text: /*-
   * 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_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_pageout_deficit;		/* Estimated number of pages deficit */
  int vm_pageout_wakeup_thresh;
  static int vm_pageout_oom_seq = 12;
  bool vm_pageout_wanted;		/* Event on which pageout daemon sleeps */
  bool vm_pages_needed;		/* Are threads waiting for free pages? */
  
  #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 write 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 boundary, 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 boundary.  This catches boundary
  	 * 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 - Free inactive pages
   *	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 that we want to free.
  	 */
  	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 that we can free.  The
  	 * scan will stop when we reach the target or we have scanned the
  	 * entire queue.  (Note that m->act_count is not used to make
  	 * 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 freeing it.  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 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 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_LITE(p);
  		PROC_UNLOCK(p);
  		sx_sunlock(&allproc_lock);
  		if (!vm_map_trylock_read(&vm->vm_map)) {
  			vmspace_free(vm);
  			sx_slock(&allproc_lock);
  			PRELE(p);
  			continue;
  		}
  		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);
  		sx_slock(&allproc_lock);
  
  		/*
  		 * 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) {
  		mtx_lock(&vm_page_queue_free_mtx);
  
  		/*
  		 * Generally, after a level >= 1 scan, if there are enough
  		 * free pages to wakeup the waiters, then they are already
  		 * awake.  A call to vm_page_free() during the scan awakened
  		 * them.  However, in the following case, this wakeup serves
  		 * to bound the amount of time that a thread might wait.
  		 * Suppose a thread's call to vm_page_alloc() fails, but
  		 * before that thread calls VM_WAIT, enough pages are freed by
  		 * other threads to alleviate the free page shortage.  The
  		 * thread will, nonetheless, wait until another page is freed
  		 * or this wakeup is performed.
  		 */
  		if (vm_pages_needed && !vm_page_count_min()) {
  			vm_pages_needed = false;
  			wakeup(&vm_cnt.v_free_count);
  		}
  
  		/*
  		 * Do not clear vm_pageout_wanted until we reach our target.
  		 * Otherwise, we may be awakened over and over again, wasting
  		 * CPU time.
  		 */
  		if (vm_pageout_wanted && !vm_paging_needed())
  			vm_pageout_wanted = false;
  
  		/*
  		 * Might the page daemon receive a wakeup call?
  		 */
  		if (vm_pageout_wanted) {
  			/*
  			 * No.  Either vm_pageout_wanted was set by another
  			 * thread during the previous scan, which must have
  			 * been a level 0 scan, or vm_pageout_wanted 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.
  			 */
  			mtx_unlock(&vm_page_queue_free_mtx);
  			if (domain->vmd_pass > 1)
  				pause("psleep", hz / 2);
  			domain->vmd_pass++;
  		} else {
  			/*
  			 * Yes.  Sleep until pages need to be reclaimed or
  			 * have their reference stats updated.
  			 */
  			if (mtx_sleep(&vm_pageout_wanted,
  			    &vm_page_queue_free_mtx, PDROP | PVM, "psleep",
  			    hz) == 0) {
  				PCPU_INC(cnt.v_pdwakeups);
  				domain->vmd_pass = 1;
  			} else
  				domain->vmd_pass = 0;
  		}
  
  		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;
  #ifdef VM_NUMA_ALLOC
  	int i;
  #endif
  
  	swap_pager_swap_init();
  #ifdef VM_NUMA_ALLOC
  	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_pageout_wanted && curthread->td_proc != pageproc) {
  		vm_pageout_wanted = true;
  		wakeup(&vm_pageout_wanted);
  	}
  }
  
  #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);
  			_PHOLD_LITE(p);
  			PROC_UNLOCK(p);
  			if (vm == NULL) {
  				PRELE(p);
  				continue;
  			}
  			sx_sunlock(&allproc_lock);
  
  			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_slock(&allproc_lock);
  			PRELE(p);
  		}
  		sx_sunlock(&allproc_lock);
  		if (tryagain != 0 && attempts <= 10)
  			goto again;
  	}
  }
  #endif			/* !defined(NO_SWAPPING) */
  