contrib/tzdata: import tzdata 2022f

[FreeBSD/FreeBSD.git] / 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 < NBPOPMAP; 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 low_index.
 */
static bool
vm_reserv_test_contig(vm_reserv_t rv, u_long npages, vm_paddr_t low,
    vm_paddr_t high, u_long alignment, vm_paddr_t boundary)
{
        vm_paddr_t pa, size;
        u_long changes;
        int bitpos, bits_left, i, hi, lo, n;

        vm_reserv_assert_locked(rv);
        size = npages << PAGE_SHIFT;
        pa = VM_PAGE_TO_PHYS(&rv->pages[0]);
        lo = (pa < low) ?
            ((low + PAGE_MASK - pa) >> PAGE_SHIFT) : 0;
        i = lo / NBPOPMAP;
        changes = rv->popmap[i] | ((1UL << (lo % NBPOPMAP)) - 1);
        hi = (pa + VM_LEVEL_0_SIZE > high) ?
            ((high + PAGE_MASK - pa) >> PAGE_SHIFT) : VM_LEVEL_0_NPAGES;
        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;
                        pa = VM_PAGE_TO_PHYS(&rv->pages[lo]);
                        if ((pa & (alignment - 1)) != 0) {
                                /* Skip to next aligned page. */
                                lo += (((pa - 1) | (alignment - 1)) + 1) >>
                                    PAGE_SHIFT;
                                if (lo >= VM_LEVEL_0_NPAGES)
                                        return (false);
                                pa = VM_PAGE_TO_PHYS(&rv->pages[lo]);
                        }
                        if (((pa ^ (pa + size - 1)) & ~(boundary - 1)) != 0) {
                                /* Skip to next boundary-matching page. */
                                lo += (((pa - 1) | (boundary - 1)) + 1) >>
                                    PAGE_SHIFT;
                                if (lo >= VM_LEVEL_0_NPAGES)
                                        return (false);
                                pa = VM_PAGE_TO_PHYS(&rv->pages[lo]);
                        }
                        if (lo * PAGE_SIZE + size <= hi * PAGE_SIZE)
                                return (true);
                        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 (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.
 */
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;

        if (npages > VM_LEVEL_0_NPAGES - 1)
                return (false);
        marker = &vm_rvd[domain].marker;
        queue = &vm_rvd[domain].partpop;
        size = npages << 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 (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);
                if (vm_reserv_test_contig(rv, npages, low, high,
                    alignment, 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 */