Fix a bug that allowed a tracing process (e.g. gdb) to write

[FreeBSD/FreeBSD.git] / sys / vm / vm_page.c

/*-
 * Copyright (c) 1991 Regents of the University of California.
 * All rights reserved.
 * Copyright (c) 1998 Matthew Dillon.  All Rights Reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * The Mach Operating System project at Carnegie-Mellon University.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      from: @(#)vm_page.c     7.4 (Berkeley) 5/7/91
 */

/*-
 * Copyright (c) 1987, 1990 Carnegie-Mellon University.
 * All rights reserved.
 *
 * Authors: Avadis Tevanian, Jr., Michael Wayne Young
 *
 * Permission to use, copy, modify and distribute this software and
 * its documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 *
 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
 * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 *
 * Carnegie Mellon requests users of this software to return to
 *
 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 *
 * any improvements or extensions that they make and grant Carnegie the
 * rights to redistribute these changes.
 */

/*
 *                      GENERAL RULES ON VM_PAGE MANIPULATION
 *
 *      - A page queue lock is required when adding or removing a page from a
 *        page queue (vm_pagequeues[]), regardless of other locks or the
 *        busy state of a page.
 *
 *              * In general, no thread besides the page daemon can acquire or
 *                hold more than one page queue lock at a time.
 *
 *              * The page daemon can acquire and hold any pair of page queue
 *                locks in any order.
 *
 *      - The object lock is required when inserting or removing
 *        pages from an object (vm_page_insert() or vm_page_remove()).
 *
 */

/*
 *      Resident memory management module.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include "opt_vm.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/lock.h>
#include <sys/kernel.h>
#include <sys/limits.h>
#include <sys/malloc.h>
#include <sys/mman.h>
#include <sys/msgbuf.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/rwlock.h>
#include <sys/sysctl.h>
#include <sys/vmmeter.h>
#include <sys/vnode.h>

#include <vm/vm.h>
#include <vm/pmap.h>
#include <vm/vm_param.h>
#include <vm/vm_kern.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
#include <vm/vm_pageout.h>
#include <vm/vm_pager.h>
#include <vm/vm_phys.h>
#include <vm/vm_radix.h>
#include <vm/vm_reserv.h>
#include <vm/vm_extern.h>
#include <vm/uma.h>
#include <vm/uma_int.h>

#include <machine/md_var.h>

/*
 *      Associated with page of user-allocatable memory is a
 *      page structure.
 */

struct vm_pagequeue vm_pagequeues[PQ_COUNT] = {
        [PQ_INACTIVE] = {
                .pq_pl = TAILQ_HEAD_INITIALIZER(
                    vm_pagequeues[PQ_INACTIVE].pq_pl),
                .pq_cnt = &cnt.v_inactive_count,
                .pq_name = "vm inactive pagequeue"
        },
        [PQ_ACTIVE] = {
                .pq_pl = TAILQ_HEAD_INITIALIZER(
                    vm_pagequeues[PQ_ACTIVE].pq_pl),
                .pq_cnt = &cnt.v_active_count,
                .pq_name = "vm active pagequeue"
        }
};
struct mtx_padalign vm_page_queue_free_mtx;

struct mtx_padalign pa_lock[PA_LOCK_COUNT];

vm_page_t vm_page_array;
long vm_page_array_size;
long first_page;
int vm_page_zero_count;

static int boot_pages = UMA_BOOT_PAGES;
TUNABLE_INT("vm.boot_pages", &boot_pages);
SYSCTL_INT(_vm, OID_AUTO, boot_pages, CTLFLAG_RD, &boot_pages, 0,
        "number of pages allocated for bootstrapping the VM system");

static int pa_tryrelock_restart;
SYSCTL_INT(_vm, OID_AUTO, tryrelock_restart, CTLFLAG_RD,
    &pa_tryrelock_restart, 0, "Number of tryrelock restarts");

static uma_zone_t fakepg_zone;

static struct vnode *vm_page_alloc_init(vm_page_t m);
static void vm_page_clear_dirty_mask(vm_page_t m, vm_page_bits_t pagebits);
static void vm_page_enqueue(int queue, vm_page_t m);
static void vm_page_init_fakepg(void *dummy);
static void vm_page_insert_after(vm_page_t m, vm_object_t object,
    vm_pindex_t pindex, vm_page_t mpred);

SYSINIT(vm_page, SI_SUB_VM, SI_ORDER_SECOND, vm_page_init_fakepg, NULL);

static void
vm_page_init_fakepg(void *dummy)
{

        fakepg_zone = uma_zcreate("fakepg", sizeof(struct vm_page), NULL, NULL,
            NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE | UMA_ZONE_VM); 
}

/* Make sure that u_long is at least 64 bits when PAGE_SIZE is 32K. */
#if PAGE_SIZE == 32768
#ifdef CTASSERT
CTASSERT(sizeof(u_long) >= 8);
#endif
#endif

/*
 * Try to acquire a physical address lock while a pmap is locked.  If we
 * fail to trylock we unlock and lock the pmap directly and cache the
 * locked pa in *locked.  The caller should then restart their loop in case
 * the virtual to physical mapping has changed.
 */
int
vm_page_pa_tryrelock(pmap_t pmap, vm_paddr_t pa, vm_paddr_t *locked)
{
        vm_paddr_t lockpa;

        lockpa = *locked;
        *locked = pa;
        if (lockpa) {
                PA_LOCK_ASSERT(lockpa, MA_OWNED);
                if (PA_LOCKPTR(pa) == PA_LOCKPTR(lockpa))
                        return (0);
                PA_UNLOCK(lockpa);
        }
        if (PA_TRYLOCK(pa))
                return (0);
        PMAP_UNLOCK(pmap);
        atomic_add_int(&pa_tryrelock_restart, 1);
        PA_LOCK(pa);
        PMAP_LOCK(pmap);
        return (EAGAIN);
}

/*
 *      vm_set_page_size:
 *
 *      Sets the page size, perhaps based upon the memory
 *      size.  Must be called before any use of page-size
 *      dependent functions.
 */
void
vm_set_page_size(void)
{
        if (cnt.v_page_size == 0)
                cnt.v_page_size = PAGE_SIZE;
        if (((cnt.v_page_size - 1) & cnt.v_page_size) != 0)
                panic("vm_set_page_size: page size not a power of two");
}

/*
 *      vm_page_blacklist_lookup:
 *
 *      See if a physical address in this page has been listed
 *      in the blacklist tunable.  Entries in the tunable are
 *      separated by spaces or commas.  If an invalid integer is
 *      encountered then the rest of the string is skipped.
 */
static int
vm_page_blacklist_lookup(char *list, vm_paddr_t pa)
{
        vm_paddr_t bad;
        char *cp, *pos;

        for (pos = list; *pos != '\0'; pos = cp) {
                bad = strtoq(pos, &cp, 0);
                if (*cp != '\0') {
                        if (*cp == ' ' || *cp == ',') {
                                cp++;
                                if (cp == pos)
                                        continue;
                        } else
                                break;
                }
                if (pa == trunc_page(bad))
                        return (1);
        }
        return (0);
}

/*
 *      vm_page_startup:
 *
 *      Initializes the resident memory module.
 *
 *      Allocates memory for the page cells, and
 *      for the object/offset-to-page hash table headers.
 *      Each page cell is initialized and placed on the free list.
 */
vm_offset_t
vm_page_startup(vm_offset_t vaddr)
{
        vm_offset_t mapped;
        vm_paddr_t page_range;
        vm_paddr_t new_end;
        int i;
        vm_paddr_t pa;
        vm_paddr_t last_pa;
        char *list;

        /* the biggest memory array is the second group of pages */
        vm_paddr_t end;
        vm_paddr_t biggestsize;
        vm_paddr_t low_water, high_water;
        int biggestone;

        biggestsize = 0;
        biggestone = 0;
        vaddr = round_page(vaddr);

        for (i = 0; phys_avail[i + 1]; i += 2) {
                phys_avail[i] = round_page(phys_avail[i]);
                phys_avail[i + 1] = trunc_page(phys_avail[i + 1]);
        }

        low_water = phys_avail[0];
        high_water = phys_avail[1];

        for (i = 0; phys_avail[i + 1]; i += 2) {
                vm_paddr_t size = phys_avail[i + 1] - phys_avail[i];

                if (size > biggestsize) {
                        biggestone = i;
                        biggestsize = size;
                }
                if (phys_avail[i] < low_water)
                        low_water = phys_avail[i];
                if (phys_avail[i + 1] > high_water)
                        high_water = phys_avail[i + 1];
        }

#ifdef XEN
        low_water = 0;
#endif  

        end = phys_avail[biggestone+1];

        /*
         * Initialize the page and queue locks.
         */
        mtx_init(&vm_page_queue_free_mtx, "vm page free queue", NULL, MTX_DEF);
        for (i = 0; i < PA_LOCK_COUNT; i++)
                mtx_init(&pa_lock[i], "vm page", NULL, MTX_DEF);
        for (i = 0; i < PQ_COUNT; i++)
                vm_pagequeue_init_lock(&vm_pagequeues[i]);

        /*
         * Allocate memory for use when boot strapping the kernel memory
         * allocator.
         */
        new_end = end - (boot_pages * UMA_SLAB_SIZE);
        new_end = trunc_page(new_end);
        mapped = pmap_map(&vaddr, new_end, end,
            VM_PROT_READ | VM_PROT_WRITE);
        bzero((void *)mapped, end - new_end);
        uma_startup((void *)mapped, boot_pages);

#if defined(__amd64__) || defined(__i386__) || defined(__arm__) || \
    defined(__mips__)
        /*
         * Allocate a bitmap to indicate that a random physical page
         * needs to be included in a minidump.
         *
         * The amd64 port needs this to indicate which direct map pages
         * need to be dumped, via calls to dump_add_page()/dump_drop_page().
         *
         * However, i386 still needs this workspace internally within the
         * minidump code.  In theory, they are not needed on i386, but are
         * included should the sf_buf code decide to use them.
         */
        last_pa = 0;
        for (i = 0; dump_avail[i + 1] != 0; i += 2)
                if (dump_avail[i + 1] > last_pa)
                        last_pa = dump_avail[i + 1];
        page_range = last_pa / PAGE_SIZE;
        vm_page_dump_size = round_page(roundup2(page_range, NBBY) / NBBY);
        new_end -= vm_page_dump_size;
        vm_page_dump = (void *)(uintptr_t)pmap_map(&vaddr, new_end,
            new_end + vm_page_dump_size, VM_PROT_READ | VM_PROT_WRITE);
        bzero((void *)vm_page_dump, vm_page_dump_size);
#endif
#ifdef __amd64__
        /*
         * Request that the physical pages underlying the message buffer be
         * included in a crash dump.  Since the message buffer is accessed
         * through the direct map, they are not automatically included.
         */
        pa = DMAP_TO_PHYS((vm_offset_t)msgbufp->msg_ptr);
        last_pa = pa + round_page(msgbufsize);
        while (pa < last_pa) {
                dump_add_page(pa);
                pa += PAGE_SIZE;
        }
#endif
        /*
         * Compute the number of pages of memory that will be available for
         * use (taking into account the overhead of a page structure per
         * page).
         */
        first_page = low_water / PAGE_SIZE;
#ifdef VM_PHYSSEG_SPARSE
        page_range = 0;
        for (i = 0; phys_avail[i + 1] != 0; i += 2)
                page_range += atop(phys_avail[i + 1] - phys_avail[i]);
#elif defined(VM_PHYSSEG_DENSE)
        page_range = high_water / PAGE_SIZE - first_page;
#else
#error "Either VM_PHYSSEG_DENSE or VM_PHYSSEG_SPARSE must be defined."
#endif
        end = new_end;

        /*
         * Reserve an unmapped guard page to trap access to vm_page_array[-1].
         */
        vaddr += PAGE_SIZE;

