kernel - Fix DEBUG_LOCKS races

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

/*
 * (MPSAFE)
 *
 * Copyright (c) 1991 Regents of the University of California.
 * 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
 * $FreeBSD: src/sys/vm/vm_page.c,v 1.147.2.18 2002/03/10 05:03:19 alc Exp $
 */

/*
 * 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.
 */
/*
 * Resident memory management module.  The module manipulates 'VM pages'.
 * A VM page is the core building block for memory management.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/malloc.h>
#include <sys/proc.h>
#include <sys/vmmeter.h>
#include <sys/vnode.h>
#include <sys/kernel.h>

#include <vm/vm.h>
#include <vm/vm_param.h>
#include <sys/lock.h>
#include <vm/vm_kern.h>
#include <vm/pmap.h>
#include <vm/vm_map.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
#include <vm/vm_pageout.h>
#include <vm/vm_pager.h>
#include <vm/vm_extern.h>
#include <vm/swap_pager.h>

#include <machine/inttypes.h>
#include <machine/md_var.h>

#include <vm/vm_page2.h>
#include <sys/spinlock2.h>

#define VMACTION_HSIZE  256
#define VMACTION_HMASK  (VMACTION_HSIZE - 1)

static void vm_page_queue_init(void);
static void vm_page_free_wakeup(void);
static vm_page_t vm_page_select_cache(u_short pg_color);
static vm_page_t _vm_page_list_find2(int basequeue, int index);
static void _vm_page_deactivate_locked(vm_page_t m, int athead);

/*
 * Array of tailq lists
 */
__cachealign struct vpgqueues vm_page_queues[PQ_COUNT];

LIST_HEAD(vm_page_action_list, vm_page_action);
struct vm_page_action_list      action_list[VMACTION_HSIZE];
static volatile int vm_pages_waiting;


RB_GENERATE2(vm_page_rb_tree, vm_page, rb_entry, rb_vm_page_compare,
             vm_pindex_t, pindex);

static void
vm_page_queue_init(void) 
{
        int i;

        for (i = 0; i < PQ_L2_SIZE; i++)
                vm_page_queues[PQ_FREE+i].cnt = &vmstats.v_free_count;
        for (i = 0; i < PQ_L2_SIZE; i++)
                vm_page_queues[PQ_CACHE+i].cnt = &vmstats.v_cache_count;
        for (i = 0; i < PQ_L2_SIZE; i++)
                vm_page_queues[PQ_INACTIVE+i].cnt = &vmstats.v_inactive_count;
        for (i = 0; i < PQ_L2_SIZE; i++)
                vm_page_queues[PQ_ACTIVE+i].cnt = &vmstats.v_active_count;
        for (i = 0; i < PQ_L2_SIZE; i++)
                vm_page_queues[PQ_HOLD+i].cnt = &vmstats.v_active_count;
        /* PQ_NONE has no queue */

        for (i = 0; i < PQ_COUNT; i++) {
                TAILQ_INIT(&vm_page_queues[i].pl);
                spin_init(&vm_page_queues[i].spin);
        }

        for (i = 0; i < VMACTION_HSIZE; i++)
                LIST_INIT(&action_list[i]);
}

/*
 * note: place in initialized data section?  Is this necessary?
 */
long first_page = 0;
int vm_page_array_size = 0;
int vm_page_zero_count = 0;
vm_page_t vm_page_array = 0;

/*
 * (low level boot)
 *
 * 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 (vmstats.v_page_size == 0)
                vmstats.v_page_size = PAGE_SIZE;
        if (((vmstats.v_page_size - 1) & vmstats.v_page_size) != 0)
                panic("vm_set_page_size: page size not a power of two");
}

/*
 * (low level boot)
 *
 * Add a new page to the freelist for use by the system.  New pages
 * are added to both the head and tail of the associated free page
 * queue in a bottom-up fashion, so both zero'd and non-zero'd page
 * requests pull 'recent' adds (higher physical addresses) first.
 *
 * Beware that the page zeroing daemon will also be running soon after
 * boot, moving pages from the head to the tail of the PQ_FREE queues.
 *
 * Must be called in a critical section.
 */
static vm_page_t
vm_add_new_page(vm_paddr_t pa)
{
        struct vpgqueues *vpq;
        vm_page_t m;

        m = PHYS_TO_VM_PAGE(pa);
        m->phys_addr = pa;
        m->flags = 0;
        m->pc = (pa >> PAGE_SHIFT) & PQ_L2_MASK;
#ifdef SMP
        /*
         * Twist for cpu localization in addition to page coloring, so
         * different cpus selecting by m->queue get different page colors.
         */
        m->pc ^= ((pa >> PAGE_SHIFT) / PQ_L2_SIZE) & PQ_L2_MASK;
        m->pc ^= ((pa >> PAGE_SHIFT) / (PQ_L2_SIZE * PQ_L2_SIZE)) & PQ_L2_MASK;
#endif
        m->queue = m->pc + PQ_FREE;
        KKASSERT(m->dirty == 0);

        atomic_add_int(&vmstats.v_page_count, 1);
        atomic_add_int(&vmstats.v_free_count, 1);
        vpq = &vm_page_queues[m->queue];
        if ((vpq->flipflop & 15) == 0) {
                pmap_zero_page(VM_PAGE_TO_PHYS(m));
                m->flags |= PG_ZERO;
                TAILQ_INSERT_TAIL(&vpq->pl, m, pageq);
                atomic_add_int(&vm_page_zero_count, 1);
        } else {
                TAILQ_INSERT_HEAD(&vpq->pl, m, pageq);
        }
        ++vpq->flipflop;
        ++vpq->lcnt;

        return (m);
}

/*
 * (low level boot)
 *
 * Initializes the resident memory module.
 *
 * Preallocates memory for critical VM structures and arrays prior to
 * kernel_map becoming available.
 *
 * Memory is allocated from (virtual2_start, virtual2_end) if available,
 * otherwise memory is allocated from (virtual_start, virtual_end).
 *
 * On x86-64 (virtual_start, virtual_end) is only 2GB and may not be
 * large enough to hold vm_page_array & other structures for machines with
 * large amounts of ram, so we want to use virtual2* when available.
 */
void
vm_page_startup(void)
{
        vm_offset_t vaddr = virtual2_start ? virtual2_start : virtual_start;
        vm_offset_t mapped;
        vm_size_t npages;
        vm_paddr_t page_range;
        vm_paddr_t new_end;
        int i;
        vm_paddr_t pa;
        int nblocks;
        vm_paddr_t last_pa;
        vm_paddr_t end;
        vm_paddr_t biggestone, biggestsize;
        vm_paddr_t total;

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

        for (i = 0; phys_avail[i + 1]; i += 2) {
                phys_avail[i] = round_page64(phys_avail[i]);
                phys_avail[i + 1] = trunc_page64(phys_avail[i + 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;
                }
                ++nblocks;
                total += size;
        }

        end = phys_avail[biggestone+1];
        end = trunc_page(end);

        /*
         * Initialize the queue headers for the free queue, the active queue
         * and the inactive queue.
         */

        vm_page_queue_init();

#if !defined(_KERNEL_VIRTUAL)
        /*
         * VKERNELs don't support minidumps and as such don't need
         * vm_page_dump
         *
         * 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.
         */
        page_range = phys_avail[(nblocks - 1) * 2 + 1] / PAGE_SIZE;
        vm_page_dump_size = round_page(roundup2(page_range, NBBY) / NBBY);
        end -= vm_page_dump_size;
        vm_page_dump = (void *)pmap_map(&vaddr, end, end + vm_page_dump_size,
            VM_PROT_READ | VM_PROT_WRITE);
        bzero((void *)vm_page_dump, vm_page_dump_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 = phys_avail[0] / PAGE_SIZE;
        page_range = phys_avail[(nblocks - 1) * 2 + 1] / PAGE_SIZE - first_page;
        npages = (total - (page_range * sizeof(struct vm_page))) / 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 defined(__x86_64__) && !defined(_KERNEL_VIRTUAL)
        /*
         * since pmap_map on amd64 returns stuff out of a direct-map region,
         * we have to manually add these pages to the minidump tracking so
         * that they can be dumped, including the vm_page_array.
         */
        for (pa = new_end; pa < phys_avail[biggestone + 1]; pa += PAGE_SIZE)
                dump_add_page(pa);
#endif

        /*
         * Clear all of the page structures
         */
        bzero((caddr_t) vm_page_array, page_range * sizeof(struct vm_page));
        vm_page_array_size = page_range;

        /*
         * Construct the free queue(s) in ascending order (by physical
         * address) so that the first 16MB of physical memory is allocated
         * last rather than first.  On large-memory machines, this avoids
         * the exhaustion of low physical memory before isa_dmainit has run.
         */
        vmstats.v_page_count = 0;
        vmstats.v_free_count = 0;
        for (i = 0; phys_avail[i + 1] && npages > 0; i += 2) {
                pa = phys_avail[i];
                if (i == biggestone)
                        last_pa = new_end;
                else
                        last_pa = phys_avail[i + 1];
                while (pa < last_pa && npages-- > 0) {
                        vm_add_new_page(pa);
                        pa += PAGE_SIZE;
                }
        }
        if (virtual2_start)
                virtual2_start = vaddr;
        else
                virtual_start = vaddr;
}

/*
 * Scan comparison function for Red-Black tree scans.  An inclusive
 * (start,end) is expected.  Other fields are not used.
 */
int
rb_vm_page_scancmp(struct vm_page *p, void *data)
{
        struct rb_vm_page_scan_info *info = data;

        if (p->pindex < info->start_pindex)
                return(-1);
        if (p->pindex > info->end_pindex)
                return(1);
        return(0);
}

int
rb_vm_page_compare(struct vm_page *p1, struct vm_page *p2)
{
        if (p1->pindex < p2->pindex)
                return(-1);
        if (p1->pindex > p2->pindex)
                return(1);
        return(0);
}

