Update llvm to trunk r256945.

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

/*-
 * Copyright (c) 1991 Regents of the University of California.
 * All rights reserved.
 * Copyright (c) 1994 John S. Dyson
 * All rights reserved.
 * Copyright (c) 1994 David Greenman
 * All rights reserved.
 * Copyright (c) 2005 Yahoo! Technologies Norway AS
 * 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_pageout.c  7.4 (Berkeley) 5/7/91
 *
 *
 * Copyright (c) 1987, 1990 Carnegie-Mellon University.
 * All rights reserved.
 *
 * Authors: Avadis Tevanian, Jr., Michael Wayne Young
 *
 * Permission to use, copy, modify and distribute this software and
 * its documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 *
 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
 * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 *
 * Carnegie Mellon requests users of this software to return to
 *
 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 *
 * any improvements or extensions that they make and grant Carnegie the
 * rights to redistribute these changes.
 */

/*
 *      The proverbial page-out daemon.
 */

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

#include "opt_vm.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/eventhandler.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/kthread.h>
#include <sys/ktr.h>
#include <sys/mount.h>
#include <sys/racct.h>
#include <sys/resourcevar.h>
#include <sys/sched.h>
#include <sys/sdt.h>
#include <sys/signalvar.h>
#include <sys/smp.h>
#include <sys/time.h>
#include <sys/vnode.h>
#include <sys/vmmeter.h>
#include <sys/rwlock.h>
#include <sys/sx.h>
#include <sys/sysctl.h>

#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
#include <vm/vm_map.h>
#include <vm/vm_pageout.h>
#include <vm/vm_pager.h>
#include <vm/vm_phys.h>
#include <vm/swap_pager.h>
#include <vm/vm_extern.h>
#include <vm/uma.h>

/*
 * System initialization
 */

/* the kernel process "vm_pageout"*/
static void vm_pageout(void);
static void vm_pageout_init(void);
static int vm_pageout_clean(vm_page_t m);
static int vm_pageout_cluster(vm_page_t m);
static void vm_pageout_scan(struct vm_domain *vmd, int pass);
static void vm_pageout_mightbe_oom(struct vm_domain *vmd, int page_shortage,
    int starting_page_shortage);

SYSINIT(pagedaemon_init, SI_SUB_KTHREAD_PAGE, SI_ORDER_FIRST, vm_pageout_init,
    NULL);

struct proc *pageproc;

static struct kproc_desc page_kp = {
        "pagedaemon",
        vm_pageout,
        &pageproc
};
SYSINIT(pagedaemon, SI_SUB_KTHREAD_PAGE, SI_ORDER_SECOND, kproc_start,
    &page_kp);

SDT_PROVIDER_DEFINE(vm);
SDT_PROBE_DEFINE(vm, , , vm__lowmem_cache);
SDT_PROBE_DEFINE(vm, , , vm__lowmem_scan);

#if !defined(NO_SWAPPING)
/* the kernel process "vm_daemon"*/
static void vm_daemon(void);
static struct   proc *vmproc;

static struct kproc_desc vm_kp = {
        "vmdaemon",
        vm_daemon,
        &vmproc
};
SYSINIT(vmdaemon, SI_SUB_KTHREAD_VM, SI_ORDER_FIRST, kproc_start, &vm_kp);
#endif


int vm_pages_needed;            /* Event on which pageout daemon sleeps */
int vm_pageout_deficit;         /* Estimated number of pages deficit */
int vm_pageout_wakeup_thresh;
static int vm_pageout_oom_seq = 12;

#if !defined(NO_SWAPPING)
static int vm_pageout_req_swapout;      /* XXX */
static int vm_daemon_needed;
static struct mtx vm_daemon_mtx;
/* Allow for use by vm_pageout before vm_daemon is initialized. */
MTX_SYSINIT(vm_daemon, &vm_daemon_mtx, "vm daemon", MTX_DEF);
#endif
static int vm_max_launder = 32;
static int vm_pageout_update_period;
static int defer_swap_pageouts;
static int disable_swap_pageouts;
static int lowmem_period = 10;
static time_t lowmem_uptime;

#if defined(NO_SWAPPING)
static int vm_swap_enabled = 0;
static int vm_swap_idle_enabled = 0;
#else
static int vm_swap_enabled = 1;
static int vm_swap_idle_enabled = 0;
#endif

static int vm_panic_on_oom = 0;

SYSCTL_INT(_vm, OID_AUTO, panic_on_oom,
        CTLFLAG_RWTUN, &vm_panic_on_oom, 0,
        "panic on out of memory instead of killing the largest process");

SYSCTL_INT(_vm, OID_AUTO, pageout_wakeup_thresh,
        CTLFLAG_RW, &vm_pageout_wakeup_thresh, 0,
        "free page threshold for waking up the pageout daemon");

SYSCTL_INT(_vm, OID_AUTO, max_launder,
        CTLFLAG_RW, &vm_max_launder, 0, "Limit dirty flushes in pageout");

SYSCTL_INT(_vm, OID_AUTO, pageout_update_period,
        CTLFLAG_RW, &vm_pageout_update_period, 0,
        "Maximum active LRU update period");
  
SYSCTL_INT(_vm, OID_AUTO, lowmem_period, CTLFLAG_RW, &lowmem_period, 0,
        "Low memory callback period");

#if defined(NO_SWAPPING)
SYSCTL_INT(_vm, VM_SWAPPING_ENABLED, swap_enabled,
        CTLFLAG_RD, &vm_swap_enabled, 0, "Enable entire process swapout");
SYSCTL_INT(_vm, OID_AUTO, swap_idle_enabled,
        CTLFLAG_RD, &vm_swap_idle_enabled, 0, "Allow swapout on idle criteria");
#else
SYSCTL_INT(_vm, VM_SWAPPING_ENABLED, swap_enabled,
        CTLFLAG_RW, &vm_swap_enabled, 0, "Enable entire process swapout");
SYSCTL_INT(_vm, OID_AUTO, swap_idle_enabled,
        CTLFLAG_RW, &vm_swap_idle_enabled, 0, "Allow swapout on idle criteria");
#endif

SYSCTL_INT(_vm, OID_AUTO, defer_swapspace_pageouts,
        CTLFLAG_RW, &defer_swap_pageouts, 0, "Give preference to dirty pages in mem");

SYSCTL_INT(_vm, OID_AUTO, disable_swapspace_pageouts,
        CTLFLAG_RW, &disable_swap_pageouts, 0, "Disallow swapout of dirty pages");

static int pageout_lock_miss;
SYSCTL_INT(_vm, OID_AUTO, pageout_lock_miss,
        CTLFLAG_RD, &pageout_lock_miss, 0, "vget() lock misses during pageout");

SYSCTL_INT(_vm, OID_AUTO, pageout_oom_seq,
        CTLFLAG_RW, &vm_pageout_oom_seq, 0,
        "back-to-back calls to oom detector to start OOM");

#define VM_PAGEOUT_PAGE_COUNT 16
int vm_pageout_page_count = VM_PAGEOUT_PAGE_COUNT;

int vm_page_max_wired;          /* XXX max # of wired pages system-wide */
SYSCTL_INT(_vm, OID_AUTO, max_wired,
        CTLFLAG_RW, &vm_page_max_wired, 0, "System-wide limit to wired page count");

static boolean_t vm_pageout_fallback_object_lock(vm_page_t, vm_page_t *);
#if !defined(NO_SWAPPING)
static void vm_pageout_map_deactivate_pages(vm_map_t, long);
static void vm_pageout_object_deactivate_pages(pmap_t, vm_object_t, long);
static void vm_req_vmdaemon(int req);
#endif
static boolean_t vm_pageout_page_lock(vm_page_t, vm_page_t *);

