kernel - Fix longstanding VM long-duration stall issues (2)

[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.
 * 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: src/sys/vm/vm_page.c,v 1.147.2.18 2002/03/10 05:03:19 alc Exp $
 * $DragonFly: src/sys/vm/vm_page.c,v 1.40 2008/08/25 17:01:42 dillon 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/md_var.h>

#include <vm/vm_page2.h>
#include <sys/mplock2.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(vm_object_t, vm_pindex_t);
static vm_page_t _vm_page_list_find2(int basequeue, int index);

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

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


#define ASSERT_IN_CRIT_SECTION()        KKASSERT(crit_test(curthread));

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;

        vm_page_queues[PQ_INACTIVE].cnt = &vmstats.v_inactive_count;
        vm_page_queues[PQ_ACTIVE].cnt = &vmstats.v_active_count;
        vm_page_queues[PQ_HOLD].cnt = &vmstats.v_active_count;
        /* PQ_NONE has no queue */

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

        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.
 *
 * Must be called in a critical section.
 */
vm_page_t
vm_add_new_page(vm_paddr_t pa)
{
        struct vpgqueues *vpq;
        vm_page_t m;

        ++vmstats.v_page_count;
        ++vmstats.v_free_count;
        m = PHYS_TO_VM_PAGE(pa);
        m->phys_addr = pa;
        m->flags = 0;
        m->pc = (pa >> PAGE_SHIFT) & PQ_L2_MASK;
        m->queue = m->pc + PQ_FREE;
        KKASSERT(m->dirty == 0);

        vpq = &vm_page_queues[m->queue];
        if (vpq->flipflop)
                TAILQ_INSERT_TAIL(&vpq->pl, m, pageq);
        else
                TAILQ_INSERT_HEAD(&vpq->pl, m, pageq);
        vpq->flipflop = 1 - vpq->flipflop;

        vm_page_queues[m->queue].lcnt++;
        return (m);
}

/*
 * (low level boot)
 *
 * 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.
 *
 * starta/enda represents the range of physical memory addresses available
 * for use (skipping memory already used by the kernel), subject to
 * phys_avail[].  Note that phys_avail[] has already mapped out memory
 * already in use by the kernel.
 */
vm_offset_t
vm_page_startup(vm_offset_t vaddr)
{
        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();

        /* VKERNELs don't support minidumps and as such don't need vm_page_dump */
#if !defined(_KERNEL_VIRTUAL)
        /*
         * 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;
                }
        }
        return (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);
}

/*
 * 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 hold vm_token.
 *
 * 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.
 */
void
vm_page_hold(vm_page_t m)
{
        ASSERT_LWKT_TOKEN_HELD(&vm_token);
        ++m->hold_count;
}

/*
 * The opposite of vm_page_hold().  A page can be freed while being held,
 * which places it on the PQ_HOLD queue.  We must call vm_page_free_toq()
 * in this case to actually free it once the hold count drops to 0.
 *
 * The caller must hold vm_token if non-blocking operation is desired,
 * but otherwise does not need to.
 */
void
vm_page_unhold(vm_page_t m)
{
        lwkt_gettoken(&vm_token);
        --m->hold_count;
        KASSERT(m->hold_count >= 0, ("vm_page_unhold: hold count < 0!!!"));
        if (m->hold_count == 0 && m->queue == PQ_HOLD) {
                vm_page_busy(m);
                vm_page_free_toq(m);
        }
        lwkt_reltoken(&vm_token);
}

/*
 * 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_token held.
 * This routine must be called with a critical section held.
 */
void
vm_page_insert(vm_page_t m, vm_object_t object, vm_pindex_t pindex)
{
        ASSERT_IN_CRIT_SECTION();
        ASSERT_LWKT_TOKEN_HELD(&vm_token);
        if (m->object != NULL)
                panic("vm_page_insert: already inserted");

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

        /*
         * Insert it into the object.
         */
        vm_page_rb_tree_RB_INSERT(&object->rb_memq, m);
        object->generation++;

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

        /*
         * Add the pv_list_cout of the page when its inserted in
         * the object
        */
        object->agg_pv_list_count = object->agg_pv_list_count + m->md.pv_list_count;

        /*
         * 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);
}

/*
 * Removes the given vm_page_t from the global (object,index) hash table
 * and from the object's memq.
 *
 * 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;

        crit_enter();
        lwkt_gettoken(&vm_token);
        if (m->object == NULL) {
                lwkt_reltoken(&vm_token);
                crit_exit();
                return;
        }

