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

     /*-
      * Copyright (c) 2002-2006 Rice University
      * Copyright (c) 2007-2008 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
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD: releng/8.0/sys/vm/vm_reserv.c 190912 2009-04-11 09:09:00Z alc $");
    
    #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/sbuf.h>
    #include <sys/sysctl.h>
    #include <sys/systm.h>
    
    #include <vm/vm.h>
    #include <vm/vm_param.h>
    #include <vm/vm_object.h>
    #include <vm/vm_page.h>
    #include <vm/vm_phys.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
    
    /*
     * The number of small pages that are contained in a level 0 reservation
     */
    #define VM_LEVEL_0_NPAGES       (1 << VM_LEVEL_0_ORDER)
    
    /*
     * 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 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.
    */
   struct vm_reserv {
           TAILQ_ENTRY(vm_reserv) partpopq;
           LIST_ENTRY(vm_reserv) objq;
           vm_object_t     object;                 /* containing object */
           vm_pindex_t     pindex;                 /* offset within object */
           vm_page_t       pages;                  /* first page of a superpage */
           int             popcnt;                 /* # of pages in use */
           char            inpartpopq;
   };
   
   /*
    * 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 partially-populated reservation queue
    *
    * This queue enables the fast recovery of an unused cached or free small page
    * from a partially-populated reservation.  The reservation at the head of
    * this queue is the least-recently-changed, partially-populated reservation.
    *
    * Access to this queue is synchronized by the free page queue lock.
    */
   static TAILQ_HEAD(, vm_reserv) vm_rvq_partpop =
                               TAILQ_HEAD_INITIALIZER(vm_rvq_partpop);
   
   static SYSCTL_NODE(_vm, OID_AUTO, reserv, CTLFLAG_RD, 0, "Reservation Info");
   
   static long vm_reserv_broken;
   SYSCTL_LONG(_vm_reserv, OID_AUTO, broken, CTLFLAG_RD,
       &vm_reserv_broken, 0, "Cumulative number of broken reservations");
   
   static long vm_reserv_freed;
   SYSCTL_LONG(_vm_reserv, OID_AUTO, freed, CTLFLAG_RD,
       &vm_reserv_freed, 0, "Cumulative number of freed reservations");
   
   static int sysctl_vm_reserv_partpopq(SYSCTL_HANDLER_ARGS);
   
   SYSCTL_OID(_vm_reserv, OID_AUTO, partpopq, CTLTYPE_STRING | CTLFLAG_RD, NULL, 0,
       sysctl_vm_reserv_partpopq, "A", "Partially-populated reservation queues");
   
   static long vm_reserv_reclaimed;
   SYSCTL_LONG(_vm_reserv, OID_AUTO, reclaimed, CTLFLAG_RD,
       &vm_reserv_reclaimed, 0, "Cumulative number of reclaimed reservations");
   
   static void             vm_reserv_depopulate(vm_reserv_t rv);
   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);
   static void             vm_reserv_reclaim(vm_reserv_t rv);
   
   /*
    * 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;
           char *cbuf;
           const int cbufsize = (VM_NRESERVLEVEL + 1) * 81;
           int counter, error, level, unused_pages;
   
           cbuf = malloc(cbufsize, M_TEMP, M_WAITOK | M_ZERO);
           sbuf_new(&sbuf, cbuf, cbufsize, SBUF_FIXEDLEN);
           sbuf_printf(&sbuf, "\nLEVEL     SIZE  NUMBER\n\n");
           for (level = -1; level <= VM_NRESERVLEVEL - 2; level++) {
                   counter = 0;
                   unused_pages = 0;
                   mtx_lock(&vm_page_queue_free_mtx);
                   TAILQ_FOREACH(rv, &vm_rvq_partpop/*[level]*/, partpopq) {
                           counter++;
                           unused_pages += VM_LEVEL_0_NPAGES - rv->popcnt;
                   }
                   mtx_unlock(&vm_page_queue_free_mtx);
                   sbuf_printf(&sbuf, "%5.5d: %6.6dK, %6.6d\n", level,
                       unused_pages * (PAGE_SIZE / 1024), counter);
           }
           sbuf_finish(&sbuf);
           error = SYSCTL_OUT(req, sbuf_data(&sbuf), sbuf_len(&sbuf));
           sbuf_delete(&sbuf);
           free(cbuf, M_TEMP);
           return (error);
   }
   
