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 292469 2015-12-19 18:42:50Z alc $");
   77 
   78 #include "opt_vm.h"
   79 
   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/time.h>
   97 #include <sys/vnode.h>
   98 #include <sys/vmmeter.h>
   99 #include <sys/rwlock.h>
  100 #include <sys/sx.h>
  101 #include <sys/sysctl.h>
  102 
  103 #include <vm/vm.h>
  104 #include <vm/vm_param.h>
  105 #include <vm/vm_object.h>
  106 #include <vm/vm_page.h>
  107 #include <vm/vm_map.h>
  108 #include <vm/vm_pageout.h>
  109 #include <vm/vm_pager.h>
  110 #include <vm/vm_phys.h>
  111 #include <vm/swap_pager.h>
  112 #include <vm/vm_extern.h>
  113 #include <vm/uma.h>
  114 
  115 /*
  116  * System initialization
  117  */
  118 
  119 /* the kernel process "vm_pageout"*/
  120 static void vm_pageout(void);
  121 static void vm_pageout_init(void);
  122 static int vm_pageout_clean(vm_page_t m);
  123 static int vm_pageout_cluster(vm_page_t m);
  124 static void vm_pageout_scan(struct vm_domain *vmd, int pass);
  125 static void vm_pageout_mightbe_oom(struct vm_domain *vmd, int page_shortage,
  126     int starting_page_shortage);
  127 
  128 SYSINIT(pagedaemon_init, SI_SUB_KTHREAD_PAGE, SI_ORDER_FIRST, vm_pageout_init,
  129     NULL);
  130 
  131 struct proc *pageproc;
  132 
  133 static struct kproc_desc page_kp = {
  134         "pagedaemon",
  135         vm_pageout,
  136         &pageproc
  137 };
  138 SYSINIT(pagedaemon, SI_SUB_KTHREAD_PAGE, SI_ORDER_SECOND, kproc_start,
  139     &page_kp);
  140 
  141 SDT_PROVIDER_DEFINE(vm);
  142 SDT_PROBE_DEFINE(vm, , , vm__lowmem_cache);
  143 SDT_PROBE_DEFINE(vm, , , vm__lowmem_scan);
  144 
  145 #if !defined(NO_SWAPPING)
  146 /* the kernel process "vm_daemon"*/
  147 static void vm_daemon(void);
  148 static struct   proc *vmproc;
  149 
  150 static struct kproc_desc vm_kp = {
  151         "vmdaemon",
  152         vm_daemon,
  153         &vmproc
  154 };
  155 SYSINIT(vmdaemon, SI_SUB_KTHREAD_VM, SI_ORDER_FIRST, kproc_start, &vm_kp);
  156 #endif
  157 
  158 
  159 int vm_pages_needed;            /* Event on which pageout daemon sleeps */
  160 int vm_pageout_deficit;         /* Estimated number of pages deficit */
  161 int vm_pageout_wakeup_thresh;
  162 static int vm_pageout_oom_seq = 12;
  163 
  164 #if !defined(NO_SWAPPING)
  165 static int vm_pageout_req_swapout;      /* XXX */
  166 static int vm_daemon_needed;
  167 static struct mtx vm_daemon_mtx;
  168 /* Allow for use by vm_pageout before vm_daemon is initialized. */
  169 MTX_SYSINIT(vm_daemon, &vm_daemon_mtx, "vm daemon", MTX_DEF);
  170 #endif
  171 static int vm_max_launder = 32;
  172 static int vm_pageout_update_period;
  173 static int defer_swap_pageouts;
  174 static int disable_swap_pageouts;
  175 static int lowmem_period = 10;
  176 static time_t lowmem_uptime;
  177 
  178 #if defined(NO_SWAPPING)
  179 static int vm_swap_enabled = 0;
  180 static int vm_swap_idle_enabled = 0;
  181 #else
  182 static int vm_swap_enabled = 1;
  183 static int vm_swap_idle_enabled = 0;
  184 #endif
  185 
  186 static int vm_panic_on_oom = 0;
  187 
  188 SYSCTL_INT(_vm, OID_AUTO, panic_on_oom,
  189         CTLFLAG_RWTUN, &vm_panic_on_oom, 0,
  190         "panic on out of memory instead of killing the largest process");
  191 
  192 SYSCTL_INT(_vm, OID_AUTO, pageout_wakeup_thresh,
  193         CTLFLAG_RW, &vm_pageout_wakeup_thresh, 0,
  194         "free page threshold for waking up the pageout daemon");
  195 
  196 SYSCTL_INT(_vm, OID_AUTO, max_launder,
  197         CTLFLAG_RW, &vm_max_launder, 0, "Limit dirty flushes in pageout");
  198 
  199 SYSCTL_INT(_vm, OID_AUTO, pageout_update_period,
  200         CTLFLAG_RW, &vm_pageout_update_period, 0,
  201         "Maximum active LRU update period");
  202   
  203 SYSCTL_INT(_vm, OID_AUTO, lowmem_period, CTLFLAG_RW, &lowmem_period, 0,
  204         "Low memory callback period");
  205 
  206 #if defined(NO_SWAPPING)
  207 SYSCTL_INT(_vm, VM_SWAPPING_ENABLED, swap_enabled,
  208         CTLFLAG_RD, &vm_swap_enabled, 0, "Enable entire process swapout");
  209 SYSCTL_INT(_vm, OID_AUTO, swap_idle_enabled,
  210         CTLFLAG_RD, &vm_swap_idle_enabled, 0, "Allow swapout on idle criteria");
  211 #else
  212 SYSCTL_INT(_vm, VM_SWAPPING_ENABLED, swap_enabled,
  213         CTLFLAG_RW, &vm_swap_enabled, 0, "Enable entire process swapout");
  214 SYSCTL_INT(_vm, OID_AUTO, swap_idle_enabled,
  215         CTLFLAG_RW, &vm_swap_idle_enabled, 0, "Allow swapout on idle criteria");
  216 #endif
  217 
  218 SYSCTL_INT(_vm, OID_AUTO, defer_swapspace_pageouts,
  219         CTLFLAG_RW, &defer_swap_pageouts, 0, "Give preference to dirty pages in mem");
  220 
  221 SYSCTL_INT(_vm, OID_AUTO, disable_swapspace_pageouts,
  222         CTLFLAG_RW, &disable_swap_pageouts, 0, "Disallow swapout of dirty pages");
  223 
  224 static int pageout_lock_miss;
  225 SYSCTL_INT(_vm, OID_AUTO, pageout_lock_miss,
  226         CTLFLAG_RD, &pageout_lock_miss, 0, "vget() lock misses during pageout");
  227 
  228 SYSCTL_INT(_vm, OID_AUTO, pageout_oom_seq,
  229         CTLFLAG_RW, &vm_pageout_oom_seq, 0,
  230         "back-to-back calls to oom detector to start OOM");
  231 
  232 #define VM_PAGEOUT_PAGE_COUNT 16
  233 int vm_pageout_page_count = VM_PAGEOUT_PAGE_COUNT;
  234 
  235 int vm_page_max_wired;          /* XXX max # of wired pages system-wide */
  236 SYSCTL_INT(_vm, OID_AUTO, max_wired,
  237         CTLFLAG_RW, &vm_page_max_wired, 0, "System-wide limit to wired page count");
  238 
  239 static boolean_t vm_pageout_fallback_object_lock(vm_page_t, vm_page_t *);
  240 #if !defined(NO_SWAPPING)
  241 static void vm_pageout_map_deactivate_pages(vm_map_t, long);
  242 static void vm_pageout_object_deactivate_pages(pmap_t, vm_object_t, long);
  243 static void vm_req_vmdaemon(int req);
  244 #endif
  245 static boolean_t vm_pageout_page_lock(vm_page_t, vm_page_t *);
  246 
  247 /*
  248  * Initialize a dummy page for marking the caller's place in the specified
  249  * paging queue.  In principle, this function only needs to set the flag
  250  * PG_MARKER.  Nonetheless, it wirte busies and initializes the hold count
  251  * to one as safety precautions.
