Remove unnecessary locking of Giant around nanotime() in clock_gettime().

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

/*
 * 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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 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
 * $FreeBSD$
 */

/*
 * 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 pageq mutex is required when adding or removing a page from a
 *        page queue (vm_page_queue[]), regardless of other mutexes or the
 *        busy state of a page.
 *
 *      - a hash chain mutex is required when associating or disassociating
 *        a page from the VM PAGE CACHE hash table (vm_page_buckets),
 *        regardless of other mutexes or the busy state of a page.
 *
 *      - either a hash chain mutex OR a busied page is required in order
 *        to modify the page flags.  A hash chain mutex must be obtained in
 *        order to busy a page.  A page's flags cannot be modified by a
 *        hash chain mutex if the page is marked busy.
 *
 *      - The object memq mutex is held when inserting or removing
 *        pages from an object (vm_page_insert() or vm_page_remove()).  This
 *        is different from the object's main mutex.
 *
 *      Generally speaking, you have to be aware of side effects when running
 *      vm_page ops.  A vm_page_lookup() will return with the hash chain
 *      locked, whether it was able to lookup the page or not.  vm_page_free(),
 *      vm_page_cache(), vm_page_activate(), and a number of other routines
 *      will release the hash chain mutex for you.  Intermediate manipulation
 *      routines such as vm_page_flag_set() expect the hash chain to be held
 *      on entry and the hash chain will remain held on return.
 *
 *      pageq scanning can only occur with the pageq in question locked.
 *      We have a known bottleneck with the active queue, but the cache
 *      and free queues are actually arrays already. 
 */

/*
 *      Resident memory management module.
 */

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

#include <vm/vm.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_extern.h>
#include <vm/uma.h>
#include <vm/uma_int.h>

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

struct mtx vm_page_queue_mtx;
struct mtx vm_page_queue_free_mtx;

vm_page_t vm_page_array = 0;
int vm_page_array_size = 0;
long first_page = 0;
int vm_page_zero_count = 0;

/*
 *      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_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 starta, vm_offset_t enda, vm_offset_t vaddr)
{
        vm_offset_t mapped;
        vm_size_t npages, page_range;
        vm_offset_t new_end;
        int i;
        vm_offset_t pa;
        int nblocks;
        vm_offset_t last_pa;

        /* the biggest memory array is the second group of pages */
        vm_offset_t end;
        vm_offset_t biggestone, biggestsize;

        vm_offset_t total;
        vm_size_t bootpages;

        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_page(phys_avail[i]);
                phys_avail[i + 1] = trunc_page(phys_avail[i + 1]);
        }

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

                if (size > biggestsize) {
                        biggestone = i;
                        biggestsize = size;
                }
                ++nblocks;
                total += size;
        }

        end = phys_avail[biggestone+1];

        /*
         * Initialize the locks.
         */
        mtx_init(&vm_page_queue_mtx, "vm page queue mutex", NULL, MTX_DEF);
        mtx_init(&vm_page_queue_free_mtx, "vm page queue free mutex", NULL,
           MTX_SPIN);

        /*
         * Initialize the queue headers for the free queue, the active queue
         * and the inactive queue.
         */
        vm_pageq_init();

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

        /*
         * 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)) -
            (end - new_end)) / PAGE_SIZE;
        end = new_end;

        /*
         * 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;

        /*
         * 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 descending 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.
         */
        cnt.v_page_count = 0;
        cnt.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_pageq_add_new_page(pa);
                        pa += PAGE_SIZE;
                }
        }
        return (vaddr);
}

void
vm_page_flag_set(vm_page_t m, unsigned short bits)
{

        mtx_assert(&vm_page_queue_mtx, MA_OWNED);
        m->flags |= bits;
} 

void
vm_page_flag_clear(vm_page_t m, unsigned short bits)
{

        mtx_assert(&vm_page_queue_mtx, MA_OWNED);
        m->flags &= ~bits;
}

void
vm_page_busy(vm_page_t m)
{
        KASSERT((m->flags & PG_BUSY) == 0,
            ("vm_page_busy: page already busy!!!"));
        vm_page_flag_set(m, PG_BUSY);
}

