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

     /*-
      * 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.
     * 4. 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.
     */
    
    /*
     *                      GENERAL RULES ON VM_PAGE MANIPULATION
     *
     *      - A page queue lock is required when adding or removing a page from a
     *        page queue regardless of other locks or the busy state of a page.
     *
     *              * In general, no thread besides the page daemon can acquire or
     *                hold more than one page queue lock at a time.
     *
     *              * The page daemon can acquire and hold any pair of page queue
     *                locks in any order.
     *
     *      - The object lock is required when inserting or removing
     *        pages from an object (vm_page_insert() or vm_page_remove()).
     *
     */
    
    /*
     *      Resident memory management module.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include "opt_vm.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/lock.h>
    #include <sys/kernel.h>
    #include <sys/limits.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/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_kern.h>
   #include <vm/vm_object.h>
   #include <vm/vm_page.h>
   #include <vm/vm_pageout.h>
   #include <vm/vm_pager.h>
   #include <vm/vm_phys.h>
   #include <vm/vm_radix.h>
   #include <vm/vm_reserv.h>
   #include <vm/vm_extern.h>
   #include <vm/uma.h>
   #include <vm/uma_int.h>
   
   #include <machine/md_var.h>
   
   /*
    *      Associated with page of user-allocatable memory is a
    *      page structure.
    */
   
   struct vm_domain vm_dom[MAXMEMDOM];
   struct mtx_padalign vm_page_queue_free_mtx;
   
   struct mtx_padalign pa_lock[PA_LOCK_COUNT];
   
   vm_page_t vm_page_array;
   long vm_page_array_size;
   long first_page;
   int vm_page_zero_count;
   
   static int boot_pages = UMA_BOOT_PAGES;
   TUNABLE_INT("vm.boot_pages", &boot_pages);
   SYSCTL_INT(_vm, OID_AUTO, boot_pages, CTLFLAG_RD, &boot_pages, 0,
           "number of pages allocated for bootstrapping the VM system");
   
   static int pa_tryrelock_restart;
   SYSCTL_INT(_vm, OID_AUTO, tryrelock_restart, CTLFLAG_RD,
       &pa_tryrelock_restart, 0, "Number of tryrelock restarts");
   
   static uma_zone_t fakepg_zone;
   
   static struct vnode *vm_page_alloc_init(vm_page_t m);
   static void vm_page_cache_turn_free(vm_page_t m);
   static void vm_page_clear_dirty_mask(vm_page_t m, vm_page_bits_t pagebits);
   static void vm_page_enqueue(int queue, vm_page_t m);
   static void vm_page_init_fakepg(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);
   
   SYSINIT(vm_page, SI_SUB_VM, SI_ORDER_SECOND, vm_page_init_fakepg, NULL);
   
   static void
   vm_page_init_fakepg(void *dummy)
   {
   
           fakepg_zone = uma_zcreate("fakepg", sizeof(struct vm_page), NULL, NULL,
               NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE | UMA_ZONE_VM); 
   }
   
   /* 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
   
   /*
    * Try to acquire a physical address lock while a pmap is locked.  If we
    * fail to trylock we unlock and lock the pmap directly and cache the
    * locked pa in *locked.  The caller should then restart their loop in case
    * the virtual to physical mapping has changed.
    */
   int
   vm_page_pa_tryrelock(pmap_t pmap, vm_paddr_t pa, vm_paddr_t *locked)
   {
           vm_paddr_t lockpa;
   
           lockpa = *locked;
           *locked = pa;
           if (lockpa) {
                   PA_LOCK_ASSERT(lockpa, MA_OWNED);
                   if (PA_LOCKPTR(pa) == PA_LOCKPTR(lockpa))
                           return (0);
                   PA_UNLOCK(lockpa);
           }
           if (PA_TRYLOCK(pa))
                   return (0);
           PMAP_UNLOCK(pmap);
           atomic_add_int(&pa_tryrelock_restart, 1);
           PA_LOCK(pa);
           PMAP_LOCK(pmap);
           return (EAGAIN);
   }
   
   /*
    *      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 (cnt.v_page_size == 0)
                   cnt.v_page_size = PAGE_SIZE;
           if (((cnt.v_page_size - 1) & cnt.v_page_size) != 0)
                   panic("vm_set_page_size: page size not a power of two");
   }
   
   /*
    *      vm_page_blacklist_lookup:
    *
    *      See if a physical address in this page has been listed
    *      in the blacklist tunable.  Entries in the tunable are
    *      separated by spaces or commas.  If an invalid integer is
    *      encountered then the rest of the string is skipped.
    */
   static int
   vm_page_blacklist_lookup(char *list, vm_paddr_t pa)
   {
           vm_paddr_t bad;
           char *cp, *pos;
   
           for (pos = list; *pos != '\0'; pos = cp) {
                   bad = strtoq(pos, &cp, 0);
                   if (*cp != '\0') {
                           if (*cp == ' ' || *cp == ',') {
                                   cp++;
                                   if (cp == pos)
                                           continue;
                           } else
                                   break;
                   }
                   if (pa == trunc_page(bad))
                           return (1);
           }
           return (0);
   }
   
   static void
   vm_page_domain_init(struct vm_domain *vmd)
   {
           struct vm_pagequeue *pq;
           int i;
   
           *__DECONST(char **, &vmd->vmd_pagequeues[PQ_INACTIVE].pq_name) =
               "vm inactive pagequeue";
           *__DECONST(u_int **, &vmd->vmd_pagequeues[PQ_INACTIVE].pq_vcnt) =
               &cnt.v_inactive_count;
           *__DECONST(char **, &vmd->vmd_pagequeues[PQ_ACTIVE].pq_name) =
               "vm active pagequeue";
           *__DECONST(u_int **, &vmd->vmd_pagequeues[PQ_ACTIVE].pq_vcnt) =
               &cnt.v_active_count;
           vmd->vmd_page_count = 0;
           vmd->vmd_free_count = 0;
           vmd->vmd_segs = 0;
           vmd->vmd_oom = FALSE;
           vmd->vmd_pass = 0;
           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);
           }
   }
   
   /*
    *      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)
   {
           vm_offset_t mapped;
           vm_paddr_t high_avail, low_avail, page_range, size;
           vm_paddr_t new_end;
           int i;
           vm_paddr_t pa;
           vm_paddr_t last_pa;
           char *list;
   
           /* the biggest memory array is the second group of pages */
           vm_paddr_t end;
           vm_paddr_t biggestsize;
           int biggestone;
   
           biggestsize = 0;
           biggestone = 0;
           vaddr = round_page(vaddr);
   
           for (i = 0; phys_avail[i + 1]; i += 2) {
                   phys_avail[i] = round_page(phys_avail[i]);
                   phys_avail[i + 1] = trunc_page(phys_avail[i + 1]);
           }
   
   #ifdef XEN
           /*
            * There is no obvious reason why i386 PV Xen needs vm_page structs
            * created for these pseudo-physical addresses.  XXX
            */
           vm_phys_add_seg(0, phys_avail[0]);
   #endif
   
           for (i = 0; phys_avail[i + 1]; i += 2) {
                   size = phys_avail[i + 1] - phys_avail[i];
                   if (size > biggestsize) {
                           biggestone = i;
                           biggestsize = size;
                   }
           }
   
           end = phys_avail[biggestone+1];
   
           /*
            * Initialize the page and queue locks.
            */
           mtx_init(&vm_page_queue_free_mtx, "vm page free queue", 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(&vm_dom[i]);
   
           /*
            * Allocate memory for use when boot strapping the kernel memory
            * allocator.
            */
           new_end = end - (boot_pages * UMA_SLAB_SIZE);
           new_end = trunc_page(new_end);
           mapped = pmap_map(&vaddr, new_end, end,
               VM_PROT_READ | VM_PROT_WRITE);
           bzero((void *)mapped, end - new_end);
           uma_startup((void *)mapped, boot_pages);
   
   #if defined(__amd64__) || defined(__i386__) || defined(__arm__) || \
       defined(__mips__)
           /*
            * 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;
           for (i = 0; dump_avail[i + 1] != 0; i += 2)
                   if (dump_avail[i + 1] > last_pa)
                           last_pa = dump_avail[i + 1];
           page_range = last_pa / PAGE_SIZE;
           vm_page_dump_size = round_page(roundup2(page_range, NBBY) / NBBY);
           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);
   #endif
   #if defined(__amd64__) || defined(__mips__)
           /*
            * Include the UMA bootstrap 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 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;
   
           /*
            * 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));
           mapped = pmap_map(&vaddr, new_end, end,
               VM_PROT_READ | VM_PROT_WRITE);
           vm_page_array = (vm_page_t) mapped;
   #if VM_NRESERVLEVEL > 0
           /*
            * Allocate physical memory for the reservation management system's
            * data structures, and map it.
            */
           if (high_avail == end)
                   high_avail = new_end;
           new_end = vm_reserv_startup(&vaddr, new_end, high_avail);
   #endif
   #if defined(__amd64__) || defined(__mips__)
           /*
            * 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)
                   vm_phys_add_seg(phys_avail[i], phys_avail[i + 1]);
   