        /*
         * Initialize the mem entry structures now, and put them in the free
         * queue.
         */
        new_end = trunc_page(end - page_range * sizeof(struct vm_page));
        mapped = pmap_map(&vaddr, new_end, end,
            VM_PROT_READ | VM_PROT_WRITE);
        vm_page_array = (vm_page_t) mapped;
#if VM_NRESERVLEVEL > 0
        /*
         * Allocate memory for the reservation management system's data
         * structures.
         */
        new_end = vm_reserv_startup(&vaddr, new_end, high_water);
#endif
#if defined(__amd64__) || defined(__mips__)
        /*
         * pmap_map on amd64 and mips can come out of the direct-map, not kvm
         * like i386, so the pages must be tracked for a crashdump to include
         * this data.  This includes the vm_page_array and the early UMA
         * bootstrap pages.
         */
        for (pa = new_end; pa < phys_avail[biggestone + 1]; pa += PAGE_SIZE)
                dump_add_page(pa);
#endif  
        phys_avail[biggestone + 1] = new_end;

        /*
         * Clear all of the page structures
         */
        bzero((caddr_t) vm_page_array, page_range * sizeof(struct vm_page));
        for (i = 0; i < page_range; i++)
                vm_page_array[i].order = VM_NFREEORDER;
        vm_page_array_size = page_range;

        /*
         * Initialize the physical memory allocator.
         */
        vm_phys_init();

        /*
         * Add every available physical page that is not blacklisted to
         * the free lists.
         */
        cnt.v_page_count = 0;
        cnt.v_free_count = 0;
        list = getenv("vm.blacklist");
        for (i = 0; phys_avail[i + 1] != 0; i += 2) {
                pa = phys_avail[i];
                last_pa = phys_avail[i + 1];
                while (pa < last_pa) {
                        if (list != NULL &&
                            vm_page_blacklist_lookup(list, pa))
                                printf("Skipping page with pa 0x%jx\n",
                                    (uintmax_t)pa);
                        else
                                vm_phys_add_page(pa);
                        pa += PAGE_SIZE;
                }
        }
        freeenv(list);
#if VM_NRESERVLEVEL > 0
        /*
         * Initialize the reservation management system.
         */
        vm_reserv_init();
#endif
        return (vaddr);
}

void
vm_page_reference(vm_page_t m)
{

        vm_page_aflag_set(m, PGA_REFERENCED);
}

void
vm_page_busy(vm_page_t m)
{

        VM_OBJECT_ASSERT_WLOCKED(m->object);
        KASSERT((m->oflags & VPO_BUSY) == 0,
            ("vm_page_busy: page already busy!!!"));
        m->oflags |= VPO_BUSY;
}

/*
 *      vm_page_flash:
 *
 *      wakeup anyone waiting for the page.
 */
void
vm_page_flash(vm_page_t m)
{

        VM_OBJECT_ASSERT_WLOCKED(m->object);
        if (m->oflags & VPO_WANTED) {
                m->oflags &= ~VPO_WANTED;
                wakeup(m);
        }
}

/*
 *      vm_page_wakeup:
 *
 *      clear the VPO_BUSY flag and wakeup anyone waiting for the
 *      page.
 *
 */
void
vm_page_wakeup(vm_page_t m)
{

        VM_OBJECT_ASSERT_WLOCKED(m->object);
        KASSERT(m->oflags & VPO_BUSY, ("vm_page_wakeup: page not busy!!!"));
        m->oflags &= ~VPO_BUSY;
        vm_page_flash(m);
}

void
vm_page_io_start(vm_page_t m)
{

        VM_OBJECT_ASSERT_WLOCKED(m->object);
        m->busy++;
}

void
vm_page_io_finish(vm_page_t m)
{

        VM_OBJECT_ASSERT_WLOCKED(m->object);
        KASSERT(m->busy > 0, ("vm_page_io_finish: page %p is not busy", m));
        m->busy--;
        if (m->busy == 0)
                vm_page_flash(m);
}

/*
 * Keep page from being freed by the page daemon
 * much of the same effect as wiring, except much lower
 * overhead and should be used only for *very* temporary
 * holding ("wiring").
 */
void
vm_page_hold(vm_page_t mem)
{

        vm_page_lock_assert(mem, MA_OWNED);
        mem->hold_count++;
}

void
vm_page_unhold(vm_page_t mem)
{

        vm_page_lock_assert(mem, MA_OWNED);
        --mem->hold_count;
        KASSERT(mem->hold_count >= 0, ("vm_page_unhold: hold count < 0!!!"));
        if (mem->hold_count == 0 && (mem->flags & PG_UNHOLDFREE) != 0)
                vm_page_free_toq(mem);
}

/*
 *      vm_page_unhold_pages:
 *
 *      Unhold each of the pages that is referenced by the given array.
 */ 
void
vm_page_unhold_pages(vm_page_t *ma, int count)
{
        struct mtx *mtx, *new_mtx;

        mtx = NULL;
        for (; count != 0; count--) {
                /*
                 * Avoid releasing and reacquiring the same page lock.
                 */
                new_mtx = vm_page_lockptr(*ma);
                if (mtx != new_mtx) {
                        if (mtx != NULL)
                                mtx_unlock(mtx);
                        mtx = new_mtx;
                        mtx_lock(mtx);
                }
                vm_page_unhold(*ma);
                ma++;
        }
        if (mtx != NULL)
                mtx_unlock(mtx);
}

vm_page_t
PHYS_TO_VM_PAGE(vm_paddr_t pa)
{
        vm_page_t m;

#ifdef VM_PHYSSEG_SPARSE
        m = vm_phys_paddr_to_vm_page(pa);
        if (m == NULL)
                m = vm_phys_fictitious_to_vm_page(pa);
        return (m);
#elif defined(VM_PHYSSEG_DENSE)
        long pi;

        pi = atop(pa);
        if (pi >= first_page && (pi - first_page) < vm_page_array_size) {
                m = &vm_page_array[pi - first_page];
                return (m);
        }
        return (vm_phys_fictitious_to_vm_page(pa));
#else
#error "Either VM_PHYSSEG_DENSE or VM_PHYSSEG_SPARSE must be defined."
#endif
}

/*
 *      vm_page_getfake:
 *
 *      Create a fictitious page with the specified physical address and
 *      memory attribute.  The memory attribute is the only the machine-
 *      dependent aspect of a fictitious page that must be initialized.
 */
vm_page_t
vm_page_getfake(vm_paddr_t paddr, vm_memattr_t memattr)
{
        vm_page_t m;

        m = uma_zalloc(fakepg_zone, M_WAITOK | M_ZERO);
        vm_page_initfake(m, paddr, memattr);
        return (m);
}

void
vm_page_initfake(vm_page_t m, vm_paddr_t paddr, vm_memattr_t memattr)
{

        if ((m->flags & PG_FICTITIOUS) != 0) {
                /*
                 * The page's memattr might have changed since the
                 * previous initialization.  Update the pmap to the
                 * new memattr.
                 */
                goto memattr;
        }
        m->phys_addr = paddr;
        m->queue = PQ_NONE;
        /* Fictitious pages don't use "segind". */
        m->flags = PG_FICTITIOUS;
        /* Fictitious pages don't use "order" or "pool". */
        m->oflags = VPO_BUSY | VPO_UNMANAGED;
        m->wire_count = 1;
memattr:
        pmap_page_set_memattr(m, memattr);
}

/*
 *      vm_page_putfake:
 *
 *      Release a fictitious page.
 */
void
vm_page_putfake(vm_page_t m)
{

        KASSERT((m->oflags & VPO_UNMANAGED) != 0, ("managed %p", m));
        KASSERT((m->flags & PG_FICTITIOUS) != 0,
            ("vm_page_putfake: bad page %p", m));
        uma_zfree(fakepg_zone, m);
}

/*
 *      vm_page_updatefake:
 *
 *      Update the given fictitious page to the specified physical address and
 *      memory attribute.
 */
void
vm_page_updatefake(vm_page_t m, vm_paddr_t paddr, vm_memattr_t memattr)
{

        KASSERT((m->flags & PG_FICTITIOUS) != 0,
            ("vm_page_updatefake: bad page %p", m));
        m->phys_addr = paddr;
        pmap_page_set_memattr(m, memattr);
}

/*
 *      vm_page_free:
 *
 *      Free a page.
 */
void
vm_page_free(vm_page_t m)
{

        m->flags &= ~PG_ZERO;
        vm_page_free_toq(m);
}

/*
 *      vm_page_free_zero:
 *
 *      Free a page to the zerod-pages queue
 */
void
vm_page_free_zero(vm_page_t m)
{

        m->flags |= PG_ZERO;
        vm_page_free_toq(m);
}

/*
 * Unbusy and handle the page queueing for a page from the VOP_GETPAGES()
 * array which is not the request page.
 */
void
vm_page_readahead_finish(vm_page_t m)
{

        if (m->valid != 0) {
                /*
                 * Since the page is not the requested page, whether
                 * it should be activated or deactivated is not
                 * obvious.  Empirical results have shown that
                 * deactivating the page is usually the best choice,
                 * unless the page is wanted by another thread.
                 */
                if (m->oflags & VPO_WANTED) {
                        vm_page_lock(m);
                        vm_page_activate(m);
                        vm_page_unlock(m);
                } else {
                        vm_page_lock(m);
                        vm_page_deactivate(m);
                        vm_page_unlock(m);
                }
                vm_page_wakeup(m);
        } else {
                /*
                 * Free the completely invalid page.  Such page state
                 * occurs due to the short read operation which did
                 * not covered our page at all, or in case when a read
                 * error happens.
                 */
                vm_page_lock(m);
                vm_page_free(m);
                vm_page_unlock(m);
        }
}

/*
 *      vm_page_sleep:
 *
 *      Sleep and release the page lock.
 *
 *      The object containing the given page must be locked.
 */
void
vm_page_sleep(vm_page_t m, const char *msg)
{

        VM_OBJECT_ASSERT_WLOCKED(m->object);
        if (mtx_owned(vm_page_lockptr(m)))
                vm_page_unlock(m);

        /*
         * It's possible that while we sleep, the page will get
         * unbusied and freed.  If we are holding the object
         * lock, we will assume we hold a reference to the object
         * such that even if m->object changes, we can re-lock
         * it.
         */
        m->oflags |= VPO_WANTED;
        VM_OBJECT_SLEEP(m->object, m, PVM, msg, 0);
}

/*
 *      vm_page_dirty_KBI:              [ internal use only ]
 *
 *      Set all bits in the page's dirty field.
 *
 *      The object containing the specified page must be locked if the
 *      call is made from the machine-independent layer.
 *
 *      See vm_page_clear_dirty_mask().
 *
 *      This function should only be called by vm_page_dirty().
 */
void
vm_page_dirty_KBI(vm_page_t m)
{

        /* These assertions refer to this operation by its public name. */
        KASSERT((m->flags & PG_CACHED) == 0,
            ("vm_page_dirty: page in cache!"));
        KASSERT(!VM_PAGE_IS_FREE(m),
            ("vm_page_dirty: page is free!"));
        KASSERT(m->valid == VM_PAGE_BITS_ALL,
            ("vm_page_dirty: page is invalid!"));
        m->dirty = VM_PAGE_BITS_ALL;
}

/*
 *      vm_page_insert:         [ internal use only ]
 *
 *      Inserts the given mem entry into the object and object list.
 *
 *      The object must be locked.
 */
void
vm_page_insert(vm_page_t m, vm_object_t object, vm_pindex_t pindex)
{
        vm_page_t mpred;

        VM_OBJECT_ASSERT_WLOCKED(object);
        mpred = vm_radix_lookup_le(&object->rtree, pindex);
        vm_page_insert_after(m, object, pindex, mpred);
}

/*
 *      vm_page_insert_after:
 *
 *      Inserts the page "m" into the specified object at offset "pindex".
 *
 *      The page "mpred" must immediately precede the offset "pindex" within
 *      the specified object.
 *
 *      The object must be locked.
 */
static void
vm_page_insert_after(vm_page_t m, vm_object_t object, vm_pindex_t pindex,
    vm_page_t mpred)
{
        vm_page_t msucc;

