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

     /*-
      * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
      *
      * Copyright (c) 2002-2006 Rice University
      * Copyright (c) 2007-2011 Alan L. Cox <alc@cs.rice.edu>
      * All rights reserved.
      *
      * This software was developed for the FreeBSD Project by Alan L. Cox,
      * Olivier Crameri, Peter Druschel, Sitaram Iyer, and Juan Navarro.
     *
     * 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.
     *
     * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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 COPYRIGHT
     * HOLDERS 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.
     */
    
    /*
     *      Superpage reservation management module
     *
     * Any external functions defined by this module are only to be used by the
     * virtual memory system.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include "opt_vm.h"
    
    #include <sys/param.h>
    #include <sys/kernel.h>
    #include <sys/lock.h>
    #include <sys/malloc.h>
    #include <sys/mutex.h>
    #include <sys/queue.h>
    #include <sys/rwlock.h>
    #include <sys/sbuf.h>
    #include <sys/sysctl.h>
    #include <sys/systm.h>
    #include <sys/counter.h>
    #include <sys/ktr.h>
    #include <sys/vmmeter.h>
    #include <sys/smp.h>
    
    #include <vm/vm.h>
    #include <vm/vm_param.h>
    #include <vm/vm_object.h>
    #include <vm/vm_page.h>
    #include <vm/vm_pageout.h>
    #include <vm/vm_phys.h>
    #include <vm/vm_pagequeue.h>
    #include <vm/vm_radix.h>
    #include <vm/vm_reserv.h>
    
    /*
     * The reservation system supports the speculative allocation of large physical
     * pages ("superpages").  Speculative allocation enables the fully automatic
     * utilization of superpages by the virtual memory system.  In other words, no
     * programmatic directives are required to use superpages.
     */
    
    #if VM_NRESERVLEVEL > 0
    
    #ifndef VM_LEVEL_0_ORDER_MAX
    #define VM_LEVEL_0_ORDER_MAX    VM_LEVEL_0_ORDER
    #endif
    
    /*
     * The number of small pages that are contained in a level 0 reservation
     */
    #define VM_LEVEL_0_NPAGES       (1 << VM_LEVEL_0_ORDER)
    #define VM_LEVEL_0_NPAGES_MAX   (1 << VM_LEVEL_0_ORDER_MAX)
    
    /*
     * The number of bits by which a physical address is shifted to obtain the
     * reservation number
     */
    #define VM_LEVEL_0_SHIFT        (VM_LEVEL_0_ORDER + PAGE_SHIFT)
    
    /*
     * The size of a level 0 reservation in bytes
     */
    #define VM_LEVEL_0_SIZE         (1 << VM_LEVEL_0_SHIFT)
   
   /*
    * Computes the index of the small page underlying the given (object, pindex)
    * within the reservation's array of small pages.
    */
   #define VM_RESERV_INDEX(object, pindex) \
       (((object)->pg_color + (pindex)) & (VM_LEVEL_0_NPAGES - 1))
   
   /*
    * The size of a population map entry
    */
   typedef u_long          popmap_t;
   
   /*
    * The number of bits in a population map entry
    */
   #define NBPOPMAP        (NBBY * sizeof(popmap_t))
   
   /*
    * The number of population map entries in a reservation
    */
   #define NPOPMAP         howmany(VM_LEVEL_0_NPAGES, NBPOPMAP)
   #define NPOPMAP_MAX     howmany(VM_LEVEL_0_NPAGES_MAX, NBPOPMAP)
   
   /*
    * Number of elapsed ticks before we update the LRU queue position.  Used
    * to reduce contention and churn on the list.
    */
   #define PARTPOPSLOP     1
   
   /*
    * Clear a bit in the population map.
    */
   static __inline void
   popmap_clear(popmap_t popmap[], int i)
   {
   
           popmap[i / NBPOPMAP] &= ~(1UL << (i % NBPOPMAP));
   }
   
   /*
    * Set a bit in the population map.
    */
   static __inline void
   popmap_set(popmap_t popmap[], int i)
   {
   
           popmap[i / NBPOPMAP] |= 1UL << (i % NBPOPMAP);
   }
   
   /*
    * Is a bit in the population map clear?
    */
   static __inline boolean_t
   popmap_is_clear(popmap_t popmap[], int i)
   {
   
           return ((popmap[i / NBPOPMAP] & (1UL << (i % NBPOPMAP))) == 0);
   }
   
   /*
    * Is a bit in the population map set?
    */
   static __inline boolean_t
   popmap_is_set(popmap_t popmap[], int i)
   {
   
           return ((popmap[i / NBPOPMAP] & (1UL << (i % NBPOPMAP))) != 0);
   }
   
   /*
    * The reservation structure
    *
    * A reservation structure is constructed whenever a large physical page is
    * speculatively allocated to an object.  The reservation provides the small
    * physical pages for the range [pindex, pindex + VM_LEVEL_0_NPAGES) of offsets
    * within that object.  The reservation's "popcnt" tracks the number of these
    * small physical pages that are in use at any given time.  When and if the
    * reservation is not fully utilized, it appears in the queue of partially
    * populated reservations.  The reservation always appears on the containing
    * object's list of reservations.
    *
    * A partially populated reservation can be broken and reclaimed at any time.
    *
    * c - constant after boot
    * d - vm_reserv_domain_lock
    * o - vm_reserv_object_lock
    * r - vm_reserv_lock
    * s - vm_reserv_domain_scan_lock
    */
   struct vm_reserv {
           struct mtx      lock;                   /* reservation lock. */
           TAILQ_ENTRY(vm_reserv) partpopq;        /* (d, r) per-domain queue. */
           LIST_ENTRY(vm_reserv) objq;             /* (o, r) object queue */
           vm_object_t     object;                 /* (o, r) containing object */
           vm_pindex_t     pindex;                 /* (o, r) offset in object */
           vm_page_t       pages;                  /* (c) first page  */
           uint16_t        popcnt;                 /* (r) # of pages in use */
           uint8_t         domain;                 /* (c) NUMA domain. */
           char            inpartpopq;             /* (d, r) */
           int             lasttick;               /* (r) last pop update tick. */
           popmap_t        popmap[NPOPMAP_MAX];    /* (r) bit vector, used pages */
   };
   
   TAILQ_HEAD(vm_reserv_queue, vm_reserv);
   
   #define vm_reserv_lockptr(rv)           (&(rv)->lock)
   #define vm_reserv_assert_locked(rv)                                     \
               mtx_assert(vm_reserv_lockptr(rv), MA_OWNED)
   #define vm_reserv_lock(rv)              mtx_lock(vm_reserv_lockptr(rv))
   #define vm_reserv_trylock(rv)           mtx_trylock(vm_reserv_lockptr(rv))
   #define vm_reserv_unlock(rv)            mtx_unlock(vm_reserv_lockptr(rv))
   
   /*
    * The reservation array
    *
    * This array is analoguous in function to vm_page_array.  It differs in the
    * respect that it may contain a greater number of useful reservation
    * structures than there are (physical) superpages.  These "invalid"
    * reservation structures exist to trade-off space for time in the
    * implementation of vm_reserv_from_page().  Invalid reservation structures are
    * distinguishable from "valid" reservation structures by inspecting the
    * reservation's "pages" field.  Invalid reservation structures have a NULL
    * "pages" field.
    *
    * vm_reserv_from_page() maps a small (physical) page to an element of this
    * array by computing a physical reservation number from the page's physical
    * address.  The physical reservation number is used as the array index.
    *
    * An "active" reservation is a valid reservation structure that has a non-NULL
    * "object" field and a non-zero "popcnt" field.  In other words, every active
    * reservation belongs to a particular object.  Moreover, every active
    * reservation has an entry in the containing object's list of reservations.  
    */
   static vm_reserv_t vm_reserv_array;
   