           /*
            * Clear all of the page structures
            */
           bzero((caddr_t) vm_page_array, page_range * sizeof(struct vm_page));
           for (i = 0; i < page_range; i++)
                   vm_page_array[i].order = VM_NFREEORDER;
           vm_page_array_size = page_range;
   
           /*
            * Initialize the physical memory allocator.
            */
           vm_phys_init();
   
           /*
            * Add every available physical page that is not blacklisted to
            * the free lists.
            */
           cnt.v_page_count = 0;
           cnt.v_free_count = 0;
           list = getenv("vm.blacklist");
           for (i = 0; phys_avail[i + 1] != 0; i += 2) {
                   pa = phys_avail[i];
                   last_pa = phys_avail[i + 1];
                   while (pa < last_pa) {
                           if (list != NULL &&
                               vm_page_blacklist_lookup(list, pa))
                                   printf("Skipping page with pa 0x%jx\n",
                                       (uintmax_t)pa);
                           else
                                   vm_phys_add_page(pa);
                           pa += PAGE_SIZE;
                   }
           }
           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_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;
           bool locked;
   
           vm_page_assert_xbusied(m);
           locked = mtx_owned(vm_page_lockptr(m));
   
           for (;;) {
                   x = m->busy_lock;
                   x &= VPB_BIT_WAITERS;
                   if (x != 0 && !locked)
                           vm_page_lock(m);
                   if (atomic_cmpset_rel_int(&m->busy_lock,
                       VPB_SINGLE_EXCLUSIVER | x, VPB_SHARERS_WORD(1)))
                           break;
                   if (x != 0 && !locked)
                           vm_page_unlock(m);
           }
           if (x != 0) {
                   wakeup(m);
                   if (!locked)
                           vm_page_unlock(m);
           }
   }
   
   /*
    *      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 = m->busy_lock;
           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);
   
           for (;;) {
                   x = m->busy_lock;
                   if (VPB_SHARERS(x) > 1) {
                           if (atomic_cmpset_int(&m->busy_lock, x,
                               x - VPB_ONE_SHARER))
                                   break;
                           continue;
                   }
                   if ((x & VPB_BIT_WAITERS) == 0) {
                           KASSERT(x == VPB_SHARERS_WORD(1),
                               ("vm_page_sunbusy: invalid lock state"));
                           if (atomic_cmpset_int(&m->busy_lock,
                               VPB_SHARERS_WORD(1), VPB_UNBUSIED))
                                   break;
                           continue;
                   }
                   KASSERT(x == (VPB_SHARERS_WORD(1) | VPB_BIT_WAITERS),
                       ("vm_page_sunbusy: invalid lock state for waiters"));
   
                   vm_page_lock(m);
                   if (!atomic_cmpset_int(&m->busy_lock, x, VPB_UNBUSIED)) {
                           vm_page_unlock(m);
                           continue;
                   }
                   wakeup(m);
                   vm_page_unlock(m);
                   break;
           }
   }
   
   /*
    *      vm_page_busy_sleep:
    *
    *      Sleep and release the page lock, using the page pointer as wchan.
    *      This is used to implement the hard-path of busying mechanism.
    *
    *      The given page must be locked.
    *
    *      If nonshared is true, sleep only if the page is xbusy.
    */
   void
   vm_page_busy_sleep(vm_page_t m, const char *wmesg, bool nonshared)
   {
           u_int x;
   
           vm_page_assert_locked(m);
   
           x = m->busy_lock;
           if (x == VPB_UNBUSIED || (nonshared && (x & VPB_BIT_SHARED) != 0) ||
               ((x & VPB_BIT_WAITERS) == 0 &&
               !atomic_cmpset_int(&m->busy_lock, x, x | VPB_BIT_WAITERS))) {
                   vm_page_unlock(m);
                   return;
           }
           msleep(m, vm_page_lockptr(m), PVM | PDROP, wmesg, 0);
   }
   
   /*
    *      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)
   {
           u_int x;
   
           for (;;) {
                   x = m->busy_lock;
                   if ((x & VPB_BIT_SHARED) == 0)
                           return (0);
                   if (atomic_cmpset_acq_int(&m->busy_lock, x, x + VPB_ONE_SHARER))
                           return (1);
           }
   }
   
   /*
    *      vm_page_xunbusy_hard:
    *
    *      Called after the first try the exclusive unbusy of a page failed.
    *      It is assumed that the waiters bit is on.
    */
   void
   vm_page_xunbusy_hard(vm_page_t m)
   {
   
           vm_page_assert_xbusied(m);
   
           vm_page_lock(m);
           atomic_store_rel_int(&m->busy_lock, VPB_UNBUSIED);
           wakeup(m);
           vm_page_unlock(m);
   }
   
   /*
    *      vm_page_flash:
    *
    *      Wakeup anyone waiting for the page.
    *      The ownership bits do not change.
    *
    *      The given page must be locked.
    */
   void
   vm_page_flash(vm_page_t m)
   {
           u_int x;
   
           vm_page_lock_assert(m, MA_OWNED);
   
           for (;;) {
                   x = m->busy_lock;
                   if ((x & VPB_BIT_WAITERS) == 0)
                           return;
                   if (atomic_cmpset_int(&m->busy_lock, x,
                       x & (~VPB_BIT_WAITERS)))
                           break;
           }
           wakeup(m);
   }
   
   /*
    * Keep page from being freed by the page daemon
    * much of the same effect as wiring, except much lower
    * overhead and should be used only for *very* temporary
    * holding ("wiring").
    */
   void
   vm_page_hold(vm_page_t mem)
   {
   
           vm_page_lock_assert(mem, MA_OWNED);
           mem->hold_count++;
   }
   
   void
   vm_page_unhold(vm_page_t mem)
   {
   
           vm_page_lock_assert(mem, MA_OWNED);
           KASSERT(mem->hold_count >= 1, ("vm_page_unhold: hold count < 0!!!"));
           --mem->hold_count;
           if (mem->hold_count == 0 && (mem->flags & PG_UNHOLDFREE) != 0)
                   vm_page_free_toq(mem);
   }
   
   /*
    *      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)
   {
           struct mtx *mtx, *new_mtx;
   
           mtx = NULL;
           for (; count != 0; count--) {
                   /*
                    * Avoid releasing and reacquiring the same page lock.
                    */
                   new_mtx = vm_page_lockptr(*ma);
                   if (mtx != new_mtx) {
                           if (mtx != NULL)
                                   mtx_unlock(mtx);
                           mtx = new_mtx;
                           mtx_lock(mtx);
                   }
                   vm_page_unhold(*ma);
                   ma++;
           }
           if (mtx != NULL)
                   mtx_unlock(mtx);
   }
   
   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->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_SINGLE_EXCLUSIVER;
           m->wire_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));
           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 the VOP_GETPAGES()
    * array which is not the request page.
    */
   void
   vm_page_readahead_finish(vm_page_t m)
   {
   
           if (m->valid != 0) {
                   /*
                    * Since the page is not the requested page, 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.
                    */
                   vm_page_lock(m);
                   if ((m->busy_lock & VPB_BIT_WAITERS) != 0)
                           vm_page_activate(m);
                   else
                           vm_page_deactivate(m);
                   vm_page_unlock(m);
                   vm_page_xunbusy(m);
           } else {
                   /*
                    * Free the completely invalid page.  Such page state
                    * occurs due to the short read operation which did
                    * not covered our page at all, or in case when a read
                    * error happens.
                    */
                   vm_page_lock(m);
                   vm_page_free(m);
                   vm_page_unlock(m);
           }
   }
   
   /*
    *      vm_page_sleep_if_busy:
    *
    *      Sleep and release the page queues 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 *msg)
   {
           vm_object_t obj;
   
           vm_page_lock_assert(m, MA_NOTOWNED);
           VM_OBJECT_ASSERT_WLOCKED(m->object);
   
           if (vm_page_busied(m)) {
                   /*
                    * 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;
                   vm_page_lock(m);
                   VM_OBJECT_WUNLOCK(obj);
                   vm_page_busy_sleep(m, msg, false);
                   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)
   {
   
           /* These assertions refer to this operation by its public name. */
           KASSERT((m->flags & PG_CACHED) == 0,
               ("vm_page_dirty: page in cache!"));
           KASSERT(!VM_PAGE_IS_FREE(m),
               ("vm_page_dirty: page is free!"));
           KASSERT(m->valid == VM_PAGE_BITS_ALL,
               ("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;
  
          /*
           * Now link into the object's ordered list of backed pages.
           */
          if (vm_radix_insert(&object->rtree, m)) {
                  m->object = NULL;
                  m->pindex = 0;
                  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));
          if (mpred != NULL) {
                  KASSERT(mpred->object == object,
                      ("vm_page_insert_after: object doesn't contain mpred"));
                  KASSERT(mpred->pindex < m->pindex,
                      ("vm_page_insert_after: 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 OBJ_MIGHTBEDIRTY flag.
           */
          if (pmap_page_is_write_mapped(m))
                  vm_object_set_writeable_dirty(object);
  }
  