        VM_OBJECT_ASSERT_WLOCKED(object);
        KASSERT(m->object == NULL,
            ("vm_page_insert_after: page already inserted"));
        if (mpred != NULL) {
                KASSERT(mpred->object == object ||
                    (mpred->flags & PG_SLAB) != 0,
                    ("vm_page_insert_after: object doesn't contain mpred"));
                KASSERT(mpred->pindex < pindex,
                    ("vm_page_insert_after: mpred doesn't precede pindex"));
                msucc = TAILQ_NEXT(mpred, listq);
        } else
                msucc = TAILQ_FIRST(&object->memq);
        if (msucc != NULL)
                KASSERT(msucc->pindex > pindex,
                    ("vm_page_insert_after: msucc doesn't succeed pindex"));

        /*
         * Record the object/offset pair in this page
         */
        m->object = object;
        m->pindex = pindex;

        /*
         * Now link into the object's ordered list of backed pages.
         */
        if (mpred != NULL)
                TAILQ_INSERT_AFTER(&object->memq, mpred, m, listq);
        else
                TAILQ_INSERT_HEAD(&object->memq, m, listq);
        vm_radix_insert(&object->rtree, m);

        /*
         * Show that the object has one more resident page.
         */
        object->resident_page_count++;

        /*
         * Hold the vnode until the last page is released.
         */
        if (object->resident_page_count == 1 && object->type == OBJT_VNODE)
                vhold(object->handle);

        /*
         * Since we are inserting a new and possibly dirty page,
         * update the object's OBJ_MIGHTBEDIRTY flag.
         */
        if (pmap_page_is_write_mapped(m))
                vm_object_set_writeable_dirty(object);
}

/*
 *      vm_page_remove:
 *
 *      Removes the given mem entry from the object/offset-page
 *      table and the object page list, but do not invalidate/terminate
 *      the backing store.
 *
 *      The object must be locked.  The page must be locked if it is managed.
 */
void
vm_page_remove(vm_page_t m)
{
        vm_object_t object;

        if ((m->oflags & VPO_UNMANAGED) == 0)
                vm_page_lock_assert(m, MA_OWNED);
        if ((object = m->object) == NULL)
                return;
        VM_OBJECT_ASSERT_WLOCKED(object);
        if (m->oflags & VPO_BUSY) {
                m->oflags &= ~VPO_BUSY;
                vm_page_flash(m);
        }

        /*
         * Now remove from the object's list of backed pages.
         */
        vm_radix_remove(&object->rtree, m->pindex);
        TAILQ_REMOVE(&object->memq, m, listq);

        /*
         * And show that the object has one fewer resident page.
         */
        object->resident_page_count--;

        /*
         * The vnode may now be recycled.
         */
        if (object->resident_page_count == 0 && object->type == OBJT_VNODE)
                vdrop(object->handle);

        m->object = NULL;
}

/*
 *      vm_page_lookup:
 *
 *      Returns the page associated with the object/offset
 *      pair specified; if none is found, NULL is returned.
 *
 *      The object must be locked.
 */
vm_page_t
vm_page_lookup(vm_object_t object, vm_pindex_t pindex)
{

        VM_OBJECT_ASSERT_LOCKED(object);
        return (vm_radix_lookup(&object->rtree, pindex));
}

/*
 *      vm_page_find_least:
 *
 *      Returns the page associated with the object with least pindex
 *      greater than or equal to the parameter pindex, or NULL.
 *
 *      The object must be locked.
 */
vm_page_t
vm_page_find_least(vm_object_t object, vm_pindex_t pindex)
{
        vm_page_t m;

        VM_OBJECT_ASSERT_LOCKED(object);
        if ((m = TAILQ_FIRST(&object->memq)) != NULL && m->pindex < pindex)
                m = vm_radix_lookup_ge(&object->rtree, pindex);
        return (m);
}

/*
 * Returns the given page's successor (by pindex) within the object if it is
 * resident; if none is found, NULL is returned.
 *
 * The object must be locked.
 */
vm_page_t
vm_page_next(vm_page_t m)
{
        vm_page_t next;

        VM_OBJECT_ASSERT_WLOCKED(m->object);
        if ((next = TAILQ_NEXT(m, listq)) != NULL &&
            next->pindex != m->pindex + 1)
                next = NULL;
        return (next);
}

/*
 * Returns the given page's predecessor (by pindex) within the object if it is
 * resident; if none is found, NULL is returned.
 *
 * The object must be locked.
 */
vm_page_t
vm_page_prev(vm_page_t m)
{
        vm_page_t prev;

        VM_OBJECT_ASSERT_WLOCKED(m->object);
        if ((prev = TAILQ_PREV(m, pglist, listq)) != NULL &&
            prev->pindex != m->pindex - 1)
                prev = NULL;
        return (prev);
}

/*
 *      vm_page_rename:
 *
 *      Move the given memory entry from its
 *      current object to the specified target object/offset.
 *
 *      Note: swap associated with the page must be invalidated by the move.  We
 *            have to do this for several reasons:  (1) we aren't freeing the
 *            page, (2) we are dirtying the page, (3) the VM system is probably
 *            moving the page from object A to B, and will then later move
 *            the backing store from A to B and we can't have a conflict.
 *
 *      Note: we *always* dirty the page.  It is necessary both for the
 *            fact that we moved it, and because we may be invalidating
 *            swap.  If the page is on the cache, we have to deactivate it
 *            or vm_page_dirty() will panic.  Dirty pages are not allowed
 *            on the cache.
 *
 *      The objects must be locked.  The page must be locked if it is managed.
 */
void
vm_page_rename(vm_page_t m, vm_object_t new_object, vm_pindex_t new_pindex)
{

        vm_page_remove(m);
        vm_page_insert(m, new_object, new_pindex);
        vm_page_dirty(m);
}

/*
 *      Convert all of the given object's cached pages that have a
 *      pindex within the given range into free pages.  If the value
 *      zero is given for "end", then the range's upper bound is
 *      infinity.  If the given object is backed by a vnode and it
 *      transitions from having one or more cached pages to none, the
 *      vnode's hold count is reduced. 
 */
void
vm_page_cache_free(vm_object_t object, vm_pindex_t start, vm_pindex_t end)
{
        vm_page_t m;
        boolean_t empty;

        mtx_lock(&vm_page_queue_free_mtx);
        if (__predict_false(vm_radix_is_empty(&object->cache))) {
                mtx_unlock(&vm_page_queue_free_mtx);
                return;
        }
        while ((m = vm_radix_lookup_ge(&object->cache, start)) != NULL) {
                if (end != 0 && m->pindex >= end)
                        break;
                vm_radix_remove(&object->cache, m->pindex);
                m->object = NULL;
                m->valid = 0;
                /* Clear PG_CACHED and set PG_FREE. */
                m->flags ^= PG_CACHED | PG_FREE;
                KASSERT((m->flags & (PG_CACHED | PG_FREE)) == PG_FREE,
                    ("vm_page_cache_free: page %p has inconsistent flags", m));
                cnt.v_cache_count--;
                cnt.v_free_count++;
        }
        empty = vm_radix_is_empty(&object->cache);
        mtx_unlock(&vm_page_queue_free_mtx);
        if (object->type == OBJT_VNODE && empty)
                vdrop(object->handle);
}

/*
 *      Returns the cached page that is associated with the given
 *      object and offset.  If, however, none exists, returns NULL.
 *
 *      The free page queue must be locked.
 */
static inline vm_page_t
vm_page_cache_lookup(vm_object_t object, vm_pindex_t pindex)
{

        mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
        return (vm_radix_lookup(&object->cache, pindex));
}

/*
 *      Remove the given cached page from its containing object's
 *      collection of cached pages.
 *
 *      The free page queue must be locked.
 */
static void
vm_page_cache_remove(vm_page_t m)
{

        mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
        KASSERT((m->flags & PG_CACHED) != 0,
            ("vm_page_cache_remove: page %p is not cached", m));
        vm_radix_remove(&m->object->cache, m->pindex);
        m->object = NULL;
        cnt.v_cache_count--;
}

/*
 *      Transfer all of the cached pages with offset greater than or
 *      equal to 'offidxstart' from the original object's cache to the
 *      new object's cache.  However, any cached pages with offset
 *      greater than or equal to the new object's size are kept in the
 *      original object.  Initially, the new object's cache must be
 *      empty.  Offset 'offidxstart' in the original object must
 *      correspond to offset zero in the new object.
 *
 *      The new object must be locked.
 */
void
vm_page_cache_transfer(vm_object_t orig_object, vm_pindex_t offidxstart,
    vm_object_t new_object)
{
        vm_page_t m;

        /*
         * Insertion into an object's collection of cached pages
         * requires the object to be locked.  In contrast, removal does
         * not.
         */
        VM_OBJECT_ASSERT_WLOCKED(new_object);
        KASSERT(vm_radix_is_empty(&new_object->cache),
            ("vm_page_cache_transfer: object %p has cached pages",
            new_object));
        mtx_lock(&vm_page_queue_free_mtx);
        while ((m = vm_radix_lookup_ge(&orig_object->cache,
            offidxstart)) != NULL) {
                /*
                 * Transfer all of the pages with offset greater than or
                 * equal to 'offidxstart' from the original object's
                 * cache to the new object's cache.
                 */
                if ((m->pindex - offidxstart) >= new_object->size)
                        break;
                vm_radix_remove(&orig_object->cache, m->pindex);
                /* Update the page's object and offset. */
                m->object = new_object;
                m->pindex -= offidxstart;
                vm_radix_insert(&new_object->cache, m);
        }
        mtx_unlock(&vm_page_queue_free_mtx);
}

/*
 *      Returns TRUE if a cached page is associated with the given object and
 *      offset, and FALSE otherwise.
 *
 *      The object must be locked.
 */
boolean_t
vm_page_is_cached(vm_object_t object, vm_pindex_t pindex)
{
        vm_page_t m;

        /*
         * Insertion into an object's collection of cached pages requires the
         * object to be locked.  Therefore, if the object is locked and the
         * object's collection is empty, there is no need to acquire the free
         * page queues lock in order to prove that the specified page doesn't
         * exist.
         */
        VM_OBJECT_ASSERT_WLOCKED(object);
        if (__predict_true(vm_object_cache_is_empty(object)))
                return (FALSE);
        mtx_lock(&vm_page_queue_free_mtx);
        m = vm_page_cache_lookup(object, pindex);
        mtx_unlock(&vm_page_queue_free_mtx);
        return (m != NULL);
}

/*
 *      vm_page_alloc:
 *
 *      Allocate and return a page that is associated with the specified
 *      object and offset pair.  By default, this page has the flag VPO_BUSY
 *      set.
 *
 *      The caller must always specify an allocation class.
 *
 *      allocation classes:
 *      VM_ALLOC_NORMAL         normal process request
 *      VM_ALLOC_SYSTEM         system *really* needs a page
 *      VM_ALLOC_INTERRUPT      interrupt time request
 *
 *      optional allocation flags:
 *      VM_ALLOC_COUNT(number)  the number of additional pages that the caller
 *                              intends to allocate
 *      VM_ALLOC_IFCACHED       return page only if it is cached
 *      VM_ALLOC_IFNOTCACHED    return NULL, do not reactivate if the page
 *                              is cached
 *      VM_ALLOC_NOBUSY         do not set the flag VPO_BUSY on the page
 *      VM_ALLOC_NODUMP         do not include the page in a kernel core dump
 *      VM_ALLOC_NOOBJ          page is not associated with an object and
 *                              should not have the flag VPO_BUSY set
 *      VM_ALLOC_WIRED          wire the allocated page
 *      VM_ALLOC_ZERO           prefer a zeroed page
 *
 *      This routine may not sleep.
 */
vm_page_t
vm_page_alloc(vm_object_t object, vm_pindex_t pindex, int req)
{
        struct vnode *vp = NULL;
        vm_object_t m_object;
        vm_page_t m, mpred;
        int flags, req_class;

        mpred = 0;      /* XXX: pacify gcc */
        KASSERT((object != NULL) == ((req & VM_ALLOC_NOOBJ) == 0),
            ("vm_page_alloc: inconsistent object/req"));
        if (object != NULL)
                VM_OBJECT_ASSERT_WLOCKED(object);

        req_class = req & VM_ALLOC_CLASS_MASK;

