_size == 0)
                   vm_cnt.v_page_size = PAGE_SIZE;
           if (((vm_cnt.v_page_size - 1) & vm_cnt.v_page_size) != 0)
                   panic("vm_set_page_size: page size not a power of two");
   }
   
   /*
    *      vm_page_blacklist_next:
    *
    *      Find the next entry in the provided string of blacklist
    *      addresses.  Entries are separated by space, comma, or newline.
    *      If an invalid integer is encountered then the rest of the
    *      string is skipped.  Updates the list pointer to the next
    *      character, or NULL if the string is exhausted or invalid.
    */
   static vm_paddr_t
   vm_page_blacklist_next(char **list, char *end)
   {
           vm_paddr_t bad;
           char *cp, *pos;
   
           if (list == NULL || *list == NULL)
                   return (0);
           if (**list =='\0') {
                   *list = NULL;
                   return (0);
           }
   
           /*
            * If there's no end pointer then the buffer is coming from
            * the kenv and we know it's null-terminated.
            */
           if (end == NULL)
                   end = *list + strlen(*list);
   
           /* Ensure that strtoq() won't walk off the end */
           if (*end != '\0') {
                   if (*end == '\n' || *end == ' ' || *end  == ',')
                           *end = '\0';
                   else {
                           printf("Blacklist not terminated, skipping\n");
                           *list = NULL;
                           return (0);
                   }
           }
   
           for (pos = *list; *pos != '\0'; pos = cp) {
                   bad = strtoq(pos, &cp, 0);
                   if (*cp == '\0' || *cp == ' ' || *cp == ',' || *cp == '\n') {
                           if (bad == 0) {
                                   if (++cp < end)
                                           continue;
                                   else
                                           break;
                           }
                   } else
                           break;
                   if (*cp == '\0' || ++cp >= end)
                           *list = NULL;
                   else
                           *list = cp;
                   return (trunc_page(bad));
           }
           printf("Garbage in RAM blacklist, skipping\n");
           *list = NULL;
           return (0);
   }
   
   bool
   vm_page_blacklist_add(vm_paddr_t pa, bool verbose)
   {
           struct vm_domain *vmd;
           vm_page_t m;
           int ret;
   
           m = vm_phys_paddr_to_vm_page(pa);
           if (m == NULL)
                   return (true); /* page does not exist, no failure */
   
           vmd = vm_pagequeue_domain(m);
           vm_domain_free_lock(vmd);
           ret = vm_phys_unfree_page(m);
           vm_domain_free_unlock(vmd);
           if (ret != 0) {
                   vm_domain_freecnt_inc(vmd, -1);
                   TAILQ_INSERT_TAIL(&blacklist_head, m, listq);
                   if (verbose)
                           printf("Skipping page with pa 0x%jx\n", (uintmax_t)pa);
           }
           return (ret);
   }
   
   /*
    *      vm_page_blacklist_check:
    *
    *      Iterate through the provided string of blacklist addresses, pulling
    *      each entry out of the physical allocator free list and putting it
    *      onto a list for reporting via the vm.page_blacklist sysctl.
    */
   static void
   vm_page_blacklist_check(char *list, char *end)
   {
           vm_paddr_t pa;
           char *next;
   
           next = list;
           while (next != NULL) {
                   if ((pa = vm_page_blacklist_next(&next, end)) == 0)
                           continue;
                   vm_page_blacklist_add(pa, bootverbose);
           }
   }
   
   /*
    *      vm_page_blacklist_load:
    *
    *      Search for a special module named "ram_blacklist".  It'll be a
    *      plain text file provided by the user via the loader directive
    *      of the same name.
    */
   static void
   vm_page_blacklist_load(char **list, char **end)
   {
           void *mod;
           u_char *ptr;
           u_int len;
   
           mod = NULL;
           ptr = NULL;
   
           mod = preload_search_by_type("ram_blacklist");
           if (mod != NULL) {
                   ptr = preload_fetch_addr(mod);
                   len = preload_fetch_size(mod);
           }
           *list = ptr;
           if (ptr != NULL)
                   *end = ptr + len;
           else
                   *end = NULL;
           return;
   }
   
   static int
   sysctl_vm_page_blacklist(SYSCTL_HANDLER_ARGS)
   {
           vm_page_t m;
           struct sbuf sbuf;
           int error, first;
   
           first = 1;
           error = sysctl_wire_old_buffer(req, 0);
           if (error != 0)
                   return (error);
           sbuf_new_for_sysctl(&sbuf, NULL, 128, req);
           TAILQ_FOREACH(m, &blacklist_head, listq) {
                   sbuf_printf(&sbuf, "%s%#jx", first ? "" : ",",
                       (uintmax_t)m->phys_addr);
                   first = 0;
           }
           error = sbuf_finish(&sbuf);
           sbuf_delete(&sbuf);
           return (error);
   }
   
   /*
    * Initialize a dummy page for use in scans of the specified paging queue.
    * In principle, this function only needs to set the flag PG_MARKER.
    * Nonetheless, it write busies the page as a safety precaution.
    */
   void
   vm_page_init_marker(vm_page_t marker, int queue, uint16_t aflags)
   {
   
           bzero(marker, sizeof(*marker));
           marker->flags = PG_MARKER;
           marker->a.flags = aflags;
           marker->busy_lock = VPB_CURTHREAD_EXCLUSIVE;
           marker->a.queue = queue;
   }
   
   static void
   vm_page_domain_init(int domain)
   {
           struct vm_domain *vmd;
           struct vm_pagequeue *pq;
           int i;
   
           vmd = VM_DOMAIN(domain);
           bzero(vmd, sizeof(*vmd));
           *__DECONST(const char **, &vmd->vmd_pagequeues[PQ_INACTIVE].pq_name) =
               "vm inactive pagequeue";
           *__DECONST(const char **, &vmd->vmd_pagequeues[PQ_ACTIVE].pq_name) =
               "vm active pagequeue";
           *__DECONST(const char **, &vmd->vmd_pagequeues[PQ_LAUNDRY].pq_name) =
               "vm laundry pagequeue";
           *__DECONST(const char **,
               &vmd->vmd_pagequeues[PQ_UNSWAPPABLE].pq_name) =
               "vm unswappable pagequeue";
           vmd->vmd_domain = domain;
           vmd->vmd_page_count = 0;
           vmd->vmd_free_count = 0;
           vmd->vmd_segs = 0;
           vmd->vmd_oom = FALSE;
           for (i = 0; i < PQ_COUNT; i++) {
                   pq = &vmd->vmd_pagequeues[i];
                   TAILQ_INIT(&pq->pq_pl);
                   mtx_init(&pq->pq_mutex, pq->pq_name, "vm pagequeue",
                       MTX_DEF | MTX_DUPOK);
                   pq->pq_pdpages = 0;
                   vm_page_init_marker(&vmd->vmd_markers[i], i, 0);
           }
           mtx_init(&vmd->vmd_free_mtx, "vm page free queue", NULL, MTX_DEF);
           mtx_init(&vmd->vmd_pageout_mtx, "vm pageout lock", NULL, MTX_DEF);
           snprintf(vmd->vmd_name, sizeof(vmd->vmd_name), "%d", domain);
   
           /*
            * inacthead is used to provide FIFO ordering for LRU-bypassing
            * insertions.
            */
           vm_page_init_marker(&vmd->vmd_inacthead, PQ_INACTIVE, PGA_ENQUEUED);
           TAILQ_INSERT_HEAD(&vmd->vmd_pagequeues[PQ_INACTIVE].pq_pl,
               &vmd->vmd_inacthead, plinks.q);
   
           /*
            * The clock pages are used to implement active queue scanning without
            * requeues.  Scans start at clock[0], which is advanced after the scan
            * ends.  When the two clock hands meet, they are reset and scanning
            * resumes from the head of the queue.
            */
           vm_page_init_marker(&vmd->vmd_clock[0], PQ_ACTIVE, PGA_ENQUEUED);
           vm_page_init_marker(&vmd->vmd_clock[1], PQ_ACTIVE, PGA_ENQUEUED);
           TAILQ_INSERT_HEAD(&vmd->vmd_pagequeues[PQ_ACTIVE].pq_pl,
               &vmd->vmd_clock[0], plinks.q);
           TAILQ_INSERT_TAIL(&vmd->vmd_pagequeues[PQ_ACTIVE].pq_pl,
               &vmd->vmd_clock[1], plinks.q);
   }
   
   /*
    * Initialize a physical page in preparation for adding it to the free
    * lists.
    */
   static void
   vm_page_init_page(vm_page_t m, vm_paddr_t pa, int segind)
   {
   
           m->object = NULL;
           m->ref_count = 0;
           m->busy_lock = VPB_FREED;
           m->flags = m->a.flags = 0;
           m->phys_addr = pa;
           m->a.queue = PQ_NONE;
           m->psind = 0;
           m->segind = segind;
           m->order = VM_NFREEORDER;
           m->pool = VM_FREEPOOL_DEFAULT;
           m->valid = m->dirty = 0;
           pmap_page_init(m);
   }
   
   #ifndef PMAP_HAS_PAGE_ARRAY
   static vm_paddr_t
   vm_page_array_alloc(vm_offset_t *vaddr, vm_paddr_t end, vm_paddr_t page_range)
   {
           vm_paddr_t new_end;
   
           /*
            * Reserve an unmapped guard page to trap access to vm_page_array[-1].
            * However, because this page is allocated from KVM, out-of-bounds
            * accesses using the direct map will not be trapped.
            */
           *vaddr += PAGE_SIZE;
   
           /*
            * Allocate physical memory for the page structures, and map it.
            */
           new_end = trunc_page(end - page_range * sizeof(struct vm_page));
           vm_page_array = (vm_page_t)pmap_map(vaddr, new_end, end,
               VM_PROT_READ | VM_PROT_WRITE);
           vm_page_array_size = page_range;
   
           return (new_end);
   }
   #endif
   
   /*
    *      vm_page_startup:
    *
    *      Initializes the resident memory module.  Allocates physical memory for
    *      bootstrapping UMA and some data structures that are used to manage
    *      physical pages.  Initializes these structures, and populates the free
    *      page queues.
    */
   vm_offset_t
   vm_page_startup(vm_offset_t vaddr)
   {
           struct vm_phys_seg *seg;
           vm_page_t m;
           char *list, *listend;
           vm_paddr_t end, high_avail, low_avail, new_end, size;
           vm_paddr_t page_range __unused;
           vm_paddr_t last_pa, pa;
           u_long pagecount;
   #if MINIDUMP_PAGE_TRACKING
           u_long vm_page_dump_size;
   #endif
           int biggestone, i, segind;
   #ifdef WITNESS
           vm_offset_t mapped;
           int witness_size;
   #endif
   #if defined(__i386__) && defined(VM_PHYSSEG_DENSE)
           long ii;
   #endif
   
           vaddr = round_page(vaddr);
   
           vm_phys_early_startup();
           biggestone = vm_phys_avail_largest();
           end = phys_avail[biggestone+1];
   
           /*
            * Initialize the page and queue locks.
            */
           mtx_init(&vm_domainset_lock, "vm domainset lock", NULL, MTX_DEF);
           for (i = 0; i < PA_LOCK_COUNT; i++)
                   mtx_init(&pa_lock[i], "vm page", NULL, MTX_DEF);
           for (i = 0; i < vm_ndomains; i++)
                   vm_page_domain_init(i);
   
           new_end = end;
   #ifdef WITNESS
           witness_size = round_page(witness_startup_count());
           new_end -= witness_size;
           mapped = pmap_map(&vaddr, new_end, new_end + witness_size,
               VM_PROT_READ | VM_PROT_WRITE);
           bzero((void *)mapped, witness_size);
           witness_startup((void *)mapped);
   #endif
   
   #if MINIDUMP_PAGE_TRACKING
           /*
            * Allocate a bitmap to indicate that a random physical page
            * needs to be included in a minidump.
            *
            * The amd64 port needs this to indicate which direct map pages
            * need to be dumped, via calls to dump_add_page()/dump_drop_page().
            *
            * However, i386 still needs this workspace internally within the
            * minidump code.  In theory, they are not needed on i386, but are
            * included should the sf_buf code decide to use them.
            */
           last_pa = 0;
           vm_page_dump_pages = 0;
           for (i = 0; dump_avail[i + 1] != 0; i += 2) {
                   vm_page_dump_pages += howmany(dump_avail[i + 1], PAGE_SIZE) -
                       dump_avail[i] / PAGE_SIZE;
                   if (dump_avail[i + 1] > last_pa)
                           last_pa = dump_avail[i + 1];
           }
           vm_page_dump_size = round_page(BITSET_SIZE(vm_page_dump_pages));
           new_end -= vm_page_dump_size;
           vm_page_dump = (void *)(uintptr_t)pmap_map(&vaddr, new_end,
               new_end + vm_page_dump_size, VM_PROT_READ | VM_PROT_WRITE);
           bzero((void *)vm_page_dump, vm_page_dump_size);
   #else
           (void)last_pa;
   #endif
   #if defined(__aarch64__) || defined(__amd64__) || defined(__mips__) || \
       defined(__riscv) || defined(__powerpc64__)
           /*
            * Include the UMA bootstrap pages, witness pages and vm_page_dump
            * in a crash dump.  When pmap_map() uses the direct map, they are
            * not automatically included.
            */
           for (pa = new_end; pa < end; pa += PAGE_SIZE)
                   dump_add_page(pa);
   #endif
           phys_avail[biggestone + 1] = new_end;
   #ifdef __amd64__
           /*
            * Request that the physical pages underlying the message buffer be
            * included in a crash dump.  Since the message buffer is accessed
            * through the direct map, they are not automatically included.
            */
           pa = DMAP_TO_PHYS((vm_offset_t)msgbufp->msg_ptr);
           last_pa = pa + round_page(msgbufsize);
           while (pa < last_pa) {
                   dump_add_page(pa);
                   pa += PAGE_SIZE;
           }
   #endif
           /*
            * Compute the number of pages of memory that will be available for
            * use, taking into account the overhead of a page structure per page.
            * In other words, solve
            *      "available physical memory" - round_page(page_range *
            *          sizeof(struct vm_page)) = page_range * PAGE_SIZE 
            * for page_range.  
            */
           low_avail = phys_avail[0];
           high_avail = phys_avail[1];
           for (i = 0; i < vm_phys_nsegs; i++) {
                   if (vm_phys_segs[i].start < low_avail)
                           low_avail = vm_phys_segs[i].start;
                   if (vm_phys_segs[i].end > high_avail)
                           high_avail = vm_phys_segs[i].end;
           }
           /* Skip the first chunk.  It is already accounted for. */
           for (i = 2; phys_avail[i + 1] != 0; i += 2) {
                   if (phys_avail[i] < low_avail)
                           low_avail = phys_avail[i];
                   if (phys_avail[i + 1] > high_avail)
                           high_avail = phys_avail[i + 1];
           }
           first_page = low_avail / PAGE_SIZE;
   #ifdef VM_PHYSSEG_SPARSE
           size = 0;
           for (i = 0; i < vm_phys_nsegs; i++)
                   size += vm_phys_segs[i].end - vm_phys_segs[i].start;
           for (i = 0; phys_avail[i + 1] != 0; i += 2)
                   size += phys_avail[i + 1] - phys_avail[i];
   #elif defined(VM_PHYSSEG_DENSE)
           size = high_avail - low_avail;
   #else
   #error "Either VM_PHYSSEG_DENSE or VM_PHYSSEG_SPARSE must be defined."
   #endif
   
   #ifdef PMAP_HAS_PAGE_ARRAY
           pmap_page_array_startup(size / PAGE_SIZE);
           biggestone = vm_phys_avail_largest();
           end = new_end = phys_avail[biggestone + 1];
   #else
   #ifdef VM_PHYSSEG_DENSE
           /*
            * In the VM_PHYSSEG_DENSE case, the number of pages can account for
            * the overhead of a page structure per page only if vm_page_array is
            * allocated from the last physical memory chunk.  Otherwise, we must
            * allocate page structures representing the physical memory
            * underlying vm_page_array, even though they will not be used.
            */
           if (new_end != high_avail)
                   page_range = size / PAGE_SIZE;
           else
   #endif
           {
                   page_range = size / (PAGE_SIZE + sizeof(struct vm_page));
   
                   /*
                    * If the partial bytes remaining are large enough for
                    * a page (PAGE_SIZE) without a corresponding
                    * 'struct vm_page', then new_end will contain an
                    * extra page after subtracting the length of the VM
                    * page array.  Compensate by subtracting an extra
                    * page from new_end.
                    */
                   if (size % (PAGE_SIZE + sizeof(struct vm_page)) >= PAGE_SIZE) {
                           if (new_end == high_avail)
                                   high_avail -= PAGE_SIZE;
                           new_end -= PAGE_SIZE;
                   }
           }
           end = new_end;
           new_end = vm_page_array_alloc(&vaddr, end, page_range);
   #endif
   
   #if VM_NRESERVLEVEL > 0
           /*
            * Allocate physical memory for the reservation management system's
            * data structures, and map it.
            */
           new_end = vm_reserv_startup(&vaddr, new_end);
   #endif
   #if defined(__aarch64__) || defined(__amd64__) || defined(__mips__) || \
       defined(__riscv) || defined(__powerpc64__)
           /*
            * Include vm_page_array and vm_reserv_array in a crash dump.
            */
           for (pa = new_end; pa < end; pa += PAGE_SIZE)
                   dump_add_page(pa);
   #endif
           phys_avail[biggestone + 1] = new_end;
   
           /*
            * Add physical memory segments corresponding to the available
            * physical pages.
            */
           for (i = 0; phys_avail[i + 1] != 0; i += 2)
                   if (vm_phys_avail_size(i) != 0)
                           vm_phys_add_seg(phys_avail[i], phys_avail[i + 1]);
   
           /*
            * Initialize the physical memory allocator.
            */
           vm_phys_init();
   
           /*
            * Initialize the page structures and add every available page to the
            * physical memory allocator's free lists.
            */
   #if defined(__i386__) && defined(VM_PHYSSEG_DENSE)
           for (ii = 0; ii < vm_page_array_size; ii++) {
                   m = &vm_page_array[ii];
                   vm_page_init_page(m, (first_page + ii) << PAGE_SHIFT, 0);
                   m->flags = PG_FICTITIOUS;
           }
   #endif
           vm_cnt.v_page_count = 0;
           for (segind = 0; segind < vm_phys_nsegs; segind++) {
                   seg = &vm_phys_segs[segind];
                   for (m = seg->first_page, pa = seg->start; pa < seg->end;
                       m++, pa += PAGE_SIZE)
                           vm_page_init_page(m, pa, segind);
   
                   /*
                    * Add the segment to the free lists only if it is covered by
                    * one of the ranges in phys_avail.  Because we've added the
                    * ranges to the vm_phys_segs array, we can assume that each
                    * segment is either entirely contained in one of the ranges,
                    * or doesn't overlap any of them.
                    */
                   for (i = 0; phys_avail[i + 1] != 0; i += 2) {
                           struct vm_domain *vmd;
   
                           if (seg->start < phys_avail[i] ||
                               seg->end > phys_avail[i + 1])
                                   continue;
   
                           m = seg->first_page;
                           pagecount = (u_long)atop(seg->end - seg->start);
   
                           vmd = VM_DOMAIN(seg->domain);
                           vm_domain_free_lock(vmd);
                           vm_phys_enqueue_contig(m, pagecount);
                           vm_domain_free_unlock(vmd);
                           vm_domain_freecnt_inc(vmd, pagecount);
                           vm_cnt.v_page_count += (u_int)pagecount;
   
                           vmd = VM_DOMAIN(seg->domain);
                           vmd->vmd_page_count += (u_int)pagecount;
                           vmd->vmd_segs |= 1UL << m->segind;
                           break;
                   }
           }
   
           /*
            * Remove blacklisted pages from the physical memory allocator.
            */
           TAILQ_INIT(&blacklist_head);
           vm_page_blacklist_load(&list, &listend);
           vm_page_blacklist_check(list, listend);
   
           list = kern_getenv("vm.blacklist");
           vm_page_blacklist_check(list, NULL);
   
           freeenv(list);
   #if VM_NRESERVLEVEL > 0
           /*
            * Initialize the reservation management system.
            */
           vm_reserv_init();
   #endif
   
           return (vaddr);
   }
   
   void
   vm_page_reference(vm_page_t m)
   {
   
           vm_page_aflag_set(m, PGA_REFERENCED);
   }
   
   /*
    *      vm_page_trybusy
    *
    *      Helper routine for grab functions to trylock busy.
    *
    *      Returns true on success and false on failure.
    */
   static bool
   vm_page_trybusy(vm_page_t m, int allocflags)
   {
   
           if ((allocflags & (VM_ALLOC_SBUSY | VM_ALLOC_IGN_SBUSY)) != 0)
                   return (vm_page_trysbusy(m));
           else
                   return (vm_page_tryxbusy(m));
   }
   
   /*
    *      vm_page_tryacquire
    *
    *      Helper routine for grab functions to trylock busy and wire.
    *
    *      Returns true on success and false on failure.
    */
   static inline bool
   vm_page_tryacquire(vm_page_t m, int allocflags)
   {
           bool locked;
   
           locked = vm_page_trybusy(m, allocflags);
           if (locked && (allocflags & VM_ALLOC_WIRED) != 0)
                   vm_page_wire(m);
           return (locked);
   }
   
   /*
    *      vm_page_busy_acquire:
    *
    *      Acquire the busy lock as described by VM_ALLOC_* flags.  Will loop
    *      and drop the object lock if necessary.
    */
   bool
   vm_page_busy_acquire(vm_page_t m, int allocflags)
   {
           vm_object_t obj;
           bool locked;
   
           /*
            * The page-specific object must be cached because page
            * identity can change during the sleep, causing the
            * re-lock of a different object.
            * It is assumed that a reference to the object is already
            * held by the callers.
            */
           obj = atomic_load_ptr(&m->object);
           for (;;) {
                   if (vm_page_tryacquire(m, allocflags))
                           return (true);
                   if ((allocflags & VM_ALLOC_NOWAIT) != 0)
                           return (false);
                   if (obj != NULL)
                           locked = VM_OBJECT_WOWNED(obj);
                   else
                           locked = false;
                   MPASS(locked || vm_page_wired(m));
                   if (_vm_page_busy_sleep(obj, m, m->pindex, "vmpba", allocflags,
                       locked) && locked)
                           VM_OBJECT_WLOCK(obj);
                   if ((allocflags & VM_ALLOC_WAITFAIL) != 0)
                           return (false);
                   KASSERT(m->object == obj || m->object == NULL,
                       ("vm_page_busy_acquire: page %p does not belong to %p",
                       m, obj));
           }
   }
   