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

        object = m->object;

        /*
         * Remove the page from the object and update the object.
         */
        vm_page_rb_tree_RB_REMOVE(&object->rb_memq, m);
        object->resident_page_count--;
        object->agg_pv_list_count = object->agg_pv_list_count - m->md.pv_list_count;
        object->generation++;
        m->object = NULL;

        lwkt_reltoken(&vm_token);
        crit_exit();
}

/*
 * Locate and return the page at (object, pindex), or NULL if the
 * page could not be found.
 *
 * The caller must hold vm_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_token);
        crit_enter();
        m = vm_page_rb_tree_RB_LOOKUP(&object->rb_memq, pindex);
        crit_exit();
        KKASSERT(m == NULL || (m->object == object && m->pindex == pindex));
        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)
{
        crit_enter();
        lwkt_gettoken(&vm_token);
        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);
        vm_page_wakeup(m);
        lwkt_reltoken(&vm_token);
        crit_exit();
}

/*
 * 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.
 *
 * The caller must hold vm_token
 * This routine may not block.
 */
void
vm_page_unqueue_nowakeup(vm_page_t m)
{
        int queue = m->queue;
        struct vpgqueues *pq;

        ASSERT_LWKT_TOKEN_HELD(&vm_token);
        if (queue != PQ_NONE) {
                pq = &vm_page_queues[queue];
                m->queue = PQ_NONE;
                TAILQ_REMOVE(&pq->pl, m, pageq);
                (*pq->cnt)--;
                pq->lcnt--;
        }
}

/*
 * vm_page_unqueue() - Remove a page from its queue, wakeup the pagedemon
 * if necessary.
 *
 * The caller must hold vm_token
 * This routine may not block.
 */
void
vm_page_unqueue(vm_page_t m)
{
        int queue = m->queue;
        struct vpgqueues *pq;

        ASSERT_LWKT_TOKEN_HELD(&vm_token);
        if (queue != PQ_NONE) {
                m->queue = PQ_NONE;
                pq = &vm_page_queues[queue];
                TAILQ_REMOVE(&pq->pl, m, pageq);
                (*pq->cnt)--;
                pq->lcnt--;
                if ((queue - m->pc) == PQ_CACHE || (queue - m->pc) == PQ_FREE)
                        pagedaemon_wakeup();
        }
}

/*
 * 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.
 *
 * Must be called with vm_token held.
 * This routine may not block.
 *
 * Note that 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.
 */
static __inline
vm_page_t
_vm_page_list_find(int basequeue, int index, boolean_t prefer_zero)
{
        vm_page_t m;

        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);
}

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) {
                if ((m = TAILQ_FIRST(&pq[(index + i) & PQ_L2_MASK].pl)) != NULL)
                        break;

                if ((m = TAILQ_FIRST(&pq[(index - i) & PQ_L2_MASK].pl)) != NULL)
                        break;
        }
        return(m);
}

/*
 * Must be called with vm_token held if the caller desired non-blocking
 * operation and a stable result.
 */
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.  As pages
 * might be found, but not applicable, they are deactivated.  This
 * keeps us from using potentially busy cached pages.
 *
 * This routine may not block.
 * Must be called with vm_token held.
 */
vm_page_t
vm_page_select_cache(vm_object_t object, vm_pindex_t pindex)
{
        vm_page_t m;

        ASSERT_LWKT_TOKEN_HELD(&vm_token);
        while (TRUE) {
                m = _vm_page_list_find(
                    PQ_CACHE,
                    (pindex + object->pg_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;
        }
        /* not reached */
}

/*
 * 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.
 *
 * This routine must be called with a critical section held.
 * This routine may not block.
 */
static __inline vm_page_t
vm_page_select_free(vm_object_t object, vm_pindex_t pindex, boolean_t prefer_zero)
{
        vm_page_t m;

        m = _vm_page_list_find(
                PQ_FREE,
                (pindex + object->pg_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         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
 *
 * The object must be locked.
 * This routine may not block.
 * The returned page will be marked PG_BUSY
 *
 * 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)
{
        vm_page_t m = NULL;

        crit_enter();
        lwkt_gettoken(&vm_token);
        