        /*
         * The page daemon is allowed to dig deeper into the free page list.
         */
        if (curproc == pageproc && req_class != VM_ALLOC_INTERRUPT)
                req_class = VM_ALLOC_SYSTEM;

        if (object != NULL) {
                mpred = vm_radix_lookup_le(&object->rtree, pindex);
                KASSERT(mpred == NULL || mpred->pindex != pindex,
                   ("vm_page_alloc: pindex already allocated"));
        }
        mtx_lock(&vm_page_queue_free_mtx);
        if (cnt.v_free_count + cnt.v_cache_count > cnt.v_free_reserved ||
            (req_class == VM_ALLOC_SYSTEM &&
            cnt.v_free_count + cnt.v_cache_count > cnt.v_interrupt_free_min) ||
            (req_class == VM_ALLOC_INTERRUPT &&
            cnt.v_free_count + cnt.v_cache_count > 0)) {
                /*
                 * Allocate from the free queue if the number of free pages
                 * exceeds the minimum for the request class.
                 */
                if (object != NULL &&
                    (m = vm_page_cache_lookup(object, pindex)) != NULL) {
                        if ((req & VM_ALLOC_IFNOTCACHED) != 0) {
                                mtx_unlock(&vm_page_queue_free_mtx);
                                return (NULL);
                        }
                        if (vm_phys_unfree_page(m))
                                vm_phys_set_pool(VM_FREEPOOL_DEFAULT, m, 0);
#if VM_NRESERVLEVEL > 0
                        else if (!vm_reserv_reactivate_page(m))
#else
                        else
#endif
                                panic("vm_page_alloc: cache page %p is missing"
                                    " from the free queue", m);
                } else if ((req & VM_ALLOC_IFCACHED) != 0) {
                        mtx_unlock(&vm_page_queue_free_mtx);
                        return (NULL);
#if VM_NRESERVLEVEL > 0
                } else if (object == NULL || (object->flags & (OBJ_COLORED |
                    OBJ_FICTITIOUS)) != OBJ_COLORED || (m =
                    vm_reserv_alloc_page(object, pindex, mpred)) == NULL) {
#else
                } else {
#endif
                        m = vm_phys_alloc_pages(object != NULL ?
                            VM_FREEPOOL_DEFAULT : VM_FREEPOOL_DIRECT, 0);
#if VM_NRESERVLEVEL > 0
                        if (m == NULL && vm_reserv_reclaim_inactive()) {
                                m = vm_phys_alloc_pages(object != NULL ?
                                    VM_FREEPOOL_DEFAULT : VM_FREEPOOL_DIRECT,
                                    0);
                        }
#endif
                }
        } else {
                /*
                 * Not allocatable, give up.
                 */
                mtx_unlock(&vm_page_queue_free_mtx);
                atomic_add_int(&vm_pageout_deficit,
                    max((u_int)req >> VM_ALLOC_COUNT_SHIFT, 1));
                pagedaemon_wakeup();
                return (NULL);
        }

        /*
         *  At this point we had better have found a good page.
         */
        KASSERT(m != NULL, ("vm_page_alloc: missing page"));
        KASSERT(m->queue == PQ_NONE,
            ("vm_page_alloc: page %p has unexpected queue %d", m, m->queue));
        KASSERT(m->wire_count == 0, ("vm_page_alloc: page %p is wired", m));
        KASSERT(m->hold_count == 0, ("vm_page_alloc: page %p is held", m));
        KASSERT(m->busy == 0, ("vm_page_alloc: page %p is busy", m));
        KASSERT(m->dirty == 0, ("vm_page_alloc: page %p is dirty", m));
        KASSERT(pmap_page_get_memattr(m) == VM_MEMATTR_DEFAULT,
            ("vm_page_alloc: page %p has unexpected memattr %d", m,
            pmap_page_get_memattr(m)));
        if ((m->flags & PG_CACHED) != 0) {
                KASSERT((m->flags & PG_ZERO) == 0,
                    ("vm_page_alloc: cached page %p is PG_ZERO", m));
                KASSERT(m->valid != 0,
                    ("vm_page_alloc: cached page %p is invalid", m));
                if (m->object == object && m->pindex == pindex)
                        cnt.v_reactivated++;
                else
                        m->valid = 0;
                m_object = m->object;
                vm_page_cache_remove(m);
                if (m_object->type == OBJT_VNODE &&
                    vm_object_cache_is_empty(m_object))
                        vp = m_object->handle;
        } else {
                KASSERT(VM_PAGE_IS_FREE(m),
                    ("vm_page_alloc: page %p is not free", m));
                KASSERT(m->valid == 0,
                    ("vm_page_alloc: free page %p is valid", m));
                cnt.v_free_count--;
        }

        /*
         * Only the PG_ZERO flag is inherited.  The PG_CACHED or PG_FREE flag
         * must be cleared before the free page queues lock is released.
         */
        flags = 0;
        if (m->flags & PG_ZERO) {
                vm_page_zero_count--;
                if (req & VM_ALLOC_ZERO)
                        flags = PG_ZERO;
        }
        if (req & VM_ALLOC_NODUMP)
                flags |= PG_NODUMP;
        m->flags = flags;
        mtx_unlock(&vm_page_queue_free_mtx);
        m->aflags = 0;
        m->oflags = object == NULL || (object->flags & OBJ_UNMANAGED) != 0 ?
            VPO_UNMANAGED : 0;
        if ((req & (VM_ALLOC_NOBUSY | VM_ALLOC_NOOBJ)) == 0)
                m->oflags |= VPO_BUSY;
        if (req & VM_ALLOC_WIRED) {
                /*
                 * The page lock is not required for wiring a page until that
                 * page is inserted into the object.
                 */
                atomic_add_int(&cnt.v_wire_count, 1);
                m->wire_count = 1;
        }
        m->act_count = 0;

        if (object != NULL) {
                /* Ignore device objects; the pager sets "memattr" for them. */
                if (object->memattr != VM_MEMATTR_DEFAULT &&
                    (object->flags & OBJ_FICTITIOUS) == 0)
                        pmap_page_set_memattr(m, object->memattr);
                vm_page_insert_after(m, object, pindex, mpred);
        } else
                m->pindex = pindex;

        /*
         * The following call to vdrop() must come after the above call
         * to vm_page_insert() in case both affect the same object and
         * vnode.  Otherwise, the affected vnode's hold count could
         * temporarily become zero.
         */
        if (vp != NULL)
                vdrop(vp);

        /*
         * Don't wakeup too often - wakeup the pageout daemon when
         * we would be nearly out of memory.
         */
        if (vm_paging_needed())
                pagedaemon_wakeup();

        return (m);
}

/*
 *      vm_page_alloc_contig:
 *
 *      Allocate a contiguous set of physical pages of the given size "npages"
 *      from the free lists.  All of the physical pages must be at or above
 *      the given physical address "low" and below the given physical address
 *      "high".  The given value "alignment" determines the alignment of the
 *      first physical page in the set.  If the given value "boundary" is
 *      non-zero, then the set of physical pages cannot cross any physical
 *      address boundary that is a multiple of that value.  Both "alignment"
 *      and "boundary" must be a power of two.
 *
 *      If the specified memory attribute, "memattr", is VM_MEMATTR_DEFAULT,
 *      then the memory attribute setting for the physical pages is configured
 *      to the object's memory attribute setting.  Otherwise, the memory
 *      attribute setting for the physical pages is configured to "memattr",
 *      overriding the object's memory attribute setting.  However, if the
 *      object's memory attribute setting is not VM_MEMATTR_DEFAULT, then the
 *      memory attribute setting for the physical pages cannot be configured
 *      to VM_MEMATTR_DEFAULT.
 *
 *      The caller must always specify an allocation class.
 *
 *      allocation classes:
 *      VM_ALLOC_NORMAL         normal process request
 *      VM_ALLOC_SYSTEM         system *really* needs a page
 *      VM_ALLOC_INTERRUPT      interrupt time request
 *
 *      optional allocation flags:
 *      VM_ALLOC_NOBUSY         do not set the flag VPO_BUSY on the page
 *      VM_ALLOC_NOOBJ          page is not associated with an object and
 *                              should not have the flag VPO_BUSY set
 *      VM_ALLOC_WIRED          wire the allocated page
 *      VM_ALLOC_ZERO           prefer a zeroed page
 *
 *      This routine may not sleep.
 */
vm_page_t
vm_page_alloc_contig(vm_object_t object, vm_pindex_t pindex, int req,
    u_long npages, vm_paddr_t low, vm_paddr_t high, u_long alignment,
    vm_paddr_t boundary, vm_memattr_t memattr)
{
        struct vnode *drop;
        vm_page_t deferred_vdrop_list, m, m_ret;
        u_int flags, oflags;
        int req_class;

        KASSERT((object != NULL) == ((req & VM_ALLOC_NOOBJ) == 0),
            ("vm_page_alloc_contig: inconsistent object/req"));
        if (object != NULL) {
                VM_OBJECT_ASSERT_WLOCKED(object);
                KASSERT(object->type == OBJT_PHYS,
                    ("vm_page_alloc_contig: object %p isn't OBJT_PHYS",
                    object));
        }
        KASSERT(npages > 0, ("vm_page_alloc_contig: npages is zero"));
        req_class = req & VM_ALLOC_CLASS_MASK;

        /*
         * The page daemon is allowed to dig deeper into the free page list.
         */
        if (curproc == pageproc && req_class != VM_ALLOC_INTERRUPT)
                req_class = VM_ALLOC_SYSTEM;

        deferred_vdrop_list = NULL;
        mtx_lock(&vm_page_queue_free_mtx);
        if (cnt.v_free_count + cnt.v_cache_count >= npages +
            cnt.v_free_reserved || (req_class == VM_ALLOC_SYSTEM &&
            cnt.v_free_count + cnt.v_cache_count >= npages +
            cnt.v_interrupt_free_min) || (req_class == VM_ALLOC_INTERRUPT &&
            cnt.v_free_count + cnt.v_cache_count >= npages)) {
#if VM_NRESERVLEVEL > 0
retry:
                if (object == NULL || (object->flags & OBJ_COLORED) == 0 ||
                    (m_ret = vm_reserv_alloc_contig(object, pindex, npages,
                    low, high, alignment, boundary)) == NULL)
#endif
                        m_ret = vm_phys_alloc_contig(npages, low, high,
                            alignment, boundary);
        } else {
                mtx_unlock(&vm_page_queue_free_mtx);
                atomic_add_int(&vm_pageout_deficit, npages);
                pagedaemon_wakeup();
                return (NULL);
        }
        if (m_ret != NULL)
                for (m = m_ret; m < &m_ret[npages]; m++) {
                        drop = vm_page_alloc_init(m);
                        if (drop != NULL) {
                                /*
                                 * Enqueue the vnode for deferred vdrop().
                                 *
                                 * Once the pages are removed from the free
                                 * page list, "pageq" can be safely abused to
                                 * construct a short-lived list of vnodes.
                                 */
                                m->pageq.tqe_prev = (void *)drop;
                                m->pageq.tqe_next = deferred_vdrop_list;
                                deferred_vdrop_list = m;
                        }
                }
        else {
#if VM_NRESERVLEVEL > 0
                if (vm_reserv_reclaim_contig(npages, low, high, alignment,
                    boundary))
                        goto retry;
#endif
        }
        mtx_unlock(&vm_page_queue_free_mtx);
        if (m_ret == NULL)
                return (NULL);