   /*
    *      vm_page_busy_downgrade:
    *
    *      Downgrade an exclusive busy page into a single shared busy page.
    */
   void
   vm_page_busy_downgrade(vm_page_t m)
   {
           u_int x;
   
           vm_page_assert_xbusied(m);
   
           x = vm_page_busy_fetch(m);
           for (;;) {
                   if (atomic_fcmpset_rel_int(&m->busy_lock,
                       &x, VPB_SHARERS_WORD(1)))
                           break;
           }
           if ((x & VPB_BIT_WAITERS) != 0)
                   wakeup(m);
   }
   
   /*
    *
    *      vm_page_busy_tryupgrade:
    *
    *      Attempt to upgrade a single shared busy into an exclusive busy.
    */
   int
   vm_page_busy_tryupgrade(vm_page_t m)
   {
           u_int ce, x;
   
           vm_page_assert_sbusied(m);
   
           x = vm_page_busy_fetch(m);
           ce = VPB_CURTHREAD_EXCLUSIVE;
           for (;;) {
                   if (VPB_SHARERS(x) > 1)
                           return (0);
                   KASSERT((x & ~VPB_BIT_WAITERS) == VPB_SHARERS_WORD(1),
                       ("vm_page_busy_tryupgrade: invalid lock state"));
                   if (!atomic_fcmpset_acq_int(&m->busy_lock, &x,
                       ce | (x & VPB_BIT_WAITERS)))
                           continue;
                   return (1);
           }
   }
   
   /*
    *      vm_page_sbusied:
    *
    *      Return a positive value if the page is shared busied, 0 otherwise.
    */
   int
   vm_page_sbusied(vm_page_t m)
   {
           u_int x;
   
           x = vm_page_busy_fetch(m);
           return ((x & VPB_BIT_SHARED) != 0 && x != VPB_UNBUSIED);
   }
   
   /*
    *      vm_page_sunbusy:
    *
    *      Shared unbusy a page.
    */
   void
   vm_page_sunbusy(vm_page_t m)
   {
           u_int x;
   
           vm_page_assert_sbusied(m);
   
           x = vm_page_busy_fetch(m);
           for (;;) {
                   KASSERT(x != VPB_FREED,
                       ("vm_page_sunbusy: Unlocking freed page."));
                   if (VPB_SHARERS(x) > 1) {
                           if (atomic_fcmpset_int(&m->busy_lock, &x,
                               x - VPB_ONE_SHARER))
                                   break;
                           continue;
                   }
                   KASSERT((x & ~VPB_BIT_WAITERS) == VPB_SHARERS_WORD(1),
                       ("vm_page_sunbusy: invalid lock state"));
                   if (!atomic_fcmpset_rel_int(&m->busy_lock, &x, VPB_UNBUSIED))
                           continue;
                   if ((x & VPB_BIT_WAITERS) == 0)
                           break;
                   wakeup(m);
                   break;
          }
  }
  
  /*
   *      vm_page_busy_sleep:
   *
   *      Sleep if the page is busy, using the page pointer as wchan.
   *      This is used to implement the hard-path of busying mechanism.
   *
   *      If nonshared is true, sleep only if the page is xbusy.
   *
   *      The object lock must be held on entry and will be released on exit.
   */
  void
  vm_page_busy_sleep(vm_page_t m, const char *wmesg, bool nonshared)
  {
          vm_object_t obj;
  
          obj = m->object;
          VM_OBJECT_ASSERT_LOCKED(obj);
          vm_page_lock_assert(m, MA_NOTOWNED);
  
          if (!_vm_page_busy_sleep(obj, m, m->pindex, wmesg,
              nonshared ? VM_ALLOC_SBUSY : 0 , true))
                  VM_OBJECT_DROP(obj);
  }
  
  /*
   *      vm_page_busy_sleep_unlocked:
   *
   *      Sleep if the page is busy, using the page pointer as wchan.
   *      This is used to implement the hard-path of busying mechanism.
   *
   *      If nonshared is true, sleep only if the page is xbusy.
   *
   *      The object lock must not be held on entry.  The operation will
   *      return if the page changes identity.
   */
  void
  vm_page_busy_sleep_unlocked(vm_object_t obj, vm_page_t m, vm_pindex_t pindex,
      const char *wmesg, bool nonshared)
  {
  
          VM_OBJECT_ASSERT_UNLOCKED(obj);
          vm_page_lock_assert(m, MA_NOTOWNED);
  
          _vm_page_busy_sleep(obj, m, pindex, wmesg,
              nonshared ? VM_ALLOC_SBUSY : 0, false);
  }
  
  /*
   *      _vm_page_busy_sleep:
   *
   *      Internal busy sleep function.  Verifies the page identity and
   *      lockstate against parameters.  Returns true if it sleeps and
   *      false otherwise.
   *
   *      If locked is true the lock will be dropped for any true returns
   *      and held for any false returns.
   */
  static bool
  _vm_page_busy_sleep(vm_object_t obj, vm_page_t m, vm_pindex_t pindex,
      const char *wmesg, int allocflags, bool locked)
  {
          bool xsleep;
          u_int x;
  
          /*
           * If the object is busy we must wait for that to drain to zero
           * before trying the page again.
           */
          if (obj != NULL && vm_object_busied(obj)) {
                  if (locked)
                          VM_OBJECT_DROP(obj);
                  vm_object_busy_wait(obj, wmesg);
                  return (true);
          }
  
          if (!vm_page_busied(m))
                  return (false);
  
          xsleep = (allocflags & (VM_ALLOC_SBUSY | VM_ALLOC_IGN_SBUSY)) != 0;
          sleepq_lock(m);
          x = vm_page_busy_fetch(m);
          do {
                  /*
                   * If the page changes objects or becomes unlocked we can
                   * simply return.
                   */
                  if (x == VPB_UNBUSIED ||
                      (xsleep && (x & VPB_BIT_SHARED) != 0) ||
                      m->object != obj || m->pindex != pindex) {
                          sleepq_release(m);
                          return (false);
                  }
                  if ((x & VPB_BIT_WAITERS) != 0)
                          break;
          } while (!atomic_fcmpset_int(&m->busy_lock, &x, x | VPB_BIT_WAITERS));
          if (locked)
                  VM_OBJECT_DROP(obj);
          DROP_GIANT();
          sleepq_add(m, NULL, wmesg, 0, 0);
          sleepq_wait(m, PVM);
          PICKUP_GIANT();
          return (true);
  }
  
  /*
   *      vm_page_trysbusy:
   *
   *      Try to shared busy a page.
   *      If the operation succeeds 1 is returned otherwise 0.
   *      The operation never sleeps.
   */
  int
  vm_page_trysbusy(vm_page_t m)
  {
          vm_object_t obj;
          u_int x;
  
          obj = m->object;
          x = vm_page_busy_fetch(m);
          for (;;) {
                  if ((x & VPB_BIT_SHARED) == 0)
                          return (0);
                  /*
                   * Reduce the window for transient busies that will trigger
                   * false negatives in vm_page_ps_test().
                   */
                  if (obj != NULL && vm_object_busied(obj))
                          return (0);
                  if (atomic_fcmpset_acq_int(&m->busy_lock, &x,
                      x + VPB_ONE_SHARER))
                          break;
          }
  
          /* Refetch the object now that we're guaranteed that it is stable. */
          obj = m->object;
          if (obj != NULL && vm_object_busied(obj)) {
                  vm_page_sunbusy(m);
                  return (0);
          }
          return (1);
  }
  
  /*
   *      vm_page_tryxbusy:
   *
   *      Try to exclusive busy a page.
   *      If the operation succeeds 1 is returned otherwise 0.
   *      The operation never sleeps.
   */
  int
  vm_page_tryxbusy(vm_page_t m)
  {
          vm_object_t obj;
  
          if (atomic_cmpset_acq_int(&m->busy_lock, VPB_UNBUSIED,
              VPB_CURTHREAD_EXCLUSIVE) == 0)
                  return (0);
  
          obj = m->object;
          if (obj != NULL && vm_object_busied(obj)) {
                  vm_page_xunbusy(m);
                  return (0);
          }
          return (1);
  }
  
  static void
  vm_page_xunbusy_hard_tail(vm_page_t m)
  {
          atomic_store_rel_int(&m->busy_lock, VPB_UNBUSIED);
          /* Wake the waiter. */
          wakeup(m);
  }
  
  /*
   *      vm_page_xunbusy_hard:
   *
   *      Called when unbusy has failed because there is a waiter.
   */
  void
  vm_page_xunbusy_hard(vm_page_t m)
  {
          vm_page_assert_xbusied(m);
          vm_page_xunbusy_hard_tail(m);
  }
  
  void
  vm_page_xunbusy_hard_unchecked(vm_page_t m)
  {
          vm_page_assert_xbusied_unchecked(m);
          vm_page_xunbusy_hard_tail(m);
  }
  
  static void
  vm_page_busy_free(vm_page_t m)
  {
          u_int x;
  
          atomic_thread_fence_rel();
          x = atomic_swap_int(&m->busy_lock, VPB_FREED);
          if ((x & VPB_BIT_WAITERS) != 0)
                  wakeup(m);
  }
  
  /*
   *      vm_page_unhold_pages:
   *
   *      Unhold each of the pages that is referenced by the given array.
   */
  void
  vm_page_unhold_pages(vm_page_t *ma, int count)
  {
  
          for (; count != 0; count--) {
                  vm_page_unwire(*ma, PQ_ACTIVE);
                  ma++;
          }
  }
  
  vm_page_t
  PHYS_TO_VM_PAGE(vm_paddr_t pa)
  {
          vm_page_t m;
  
  #ifdef VM_PHYSSEG_SPARSE
          m = vm_phys_paddr_to_vm_page(pa);
          if (m == NULL)
                  m = vm_phys_fictitious_to_vm_page(pa);
          return (m);
  #elif defined(VM_PHYSSEG_DENSE)
          long pi;
  
          pi = atop(pa);
          if (pi >= first_page && (pi - first_page) < vm_page_array_size) {
                  m = &vm_page_array[pi - first_page];
                  return (m);
          }
          return (vm_phys_fictitious_to_vm_page(pa));
  #else
  #error "Either VM_PHYSSEG_DENSE or VM_PHYSSEG_SPARSE must be defined."
  #endif
  }
  
  /*
   *      vm_page_getfake:
   *
   *      Create a fictitious page with the specified physical address and
   *      memory attribute.  The memory attribute is the only the machine-
   *      dependent aspect of a fictitious page that must be initialized.
   */
  vm_page_t
  vm_page_getfake(vm_paddr_t paddr, vm_memattr_t memattr)
  {
          vm_page_t m;
  
          m = uma_zalloc(fakepg_zone, M_WAITOK | M_ZERO);
          vm_page_initfake(m, paddr, memattr);
          return (m);
  }
  
  void
  vm_page_initfake(vm_page_t m, vm_paddr_t paddr, vm_memattr_t memattr)
  {
  
          if ((m->flags & PG_FICTITIOUS) != 0) {
                  /*
                   * The page's memattr might have changed since the
                   * previous initialization.  Update the pmap to the
                   * new memattr.
                   */
                  goto memattr;
          }
          m->phys_addr = paddr;
          m->a.queue = PQ_NONE;
          /* Fictitious pages don't use "segind". */
          m->flags = PG_FICTITIOUS;
          /* Fictitious pages don't use "order" or "pool". */
          m->oflags = VPO_UNMANAGED;
          m->busy_lock = VPB_CURTHREAD_EXCLUSIVE;
          /* Fictitious pages are unevictable. */
          m->ref_count = 1;
          pmap_page_init(m);
  memattr:
          pmap_page_set_memattr(m, memattr);
  }
  
  /*
   *      vm_page_putfake:
   *
   *      Release a fictitious page.
   */
  void
  vm_page_putfake(vm_page_t m)
  {
  
          KASSERT((m->oflags & VPO_UNMANAGED) != 0, ("managed %p", m));
          KASSERT((m->flags & PG_FICTITIOUS) != 0,
              ("vm_page_putfake: bad page %p", m));
          vm_page_assert_xbusied(m);
          vm_page_busy_free(m);
          uma_zfree(fakepg_zone, m);
  }
  
  /*
   *      vm_page_updatefake:
   *
   *      Update the given fictitious page to the specified physical address and
   *      memory attribute.
   */
  void
  vm_page_updatefake(vm_page_t m, vm_paddr_t paddr, vm_memattr_t memattr)
  {
  
          KASSERT((m->flags & PG_FICTITIOUS) != 0,
              ("vm_page_updatefake: bad page %p", m));
          m->phys_addr = paddr;
          pmap_page_set_memattr(m, memattr);
  }
  
  /*
   *      vm_page_free:
   *
   *      Free a page.
   */
  void
  vm_page_free(vm_page_t m)
  {
  
          m->flags &= ~PG_ZERO;
          vm_page_free_toq(m);
  }
  
  /*
   *      vm_page_free_zero:
   *
   *      Free a page to the zerod-pages queue
   */
  void
  vm_page_free_zero(vm_page_t m)
  {
  
          m->flags |= PG_ZERO;
          vm_page_free_toq(m);
  }
  
  /*
   * Unbusy and handle the page queueing for a page from a getpages request that
   * was optionally read ahead or behind.
   */
  void
  vm_page_readahead_finish(vm_page_t m)
  {
  
          /* We shouldn't put invalid pages on queues. */
          KASSERT(!vm_page_none_valid(m), ("%s: %p is invalid", __func__, m));
  
          /*
           * Since the page is not the actually needed one, whether it should
           * be activated or deactivated is not obvious.  Empirical results
           * have shown that deactivating the page is usually the best choice,
           * unless the page is wanted by another thread.
           */
          if ((vm_page_busy_fetch(m) & VPB_BIT_WAITERS) != 0)
                  vm_page_activate(m);
          else
                  vm_page_deactivate(m);
          vm_page_xunbusy_unchecked(m);
  }
  
  /*
   * Destroy the identity of an invalid page and free it if possible.
   * This is intended to be used when reading a page from backing store fails.
   */
  void
  vm_page_free_invalid(vm_page_t m)
  {
  
          KASSERT(vm_page_none_valid(m), ("page %p is valid", m));
          KASSERT(!pmap_page_is_mapped(m), ("page %p is mapped", m));
          KASSERT(m->object != NULL, ("page %p has no object", m));
          VM_OBJECT_ASSERT_WLOCKED(m->object);
  
          /*
           * We may be attempting to free the page as part of the handling for an
           * I/O error, in which case the page was xbusied by a different thread.
           */
          vm_page_xbusy_claim(m);
  
          /*
           * If someone has wired this page while the object lock
           * was not held, then the thread that unwires is responsible
           * for freeing the page.  Otherwise just free the page now.
           * The wire count of this unmapped page cannot change while
           * we have the page xbusy and the page's object wlocked.
           */
          if (vm_page_remove(m))
                  vm_page_free(m);
  }
  
  /*
   *      vm_page_sleep_if_busy:
   *
   *      Sleep and release the object lock if the page is busied.
   *      Returns TRUE if the thread slept.
   *
   *      The given page must be unlocked and object containing it must
   *      be locked.
   */
  int
  vm_page_sleep_if_busy(vm_page_t m, const char *wmesg)
  {
          vm_object_t obj;
  
          vm_page_lock_assert(m, MA_NOTOWNED);
          VM_OBJECT_ASSERT_WLOCKED(m->object);
  
          /*
           * The page-specific object must be cached because page
           * identity can change during the sleep, causing the
           * re-lock of a different object.
           * It is assumed that a reference to the object is already
           * held by the callers.
           */
          obj = m->object;
          if (_vm_page_busy_sleep(obj, m, m->pindex, wmesg, 0, true)) {
                  VM_OBJECT_WLOCK(obj);
                  return (TRUE);
          }
          return (FALSE);
  }
  
  /*
   *      vm_page_sleep_if_xbusy:
   *
   *      Sleep and release the object lock if the page is xbusied.
   *      Returns TRUE if the thread slept.
   *
   *      The given page must be unlocked and object containing it must
   *      be locked.
   */
  int
  vm_page_sleep_if_xbusy(vm_page_t m, const char *wmesg)
  {
          vm_object_t obj;
  
          vm_page_lock_assert(m, MA_NOTOWNED);
          VM_OBJECT_ASSERT_WLOCKED(m->object);
  
          /*
           * The page-specific object must be cached because page
           * identity can change during the sleep, causing the
           * re-lock of a different object.
           * It is assumed that a reference to the object is already
           * held by the callers.
           */
          obj = m->object;
          if (_vm_page_busy_sleep(obj, m, m->pindex, wmesg, VM_ALLOC_SBUSY,
              true)) {
                  VM_OBJECT_WLOCK(obj);
                  return (TRUE);
          }
          return (FALSE);
  }
  
  /*
   *      vm_page_dirty_KBI:              [ internal use only ]
   *
   *      Set all bits in the page's dirty field.
   *
   *      The object containing the specified page must be locked if the
   *      call is made from the machine-independent layer.
   *
   *      See vm_page_clear_dirty_mask().
   *
   *      This function should only be called by vm_page_dirty().
   */
  void
  vm_page_dirty_KBI(vm_page_t m)
  {
  
          /* Refer to this operation by its public name. */
          KASSERT(vm_page_all_valid(m), ("vm_page_dirty: page is invalid!"));
          m->dirty = VM_PAGE_BITS_ALL;
  }
  
  /*
   *      vm_page_insert:         [ internal use only ]
   *
   *      Inserts the given mem entry into the object and object list.
   *
   *      The object must be locked.
   */
  int
  vm_page_insert(vm_page_t m, vm_object_t object, vm_pindex_t pindex)
  {
          vm_page_t mpred;
  
          VM_OBJECT_ASSERT_WLOCKED(object);
          mpred = vm_radix_lookup_le(&object->rtree, pindex);
          return (vm_page_insert_after(m, object, pindex, mpred));
  }
  
  /*
   *      vm_page_insert_after:
   *
   *      Inserts the page "m" into the specified object at offset "pindex".
   *
   *      The page "mpred" must immediately precede the offset "pindex" within
   *      the specified object.
   *
   *      The object must be locked.
   */
  static int
  vm_page_insert_after(vm_page_t m, vm_object_t object, vm_pindex_t pindex,
      vm_page_t mpred)
  {
          vm_page_t msucc;
  
          VM_OBJECT_ASSERT_WLOCKED(object);
          KASSERT(m->object == NULL,
              ("vm_page_insert_after: page already inserted"));
          if (mpred != NULL) {
                  KASSERT(mpred->object == object,
                      ("vm_page_insert_after: object doesn't contain mpred"));
                  KASSERT(mpred->pindex < pindex,
                      ("vm_page_insert_after: mpred doesn't precede pindex"));
                  msucc = TAILQ_NEXT(mpred, listq);
          } else
                  msucc = TAILQ_FIRST(&object->memq);
          if (msucc != NULL)
                  KASSERT(msucc->pindex > pindex,
                      ("vm_page_insert_after: msucc doesn't succeed pindex"));
  
          /*
           * Record the object/offset pair in this page.
           */
          m->object = object;
          m->pindex = pindex;
          m->ref_count |= VPRC_OBJREF;
  
          /*
           * Now link into the object's ordered list of backed pages.
           */
          if (vm_radix_insert(&object->rtree, m)) {
                  m->object = NULL;
                  m->pindex = 0;
                  m->ref_count &= ~VPRC_OBJREF;
                  return (1);
          }
          vm_page_insert_radixdone(m, object, mpred);
          return (0);
  }
  
  /*
   *      vm_page_insert_radixdone:
   *
   *      Complete page "m" insertion into the specified object after the
   *      radix trie hooking.
   *
   *      The page "mpred" must precede the offset "m->pindex" within the
   *      specified object.
   *
   *      The object must be locked.
   */
  static void
  vm_page_insert_radixdone(vm_page_t m, vm_object_t object, vm_page_t mpred)
  {
  
          VM_OBJECT_ASSERT_WLOCKED(object);
          KASSERT(object != NULL && m->object == object,
              ("vm_page_insert_radixdone: page %p has inconsistent object", m));
          KASSERT((m->ref_count & VPRC_OBJREF) != 0,
              ("vm_page_insert_radixdone: page %p is missing object ref", m));
          if (mpred != NULL) {
                  KASSERT(mpred->object == object,
                      ("vm_page_insert_radixdone: object doesn't contain mpred"));
                  KASSERT(mpred->pindex < m->pindex,
                      ("vm_page_insert_radixdone: mpred doesn't precede pindex"));
          }
  
          if (mpred != NULL)
                  TAILQ_INSERT_AFTER(&object->memq, mpred, m, listq);
          else
                  TAILQ_INSERT_HEAD(&object->memq, m, listq);
  
          /*
           * Show that the object has one more resident page.
           */
          object->resident_page_count++;
  
          /*
           * Hold the vnode until the last page is released.
           */
          if (object->resident_page_count == 1 && object->type == OBJT_VNODE)
                  vhold(object->handle);
  
          /*
           * Since we are inserting a new and possibly dirty page,
           * update the object's generation count.
           */
          if (pmap_page_is_write_mapped(m))
                  vm_object_set_writeable_dirty(object);
  }
  
  /*
   * Do the work to remove a page from its object.  The caller is responsible for
   * updating the page's fields to reflect this removal.
   */
  static void
  vm_page_object_remove(vm_page_t m)
  {
          vm_object_t object;
          vm_page_t mrem;
  
          vm_page_assert_xbusied(m);
          object = m->object;
          VM_OBJECT_ASSERT_WLOCKED(object);
          KASSERT((m->ref_count & VPRC_OBJREF) != 0,
              ("page %p is missing its object ref", m));
  
          /* Deferred free of swap space. */
          if ((m->a.flags & PGA_SWAP_FREE) != 0)
                  vm_pager_page_unswapped(m);
  
          m->object = NULL;
          mrem = vm_radix_remove(&object->rtree, m->pindex);
          KASSERT(mrem == m, ("removed page %p, expected page %p", mrem, m));
  
          /*
           * Now remove from the object's list of backed pages.
           */
          TAILQ_REMOVE(&object->memq, m, listq);
  
          /*
           * And show that the object has one fewer resident page.
           */
          object->resident_page_count--;
  
          /*
           * The vnode may now be recycled.
           */
          if (object->resident_page_count == 0 && object->type == OBJT_VNODE)
                  vdrop(object->handle);
  }
  