   /*
    * The per-domain partially populated reservation queues
    *
    * These queues enable the fast recovery of an unused free small page from a
    * partially populated reservation.  The reservation at the head of a queue
    * is the least recently changed, partially populated reservation.
    *
    * Access to this queue is synchronized by the per-domain reservation lock.
    * Threads reclaiming free pages from the queue must hold the per-domain scan
    * lock.
    */
   struct vm_reserv_domain {
           struct mtx              lock;
           struct vm_reserv_queue  partpop;        /* (d) */
           struct vm_reserv        marker;         /* (d, s) scan marker/lock */
   } __aligned(CACHE_LINE_SIZE);
   
   static struct vm_reserv_domain vm_rvd[MAXMEMDOM];
   
   #define vm_reserv_domain_lockptr(d)     (&vm_rvd[(d)].lock)
   #define vm_reserv_domain_assert_locked(d)       \
           mtx_assert(vm_reserv_domain_lockptr(d), MA_OWNED)
   #define vm_reserv_domain_lock(d)        mtx_lock(vm_reserv_domain_lockptr(d))
   #define vm_reserv_domain_unlock(d)      mtx_unlock(vm_reserv_domain_lockptr(d))
   
   #define vm_reserv_domain_scan_lock(d)   mtx_lock(&vm_rvd[(d)].marker.lock)
   #define vm_reserv_domain_scan_unlock(d) mtx_unlock(&vm_rvd[(d)].marker.lock)
   
   static SYSCTL_NODE(_vm, OID_AUTO, reserv, CTLFLAG_RD, 0, "Reservation Info");
   
   static counter_u64_t vm_reserv_broken = EARLY_COUNTER;
   SYSCTL_COUNTER_U64(_vm_reserv, OID_AUTO, broken, CTLFLAG_RD,
       &vm_reserv_broken, "Cumulative number of broken reservations");
   
   static counter_u64_t vm_reserv_freed = EARLY_COUNTER;
   SYSCTL_COUNTER_U64(_vm_reserv, OID_AUTO, freed, CTLFLAG_RD,
       &vm_reserv_freed, "Cumulative number of freed reservations");
   
   static int sysctl_vm_reserv_fullpop(SYSCTL_HANDLER_ARGS);
   
   SYSCTL_PROC(_vm_reserv, OID_AUTO, fullpop, CTLTYPE_INT | CTLFLAG_RD, NULL, 0,
       sysctl_vm_reserv_fullpop, "I", "Current number of full reservations");
   
   static int sysctl_vm_reserv_partpopq(SYSCTL_HANDLER_ARGS);
   
   SYSCTL_OID(_vm_reserv, OID_AUTO, partpopq,
       CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MPSAFE, NULL, 0,
       sysctl_vm_reserv_partpopq, "A",
       "Partially populated reservation queues");
   
   static counter_u64_t vm_reserv_reclaimed = EARLY_COUNTER;
   SYSCTL_COUNTER_U64(_vm_reserv, OID_AUTO, reclaimed, CTLFLAG_RD,
       &vm_reserv_reclaimed, "Cumulative number of reclaimed reservations");
   
   /*
    * The object lock pool is used to synchronize the rvq.  We can not use a
    * pool mutex because it is required before malloc works.
    *
    * The "hash" function could be made faster without divide and modulo.
    */
   #define VM_RESERV_OBJ_LOCK_COUNT        MAXCPU
   
   struct mtx_padalign vm_reserv_object_mtx[VM_RESERV_OBJ_LOCK_COUNT];
   
   #define vm_reserv_object_lock_idx(object)                       \
               (((uintptr_t)object / sizeof(*object)) % VM_RESERV_OBJ_LOCK_COUNT)
   #define vm_reserv_object_lock_ptr(object)                       \
               &vm_reserv_object_mtx[vm_reserv_object_lock_idx((object))]
   #define vm_reserv_object_lock(object)                           \
               mtx_lock(vm_reserv_object_lock_ptr((object)))
   #define vm_reserv_object_unlock(object)                         \
               mtx_unlock(vm_reserv_object_lock_ptr((object)))
   
   static void             vm_reserv_break(vm_reserv_t rv);
   static void             vm_reserv_depopulate(vm_reserv_t rv, int index);
   static vm_reserv_t      vm_reserv_from_page(vm_page_t m);
   static boolean_t        vm_reserv_has_pindex(vm_reserv_t rv,
                               vm_pindex_t pindex);
   static void             vm_reserv_populate(vm_reserv_t rv, int index);
   static void             vm_reserv_reclaim(vm_reserv_t rv);
   
   /*
    * Returns the current number of full reservations.
    *
    * Since the number of full reservations is computed without acquiring any
    * locks, the returned value is inexact.
    */
   static int
   sysctl_vm_reserv_fullpop(SYSCTL_HANDLER_ARGS)
   {
           vm_paddr_t paddr;
           struct vm_phys_seg *seg;
           vm_reserv_t rv;
           int fullpop, segind;
   
           fullpop = 0;
           for (segind = 0; segind < vm_phys_nsegs; segind++) {
                   seg = &vm_phys_segs[segind];
                   paddr = roundup2(seg->start, VM_LEVEL_0_SIZE);
                   while (paddr + VM_LEVEL_0_SIZE > paddr && paddr +
                       VM_LEVEL_0_SIZE <= seg->end) {
                           rv = &vm_reserv_array[paddr >> VM_LEVEL_0_SHIFT];
                           fullpop += rv->popcnt == VM_LEVEL_0_NPAGES;
                           paddr += VM_LEVEL_0_SIZE;
                   }
           }
           return (sysctl_handle_int(oidp, &fullpop, 0, req));
   }
   
   /*
    * Describes the current state of the partially populated reservation queue.
    */
   static int
   sysctl_vm_reserv_partpopq(SYSCTL_HANDLER_ARGS)
   {
           struct sbuf sbuf;
           vm_reserv_t rv;
           int counter, error, domain, level, unused_pages;
   
           error = sysctl_wire_old_buffer(req, 0);
           if (error != 0)
                   return (error);
           sbuf_new_for_sysctl(&sbuf, NULL, 128, req);
           sbuf_printf(&sbuf, "\nDOMAIN    LEVEL     SIZE  NUMBER\n\n");
           for (domain = 0; domain < vm_ndomains; domain++) {
                   for (level = -1; level <= VM_NRESERVLEVEL - 2; level++) {
                           counter = 0;
                           unused_pages = 0;
                           vm_reserv_domain_lock(domain);
                           TAILQ_FOREACH(rv, &vm_rvd[domain].partpop, partpopq) {
                                   if (rv == &vm_rvd[domain].marker)
                                           continue;
                                   counter++;
                                   unused_pages += VM_LEVEL_0_NPAGES - rv->popcnt;
                           }
                           vm_reserv_domain_unlock(domain);
                           sbuf_printf(&sbuf, "%6d, %7d, %6dK, %6d\n",
                               domain, level,
                               unused_pages * ((int)PAGE_SIZE / 1024), counter);
                   }
           }
           error = sbuf_finish(&sbuf);
           sbuf_delete(&sbuf);
           return (error);
   }
   