/*
 * Initialize a dummy page for marking the caller's place in the specified
 * paging queue.  In principle, this function only needs to set the flag
 * PG_MARKER.  Nonetheless, it wirte busies and initializes the hold count
 * to one as safety precautions.
 */ 
static void
vm_pageout_init_marker(vm_page_t marker, u_short queue)
{

        bzero(marker, sizeof(*marker));
        marker->flags = PG_MARKER;
        marker->busy_lock = VPB_SINGLE_EXCLUSIVER;
        marker->queue = queue;
        marker->hold_count = 1;
}

/*
 * vm_pageout_fallback_object_lock:
 * 
 * Lock vm object currently associated with `m'. VM_OBJECT_TRYWLOCK is
 * known to have failed and page queue must be either PQ_ACTIVE or
 * PQ_INACTIVE.  To avoid lock order violation, unlock the page queues
 * while locking the vm object.  Use marker page to detect page queue
 * changes and maintain notion of next page on page queue.  Return
 * TRUE if no changes were detected, FALSE otherwise.  vm object is
 * locked on return.
 * 
 * This function depends on both the lock portion of struct vm_object
 * and normal struct vm_page being type stable.
 */
static boolean_t
vm_pageout_fallback_object_lock(vm_page_t m, vm_page_t *next)
{
        struct vm_page marker;
        struct vm_pagequeue *pq;
        boolean_t unchanged;
        u_short queue;
        vm_object_t object;

        queue = m->queue;
        vm_pageout_init_marker(&marker, queue);
        pq = vm_page_pagequeue(m);
        object = m->object;
        
        TAILQ_INSERT_AFTER(&pq->pq_pl, m, &marker, plinks.q);
        vm_pagequeue_unlock(pq);
        vm_page_unlock(m);
        VM_OBJECT_WLOCK(object);
        vm_page_lock(m);
        vm_pagequeue_lock(pq);

        /*
         * The page's object might have changed, and/or the page might
         * have moved from its original position in the queue.  If the
         * page's object has changed, then the caller should abandon
         * processing the page because the wrong object lock was
         * acquired.  Use the marker's plinks.q, not the page's, to
         * determine if the page has been moved.  The state of the
         * page's plinks.q can be indeterminate; whereas, the marker's
         * plinks.q must be valid.
         */
        *next = TAILQ_NEXT(&marker, plinks.q);
        unchanged = m->object == object &&
            m == TAILQ_PREV(&marker, pglist, plinks.q);
        KASSERT(!unchanged || m->queue == queue,
            ("page %p queue %d %d", m, queue, m->queue));
        TAILQ_REMOVE(&pq->pq_pl, &marker, plinks.q);
        return (unchanged);
}

/*
 * Lock the page while holding the page queue lock.  Use marker page
 * to detect page queue changes and maintain notion of next page on
 * page queue.  Return TRUE if no changes were detected, FALSE
 * otherwise.  The page is locked on return. The page queue lock might
 * be dropped and reacquired.
 *
 * This function depends on normal struct vm_page being type stable.
 */
static boolean_t
vm_pageout_page_lock(vm_page_t m, vm_page_t *next)
{
        struct vm_page marker;
        struct vm_pagequeue *pq;
        boolean_t unchanged;
        u_short queue;

        vm_page_lock_assert(m, MA_NOTOWNED);
        if (vm_page_trylock(m))
                return (TRUE);

        queue = m->queue;
        vm_pageout_init_marker(&marker, queue);
        pq = vm_page_pagequeue(m);

        TAILQ_INSERT_AFTER(&pq->pq_pl, m, &marker, plinks.q);
        vm_pagequeue_unlock(pq);
        vm_page_lock(m);
        vm_pagequeue_lock(pq);

        /* Page queue might have changed. */
        *next = TAILQ_NEXT(&marker, plinks.q);
        unchanged = m == TAILQ_PREV(&marker, pglist, plinks.q);
        KASSERT(!unchanged || m->queue == queue,
            ("page %p queue %d %d", m, queue, m->queue));
        TAILQ_REMOVE(&pq->pq_pl, &marker, plinks.q);
        return (unchanged);
}

/*
 * vm_pageout_clean:
 *
 * Clean the page and remove it from the laundry.
 * 
 * We set the busy bit to cause potential page faults on this page to
 * block.  Note the careful timing, however, the busy bit isn't set till
 * late and we cannot do anything that will mess with the page.
 */
static int
vm_pageout_cluster(vm_page_t m)
{
        vm_object_t object;
        vm_page_t mc[2*vm_pageout_page_count], pb, ps;
        int pageout_count;
        int ib, is, page_base;
        vm_pindex_t pindex = m->pindex;

        vm_page_lock_assert(m, MA_OWNED);
        object = m->object;
        VM_OBJECT_ASSERT_WLOCKED(object);

        /*
         * It doesn't cost us anything to pageout OBJT_DEFAULT or OBJT_SWAP
         * with the new swapper, but we could have serious problems paging
         * out other object types if there is insufficient memory.  
         *
         * Unfortunately, checking free memory here is far too late, so the
         * check has been moved up a procedural level.
         */

        /*
         * Can't clean the page if it's busy or held.
         */
        vm_page_assert_unbusied(m);
        KASSERT(m->hold_count == 0, ("vm_pageout_clean: page %p is held", m));
        vm_page_unlock(m);

        mc[vm_pageout_page_count] = pb = ps = m;
        pageout_count = 1;
        page_base = vm_pageout_page_count;
        ib = 1;
        is = 1;

        /*
         * Scan object for clusterable pages.
         *
         * We can cluster ONLY if: ->> the page is NOT
         * clean, wired, busy, held, or mapped into a
         * buffer, and one of the following:
         * 1) The page is inactive, or a seldom used
         *    active page.
         * -or-
         * 2) we force the issue.
         *
         * During heavy mmap/modification loads the pageout
         * daemon can really fragment the underlying file
         * due to flushing pages out of order and not trying
         * align the clusters (which leave sporatic out-of-order
         * holes).  To solve this problem we do the reverse scan
         * first and attempt to align our cluster, then do a 
         * forward scan if room remains.
         */
more:
        while (ib && pageout_count < vm_pageout_page_count) {
                vm_page_t p;

                if (ib > pindex) {
                        ib = 0;
                        break;
                }

                if ((p = vm_page_prev(pb)) == NULL || vm_page_busied(p)) {
                        ib = 0;
                        break;
                }
                vm_page_test_dirty(p);
                if (p->dirty == 0) {
                        ib = 0;
                        break;
                }
                vm_page_lock(p);
                if (p->queue != PQ_INACTIVE ||
                    p->hold_count != 0) {       /* may be undergoing I/O */
                        vm_page_unlock(p);
                        ib = 0;
                        break;
                }
                vm_page_unlock(p);
                mc[--page_base] = pb = p;
                ++pageout_count;
                ++ib;
                /*
                 * alignment boundry, stop here and switch directions.  Do
                 * not clear ib.
                 */
                if ((pindex - (ib - 1)) % vm_pageout_page_count == 0)
                        break;
        }

        while (pageout_count < vm_pageout_page_count && 
            pindex + is < object->size) {
                vm_page_t p;

                if ((p = vm_page_next(ps)) == NULL || vm_page_busied(p))
                        break;
                vm_page_test_dirty(p);
                if (p->dirty == 0)
                        break;
                vm_page_lock(p);
                if (p->queue != PQ_INACTIVE ||
                    p->hold_count != 0) {       /* may be undergoing I/O */
                        vm_page_unlock(p);
                        break;
                }
                vm_page_unlock(p);
                mc[page_base + pageout_count] = ps = p;
                ++pageout_count;
                ++is;
        }