  /*
   *      vm_page_remove:
   *
   *      Removes the specified page from its containing object, but does not
   *      invalidate any backing storage.  Returns true if the object's reference
   *      was the last reference to the page, and false otherwise.
   *
   *      The object must be locked and the page must be exclusively busied.
   *      The exclusive busy will be released on return.  If this is not the
   *      final ref and the caller does not hold a wire reference it may not
   *      continue to access the page.
   */
  bool
  vm_page_remove(vm_page_t m)
  {
          bool dropped;
  
          dropped = vm_page_remove_xbusy(m);
          vm_page_xunbusy(m);
  
          return (dropped);
  }
  
  /*
   *      vm_page_remove_xbusy
   *
   *      Removes the page but leaves the xbusy held.  Returns true if this
   *      removed the final ref and false otherwise.
   */
  bool
  vm_page_remove_xbusy(vm_page_t m)
  {
  
          vm_page_object_remove(m);
          return (vm_page_drop(m, VPRC_OBJREF) == VPRC_OBJREF);
  }
  
  /*
   *      vm_page_lookup:
   *
   *      Returns the page associated with the object/offset
   *      pair specified; if none is found, NULL is returned.
   *
   *      The object must be locked.
   */
  vm_page_t
  vm_page_lookup(vm_object_t object, vm_pindex_t pindex)
  {
  
          VM_OBJECT_ASSERT_LOCKED(object);
          return (vm_radix_lookup(&object->rtree, pindex));
  }
  
  /*
   *      vm_page_lookup_unlocked:
   *
   *      Returns the page associated with the object/offset pair specified;
   *      if none is found, NULL is returned.  The page may be no longer be
   *      present in the object at the time that this function returns.  Only
   *      useful for opportunistic checks such as inmem().
   */
  vm_page_t
  vm_page_lookup_unlocked(vm_object_t object, vm_pindex_t pindex)
  {
  
          return (vm_radix_lookup_unlocked(&object->rtree, pindex));
  }
  
  /*
   *      vm_page_relookup:
   *
   *      Returns a page that must already have been busied by
   *      the caller.  Used for bogus page replacement.
   */
  vm_page_t
  vm_page_relookup(vm_object_t object, vm_pindex_t pindex)
  {
          vm_page_t m;
  
          m = vm_radix_lookup_unlocked(&object->rtree, pindex);
          KASSERT(m != NULL && (vm_page_busied(m) || vm_page_wired(m)) &&
              m->object == object && m->pindex == pindex,
              ("vm_page_relookup: Invalid page %p", m));
          return (m);
  }
  
  /*
   * This should only be used by lockless functions for releasing transient
   * incorrect acquires.  The page may have been freed after we acquired a
   * busy lock.  In this case busy_lock == VPB_FREED and we have nothing
   * further to do.
   */
  static void
  vm_page_busy_release(vm_page_t m)
  {
          u_int x;
  
          x = vm_page_busy_fetch(m);
          for (;;) {
                  if (x == VPB_FREED)
                          break;
                  if ((x & VPB_BIT_SHARED) != 0 && VPB_SHARERS(x) > 1) {
                          if (atomic_fcmpset_int(&m->busy_lock, &x,
                              x - VPB_ONE_SHARER))
                                  break;
                          continue;
                  }
                  KASSERT((x & VPB_BIT_SHARED) != 0 ||
                      (x & ~VPB_BIT_WAITERS) == VPB_CURTHREAD_EXCLUSIVE,
                      ("vm_page_busy_release: %p xbusy not owned.", m));
                  if (!atomic_fcmpset_rel_int(&m->busy_lock, &x, VPB_UNBUSIED))
                          continue;
                  if ((x & VPB_BIT_WAITERS) != 0)
                          wakeup(m);
                  break;
          }
  }
  
  /*
   *      vm_page_find_least:
   *
   *      Returns the page associated with the object with least pindex
   *      greater than or equal to the parameter pindex, or NULL.
   *
   *      The object must be locked.
   */
  vm_page_t
  vm_page_find_least(vm_object_t object, vm_pindex_t pindex)
  {
          vm_page_t m;
  
          VM_OBJECT_ASSERT_LOCKED(object);
          if ((m = TAILQ_FIRST(&object->memq)) != NULL && m->pindex < pindex)
                  m = vm_radix_lookup_ge(&object->rtree, pindex);
          return (m);
  }
  
  /*
   * Returns the given page's successor (by pindex) within the object if it is
   * resident; if none is found, NULL is returned.
   *
   * The object must be locked.
   */
  vm_page_t
  vm_page_next(vm_page_t m)
  {
          vm_page_t next;
  
          VM_OBJECT_ASSERT_LOCKED(m->object);
          if ((next = TAILQ_NEXT(m, listq)) != NULL) {
                  MPASS(next->object == m->object);
                  if (next->pindex != m->pindex + 1)
                          next = NULL;
          }
          return (next);
  }
  
  /*
   * Returns the given page's predecessor (by pindex) within the object if it is
   * resident; if none is found, NULL is returned.
   *
   * The object must be locked.
   */
  vm_page_t
  vm_page_prev(vm_page_t m)
  {
          vm_page_t prev;
  
          VM_OBJECT_ASSERT_LOCKED(m->object);
          if ((prev = TAILQ_PREV(m, pglist, listq)) != NULL) {
                  MPASS(prev->object == m->object);
                  if (prev->pindex != m->pindex - 1)
                          prev = NULL;
          }
          return (prev);
  }
  
  /*
   * Uses the page mnew as a replacement for an existing page at index
   * pindex which must be already present in the object.
   *
   * Both pages must be exclusively busied on enter.  The old page is
   * unbusied on exit.
   *
   * A return value of true means mold is now free.  If this is not the
   * final ref and the caller does not hold a wire reference it may not
   * continue to access the page.
   */
  static bool
  vm_page_replace_hold(vm_page_t mnew, vm_object_t object, vm_pindex_t pindex,
      vm_page_t mold)
  {
          vm_page_t mret;
          bool dropped;
  
          VM_OBJECT_ASSERT_WLOCKED(object);
          vm_page_assert_xbusied(mold);
          KASSERT(mnew->object == NULL && (mnew->ref_count & VPRC_OBJREF) == 0,
              ("vm_page_replace: page %p already in object", mnew));
  
          /*
           * This function mostly follows vm_page_insert() and
           * vm_page_remove() without the radix, object count and vnode
           * dance.  Double check such functions for more comments.
           */
  
          mnew->object = object;
          mnew->pindex = pindex;
          atomic_set_int(&mnew->ref_count, VPRC_OBJREF);
          mret = vm_radix_replace(&object->rtree, mnew);
          KASSERT(mret == mold,
              ("invalid page replacement, mold=%p, mret=%p", mold, mret));
          KASSERT((mold->oflags & VPO_UNMANAGED) ==
              (mnew->oflags & VPO_UNMANAGED),
              ("vm_page_replace: mismatched VPO_UNMANAGED"));
  
          /* Keep the resident page list in sorted order. */
          TAILQ_INSERT_AFTER(&object->memq, mold, mnew, listq);
          TAILQ_REMOVE(&object->memq, mold, listq);
          mold->object = NULL;
  
          /*
           * The object's resident_page_count does not change because we have
           * swapped one page for another, but the generation count should
           * change if the page is dirty.
           */
          if (pmap_page_is_write_mapped(mnew))
                  vm_object_set_writeable_dirty(object);
          dropped = vm_page_drop(mold, VPRC_OBJREF) == VPRC_OBJREF;
          vm_page_xunbusy(mold);
  
          return (dropped);
  }
  
  void
  vm_page_replace(vm_page_t mnew, vm_object_t object, vm_pindex_t pindex,
      vm_page_t mold)
  {
  
          vm_page_assert_xbusied(mnew);
  
          if (vm_page_replace_hold(mnew, object, pindex, mold))
                  vm_page_free(mold);
  }
  
  /*
   *      vm_page_rename:
   *
   *      Move the given memory entry from its
   *      current object to the specified target object/offset.
   *
   *      Note: swap associated with the page must be invalidated by the move.  We
   *            have to do this for several reasons:  (1) we aren't freeing the
   *            page, (2) we are dirtying the page, (3) the VM system is probably
   *            moving the page from object A to B, and will then later move
   *            the backing store from A to B and we can't have a conflict.
   *
   *      Note: we *always* dirty the page.  It is necessary both for the
   *            fact that we moved it, and because we may be invalidating
   *            swap.
   *
   *      The objects must be locked.
   */
  int
  vm_page_rename(vm_page_t m, vm_object_t new_object, vm_pindex_t new_pindex)
  {
          vm_page_t mpred;
          vm_pindex_t opidx;
  
          VM_OBJECT_ASSERT_WLOCKED(new_object);
  
          KASSERT(m->ref_count != 0, ("vm_page_rename: page %p has no refs", m));
          mpred = vm_radix_lookup_le(&new_object->rtree, new_pindex);
          KASSERT(mpred == NULL || mpred->pindex != new_pindex,
              ("vm_page_rename: pindex already renamed"));
  
          /*
           * Create a custom version of vm_page_insert() which does not depend
           * by m_prev and can cheat on the implementation aspects of the
           * function.
           */
          opidx = m->pindex;
          m->pindex = new_pindex;
          if (vm_radix_insert(&new_object->rtree, m)) {
                  m->pindex = opidx;
                  return (1);
          }
  
          /*
           * The operation cannot fail anymore.  The removal must happen before
           * the listq iterator is tainted.
           */
          m->pindex = opidx;
          vm_page_object_remove(m);
  
          /* Return back to the new pindex to complete vm_page_insert(). */
          m->pindex = new_pindex;
          m->object = new_object;
  
          vm_page_insert_radixdone(m, new_object, mpred);
          vm_page_dirty(m);
          return (0);
  }
  
  /*
   *      vm_page_alloc:
   *
   *      Allocate and return a page that is associated with the specified
   *      object and offset pair.  By default, this page is exclusive busied.
   *
   *      The caller must always specify an allocation class.
   *
   *      allocation classes:
   *      VM_ALLOC_NORMAL         normal process request
   *      VM_ALLOC_SYSTEM         system *really* needs a page
   *      VM_ALLOC_INTERRUPT      interrupt time request
   *
   *      optional allocation flags:
   *      VM_ALLOC_COUNT(number)  the number of additional pages that the caller
   *                              intends to allocate
   *      VM_ALLOC_NOBUSY         do not exclusive busy the page
   *      VM_ALLOC_NODUMP         do not include the page in a kernel core dump
   *      VM_ALLOC_NOOBJ          page is not associated with an object and
   *                              should not be exclusive busy
   *      VM_ALLOC_SBUSY          shared busy the allocated page
   *      VM_ALLOC_WIRED          wire the allocated page
   *      VM_ALLOC_ZERO           prefer a zeroed page
   */
  vm_page_t
  vm_page_alloc(vm_object_t object, vm_pindex_t pindex, int req)
  {
  
          return (vm_page_alloc_after(object, pindex, req, object != NULL ?
              vm_radix_lookup_le(&object->rtree, pindex) : NULL));
  }
  
  vm_page_t
  vm_page_alloc_domain(vm_object_t object, vm_pindex_t pindex, int domain,
      int req)
  {
  
          return (vm_page_alloc_domain_after(object, pindex, domain, req,
              object != NULL ? vm_radix_lookup_le(&object->rtree, pindex) :
              NULL));
  }
  
  /*
   * Allocate a page in the specified object with the given page index.  To
   * optimize insertion of the page into the object, the caller must also specifiy
   * the resident page in the object with largest index smaller than the given
   * page index, or NULL if no such page exists.
   */
  vm_page_t
  vm_page_alloc_after(vm_object_t object, vm_pindex_t pindex,
      int req, vm_page_t mpred)
  {
          struct vm_domainset_iter di;
          vm_page_t m;
          int domain;
  
          vm_domainset_iter_page_init(&di, object, pindex, &domain, &req);
          do {
                  m = vm_page_alloc_domain_after(object, pindex, domain, req,
                      mpred);
                  if (m != NULL)
                          break;
          } while (vm_domainset_iter_page(&di, object, &domain) == 0);
  
          return (m);
  }
  
  /*
   * Returns true if the number of free pages exceeds the minimum
   * for the request class and false otherwise.
   */
  static int
  _vm_domain_allocate(struct vm_domain *vmd, int req_class, int npages)
  {
          u_int limit, old, new;
  
          if (req_class == VM_ALLOC_INTERRUPT)
                  limit = 0;
          else if (req_class == VM_ALLOC_SYSTEM)
                  limit = vmd->vmd_interrupt_free_min;
          else
                  limit = vmd->vmd_free_reserved;
  
          /*
           * Attempt to reserve the pages.  Fail if we're below the limit.
           */
          limit += npages;
          old = vmd->vmd_free_count;
          do {
                  if (old < limit)
                          return (0);
                  new = old - npages;
          } while (atomic_fcmpset_int(&vmd->vmd_free_count, &old, new) == 0);
  
          /* Wake the page daemon if we've crossed the threshold. */
          if (vm_paging_needed(vmd, new) && !vm_paging_needed(vmd, old))
                  pagedaemon_wakeup(vmd->vmd_domain);
  
          /* Only update bitsets on transitions. */
          if ((old >= vmd->vmd_free_min && new < vmd->vmd_free_min) ||
              (old >= vmd->vmd_free_severe && new < vmd->vmd_free_severe))
                  vm_domain_set(vmd);
  
          return (1);
  }
  
  int
  vm_domain_allocate(struct vm_domain *vmd, int req, int npages)
  {
          int req_class;
  
          /*
           * The page daemon is allowed to dig deeper into the free page list.
           */
          req_class = req & VM_ALLOC_CLASS_MASK;
          if (curproc == pageproc && req_class != VM_ALLOC_INTERRUPT)
                  req_class = VM_ALLOC_SYSTEM;
          return (_vm_domain_allocate(vmd, req_class, npages));
  }
  
  vm_page_t
  vm_page_alloc_domain_after(vm_object_t object, vm_pindex_t pindex, int domain,
      int req, vm_page_t mpred)
  {
          struct vm_domain *vmd;
          vm_page_t m;
          int flags, pool;
  
          KASSERT((object != NULL) == ((req & VM_ALLOC_NOOBJ) == 0) &&
              (object != NULL || (req & VM_ALLOC_SBUSY) == 0) &&
              ((req & (VM_ALLOC_NOBUSY | VM_ALLOC_SBUSY)) !=
              (VM_ALLOC_NOBUSY | VM_ALLOC_SBUSY)),
              ("inconsistent object(%p)/req(%x)", object, req));
          KASSERT(object == NULL || (req & VM_ALLOC_WAITOK) == 0,
              ("Can't sleep and retry object insertion."));
          KASSERT(mpred == NULL || mpred->pindex < pindex,
              ("mpred %p doesn't precede pindex 0x%jx", mpred,
              (uintmax_t)pindex));
          if (object != NULL)
                  VM_OBJECT_ASSERT_WLOCKED(object);
  
          flags = 0;
          m = NULL;
          pool = object != NULL ? VM_FREEPOOL_DEFAULT : VM_FREEPOOL_DIRECT;
  again:
  #if VM_NRESERVLEVEL > 0
          /*
           * Can we allocate the page from a reservation?
           */
          if (vm_object_reserv(object) &&
              (m = vm_reserv_alloc_page(object, pindex, domain, req, mpred)) !=
              NULL) {
                  goto found;
          }
  #endif
          vmd = VM_DOMAIN(domain);
          if (vmd->vmd_pgcache[pool].zone != NULL) {
                  m = uma_zalloc(vmd->vmd_pgcache[pool].zone, M_NOWAIT | M_NOVM);
                  if (m != NULL) {
                          flags |= PG_PCPU_CACHE;
                          goto found;
                  }
          }
          if (vm_domain_allocate(vmd, req, 1)) {
                  /*
                   * If not, allocate it from the free page queues.
                   */
                  vm_domain_free_lock(vmd);
                  m = vm_phys_alloc_pages(domain, pool, 0);
                  vm_domain_free_unlock(vmd);
                  if (m == NULL) {
                          vm_domain_freecnt_inc(vmd, 1);
  #if VM_NRESERVLEVEL > 0
                          if (vm_reserv_reclaim_inactive(domain))
                                  goto again;
  #endif
                  }
          }
          if (m == NULL) {
                  /*
                   * Not allocatable, give up.
                   */
                  if (vm_domain_alloc_fail(vmd, object, req))
                          goto again;
                  return (NULL);
          }
  
          /*
           * At this point we had better have found a good page.
           */
  found:
          vm_page_dequeue(m);
          vm_page_alloc_check(m);
  
          /*
           * Initialize the page.  Only the PG_ZERO flag is inherited.
           */
          if ((req & VM_ALLOC_ZERO) != 0)
                  flags |= (m->flags & PG_ZERO);
          if ((req & VM_ALLOC_NODUMP) != 0)
                  flags |= PG_NODUMP;
          m->flags = flags;
          m->a.flags = 0;
          m->oflags = object == NULL || (object->flags & OBJ_UNMANAGED) != 0 ?
              VPO_UNMANAGED : 0;
          if ((req & (VM_ALLOC_NOBUSY | VM_ALLOC_NOOBJ | VM_ALLOC_SBUSY)) == 0)
                  m->busy_lock = VPB_CURTHREAD_EXCLUSIVE;
          else if ((req & VM_ALLOC_SBUSY) != 0)
                  m->busy_lock = VPB_SHARERS_WORD(1);
          else
                  m->busy_lock = VPB_UNBUSIED;
          if (req & VM_ALLOC_WIRED) {
                  vm_wire_add(1);
                  m->ref_count = 1;
          }
          m->a.act_count = 0;
  
          if (object != NULL) {
                  if (vm_page_insert_after(m, object, pindex, mpred)) {
                          if (req & VM_ALLOC_WIRED) {
                                  vm_wire_sub(1);
                                  m->ref_count = 0;
                          }
                          KASSERT(m->object == NULL, ("page %p has object", m));
                          m->oflags = VPO_UNMANAGED;
                          m->busy_lock = VPB_UNBUSIED;
                          /* Don't change PG_ZERO. */
                          vm_page_free_toq(m);
                          if (req & VM_ALLOC_WAITFAIL) {
                                  VM_OBJECT_WUNLOCK(object);
                                  vm_radix_wait();
                                  VM_OBJECT_WLOCK(object);
                          }
                          return (NULL);
                  }
  
                  /* Ignore device objects; the pager sets "memattr" for them. */
                  if (object->memattr != VM_MEMATTR_DEFAULT &&
                      (object->flags & OBJ_FICTITIOUS) == 0)
                          pmap_page_set_memattr(m, object->memattr);
          } else
                  m->pindex = pindex;
  
          return (m);
  }
  
  /*
   *      vm_page_alloc_contig:
   *
   *      Allocate a contiguous set of physical pages of the given size "npages"
   *      from the free lists.  All of the physical pages must be at or above
   *      the given physical address "low" and below the given physical address
   *      "high".  The given value "alignment" determines the alignment of the
   *      first physical page in the set.  If the given value "boundary" is
   *      non-zero, then the set of physical pages cannot cross any physical
   *      address boundary that is a multiple of that value.  Both "alignment"
   *      and "boundary" must be a power of two.
   *
   *      If the specified memory attribute, "memattr", is VM_MEMATTR_DEFAULT,
   *      then the memory attribute setting for the physical pages is configured
   *      to the object's memory attribute setting.  Otherwise, the memory
   *      attribute setting for the physical pages is configured to "memattr",
   *      overriding the object's memory attribute setting.  However, if the
   *      object's memory attribute setting is not VM_MEMATTR_DEFAULT, then the
   *      memory attribute setting for the physical pages cannot be configured
   *      to VM_MEMATTR_DEFAULT.
   *
   *      The specified object may not contain fictitious pages.
   *
   *      The caller must always specify an allocation class.
   *
   *      allocation classes:
   *      VM_ALLOC_NORMAL         normal process request
   *      VM_ALLOC_SYSTEM         system *really* needs a page
   *      VM_ALLOC_INTERRUPT      interrupt time request
   *
   *      optional allocation flags:
   *      VM_ALLOC_NOBUSY         do not exclusive busy the page
   *      VM_ALLOC_NODUMP         do not include the page in a kernel core dump
   *      VM_ALLOC_NOOBJ          page is not associated with an object and
   *                              should not be exclusive busy
   *      VM_ALLOC_SBUSY          shared busy the allocated page
   *      VM_ALLOC_WIRED          wire the allocated page
   *      VM_ALLOC_ZERO           prefer a zeroed page
   */
  vm_page_t
  vm_page_alloc_contig(vm_object_t object, vm_pindex_t pindex, int req,
      u_long npages, vm_paddr_t low, vm_paddr_t high, u_long alignment,
      vm_paddr_t boundary, vm_memattr_t memattr)
  {
          struct vm_domainset_iter di;
          vm_page_t m;
          int domain;
  
          vm_domainset_iter_page_init(&di, object, pindex, &domain, &req);
          do {
                  m = vm_page_alloc_contig_domain(object, pindex, domain, req,
                      npages, low, high, alignment, boundary, memattr);
                  if (m != NULL)
                          break;
          } while (vm_domainset_iter_page(&di, object, &domain) == 0);
  
          return (m);
  }
  
  vm_page_t
  vm_page_alloc_contig_domain(vm_object_t object, vm_pindex_t pindex, int domain,
      int req, u_long npages, vm_paddr_t low, vm_paddr_t high, u_long alignment,
      vm_paddr_t boundary, vm_memattr_t memattr)
  {
          struct vm_domain *vmd;
          vm_page_t m, m_ret, mpred;
          u_int busy_lock, flags, oflags;
  
          mpred = NULL;   /* XXX: pacify gcc */
          KASSERT((object != NULL) == ((req & VM_ALLOC_NOOBJ) == 0) &&
              (object != NULL || (req & VM_ALLOC_SBUSY) == 0) &&
              ((req & (VM_ALLOC_NOBUSY | VM_ALLOC_SBUSY)) !=
              (VM_ALLOC_NOBUSY | VM_ALLOC_SBUSY)),
              ("vm_page_alloc_contig: inconsistent object(%p)/req(%x)", object,
              req));
          KASSERT(object == NULL || (req & VM_ALLOC_WAITOK) == 0,
              ("Can't sleep and retry object insertion."));
          if (object != NULL) {
                  VM_OBJECT_ASSERT_WLOCKED(object);
                  KASSERT((object->flags & OBJ_FICTITIOUS) == 0,
                      ("vm_page_alloc_contig: object %p has fictitious pages",
                      object));
          }
          KASSERT(npages > 0, ("vm_page_alloc_contig: npages is zero"));
  
          if (object != NULL) {
                  mpred = vm_radix_lookup_le(&object->rtree, pindex);
                  KASSERT(mpred == NULL || mpred->pindex != pindex,
                      ("vm_page_alloc_contig: pindex already allocated"));
          }
  
