The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/vm/vm_pageout.c

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    1 /*-
    2  * Copyright (c) 1991 Regents of the University of California.
    3  * All rights reserved.
    4  * Copyright (c) 1994 John S. Dyson
    5  * All rights reserved.
    6  * Copyright (c) 1994 David Greenman
    7  * All rights reserved.
    8  * Copyright (c) 2005 Yahoo! Technologies Norway AS
    9  * All rights reserved.
   10  *
   11  * This code is derived from software contributed to Berkeley by
   12  * The Mach Operating System project at Carnegie-Mellon University.
   13  *
   14  * Redistribution and use in source and binary forms, with or without
   15  * modification, are permitted provided that the following conditions
   16  * are met:
   17  * 1. Redistributions of source code must retain the above copyright
   18  *    notice, this list of conditions and the following disclaimer.
   19  * 2. Redistributions in binary form must reproduce the above copyright
   20  *    notice, this list of conditions and the following disclaimer in the
   21  *    documentation and/or other materials provided with the distribution.
   22  * 3. All advertising materials mentioning features or use of this software
   23  *    must display the following acknowledgement:
   24  *      This product includes software developed by the University of
   25  *      California, Berkeley and its contributors.
   26  * 4. Neither the name of the University nor the names of its contributors
   27  *    may be used to endorse or promote products derived from this software
   28  *    without specific prior written permission.
   29  *
   30  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   31  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   32  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   33  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   34  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   35  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   36  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   37  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   38  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   39  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   40  * SUCH DAMAGE.
   41  *
   42  *      from: @(#)vm_pageout.c  7.4 (Berkeley) 5/7/91
   43  *
   44  *
   45  * Copyright (c) 1987, 1990 Carnegie-Mellon University.
   46  * All rights reserved.
   47  *
   48  * Authors: Avadis Tevanian, Jr., Michael Wayne Young
   49  *
   50  * Permission to use, copy, modify and distribute this software and
   51  * its documentation is hereby granted, provided that both the copyright
   52  * notice and this permission notice appear in all copies of the
   53  * software, derivative works or modified versions, and any portions
   54  * thereof, and that both notices appear in supporting documentation.
   55  *
   56  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
   57  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
   58  * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
   59  *
   60  * Carnegie Mellon requests users of this software to return to
   61  *
   62  *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
   63  *  School of Computer Science
   64  *  Carnegie Mellon University
   65  *  Pittsburgh PA 15213-3890
   66  *
   67  * any improvements or extensions that they make and grant Carnegie the
   68  * rights to redistribute these changes.
   69  */
   70 
   71 /*
   72  *      The proverbial page-out daemon.
   73  */
   74 
   75 #include <sys/cdefs.h>
   76 __FBSDID("$FreeBSD: head/sys/vm/vm_pageout.c 272483 2014-10-03 20:34:55Z smh $");
   77 
   78 #include "opt_vm.h"
   79 #include "opt_kdtrace.h"
   80 #include <sys/param.h>
   81 #include <sys/systm.h>
   82 #include <sys/kernel.h>
   83 #include <sys/eventhandler.h>
   84 #include <sys/lock.h>
   85 #include <sys/mutex.h>
   86 #include <sys/proc.h>
   87 #include <sys/kthread.h>
   88 #include <sys/ktr.h>
   89 #include <sys/mount.h>
   90 #include <sys/racct.h>
   91 #include <sys/resourcevar.h>
   92 #include <sys/sched.h>
   93 #include <sys/sdt.h>
   94 #include <sys/signalvar.h>
   95 #include <sys/smp.h>
   96 #include <sys/vnode.h>
   97 #include <sys/vmmeter.h>
   98 #include <sys/rwlock.h>
   99 #include <sys/sx.h>
  100 #include <sys/sysctl.h>
  101 
  102 #include <vm/vm.h>
  103 #include <vm/vm_param.h>
  104 #include <vm/vm_object.h>
  105 #include <vm/vm_page.h>
  106 #include <vm/vm_map.h>
  107 #include <vm/vm_pageout.h>
  108 #include <vm/vm_pager.h>
  109 #include <vm/vm_phys.h>
  110 #include <vm/swap_pager.h>
  111 #include <vm/vm_extern.h>
  112 #include <vm/uma.h>
  113 
  114 /*
  115  * System initialization
  116  */
  117 
  118 /* the kernel process "vm_pageout"*/
  119 static void vm_pageout(void);
  120 static void vm_pageout_init(void);
  121 static int vm_pageout_clean(vm_page_t);
  122 static void vm_pageout_scan(struct vm_domain *vmd, int pass);
  123 static void vm_pageout_mightbe_oom(struct vm_domain *vmd, int pass);
  124 
  125 SYSINIT(pagedaemon_init, SI_SUB_KTHREAD_PAGE, SI_ORDER_FIRST, vm_pageout_init,
  126     NULL);
  127 
  128 struct proc *pageproc;
  129 
  130 static struct kproc_desc page_kp = {
  131         "pagedaemon",
  132         vm_pageout,
  133         &pageproc
  134 };
  135 SYSINIT(pagedaemon, SI_SUB_KTHREAD_PAGE, SI_ORDER_SECOND, kproc_start,
  136     &page_kp);
  137 
  138 SDT_PROVIDER_DEFINE(vm);
  139 SDT_PROBE_DEFINE(vm, , , vm__lowmem_cache);
  140 SDT_PROBE_DEFINE(vm, , , vm__lowmem_scan);
  141 
  142 #if !defined(NO_SWAPPING)
  143 /* the kernel process "vm_daemon"*/
  144 static void vm_daemon(void);
  145 static struct   proc *vmproc;
  146 
  147 static struct kproc_desc vm_kp = {
  148         "vmdaemon",
  149         vm_daemon,
  150         &vmproc
  151 };
  152 SYSINIT(vmdaemon, SI_SUB_KTHREAD_VM, SI_ORDER_FIRST, kproc_start, &vm_kp);
  153 #endif
  154 
  155 
  156 int vm_pages_needed;            /* Event on which pageout daemon sleeps */
  157 int vm_pageout_deficit;         /* Estimated number of pages deficit */
  158 int vm_pageout_pages_needed;    /* flag saying that the pageout daemon needs pages */
  159 int vm_pageout_wakeup_thresh;
  160 
  161 #if !defined(NO_SWAPPING)
  162 static int vm_pageout_req_swapout;      /* XXX */
  163 static int vm_daemon_needed;
  164 static struct mtx vm_daemon_mtx;
  165 /* Allow for use by vm_pageout before vm_daemon is initialized. */
  166 MTX_SYSINIT(vm_daemon, &vm_daemon_mtx, "vm daemon", MTX_DEF);
  167 #endif
  168 static int vm_max_launder = 32;
  169 static int vm_pageout_update_period;
  170 static int defer_swap_pageouts;
  171 static int disable_swap_pageouts;
  172 static int lowmem_period = 10;
  173 static int lowmem_ticks;
  174 
  175 #if defined(NO_SWAPPING)
  176 static int vm_swap_enabled = 0;
  177 static int vm_swap_idle_enabled = 0;
  178 #else
  179 static int vm_swap_enabled = 1;
  180 static int vm_swap_idle_enabled = 0;
  181 #endif
  182 
  183 SYSCTL_INT(_vm, OID_AUTO, pageout_wakeup_thresh,
  184         CTLFLAG_RW, &vm_pageout_wakeup_thresh, 0,
  185         "free page threshold for waking up the pageout daemon");
  186 
  187 SYSCTL_INT(_vm, OID_AUTO, max_launder,
  188         CTLFLAG_RW, &vm_max_launder, 0, "Limit dirty flushes in pageout");
  189 
  190 SYSCTL_INT(_vm, OID_AUTO, pageout_update_period,
  191         CTLFLAG_RW, &vm_pageout_update_period, 0,
  192         "Maximum active LRU update period");
  193   
  194 SYSCTL_INT(_vm, OID_AUTO, lowmem_period, CTLFLAG_RW, &lowmem_period, 0,
  195         "Low memory callback period");
  196 
  197 #if defined(NO_SWAPPING)
  198 SYSCTL_INT(_vm, VM_SWAPPING_ENABLED, swap_enabled,
  199         CTLFLAG_RD, &vm_swap_enabled, 0, "Enable entire process swapout");
  200 SYSCTL_INT(_vm, OID_AUTO, swap_idle_enabled,
  201         CTLFLAG_RD, &vm_swap_idle_enabled, 0, "Allow swapout on idle criteria");
  202 #else
  203 SYSCTL_INT(_vm, VM_SWAPPING_ENABLED, swap_enabled,
  204         CTLFLAG_RW, &vm_swap_enabled, 0, "Enable entire process swapout");
  205 SYSCTL_INT(_vm, OID_AUTO, swap_idle_enabled,
  206         CTLFLAG_RW, &vm_swap_idle_enabled, 0, "Allow swapout on idle criteria");
  207 #endif
  208 
  209 SYSCTL_INT(_vm, OID_AUTO, defer_swapspace_pageouts,
  210         CTLFLAG_RW, &defer_swap_pageouts, 0, "Give preference to dirty pages in mem");
  211 
  212 SYSCTL_INT(_vm, OID_AUTO, disable_swapspace_pageouts,
  213         CTLFLAG_RW, &disable_swap_pageouts, 0, "Disallow swapout of dirty pages");
  214 
  215 static int pageout_lock_miss;
  216 SYSCTL_INT(_vm, OID_AUTO, pageout_lock_miss,
  217         CTLFLAG_RD, &pageout_lock_miss, 0, "vget() lock misses during pageout");
  218 
  219 #define VM_PAGEOUT_PAGE_COUNT 16
  220 int vm_pageout_page_count = VM_PAGEOUT_PAGE_COUNT;
  221 
  222 int vm_page_max_wired;          /* XXX max # of wired pages system-wide */
  223 SYSCTL_INT(_vm, OID_AUTO, max_wired,
  224         CTLFLAG_RW, &vm_page_max_wired, 0, "System-wide limit to wired page count");
  225 
  226 static boolean_t vm_pageout_fallback_object_lock(vm_page_t, vm_page_t *);
  227 static boolean_t vm_pageout_launder(struct vm_pagequeue *pq, int, vm_paddr_t,
  228     vm_paddr_t);
  229 #if !defined(NO_SWAPPING)
  230 static void vm_pageout_map_deactivate_pages(vm_map_t, long);
  231 static void vm_pageout_object_deactivate_pages(pmap_t, vm_object_t, long);
  232 static void vm_req_vmdaemon(int req);
  233 #endif
  234 static boolean_t vm_pageout_page_lock(vm_page_t, vm_page_t *);
  235 
  236 /*
  237  * Initialize a dummy page for marking the caller's place in the specified
  238  * paging queue.  In principle, this function only needs to set the flag
  239  * PG_MARKER.  Nonetheless, it wirte busies and initializes the hold count
  240  * to one as safety precautions.
