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

     /*-
      * 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/vmmeter.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_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
    
    /*
     * 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 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)
   
   /*
    * 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.
    */
   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;
           popmap_t        popmap[NPOPMAP];        /* bit vector of used pages */
   };
   
   /*
    * 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 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_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, 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_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 the
    * free page queue lock, the returned value may be 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, 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, "\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, "%5d: %6dK, %6d\n", level,
                       unused_pages * ((int)PAGE_SIZE / 1024), counter);
           }
           error = sbuf_finish(&sbuf);
           sbuf_delete(&sbuf);
           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 reservation 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, int index)
   {
   
           mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
           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));
           if (rv->inpartpopq) {
                   TAILQ_REMOVE(&vm_rvq_partpop, rv, partpopq);
                   rv->inpartpopq = FALSE;
           } else {
                   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 (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, int index)
   {
   
           mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
           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));
           if (rv->inpartpopq) {
                   TAILQ_REMOVE(&vm_rvq_partpop, rv, partpopq);
                   rv->inpartpopq = FALSE;
           }
           popmap_set(rv->popmap, index);
           rv->popcnt++;
           if (rv->popcnt < VM_LEVEL_0_NPAGES) {
                   rv->inpartpopq = TRUE;
                   TAILQ_INSERT_TAIL(&vm_rvq_partpop, rv, partpopq);
           } else
                   rv->pages->psind = 1;
   }
   
   /*
    * Allocates a contiguous set of physical pages of the given size "npages"
    * from existing or 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.
    *
    * 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(vm_object_t object, vm_pindex_t pindex, u_long npages,
       vm_paddr_t low, vm_paddr_t high, u_long alignment, vm_paddr_t boundary,
       vm_page_t mpred)
   {
           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;
   
           mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
           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);
   
           /*
            * Look for an existing reservation.
            */
           if (mpred != NULL) {
                   KASSERT(mpred->object == object,
                       ("vm_reserv_alloc_contig: object doesn't contain mpred"));
                   KASSERT(mpred->pindex < pindex,
                       ("vm_reserv_alloc_contig: 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_alloc_contig: msucc doesn't succeed pindex"));
                   rv = vm_reserv_from_page(msucc);
                   if (rv->object == object && vm_reserv_has_pindex(rv, pindex))
                           goto found;
           }
   
           /*
            * 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")?
            */
           first = pindex - VM_RESERV_INDEX(object, pindex);
           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)
                           return (NULL);
           }
           minpages = VM_RESERV_INDEX(object, pindex) + npages;
           maxpages = roundup2(minpages, VM_LEVEL_0_NPAGES);
           allocpages = maxpages;
           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)
                                   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;
                   }
           }
   
           /*
            * 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 = vm_phys_alloc_contig(allocpages, low, high, ulmax(alignment,
               VM_LEVEL_0_SIZE), boundary > VM_LEVEL_0_SIZE ? boundary : 0);
           if (m == NULL)
                   return (NULL);
   
           /*
            * 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));
                   KASSERT(rv->object == NULL,
                       ("vm_reserv_alloc_contig: 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_contig: reserv %p's popcnt is corrupted",
                       rv));
                   KASSERT(!rv->inpartpopq,
                       ("vm_reserv_alloc_contig: reserv %p's inpartpopq is TRUE",
                       rv));
                   for (i = 0; i < NPOPMAP; i++)
                           KASSERT(rv->popmap[i] == 0,
                       ("vm_reserv_alloc_contig: reserv %p's popmap is corrupted",
                               rv));
                   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;
                   }
                   m += VM_LEVEL_0_NPAGES;
                   first += VM_LEVEL_0_NPAGES;
                   allocpages -= VM_LEVEL_0_NPAGES;
           } while (allocpages >= VM_LEVEL_0_NPAGES);
           return (m_ret);
   