/*
 *      vm_page_flash:
 *
 *      wakeup anyone waiting for the page.
 */
void
vm_page_flash(vm_page_t m)
{
        if (m->flags & PG_WANTED) {
                vm_page_flag_clear(m, PG_WANTED);
                wakeup(m);
        }
}

/*
 *      vm_page_wakeup:
 *
 *      clear the PG_BUSY flag and wakeup anyone waiting for the
 *      page.
 *
 */
void
vm_page_wakeup(vm_page_t m)
{
        KASSERT(m->flags & PG_BUSY, ("vm_page_wakeup: page not busy!!!"));
        vm_page_flag_clear(m, PG_BUSY);
        vm_page_flash(m);
}

/*
 *
 *
 */
void
vm_page_io_start(vm_page_t m)
{

        mtx_assert(&vm_page_queue_mtx, MA_OWNED);
        m->busy++;
}

void
vm_page_io_finish(vm_page_t m)
{

        mtx_assert(&vm_page_queue_mtx, MA_OWNED);
        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)
{
        GIANT_REQUIRED;
        mem->hold_count++;
}

void
vm_page_unhold(vm_page_t mem)
{

        mtx_assert(&vm_page_queue_mtx, MA_OWNED);
        --mem->hold_count;
        KASSERT(mem->hold_count >= 0, ("vm_page_unhold: hold count < 0!!!"));
        if (mem->hold_count == 0 && mem->queue == PQ_HOLD)
                vm_page_free_toq(mem);
}

/*
 *      vm_page_copy:
 *
 *      Copy one page to another
 */
void
vm_page_copy(vm_page_t src_m, vm_page_t dest_m)
{
        pmap_copy_page(src_m, dest_m);
        dest_m->valid = VM_PAGE_BITS_ALL;
}

/*
 *      vm_page_free:
 *
 *      Free a page
 *
 *      The clearing of PG_ZERO is a temporary safety until the code can be
 *      reviewed to determine that PG_ZERO is being properly cleared on
 *      write faults or maps.  PG_ZERO was previously cleared in
 *      vm_page_alloc().
 */
void
vm_page_free(vm_page_t m)
{
        vm_page_flag_clear(m, PG_ZERO);
        vm_page_free_toq(m);
        vm_page_zero_idle_wakeup();
}

/*
 *      vm_page_free_zero:
 *
 *      Free a page to the zerod-pages queue
 */
void
vm_page_free_zero(vm_page_t m)
{
        vm_page_flag_set(m, PG_ZERO);
        vm_page_free_toq(m);
}

/*
 *      vm_page_sleep_if_busy:
 *
 *      Sleep and release the page queues lock if PG_BUSY is set or,
 *      if also_m_busy is TRUE, busy is non-zero.  Returns TRUE if the
 *      thread slept and the page queues lock was released.
 *      Otherwise, retains the page queues lock and returns FALSE.
 */
int
vm_page_sleep_if_busy(vm_page_t m, int also_m_busy, const char *msg)
{

        mtx_assert(&vm_page_queue_mtx, MA_OWNED);
        if ((m->flags & PG_BUSY) || (also_m_busy && m->busy)) {
                vm_page_flag_set(m, PG_WANTED | PG_REFERENCED);
                msleep(m, &vm_page_queue_mtx, PDROP | PVM, msg, 0);
                return (TRUE);
        }
        return (FALSE);
}

/*
 *      vm_page_dirty:
 *
 *      make page all dirty
 */
void
vm_page_dirty(vm_page_t m)
{
        KASSERT(m->queue - m->pc != PQ_CACHE,
            ("vm_page_dirty: page in cache!"));
        m->dirty = VM_PAGE_BITS_ALL;
}