  241  */ 
  242 static void
  243 vm_pageout_init_marker(vm_page_t marker, u_short queue)
  244 {
  245 
  246         bzero(marker, sizeof(*marker));
  247         marker->flags = PG_MARKER;
  248         marker->busy_lock = VPB_SINGLE_EXCLUSIVER;
  249         marker->queue = queue;
  250         marker->hold_count = 1;
  251 }
  252 
  253 /*
  254  * vm_pageout_fallback_object_lock:
  255  * 
  256  * Lock vm object currently associated with `m'. VM_OBJECT_TRYWLOCK is
  257  * known to have failed and page queue must be either PQ_ACTIVE or
  258  * PQ_INACTIVE.  To avoid lock order violation, unlock the page queues
  259  * while locking the vm object.  Use marker page to detect page queue
  260  * changes and maintain notion of next page on page queue.  Return
  261  * TRUE if no changes were detected, FALSE otherwise.  vm object is
  262  * locked on return.
  263  * 
  264  * This function depends on both the lock portion of struct vm_object
  265  * and normal struct vm_page being type stable.
  266  */
  267 static boolean_t
  268 vm_pageout_fallback_object_lock(vm_page_t m, vm_page_t *next)
  269 {
  270         struct vm_page marker;
  271         struct vm_pagequeue *pq;
  272         boolean_t unchanged;
  273         u_short queue;
  274         vm_object_t object;
  275 
  276         queue = m->queue;
  277         vm_pageout_init_marker(&marker, queue);
  278         pq = vm_page_pagequeue(m);
  279         object = m->object;
  280         
  281         TAILQ_INSERT_AFTER(&pq->pq_pl, m, &marker, plinks.q);
  282         vm_pagequeue_unlock(pq);
  283         vm_page_unlock(m);
  284         VM_OBJECT_WLOCK(object);
  285         vm_page_lock(m);
  286         vm_pagequeue_lock(pq);
  287 
  288         /* Page queue might have changed. */
  289         *next = TAILQ_NEXT(&marker, plinks.q);
  290         unchanged = (m->queue == queue &&
  291                      m->object == object &&
  292                      &marker == TAILQ_NEXT(m, plinks.q));
  293         TAILQ_REMOVE(&pq->pq_pl, &marker, plinks.q);
  294         return (unchanged);
  295 }
  296 
  297 /*
  298  * Lock the page while holding the page queue lock.  Use marker page
  299  * to detect page queue changes and maintain notion of next page on
  300  * page queue.  Return TRUE if no changes were detected, FALSE
  301  * otherwise.  The page is locked on return. The page queue lock might
  302  * be dropped and reacquired.
  303  *
  304  * This function depends on normal struct vm_page being type stable.
  305  */
  306 static boolean_t
  307 vm_pageout_page_lock(vm_page_t m, vm_page_t *next)
  308 {
  309         struct vm_page marker;
  310         struct vm_pagequeue *pq;
  311         boolean_t unchanged;
  312         u_short queue;
  313 
  314         vm_page_lock_assert(m, MA_NOTOWNED);
  315         if (vm_page_trylock(m))
  316                 return (TRUE);
  317 
  318         queue = m->queue;
  319         vm_pageout_init_marker(&marker, queue);
  320         pq = vm_page_pagequeue(m);
  321 
  322         TAILQ_INSERT_AFTER(&pq->pq_pl, m, &marker, plinks.q);
  323         vm_pagequeue_unlock(pq);
  324         vm_page_lock(m);
  325         vm_pagequeue_lock(pq);
  326 
  327         /* Page queue might have changed. */
  328         *next = TAILQ_NEXT(&marker, plinks.q);
  329         unchanged = (m->queue == queue && &marker == TAILQ_NEXT(m, plinks.q));
  330         TAILQ_REMOVE(&pq->pq_pl, &marker, plinks.q);
  331         return (unchanged);
  332 }
  333 
  334 /*
  335  * vm_pageout_clean:
  336  *
  337  * Clean the page and remove it from the laundry.
  338  * 
  339  * We set the busy bit to cause potential page faults on this page to
  340  * block.  Note the careful timing, however, the busy bit isn't set till
  341  * late and we cannot do anything that will mess with the page.
  342  */
  343 static int
  344 vm_pageout_clean(vm_page_t m)
  345 {
  346         vm_object_t object;
  347         vm_page_t mc[2*vm_pageout_page_count], pb, ps;
  348         int pageout_count;
  349         int ib, is, page_base;
  350         vm_pindex_t pindex = m->pindex;
  351 
  352         vm_page_lock_assert(m, MA_OWNED);
  353         object = m->object;
  354         VM_OBJECT_ASSERT_WLOCKED(object);
  355 
  356         /*
  357          * It doesn't cost us anything to pageout OBJT_DEFAULT or OBJT_SWAP
  358          * with the new swapper, but we could have serious problems paging
  359          * out other object types if there is insufficient memory.  
  360          *
  361          * Unfortunately, checking free memory here is far too late, so the
  362          * check has been moved up a procedural level.
  363          */
  364 
  365         /*
  366          * Can't clean the page if it's busy or held.
  367          */
  368         vm_page_assert_unbusied(m);
  369         KASSERT(m->hold_count == 0, ("vm_pageout_clean: page %p is held", m));
  370         vm_page_unlock(m);
  371 
  372         mc[vm_pageout_page_count] = pb = ps = m;
  373         pageout_count = 1;
  374         page_base = vm_pageout_page_count;
  375         ib = 1;
  376         is = 1;
  377 
  378         /*
  379          * Scan object for clusterable pages.
  380          *
  381          * We can cluster ONLY if: ->> the page is NOT
  382          * clean, wired, busy, held, or mapped into a
  383          * buffer, and one of the following:
  384          * 1) The page is inactive, or a seldom used
  385          *    active page.
  386          * -or-
  387          * 2) we force the issue.
  388          *
  389          * During heavy mmap/modification loads the pageout
  390          * daemon can really fragment the underlying file
  391          * due to flushing pages out of order and not trying
  392          * align the clusters (which leave sporatic out-of-order
  393          * holes).  To solve this problem we do the reverse scan
  394          * first and attempt to align our cluster, then do a 
  395          * forward scan if room remains.
  396          */
  397 more:
  398         while (ib && pageout_count < vm_pageout_page_count) {
  399                 vm_page_t p;
  400 
  401                 if (ib > pindex) {
  402                         ib = 0;
  403                         break;
  404                 }
  405 
  406                 if ((p = vm_page_prev(pb)) == NULL || vm_page_busied(p)) {
  407                         ib = 0;
  408                         break;
  409                 }
  410                 vm_page_lock(p);
  411                 vm_page_test_dirty(p);
  412                 if (p->dirty == 0 ||
  413                     p->queue != PQ_INACTIVE ||
  414                     p->hold_count != 0) {       /* may be undergoing I/O */
  415                         vm_page_unlock(p);
  416                         ib = 0;
  417                         break;
  418                 }
  419                 vm_page_unlock(p);
  420                 mc[--page_base] = pb = p;
  421                 ++pageout_count;
  422                 ++ib;
  423                 /*
  424                  * alignment boundry, stop here and switch directions.  Do
  425                  * not clear ib.
  426                  */
  427                 if ((pindex - (ib - 1)) % vm_pageout_page_count == 0)
  428                         break;
  429         }
  430 
  431         while (pageout_count < vm_pageout_page_count && 
  432             pindex + is < object->size) {
  433                 vm_page_t p;
  434 
  435                 if ((p = vm_page_next(ps)) == NULL || vm_page_busied(p))
  436                         break;
  437                 vm_page_lock(p);
  438                 vm_page_test_dirty(p);
  439                 if (p->dirty == 0 ||
  440                     p->queue != PQ_INACTIVE ||
  441                     p->hold_count != 0) {       /* may be undergoing I/O */
  442                         vm_page_unlock(p);
  443                         break;
  444                 }
  445                 vm_page_unlock(p);
  446                 mc[page_base + pageout_count] = ps = p;
  447                 ++pageout_count;
  448                 ++is;
  449         }
  450 
  451         /*
  452          * If we exhausted our forward scan, continue with the reverse scan
  453          * when possible, even past a page boundry.  This catches boundry
  454          * conditions.
  455          */
  456         if (ib && pageout_count < vm_pageout_page_count)
  457                 goto more;
  458 
  459         /*
  460          * we allow reads during pageouts...
  461          */
  462         return (vm_pageout_flush(&mc[page_base], pageout_count, 0, 0, NULL,
  463             NULL));
  464 }
  465 
  466 /*
  467  * vm_pageout_flush() - launder the given pages
  468  *
  469  *      The given pages are laundered.  Note that we setup for the start of
  470  *      I/O ( i.e. busy the page ), mark it read-only, and bump the object
  471  *      reference count all in here rather then in the parent.  If we want
  472  *      the parent to do more sophisticated things we may have to change
  473  *      the ordering.