        /*
         * Initialize the pages.  Only the PG_ZERO flag is inherited.
         */
        flags = 0;
        if ((req & VM_ALLOC_ZERO) != 0)
                flags = PG_ZERO;
        if ((req & VM_ALLOC_NODUMP) != 0)
                flags |= PG_NODUMP;
        if ((req & VM_ALLOC_WIRED) != 0)
                atomic_add_int(&cnt.v_wire_count, npages);
        oflags = VPO_UNMANAGED;
        if (object != NULL) {
                if ((req & VM_ALLOC_NOBUSY) == 0)
                        oflags |= VPO_BUSY;
                if (object->memattr != VM_MEMATTR_DEFAULT &&
                    memattr == VM_MEMATTR_DEFAULT)
                        memattr = object->memattr;
        }
        for (m = m_ret; m < &m_ret[npages]; m++) {
                m->aflags = 0;
                m->flags = (m->flags | PG_NODUMP) & flags;
                if ((req & VM_ALLOC_WIRED) != 0)
                        m->wire_count = 1;
                /* Unmanaged pages don't use "act_count". */
                m->oflags = oflags;
                if (memattr != VM_MEMATTR_DEFAULT)
                        pmap_page_set_memattr(m, memattr);
                if (object != NULL)
                        vm_page_insert(m, object, pindex);
                else
                        m->pindex = pindex;
                pindex++;
        }
        while (deferred_vdrop_list != NULL) {
                vdrop((struct vnode *)deferred_vdrop_list->pageq.tqe_prev);
                deferred_vdrop_list = deferred_vdrop_list->pageq.tqe_next;
        }
        if (vm_paging_needed())
                pagedaemon_wakeup();
        return (m_ret);
}

/*
 * Initialize a page that has been freshly dequeued from a freelist.
 * The caller has to drop the vnode returned, if it is not NULL.
 *
 * This function may only be used to initialize unmanaged pages.
 *
 * To be called with vm_page_queue_free_mtx held.
 */
static struct vnode *
vm_page_alloc_init(vm_page_t m)
{
        struct vnode *drop;
        vm_object_t m_object;

        KASSERT(m->queue == PQ_NONE,
            ("vm_page_alloc_init: page %p has unexpected queue %d",
            m, m->queue));
        KASSERT(m->wire_count == 0,
            ("vm_page_alloc_init: page %p is wired", m));
        KASSERT(m->hold_count == 0,
            ("vm_page_alloc_init: page %p is held", m));
        KASSERT(m->busy == 0,
            ("vm_page_alloc_init: page %p is busy", m));
        KASSERT(m->dirty == 0,
            ("vm_page_alloc_init: page %p is dirty", m));
        KASSERT(pmap_page_get_memattr(m) == VM_MEMATTR_DEFAULT,
            ("vm_page_alloc_init: page %p has unexpected memattr %d",
            m, pmap_page_get_memattr(m)));
        mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
        drop = NULL;
        if ((m->flags & PG_CACHED) != 0) {
                KASSERT((m->flags & PG_ZERO) == 0,
                    ("vm_page_alloc_init: cached page %p is PG_ZERO", m));
                m->valid = 0;
                m_object = m->object;
                vm_page_cache_remove(m);
                if (m_object->type == OBJT_VNODE &&
                    vm_object_cache_is_empty(m_object))
                        drop = m_object->handle;
        } else {
                KASSERT(VM_PAGE_IS_FREE(m),
                    ("vm_page_alloc_init: page %p is not free", m));
                KASSERT(m->valid == 0,
                    ("vm_page_alloc_init: free page %p is valid", m));
                cnt.v_free_count--;
                if ((m->flags & PG_ZERO) != 0)
                        vm_page_zero_count--;
        }
        /* Don't clear the PG_ZERO flag; we'll need it later. */
        m->flags &= PG_ZERO;
        return (drop);
}

/*
 *      vm_page_alloc_freelist:
 *
 *      Allocate a physical page from the specified free page list.
 *
 *      The caller must always specify an allocation class.
 *
 *      allocation classes:
 *      VM_ALLOC_NORMAL         normal process request
 *      VM_ALLOC_SYSTEM         system *really* needs a page
 *      VM_ALLOC_INTERRUPT      interrupt time request
 *
 *      optional allocation flags:
 *      VM_ALLOC_COUNT(number)  the number of additional pages that the caller
 *                              intends to allocate
 *      VM_ALLOC_WIRED          wire the allocated page
 *      VM_ALLOC_ZERO           prefer a zeroed page
 *
 *      This routine may not sleep.
 */
vm_page_t
vm_page_alloc_freelist(int flind, int req)
{
        struct vnode *drop;
        vm_page_t m;
        u_int flags;
        int req_class;

        req_class = req & VM_ALLOC_CLASS_MASK;

        /*
         * The page daemon is allowed to dig deeper into the free page list.
         */
        if (curproc == pageproc && req_class != VM_ALLOC_INTERRUPT)
                req_class = VM_ALLOC_SYSTEM;

        /*
         * Do not allocate reserved pages unless the req has asked for it.
         */
        mtx_lock(&vm_page_queue_free_mtx);
        if (cnt.v_free_count + cnt.v_cache_count > cnt.v_free_reserved ||
            (req_class == VM_ALLOC_SYSTEM &&
            cnt.v_free_count + cnt.v_cache_count > cnt.v_interrupt_free_min) ||
            (req_class == VM_ALLOC_INTERRUPT &&
            cnt.v_free_count + cnt.v_cache_count > 0))
                m = vm_phys_alloc_freelist_pages(flind, VM_FREEPOOL_DIRECT, 0);
        else {
                mtx_unlock(&vm_page_queue_free_mtx);
                atomic_add_int(&vm_pageout_deficit,
                    max((u_int)req >> VM_ALLOC_COUNT_SHIFT, 1));
                pagedaemon_wakeup();
                return (NULL);
        }
        if (m == NULL) {
                mtx_unlock(&vm_page_queue_free_mtx);
                return (NULL);
        }
        drop = vm_page_alloc_init(m);
        mtx_unlock(&vm_page_queue_free_mtx);

        /*
         * Initialize the page.  Only the PG_ZERO flag is inherited.
         */
        m->aflags = 0;
        flags = 0;
        if ((req & VM_ALLOC_ZERO) != 0)
                flags = PG_ZERO;
        m->flags &= flags;
        if ((req & VM_ALLOC_WIRED) != 0) {
                /*
                 * The page lock is not required for wiring a page that does
                 * not belong to an object.
                 */
                atomic_add_int(&cnt.v_wire_count, 1);
                m->wire_count = 1;
        }
        /* Unmanaged pages don't use "act_count". */
        m->oflags = VPO_UNMANAGED;
        if (drop != NULL)
                vdrop(drop);
        if (vm_paging_needed())
                pagedaemon_wakeup();
        return (m);
}

/*
 *      vm_wait:        (also see VM_WAIT macro)
 *
 *      Sleep until free pages are available for allocation.
 *      - Called in various places before memory allocations.
 */
void
vm_wait(void)
{

        mtx_lock(&vm_page_queue_free_mtx);
        if (curproc == pageproc) {
                vm_pageout_pages_needed = 1;
                msleep(&vm_pageout_pages_needed, &vm_page_queue_free_mtx,
                    PDROP | PSWP, "VMWait", 0);
        } else {
                if (!vm_pages_needed) {
                        vm_pages_needed = 1;
                        wakeup(&vm_pages_needed);
                }
                msleep(&cnt.v_free_count, &vm_page_queue_free_mtx, PDROP | PVM,
                    "vmwait", 0);
        }
}

/*
 *      vm_waitpfault:  (also see VM_WAITPFAULT macro)
 *
 *      Sleep until free pages are available for allocation.
 *      - Called only in vm_fault so that processes page faulting
 *        can be easily tracked.
 *      - Sleeps at a lower priority than vm_wait() so that vm_wait()ing
 *        processes will be able to grab memory first.  Do not change
 *        this balance without careful testing first.
 */
void
vm_waitpfault(void)
{

        mtx_lock(&vm_page_queue_free_mtx);
        if (!vm_pages_needed) {
                vm_pages_needed = 1;
                wakeup(&vm_pages_needed);
        }
        msleep(&cnt.v_free_count, &vm_page_queue_free_mtx, PDROP | PUSER,
            "pfault", 0);
}

/*
 *      vm_page_dequeue:
 *
 *      Remove the given page from its current page queue.
 *
 *      The page must be locked.
 */
void
vm_page_dequeue(vm_page_t m)
{
        struct vm_pagequeue *pq;

        vm_page_lock_assert(m, MA_OWNED);
        KASSERT(m->queue != PQ_NONE,
            ("vm_page_dequeue: page %p is not queued", m));
        pq = &vm_pagequeues[m->queue];
        vm_pagequeue_lock(pq);
        m->queue = PQ_NONE;
        TAILQ_REMOVE(&pq->pq_pl, m, pageq);
        (*pq->pq_cnt)--;
        vm_pagequeue_unlock(pq);
}

/*
 *      vm_page_dequeue_locked:
 *
 *      Remove the given page from its current page queue.
 *
 *      The page and page queue must be locked.
 */
void
vm_page_dequeue_locked(vm_page_t m)
{
        struct vm_pagequeue *pq;

        vm_page_lock_assert(m, MA_OWNED);
        pq = &vm_pagequeues[m->queue];
        vm_pagequeue_assert_locked(pq);
        m->queue = PQ_NONE;
        TAILQ_REMOVE(&pq->pq_pl, m, pageq);
        (*pq->pq_cnt)--;
}

/*
 *      vm_page_enqueue:
 *
 *      Add the given page to the specified page queue.
 *
 *      The page must be locked.
 */
static void
vm_page_enqueue(int queue, vm_page_t m)
{
        struct vm_pagequeue *pq;

        vm_page_lock_assert(m, MA_OWNED);
        pq = &vm_pagequeues[queue];
        vm_pagequeue_lock(pq);
        m->queue = queue;
        TAILQ_INSERT_TAIL(&pq->pq_pl, m, pageq);
        ++*pq->pq_cnt;
        vm_pagequeue_unlock(pq);
}

/*
 *      vm_page_requeue:
 *
 *      Move the given page to the tail of its current page queue.
 *
 *      The page must be locked.
 */
void
vm_page_requeue(vm_page_t m)
{
        struct vm_pagequeue *pq;

        vm_page_lock_assert(m, MA_OWNED);
        KASSERT(m->queue != PQ_NONE,
            ("vm_page_requeue: page %p is not queued", m));
        pq = &vm_pagequeues[m->queue];
        vm_pagequeue_lock(pq);
        TAILQ_REMOVE(&pq->pq_pl, m, pageq);
        TAILQ_INSERT_TAIL(&pq->pq_pl, m, pageq);
        vm_pagequeue_unlock(pq);
}

/*
 *      vm_page_requeue_locked:
 *
 *      Move the given page to the tail of its current page queue.
 *
 *      The page queue must be locked.
 */
void
vm_page_requeue_locked(vm_page_t m)
{
        struct vm_pagequeue *pq;

        KASSERT(m->queue != PQ_NONE,
            ("vm_page_requeue_locked: page %p is not queued", m));
        pq = &vm_pagequeues[m->queue];
        vm_pagequeue_assert_locked(pq);
        TAILQ_REMOVE(&pq->pq_pl, m, pageq);
        TAILQ_INSERT_TAIL(&pq->pq_pl, m, pageq);
}

/*
 *      vm_page_activate:
 *
 *      Put the specified page on the active list (if appropriate).
 *      Ensure that act_count is at least ACT_INIT but do not otherwise
 *      mess with it.
 *
 *      The page must be locked.
 */
void
vm_page_activate(vm_page_t m)
{
        int queue;

        vm_page_lock_assert(m, MA_OWNED);
        if ((queue = m->queue) != PQ_ACTIVE) {
                if (m->wire_count == 0 && (m->oflags & VPO_UNMANAGED) == 0) {
                        if (m->act_count < ACT_INIT)
                                m->act_count = ACT_INIT;
                        if (queue != PQ_NONE)
                                vm_page_dequeue(m);
                        vm_page_enqueue(PQ_ACTIVE, m);
                } else
                        KASSERT(queue == PQ_NONE,
                            ("vm_page_activate: wired page %p is queued", m));
        } else {
                if (m->act_count < ACT_INIT)
                        m->act_count = ACT_INIT;
        }
}