   /*
    * 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 reservations queue if the
    * population count is non-zero.
    *
    * The free page queue lock must be held.
    */
   static void
   vm_reserv_depopulate(vm_reserv_t rv)
   {
   
           mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
           KASSERT(rv->object != NULL,
               ("vm_reserv_depopulate: reserv %p is free", rv));
           KASSERT(rv->popcnt > 0,
               ("vm_reserv_depopulate: reserv %p's popcnt is corrupted", rv));
           if (rv->inpartpopq) {
                   TAILQ_REMOVE(&vm_rvq_partpop, rv, partpopq);
                   rv->inpartpopq = FALSE;
           }
           rv->popcnt--;
           if (rv->popcnt == 0) {
                   LIST_REMOVE(rv, objq);
                   rv->object = NULL;
                   vm_phys_free_pages(rv->pages, VM_LEVEL_0_ORDER);
                   vm_reserv_freed++;
           } else {
                   rv->inpartpopq = TRUE;
                   TAILQ_INSERT_TAIL(&vm_rvq_partpop, rv, partpopq);
           }
   }
   
   /*
    * 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 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.
    *
    * The free page queue must be locked.
    */
   static void
   vm_reserv_populate(vm_reserv_t rv)
   {
   
           mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
           KASSERT(rv->object != NULL,
               ("vm_reserv_populate: reserv %p is free", rv));
           KASSERT(rv->popcnt < VM_LEVEL_0_NPAGES,
               ("vm_reserv_populate: reserv %p is already full", rv));
           if (rv->inpartpopq) {
                   TAILQ_REMOVE(&vm_rvq_partpop, rv, partpopq);
                   rv->inpartpopq = FALSE;
           }
           rv->popcnt++;
           if (rv->popcnt < VM_LEVEL_0_NPAGES) {
                   rv->inpartpopq = TRUE;
                   TAILQ_INSERT_TAIL(&vm_rvq_partpop, rv, partpopq);
           }
   }
   
   /*
    * Allocates a page from an existing or newly-created reservation.
    *
    * The object and free page queue must be locked.
    */
   vm_page_t
   vm_reserv_alloc_page(vm_object_t object, vm_pindex_t pindex)
   {
           vm_page_t m, mpred, msucc;
           vm_pindex_t first, leftcap, rightcap;
           vm_reserv_t rv;
   
           mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
   
           /*
            * Is a reservation fundamentally not possible?
            */
           VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
           if (pindex < VM_RESERV_INDEX(object, pindex) ||
               pindex >= object->size)
                   return (NULL);
   
           /*
            * Look for an existing reservation.
            */
           msucc = NULL;
           mpred = object->root;
           while (mpred != NULL) {
                   KASSERT(mpred->pindex != pindex,
                       ("vm_reserv_alloc_page: pindex already allocated"));
                   rv = vm_reserv_from_page(mpred);
                   if (rv->object == object && vm_reserv_has_pindex(rv, pindex)) {
                           m = &rv->pages[VM_RESERV_INDEX(object, pindex)];
                           /* Handle vm_page_rename(m, new_object, ...). */
                           if ((m->flags & (PG_CACHED | PG_FREE)) == 0)
                                   return (NULL);
                           vm_reserv_populate(rv);
                           return (m);
                   } else if (mpred->pindex < pindex) {
                           if (msucc != NULL ||
                               (msucc = TAILQ_NEXT(mpred, listq)) == NULL)
                                   break;
                           KASSERT(msucc->pindex != pindex,
                               ("vm_reserv_alloc_page: pindex already allocated"));
                           rv = vm_reserv_from_page(msucc);
                           if (rv->object == object &&
                               vm_reserv_has_pindex(rv, pindex)) {
                                   m = &rv->pages[VM_RESERV_INDEX(object, pindex)];
                                   /* Handle vm_page_rename(m, new_object, ...). */
                                   if ((m->flags & (PG_CACHED | PG_FREE)) == 0)
                                           return (NULL);
                                   vm_reserv_populate(rv);
                                   return (m);
                           } else if (pindex < msucc->pindex)
                                   break;
                   } else if (msucc == NULL) {
                           msucc = mpred;
                           mpred = TAILQ_PREV(msucc, pglist, listq);
                           continue;
                   }
                   msucc = NULL;
                   mpred = object->root = vm_page_splay(pindex, object->root);
           }
   