          /*
           * Can we allocate the pages without the number of free pages falling
           * below the lower bound for the allocation class?
           */
          m_ret = NULL;
  again:
  #if VM_NRESERVLEVEL > 0
          /*
           * Can we allocate the pages from a reservation?
           */
          if (vm_object_reserv(object) &&
              (m_ret = vm_reserv_alloc_contig(object, pindex, domain, req,
              mpred, npages, low, high, alignment, boundary)) != NULL) {
                  goto found;
          }
  #endif
          vmd = VM_DOMAIN(domain);
          if (vm_domain_allocate(vmd, req, npages)) {
                  /*
                   * allocate them from the free page queues.
                   */
                  vm_domain_free_lock(vmd);
                  m_ret = vm_phys_alloc_contig(domain, npages, low, high,
                      alignment, boundary);
                  vm_domain_free_unlock(vmd);
                  if (m_ret == NULL) {
                          vm_domain_freecnt_inc(vmd, npages);
  #if VM_NRESERVLEVEL > 0
                          if (vm_reserv_reclaim_contig(domain, npages, low,
                              high, alignment, boundary))
                                  goto again;
  #endif
                  }
          }
          if (m_ret == NULL) {
                  if (vm_domain_alloc_fail(vmd, object, req))
                          goto again;
                  return (NULL);
          }
  #if VM_NRESERVLEVEL > 0
  found:
  #endif
          for (m = m_ret; m < &m_ret[npages]; m++) {
                  vm_page_dequeue(m);
                  vm_page_alloc_check(m);
          }
  
          /*
           * Initialize the pages.  Only the PG_ZERO flag is inherited.
           */
          flags = 0;
          if ((req & VM_ALLOC_ZERO) != 0)
                  flags = PG_ZERO;
          if ((req & VM_ALLOC_NODUMP) != 0)
                  flags |= PG_NODUMP;
          oflags = object == NULL || (object->flags & OBJ_UNMANAGED) != 0 ?
              VPO_UNMANAGED : 0;
          if ((req & (VM_ALLOC_NOBUSY | VM_ALLOC_NOOBJ | VM_ALLOC_SBUSY)) == 0)
                  busy_lock = VPB_CURTHREAD_EXCLUSIVE;
          else if ((req & VM_ALLOC_SBUSY) != 0)
                  busy_lock = VPB_SHARERS_WORD(1);
          else
                  busy_lock = VPB_UNBUSIED;
          if ((req & VM_ALLOC_WIRED) != 0)
                  vm_wire_add(npages);
          if (object != NULL) {
                  if (object->memattr != VM_MEMATTR_DEFAULT &&
                      memattr == VM_MEMATTR_DEFAULT)
                          memattr = object->memattr;
          }
          for (m = m_ret; m < &m_ret[npages]; m++) {
                  m->a.flags = 0;
                  m->flags = (m->flags | PG_NODUMP) & flags;
                  m->busy_lock = busy_lock;
                  if ((req & VM_ALLOC_WIRED) != 0)
                          m->ref_count = 1;
                  m->a.act_count = 0;
                  m->oflags = oflags;
                  if (object != NULL) {
                          if (vm_page_insert_after(m, object, pindex, mpred)) {
                                  if ((req & VM_ALLOC_WIRED) != 0)
                                          vm_wire_sub(npages);
                                  KASSERT(m->object == NULL,
                                      ("page %p has object", m));
                                  mpred = m;
                                  for (m = m_ret; m < &m_ret[npages]; m++) {
                                          if (m <= mpred &&
                                              (req & VM_ALLOC_WIRED) != 0)
                                                  m->ref_count = 0;
                                          m->oflags = VPO_UNMANAGED;
                                          m->busy_lock = VPB_UNBUSIED;
                                          /* Don't change PG_ZERO. */
                                          vm_page_free_toq(m);
                                  }
                                  if (req & VM_ALLOC_WAITFAIL) {
                                          VM_OBJECT_WUNLOCK(object);
                                          vm_radix_wait();
                                          VM_OBJECT_WLOCK(object);
                                  }
                                  return (NULL);
                          }
                          mpred = m;
                  } else
                          m->pindex = pindex;
                  if (memattr != VM_MEMATTR_DEFAULT)
                          pmap_page_set_memattr(m, memattr);
                  pindex++;
          }
          return (m_ret);
  }
  
  /*
   * Check a page that has been freshly dequeued from a freelist.
   */
  static void
  vm_page_alloc_check(vm_page_t m)
  {
  
          KASSERT(m->object == NULL, ("page %p has object", m));
          KASSERT(m->a.queue == PQ_NONE &&
              (m->a.flags & PGA_QUEUE_STATE_MASK) == 0,
              ("page %p has unexpected queue %d, flags %#x",
              m, m->a.queue, (m->a.flags & PGA_QUEUE_STATE_MASK)));
          KASSERT(m->ref_count == 0, ("page %p has references", m));
          KASSERT(vm_page_busy_freed(m), ("page %p is not freed", m));
          KASSERT(m->dirty == 0, ("page %p is dirty", m));
          KASSERT(pmap_page_get_memattr(m) == VM_MEMATTR_DEFAULT,
              ("page %p has unexpected memattr %d",
              m, pmap_page_get_memattr(m)));
          KASSERT(m->valid == 0, ("free page %p is valid", m));
  }
  
  /*
   *      vm_page_alloc_freelist:
   *
   *      Allocate a physical page from the specified free page list.
   *
   *      The caller must always specify an allocation class.
   *
   *      allocation classes:
   *      VM_ALLOC_NORMAL         normal process request
   *      VM_ALLOC_SYSTEM         system *really* needs a page
   *      VM_ALLOC_INTERRUPT      interrupt time request
   *
   *      optional allocation flags:
   *      VM_ALLOC_COUNT(number)  the number of additional pages that the caller
   *                              intends to allocate
   *      VM_ALLOC_WIRED          wire the allocated page
   *      VM_ALLOC_ZERO           prefer a zeroed page
   */
  vm_page_t
  vm_page_alloc_freelist(int freelist, int req)
  {
          struct vm_domainset_iter di;
          vm_page_t m;
          int domain;
  
          vm_domainset_iter_page_init(&di, NULL, 0, &domain, &req);
          do {
                  m = vm_page_alloc_freelist_domain(domain, freelist, req);
                  if (m != NULL)
                          break;
          } while (vm_domainset_iter_page(&di, NULL, &domain) == 0);
  
          return (m);
  }
  
  vm_page_t
  vm_page_alloc_freelist_domain(int domain, int freelist, int req)
  {
          struct vm_domain *vmd;
          vm_page_t m;
          u_int flags;
  
          m = NULL;
          vmd = VM_DOMAIN(domain);
  again:
          if (vm_domain_allocate(vmd, req, 1)) {
                  vm_domain_free_lock(vmd);
                  m = vm_phys_alloc_freelist_pages(domain, freelist,
                      VM_FREEPOOL_DIRECT, 0);
                  vm_domain_free_unlock(vmd);
                  if (m == NULL)
                          vm_domain_freecnt_inc(vmd, 1);
          }
          if (m == NULL) {
                  if (vm_domain_alloc_fail(vmd, NULL, req))
                          goto again;
                  return (NULL);
          }
          vm_page_dequeue(m);
          vm_page_alloc_check(m);
  
          /*
           * Initialize the page.  Only the PG_ZERO flag is inherited.
           */
          m->a.flags = 0;
          flags = 0;
          if ((req & VM_ALLOC_ZERO) != 0)
                  flags = PG_ZERO;
          m->flags &= flags;
          if ((req & VM_ALLOC_WIRED) != 0) {
                  vm_wire_add(1);
                  m->ref_count = 1;
          }
          /* Unmanaged pages don't use "act_count". */
          m->oflags = VPO_UNMANAGED;
          return (m);
  }
  
  static int
  vm_page_zone_import(void *arg, void **store, int cnt, int domain, int flags)
  {
          struct vm_domain *vmd;
          struct vm_pgcache *pgcache;
          int i;
  
          pgcache = arg;
          vmd = VM_DOMAIN(pgcache->domain);
  
          /*
           * The page daemon should avoid creating extra memory pressure since its
           * main purpose is to replenish the store of free pages.
           */
          if (vmd->vmd_severeset || curproc == pageproc ||
              !_vm_domain_allocate(vmd, VM_ALLOC_NORMAL, cnt))
                  return (0);
          domain = vmd->vmd_domain;
          vm_domain_free_lock(vmd);
          i = vm_phys_alloc_npages(domain, pgcache->pool, cnt,
              (vm_page_t *)store);
          vm_domain_free_unlock(vmd);
          if (cnt != i)
                  vm_domain_freecnt_inc(vmd, cnt - i);
  
          return (i);
  }
  
  static void
  vm_page_zone_release(void *arg, void **store, int cnt)
  {
          struct vm_domain *vmd;
          struct vm_pgcache *pgcache;
          vm_page_t m;
          int i;
  
          pgcache = arg;
          vmd = VM_DOMAIN(pgcache->domain);
          vm_domain_free_lock(vmd);
          for (i = 0; i < cnt; i++) {
                  m = (vm_page_t)store[i];
                  vm_phys_free_pages(m, 0);
          }
          vm_domain_free_unlock(vmd);
          vm_domain_freecnt_inc(vmd, cnt);
  }
  
  #define VPSC_ANY        0       /* No restrictions. */
  #define VPSC_NORESERV   1       /* Skip reservations; implies VPSC_NOSUPER. */
  #define VPSC_NOSUPER    2       /* Skip superpages. */
  
  /*
   *      vm_page_scan_contig:
   *
   *      Scan vm_page_array[] between the specified entries "m_start" and
   *      "m_end" for a run of contiguous physical pages that satisfy the
   *      specified conditions, and return the lowest page in the run.  The
   *      specified "alignment" determines the alignment of the lowest physical
   *      page in the run.  If the specified "boundary" is non-zero, then the
   *      run of physical pages cannot span a physical address that is a
   *      multiple of "boundary".
   *
   *      "m_end" is never dereferenced, so it need not point to a vm_page
   *      structure within vm_page_array[].
   *
   *      "npages" must be greater than zero.  "m_start" and "m_end" must not
   *      span a hole (or discontiguity) in the physical address space.  Both
   *      "alignment" and "boundary" must be a power of two.
   */
  vm_page_t
  vm_page_scan_contig(u_long npages, vm_page_t m_start, vm_page_t m_end,
      u_long alignment, vm_paddr_t boundary, int options)
  {
          vm_object_t object;
          vm_paddr_t pa;
          vm_page_t m, m_run;
  #if VM_NRESERVLEVEL > 0
          int level;
  #endif
          int m_inc, order, run_ext, run_len;
  
          KASSERT(npages > 0, ("npages is 0"));
          KASSERT(powerof2(alignment), ("alignment is not a power of 2"));
          KASSERT(powerof2(boundary), ("boundary is not a power of 2"));
          m_run = NULL;
          run_len = 0;
          for (m = m_start; m < m_end && run_len < npages; m += m_inc) {
                  KASSERT((m->flags & PG_MARKER) == 0,
                      ("page %p is PG_MARKER", m));
                  KASSERT((m->flags & PG_FICTITIOUS) == 0 || m->ref_count >= 1,
                      ("fictitious page %p has invalid ref count", m));
  
                  /*
                   * If the current page would be the start of a run, check its
                   * physical address against the end, alignment, and boundary
                   * conditions.  If it doesn't satisfy these conditions, either
                   * terminate the scan or advance to the next page that
                   * satisfies the failed condition.
                   */
                  if (run_len == 0) {
                          KASSERT(m_run == NULL, ("m_run != NULL"));
                          if (m + npages > m_end)
                                  break;
                          pa = VM_PAGE_TO_PHYS(m);
                          if ((pa & (alignment - 1)) != 0) {
                                  m_inc = atop(roundup2(pa, alignment) - pa);
                                  continue;
                          }
                          if (rounddown2(pa ^ (pa + ptoa(npages) - 1),
                              boundary) != 0) {
                                  m_inc = atop(roundup2(pa, boundary) - pa);
                                  continue;
                          }
                  } else
                          KASSERT(m_run != NULL, ("m_run == NULL"));
  
  retry:
                  m_inc = 1;
                  if (vm_page_wired(m))
                          run_ext = 0;
  #if VM_NRESERVLEVEL > 0
                  else if ((level = vm_reserv_level(m)) >= 0 &&
                      (options & VPSC_NORESERV) != 0) {
                          run_ext = 0;
                          /* Advance to the end of the reservation. */
                          pa = VM_PAGE_TO_PHYS(m);
                          m_inc = atop(roundup2(pa + 1, vm_reserv_size(level)) -
                              pa);
                  }
  #endif
                  else if ((object = atomic_load_ptr(&m->object)) != NULL) {
                          /*
                           * The page is considered eligible for relocation if
                           * and only if it could be laundered or reclaimed by
                           * the page daemon.
                           */
                          VM_OBJECT_RLOCK(object);
                          if (object != m->object) {
                                  VM_OBJECT_RUNLOCK(object);
                                  goto retry;
                          }
                          /* Don't care: PG_NODUMP, PG_ZERO. */
                          if (object->type != OBJT_DEFAULT &&
                              object->type != OBJT_SWAP &&
                              object->type != OBJT_VNODE) {
                                  run_ext = 0;
  #if VM_NRESERVLEVEL > 0
                          } else if ((options & VPSC_NOSUPER) != 0 &&
                              (level = vm_reserv_level_iffullpop(m)) >= 0) {
                                  run_ext = 0;
                                  /* Advance to the end of the superpage. */
                                  pa = VM_PAGE_TO_PHYS(m);
                                  m_inc = atop(roundup2(pa + 1,
                                      vm_reserv_size(level)) - pa);
  #endif
                          } else if (object->memattr == VM_MEMATTR_DEFAULT &&
                              vm_page_queue(m) != PQ_NONE && !vm_page_busied(m)) {
                                  /*
                                   * The page is allocated but eligible for
                                   * relocation.  Extend the current run by one
                                   * page.
                                   */
                                  KASSERT(pmap_page_get_memattr(m) ==
                                      VM_MEMATTR_DEFAULT,
                                      ("page %p has an unexpected memattr", m));
                                  KASSERT((m->oflags & (VPO_SWAPINPROG |
                                      VPO_SWAPSLEEP | VPO_UNMANAGED)) == 0,
                                      ("page %p has unexpected oflags", m));
                                  /* Don't care: PGA_NOSYNC. */
                                  run_ext = 1;
                          } else
                                  run_ext = 0;
                          VM_OBJECT_RUNLOCK(object);
  #if VM_NRESERVLEVEL > 0
                  } else if (level >= 0) {
                          /*
                           * The page is reserved but not yet allocated.  In
                           * other words, it is still free.  Extend the current
                           * run by one page.
                           */
                          run_ext = 1;
  #endif
                  } else if ((order = m->order) < VM_NFREEORDER) {
                          /*
                           * The page is enqueued in the physical memory
                           * allocator's free page queues.  Moreover, it is the
                           * first page in a power-of-two-sized run of
                           * contiguous free pages.  Add these pages to the end
                           * of the current run, and jump ahead.
                           */
                          run_ext = 1 << order;
                          m_inc = 1 << order;
                  } else {
                          /*
                           * Skip the page for one of the following reasons: (1)
                           * It is enqueued in the physical memory allocator's
                           * free page queues.  However, it is not the first
                           * page in a run of contiguous free pages.  (This case
                           * rarely occurs because the scan is performed in
                           * ascending order.) (2) It is not reserved, and it is
                           * transitioning from free to allocated.  (Conversely,
                           * the transition from allocated to free for managed
                           * pages is blocked by the page busy lock.) (3) It is
                           * allocated but not contained by an object and not
                           * wired, e.g., allocated by Xen's balloon driver.
                           */
                          run_ext = 0;
                  }
  
                  /*
                   * Extend or reset the current run of pages.
                   */
                  if (run_ext > 0) {
                          if (run_len == 0)
                                  m_run = m;
                          run_len += run_ext;
                  } else {
                          if (run_len > 0) {
                                  m_run = NULL;
                                  run_len = 0;
                          }
                  }
          }
          if (run_len >= npages)
                  return (m_run);
          return (NULL);
  }
  
  /*
   *      vm_page_reclaim_run:
   *
   *      Try to relocate each of the allocated virtual pages within the
   *      specified run of physical pages to a new physical address.  Free the
   *      physical pages underlying the relocated virtual pages.  A virtual page
   *      is relocatable if and only if it could be laundered or reclaimed by
   *      the page daemon.  Whenever possible, a virtual page is relocated to a
   *      physical address above "high".
   *
   *      Returns 0 if every physical page within the run was already free or
   *      just freed by a successful relocation.  Otherwise, returns a non-zero
   *      value indicating why the last attempt to relocate a virtual page was
   *      unsuccessful.
   *
   *      "req_class" must be an allocation class.
   */
  static int
  vm_page_reclaim_run(int req_class, int domain, u_long npages, vm_page_t m_run,
      vm_paddr_t high)
  {
          struct vm_domain *vmd;
          struct spglist free;
          vm_object_t object;
          vm_paddr_t pa;
          vm_page_t m, m_end, m_new;
          int error, order, req;
  
          KASSERT((req_class & VM_ALLOC_CLASS_MASK) == req_class,
              ("req_class is not an allocation class"));
          SLIST_INIT(&free);
          error = 0;
          m = m_run;
          m_end = m_run + npages;
          for (; error == 0 && m < m_end; m++) {
                  KASSERT((m->flags & (PG_FICTITIOUS | PG_MARKER)) == 0,
                      ("page %p is PG_FICTITIOUS or PG_MARKER", m));
  
                  /*
                   * Racily check for wirings.  Races are handled once the object
                   * lock is held and the page is unmapped.
                   */
                  if (vm_page_wired(m))
                          error = EBUSY;
                  else if ((object = atomic_load_ptr(&m->object)) != NULL) {
                          /*
                           * The page is relocated if and only if it could be
                           * laundered or reclaimed by the page daemon.
                           */
                          VM_OBJECT_WLOCK(object);
                          /* Don't care: PG_NODUMP, PG_ZERO. */
                          if (m->object != object ||
                              (object->type != OBJT_DEFAULT &&
                              object->type != OBJT_SWAP &&
                              object->type != OBJT_VNODE))
                                  error = EINVAL;
                          else if (object->memattr != VM_MEMATTR_DEFAULT)
                                  error = EINVAL;
                          else if (vm_page_queue(m) != PQ_NONE &&
                              vm_page_tryxbusy(m) != 0) {
                                  if (vm_page_wired(m)) {
                                          vm_page_xunbusy(m);
                                          error = EBUSY;
                                          goto unlock;
                                  }
                                  KASSERT(pmap_page_get_memattr(m) ==
                                      VM_MEMATTR_DEFAULT,
                                      ("page %p has an unexpected memattr", m));
                                  KASSERT(m->oflags == 0,
                                      ("page %p has unexpected oflags", m));
                                  /* Don't care: PGA_NOSYNC. */
                                  if (!vm_page_none_valid(m)) {
                                          /*
                                           * First, try to allocate a new page
                                           * that is above "high".  Failing
                                           * that, try to allocate a new page
                                           * that is below "m_run".  Allocate
                                           * the new page between the end of
                                           * "m_run" and "high" only as a last
                                           * resort.
                                           */
                                          req = req_class | VM_ALLOC_NOOBJ;
                                          if ((m->flags & PG_NODUMP) != 0)
                                                  req |= VM_ALLOC_NODUMP;
                                          if (trunc_page(high) !=
                                              ~(vm_paddr_t)PAGE_MASK) {
                                                  m_new = vm_page_alloc_contig(
                                                      NULL, 0, req, 1,
                                                      round_page(high),
                                                      ~(vm_paddr_t)0,
                                                      PAGE_SIZE, 0,
                                                      VM_MEMATTR_DEFAULT);
                                          } else
                                                  m_new = NULL;
                                          if (m_new == NULL) {
                                                  pa = VM_PAGE_TO_PHYS(m_run);
                                                  m_new = vm_page_alloc_contig(
                                                      NULL, 0, req, 1,
                                                      0, pa - 1, PAGE_SIZE, 0,
                                                      VM_MEMATTR_DEFAULT);
                                          }
                                          if (m_new == NULL) {
                                                  pa += ptoa(npages);
                                                  m_new = vm_page_alloc_contig(
                                                      NULL, 0, req, 1,
                                                      pa, high, PAGE_SIZE, 0,
                                                      VM_MEMATTR_DEFAULT);
                                          }
                                          if (m_new == NULL) {
                                                  vm_page_xunbusy(m);
                                                  error = ENOMEM;
                                                  goto unlock;
                                          }
  
                                          /*
                                           * Unmap the page and check for new
                                           * wirings that may have been acquired
                                           * through a pmap lookup.
                                           */
                                          if (object->ref_count != 0 &&
                                              !vm_page_try_remove_all(m)) {
                                                  vm_page_xunbusy(m);
                                                  vm_page_free(m_new);
                                                  error = EBUSY;
                                                  goto unlock;
                                          }
  
                                          /*
                                           * Replace "m" with the new page.  For
                                           * vm_page_replace(), "m" must be busy
                                           * and dequeued.  Finally, change "m"
                                           * as if vm_page_free() was called.
                                           */
                                          m_new->a.flags = m->a.flags &
                                              ~PGA_QUEUE_STATE_MASK;
                                          KASSERT(m_new->oflags == VPO_UNMANAGED,
                                              ("page %p is managed", m_new));
                                          m_new->oflags = 0;
                                          pmap_copy_page(m, m_new);
                                          m_new->valid = m->valid;
                                          m_new->dirty = m->dirty;
                                          m->flags &= ~PG_ZERO;
                                          vm_page_dequeue(m);
                                          if (vm_page_replace_hold(m_new, object,
                                              m->pindex, m) &&
                                              vm_page_free_prep(m))
                                                  SLIST_INSERT_HEAD(&free, m,
                                                      plinks.s.ss);
  
                                          /*
                                           * The new page must be deactivated
                                           * before the object is unlocked.
                                           */
                                          vm_page_deactivate(m_new);
                                  } else {
                                          m->flags &= ~PG_ZERO;
                                          vm_page_dequeue(m);
                                          if (vm_page_free_prep(m))
                                                  SLIST_INSERT_HEAD(&free, m,
                                                      plinks.s.ss);
                                          KASSERT(m->dirty == 0,
                                              ("page %p is dirty", m));
                                  }
                          } else
                                  error = EBUSY;
  unlock:
                          VM_OBJECT_WUNLOCK(object);
                  } else {
                          MPASS(vm_page_domain(m) == domain);
                          vmd = VM_DOMAIN(domain);
                          vm_domain_free_lock(vmd);
                          order = m->order;
                          if (order < VM_NFREEORDER) {
                                  /*
                                   * The page is enqueued in the physical memory
                                   * allocator's free page queues.  Moreover, it
                                   * is the first page in a power-of-two-sized
                                   * run of contiguous free pages.  Jump ahead
                                   * to the last page within that run, and
                                   * continue from there.
                                   */
                                  m += (1 << order) - 1;
                          }
  #if VM_NRESERVLEVEL > 0
                          else if (vm_reserv_is_page_free(m))
                                  order = 0;
  #endif
                          vm_domain_free_unlock(vmd);
                          if (order == VM_NFREEORDER)
                                  error = EINVAL;
                  }
          }
          if ((m = SLIST_FIRST(&free)) != NULL) {
                  int cnt;
  
                  vmd = VM_DOMAIN(domain);
                  cnt = 0;
                  vm_domain_free_lock(vmd);
                  do {
                          MPASS(vm_page_domain(m) == domain);
                          SLIST_REMOVE_HEAD(&free, plinks.s.ss);
                          vm_phys_free_pages(m, 0);
                          cnt++;
                  } while ((m = SLIST_FIRST(&free)) != NULL);
                  vm_domain_free_unlock(vmd);
                  vm_domain_freecnt_inc(vmd, cnt);
          }
          return (error);
  }
  