/*
 * Each page queue has its own spin lock, which is fairly optimal for
 * allocating and freeing pages at least.
 *
 * The caller must hold the vm_page_spin_lock() before locking a vm_page's
 * queue spinlock via this function.  Also note that m->queue cannot change
 * unless both the page and queue are locked.
 */
static __inline
void
_vm_page_queue_spin_lock(vm_page_t m)
{
        u_short queue;

        queue = m->queue;
        if (queue != PQ_NONE) {
                spin_lock(&vm_page_queues[queue].spin);
                KKASSERT(queue == m->queue);
        }
}

static __inline
void
_vm_page_queue_spin_unlock(vm_page_t m)
{
        u_short queue;

        queue = m->queue;
        cpu_ccfence();
        if (queue != PQ_NONE)
                spin_unlock(&vm_page_queues[queue].spin);
}

static __inline
void
_vm_page_queues_spin_lock(u_short queue)
{
        cpu_ccfence();
        if (queue != PQ_NONE)
                spin_lock(&vm_page_queues[queue].spin);
}


static __inline
void
_vm_page_queues_spin_unlock(u_short queue)
{
        cpu_ccfence();
        if (queue != PQ_NONE)
                spin_unlock(&vm_page_queues[queue].spin);
}

void
vm_page_queue_spin_lock(vm_page_t m)
{
        _vm_page_queue_spin_lock(m);
}

void
vm_page_queues_spin_lock(u_short queue)
{
        _vm_page_queues_spin_lock(queue);
}

void
vm_page_queue_spin_unlock(vm_page_t m)
{
        _vm_page_queue_spin_unlock(m);
}

void
vm_page_queues_spin_unlock(u_short queue)
{
        _vm_page_queues_spin_unlock(queue);
}

/*
 * This locks the specified vm_page and its queue in the proper order
 * (page first, then queue).  The queue may change so the caller must
 * recheck on return.
 */
static __inline
void
_vm_page_and_queue_spin_lock(vm_page_t m)
{
        vm_page_spin_lock(m);
        _vm_page_queue_spin_lock(m);
}

static __inline
void
_vm_page_and_queue_spin_unlock(vm_page_t m)
{
        _vm_page_queues_spin_unlock(m->queue);
        vm_page_spin_unlock(m);
}

void
vm_page_and_queue_spin_unlock(vm_page_t m)
{
        _vm_page_and_queue_spin_unlock(m);
}

void
vm_page_and_queue_spin_lock(vm_page_t m)
{
        _vm_page_and_queue_spin_lock(m);
}

/*
 * Helper function removes vm_page from its current queue.
 * Returns the base queue the page used to be on.
 *
 * The vm_page and the queue must be spinlocked.
 * This function will unlock the queue but leave the page spinlocked.
 */
static __inline u_short
_vm_page_rem_queue_spinlocked(vm_page_t m)
{
        struct vpgqueues *pq;
        u_short queue;

        queue = m->queue;
        if (queue != PQ_NONE) {
                pq = &vm_page_queues[queue];
                TAILQ_REMOVE(&pq->pl, m, pageq);
                atomic_add_int(pq->cnt, -1);
                pq->lcnt--;
                m->queue = PQ_NONE;
                vm_page_queues_spin_unlock(queue);
                if ((queue - m->pc) == PQ_FREE && (m->flags & PG_ZERO))
                        atomic_subtract_int(&vm_page_zero_count, 1);
                if ((queue - m->pc) == PQ_CACHE || (queue - m->pc) == PQ_FREE)
                        return (queue - m->pc);
        }
        return queue;
}

/*
 * Helper function places the vm_page on the specified queue.
 *
 * The vm_page must be spinlocked.
 * This function will return with both the page and the queue locked.
 */
static __inline void
_vm_page_add_queue_spinlocked(vm_page_t m, u_short queue, int athead)
{
        struct vpgqueues *pq;

        KKASSERT(m->queue == PQ_NONE);

        if (queue != PQ_NONE) {
                vm_page_queues_spin_lock(queue);
                pq = &vm_page_queues[queue];
                ++pq->lcnt;
                atomic_add_int(pq->cnt, 1);
                m->queue = queue;

                /*
                 * Put zero'd pages on the end ( where we look for zero'd pages
                 * first ) and non-zerod pages at the head.
                 */
                if (queue - m->pc == PQ_FREE) {
                        if (m->flags & PG_ZERO) {
                                TAILQ_INSERT_TAIL(&pq->pl, m, pageq);
                                atomic_add_int(&vm_page_zero_count, 1);
                        } else {
                                TAILQ_INSERT_HEAD(&pq->pl, m, pageq);
                        }
                } else if (athead) {
                        TAILQ_INSERT_HEAD(&pq->pl, m, pageq);
                } else {
                        TAILQ_INSERT_TAIL(&pq->pl, m, pageq);
                }
                /* leave the queue spinlocked */
        }
}

/*
 * Wait until page is no longer PG_BUSY or (if also_m_busy is TRUE)
 * m->busy is zero.  Returns TRUE if it had to sleep, FALSE if we
 * did not.  Only one sleep call will be made before returning.
 *
 * This function does NOT busy the page and on return the page is not
 * guaranteed to be available.
 */
void
vm_page_sleep_busy(vm_page_t m, int also_m_busy, const char *msg)
{
        u_int32_t flags;

        for (;;) {
                flags = m->flags;
                cpu_ccfence();

                if ((flags & PG_BUSY) == 0 &&
                    (also_m_busy == 0 || (flags & PG_SBUSY) == 0)) {
                        break;
                }
                tsleep_interlock(m, 0);
                if (atomic_cmpset_int(&m->flags, flags,
                                      flags | PG_WANTED | PG_REFERENCED)) {
                        tsleep(m, PINTERLOCKED, msg, 0);
                        break;
                }
        }
}

/*
 * Wait until PG_BUSY can be set, then set it.  If also_m_busy is TRUE we
 * also wait for m->busy to become 0 before setting PG_BUSY.
 */
void
VM_PAGE_DEBUG_EXT(vm_page_busy_wait)(vm_page_t m,
                                     int also_m_busy, const char *msg
                                     VM_PAGE_DEBUG_ARGS)
{
        u_int32_t flags;

        for (;;) {
                flags = m->flags;
                cpu_ccfence();
                if (flags & PG_BUSY) {
                        tsleep_interlock(m, 0);
                        if (atomic_cmpset_int(&m->flags, flags,
                                          flags | PG_WANTED | PG_REFERENCED)) {
                                tsleep(m, PINTERLOCKED, msg, 0);
                        }
                } else if (also_m_busy && (flags & PG_SBUSY)) {
                        tsleep_interlock(m, 0);
                        if (atomic_cmpset_int(&m->flags, flags,
                                          flags | PG_WANTED | PG_REFERENCED)) {
                                tsleep(m, PINTERLOCKED, msg, 0);
                        }
                } else {
                        if (atomic_cmpset_int(&m->flags, flags,
                                              flags | PG_BUSY)) {
#ifdef VM_PAGE_DEBUG
                                m->busy_func = func;
                                m->busy_line = lineno;
#endif
                                break;
                        }
                }
        }
}

/*
 * Attempt to set PG_BUSY.  If also_m_busy is TRUE we only succeed if m->busy
 * is also 0.
 *
 * Returns non-zero on failure.
 */
int
VM_PAGE_DEBUG_EXT(vm_page_busy_try)(vm_page_t m, int also_m_busy
                                    VM_PAGE_DEBUG_ARGS)
{
        u_int32_t flags;

        for (;;) {
                flags = m->flags;
                cpu_ccfence();
                if (flags & PG_BUSY)
                        return TRUE;
                if (also_m_busy && (flags & PG_SBUSY))
                        return TRUE;
                if (atomic_cmpset_int(&m->flags, flags, flags | PG_BUSY)) {
#ifdef VM_PAGE_DEBUG
                                m->busy_func = func;
                                m->busy_line = lineno;
#endif
                        return FALSE;
                }
        }
}

/*
 * Clear the PG_BUSY flag and return non-zero to indicate to the caller
 * that a wakeup() should be performed.
 *
 * The vm_page must be spinlocked and will remain spinlocked on return.
 * The related queue must NOT be spinlocked (which could deadlock us).
 *
 * (inline version)
 */
static __inline
int
_vm_page_wakeup(vm_page_t m)
{
        u_int32_t flags;

        for (;;) {
                flags = m->flags;
                cpu_ccfence();
                if (atomic_cmpset_int(&m->flags, flags,
                                      flags & ~(PG_BUSY | PG_WANTED))) {
                        break;
                }
        }
        return(flags & PG_WANTED);
}

/*
 * Clear the PG_BUSY flag and wakeup anyone waiting for the page.  This
 * is typically the last call you make on a page before moving onto
 * other things.
 */
void
vm_page_wakeup(vm_page_t m)
{
        KASSERT(m->flags & PG_BUSY, ("vm_page_wakeup: page not busy!!!"));
        vm_page_spin_lock(m);
        if (_vm_page_wakeup(m)) {
                vm_page_spin_unlock(m);
                wakeup(m);
        } else {
                vm_page_spin_unlock(m);
        }
}