  /*
   *      vm_page_remove:
   *
   *      Removes the given mem entry from the object/offset-page
   *      table and the object page list, but do not invalidate/terminate
   *      the backing store.
   *
   *      The object must be locked.  The page must be locked if it is managed.
   */
  void
  vm_page_remove(vm_page_t m)
  {
          vm_object_t object;
          boolean_t lockacq;
  
          if ((m->oflags & VPO_UNMANAGED) == 0)
                  vm_page_lock_assert(m, MA_OWNED);
          if ((object = m->object) == NULL)
                  return;
          VM_OBJECT_ASSERT_WLOCKED(object);
          if (vm_page_xbusied(m)) {
                  lockacq = FALSE;
                  if ((m->oflags & VPO_UNMANAGED) != 0 &&
                      !mtx_owned(vm_page_lockptr(m))) {
                          lockacq = TRUE;
                          vm_page_lock(m);
                  }
                  vm_page_flash(m);
                  atomic_store_rel_int(&m->busy_lock, VPB_UNBUSIED);
                  if (lockacq)
                          vm_page_unlock(m);
          }
  
          /*
           * Now remove from the object's list of backed pages.
           */
          vm_radix_remove(&object->rtree, m->pindex);
          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);
  
          m->object = NULL;
  }
  
  /*
   *      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_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_WLOCKED(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_WLOCKED(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.
   *
   * The existing page must not be on a paging queue.
   */
  vm_page_t
  vm_page_replace(vm_page_t mnew, vm_object_t object, vm_pindex_t pindex)
  {
          vm_page_t mold, mpred;
  
          VM_OBJECT_ASSERT_WLOCKED(object);
  
          /*
           * 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.
           */
          mpred = vm_radix_lookup(&object->rtree, pindex);
          KASSERT(mpred != NULL,
              ("vm_page_replace: replacing page not present with pindex"));
          mpred = TAILQ_PREV(mpred, respgs, listq);
          if (mpred != NULL)
                  KASSERT(mpred->pindex < pindex,
                      ("vm_page_insert_after: mpred doesn't precede pindex"));
  
          mnew->object = object;
          mnew->pindex = pindex;
          mold = vm_radix_replace(&object->rtree, mnew);
          KASSERT(mold->queue == PQ_NONE,
              ("vm_page_replace: mold is on a paging queue"));
  
          /* Detach the old page from the resident tailq. */
          TAILQ_REMOVE(&object->memq, mold, listq);
  
          mold->object = NULL;
          vm_page_xunbusy(mold);
  
          /* Insert the new page in the resident tailq. */
          if (mpred != NULL)
                  TAILQ_INSERT_AFTER(&object->memq, mpred, mnew, listq);
          else
                  TAILQ_INSERT_HEAD(&object->memq, mnew, listq);
          if (pmap_page_is_write_mapped(mnew))
                  vm_object_set_writeable_dirty(object);
          return (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.  If the page is on the cache, we have to deactivate it
   *            or vm_page_dirty() will panic.  Dirty pages are not allowed
   *            on the cache.
   *
   *      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);
  
          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_lock(m);
          vm_page_remove(m);
  
          /* Return back to the new pindex to complete vm_page_insert(). */
          m->pindex = new_pindex;
          m->object = new_object;
          vm_page_unlock(m);
          vm_page_insert_radixdone(m, new_object, mpred);
          vm_page_dirty(m);
          return (0);
  }
  
  /*
   *      Convert all of the given object's cached pages that have a
   *      pindex within the given range into free pages.  If the value
   *      zero is given for "end", then the range's upper bound is
   *      infinity.  If the given object is backed by a vnode and it
   *      transitions from having one or more cached pages to none, the
   *      vnode's hold count is reduced. 
   */
  void
  vm_page_cache_free(vm_object_t object, vm_pindex_t start, vm_pindex_t end)
  {
          vm_page_t m;
          boolean_t empty;
  
          mtx_lock(&vm_page_queue_free_mtx);
          if (__predict_false(vm_radix_is_empty(&object->cache))) {
                  mtx_unlock(&vm_page_queue_free_mtx);
                  return;
          }
          while ((m = vm_radix_lookup_ge(&object->cache, start)) != NULL) {
                  if (end != 0 && m->pindex >= end)
                          break;
                  vm_radix_remove(&object->cache, m->pindex);
                  vm_page_cache_turn_free(m);
          }
          empty = vm_radix_is_empty(&object->cache);
          mtx_unlock(&vm_page_queue_free_mtx);
          if (object->type == OBJT_VNODE && empty)
                  vdrop(object->handle);
  }
  
  /*
   *      Returns the cached page that is associated with the given
   *      object and offset.  If, however, none exists, returns NULL.
   *
   *      The free page queue must be locked.
   */
  static inline vm_page_t
  vm_page_cache_lookup(vm_object_t object, vm_pindex_t pindex)
  {
  
          mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
          return (vm_radix_lookup(&object->cache, pindex));
  }
  
  /*
   *      Remove the given cached page from its containing object's
   *      collection of cached pages.
   *
   *      The free page queue must be locked.
   */
  static void
  vm_page_cache_remove(vm_page_t m)
  {
  
          mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
          KASSERT((m->flags & PG_CACHED) != 0,
              ("vm_page_cache_remove: page %p is not cached", m));
          vm_radix_remove(&m->object->cache, m->pindex);
          m->object = NULL;
          cnt.v_cache_count--;
  }
  
  /*
   *      Transfer all of the cached pages with offset greater than or
   *      equal to 'offidxstart' from the original object's cache to the
   *      new object's cache.  However, any cached pages with offset
   *      greater than or equal to the new object's size are kept in the
   *      original object.  Initially, the new object's cache must be
   *      empty.  Offset 'offidxstart' in the original object must
   *      correspond to offset zero in the new object.
   *
   *      The new object must be locked.
   */
  void
  vm_page_cache_transfer(vm_object_t orig_object, vm_pindex_t offidxstart,
      vm_object_t new_object)
  {
          vm_page_t m;
  
          /*
           * Insertion into an object's collection of cached pages
           * requires the object to be locked.  In contrast, removal does
           * not.
           */
          VM_OBJECT_ASSERT_WLOCKED(new_object);
          KASSERT(vm_radix_is_empty(&new_object->cache),
              ("vm_page_cache_transfer: object %p has cached pages",
              new_object));
          mtx_lock(&vm_page_queue_free_mtx);
          while ((m = vm_radix_lookup_ge(&orig_object->cache,
              offidxstart)) != NULL) {
                  /*
                   * Transfer all of the pages with offset greater than or
                   * equal to 'offidxstart' from the original object's
                   * cache to the new object's cache.
                   */
                  if ((m->pindex - offidxstart) >= new_object->size)
                          break;
                  vm_radix_remove(&orig_object->cache, m->pindex);
                  /* Update the page's object and offset. */
                  m->object = new_object;
                  m->pindex -= offidxstart;
                  if (vm_radix_insert(&new_object->cache, m))
                          vm_page_cache_turn_free(m);
          }
          mtx_unlock(&vm_page_queue_free_mtx);
  }
  
  /*
   *      Returns TRUE if a cached page is associated with the given object and
   *      offset, and FALSE otherwise.
   *
   *      The object must be locked.
   */
  boolean_t
  vm_page_is_cached(vm_object_t object, vm_pindex_t pindex)
  {
          vm_page_t m;
  
          /*
           * Insertion into an object's collection of cached pages requires the
           * object to be locked.  Therefore, if the object is locked and the
           * object's collection is empty, there is no need to acquire the free
           * page queues lock in order to prove that the specified page doesn't
           * exist.
           */
          VM_OBJECT_ASSERT_WLOCKED(object);
          if (__predict_true(vm_object_cache_is_empty(object)))
                  return (FALSE);
          mtx_lock(&vm_page_queue_free_mtx);
          m = vm_page_cache_lookup(object, pindex);
          mtx_unlock(&vm_page_queue_free_mtx);
          return (m != NULL);
  }
  
  /*
   *      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_IFCACHED       return page only if it is cached
   *      VM_ALLOC_IFNOTCACHED    return NULL, do not reactivate if the page
   *                              is cached
   *      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
   *
   *      This routine may not sleep.
   */
  vm_page_t
  vm_page_alloc(vm_object_t object, vm_pindex_t pindex, int req)
  {
          struct vnode *vp = NULL;
          vm_object_t m_object;
          vm_page_t m, mpred;
          int flags, req_class;
  
          mpred = 0;      /* 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: inconsistent object(%p)/req(%x)", (void *)object,
              req));
          if (object != NULL)
                  VM_OBJECT_ASSERT_WLOCKED(object);
  
          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;
  
          if (object != NULL) {
                  mpred = vm_radix_lookup_le(&object->rtree, pindex);
                  KASSERT(mpred == NULL || mpred->pindex != pindex,
                     ("vm_page_alloc: pindex already allocated"));
          }
  