        KKASSERT(object != NULL);
        KASSERT(!vm_page_lookup(object, pindex),
                ("vm_page_alloc: page already allocated"));
        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)
                        m = vm_page_select_free(object, pindex, TRUE);
                else
                        m = vm_page_select_free(object, pindex, 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(object, pindex);
                }
#else
                m = vm_page_select_cache(object, pindex);
#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_busy(m);
                        vm_page_protect(m, VM_PROT_NONE);
                        vm_page_free(m);
                        goto loop;
                }

                /*
                 * On failure return NULL
                 */
                lwkt_reltoken(&vm_token);
                crit_exit();
#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.
                 */
                lwkt_reltoken(&vm_token);
                crit_exit();
                vm_pageout_deficit++;
                pagedaemon_wakeup();
                return (NULL);
        }

        /*
         * Good page found.  The page has not yet been busied.  We are in
         * a critical section.
         */
        KASSERT(m != NULL, ("vm_page_alloc(): missing page on free queue\n"));
        KASSERT(m->dirty == 0, 
                ("vm_page_alloc: free/cache page %p was dirty", m));

        /*
         * Remove from free queue
         */
        vm_page_unqueue_nowakeup(m);

        /*
         * Initialize structure.  Only the PG_ZERO flag is inherited.  Set
         * the page PG_BUSY
         */
        if (m->flags & PG_ZERO) {
                vm_page_zero_count--;
                m->flags = PG_ZERO | PG_BUSY;
        } else {
                m->flags = PG_BUSY;
        }
        m->wire_count = 0;
        m->hold_count = 0;
        m->act_count = 0;
        m->busy = 0;
        m->valid = 0;

        /*
         * vm_page_insert() is safe prior to the crit_exit().  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.
         */
        vm_page_insert(m, object, pindex);

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

        lwkt_reltoken(&vm_token);
        crit_exit();

        /*
         * 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 page queues must be locked.
 * This routine may not block.
 */
void
vm_page_activate(vm_page_t m)
{
        crit_enter();
        lwkt_gettoken(&vm_token);
        if (m->queue != PQ_ACTIVE) {
                if ((m->queue - m->pc) == PQ_CACHE)
                        mycpu->gd_cnt.v_reactivated++;

                vm_page_unqueue(m);

                if (m->wire_count == 0 && (m->flags & PG_UNMANAGED) == 0) {
                        m->queue = PQ_ACTIVE;
                        vm_page_queues[PQ_ACTIVE].lcnt++;
                        TAILQ_INSERT_TAIL(&vm_page_queues[PQ_ACTIVE].pl,
                                            m, pageq);
                        if (m->act_count < ACT_INIT)
                                m->act_count = ACT_INIT;
                        vmstats.v_active_count++;
                }
        } else {
                if (m->act_count < ACT_INIT)
                        m->act_count = ACT_INIT;
        }
        lwkt_reltoken(&vm_token);
        crit_exit();
}

/*
 * 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 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;
                }
        }
}

/*
 *      vm_page_free_toq:
 *
 *      Returns the given page to the PQ_FREE list, disassociating it with
 *      any VM object.
 *
 *      The vm_page must be PG_BUSY on entry.  PG_BUSY will be released on
 *      return (the page will have been freed).  No particular spl is required
 *      on entry.
 *
 *      This routine may not block.
 */
void
vm_page_free_toq(vm_page_t m)
{
        struct vpgqueues *pq;

        crit_enter();
        lwkt_gettoken(&vm_token);
        mycpu->gd_cnt.v_tfree++;

        KKASSERT((m->flags & PG_MAPPED) == 0);

        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");
        }

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

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

        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];
        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);
        }
        vm_page_wakeup(m);
        vm_page_free_wakeup();
        lwkt_reltoken(&vm_token);
        crit_exit();
}

/*
 * 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.
 *
 * MPUNSAFE
 */
vm_page_t
vm_page_free_fromq_fast(void)
{
        static int qi;
        vm_page_t m;
        int i;