/*
 * Holding a page keeps it from being reused.  Other parts of the system
 * can still disassociate the page from its current object and free it, or
 * perform read or write I/O on it and/or otherwise manipulate the page,
 * but if the page is held the VM system will leave the page and its data
 * intact and not reuse the page for other purposes until the last hold
 * reference is released.  (see vm_page_wire() if you want to prevent the
 * page from being disassociated from its object too).
 *
 * The caller must still validate the contents of the page and, if necessary,
 * wait for any pending I/O (e.g. vm_page_sleep_busy() loop) to complete
 * before manipulating the page.
 *
 * XXX get vm_page_spin_lock() here and move FREE->HOLD if necessary
 */
void
vm_page_hold(vm_page_t m)
{
        vm_page_spin_lock(m);
        atomic_add_int(&m->hold_count, 1);
        if (m->queue - m->pc == PQ_FREE) {
                _vm_page_queue_spin_lock(m);
                _vm_page_rem_queue_spinlocked(m);
                _vm_page_add_queue_spinlocked(m, PQ_HOLD + m->pc, 0);
                _vm_page_queue_spin_unlock(m);
        }
        vm_page_spin_unlock(m);
}

/*
 * The opposite of vm_page_hold().  A page can be freed while being held,
 * which places it on the PQ_HOLD queue.  If we are able to busy the page
 * after the hold count drops to zero we will move the page to the
 * appropriate PQ_FREE queue by calling vm_page_free_toq().
 */
void
vm_page_unhold(vm_page_t m)
{
        vm_page_spin_lock(m);
        atomic_add_int(&m->hold_count, -1);
        if (m->hold_count == 0 && m->queue - m->pc == PQ_HOLD) {
                _vm_page_queue_spin_lock(m);
                _vm_page_rem_queue_spinlocked(m);
                _vm_page_add_queue_spinlocked(m, PQ_FREE + m->pc, 0);
                _vm_page_queue_spin_unlock(m);
        }
        vm_page_spin_unlock(m);
}

/*
 * Inserts the given vm_page into the object and object list.
 *
 * The pagetables are not updated but will presumably fault the page
 * in if necessary, or if a kernel page the caller will at some point
 * enter the page into the kernel's pmap.  We are not allowed to block
 * here so we *can't* do this anyway.
 *
 * This routine may not block.
 * This routine must be called with the vm_object held.
 * This routine must be called with a critical section held.
 *
 * This routine returns TRUE if the page was inserted into the object
 * successfully, and FALSE if the page already exists in the object.
 */
int
vm_page_insert(vm_page_t m, vm_object_t object, vm_pindex_t pindex)
{
        ASSERT_LWKT_TOKEN_HELD(vm_object_token(object));
        if (m->object != NULL)
                panic("vm_page_insert: already inserted");

        object->generation++;

        /*
         * Record the object/offset pair in this page and add the
         * pv_list_count of the page to the object.
         *
         * The vm_page spin lock is required for interactions with the pmap.
         */
        vm_page_spin_lock(m);
        m->object = object;
        m->pindex = pindex;
        if (vm_page_rb_tree_RB_INSERT(&object->rb_memq, m)) {
                m->object = NULL;
                m->pindex = 0;
                vm_page_spin_unlock(m);
                return FALSE;
        }
        object->resident_page_count++;
        /* atomic_add_int(&object->agg_pv_list_count, m->md.pv_list_count); */
        vm_page_spin_unlock(m);

        /*
         * Since we are inserting a new and possibly dirty page,
         * update the object's OBJ_WRITEABLE and OBJ_MIGHTBEDIRTY flags.
         */
        if ((m->valid & m->dirty) || (m->flags & PG_WRITEABLE))
                vm_object_set_writeable_dirty(object);

        /*
         * Checks for a swap assignment and sets PG_SWAPPED if appropriate.
         */
        swap_pager_page_inserted(m);
        return TRUE;
}

/*
 * Removes the given vm_page_t from the (object,index) table
 *
 * The underlying pmap entry (if any) is NOT removed here.
 * This routine may not block.
 *
 * The page must be BUSY and will remain BUSY on return.
 * No other requirements.
 *
 * NOTE: FreeBSD side effect was to unbusy the page on return.  We leave
 *       it busy.
 */
void
vm_page_remove(vm_page_t m)
{
        vm_object_t object;

        if (m->object == NULL) {
                return;
        }

        if ((m->flags & PG_BUSY) == 0)
                panic("vm_page_remove: page not busy");

        object = m->object;

        vm_object_hold(object);

        /*
         * Remove the page from the object and update the object.
         *
         * The vm_page spin lock is required for interactions with the pmap.
         */
        vm_page_spin_lock(m);
        vm_page_rb_tree_RB_REMOVE(&object->rb_memq, m);
        object->resident_page_count--;
        /* atomic_add_int(&object->agg_pv_list_count, -m->md.pv_list_count); */
        m->object = NULL;
        vm_page_spin_unlock(m);

        object->generation++;

        vm_object_drop(object);
}

/*
 * Locate and return the page at (object, pindex), or NULL if the
 * page could not be found.
 *
 * The caller must hold the vm_object token.
 */
vm_page_t
vm_page_lookup(vm_object_t object, vm_pindex_t pindex)
{
        vm_page_t m;

        /*
         * Search the hash table for this object/offset pair
         */
        ASSERT_LWKT_TOKEN_HELD(vm_object_token(object));
        m = vm_page_rb_tree_RB_LOOKUP(&object->rb_memq, pindex);
        KKASSERT(m == NULL || (m->object == object && m->pindex == pindex));
        return(m);
}

vm_page_t
VM_PAGE_DEBUG_EXT(vm_page_lookup_busy_wait)(struct vm_object *object,
                                            vm_pindex_t pindex,
                                            int also_m_busy, const char *msg
                                            VM_PAGE_DEBUG_ARGS)
{
        u_int32_t flags;
        vm_page_t m;

        ASSERT_LWKT_TOKEN_HELD(vm_object_token(object));
        m = vm_page_rb_tree_RB_LOOKUP(&object->rb_memq, pindex);
        while (m) {
                KKASSERT(m->object == object && m->pindex == pindex);
                flags = m->flags;
                cpu_ccfence();
                if (flags & PG_BUSY) {
                        tsleep_interlock(m, 0);
                        if (atomic_cmpset_int(&m->flags, flags,
                                          flags | PG_WANTED | PG_REFERENCED)) {
                                tsleep(m, PINTERLOCKED, msg, 0);
                                m = vm_page_rb_tree_RB_LOOKUP(&object->rb_memq,
                                                              pindex);
                        }
                } else if (also_m_busy && (flags & PG_SBUSY)) {
                        tsleep_interlock(m, 0);
                        if (atomic_cmpset_int(&m->flags, flags,
                                          flags | PG_WANTED | PG_REFERENCED)) {
                                tsleep(m, PINTERLOCKED, msg, 0);
                                m = vm_page_rb_tree_RB_LOOKUP(&object->rb_memq,
                                                              pindex);
                        }
                } else if (atomic_cmpset_int(&m->flags, flags,
                                             flags | PG_BUSY)) {
#ifdef VM_PAGE_DEBUG
                        m->busy_func = func;
                        m->busy_line = lineno;
#endif
                        break;
                }
        }
        return m;
}

/*
 * Attempt to lookup and busy a page.
 *
 * Returns NULL if the page could not be found
 *
 * Returns a vm_page and error == TRUE if the page exists but could not
 * be busied.
 *
 * Returns a vm_page and error == FALSE on success.
 */
vm_page_t
VM_PAGE_DEBUG_EXT(vm_page_lookup_busy_try)(struct vm_object *object,
                                           vm_pindex_t pindex,
                                           int also_m_busy, int *errorp
                                           VM_PAGE_DEBUG_ARGS)
{
        u_int32_t flags;
        vm_page_t m;

        ASSERT_LWKT_TOKEN_HELD(vm_object_token(object));
        m = vm_page_rb_tree_RB_LOOKUP(&object->rb_memq, pindex);
        *errorp = FALSE;
        while (m) {
                KKASSERT(m->object == object && m->pindex == pindex);
                flags = m->flags;
                cpu_ccfence();
                if (flags & PG_BUSY) {
                        *errorp = TRUE;
                        break;
                }
                if (also_m_busy && (flags & PG_SBUSY)) {
                        *errorp = TRUE;
                        break;
                }
                if (atomic_cmpset_int(&m->flags, flags, flags | PG_BUSY)) {
#ifdef VM_PAGE_DEBUG
                        m->busy_func = func;
                        m->busy_line = lineno;
#endif
                        break;
                }
        }
        return m;
}

/*
 * Caller must hold the related vm_object
 */
vm_page_t
vm_page_next(vm_page_t m)
{
        vm_page_t next;

        next = vm_page_rb_tree_RB_NEXT(m);
        if (next && next->pindex != m->pindex + 1)
                next = NULL;
        return (next);
}

/*
 * vm_page_rename()
 *
 * Move the given vm_page from its current object to the specified
 * target object/offset.  The page must be busy and will remain so
 * on return.
 *
 * new_object must be held.
 * This routine might block. XXX ?
 *
 * 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.
 */
void
vm_page_rename(vm_page_t m, vm_object_t new_object, vm_pindex_t new_pindex)
{
        KKASSERT(m->flags & PG_BUSY);
        ASSERT_LWKT_TOKEN_HELD(vm_object_token(new_object));
        if (m->object) {
                ASSERT_LWKT_TOKEN_HELD(vm_object_token(m->object));
                vm_page_remove(m);
        }
        if (vm_page_insert(m, new_object, new_pindex) == FALSE) {
                panic("vm_page_rename: target exists (%p,%"PRIu64")",
                      new_object, new_pindex);
        }
        if (m->queue - m->pc == PQ_CACHE)
                vm_page_deactivate(m);
        vm_page_dirty(m);
}

/*
 * vm_page_unqueue() without any wakeup.  This routine is used when a page
 * is being moved between queues or otherwise is to remain BUSYied by the
 * caller.
 *
 * This routine may not block.
 */
void
vm_page_unqueue_nowakeup(vm_page_t m)
{
        vm_page_and_queue_spin_lock(m);
        (void)_vm_page_rem_queue_spinlocked(m);
        vm_page_spin_unlock(m);
}