          /*
           * The page allocation request can came from consumers which already
           * hold the free page queue mutex, like vm_page_insert() in
           * vm_page_cache().
           */
          mtx_lock_flags(&vm_page_queue_free_mtx, MTX_RECURSE);
          if (cnt.v_free_count + cnt.v_cache_count > cnt.v_free_reserved ||
              (req_class == VM_ALLOC_SYSTEM &&
              cnt.v_free_count + cnt.v_cache_count > cnt.v_interrupt_free_min) ||
              (req_class == VM_ALLOC_INTERRUPT &&
              cnt.v_free_count + cnt.v_cache_count > 0)) {
                  /*
                   * Allocate from the free queue if the number of free pages
                   * exceeds the minimum for the request class.
                   */
                  if (object != NULL &&
                      (m = vm_page_cache_lookup(object, pindex)) != NULL) {
                          if ((req & VM_ALLOC_IFNOTCACHED) != 0) {
                                  mtx_unlock(&vm_page_queue_free_mtx);
                                  return (NULL);
                          }
                          if (vm_phys_unfree_page(m))
                                  vm_phys_set_pool(VM_FREEPOOL_DEFAULT, m, 0);
  #if VM_NRESERVLEVEL > 0
                          else if (!vm_reserv_reactivate_page(m))
  #else
                          else
  #endif
                                  panic("vm_page_alloc: cache page %p is missing"
                                      " from the free queue", m);
                  } else if ((req & VM_ALLOC_IFCACHED) != 0) {
                          mtx_unlock(&vm_page_queue_free_mtx);
                          return (NULL);
  #if VM_NRESERVLEVEL > 0
                  } else if (object == NULL || (object->flags & (OBJ_COLORED |
                      OBJ_FICTITIOUS)) != OBJ_COLORED || (m =
                      vm_reserv_alloc_page(object, pindex, mpred)) == NULL) {
  #else
                  } else {
  #endif
                          m = vm_phys_alloc_pages(object != NULL ?
                              VM_FREEPOOL_DEFAULT : VM_FREEPOOL_DIRECT, 0);
  #if VM_NRESERVLEVEL > 0
                          if (m == NULL && vm_reserv_reclaim_inactive()) {
                                  m = vm_phys_alloc_pages(object != NULL ?
                                      VM_FREEPOOL_DEFAULT : VM_FREEPOOL_DIRECT,
                                      0);
                          }
  #endif
                  }
          } else {
                  /*
                   * Not allocatable, give up.
                   */
                  mtx_unlock(&vm_page_queue_free_mtx);
                  atomic_add_int(&vm_pageout_deficit,
                      max((u_int)req >> VM_ALLOC_COUNT_SHIFT, 1));
                  pagedaemon_wakeup();
                  return (NULL);
          }
  
          /*
           *  At this point we had better have found a good page.
           */
          KASSERT(m != NULL, ("vm_page_alloc: missing page"));
          KASSERT(m->queue == PQ_NONE,
              ("vm_page_alloc: page %p has unexpected queue %d", m, m->queue));
          KASSERT(m->wire_count == 0, ("vm_page_alloc: page %p is wired", m));
          KASSERT(m->hold_count == 0, ("vm_page_alloc: page %p is held", m));
          KASSERT(!vm_page_busied(m), ("vm_page_alloc: page %p is busy", m));
          KASSERT(m->dirty == 0, ("vm_page_alloc: page %p is dirty", m));
          KASSERT(pmap_page_get_memattr(m) == VM_MEMATTR_DEFAULT,
              ("vm_page_alloc: page %p has unexpected memattr %d", m,
              pmap_page_get_memattr(m)));
          if ((m->flags & PG_CACHED) != 0) {
                  KASSERT((m->flags & PG_ZERO) == 0,
                      ("vm_page_alloc: cached page %p is PG_ZERO", m));
                  KASSERT(m->valid != 0,
                      ("vm_page_alloc: cached page %p is invalid", m));
                  if (m->object == object && m->pindex == pindex)
                          cnt.v_reactivated++;
                  else
                          m->valid = 0;
                  m_object = m->object;
                  vm_page_cache_remove(m);
                  if (m_object->type == OBJT_VNODE &&
                      vm_object_cache_is_empty(m_object))
                          vp = m_object->handle;
          } else {
                  KASSERT(VM_PAGE_IS_FREE(m),
                      ("vm_page_alloc: page %p is not free", m));
                  KASSERT(m->valid == 0,
                      ("vm_page_alloc: free page %p is valid", m));
                  vm_phys_freecnt_adj(m, -1);
          }
  
          /*
           * Only the PG_ZERO flag is inherited.  The PG_CACHED or PG_FREE flag
           * must be cleared before the free page queues lock is released.
           */
          flags = 0;
          if (m->flags & PG_ZERO) {
                  vm_page_zero_count--;
                  if (req & VM_ALLOC_ZERO)
                          flags = PG_ZERO;
          }
          if (req & VM_ALLOC_NODUMP)
                  flags |= PG_NODUMP;
          m->flags = flags;
          mtx_unlock(&vm_page_queue_free_mtx);
          m->aflags = 0;
          m->oflags = object == NULL || (object->flags & OBJ_UNMANAGED) != 0 ?
              VPO_UNMANAGED : 0;
          m->busy_lock = VPB_UNBUSIED;
          if ((req & (VM_ALLOC_NOBUSY | VM_ALLOC_NOOBJ | VM_ALLOC_SBUSY)) == 0)
                  m->busy_lock = VPB_SINGLE_EXCLUSIVER;
          if ((req & VM_ALLOC_SBUSY) != 0)
                  m->busy_lock = VPB_SHARERS_WORD(1);
          if (req & VM_ALLOC_WIRED) {
                  /*
                   * The page lock is not required for wiring a page until that
                   * page is inserted into the object.
                   */
                  atomic_add_int(&cnt.v_wire_count, 1);
                  m->wire_count = 1;
          }
          m->act_count = 0;
  
          if (object != NULL) {
                  if (vm_page_insert_after(m, object, pindex, mpred)) {
                          /* See the comment below about hold count. */
                          if (vp != NULL)
                                  vdrop(vp);
                          pagedaemon_wakeup();
                          if (req & VM_ALLOC_WIRED) {
                                  atomic_subtract_int(&cnt.v_wire_count, 1);
                                  m->wire_count = 0;
                          }
                          m->object = NULL;
                          m->oflags = VPO_UNMANAGED;
                          m->busy_lock = VPB_UNBUSIED;
                          vm_page_free(m);
                          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;
  
          /*
           * The following call to vdrop() must come after the above call
           * to vm_page_insert() in case both affect the same object and
           * vnode.  Otherwise, the affected vnode's hold count could
           * temporarily become zero.
           */
          if (vp != NULL)
                  vdrop(vp);
  
          /*
           * Don't wakeup too often - wakeup the pageout daemon when
           * we would be nearly out of memory.
           */
          if (vm_paging_needed())
                  pagedaemon_wakeup();
  
          return (m);
  }
  
  static void
  vm_page_alloc_contig_vdrop(struct spglist *lst)
  {
  
          while (!SLIST_EMPTY(lst)) {
                  vdrop((struct vnode *)SLIST_FIRST(lst)-> plinks.s.pv);
                  SLIST_REMOVE_HEAD(lst, plinks.s.ss);
          }
  }
  
  /*
   *      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 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
   *
   *      This routine may not sleep.
   */
  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 vnode *drop;
          struct spglist deferred_vdrop_list;
          vm_page_t m, m_tmp, m_ret;
          u_int flags, oflags;
          int req_class;
  
          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: inconsistent object(%p)/req(%x)", (void *)object,
              req));
          if (object != NULL) {
                  VM_OBJECT_ASSERT_WLOCKED(object);
                  KASSERT(object->type == OBJT_PHYS,
                      ("vm_page_alloc_contig: object %p isn't OBJT_PHYS",
                      object));
          }
          KASSERT(npages > 0, ("vm_page_alloc_contig: npages is zero"));
          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;
  
          SLIST_INIT(&deferred_vdrop_list);
          mtx_lock(&vm_page_queue_free_mtx);
          if (cnt.v_free_count + cnt.v_cache_count >= npages +
              cnt.v_free_reserved || (req_class == VM_ALLOC_SYSTEM &&
              cnt.v_free_count + cnt.v_cache_count >= npages +
              cnt.v_interrupt_free_min) || (req_class == VM_ALLOC_INTERRUPT &&
              cnt.v_free_count + cnt.v_cache_count >= npages)) {
  #if VM_NRESERVLEVEL > 0
  retry:
                  if (object == NULL || (object->flags & OBJ_COLORED) == 0 ||
                      (m_ret = vm_reserv_alloc_contig(object, pindex, npages,
                      low, high, alignment, boundary)) == NULL)
  #endif
                          m_ret = vm_phys_alloc_contig(npages, low, high,
                              alignment, boundary);
          } else {
                  mtx_unlock(&vm_page_queue_free_mtx);
                  atomic_add_int(&vm_pageout_deficit, npages);
                  pagedaemon_wakeup();
                  return (NULL);
          }
          if (m_ret != NULL)
                  for (m = m_ret; m < &m_ret[npages]; m++) {
                          drop = vm_page_alloc_init(m);
                          if (drop != NULL) {
                                  /*
                                   * Enqueue the vnode for deferred vdrop().
                                   */
                                  m->plinks.s.pv = drop;
                                  SLIST_INSERT_HEAD(&deferred_vdrop_list, m,
                                      plinks.s.ss);
                          }
                  }
          else {
  #if VM_NRESERVLEVEL > 0
                  if (vm_reserv_reclaim_contig(npages, low, high, alignment,
                      boundary))
                          goto retry;
  #endif
          }
          mtx_unlock(&vm_page_queue_free_mtx);
          if (m_ret == NULL)
                  return (NULL);
  