  252  */ 
  253 static void
  254 vm_pageout_init_marker(vm_page_t marker, u_short queue)
  255 {
  256 
  257         bzero(marker, sizeof(*marker));
  258         marker->flags = PG_MARKER;
  259         marker->busy_lock = VPB_SINGLE_EXCLUSIVER;
  260         marker->queue = queue;
  261         marker->hold_count = 1;
  262 }
  263 
  264 /*
  265  * vm_pageout_fallback_object_lock:
  266  * 
  267  * Lock vm object currently associated with `m'. VM_OBJECT_TRYWLOCK is
  268  * known to have failed and page queue must be either PQ_ACTIVE or
  269  * PQ_INACTIVE.  To avoid lock order violation, unlock the page queues
  270  * while locking the vm object.  Use marker page to detect page queue
  271  * changes and maintain notion of next page on page queue.  Return
  272  * TRUE if no changes were detected, FALSE otherwise.  vm object is
  273  * locked on return.
  274  * 
  275  * This function depends on both the lock portion of struct vm_object
  276  * and normal struct vm_page being type stable.
  277  */
  278 static boolean_t
  279 vm_pageout_fallback_object_lock(vm_page_t m, vm_page_t *next)
  280 {
  281         struct vm_page marker;
  282         struct vm_pagequeue *pq;
  283         boolean_t unchanged;
  284         u_short queue;
  285         vm_object_t object;
  286 
  287         queue = m->queue;
  288         vm_pageout_init_marker(&marker, queue);
  289         pq = vm_page_pagequeue(m);
  290         object = m->object;
  291         
  292         TAILQ_INSERT_AFTER(&pq->pq_pl, m, &marker, plinks.q);
  293         vm_pagequeue_unlock(pq);
  294         vm_page_unlock(m);
  295         VM_OBJECT_WLOCK(object);
  296         vm_page_lock(m);
  297         vm_pagequeue_lock(pq);
  298 
  299         /*
  300          * The page's object might have changed, and/or the page might
  301          * have moved from its original position in the queue.  If the
  302          * page's object has changed, then the caller should abandon
  303          * processing the page because the wrong object lock was
  304          * acquired.  Use the marker's plinks.q, not the page's, to
  305          * determine if the page has been moved.  The state of the
  306          * page's plinks.q can be indeterminate; whereas, the marker's
  307          * plinks.q must be valid.
  308          */
  309         *next = TAILQ_NEXT(&marker, plinks.q);
  310         unchanged = m->object == object &&
  311             m == TAILQ_PREV(&marker, pglist, plinks.q);
  312         KASSERT(!unchanged || m->queue == queue,
  313             ("page %p queue %d %d", m, queue, m->queue));
  314         TAILQ_REMOVE(&pq->pq_pl, &marker, plinks.q);
  315         return (unchanged);
  316 }
  317 
  318 /*
  319  * Lock the page while holding the page queue lock.  Use marker page
  320  * to detect page queue changes and maintain notion of next page on
  321  * page queue.  Return TRUE if no changes were detected, FALSE
  322  * otherwise.  The page is locked on return. The page queue lock might
  323  * be dropped and reacquired.
  324  *
  325  * This function depends on normal struct vm_page being type stable.
  326  */
  327 static boolean_t
  328 vm_pageout_page_lock(vm_page_t m, vm_page_t *next)
  329 {
  330         struct vm_page marker;
  331         struct vm_pagequeue *pq;
  332         boolean_t unchanged;
  333         u_short queue;
  334 
  335         vm_page_lock_assert(m, MA_NOTOWNED);
  336         if (vm_page_trylock(m))
  337                 return (TRUE);
  338 
  339         queue = m->queue;
  340         vm_pageout_init_marker(&marker, queue);
  341         pq = vm_page_pagequeue(m);
  342 
  343         TAILQ_INSERT_AFTER(&pq->pq_pl, m, &marker, plinks.q);
  344         vm_pagequeue_unlock(pq);
  345         vm_page_lock(m);
  346         vm_pagequeue_lock(pq);
  347 
  348         /* Page queue might have changed. */
  349         *next = TAILQ_NEXT(&marker, plinks.q);
  350         unchanged = m == TAILQ_PREV(&marker, pglist, plinks.q);
  351         KASSERT(!unchanged || m->queue == queue,
  352             ("page %p queue %d %d", m, queue, m->queue));
  353         TAILQ_REMOVE(&pq->pq_pl, &marker, plinks.q);
  354         return (unchanged);
  355 }
  356 
  357 /*
  358  * vm_pageout_clean:
  359  *
  360  * Clean the page and remove it from the laundry.
  361  * 
  362  * We set the busy bit to cause potential page faults on this page to
  363  * block.  Note the careful timing, however, the busy bit isn't set till
  364  * late and we cannot do anything that will mess with the page.
  365  */
  366 static int
  367 vm_pageout_cluster(vm_page_t m)
  368 {
  369         vm_object_t object;
  370         vm_page_t mc[2*vm_pageout_page_count], pb, ps;
  371         int pageout_count;
  372         int ib, is, page_base;
  373         vm_pindex_t pindex = m->pindex;
  374 
  375         vm_page_lock_assert(m, MA_OWNED);
  376         object = m->object;
  377         VM_OBJECT_ASSERT_WLOCKED(object);
  378 
  379         /*
  380          * It doesn't cost us anything to pageout OBJT_DEFAULT or OBJT_SWAP
  381          * with the new swapper, but we could have serious problems paging
  382          * out other object types if there is insufficient memory.  
  383          *
  384          * Unfortunately, checking free memory here is far too late, so the
  385          * check has been moved up a procedural level.
  386          */
  387 
  388         /*
  389          * Can't clean the page if it's busy or held.
  390          */
  391         vm_page_assert_unbusied(m);
  392         KASSERT(m->hold_count == 0, ("vm_pageout_clean: page %p is held", m));
  393         vm_page_unlock(m);
  394 
  395         mc[vm_pageout_page_count] = pb = ps = m;
  396         pageout_count = 1;
  397         page_base = vm_pageout_page_count;
  398         ib = 1;
  399         is = 1;
  400 
  401         /*
  402          * Scan object for clusterable pages.
  403          *
  404          * We can cluster ONLY if: ->> the page is NOT
  405          * clean, wired, busy, held, or mapped into a
  406          * buffer, and one of the following:
  407          * 1) The page is inactive, or a seldom used
  408          *    active page.
  409          * -or-
  410          * 2) we force the issue.
  411          *
  412          * During heavy mmap/modification loads the pageout
  413          * daemon can really fragment the underlying file
  414          * due to flushing pages out of order and not trying
  415          * align the clusters (which leave sporatic out-of-order
  416          * holes).  To solve this problem we do the reverse scan
  417          * first and attempt to align our cluster, then do a 
  418          * forward scan if room remains.