   /*
    * Remove a reservation from the object's objq.
    */
   static void
   vm_reserv_remove(vm_reserv_t rv)
   {
           vm_object_t object;
   
           vm_reserv_assert_locked(rv);
           CTR5(KTR_VM, "%s: rv %p object %p popcnt %d inpartpop %d",
               __FUNCTION__, rv, rv->object, rv->popcnt, rv->inpartpopq);
           KASSERT(rv->object != NULL,
               ("vm_reserv_remove: reserv %p is free", rv));
           KASSERT(!rv->inpartpopq,
               ("vm_reserv_remove: reserv %p's inpartpopq is TRUE", rv));
           object = rv->object;
           vm_reserv_object_lock(object);
           LIST_REMOVE(rv, objq);
           rv->object = NULL;
           vm_reserv_object_unlock(object);
   }
   
   /*
    * Insert a new reservation into the object's objq.
    */
   static void
   vm_reserv_insert(vm_reserv_t rv, vm_object_t object, vm_pindex_t pindex)
   {
           int i;
   
           vm_reserv_assert_locked(rv);
           CTR6(KTR_VM,
               "%s: rv %p(%p) object %p new %p popcnt %d",
               __FUNCTION__, rv, rv->pages, rv->object, object,
              rv->popcnt);
           KASSERT(rv->object == NULL,
               ("vm_reserv_insert: reserv %p isn't free", rv));
           KASSERT(rv->popcnt == 0,
               ("vm_reserv_insert: reserv %p's popcnt is corrupted", rv));
           KASSERT(!rv->inpartpopq,
               ("vm_reserv_insert: reserv %p's inpartpopq is TRUE", rv));
           for (i = 0; i < NPOPMAP; i++)
                   KASSERT(rv->popmap[i] == 0,
                       ("vm_reserv_insert: reserv %p's popmap is corrupted", rv));
           vm_reserv_object_lock(object);
           rv->pindex = pindex;
           rv->object = object;
           rv->lasttick = ticks;
           LIST_INSERT_HEAD(&object->rvq, rv, objq);
           vm_reserv_object_unlock(object);
   }
   
   /*
    * Reduces the given reservation's population count.  If the population count
    * becomes zero, the reservation is destroyed.  Additionally, moves the
    * reservation to the tail of the partially populated reservation queue if the
    * population count is non-zero.
    */
   static void
   vm_reserv_depopulate(vm_reserv_t rv, int index)
   {
           struct vm_domain *vmd;
   
           vm_reserv_assert_locked(rv);
           CTR5(KTR_VM, "%s: rv %p object %p popcnt %d inpartpop %d",
               __FUNCTION__, rv, rv->object, rv->popcnt, rv->inpartpopq);
           KASSERT(rv->object != NULL,
               ("vm_reserv_depopulate: reserv %p is free", rv));
           KASSERT(popmap_is_set(rv->popmap, index),
               ("vm_reserv_depopulate: reserv %p's popmap[%d] is clear", rv,
               index));
           KASSERT(rv->popcnt > 0,
               ("vm_reserv_depopulate: reserv %p's popcnt is corrupted", rv));
           KASSERT(rv->domain < vm_ndomains,
               ("vm_reserv_depopulate: reserv %p's domain is corrupted %d",
               rv, rv->domain));
           if (rv->popcnt == VM_LEVEL_0_NPAGES) {
                   KASSERT(rv->pages->psind == 1,
                       ("vm_reserv_depopulate: reserv %p is already demoted",
                       rv));
                   rv->pages->psind = 0;
           }
           popmap_clear(rv->popmap, index);
           rv->popcnt--;
           if ((unsigned)(ticks - rv->lasttick) >= PARTPOPSLOP ||
               rv->popcnt == 0) {
                   vm_reserv_domain_lock(rv->domain);
                   if (rv->inpartpopq) {
                           TAILQ_REMOVE(&vm_rvd[rv->domain].partpop, rv, partpopq);
                           rv->inpartpopq = FALSE;
                   }
                   if (rv->popcnt != 0) {
                           rv->inpartpopq = TRUE;
                           TAILQ_INSERT_TAIL(&vm_rvd[rv->domain].partpop, rv,
                               partpopq);
                   }
                   vm_reserv_domain_unlock(rv->domain);
                   rv->lasttick = ticks;
           }
           vmd = VM_DOMAIN(rv->domain);
           if (rv->popcnt == 0) {
                   vm_reserv_remove(rv);
                   vm_domain_free_lock(vmd);
                   vm_phys_free_pages(rv->pages, VM_LEVEL_0_ORDER);
                   vm_domain_free_unlock(vmd);
                   counter_u64_add(vm_reserv_freed, 1);
           }
           vm_domain_freecnt_inc(vmd, 1);
   }
   
   /*
    * Returns the reservation to which the given page might belong.
    */
   static __inline vm_reserv_t
   vm_reserv_from_page(vm_page_t m)
   {
   
           return (&vm_reserv_array[VM_PAGE_TO_PHYS(m) >> VM_LEVEL_0_SHIFT]);
   }
   
   /*
    * Returns an existing reservation or NULL and initialized successor pointer.
    */
   static vm_reserv_t
   vm_reserv_from_object(vm_object_t object, vm_pindex_t pindex,
       vm_page_t mpred, vm_page_t *msuccp)
   {
           vm_reserv_t rv;
           vm_page_t msucc;
   
           msucc = NULL;
           if (mpred != NULL) {
                   KASSERT(mpred->object == object,
                       ("vm_reserv_from_object: object doesn't contain mpred"));
                   KASSERT(mpred->pindex < pindex,
                       ("vm_reserv_from_object: mpred doesn't precede pindex"));
                   rv = vm_reserv_from_page(mpred);
                   if (rv->object == object && vm_reserv_has_pindex(rv, pindex))
                           goto found;
                   msucc = TAILQ_NEXT(mpred, listq);
           } else
                   msucc = TAILQ_FIRST(&object->memq);
           if (msucc != NULL) {
                   KASSERT(msucc->pindex > pindex,
                       ("vm_reserv_from_object: msucc doesn't succeed pindex"));
                   rv = vm_reserv_from_page(msucc);
                   if (rv->object == object && vm_reserv_has_pindex(rv, pindex))
                           goto found;
           }
           rv = NULL;
   
   found:
           *msuccp = msucc;
   
           return (rv);
   }
   
   /*
    * Returns TRUE if the given reservation contains the given page index and
    * FALSE otherwise.
    */
   static __inline boolean_t
   vm_reserv_has_pindex(vm_reserv_t rv, vm_pindex_t pindex)
   {
   
           return (((pindex - rv->pindex) & ~(VM_LEVEL_0_NPAGES - 1)) == 0);
   }
   
   /*
    * Increases the given reservation's population count.  Moves the reservation
    * to the tail of the partially populated reservation queue.
    */
   static void
   vm_reserv_populate(vm_reserv_t rv, int index)
   {
   
           vm_reserv_assert_locked(rv);
           CTR5(KTR_VM, "%s: rv %p object %p popcnt %d inpartpop %d",
               __FUNCTION__, rv, rv->object, rv->popcnt, rv->inpartpopq);
           KASSERT(rv->object != NULL,
               ("vm_reserv_populate: reserv %p is free", rv));
           KASSERT(popmap_is_clear(rv->popmap, index),
               ("vm_reserv_populate: reserv %p's popmap[%d] is set", rv,
               index));
           KASSERT(rv->popcnt < VM_LEVEL_0_NPAGES,
               ("vm_reserv_populate: reserv %p is already full", rv));
           KASSERT(rv->pages->psind == 0,
               ("vm_reserv_populate: reserv %p is already promoted", rv));
           KASSERT(rv->domain < vm_ndomains,
               ("vm_reserv_populate: reserv %p's domain is corrupted %d",
               rv, rv->domain));
           popmap_set(rv->popmap, index);
           rv->popcnt++;
           if ((unsigned)(ticks - rv->lasttick) < PARTPOPSLOP &&
               rv->inpartpopq && rv->popcnt != VM_LEVEL_0_NPAGES)
                   return;
           rv->lasttick = ticks;
           vm_reserv_domain_lock(rv->domain);
           if (rv->inpartpopq) {
                   TAILQ_REMOVE(&vm_rvd[rv->domain].partpop, rv, partpopq);
                   rv->inpartpopq = FALSE;
           }
           if (rv->popcnt < VM_LEVEL_0_NPAGES) {
                   rv->inpartpopq = TRUE;
                   TAILQ_INSERT_TAIL(&vm_rvd[rv->domain].partpop, rv, partpopq);
           } else {
                   KASSERT(rv->pages->psind == 0,
                       ("vm_reserv_populate: reserv %p is already promoted",
                       rv));
                   rv->pages->psind = 1;
           }
           vm_reserv_domain_unlock(rv->domain);
   }
   