  474  *
  475  *      Returned runlen is the count of pages between mreq and first
  476  *      page after mreq with status VM_PAGER_AGAIN.
  477  *      *eio is set to TRUE if pager returned VM_PAGER_ERROR or VM_PAGER_FAIL
  478  *      for any page in runlen set.
  479  */
  480 int
  481 vm_pageout_flush(vm_page_t *mc, int count, int flags, int mreq, int *prunlen,
  482     boolean_t *eio)
  483 {
  484         vm_object_t object = mc[0]->object;
  485         int pageout_status[count];
  486         int numpagedout = 0;
  487         int i, runlen;
  488 
  489         VM_OBJECT_ASSERT_WLOCKED(object);
  490 
  491         /*
  492          * Initiate I/O.  Bump the vm_page_t->busy counter and
  493          * mark the pages read-only.
  494          *
  495          * We do not have to fixup the clean/dirty bits here... we can
  496          * allow the pager to do it after the I/O completes.
  497          *
  498          * NOTE! mc[i]->dirty may be partial or fragmented due to an
  499          * edge case with file fragments.
  500          */
  501         for (i = 0; i < count; i++) {
  502                 KASSERT(mc[i]->valid == VM_PAGE_BITS_ALL,
  503                     ("vm_pageout_flush: partially invalid page %p index %d/%d",
  504                         mc[i], i, count));
  505                 vm_page_sbusy(mc[i]);
  506                 pmap_remove_write(mc[i]);
  507         }
  508         vm_object_pip_add(object, count);
  509 
  510         vm_pager_put_pages(object, mc, count, flags, pageout_status);
  511 
  512         runlen = count - mreq;
  513         if (eio != NULL)
  514                 *eio = FALSE;
  515         for (i = 0; i < count; i++) {
  516                 vm_page_t mt = mc[i];
  517 
  518                 KASSERT(pageout_status[i] == VM_PAGER_PEND ||
  519                     !pmap_page_is_write_mapped(mt),
  520                     ("vm_pageout_flush: page %p is not write protected", mt));
  521                 switch (pageout_status[i]) {
  522                 case VM_PAGER_OK:
  523                 case VM_PAGER_PEND:
  524                         numpagedout++;
  525                         break;
  526                 case VM_PAGER_BAD:
  527                         /*
  528                          * Page outside of range of object. Right now we
  529                          * essentially lose the changes by pretending it
  530                          * worked.
  531                          */
  532                         vm_page_undirty(mt);
  533                         break;
  534                 case VM_PAGER_ERROR:
  535                 case VM_PAGER_FAIL:
  536                         /*
  537                          * If page couldn't be paged out, then reactivate the
  538                          * page so it doesn't clog the inactive list.  (We
  539                          * will try paging out it again later).
  540                          */
  541                         vm_page_lock(mt);
  542                         vm_page_activate(mt);
  543                         vm_page_unlock(mt);
  544                         if (eio != NULL && i >= mreq && i - mreq < runlen)
  545                                 *eio = TRUE;
  546                         break;
  547                 case VM_PAGER_AGAIN:
  548                         if (i >= mreq && i - mreq < runlen)
  549                                 runlen = i - mreq;
  550                         break;
  551                 }
  552 
  553                 /*
  554                  * If the operation is still going, leave the page busy to
  555                  * block all other accesses. Also, leave the paging in
  556                  * progress indicator set so that we don't attempt an object
  557                  * collapse.
  558                  */
  559                 if (pageout_status[i] != VM_PAGER_PEND) {
  560                         vm_object_pip_wakeup(object);
  561                         vm_page_sunbusy(mt);
  562                         if (vm_page_count_severe()) {
  563                                 vm_page_lock(mt);
  564                                 vm_page_try_to_cache(mt);
  565                                 vm_page_unlock(mt);
  566                         }
  567                 }
  568         }
  569         if (prunlen != NULL)
  570                 *prunlen = runlen;
  571         return (numpagedout);
  572 }
  573 
  574 static boolean_t
  575 vm_pageout_launder(struct vm_pagequeue *pq, int tries, vm_paddr_t low,
  576     vm_paddr_t high)
  577 {
  578         struct mount *mp;
  579         struct vnode *vp;
  580         vm_object_t object;
  581         vm_paddr_t pa;
  582         vm_page_t m, m_tmp, next;
  583         int lockmode;
  584 
  585         vm_pagequeue_lock(pq);
  586         TAILQ_FOREACH_SAFE(m, &pq->pq_pl, plinks.q, next) {
  587                 if ((m->flags & PG_MARKER) != 0)
  588                         continue;
  589                 pa = VM_PAGE_TO_PHYS(m);
  590                 if (pa < low || pa + PAGE_SIZE > high)
  591                         continue;
  592                 if (!vm_pageout_page_lock(m, &next) || m->hold_count != 0) {
  593                         vm_page_unlock(m);
  594                         continue;
  595                 }
  596                 object = m->object;
  597                 if ((!VM_OBJECT_TRYWLOCK(object) &&
  598                     (!vm_pageout_fallback_object_lock(m, &next) ||
  599                     m->hold_count != 0)) || vm_page_busied(m)) {
  600                         vm_page_unlock(m);
  601                         VM_OBJECT_WUNLOCK(object);
  602                         continue;
  603                 }
  604                 vm_page_test_dirty(m);
  605                 if (m->dirty == 0 && object->ref_count != 0)
  606                         pmap_remove_all(m);
  607                 if (m->dirty != 0) {
  608                         vm_page_unlock(m);
  609                         if (tries == 0 || (object->flags & OBJ_DEAD) != 0) {
  610                                 VM_OBJECT_WUNLOCK(object);
  611                                 continue;
  612                         }
  613                         if (object->type == OBJT_VNODE) {
  614                                 vm_pagequeue_unlock(pq);
  615                                 vp = object->handle;
  616                                 vm_object_reference_locked(object);
  617                                 VM_OBJECT_WUNLOCK(object);
  618                                 (void)vn_start_write(vp, &mp, V_WAIT);
  619                                 lockmode = MNT_SHARED_WRITES(vp->v_mount) ?
  620                                     LK_SHARED : LK_EXCLUSIVE;
  621                                 vn_lock(vp, lockmode | LK_RETRY);
  622                                 VM_OBJECT_WLOCK(object);
  623                                 vm_object_page_clean(object, 0, 0, OBJPC_SYNC);
  624                                 VM_OBJECT_WUNLOCK(object);
  625                                 VOP_UNLOCK(vp, 0);
  626                                 vm_object_deallocate(object);
  627                                 vn_finished_write(mp);
  628                                 return (TRUE);
  629                         } else if (object->type == OBJT_SWAP ||
  630                             object->type == OBJT_DEFAULT) {
  631                                 vm_pagequeue_unlock(pq);
  632                                 m_tmp = m;
  633                                 vm_pageout_flush(&m_tmp, 1, VM_PAGER_PUT_SYNC,
  634                                     0, NULL, NULL);
  635                                 VM_OBJECT_WUNLOCK(object);
  636                                 return (TRUE);
  637                         }
  638                 } else {
  639                         /*
  640                          * Dequeue here to prevent lock recursion in
  641                          * vm_page_cache().
  642                          */
  643                         vm_page_dequeue_locked(m);
  644                         vm_page_cache(m);
  645                         vm_page_unlock(m);
  646                 }
  647                 VM_OBJECT_WUNLOCK(object);
  648         }
  649         vm_pagequeue_unlock(pq);
  650         return (FALSE);
  651 }
  652 
  653 /*
  654  * Increase the number of cached pages.  The specified value, "tries",
  655  * determines which categories of pages are cached:
  656  *
  657  *  0: All clean, inactive pages within the specified physical address range
  658  *     are cached.  Will not sleep.
  659  *  1: The vm_lowmem handlers are called.  All inactive pages within
  660  *     the specified physical address range are cached.  May sleep.
  661  *  2: The vm_lowmem handlers are called.  All inactive and active pages
  662  *     within the specified physical address range are cached.  May sleep.
  663  */
  664 void
  665 vm_pageout_grow_cache(int tries, vm_paddr_t low, vm_paddr_t high)
  666 {
  667         int actl, actmax, inactl, inactmax, dom, initial_dom;
  668         static int start_dom = 0;
  669 
  670         if (tries > 0) {
  671                 /*
  672                  * Decrease registered cache sizes.  The vm_lowmem handlers
  673                  * may acquire locks and/or sleep, so they can only be invoked
  674                  * when "tries" is greater than zero.
  675                  */
  676                 SDT_PROBE0(vm, , , vm__lowmem_cache);
  677                 EVENTHANDLER_INVOKE(vm_lowmem, 0);
  678 
  679                 /*
  680                  * We do this explicitly after the caches have been drained
  681                  * above.
  682                  */
  683                 uma_reclaim();
  684         }
  685 
  686         /*
  687          * Make the next scan start on the next domain.
  688          */
  689         initial_dom = atomic_fetchadd_int(&start_dom, 1) % vm_ndomains;
  690 
  691         inactl = 0;
  692         inactmax = vm_cnt.v_inactive_count;
  693         actl = 0;
  694         actmax = tries < 2 ? 0 : vm_cnt.v_active_count;
  695         dom = initial_dom;
  696 
  697         /*
  698          * Scan domains in round-robin order, first inactive queues,
  699          * then active.  Since domain usually owns large physically
  700          * contiguous chunk of memory, it makes sense to completely
  701          * exhaust one domain before switching to next, while growing
  702          * the pool of contiguous physical pages.
  703          *
  704          * Do not even start launder a domain which cannot contain
  705          * the specified address range, as indicated by segments
  706          * constituting the domain.