  419          */
  420 more:
  421         while (ib && pageout_count < vm_pageout_page_count) {
  422                 vm_page_t p;
  423 
  424                 if (ib > pindex) {
  425                         ib = 0;
  426                         break;
  427                 }
  428 
  429                 if ((p = vm_page_prev(pb)) == NULL || vm_page_busied(p)) {
  430                         ib = 0;
  431                         break;
  432                 }
  433                 vm_page_test_dirty(p);
  434                 if (p->dirty == 0) {
  435                         ib = 0;
  436                         break;
  437                 }
  438                 vm_page_lock(p);
  439                 if (p->queue != PQ_INACTIVE ||
  440                     p->hold_count != 0) {       /* may be undergoing I/O */
  441                         vm_page_unlock(p);
  442                         ib = 0;
  443                         break;
  444                 }
  445                 vm_page_unlock(p);
  446                 mc[--page_base] = pb = p;
  447                 ++pageout_count;
  448                 ++ib;
  449                 /*
  450                  * alignment boundry, stop here and switch directions.  Do
  451                  * not clear ib.
  452                  */
  453                 if ((pindex - (ib - 1)) % vm_pageout_page_count == 0)
  454                         break;
  455         }
  456 
  457         while (pageout_count < vm_pageout_page_count && 
  458             pindex + is < object->size) {
  459                 vm_page_t p;
  460 
  461                 if ((p = vm_page_next(ps)) == NULL || vm_page_busied(p))
  462                         break;
  463                 vm_page_test_dirty(p);
  464                 if (p->dirty == 0)
  465                         break;
  466                 vm_page_lock(p);
  467                 if (p->queue != PQ_INACTIVE ||
  468                     p->hold_count != 0) {       /* may be undergoing I/O */
  469                         vm_page_unlock(p);
  470                         break;
  471                 }
  472                 vm_page_unlock(p);
  473                 mc[page_base + pageout_count] = ps = p;
  474                 ++pageout_count;
  475                 ++is;
  476         }
  477 
  478         /*
  479          * If we exhausted our forward scan, continue with the reverse scan
  480          * when possible, even past a page boundry.  This catches boundry
  481          * conditions.
  482          */
  483         if (ib && pageout_count < vm_pageout_page_count)
  484                 goto more;
  485 
  486         /*
  487          * we allow reads during pageouts...
  488          */
  489         return (vm_pageout_flush(&mc[page_base], pageout_count, 0, 0, NULL,
  490             NULL));
  491 }
  492 
  493 /*
  494  * vm_pageout_flush() - launder the given pages
  495  *
  496  *      The given pages are laundered.  Note that we setup for the start of
  497  *      I/O ( i.e. busy the page ), mark it read-only, and bump the object
  498  *      reference count all in here rather then in the parent.  If we want
  499  *      the parent to do more sophisticated things we may have to change
  500  *      the ordering.
  501  *
  502  *      Returned runlen is the count of pages between mreq and first
  503  *      page after mreq with status VM_PAGER_AGAIN.
  504  *      *eio is set to TRUE if pager returned VM_PAGER_ERROR or VM_PAGER_FAIL
  505  *      for any page in runlen set.
  506  */
  507 int
  508 vm_pageout_flush(vm_page_t *mc, int count, int flags, int mreq, int *prunlen,
  509     boolean_t *eio)
  510 {
  511         vm_object_t object = mc[0]->object;
  512         int pageout_status[count];
  513         int numpagedout = 0;
  514         int i, runlen;
  515 
  516         VM_OBJECT_ASSERT_WLOCKED(object);
  517 
  518         /*
  519          * Initiate I/O.  Bump the vm_page_t->busy counter and
  520          * mark the pages read-only.
  521          *
  522          * We do not have to fixup the clean/dirty bits here... we can
  523          * allow the pager to do it after the I/O completes.
  524          *
  525          * NOTE! mc[i]->dirty may be partial or fragmented due to an
  526          * edge case with file fragments.
  527          */
  528         for (i = 0; i < count; i++) {
  529                 KASSERT(mc[i]->valid == VM_PAGE_BITS_ALL,
  530                     ("vm_pageout_flush: partially invalid page %p index %d/%d",
  531                         mc[i], i, count));
  532                 vm_page_sbusy(mc[i]);
  533                 pmap_remove_write(mc[i]);
  534         }
  535         vm_object_pip_add(object, count);
  536 
  537         vm_pager_put_pages(object, mc, count, flags, pageout_status);
  538 
  539         runlen = count - mreq;
  540         if (eio != NULL)
  541                 *eio = FALSE;
  542         for (i = 0; i < count; i++) {
  543                 vm_page_t mt = mc[i];
  544 
  545                 KASSERT(pageout_status[i] == VM_PAGER_PEND ||
  546                     !pmap_page_is_write_mapped(mt),
  547                     ("vm_pageout_flush: page %p is not write protected", mt));
  548                 switch (pageout_status[i]) {
  549                 case VM_PAGER_OK:
  550                 case VM_PAGER_PEND:
  551                         numpagedout++;
  552                         break;
  553                 case VM_PAGER_BAD:
  554                         /*
  555                          * Page outside of range of object. Right now we
  556                          * essentially lose the changes by pretending it
  557                          * worked.
  558                          */
  559                         vm_page_undirty(mt);
  560                         break;
  561                 case VM_PAGER_ERROR:
  562                 case VM_PAGER_FAIL:
  563                         /*
  564                          * If page couldn't be paged out, then reactivate the
  565                          * page so it doesn't clog the inactive list.  (We
  566                          * will try paging out it again later).
  567                          */
  568                         vm_page_lock(mt);
  569                         vm_page_activate(mt);
  570                         vm_page_unlock(mt);
  571                         if (eio != NULL && i >= mreq && i - mreq < runlen)
  572                                 *eio = TRUE;
  573                         break;
  574                 case VM_PAGER_AGAIN:
  575                         if (i >= mreq && i - mreq < runlen)
  576                                 runlen = i - mreq;
  577                         break;
  578                 }
  579 
  580                 /*
  581                  * If the operation is still going, leave the page busy to
  582                  * block all other accesses. Also, leave the paging in
  583                  * progress indicator set so that we don't attempt an object
  584                  * collapse.
  585                  */
  586                 if (pageout_status[i] != VM_PAGER_PEND) {
  587                         vm_object_pip_wakeup(object);
  588                         vm_page_sunbusy(mt);
  589                 }
  590         }
  591         if (prunlen != NULL)
  592                 *prunlen = runlen;
  593         return (numpagedout);
  594 }
  595 
  596 #if !defined(NO_SWAPPING)
  597 /*
  598  *      vm_pageout_object_deactivate_pages
  599  *
  600  *      Deactivate enough pages to satisfy the inactive target
  601  *      requirements.
  602  *
  603  *      The object and map must be locked.
  604  */
  605 static void
  606 vm_pageout_object_deactivate_pages(pmap_t pmap, vm_object_t first_object,
  607     long desired)
  608 {
  609         vm_object_t backing_object, object;
  610         vm_page_t p;
  611         int act_delta, remove_mode;
  612 
  613         VM_OBJECT_ASSERT_LOCKED(first_object);
  614         if ((first_object->flags & OBJ_FICTITIOUS) != 0)
  615                 return;
  616         for (object = first_object;; object = backing_object) {
  617                 if (pmap_resident_count(pmap) <= desired)
  618                         goto unlock_return;
  619                 VM_OBJECT_ASSERT_LOCKED(object);
  620                 if ((object->flags & OBJ_UNMANAGED) != 0 ||
  621                     object->paging_in_progress != 0)
  622                         goto unlock_return;
  623 
  624                 remove_mode = 0;
  625                 if (object->shadow_count > 1)
  626                         remove_mode = 1;
  627                 /*
  628                  * Scan the object's entire memory queue.