/*
 * vm_page_unqueue() - Remove a page from its queue, wakeup the pagedemon
 * if necessary.
 *
 * This routine may not block.
 */
void
vm_page_unqueue(vm_page_t m)
{
        u_short queue;

        vm_page_and_queue_spin_lock(m);
        queue = _vm_page_rem_queue_spinlocked(m);
        if (queue == PQ_FREE || queue == PQ_CACHE) {
                vm_page_spin_unlock(m);
                pagedaemon_wakeup();
        } else {
                vm_page_spin_unlock(m);
        }
}

/*
 * vm_page_list_find()
 *
 * Find a page on the specified queue with color optimization.
 *
 * The page coloring optimization attempts to locate a page that does
 * not overload other nearby pages in the object in the cpu's L1 or L2
 * caches.  We need this optimization because cpu caches tend to be
 * physical caches, while object spaces tend to be virtual.
 *
 * On MP systems each PQ_FREE and PQ_CACHE color queue has its own spinlock
 * and the algorithm is adjusted to localize allocations on a per-core basis.
 * This is done by 'twisting' the colors.
 *
 * The page is returned spinlocked and removed from its queue (it will
 * be on PQ_NONE), or NULL. The page is not PG_BUSY'd.  The caller
 * is responsible for dealing with the busy-page case (usually by
 * deactivating the page and looping).
 *
 * NOTE:  This routine is carefully inlined.  A non-inlined version
 *        is available for outside callers but the only critical path is
 *        from within this source file.
 *
 * NOTE:  This routine assumes that the vm_pages found in PQ_CACHE and PQ_FREE
 *        represent stable storage, allowing us to order our locks vm_page
 *        first, then queue.
 */
static __inline
vm_page_t
_vm_page_list_find(int basequeue, int index, boolean_t prefer_zero)
{
        vm_page_t m;

        for (;;) {
                if (prefer_zero)
                        m = TAILQ_LAST(&vm_page_queues[basequeue+index].pl, pglist);
                else
                        m = TAILQ_FIRST(&vm_page_queues[basequeue+index].pl);
                if (m == NULL) {
                        m = _vm_page_list_find2(basequeue, index);
                        return(m);
                }
                vm_page_and_queue_spin_lock(m);
                if (m->queue == basequeue + index) {
                        _vm_page_rem_queue_spinlocked(m);
                        /* vm_page_t spin held, no queue spin */
                        break;
                }
                vm_page_and_queue_spin_unlock(m);
        }
        return(m);
}

static vm_page_t
_vm_page_list_find2(int basequeue, int index)
{
        int i;
        vm_page_t m = NULL;
        struct vpgqueues *pq;

        pq = &vm_page_queues[basequeue];

        /*
         * Note that for the first loop, index+i and index-i wind up at the
         * same place.  Even though this is not totally optimal, we've already
         * blown it by missing the cache case so we do not care.
         */
        for (i = PQ_L2_SIZE / 2; i > 0; --i) {
                for (;;) {
                        m = TAILQ_FIRST(&pq[(index + i) & PQ_L2_MASK].pl);
                        if (m) {
                                _vm_page_and_queue_spin_lock(m);
                                if (m->queue ==
                                    basequeue + ((index + i) & PQ_L2_MASK)) {
                                        _vm_page_rem_queue_spinlocked(m);
                                        return(m);
                                }
                                _vm_page_and_queue_spin_unlock(m);
                                continue;
                        }
                        m = TAILQ_FIRST(&pq[(index - i) & PQ_L2_MASK].pl);
                        if (m) {
                                _vm_page_and_queue_spin_lock(m);
                                if (m->queue ==
                                    basequeue + ((index - i) & PQ_L2_MASK)) {
                                        _vm_page_rem_queue_spinlocked(m);
                                        return(m);
                                }
                                _vm_page_and_queue_spin_unlock(m);
                                continue;
                        }
                        break;  /* next i */
                }
        }
        return(m);
}

/*
 * Returns a vm_page candidate for allocation.  The page is not busied so
 * it can move around.  The caller must busy the page (and typically
 * deactivate it if it cannot be busied!)
 *
 * Returns a spinlocked vm_page that has been removed from its queue.
 */
vm_page_t
vm_page_list_find(int basequeue, int index, boolean_t prefer_zero)
{
        return(_vm_page_list_find(basequeue, index, prefer_zero));
}

/*
 * Find a page on the cache queue with color optimization, remove it
 * from the queue, and busy it.  The returned page will not be spinlocked.
 *
 * A candidate failure will be deactivated.  Candidates can fail due to
 * being busied by someone else, in which case they will be deactivated.
 *
 * This routine may not block.
 *
 */
static vm_page_t
vm_page_select_cache(u_short pg_color)
{
        vm_page_t m;

        for (;;) {
                m = _vm_page_list_find(PQ_CACHE, pg_color & PQ_L2_MASK, FALSE);
                if (m == NULL)
                        break;
                /*
                 * (m) has been removed from its queue and spinlocked
                 */
                if (vm_page_busy_try(m, TRUE)) {
                        _vm_page_deactivate_locked(m, 0);
                        vm_page_spin_unlock(m);
#ifdef INVARIANTS
                        kprintf("Warning: busy page %p found in cache\n", m);
#endif
                } else {
                        /*
                         * We successfully busied the page
                         */
                        if ((m->flags & PG_UNMANAGED) == 0 &&
                            m->hold_count == 0 &&
                            m->wire_count == 0) {
                                vm_page_spin_unlock(m);
                                pagedaemon_wakeup();
                                return(m);
                        }
                        _vm_page_deactivate_locked(m, 0);
                        if (_vm_page_wakeup(m)) {
                                vm_page_spin_unlock(m);
                                wakeup(m);
                        } else {
                                vm_page_spin_unlock(m);
                        }
                }
        }
        return (m);
}

/*
 * Find a free or zero page, with specified preference.  We attempt to
 * inline the nominal case and fall back to _vm_page_select_free() 
 * otherwise.  A busied page is removed from the queue and returned.
 *
 * This routine may not block.
 */
static __inline vm_page_t
vm_page_select_free(u_short pg_color, boolean_t prefer_zero)
{
        vm_page_t m;

        for (;;) {
                m = _vm_page_list_find(PQ_FREE, pg_color & PQ_L2_MASK,
                                       prefer_zero);
                if (m == NULL)
                        break;
                if (vm_page_busy_try(m, TRUE)) {
                        /*
                         * Various mechanisms such as a pmap_collect can
                         * result in a busy page on the free queue.  We
                         * have to move the page out of the way so we can
                         * retry the allocation.  If the other thread is not
                         * allocating the page then m->valid will remain 0 and
                         * the pageout daemon will free the page later on.
                         *
                         * Since we could not busy the page, however, we
                         * cannot make assumptions as to whether the page
                         * will be allocated by the other thread or not,
                         * so all we can do is deactivate it to move it out
                         * of the way.  In particular, if the other thread
                         * wires the page it may wind up on the inactive
                         * queue and the pageout daemon will have to deal
                         * with that case too.
                         */
                        _vm_page_deactivate_locked(m, 0);
                        vm_page_spin_unlock(m);
#ifdef INVARIANTS
                        kprintf("Warning: busy page %p found in cache\n", m);
#endif
                } else {
                        /*
                         * Theoretically if we are able to busy the page
                         * atomic with the queue removal (using the vm_page
                         * lock) nobody else should be able to mess with the
                         * page before us.
                         */
                        KKASSERT((m->flags & PG_UNMANAGED) == 0);
                        KKASSERT(m->hold_count == 0);
                        KKASSERT(m->wire_count == 0);
                        vm_page_spin_unlock(m);
                        pagedaemon_wakeup();

                        /* return busied and removed page */
                        return(m);
                }
        }
        return(m);
}

/*
 * This implements a per-cpu cache of free, zero'd, ready-to-go pages.
 * The idea is to populate this cache prior to acquiring any locks so
 * we don't wind up potentially zeroing VM pages (under heavy loads) while
 * holding potentialy contending locks.
 *
 * Note that we allocate the page uninserted into anything and use a pindex
 * of 0, the vm_page_alloc() will effectively add gd_cpuid so these
 * allocations should wind up being uncontended.  However, we still want
 * to rove across PQ_L2_SIZE.
 */
void
vm_page_pcpu_cache(void)
{
#if 0
        globaldata_t gd = mycpu;
        vm_page_t m;

        if (gd->gd_vmpg_count < GD_MINVMPG) {
                crit_enter_gd(gd);
                while (gd->gd_vmpg_count < GD_MAXVMPG) {
                        m = vm_page_alloc(NULL, ticks & ~ncpus2_mask,
                                          VM_ALLOC_NULL_OK | VM_ALLOC_NORMAL |
                                          VM_ALLOC_NULL_OK | VM_ALLOC_ZERO);
                        if (gd->gd_vmpg_count < GD_MAXVMPG) {
                                if ((m->flags & PG_ZERO) == 0) {
                                        pmap_zero_page(VM_PAGE_TO_PHYS(m));
                                        vm_page_flag_set(m, PG_ZERO);
                                }
                                gd->gd_vmpg_array[gd->gd_vmpg_count++] = m;
                        } else {
                                vm_page_free(m);
                        }
                }
                crit_exit_gd(gd);
        }
#endif
}