          /*
           * 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;
          if ((req & VM_ALLOC_WIRED) != 0)
                  atomic_add_int(&cnt.v_wire_count, npages);
          oflags = VPO_UNMANAGED;
          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->aflags = 0;
                  m->flags = (m->flags | PG_NODUMP) & flags;
                  m->busy_lock = VPB_UNBUSIED;
                  if (object != NULL) {
                          if ((req & (VM_ALLOC_NOBUSY | VM_ALLOC_SBUSY)) == 0)
                                  m->busy_lock = VPB_SINGLE_EXCLUSIVER;
                          if ((req & VM_ALLOC_SBUSY) != 0)
                                  m->busy_lock = VPB_SHARERS_WORD(1);
                  }
                  if ((req & VM_ALLOC_WIRED) != 0)
                          m->wire_count = 1;
                  /* Unmanaged pages don't use "act_count". */
                  m->oflags = oflags;
                  if (object != NULL) {
                          if (vm_page_insert(m, object, pindex)) {
                                  vm_page_alloc_contig_vdrop(
                                      &deferred_vdrop_list);
                                  if (vm_paging_needed())
                                          pagedaemon_wakeup();
                                  if ((req & VM_ALLOC_WIRED) != 0)
                                          atomic_subtract_int(&cnt.v_wire_count,
                                              npages);
                                  for (m_tmp = m, m = m_ret;
                                      m < &m_ret[npages]; m++) {
                                          if ((req & VM_ALLOC_WIRED) != 0)
                                                  m->wire_count = 0;
                                          if (m >= m_tmp) {
                                                  m->object = NULL;
                                                  m->oflags |= VPO_UNMANAGED;
                                          }
                                          m->busy_lock = VPB_UNBUSIED;
                                          vm_page_free(m);
                                  }
                                  return (NULL);
                          }
                  } else
                          m->pindex = pindex;
                  if (memattr != VM_MEMATTR_DEFAULT)
                          pmap_page_set_memattr(m, memattr);
                  pindex++;
          }
          vm_page_alloc_contig_vdrop(&deferred_vdrop_list);
          if (vm_paging_needed())
                  pagedaemon_wakeup();
          return (m_ret);
  }
  
  /*
   * Initialize a page that has been freshly dequeued from a freelist.
   * The caller has to drop the vnode returned, if it is not NULL.
   *
   * This function may only be used to initialize unmanaged pages.
   *
   * To be called with vm_page_queue_free_mtx held.
   */
  static struct vnode *
  vm_page_alloc_init(vm_page_t m)
  {
          struct vnode *drop;
          vm_object_t m_object;
  
          KASSERT(m->queue == PQ_NONE,
              ("vm_page_alloc_init: page %p has unexpected queue %d",
              m, m->queue));
          KASSERT(m->wire_count == 0,
              ("vm_page_alloc_init: page %p is wired", m));
          KASSERT(m->hold_count == 0,
              ("vm_page_alloc_init: page %p is held", m));
          KASSERT(!vm_page_busied(m),
              ("vm_page_alloc_init: page %p is busy", m));
          KASSERT(m->dirty == 0,
              ("vm_page_alloc_init: page %p is dirty", m));
          KASSERT(pmap_page_get_memattr(m) == VM_MEMATTR_DEFAULT,
              ("vm_page_alloc_init: page %p has unexpected memattr %d",
              m, pmap_page_get_memattr(m)));
          mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
          drop = NULL;
          if ((m->flags & PG_CACHED) != 0) {
                  KASSERT((m->flags & PG_ZERO) == 0,
                      ("vm_page_alloc_init: cached page %p is PG_ZERO", m));
                  m->valid = 0;
                  m_object = m->object;
                  vm_page_cache_remove(m);
                  if (m_object->type == OBJT_VNODE &&
                      vm_object_cache_is_empty(m_object))
                          drop = m_object->handle;
          } else {
                  KASSERT(VM_PAGE_IS_FREE(m),
                      ("vm_page_alloc_init: page %p is not free", m));
                  KASSERT(m->valid == 0,
                      ("vm_page_alloc_init: free page %p is valid", m));
                  vm_phys_freecnt_adj(m, -1);
                  if ((m->flags & PG_ZERO) != 0)
                          vm_page_zero_count--;
          }
          /* Don't clear the PG_ZERO flag; we'll need it later. */
          m->flags &= PG_ZERO;
          return (drop);
  }
  
  /*
   *      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
   *
   *      This routine may not sleep.
   */
  vm_page_t
  vm_page_alloc_freelist(int flind, int req)
  {
          struct vnode *drop;
          vm_page_t m;
          u_int flags;
          int req_class;
  
          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;
  
          /*
           * Do not allocate reserved pages unless the req has asked for it.
           */
          mtx_lock_flags(&vm_page_queue_free_mtx, MTX_RECURSE);
          if (cnt.v_free_count + cnt.v_cache_count > cnt.v_free_reserved ||
              (req_class == VM_ALLOC_SYSTEM &&
              cnt.v_free_count + cnt.v_cache_count > cnt.v_interrupt_free_min) ||
              (req_class == VM_ALLOC_INTERRUPT &&
              cnt.v_free_count + cnt.v_cache_count > 0))
                  m = vm_phys_alloc_freelist_pages(flind, VM_FREEPOOL_DIRECT, 0);
          else {
                  mtx_unlock(&vm_page_queue_free_mtx);
                  atomic_add_int(&vm_pageout_deficit,
                      max((u_int)req >> VM_ALLOC_COUNT_SHIFT, 1));
                  pagedaemon_wakeup();
                  return (NULL);
          }
          if (m == NULL) {
                  mtx_unlock(&vm_page_queue_free_mtx);
                  return (NULL);
          }
          drop = vm_page_alloc_init(m);
          mtx_unlock(&vm_page_queue_free_mtx);
  
          /*
           * Initialize the page.  Only the PG_ZERO flag is inherited.
           */
          m->aflags = 0;
          flags = 0;
          if ((req & VM_ALLOC_ZERO) != 0)
                  flags = PG_ZERO;
          m->flags &= flags;
          if ((req & VM_ALLOC_WIRED) != 0) {
                  /*
                   * The page lock is not required for wiring a page that does
                   * not belong to an object.
                   */
                  atomic_add_int(&cnt.v_wire_count, 1);
                  m->wire_count = 1;
          }
          /* Unmanaged pages don't use "act_count". */
          m->oflags = VPO_UNMANAGED;
          if (drop != NULL)
                  vdrop(drop);
          if (vm_paging_needed())
                  pagedaemon_wakeup();
          return (m);
  }
  
  /*
   *      vm_wait:        (also see VM_WAIT macro)
   *
   *      Sleep until free pages are available for allocation.
   *      - Called in various places before memory allocations.
   */
  void
  vm_wait(void)
  {
  
          mtx_lock(&vm_page_queue_free_mtx);
          if (curproc == pageproc) {
                  vm_pageout_pages_needed = 1;
                  msleep(&vm_pageout_pages_needed, &vm_page_queue_free_mtx,
                      PDROP | PSWP, "VMWait", 0);
          } else {
                  if (!vm_pages_needed) {
                          vm_pages_needed = 1;
                          wakeup(&vm_pages_needed);
                  }
                  msleep(&cnt.v_free_count, &vm_page_queue_free_mtx, PDROP | PVM,
                      "vmwait", 0);
          }
  }
  
  /*
   *      vm_waitpfault:  (also see VM_WAITPFAULT macro)
   *
   *      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(void)
  {
  
          mtx_lock(&vm_page_queue_free_mtx);
          if (!vm_pages_needed) {
                  vm_pages_needed = 1;
                  wakeup(&vm_pages_needed);
          }
          msleep(&cnt.v_free_count, &vm_page_queue_free_mtx, PDROP | PUSER,
              "pfault", 0);
  }
  
  struct vm_pagequeue *
  vm_page_pagequeue(vm_page_t m)
  {
  
          return (&vm_phys_domain(m)->vmd_pagequeues[m->queue]);
  }
  
  /*
   *      vm_page_dequeue:
   *
   *      Remove the given page from its current page queue.
   *
   *      The page must be locked.
   */
  void
  vm_page_dequeue(vm_page_t m)
  {
          struct vm_pagequeue *pq;
  
          vm_page_lock_assert(m, MA_OWNED);
          KASSERT(m->queue != PQ_NONE,
              ("vm_page_dequeue: page %p is not queued", m));
          pq = vm_page_pagequeue(m);
          vm_pagequeue_lock(pq);
          m->queue = PQ_NONE;
          TAILQ_REMOVE(&pq->pq_pl, m, plinks.q);
          vm_pagequeue_cnt_dec(pq);
          vm_pagequeue_unlock(pq);
  }
  
  /*
   *      vm_page_dequeue_locked:
   *
   *      Remove the given page from its current page queue.
   *
   *      The page and page queue must be locked.
   */
  void
  vm_page_dequeue_locked(vm_page_t m)
  {
          struct vm_pagequeue *pq;
  
          vm_page_lock_assert(m, MA_OWNED);
          pq = vm_page_pagequeue(m);
          vm_pagequeue_assert_locked(pq);
          m->queue = PQ_NONE;
          TAILQ_REMOVE(&pq->pq_pl, m, plinks.q);
          vm_pagequeue_cnt_dec(pq);
  }
  