  629                  */
  630                 TAILQ_FOREACH(p, &object->memq, listq) {
  631                         if (pmap_resident_count(pmap) <= desired)
  632                                 goto unlock_return;
  633                         if (vm_page_busied(p))
  634                                 continue;
  635                         PCPU_INC(cnt.v_pdpages);
  636                         vm_page_lock(p);
  637                         if (p->wire_count != 0 || p->hold_count != 0 ||
  638                             !pmap_page_exists_quick(pmap, p)) {
  639                                 vm_page_unlock(p);
  640                                 continue;
  641                         }
  642                         act_delta = pmap_ts_referenced(p);
  643                         if ((p->aflags & PGA_REFERENCED) != 0) {
  644                                 if (act_delta == 0)
  645                                         act_delta = 1;
  646                                 vm_page_aflag_clear(p, PGA_REFERENCED);
  647                         }
  648                         if (p->queue != PQ_ACTIVE && act_delta != 0) {
  649                                 vm_page_activate(p);
  650                                 p->act_count += act_delta;
  651                         } else if (p->queue == PQ_ACTIVE) {
  652                                 if (act_delta == 0) {
  653                                         p->act_count -= min(p->act_count,
  654                                             ACT_DECLINE);
  655                                         if (!remove_mode && p->act_count == 0) {
  656                                                 pmap_remove_all(p);
  657                                                 vm_page_deactivate(p);
  658                                         } else
  659                                                 vm_page_requeue(p);
  660                                 } else {
  661                                         vm_page_activate(p);
  662                                         if (p->act_count < ACT_MAX -
  663                                             ACT_ADVANCE)
  664                                                 p->act_count += ACT_ADVANCE;
  665                                         vm_page_requeue(p);
  666                                 }
  667                         } else if (p->queue == PQ_INACTIVE)
  668                                 pmap_remove_all(p);
  669                         vm_page_unlock(p);
  670                 }
  671                 if ((backing_object = object->backing_object) == NULL)
  672                         goto unlock_return;
  673                 VM_OBJECT_RLOCK(backing_object);
  674                 if (object != first_object)
  675                         VM_OBJECT_RUNLOCK(object);
  676         }
  677 unlock_return:
  678         if (object != first_object)
  679                 VM_OBJECT_RUNLOCK(object);
  680 }
  681 
  682 /*
  683  * deactivate some number of pages in a map, try to do it fairly, but
  684  * that is really hard to do.
  685  */
  686 static void
  687 vm_pageout_map_deactivate_pages(map, desired)
  688         vm_map_t map;
  689         long desired;
  690 {
  691         vm_map_entry_t tmpe;
  692         vm_object_t obj, bigobj;
  693         int nothingwired;
  694 
  695         if (!vm_map_trylock(map))
  696                 return;
  697 
  698         bigobj = NULL;
  699         nothingwired = TRUE;
  700 
  701         /*
  702          * first, search out the biggest object, and try to free pages from
  703          * that.
  704          */
  705         tmpe = map->header.next;
  706         while (tmpe != &map->header) {
  707                 if ((tmpe->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
  708                         obj = tmpe->object.vm_object;
  709                         if (obj != NULL && VM_OBJECT_TRYRLOCK(obj)) {
  710                                 if (obj->shadow_count <= 1 &&
  711                                     (bigobj == NULL ||
  712                                      bigobj->resident_page_count < obj->resident_page_count)) {
  713                                         if (bigobj != NULL)
  714                                                 VM_OBJECT_RUNLOCK(bigobj);
  715                                         bigobj = obj;
  716                                 } else
  717                                         VM_OBJECT_RUNLOCK(obj);
  718                         }
  719                 }
  720                 if (tmpe->wired_count > 0)
  721                         nothingwired = FALSE;
  722                 tmpe = tmpe->next;
  723         }
  724 
  725         if (bigobj != NULL) {
  726                 vm_pageout_object_deactivate_pages(map->pmap, bigobj, desired);
  727                 VM_OBJECT_RUNLOCK(bigobj);
  728         }
  729         /*
  730          * Next, hunt around for other pages to deactivate.  We actually
  731          * do this search sort of wrong -- .text first is not the best idea.
  732          */
  733         tmpe = map->header.next;
  734         while (tmpe != &map->header) {
  735                 if (pmap_resident_count(vm_map_pmap(map)) <= desired)
  736                         break;
  737                 if ((tmpe->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
  738                         obj = tmpe->object.vm_object;
  739                         if (obj != NULL) {
  740                                 VM_OBJECT_RLOCK(obj);
  741                                 vm_pageout_object_deactivate_pages(map->pmap, obj, desired);
  742                                 VM_OBJECT_RUNLOCK(obj);
  743                         }
  744                 }
  745                 tmpe = tmpe->next;
  746         }
  747 
  748         /*
  749          * Remove all mappings if a process is swapped out, this will free page
  750          * table pages.
  751          */
  752         if (desired == 0 && nothingwired) {
  753                 pmap_remove(vm_map_pmap(map), vm_map_min(map),
  754                     vm_map_max(map));
  755         }
  756 
  757         vm_map_unlock(map);
  758 }
  759 #endif          /* !defined(NO_SWAPPING) */
  760 
  761 /*
  762  * Attempt to acquire all of the necessary locks to launder a page and
  763  * then call through the clustering layer to PUTPAGES.  Wait a short
  764  * time for a vnode lock.
  765  *
  766  * Requires the page and object lock on entry, releases both before return.
  767  * Returns 0 on success and an errno otherwise.
  768  */
  769 static int
  770 vm_pageout_clean(vm_page_t m)
  771 {
  772         struct vnode *vp;
  773         struct mount *mp;
  774         vm_object_t object;
  775         vm_pindex_t pindex;
  776         int error, lockmode;
  777 
  778         vm_page_assert_locked(m);
  779         object = m->object;
  780         VM_OBJECT_ASSERT_WLOCKED(object);
  781         error = 0;
  782         vp = NULL;
  783         mp = NULL;
  784 
  785         /*
  786          * The object is already known NOT to be dead.   It
  787          * is possible for the vget() to block the whole
  788          * pageout daemon, but the new low-memory handling
  789          * code should prevent it.
  790          *
  791          * We can't wait forever for the vnode lock, we might
  792          * deadlock due to a vn_read() getting stuck in
  793          * vm_wait while holding this vnode.  We skip the 
  794          * vnode if we can't get it in a reasonable amount
  795          * of time.
  796          */
  797         if (object->type == OBJT_VNODE) {
  798                 vm_page_unlock(m);
  799                 vp = object->handle;
  800                 if (vp->v_type == VREG &&
  801                     vn_start_write(vp, &mp, V_NOWAIT) != 0) {
  802                         mp = NULL;
  803                         error = EDEADLK;
  804                         goto unlock_all;
  805                 }
  806                 KASSERT(mp != NULL,
  807                     ("vp %p with NULL v_mount", vp));
  808                 vm_object_reference_locked(object);
  809                 pindex = m->pindex;
  810                 VM_OBJECT_WUNLOCK(object);
  811                 lockmode = MNT_SHARED_WRITES(vp->v_mount) ?
  812                     LK_SHARED : LK_EXCLUSIVE;
  813                 if (vget(vp, lockmode | LK_TIMELOCK, curthread)) {
  814                         vp = NULL;
  815                         error = EDEADLK;
  816                         goto unlock_mp;
  817                 }
  818                 VM_OBJECT_WLOCK(object);
  819                 vm_page_lock(m);
  820                 /*
  821                  * While the object and page were unlocked, the page
  822                  * may have been:
  823                  * (1) moved to a different queue,
  824                  * (2) reallocated to a different object,
  825                  * (3) reallocated to a different offset, or
  826                  * (4) cleaned.