           /*
            * Determine the first index to the left that can be used.
            */
           if (mpred == NULL)
                   leftcap = 0;
           else if ((rv = vm_reserv_from_page(mpred))->object != object)
                   leftcap = mpred->pindex + 1;
           else
                   leftcap = rv->pindex + VM_LEVEL_0_NPAGES;
   
           /*
            * Determine the first index to the right that cannot be used.
            */
           if (msucc == NULL)
                   rightcap = pindex + VM_LEVEL_0_NPAGES;
           else if ((rv = vm_reserv_from_page(msucc))->object != object)
                   rightcap = msucc->pindex;
           else
                   rightcap = rv->pindex;
   
           /*
            * Determine if a reservation fits between the first index to
            * the left that can be used and the first index to the right
            * that cannot be used. 
            */
           first = pindex - VM_RESERV_INDEX(object, pindex);
           if (first < leftcap || first + VM_LEVEL_0_NPAGES > rightcap)
                   return (NULL);
   
           /*
            * Would a new reservation extend past the end of the given object? 
            */
           if (object->size < first + VM_LEVEL_0_NPAGES) {
                   /*
                    * 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 a new reservation.
            */
           m = vm_phys_alloc_pages(VM_FREEPOOL_DEFAULT, VM_LEVEL_0_ORDER);
           if (m != NULL) {
                   rv = vm_reserv_from_page(m);
                   KASSERT(rv->pages == m,
                       ("vm_reserv_alloc_page: reserv %p's pages is corrupted",
                       rv));
                   KASSERT(rv->object == NULL,
                       ("vm_reserv_alloc_page: reserv %p isn't free", rv));
                   LIST_INSERT_HEAD(&object->rvq, rv, objq);
                   rv->object = object;
                   rv->pindex = first;
                   KASSERT(rv->popcnt == 0,
                       ("vm_reserv_alloc_page: reserv %p's popcnt is corrupted",
                       rv));
                   KASSERT(!rv->inpartpopq,
                       ("vm_reserv_alloc_page: reserv %p's inpartpopq is TRUE",
                       rv));
                   vm_reserv_populate(rv);
                   m = &rv->pages[VM_RESERV_INDEX(object, pindex)];
           }
           return (m);
   }
   
   /*
    * Breaks all reservations belonging to the given object.
    */
   void
   vm_reserv_break_all(vm_object_t object)
   {
           vm_reserv_t rv;
           int i;
   
           mtx_lock(&vm_page_queue_free_mtx);
           while ((rv = LIST_FIRST(&object->rvq)) != NULL) {
                   KASSERT(rv->object == object,
                       ("vm_reserv_break_all: reserv %p is corrupted", rv));
                   if (rv->inpartpopq) {
                           TAILQ_REMOVE(&vm_rvq_partpop, rv, partpopq);
                           rv->inpartpopq = FALSE;
                   }
                   LIST_REMOVE(rv, objq);
                   rv->object = NULL;
                   for (i = 0; i < VM_LEVEL_0_NPAGES; i++) {
                           if ((rv->pages[i].flags & (PG_CACHED | PG_FREE)) != 0)
                                   vm_phys_free_pages(&rv->pages[i], 0);
                           else
                                   rv->popcnt--;
                   }
                   KASSERT(rv->popcnt == 0,
                       ("vm_reserv_break_all: reserv %p's popcnt is corrupted",
                       rv));
                   vm_reserv_broken++;
           }
           mtx_unlock(&vm_page_queue_free_mtx);
   }
   