  707          */
  708 again:
  709         if (inactl < inactmax) {
  710                 if (vm_phys_domain_intersects(vm_dom[dom].vmd_segs,
  711                     low, high) &&
  712                     vm_pageout_launder(&vm_dom[dom].vmd_pagequeues[PQ_INACTIVE],
  713                     tries, low, high)) {
  714                         inactl++;
  715                         goto again;
  716                 }
  717                 if (++dom == vm_ndomains)
  718                         dom = 0;
  719                 if (dom != initial_dom)
  720                         goto again;
  721         }
  722         if (actl < actmax) {
  723                 if (vm_phys_domain_intersects(vm_dom[dom].vmd_segs,
  724                     low, high) &&
  725                     vm_pageout_launder(&vm_dom[dom].vmd_pagequeues[PQ_ACTIVE],
  726                       tries, low, high)) {
  727                         actl++;
  728                         goto again;
  729                 }
  730                 if (++dom == vm_ndomains)
  731                         dom = 0;
  732                 if (dom != initial_dom)
  733                         goto again;
  734         }
  735 }
  736 
  737 #if !defined(NO_SWAPPING)
  738 /*
  739  *      vm_pageout_object_deactivate_pages
  740  *
  741  *      Deactivate enough pages to satisfy the inactive target
  742  *      requirements.
  743  *
  744  *      The object and map must be locked.
  745  */
  746 static void
  747 vm_pageout_object_deactivate_pages(pmap_t pmap, vm_object_t first_object,
  748     long desired)
  749 {
  750         vm_object_t backing_object, object;
  751         vm_page_t p;
  752         int act_delta, remove_mode;
  753 
  754         VM_OBJECT_ASSERT_LOCKED(first_object);
  755         if ((first_object->flags & OBJ_FICTITIOUS) != 0)
  756                 return;
  757         for (object = first_object;; object = backing_object) {
  758                 if (pmap_resident_count(pmap) <= desired)
  759                         goto unlock_return;
  760                 VM_OBJECT_ASSERT_LOCKED(object);
  761                 if ((object->flags & OBJ_UNMANAGED) != 0 ||
  762                     object->paging_in_progress != 0)
  763                         goto unlock_return;
  764 
  765                 remove_mode = 0;
  766                 if (object->shadow_count > 1)
  767                         remove_mode = 1;
  768                 /*
  769                  * Scan the object's entire memory queue.
  770                  */
  771                 TAILQ_FOREACH(p, &object->memq, listq) {
  772                         if (pmap_resident_count(pmap) <= desired)
  773                                 goto unlock_return;
  774                         if (vm_page_busied(p))
  775                                 continue;
  776                         PCPU_INC(cnt.v_pdpages);
  777                         vm_page_lock(p);
  778                         if (p->wire_count != 0 || p->hold_count != 0 ||
  779                             !pmap_page_exists_quick(pmap, p)) {
  780                                 vm_page_unlock(p);
  781                                 continue;
  782                         }
  783                         act_delta = pmap_ts_referenced(p);
  784                         if ((p->aflags & PGA_REFERENCED) != 0) {
  785                                 if (act_delta == 0)
  786                                         act_delta = 1;
  787                                 vm_page_aflag_clear(p, PGA_REFERENCED);
  788                         }
  789                         if (p->queue != PQ_ACTIVE && act_delta != 0) {
  790                                 vm_page_activate(p);
  791                                 p->act_count += act_delta;
  792                         } else if (p->queue == PQ_ACTIVE) {
  793                                 if (act_delta == 0) {
  794                                         p->act_count -= min(p->act_count,
  795                                             ACT_DECLINE);
  796                                         if (!remove_mode && p->act_count == 0) {
  797                                                 pmap_remove_all(p);
  798                                                 vm_page_deactivate(p);
  799                                         } else
  800                                                 vm_page_requeue(p);
  801                                 } else {
  802                                         vm_page_activate(p);
  803                                         if (p->act_count < ACT_MAX -
  804                                             ACT_ADVANCE)
  805                                                 p->act_count += ACT_ADVANCE;
  806                                         vm_page_requeue(p);
  807                                 }
  808                         } else if (p->queue == PQ_INACTIVE)
  809                                 pmap_remove_all(p);
  810                         vm_page_unlock(p);
  811                 }
  812                 if ((backing_object = object->backing_object) == NULL)
  813                         goto unlock_return;
  814                 VM_OBJECT_RLOCK(backing_object);
  815                 if (object != first_object)
  816                         VM_OBJECT_RUNLOCK(object);
  817         }
  818 unlock_return:
  819         if (object != first_object)
  820                 VM_OBJECT_RUNLOCK(object);
  821 }
  822 
  823 /*
  824  * deactivate some number of pages in a map, try to do it fairly, but
  825  * that is really hard to do.
  826  */
  827 static void
  828 vm_pageout_map_deactivate_pages(map, desired)
  829         vm_map_t map;
  830         long desired;
  831 {
  832         vm_map_entry_t tmpe;
  833         vm_object_t obj, bigobj;
  834         int nothingwired;
  835 
  836         if (!vm_map_trylock(map))
  837                 return;
  838 
  839         bigobj = NULL;
  840         nothingwired = TRUE;
  841 
  842         /*
  843          * first, search out the biggest object, and try to free pages from
  844          * that.
  845          */
  846         tmpe = map->header.next;
  847         while (tmpe != &map->header) {
  848                 if ((tmpe->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
  849                         obj = tmpe->object.vm_object;
  850                         if (obj != NULL && VM_OBJECT_TRYRLOCK(obj)) {
  851                                 if (obj->shadow_count <= 1 &&
  852                                     (bigobj == NULL ||
  853                                      bigobj->resident_page_count < obj->resident_page_count)) {
  854                                         if (bigobj != NULL)
  855                                                 VM_OBJECT_RUNLOCK(bigobj);
  856                                         bigobj = obj;
  857                                 } else
  858                                         VM_OBJECT_RUNLOCK(obj);
  859                         }
  860                 }
  861                 if (tmpe->wired_count > 0)
  862                         nothingwired = FALSE;
  863                 tmpe = tmpe->next;
  864         }
  865 
  866         if (bigobj != NULL) {
  867                 vm_pageout_object_deactivate_pages(map->pmap, bigobj, desired);
  868                 VM_OBJECT_RUNLOCK(bigobj);
  869         }
  870         /*
  871          * Next, hunt around for other pages to deactivate.  We actually
  872          * do this search sort of wrong -- .text first is not the best idea.
  873          */
  874         tmpe = map->header.next;
  875         while (tmpe != &map->header) {
  876                 if (pmap_resident_count(vm_map_pmap(map)) <= desired)
  877                         break;
  878                 if ((tmpe->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
  879                         obj = tmpe->object.vm_object;
  880                         if (obj != NULL) {
  881                                 VM_OBJECT_RLOCK(obj);
  882                                 vm_pageout_object_deactivate_pages(map->pmap, obj, desired);
  883                                 VM_OBJECT_RUNLOCK(obj);
  884                         }
  885                 }
  886                 tmpe = tmpe->next;
  887         }
  888 
  889         /*
  890          * Remove all mappings if a process is swapped out, this will free page
  891          * table pages.
  892          */
  893         if (desired == 0 && nothingwired) {
  894                 pmap_remove(vm_map_pmap(map), vm_map_min(map),
  895                     vm_map_max(map));
  896         }
  897 
  898         vm_map_unlock(map);
  899 }
  900 #endif          /* !defined(NO_SWAPPING) */
  901 
  902 /*
  903  *      vm_pageout_scan does the dirty work for the pageout daemon.
  904  *
  905  *      pass 0 - Update active LRU/deactivate pages
  906  *      pass 1 - Move inactive to cache or free
  907  *      pass 2 - Launder dirty pages
  908  */
  909 static void
  910 vm_pageout_scan(struct vm_domain *vmd, int pass)
  911 {
  912         vm_page_t m, next;
  913         struct vm_pagequeue *pq;
  914         vm_object_t object;
  915         int act_delta, addl_page_shortage, deficit, maxscan, page_shortage;
  916         int vnodes_skipped = 0;
  917         int maxlaunder;
  918         int lockmode;
  919         boolean_t queues_locked;
  920 
  921         /*
  922          * If we need to reclaim memory ask kernel caches to return
  923          * some.  We rate limit to avoid thrashing.
  924          */
  925         if (vmd == &vm_dom[0] && pass > 0 &&
  926             (ticks - lowmem_ticks) / hz >= lowmem_period) {
  927                 /*
  928                  * Decrease registered cache sizes.
  929                  */
  930                 SDT_PROBE0(vm, , , vm__lowmem_scan);
  931                 EVENTHANDLER_INVOKE(vm_lowmem, 0);
  932                 /*
  933                  * We do this explicitly after the caches have been
  934                  * drained above.
  935                  */
  936                 uma_reclaim();
  937                 lowmem_ticks = ticks;
  938         }
  939 
  940         /*
  941          * The addl_page_shortage is the number of temporarily
  942          * stuck pages in the inactive queue.  In other words, the
  943          * number of pages from the inactive count that should be
  944          * discounted in setting the target for the active queue scan.
  945          */
  946         addl_page_shortage = 0;
  947 
  948         /*
  949          * Calculate the number of pages we want to either free or move
  950          * to the cache.
  951          */
  952         if (pass > 0) {
  953                 deficit = atomic_readandclear_int(&vm_pageout_deficit);
  954                 page_shortage = vm_paging_target() + deficit;
  955         } else
  956                 page_shortage = deficit = 0;
  957 
  958         /*
  959          * maxlaunder limits the number of dirty pages we flush per scan.