  #define NRUNS   16
  
  CTASSERT(powerof2(NRUNS));
  
  #define RUN_INDEX(count)        ((count) & (NRUNS - 1))
  
  #define MIN_RECLAIM     8
  
  /*
   *      vm_page_reclaim_contig:
   *
   *      Reclaim allocated, contiguous physical memory satisfying the specified
   *      conditions by relocating the virtual pages using that physical memory.
   *      Returns true if reclamation is successful and false otherwise.  Since
   *      relocation requires the allocation of physical pages, reclamation may
   *      fail due to a shortage of free pages.  When reclamation fails, callers
   *      are expected to perform vm_wait() before retrying a failed allocation
   *      operation, e.g., vm_page_alloc_contig().
   *
   *      The caller must always specify an allocation class through "req".
   *
   *      allocation classes:
   *      VM_ALLOC_NORMAL         normal process request
   *      VM_ALLOC_SYSTEM         system *really* needs a page
   *      VM_ALLOC_INTERRUPT      interrupt time request
   *
   *      The optional allocation flags are ignored.
   *
   *      "npages" must be greater than zero.  Both "alignment" and "boundary"
   *      must be a power of two.
   */
  bool
  vm_page_reclaim_contig_domain(int domain, int req, u_long npages,
      vm_paddr_t low, vm_paddr_t high, u_long alignment, vm_paddr_t boundary)
  {
          struct vm_domain *vmd;
          vm_paddr_t curr_low;
          vm_page_t m_run, m_runs[NRUNS];
          u_long count, reclaimed;
          int error, i, options, req_class;
  
          KASSERT(npages > 0, ("npages is 0"));
          KASSERT(powerof2(alignment), ("alignment is not a power of 2"));
          KASSERT(powerof2(boundary), ("boundary is not a power of 2"));
          req_class = req & VM_ALLOC_CLASS_MASK;
  
          /*
           * The page daemon is allowed to dig deeper into the free page list.
           */
          if (curproc == pageproc && req_class != VM_ALLOC_INTERRUPT)
                  req_class = VM_ALLOC_SYSTEM;
  
          /*
           * Return if the number of free pages cannot satisfy the requested
           * allocation.
           */
          vmd = VM_DOMAIN(domain);
          count = vmd->vmd_free_count;
          if (count < npages + vmd->vmd_free_reserved || (count < npages +
              vmd->vmd_interrupt_free_min && req_class == VM_ALLOC_SYSTEM) ||
              (count < npages && req_class == VM_ALLOC_INTERRUPT))
                  return (false);
  
          /*
           * Scan up to three times, relaxing the restrictions ("options") on
           * the reclamation of reservations and superpages each time.
           */
          for (options = VPSC_NORESERV;;) {
                  /*
                   * Find the highest runs that satisfy the given constraints
                   * and restrictions, and record them in "m_runs".
                   */
                  curr_low = low;
                  count = 0;
                  for (;;) {
                          m_run = vm_phys_scan_contig(domain, npages, curr_low,
                              high, alignment, boundary, options);
                          if (m_run == NULL)
                                  break;
                          curr_low = VM_PAGE_TO_PHYS(m_run) + ptoa(npages);
                          m_runs[RUN_INDEX(count)] = m_run;
                          count++;
                  }
  
                  /*
                   * Reclaim the highest runs in LIFO (descending) order until
                   * the number of reclaimed pages, "reclaimed", is at least
                   * MIN_RECLAIM.  Reset "reclaimed" each time because each
                   * reclamation is idempotent, and runs will (likely) recur
                   * from one scan to the next as restrictions are relaxed.
                   */
                  reclaimed = 0;
                  for (i = 0; count > 0 && i < NRUNS; i++) {
                          count--;
                          m_run = m_runs[RUN_INDEX(count)];
                          error = vm_page_reclaim_run(req_class, domain, npages,
                              m_run, high);
                          if (error == 0) {
                                  reclaimed += npages;
                                  if (reclaimed >= MIN_RECLAIM)
                                          return (true);
                          }
                  }
  
                  /*
                   * Either relax the restrictions on the next scan or return if
                   * the last scan had no restrictions.
                   */
                  if (options == VPSC_NORESERV)
                          options = VPSC_NOSUPER;
                  else if (options == VPSC_NOSUPER)
                          options = VPSC_ANY;
                  else if (options == VPSC_ANY)
                          return (reclaimed != 0);
          }
  }
  
  bool
  vm_page_reclaim_contig(int req, u_long npages, vm_paddr_t low, vm_paddr_t high,
      u_long alignment, vm_paddr_t boundary)
  {
          struct vm_domainset_iter di;
          int domain;
          bool ret;
  
          vm_domainset_iter_page_init(&di, NULL, 0, &domain, &req);
          do {
                  ret = vm_page_reclaim_contig_domain(domain, req, npages, low,
                      high, alignment, boundary);
                  if (ret)
                          break;
          } while (vm_domainset_iter_page(&di, NULL, &domain) == 0);
  
          return (ret);
  }
  
  /*
   * Set the domain in the appropriate page level domainset.
   */
  void
  vm_domain_set(struct vm_domain *vmd)
  {
  
          mtx_lock(&vm_domainset_lock);
          if (!vmd->vmd_minset && vm_paging_min(vmd)) {
                  vmd->vmd_minset = 1;
                  DOMAINSET_SET(vmd->vmd_domain, &vm_min_domains);
          }
          if (!vmd->vmd_severeset && vm_paging_severe(vmd)) {
                  vmd->vmd_severeset = 1;
                  DOMAINSET_SET(vmd->vmd_domain, &vm_severe_domains);
          }
          mtx_unlock(&vm_domainset_lock);
  }
  
  /*
   * Clear the domain from the appropriate page level domainset.
   */
  void
  vm_domain_clear(struct vm_domain *vmd)
  {
  
          mtx_lock(&vm_domainset_lock);
          if (vmd->vmd_minset && !vm_paging_min(vmd)) {
                  vmd->vmd_minset = 0;
                  DOMAINSET_CLR(vmd->vmd_domain, &vm_min_domains);
                  if (vm_min_waiters != 0) {
                          vm_min_waiters = 0;
                          wakeup(&vm_min_domains);
                  }
          }
          if (vmd->vmd_severeset && !vm_paging_severe(vmd)) {
                  vmd->vmd_severeset = 0;
                  DOMAINSET_CLR(vmd->vmd_domain, &vm_severe_domains);
                  if (vm_severe_waiters != 0) {
                          vm_severe_waiters = 0;
                          wakeup(&vm_severe_domains);
                  }
          }
  
          /*
           * If pageout daemon needs pages, then tell it that there are
           * some free.
           */
          if (vmd->vmd_pageout_pages_needed &&
              vmd->vmd_free_count >= vmd->vmd_pageout_free_min) {
                  wakeup(&vmd->vmd_pageout_pages_needed);
                  vmd->vmd_pageout_pages_needed = 0;
          }
  
          /* See comments in vm_wait_doms(). */
          if (vm_pageproc_waiters) {
                  vm_pageproc_waiters = 0;
                  wakeup(&vm_pageproc_waiters);
          }
          mtx_unlock(&vm_domainset_lock);
  }
  
  /*
   * Wait for free pages to exceed the min threshold globally.
   */
  void
  vm_wait_min(void)
  {
  
          mtx_lock(&vm_domainset_lock);
          while (vm_page_count_min()) {
                  vm_min_waiters++;
                  msleep(&vm_min_domains, &vm_domainset_lock, PVM, "vmwait", 0);
          }
          mtx_unlock(&vm_domainset_lock);
  }
  
  /*
   * Wait for free pages to exceed the severe threshold globally.
   */
  void
  vm_wait_severe(void)
  {
  
          mtx_lock(&vm_domainset_lock);
          while (vm_page_count_severe()) {
                  vm_severe_waiters++;
                  msleep(&vm_severe_domains, &vm_domainset_lock, PVM,
                      "vmwait", 0);
          }
          mtx_unlock(&vm_domainset_lock);
  }
  
  u_int
  vm_wait_count(void)
  {
  
          return (vm_severe_waiters + vm_min_waiters + vm_pageproc_waiters);
  }
  
  int
  vm_wait_doms(const domainset_t *wdoms, int mflags)
  {
          int error;
  
          error = 0;
  
          /*
           * We use racey wakeup synchronization to avoid expensive global
           * locking for the pageproc when sleeping with a non-specific vm_wait.
           * To handle this, we only sleep for one tick in this instance.  It
           * is expected that most allocations for the pageproc will come from
           * kmem or vm_page_grab* which will use the more specific and
           * race-free vm_wait_domain().
           */
          if (curproc == pageproc) {
                  mtx_lock(&vm_domainset_lock);
                  vm_pageproc_waiters++;
                  error = msleep(&vm_pageproc_waiters, &vm_domainset_lock,
                      PVM | PDROP | mflags, "pageprocwait", 1);
          } else {
                  /*
                   * XXX Ideally we would wait only until the allocation could
                   * be satisfied.  This condition can cause new allocators to
                   * consume all freed pages while old allocators wait.
                   */
                  mtx_lock(&vm_domainset_lock);
                  if (vm_page_count_min_set(wdoms)) {
                          vm_min_waiters++;
                          error = msleep(&vm_min_domains, &vm_domainset_lock,
                              PVM | PDROP | mflags, "vmwait", 0);
                  } else
                          mtx_unlock(&vm_domainset_lock);
          }
          return (error);
  }
  
  /*
   *      vm_wait_domain:
   *
   *      Sleep until free pages are available for allocation.
   *      - Called in various places after failed memory allocations.
   */
  void
  vm_wait_domain(int domain)
  {
          struct vm_domain *vmd;
          domainset_t wdom;
  
          vmd = VM_DOMAIN(domain);
          vm_domain_free_assert_unlocked(vmd);
  
          if (curproc == pageproc) {
                  mtx_lock(&vm_domainset_lock);
                  if (vmd->vmd_free_count < vmd->vmd_pageout_free_min) {
                          vmd->vmd_pageout_pages_needed = 1;
                          msleep(&vmd->vmd_pageout_pages_needed,
                              &vm_domainset_lock, PDROP | PSWP, "VMWait", 0);
                  } else
                          mtx_unlock(&vm_domainset_lock);
          } else {
                  if (pageproc == NULL)
                          panic("vm_wait in early boot");
                  DOMAINSET_ZERO(&wdom);
                  DOMAINSET_SET(vmd->vmd_domain, &wdom);
                  vm_wait_doms(&wdom, 0);
          }
  }
  
  static int
  vm_wait_flags(vm_object_t obj, int mflags)
  {
          struct domainset *d;
  
          d = NULL;
  
          /*
           * Carefully fetch pointers only once: the struct domainset
           * itself is ummutable but the pointer might change.
           */
          if (obj != NULL)
                  d = obj->domain.dr_policy;
          if (d == NULL)
                  d = curthread->td_domain.dr_policy;
  
          return (vm_wait_doms(&d->ds_mask, mflags));
  }
  
  /*
   *      vm_wait:
   *
   *      Sleep until free pages are available for allocation in the
   *      affinity domains of the obj.  If obj is NULL, the domain set
   *      for the calling thread is used.
   *      Called in various places after failed memory allocations.
   */
  void
  vm_wait(vm_object_t obj)
  {
          (void)vm_wait_flags(obj, 0);
  }
  
  int
  vm_wait_intr(vm_object_t obj)
  {
          return (vm_wait_flags(obj, PCATCH));
  }
  
  /*
   *      vm_domain_alloc_fail:
   *
   *      Called when a page allocation function fails.  Informs the
   *      pagedaemon and performs the requested wait.  Requires the
   *      domain_free and object lock on entry.  Returns with the
   *      object lock held and free lock released.  Returns an error when
   *      retry is necessary.
   *
   */
  static int
  vm_domain_alloc_fail(struct vm_domain *vmd, vm_object_t object, int req)
  {
  
          vm_domain_free_assert_unlocked(vmd);
  
          atomic_add_int(&vmd->vmd_pageout_deficit,
              max((u_int)req >> VM_ALLOC_COUNT_SHIFT, 1));
          if (req & (VM_ALLOC_WAITOK | VM_ALLOC_WAITFAIL)) {
                  if (object != NULL) 
                          VM_OBJECT_WUNLOCK(object);
                  vm_wait_domain(vmd->vmd_domain);
                  if (object != NULL) 
                          VM_OBJECT_WLOCK(object);
                  if (req & VM_ALLOC_WAITOK)
                          return (EAGAIN);
          }
  
          return (0);
  }
  
  /*
   *      vm_waitpfault:
   *
   *      Sleep until free pages are available for allocation.
   *      - Called only in vm_fault so that processes page faulting
   *        can be easily tracked.
   *      - Sleeps at a lower priority than vm_wait() so that vm_wait()ing
   *        processes will be able to grab memory first.  Do not change
   *        this balance without careful testing first.
   */
  void
  vm_waitpfault(struct domainset *dset, int timo)
  {
  
          /*
           * XXX Ideally we would wait only until the allocation could
           * be satisfied.  This condition can cause new allocators to
           * consume all freed pages while old allocators wait.
           */
          mtx_lock(&vm_domainset_lock);
          if (vm_page_count_min_set(&dset->ds_mask)) {
                  vm_min_waiters++;
                  msleep(&vm_min_domains, &vm_domainset_lock, PUSER | PDROP,
                      "pfault", timo);
          } else
                  mtx_unlock(&vm_domainset_lock);
  }
  
  static struct vm_pagequeue *
  _vm_page_pagequeue(vm_page_t m, uint8_t queue)
  {
  
          return (&vm_pagequeue_domain(m)->vmd_pagequeues[queue]);
  }
  
  #ifdef INVARIANTS
  static struct vm_pagequeue *
  vm_page_pagequeue(vm_page_t m)
  {
  
          return (_vm_page_pagequeue(m, vm_page_astate_load(m).queue));
  }
  #endif
  
  static __always_inline bool
  vm_page_pqstate_fcmpset(vm_page_t m, vm_page_astate_t *old, vm_page_astate_t new)
  {
          vm_page_astate_t tmp;
  
          tmp = *old;
          do {
                  if (__predict_true(vm_page_astate_fcmpset(m, old, new)))
                          return (true);
                  counter_u64_add(pqstate_commit_retries, 1);
          } while (old->_bits == tmp._bits);
  
          return (false);
  }
  
  /*
   * Do the work of committing a queue state update that moves the page out of
   * its current queue.
   */
  static bool
  _vm_page_pqstate_commit_dequeue(struct vm_pagequeue *pq, vm_page_t m,
      vm_page_astate_t *old, vm_page_astate_t new)
  {
          vm_page_t next;
  
          vm_pagequeue_assert_locked(pq);
          KASSERT(vm_page_pagequeue(m) == pq,
              ("%s: queue %p does not match page %p", __func__, pq, m));
          KASSERT(old->queue != PQ_NONE && new.queue != old->queue,
              ("%s: invalid queue indices %d %d",
              __func__, old->queue, new.queue));
  
          /*
           * Once the queue index of the page changes there is nothing
           * synchronizing with further updates to the page's physical
           * queue state.  Therefore we must speculatively remove the page
           * from the queue now and be prepared to roll back if the queue
           * state update fails.  If the page is not physically enqueued then
           * we just update its queue index.
           */
          if ((old->flags & PGA_ENQUEUED) != 0) {
                  new.flags &= ~PGA_ENQUEUED;
                  next = TAILQ_NEXT(m, plinks.q);
                  TAILQ_REMOVE(&pq->pq_pl, m, plinks.q);
                  vm_pagequeue_cnt_dec(pq);
                  if (!vm_page_pqstate_fcmpset(m, old, new)) {
                          if (next == NULL)
                                  TAILQ_INSERT_TAIL(&pq->pq_pl, m, plinks.q);
                          else
                                  TAILQ_INSERT_BEFORE(next, m, plinks.q);
                          vm_pagequeue_cnt_inc(pq);
                          return (false);
                  } else {
                          return (true);
                  }
          } else {
                  return (vm_page_pqstate_fcmpset(m, old, new));
          }
  }
  
  static bool
  vm_page_pqstate_commit_dequeue(vm_page_t m, vm_page_astate_t *old,
      vm_page_astate_t new)
  {
          struct vm_pagequeue *pq;
          vm_page_astate_t as;
          bool ret;
  
          pq = _vm_page_pagequeue(m, old->queue);
  
          /*
           * The queue field and PGA_ENQUEUED flag are stable only so long as the
           * corresponding page queue lock is held.
           */
          vm_pagequeue_lock(pq);
          as = vm_page_astate_load(m);
          if (__predict_false(as._bits != old->_bits)) {
                  *old = as;
                  ret = false;
          } else {
                  ret = _vm_page_pqstate_commit_dequeue(pq, m, old, new);
          }
          vm_pagequeue_unlock(pq);
          return (ret);
  }
  
  /*
   * Commit a queue state update that enqueues or requeues a page.
   */
  static bool
  _vm_page_pqstate_commit_requeue(struct vm_pagequeue *pq, vm_page_t m,
      vm_page_astate_t *old, vm_page_astate_t new)
  {
          struct vm_domain *vmd;
  
          vm_pagequeue_assert_locked(pq);
          KASSERT(old->queue != PQ_NONE && new.queue == old->queue,
              ("%s: invalid queue indices %d %d",
              __func__, old->queue, new.queue));
  
          new.flags |= PGA_ENQUEUED;
          if (!vm_page_pqstate_fcmpset(m, old, new))
                  return (false);
  
          if ((old->flags & PGA_ENQUEUED) != 0)
                  TAILQ_REMOVE(&pq->pq_pl, m, plinks.q);
          else
                  vm_pagequeue_cnt_inc(pq);
  
          /*
           * Give PGA_REQUEUE_HEAD precedence over PGA_REQUEUE.  In particular, if
           * both flags are set in close succession, only PGA_REQUEUE_HEAD will be
           * applied, even if it was set first.
           */
          if ((old->flags & PGA_REQUEUE_HEAD) != 0) {
                  vmd = vm_pagequeue_domain(m);
                  KASSERT(pq == &vmd->vmd_pagequeues[PQ_INACTIVE],
                      ("%s: invalid page queue for page %p", __func__, m));
                  TAILQ_INSERT_BEFORE(&vmd->vmd_inacthead, m, plinks.q);
          } else {
                  TAILQ_INSERT_TAIL(&pq->pq_pl, m, plinks.q);
          }
          return (true);
  }
  
  /*
   * Commit a queue state update that encodes a request for a deferred queue
   * operation.
   */
  static bool
  vm_page_pqstate_commit_request(vm_page_t m, vm_page_astate_t *old,
      vm_page_astate_t new)
  {
  
          KASSERT(old->queue == new.queue || new.queue != PQ_NONE,
              ("%s: invalid state, queue %d flags %x",
              __func__, new.queue, new.flags));
  
          if (old->_bits != new._bits &&
              !vm_page_pqstate_fcmpset(m, old, new))
                  return (false);
          vm_page_pqbatch_submit(m, new.queue);
          return (true);
  }
  
  /*
   * A generic queue state update function.  This handles more cases than the
   * specialized functions above.
   */
  bool
  vm_page_pqstate_commit(vm_page_t m, vm_page_astate_t *old, vm_page_astate_t new)
  {
  
          if (old->_bits == new._bits)
                  return (true);
  
          if (old->queue != PQ_NONE && new.queue != old->queue) {
                  if (!vm_page_pqstate_commit_dequeue(m, old, new))
                          return (false);
                  if (new.queue != PQ_NONE)
                          vm_page_pqbatch_submit(m, new.queue);
          } else {
                  if (!vm_page_pqstate_fcmpset(m, old, new))
                          return (false);
                  if (new.queue != PQ_NONE &&
                      ((new.flags & ~old->flags) & PGA_QUEUE_OP_MASK) != 0)
                          vm_page_pqbatch_submit(m, new.queue);
          }
          return (true);
  }
  
  /*
   * Apply deferred queue state updates to a page.
   */
  static inline void
  vm_pqbatch_process_page(struct vm_pagequeue *pq, vm_page_t m, uint8_t queue)
  {
          vm_page_astate_t new, old;
  
          CRITICAL_ASSERT(curthread);
          vm_pagequeue_assert_locked(pq);
          KASSERT(queue < PQ_COUNT,
              ("%s: invalid queue index %d", __func__, queue));
          KASSERT(pq == _vm_page_pagequeue(m, queue),
              ("%s: page %p does not belong to queue %p", __func__, m, pq));
  
          for (old = vm_page_astate_load(m);;) {
                  if (__predict_false(old.queue != queue ||
                      (old.flags & PGA_QUEUE_OP_MASK) == 0)) {
                          counter_u64_add(queue_nops, 1);
                          break;
                  }
                  KASSERT(old.queue != PQ_NONE ||
                      (old.flags & PGA_QUEUE_STATE_MASK) == 0,
                      ("%s: page %p has unexpected queue state", __func__, m));
  
                  new = old;
                  if ((old.flags & PGA_DEQUEUE) != 0) {
                          new.flags &= ~PGA_QUEUE_OP_MASK;
                          new.queue = PQ_NONE;
                          if (__predict_true(_vm_page_pqstate_commit_dequeue(pq,
                              m, &old, new))) {
                                  counter_u64_add(queue_ops, 1);
                                  break;
                          }
                  } else {
                          new.flags &= ~(PGA_REQUEUE | PGA_REQUEUE_HEAD);
                          if (__predict_true(_vm_page_pqstate_commit_requeue(pq,
                              m, &old, new))) {
                                  counter_u64_add(queue_ops, 1);
                                  break;
                          }
                  }
          }
  }
  
  static void
  vm_pqbatch_process(struct vm_pagequeue *pq, struct vm_batchqueue *bq,
      uint8_t queue)
  {
          int i;
  
          for (i = 0; i < bq->bq_cnt; i++)
                  vm_pqbatch_process_page(pq, bq->bq_pa[i], queue);
          vm_batchqueue_init(bq);
  }
  