/*
 *      vm_page_splay:
 *
 *      Implements Sleator and Tarjan's top-down splay algorithm.  Returns
 *      the vm_page containing the given pindex.  If, however, that
 *      pindex is not found in the vm_object, returns a vm_page that is
 *      adjacent to the pindex, coming before or after it.
 */
vm_page_t
vm_page_splay(vm_pindex_t pindex, vm_page_t root)
{
        struct vm_page dummy;
        vm_page_t lefttreemax, righttreemin, y;

        if (root == NULL)
                return (root);
        lefttreemax = righttreemin = &dummy;
        for (;; root = y) {
                if (pindex < root->pindex) {
                        if ((y = root->left) == NULL)
                                break;
                        if (pindex < y->pindex) {
                                /* Rotate right. */
                                root->left = y->right;
                                y->right = root;
                                root = y;
                                if ((y = root->left) == NULL)
                                        break;
                        }
                        /* Link into the new root's right tree. */
                        righttreemin->left = root;
                        righttreemin = root;
                } else if (pindex > root->pindex) {
                        if ((y = root->right) == NULL)
                                break;
                        if (pindex > y->pindex) {
                                /* Rotate left. */
                                root->right = y->left;
                                y->left = root;
                                root = y;
                                if ((y = root->right) == NULL)
                                        break;
                        }
                        /* Link into the new root's left tree. */
                        lefttreemax->right = root;
                        lefttreemax = root;
                } else
                        break;
        }
        /* Assemble the new root. */
        lefttreemax->right = root->left;
        righttreemin->left = root->right;
        root->left = dummy.right;
        root->right = dummy.left;
        return (root);
}

/*
 *      vm_page_insert:         [ internal use only ]
 *
 *      Inserts the given mem entry 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.
 *
 *      The object and page must be locked, and must be splhigh.
 *      This routine may not block.
 */
void
vm_page_insert(vm_page_t m, vm_object_t object, vm_pindex_t pindex)
{
        vm_page_t root;

        if (m->object != NULL)
                panic("vm_page_insert: already inserted");

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

        mtx_assert(object == kmem_object ? &object->mtx : &Giant, MA_OWNED);
        /*
         * Now link into the object's ordered list of backed pages.
         */
        root = object->root;
        if (root == NULL) {
                m->left = NULL;
                m->right = NULL;
                TAILQ_INSERT_TAIL(&object->memq, m, listq);
        } else {
                root = vm_page_splay(pindex, root);
                if (pindex < root->pindex) {
                        m->left = root->left;
                        m->right = root;
                        root->left = NULL;
                        TAILQ_INSERT_BEFORE(root, m, listq);
                } else {
                        m->right = root->right;
                        m->left = root;
                        root->right = NULL;
                        TAILQ_INSERT_AFTER(&object->memq, root, m, listq);
                }
        }
        object->root = m;
        object->generation++;

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

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

/*
 *      vm_page_remove:
 *                              NOTE: used by device pager as well -wfj
 *
 *      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 and page must be locked, and at splhigh.
 *      The underlying pmap entry (if any) is NOT removed here.
 *      This routine may not block.
 */
void
vm_page_remove(vm_page_t m)
{
        vm_object_t object;
        vm_page_t root;

        GIANT_REQUIRED;
        mtx_assert(&vm_page_queue_mtx, MA_OWNED);
        if (m->object == NULL)
                return;

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

        /*
         * Basically destroy the page.
         */
        vm_page_wakeup(m);

        object = m->object;

        /*
         * Now remove from the object's list of backed pages.
         */
        if (m != object->root)
                vm_page_splay(m->pindex, object->root);
        if (m->left == NULL)
                root = m->right;
        else {
                root = vm_page_splay(m->pindex, m->left);
                root->right = m->right;
        }
        object->root = root;
        TAILQ_REMOVE(&object->memq, m, listq);

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

        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.
 *      This routine may not block.
 *      This is a critical path routine
 */
vm_page_t
vm_page_lookup(vm_object_t object, vm_pindex_t pindex)
{
        vm_page_t m;

        mtx_assert(object == kmem_object ? &object->mtx : &Giant, MA_OWNED);
        m = vm_page_splay(pindex, object->root);
        if ((object->root = m) != NULL && m->pindex != pindex)
                m = NULL;
        return (m);
}