  827                  */
  828                 if (m->queue != PQ_INACTIVE || m->object != object ||
  829                     m->pindex != pindex || m->dirty == 0) {
  830                         vm_page_unlock(m);
  831                         error = ENXIO;
  832                         goto unlock_all;
  833                 }
  834 
  835                 /*
  836                  * The page may have been busied or held while the object
  837                  * and page locks were released.
  838                  */
  839                 if (vm_page_busied(m) || m->hold_count != 0) {
  840                         vm_page_unlock(m);
  841                         error = EBUSY;
  842                         goto unlock_all;
  843                 }
  844         }
  845 
  846         /*
  847          * If a page is dirty, then it is either being washed
  848          * (but not yet cleaned) or it is still in the
  849          * laundry.  If it is still in the laundry, then we
  850          * start the cleaning operation. 
  851          */
  852         if (vm_pageout_cluster(m) == 0)
  853                 error = EIO;
  854 
  855 unlock_all:
  856         VM_OBJECT_WUNLOCK(object);
  857 
  858 unlock_mp:
  859         vm_page_lock_assert(m, MA_NOTOWNED);
  860         if (mp != NULL) {
  861                 if (vp != NULL)
  862                         vput(vp);
  863                 vm_object_deallocate(object);
  864                 vn_finished_write(mp);
  865         }
  866 
  867         return (error);
  868 }
  869 
  870 /*
  871  *      vm_pageout_scan does the dirty work for the pageout daemon.
  872  *
  873  *      pass 0 - Update active LRU/deactivate pages
  874  *      pass 1 - Move inactive to cache or free
  875  *      pass 2 - Launder dirty pages
  876  */
  877 static void
  878 vm_pageout_scan(struct vm_domain *vmd, int pass)
  879 {
  880         vm_page_t m, next;
  881         struct vm_pagequeue *pq;
  882         vm_object_t object;
  883         long min_scan;
  884         int act_delta, addl_page_shortage, deficit, error, maxlaunder, maxscan;
  885         int page_shortage, scan_tick, scanned, starting_page_shortage;
  886         int vnodes_skipped;
  887         boolean_t pageout_ok, queues_locked;
  888 
  889         /*
  890          * If we need to reclaim memory ask kernel caches to return
  891          * some.  We rate limit to avoid thrashing.
  892          */
  893         if (vmd == &vm_dom[0] && pass > 0 &&
  894             (time_uptime - lowmem_uptime) >= lowmem_period) {
  895                 /*
  896                  * Decrease registered cache sizes.
  897                  */
  898                 SDT_PROBE0(vm, , , vm__lowmem_scan);
  899                 EVENTHANDLER_INVOKE(vm_lowmem, 0);
  900                 /*
  901                  * We do this explicitly after the caches have been
  902                  * drained above.
  903                  */
  904                 uma_reclaim();
  905                 lowmem_uptime = time_uptime;
  906         }
  907 
  908         /*
  909          * The addl_page_shortage is the number of temporarily
  910          * stuck pages in the inactive queue.  In other words, the
  911          * number of pages from the inactive count that should be
  912          * discounted in setting the target for the active queue scan.
  913          */
  914         addl_page_shortage = 0;
  915 
  916         /*
  917          * Calculate the number of pages we want to either free or move
  918          * to the cache.
  919          */
  920         if (pass > 0) {
  921                 deficit = atomic_readandclear_int(&vm_pageout_deficit);
  922                 page_shortage = vm_paging_target() + deficit;
  923         } else
  924                 page_shortage = deficit = 0;
  925         starting_page_shortage = page_shortage;
  926 
  927         /*
  928          * maxlaunder limits the number of dirty pages we flush per scan.
  929          * For most systems a smaller value (16 or 32) is more robust under
  930          * extreme memory and disk pressure because any unnecessary writes
  931          * to disk can result in extreme performance degredation.  However,
  932          * systems with excessive dirty pages (especially when MAP_NOSYNC is
  933          * used) will die horribly with limited laundering.  If the pageout
  934          * daemon cannot clean enough pages in the first pass, we let it go
  935          * all out in succeeding passes.
  936          */
  937         if ((maxlaunder = vm_max_launder) <= 1)
  938                 maxlaunder = 1;
  939         if (pass > 1)
  940                 maxlaunder = 10000;
  941 
  942         vnodes_skipped = 0;
  943 
  944         /*
  945          * Start scanning the inactive queue for pages we can move to the
  946          * cache or free.  The scan will stop when the target is reached or
  947          * we have scanned the entire inactive queue.  Note that m->act_count
  948          * is not used to form decisions for the inactive queue, only for the
  949          * active queue.
  950          */
  951         pq = &vmd->vmd_pagequeues[PQ_INACTIVE];
  952         maxscan = pq->pq_cnt;
  953         vm_pagequeue_lock(pq);
  954         queues_locked = TRUE;
  955         for (m = TAILQ_FIRST(&pq->pq_pl);
  956              m != NULL && maxscan-- > 0 && page_shortage > 0;
  957              m = next) {
  958                 vm_pagequeue_assert_locked(pq);
  959                 KASSERT(queues_locked, ("unlocked queues"));
  960                 KASSERT(m->queue == PQ_INACTIVE, ("Inactive queue %p", m));
  961 
  962                 PCPU_INC(cnt.v_pdpages);
  963                 next = TAILQ_NEXT(m, plinks.q);
  964 
  965                 /*
  966                  * skip marker pages
  967                  */
  968                 if (m->flags & PG_MARKER)
  969                         continue;
  970 
  971                 KASSERT((m->flags & PG_FICTITIOUS) == 0,
  972                     ("Fictitious page %p cannot be in inactive queue", m));
  973                 KASSERT((m->oflags & VPO_UNMANAGED) == 0,
  974                     ("Unmanaged page %p cannot be in inactive queue", m));
  975 
  976                 /*
  977                  * The page or object lock acquisitions fail if the
  978                  * page was removed from the queue or moved to a
  979                  * different position within the queue.  In either
  980                  * case, addl_page_shortage should not be incremented.
  981                  */
  982                 if (!vm_pageout_page_lock(m, &next))
  983                         goto unlock_page;
  984                 else if (m->hold_count != 0) {
  985                         /*
  986                          * Held pages are essentially stuck in the
  987                          * queue.  So, they ought to be discounted
  988                          * from the inactive count.  See the
  989                          * calculation of the page_shortage for the
  990                          * loop over the active queue below.
  991                          */
  992                         addl_page_shortage++;
  993                         goto unlock_page;
  994                 }
  995                 object = m->object;
  996                 if (!VM_OBJECT_TRYWLOCK(object)) {
  997                         if (!vm_pageout_fallback_object_lock(m, &next))
  998                                 goto unlock_object;
  999                         else if (m->hold_count != 0) {
 1000                                 addl_page_shortage++;
 1001                                 goto unlock_object;
 1002                         }
 1003                 }
 1004                 if (vm_page_busied(m)) {
 1005                         /*
 1006                          * Don't mess with busy pages.  Leave them at
 1007                          * the front of the queue.  Most likely, they
 1008                          * are being paged out and will leave the
 1009                          * queue shortly after the scan finishes.  So,
 1010                          * they ought to be discounted from the
 1011                          * inactive count.
 1012                          */
 1013                         addl_page_shortage++;
 1014 unlock_object:
 1015                         VM_OBJECT_WUNLOCK(object);
 1016 unlock_page:
 1017                         vm_page_unlock(m);
 1018                         continue;
 1019                 }
 1020                 KASSERT(m->hold_count == 0, ("Held page %p", m));
 1021 
 1022                 /*
 1023                  * We unlock the inactive page queue, invalidating the
 1024                  * 'next' pointer.  Use our marker to remember our
 1025                  * place.