  960          * For most systems a smaller value (16 or 32) is more robust under
  961          * extreme memory and disk pressure because any unnecessary writes
  962          * to disk can result in extreme performance degredation.  However,
  963          * systems with excessive dirty pages (especially when MAP_NOSYNC is
  964          * used) will die horribly with limited laundering.  If the pageout
  965          * daemon cannot clean enough pages in the first pass, we let it go
  966          * all out in succeeding passes.
  967          */
  968         if ((maxlaunder = vm_max_launder) <= 1)
  969                 maxlaunder = 1;
  970         if (pass > 1)
  971                 maxlaunder = 10000;
  972 
  973         /*
  974          * Start scanning the inactive queue for pages we can move to the
  975          * cache or free.  The scan will stop when the target is reached or
  976          * we have scanned the entire inactive queue.  Note that m->act_count
  977          * is not used to form decisions for the inactive queue, only for the
  978          * active queue.
  979          */
  980         pq = &vmd->vmd_pagequeues[PQ_INACTIVE];
  981         maxscan = pq->pq_cnt;
  982         vm_pagequeue_lock(pq);
  983         queues_locked = TRUE;
  984         for (m = TAILQ_FIRST(&pq->pq_pl);
  985              m != NULL && maxscan-- > 0 && page_shortage > 0;
  986              m = next) {
  987                 vm_pagequeue_assert_locked(pq);
  988                 KASSERT(queues_locked, ("unlocked queues"));
  989                 KASSERT(m->queue == PQ_INACTIVE, ("Inactive queue %p", m));
  990 
  991                 PCPU_INC(cnt.v_pdpages);
  992                 next = TAILQ_NEXT(m, plinks.q);
  993 
  994                 /*
  995                  * skip marker pages
  996                  */
  997                 if (m->flags & PG_MARKER)
  998                         continue;
  999 
 1000                 KASSERT((m->flags & PG_FICTITIOUS) == 0,
 1001                     ("Fictitious page %p cannot be in inactive queue", m));
 1002                 KASSERT((m->oflags & VPO_UNMANAGED) == 0,
 1003                     ("Unmanaged page %p cannot be in inactive queue", m));
 1004 
 1005                 /*
 1006                  * The page or object lock acquisitions fail if the
 1007                  * page was removed from the queue or moved to a
 1008                  * different position within the queue.  In either
 1009                  * case, addl_page_shortage should not be incremented.
 1010                  */
 1011                 if (!vm_pageout_page_lock(m, &next)) {
 1012                         vm_page_unlock(m);
 1013                         continue;
 1014                 }
 1015                 object = m->object;
 1016                 if (!VM_OBJECT_TRYWLOCK(object) &&
 1017                     !vm_pageout_fallback_object_lock(m, &next)) {
 1018                         vm_page_unlock(m);
 1019                         VM_OBJECT_WUNLOCK(object);
 1020                         continue;
 1021                 }
 1022 
 1023                 /*
 1024                  * Don't mess with busy pages, keep them at at the
 1025                  * front of the queue, most likely they are being
 1026                  * paged out.  Increment addl_page_shortage for busy
 1027                  * pages, because they may leave the inactive queue
 1028                  * shortly after page scan is finished.
 1029                  */
 1030                 if (vm_page_busied(m)) {
 1031                         vm_page_unlock(m);
 1032                         VM_OBJECT_WUNLOCK(object);
 1033                         addl_page_shortage++;
 1034                         continue;
 1035                 }
 1036 
 1037                 /*
 1038                  * We unlock the inactive page queue, invalidating the
 1039                  * 'next' pointer.  Use our marker to remember our
 1040                  * place.
 1041                  */
 1042                 TAILQ_INSERT_AFTER(&pq->pq_pl, m, &vmd->vmd_marker, plinks.q);
 1043                 vm_pagequeue_unlock(pq);
 1044                 queues_locked = FALSE;
 1045 
 1046                 /*
 1047                  * We bump the activation count if the page has been
 1048                  * referenced while in the inactive queue.  This makes
 1049                  * it less likely that the page will be added back to the
 1050                  * inactive queue prematurely again.  Here we check the 
 1051                  * page tables (or emulated bits, if any), given the upper 
 1052                  * level VM system not knowing anything about existing 
 1053                  * references.
 1054                  */
 1055                 if ((m->aflags & PGA_REFERENCED) != 0) {
 1056                         vm_page_aflag_clear(m, PGA_REFERENCED);
 1057                         act_delta = 1;
 1058                 } else
 1059                         act_delta = 0;
 1060                 if (object->ref_count != 0) {
 1061                         act_delta += pmap_ts_referenced(m);
 1062                 } else {
 1063                         KASSERT(!pmap_page_is_mapped(m),
 1064                             ("vm_pageout_scan: page %p is mapped", m));
 1065                 }
 1066 
 1067                 /*
 1068                  * If the upper level VM system knows about any page 
 1069                  * references, we reactivate the page or requeue it.
 1070                  */
 1071                 if (act_delta != 0) {
 1072                         if (object->ref_count != 0) {
 1073                                 vm_page_activate(m);
 1074                                 m->act_count += act_delta + ACT_ADVANCE;
 1075                         } else {
 1076                                 vm_pagequeue_lock(pq);
 1077                                 queues_locked = TRUE;
 1078                                 vm_page_requeue_locked(m);
 1079                         }
 1080                         VM_OBJECT_WUNLOCK(object);
 1081                         vm_page_unlock(m);
 1082                         goto relock_queues;
 1083                 }
 1084 
 1085                 if (m->hold_count != 0) {
 1086                         vm_page_unlock(m);
 1087                         VM_OBJECT_WUNLOCK(object);
 1088 
 1089                         /*
 1090                          * Held pages are essentially stuck in the
 1091                          * queue.  So, they ought to be discounted
 1092                          * from the inactive count.  See the
 1093                          * calculation of the page_shortage for the
 1094                          * loop over the active queue below.
 1095                          */
 1096                         addl_page_shortage++;
 1097                         goto relock_queues;
 1098                 }
 1099 
 1100                 /*
 1101                  * If the page appears to be clean at the machine-independent
 1102                  * layer, then remove all of its mappings from the pmap in
 1103                  * anticipation of placing it onto the cache queue.  If,
 1104                  * however, any of the page's mappings allow write access,
 1105                  * then the page may still be modified until the last of those
 1106                  * mappings are removed.
 1107                  */
 1108                 vm_page_test_dirty(m);
 1109                 if (m->dirty == 0 && object->ref_count != 0)
 1110                         pmap_remove_all(m);
 1111 
 1112                 if (m->valid == 0) {
 1113                         /*
 1114                          * Invalid pages can be easily freed
 1115                          */
 1116                         vm_page_free(m);
 1117                         PCPU_INC(cnt.v_dfree);
 1118                         --page_shortage;
 1119                 } else if (m->dirty == 0) {
 1120                         /*
 1121                          * Clean pages can be placed onto the cache queue.
 1122                          * This effectively frees them.
 1123                          */
 1124                         vm_page_cache(m);
 1125                         --page_shortage;
 1126                 } else if ((m->flags & PG_WINATCFLS) == 0 && pass < 2) {
 1127                         /*
 1128                          * Dirty pages need to be paged out, but flushing
 1129                          * a page is extremely expensive versus freeing
 1130                          * a clean page.  Rather then artificially limiting
 1131                          * the number of pages we can flush, we instead give
 1132                          * dirty pages extra priority on the inactive queue
 1133                          * by forcing them to be cycled through the queue
 1134                          * twice before being flushed, after which the
 1135                          * (now clean) page will cycle through once more
 1136                          * before being freed.  This significantly extends
 1137                          * the thrash point for a heavily loaded machine.
 1138                          */
 1139                         m->flags |= PG_WINATCFLS;
 1140                         vm_pagequeue_lock(pq);
 1141                         queues_locked = TRUE;
 1142                         vm_page_requeue_locked(m);
 1143                 } else if (maxlaunder > 0) {
 1144                         /*
 1145                          * We always want to try to flush some dirty pages if
 1146                          * we encounter them, to keep the system stable.
 1147                          * Normally this number is small, but under extreme
 1148                          * pressure where there are insufficient clean pages
 1149                          * on the inactive queue, we may have to go all out.
 1150                          */
 1151                         int swap_pageouts_ok;
 1152                         struct vnode *vp = NULL;
 1153                         struct mount *mp = NULL;
 1154 
 1155                         if ((object->type != OBJT_SWAP) && (object->type != OBJT_DEFAULT)) {
 1156                                 swap_pageouts_ok = 1;
 1157                         } else {
 1158                                 swap_pageouts_ok = !(defer_swap_pageouts || disable_swap_pageouts);
 1159                                 swap_pageouts_ok |= (!disable_swap_pageouts && defer_swap_pageouts &&
 1160                                 vm_page_count_min());
 1161                                                                                 
 1162                         }
 1163 
 1164                         /*
 1165                          * We don't bother paging objects that are "dead".  
 1166                          * Those objects are in a "rundown" state.
 1167                          */
 1168                         if (!swap_pageouts_ok || (object->flags & OBJ_DEAD)) {
 1169                                 vm_pagequeue_lock(pq);
 1170                                 vm_page_unlock(m);
 1171                                 VM_OBJECT_WUNLOCK(object);
 1172                                 queues_locked = TRUE;
 1173                                 vm_page_requeue_locked(m);
 1174                                 goto relock_queues;
 1175                         }
 1176 
 1177                         /*
 1178                          * The object is already known NOT to be dead.   It
 1179                          * is possible for the vget() to block the whole
 1180                          * pageout daemon, but the new low-memory handling
 1181                          * code should prevent it.
 1182                          *
 1183                          * The previous code skipped locked vnodes and, worse,
 1184                          * reordered pages in the queue.  This results in
 1185                          * completely non-deterministic operation and, on a
 1186                          * busy system, can lead to extremely non-optimal
 1187                          * pageouts.  For example, it can cause clean pages
 1188                          * to be freed and dirty pages to be moved to the end
 1189                          * of the queue.  Since dirty pages are also moved to
 1190                          * the end of the queue once-cleaned, this gives
 1191                          * way too large a weighting to deferring the freeing
 1192                          * of dirty pages.