   /*
    * Frees the given page if it belongs to a reservation.  Returns TRUE if the
    * page is freed and FALSE otherwise.
    *
    * The free page queue lock must be held.
    */
   boolean_t
   vm_reserv_free_page(vm_page_t m)
   {
           vm_reserv_t rv;
   
           mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
           rv = vm_reserv_from_page(m);
           if (rv->object != NULL) {
                   vm_reserv_depopulate(rv);
                   return (TRUE);
           }
           return (FALSE);
   }
   
   /*
    * 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;
           int i;
   
           /*
            * Initialize the reservation array.  Specifically, initialize the
            * "pages" field for every element that has an underlying superpage.
            */
           for (i = 0; phys_avail[i + 1] != 0; i += 2) {
                   paddr = roundup2(phys_avail[i], VM_LEVEL_0_SIZE);
                   while (paddr + VM_LEVEL_0_SIZE <= phys_avail[i + 1]) {
                           vm_reserv_array[paddr >> VM_LEVEL_0_SHIFT].pages =
                               PHYS_TO_VM_PAGE(paddr);
                           paddr += VM_LEVEL_0_SIZE;
                   }
           }
   }
   
   /*
    * 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);
   }
   
   /*
    * Prepare for the reactivation of a cached page.
    *
    * First, suppose that the given page "m" was allocated individually, i.e., not
    * as part of a reservation, and cached.  Then, suppose a reservation
    * containing "m" is allocated by the same object.  Although "m" and the
    * reservation belong to the same object, "m"'s pindex may not match the
    * reservation's.
    *
    * The free page queue must be locked.
    */
   boolean_t
   vm_reserv_reactivate_page(vm_page_t m)
   {
           vm_reserv_t rv;
           int i, m_index;
   
           mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
           rv = vm_reserv_from_page(m);
           if (rv->object == NULL)
                   return (FALSE);
           KASSERT((m->flags & PG_CACHED) != 0,
               ("vm_reserv_uncache_page: page %p is not cached", m));
           if (m->object == rv->object &&
               m->pindex - rv->pindex == VM_RESERV_INDEX(m->object, m->pindex))
                   vm_reserv_populate(rv);
           else {
                   KASSERT(rv->inpartpopq,
                       ("vm_reserv_uncache_page: reserv %p's inpartpopq is FALSE",
                       rv));
                   TAILQ_REMOVE(&vm_rvq_partpop, rv, partpopq);
                   rv->inpartpopq = FALSE;
                   LIST_REMOVE(rv, objq);
                   rv->object = NULL;
                   /* Don't vm_phys_free_pages(m, 0). */
                   m_index = m - rv->pages;
                   for (i = 0; i < m_index; i++) {
                           if ((rv->pages[i].flags & (PG_CACHED | PG_FREE)) != 0)
                                   vm_phys_free_pages(&rv->pages[i], 0);
                           else
                                   rv->popcnt--;
                   }
                   for (i++; i < VM_LEVEL_0_NPAGES; i++) {
                           if ((rv->pages[i].flags & (PG_CACHED | PG_FREE)) != 0)
                                   vm_phys_free_pages(&rv->pages[i], 0);
                           else
                                   rv->popcnt--;
                   }
                   KASSERT(rv->popcnt == 0,
                       ("vm_reserv_uncache_page: reserv %p's popcnt is corrupted",
                       rv));
                   vm_reserv_broken++;
           }
           return (TRUE);
   }
   