/*
 *      vm_page_free_wakeup:
 *
 *      Helper routine for vm_page_free_toq() and vm_page_cache().  This
 *      routine is called when a page has been added to the cache or free
 *      queues.
 *
 *      The page queues must be locked.
 */
static inline void
vm_page_free_wakeup(void)
{

        mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
        /*
         * if pageout daemon needs pages, then tell it that there are
         * some free.
         */
        if (vm_pageout_pages_needed &&
            cnt.v_cache_count + cnt.v_free_count >= cnt.v_pageout_free_min) {
                wakeup(&vm_pageout_pages_needed);
                vm_pageout_pages_needed = 0;
        }
        /*
         * wakeup processes that are waiting on memory if we hit a
         * high water mark. And wakeup scheduler process if we have
         * lots of memory. this process will swapin processes.
         */
        if (vm_pages_needed && !vm_page_count_min()) {
                vm_pages_needed = 0;
                wakeup(&cnt.v_free_count);
        }
}

/*
 *      vm_page_free_toq:
 *
 *      Returns the given page to the free list,
 *      disassociating it with any VM object.
 *
 *      The object must be locked.  The page must be locked if it is managed.
 */
void
vm_page_free_toq(vm_page_t m)
{

        if ((m->oflags & VPO_UNMANAGED) == 0) {
                vm_page_lock_assert(m, MA_OWNED);
                KASSERT(!pmap_page_is_mapped(m),
                    ("vm_page_free_toq: freeing mapped page %p", m));
        } else
                KASSERT(m->queue == PQ_NONE,
                    ("vm_page_free_toq: unmanaged page %p is queued", m));
        PCPU_INC(cnt.v_tfree);

        if (VM_PAGE_IS_FREE(m))
                panic("vm_page_free: freeing free page %p", m);
        else if (m->busy != 0)
                panic("vm_page_free: freeing busy page %p", m);

        /*
         * Unqueue, then remove page.  Note that we cannot destroy
         * the page here because we do not want to call the pager's
         * callback routine until after we've put the page on the
         * appropriate free queue.
         */
        vm_page_remque(m);
        vm_page_remove(m);

        /*
         * If fictitious remove object association and
         * return, otherwise delay object association removal.
         */
        if ((m->flags & PG_FICTITIOUS) != 0) {
                return;
        }

        m->valid = 0;
        vm_page_undirty(m);

        if (m->wire_count != 0)
                panic("vm_page_free: freeing wired page %p", m);
        if (m->hold_count != 0) {
                m->flags &= ~PG_ZERO;
                KASSERT((m->flags & PG_UNHOLDFREE) == 0,
                    ("vm_page_free: freeing PG_UNHOLDFREE page %p", m));
                m->flags |= PG_UNHOLDFREE;
        } else {
                /*
                 * Restore the default memory attribute to the page.
                 */
                if (pmap_page_get_memattr(m) != VM_MEMATTR_DEFAULT)
                        pmap_page_set_memattr(m, VM_MEMATTR_DEFAULT);

                /*
                 * Insert the page into the physical memory allocator's
                 * cache/free page queues.
                 */
                mtx_lock(&vm_page_queue_free_mtx);
                m->flags |= PG_FREE;
                cnt.v_free_count++;
#if VM_NRESERVLEVEL > 0
                if (!vm_reserv_free_page(m))
#else
                if (TRUE)
#endif
                        vm_phys_free_pages(m, 0);
                if ((m->flags & PG_ZERO) != 0)
                        ++vm_page_zero_count;
                else
                        vm_page_zero_idle_wakeup();
                vm_page_free_wakeup();
                mtx_unlock(&vm_page_queue_free_mtx);
        }
}

/*
 *      vm_page_wire:
 *
 *      Mark this page as wired down by yet
 *      another map, removing it from paging queues
 *      as necessary.
 *
 *      If the page is fictitious, then its wire count must remain one.
 *
 *      The page must be locked.
 */
void
vm_page_wire(vm_page_t m)
{

        /*
         * Only bump the wire statistics if the page is not already wired,
         * and only unqueue the page if it is on some queue (if it is unmanaged
         * it is already off the queues).
         */
        vm_page_lock_assert(m, MA_OWNED);
        if ((m->flags & PG_FICTITIOUS) != 0) {
                KASSERT(m->wire_count == 1,
                    ("vm_page_wire: fictitious page %p's wire count isn't one",
                    m));
                return;
        }
        if (m->wire_count == 0) {
                KASSERT((m->oflags & VPO_UNMANAGED) == 0 ||
                    m->queue == PQ_NONE,
                    ("vm_page_wire: unmanaged page %p is queued", m));
                vm_page_remque(m);
                atomic_add_int(&cnt.v_wire_count, 1);
        }
        m->wire_count++;
        KASSERT(m->wire_count != 0, ("vm_page_wire: wire_count overflow m=%p", m));
}

/*
 * vm_page_unwire:
 *
 * Release one wiring of the specified page, potentially enabling it to be
 * paged again.  If paging is enabled, then the value of the parameter
 * "activate" determines to which queue the page is added.  If "activate" is
 * non-zero, then the page is added to the active queue.  Otherwise, it is
 * added to the inactive queue.
 *
 * However, unless the page belongs to an object, it is not enqueued because
 * it cannot be paged out.
 *
 * If a page is fictitious, then its wire count must alway be one.
 *
 * A managed page must be locked.
 */
void
vm_page_unwire(vm_page_t m, int activate)
{

        if ((m->oflags & VPO_UNMANAGED) == 0)
                vm_page_lock_assert(m, MA_OWNED);
        if ((m->flags & PG_FICTITIOUS) != 0) {
                KASSERT(m->wire_count == 1,
            ("vm_page_unwire: fictitious page %p's wire count isn't one", m));
                return;
        }
        if (m->wire_count > 0) {
                m->wire_count--;
                if (m->wire_count == 0) {
                        atomic_subtract_int(&cnt.v_wire_count, 1);
                        if ((m->oflags & VPO_UNMANAGED) != 0 ||
                            m->object == NULL)
                                return;
                        if (!activate)
                                m->flags &= ~PG_WINATCFLS;
                        vm_page_enqueue(activate ? PQ_ACTIVE : PQ_INACTIVE, m);
                }
        } else
                panic("vm_page_unwire: page %p's wire count is zero", m);
}

/*
 * Move the specified page to the inactive queue.
 *
 * Many pages placed on the inactive queue should actually go
 * into the cache, but it is difficult to figure out which.  What
 * we do instead, if the inactive target is well met, is to put
 * clean pages at the head of the inactive queue instead of the tail.
 * This will cause them to be moved to the cache more quickly and
 * if not actively re-referenced, reclaimed more quickly.  If we just
 * stick these pages at the end of the inactive queue, heavy filesystem
 * meta-data accesses can cause an unnecessary paging load on memory bound 
 * processes.  This optimization causes one-time-use metadata to be
 * reused more quickly.
 *
 * Normally athead is 0 resulting in LRU operation.  athead is set
 * to 1 if we want this page to be 'as if it were placed in the cache',
 * except without unmapping it from the process address space.
 *
 * The page must be locked.
 */
static inline void
_vm_page_deactivate(vm_page_t m, int athead)
{
        struct vm_pagequeue *pq;
        int queue;

        vm_page_lock_assert(m, MA_OWNED);

        /*
         * Ignore if already inactive.
         */
        if ((queue = m->queue) == PQ_INACTIVE)
                return;
        if (m->wire_count == 0 && (m->oflags & VPO_UNMANAGED) == 0) {
                if (queue != PQ_NONE)
                        vm_page_dequeue(m);
                m->flags &= ~PG_WINATCFLS;
                pq = &vm_pagequeues[PQ_INACTIVE];
                vm_pagequeue_lock(pq);
                m->queue = PQ_INACTIVE;
                if (athead)
                        TAILQ_INSERT_HEAD(&pq->pq_pl, m, pageq);
                else
                        TAILQ_INSERT_TAIL(&pq->pq_pl, m, pageq);
                cnt.v_inactive_count++;
                vm_pagequeue_unlock(pq);
        }
}

/*
 * Move the specified page to the inactive queue.
 *
 * The page must be locked.
 */
void
vm_page_deactivate(vm_page_t m)
{

        _vm_page_deactivate(m, 0);
}

/*
 * vm_page_try_to_cache:
 *
 * Returns 0 on failure, 1 on success
 */
int
vm_page_try_to_cache(vm_page_t m)
{

        vm_page_lock_assert(m, MA_OWNED);
        VM_OBJECT_ASSERT_WLOCKED(m->object);
        if (m->dirty || m->hold_count || m->busy || m->wire_count ||
            (m->oflags & (VPO_BUSY | VPO_UNMANAGED)) != 0)
                return (0);
        pmap_remove_all(m);
        if (m->dirty)
                return (0);
        vm_page_cache(m);
        return (1);
}

/*
 * vm_page_try_to_free()
 *
 *      Attempt to free the page.  If we cannot free it, we do nothing.
 *      1 is returned on success, 0 on failure.
 */
int
vm_page_try_to_free(vm_page_t m)
{

        vm_page_lock_assert(m, MA_OWNED);
        if (m->object != NULL)
                VM_OBJECT_ASSERT_WLOCKED(m->object);
        if (m->dirty || m->hold_count || m->busy || m->wire_count ||
            (m->oflags & (VPO_BUSY | VPO_UNMANAGED)) != 0)
                return (0);
        pmap_remove_all(m);
        if (m->dirty)
                return (0);
        vm_page_free(m);
        return (1);
}

/*
 * vm_page_cache
 *
 * Put the specified page onto the page cache queue (if appropriate).
 *
 * The object and page must be locked.
 */
void
vm_page_cache(vm_page_t m)
{
        vm_object_t object;
        boolean_t cache_was_empty;

        vm_page_lock_assert(m, MA_OWNED);
        object = m->object;
        VM_OBJECT_ASSERT_WLOCKED(object);
        if ((m->oflags & (VPO_UNMANAGED | VPO_BUSY)) || m->busy ||
            m->hold_count || m->wire_count)
                panic("vm_page_cache: attempting to cache busy page");
        KASSERT(!pmap_page_is_mapped(m),
            ("vm_page_cache: page %p is mapped", m));
        KASSERT(m->dirty == 0, ("vm_page_cache: page %p is dirty", m));
        if (m->valid == 0 || object->type == OBJT_DEFAULT ||
            (object->type == OBJT_SWAP &&
            !vm_pager_has_page(object, m->pindex, NULL, NULL))) {
                /*
                 * Hypothesis: A cache-elgible page belonging to a
                 * default object or swap object but without a backing
                 * store must be zero filled.
                 */
                vm_page_free(m);
                return;
        }
        KASSERT((m->flags & PG_CACHED) == 0,
            ("vm_page_cache: page %p is already cached", m));
        PCPU_INC(cnt.v_tcached);

        /*
         * Remove the page from the paging queues.
         */
        vm_page_remque(m);

        /*
         * Remove the page from the object's collection of resident
         * pages. 
         */
        vm_radix_remove(&object->rtree, m->pindex);
        TAILQ_REMOVE(&object->memq, m, listq);
        object->resident_page_count--;

        /*
         * Restore the default memory attribute to the page.
         */
        if (pmap_page_get_memattr(m) != VM_MEMATTR_DEFAULT)
                pmap_page_set_memattr(m, VM_MEMATTR_DEFAULT);

        /*
         * Insert the page into the object's collection of cached pages
         * and the physical memory allocator's cache/free page queues.
         */
        m->flags &= ~PG_ZERO;
        mtx_lock(&vm_page_queue_free_mtx);
        m->flags |= PG_CACHED;
        cnt.v_cache_count++;
        cache_was_empty = vm_radix_is_empty(&object->cache);
        vm_radix_insert(&object->cache, m);
#if VM_NRESERVLEVEL > 0
        if (!vm_reserv_free_page(m)) {
#else
        if (TRUE) {
#endif
                vm_phys_set_pool(VM_FREEPOOL_CACHE, m, 0);
                vm_phys_free_pages(m, 0);
        }
        vm_page_free_wakeup();
        mtx_unlock(&vm_page_queue_free_mtx);