 1026                  */
 1027                 TAILQ_INSERT_AFTER(&pq->pq_pl, m, &vmd->vmd_marker, plinks.q);
 1028                 vm_pagequeue_unlock(pq);
 1029                 queues_locked = FALSE;
 1030 
 1031                 /*
 1032                  * Invalid pages can be easily freed. They cannot be
 1033                  * mapped, vm_page_free() asserts this.
 1034                  */
 1035                 if (m->valid == 0)
 1036                         goto free_page;
 1037 
 1038                 /*
 1039                  * If the page has been referenced and the object is not dead,
 1040                  * reactivate or requeue the page depending on whether the
 1041                  * object is mapped.
 1042                  */
 1043                 if ((m->aflags & PGA_REFERENCED) != 0) {
 1044                         vm_page_aflag_clear(m, PGA_REFERENCED);
 1045                         act_delta = 1;
 1046                 } else
 1047                         act_delta = 0;
 1048                 if (object->ref_count != 0) {
 1049                         act_delta += pmap_ts_referenced(m);
 1050                 } else {
 1051                         KASSERT(!pmap_page_is_mapped(m),
 1052                             ("vm_pageout_scan: page %p is mapped", m));
 1053                 }
 1054                 if (act_delta != 0) {
 1055                         if (object->ref_count != 0) {
 1056                                 vm_page_activate(m);
 1057 
 1058                                 /*
 1059                                  * Increase the activation count if the page
 1060                                  * was referenced while in the inactive queue.
 1061                                  * This makes it less likely that the page will
 1062                                  * be returned prematurely to the inactive
 1063                                  * queue.
 1064                                  */
 1065                                 m->act_count += act_delta + ACT_ADVANCE;
 1066                                 goto drop_page;
 1067                         } else if ((object->flags & OBJ_DEAD) == 0)
 1068                                 goto requeue_page;
 1069                 }
 1070 
 1071                 /*
 1072                  * If the page appears to be clean at the machine-independent
 1073                  * layer, then remove all of its mappings from the pmap in
 1074                  * anticipation of placing it onto the cache queue.  If,
 1075                  * however, any of the page's mappings allow write access,
 1076                  * then the page may still be modified until the last of those
 1077                  * mappings are removed.
 1078                  */
 1079                 if (object->ref_count != 0) {
 1080                         vm_page_test_dirty(m);
 1081                         if (m->dirty == 0)
 1082                                 pmap_remove_all(m);
 1083                 }
 1084 
 1085                 if (m->dirty == 0) {
 1086                         /*
 1087                          * Clean pages can be freed.
 1088                          */
 1089 free_page:
 1090                         vm_page_free(m);
 1091                         PCPU_INC(cnt.v_dfree);
 1092                         --page_shortage;
 1093                 } else if ((object->flags & OBJ_DEAD) != 0) {
 1094                         /*
 1095                          * Leave dirty pages from dead objects at the front of
 1096                          * the queue.  They are being paged out and freed by
 1097                          * the thread that destroyed the object.  They will
 1098                          * leave the queue shortly after the scan finishes, so 
 1099                          * they should be discounted from the inactive count.
 1100                          */
 1101                         addl_page_shortage++;
 1102                 } else if ((m->flags & PG_WINATCFLS) == 0 && pass < 2) {
 1103                         /*
 1104                          * Dirty pages need to be paged out, but flushing
 1105                          * a page is extremely expensive versus freeing
 1106                          * a clean page.  Rather then artificially limiting
 1107                          * the number of pages we can flush, we instead give
 1108                          * dirty pages extra priority on the inactive queue
 1109                          * by forcing them to be cycled through the queue
 1110                          * twice before being flushed, after which the
 1111                          * (now clean) page will cycle through once more
 1112                          * before being freed.  This significantly extends
 1113                          * the thrash point for a heavily loaded machine.
 1114                          */
 1115                         m->flags |= PG_WINATCFLS;
 1116 requeue_page:
 1117                         vm_pagequeue_lock(pq);
 1118                         queues_locked = TRUE;
 1119                         vm_page_requeue_locked(m);
 1120                 } else if (maxlaunder > 0) {
 1121                         /*
 1122                          * We always want to try to flush some dirty pages if
 1123                          * we encounter them, to keep the system stable.
 1124                          * Normally this number is small, but under extreme
 1125                          * pressure where there are insufficient clean pages
 1126                          * on the inactive queue, we may have to go all out.
 1127                          */
 1128 
 1129                         if (object->type != OBJT_SWAP &&
 1130                             object->type != OBJT_DEFAULT)
 1131                                 pageout_ok = TRUE;
 1132                         else if (disable_swap_pageouts)
 1133                                 pageout_ok = FALSE;
 1134                         else if (defer_swap_pageouts)
 1135                                 pageout_ok = vm_page_count_min();
 1136                         else
 1137                                 pageout_ok = TRUE;
 1138                         if (!pageout_ok)
 1139                                 goto requeue_page;
 1140                         error = vm_pageout_clean(m);
 1141                         /*
 1142                          * Decrement page_shortage on success to account for
 1143                          * the (future) cleaned page.  Otherwise we could wind
 1144                          * up laundering or cleaning too many pages.
 1145                          */
 1146                         if (error == 0) {
 1147                                 page_shortage--;
 1148                                 maxlaunder--;
 1149                         } else if (error == EDEADLK) {
 1150                                 pageout_lock_miss++;
 1151                                 vnodes_skipped++;
 1152                         } else if (error == EBUSY) {
 1153                                 addl_page_shortage++;
 1154                         }
 1155                         vm_page_lock_assert(m, MA_NOTOWNED);
 1156                         goto relock_queues;
 1157                 }
 1158 drop_page:
 1159                 vm_page_unlock(m);
 1160                 VM_OBJECT_WUNLOCK(object);
 1161 relock_queues:
 1162                 if (!queues_locked) {
 1163                         vm_pagequeue_lock(pq);
 1164                         queues_locked = TRUE;
 1165                 }
 1166                 next = TAILQ_NEXT(&vmd->vmd_marker, plinks.q);
 1167                 TAILQ_REMOVE(&pq->pq_pl, &vmd->vmd_marker, plinks.q);
 1168         }
 1169         vm_pagequeue_unlock(pq);
 1170 
 1171 #if !defined(NO_SWAPPING)
 1172         /*
 1173          * Wakeup the swapout daemon if we didn't cache or free the targeted
 1174          * number of pages. 
 1175          */
 1176         if (vm_swap_enabled && page_shortage > 0)
 1177                 vm_req_vmdaemon(VM_SWAP_NORMAL);
 1178 #endif
 1179 
 1180         /*
 1181          * Wakeup the sync daemon if we skipped a vnode in a writeable object
 1182          * and we didn't cache or free enough pages.
 1183          */
 1184         if (vnodes_skipped > 0 && page_shortage > vm_cnt.v_free_target -
 1185             vm_cnt.v_free_min)
 1186                 (void)speedup_syncer();
 1187 
 1188         /*
 1189          * If the inactive queue scan fails repeatedly to meet its
 1190          * target, kill the largest process.
 1191          */
 1192         vm_pageout_mightbe_oom(vmd, page_shortage, starting_page_shortage);
 1193 
 1194         /*
 1195          * Compute the number of pages we want to try to move from the
 1196          * active queue to the inactive queue.