  /*
   *      vm_page_pqbatch_submit:         [ internal use only ]
   *
   *      Enqueue a page in the specified page queue's batched work queue.
   *      The caller must have encoded the requested operation in the page
   *      structure's a.flags field.
   */
  void
  vm_page_pqbatch_submit(vm_page_t m, uint8_t queue)
  {
          struct vm_batchqueue *bq;
          struct vm_pagequeue *pq;
          int domain;
  
          KASSERT((m->oflags & VPO_UNMANAGED) == 0,
              ("page %p is unmanaged", m));
          KASSERT(queue < PQ_COUNT, ("invalid queue %d", queue));
  
          domain = vm_page_domain(m);
          critical_enter();
          bq = DPCPU_PTR(pqbatch[domain][queue]);
          if (vm_batchqueue_insert(bq, m)) {
                  critical_exit();
                  return;
          }
          critical_exit();
  
          pq = &VM_DOMAIN(domain)->vmd_pagequeues[queue];
          vm_pagequeue_lock(pq);
          critical_enter();
          bq = DPCPU_PTR(pqbatch[domain][queue]);
          vm_pqbatch_process(pq, bq, queue);
          vm_pqbatch_process_page(pq, m, queue);
          vm_pagequeue_unlock(pq);
          critical_exit();
  }
  
  /*
   *      vm_page_pqbatch_drain:          [ internal use only ]
   *
   *      Force all per-CPU page queue batch queues to be drained.  This is
   *      intended for use in severe memory shortages, to ensure that pages
   *      do not remain stuck in the batch queues.
   */
  void
  vm_page_pqbatch_drain(void)
  {
          struct thread *td;
          struct vm_domain *vmd;
          struct vm_pagequeue *pq;
          int cpu, domain, queue;
  
          td = curthread;
          CPU_FOREACH(cpu) {
                  thread_lock(td);
                  sched_bind(td, cpu);
                  thread_unlock(td);
  
                  for (domain = 0; domain < vm_ndomains; domain++) {
                          vmd = VM_DOMAIN(domain);
                          for (queue = 0; queue < PQ_COUNT; queue++) {
                                  pq = &vmd->vmd_pagequeues[queue];
                                  vm_pagequeue_lock(pq);
                                  critical_enter();
                                  vm_pqbatch_process(pq,
                                      DPCPU_PTR(pqbatch[domain][queue]), queue);
                                  critical_exit();
                                  vm_pagequeue_unlock(pq);
                          }
                  }
          }
          thread_lock(td);
          sched_unbind(td);
          thread_unlock(td);
  }
  
  /*
   *      vm_page_dequeue_deferred:       [ internal use only ]
   *
   *      Request removal of the given page from its current page
   *      queue.  Physical removal from the queue may be deferred
   *      indefinitely.
   */
  void
  vm_page_dequeue_deferred(vm_page_t m)
  {
          vm_page_astate_t new, old;
  
          old = vm_page_astate_load(m);
          do {
                  if (old.queue == PQ_NONE) {
                          KASSERT((old.flags & PGA_QUEUE_STATE_MASK) == 0,
                              ("%s: page %p has unexpected queue state",
                              __func__, m));
                          break;
                  }
                  new = old;
                  new.flags |= PGA_DEQUEUE;
          } while (!vm_page_pqstate_commit_request(m, &old, new));
  }
  
  /*
   *      vm_page_dequeue:
   *
   *      Remove the page from whichever page queue it's in, if any, before
   *      returning.
   */
  void
  vm_page_dequeue(vm_page_t m)
  {
          vm_page_astate_t new, old;
  
          old = vm_page_astate_load(m);
          do {
                  if (old.queue == PQ_NONE) {
                          KASSERT((old.flags & PGA_QUEUE_STATE_MASK) == 0,
                              ("%s: page %p has unexpected queue state",
                              __func__, m));
                          break;
                  }
                  new = old;
                  new.flags &= ~PGA_QUEUE_OP_MASK;
                  new.queue = PQ_NONE;
          } while (!vm_page_pqstate_commit_dequeue(m, &old, new));
  
  }
  
  /*
   * Schedule the given page for insertion into the specified page queue.
   * Physical insertion of the page may be deferred indefinitely.
   */
  static void
  vm_page_enqueue(vm_page_t m, uint8_t queue)
  {
  
          KASSERT(m->a.queue == PQ_NONE &&
              (m->a.flags & PGA_QUEUE_STATE_MASK) == 0,
              ("%s: page %p is already enqueued", __func__, m));
          KASSERT(m->ref_count > 0,
              ("%s: page %p does not carry any references", __func__, m));
  
          m->a.queue = queue;
          if ((m->a.flags & PGA_REQUEUE) == 0)
                  vm_page_aflag_set(m, PGA_REQUEUE);
          vm_page_pqbatch_submit(m, queue);
  }
  
  /*
   *      vm_page_free_prep:
   *
   *      Prepares the given page to be put on the free list,
   *      disassociating it from any VM object. The caller may return
   *      the page to the free list only if this function returns true.
   *
   *      The object, if it exists, must be locked, and then the page must
   *      be xbusy.  Otherwise the page must be not busied.  A managed
   *      page must be unmapped.
   */
  static bool
  vm_page_free_prep(vm_page_t m)
  {
  
          /*
           * Synchronize with threads that have dropped a reference to this
           * page.
           */
          atomic_thread_fence_acq();
  
  #if defined(DIAGNOSTIC) && defined(PHYS_TO_DMAP)
          if (PMAP_HAS_DMAP && (m->flags & PG_ZERO) != 0) {
                  uint64_t *p;
                  int i;
                  p = (uint64_t *)PHYS_TO_DMAP(VM_PAGE_TO_PHYS(m));
                  for (i = 0; i < PAGE_SIZE / sizeof(uint64_t); i++, p++)
                          KASSERT(*p == 0, ("vm_page_free_prep %p PG_ZERO %d %jx",
                              m, i, (uintmax_t)*p));
          }
  #endif
          if ((m->oflags & VPO_UNMANAGED) == 0) {
                  KASSERT(!pmap_page_is_mapped(m),
                      ("vm_page_free_prep: freeing mapped page %p", m));
                  KASSERT((m->a.flags & (PGA_EXECUTABLE | PGA_WRITEABLE)) == 0,
                      ("vm_page_free_prep: mapping flags set in page %p", m));
          } else {
                  KASSERT(m->a.queue == PQ_NONE,
                      ("vm_page_free_prep: unmanaged page %p is queued", m));
          }
          VM_CNT_INC(v_tfree);
  
          if (m->object != NULL) {
                  KASSERT(((m->oflags & VPO_UNMANAGED) != 0) ==
                      ((m->object->flags & OBJ_UNMANAGED) != 0),
                      ("vm_page_free_prep: managed flag mismatch for page %p",
                      m));
                  vm_page_assert_xbusied(m);
  
                  /*
                   * The object reference can be released without an atomic
                   * operation.
                   */
                  KASSERT((m->flags & PG_FICTITIOUS) != 0 ||
                      m->ref_count == VPRC_OBJREF,
                      ("vm_page_free_prep: page %p has unexpected ref_count %u",
                      m, m->ref_count));
                  vm_page_object_remove(m);
                  m->ref_count -= VPRC_OBJREF;
          } else
                  vm_page_assert_unbusied(m);
  
          vm_page_busy_free(m);
  
          /*
           * If fictitious remove object association and
           * return.
           */
          if ((m->flags & PG_FICTITIOUS) != 0) {
                  KASSERT(m->ref_count == 1,
                      ("fictitious page %p is referenced", m));
                  KASSERT(m->a.queue == PQ_NONE,
                      ("fictitious page %p is queued", m));
                  return (false);
          }
  
          /*
           * Pages need not be dequeued before they are returned to the physical
           * memory allocator, but they must at least be marked for a deferred
           * dequeue.
           */
          if ((m->oflags & VPO_UNMANAGED) == 0)
                  vm_page_dequeue_deferred(m);
  
          m->valid = 0;
          vm_page_undirty(m);
  
          if (m->ref_count != 0)
                  panic("vm_page_free_prep: page %p has references", m);
  
          /*
           * Restore the default memory attribute to the page.
           */
          if (pmap_page_get_memattr(m) != VM_MEMATTR_DEFAULT)
                  pmap_page_set_memattr(m, VM_MEMATTR_DEFAULT);
  
  #if VM_NRESERVLEVEL > 0
          /*
           * Determine whether the page belongs to a reservation.  If the page was
           * allocated from a per-CPU cache, it cannot belong to a reservation, so
           * as an optimization, we avoid the check in that case.
           */
          if ((m->flags & PG_PCPU_CACHE) == 0 && vm_reserv_free_page(m))
                  return (false);
  #endif
  
          return (true);
  }
  
  /*
   *      vm_page_free_toq:
   *
   *      Returns the given page to the free list, disassociating it
   *      from any VM object.
   *
   *      The object must be locked.  The page must be exclusively busied if it
   *      belongs to an object.
   */
  static void
  vm_page_free_toq(vm_page_t m)
  {
          struct vm_domain *vmd;
          uma_zone_t zone;
  
          if (!vm_page_free_prep(m))
                  return;
  
          vmd = vm_pagequeue_domain(m);
          zone = vmd->vmd_pgcache[m->pool].zone;
          if ((m->flags & PG_PCPU_CACHE) != 0 && zone != NULL) {
                  uma_zfree(zone, m);
                  return;
          }
          vm_domain_free_lock(vmd);
          vm_phys_free_pages(m, 0);
          vm_domain_free_unlock(vmd);
          vm_domain_freecnt_inc(vmd, 1);
  }
  
  /*
   *      vm_page_free_pages_toq:
   *
   *      Returns a list of pages to the free list, disassociating it
   *      from any VM object.  In other words, this is equivalent to
   *      calling vm_page_free_toq() for each page of a list of VM objects.
   */
  void
  vm_page_free_pages_toq(struct spglist *free, bool update_wire_count)
  {
          vm_page_t m;
          int count;
  
          if (SLIST_EMPTY(free))
                  return;
  
          count = 0;
          while ((m = SLIST_FIRST(free)) != NULL) {
                  count++;
                  SLIST_REMOVE_HEAD(free, plinks.s.ss);
                  vm_page_free_toq(m);
          }
  
          if (update_wire_count)
                  vm_wire_sub(count);
  }
  
  /*
   * Mark this page as wired down.  For managed pages, this prevents reclamation
   * by the page daemon, or when the containing object, if any, is destroyed.
   */
  void
  vm_page_wire(vm_page_t m)
  {
          u_int old;
  
  #ifdef INVARIANTS
          if (m->object != NULL && !vm_page_busied(m) &&
              !vm_object_busied(m->object))
                  VM_OBJECT_ASSERT_LOCKED(m->object);
  #endif
          KASSERT((m->flags & PG_FICTITIOUS) == 0 ||
              VPRC_WIRE_COUNT(m->ref_count) >= 1,
              ("vm_page_wire: fictitious page %p has zero wirings", m));
  
          old = atomic_fetchadd_int(&m->ref_count, 1);
          KASSERT(VPRC_WIRE_COUNT(old) != VPRC_WIRE_COUNT_MAX,
              ("vm_page_wire: counter overflow for page %p", m));
          if (VPRC_WIRE_COUNT(old) == 0) {
                  if ((m->oflags & VPO_UNMANAGED) == 0)
                          vm_page_aflag_set(m, PGA_DEQUEUE);
                  vm_wire_add(1);
          }
  }
  
  /*
   * Attempt to wire a mapped page following a pmap lookup of that page.
   * This may fail if a thread is concurrently tearing down mappings of the page.
   * The transient failure is acceptable because it translates to the
   * failure of the caller pmap_extract_and_hold(), which should be then
   * followed by the vm_fault() fallback, see e.g. vm_fault_quick_hold_pages().
   */
  bool
  vm_page_wire_mapped(vm_page_t m)
  {
          u_int old;
  
          old = m->ref_count;
          do {
                  KASSERT(old > 0,
                      ("vm_page_wire_mapped: wiring unreferenced page %p", m));
                  if ((old & VPRC_BLOCKED) != 0)
                          return (false);
          } while (!atomic_fcmpset_int(&m->ref_count, &old, old + 1));
  
          if (VPRC_WIRE_COUNT(old) == 0) {
                  if ((m->oflags & VPO_UNMANAGED) == 0)
                          vm_page_aflag_set(m, PGA_DEQUEUE);
                  vm_wire_add(1);
          }
          return (true);
  }
  
  /*
   * Release a wiring reference to a managed page.  If the page still belongs to
   * an object, update its position in the page queues to reflect the reference.
   * If the wiring was the last reference to the page, free the page.
   */
  static void
  vm_page_unwire_managed(vm_page_t m, uint8_t nqueue, bool noreuse)
  {
          u_int old;
  
          KASSERT((m->oflags & VPO_UNMANAGED) == 0,
              ("%s: page %p is unmanaged", __func__, m));
  
          /*
           * Update LRU state before releasing the wiring reference.
           * Use a release store when updating the reference count to
           * synchronize with vm_page_free_prep().
           */
          old = m->ref_count;
          do {
                  KASSERT(VPRC_WIRE_COUNT(old) > 0,
                      ("vm_page_unwire: wire count underflow for page %p", m));
  
                  if (old > VPRC_OBJREF + 1) {
                          /*
                           * The page has at least one other wiring reference.  An
                           * earlier iteration of this loop may have called
                           * vm_page_release_toq() and cleared PGA_DEQUEUE, so
                           * re-set it if necessary.
                           */
                          if ((vm_page_astate_load(m).flags & PGA_DEQUEUE) == 0)
                                  vm_page_aflag_set(m, PGA_DEQUEUE);
                  } else if (old == VPRC_OBJREF + 1) {
                          /*
                           * This is the last wiring.  Clear PGA_DEQUEUE and
                           * update the page's queue state to reflect the
                           * reference.  If the page does not belong to an object
                           * (i.e., the VPRC_OBJREF bit is clear), we only need to
                           * clear leftover queue state.
                           */
                          vm_page_release_toq(m, nqueue, noreuse);
                  } else if (old == 1) {
                          vm_page_aflag_clear(m, PGA_DEQUEUE);
                  }
          } while (!atomic_fcmpset_rel_int(&m->ref_count, &old, old - 1));
  
          if (VPRC_WIRE_COUNT(old) == 1) {
                  vm_wire_sub(1);
                  if (old == 1)
                          vm_page_free(m);
          }
  }
  
  /*
   * Release one wiring of the specified page, potentially allowing it to be
   * paged out.
   *
   * Only managed pages belonging to an object can be paged out.  If the number
   * of wirings transitions to zero and the page is eligible for page out, then
   * the page is added to the specified paging queue.  If the released wiring
   * represented the last reference to the page, the page is freed.
   */
  void
  vm_page_unwire(vm_page_t m, uint8_t nqueue)
  {
  
          KASSERT(nqueue < PQ_COUNT,
              ("vm_page_unwire: invalid queue %u request for page %p",
              nqueue, m));
  
          if ((m->oflags & VPO_UNMANAGED) != 0) {
                  if (vm_page_unwire_noq(m) && m->ref_count == 0)
                          vm_page_free(m);
                  return;
          }
          vm_page_unwire_managed(m, nqueue, false);
  }
  
  /*
   * Unwire a page without (re-)inserting it into a page queue.  It is up
   * to the caller to enqueue, requeue, or free the page as appropriate.
   * In most cases involving managed pages, vm_page_unwire() should be used
   * instead.
   */
  bool
  vm_page_unwire_noq(vm_page_t m)
  {
          u_int old;
  
          old = vm_page_drop(m, 1);
          KASSERT(VPRC_WIRE_COUNT(old) != 0,
              ("vm_page_unref: counter underflow for page %p", m));
          KASSERT((m->flags & PG_FICTITIOUS) == 0 || VPRC_WIRE_COUNT(old) > 1,
              ("vm_page_unref: missing ref on fictitious page %p", m));
  
          if (VPRC_WIRE_COUNT(old) > 1)
                  return (false);
          if ((m->oflags & VPO_UNMANAGED) == 0)
                  vm_page_aflag_clear(m, PGA_DEQUEUE);
          vm_wire_sub(1);
          return (true);
  }
  
  /*
   * Ensure that the page ends up in the specified page queue.  If the page is
   * active or being moved to the active queue, ensure that its act_count is
   * at least ACT_INIT but do not otherwise mess with it.
   */
  static __always_inline void
  vm_page_mvqueue(vm_page_t m, const uint8_t nqueue, const uint16_t nflag)
  {
          vm_page_astate_t old, new;
  
          KASSERT(m->ref_count > 0,
              ("%s: page %p does not carry any references", __func__, m));
          KASSERT(nflag == PGA_REQUEUE || nflag == PGA_REQUEUE_HEAD,
              ("%s: invalid flags %x", __func__, nflag));
  
          if ((m->oflags & VPO_UNMANAGED) != 0 || vm_page_wired(m))
                  return;
  
          old = vm_page_astate_load(m);
          do {
                  if ((old.flags & PGA_DEQUEUE) != 0)
                          break;
                  new = old;
                  new.flags &= ~PGA_QUEUE_OP_MASK;
                  if (nqueue == PQ_ACTIVE)
                          new.act_count = max(old.act_count, ACT_INIT);
                  if (old.queue == nqueue) {
                          if (nqueue != PQ_ACTIVE)
                                  new.flags |= nflag;
                  } else {
                          new.flags |= nflag;
                          new.queue = nqueue;
                  }
          } while (!vm_page_pqstate_commit(m, &old, new));
  }
  
  /*
   * Put the specified page on the active list (if appropriate).
   */
  void
  vm_page_activate(vm_page_t m)
  {
  
          vm_page_mvqueue(m, PQ_ACTIVE, PGA_REQUEUE);
  }
  
  /*
   * Move the specified page to the tail of the inactive queue, or requeue
   * the page if it is already in the inactive queue.
   */
  void
  vm_page_deactivate(vm_page_t m)
  {
  
          vm_page_mvqueue(m, PQ_INACTIVE, PGA_REQUEUE);
  }
  
  void
  vm_page_deactivate_noreuse(vm_page_t m)
  {
  
          vm_page_mvqueue(m, PQ_INACTIVE, PGA_REQUEUE_HEAD);
  }
  
  /*
   * Put a page in the laundry, or requeue it if it is already there.
   */
  void
  vm_page_launder(vm_page_t m)
  {
  
          vm_page_mvqueue(m, PQ_LAUNDRY, PGA_REQUEUE);
  }
  
  /*
   * Put a page in the PQ_UNSWAPPABLE holding queue.
   */
  void
  vm_page_unswappable(vm_page_t m)
  {
  
          KASSERT(!vm_page_wired(m) && (m->oflags & VPO_UNMANAGED) == 0,
              ("page %p already unswappable", m));
  
          vm_page_dequeue(m);
          vm_page_enqueue(m, PQ_UNSWAPPABLE);
  }
  
  /*
   * Release a page back to the page queues in preparation for unwiring.
   */
  static void
  vm_page_release_toq(vm_page_t m, uint8_t nqueue, const bool noreuse)
  {
          vm_page_astate_t old, new;
          uint16_t nflag;
  
          /*
           * Use a check of the valid bits to determine whether we should
           * accelerate reclamation of the page.  The object lock might not be
           * held here, in which case the check is racy.  At worst we will either
           * accelerate reclamation of a valid page and violate LRU, or
           * unnecessarily defer reclamation of an invalid page.
           *
           * If we were asked to not cache the page, place it near the head of the
           * inactive queue so that is reclaimed sooner.
           */
          if (noreuse || m->valid == 0) {
                  nqueue = PQ_INACTIVE;
                  nflag = PGA_REQUEUE_HEAD;
          } else {
                  nflag = PGA_REQUEUE;
          }
  
          old = vm_page_astate_load(m);
          do {
                  new = old;
  
                  /*
                   * If the page is already in the active queue and we are not
                   * trying to accelerate reclamation, simply mark it as
                   * referenced and avoid any queue operations.
                   */
                  new.flags &= ~PGA_QUEUE_OP_MASK;
                  if (nflag != PGA_REQUEUE_HEAD && old.queue == PQ_ACTIVE)
                          new.flags |= PGA_REFERENCED;
                  else {
                          new.flags |= nflag;
                          new.queue = nqueue;
                  }
          } while (!vm_page_pqstate_commit(m, &old, new));
  }
  
  /*
   * Unwire a page and either attempt to free it or re-add it to the page queues.
   */
  void
  vm_page_release(vm_page_t m, int flags)
  {
          vm_object_t object;
  
          KASSERT((m->oflags & VPO_UNMANAGED) == 0,
              ("vm_page_release: page %p is unmanaged", m));
  
          if ((flags & VPR_TRYFREE) != 0) {
                  for (;;) {
                          object = atomic_load_ptr(&m->object);
                          if (object == NULL)
                                  break;
                          /* Depends on type-stability. */
                          if (vm_page_busied(m) || !VM_OBJECT_TRYWLOCK(object))
                                  break;
                          if (object == m->object) {
                                  vm_page_release_locked(m, flags);
                                  VM_OBJECT_WUNLOCK(object);
                                  return;
                          }
                          VM_OBJECT_WUNLOCK(object);
                  }
          }
          vm_page_unwire_managed(m, PQ_INACTIVE, flags != 0);
  }
  
  /* See vm_page_release(). */
  void
  vm_page_release_locked(vm_page_t m, int flags)
  {
  
          VM_OBJECT_ASSERT_WLOCKED(m->object);
          KASSERT((m->oflags & VPO_UNMANAGED) == 0,
              ("vm_page_release_locked: page %p is unmanaged", m));
  
          if (vm_page_unwire_noq(m)) {
                  if ((flags & VPR_TRYFREE) != 0 &&
                      (m->object->ref_count == 0 || !pmap_page_is_mapped(m)) &&
                      m->dirty == 0 && vm_page_tryxbusy(m)) {
                          /*
                           * An unlocked lookup may have wired the page before the
                           * busy lock was acquired, in which case the page must
                           * not be freed.
                           */
                          if (__predict_true(!vm_page_wired(m))) {
                                  vm_page_free(m);
                                  return;
                          }
                          vm_page_xunbusy(m);
                  } else {
                          vm_page_release_toq(m, PQ_INACTIVE, flags != 0);
                  }
          }
  }
  
  static bool
  vm_page_try_blocked_op(vm_page_t m, void (*op)(vm_page_t))
  {
          u_int old;
  