/*
 * vm_page_alloc()
 *
 * Allocate and return a memory cell associated with this VM object/offset
 * pair.  If object is NULL an unassociated page will be allocated.
 *
 * The returned page will be busied and removed from its queues.  This
 * routine can block and may return NULL if a race occurs and the page
 * is found to already exist at the specified (object, pindex).
 *
 *      VM_ALLOC_NORMAL         allow use of cache pages, nominal free drain
 *      VM_ALLOC_QUICK          like normal but cannot use cache
 *      VM_ALLOC_SYSTEM         greater free drain
 *      VM_ALLOC_INTERRUPT      allow free list to be completely drained
 *      VM_ALLOC_ZERO           advisory request for pre-zero'd page only
 *      VM_ALLOC_FORCE_ZERO     advisory request for pre-zero'd page only
 *      VM_ALLOC_NULL_OK        ok to return NULL on insertion collision
 *                              (see vm_page_grab())
 *      VM_ALLOC_USE_GD         ok to use per-gd cache
 *
 * The object must be held if not NULL
 * This routine may not block
 *
 * Additional special handling is required when called from an interrupt
 * (VM_ALLOC_INTERRUPT).  We are not allowed to mess with the page cache
 * in this case.
 */
vm_page_t
vm_page_alloc(vm_object_t object, vm_pindex_t pindex, int page_req)
{
#ifdef SMP
        globaldata_t gd = mycpu;
#endif
        vm_page_t m;
        u_short pg_color;

#if 0
        /*
         * Special per-cpu free VM page cache.  The pages are pre-busied
         * and pre-zerod for us.
         */
        if (gd->gd_vmpg_count && (page_req & VM_ALLOC_USE_GD)) {
                crit_enter_gd(gd);
                if (gd->gd_vmpg_count) {
                        m = gd->gd_vmpg_array[--gd->gd_vmpg_count];
                        crit_exit_gd(gd);
                        goto done;
                }
                crit_exit_gd(gd);
        }
#endif
        m = NULL;

#ifdef SMP
        /*
         * Cpu twist - cpu localization algorithm
         */
        if (object) {
                pg_color = gd->gd_cpuid + (pindex & ~ncpus_fit_mask) +
                           (object->pg_color & ~ncpus_fit_mask);
        } else {
                pg_color = gd->gd_cpuid + (pindex & ~ncpus_fit_mask);
        }
#else
        /*
         * Normal page coloring algorithm
         */
        if (object) {
                pg_color = object->pg_color + pindex;
        } else {
                pg_color = pindex;
        }
#endif
        KKASSERT(page_req & 
                (VM_ALLOC_NORMAL|VM_ALLOC_QUICK|
                 VM_ALLOC_INTERRUPT|VM_ALLOC_SYSTEM));

        /*
         * Certain system threads (pageout daemon, buf_daemon's) are
         * allowed to eat deeper into the free page list.
         */
        if (curthread->td_flags & TDF_SYSTHREAD)
                page_req |= VM_ALLOC_SYSTEM;

loop:
        if (vmstats.v_free_count > vmstats.v_free_reserved ||
            ((page_req & VM_ALLOC_INTERRUPT) && vmstats.v_free_count > 0) ||
            ((page_req & VM_ALLOC_SYSTEM) && vmstats.v_cache_count == 0 &&
                vmstats.v_free_count > vmstats.v_interrupt_free_min)
        ) {
                /*
                 * The free queue has sufficient free pages to take one out.
                 */
                if (page_req & (VM_ALLOC_ZERO | VM_ALLOC_FORCE_ZERO))
                        m = vm_page_select_free(pg_color, TRUE);
                else
                        m = vm_page_select_free(pg_color, FALSE);
        } else if (page_req & VM_ALLOC_NORMAL) {
                /*
                 * Allocatable from the cache (non-interrupt only).  On
                 * success, we must free the page and try again, thus
                 * ensuring that vmstats.v_*_free_min counters are replenished.
                 */
#ifdef INVARIANTS
                if (curthread->td_preempted) {
                        kprintf("vm_page_alloc(): warning, attempt to allocate"
                                " cache page from preempting interrupt\n");
                        m = NULL;
                } else {
                        m = vm_page_select_cache(pg_color);
                }
#else
                m = vm_page_select_cache(pg_color);
#endif
                /*
                 * On success move the page into the free queue and loop.
                 */
                if (m != NULL) {
                        KASSERT(m->dirty == 0,
                                ("Found dirty cache page %p", m));
                        vm_page_protect(m, VM_PROT_NONE);
                        vm_page_free(m);
                        goto loop;
                }

                /*
                 * On failure return NULL
                 */
#if defined(DIAGNOSTIC)
                if (vmstats.v_cache_count > 0)
                        kprintf("vm_page_alloc(NORMAL): missing pages on cache queue: %d\n", vmstats.v_cache_count);
#endif
                vm_pageout_deficit++;
                pagedaemon_wakeup();
                return (NULL);
        } else {
                /*
                 * No pages available, wakeup the pageout daemon and give up.
                 */
                vm_pageout_deficit++;
                pagedaemon_wakeup();
                return (NULL);
        }

        /*
         * v_free_count can race so loop if we don't find the expected
         * page.
         */
        if (m == NULL)
                goto loop;

        /*
         * Good page found.  The page has already been busied for us and
         * removed from its queues.
         */
        KASSERT(m->dirty == 0,
                ("vm_page_alloc: free/cache page %p was dirty", m));
        KKASSERT(m->queue == PQ_NONE);

#if 0
done:
#endif
        /*
         * Initialize the structure, inheriting some flags but clearing
         * all the rest.  The page has already been busied for us.
         */
        vm_page_flag_clear(m, ~(PG_ZERO | PG_BUSY | PG_SBUSY));
        KKASSERT(m->wire_count == 0);
        KKASSERT(m->busy == 0);
        m->act_count = 0;
        m->valid = 0;

        /*
         * Caller must be holding the object lock (asserted by
         * vm_page_insert()).
         *
         * NOTE: Inserting a page here does not insert it into any pmaps
         *       (which could cause us to block allocating memory).
         *
         * NOTE: If no object an unassociated page is allocated, m->pindex
         *       can be used by the caller for any purpose.
         */
        if (object) {
                if (vm_page_insert(m, object, pindex) == FALSE) {
                        kprintf("PAGE RACE (%p:%d,%"PRIu64")\n",
                                object, object->type, pindex);
                        vm_page_free(m);
                        m = NULL;
                        if ((page_req & VM_ALLOC_NULL_OK) == 0)
                                panic("PAGE RACE");
                }
        } else {
                m->pindex = pindex;
        }

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

        /*
         * A PG_BUSY page is returned.
         */
        return (m);
}

/*
 * Wait for sufficient free memory for nominal heavy memory use kernel
 * operations.
 */
void
vm_wait_nominal(void)
{
        while (vm_page_count_min(0))
                vm_wait(0);
}

/*
 * Test if vm_wait_nominal() would block.
 */
int
vm_test_nominal(void)
{
        if (vm_page_count_min(0))
                return(1);
        return(0);
}

/*
 * Block until free pages are available for allocation, called in various
 * places before memory allocations.
 *
 * The caller may loop if vm_page_count_min() == FALSE so we cannot be
 * more generous then that.
 */
void
vm_wait(int timo)
{
        /*
         * never wait forever
         */
        if (timo == 0)
                timo = hz;
        lwkt_gettoken(&vm_token);

        if (curthread == pagethread) {
                /*
                 * The pageout daemon itself needs pages, this is bad.
                 */
                if (vm_page_count_min(0)) {
                        vm_pageout_pages_needed = 1;
                        tsleep(&vm_pageout_pages_needed, 0, "VMWait", timo);
                }
        } else {
                /*
                 * Wakeup the pageout daemon if necessary and wait.
                 */
                if (vm_page_count_target()) {
                        if (vm_pages_needed == 0) {
                                vm_pages_needed = 1;
                                wakeup(&vm_pages_needed);
                        }
                        ++vm_pages_waiting;     /* SMP race ok */
                        tsleep(&vmstats.v_free_count, 0, "vmwait", timo);
                }
        }
        lwkt_reltoken(&vm_token);
}

/*
 * Block until free pages are available for allocation
 *
 * Called only from vm_fault so that processes page faulting can be
 * easily tracked.
 */
void
vm_waitpfault(void)
{
        /*
         * Wakeup the pageout daemon if necessary and wait.
         */
        if (vm_page_count_target()) {
                lwkt_gettoken(&vm_token);
                if (vm_page_count_target()) {
                        if (vm_pages_needed == 0) {
                                vm_pages_needed = 1;
                                wakeup(&vm_pages_needed);
                        }
                        ++vm_pages_waiting;     /* SMP race ok */
                        tsleep(&vmstats.v_free_count, 0, "pfault", hz);
                }
                lwkt_reltoken(&vm_token);
        }
}

/*
 * 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 caller should be holding the page busied ? XXX
 * This routine may not block.
 */
void
vm_page_activate(vm_page_t m)
{
        u_short oqueue;

        vm_page_spin_lock(m);
        if (m->queue - m->pc != PQ_ACTIVE) {
                _vm_page_queue_spin_lock(m);
                oqueue = _vm_page_rem_queue_spinlocked(m);
                /* page is left spinlocked, queue is unlocked */

                if (oqueue == PQ_CACHE)
                        mycpu->gd_cnt.v_reactivated++;
                if (m->wire_count == 0 && (m->flags & PG_UNMANAGED) == 0) {
                        if (m->act_count < ACT_INIT)
                                m->act_count = ACT_INIT;
                        _vm_page_add_queue_spinlocked(m, PQ_ACTIVE + m->pc, 0);
                }
                _vm_page_and_queue_spin_unlock(m);
                if (oqueue == PQ_CACHE || oqueue == PQ_FREE)
                        pagedaemon_wakeup();
        } else {
                if (m->act_count < ACT_INIT)
                        m->act_count = ACT_INIT;
                vm_page_spin_unlock(m);
        }
}