        /*
         * If we exhausted our forward scan, continue with the reverse scan
         * when possible, even past a page boundry.  This catches boundry
         * conditions.
         */
        if (ib && pageout_count < vm_pageout_page_count)
                goto more;

        /*
         * we allow reads during pageouts...
         */
        return (vm_pageout_flush(&mc[page_base], pageout_count, 0, 0, NULL,
            NULL));
}

/*
 * vm_pageout_flush() - launder the given pages
 *
 *      The given pages are laundered.  Note that we setup for the start of
 *      I/O ( i.e. busy the page ), mark it read-only, and bump the object
 *      reference count all in here rather then in the parent.  If we want
 *      the parent to do more sophisticated things we may have to change
 *      the ordering.
 *
 *      Returned runlen is the count of pages between mreq and first
 *      page after mreq with status VM_PAGER_AGAIN.
 *      *eio is set to TRUE if pager returned VM_PAGER_ERROR or VM_PAGER_FAIL
 *      for any page in runlen set.
 */
int
vm_pageout_flush(vm_page_t *mc, int count, int flags, int mreq, int *prunlen,
    boolean_t *eio)
{
        vm_object_t object = mc[0]->object;
        int pageout_status[count];
        int numpagedout = 0;
        int i, runlen;

        VM_OBJECT_ASSERT_WLOCKED(object);

        /*
         * Initiate I/O.  Bump the vm_page_t->busy counter and
         * mark the pages read-only.
         *
         * We do not have to fixup the clean/dirty bits here... we can
         * allow the pager to do it after the I/O completes.
         *
         * NOTE! mc[i]->dirty may be partial or fragmented due to an
         * edge case with file fragments.
         */
        for (i = 0; i < count; i++) {
                KASSERT(mc[i]->valid == VM_PAGE_BITS_ALL,
                    ("vm_pageout_flush: partially invalid page %p index %d/%d",
                        mc[i], i, count));
                vm_page_sbusy(mc[i]);
                pmap_remove_write(mc[i]);
        }
        vm_object_pip_add(object, count);

        vm_pager_put_pages(object, mc, count, flags, pageout_status);

        runlen = count - mreq;
        if (eio != NULL)
                *eio = FALSE;
        for (i = 0; i < count; i++) {
                vm_page_t mt = mc[i];

                KASSERT(pageout_status[i] == VM_PAGER_PEND ||
                    !pmap_page_is_write_mapped(mt),
                    ("vm_pageout_flush: page %p is not write protected", mt));
                switch (pageout_status[i]) {
                case VM_PAGER_OK:
                case VM_PAGER_PEND:
                        numpagedout++;
                        break;
                case VM_PAGER_BAD:
                        /*
                         * Page outside of range of object. Right now we
                         * essentially lose the changes by pretending it
                         * worked.
                         */
                        vm_page_undirty(mt);
                        break;
                case VM_PAGER_ERROR:
                case VM_PAGER_FAIL:
                        /*
                         * If page couldn't be paged out, then reactivate the
                         * page so it doesn't clog the inactive list.  (We
                         * will try paging out it again later).
                         */
                        vm_page_lock(mt);
                        vm_page_activate(mt);
                        vm_page_unlock(mt);
                        if (eio != NULL && i >= mreq && i - mreq < runlen)
                                *eio = TRUE;
                        break;
                case VM_PAGER_AGAIN:
                        if (i >= mreq && i - mreq < runlen)
                                runlen = i - mreq;
                        break;
                }

                /*
                 * If the operation is still going, leave the page busy to
                 * block all other accesses. Also, leave the paging in
                 * progress indicator set so that we don't attempt an object
                 * collapse.
                 */
                if (pageout_status[i] != VM_PAGER_PEND) {
                        vm_object_pip_wakeup(object);
                        vm_page_sunbusy(mt);
                }
        }
        if (prunlen != NULL)
                *prunlen = runlen;
        return (numpagedout);
}

#if !defined(NO_SWAPPING)
/*
 *      vm_pageout_object_deactivate_pages
 *
 *      Deactivate enough pages to satisfy the inactive target
 *      requirements.
 *
 *      The object and map must be locked.
 */
static void
vm_pageout_object_deactivate_pages(pmap_t pmap, vm_object_t first_object,
    long desired)
{
        vm_object_t backing_object, object;
        vm_page_t p;
        int act_delta, remove_mode;

        VM_OBJECT_ASSERT_LOCKED(first_object);
        if ((first_object->flags & OBJ_FICTITIOUS) != 0)
                return;
        for (object = first_object;; object = backing_object) {
                if (pmap_resident_count(pmap) <= desired)
                        goto unlock_return;
                VM_OBJECT_ASSERT_LOCKED(object);
                if ((object->flags & OBJ_UNMANAGED) != 0 ||
                    object->paging_in_progress != 0)
                        goto unlock_return;

                remove_mode = 0;
                if (object->shadow_count > 1)
                        remove_mode = 1;
                /*
                 * Scan the object's entire memory queue.
                 */
                TAILQ_FOREACH(p, &object->memq, listq) {
                        if (pmap_resident_count(pmap) <= desired)
                                goto unlock_return;
                        if (vm_page_busied(p))
                                continue;
                        PCPU_INC(cnt.v_pdpages);
                        vm_page_lock(p);
                        if (p->wire_count != 0 || p->hold_count != 0 ||
                            !pmap_page_exists_quick(pmap, p)) {
                                vm_page_unlock(p);
                                continue;
                        }
                        act_delta = pmap_ts_referenced(p);
                        if ((p->aflags & PGA_REFERENCED) != 0) {
                                if (act_delta == 0)
                                        act_delta = 1;
                                vm_page_aflag_clear(p, PGA_REFERENCED);
                        }
                        if (p->queue != PQ_ACTIVE && act_delta != 0) {
                                vm_page_activate(p);
                                p->act_count += act_delta;
                        } else if (p->queue == PQ_ACTIVE) {
                                if (act_delta == 0) {
                                        p->act_count -= min(p->act_count,
                                            ACT_DECLINE);
                                        if (!remove_mode && p->act_count == 0) {
                                                pmap_remove_all(p);
                                                vm_page_deactivate(p);
                                        } else
                                                vm_page_requeue(p);
                                } else {
                                        vm_page_activate(p);
                                        if (p->act_count < ACT_MAX -
                                            ACT_ADVANCE)
                                                p->act_count += ACT_ADVANCE;
                                        vm_page_requeue(p);
                                }
                        } else if (p->queue == PQ_INACTIVE)
                                pmap_remove_all(p);
                        vm_page_unlock(p);
                }
                if ((backing_object = object->backing_object) == NULL)
                        goto unlock_return;
                VM_OBJECT_RLOCK(backing_object);
                if (object != first_object)
                        VM_OBJECT_RUNLOCK(object);
        }
unlock_return:
        if (object != first_object)
                VM_OBJECT_RUNLOCK(object);
}

/*
 * deactivate some number of pages in a map, try to do it fairly, but
 * that is really hard to do.
 */
static void
vm_pageout_map_deactivate_pages(map, desired)
        vm_map_t map;
        long desired;
{
        vm_map_entry_t tmpe;
        vm_object_t obj, bigobj;
        int nothingwired;

        if (!vm_map_trylock(map))
                return;

        bigobj = NULL;
        nothingwired = TRUE;