 1193                          *
 1194                          * We can't wait forever for the vnode lock, we might
 1195                          * deadlock due to a vn_read() getting stuck in
 1196                          * vm_wait while holding this vnode.  We skip the 
 1197                          * vnode if we can't get it in a reasonable amount
 1198                          * of time.
 1199                          */
 1200                         if (object->type == OBJT_VNODE) {
 1201                                 vm_page_unlock(m);
 1202                                 vp = object->handle;
 1203                                 if (vp->v_type == VREG &&
 1204                                     vn_start_write(vp, &mp, V_NOWAIT) != 0) {
 1205                                         mp = NULL;
 1206                                         ++pageout_lock_miss;
 1207                                         if (object->flags & OBJ_MIGHTBEDIRTY)
 1208                                                 vnodes_skipped++;
 1209                                         goto unlock_and_continue;
 1210                                 }
 1211                                 KASSERT(mp != NULL,
 1212                                     ("vp %p with NULL v_mount", vp));
 1213                                 vm_object_reference_locked(object);
 1214                                 VM_OBJECT_WUNLOCK(object);
 1215                                 lockmode = MNT_SHARED_WRITES(vp->v_mount) ?
 1216                                     LK_SHARED : LK_EXCLUSIVE;
 1217                                 if (vget(vp, lockmode | LK_TIMELOCK,
 1218                                     curthread)) {
 1219                                         VM_OBJECT_WLOCK(object);
 1220                                         ++pageout_lock_miss;
 1221                                         if (object->flags & OBJ_MIGHTBEDIRTY)
 1222                                                 vnodes_skipped++;
 1223                                         vp = NULL;
 1224                                         goto unlock_and_continue;
 1225                                 }
 1226                                 VM_OBJECT_WLOCK(object);
 1227                                 vm_page_lock(m);
 1228                                 vm_pagequeue_lock(pq);
 1229                                 queues_locked = TRUE;
 1230                                 /*
 1231                                  * The page might have been moved to another
 1232                                  * queue during potential blocking in vget()
 1233                                  * above.  The page might have been freed and
 1234                                  * reused for another vnode.
 1235                                  */
 1236                                 if (m->queue != PQ_INACTIVE ||
 1237                                     m->object != object ||
 1238                                     TAILQ_NEXT(m, plinks.q) != &vmd->vmd_marker) {
 1239                                         vm_page_unlock(m);
 1240                                         if (object->flags & OBJ_MIGHTBEDIRTY)
 1241                                                 vnodes_skipped++;
 1242                                         goto unlock_and_continue;
 1243                                 }
 1244         
 1245                                 /*
 1246                                  * The page may have been busied during the
 1247                                  * blocking in vget().  We don't move the
 1248                                  * page back onto the end of the queue so that
 1249                                  * statistics are more correct if we don't.
 1250                                  */
 1251                                 if (vm_page_busied(m)) {
 1252                                         vm_page_unlock(m);
 1253                                         addl_page_shortage++;
 1254                                         goto unlock_and_continue;
 1255                                 }
 1256 
 1257                                 /*
 1258                                  * If the page has become held it might
 1259                                  * be undergoing I/O, so skip it
 1260                                  */
 1261                                 if (m->hold_count != 0) {
 1262                                         vm_page_unlock(m);
 1263                                         addl_page_shortage++;
 1264                                         if (object->flags & OBJ_MIGHTBEDIRTY)
 1265                                                 vnodes_skipped++;
 1266                                         goto unlock_and_continue;
 1267                                 }
 1268                                 vm_pagequeue_unlock(pq);
 1269                                 queues_locked = FALSE;
 1270                         }
 1271 
 1272                         /*
 1273                          * If a page is dirty, then it is either being washed
 1274                          * (but not yet cleaned) or it is still in the
 1275                          * laundry.  If it is still in the laundry, then we
 1276                          * start the cleaning operation. 
 1277                          *
 1278                          * decrement page_shortage on success to account for
 1279                          * the (future) cleaned page.  Otherwise we could wind
 1280                          * up laundering or cleaning too many pages.
 1281                          */
 1282                         if (vm_pageout_clean(m) != 0) {
 1283                                 --page_shortage;
 1284                                 --maxlaunder;
 1285                         }
 1286 unlock_and_continue:
 1287                         vm_page_lock_assert(m, MA_NOTOWNED);
 1288                         VM_OBJECT_WUNLOCK(object);
 1289                         if (mp != NULL) {
 1290                                 if (queues_locked) {
 1291                                         vm_pagequeue_unlock(pq);
 1292                                         queues_locked = FALSE;
 1293                                 }
 1294                                 if (vp != NULL)
 1295                                         vput(vp);
 1296                                 vm_object_deallocate(object);
 1297                                 vn_finished_write(mp);
 1298                         }
 1299                         vm_page_lock_assert(m, MA_NOTOWNED);
 1300                         goto relock_queues;
 1301                 }
 1302                 vm_page_unlock(m);
 1303                 VM_OBJECT_WUNLOCK(object);
 1304 relock_queues:
 1305                 if (!queues_locked) {
 1306                         vm_pagequeue_lock(pq);
 1307                         queues_locked = TRUE;
 1308                 }
 1309                 next = TAILQ_NEXT(&vmd->vmd_marker, plinks.q);
 1310                 TAILQ_REMOVE(&pq->pq_pl, &vmd->vmd_marker, plinks.q);
 1311         }
 1312         vm_pagequeue_unlock(pq);
 1313 
 1314 #if !defined(NO_SWAPPING)
 1315         /*
 1316          * Wakeup the swapout daemon if we didn't cache or free the targeted
 1317          * number of pages. 
 1318          */
 1319         if (vm_swap_enabled && page_shortage > 0)
 1320                 vm_req_vmdaemon(VM_SWAP_NORMAL);
 1321 #endif
 1322 
 1323         /*
 1324          * Wakeup the sync daemon if we skipped a vnode in a writeable object
 1325          * and we didn't cache or free enough pages.
 1326          */
 1327         if (vnodes_skipped > 0 && page_shortage > vm_cnt.v_free_target -
 1328             vm_cnt.v_free_min)
 1329                 (void)speedup_syncer();
 1330 
 1331         /*
 1332          * Compute the number of pages we want to try to move from the
 1333          * active queue to the inactive queue.
 1334          */
 1335         page_shortage = vm_cnt.v_inactive_target - vm_cnt.v_inactive_count +
 1336             vm_paging_target() + deficit + addl_page_shortage;
 1337 
 1338         pq = &vmd->vmd_pagequeues[PQ_ACTIVE];
 1339         vm_pagequeue_lock(pq);
 1340         maxscan = pq->pq_cnt;
 1341 
 1342         /*
 1343          * If we're just idle polling attempt to visit every
 1344          * active page within 'update_period' seconds.
 1345          */
 1346         if (pass == 0 && vm_pageout_update_period != 0) {
 1347                 maxscan /= vm_pageout_update_period;
 1348                 page_shortage = maxscan;
 1349         }
 1350 
 1351         /*
 1352          * Scan the active queue for things we can deactivate. We nominally
 1353          * track the per-page activity counter and use it to locate
 1354          * deactivation candidates.
 1355          */
 1356         m = TAILQ_FIRST(&pq->pq_pl);
 1357         while (m != NULL && maxscan-- > 0 && page_shortage > 0) {
 1358 
 1359                 KASSERT(m->queue == PQ_ACTIVE,
 1360                     ("vm_pageout_scan: page %p isn't active", m));
 1361 
 1362                 next = TAILQ_NEXT(m, plinks.q);
 1363                 if ((m->flags & PG_MARKER) != 0) {
 1364                         m = next;
 1365                         continue;
 1366                 }
 1367                 KASSERT((m->flags & PG_FICTITIOUS) == 0,
 1368                     ("Fictitious page %p cannot be in active queue", m));
 1369                 KASSERT((m->oflags & VPO_UNMANAGED) == 0,
 1370                     ("Unmanaged page %p cannot be in active queue", m));
 1371                 if (!vm_pageout_page_lock(m, &next)) {
 1372                         vm_page_unlock(m);
 1373                         m = next;
 1374                         continue;
 1375                 }
 1376 
 1377                 /*
 1378                  * The count for pagedaemon pages is done after checking the
 1379                  * page for eligibility...
 1380                  */
 1381                 PCPU_INC(cnt.v_pdpages);
 1382 
 1383                 /*
 1384                  * Check to see "how much" the page has been used.
 1385                  */
 1386                 if ((m->aflags & PGA_REFERENCED) != 0) {
 1387                         vm_page_aflag_clear(m, PGA_REFERENCED);
 1388                         act_delta = 1;
 1389                 } else
 1390                         act_delta = 0;
 1391 
 1392                 /*
 1393                  * Unlocked object ref count check.  Two races are possible.
 1394                  * 1) The ref was transitioning to zero and we saw non-zero,
 1395                  *    the pmap bits will be checked unnecessarily.
 1396                  * 2) The ref was transitioning to one and we saw zero. 
 1397                  *    The page lock prevents a new reference to this page so
 1398                  *    we need not check the reference bits.
 1399                  */
 1400                 if (m->object->ref_count != 0)
 1401                         act_delta += pmap_ts_referenced(m);
 1402 
 1403                 /*
 1404                  * Advance or decay the act_count based on recent usage.
 1405                  */
 1406                 if (act_delta != 0) {
 1407                         m->act_count += ACT_ADVANCE + act_delta;
 1408                         if (m->act_count > ACT_MAX)
 1409                                 m->act_count = ACT_MAX;
 1410                 } else
 1411                         m->act_count -= min(m->act_count, ACT_DECLINE);
 1412 
 1413                 /*
 1414                  * Move this page to the tail of the active or inactive
 1415                  * queue depending on usage.