/*
 * 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.
 *
 * This routine may not block.
 */
static __inline void
vm_page_free_wakeup(void)
{
        /*
         * If the pageout daemon itself needs pages, then tell it that
         * there are some free.
         */
        if (vm_pageout_pages_needed &&
            vmstats.v_cache_count + vmstats.v_free_count >= 
            vmstats.v_pageout_free_min
        ) {
                wakeup(&vm_pageout_pages_needed);
                vm_pageout_pages_needed = 0;
        }

        /*
         * Wakeup processes that are waiting on memory.
         *
         * NOTE: vm_paging_target() is the pageout daemon's target, while
         *       vm_page_count_target() is somewhere inbetween.  We want
         *       to wake processes up prior to the pageout daemon reaching
         *       its target to provide some hysteresis.
         */
        if (vm_pages_waiting) {
                if (!vm_page_count_target()) {
                        /*
                         * Plenty of pages are free, wakeup everyone.
                         */
                        vm_pages_waiting = 0;
                        wakeup(&vmstats.v_free_count);
                        ++mycpu->gd_cnt.v_ppwakeups;
                } else if (!vm_page_count_min(0)) {
                        /*
                         * Some pages are free, wakeup someone.
                         */
                        int wcount = vm_pages_waiting;
                        if (wcount > 0)
                                --wcount;
                        vm_pages_waiting = wcount;
                        wakeup_one(&vmstats.v_free_count);
                        ++mycpu->gd_cnt.v_ppwakeups;
                }
        }
}

/*
 * Returns the given page to the PQ_FREE or PQ_HOLD list and disassociates
 * it from its VM object.
 *
 * The vm_page must be PG_BUSY on entry.  PG_BUSY will be released on
 * return (the page will have been freed).
 */
void
vm_page_free_toq(vm_page_t m)
{
        mycpu->gd_cnt.v_tfree++;
        KKASSERT((m->flags & PG_MAPPED) == 0);
        KKASSERT(m->flags & PG_BUSY);

        if (m->busy || ((m->queue - m->pc) == PQ_FREE)) {
                kprintf(
                "vm_page_free: pindex(%lu), busy(%d), PG_BUSY(%d), hold(%d)\n",
                    (u_long)m->pindex, m->busy, (m->flags & PG_BUSY) ? 1 : 0,
                    m->hold_count);
                if ((m->queue - m->pc) == PQ_FREE)
                        panic("vm_page_free: freeing free page");
                else
                        panic("vm_page_free: freeing busy page");
        }

        /*
         * Remove from object, spinlock the page and its queues and
         * remove from any queue.  No queue spinlock will be held
         * after this section (because the page was removed from any
         * queue).
         */
        vm_page_remove(m);
        vm_page_and_queue_spin_lock(m);
        _vm_page_rem_queue_spinlocked(m);

        /*
         * No further management of fictitious pages occurs beyond object
         * and queue removal.
         */
        if ((m->flags & PG_FICTITIOUS) != 0) {
                vm_page_spin_unlock(m);
                vm_page_wakeup(m);
                return;
        }

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

        if (m->wire_count != 0) {
                if (m->wire_count > 1) {
                    panic(
                        "vm_page_free: invalid wire count (%d), pindex: 0x%lx",
                        m->wire_count, (long)m->pindex);
                }
                panic("vm_page_free: freeing wired page");
        }

        /*
         * Clear the UNMANAGED flag when freeing an unmanaged page.
         */
        if (m->flags & PG_UNMANAGED) {
                vm_page_flag_clear(m, PG_UNMANAGED);
        }

        if (m->hold_count != 0) {
                vm_page_flag_clear(m, PG_ZERO);
                _vm_page_add_queue_spinlocked(m, PQ_HOLD + m->pc, 0);
        } else {
                _vm_page_add_queue_spinlocked(m, PQ_FREE + m->pc, 0);
        }

        /*
         * This sequence allows us to clear PG_BUSY while still holding
         * its spin lock, which reduces contention vs allocators.  We
         * must not leave the queue locked or _vm_page_wakeup() may
         * deadlock.
         */
        _vm_page_queue_spin_unlock(m);
        if (_vm_page_wakeup(m)) {
                vm_page_spin_unlock(m);
                wakeup(m);
        } else {
                vm_page_spin_unlock(m);
        }
        vm_page_free_wakeup();
}

/*
 * vm_page_free_fromq_fast()
 *
 * Remove a non-zero page from one of the free queues; the page is removed for
 * zeroing, so do not issue a wakeup.
 */
vm_page_t
vm_page_free_fromq_fast(void)
{
        static int qi;
        vm_page_t m;
        int i;

        for (i = 0; i < PQ_L2_SIZE; ++i) {
                m = vm_page_list_find(PQ_FREE, qi, FALSE);
                /* page is returned spinlocked and removed from its queue */
                if (m) {
                        if (vm_page_busy_try(m, TRUE)) {
                                /*
                                 * We were unable to busy the page, deactivate
                                 * it and loop.
                                 */
                                _vm_page_deactivate_locked(m, 0);
                                vm_page_spin_unlock(m);
                        } else if (m->flags & PG_ZERO) {
                                /*
                                 * The page is PG_ZERO, requeue it and loop
                                 */
                                _vm_page_add_queue_spinlocked(m,
                                                              PQ_FREE + m->pc,
                                                              0);
                                vm_page_queue_spin_unlock(m);
                                if (_vm_page_wakeup(m)) {
                                        vm_page_spin_unlock(m);
                                        wakeup(m);
                                } else {
                                        vm_page_spin_unlock(m);
                                }
                        } else {
                                /*
                                 * The page is not PG_ZERO'd so return it.
                                 */
                                vm_page_spin_unlock(m);
                                KKASSERT((m->flags & PG_UNMANAGED) == 0);
                                KKASSERT(m->hold_count == 0);
                                KKASSERT(m->wire_count == 0);
                                break;
                        }
                        m = NULL;
                }
                qi = (qi + PQ_PRIME2) & PQ_L2_MASK;
        }
        return (m);
}

/*
 * vm_page_unmanage()
 *
 * Prevent PV management from being done on the page.  The page is
 * removed from the paging queues as if it were wired, and as a 
 * consequence of no longer being managed the pageout daemon will not
 * touch it (since there is no way to locate the pte mappings for the
 * page).  madvise() calls that mess with the pmap will also no longer
 * operate on the page.
 *
 * Beyond that the page is still reasonably 'normal'.  Freeing the page
 * will clear the flag.
 *
 * This routine is used by OBJT_PHYS objects - objects using unswappable
 * physical memory as backing store rather then swap-backed memory and
 * will eventually be extended to support 4MB unmanaged physical 
 * mappings.
 *
 * Caller must be holding the page busy.
 */
void
vm_page_unmanage(vm_page_t m)
{
        KKASSERT(m->flags & PG_BUSY);
        if ((m->flags & PG_UNMANAGED) == 0) {
                if (m->wire_count == 0)
                        vm_page_unqueue(m);
        }
        vm_page_flag_set(m, PG_UNMANAGED);
}

/*
 * Mark this page as wired down by yet another map, removing it from
 * paging queues as necessary.
 *
 * Caller must be holding the page busy.
 */
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).  Don't do anything with fictitious
         * pages because they are always wired.
         */
        KKASSERT(m->flags & PG_BUSY);
        if ((m->flags & PG_FICTITIOUS) == 0) {
                if (atomic_fetchadd_int(&m->wire_count, 1) == 0) {
                        if ((m->flags & PG_UNMANAGED) == 0)
                                vm_page_unqueue(m);
                        atomic_add_int(&vmstats.v_wire_count, 1);
                }
                KASSERT(m->wire_count != 0,
                        ("vm_page_wire: wire_count overflow m=%p", m));
        }
}

/*
 * Release one wiring of this page, potentially enabling it to be paged again.
 *
 * 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, freed 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.
 *
 * BUT, if we are in a low-memory situation we have no choice but to
 * put clean pages on the cache queue.
 *
 * A number of routines use vm_page_unwire() to guarantee that the page
 * will go into either the inactive or active queues, and will NEVER
 * be placed in the cache - for example, just after dirtying a page.
 * dirty pages in the cache are not allowed.
 *
 * The page queues must be locked.
 * This routine may not block.
 */
void
vm_page_unwire(vm_page_t m, int activate)
{
        KKASSERT(m->flags & PG_BUSY);
        if (m->flags & PG_FICTITIOUS) {
                /* do nothing */
        } else if (m->wire_count <= 0) {
                panic("vm_page_unwire: invalid wire count: %d", m->wire_count);
        } else {
                if (atomic_fetchadd_int(&m->wire_count, -1) == 1) {
                        atomic_add_int(&vmstats.v_wire_count, -1);
                        if (m->flags & PG_UNMANAGED) {
                                ;
                        } else if (activate) {
                                vm_page_spin_lock(m);
                                _vm_page_add_queue_spinlocked(m,
                                                        PQ_ACTIVE + m->pc, 0);
                                _vm_page_and_queue_spin_unlock(m);
                        } else {
                                vm_page_spin_lock(m);
                                vm_page_flag_clear(m, PG_WINATCFLS);
                                _vm_page_add_queue_spinlocked(m,
                                                        PQ_INACTIVE + m->pc, 0);
                                ++vm_swapcache_inactive_heuristic;
                                _vm_page_and_queue_spin_unlock(m);
                        }
                }
        }
}

/*
 * Move the specified page to the inactive queue.  If the page has
 * any associated swap, the swap is deallocated.
 *
 * 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.
 *
 * vm_page's spinlock must be held on entry and will remain held on return.
 * This routine may not block.
 */
static void
_vm_page_deactivate_locked(vm_page_t m, int athead)
{
        u_short oqueue;