/*
 *      vm_page_rename:
 *
 *      Move the given memory entry from its
 *      current object to the specified target object/offset.
 *
 *      The object must be locked.
 *      This routine may not block.
 *
 *      Note: this routine will raise itself to splvm(), the caller need not. 
 *
 *      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)
{
        int s;

        s = splvm();
        vm_page_remove(m);
        vm_page_insert(m, new_object, new_pindex);
        if (m->queue - m->pc == PQ_CACHE)
                vm_page_deactivate(m);
        vm_page_dirty(m);
        splx(s);
}

/*
 *      vm_page_select_cache:
 *
 *      Find a page on the cache queue with color optimization.  As pages
 *      might be found, but not applicable, they are deactivated.  This
 *      keeps us from using potentially busy cached pages.
 *
 *      This routine must be called at splvm().
 *      This routine may not block.
 */
static vm_page_t
vm_page_select_cache(vm_pindex_t color)
{
        vm_page_t m;

        mtx_assert(&vm_page_queue_mtx, MA_OWNED);
        while (TRUE) {
                m = vm_pageq_find(PQ_CACHE, color & PQ_L2_MASK, FALSE);
                if (m && ((m->flags & (PG_BUSY|PG_UNMANAGED)) || m->busy ||
                               m->hold_count || m->wire_count)) {
                        vm_page_deactivate(m);
                        continue;
                }
                return m;
        }
}

/*
 *      vm_page_select_free:
 *
 *      Find a free or zero page, with specified preference. 
 *
 *      This routine must be called at splvm().
 *      This routine may not block.
 */
static __inline vm_page_t
vm_page_select_free(vm_pindex_t color, boolean_t prefer_zero)
{
        vm_page_t m;

        m = vm_pageq_find(PQ_FREE, color & PQ_L2_MASK, prefer_zero);
        return (m);
}

/*
 *      vm_page_alloc:
 *
 *      Allocate and return a memory cell associated
 *      with this VM object/offset pair.
 *
 *      page_req classes:
 *      VM_ALLOC_NORMAL         normal process request
 *      VM_ALLOC_SYSTEM         system *really* needs a page
 *      VM_ALLOC_INTERRUPT      interrupt time request
 *      VM_ALLOC_ZERO           zero page
 *
 *      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 req)
{
        vm_page_t m = NULL;
        vm_pindex_t color;
        int flags, page_req, s;

        page_req = req & VM_ALLOC_CLASS_MASK;

        if ((req & VM_ALLOC_NOOBJ) == 0) {
                KASSERT(object != NULL,
                    ("vm_page_alloc: NULL object."));
                mtx_assert(object == kmem_object ? &object->mtx : &Giant,
                    MA_OWNED);
                KASSERT(!vm_page_lookup(object, pindex),
                    ("vm_page_alloc: page already allocated"));
                color = pindex + object->pg_color;
        } else
                color = pindex;

        /*
         * The pager is allowed to eat deeper into the free page list.
         */
        if ((curproc == pageproc) && (page_req != VM_ALLOC_INTERRUPT)) {
                page_req = VM_ALLOC_SYSTEM;
        };