 1416                  */
 1417                 if (m->act_count == 0) {
 1418                         /* Dequeue to avoid later lock recursion. */
 1419                         vm_page_dequeue_locked(m);
 1420                         vm_page_deactivate(m);
 1421                         page_shortage--;
 1422                 } else
 1423                         vm_page_requeue_locked(m);
 1424                 vm_page_unlock(m);
 1425                 m = next;
 1426         }
 1427         vm_pagequeue_unlock(pq);
 1428 #if !defined(NO_SWAPPING)
 1429         /*
 1430          * Idle process swapout -- run once per second.
 1431          */
 1432         if (vm_swap_idle_enabled) {
 1433                 static long lsec;
 1434                 if (time_second != lsec) {
 1435                         vm_req_vmdaemon(VM_SWAP_IDLE);
 1436                         lsec = time_second;
 1437                 }
 1438         }
 1439 #endif
 1440 
 1441         /*
 1442          * If we are critically low on one of RAM or swap and low on
 1443          * the other, kill the largest process.  However, we avoid
 1444          * doing this on the first pass in order to give ourselves a
 1445          * chance to flush out dirty vnode-backed pages and to allow
 1446          * active pages to be moved to the inactive queue and reclaimed.
 1447          */
 1448         vm_pageout_mightbe_oom(vmd, pass);
 1449 }
 1450 
 1451 static int vm_pageout_oom_vote;
 1452 
 1453 /*
 1454  * The pagedaemon threads randlomly select one to perform the
 1455  * OOM.  Trying to kill processes before all pagedaemons
 1456  * failed to reach free target is premature.
 1457  */
 1458 static void
 1459 vm_pageout_mightbe_oom(struct vm_domain *vmd, int pass)
 1460 {
 1461         int old_vote;
 1462 
 1463         if (pass <= 1 || !((swap_pager_avail < 64 && vm_page_count_min()) ||
 1464             (swap_pager_full && vm_paging_target() > 0))) {
 1465                 if (vmd->vmd_oom) {
 1466                         vmd->vmd_oom = FALSE;
 1467                         atomic_subtract_int(&vm_pageout_oom_vote, 1);
 1468                 }
 1469                 return;
 1470         }
 1471 
 1472         if (vmd->vmd_oom)
 1473                 return;
 1474 
 1475         vmd->vmd_oom = TRUE;
 1476         old_vote = atomic_fetchadd_int(&vm_pageout_oom_vote, 1);
 1477         if (old_vote != vm_ndomains - 1)
 1478                 return;
 1479 
 1480         /*
 1481          * The current pagedaemon thread is the last in the quorum to
 1482          * start OOM.  Initiate the selection and signaling of the
 1483          * victim.
 1484          */
 1485         vm_pageout_oom(VM_OOM_MEM);
 1486 
 1487         /*
 1488          * After one round of OOM terror, recall our vote.  On the
 1489          * next pass, current pagedaemon would vote again if the low
 1490          * memory condition is still there, due to vmd_oom being
 1491          * false.
 1492          */
 1493         vmd->vmd_oom = FALSE;
 1494         atomic_subtract_int(&vm_pageout_oom_vote, 1);
 1495 }
 1496 
 1497 void
 1498 vm_pageout_oom(int shortage)
 1499 {
 1500         struct proc *p, *bigproc;
 1501         vm_offset_t size, bigsize;
 1502         struct thread *td;
 1503         struct vmspace *vm;
 1504 
 1505         /*
 1506          * We keep the process bigproc locked once we find it to keep anyone
 1507          * from messing with it; however, there is a possibility of
 1508          * deadlock if process B is bigproc and one of it's child processes
 1509          * attempts to propagate a signal to B while we are waiting for A's
 1510          * lock while walking this list.  To avoid this, we don't block on
 1511          * the process lock but just skip a process if it is already locked.
 1512          */
 1513         bigproc = NULL;
 1514         bigsize = 0;
 1515         sx_slock(&allproc_lock);
 1516         FOREACH_PROC_IN_SYSTEM(p) {
 1517                 int breakout;
 1518 
 1519                 if (PROC_TRYLOCK(p) == 0)
 1520                         continue;
 1521                 /*
 1522                  * If this is a system, protected or killed process, skip it.
 1523                  */
 1524                 if (p->p_state != PRS_NORMAL ||
 1525                     (p->p_flag & (P_INEXEC | P_PROTECTED | P_SYSTEM)) ||
 1526                     (p->p_pid == 1) || P_KILLED(p) ||
 1527                     ((p->p_pid < 48) && (swap_pager_avail != 0))) {
 1528                         PROC_UNLOCK(p);
 1529                         continue;
 1530                 }
 1531                 /*
 1532                  * If the process is in a non-running type state,
 1533                  * don't touch it.  Check all the threads individually.
 1534                  */
 1535                 breakout = 0;
 1536                 FOREACH_THREAD_IN_PROC(p, td) {
 1537                         thread_lock(td);
 1538                         if (!TD_ON_RUNQ(td) &&
 1539                             !TD_IS_RUNNING(td) &&
 1540                             !TD_IS_SLEEPING(td) &&
 1541                             !TD_IS_SUSPENDED(td)) {
 1542                                 thread_unlock(td);
 1543                                 breakout = 1;
 1544                                 break;
 1545                         }
 1546                         thread_unlock(td);
 1547                 }
 1548                 if (breakout) {
 1549                         PROC_UNLOCK(p);
 1550                         continue;
 1551                 }
 1552                 /*
 1553                  * get the process size
 1554                  */
 1555                 vm = vmspace_acquire_ref(p);
 1556                 if (vm == NULL) {
 1557                         PROC_UNLOCK(p);
 1558                         continue;
 1559                 }
 1560                 if (!vm_map_trylock_read(&vm->vm_map)) {
 1561                         vmspace_free(vm);
 1562                         PROC_UNLOCK(p);
 1563                         continue;
 1564                 }
 1565                 size = vmspace_swap_count(vm);
 1566                 vm_map_unlock_read(&vm->vm_map);
 1567                 if (shortage == VM_OOM_MEM)
 1568                         size += vmspace_resident_count(vm);
 1569                 vmspace_free(vm);
 1570                 /*
 1571                  * if the this process is bigger than the biggest one
 1572                  * remember it.
 1573                  */
 1574                 if (size > bigsize) {
 1575                         if (bigproc != NULL)
 1576                                 PROC_UNLOCK(bigproc);
 1577                         bigproc = p;
 1578                         bigsize = size;
 1579                 } else
 1580                         PROC_UNLOCK(p);
 1581         }
 1582         sx_sunlock(&allproc_lock);
 1583         if (bigproc != NULL) {
 1584                 killproc(bigproc, "out of swap space");
 1585                 sched_nice(bigproc, PRIO_MIN);
 1586                 PROC_UNLOCK(bigproc);
 1587                 wakeup(&vm_cnt.v_free_count);
 1588         }
 1589 }
 1590 
 1591 static void
 1592 vm_pageout_worker(void *arg)
 1593 {
 1594         struct vm_domain *domain;
 1595         int domidx;
 1596 
 1597         domidx = (uintptr_t)arg;
 1598         domain = &vm_dom[domidx];
 1599 
 1600         /*
 1601          * XXXKIB It could be useful to bind pageout daemon threads to
 1602          * the cores belonging to the domain, from which vm_page_array
 1603          * is allocated.
 1604          */
 1605 
 1606         KASSERT(domain->vmd_segs != 0, ("domain without segments"));
 1607         vm_pageout_init_marker(&domain->vmd_marker, PQ_INACTIVE);
 1608 
 1609         /*
 1610          * The pageout daemon worker is never done, so loop forever.
 1611          */
 1612         while (TRUE) {
 1613                 /*
 1614                  * If we have enough free memory, wakeup waiters.  Do
 1615                  * not clear vm_pages_needed until we reach our target,
 1616                  * otherwise we may be woken up over and over again and
 1617                  * waste a lot of cpu.
 1618                  */
 1619                 mtx_lock(&vm_page_queue_free_mtx);
 1620                 if (vm_pages_needed && !vm_page_count_min()) {
 1621                         if (!vm_paging_needed())
 1622                                 vm_pages_needed = 0;
 1623                         wakeup(&vm_cnt.v_free_count);
 1624                 }
 1625                 if (vm_pages_needed) {
 1626                         /*
 1627                          * Still not done, take a second pass without waiting
 1628                          * (unlimited dirty cleaning), otherwise sleep a bit
 1629                          * and try again.
 1630                          */
 1631                         if (domain->vmd_pass > 1)
 1632                                 msleep(&vm_pages_needed,
 1633                                     &vm_page_queue_free_mtx, PVM, "psleep",
 1634                                     hz / 2);
 1635                 } else {
 1636                         /*
 1637                          * Good enough, sleep until required to refresh
 1638                          * stats.
 1639                          */
 1640                         domain->vmd_pass = 0;
 1641                         msleep(&vm_pages_needed, &vm_page_queue_free_mtx,
 1642                             PVM, "psleep", hz);
 1643 
 1644                 }
 1645                 if (vm_pages_needed) {
 1646                         vm_cnt.v_pdwakeups++;
 1647                         domain->vmd_pass++;
 1648                 }
 1649                 mtx_unlock(&vm_page_queue_free_mtx);
 1650                 vm_pageout_scan(domain, domain->vmd_pass);
 1651         }
 1652 }
 1653 
 1654 /*
 1655  *      vm_pageout_init initialises basic pageout daemon settings.
 1656  */
 1657 static void
 1658 vm_pageout_init(void)
 1659 {
 1660         /*
 1661          * Initialize some paging parameters.