  /*
   *      vm_page_enqueue:
   *
   *      Add the given page to the specified page queue.
   *
   *      The page must be locked.
   */
  static void
  vm_page_enqueue(int queue, vm_page_t m)
  {
          struct vm_pagequeue *pq;
  
          vm_page_lock_assert(m, MA_OWNED);
          pq = &vm_phys_domain(m)->vmd_pagequeues[queue];
          vm_pagequeue_lock(pq);
          m->queue = queue;
          TAILQ_INSERT_TAIL(&pq->pq_pl, m, plinks.q);
          vm_pagequeue_cnt_inc(pq);
          vm_pagequeue_unlock(pq);
  }
  
  /*
   *      vm_page_requeue:
   *
   *      Move the given page to the tail of its current page queue.
   *
   *      The page must be locked.
   */
  void
  vm_page_requeue(vm_page_t m)
  {
          struct vm_pagequeue *pq;
  
          vm_page_lock_assert(m, MA_OWNED);
          KASSERT(m->queue != PQ_NONE,
              ("vm_page_requeue: page %p is not queued", m));
          pq = vm_page_pagequeue(m);
          vm_pagequeue_lock(pq);
          TAILQ_REMOVE(&pq->pq_pl, m, plinks.q);
          TAILQ_INSERT_TAIL(&pq->pq_pl, m, plinks.q);
          vm_pagequeue_unlock(pq);
  }
  
  /*
   *      vm_page_requeue_locked:
   *
   *      Move the given page to the tail of its current page queue.
   *
   *      The page queue must be locked.
   */
  void
  vm_page_requeue_locked(vm_page_t m)
  {
          struct vm_pagequeue *pq;
  
          KASSERT(m->queue != PQ_NONE,
              ("vm_page_requeue_locked: page %p is not queued", m));
          pq = vm_page_pagequeue(m);
          vm_pagequeue_assert_locked(pq);
          TAILQ_REMOVE(&pq->pq_pl, m, plinks.q);
          TAILQ_INSERT_TAIL(&pq->pq_pl, m, plinks.q);
  }
  
  /*
   *      vm_page_activate:
   *
   *      Put the specified page on the active list (if appropriate).
   *      Ensure that act_count is at least ACT_INIT but do not otherwise
   *      mess with it.
   *
   *      The page must be locked.
   */
  void
  vm_page_activate(vm_page_t m)
  {
          int queue;
  
          vm_page_lock_assert(m, MA_OWNED);
          if ((queue = m->queue) != PQ_ACTIVE) {
                  if (m->wire_count == 0 && (m->oflags & VPO_UNMANAGED) == 0) {
                          if (m->act_count < ACT_INIT)
                                  m->act_count = ACT_INIT;
                          if (queue != PQ_NONE)
                                  vm_page_dequeue(m);
                          vm_page_enqueue(PQ_ACTIVE, m);
                  } else
                          KASSERT(queue == PQ_NONE,
                              ("vm_page_activate: wired page %p is queued", m));
          } else {
                  if (m->act_count < ACT_INIT)
                          m->act_count = ACT_INIT;
          }
  }
  
  /*
   *      vm_page_free_wakeup:
   *
   *      Helper routine for vm_page_free_toq() and vm_page_cache().  This
   *      routine is called when a page has been added to the cache or free
   *      queues.
   *
   *      The page queues must be locked.
   */
  static inline void
  vm_page_free_wakeup(void)
  {
  
          mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
          /*
           * if pageout daemon needs pages, then tell it that there are
           * some free.
           */
          if (vm_pageout_pages_needed &&
              cnt.v_cache_count + cnt.v_free_count >= cnt.v_pageout_free_min) {
                  wakeup(&vm_pageout_pages_needed);
                  vm_pageout_pages_needed = 0;
          }
          /*
           * wakeup processes that are waiting on memory if we hit a
           * high water mark. And wakeup scheduler process if we have
           * lots of memory. this process will swapin processes.
           */
          if (vm_pages_needed && !vm_page_count_min()) {
                  vm_pages_needed = 0;
                  wakeup(&cnt.v_free_count);
          }
  }
  
  /*
   *      Turn a cached page into a free page, by changing its attributes.
   *      Keep the statistics up-to-date.
   *
   *      The free page queue must be locked.
   */
  static void
  vm_page_cache_turn_free(vm_page_t m)
  {
  
          mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
  
          m->object = NULL;
          m->valid = 0;
          /* Clear PG_CACHED and set PG_FREE. */
          m->flags ^= PG_CACHED | PG_FREE;
          KASSERT((m->flags & (PG_CACHED | PG_FREE)) == PG_FREE,
              ("vm_page_cache_free: page %p has inconsistent flags", m));
          cnt.v_cache_count--;
          vm_phys_freecnt_adj(m, 1);
  }
  
  /*
   *      vm_page_free_toq:
   *
   *      Returns the given page to the free list,
   *      disassociating it with any VM object.
   *
   *      The object must be locked.  The page must be locked if it is managed.
   */
  void
  vm_page_free_toq(vm_page_t m)
  {
  
          if ((m->oflags & VPO_UNMANAGED) == 0) {
                  vm_page_lock_assert(m, MA_OWNED);
                  KASSERT(!pmap_page_is_mapped(m),
                      ("vm_page_free_toq: freeing mapped page %p", m));
          } else
                  KASSERT(m->queue == PQ_NONE,
                      ("vm_page_free_toq: unmanaged page %p is queued", m));
          PCPU_INC(cnt.v_tfree);
  
          if (VM_PAGE_IS_FREE(m))
                  panic("vm_page_free: freeing free page %p", m);
          else if (vm_page_sbusied(m))
                  panic("vm_page_free: freeing busy page %p", m);
  
          /*
           * Unqueue, then remove page.  Note that we cannot destroy
           * the page here because we do not want to call the pager's
           * callback routine until after we've put the page on the
           * appropriate free queue.
           */
          vm_page_remque(m);
          vm_page_remove(m);
  
          /*
           * If fictitious remove object association and
           * return, otherwise delay object association removal.
           */
          if ((m->flags & PG_FICTITIOUS) != 0) {
                  return;
          }
  
          m->valid = 0;
          vm_page_undirty(m);
  
          if (m->wire_count != 0)
                  panic("vm_page_free: freeing wired page %p", m);
          if (m->hold_count != 0) {
                  m->flags &= ~PG_ZERO;
                  KASSERT((m->flags & PG_UNHOLDFREE) == 0,
                      ("vm_page_free: freeing PG_UNHOLDFREE page %p", m));
                  m->flags |= PG_UNHOLDFREE;
          } else {
                  /*
                   * 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);
  
                  /*
                   * Insert the page into the physical memory allocator's
                   * cache/free page queues.
                   */
                  mtx_lock(&vm_page_queue_free_mtx);
                  m->flags |= PG_FREE;
                  vm_phys_freecnt_adj(m, 1);
  #if VM_NRESERVLEVEL > 0
                  if (!vm_reserv_free_page(m))
  #else
                  if (TRUE)
  #endif
                          vm_phys_free_pages(m, 0);
                  if ((m->flags & PG_ZERO) != 0)
                          ++vm_page_zero_count;
                  else
                          vm_page_zero_idle_wakeup();
                  vm_page_free_wakeup();
                  mtx_unlock(&vm_page_queue_free_mtx);
          }
  }
  
  /*
   *      vm_page_wire:
   *
   *      Mark this page as wired down by yet
   *      another map, removing it from paging queues
   *      as necessary.
   *
   *      If the page is fictitious, then its wire count must remain one.
   *
   *      The page must be locked.
   */
  void
  vm_page_wire(vm_page_t m)
  {
  
          /*
           * Only bump the wire statistics if the page is not already wired,
           * and only unqueue the page if it is on some queue (if it is unmanaged
           * it is already off the queues).
           */
          vm_page_lock_assert(m, MA_OWNED);
          if ((m->flags & PG_FICTITIOUS) != 0) {
                  KASSERT(m->wire_count == 1,
                      ("vm_page_wire: fictitious page %p's wire count isn't one",
                      m));
                  return;
          }
          if (m->wire_count == 0) {
                  KASSERT((m->oflags & VPO_UNMANAGED) == 0 ||
                      m->queue == PQ_NONE,
                      ("vm_page_wire: unmanaged page %p is queued", m));
                  vm_page_remque(m);
                  atomic_add_int(&cnt.v_wire_count, 1);
          }
          m->wire_count++;
          KASSERT(m->wire_count != 0, ("vm_page_wire: wire_count overflow m=%p", m));
  }
  