        /*
         * first, search out the biggest object, and try to free pages from
         * that.
         */
        tmpe = map->header.next;
        while (tmpe != &map->header) {
                if ((tmpe->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
                        obj = tmpe->object.vm_object;
                        if (obj != NULL && VM_OBJECT_TRYRLOCK(obj)) {
                                if (obj->shadow_count <= 1 &&
                                    (bigobj == NULL ||
                                     bigobj->resident_page_count < obj->resident_page_count)) {
                                        if (bigobj != NULL)
                                                VM_OBJECT_RUNLOCK(bigobj);
                                        bigobj = obj;
                                } else
                                        VM_OBJECT_RUNLOCK(obj);
                        }
                }
                if (tmpe->wired_count > 0)
                        nothingwired = FALSE;
                tmpe = tmpe->next;
        }

        if (bigobj != NULL) {
                vm_pageout_object_deactivate_pages(map->pmap, bigobj, desired);
                VM_OBJECT_RUNLOCK(bigobj);
        }
        /*
         * Next, hunt around for other pages to deactivate.  We actually
         * do this search sort of wrong -- .text first is not the best idea.
         */
        tmpe = map->header.next;
        while (tmpe != &map->header) {
                if (pmap_resident_count(vm_map_pmap(map)) <= desired)
                        break;
                if ((tmpe->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
                        obj = tmpe->object.vm_object;
                        if (obj != NULL) {
                                VM_OBJECT_RLOCK(obj);
                                vm_pageout_object_deactivate_pages(map->pmap, obj, desired);
                                VM_OBJECT_RUNLOCK(obj);
                        }
                }
                tmpe = tmpe->next;
        }

        /*
         * Remove all mappings if a process is swapped out, this will free page
         * table pages.
         */
        if (desired == 0 && nothingwired) {
                pmap_remove(vm_map_pmap(map), vm_map_min(map),
                    vm_map_max(map));
        }

        vm_map_unlock(map);
}
#endif          /* !defined(NO_SWAPPING) */

/*
 * Attempt to acquire all of the necessary locks to launder a page and
 * then call through the clustering layer to PUTPAGES.  Wait a short
 * time for a vnode lock.
 *
 * Requires the page and object lock on entry, releases both before return.
 * Returns 0 on success and an errno otherwise.
 */
static int
vm_pageout_clean(vm_page_t m)
{
        struct vnode *vp;
        struct mount *mp;
        vm_object_t object;
        vm_pindex_t pindex;
        int error, lockmode;

        vm_page_assert_locked(m);
        object = m->object;
        VM_OBJECT_ASSERT_WLOCKED(object);
        error = 0;
        vp = NULL;
        mp = NULL;

        /*
         * The object is already known NOT to be dead.   It
         * is possible for the vget() to block the whole
         * pageout daemon, but the new low-memory handling
         * code should prevent it.
         *
         * We can't wait forever for the vnode lock, we might
         * deadlock due to a vn_read() getting stuck in
         * vm_wait while holding this vnode.  We skip the 
         * vnode if we can't get it in a reasonable amount
         * of time.
         */
        if (object->type == OBJT_VNODE) {
                vm_page_unlock(m);
                vp = object->handle;
                if (vp->v_type == VREG &&
                    vn_start_write(vp, &mp, V_NOWAIT) != 0) {
                        mp = NULL;
                        error = EDEADLK;
                        goto unlock_all;
                }
                KASSERT(mp != NULL,
                    ("vp %p with NULL v_mount", vp));
                vm_object_reference_locked(object);
                pindex = m->pindex;
                VM_OBJECT_WUNLOCK(object);
                lockmode = MNT_SHARED_WRITES(vp->v_mount) ?
                    LK_SHARED : LK_EXCLUSIVE;
                if (vget(vp, lockmode | LK_TIMELOCK, curthread)) {
                        vp = NULL;
                        error = EDEADLK;
                        goto unlock_mp;
                }
                VM_OBJECT_WLOCK(object);
                vm_page_lock(m);
                /*
                 * While the object and page were unlocked, the page
                 * may have been:
                 * (1) moved to a different queue,
                 * (2) reallocated to a different object,
                 * (3) reallocated to a different offset, or
                 * (4) cleaned.
                 */
                if (m->queue != PQ_INACTIVE || m->object != object ||
                    m->pindex != pindex || m->dirty == 0) {
                        vm_page_unlock(m);
                        error = ENXIO;
                        goto unlock_all;
                }

                /*
                 * The page may have been busied or held while the object
                 * and page locks were released.
                 */
                if (vm_page_busied(m) || m->hold_count != 0) {
                        vm_page_unlock(m);
                        error = EBUSY;
                        goto unlock_all;
                }
        }

        /*
         * If a page is dirty, then it is either being washed
         * (but not yet cleaned) or it is still in the
         * laundry.  If it is still in the laundry, then we
         * start the cleaning operation. 
         */
        if (vm_pageout_cluster(m) == 0)
                error = EIO;

unlock_all:
        VM_OBJECT_WUNLOCK(object);

unlock_mp:
        vm_page_lock_assert(m, MA_NOTOWNED);
        if (mp != NULL) {
                if (vp != NULL)
                        vput(vp);
                vm_object_deallocate(object);
                vn_finished_write(mp);
        }

        return (error);
}

/*
 *      vm_pageout_scan does the dirty work for the pageout daemon.
 *
 *      pass 0 - Update active LRU/deactivate pages
 *      pass 1 - Move inactive to cache or free
 *      pass 2 - Launder dirty pages
 */
static void
vm_pageout_scan(struct vm_domain *vmd, int pass)
{
        vm_page_t m, next;
        struct vm_pagequeue *pq;
        vm_object_t object;
        long min_scan;
        int act_delta, addl_page_shortage, deficit, error, maxlaunder, maxscan;
        int page_shortage, scan_tick, scanned, starting_page_shortage;
        int vnodes_skipped;
        boolean_t pageout_ok, queues_locked;

        /*
         * If we need to reclaim memory ask kernel caches to return
         * some.  We rate limit to avoid thrashing.
         */
        if (vmd == &vm_dom[0] && pass > 0 &&
            (time_uptime - lowmem_uptime) >= lowmem_period) {
                /*
                 * Decrease registered cache sizes.
                 */
                SDT_PROBE0(vm, , , vm__lowmem_scan);
                EVENTHANDLER_INVOKE(vm_lowmem, 0);
                /*
                 * We do this explicitly after the caches have been
                 * drained above.
                 */
                uma_reclaim();
                lowmem_uptime = time_uptime;
        }

        /*
         * The addl_page_shortage is the number of temporarily
         * stuck pages in the inactive queue.  In other words, the
         * number of pages from the inactive count that should be
         * discounted in setting the target for the active queue scan.
         */
        addl_page_shortage = 0;

        /*
         * Calculate the number of pages we want to either free or move
         * to the cache.
         */
        if (pass > 0) {
                deficit = atomic_readandclear_int(&vm_pageout_deficit);
                page_shortage = vm_paging_target() + deficit;
        } else
                page_shortage = deficit = 0;
        starting_page_shortage = page_shortage;

        /*
         * maxlaunder limits the number of dirty pages we flush per scan.
         * For most systems a smaller value (16 or 32) is more robust under
         * extreme memory and disk pressure because any unnecessary writes
         * to disk can result in extreme performance degredation.  However,
         * systems with excessive dirty pages (especially when MAP_NOSYNC is
         * used) will die horribly with limited laundering.  If the pageout
         * daemon cannot clean enough pages in the first pass, we let it go
         * all out in succeeding passes.
         */
        if ((maxlaunder = vm_max_launder) <= 1)
                maxlaunder = 1;
        if (pass > 1)
                maxlaunder = 10000;

        vnodes_skipped = 0;