        s = splvm();
loop:
        mtx_lock_spin(&vm_page_queue_free_mtx);
        if (cnt.v_free_count > cnt.v_free_reserved ||
            (page_req == VM_ALLOC_SYSTEM && 
             cnt.v_cache_count == 0 && 
             cnt.v_free_count > cnt.v_interrupt_free_min) ||
            (page_req == VM_ALLOC_INTERRUPT && cnt.v_free_count > 0)) {
                /*
                 * Allocate from the free queue if the number of free pages
                 * exceeds the minimum for the request class.
                 */
                m = vm_page_select_free(color, (req & VM_ALLOC_ZERO) != 0);
        } else if (page_req != VM_ALLOC_INTERRUPT) {
                mtx_unlock_spin(&vm_page_queue_free_mtx);
                /*
                 * Allocatable from cache (non-interrupt only).  On success,
                 * we must free the page and try again, thus ensuring that
                 * cnt.v_*_free_min counters are replenished.
                 */
                vm_page_lock_queues();
                if ((m = vm_page_select_cache(color)) == NULL) {
                        vm_page_unlock_queues();
                        splx(s);
#if defined(DIAGNOSTIC)
                        if (cnt.v_cache_count > 0)
                                printf("vm_page_alloc(NORMAL): missing pages on cache queue: %d\n", cnt.v_cache_count);
#endif
                        atomic_add_int(&vm_pageout_deficit, 1);
                        pagedaemon_wakeup();
                        return (NULL);
                }
                KASSERT(m->dirty == 0, ("Found dirty cache page %p", m));
                vm_page_busy(m);
                pmap_remove_all(m);
                vm_page_free(m);
                vm_page_unlock_queues();
                goto loop;
        } else {
                /*
                 * Not allocatable from cache from interrupt, give up.
                 */
                mtx_unlock_spin(&vm_page_queue_free_mtx);
                splx(s);
                atomic_add_int(&vm_pageout_deficit, 1);
                pagedaemon_wakeup();
                return (NULL);
        }

        /*
         *  At this point we had better have found a good page.
         */

        KASSERT(
            m != NULL,
            ("vm_page_alloc(): missing page on free queue\n")
        );

        /*
         * Remove from free queue
         */

        vm_pageq_remove_nowakeup(m);

        /*
         * Initialize structure.  Only the PG_ZERO flag is inherited.
         */
        flags = PG_BUSY;
        if (m->flags & PG_ZERO) {
                vm_page_zero_count--;
                if (req & VM_ALLOC_ZERO)
                        flags = PG_ZERO | PG_BUSY;
        }
        m->flags = flags;
        if (req & VM_ALLOC_WIRED) {
                atomic_add_int(&cnt.v_wire_count, 1);
                m->wire_count = 1;
        } else
                m->wire_count = 0;
        m->hold_count = 0;
        m->act_count = 0;
        m->busy = 0;
        m->valid = 0;
        KASSERT(m->dirty == 0, ("vm_page_alloc: free/cache page %p was dirty", m));
        mtx_unlock_spin(&vm_page_queue_free_mtx);

        /*
         * vm_page_insert() is safe prior to the splx().  Note also that
         * inserting a page here does not insert it into the pmap (which
         * could cause us to block allocating memory).  We cannot block 
         * anywhere.
         */
        if ((req & VM_ALLOC_NOOBJ) == 0)
                vm_page_insert(m, object, pindex);

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

        splx(s);
        return (m);
}

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

        s = splvm();
        if (curproc == pageproc) {
                vm_pageout_pages_needed = 1;
                tsleep(&vm_pageout_pages_needed, PSWP, "VMWait", 0);
        } else {
                if (!vm_pages_needed) {
                        vm_pages_needed = 1;
                        wakeup(&vm_pages_needed);
                }
                tsleep(&cnt.v_free_count, PVM, "vmwait", 0);
        }
        splx(s);
}

/*
 *      vm_waitpfault:  (also see VM_WAITPFAULT macro)
 *
 *      Block 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)
{
        int s;

        s = splvm();
        if (!vm_pages_needed) {
                vm_pages_needed = 1;
                wakeup(&vm_pages_needed);
        }
        tsleep(&cnt.v_free_count, PUSER, "pfault", 0);
        splx(s);
}

/*
 *      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 queues must be locked.
 *      This routine may not block.
 */
void
vm_page_activate(vm_page_t m)
{
        int s;

        mtx_assert(&vm_page_queue_mtx, MA_OWNED);
        s = splvm();
        if (m->queue != PQ_ACTIVE) {
                if ((m->queue - m->pc) == PQ_CACHE)
                        cnt.v_reactivated++;
                vm_pageq_remove(m);
                if (m->wire_count == 0 && (m->flags & PG_UNMANAGED) == 0) {
                        if (m->act_count < ACT_INIT)
                                m->act_count = ACT_INIT;
                        vm_pageq_enqueue(PQ_ACTIVE, m);
                }
        } else {
                if (m->act_count < ACT_INIT)
                        m->act_count = ACT_INIT;
        }
        splx(s);
}