  /*
   * vm_page_unwire:
   *
   * Release one wiring of the specified page, potentially enabling it to be
   * paged again.  If paging is enabled, then the value of the parameter
   * "activate" determines to which queue the page is added.  If "activate" is
   * non-zero, then the page is added to the active queue.  Otherwise, it is
   * added to the inactive queue.
   *
   * However, unless the page belongs to an object, it is not enqueued because
   * it cannot be paged out.
   *
   * If a page is fictitious, then its wire count must always be one.
   *
   * A managed page must be locked.
   */
  void
  vm_page_unwire(vm_page_t m, int activate)
  {
  
          if ((m->oflags & VPO_UNMANAGED) == 0)
                  vm_page_lock_assert(m, MA_OWNED);
          if ((m->flags & PG_FICTITIOUS) != 0) {
                  KASSERT(m->wire_count == 1,
              ("vm_page_unwire: fictitious page %p's wire count isn't one", m));
                  return;
          }
          if (m->wire_count > 0) {
                  m->wire_count--;
                  if (m->wire_count == 0) {
                          atomic_subtract_int(&cnt.v_wire_count, 1);
                          if ((m->oflags & VPO_UNMANAGED) != 0 ||
                              m->object == NULL)
                                  return;
                          if (!activate)
                                  m->flags &= ~PG_WINATCFLS;
                          vm_page_enqueue(activate ? PQ_ACTIVE : PQ_INACTIVE, m);
                  }
          } else
                  panic("vm_page_unwire: page %p's wire count is zero", m);
  }
  
  /*
   * Move the specified page to the inactive queue.
   *
   * Many pages placed on the inactive queue should actually go
   * into the cache, but it is difficult to figure out which.  What
   * we do instead, if the inactive target is well met, is to put
   * clean pages at the head of the inactive queue instead of the tail.
   * This will cause them to be moved to the cache more quickly and
   * if not actively re-referenced, reclaimed more quickly.  If we just
   * stick these pages at the end of the inactive queue, heavy filesystem
   * meta-data accesses can cause an unnecessary paging load on memory bound 
   * processes.  This optimization causes one-time-use metadata to be
   * reused more quickly.
   *
   * Normally athead is 0 resulting in LRU operation.  athead is set
   * to 1 if we want this page to be 'as if it were placed in the cache',
   * except without unmapping it from the process address space.
   *
   * The page must be locked.
   */
  static inline void
  _vm_page_deactivate(vm_page_t m, int athead)
  {
          struct vm_pagequeue *pq;
          int queue;
  
          vm_page_assert_locked(m);
  
          /*
           * Ignore if the page is already inactive, unless it is unlikely to be
           * reactivated.
           */
          if ((queue = m->queue) == PQ_INACTIVE && !athead)
                  return;
          if (m->wire_count == 0 && (m->oflags & VPO_UNMANAGED) == 0) {
                  pq = &vm_phys_domain(m)->vmd_pagequeues[PQ_INACTIVE];
                  /* Avoid multiple acquisitions of the inactive queue lock. */
                  if (queue == PQ_INACTIVE) {
                          vm_pagequeue_lock(pq);
                          vm_page_dequeue_locked(m);
                  } else {
                          if (queue != PQ_NONE)
                                  vm_page_dequeue(m);
                          m->flags &= ~PG_WINATCFLS;
                          vm_pagequeue_lock(pq);
                  }
                  m->queue = PQ_INACTIVE;
                  if (athead)
                          TAILQ_INSERT_HEAD(&pq->pq_pl, m, plinks.q);
                  else
                          TAILQ_INSERT_TAIL(&pq->pq_pl, m, plinks.q);
                  vm_pagequeue_cnt_inc(pq);
                  vm_pagequeue_unlock(pq);
          }
  }
  
  /*
   * Move the specified page to the inactive queue.
   *
   * The page must be locked.
   */
  void
  vm_page_deactivate(vm_page_t m)
  {
  
          _vm_page_deactivate(m, 0);
  }
  
  /*
   * vm_page_try_to_cache:
   *
   * Returns 0 on failure, 1 on success
   */
  int
  vm_page_try_to_cache(vm_page_t m)
  {
  
          vm_page_lock_assert(m, MA_OWNED);
          VM_OBJECT_ASSERT_WLOCKED(m->object);
          if (m->dirty || m->hold_count || m->wire_count ||
              (m->oflags & VPO_UNMANAGED) != 0 || vm_page_busied(m))
                  return (0);
          pmap_remove_all(m);
          if (m->dirty)
                  return (0);
          vm_page_cache(m);
          return (1);
  }
  
  /*
   * vm_page_try_to_free()
   *
   *      Attempt to free the page.  If we cannot free it, we do nothing.
   *      1 is returned on success, 0 on failure.
   */
  int
  vm_page_try_to_free(vm_page_t m)
  {
  
          vm_page_lock_assert(m, MA_OWNED);
          if (m->object != NULL)
                  VM_OBJECT_ASSERT_WLOCKED(m->object);
          if (m->dirty || m->hold_count || m->wire_count ||
              (m->oflags & VPO_UNMANAGED) != 0 || vm_page_busied(m))
                  return (0);
          pmap_remove_all(m);
          if (m->dirty)
                  return (0);
          vm_page_free(m);
          return (1);
  }
  
  /*
   * vm_page_cache
   *
   * Put the specified page onto the page cache queue (if appropriate).
   *
   * The object and page must be locked.
   */
  void
  vm_page_cache(vm_page_t m)
  {
          vm_object_t object;
          boolean_t cache_was_empty;
  
          vm_page_lock_assert(m, MA_OWNED);
          object = m->object;
          VM_OBJECT_ASSERT_WLOCKED(object);
          if (vm_page_busied(m) || (m->oflags & VPO_UNMANAGED) ||
              m->hold_count || m->wire_count)
                  panic("vm_page_cache: attempting to cache busy page");
          KASSERT(!pmap_page_is_mapped(m),
              ("vm_page_cache: page %p is mapped", m));
          KASSERT(m->dirty == 0, ("vm_page_cache: page %p is dirty", m));
          if (m->valid == 0 || object->type == OBJT_DEFAULT ||
              (object->type == OBJT_SWAP &&
              !vm_pager_has_page(object, m->pindex, NULL, NULL))) {
                  /*
                   * Hypothesis: A cache-elgible page belonging to a
                   * default object or swap object but without a backing
                   * store must be zero filled.
                   */
                  vm_page_free(m);
                  return;
          }
          KASSERT((m->flags & PG_CACHED) == 0,
              ("vm_page_cache: page %p is already cached", m));
  
          /*
           * Remove the page from the paging queues.
           */
          vm_page_remque(m);
  
          /*
           * Remove the page from the object's collection of resident
           * pages. 
           */
          vm_radix_remove(&object->rtree, m->pindex);
          TAILQ_REMOVE(&object->memq, m, listq);
          object->resident_page_count--;
  
          /*
           * 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);
  
          /*
           * Insert the page into the object's collection of cached pages
           * and the physical memory allocator's cache/free page queues.
           */
          m->flags &= ~PG_ZERO;
          mtx_lock(&vm_page_queue_free_mtx);
          cache_was_empty = vm_radix_is_empty(&object->cache);
          if (vm_radix_insert(&object->cache, m)) {
                  mtx_unlock(&vm_page_queue_free_mtx);
                  if (object->type == OBJT_VNODE &&
                      object->resident_page_count == 0)
                          vdrop(object->handle);
                  m->object = NULL;
                  vm_page_free(m);
                  return;
          }
  
          /*
           * The above call to vm_radix_insert() could reclaim the one pre-
           * existing cached page from this object, resulting in a call to
           * vdrop().
           */
          if (!cache_was_empty)
                  cache_was_empty = vm_radix_is_singleton(&object->cache);
  
          m->flags |= PG_CACHED;
          cnt.v_cache_count++;
          PCPU_INC(cnt.v_tcached);
  #if VM_NRESERVLEVEL > 0
          if (!vm_reserv_free_page(m)) {
  #else
          if (TRUE) {
  #endif
                  vm_phys_set_pool(VM_FREEPOOL_CACHE, m, 0);
                  vm_phys_free_pages(m, 0);
          }
          vm_page_free_wakeup();
          mtx_unlock(&vm_page_queue_free_mtx);
  
          /*
           * Increment the vnode's hold count if this is the object's only
           * cached page.  Decrement the vnode's hold count if this was
           * the object's only resident page.
           */
          if (object->type == OBJT_VNODE) {
                  if (cache_was_empty && object->resident_page_count != 0)
                          vhold(object->handle);
                  else if (!cache_was_empty && object->resident_page_count == 0)
                          vdrop(object->handle);
          }
  }
  
  /*
   * vm_page_advise
   *
   *      Deactivate or do nothing, as appropriate.  This routine is used
   *      by madvise() and vop_stdadvise().
   *
   *      The object and page must be locked.
   */
  void
  vm_page_advise(vm_page_t m, int advice)
  {
  
          vm_page_assert_locked(m);
          VM_OBJECT_ASSERT_WLOCKED(m->object);
          if (advice == MADV_FREE)
                  /*
                   * Mark the page clean.  This will allow the page to be freed
                   * up by the system.  However, such pages are often reused
                   * quickly by malloc() so we do not do anything that would
                   * cause a page fault if we can help it.
                   *
                   * Specifically, we do not try to actually free the page now
                   * nor do we try to put it in the cache (which would cause a
                   * page fault on reuse).
                   *
                   * But we do make the page as freeable as we can without
                   * actually taking the step of unmapping it.
                   */
                  vm_page_undirty(m);
          else if (advice != MADV_DONTNEED)
                  return;
  