        /*
         * Increment the vnode's hold count if this is the object's only
         * cached page.  Decrement the vnode's hold count if this was
         * the object's only resident page.
         */
        if (object->type == OBJT_VNODE) {
                if (cache_was_empty && object->resident_page_count != 0)
                        vhold(object->handle);
                else if (!cache_was_empty && object->resident_page_count == 0)
                        vdrop(object->handle);
        }
}

/*
 * vm_page_advise
 *
 *      Cache, deactivate, or do nothing as appropriate.  This routine
 *      is used by madvise().
 *
 *      Generally speaking we want to move the page into the cache so
 *      it gets reused quickly.  However, this can result in a silly syndrome
 *      due to the page recycling too quickly.  Small objects will not be
 *      fully cached.  On the other hand, if we move the page to the inactive
 *      queue we wind up with a problem whereby very large objects 
 *      unnecessarily blow away our inactive and cache queues.
 *
 *      The solution is to move the pages based on a fixed weighting.  We
 *      either leave them alone, deactivate them, or move them to the cache,
 *      where moving them to the cache has the highest weighting.
 *      By forcing some pages into other queues we eventually force the
 *      system to balance the queues, potentially recovering other unrelated
 *      space from active.  The idea is to not force this to happen too
 *      often.
 *
 *      The object and page must be locked.
 */
void
vm_page_advise(vm_page_t m, int advice)
{
        int dnw, head;

        vm_page_assert_locked(m);
        VM_OBJECT_ASSERT_WLOCKED(m->object);
        if (advice == MADV_FREE) {
                /*
                 * Mark the page clean.  This will allow the page to be freed
                 * up by the system.  However, such pages are often reused
                 * quickly by malloc() so we do not do anything that would
                 * cause a page fault if we can help it.
                 *
                 * Specifically, we do not try to actually free the page now
                 * nor do we try to put it in the cache (which would cause a
                 * page fault on reuse).
                 *
                 * But we do make the page is freeable as we can without
                 * actually taking the step of unmapping it.
                 */
                pmap_clear_modify(m);
                m->dirty = 0;
                m->act_count = 0;
        } else if (advice != MADV_DONTNEED)
                return;
        dnw = PCPU_GET(dnweight);
        PCPU_INC(dnweight);

        /*
         * Occasionally leave the page alone.
         */
        if ((dnw & 0x01F0) == 0 || m->queue == PQ_INACTIVE) {
                if (m->act_count >= ACT_INIT)
                        --m->act_count;
                return;
        }

        /*
         * Clear any references to the page.  Otherwise, the page daemon will
         * immediately reactivate the page.
         *
         * Perform the pmap_clear_reference() first.  Otherwise, a concurrent
         * pmap operation, such as pmap_remove(), could clear a reference in
         * the pmap and set PGA_REFERENCED on the page before the
         * pmap_clear_reference() had completed.  Consequently, the page would
         * appear referenced based upon an old reference that occurred before
         * this function ran.
         */
        pmap_clear_reference(m);
        vm_page_aflag_clear(m, PGA_REFERENCED);

        if (advice != MADV_FREE && m->dirty == 0 && pmap_is_modified(m))
                vm_page_dirty(m);

        if (m->dirty || (dnw & 0x0070) == 0) {
                /*
                 * Deactivate the page 3 times out of 32.
                 */
                head = 0;
        } else {
                /*
                 * Cache the page 28 times out of every 32.  Note that
                 * the page is deactivated instead of cached, but placed
                 * at the head of the queue instead of the tail.
                 */
                head = 1;
        }
        _vm_page_deactivate(m, head);
}

/*
 * Grab a page, waiting until we are waken up due to the page
 * changing state.  We keep on waiting, if the page continues
 * to be in the object.  If the page doesn't exist, first allocate it
 * and then conditionally zero it.
 *
 * The caller must always specify the VM_ALLOC_RETRY flag.  This is intended
 * to facilitate its eventual removal.
 *
 * This routine may sleep.
 *
 * The object must be locked on entry.  The lock will, however, be released
 * and reacquired if the routine sleeps.
 */
vm_page_t
vm_page_grab(vm_object_t object, vm_pindex_t pindex, int allocflags)
{
        vm_page_t m;

        VM_OBJECT_ASSERT_WLOCKED(object);
        KASSERT((allocflags & VM_ALLOC_RETRY) != 0,
            ("vm_page_grab: VM_ALLOC_RETRY is required"));
retrylookup:
        if ((m = vm_page_lookup(object, pindex)) != NULL) {
                if ((m->oflags & VPO_BUSY) != 0 ||
                    ((allocflags & VM_ALLOC_IGN_SBUSY) == 0 && m->busy != 0)) {
                        /*
                         * Reference the page before unlocking and
                         * sleeping so that the page daemon is less
                         * likely to reclaim it.
                         */
                        vm_page_aflag_set(m, PGA_REFERENCED);
                        vm_page_sleep(m, "pgrbwt");
                        goto retrylookup;
                } else {
                        if ((allocflags & VM_ALLOC_WIRED) != 0) {
                                vm_page_lock(m);
                                vm_page_wire(m);
                                vm_page_unlock(m);
                        }
                        if ((allocflags & VM_ALLOC_NOBUSY) == 0)
                                vm_page_busy(m);
                        return (m);
                }
        }
        m = vm_page_alloc(object, pindex, allocflags & ~(VM_ALLOC_RETRY |
            VM_ALLOC_IGN_SBUSY));
        if (m == NULL) {
                VM_OBJECT_WUNLOCK(object);
                VM_WAIT;
                VM_OBJECT_WLOCK(object);
                goto retrylookup;
        } else if (m->valid != 0)
                return (m);
        if (allocflags & VM_ALLOC_ZERO && (m->flags & PG_ZERO) == 0)
                pmap_zero_page(m);
        return (m);
}

/*
 * Mapping function for valid or dirty bits in a page.
 *
 * Inputs are required to range within a page.
 */
vm_page_bits_t
vm_page_bits(int base, int size)
{
        int first_bit;
        int last_bit;

        KASSERT(
            base + size <= PAGE_SIZE,
            ("vm_page_bits: illegal base/size %d/%d", base, size)
        );

        if (size == 0)          /* handle degenerate case */
                return (0);

        first_bit = base >> DEV_BSHIFT;
        last_bit = (base + size - 1) >> DEV_BSHIFT;

        return (((vm_page_bits_t)2 << last_bit) -
            ((vm_page_bits_t)1 << first_bit));
}

/*
 *      vm_page_set_valid_range:
 *
 *      Sets portions of a page valid.  The arguments are expected
 *      to be DEV_BSIZE aligned but if they aren't the bitmap is inclusive
 *      of any partial chunks touched by the range.  The invalid portion of
 *      such chunks will be zeroed.
 *
 *      (base + size) must be less then or equal to PAGE_SIZE.
 */
void
vm_page_set_valid_range(vm_page_t m, int base, int size)
{
        int endoff, frag;

        VM_OBJECT_ASSERT_WLOCKED(m->object);
        if (size == 0)  /* handle degenerate case */
                return;

        /*
         * If the base is not DEV_BSIZE aligned and the valid
         * bit is clear, we have to zero out a portion of the
         * first block.
         */
        if ((frag = base & ~(DEV_BSIZE - 1)) != base &&
            (m->valid & (1 << (base >> DEV_BSHIFT))) == 0)
                pmap_zero_page_area(m, frag, base - frag);

        /*
         * If the ending offset is not DEV_BSIZE aligned and the 
         * valid bit is clear, we have to zero out a portion of
         * the last block.
         */
        endoff = base + size;
        if ((frag = endoff & ~(DEV_BSIZE - 1)) != endoff &&
            (m->valid & (1 << (endoff >> DEV_BSHIFT))) == 0)
                pmap_zero_page_area(m, endoff,
                    DEV_BSIZE - (endoff & (DEV_BSIZE - 1)));

        /*
         * Assert that no previously invalid block that is now being validated
         * is already dirty. 
         */
        KASSERT((~m->valid & vm_page_bits(base, size) & m->dirty) == 0,
            ("vm_page_set_valid_range: page %p is dirty", m));

        /*
         * Set valid bits inclusive of any overlap.
         */
        m->valid |= vm_page_bits(base, size);
}

/*
 * Clear the given bits from the specified page's dirty field.
 */
static __inline void
vm_page_clear_dirty_mask(vm_page_t m, vm_page_bits_t pagebits)
{
        uintptr_t addr;
#if PAGE_SIZE < 16384
        int shift;
#endif

        /*
         * If the object is locked and the page is neither VPO_BUSY nor
         * write mapped, then the page's dirty field cannot possibly be
         * set by a concurrent pmap operation.
         */
        VM_OBJECT_ASSERT_WLOCKED(m->object);
        if ((m->oflags & VPO_BUSY) == 0 && !pmap_page_is_write_mapped(m))
                m->dirty &= ~pagebits;
        else {
                /*
                 * The pmap layer can call vm_page_dirty() without
                 * holding a distinguished lock.  The combination of
                 * the object's lock and an atomic operation suffice
                 * to guarantee consistency of the page dirty field.
                 *
                 * For PAGE_SIZE == 32768 case, compiler already
                 * properly aligns the dirty field, so no forcible
                 * alignment is needed. Only require existence of
                 * atomic_clear_64 when page size is 32768.
                 */
                addr = (uintptr_t)&m->dirty;
#if PAGE_SIZE == 32768
                atomic_clear_64((uint64_t *)addr, pagebits);
#elif PAGE_SIZE == 16384
                atomic_clear_32((uint32_t *)addr, pagebits);
#else           /* PAGE_SIZE <= 8192 */
                /*
                 * Use a trick to perform a 32-bit atomic on the
                 * containing aligned word, to not depend on the existence
                 * of atomic_clear_{8, 16}.
                 */
                shift = addr & (sizeof(uint32_t) - 1);
#if BYTE_ORDER == BIG_ENDIAN
                shift = (sizeof(uint32_t) - sizeof(m->dirty) - shift) * NBBY;
#else
                shift *= NBBY;
#endif
                addr &= ~(sizeof(uint32_t) - 1);
                atomic_clear_32((uint32_t *)addr, pagebits << shift);
#endif          /* PAGE_SIZE */
        }
}

/*
 *      vm_page_set_validclean:
 *
 *      Sets portions of a page valid and clean.  The arguments are expected
 *      to be DEV_BSIZE aligned but if they aren't the bitmap is inclusive
 *      of any partial chunks touched by the range.  The invalid portion of
 *      such chunks will be zero'd.
 *
 *      (base + size) must be less then or equal to PAGE_SIZE.
 */
void
vm_page_set_validclean(vm_page_t m, int base, int size)
{
        vm_page_bits_t oldvalid, pagebits;
        int endoff, frag;

        VM_OBJECT_ASSERT_WLOCKED(m->object);
        if (size == 0)  /* handle degenerate case */
                return;

        /*
         * If the base is not DEV_BSIZE aligned and the valid
         * bit is clear, we have to zero out a portion of the
         * first block.
         */
        if ((frag = base & ~(DEV_BSIZE - 1)) != base &&
            (m->valid & ((vm_page_bits_t)1 << (base >> DEV_BSHIFT))) == 0)
                pmap_zero_page_area(m, frag, base - frag);

        /*
         * If the ending offset is not DEV_BSIZE aligned and the 
         * valid bit is clear, we have to zero out a portion of
         * the last block.
         */
        endoff = base + size;
        if ((frag = endoff & ~(DEV_BSIZE - 1)) != endoff &&
            (m->valid & ((vm_page_bits_t)1 << (endoff >> DEV_BSHIFT))) == 0)
                pmap_zero_page_area(m, endoff,
                    DEV_BSIZE - (endoff & (DEV_BSIZE - 1)));