        crit_enter();
        lwkt_gettoken(&vm_token);
        for (i = 0; i < PQ_L2_SIZE; ++i) {
                m = vm_page_list_find(PQ_FREE, qi, FALSE);
                qi = (qi + PQ_PRIME2) & PQ_L2_MASK;
                if (m && (m->flags & PG_ZERO) == 0) {
                        vm_page_unqueue_nowakeup(m);
                        vm_page_busy(m);
                        break;
                }
                m = NULL;
        }
        lwkt_reltoken(&vm_token);
        crit_exit();
        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.
 *
 * Must be called with a critical section held.
 * Must be called with vm_token held.
 */
void
vm_page_unmanage(vm_page_t m)
{
        ASSERT_IN_CRIT_SECTION();
        ASSERT_LWKT_TOKEN_HELD(&vm_token);
        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.
 *
 * The page queues must be locked.
 * This routine may not block.
 */
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.
         */
        crit_enter();
        lwkt_gettoken(&vm_token);
        if ((m->flags & PG_FICTITIOUS) == 0) {
                if (m->wire_count == 0) {
                        if ((m->flags & PG_UNMANAGED) == 0)
                                vm_page_unqueue(m);
                        vmstats.v_wire_count++;
                }
                m->wire_count++;
                KASSERT(m->wire_count != 0,
                        ("vm_page_wire: wire_count overflow m=%p", m));
        }
        lwkt_reltoken(&vm_token);
        crit_exit();
}

/*
 * 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)
{
        crit_enter();
        lwkt_gettoken(&vm_token);
        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 (--m->wire_count == 0) {
                        --vmstats.v_wire_count;
                        if (m->flags & PG_UNMANAGED) {
                                ;
                        } else if (activate) {
                                TAILQ_INSERT_TAIL(
                                    &vm_page_queues[PQ_ACTIVE].pl, m, pageq);
                                m->queue = PQ_ACTIVE;
                                vm_page_queues[PQ_ACTIVE].lcnt++;
                                vmstats.v_active_count++;
                        } else {
                                vm_page_flag_clear(m, PG_WINATCFLS);
                                TAILQ_INSERT_TAIL(
                                    &vm_page_queues[PQ_INACTIVE].pl, m, pageq);
                                m->queue = PQ_INACTIVE;
                                vm_page_queues[PQ_INACTIVE].lcnt++;
                                vmstats.v_inactive_count++;
                                ++vm_swapcache_inactive_heuristic;
                        }
                }
        }
        lwkt_reltoken(&vm_token);
        crit_exit();
}


/*
 * 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.
 * The caller must hold vm_token.
 */
static __inline void
_vm_page_deactivate(vm_page_t m, int athead)
{
        /*
         * Ignore if already inactive.
         */
        if (m->queue == PQ_INACTIVE)
                return;

        if (m->wire_count == 0 && (m->flags & PG_UNMANAGED) == 0) {
                if ((m->queue - m->pc) == PQ_CACHE)
                        mycpu->gd_cnt.v_reactivated++;
                vm_page_flag_clear(m, PG_WINATCFLS);
                vm_page_unqueue(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);
                        ++vm_swapcache_inactive_heuristic;
                }
                m->queue = PQ_INACTIVE;
                vm_page_queues[PQ_INACTIVE].lcnt++;
                vmstats.v_inactive_count++;
        }
}

/*
 * Attempt to deactivate a page.
 *
 * No requirements.
 */
void
vm_page_deactivate(vm_page_t m)
{
        crit_enter();
        lwkt_gettoken(&vm_token);
        _vm_page_deactivate(m, 0);
        lwkt_reltoken(&vm_token);
        crit_exit();
}

/*
 * Attempt to move a page to PQ_CACHE.
 * Returns 0 on failure, 1 on success
 *
 * No requirements.
 */
int
vm_page_try_to_cache(vm_page_t m)
{
        crit_enter();
        lwkt_gettoken(&vm_token);
        if (m->dirty || m->hold_count || m->busy || m->wire_count ||
            (m->flags & (PG_BUSY|PG_UNMANAGED))) {
                lwkt_reltoken(&vm_token);
                crit_exit();
                return(0);
        }
        vm_page_test_dirty(m);
        if (m->dirty) {
                lwkt_reltoken(&vm_token);
                crit_exit();
                return(0);
        }
        vm_page_cache(m);
        lwkt_reltoken(&vm_token);
        crit_exit();
        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)
{
        crit_enter();
        lwkt_gettoken(&vm_token);
        if (m->dirty || m->hold_count || m->busy || m->wire_count ||
            (m->flags & (PG_BUSY|PG_UNMANAGED))) {
                lwkt_reltoken(&vm_token);
                crit_exit();
                return(0);
        }
        vm_page_test_dirty(m);
        if (m->dirty) {
                lwkt_reltoken(&vm_token);
                crit_exit();
                return(0);
        }
        vm_page_busy(m);
        vm_page_protect(m, VM_PROT_NONE);
        vm_page_free(m);
        lwkt_reltoken(&vm_token);
        crit_exit();
        return(1);
}