        /*
         * Start scanning the inactive queue for pages we can move to the
         * cache or free.  The scan will stop when the target is reached or
         * we have scanned the entire inactive queue.  Note that m->act_count
         * is not used to form decisions for the inactive queue, only for the
         * active queue.
         */
        pq = &vmd->vmd_pagequeues[PQ_INACTIVE];
        maxscan = pq->pq_cnt;
        vm_pagequeue_lock(pq);
        queues_locked = TRUE;
        for (m = TAILQ_FIRST(&pq->pq_pl);
             m != NULL && maxscan-- > 0 && page_shortage > 0;
             m = next) {
                vm_pagequeue_assert_locked(pq);
                KASSERT(queues_locked, ("unlocked queues"));
                KASSERT(m->queue == PQ_INACTIVE, ("Inactive queue %p", m));

                PCPU_INC(cnt.v_pdpages);
                next = TAILQ_NEXT(m, plinks.q);

                /*
                 * skip marker pages
                 */
                if (m->flags & PG_MARKER)
                        continue;

                KASSERT((m->flags & PG_FICTITIOUS) == 0,
                    ("Fictitious page %p cannot be in inactive queue", m));
                KASSERT((m->oflags & VPO_UNMANAGED) == 0,
                    ("Unmanaged page %p cannot be in inactive queue", m));

                /*
                 * The page or object lock acquisitions fail if the
                 * page was removed from the queue or moved to a
                 * different position within the queue.  In either
                 * case, addl_page_shortage should not be incremented.
                 */
                if (!vm_pageout_page_lock(m, &next))
                        goto unlock_page;
                else if (m->hold_count != 0) {
                        /*
                         * Held pages are essentially stuck in the
                         * queue.  So, they ought to be discounted
                         * from the inactive count.  See the
                         * calculation of the page_shortage for the
                         * loop over the active queue below.
                         */
                        addl_page_shortage++;
                        goto unlock_page;
                }
                object = m->object;
                if (!VM_OBJECT_TRYWLOCK(object)) {
                        if (!vm_pageout_fallback_object_lock(m, &next))
                                goto unlock_object;
                        else if (m->hold_count != 0) {
                                addl_page_shortage++;
                                goto unlock_object;
                        }
                }
                if (vm_page_busied(m)) {
                        /*
                         * Don't mess with busy pages.  Leave them at
                         * the front of the queue.  Most likely, they
                         * are being paged out and will leave the
                         * queue shortly after the scan finishes.  So,
                         * they ought to be discounted from the
                         * inactive count.
                         */
                        addl_page_shortage++;
unlock_object:
                        VM_OBJECT_WUNLOCK(object);
unlock_page:
                        vm_page_unlock(m);
                        continue;
                }
                KASSERT(m->hold_count == 0, ("Held page %p", m));

                /*
                 * We unlock the inactive page queue, invalidating the
                 * 'next' pointer.  Use our marker to remember our
                 * place.
                 */
                TAILQ_INSERT_AFTER(&pq->pq_pl, m, &vmd->vmd_marker, plinks.q);
                vm_pagequeue_unlock(pq);
                queues_locked = FALSE;

                /*
                 * Invalid pages can be easily freed. They cannot be
                 * mapped, vm_page_free() asserts this.
                 */
                if (m->valid == 0)
                        goto free_page;

                /*
                 * If the page has been referenced and the object is not dead,
                 * reactivate or requeue the page depending on whether the
                 * object is mapped.
                 */
                if ((m->aflags & PGA_REFERENCED) != 0) {
                        vm_page_aflag_clear(m, PGA_REFERENCED);
                        act_delta = 1;
                } else
                        act_delta = 0;
                if (object->ref_count != 0) {
                        act_delta += pmap_ts_referenced(m);
                } else {
                        KASSERT(!pmap_page_is_mapped(m),
                            ("vm_pageout_scan: page %p is mapped", m));
                }
                if (act_delta != 0) {
                        if (object->ref_count != 0) {
                                vm_page_activate(m);

                                /*
                                 * Increase the activation count if the page
                                 * was referenced while in the inactive queue.
                                 * This makes it less likely that the page will
                                 * be returned prematurely to the inactive
                                 * queue.
                                 */
                                m->act_count += act_delta + ACT_ADVANCE;
                                goto drop_page;
                        } else if ((object->flags & OBJ_DEAD) == 0)
                                goto requeue_page;
                }

                /*
                 * If the page appears to be clean at the machine-independent
                 * layer, then remove all of its mappings from the pmap in
                 * anticipation of placing it onto the cache queue.  If,
                 * however, any of the page's mappings allow write access,
                 * then the page may still be modified until the last of those
                 * mappings are removed.
                 */
                if (object->ref_count != 0) {
                        vm_page_test_dirty(m);
                        if (m->dirty == 0)
                                pmap_remove_all(m);
                }

                if (m->dirty == 0) {
                        /*
                         * Clean pages can be freed.
                         */
free_page:
                        vm_page_free(m);
                        PCPU_INC(cnt.v_dfree);
                        --page_shortage;
                } else if ((object->flags & OBJ_DEAD) != 0) {
                        /*
                         * Leave dirty pages from dead objects at the front of
                         * the queue.  They are being paged out and freed by
                         * the thread that destroyed the object.  They will
                         * leave the queue shortly after the scan finishes, so 
                         * they should be discounted from the inactive count.
                         */
                        addl_page_shortage++;
                } else if ((m->flags & PG_WINATCFLS) == 0 && pass < 2) {
                        /*
                         * Dirty pages need to be paged out, but flushing
                         * a page is extremely expensive versus freeing
                         * a clean page.  Rather then artificially limiting
                         * the number of pages we can flush, we instead give
                         * dirty pages extra priority on the inactive queue
                         * by forcing them to be cycled through the queue
                         * twice before being flushed, after which the
                         * (now clean) page will cycle through once more
                         * before being freed.  This significantly extends
                         * the thrash point for a heavily loaded machine.
                         */
                        m->flags |= PG_WINATCFLS;
requeue_page:
                        vm_pagequeue_lock(pq);
                        queues_locked = TRUE;
                        vm_page_requeue_locked(m);
                } else if (maxlaunder > 0) {
                        /*
                         * We always want to try to flush some dirty pages if
                         * we encounter them, to keep the system stable.
                         * Normally this number is small, but under extreme
                         * pressure where there are insufficient clean pages
                         * on the inactive queue, we may have to go all out.
                         */

                        if (object->type != OBJT_SWAP &&
                            object->type != OBJT_DEFAULT)
                                pageout_ok = TRUE;
                        else if (disable_swap_pageouts)
                                pageout_ok = FALSE;
                        else if (defer_swap_pageouts)
                                pageout_ok = vm_page_count_min();
                        else
                                pageout_ok = TRUE;
                        if (!pageout_ok)
                                goto requeue_page;
                        error = vm_pageout_clean(m);
                        /*
                         * Decrement page_shortage on success to account for
                         * the (future) cleaned page.  Otherwise we could wind
                         * up laundering or cleaning too many pages.
                         */
                        if (error == 0) {
                                page_shortage--;
                                maxlaunder--;
                        } else if (error == EDEADLK) {
                                pageout_lock_miss++;
                                vnodes_skipped++;
                        } else if (error == EBUSY) {
                                addl_page_shortage++;
                        }
                        vm_page_lock_assert(m, MA_NOTOWNED);
                        goto relock_queues;
                }
drop_page:
                vm_page_unlock(m);
                VM_OBJECT_WUNLOCK(object);
relock_queues:
                if (!queues_locked) {
                        vm_pagequeue_lock(pq);
                        queues_locked = TRUE;
                }
                next = TAILQ_NEXT(&vmd->vmd_marker, plinks.q);
                TAILQ_REMOVE(&pq->pq_pl, &vmd->vmd_marker, plinks.q);
        }
        vm_pagequeue_unlock(pq);