        /*
         * Ignore if already inactive.
         */
        if (m->queue - m->pc == PQ_INACTIVE)
                return;
        _vm_page_queue_spin_lock(m);
        oqueue = _vm_page_rem_queue_spinlocked(m);

        if (m->wire_count == 0 && (m->flags & PG_UNMANAGED) == 0) {
                if (oqueue == PQ_CACHE)
                        mycpu->gd_cnt.v_reactivated++;
                vm_page_flag_clear(m, PG_WINATCFLS);
                _vm_page_add_queue_spinlocked(m, PQ_INACTIVE + m->pc, athead);
                if (athead == 0)
                        ++vm_swapcache_inactive_heuristic;
        }
        _vm_page_queue_spin_unlock(m);
        /* leaves vm_page spinlocked */
}

/*
 * Attempt to deactivate a page.
 *
 * No requirements.
 */
void
vm_page_deactivate(vm_page_t m)
{
        vm_page_spin_lock(m);
        _vm_page_deactivate_locked(m, 0);
        vm_page_spin_unlock(m);
}

void
vm_page_deactivate_locked(vm_page_t m)
{
        _vm_page_deactivate_locked(m, 0);
}

/*
 * Attempt to move a page to PQ_CACHE.
 *
 * Returns 0 on failure, 1 on success
 *
 * The page should NOT be busied by the caller.  This function will validate
 * whether the page can be safely moved to the cache.
 */
int
vm_page_try_to_cache(vm_page_t m)
{
        vm_page_spin_lock(m);
        if (vm_page_busy_try(m, TRUE)) {
                vm_page_spin_unlock(m);
                return(0);
        }
        if (m->dirty || m->hold_count || m->wire_count ||
            (m->flags & PG_UNMANAGED)) {
                if (_vm_page_wakeup(m)) {
                        vm_page_spin_unlock(m);
                        wakeup(m);
                } else {
                        vm_page_spin_unlock(m);
                }
                return(0);
        }
        vm_page_spin_unlock(m);

        /*
         * Page busied by us and no longer spinlocked.  Dirty pages cannot
         * be moved to the cache.
         */
        vm_page_test_dirty(m);
        if (m->dirty) {
                vm_page_wakeup(m);
                return(0);
        }
        vm_page_cache(m);
        return(1);
}

/*
 * Attempt to free the page.  If we cannot free it, we do nothing.
 * 1 is returned on success, 0 on failure.
 *
 * No requirements.
 */
int
vm_page_try_to_free(vm_page_t m)
{
        vm_page_spin_lock(m);
        if (vm_page_busy_try(m, TRUE)) {
                vm_page_spin_unlock(m);
                return(0);
        }
        if (m->dirty || m->hold_count || m->wire_count ||
            (m->flags & PG_UNMANAGED)) {
                if (_vm_page_wakeup(m)) {
                        vm_page_spin_unlock(m);
                        wakeup(m);
                } else {
                        vm_page_spin_unlock(m);
                }
                return(0);
        }
        vm_page_spin_unlock(m);

        /*
         * Page busied by us and no longer spinlocked.  Dirty pages will
         * not be freed by this function.    We have to re-test the
         * dirty bit after cleaning out the pmaps.
         */
        vm_page_test_dirty(m);
        if (m->dirty) {
                vm_page_wakeup(m);
                return(0);
        }
        vm_page_protect(m, VM_PROT_NONE);
        if (m->dirty) {
                vm_page_wakeup(m);
                return(0);
        }
        vm_page_free(m);
        return(1);
}

/*
 * vm_page_cache
 *
 * Put the specified page onto the page cache queue (if appropriate).
 *
 * The page must be busy, and this routine will release the busy and
 * possibly even free the page.
 */
void
vm_page_cache(vm_page_t m)
{
        if ((m->flags & PG_UNMANAGED) || m->busy ||
            m->wire_count || m->hold_count) {
                kprintf("vm_page_cache: attempting to cache busy/held page\n");
                vm_page_wakeup(m);
                return;
        }

        /*
         * Already in the cache (and thus not mapped)
         */
        if ((m->queue - m->pc) == PQ_CACHE) {
                KKASSERT((m->flags & PG_MAPPED) == 0);
                vm_page_wakeup(m);
                return;
        }

        /*
         * Caller is required to test m->dirty, but note that the act of
         * removing the page from its maps can cause it to become dirty
         * on an SMP system due to another cpu running in usermode.
         */
        if (m->dirty) {
                panic("vm_page_cache: caching a dirty page, pindex: %ld",
                        (long)m->pindex);
        }

        /*
         * Remove all pmaps and indicate that the page is not
         * writeable or mapped.  Our vm_page_protect() call may
         * have blocked (especially w/ VM_PROT_NONE), so recheck
         * everything.
         */
        vm_page_protect(m, VM_PROT_NONE);
        if ((m->flags & (PG_UNMANAGED|PG_MAPPED)) || m->busy ||
                        m->wire_count || m->hold_count) {
                vm_page_wakeup(m);
        } else if (m->dirty) {
                vm_page_deactivate(m);
                vm_page_wakeup(m);
        } else {
                _vm_page_and_queue_spin_lock(m);
                _vm_page_rem_queue_spinlocked(m);
                _vm_page_add_queue_spinlocked(m, PQ_CACHE + m->pc, 0);
                _vm_page_queue_spin_unlock(m);
                if (_vm_page_wakeup(m)) {
                        vm_page_spin_unlock(m);
                        wakeup(m);
                } else {
                        vm_page_spin_unlock(m);
                }
                vm_page_free_wakeup();
        }
}

/*
 * vm_page_dontneed()
 *
 * Cache, deactivate, or do nothing as appropriate.  This routine
 * is typically used by madvise() MADV_DONTNEED.
 *
 * 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 otherhand, 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 page must be busied.
 */
void
vm_page_dontneed(vm_page_t m)
{
        static int dnweight;
        int dnw;
        int head;

        dnw = ++dnweight;

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

        /*
         * If vm_page_dontneed() is inactivating a page, it must clear
         * the referenced flag; otherwise the pagedaemon will see references
         * on the page in the inactive queue and reactivate it. Until the 
         * page can move to the cache queue, madvise's job is not done.
         */
        vm_page_flag_clear(m, PG_REFERENCED);
        pmap_clear_reference(m);

        if (m->dirty == 0)
                vm_page_test_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_spin_lock(m);
        _vm_page_deactivate_locked(m, head);
        vm_page_spin_unlock(m);
}

/*
 * These routines manipulate the 'soft busy' count for a page.  A soft busy
 * is almost like PG_BUSY except that it allows certain compatible operations
 * to occur on the page while it is busy.  For example, a page undergoing a
 * write can still be mapped read-only.
 *
 * Because vm_pages can overlap buffers m->busy can be > 1.  m->busy is only
 * adjusted while the vm_page is PG_BUSY so the flash will occur when the
 * busy bit is cleared.
 */
void
vm_page_io_start(vm_page_t m)
{
        KASSERT(m->flags & PG_BUSY, ("vm_page_io_start: page not busy!!!"));
        atomic_add_char(&m->busy, 1);
        vm_page_flag_set(m, PG_SBUSY);
}

void
vm_page_io_finish(vm_page_t m)
{
        KASSERT(m->flags & PG_BUSY, ("vm_page_io_finish: page not busy!!!"));
        atomic_subtract_char(&m->busy, 1);
        if (m->busy == 0)
                vm_page_flag_clear(m, PG_SBUSY);
}

/*
 * Grab a page, blocking if it is busy and allocating a page if necessary.
 * A busy page is returned or NULL.  The page may or may not be valid and
 * might not be on a queue (the caller is responsible for the disposition of
 * the page).
 *
 * If VM_ALLOC_ZERO is specified and the grab must allocate a new page, the
 * page will be zero'd and marked valid.
 *
 * If VM_ALLOC_FORCE_ZERO is specified the page will be zero'd and marked
 * valid even if it already exists.
 *
 * If VM_ALLOC_RETRY is specified this routine will never return NULL.  Also
 * note that VM_ALLOC_NORMAL must be specified if VM_ALLOC_RETRY is specified.
 *
 * This routine may block, but if VM_ALLOC_RETRY is not set then NULL is
 * always returned if we had blocked.  
 *
 * This routine may not be called from an interrupt.
 *
 * PG_ZERO is *ALWAYS* cleared by this routine.
 *
 * No other requirements.
 */
vm_page_t
vm_page_grab(vm_object_t object, vm_pindex_t pindex, int allocflags)
{
        vm_page_t m;
        int error;

        KKASSERT(allocflags &
                (VM_ALLOC_NORMAL|VM_ALLOC_INTERRUPT|VM_ALLOC_SYSTEM));
        vm_object_hold(object);
        for (;;) {
                m = vm_page_lookup_busy_try(object, pindex, TRUE, &error);
                if (error) {
                        vm_page_sleep_busy(m, TRUE, "pgrbwt");
                        if ((allocflags & VM_ALLOC_RETRY) == 0) {
                                m = NULL;
                                break;
                        }
                        /* retry */
                } else if (m == NULL) {
                        m = vm_page_alloc(object, pindex,
                                          allocflags & ~VM_ALLOC_RETRY);
                        if (m)
                                break;
                        vm_wait(0);
                        if ((allocflags & VM_ALLOC_RETRY) == 0)
                                goto failed;
                } else {
                        /* m found */
                        break;
                }
        }

        /*
         * If VM_ALLOC_ZERO an invalid page will be zero'd and set valid.
         *
         * If VM_ALLOC_FORCE_ZERO the page is unconditionally zero'd and set
         * valid even if already valid.
         */
        if (m->valid == 0) {
                if (allocflags & (VM_ALLOC_ZERO | VM_ALLOC_FORCE_ZERO)) {
                        if ((m->flags & PG_ZERO) == 0)
                                pmap_zero_page(VM_PAGE_TO_PHYS(m));
                        m->valid = VM_PAGE_BITS_ALL;
                }
        } else if (allocflags & VM_ALLOC_FORCE_ZERO) {
                pmap_zero_page(VM_PAGE_TO_PHYS(m));
                m->valid = VM_PAGE_BITS_ALL;
        }
        vm_page_flag_clear(m, PG_ZERO);
failed:
        vm_object_drop(object);
        return(m);
}