           /*
            * Found a matching reservation.
            */
   found:
           index = VM_RESERV_INDEX(object, pindex);
           /* Does the allocation fit within the reservation? */
           if (index + npages > VM_LEVEL_0_NPAGES)
                   return (NULL);
           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)
                   return (NULL);
           /* Handle vm_page_rename(m, new_object, ...). */
           for (i = 0; i < npages; i++)
                   if (popmap_is_set(rv->popmap, index + i))
                           return (NULL);
           for (i = 0; i < npages; i++)
                   vm_reserv_populate(rv, index + i);
           return (m);
   }
   
   /*
    * Allocates a page from an existing or newly created 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(vm_object_t object, vm_pindex_t pindex, vm_page_t mpred)
   {
           vm_page_t m, msucc;
           vm_pindex_t first, leftcap, rightcap;
           vm_reserv_t rv;
           int i, index;
   
           mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
           VM_OBJECT_ASSERT_WLOCKED(object);
   
           /*
            * Is a reservation fundamentally impossible?
            */
           if (pindex < VM_RESERV_INDEX(object, pindex) ||
               pindex >= object->size)
                   return (NULL);
   
           /*
            * Look for an existing reservation.
            */
           if (mpred != NULL) {
                   KASSERT(mpred->object == object,
                       ("vm_reserv_alloc_page: object doesn't contain mpred"));
                   KASSERT(mpred->pindex < pindex,
                       ("vm_reserv_alloc_page: 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_alloc_page: msucc doesn't succeed pindex"));
                   rv = vm_reserv_from_page(msucc);
                   if (rv->object == object && vm_reserv_has_pindex(rv, pindex))
                           goto found;
           }
   
           /*
            * 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?
            */
           first = pindex - VM_RESERV_INDEX(object, pindex);
           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)
                           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)
                           return (NULL);
           }
   
           /*
            * 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 = vm_phys_alloc_pages(VM_FREEPOOL_DEFAULT, VM_LEVEL_0_ORDER);
           if (m == NULL)
                   return (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));
           for (i = 0; i < NPOPMAP; i++)
                   KASSERT(rv->popmap[i] == 0,
                       ("vm_reserv_alloc_page: reserv %p's popmap is corrupted",
                       rv));
           index = VM_RESERV_INDEX(object, pindex);
           vm_reserv_populate(rv, index);
           return (&rv->pages[index]);
   
           /*
            * Found a matching reservation.
            */
   found:
           index = VM_RESERV_INDEX(object, pindex);
           m = &rv->pages[index];
           /* Handle vm_page_rename(m, new_object, ...). */
           if (popmap_is_set(rv->popmap, index))
                   return (NULL);
           vm_reserv_populate(rv, index);
           return (m);
   }
   
   /*
    * 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.  The free page queue lock must be held.
    */
   static void
   vm_reserv_break(vm_reserv_t rv)
   {
           int begin_zeroes, hi, i, lo;
   
           mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
           KASSERT(rv->object != NULL,
               ("vm_reserv_break: reserv %p is free", rv));
           KASSERT(!rv->inpartpopq,
               ("vm_reserv_break: reserv %p's inpartpopq is TRUE", rv));
           LIST_REMOVE(rv, objq);
           rv->object = NULL;
           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_phys_free_contig(&rv->pages[begin_zeroes], NBPOPMAP * i +
                       hi - begin_zeroes);
           } while (i < NPOPMAP);
           KASSERT(rv->popcnt == 0,
               ("vm_reserv_break: reserv %p's popcnt is corrupted", rv));
           vm_reserv_broken++;
   }
   
   /*
    * Breaks all reservations belonging to the given object.
    */
   void
   vm_reserv_break_all(vm_object_t object)
   {
           vm_reserv_t rv;
   
           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;
                   }
                   vm_reserv_break(rv);
           }
           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)
                   return (FALSE);
           vm_reserv_depopulate(rv, m - rv->pages);
           return (TRUE);
   }
   
   /*
    * 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;
           int 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) {
                           vm_reserv_array[paddr >> VM_LEVEL_0_SHIFT].pages =
                               PHYS_TO_VM_PAGE(paddr);
                           paddr += VM_LEVEL_0_SIZE;
                   }
           }
   }
   
   /*
    * 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;
   
           mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
           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);
   }
   