 1197          */
 1198         page_shortage = vm_cnt.v_inactive_target - vm_cnt.v_inactive_count +
 1199             vm_paging_target() + deficit + addl_page_shortage;
 1200 
 1201         pq = &vmd->vmd_pagequeues[PQ_ACTIVE];
 1202         vm_pagequeue_lock(pq);
 1203         maxscan = pq->pq_cnt;
 1204 
 1205         /*
 1206          * If we're just idle polling attempt to visit every
 1207          * active page within 'update_period' seconds.
 1208          */
 1209         scan_tick = ticks;
 1210         if (vm_pageout_update_period != 0) {
 1211                 min_scan = pq->pq_cnt;
 1212                 min_scan *= scan_tick - vmd->vmd_last_active_scan;
 1213                 min_scan /= hz * vm_pageout_update_period;
 1214         } else
 1215                 min_scan = 0;
 1216         if (min_scan > 0 || (page_shortage > 0 && maxscan > 0))
 1217                 vmd->vmd_last_active_scan = scan_tick;
 1218 
 1219         /*
 1220          * Scan the active queue for pages that can be deactivated.  Update
 1221          * the per-page activity counter and use it to identify deactivation
 1222          * candidates.
 1223          */
 1224         for (m = TAILQ_FIRST(&pq->pq_pl), scanned = 0; m != NULL && (scanned <
 1225             min_scan || (page_shortage > 0 && scanned < maxscan)); m = next,
 1226             scanned++) {
 1227 
 1228                 KASSERT(m->queue == PQ_ACTIVE,
 1229                     ("vm_pageout_scan: page %p isn't active", m));
 1230 
 1231                 next = TAILQ_NEXT(m, plinks.q);
 1232                 if ((m->flags & PG_MARKER) != 0)
 1233                         continue;
 1234                 KASSERT((m->flags & PG_FICTITIOUS) == 0,
 1235                     ("Fictitious page %p cannot be in active queue", m));
 1236                 KASSERT((m->oflags & VPO_UNMANAGED) == 0,
 1237                     ("Unmanaged page %p cannot be in active queue", m));
 1238                 if (!vm_pageout_page_lock(m, &next)) {
 1239                         vm_page_unlock(m);
 1240                         continue;
 1241                 }
 1242 
 1243                 /*
 1244                  * The count for pagedaemon pages is done after checking the
 1245                  * page for eligibility...
 1246                  */
 1247                 PCPU_INC(cnt.v_pdpages);
 1248 
 1249                 /*
 1250                  * Check to see "how much" the page has been used.
 1251                  */
 1252                 if ((m->aflags & PGA_REFERENCED) != 0) {
 1253                         vm_page_aflag_clear(m, PGA_REFERENCED);
 1254                         act_delta = 1;
 1255                 } else
 1256                         act_delta = 0;
 1257 
 1258                 /*
 1259                  * Unlocked object ref count check.  Two races are possible.
 1260                  * 1) The ref was transitioning to zero and we saw non-zero,
 1261                  *    the pmap bits will be checked unnecessarily.
 1262                  * 2) The ref was transitioning to one and we saw zero. 
 1263                  *    The page lock prevents a new reference to this page so
 1264                  *    we need not check the reference bits.
 1265                  */
 1266                 if (m->object->ref_count != 0)
 1267                         act_delta += pmap_ts_referenced(m);
 1268 
 1269                 /*
 1270                  * Advance or decay the act_count based on recent usage.
 1271                  */
 1272                 if (act_delta != 0) {
 1273                         m->act_count += ACT_ADVANCE + act_delta;
 1274                         if (m->act_count > ACT_MAX)
 1275                                 m->act_count = ACT_MAX;
 1276                 } else
 1277                         m->act_count -= min(m->act_count, ACT_DECLINE);
 1278 
 1279                 /*
 1280                  * Move this page to the tail of the active or inactive
 1281                  * queue depending on usage.
 1282                  */
 1283                 if (m->act_count == 0) {
 1284                         /* Dequeue to avoid later lock recursion. */
 1285                         vm_page_dequeue_locked(m);
 1286                         vm_page_deactivate(m);
 1287                         page_shortage--;
 1288                 } else
 1289                         vm_page_requeue_locked(m);
 1290                 vm_page_unlock(m);
 1291         }
 1292         vm_pagequeue_unlock(pq);
 1293 #if !defined(NO_SWAPPING)
 1294         /*
 1295          * Idle process swapout -- run once per second.
 1296          */
 1297         if (vm_swap_idle_enabled) {
 1298                 static long lsec;
 1299                 if (time_second != lsec) {
 1300                         vm_req_vmdaemon(VM_SWAP_IDLE);
 1301                         lsec = time_second;
 1302                 }
 1303         }
 1304 #endif
 1305 }
 1306 
 1307 static int vm_pageout_oom_vote;
 1308 
 1309 /*
 1310  * The pagedaemon threads randlomly select one to perform the
 1311  * OOM.  Trying to kill processes before all pagedaemons
 1312  * failed to reach free target is premature.
 1313  */
 1314 static void
 1315 vm_pageout_mightbe_oom(struct vm_domain *vmd, int page_shortage,
 1316     int starting_page_shortage)
 1317 {
 1318         int old_vote;
 1319 
 1320         if (starting_page_shortage <= 0 || starting_page_shortage !=
 1321             page_shortage)
 1322                 vmd->vmd_oom_seq = 0;
 1323         else
 1324                 vmd->vmd_oom_seq++;
 1325         if (vmd->vmd_oom_seq < vm_pageout_oom_seq) {
 1326                 if (vmd->vmd_oom) {
 1327                         vmd->vmd_oom = FALSE;
 1328                         atomic_subtract_int(&vm_pageout_oom_vote, 1);
 1329                 }
 1330                 return;
 1331         }
 1332 
 1333         /*
 1334          * Do not follow the call sequence until OOM condition is
 1335          * cleared.
 1336          */
 1337         vmd->vmd_oom_seq = 0;
 1338 
 1339         if (vmd->vmd_oom)
 1340                 return;
 1341 
 1342         vmd->vmd_oom = TRUE;
 1343         old_vote = atomic_fetchadd_int(&vm_pageout_oom_vote, 1);
 1344         if (old_vote != vm_ndomains - 1)
 1345                 return;
 1346 
 1347         /*
 1348          * The current pagedaemon thread is the last in the quorum to
 1349          * start OOM.  Initiate the selection and signaling of the
 1350          * victim.
 1351          */
 1352         vm_pageout_oom(VM_OOM_MEM);
 1353 
 1354         /*
 1355          * After one round of OOM terror, recall our vote.  On the
 1356          * next pass, current pagedaemon would vote again if the low
 1357          * memory condition is still there, due to vmd_oom being
 1358          * false.
 1359          */
 1360         vmd->vmd_oom = FALSE;
 1361         atomic_subtract_int(&vm_pageout_oom_vote, 1);
 1362 }
 1363 
 1364 /*
 1365  * The OOM killer is the page daemon's action of last resort when
 1366  * memory allocation requests have been stalled for a prolonged period
 1367  * of time because it cannot reclaim memory.  This function computes
 1368  * the approximate number of physical pages that could be reclaimed if
 1369  * the specified address space is destroyed.
 1370  *
 1371  * Private, anonymous memory owned by the address space is the
 1372  * principal resource that we expect to recover after an OOM kill.
 1373  * Since the physical pages mapped by the address space's COW entries
 1374  * are typically shared pages, they are unlikely to be released and so
 1375  * they are not counted.