/*
 * vm_page_cache
 *
 * Put the specified page onto the page cache queue (if appropriate).
 *
 * The caller must hold vm_token.
 * This routine may not block.
 */
void
vm_page_cache(vm_page_t m)
{
        ASSERT_IN_CRIT_SECTION();
        ASSERT_LWKT_TOKEN_HELD(&vm_token);

        if ((m->flags & (PG_BUSY|PG_UNMANAGED)) || m->busy ||
                        m->wire_count || m->hold_count) {
                kprintf("vm_page_cache: attempting to cache busy/held page\n");
                return;
        }

        /*
         * Already in the cache (and thus not mapped)
         */
        if ((m->queue - m->pc) == PQ_CACHE) {
                KKASSERT((m->flags & PG_MAPPED) == 0);
                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_busy(m);
        vm_page_protect(m, VM_PROT_NONE);
        vm_page_wakeup(m);
        if ((m->flags & (PG_BUSY|PG_UNMANAGED|PG_MAPPED)) || m->busy ||
                        m->wire_count || m->hold_count) {
                /* do nothing */
        } else if (m->dirty) {
                vm_page_deactivate(m);
        } else {
                vm_page_unqueue_nowakeup(m);
                m->queue = PQ_CACHE + m->pc;
                vm_page_queues[m->queue].lcnt++;
                TAILQ_INSERT_TAIL(&vm_page_queues[m->queue].pl, m, pageq);
                vmstats.v_cache_count++;
                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.
 *
 * No requirements.
 */
void
vm_page_dontneed(vm_page_t m)
{
        static int dnweight;
        int dnw;
        int head;

        dnw = ++dnweight;

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

/*
 * Grab a page, blocking if it is busy and allocating a page if necessary.
 * A busy page is returned or NULL.
 *
 * If VM_ALLOC_RETRY is specified VM_ALLOC_NORMAL must also be specified.
 * If VM_ALLOC_RETRY is not specified
 *
 * This routine may block, but if VM_ALLOC_RETRY is not set then NULL is
 * always returned if we had blocked.  
 * This routine will never return NULL if VM_ALLOC_RETRY is set.
 * This routine may not be called from an interrupt.
 * The returned page may not be entirely valid.
 *
 * This routine may be called from mainline code without spl protection and
 * be guarenteed a busied page associated with the object at the specified
 * index.
 *
 * No requirements.
 */
vm_page_t
vm_page_grab(vm_object_t object, vm_pindex_t pindex, int allocflags)
{
        vm_page_t m;
        int generation;

        KKASSERT(allocflags &
                (VM_ALLOC_NORMAL|VM_ALLOC_INTERRUPT|VM_ALLOC_SYSTEM));
        crit_enter();
        lwkt_gettoken(&vm_token);
retrylookup:
        if ((m = vm_page_lookup(object, pindex)) != NULL) {
                if (m->busy || (m->flags & PG_BUSY)) {
                        generation = object->generation;

                        while ((object->generation == generation) &&
                                        (m->busy || (m->flags & PG_BUSY))) {
                                vm_page_flag_set(m, PG_WANTED | PG_REFERENCED);
                                tsleep(m, 0, "pgrbwt", 0);
                                if ((allocflags & VM_ALLOC_RETRY) == 0) {
                                        m = NULL;
                                        goto done;
                                }
                        }
                        goto retrylookup;
                } else {
                        vm_page_busy(m);
                        goto done;
                }
        }
        m = vm_page_alloc(object, pindex, allocflags & ~VM_ALLOC_RETRY);
        if (m == NULL) {
                vm_wait(0);
                if ((allocflags & VM_ALLOC_RETRY) == 0)
                        goto done;
                goto retrylookup;
        }
done:
        lwkt_reltoken(&vm_token);
        crit_exit();
        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.
 *
 * Page must be busied?
 * 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()
 *
 * Page must be busied?
 * 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 vm_token if non-blocking operation desired.
 * No other requirements.
 */
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: %d, PQ_INACTIVE: %d\n",
                vm_page_queues[PQ_ACTIVE].lcnt,
                vm_page_queues[PQ_INACTIVE].lcnt);
}
#endif /* DDB */