#if !defined(NO_SWAPPING)
        /*
         * Wakeup the swapout daemon if we didn't cache or free the targeted
         * number of pages. 
         */
        if (vm_swap_enabled && page_shortage > 0)
                vm_req_vmdaemon(VM_SWAP_NORMAL);
#endif

        /*
         * Wakeup the sync daemon if we skipped a vnode in a writeable object
         * and we didn't cache or free enough pages.
         */
        if (vnodes_skipped > 0 && page_shortage > vm_cnt.v_free_target -
            vm_cnt.v_free_min)
                (void)speedup_syncer();

        /*
         * If the inactive queue scan fails repeatedly to meet its
         * target, kill the largest process.
         */
        vm_pageout_mightbe_oom(vmd, page_shortage, starting_page_shortage);

        /*
         * Compute the number of pages we want to try to move from the
         * active queue to the inactive queue.
         */
        page_shortage = vm_cnt.v_inactive_target - vm_cnt.v_inactive_count +
            vm_paging_target() + deficit + addl_page_shortage;

        pq = &vmd->vmd_pagequeues[PQ_ACTIVE];
        vm_pagequeue_lock(pq);
        maxscan = pq->pq_cnt;

        /*
         * If we're just idle polling attempt to visit every
         * active page within 'update_period' seconds.
         */
        scan_tick = ticks;
        if (vm_pageout_update_period != 0) {
                min_scan = pq->pq_cnt;
                min_scan *= scan_tick - vmd->vmd_last_active_scan;
                min_scan /= hz * vm_pageout_update_period;
        } else
                min_scan = 0;
        if (min_scan > 0 || (page_shortage > 0 && maxscan > 0))
                vmd->vmd_last_active_scan = scan_tick;

        /*
         * Scan the active queue for pages that can be deactivated.  Update
         * the per-page activity counter and use it to identify deactivation
         * candidates.
         */
        for (m = TAILQ_FIRST(&pq->pq_pl), scanned = 0; m != NULL && (scanned <
            min_scan || (page_shortage > 0 && scanned < maxscan)); m = next,
            scanned++) {

                KASSERT(m->queue == PQ_ACTIVE,
                    ("vm_pageout_scan: page %p isn't active", m));

                next = TAILQ_NEXT(m, plinks.q);
                if ((m->flags & PG_MARKER) != 0)
                        continue;
                KASSERT((m->flags & PG_FICTITIOUS) == 0,
                    ("Fictitious page %p cannot be in active queue", m));
                KASSERT((m->oflags & VPO_UNMANAGED) == 0,
                    ("Unmanaged page %p cannot be in active queue", m));
                if (!vm_pageout_page_lock(m, &next)) {
                        vm_page_unlock(m);
                        continue;
                }

                /*
                 * The count for pagedaemon pages is done after checking the
                 * page for eligibility...
                 */
                PCPU_INC(cnt.v_pdpages);

                /*
                 * Check to see "how much" the page has been used.
                 */
                if ((m->aflags & PGA_REFERENCED) != 0) {
                        vm_page_aflag_clear(m, PGA_REFERENCED);
                        act_delta = 1;
                } else
                        act_delta = 0;

                /*
                 * Unlocked object ref count check.  Two races are possible.
                 * 1) The ref was transitioning to zero and we saw non-zero,
                 *    the pmap bits will be checked unnecessarily.
                 * 2) The ref was transitioning to one and we saw zero. 
                 *    The page lock prevents a new reference to this page so
                 *    we need not check the reference bits.
                 */
                if (m->object->ref_count != 0)
                        act_delta += pmap_ts_referenced(m);

                /*
                 * Advance or decay the act_count based on recent usage.
                 */
                if (act_delta != 0) {
                        m->act_count += ACT_ADVANCE + act_delta;
                        if (m->act_count > ACT_MAX)
                                m->act_count = ACT_MAX;
                } else
                        m->act_count -= min(m->act_count, ACT_DECLINE);

                /*
                 * Move this page to the tail of the active or inactive
                 * queue depending on usage.
                 */
                if (m->act_count == 0) {
                        /* Dequeue to avoid later lock recursion. */
                        vm_page_dequeue_locked(m);
                        vm_page_deactivate(m);
                        page_shortage--;
                } else
                        vm_page_requeue_locked(m);
                vm_page_unlock(m);
        }
        vm_pagequeue_unlock(pq);
#if !defined(NO_SWAPPING)
        /*
         * Idle process swapout -- run once per second.
         */
        if (vm_swap_idle_enabled) {
                static long lsec;
                if (time_second != lsec) {
                        vm_req_vmdaemon(VM_SWAP_IDLE);
                        lsec = time_second;
                }
        }
#endif
}

static int vm_pageout_oom_vote;

/*
 * The pagedaemon threads randlomly select one to perform the
 * OOM.  Trying to kill processes before all pagedaemons
 * failed to reach free target is premature.
 */
static void
vm_pageout_mightbe_oom(struct vm_domain *vmd, int page_shortage,
    int starting_page_shortage)
{
        int old_vote;

        if (starting_page_shortage <= 0 || starting_page_shortage !=
            page_shortage)
                vmd->vmd_oom_seq = 0;
        else
                vmd->vmd_oom_seq++;
        if (vmd->vmd_oom_seq < vm_pageout_oom_seq) {
                if (vmd->vmd_oom) {
                        vmd->vmd_oom = FALSE;
                        atomic_subtract_int(&vm_pageout_oom_vote, 1);
                }
                return;
        }

        /*
         * Do not follow the call sequence until OOM condition is
         * cleared.
         */
        vmd->vmd_oom_seq = 0;

        if (vmd->vmd_oom)
                return;

        vmd->vmd_oom = TRUE;
        old_vote = atomic_fetchadd_int(&vm_pageout_oom_vote, 1);
        if (old_vote != vm_ndomains - 1)
                return;

        /*
         * The current pagedaemon thread is the last in the quorum to
         * start OOM.  Initiate the selection and signaling of the
         * victim.
         */
        vm_pageout_oom(VM_OOM_MEM);

        /*
         * After one round of OOM terror, recall our vote.  On the
         * next pass, current pagedaemon would vote again if the low
         * memory condition is still there, due to vmd_oom being
         * false.
         */
        vmd->vmd_oom = FALSE;
        atomic_subtract_int(&vm_pageout_oom_vote, 1);
}