   /*
    * Attempts to allocate a contiguous set of physical pages from existing
    * reservations.  See vm_reserv_alloc_contig() for a description of the
    * function's parameters.
    *
    * The page "mpred" must immediately precede the offset "pindex" within the
    * specified object.
    *
    * The object must be locked.
    */
   vm_page_t
   vm_reserv_extend_contig(int req, vm_object_t object, vm_pindex_t pindex,
       int domain, u_long npages, vm_paddr_t low, vm_paddr_t high,
       u_long alignment, vm_paddr_t boundary, vm_page_t mpred)
   {
           struct vm_domain *vmd;
           vm_paddr_t pa, size;
           vm_page_t m, msucc;
           vm_reserv_t rv;
           int i, index;
   
           VM_OBJECT_ASSERT_WLOCKED(object);
           KASSERT(npages != 0, ("vm_reserv_alloc_contig: npages is 0"));
   
           /*
            * Is a reservation fundamentally impossible?
            */
           if (pindex < VM_RESERV_INDEX(object, pindex) ||
               pindex + npages > object->size || object->resident_page_count == 0)
                   return (NULL);
   
           /*
            * All reservations of a particular size have the same alignment.
            * Assuming that the first page is allocated from a reservation, the
            * least significant bits of its physical address can be determined
            * from its offset from the beginning of the reservation and the size
            * of the reservation.
            *
            * Could the specified index within a reservation of the smallest
            * possible size satisfy the alignment and boundary requirements?
            */
           pa = VM_RESERV_INDEX(object, pindex) << PAGE_SHIFT;
           if ((pa & (alignment - 1)) != 0)
                   return (NULL);
           size = npages << PAGE_SHIFT;
           if (((pa ^ (pa + size - 1)) & ~(boundary - 1)) != 0)
                   return (NULL);
   
           /*
            * Look for an existing reservation.
            */
           rv = vm_reserv_from_object(object, pindex, mpred, &msucc);
           if (rv == NULL)
                   return (NULL);
           KASSERT(object != kernel_object || rv->domain == domain,
               ("vm_reserv_extend_contig: Domain mismatch from reservation."));
           index = VM_RESERV_INDEX(object, pindex);
           /* Does the allocation fit within the reservation? */
           if (index + npages > VM_LEVEL_0_NPAGES)
                   return (NULL);
           domain = rv->domain;
           vmd = VM_DOMAIN(domain);
           vm_reserv_lock(rv);
           if (rv->object != object)
                   goto out;
           m = &rv->pages[index];
           pa = VM_PAGE_TO_PHYS(m);
           if (pa < low || pa + size > high || (pa & (alignment - 1)) != 0 ||
               ((pa ^ (pa + size - 1)) & ~(boundary - 1)) != 0)
                   goto out;
           /* Handle vm_page_rename(m, new_object, ...). */
           for (i = 0; i < npages; i++) {
                   if (popmap_is_set(rv->popmap, index + i))
                           goto out;
           }
           if (!vm_domain_allocate(vmd, req, npages))
                   goto out;
           for (i = 0; i < npages; i++)
                   vm_reserv_populate(rv, index + i);
           vm_reserv_unlock(rv);
           return (m);
   
   out:
           vm_reserv_unlock(rv);
           return (NULL);
   }
   
   /*
    * Allocates a contiguous set of physical pages of the given size "npages"
    * from newly created reservations.  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.
    *
    * Callers should first invoke vm_reserv_extend_contig() to attempt an
    * allocation from existing reservations.
    *
    * The page "mpred" must immediately precede the offset "pindex" within the
    * specified object.
    *
    * The object and free page queue must be locked.
    */
   vm_page_t
   vm_reserv_alloc_contig(int req, vm_object_t object, vm_pindex_t pindex, int domain,
       u_long npages, vm_paddr_t low, vm_paddr_t high, u_long alignment,
       vm_paddr_t boundary, vm_page_t mpred)
   {
           struct vm_domain *vmd;
           vm_paddr_t pa, size;
           vm_page_t m, m_ret, msucc;
           vm_pindex_t first, leftcap, rightcap;
           vm_reserv_t rv;
           u_long allocpages, maxpages, minpages;
           int i, index, n;
   
           VM_OBJECT_ASSERT_WLOCKED(object);
           KASSERT(npages != 0, ("vm_reserv_alloc_contig: npages is 0"));
   
           /*
            * Is a reservation fundamentally impossible?
            */
           if (pindex < VM_RESERV_INDEX(object, pindex) ||
               pindex + npages > object->size)
                   return (NULL);
   
           /*
            * All reservations of a particular size have the same alignment.
            * Assuming that the first page is allocated from a reservation, the
            * least significant bits of its physical address can be determined
            * from its offset from the beginning of the reservation and the size
            * of the reservation.
            *
            * Could the specified index within a reservation of the smallest
            * possible size satisfy the alignment and boundary requirements?
            */
           pa = VM_RESERV_INDEX(object, pindex) << PAGE_SHIFT;
           if ((pa & (alignment - 1)) != 0)
                   return (NULL);
           size = npages << PAGE_SHIFT;
           if (((pa ^ (pa + size - 1)) & ~(boundary - 1)) != 0)
                   return (NULL);
   
           /*
            * Callers should've extended an existing reservation prior to
            * calling this function.  If a reservation exists it is
            * incompatible with the allocation.
            */
           rv = vm_reserv_from_object(object, pindex, mpred, &msucc);
           if (rv != NULL)
                   return (NULL);
   
           /*
            * Could at least one reservation fit between the first index to the
            * left that can be used ("leftcap") and the first index to the right
            * that cannot be used ("rightcap")?
            *
            * We must synchronize with the reserv object lock to protect the
            * pindex/object of the resulting reservations against rename while
            * we are inspecting.
            */
           first = pindex - VM_RESERV_INDEX(object, pindex);
           minpages = VM_RESERV_INDEX(object, pindex) + npages;
           maxpages = roundup2(minpages, VM_LEVEL_0_NPAGES);
           allocpages = maxpages;
           vm_reserv_object_lock(object);
           if (mpred != NULL) {
                   if ((rv = vm_reserv_from_page(mpred))->object != object)
                           leftcap = mpred->pindex + 1;
                   else
                           leftcap = rv->pindex + VM_LEVEL_0_NPAGES;
                   if (leftcap > first) {
                           vm_reserv_object_unlock(object);
                           return (NULL);
                   }
           }
           if (msucc != NULL) {
                   if ((rv = vm_reserv_from_page(msucc))->object != object)
                           rightcap = msucc->pindex;
                   else
                           rightcap = rv->pindex;
                   if (first + maxpages > rightcap) {
                           if (maxpages == VM_LEVEL_0_NPAGES) {
                                   vm_reserv_object_unlock(object);
                                   return (NULL);
                           }
   