          KASSERT(m->object != NULL && (m->oflags & VPO_UNMANAGED) == 0,
              ("vm_page_try_blocked_op: page %p has no object", m));
          KASSERT(vm_page_busied(m),
              ("vm_page_try_blocked_op: page %p is not busy", m));
          VM_OBJECT_ASSERT_LOCKED(m->object);
  
          old = m->ref_count;
          do {
                  KASSERT(old != 0,
                      ("vm_page_try_blocked_op: page %p has no references", m));
                  if (VPRC_WIRE_COUNT(old) != 0)
                          return (false);
          } while (!atomic_fcmpset_int(&m->ref_count, &old, old | VPRC_BLOCKED));
  
          (op)(m);
  
          /*
           * If the object is read-locked, new wirings may be created via an
           * object lookup.
           */
          old = vm_page_drop(m, VPRC_BLOCKED);
          KASSERT(!VM_OBJECT_WOWNED(m->object) ||
              old == (VPRC_BLOCKED | VPRC_OBJREF),
              ("vm_page_try_blocked_op: unexpected refcount value %u for %p",
              old, m));
          return (true);
  }
  
  /*
   * Atomically check for wirings and remove all mappings of the page.
   */
  bool
  vm_page_try_remove_all(vm_page_t m)
  {
  
          return (vm_page_try_blocked_op(m, pmap_remove_all));
  }
  
  /*
   * Atomically check for wirings and remove all writeable mappings of the page.
   */
  bool
  vm_page_try_remove_write(vm_page_t m)
  {
  
          return (vm_page_try_blocked_op(m, pmap_remove_write));
  }
  
  /*
   * vm_page_advise
   *
   *      Apply the specified advice to the given page.
   */
  void
  vm_page_advise(vm_page_t m, int advice)
  {
  
          VM_OBJECT_ASSERT_WLOCKED(m->object);
          vm_page_assert_xbusied(m);
  
          if (advice == MADV_FREE)
                  /*
                   * Mark the page clean.  This will allow the page to be freed
                   * without first paging it out.  MADV_FREE pages are often
                   * quickly reused by malloc(3), so we do not do anything that
                   * would result in a page fault on a later access.
                   */
                  vm_page_undirty(m);
          else if (advice != MADV_DONTNEED) {
                  if (advice == MADV_WILLNEED)
                          vm_page_activate(m);
                  return;
          }
  
          if (advice != MADV_FREE && m->dirty == 0 && pmap_is_modified(m))
                  vm_page_dirty(m);
  
          /*
           * Clear any references to the page.  Otherwise, the page daemon will
           * immediately reactivate the page.
           */
          vm_page_aflag_clear(m, PGA_REFERENCED);
  
          /*
           * Place clean pages near the head of the inactive queue rather than
           * the tail, thus defeating the queue's LRU operation and ensuring that
           * the page will be reused quickly.  Dirty pages not already in the
           * laundry are moved there.
           */
          if (m->dirty == 0)
                  vm_page_deactivate_noreuse(m);
          else if (!vm_page_in_laundry(m))
                  vm_page_launder(m);
  }
  
  /*
   *      vm_page_grab_release
   *
   *      Helper routine for grab functions to release busy on return.
   */
  static inline void
  vm_page_grab_release(vm_page_t m, int allocflags)
  {
  
          if ((allocflags & VM_ALLOC_NOBUSY) != 0) {
                  if ((allocflags & VM_ALLOC_IGN_SBUSY) != 0)
                          vm_page_sunbusy(m);
                  else
                          vm_page_xunbusy(m);
          }
  }
  
  /*
   *      vm_page_grab_sleep
   *
   *      Sleep for busy according to VM_ALLOC_ parameters.  Returns true
   *      if the caller should retry and false otherwise.
   *
   *      If the object is locked on entry the object will be unlocked with
   *      false returns and still locked but possibly having been dropped
   *      with true returns.
   */
  static bool
  vm_page_grab_sleep(vm_object_t object, vm_page_t m, vm_pindex_t pindex,
      const char *wmesg, int allocflags, bool locked)
  {
  
          if ((allocflags & VM_ALLOC_NOWAIT) != 0)
                  return (false);
  
          /*
           * Reference the page before unlocking and sleeping so that
           * the page daemon is less likely to reclaim it.
           */
          if (locked && (allocflags & VM_ALLOC_NOCREAT) == 0)
                  vm_page_reference(m);
  
          if (_vm_page_busy_sleep(object, m, pindex, wmesg, allocflags, locked) &&
              locked)
                  VM_OBJECT_WLOCK(object);
          if ((allocflags & VM_ALLOC_WAITFAIL) != 0)
                  return (false);
  
          return (true);
  }
  
  /*
   * Assert that the grab flags are valid.
   */
  static inline void
  vm_page_grab_check(int allocflags)
  {
  
          KASSERT((allocflags & VM_ALLOC_NOBUSY) == 0 ||
              (allocflags & VM_ALLOC_WIRED) != 0,
              ("vm_page_grab*: the pages must be busied or wired"));
  
          KASSERT((allocflags & VM_ALLOC_SBUSY) == 0 ||
              (allocflags & VM_ALLOC_IGN_SBUSY) != 0,
              ("vm_page_grab*: VM_ALLOC_SBUSY/VM_ALLOC_IGN_SBUSY mismatch"));
  }
  
  /*
   * Calculate the page allocation flags for grab.
   */
  static inline int
  vm_page_grab_pflags(int allocflags)
  {
          int pflags;
  
          pflags = allocflags &
              ~(VM_ALLOC_NOWAIT | VM_ALLOC_WAITOK | VM_ALLOC_WAITFAIL |
              VM_ALLOC_NOBUSY);
          if ((allocflags & VM_ALLOC_NOWAIT) == 0)
                  pflags |= VM_ALLOC_WAITFAIL;
          if ((allocflags & VM_ALLOC_IGN_SBUSY) != 0)
                  pflags |= VM_ALLOC_SBUSY;
  
          return (pflags);
  }
  
  /*
   * Grab a page, waiting until we are waken up due to the page
   * changing state.  We keep on waiting, if the page continues
   * to be in the object.  If the page doesn't exist, first allocate it
   * and then conditionally zero it.
   *
   * This routine may sleep.
   *
   * The object must be locked on entry.  The lock will, however, be released
   * and reacquired if the routine sleeps.
   */
  vm_page_t
  vm_page_grab(vm_object_t object, vm_pindex_t pindex, int allocflags)
  {
          vm_page_t m;
  
          VM_OBJECT_ASSERT_WLOCKED(object);
          vm_page_grab_check(allocflags);
  
  retrylookup:
          if ((m = vm_page_lookup(object, pindex)) != NULL) {
                  if (!vm_page_tryacquire(m, allocflags)) {
                          if (vm_page_grab_sleep(object, m, pindex, "pgrbwt",
                              allocflags, true))
                                  goto retrylookup;
                          return (NULL);
                  }
                  goto out;
          }
          if ((allocflags & VM_ALLOC_NOCREAT) != 0)
                  return (NULL);
          m = vm_page_alloc(object, pindex, vm_page_grab_pflags(allocflags));
          if (m == NULL) {
                  if ((allocflags & (VM_ALLOC_NOWAIT | VM_ALLOC_WAITFAIL)) != 0)
                          return (NULL);
                  goto retrylookup;
          }
          if (allocflags & VM_ALLOC_ZERO && (m->flags & PG_ZERO) == 0)
                  pmap_zero_page(m);
  
  out:
          vm_page_grab_release(m, allocflags);
  
          return (m);
  }
  
  /*
   * Locklessly attempt to acquire a page given a (object, pindex) tuple
   * and an optional previous page to avoid the radix lookup.  The resulting
   * page will be validated against the identity tuple and busied or wired
   * as requested.  A NULL *mp return guarantees that the page was not in
   * radix at the time of the call but callers must perform higher level
   * synchronization or retry the operation under a lock if they require
   * an atomic answer.  This is the only lock free validation routine,
   * other routines can depend on the resulting page state.
   *
   * The return value indicates whether the operation failed due to caller
   * flags.  The return is tri-state with mp:
   *
   * (true, *mp != NULL) - The operation was successful.
   * (true, *mp == NULL) - The page was not found in tree.
   * (false, *mp == NULL) - WAITFAIL or NOWAIT prevented acquisition.
   */
  static bool
  vm_page_acquire_unlocked(vm_object_t object, vm_pindex_t pindex,
      vm_page_t prev, vm_page_t *mp, int allocflags)
  {
          vm_page_t m;
  
          vm_page_grab_check(allocflags);
          MPASS(prev == NULL || vm_page_busied(prev) || vm_page_wired(prev));
  
          *mp = NULL;
          for (;;) {
                  /*
                   * We may see a false NULL here because the previous page
                   * has been removed or just inserted and the list is loaded
                   * without barriers.  Switch to radix to verify.
                   */
                  if (prev == NULL || (m = TAILQ_NEXT(prev, listq)) == NULL ||
                      QMD_IS_TRASHED(m) || m->pindex != pindex ||
                      atomic_load_ptr(&m->object) != object) {
                          prev = NULL;
                          /*
                           * This guarantees the result is instantaneously
                           * correct.
                           */
                          m = vm_radix_lookup_unlocked(&object->rtree, pindex);
                  }
                  if (m == NULL)
                          return (true);
                  if (vm_page_trybusy(m, allocflags)) {
                          if (m->object == object && m->pindex == pindex)
                                  break;
                          /* relookup. */
                          vm_page_busy_release(m);
                          cpu_spinwait();
                          continue;
                  }
                  if (!vm_page_grab_sleep(object, m, pindex, "pgnslp",
                      allocflags, false))
                          return (false);
          }
          if ((allocflags & VM_ALLOC_WIRED) != 0)
                  vm_page_wire(m);
          vm_page_grab_release(m, allocflags);
          *mp = m;
          return (true);
  }
  
  /*
   * Try to locklessly grab a page and fall back to the object lock if NOCREAT
   * is not set.
   */
  vm_page_t
  vm_page_grab_unlocked(vm_object_t object, vm_pindex_t pindex, int allocflags)
  {
          vm_page_t m;
  
          vm_page_grab_check(allocflags);
  
          if (!vm_page_acquire_unlocked(object, pindex, NULL, &m, allocflags))
                  return (NULL);
          if (m != NULL)
                  return (m);
  
          /*
           * The radix lockless lookup should never return a false negative
           * errors.  If the user specifies NOCREAT they are guaranteed there
           * was no page present at the instant of the call.  A NOCREAT caller
           * must handle create races gracefully.
           */
          if ((allocflags & VM_ALLOC_NOCREAT) != 0)
                  return (NULL);
  
          VM_OBJECT_WLOCK(object);
          m = vm_page_grab(object, pindex, allocflags);
          VM_OBJECT_WUNLOCK(object);
  
          return (m);
  }
  
  /*
   * Grab a page and make it valid, paging in if necessary.  Pages missing from
   * their pager are zero filled and validated.  If a VM_ALLOC_COUNT is supplied
   * and the page is not valid as many as VM_INITIAL_PAGEIN pages can be brought
   * in simultaneously.  Additional pages will be left on a paging queue but
   * will neither be wired nor busy regardless of allocflags.
   */
  int
  vm_page_grab_valid(vm_page_t *mp, vm_object_t object, vm_pindex_t pindex, int allocflags)
  {
          vm_page_t m;
          vm_page_t ma[VM_INITIAL_PAGEIN];
          int after, i, pflags, rv;
  
          KASSERT((allocflags & VM_ALLOC_SBUSY) == 0 ||
              (allocflags & VM_ALLOC_IGN_SBUSY) != 0,
              ("vm_page_grab_valid: VM_ALLOC_SBUSY/VM_ALLOC_IGN_SBUSY mismatch"));
          KASSERT((allocflags &
              (VM_ALLOC_NOWAIT | VM_ALLOC_WAITFAIL | VM_ALLOC_ZERO)) == 0,
              ("vm_page_grab_valid: Invalid flags 0x%X", allocflags));
          VM_OBJECT_ASSERT_WLOCKED(object);
          pflags = allocflags & ~(VM_ALLOC_NOBUSY | VM_ALLOC_SBUSY |
              VM_ALLOC_WIRED);
          pflags |= VM_ALLOC_WAITFAIL;
  
  retrylookup:
          if ((m = vm_page_lookup(object, pindex)) != NULL) {
                  /*
                   * If the page is fully valid it can only become invalid
                   * with the object lock held.  If it is not valid it can
                   * become valid with the busy lock held.  Therefore, we
                   * may unnecessarily lock the exclusive busy here if we
                   * race with I/O completion not using the object lock.
                   * However, we will not end up with an invalid page and a
                   * shared lock.
                   */
                  if (!vm_page_trybusy(m,
                      vm_page_all_valid(m) ? allocflags : 0)) {
                          (void)vm_page_grab_sleep(object, m, pindex, "pgrbwt",
                              allocflags, true);
                          goto retrylookup;
                  }
                  if (vm_page_all_valid(m))
                          goto out;
                  if ((allocflags & VM_ALLOC_NOCREAT) != 0) {
                          vm_page_busy_release(m);
                          *mp = NULL;
                          return (VM_PAGER_FAIL);
                  }
          } else if ((allocflags & VM_ALLOC_NOCREAT) != 0) {
                  *mp = NULL;
                  return (VM_PAGER_FAIL);
          } else if ((m = vm_page_alloc(object, pindex, pflags)) == NULL) {
                  goto retrylookup;
          }
  
          vm_page_assert_xbusied(m);
          if (vm_pager_has_page(object, pindex, NULL, &after)) {
                  after = MIN(after, VM_INITIAL_PAGEIN);
                  after = MIN(after, allocflags >> VM_ALLOC_COUNT_SHIFT);
                  after = MAX(after, 1);
                  ma[0] = m;
                  for (i = 1; i < after; i++) {
                          if ((ma[i] = vm_page_next(ma[i - 1])) != NULL) {
                                  if (ma[i]->valid || !vm_page_tryxbusy(ma[i]))
                                          break;
                          } else {
                                  ma[i] = vm_page_alloc(object, m->pindex + i,
                                      VM_ALLOC_NORMAL);
                                  if (ma[i] == NULL)
                                          break;
                          }
                  }
                  after = i;
                  vm_object_pip_add(object, after);
                  VM_OBJECT_WUNLOCK(object);
                  rv = vm_pager_get_pages(object, ma, after, NULL, NULL);
                  VM_OBJECT_WLOCK(object);
                  vm_object_pip_wakeupn(object, after);
                  /* Pager may have replaced a page. */
                  m = ma[0];
                  if (rv != VM_PAGER_OK) {
                          for (i = 0; i < after; i++) {
                                  if (!vm_page_wired(ma[i]))
                                          vm_page_free(ma[i]);
                                  else
                                          vm_page_xunbusy(ma[i]);
                          }
                          *mp = NULL;
                          return (rv);
                  }
                  for (i = 1; i < after; i++)
                          vm_page_readahead_finish(ma[i]);
                  MPASS(vm_page_all_valid(m));
          } else {
                  vm_page_zero_invalid(m, TRUE);
          }
  out:
          if ((allocflags & VM_ALLOC_WIRED) != 0)
                  vm_page_wire(m);
          if ((allocflags & VM_ALLOC_SBUSY) != 0 && vm_page_xbusied(m))
                  vm_page_busy_downgrade(m);
          else if ((allocflags & VM_ALLOC_NOBUSY) != 0)
                  vm_page_busy_release(m);
          *mp = m;
          return (VM_PAGER_OK);
  }
  
  /*
   * Locklessly grab a valid page.  If the page is not valid or not yet
   * allocated this will fall back to the object lock method.
   */
  int
  vm_page_grab_valid_unlocked(vm_page_t *mp, vm_object_t object,
      vm_pindex_t pindex, int allocflags)
  {
          vm_page_t m;
          int flags;
          int error;
  
          KASSERT((allocflags & VM_ALLOC_SBUSY) == 0 ||
              (allocflags & VM_ALLOC_IGN_SBUSY) != 0,
              ("vm_page_grab_valid_unlocked: VM_ALLOC_SBUSY/VM_ALLOC_IGN_SBUSY "
              "mismatch"));
          KASSERT((allocflags &
              (VM_ALLOC_NOWAIT | VM_ALLOC_WAITFAIL | VM_ALLOC_ZERO)) == 0,
              ("vm_page_grab_valid_unlocked: Invalid flags 0x%X", allocflags));
  
          /*
           * Attempt a lockless lookup and busy.  We need at least an sbusy
           * before we can inspect the valid field and return a wired page.
           */
          flags = allocflags & ~(VM_ALLOC_NOBUSY | VM_ALLOC_WIRED);
          if (!vm_page_acquire_unlocked(object, pindex, NULL, mp, flags))
                  return (VM_PAGER_FAIL);
          if ((m = *mp) != NULL) {
                  if (vm_page_all_valid(m)) {
                          if ((allocflags & VM_ALLOC_WIRED) != 0)
                                  vm_page_wire(m);
                          vm_page_grab_release(m, allocflags);
                          return (VM_PAGER_OK);
                  }
                  vm_page_busy_release(m);
          }
          if ((allocflags & VM_ALLOC_NOCREAT) != 0) {
                  *mp = NULL;
                  return (VM_PAGER_FAIL);
          }
          VM_OBJECT_WLOCK(object);
          error = vm_page_grab_valid(mp, object, pindex, allocflags);
          VM_OBJECT_WUNLOCK(object);
  
          return (error);
  }
  
  /*
   * Return the specified range of pages from the given object.  For each
   * page offset within the range, if a page already exists within the object
   * at that offset and it is busy, then wait for it to change state.  If,
   * instead, the page doesn't exist, then allocate it.
   *
   * The caller must always specify an allocation class.
   *
   * allocation classes:
   *      VM_ALLOC_NORMAL         normal process request
   *      VM_ALLOC_SYSTEM         system *really* needs the pages
   *
   * The caller must always specify that the pages are to be busied and/or
   * wired.
   *
   * optional allocation flags:
   *      VM_ALLOC_IGN_SBUSY      do not sleep on soft busy pages
   *      VM_ALLOC_NOBUSY         do not exclusive busy the page
   *      VM_ALLOC_NOWAIT         do not sleep
   *      VM_ALLOC_SBUSY          set page to sbusy state
   *      VM_ALLOC_WIRED          wire the pages
   *      VM_ALLOC_ZERO           zero and validate any invalid pages
   *
   * If VM_ALLOC_NOWAIT is not specified, this routine may sleep.  Otherwise, it
   * may return a partial prefix of the requested range.
   */
  int
  vm_page_grab_pages(vm_object_t object, vm_pindex_t pindex, int allocflags,
      vm_page_t *ma, int count)
  {
          vm_page_t m, mpred;
          int pflags;
          int i;
  
          VM_OBJECT_ASSERT_WLOCKED(object);
          KASSERT(((u_int)allocflags >> VM_ALLOC_COUNT_SHIFT) == 0,
              ("vm_page_grap_pages: VM_ALLOC_COUNT() is not allowed"));
          KASSERT(count > 0,
              ("vm_page_grab_pages: invalid page count %d", count));
          vm_page_grab_check(allocflags);
  
          pflags = vm_page_grab_pflags(allocflags);
          i = 0;
  retrylookup:
          m = vm_radix_lookup_le(&object->rtree, pindex + i);
          if (m == NULL || m->pindex != pindex + i) {
                  mpred = m;
                  m = NULL;
          } else
                  mpred = TAILQ_PREV(m, pglist, listq);
          for (; i < count; i++) {
                  if (m != NULL) {
                          if (!vm_page_tryacquire(m, allocflags)) {
                                  if (vm_page_grab_sleep(object, m, pindex + i,
                                      "grbmaw", allocflags, true))
                                          goto retrylookup;
                                  break;
                          }
                  } else {
                          if ((allocflags & VM_ALLOC_NOCREAT) != 0)
                                  break;
                          m = vm_page_alloc_after(object, pindex + i,
                              pflags | VM_ALLOC_COUNT(count - i), mpred);
                          if (m == NULL) {
                                  if ((allocflags & (VM_ALLOC_NOWAIT |
                                      VM_ALLOC_WAITFAIL)) != 0)
                                          break;
                                  goto retrylookup;
                          }
                  }
                  if (vm_page_none_valid(m) &&
                      (allocflags & VM_ALLOC_ZERO) != 0) {
                          if ((m->flags & PG_ZERO) == 0)
                                  pmap_zero_page(m);
                          vm_page_valid(m);
                  }
                  vm_page_grab_release(m, allocflags);
                  ma[i] = mpred = m;
                  m = vm_page_next(m);
          }
          return (i);
  }
  
  /*
   * Unlocked variant of vm_page_grab_pages().  This accepts the same flags
   * and will fall back to the locked variant to handle allocation.
   */
  int
  vm_page_grab_pages_unlocked(vm_object_t object, vm_pindex_t pindex,
      int allocflags, vm_page_t *ma, int count)
  {
          vm_page_t m, pred;
          int flags;
          int i;
  
          KASSERT(count > 0,
              ("vm_page_grab_pages_unlocked: invalid page count %d", count));
          vm_page_grab_check(allocflags);
  
          /*
           * Modify flags for lockless acquire to hold the page until we
           * set it valid if necessary.
           */
          flags = allocflags & ~VM_ALLOC_NOBUSY;
          pred = NULL;
          for (i = 0; i < count; i++, pindex++) {
                  if (!vm_page_acquire_unlocked(object, pindex, pred, &m, flags))
                          return (i);
                  if (m == NULL)
                          break;
                  if ((flags & VM_ALLOC_ZERO) != 0 && vm_page_none_valid(m)) {
                          if ((m->flags & PG_ZERO) == 0)
                                  pmap_zero_page(m);
                          vm_page_valid(m);
                  }
                  /* m will still be wired or busy according to flags. */
                  vm_page_grab_release(m, allocflags);
                  pred = ma[i] = m;
          }
          if (i == count || (allocflags & VM_ALLOC_NOCREAT) != 0)
                  return (i);
          count -= i;
          VM_OBJECT_WLOCK(object);
          i += vm_page_grab_pages(object, pindex, allocflags, &ma[i], count);
          VM_OBJECT_WUNLOCK(object);
  
          return (i);
  }
  
  /*
   * Mapping function for valid or dirty bits in a page.
   *
   * Inputs are required to range within a page.
   */
  vm_page_bits_t
  vm_page_bits(int base, int size)
  {
          int first_bit;
          int last_bit;
  
          KASSERT(
              base + size <= PAGE_SIZE,
              ("vm_page_bits: illegal base/size %d/%d", base, size)
          );
  
          if (size == 0)          /* handle degenerate case */
                  return (0);
  
          first_bit = base >> DEV_BSHIFT;
          last_bit = (base + size - 1) >> DEV_BSHIFT;
  
          return (((vm_page_bits_t)2 << last_bit) -
              ((vm_page_bits_t)1 << first_bit));
  }
  
  void
  vm_page_bits_set(vm_page_t m, vm_page_bits_t *bits, vm_page_bits_t set)
  {
  