        /*
         * Set valid, clear dirty bits.  If validating the entire
         * page we can safely clear the pmap modify bit.  We also
         * use this opportunity to clear the VPO_NOSYNC flag.  If a process
         * takes a write fault on a MAP_NOSYNC memory area the flag will
         * be set again.
         *
         * We set valid bits inclusive of any overlap, but we can only
         * clear dirty bits for DEV_BSIZE chunks that are fully within
         * the range.
         */
        oldvalid = m->valid;
        pagebits = vm_page_bits(base, size);
        m->valid |= pagebits;
#if 0   /* NOT YET */
        if ((frag = base & (DEV_BSIZE - 1)) != 0) {
                frag = DEV_BSIZE - frag;
                base += frag;
                size -= frag;
                if (size < 0)
                        size = 0;
        }
        pagebits = vm_page_bits(base, size & (DEV_BSIZE - 1));
#endif
        if (base == 0 && size == PAGE_SIZE) {
                /*
                 * The page can only be modified within the pmap if it is
                 * mapped, and it can only be mapped if it was previously
                 * fully valid.
                 */
                if (oldvalid == VM_PAGE_BITS_ALL)
                        /*
                         * Perform the pmap_clear_modify() first.  Otherwise,
                         * a concurrent pmap operation, such as
                         * pmap_protect(), could clear a modification in the
                         * pmap and set the dirty field on the page before
                         * pmap_clear_modify() had begun and after the dirty
                         * field was cleared here.
                         */
                        pmap_clear_modify(m);
                m->dirty = 0;
                m->oflags &= ~VPO_NOSYNC;
        } else if (oldvalid != VM_PAGE_BITS_ALL)
                m->dirty &= ~pagebits;
        else
                vm_page_clear_dirty_mask(m, pagebits);
}

void
vm_page_clear_dirty(vm_page_t m, int base, int size)
{

        vm_page_clear_dirty_mask(m, vm_page_bits(base, size));
}

/*
 *      vm_page_set_invalid:
 *
 *      Invalidates DEV_BSIZE'd chunks within a page.  Both the
 *      valid and dirty bits for the effected areas are cleared.
 */
void
vm_page_set_invalid(vm_page_t m, int base, int size)
{
        vm_page_bits_t bits;

        VM_OBJECT_ASSERT_WLOCKED(m->object);
        KASSERT((m->oflags & VPO_BUSY) == 0,
            ("vm_page_set_invalid: page %p is busy", m));
        bits = vm_page_bits(base, size);
        if (m->valid == VM_PAGE_BITS_ALL && bits != 0)
                pmap_remove_all(m);
        KASSERT(!pmap_page_is_mapped(m),
            ("vm_page_set_invalid: page %p is mapped", m));
        m->valid &= ~bits;
        m->dirty &= ~bits;
}

/*
 * vm_page_zero_invalid()
 *
 *      The kernel assumes that the invalid portions of a page contain 
 *      garbage, but such pages can be mapped into memory by user code.
 *      When this occurs, we must zero out the non-valid portions of the
 *      page so user code sees what it expects.
 *
 *      Pages are most often semi-valid when the end of a file is mapped 
 *      into memory and the file's size is not page aligned.
 */
void
vm_page_zero_invalid(vm_page_t m, boolean_t setvalid)
{
        int b;
        int i;

        VM_OBJECT_ASSERT_WLOCKED(m->object);
        /*
         * Scan the valid bits looking for invalid sections that
         * must be zerod.  Invalid sub-DEV_BSIZE'd areas ( where the
         * valid bit may be set ) have already been zerod by
         * vm_page_set_validclean().
         */
        for (b = i = 0; i <= PAGE_SIZE / DEV_BSIZE; ++i) {
                if (i == (PAGE_SIZE / DEV_BSIZE) || 
                    (m->valid & ((vm_page_bits_t)1 << i))) {
                        if (i > b) {
                                pmap_zero_page_area(m, 
                                    b << DEV_BSHIFT, (i - b) << DEV_BSHIFT);
                        }
                        b = i + 1;
                }
        }

        /*
         * setvalid is TRUE when we can safely set the zero'd areas
         * as being valid.  We can do this if there are no cache consistancy
         * issues.  e.g. it is ok to do with UFS, but not ok to do with NFS.
         */
        if (setvalid)
                m->valid = VM_PAGE_BITS_ALL;
}

/*
 *      vm_page_is_valid:
 *
 *      Is (partial) page valid?  Note that the case where size == 0
 *      will return FALSE in the degenerate case where the page is
 *      entirely invalid, and TRUE otherwise.
 */
int
vm_page_is_valid(vm_page_t m, int base, int size)
{
        vm_page_bits_t bits;

        VM_OBJECT_ASSERT_WLOCKED(m->object);
        bits = vm_page_bits(base, size);
        return (m->valid != 0 && (m->valid & bits) == bits);
}

/*
 * Set the page's dirty bits if the page is modified.
 */
void
vm_page_test_dirty(vm_page_t m)
{

        VM_OBJECT_ASSERT_WLOCKED(m->object);
        if (m->dirty != VM_PAGE_BITS_ALL && pmap_is_modified(m))
                vm_page_dirty(m);
}

void
vm_page_lock_KBI(vm_page_t m, const char *file, int line)
{

        mtx_lock_flags_(vm_page_lockptr(m), 0, file, line);
}

void
vm_page_unlock_KBI(vm_page_t m, const char *file, int line)
{

        mtx_unlock_flags_(vm_page_lockptr(m), 0, file, line);
}

int
vm_page_trylock_KBI(vm_page_t m, const char *file, int line)
{

        return (mtx_trylock_flags_(vm_page_lockptr(m), 0, file, line));
}

#if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
void
vm_page_assert_locked_KBI(vm_page_t m, const char *file, int line)
{

        vm_page_lock_assert_KBI(m, MA_OWNED, file, line);
}

void
vm_page_lock_assert_KBI(vm_page_t m, int a, const char *file, int line)
{

        mtx_assert_(vm_page_lockptr(m), a, file, line);
}
#endif

int so_zerocp_fullpage = 0;

/*
 *      Replace the given page with a copy.  The copied page assumes
 *      the portion of the given page's "wire_count" that is not the
 *      responsibility of this copy-on-write mechanism.
 *
 *      The object containing the given page must have a non-zero
 *      paging-in-progress count and be locked.
 */
void
vm_page_cowfault(vm_page_t m)
{
        vm_page_t mnew;
        vm_object_t object;
        vm_pindex_t pindex;

        vm_page_lock_assert(m, MA_OWNED);
        object = m->object;
        VM_OBJECT_ASSERT_WLOCKED(object);
        KASSERT(object->paging_in_progress != 0,
            ("vm_page_cowfault: object %p's paging-in-progress count is zero.",
            object)); 
        pindex = m->pindex;

 retry_alloc:
        pmap_remove_all(m);
        vm_page_remove(m);
        mnew = vm_page_alloc(object, pindex, VM_ALLOC_NORMAL | VM_ALLOC_NOBUSY);
        if (mnew == NULL) {
                vm_page_insert(m, object, pindex);
                vm_page_unlock(m);
                VM_OBJECT_WUNLOCK(object);
                VM_WAIT;
                VM_OBJECT_WLOCK(object);
                if (m == vm_page_lookup(object, pindex)) {
                        vm_page_lock(m);
                        goto retry_alloc;
                } else {
                        /*
                         * Page disappeared during the wait.
                         */
                        return;
                }
        }

        if (m->cow == 0) {
                /* 
                 * check to see if we raced with an xmit complete when 
                 * waiting to allocate a page.  If so, put things back 
                 * the way they were 
                 */
                vm_page_unlock(m);
                vm_page_lock(mnew);
                vm_page_free(mnew);
                vm_page_unlock(mnew);
                vm_page_insert(m, object, pindex);
        } else { /* clear COW & copy page */
                if (!so_zerocp_fullpage)
                        pmap_copy_page(m, mnew);
                mnew->valid = VM_PAGE_BITS_ALL;
                vm_page_dirty(mnew);
                mnew->wire_count = m->wire_count - m->cow;
                m->wire_count = m->cow;
                vm_page_unlock(m);
        }
}

void 
vm_page_cowclear(vm_page_t m)
{

        vm_page_lock_assert(m, MA_OWNED);
        if (m->cow) {
                m->cow--;
                /* 
                 * let vm_fault add back write permission  lazily
                 */
        } 
        /*
         *  sf_buf_free() will free the page, so we needn't do it here
         */ 
}

int
vm_page_cowsetup(vm_page_t m)
{

        vm_page_lock_assert(m, MA_OWNED);
        if ((m->flags & PG_FICTITIOUS) != 0 ||
            (m->oflags & VPO_UNMANAGED) != 0 ||
            m->cow == USHRT_MAX - 1 || !VM_OBJECT_TRYWLOCK(m->object))
                return (EBUSY);
        m->cow++;
        pmap_remove_write(m);
        VM_OBJECT_WUNLOCK(m->object);
        return (0);
}

#ifdef INVARIANTS
void
vm_page_object_lock_assert(vm_page_t m)
{

        /*
         * Certain of the page's fields may only be modified by the
         * holder of the containing object's lock or the setter of the
         * page's VPO_BUSY flag.  Unfortunately, the setter of the
         * VPO_BUSY flag is not recorded, and thus cannot be checked
         * here.
         */
        if (m->object != NULL && (m->oflags & VPO_BUSY) == 0)
                VM_OBJECT_ASSERT_WLOCKED(m->object);
}
#endif

#include "opt_ddb.h"
#ifdef DDB
#include <sys/kernel.h>

#include <ddb/ddb.h>

DB_SHOW_COMMAND(page, vm_page_print_page_info)
{
        db_printf("cnt.v_free_count: %d\n", cnt.v_free_count);
        db_printf("cnt.v_cache_count: %d\n", cnt.v_cache_count);
        db_printf("cnt.v_inactive_count: %d\n", cnt.v_inactive_count);
        db_printf("cnt.v_active_count: %d\n", cnt.v_active_count);
        db_printf("cnt.v_wire_count: %d\n", cnt.v_wire_count);
        db_printf("cnt.v_free_reserved: %d\n", cnt.v_free_reserved);
        db_printf("cnt.v_free_min: %d\n", cnt.v_free_min);
        db_printf("cnt.v_free_target: %d\n", cnt.v_free_target);
        db_printf("cnt.v_cache_min: %d\n", cnt.v_cache_min);
        db_printf("cnt.v_inactive_target: %d\n", cnt.v_inactive_target);
}

DB_SHOW_COMMAND(pageq, vm_page_print_pageq_info)
{
                
        db_printf("PQ_FREE:");
        db_printf(" %d", cnt.v_free_count);
        db_printf("\n");
                
        db_printf("PQ_CACHE:");
        db_printf(" %d", cnt.v_cache_count);
        db_printf("\n");

        db_printf("PQ_ACTIVE: %d, PQ_INACTIVE: %d\n",
                *vm_pagequeues[PQ_ACTIVE].pq_cnt,
                *vm_pagequeues[PQ_INACTIVE].pq_cnt);
}

DB_SHOW_COMMAND(pginfo, vm_page_print_pginfo)
{
        vm_page_t m;
        boolean_t phys;

        if (!have_addr) {
                db_printf("show pginfo addr\n");
                return;
        }

        phys = strchr(modif, 'p') != NULL;
        if (phys)
                m = PHYS_TO_VM_PAGE(addr);
        else
                m = (vm_page_t)addr;
        db_printf(
    "page %p obj %p pidx 0x%jx phys 0x%jx q %d hold %d wire %d\n"
    "  af 0x%x of 0x%x f 0x%x act %d busy %d valid 0x%x dirty 0x%x\n",
            m, m->object, (uintmax_t)m->pindex, (uintmax_t)m->phys_addr,
            m->queue, m->hold_count, m->wire_count, m->aflags, m->oflags,
            m->flags, m->act_count, m->busy, m->valid, m->dirty);
}
#endif /* DDB */