                           /*
                            * At least one reservation will fit between "leftcap"
                            * and "rightcap".  However, a reservation for the
                            * last of the requested pages will not fit.  Reduce
                            * the size of the upcoming allocation accordingly.
                            */
                           allocpages = minpages;
                   }
           }
           vm_reserv_object_unlock(object);
   
           /*
            * Would the last new reservation extend past the end of the object?
            */
           if (first + maxpages > object->size) {
                   /*
                    * Don't allocate the last new reservation if the object is a
                    * vnode or backed by another object that is a vnode. 
                    */
                   if (object->type == OBJT_VNODE ||
                       (object->backing_object != NULL &&
                       object->backing_object->type == OBJT_VNODE)) {
                           if (maxpages == VM_LEVEL_0_NPAGES)
                                   return (NULL);
                           allocpages = minpages;
                   }
                   /* Speculate that the object may grow. */
           }
   
           /*
            * Allocate the physical pages.  The alignment and boundary specified
            * for this allocation may be different from the alignment and
            * boundary specified for the requested pages.  For instance, the
            * specified index may not be the first page within the first new
            * reservation.
            */
           m = NULL;
           vmd = VM_DOMAIN(domain);
           if (vm_domain_allocate(vmd, req, npages)) {
                   vm_domain_free_lock(vmd);
                   m = vm_phys_alloc_contig(domain, allocpages, low, high,
                       ulmax(alignment, VM_LEVEL_0_SIZE),
                       boundary > VM_LEVEL_0_SIZE ? boundary : 0);
                   vm_domain_free_unlock(vmd);
                   if (m == NULL) {
                           vm_domain_freecnt_inc(vmd, npages);
                           return (NULL);
                   }
           } else
                   return (NULL);
           KASSERT(vm_phys_domain(m) == domain,
               ("vm_reserv_alloc_contig: Page domain does not match requested."));
   
           /*
            * The allocated physical pages always begin at a reservation
            * boundary, but they do not always end at a reservation boundary.
            * Initialize every reservation that is completely covered by the
            * allocated physical pages.
            */
           m_ret = NULL;
           index = VM_RESERV_INDEX(object, pindex);
           do {
                   rv = vm_reserv_from_page(m);
                   KASSERT(rv->pages == m,
                       ("vm_reserv_alloc_contig: reserv %p's pages is corrupted",
                       rv));
                   vm_reserv_lock(rv);
                   vm_reserv_insert(rv, object, first);
                   n = ulmin(VM_LEVEL_0_NPAGES - index, npages);
                   for (i = 0; i < n; i++)
                           vm_reserv_populate(rv, index + i);
                   npages -= n;
                   if (m_ret == NULL) {
                           m_ret = &rv->pages[index];
                           index = 0;
                   }
                   vm_reserv_unlock(rv);
                   m += VM_LEVEL_0_NPAGES;
                   first += VM_LEVEL_0_NPAGES;
                   allocpages -= VM_LEVEL_0_NPAGES;
           } while (allocpages >= VM_LEVEL_0_NPAGES);
           return (m_ret);
   }
   
   /*
    * Attempts to extend an existing reservation and allocate the page to the
    * object.
    *
    * The page "mpred" must immediately precede the offset "pindex" within the
    * specified object.
    *
    * The object must be locked.
    */
   vm_page_t
   vm_reserv_extend(int req, vm_object_t object, vm_pindex_t pindex, int domain,
       vm_page_t mpred)
   {
           struct vm_domain *vmd;
           vm_page_t m, msucc;
           vm_reserv_t rv;
           int index;
   
           VM_OBJECT_ASSERT_WLOCKED(object);
   
           /*
            * Could a reservation currently exist?
            */
           if (pindex < VM_RESERV_INDEX(object, pindex) ||
               pindex >= object->size || object->resident_page_count == 0)
                   return (NULL);
   
           /*
            * Look for an existing reservation.
            */
           rv = vm_reserv_from_object(object, pindex, mpred, &msucc);
           if (rv == NULL)
                   return (NULL);
   
           KASSERT(object != kernel_object || rv->domain == domain,
               ("vm_reserv_extend: Domain mismatch from reservation."));
           domain = rv->domain;
           vmd = VM_DOMAIN(domain);
           index = VM_RESERV_INDEX(object, pindex);
           m = &rv->pages[index];
           vm_reserv_lock(rv);
           /* Handle reclaim race. */
           if (rv->object != object ||
               /* Handle vm_page_rename(m, new_object, ...). */
               popmap_is_set(rv->popmap, index)) {
                   m = NULL;
                   goto out;
           }
           if (vm_domain_allocate(vmd, req, 1) == 0)
                   m = NULL;
           else
                   vm_reserv_populate(rv, index);
   out:
           vm_reserv_unlock(rv);
   
           return (m);
   }
   
   /*
    * Attempts to allocate a new reservation for the object, and allocates a
    * page from that reservation.  Callers should first invoke vm_reserv_extend()
    * to attempt an allocation from an existing reservation.
    *
    * The page "mpred" must immediately precede the offset "pindex" within the
    * specified object.
    *
    * The object and free page queue must be locked.
    */
   vm_page_t
   vm_reserv_alloc_page(int req, vm_object_t object, vm_pindex_t pindex, int domain,
       vm_page_t mpred)
   {
           struct vm_domain *vmd;
           vm_page_t m, msucc;
           vm_pindex_t first, leftcap, rightcap;
           vm_reserv_t rv;
           int index;
   
           VM_OBJECT_ASSERT_WLOCKED(object);
   
           /*
            * Is a reservation fundamentally impossible?
            */
           if (pindex < VM_RESERV_INDEX(object, pindex) ||
               pindex >= object->size)
                   return (NULL);
   
           /*
            * Callers should've extended an existing reservation prior to
            * calling this function.  If a reservation exists it is
            * incompatible with the allocation.
            */
           rv = vm_reserv_from_object(object, pindex, mpred, &msucc);
           if (rv != NULL)
                   return (NULL);
   
           /*
            * Could a reservation fit between the first index to the left that
            * can be used and the first index to the right that cannot be used?
            *
            * We must synchronize with the reserv object lock to protect the
            * pindex/object of the resulting reservations against rename while
            * we are inspecting.
            */
           first = pindex - VM_RESERV_INDEX(object, pindex);
           vm_reserv_object_lock(object);
           if (mpred != NULL) {
                   if ((rv = vm_reserv_from_page(mpred))->object != object)
                           leftcap = mpred->pindex + 1;
                   else
                           leftcap = rv->pindex + VM_LEVEL_0_NPAGES;
                   if (leftcap > first) {
                           vm_reserv_object_unlock(object);
                           return (NULL);
                   }
           }
           if (msucc != NULL) {
                   if ((rv = vm_reserv_from_page(msucc))->object != object)
                           rightcap = msucc->pindex;
                   else
                           rightcap = rv->pindex;
                   if (first + VM_LEVEL_0_NPAGES > rightcap) {
                           vm_reserv_object_unlock(object);
                           return (NULL);
                   }
           }
           vm_reserv_object_unlock(object);
   
           /*
            * Would a new reservation extend past the end of the object? 
            */
          if (first + VM_LEVEL_0_NPAGES > object->size) {
                  /*
                   * Don't allocate a new reservation if the object is a vnode or
                   * backed by another object that is a vnode. 
                   */
                  if (object->type == OBJT_VNODE ||
                      (object->backing_object != NULL &&
                      object->backing_object->type == OBJT_VNODE))
                          return (NULL);
                  /* Speculate that the object may grow. */
          }
  