   /*
    * Breaks the given partially-populated reservation, releasing its cached and
    * free pages to the physical memory allocator.
    *
    * The free page queue lock must be held.
    */
   static void
   vm_reserv_reclaim(vm_reserv_t rv)
   {
           int i;
   
           mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
           KASSERT(rv->inpartpopq,
               ("vm_reserv_reclaim: reserv %p's inpartpopq is corrupted", rv));
           TAILQ_REMOVE(&vm_rvq_partpop, rv, partpopq);
           rv->inpartpopq = FALSE;
           KASSERT(rv->object != NULL,
               ("vm_reserv_reclaim: reserv %p is free", rv));
           LIST_REMOVE(rv, objq);
           rv->object = NULL;
           for (i = 0; i < VM_LEVEL_0_NPAGES; i++) {
                   if ((rv->pages[i].flags & (PG_CACHED | PG_FREE)) != 0)
                           vm_phys_free_pages(&rv->pages[i], 0);
                   else
                           rv->popcnt--;
           }
           KASSERT(rv->popcnt == 0,
               ("vm_reserv_reclaim: reserv %p's popcnt is corrupted", rv));
           vm_reserv_reclaimed++;
   }
   
   /*
    * Breaks the reservation at the head of the partially-populated reservation
    * queue, releasing its cached and free pages to the physical memory
    * allocator.  Returns TRUE if a reservation is broken and FALSE otherwise.
    *
    * The free page queue lock must be held.
    */
   boolean_t
   vm_reserv_reclaim_inactive(void)
   {
           vm_reserv_t rv;
   
           mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
           if ((rv = TAILQ_FIRST(&vm_rvq_partpop)) != NULL) {
                   vm_reserv_reclaim(rv);
                   return (TRUE);
           }
           return (FALSE);
   }
   
   /*
    * Searches the partially-populated reservation queue for the least recently
    * active reservation with unused pages, i.e., cached or free, 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.
    *
    * The free page queue lock must be held.
    */
   boolean_t
   vm_reserv_reclaim_contig(vm_paddr_t size, vm_paddr_t low, vm_paddr_t high,
       unsigned long alignment, unsigned long boundary)
   {
           vm_paddr_t pa, pa_length;
           vm_reserv_t rv;
           int i;
   
           mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
           if (size > VM_LEVEL_0_SIZE - PAGE_SIZE)
                   return (FALSE);
           TAILQ_FOREACH(rv, &vm_rvq_partpop, partpopq) {
                   pa = VM_PAGE_TO_PHYS(&rv->pages[VM_LEVEL_0_NPAGES - 1]);
                   if (pa + PAGE_SIZE - size < low) {
                           /* this entire reservation is too low; go to next */
                           continue;
                   }
                   pa_length = 0;
                   for (i = 0; i < VM_LEVEL_0_NPAGES; i++)
                           if ((rv->pages[i].flags & (PG_CACHED | PG_FREE)) != 0) {
                                   pa_length += PAGE_SIZE;
                                   if (pa_length == PAGE_SIZE) {
                                           pa = VM_PAGE_TO_PHYS(&rv->pages[i]);
                                           if (pa + size > high) {
                                                   /* skip to next reservation */
                                                   break;
                                           } else if (pa < low ||
                                               (pa & (alignment - 1)) != 0 ||
                                               ((pa ^ (pa + size - 1)) &
                                               ~(boundary - 1)) != 0)
                                                   pa_length = 0;
                                   } else if (pa_length >= size) {
                                           vm_reserv_reclaim(rv);
                                           return (TRUE);
                                   }
                           } else
                                   pa_length = 0;
           }
           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_LOCK_ASSERT(new_object, MA_OWNED);
           rv = vm_reserv_from_page(m);
           if (rv->object == old_object) {
                   mtx_lock(&vm_page_queue_free_mtx);
                   if (rv->object == old_object) {
                           LIST_REMOVE(rv, objq);
                           LIST_INSERT_HEAD(&new_object->rvq, rv, objq);
                           rv->object = new_object;
                           rv->pindex -= old_object_offset;
                   }
                   mtx_unlock(&vm_page_queue_free_mtx);
           }
   }
   
   /*
    * 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);
   }
   
   #endif  /* VM_NRESERVLEVEL > 0 */

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