/*
 * The OOM killer is the page daemon's action of last resort when
 * memory allocation requests have been stalled for a prolonged period
 * of time because it cannot reclaim memory.  This function computes
 * the approximate number of physical pages that could be reclaimed if
 * the specified address space is destroyed.
 *
 * Private, anonymous memory owned by the address space is the
 * principal resource that we expect to recover after an OOM kill.
 * Since the physical pages mapped by the address space's COW entries
 * are typically shared pages, they are unlikely to be released and so
 * they are not counted.
 *
 * To get to the point where the page daemon runs the OOM killer, its
 * efforts to write-back vnode-backed pages may have stalled.  This
 * could be caused by a memory allocation deadlock in the write path
 * that might be resolved by an OOM kill.  Therefore, physical pages
 * belonging to vnode-backed objects are counted, because they might
 * be freed without being written out first if the address space holds
 * the last reference to an unlinked vnode.
 *
 * Similarly, physical pages belonging to OBJT_PHYS objects are
 * counted because the address space might hold the last reference to
 * the object.
 */
static long
vm_pageout_oom_pagecount(struct vmspace *vmspace)
{
        vm_map_t map;
        vm_map_entry_t entry;
        vm_object_t obj;
        long res;

        map = &vmspace->vm_map;
        KASSERT(!map->system_map, ("system map"));
        sx_assert(&map->lock, SA_LOCKED);
        res = 0;
        for (entry = map->header.next; entry != &map->header;
            entry = entry->next) {
                if ((entry->eflags & MAP_ENTRY_IS_SUB_MAP) != 0)
                        continue;
                obj = entry->object.vm_object;
                if (obj == NULL)
                        continue;
                if ((entry->eflags & MAP_ENTRY_NEEDS_COPY) != 0 &&
                    obj->ref_count != 1)
                        continue;
                switch (obj->type) {
                case OBJT_DEFAULT:
                case OBJT_SWAP:
                case OBJT_PHYS:
                case OBJT_VNODE:
                        res += obj->resident_page_count;
                        break;
                }
        }
        return (res);
}

void
vm_pageout_oom(int shortage)
{
        struct proc *p, *bigproc;
        vm_offset_t size, bigsize;
        struct thread *td;
        struct vmspace *vm;

        /*
         * We keep the process bigproc locked once we find it to keep anyone
         * from messing with it; however, there is a possibility of
         * deadlock if process B is bigproc and one of it's child processes
         * attempts to propagate a signal to B while we are waiting for A's
         * lock while walking this list.  To avoid this, we don't block on
         * the process lock but just skip a process if it is already locked.
         */
        bigproc = NULL;
        bigsize = 0;
        sx_slock(&allproc_lock);
        FOREACH_PROC_IN_SYSTEM(p) {
                int breakout;

                PROC_LOCK(p);

                /*
                 * If this is a system, protected or killed process, skip it.
                 */
                if (p->p_state != PRS_NORMAL || (p->p_flag & (P_INEXEC |
                    P_PROTECTED | P_SYSTEM | P_WEXIT)) != 0 ||
                    p->p_pid == 1 || P_KILLED(p) ||
                    (p->p_pid < 48 && swap_pager_avail != 0)) {
                        PROC_UNLOCK(p);
                        continue;
                }
                /*
                 * If the process is in a non-running type state,
                 * don't touch it.  Check all the threads individually.
                 */
                breakout = 0;
                FOREACH_THREAD_IN_PROC(p, td) {
                        thread_lock(td);
                        if (!TD_ON_RUNQ(td) &&
                            !TD_IS_RUNNING(td) &&
                            !TD_IS_SLEEPING(td) &&
                            !TD_IS_SUSPENDED(td) &&
                            !TD_IS_SWAPPED(td)) {
                                thread_unlock(td);
                                breakout = 1;
                                break;
                        }
                        thread_unlock(td);
                }
                if (breakout) {
                        PROC_UNLOCK(p);
                        continue;
                }
                /*
                 * get the process size
                 */
                vm = vmspace_acquire_ref(p);
                if (vm == NULL) {
                        PROC_UNLOCK(p);
                        continue;
                }
                _PHOLD(p);
                if (!vm_map_trylock_read(&vm->vm_map)) {
                        _PRELE(p);
                        PROC_UNLOCK(p);
                        vmspace_free(vm);
                        continue;
                }
                PROC_UNLOCK(p);
                size = vmspace_swap_count(vm);
                if (shortage == VM_OOM_MEM)
                        size += vm_pageout_oom_pagecount(vm);
                vm_map_unlock_read(&vm->vm_map);
                vmspace_free(vm);

                /*
                 * If this process is bigger than the biggest one,
                 * remember it.
                 */
                if (size > bigsize) {
                        if (bigproc != NULL)
                                PRELE(bigproc);
                        bigproc = p;
                        bigsize = size;
                } else {
                        PRELE(p);
                }
        }
        sx_sunlock(&allproc_lock);
        if (bigproc != NULL) {
                if (vm_panic_on_oom != 0)
                        panic("out of swap space");
                PROC_LOCK(bigproc);
                killproc(bigproc, "out of swap space");
                sched_nice(bigproc, PRIO_MIN);
                _PRELE(bigproc);
                PROC_UNLOCK(bigproc);
                wakeup(&vm_cnt.v_free_count);
        }
}

static void
vm_pageout_worker(void *arg)
{
        struct vm_domain *domain;
        int domidx;

        domidx = (uintptr_t)arg;
        domain = &vm_dom[domidx];

        /*
         * XXXKIB It could be useful to bind pageout daemon threads to
         * the cores belonging to the domain, from which vm_page_array
         * is allocated.
         */

        KASSERT(domain->vmd_segs != 0, ("domain without segments"));
        domain->vmd_last_active_scan = ticks;
        vm_pageout_init_marker(&domain->vmd_marker, PQ_INACTIVE);
        vm_pageout_init_marker(&domain->vmd_inacthead, PQ_INACTIVE);
        TAILQ_INSERT_HEAD(&domain->vmd_pagequeues[PQ_INACTIVE].pq_pl,
            &domain->vmd_inacthead, plinks.q);

        /*
         * The pageout daemon worker is never done, so loop forever.
         */
        while (TRUE) {
                /*
                 * If we have enough free memory, wakeup waiters.  Do
                 * not clear vm_pages_needed until we reach our target,
                 * otherwise we may be woken up over and over again and
                 * waste a lot of cpu.
                 */
                mtx_lock(&vm_page_queue_free_mtx);
                if (vm_pages_needed && !vm_page_count_min()) {
                        if (!vm_paging_needed())
                                vm_pages_needed = 0;
                        wakeup(&vm_cnt.v_free_count);
                }
                if (vm_pages_needed) {
                        /*
                         * We're still not done.  Either vm_pages_needed was
                         * set by another thread during the previous scan
                         * (typically, this happens during a level 0 scan) or
                         * vm_pages_needed was already set and the scan failed
                         * to free enough pages.  If we haven't yet performed
                         * a level >= 2 scan (unlimited dirty cleaning), then
                         * upgrade the level and scan again now.  Otherwise,
                         * sleep a bit and try again later.  While sleeping,
                         * vm_pages_needed can be cleared.
                         */
                        if (domain->vmd_pass > 1)
                                msleep(&vm_pages_needed,
                                    &vm_page_queue_free_mtx, PVM, "psleep",
                                    hz / 2);
                } else {
                        /*
                         * Good enough, sleep until required to refresh
                         * stats.
                         */
                        msleep(&vm_pages_needed, &vm_page_queue_free_mtx,
                            PVM, "psleep", hz);
                }
                if (vm_pages_needed) {
                        vm_cnt.v_pdwakeups++;
                        domain->vmd_pass++;
                } else
                        domain->vmd_pass = 0;
                mtx_unlock(&vm_page_queue_free_mtx);
                vm_pageout_scan(domain, domain->vmd_pass);
        }
}

/*
 *      vm_pageout_init initialises basic pageout daemon settings.
 */
static void
vm_pageout_init(void)
{
        /*
         * Initialize some paging parameters.
         */
        vm_cnt.v_interrupt_free_min = 2;
        if (vm_cnt.v_page_count < 2000)
                vm_pageout_page_count = 8;