 1662          */
 1663         vm_cnt.v_interrupt_free_min = 2;
 1664         if (vm_cnt.v_page_count < 2000)
 1665                 vm_pageout_page_count = 8;
 1666 
 1667         /*
 1668          * v_free_reserved needs to include enough for the largest
 1669          * swap pager structures plus enough for any pv_entry structs
 1670          * when paging. 
 1671          */
 1672         if (vm_cnt.v_page_count > 1024)
 1673                 vm_cnt.v_free_min = 4 + (vm_cnt.v_page_count - 1024) / 200;
 1674         else
 1675                 vm_cnt.v_free_min = 4;
 1676         vm_cnt.v_pageout_free_min = (2*MAXBSIZE)/PAGE_SIZE +
 1677             vm_cnt.v_interrupt_free_min;
 1678         vm_cnt.v_free_reserved = vm_pageout_page_count +
 1679             vm_cnt.v_pageout_free_min + (vm_cnt.v_page_count / 768);
 1680         vm_cnt.v_free_severe = vm_cnt.v_free_min / 2;
 1681         vm_cnt.v_free_target = 4 * vm_cnt.v_free_min + vm_cnt.v_free_reserved;
 1682         vm_cnt.v_free_min += vm_cnt.v_free_reserved;
 1683         vm_cnt.v_free_severe += vm_cnt.v_free_reserved;
 1684         vm_cnt.v_inactive_target = (3 * vm_cnt.v_free_target) / 2;
 1685         if (vm_cnt.v_inactive_target > vm_cnt.v_free_count / 3)
 1686                 vm_cnt.v_inactive_target = vm_cnt.v_free_count / 3;
 1687 
 1688         /*
 1689          * Set the default wakeup threshold to be 10% above the minimum
 1690          * page limit.  This keeps the steady state out of shortfall.
 1691          */
 1692         vm_pageout_wakeup_thresh = (vm_cnt.v_free_min / 10) * 11;
 1693 
 1694         /*
 1695          * Set interval in seconds for active scan.  We want to visit each
 1696          * page at least once every ten minutes.  This is to prevent worst
 1697          * case paging behaviors with stale active LRU.
 1698          */
 1699         if (vm_pageout_update_period == 0)
 1700                 vm_pageout_update_period = 600;
 1701 
 1702         /* XXX does not really belong here */
 1703         if (vm_page_max_wired == 0)
 1704                 vm_page_max_wired = vm_cnt.v_free_count / 3;
 1705 }
 1706 
 1707 /*
 1708  *     vm_pageout is the high level pageout daemon.
 1709  */
 1710 static void
 1711 vm_pageout(void)
 1712 {
 1713 #if MAXMEMDOM > 1
 1714         int error, i;
 1715 #endif
 1716 
 1717         swap_pager_swap_init();
 1718 #if MAXMEMDOM > 1
 1719         for (i = 1; i < vm_ndomains; i++) {
 1720                 error = kthread_add(vm_pageout_worker, (void *)(uintptr_t)i,
 1721                     curproc, NULL, 0, 0, "dom%d", i);
 1722                 if (error != 0) {
 1723                         panic("starting pageout for domain %d, error %d\n",
 1724                             i, error);
 1725                 }
 1726         }
 1727 #endif
 1728         vm_pageout_worker((void *)(uintptr_t)0);
 1729 }
 1730 
 1731 /*
 1732  * Unless the free page queue lock is held by the caller, this function
 1733  * should be regarded as advisory.  Specifically, the caller should
 1734  * not msleep() on &vm_cnt.v_free_count following this function unless
 1735  * the free page queue lock is held until the msleep() is performed.
 1736  */
 1737 void
 1738 pagedaemon_wakeup(void)
 1739 {
 1740 
 1741         if (!vm_pages_needed && curthread->td_proc != pageproc) {
 1742                 vm_pages_needed = 1;
 1743                 wakeup(&vm_pages_needed);
 1744         }
 1745 }
 1746 
 1747 #if !defined(NO_SWAPPING)
 1748 static void
 1749 vm_req_vmdaemon(int req)
 1750 {
 1751         static int lastrun = 0;
 1752 
 1753         mtx_lock(&vm_daemon_mtx);
 1754         vm_pageout_req_swapout |= req;
 1755         if ((ticks > (lastrun + hz)) || (ticks < lastrun)) {
 1756                 wakeup(&vm_daemon_needed);
 1757                 lastrun = ticks;
 1758         }
 1759         mtx_unlock(&vm_daemon_mtx);
 1760 }
 1761 
 1762 static void
 1763 vm_daemon(void)
 1764 {
 1765         struct rlimit rsslim;
 1766         struct proc *p;
 1767         struct thread *td;
 1768         struct vmspace *vm;
 1769         int breakout, swapout_flags, tryagain, attempts;
 1770 #ifdef RACCT
 1771         uint64_t rsize, ravailable;
 1772 #endif
 1773 
 1774         while (TRUE) {
 1775                 mtx_lock(&vm_daemon_mtx);
 1776 #ifdef RACCT
 1777                 msleep(&vm_daemon_needed, &vm_daemon_mtx, PPAUSE, "psleep", hz);
 1778 #else
 1779                 msleep(&vm_daemon_needed, &vm_daemon_mtx, PPAUSE, "psleep", 0);
 1780 #endif
 1781                 swapout_flags = vm_pageout_req_swapout;
 1782                 vm_pageout_req_swapout = 0;
 1783                 mtx_unlock(&vm_daemon_mtx);
 1784                 if (swapout_flags)
 1785                         swapout_procs(swapout_flags);
 1786 
 1787                 /*
 1788                  * scan the processes for exceeding their rlimits or if
 1789                  * process is swapped out -- deactivate pages
 1790                  */
 1791                 tryagain = 0;
 1792                 attempts = 0;
 1793 again:
 1794                 attempts++;
 1795                 sx_slock(&allproc_lock);
 1796                 FOREACH_PROC_IN_SYSTEM(p) {
 1797                         vm_pindex_t limit, size;
 1798 
 1799                         /*
 1800                          * if this is a system process or if we have already
 1801                          * looked at this process, skip it.
 1802                          */
 1803                         PROC_LOCK(p);
 1804                         if (p->p_state != PRS_NORMAL ||
 1805                             p->p_flag & (P_INEXEC | P_SYSTEM | P_WEXIT)) {
 1806                                 PROC_UNLOCK(p);
 1807                                 continue;
 1808                         }
 1809                         /*
 1810                          * if the process is in a non-running type state,
 1811                          * don't touch it.
 1812                          */
 1813                         breakout = 0;
 1814                         FOREACH_THREAD_IN_PROC(p, td) {
 1815                                 thread_lock(td);
 1816                                 if (!TD_ON_RUNQ(td) &&
 1817                                     !TD_IS_RUNNING(td) &&
 1818                                     !TD_IS_SLEEPING(td) &&
 1819                                     !TD_IS_SUSPENDED(td)) {
 1820                                         thread_unlock(td);
 1821                                         breakout = 1;
 1822                                         break;
 1823                                 }
 1824                                 thread_unlock(td);
 1825                         }
 1826                         if (breakout) {
 1827                                 PROC_UNLOCK(p);
 1828                                 continue;
 1829                         }
 1830                         /*
 1831                          * get a limit
 1832                          */
 1833                         lim_rlimit(p, RLIMIT_RSS, &rsslim);
 1834                         limit = OFF_TO_IDX(
 1835                             qmin(rsslim.rlim_cur, rsslim.rlim_max));
 1836 
 1837                         /*
 1838                          * let processes that are swapped out really be
 1839                          * swapped out set the limit to nothing (will force a
 1840                          * swap-out.)
 1841                          */
 1842                         if ((p->p_flag & P_INMEM) == 0)
 1843                                 limit = 0;      /* XXX */
 1844                         vm = vmspace_acquire_ref(p);
 1845                         PROC_UNLOCK(p);
 1846                         if (vm == NULL)
 1847                                 continue;
 1848 
 1849                         size = vmspace_resident_count(vm);
 1850                         if (size >= limit) {
 1851                                 vm_pageout_map_deactivate_pages(
 1852                                     &vm->vm_map, limit);
 1853                         }
 1854 #ifdef RACCT
 1855                         rsize = IDX_TO_OFF(size);
 1856                         PROC_LOCK(p);
 1857                         racct_set(p, RACCT_RSS, rsize);
 1858                         ravailable = racct_get_available(p, RACCT_RSS);
 1859                         PROC_UNLOCK(p);
 1860                         if (rsize > ravailable) {
 1861                                 /*
 1862                                  * Don't be overly aggressive; this might be
 1863                                  * an innocent process, and the limit could've
 1864                                  * been exceeded by some memory hog.  Don't
 1865                                  * try to deactivate more than 1/4th of process'
 1866                                  * resident set size.
 1867                                  */
 1868                                 if (attempts <= 8) {
 1869                                         if (ravailable < rsize - (rsize / 4))
 1870                                                 ravailable = rsize - (rsize / 4);
 1871                                 }
 1872                                 vm_pageout_map_deactivate_pages(
 1873                                     &vm->vm_map, OFF_TO_IDX(ravailable));
 1874                                 /* Update RSS usage after paging out. */
 1875                                 size = vmspace_resident_count(vm);
 1876                                 rsize = IDX_TO_OFF(size);
 1877                                 PROC_LOCK(p);
 1878                                 racct_set(p, RACCT_RSS, rsize);
 1879                                 PROC_UNLOCK(p);
 1880                                 if (rsize > ravailable)
 1881                                         tryagain = 1;
 1882                         }
 1883 #endif
 1884                         vmspace_free(vm);
 1885                 }
 1886                 sx_sunlock(&allproc_lock);
 1887                 if (tryagain != 0 && attempts <= 10)
 1888                         goto again;
 1889         }
 1890 }
 1891 #endif                  /* !defined(NO_SWAPPING) */

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