/*
 * Mapping function for valid bits or for dirty bits in
 * a page.  May not block.
 *
 * Inputs are required to range within a page.
 *
 * No requirements.
 * Non blocking.
 */
int
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 ((2 << last_bit) - (1 << first_bit));
}

/*
 * 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.
 *
 * NOTE: When truncating a buffer vnode_pager_setsize() will automatically
 *       align base to DEV_BSIZE so as not to mark clean a partially
 *       truncated device block.  Otherwise the dirty page status might be
 *       lost.
 *
 * This routine may not block.
 *
 * (base + size) must be less then or equal to PAGE_SIZE.
 */
static void
_vm_page_zero_valid(vm_page_t m, int base, int size)
{
        int frag;
        int endoff;

        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(
                    VM_PAGE_TO_PHYS(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(
                    VM_PAGE_TO_PHYS(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 PG_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.
 *
 * Page must be busied?
 * No other requirements.
 */
void
vm_page_set_valid(vm_page_t m, int base, int size)
{
        _vm_page_zero_valid(m, base, size);
        m->valid |= vm_page_bits(base, size);
}


/*
 * Set valid bits and clear dirty bits.
 *
 * NOTE: This function does not clear the pmap modified bit.
 *       Also note that e.g. NFS may use a byte-granular base
 *       and size.
 *
 * WARNING: Page must be busied?  But vfs_clean_one_page() will call
 *          this without necessarily busying the page (via bdwrite()).
 *          So for now vm_token must also be held.
 *
 * No other requirements.
 */
void
vm_page_set_validclean(vm_page_t m, int base, int size)
{
        int pagebits;

        _vm_page_zero_valid(m, base, size);
        pagebits = vm_page_bits(base, size);
        m->valid |= pagebits;
        m->dirty &= ~pagebits;
        if (base == 0 && size == PAGE_SIZE) {
                /*pmap_clear_modify(m);*/
                vm_page_flag_clear(m, PG_NOSYNC);
        }
}

/*
 * Set valid & dirty.  Used by buwrite()
 *
 * WARNING: Page must be busied?  But vfs_dirty_one_page() will
 *          call this function in buwrite() so for now vm_token must
 *          be held.
 *
 * No other requirements.
 */
void
vm_page_set_validdirty(vm_page_t m, int base, int size)
{
        int pagebits;

        pagebits = vm_page_bits(base, size);
        m->valid |= pagebits;
        m->dirty |= pagebits;
        if (m->object)
                vm_object_set_writeable_dirty(m->object);
}

/*
 * Clear dirty bits.
 *
 * NOTE: This function does not clear the pmap modified bit.
 *       Also note that e.g. NFS may use a byte-granular base
 *       and size.
 *
 * Page must be busied?
 * No other requirements.
 */
void
vm_page_clear_dirty(vm_page_t m, int base, int size)
{
        m->dirty &= ~vm_page_bits(base, size);
        if (base == 0 && size == PAGE_SIZE) {
                /*pmap_clear_modify(m);*/
                vm_page_flag_clear(m, PG_NOSYNC);
        }
}

/*
 * Make the page all-dirty.
 *
 * Also make sure the related object and vnode reflect the fact that the
 * object may now contain a dirty page.
 *
 * Page must be busied?
 * No other requirements.
 */
void
vm_page_dirty(vm_page_t m)
{
#ifdef INVARIANTS
        int pqtype = m->queue - m->pc;
#endif
        KASSERT(pqtype != PQ_CACHE && pqtype != PQ_FREE,
                ("vm_page_dirty: page in free/cache queue!"));
        if (m->dirty != VM_PAGE_BITS_ALL) {
                m->dirty = VM_PAGE_BITS_ALL;
                if (m->object)
                        vm_object_set_writeable_dirty(m->object);
        }
}

/*
 * Invalidates DEV_BSIZE'd chunks within a page.  Both the
 * valid and dirty bits for the effected areas are cleared.
 *
 * Page must be busied?
 * Does not block.
 * No other requirements.
 */
void
vm_page_set_invalid(vm_page_t m, int base, int size)
{
        int bits;

        bits = vm_page_bits(base, size);
        m->valid &= ~bits;
        m->dirty &= ~bits;
        m->object->generation++;
}

/*
 * 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.
 *
 * Page must be busied?
 * No other requirements.
 */
void
vm_page_zero_invalid(vm_page_t m, boolean_t setvalid)
{
        int b;
        int i;

        /*
         * 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 & (1 << i))
                ) {
                        if (i > b) {
                                pmap_zero_page_area(
                                    VM_PAGE_TO_PHYS(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 consistency
         * 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;
}

/*
 * Is a (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.
 *
 * Does not block.
 * No other requirements.
 */
int
vm_page_is_valid(vm_page_t m, int base, int size)
{
        int bits = vm_page_bits(base, size);

        if (m->valid && ((m->valid & bits) == bits))
                return 1;
        else
                return 0;
}

/*
 * update dirty bits from pmap/mmu.  May not block.
 *
 * Caller must hold the page busy
 */
void
vm_page_test_dirty(vm_page_t m)
{
        if ((m->dirty != VM_PAGE_BITS_ALL) && pmap_is_modified(m)) {
                vm_page_dirty(m);
        }
}

/*
 * Register an action, associating it with its vm_page
 */
void
vm_page_register_action(vm_page_action_t action, vm_page_event_t event)
{
        struct vm_page_action_list *list;
        int hv;

        hv = (int)((intptr_t)action->m >> 8) & VMACTION_HMASK;
        list = &action_list[hv];

        lwkt_gettoken(&vm_token);
        vm_page_flag_set(action->m, PG_ACTIONLIST);
        action->event = event;
        LIST_INSERT_HEAD(list, action, entry);
        lwkt_reltoken(&vm_token);
}

/*
 * Unregister an action, disassociating it from its related vm_page
 */
void
vm_page_unregister_action(vm_page_action_t action)
{
        struct vm_page_action_list *list;
        int hv;

        lwkt_gettoken(&vm_token);
        if (action->event != VMEVENT_NONE) {
                action->event = VMEVENT_NONE;
                LIST_REMOVE(action, entry);

                hv = (int)((intptr_t)action->m >> 8) & VMACTION_HMASK;
                list = &action_list[hv];
                if (LIST_EMPTY(list))
                        vm_page_flag_clear(action->m, PG_ACTIONLIST);
        }
        lwkt_reltoken(&vm_token);
}

/*
 * Issue an event on a VM page.  Corresponding action structures are
 * removed from the page's list and called.
 *
 * If the vm_page has no more pending action events we clear its
 * PG_ACTIONLIST flag.
 */
void
vm_page_event_internal(vm_page_t m, vm_page_event_t event)
{
        struct vm_page_action_list *list;
        struct vm_page_action *scan;
        struct vm_page_action *next;
        int hv;
        int all;

        hv = (int)((intptr_t)m >> 8) & VMACTION_HMASK;
        list = &action_list[hv];
        all = 1;

        lwkt_gettoken(&vm_token);
        LIST_FOREACH_MUTABLE(scan, list, entry, next) {
                if (scan->m == m) {
                        if (scan->event == event) {
                                scan->event = VMEVENT_NONE;
                                LIST_REMOVE(scan, entry);
                                scan->func(m, scan);
                                /* XXX */
                        } else {
                                all = 0;
                        }
                }
        }
        if (all)
                vm_page_flag_clear(m, PG_ACTIONLIST);
        lwkt_reltoken(&vm_token);
}

#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("vmstats.v_free_count: %d\n", vmstats.v_free_count);
        db_printf("vmstats.v_cache_count: %d\n", vmstats.v_cache_count);
        db_printf("vmstats.v_inactive_count: %d\n", vmstats.v_inactive_count);
        db_printf("vmstats.v_active_count: %d\n", vmstats.v_active_count);
        db_printf("vmstats.v_wire_count: %d\n", vmstats.v_wire_count);
        db_printf("vmstats.v_free_reserved: %d\n", vmstats.v_free_reserved);
        db_printf("vmstats.v_free_min: %d\n", vmstats.v_free_min);
        db_printf("vmstats.v_free_target: %d\n", vmstats.v_free_target);
        db_printf("vmstats.v_cache_min: %d\n", vmstats.v_cache_min);
        db_printf("vmstats.v_inactive_target: %d\n", vmstats.v_inactive_target);
}

DB_SHOW_COMMAND(pageq, vm_page_print_pageq_info)
{
        int i;
        db_printf("PQ_FREE:");
        for(i=0;i<PQ_L2_SIZE;i++) {
                db_printf(" %d", vm_page_queues[PQ_FREE + i].lcnt);
        }
        db_printf("\n");
                
        db_printf("PQ_CACHE:");
        for(i=0;i<PQ_L2_SIZE;i++) {
                db_printf(" %d", vm_page_queues[PQ_CACHE + i].lcnt);
        }
        db_printf("\n");

        db_printf("PQ_ACTIVE:");
        for(i=0;i<PQ_L2_SIZE;i++) {
                db_printf(" %d", vm_page_queues[PQ_ACTIVE + i].lcnt);
        }
        db_printf("\n");

        db_printf("PQ_INACTIVE:");
        for(i=0;i<PQ_L2_SIZE;i++) {
                db_printf(" %d", vm_page_queues[PQ_INACTIVE + i].lcnt);
        }
        db_printf("\n");
}
#endif /* DDB */