/*
 *      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.
 *
 *      This routine may not block.
 *      This routine must be called at splvm()
 */
static __inline void
vm_page_free_wakeup(void)
{
        /*
         * 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 PQ_FREE list,
 *      disassociating it with any VM object.
 *
 *      Object and page must be locked prior to entry.
 *      This routine may not block.
 */

void
vm_page_free_toq(vm_page_t m)
{
        int s;
        struct vpgqueues *pq;
        vm_object_t object = m->object;

        GIANT_REQUIRED;
        mtx_assert(&vm_page_queue_mtx, MA_OWNED);
        s = splvm();
        cnt.v_tfree++;

        if (m->busy || ((m->queue - m->pc) == PQ_FREE)) {
                printf(
                "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");
        }

        /*
         * 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_pageq_remove_nowakeup(m);
        vm_page_remove(m);

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

        /*
         * If we've exhausted the object's resident pages we want to free
         * it up.
         */
        if (object && 
            (object->type == OBJT_VNODE) &&
            ((object->flags & OBJ_DEAD) == 0)
        ) {
                struct vnode *vp = (struct vnode *)object->handle;

                if (vp) {
                        VI_LOCK(vp);
                        if (VSHOULDFREE(vp))
                                vfree(vp);
                        VI_UNLOCK(vp);
                }
        }

        /*
         * Clear the UNMANAGED flag when freeing an unmanaged page.
         */
        if (m->flags & PG_UNMANAGED) {
                m->flags &= ~PG_UNMANAGED;
        } else {
#ifdef __alpha__
                pmap_page_is_free(m);
#endif
        }

        if (m->hold_count != 0) {
                m->flags &= ~PG_ZERO;
                m->queue = PQ_HOLD;
        } else
                m->queue = PQ_FREE + m->pc;
        pq = &vm_page_queues[m->queue];
        mtx_lock_spin(&vm_page_queue_free_mtx);
        pq->lcnt++;
        ++(*pq->cnt);

        /*
         * Put zero'd pages on the end ( where we look for zero'd pages
         * first ) and non-zerod pages at the head.
         */
        if (m->flags & PG_ZERO) {
                TAILQ_INSERT_TAIL(&pq->pl, m, pageq);
                ++vm_page_zero_count;
        } else {
                TAILQ_INSERT_HEAD(&pq->pl, m, pageq);
        }
        mtx_unlock_spin(&vm_page_queue_free_mtx);
        vm_page_free_wakeup();
        splx(s);
}

/*
 *      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.
 */
void
vm_page_unmanage(vm_page_t m)
{
        int s;

        s = splvm();
        mtx_assert(&vm_page_queue_mtx, MA_OWNED);
        if ((m->flags & PG_UNMANAGED) == 0) {
                if (m->wire_count == 0)
                        vm_pageq_remove(m);
        }
        vm_page_flag_set(m, PG_UNMANAGED);
        splx(s);
}

/*
 *      vm_page_wire:
 *
 *      Mark this page as wired down by yet
 *      another map, removing it from paging queues
 *      as necessary.
 *
 *      The page queues must be locked.
 *      This routine may not block.
 */
void
vm_page_wire(vm_page_t m)
{
        int s;

        /*
         * 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).
         */
        s = splvm();
        mtx_assert(&vm_page_queue_mtx, MA_OWNED);
        if (m->wire_count == 0) {
                if ((m->flags & PG_UNMANAGED) == 0)
                        vm_pageq_remove(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));
        splx(s);
}