          /*
           * Allocate and populate the new reservation.
           */
          m = NULL;
          vmd = VM_DOMAIN(domain);
          if (vm_domain_allocate(vmd, req, 1)) {
                  vm_domain_free_lock(vmd);
                  m = vm_phys_alloc_pages(domain, VM_FREEPOOL_DEFAULT,
                      VM_LEVEL_0_ORDER);
                  vm_domain_free_unlock(vmd);
                  if (m == NULL) {
                          vm_domain_freecnt_inc(vmd, 1);
                          return (NULL);
                  }
          } else
                  return (NULL);
          rv = vm_reserv_from_page(m);
          vm_reserv_lock(rv);
          KASSERT(rv->pages == m,
              ("vm_reserv_alloc_page: reserv %p's pages is corrupted", rv));
          vm_reserv_insert(rv, object, first);
          index = VM_RESERV_INDEX(object, pindex);
          vm_reserv_populate(rv, index);
          vm_reserv_unlock(rv);
  
          return (&rv->pages[index]);
  }
  
  /*
   * Breaks the given reservation.  All free pages in the reservation
   * are returned to the physical memory allocator.  The reservation's
   * population count and map are reset to their initial state.
   *
   * The given reservation must not be in the partially populated reservation
   * queue.
   */
  static void
  vm_reserv_break(vm_reserv_t rv)
  {
          int begin_zeroes, hi, i, lo;
  
          vm_reserv_assert_locked(rv);
          CTR5(KTR_VM, "%s: rv %p object %p popcnt %d inpartpop %d",
              __FUNCTION__, rv, rv->object, rv->popcnt, rv->inpartpopq);
          vm_reserv_remove(rv);
          rv->pages->psind = 0;
          i = hi = 0;
          do {
                  /* Find the next 0 bit.  Any previous 0 bits are < "hi". */
                  lo = ffsl(~(((1UL << hi) - 1) | rv->popmap[i]));
                  if (lo == 0) {
                          /* Redundantly clears bits < "hi". */
                          rv->popmap[i] = 0;
                          rv->popcnt -= NBPOPMAP - hi;
                          while (++i < NPOPMAP) {
                                  lo = ffsl(~rv->popmap[i]);
                                  if (lo == 0) {
                                          rv->popmap[i] = 0;
                                          rv->popcnt -= NBPOPMAP;
                                  } else
                                          break;
                          }
                          if (i == NPOPMAP)
                                  break;
                          hi = 0;
                  }
                  KASSERT(lo > 0, ("vm_reserv_break: lo is %d", lo));
                  /* Convert from ffsl() to ordinary bit numbering. */
                  lo--;
                  if (lo > 0) {
                          /* Redundantly clears bits < "hi". */
                          rv->popmap[i] &= ~((1UL << lo) - 1);
                          rv->popcnt -= lo - hi;
                  }
                  begin_zeroes = NBPOPMAP * i + lo;
                  /* Find the next 1 bit. */
                  do
                          hi = ffsl(rv->popmap[i]);
                  while (hi == 0 && ++i < NPOPMAP);
                  if (i != NPOPMAP)
                          /* Convert from ffsl() to ordinary bit numbering. */
                          hi--;
                  vm_domain_free_lock(VM_DOMAIN(rv->domain));
                  vm_phys_free_contig(&rv->pages[begin_zeroes], NBPOPMAP * i +
                      hi - begin_zeroes);
                  vm_domain_free_unlock(VM_DOMAIN(rv->domain));
          } while (i < NPOPMAP);
          KASSERT(rv->popcnt == 0,
              ("vm_reserv_break: reserv %p's popcnt is corrupted", rv));
          counter_u64_add(vm_reserv_broken, 1);
  }
  
  /*
   * Breaks all reservations belonging to the given object.
   */
  void
  vm_reserv_break_all(vm_object_t object)
  {
          vm_reserv_t rv;
  
          /*
           * This access of object->rvq is unsynchronized so that the
           * object rvq lock can nest after the domain_free lock.  We
           * must check for races in the results.  However, the object
           * lock prevents new additions, so we are guaranteed that when
           * it returns NULL the object is properly empty.
           */
          while ((rv = LIST_FIRST(&object->rvq)) != NULL) {
                  vm_reserv_lock(rv);
                  /* Reclaim race. */
                  if (rv->object != object) {
                          vm_reserv_unlock(rv);
                          continue;
                  }
                  vm_reserv_domain_lock(rv->domain);
                  if (rv->inpartpopq) {
                          TAILQ_REMOVE(&vm_rvd[rv->domain].partpop, rv, partpopq);
                          rv->inpartpopq = FALSE;
                  }
                  vm_reserv_domain_unlock(rv->domain);
                  vm_reserv_break(rv);
                  vm_reserv_unlock(rv);
          }
  }
  
  /*
   * Frees the given page if it belongs to a reservation.  Returns TRUE if the
   * page is freed and FALSE otherwise.
   */
  boolean_t
  vm_reserv_free_page(vm_page_t m)
  {
          vm_reserv_t rv;
          boolean_t ret;
  
          rv = vm_reserv_from_page(m);
          if (rv->object == NULL)
                  return (FALSE);
          vm_reserv_lock(rv);
          /* Re-validate after lock. */
          if (rv->object != NULL) {
                  vm_reserv_depopulate(rv, m - rv->pages);
                  ret = TRUE;
          } else
                  ret = FALSE;
          vm_reserv_unlock(rv);
  
          return (ret);
  }
  
  /*
   * Initializes the reservation management system.  Specifically, initializes
   * the reservation array.
   *
   * Requires that vm_page_array and first_page are initialized!
   */
  void
  vm_reserv_init(void)
  {
          vm_paddr_t paddr;
          struct vm_phys_seg *seg;
          struct vm_reserv *rv;
          struct vm_reserv_domain *rvd;
          int i, j, segind;
  
          /*
           * Initialize the reservation array.  Specifically, initialize the
           * "pages" field for every element that has an underlying superpage.
           */
          for (segind = 0; segind < vm_phys_nsegs; segind++) {
                  seg = &vm_phys_segs[segind];
                  paddr = roundup2(seg->start, VM_LEVEL_0_SIZE);
                  while (paddr + VM_LEVEL_0_SIZE > paddr && paddr +
                      VM_LEVEL_0_SIZE <= seg->end) {
                          rv = &vm_reserv_array[paddr >> VM_LEVEL_0_SHIFT];
                          rv->pages = PHYS_TO_VM_PAGE(paddr);
                          rv->domain = seg->domain;
                          mtx_init(&rv->lock, "vm reserv", NULL, MTX_DEF);
                          paddr += VM_LEVEL_0_SIZE;
                  }
          }
          for (i = 0; i < MAXMEMDOM; i++) {
                  rvd = &vm_rvd[i];
                  mtx_init(&rvd->lock, "vm reserv domain", NULL, MTX_DEF);
                  TAILQ_INIT(&rvd->partpop);
                  mtx_init(&rvd->marker.lock, "vm reserv marker", NULL, MTX_DEF);
  
                  /*
                   * Fully populated reservations should never be present in the
                   * partially populated reservation queues.
                   */
                  rvd->marker.popcnt = VM_LEVEL_0_NPAGES;
                  for (j = 0; j < VM_LEVEL_0_NPAGES; j++)
                          popmap_set(rvd->marker.popmap, j);
          }
  
          for (i = 0; i < VM_RESERV_OBJ_LOCK_COUNT; i++)
                  mtx_init(&vm_reserv_object_mtx[i], "resv obj lock", NULL,
                      MTX_DEF);
  }
  