   /*
    * Breaks the given partially populated reservation, releasing its free pages
    * to the physical memory allocator.
    *
    * The free page queue lock must be held.
    */
   static void
   vm_reserv_reclaim(vm_reserv_t rv)
   {
   
           mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
           KASSERT(rv->inpartpopq,
               ("vm_reserv_reclaim: reserv %p's inpartpopq is FALSE", rv));
           TAILQ_REMOVE(&vm_rvq_partpop, rv, partpopq);
           rv->inpartpopq = FALSE;
           vm_reserv_break(rv);
           vm_reserv_reclaimed++;
   }
   
   /*
    * Breaks the reservation at 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.
    *
    * 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
    * 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.
    *
    * The free page queue lock must be held.
    */
   boolean_t
   vm_reserv_reclaim_contig(u_long npages, vm_paddr_t low, vm_paddr_t high,
       u_long alignment, vm_paddr_t boundary)
   {
           vm_paddr_t pa, size;
           vm_reserv_t rv;
           int hi, i, lo, low_index, next_free;
   
           mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
           if (npages > VM_LEVEL_0_NPAGES - 1)
                   return (FALSE);
           size = npages << PAGE_SHIFT;
           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 = VM_PAGE_TO_PHYS(&rv->pages[0]);
                   if (pa + size > high) {
                           /* This entire reservation is too high; go to next. */
                           continue;
                   }
                   if (pa < low) {
                           /* Start the search for free pages at "low". */
                           low_index = (low + PAGE_MASK - pa) >> PAGE_SHIFT;
                           i = low_index / NBPOPMAP;
                           hi = low_index % NBPOPMAP;
                   } else
                           i = hi = 0;
                   do {
                           /* Find the next free page. */
                           lo = ffsl(~(((1UL << hi) - 1) | rv->popmap[i]));
                           while (lo == 0 && ++i < NPOPMAP)
                                   lo = ffsl(~rv->popmap[i]);
                           if (i == NPOPMAP)
                                   break;
                           /* Convert from ffsl() to ordinary bit numbering. */
                           lo--;
                           next_free = NBPOPMAP * i + lo;
                           pa = VM_PAGE_TO_PHYS(&rv->pages[next_free]);
                           KASSERT(pa >= low,
                               ("vm_reserv_reclaim_contig: pa is too low"));
                           if (pa + size > high) {
                                   /* The rest of this reservation is too high. */
                                   break;
                           } else if ((pa & (alignment - 1)) != 0 ||
                              ((pa ^ (pa + size - 1)) & ~(boundary - 1)) != 0) {
                                  /*
                                   * The current page doesn't meet the alignment
                                   * and/or boundary requirements.  Continue
                                   * searching this reservation until the rest
                                   * of its free pages are either excluded or
                                   * exhausted.
                                   */
                                  hi = lo + 1;
                                  if (hi >= NBPOPMAP) {
                                          hi = 0;
                                          i++;
                                  }
                                  continue;
                          }
                          /* Find the next used page. */
                          hi = ffsl(rv->popmap[i] & ~((1UL << lo) - 1));
                          while (hi == 0 && ++i < NPOPMAP) {
                                  if ((NBPOPMAP * i - next_free) * PAGE_SIZE >=
                                      size) {
                                          vm_reserv_reclaim(rv);
                                          return (TRUE);
                                  }
                                  hi = ffsl(rv->popmap[i]);
                          }
                          /* Convert from ffsl() to ordinary bit numbering. */
                          if (i != NPOPMAP)
                                  hi--;
                          if ((NBPOPMAP * i + hi - next_free) * PAGE_SIZE >=
                              size) {
                                  vm_reserv_reclaim(rv);
                                  return (TRUE);
                          }
                  } while (i < NPOPMAP);
          }
          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) {
                  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);
          }
  }
  
  /*
   * 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);
  }
  
  /*
   * 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);
          return (rv->object == m->object && rv->popcnt == VM_LEVEL_0_NPAGES ?
              rv->pages : NULL);
  }
  
  #endif  /* VM_NRESERVLEVEL > 0 */

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