/*
 *      vm_page_unwire:
 *
 *      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)
{
        int s;

        s = splvm();
        mtx_assert(&vm_page_queue_mtx, MA_OWNED);
        if (m->wire_count > 0) {
                m->wire_count--;
                if (m->wire_count == 0) {
                        atomic_subtract_int(&cnt.v_wire_count, 1);
                        if (m->flags & PG_UNMANAGED) {
                                ;
                        } else if (activate)
                                vm_pageq_enqueue(PQ_ACTIVE, m);
                        else {
                                vm_page_flag_clear(m, PG_WINATCFLS);
                                vm_pageq_enqueue(PQ_INACTIVE, m);
                        }
                }
        } else {
                panic("vm_page_unwire: invalid wire count: %d\n", m->wire_count);
        }
        splx(s);
}


/*
 * 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.
 *
 * This routine may not block.
 */
static __inline void
_vm_page_deactivate(vm_page_t m, int athead)
{
        int s;

        mtx_assert(&vm_page_queue_mtx, MA_OWNED);
        /*
         * Ignore if already inactive.
         */
        if (m->queue == PQ_INACTIVE)
                return;

        s = splvm();
        if (m->wire_count == 0 && (m->flags & PG_UNMANAGED) == 0) {
                if ((m->queue - m->pc) == PQ_CACHE)
                        cnt.v_reactivated++;
                vm_page_flag_clear(m, PG_WINATCFLS);
                vm_pageq_remove(m);
                if (athead)
                        TAILQ_INSERT_HEAD(&vm_page_queues[PQ_INACTIVE].pl, m, pageq);
                else
                        TAILQ_INSERT_TAIL(&vm_page_queues[PQ_INACTIVE].pl, m, pageq);
                m->queue = PQ_INACTIVE;
                vm_page_queues[PQ_INACTIVE].lcnt++;
                cnt.v_inactive_count++;
        }
        splx(s);
}

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)
{

        mtx_assert(&vm_page_queue_mtx, MA_OWNED);
        if (m->dirty || m->hold_count || m->busy || m->wire_count ||
            (m->flags & (PG_BUSY|PG_UNMANAGED))) {
                return (0);
        }
        vm_page_test_dirty(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)
{

        mtx_assert(&vm_page_queue_mtx, MA_OWNED);
        if (m->dirty || m->hold_count || m->busy || m->wire_count ||
            (m->flags & (PG_BUSY|PG_UNMANAGED))) {
                return (0);
        }
        vm_page_test_dirty(m);
        if (m->dirty)
                return (0);
        vm_page_busy(m);
        pmap_remove_all(m);
        vm_page_free(m);
        return (1);
}

/*
 * vm_page_cache
 *
 * Put the specified page onto the page cache queue (if appropriate).
 *
 * This routine may not block.
 */
void
vm_page_cache(vm_page_t m)
{
        int s;

        mtx_assert(&vm_page_queue_mtx, MA_OWNED);
        if ((m->flags & (PG_BUSY|PG_UNMANAGED)) || m->busy || m->wire_count) {
                printf("vm_page_cache: attempting to cache busy page\n");
                return;
        }
        if ((m->queue - m->pc) == PQ_CACHE)
                return;

        /*
         * Remove all pmaps and indicate that the page is not
         * writeable or mapped.
         */
        pmap_remove_all(m);
        if (m->dirty != 0) {
                panic("vm_page_cache: caching a dirty page, pindex: %ld",
                        (long)m->pindex);
        }
        s = splvm();
        vm_pageq_remove_nowakeup(m);
        vm_pageq_enqueue(PQ_CACHE + m->pc, m);
        vm_page_free_wakeup();
        splx(s);
}

/*
 * 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.
 */
void
vm_page_dontneed(vm_page_t m)
{
        static int dnweight;
        int dnw;
        int head;

        mtx_assert(&vm_page_queue_mtx, MA_OWNED);
        dnw = ++dnweight;

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

        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_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, allocate it.
 *
 * This routine may block.
 */
vm_page_t
vm_page_grab(vm_object_t object, vm_pindex_t pindex, int allocflags)
{
        vm_page_t m;
        int s, generation;

        GIANT_REQUIRED;
retrylookup:
        if ((m = vm_page_lookup(object, pindex)) != NULL) {
                vm_page_lock_queues();
                if (m->busy || (m->flags & PG_BUSY)) {
                        generation = object->generation;