  /*
   * Returns true if the given page belongs to a reservation and that page is
   * free.  Otherwise, returns false.
   */
  bool
  vm_reserv_is_page_free(vm_page_t m)
  {
          vm_reserv_t rv;
  
          rv = vm_reserv_from_page(m);
          if (rv->object == NULL)
                  return (false);
          return (popmap_is_clear(rv->popmap, m - rv->pages));
  }
  
  /*
   * If the given page belongs to a reservation, returns the level of that
   * reservation.  Otherwise, returns -1.
   */
  int
  vm_reserv_level(vm_page_t m)
  {
          vm_reserv_t rv;
  
          rv = vm_reserv_from_page(m);
          return (rv->object != NULL ? 0 : -1);
  }
  
  /*
   * Returns a reservation level if the given page belongs to a fully populated
   * reservation and -1 otherwise.
   */
  int
  vm_reserv_level_iffullpop(vm_page_t m)
  {
          vm_reserv_t rv;
  
          rv = vm_reserv_from_page(m);
          return (rv->popcnt == VM_LEVEL_0_NPAGES ? 0 : -1);
  }
  
  /*
   * Remove a partially populated reservation from the queue.
   */
  static void
  vm_reserv_dequeue(vm_reserv_t rv)
  {
  
          vm_reserv_domain_assert_locked(rv->domain);
          vm_reserv_assert_locked(rv);
          CTR5(KTR_VM, "%s: rv %p object %p popcnt %d inpartpop %d",
              __FUNCTION__, rv, rv->object, rv->popcnt, rv->inpartpopq);
          KASSERT(rv->inpartpopq,
              ("vm_reserv_reclaim: reserv %p's inpartpopq is FALSE", rv));
  
          TAILQ_REMOVE(&vm_rvd[rv->domain].partpop, rv, partpopq);
          rv->inpartpopq = FALSE;
  }
  
  /*
   * Breaks the given partially populated reservation, releasing its free pages
   * to the physical memory allocator.
   */
  static void
  vm_reserv_reclaim(vm_reserv_t rv)
  {
  
          vm_reserv_assert_locked(rv);
          CTR5(KTR_VM, "%s: rv %p object %p popcnt %d inpartpop %d",
              __FUNCTION__, rv, rv->object, rv->popcnt, rv->inpartpopq);
          if (rv->inpartpopq) {
                  vm_reserv_domain_lock(rv->domain);
                  vm_reserv_dequeue(rv);
                  vm_reserv_domain_unlock(rv->domain);
          }
          vm_reserv_break(rv);
          counter_u64_add(vm_reserv_reclaimed, 1);
  }
  
  /*
   * Breaks a reservation near the head of the partially populated reservation
   * queue, releasing its free pages to the physical memory allocator.  Returns
   * TRUE if a reservation is broken and FALSE otherwise.
   */
  bool
  vm_reserv_reclaim_inactive(int domain)
  {
          vm_reserv_t rv;
  
          vm_reserv_domain_lock(domain);
          TAILQ_FOREACH(rv, &vm_rvd[domain].partpop, partpopq) {
                  /*
                   * A locked reservation is likely being updated or reclaimed,
                   * so just skip ahead.
                   */
                  if (rv != &vm_rvd[domain].marker && vm_reserv_trylock(rv)) {
                          vm_reserv_dequeue(rv);
                          break;
                  }
          }
          vm_reserv_domain_unlock(domain);
          if (rv != NULL) {
                  vm_reserv_reclaim(rv);
                  vm_reserv_unlock(rv);
                  return (true);
          }
          return (false);
  }
  
  /*
   * Determine whether this reservation has free pages that satisfy the given
   * request for contiguous physical memory.  Start searching from the lower
   * bound, defined by lo, and stop at the upper bound, hi.  Return the index
   * of the first satisfactory free page, or -1 if none is found.
   */
  static int
  vm_reserv_find_contig(vm_reserv_t rv, int npages, int lo,
      int hi, int ppn_align, int ppn_bound)
  {
          u_long changes;
          int bitpos, bits_left, i, n;
  
          vm_reserv_assert_locked(rv);
          KASSERT(npages <= VM_LEVEL_0_NPAGES - 1,
              ("%s: Too many pages", __func__));
          KASSERT(ppn_bound <= VM_LEVEL_0_NPAGES,
              ("%s: Too big a boundary for reservation size", __func__));
          KASSERT(npages <= ppn_bound,
              ("%s: Too many pages for given boundary", __func__));
          KASSERT(ppn_align != 0 && powerof2(ppn_align),
              ("ppn_align is not a positive power of 2"));
          KASSERT(ppn_bound != 0 && powerof2(ppn_bound),
              ("ppn_bound is not a positive power of 2"));
          i = lo / NBPOPMAP;
          changes = rv->popmap[i] | ((1UL << (lo % NBPOPMAP)) - 1);
          n = hi / NBPOPMAP;
          bits_left = hi % NBPOPMAP;
          hi = lo = -1;
          for (;;) {
                  /*
                   * "changes" is a bitmask that marks where a new sequence of
                   * 0s or 1s begins in popmap[i], with last bit in popmap[i-1]
                   * considered to be 1 if and only if lo == hi.  The bits of
                   * popmap[-1] and popmap[NPOPMAP] are considered all 1s.
                   */
                  changes ^= (changes << 1) | (lo == hi);
                  while (changes != 0) {
                          /*
                           * If the next change marked begins a run of 0s, set
                           * lo to mark that position.  Otherwise set hi and
                           * look for a satisfactory first page from lo up to hi.
                           */
                          bitpos = ffsl(changes) - 1;
                          changes ^= 1UL << bitpos;
                          if (lo == hi) {
                                  lo = NBPOPMAP * i + bitpos;
                                  continue;
                          }
                          hi = NBPOPMAP * i + bitpos;
                          if (lo < roundup2(lo, ppn_align)) {
                                  /* Skip to next aligned page. */
                                  lo = roundup2(lo, ppn_align);
                                  if (lo >= VM_LEVEL_0_NPAGES)
                                          return (-1);
                          }
                          if (lo + npages > roundup2(lo, ppn_bound)) {
                                  /* Skip to next boundary-matching page. */
                                  lo = roundup2(lo, ppn_bound);
                                  if (lo >= VM_LEVEL_0_NPAGES)
                                          return (-1);
                          }
                          if (lo + npages <= hi)
                                  return (lo);
                          lo = hi;
                  }
                  if (++i < n)
                          changes = rv->popmap[i];
                  else if (i == n)
                          changes = bits_left == 0 ? -1UL :
                              (rv->popmap[n] | (-1UL << bits_left));
                  else
                          return (-1);
          }
  }
  
  /*
   * Searches the partially populated reservation queue for the least recently
   * changed reservation with free pages that satisfy the given request for
   * contiguous physical memory.  If a satisfactory reservation is found, it is
   * broken.  Returns true if a reservation is broken and false otherwise.
   */
  bool
  vm_reserv_reclaim_contig(int domain, u_long npages, vm_paddr_t low,
      vm_paddr_t high, u_long alignment, vm_paddr_t boundary)
  {
          struct vm_reserv_queue *queue;
          vm_paddr_t pa, size;
          vm_reserv_t marker, rv, rvn;
          int hi, lo, posn, ppn_align, ppn_bound;
  