        /*
         * v_free_reserved needs to include enough for the largest
         * swap pager structures plus enough for any pv_entry structs
         * when paging. 
         */
        if (vm_cnt.v_page_count > 1024)
                vm_cnt.v_free_min = 4 + (vm_cnt.v_page_count - 1024) / 200;
        else
                vm_cnt.v_free_min = 4;
        vm_cnt.v_pageout_free_min = (2*MAXBSIZE)/PAGE_SIZE +
            vm_cnt.v_interrupt_free_min;
        vm_cnt.v_free_reserved = vm_pageout_page_count +
            vm_cnt.v_pageout_free_min + (vm_cnt.v_page_count / 768);
        vm_cnt.v_free_severe = vm_cnt.v_free_min / 2;
        vm_cnt.v_free_target = 4 * vm_cnt.v_free_min + vm_cnt.v_free_reserved;
        vm_cnt.v_free_min += vm_cnt.v_free_reserved;
        vm_cnt.v_free_severe += vm_cnt.v_free_reserved;
        vm_cnt.v_inactive_target = (3 * vm_cnt.v_free_target) / 2;
        if (vm_cnt.v_inactive_target > vm_cnt.v_free_count / 3)
                vm_cnt.v_inactive_target = vm_cnt.v_free_count / 3;

        /*
         * Set the default wakeup threshold to be 10% above the minimum
         * page limit.  This keeps the steady state out of shortfall.
         */
        vm_pageout_wakeup_thresh = (vm_cnt.v_free_min / 10) * 11;

        /*
         * Set interval in seconds for active scan.  We want to visit each
         * page at least once every ten minutes.  This is to prevent worst
         * case paging behaviors with stale active LRU.
         */
        if (vm_pageout_update_period == 0)
                vm_pageout_update_period = 600;

        /* XXX does not really belong here */
        if (vm_page_max_wired == 0)
                vm_page_max_wired = vm_cnt.v_free_count / 3;
}

/*
 *     vm_pageout is the high level pageout daemon.
 */
static void
vm_pageout(void)
{
        int error;
#if MAXMEMDOM > 1
        int i;
#endif

        swap_pager_swap_init();
#if MAXMEMDOM > 1
        for (i = 1; i < vm_ndomains; i++) {
                error = kthread_add(vm_pageout_worker, (void *)(uintptr_t)i,
                    curproc, NULL, 0, 0, "dom%d", i);
                if (error != 0) {
                        panic("starting pageout for domain %d, error %d\n",
                            i, error);
                }
        }
#endif
        error = kthread_add(uma_reclaim_worker, NULL, curproc, NULL,
            0, 0, "uma");
        if (error != 0)
                panic("starting uma_reclaim helper, error %d\n", error);
        vm_pageout_worker((void *)(uintptr_t)0);
}

/*
 * Unless the free page queue lock is held by the caller, this function
 * should be regarded as advisory.  Specifically, the caller should
 * not msleep() on &vm_cnt.v_free_count following this function unless
 * the free page queue lock is held until the msleep() is performed.
 */
void
pagedaemon_wakeup(void)
{

        if (!vm_pages_needed && curthread->td_proc != pageproc) {
                vm_pages_needed = 1;
                wakeup(&vm_pages_needed);
        }
}

#if !defined(NO_SWAPPING)
static void
vm_req_vmdaemon(int req)
{
        static int lastrun = 0;

        mtx_lock(&vm_daemon_mtx);
        vm_pageout_req_swapout |= req;
        if ((ticks > (lastrun + hz)) || (ticks < lastrun)) {
                wakeup(&vm_daemon_needed);
                lastrun = ticks;
        }
        mtx_unlock(&vm_daemon_mtx);
}

static void
vm_daemon(void)
{
        struct rlimit rsslim;
        struct proc *p;
        struct thread *td;
        struct vmspace *vm;
        int breakout, swapout_flags, tryagain, attempts;
#ifdef RACCT
        uint64_t rsize, ravailable;
#endif

        while (TRUE) {
                mtx_lock(&vm_daemon_mtx);
                msleep(&vm_daemon_needed, &vm_daemon_mtx, PPAUSE, "psleep",
#ifdef RACCT
                    racct_enable ? hz : 0
#else
                    0
#endif
                );
                swapout_flags = vm_pageout_req_swapout;
                vm_pageout_req_swapout = 0;
                mtx_unlock(&vm_daemon_mtx);
                if (swapout_flags)
                        swapout_procs(swapout_flags);

                /*
                 * scan the processes for exceeding their rlimits or if
                 * process is swapped out -- deactivate pages
                 */
                tryagain = 0;
                attempts = 0;
again:
                attempts++;
                sx_slock(&allproc_lock);
                FOREACH_PROC_IN_SYSTEM(p) {
                        vm_pindex_t limit, size;

                        /*
                         * if this is a system process or if we have already
                         * looked at this process, skip it.
                         */
                        PROC_LOCK(p);
                        if (p->p_state != PRS_NORMAL ||
                            p->p_flag & (P_INEXEC | P_SYSTEM | P_WEXIT)) {
                                PROC_UNLOCK(p);
                                continue;
                        }
                        /*
                         * if the process is in a non-running type state,
                         * don't touch it.
                         */
                        breakout = 0;
                        FOREACH_THREAD_IN_PROC(p, td) {
                                thread_lock(td);
                                if (!TD_ON_RUNQ(td) &&
                                    !TD_IS_RUNNING(td) &&
                                    !TD_IS_SLEEPING(td) &&
                                    !TD_IS_SUSPENDED(td)) {
                                        thread_unlock(td);
                                        breakout = 1;
                                        break;
                                }
                                thread_unlock(td);
                        }
                        if (breakout) {
                                PROC_UNLOCK(p);
                                continue;
                        }
                        /*
                         * get a limit
                         */
                        lim_rlimit_proc(p, RLIMIT_RSS, &rsslim);
                        limit = OFF_TO_IDX(
                            qmin(rsslim.rlim_cur, rsslim.rlim_max));

                        /*
                         * let processes that are swapped out really be
                         * swapped out set the limit to nothing (will force a
                         * swap-out.)
                         */
                        if ((p->p_flag & P_INMEM) == 0)
                                limit = 0;      /* XXX */
                        vm = vmspace_acquire_ref(p);
                        PROC_UNLOCK(p);
                        if (vm == NULL)
                                continue;

                        size = vmspace_resident_count(vm);
                        if (size >= limit) {
                                vm_pageout_map_deactivate_pages(
                                    &vm->vm_map, limit);
                        }
#ifdef RACCT
                        if (racct_enable) {
                                rsize = IDX_TO_OFF(size);
                                PROC_LOCK(p);
                                racct_set(p, RACCT_RSS, rsize);
                                ravailable = racct_get_available(p, RACCT_RSS);
                                PROC_UNLOCK(p);
                                if (rsize > ravailable) {
                                        /*
                                         * Don't be overly aggressive; this
                                         * might be an innocent process,
                                         * and the limit could've been exceeded
                                         * by some memory hog.  Don't try
                                         * to deactivate more than 1/4th
                                         * of process' resident set size.
                                         */
                                        if (attempts <= 8) {
                                                if (ravailable < rsize -
                                                    (rsize / 4)) {
                                                        ravailable = rsize -
                                                            (rsize / 4);
                                                }
                                        }
                                        vm_pageout_map_deactivate_pages(
                                            &vm->vm_map,
                                            OFF_TO_IDX(ravailable));
                                        /* Update RSS usage after paging out. */
                                        size = vmspace_resident_count(vm);
                                        rsize = IDX_TO_OFF(size);
                                        PROC_LOCK(p);
                                        racct_set(p, RACCT_RSS, rsize);
                                        PROC_UNLOCK(p);
                                        if (rsize > ravailable)
                                                tryagain = 1;
                                }
                        }
#endif
                        vmspace_free(vm);
                }
                sx_sunlock(&allproc_lock);
                if (tryagain != 0 && attempts <= 10)
                        goto again;
        }
}
#endif                  /* !defined(NO_SWAPPING) */