  #if PAGE_SIZE == 32768
          atomic_set_64((uint64_t *)bits, set);
  #elif PAGE_SIZE == 16384
          atomic_set_32((uint32_t *)bits, set);
  #elif (PAGE_SIZE == 8192) && defined(atomic_set_16)
          atomic_set_16((uint16_t *)bits, set);
  #elif (PAGE_SIZE == 4096) && defined(atomic_set_8)
          atomic_set_8((uint8_t *)bits, set);
  #else           /* PAGE_SIZE <= 8192 */
          uintptr_t addr;
          int shift;
  
          addr = (uintptr_t)bits;
          /*
           * Use a trick to perform a 32-bit atomic on the
           * containing aligned word, to not depend on the existence
           * of atomic_{set, clear}_{8, 16}.
           */
          shift = addr & (sizeof(uint32_t) - 1);
  #if BYTE_ORDER == BIG_ENDIAN
          shift = (sizeof(uint32_t) - sizeof(vm_page_bits_t) - shift) * NBBY;
  #else
          shift *= NBBY;
  #endif
          addr &= ~(sizeof(uint32_t) - 1);
          atomic_set_32((uint32_t *)addr, set << shift);
  #endif          /* PAGE_SIZE */
  }
  
  static inline void
  vm_page_bits_clear(vm_page_t m, vm_page_bits_t *bits, vm_page_bits_t clear)
  {
  
  #if PAGE_SIZE == 32768
          atomic_clear_64((uint64_t *)bits, clear);
  #elif PAGE_SIZE == 16384
          atomic_clear_32((uint32_t *)bits, clear);
  #elif (PAGE_SIZE == 8192) && defined(atomic_clear_16)
          atomic_clear_16((uint16_t *)bits, clear);
  #elif (PAGE_SIZE == 4096) && defined(atomic_clear_8)
          atomic_clear_8((uint8_t *)bits, clear);
  #else           /* PAGE_SIZE <= 8192 */
          uintptr_t addr;
          int shift;
  
          addr = (uintptr_t)bits;
          /*
           * Use a trick to perform a 32-bit atomic on the
           * containing aligned word, to not depend on the existence
           * of atomic_{set, clear}_{8, 16}.
           */
          shift = addr & (sizeof(uint32_t) - 1);
  #if BYTE_ORDER == BIG_ENDIAN
          shift = (sizeof(uint32_t) - sizeof(vm_page_bits_t) - shift) * NBBY;
  #else
          shift *= NBBY;
  #endif
          addr &= ~(sizeof(uint32_t) - 1);
          atomic_clear_32((uint32_t *)addr, clear << shift);
  #endif          /* PAGE_SIZE */
  }
  
  static inline vm_page_bits_t
  vm_page_bits_swap(vm_page_t m, vm_page_bits_t *bits, vm_page_bits_t newbits)
  {
  #if PAGE_SIZE == 32768
          uint64_t old;
  
          old = *bits;
          while (atomic_fcmpset_64(bits, &old, newbits) == 0);
          return (old);
  #elif PAGE_SIZE == 16384
          uint32_t old;
  
          old = *bits;
          while (atomic_fcmpset_32(bits, &old, newbits) == 0);
          return (old);
  #elif (PAGE_SIZE == 8192) && defined(atomic_fcmpset_16)
          uint16_t old;
  
          old = *bits;
          while (atomic_fcmpset_16(bits, &old, newbits) == 0);
          return (old);
  #elif (PAGE_SIZE == 4096) && defined(atomic_fcmpset_8)
          uint8_t old;
  
          old = *bits;
          while (atomic_fcmpset_8(bits, &old, newbits) == 0);
          return (old);
  #else           /* PAGE_SIZE <= 4096*/
          uintptr_t addr;
          uint32_t old, new, mask;
          int shift;
  
          addr = (uintptr_t)bits;
          /*
           * Use a trick to perform a 32-bit atomic on the
           * containing aligned word, to not depend on the existence
           * of atomic_{set, swap, clear}_{8, 16}.
           */
          shift = addr & (sizeof(uint32_t) - 1);
  #if BYTE_ORDER == BIG_ENDIAN
          shift = (sizeof(uint32_t) - sizeof(vm_page_bits_t) - shift) * NBBY;
  #else
          shift *= NBBY;
  #endif
          addr &= ~(sizeof(uint32_t) - 1);
          mask = VM_PAGE_BITS_ALL << shift;
  
          old = *bits;
          do {
                  new = old & ~mask;
                  new |= newbits << shift;
          } while (atomic_fcmpset_32((uint32_t *)addr, &old, new) == 0);
          return (old >> shift);
  #endif          /* PAGE_SIZE */
  }
  
  /*
   *      vm_page_set_valid_range:
   *
   *      Sets portions of a page valid.  The arguments are expected
   *      to be DEV_BSIZE aligned but if they aren't the bitmap is inclusive
   *      of any partial chunks touched by the range.  The invalid portion of
   *      such chunks will be zeroed.
   *
   *      (base + size) must be less then or equal to PAGE_SIZE.
   */
  void
  vm_page_set_valid_range(vm_page_t m, int base, int size)
  {
          int endoff, frag;
          vm_page_bits_t pagebits;
  
          vm_page_assert_busied(m);
          if (size == 0)  /* handle degenerate case */
                  return;
  
          /*
           * If the base is not DEV_BSIZE aligned and the valid
           * bit is clear, we have to zero out a portion of the
           * first block.
           */
          if ((frag = rounddown2(base, DEV_BSIZE)) != base &&
              (m->valid & (1 << (base >> DEV_BSHIFT))) == 0)
                  pmap_zero_page_area(m, frag, base - frag);
  
          /*
           * If the ending offset is not DEV_BSIZE aligned and the
           * valid bit is clear, we have to zero out a portion of
           * the last block.
           */
          endoff = base + size;
          if ((frag = rounddown2(endoff, DEV_BSIZE)) != endoff &&
              (m->valid & (1 << (endoff >> DEV_BSHIFT))) == 0)
                  pmap_zero_page_area(m, endoff,
                      DEV_BSIZE - (endoff & (DEV_BSIZE - 1)));
  
          /*
           * Assert that no previously invalid block that is now being validated
           * is already dirty.
           */
          KASSERT((~m->valid & vm_page_bits(base, size) & m->dirty) == 0,
              ("vm_page_set_valid_range: page %p is dirty", m));
  
          /*
           * Set valid bits inclusive of any overlap.
           */
          pagebits = vm_page_bits(base, size);
          if (vm_page_xbusied(m))
                  m->valid |= pagebits;
          else
                  vm_page_bits_set(m, &m->valid, pagebits);
  }
  
  /*
   * Set the page dirty bits and free the invalid swap space if
   * present.  Returns the previous dirty bits.
   */
  vm_page_bits_t
  vm_page_set_dirty(vm_page_t m)
  {
          vm_page_bits_t old;
  
          VM_PAGE_OBJECT_BUSY_ASSERT(m);
  
          if (vm_page_xbusied(m) && !pmap_page_is_write_mapped(m)) {
                  old = m->dirty;
                  m->dirty = VM_PAGE_BITS_ALL;
          } else
                  old = vm_page_bits_swap(m, &m->dirty, VM_PAGE_BITS_ALL);
          if (old == 0 && (m->a.flags & PGA_SWAP_SPACE) != 0)
                  vm_pager_page_unswapped(m);
  
          return (old);
  }
  
  /*
   * Clear the given bits from the specified page's dirty field.
   */
  static __inline void
  vm_page_clear_dirty_mask(vm_page_t m, vm_page_bits_t pagebits)
  {
  
          vm_page_assert_busied(m);
  
          /*
           * If the page is xbusied and not write mapped we are the
           * only thread that can modify dirty bits.  Otherwise, The pmap
           * layer can call vm_page_dirty() without holding a distinguished
           * lock.  The combination of page busy and atomic operations
           * suffice to guarantee consistency of the page dirty field.
           */
          if (vm_page_xbusied(m) && !pmap_page_is_write_mapped(m))
                  m->dirty &= ~pagebits;
          else
                  vm_page_bits_clear(m, &m->dirty, pagebits);
  }
  
  /*
   *      vm_page_set_validclean:
   *
   *      Sets portions of a page valid and clean.  The arguments are expected
   *      to be DEV_BSIZE aligned but if they aren't the bitmap is inclusive
   *      of any partial chunks touched by the range.  The invalid portion of
   *      such chunks will be zero'd.
   *
   *      (base + size) must be less then or equal to PAGE_SIZE.
   */
  void
  vm_page_set_validclean(vm_page_t m, int base, int size)
  {
          vm_page_bits_t oldvalid, pagebits;
          int endoff, frag;
  
          vm_page_assert_busied(m);
          if (size == 0)  /* handle degenerate case */
                  return;
  
          /*
           * If the base is not DEV_BSIZE aligned and the valid
           * bit is clear, we have to zero out a portion of the
           * first block.
           */
          if ((frag = rounddown2(base, DEV_BSIZE)) != base &&
              (m->valid & ((vm_page_bits_t)1 << (base >> DEV_BSHIFT))) == 0)
                  pmap_zero_page_area(m, frag, base - frag);
  
          /*
           * If the ending offset is not DEV_BSIZE aligned and the
           * valid bit is clear, we have to zero out a portion of
           * the last block.
           */
          endoff = base + size;
          if ((frag = rounddown2(endoff, DEV_BSIZE)) != endoff &&
              (m->valid & ((vm_page_bits_t)1 << (endoff >> DEV_BSHIFT))) == 0)
                  pmap_zero_page_area(m, endoff,
                      DEV_BSIZE - (endoff & (DEV_BSIZE - 1)));
  
          /*
           * Set valid, clear dirty bits.  If validating the entire
           * page we can safely clear the pmap modify bit.  We also
           * use this opportunity to clear the PGA_NOSYNC flag.  If a process
           * takes a write fault on a MAP_NOSYNC memory area the flag will
           * be set again.
           *
           * We set valid bits inclusive of any overlap, but we can only
           * clear dirty bits for DEV_BSIZE chunks that are fully within
           * the range.
           */
          oldvalid = m->valid;
          pagebits = vm_page_bits(base, size);
          if (vm_page_xbusied(m))
                  m->valid |= pagebits;
          else
                  vm_page_bits_set(m, &m->valid, pagebits);
  #if 0   /* NOT YET */
          if ((frag = base & (DEV_BSIZE - 1)) != 0) {
                  frag = DEV_BSIZE - frag;
                  base += frag;
                  size -= frag;
                  if (size < 0)
                          size = 0;
          }
          pagebits = vm_page_bits(base, size & (DEV_BSIZE - 1));
  #endif
          if (base == 0 && size == PAGE_SIZE) {
                  /*
                   * The page can only be modified within the pmap if it is
                   * mapped, and it can only be mapped if it was previously
                   * fully valid.
                   */
                  if (oldvalid == VM_PAGE_BITS_ALL)
                          /*
                           * Perform the pmap_clear_modify() first.  Otherwise,
                           * a concurrent pmap operation, such as
                           * pmap_protect(), could clear a modification in the
                           * pmap and set the dirty field on the page before
                           * pmap_clear_modify() had begun and after the dirty
                           * field was cleared here.
                           */
                          pmap_clear_modify(m);
                  m->dirty = 0;
                  vm_page_aflag_clear(m, PGA_NOSYNC);
          } else if (oldvalid != VM_PAGE_BITS_ALL && vm_page_xbusied(m))
                  m->dirty &= ~pagebits;
          else
                  vm_page_clear_dirty_mask(m, pagebits);
  }
  
  void
  vm_page_clear_dirty(vm_page_t m, int base, int size)
  {
  
          vm_page_clear_dirty_mask(m, vm_page_bits(base, size));
  }
  
  /*
   *      vm_page_set_invalid:
   *
   *      Invalidates DEV_BSIZE'd chunks within a page.  Both the
   *      valid and dirty bits for the effected areas are cleared.
   */
  void
  vm_page_set_invalid(vm_page_t m, int base, int size)
  {
          vm_page_bits_t bits;
          vm_object_t object;
  
          /*
           * The object lock is required so that pages can't be mapped
           * read-only while we're in the process of invalidating them.
           */
          object = m->object;
          VM_OBJECT_ASSERT_WLOCKED(object);
          vm_page_assert_busied(m);
  
          if (object->type == OBJT_VNODE && base == 0 && IDX_TO_OFF(m->pindex) +
              size >= object->un_pager.vnp.vnp_size)
                  bits = VM_PAGE_BITS_ALL;
          else
                  bits = vm_page_bits(base, size);
          if (object->ref_count != 0 && vm_page_all_valid(m) && bits != 0)
                  pmap_remove_all(m);
          KASSERT((bits == 0 && vm_page_all_valid(m)) ||
              !pmap_page_is_mapped(m),
              ("vm_page_set_invalid: page %p is mapped", m));
          if (vm_page_xbusied(m)) {
                  m->valid &= ~bits;
                  m->dirty &= ~bits;
          } else {
                  vm_page_bits_clear(m, &m->valid, bits);
                  vm_page_bits_clear(m, &m->dirty, bits);
          }
  }
  
  /*
   *      vm_page_invalid:
   *
   *      Invalidates the entire page.  The page must be busy, unmapped, and
   *      the enclosing object must be locked.  The object locks protects
   *      against concurrent read-only pmap enter which is done without
   *      busy.
   */
  void
  vm_page_invalid(vm_page_t m)
  {
  
          vm_page_assert_busied(m);
          VM_OBJECT_ASSERT_LOCKED(m->object);
          MPASS(!pmap_page_is_mapped(m));
  
          if (vm_page_xbusied(m))
                  m->valid = 0;
          else
                  vm_page_bits_clear(m, &m->valid, VM_PAGE_BITS_ALL);
  }
  
  /*
   * vm_page_zero_invalid()
   *
   *      The kernel assumes that the invalid portions of a page contain
   *      garbage, but such pages can be mapped into memory by user code.
   *      When this occurs, we must zero out the non-valid portions of the
   *      page so user code sees what it expects.
   *
   *      Pages are most often semi-valid when the end of a file is mapped
   *      into memory and the file's size is not page aligned.
   */
  void
  vm_page_zero_invalid(vm_page_t m, boolean_t setvalid)
  {
          int b;
          int i;
  
          /*
           * Scan the valid bits looking for invalid sections that
           * must be zeroed.  Invalid sub-DEV_BSIZE'd areas ( where the
           * valid bit may be set ) have already been zeroed by
           * vm_page_set_validclean().
           */
          for (b = i = 0; i <= PAGE_SIZE / DEV_BSIZE; ++i) {
                  if (i == (PAGE_SIZE / DEV_BSIZE) ||
                      (m->valid & ((vm_page_bits_t)1 << i))) {
                          if (i > b) {
                                  pmap_zero_page_area(m,
                                      b << DEV_BSHIFT, (i - b) << DEV_BSHIFT);
                          }
                          b = i + 1;
                  }
          }
  
          /*
           * setvalid is TRUE when we can safely set the zero'd areas
           * as being valid.  We can do this if there are no cache consistancy
           * issues.  e.g. it is ok to do with UFS, but not ok to do with NFS.
           */
          if (setvalid)
                  vm_page_valid(m);
  }
  
  /*
   *      vm_page_is_valid:
   *
   *      Is (partial) page valid?  Note that the case where size == 0
   *      will return FALSE in the degenerate case where the page is
   *      entirely invalid, and TRUE otherwise.
   *
   *      Some callers envoke this routine without the busy lock held and
   *      handle races via higher level locks.  Typical callers should
   *      hold a busy lock to prevent invalidation.
   */
  int
  vm_page_is_valid(vm_page_t m, int base, int size)
  {
          vm_page_bits_t bits;
  
          bits = vm_page_bits(base, size);
          return (m->valid != 0 && (m->valid & bits) == bits);
  }
  
  /*
   * Returns true if all of the specified predicates are true for the entire
   * (super)page and false otherwise.
   */
  bool
  vm_page_ps_test(vm_page_t m, int flags, vm_page_t skip_m)
  {
          vm_object_t object;
          int i, npages;
  
          object = m->object;
          if (skip_m != NULL && skip_m->object != object)
                  return (false);
          VM_OBJECT_ASSERT_LOCKED(object);
          npages = atop(pagesizes[m->psind]);
  
          /*
           * The physically contiguous pages that make up a superpage, i.e., a
           * page with a page size index ("psind") greater than zero, will
           * occupy adjacent entries in vm_page_array[].
           */
          for (i = 0; i < npages; i++) {
                  /* Always test object consistency, including "skip_m". */
                  if (m[i].object != object)
                          return (false);
                  if (&m[i] == skip_m)
                          continue;
                  if ((flags & PS_NONE_BUSY) != 0 && vm_page_busied(&m[i]))
                          return (false);
                  if ((flags & PS_ALL_DIRTY) != 0) {
                          /*
                           * Calling vm_page_test_dirty() or pmap_is_modified()
                           * might stop this case from spuriously returning
                           * "false".  However, that would require a write lock
                           * on the object containing "m[i]".
                           */
                          if (m[i].dirty != VM_PAGE_BITS_ALL)
                                  return (false);
                  }
                  if ((flags & PS_ALL_VALID) != 0 &&
                      m[i].valid != VM_PAGE_BITS_ALL)
                          return (false);
          }
          return (true);
  }
  
  /*
   * Set the page's dirty bits if the page is modified.
   */
  void
  vm_page_test_dirty(vm_page_t m)
  {
  
          vm_page_assert_busied(m);
          if (m->dirty != VM_PAGE_BITS_ALL && pmap_is_modified(m))
                  vm_page_dirty(m);
  }
  
  void
  vm_page_valid(vm_page_t m)
  {
  
          vm_page_assert_busied(m);
          if (vm_page_xbusied(m))
                  m->valid = VM_PAGE_BITS_ALL;
          else
                  vm_page_bits_set(m, &m->valid, VM_PAGE_BITS_ALL);
  }
  
  void
  vm_page_lock_KBI(vm_page_t m, const char *file, int line)
  {
  
          mtx_lock_flags_(vm_page_lockptr(m), 0, file, line);
  }
  
  void
  vm_page_unlock_KBI(vm_page_t m, const char *file, int line)
  {
  
          mtx_unlock_flags_(vm_page_lockptr(m), 0, file, line);
  }
  
  int
  vm_page_trylock_KBI(vm_page_t m, const char *file, int line)
  {
  
          return (mtx_trylock_flags_(vm_page_lockptr(m), 0, file, line));
  }
  
  #if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
  void
  vm_page_assert_locked_KBI(vm_page_t m, const char *file, int line)
  {
  
          vm_page_lock_assert_KBI(m, MA_OWNED, file, line);
  }
  
  void
  vm_page_lock_assert_KBI(vm_page_t m, int a, const char *file, int line)
  {
  
          mtx_assert_(vm_page_lockptr(m), a, file, line);
  }
  #endif
  
  #ifdef INVARIANTS
  void
  vm_page_object_busy_assert(vm_page_t m)
  {
  
          /*
           * Certain of the page's fields may only be modified by the
           * holder of a page or object busy.
           */
          if (m->object != NULL && !vm_page_busied(m))
                  VM_OBJECT_ASSERT_BUSY(m->object);
  }
  
  void
  vm_page_assert_pga_writeable(vm_page_t m, uint16_t bits)
  {
  
          if ((bits & PGA_WRITEABLE) == 0)
                  return;
  
          /*
           * The PGA_WRITEABLE flag can only be set if the page is
           * managed, is exclusively busied or the object is locked.
           * Currently, this flag is only set by pmap_enter().
           */
          KASSERT((m->oflags & VPO_UNMANAGED) == 0,
              ("PGA_WRITEABLE on unmanaged page"));
          if (!vm_page_xbusied(m))
                  VM_OBJECT_ASSERT_BUSY(m->object);
  }
  #endif
  
  #include "opt_ddb.h"
  #ifdef DDB
  #include <sys/kernel.h>
  
  #include <ddb/ddb.h>
  
  DB_SHOW_COMMAND(page, vm_page_print_page_info)
  {
  
          db_printf("vm_cnt.v_free_count: %d\n", vm_free_count());
          db_printf("vm_cnt.v_inactive_count: %d\n", vm_inactive_count());
          db_printf("vm_cnt.v_active_count: %d\n", vm_active_count());
          db_printf("vm_cnt.v_laundry_count: %d\n", vm_laundry_count());
          db_printf("vm_cnt.v_wire_count: %d\n", vm_wire_count());
          db_printf("vm_cnt.v_free_reserved: %d\n", vm_cnt.v_free_reserved);
          db_printf("vm_cnt.v_free_min: %d\n", vm_cnt.v_free_min);
          db_printf("vm_cnt.v_free_target: %d\n", vm_cnt.v_free_target);
          db_printf("vm_cnt.v_inactive_target: %d\n", vm_cnt.v_inactive_target);
  }
  
  DB_SHOW_COMMAND(pageq, vm_page_print_pageq_info)
  {
          int dom;
  
          db_printf("pq_free %d\n", vm_free_count());
          for (dom = 0; dom < vm_ndomains; dom++) {
                  db_printf(
      "dom %d page_cnt %d free %d pq_act %d pq_inact %d pq_laund %d pq_unsw %d\n",
                      dom,
                      vm_dom[dom].vmd_page_count,
                      vm_dom[dom].vmd_free_count,
                      vm_dom[dom].vmd_pagequeues[PQ_ACTIVE].pq_cnt,
                      vm_dom[dom].vmd_pagequeues[PQ_INACTIVE].pq_cnt,
                      vm_dom[dom].vmd_pagequeues[PQ_LAUNDRY].pq_cnt,
                      vm_dom[dom].vmd_pagequeues[PQ_UNSWAPPABLE].pq_cnt);
          }
  }
  
  DB_SHOW_COMMAND(pginfo, vm_page_print_pginfo)
  {
          vm_page_t m;
          boolean_t phys, virt;
  
          if (!have_addr) {
                  db_printf("show pginfo addr\n");
                  return;
          }
  
          phys = strchr(modif, 'p') != NULL;
          virt = strchr(modif, 'v') != NULL;
          if (virt)
                  m = PHYS_TO_VM_PAGE(pmap_kextract(addr));
          else if (phys)
                  m = PHYS_TO_VM_PAGE(addr);
          else
                  m = (vm_page_t)addr;
          db_printf(
      "page %p obj %p pidx 0x%jx phys 0x%jx q %d ref 0x%x\n"
      "  af 0x%x of 0x%x f 0x%x act %d busy %x valid 0x%x dirty 0x%x\n",
              m, m->object, (uintmax_t)m->pindex, (uintmax_t)m->phys_addr,
              m->a.queue, m->ref_count, m->a.flags, m->oflags,
              m->flags, m->a.act_count, m->busy_lock, m->valid, m->dirty);
  }
  #endif /* DDB */