          KASSERT(npages > 0, ("npages is 0"));
          KASSERT(powerof2(alignment), ("alignment is not a power of 2"));
          KASSERT(powerof2(boundary), ("boundary is not a power of 2"));
          if (npages > VM_LEVEL_0_NPAGES - 1)
                  return (false);
          size = npages << PAGE_SHIFT;
          /* 
           * Ensure that a free range starting at a boundary-multiple
           * doesn't include a boundary-multiple within it.  Otherwise,
           * no boundary-constrained allocation is possible.
           */
          if (size > boundary && boundary > 0)
                  return (false);
          marker = &vm_rvd[domain].marker;
          queue = &vm_rvd[domain].partpop;
          /*
           * Compute shifted alignment, boundary values for page-based
           * calculations.  Constrain to range [1, VM_LEVEL_0_NPAGES] to
           * avoid overflow.
           */
          ppn_align = (int)(ulmin(ulmax(PAGE_SIZE, alignment),
              VM_LEVEL_0_SIZE) >> PAGE_SHIFT);
          ppn_bound = boundary == 0 ? VM_LEVEL_0_NPAGES :
              (int)(MIN(MAX(PAGE_SIZE, boundary),
              VM_LEVEL_0_SIZE) >> PAGE_SHIFT);
  
          vm_reserv_domain_scan_lock(domain);
          vm_reserv_domain_lock(domain);
          TAILQ_FOREACH_SAFE(rv, queue, partpopq, rvn) {
                  pa = VM_PAGE_TO_PHYS(&rv->pages[0]);
                  if (pa + VM_LEVEL_0_SIZE - size < low) {
                          /* This entire reservation is too low; go to next. */
                          continue;
                  }
                  if (pa + size > high) {
                          /* This entire reservation is too high; go to next. */
                          continue;
                  }
                  if ((pa & (alignment - 1)) != 0) {
                          /* This entire reservation is unaligned; go to next. */
                          continue;
                  }
  
                  if (vm_reserv_trylock(rv) == 0) {
                          TAILQ_INSERT_AFTER(queue, rv, marker, partpopq);
                          vm_reserv_domain_unlock(domain);
                          vm_reserv_lock(rv);
                          if (!rv->inpartpopq ||
                              TAILQ_NEXT(rv, partpopq) != marker) {
                                  vm_reserv_unlock(rv);
                                  vm_reserv_domain_lock(domain);
                                  rvn = TAILQ_NEXT(marker, partpopq);
                                  TAILQ_REMOVE(queue, marker, partpopq);
                                  continue;
                          }
                          vm_reserv_domain_lock(domain);
                          TAILQ_REMOVE(queue, marker, partpopq);
                  }
                  vm_reserv_domain_unlock(domain);
                  lo = (pa >= low) ? 0 :
                      (int)((low + PAGE_MASK - pa) >> PAGE_SHIFT);
                  hi = (pa + VM_LEVEL_0_SIZE <= high) ? VM_LEVEL_0_NPAGES :
                      (int)((high - pa) >> PAGE_SHIFT);
                  posn = vm_reserv_find_contig(rv, (int)npages, lo, hi,
                      ppn_align, ppn_bound);
                  if (posn >= 0) {
                          pa = VM_PAGE_TO_PHYS(&rv->pages[posn]);
                          KASSERT((pa & (alignment - 1)) == 0,
                              ("%s: adjusted address does not align to %lx",
                              __func__, alignment));
                          KASSERT(((pa ^ (pa + size - 1)) & -boundary) == 0,
                              ("%s: adjusted address spans boundary to %jx",
                              __func__, (uintmax_t)boundary));
  
                          vm_reserv_domain_scan_unlock(domain);
                          vm_reserv_reclaim(rv);
                          vm_reserv_unlock(rv);
                          return (true);
                  }
                  vm_reserv_unlock(rv);
                  vm_reserv_domain_lock(domain);
          }
          vm_reserv_domain_unlock(domain);
          vm_reserv_domain_scan_unlock(domain);
          return (false);
  }
  
  /*
   * Transfers the reservation underlying the given page to a new object.
   *
   * The object must be locked.
   */
  void
  vm_reserv_rename(vm_page_t m, vm_object_t new_object, vm_object_t old_object,
      vm_pindex_t old_object_offset)
  {
          vm_reserv_t rv;
  
          VM_OBJECT_ASSERT_WLOCKED(new_object);
          rv = vm_reserv_from_page(m);
          if (rv->object == old_object) {
                  vm_reserv_lock(rv);
                  CTR6(KTR_VM,
                      "%s: rv %p object %p new %p popcnt %d inpartpop %d",
                      __FUNCTION__, rv, rv->object, new_object, rv->popcnt,
                      rv->inpartpopq);
                  if (rv->object == old_object) {
                          vm_reserv_object_lock(old_object);
                          rv->object = NULL;
                          LIST_REMOVE(rv, objq);
                          vm_reserv_object_unlock(old_object);
                          vm_reserv_object_lock(new_object);
                          rv->object = new_object;
                          rv->pindex -= old_object_offset;
                          LIST_INSERT_HEAD(&new_object->rvq, rv, objq);
                          vm_reserv_object_unlock(new_object);
                  }
                  vm_reserv_unlock(rv);
          }
  }
  
  /*
   * Returns the size (in bytes) of a reservation of the specified level.
   */
  int
  vm_reserv_size(int level)
  {
  
          switch (level) {
          case 0:
                  return (VM_LEVEL_0_SIZE);
          case -1:
                  return (PAGE_SIZE);
          default:
                  return (0);
          }
  }
  
  /*
   * Allocates the virtual and physical memory required by the reservation
   * management system's data structures, in particular, the reservation array.
   */
  vm_paddr_t
  vm_reserv_startup(vm_offset_t *vaddr, vm_paddr_t end, vm_paddr_t high_water)
  {
          vm_paddr_t new_end;
          size_t size;
  
          /*
           * Calculate the size (in bytes) of the reservation array.  Round up
           * from "high_water" because every small page is mapped to an element
           * in the reservation array based on its physical address.  Thus, the
           * number of elements in the reservation array can be greater than the
           * number of superpages. 
           */
          size = howmany(high_water, VM_LEVEL_0_SIZE) * sizeof(struct vm_reserv);
  
          /*
           * Allocate and map the physical memory for the reservation array.  The
           * next available virtual address is returned by reference.
           */
          new_end = end - round_page(size);
          vm_reserv_array = (void *)(uintptr_t)pmap_map(vaddr, new_end, end,
              VM_PROT_READ | VM_PROT_WRITE);
          bzero(vm_reserv_array, size);
  
          /*
           * Return the next available physical address.
           */
          return (new_end);
  }
  
  /*
   * Initializes the reservation management system.  Specifically, initializes
   * the reservation counters.
   */
  static void
  vm_reserv_counter_init(void *unused)
  {
  
          vm_reserv_freed = counter_u64_alloc(M_WAITOK); 
          vm_reserv_broken = counter_u64_alloc(M_WAITOK); 
          vm_reserv_reclaimed = counter_u64_alloc(M_WAITOK); 
  }
  SYSINIT(vm_reserv_counter_init, SI_SUB_CPU, SI_ORDER_ANY,
      vm_reserv_counter_init, NULL);
  
  /*
   * Returns the superpage containing the given page.
   */
  vm_page_t
  vm_reserv_to_superpage(vm_page_t m)
  {
          vm_reserv_t rv;
  
          VM_OBJECT_ASSERT_LOCKED(m->object);
          rv = vm_reserv_from_page(m);
          if (rv->object == m->object && rv->popcnt == VM_LEVEL_0_NPAGES)
                  m = rv->pages;
          else
                  m = NULL;
  
          return (m);
  }
  
  #endif  /* VM_NRESERVLEVEL > 0 */

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