                        s = splvm();
                        while ((object->generation == generation) &&
                                        (m->busy || (m->flags & PG_BUSY))) {
                                vm_page_flag_set(m, PG_WANTED | PG_REFERENCED);
                                msleep(m, &vm_page_queue_mtx, PVM, "pgrbwt", 0);
                                if ((allocflags & VM_ALLOC_RETRY) == 0) {
                                        vm_page_unlock_queues();
                                        splx(s);
                                        return NULL;
                                }
                        }
                        vm_page_unlock_queues();
                        splx(s);
                        goto retrylookup;
                } else {
                        if (allocflags & VM_ALLOC_WIRED)
                                vm_page_wire(m);
                        vm_page_busy(m);
                        vm_page_unlock_queues();
                        return m;
                }
        }

        m = vm_page_alloc(object, pindex, allocflags & ~VM_ALLOC_RETRY);
        if (m == NULL) {
                VM_WAIT;
                if ((allocflags & VM_ALLOC_RETRY) == 0)
                        return NULL;
                goto retrylookup;
        }

        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.
 */
__inline 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));
}

/*
 *      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.
 *
 *      This routine may not block.
 *
 *      (base + size) must be less then or equal to PAGE_SIZE.
 */
void
vm_page_set_validclean(vm_page_t m, int base, int size)
{
        int pagebits;
        int frag;
        int endoff;

        mtx_assert(&vm_page_queue_mtx, MA_OWNED);
        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)));

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

#if 0

void
vm_page_set_dirty(vm_page_t m, int base, int size)
{
        m->dirty |= vm_page_bits(base, size);
}

#endif

void
vm_page_clear_dirty(vm_page_t m, int base, int size)
{
        GIANT_REQUIRED;
        m->dirty &= ~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.
 *
 *      May not block.
 */
void
vm_page_set_invalid(vm_page_t m, int base, int size)
{
        int bits;

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

/*
 * 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;

        /*
         * 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(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.
 *
 *      May not block.
 */
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.
 */
void
vm_page_test_dirty(vm_page_t m)
{
        if ((m->dirty != VM_PAGE_BITS_ALL) && pmap_is_modified(m)) {
                vm_page_dirty(m);
        }
}

int so_zerocp_fullpage = 0;

void
vm_page_cowfault(vm_page_t m)
{
        vm_page_t mnew;
        vm_object_t object;
        vm_pindex_t pindex;

        object = m->object;
        pindex = m->pindex;
        vm_page_busy(m);

 retry_alloc:
        vm_page_remove(m);
        /*
         * An interrupt allocation is requested because the page
         * queues lock is held. 
         */
        mnew = vm_page_alloc(object, pindex, VM_ALLOC_INTERRUPT);
        if (mnew == NULL) {
                vm_page_insert(m, object, pindex);
                vm_page_unlock_queues();
                VM_WAIT;
                vm_page_lock_queues();
                goto retry_alloc;
        }

        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_busy(mnew);
                vm_page_free(mnew);
                vm_page_insert(m, object, pindex);
        } else { /* clear COW & copy page */
                if (so_zerocp_fullpage) {
                        mnew->valid = VM_PAGE_BITS_ALL;
                } else {
                        vm_page_copy(m, mnew);
                }
                vm_page_dirty(mnew);
                vm_page_flag_clear(mnew, PG_BUSY);
        }
}

void 
vm_page_cowclear(vm_page_t m)
{

        mtx_assert(&vm_page_queue_mtx, 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
         */ 
}

void
vm_page_cowsetup(vm_page_t m)
{

        mtx_assert(&vm_page_queue_mtx, MA_OWNED);
        m->cow++;
        pmap_page_protect(m, VM_PROT_READ);
}

#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)
{
        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: %d, PQ_INACTIVE: %d\n",
                vm_page_queues[PQ_ACTIVE].lcnt,
                vm_page_queues[PQ_INACTIVE].lcnt);
}
#endif /* DDB */