          /*
           * Clear any references to the page.  Otherwise, the page daemon will
           * immediately reactivate the page.
           */
          vm_page_aflag_clear(m, PGA_REFERENCED);
  
          if (advice != MADV_FREE && m->dirty == 0 && pmap_is_modified(m))
                  vm_page_dirty(m);
  
          /*
           * Place clean pages at 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.
           */
          _vm_page_deactivate(m, m->dirty == 0);
  }
  
  /*
   * 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;
          int sleep;
  
          VM_OBJECT_ASSERT_WLOCKED(object);
          KASSERT((allocflags & VM_ALLOC_SBUSY) == 0 ||
              (allocflags & VM_ALLOC_IGN_SBUSY) != 0,
              ("vm_page_grab: VM_ALLOC_SBUSY/VM_ALLOC_IGN_SBUSY mismatch"));
  retrylookup:
          if ((m = vm_page_lookup(object, pindex)) != NULL) {
                  sleep = (allocflags & VM_ALLOC_IGN_SBUSY) != 0 ?
                      vm_page_xbusied(m) : vm_page_busied(m);
                  if (sleep) {
                          /*
                           * Reference the page before unlocking and
                           * sleeping so that the page daemon is less
                           * likely to reclaim it.
                           */
                          vm_page_aflag_set(m, PGA_REFERENCED);
                          vm_page_lock(m);
                          VM_OBJECT_WUNLOCK(object);
                          vm_page_busy_sleep(m, "pgrbwt", (allocflags &
                              VM_ALLOC_IGN_SBUSY) != 0);
                          VM_OBJECT_WLOCK(object);
                          goto retrylookup;
                  } else {
                          if ((allocflags & VM_ALLOC_WIRED) != 0) {
                                  vm_page_lock(m);
                                  vm_page_wire(m);
                                  vm_page_unlock(m);
                          }
                          if ((allocflags &
                              (VM_ALLOC_NOBUSY | VM_ALLOC_SBUSY)) == 0)
                                  vm_page_xbusy(m);
                          if ((allocflags & VM_ALLOC_SBUSY) != 0)
                                  vm_page_sbusy(m);
                          return (m);
                  }
          }
          m = vm_page_alloc(object, pindex, allocflags & ~VM_ALLOC_IGN_SBUSY);
          if (m == NULL) {
                  VM_OBJECT_WUNLOCK(object);
                  VM_WAIT;
                  VM_OBJECT_WLOCK(object);
                  goto retrylookup;
          } else if (m->valid != 0)
                  return (m);
          if (allocflags & VM_ALLOC_ZERO && (m->flags & PG_ZERO) == 0)
                  pmap_zero_page(m);
          return (m);
  }
  
  /*
   * 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));
  }
  
  /*
   *      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_OBJECT_ASSERT_WLOCKED(m->object);
          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 = base & ~(DEV_BSIZE - 1)) != 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 = endoff & ~(DEV_BSIZE - 1)) != 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.
           */
          m->valid |= vm_page_bits(base, size);
  }
  
  /*
   * 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)
  {
          uintptr_t addr;
  #if PAGE_SIZE < 16384
          int shift;
  #endif
  
          /*
           * If the object is locked and the page is neither exclusive busy nor
           * write mapped, then the page's dirty field cannot possibly be
           * set by a concurrent pmap operation.
           */
          VM_OBJECT_ASSERT_WLOCKED(m->object);
          if (!vm_page_xbusied(m) && !pmap_page_is_write_mapped(m))
                  m->dirty &= ~pagebits;
          else {
                  /*
                   * The pmap layer can call vm_page_dirty() without
                   * holding a distinguished lock.  The combination of
                   * the object's lock and an atomic operation suffice
                   * to guarantee consistency of the page dirty field.
                   *
                   * For PAGE_SIZE == 32768 case, compiler already
                   * properly aligns the dirty field, so no forcible
                   * alignment is needed. Only require existence of
                   * atomic_clear_64 when page size is 32768.
                   */
                  addr = (uintptr_t)&m->dirty;
  #if PAGE_SIZE == 32768
                  atomic_clear_64((uint64_t *)addr, pagebits);
  #elif PAGE_SIZE == 16384
                  atomic_clear_32((uint32_t *)addr, pagebits);
  #else           /* PAGE_SIZE <= 8192 */
                  /*
                   * Use a trick to perform a 32-bit atomic on the
                   * containing aligned word, to not depend on the existence
                   * of atomic_clear_{8, 16}.
                   */
                  shift = addr & (sizeof(uint32_t) - 1);
  #if BYTE_ORDER == BIG_ENDIAN
                  shift = (sizeof(uint32_t) - sizeof(m->dirty) - shift) * NBBY;
  #else
                  shift *= NBBY;
  #endif
                  addr &= ~(sizeof(uint32_t) - 1);
                  atomic_clear_32((uint32_t *)addr, pagebits << shift);
  #endif          /* PAGE_SIZE */
          }
  }
  
  /*
   *      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_OBJECT_ASSERT_WLOCKED(m->object);
          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 = base & ~(DEV_BSIZE - 1)) != 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 = endoff & ~(DEV_BSIZE - 1)) != 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 VPO_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);
          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;
                  m->oflags &= ~VPO_NOSYNC;
          } else if (oldvalid != VM_PAGE_BITS_ALL)
                  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;
  
          object = m->object;
          VM_OBJECT_ASSERT_WLOCKED(object);
          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 && m->valid == VM_PAGE_BITS_ALL &&
              bits != 0)
                  pmap_remove_all(m);
          KASSERT((bits == 0 && m->valid == VM_PAGE_BITS_ALL) ||
              !pmap_page_is_mapped(m),
              ("vm_page_set_invalid: page %p is mapped", m));
          m->valid &= ~bits;
          m->dirty &= ~bits;
  }
  
  /*
   * 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;
  
          VM_OBJECT_ASSERT_WLOCKED(m->object);
          /*
           * 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)
                  m->valid = VM_PAGE_BITS_ALL;
  }
  
  /*
   *      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.
   */
  int
  vm_page_is_valid(vm_page_t m, int base, int size)
  {
          vm_page_bits_t bits;
  
          VM_OBJECT_ASSERT_LOCKED(m->object);
          bits = vm_page_bits(base, size);
          return (m->valid != 0 && (m->valid & bits) == bits);
  }
  
  /*
   *      vm_page_ps_is_valid:
   *
   *      Returns TRUE if the entire (super)page is valid and FALSE otherwise.
   */
  boolean_t
  vm_page_ps_is_valid(vm_page_t m)
  {
          int i, npages;
  
          VM_OBJECT_ASSERT_LOCKED(m->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++) {
                  if (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_OBJECT_ASSERT_WLOCKED(m->object);
          if (m->dirty != VM_PAGE_BITS_ALL && pmap_is_modified(m))
                  vm_page_dirty(m);
  }
  
  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_lock_assert(vm_page_t m)
  {
  
          /*
           * Certain of the page's fields may only be modified by the
           * holder of the containing object's lock or the exclusive busy.
           * holder.  Unfortunately, the holder of the write busy is
           * not recorded, and thus cannot be checked here.
           */
          if (m->object != NULL && !vm_page_xbusied(m))
                  VM_OBJECT_ASSERT_WLOCKED(m->object);
  }
  
  void
  vm_page_assert_pga_writeable(vm_page_t m, uint8_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_LOCKED(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("cnt.v_free_count: %d\n", cnt.v_free_count);
          db_printf("cnt.v_cache_count: %d\n", cnt.v_cache_count);
          db_printf("cnt.v_inactive_count: %d\n", cnt.v_inactive_count);
          db_printf("cnt.v_active_count: %d\n", cnt.v_active_count);
          db_printf("cnt.v_wire_count: %d\n", cnt.v_wire_count);
          db_printf("cnt.v_free_reserved: %d\n", cnt.v_free_reserved);
          db_printf("cnt.v_free_min: %d\n", cnt.v_free_min);
          db_printf("cnt.v_free_target: %d\n", cnt.v_free_target);
          db_printf("cnt.v_cache_min: %d\n", cnt.v_cache_min);
          db_printf("cnt.v_inactive_target: %d\n", cnt.v_inactive_target);
  }
  
  DB_SHOW_COMMAND(pageq, vm_page_print_pageq_info)
  {
          int dom;
  
          db_printf("pq_free %d pq_cache %d\n",
              cnt.v_free_count, cnt.v_cache_count);
          for (dom = 0; dom < vm_ndomains; dom++) {
                  db_printf(
          "dom %d page_cnt %d free %d pq_act %d pq_inact %d pass %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_pass);
          }
  }
  
  DB_SHOW_COMMAND(pginfo, vm_page_print_pginfo)
  {
          vm_page_t m;
          boolean_t phys;
  
          if (!have_addr) {
                  db_printf("show pginfo addr\n");
                  return;
          }
  
          phys = strchr(modif, 'p') != NULL;
          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 hold %d wire %d\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->queue, m->hold_count, m->wire_count, m->aflags, m->oflags,
              m->flags, m->act_count, m->busy_lock, m->valid, m->dirty);
  }
  #endif /* DDB */