 1376  *
 1377  * To get to the point where the page daemon runs the OOM killer, its
 1378  * efforts to write-back vnode-backed pages may have stalled.  This
 1379  * could be caused by a memory allocation deadlock in the write path
 1380  * that might be resolved by an OOM kill.  Therefore, physical pages
 1381  * belonging to vnode-backed objects are counted, because they might
 1382  * be freed without being written out first if the address space holds
 1383  * the last reference to an unlinked vnode.
 1384  *
 1385  * Similarly, physical pages belonging to OBJT_PHYS objects are
 1386  * counted because the address space might hold the last reference to
 1387  * the object.
 1388  */
 1389 static long
 1390 vm_pageout_oom_pagecount(struct vmspace *vmspace)
 1391 {
 1392         vm_map_t map;
 1393         vm_map_entry_t entry;
 1394         vm_object_t obj;
 1395         long res;
 1396 
 1397         map = &vmspace->vm_map;
 1398         KASSERT(!map->system_map, ("system map"));
 1399         sx_assert(&map->lock, SA_LOCKED);
 1400         res = 0;
 1401         for (entry = map->header.next; entry != &map->header;
 1402             entry = entry->next) {
 1403                 if ((entry->eflags & MAP_ENTRY_IS_SUB_MAP) != 0)
 1404                         continue;
 1405                 obj = entry->object.vm_object;
 1406                 if (obj == NULL)
 1407                         continue;
 1408                 if ((entry->eflags & MAP_ENTRY_NEEDS_COPY) != 0 &&
 1409                     obj->ref_count != 1)
 1410                         continue;
 1411                 switch (obj->type) {
 1412                 case OBJT_DEFAULT:
 1413                 case OBJT_SWAP:
 1414                 case OBJT_PHYS:
 1415                 case OBJT_VNODE:
 1416                         res += obj->resident_page_count;
 1417                         break;
 1418                 }
 1419         }
 1420         return (res);
 1421 }
 1422 
 1423 void
 1424 vm_pageout_oom(int shortage)
 1425 {
 1426         struct proc *p, *bigproc;
 1427         vm_offset_t size, bigsize;
 1428         struct thread *td;
 1429         struct vmspace *vm;
 1430 
 1431         /*
 1432          * We keep the process bigproc locked once we find it to keep anyone
 1433          * from messing with it; however, there is a possibility of
 1434          * deadlock if process B is bigproc and one of it's child processes
 1435          * attempts to propagate a signal to B while we are waiting for A's
 1436          * lock while walking this list.  To avoid this, we don't block on
 1437          * the process lock but just skip a process if it is already locked.
 1438          */
 1439         bigproc = NULL;
 1440         bigsize = 0;
 1441         sx_slock(&allproc_lock);
 1442         FOREACH_PROC_IN_SYSTEM(p) {
 1443                 int breakout;
 1444 
 1445                 PROC_LOCK(p);
 1446 
 1447                 /*
 1448                  * If this is a system, protected or killed process, skip it.
 1449                  */
 1450                 if (p->p_state != PRS_NORMAL || (p->p_flag & (P_INEXEC |
 1451                     P_PROTECTED | P_SYSTEM | P_WEXIT)) != 0 ||
 1452                     p->p_pid == 1 || P_KILLED(p) ||
 1453                     (p->p_pid < 48 && swap_pager_avail != 0)) {
 1454                         PROC_UNLOCK(p);
 1455                         continue;
 1456                 }
 1457                 /*
 1458                  * If the process is in a non-running type state,
 1459                  * don't touch it.  Check all the threads individually.
 1460                  */
 1461                 breakout = 0;
 1462                 FOREACH_THREAD_IN_PROC(p, td) {
 1463                         thread_lock(td);
 1464                         if (!TD_ON_RUNQ(td) &&
 1465                             !TD_IS_RUNNING(td) &&
 1466                             !TD_IS_SLEEPING(td) &&
 1467                             !TD_IS_SUSPENDED(td) &&
 1468                             !TD_IS_SWAPPED(td)) {
 1469                                 thread_unlock(td);
 1470                                 breakout = 1;
 1471                                 break;
 1472                         }
 1473                         thread_unlock(td);
 1474                 }
 1475                 if (breakout) {
 1476                         PROC_UNLOCK(p);
 1477                         continue;
 1478                 }
 1479                 /*
 1480                  * get the process size
 1481                  */
 1482                 vm = vmspace_acquire_ref(p);
 1483                 if (vm == NULL) {
 1484                         PROC_UNLOCK(p);
 1485                         continue;
 1486                 }
 1487                 _PHOLD(p);
 1488                 if (!vm_map_trylock_read(&vm->vm_map)) {
 1489                         _PRELE(p);
 1490                         PROC_UNLOCK(p);
 1491                         vmspace_free(vm);
 1492                         continue;
 1493                 }
 1494                 PROC_UNLOCK(p);
 1495                 size = vmspace_swap_count(vm);
 1496                 if (shortage == VM_OOM_MEM)
 1497                         size += vm_pageout_oom_pagecount(vm);
 1498                 vm_map_unlock_read(&vm->vm_map);
 1499                 vmspace_free(vm);
 1500 
 1501                 /*
 1502                  * If this process is bigger than the biggest one,
 1503                  * remember it.
 1504                  */
 1505                 if (size > bigsize) {
 1506                         if (bigproc != NULL)
 1507                                 PRELE(bigproc);
 1508                         bigproc = p;
 1509                         bigsize = size;
 1510                 } else {
 1511                         PRELE(p);
 1512                 }
 1513         }
 1514         sx_sunlock(&allproc_lock);
 1515         if (bigproc != NULL) {
 1516                 if (vm_panic_on_oom != 0)
 1517                         panic("out of swap space");
 1518                 PROC_LOCK(bigproc);
 1519                 killproc(bigproc, "out of swap space");
 1520                 sched_nice(bigproc, PRIO_MIN);
 1521                 _PRELE(bigproc);
 1522                 PROC_UNLOCK(bigproc);
 1523                 wakeup(&vm_cnt.v_free_count);
 1524         }
 1525 }
 1526 
 1527 static void
 1528 vm_pageout_worker(void *arg)
 1529 {
 1530         struct vm_domain *domain;
 1531         int domidx;
 1532 
 1533         domidx = (uintptr_t)arg;
 1534         domain = &vm_dom[domidx];
 1535 
 1536         /*
 1537          * XXXKIB It could be useful to bind pageout daemon threads to
 1538          * the cores belonging to the domain, from which vm_page_array
 1539          * is allocated.
 1540          */
 1541 
 1542         KASSERT(domain->vmd_segs != 0, ("domain without segments"));
 1543         domain->vmd_last_active_scan = ticks;
 1544         vm_pageout_init_marker(&domain->vmd_marker, PQ_INACTIVE);
 1545         vm_pageout_init_marker(&domain->vmd_inacthead, PQ_INACTIVE);
 1546         TAILQ_INSERT_HEAD(&domain->vmd_pagequeues[PQ_INACTIVE].pq_pl,
 1547             &domain->vmd_inacthead, plinks.q);
 1548 
 1549         /*
 1550          * The pageout daemon worker is never done, so loop forever.
 1551          */
 1552         while (TRUE) {
 1553                 /*
 1554                  * If we have enough free memory, wakeup waiters.  Do
 1555                  * not clear vm_pages_needed until we reach our target,
 1556                  * otherwise we may be woken up over and over again and
 1557                  * waste a lot of cpu.
 1558                  */
 1559                 mtx_lock(&vm_page_queue_free_mtx);
 1560                 if (vm_pages_needed && !vm_page_count_min()) {
 1561                         if (!vm_paging_needed())
 1562                                 vm_pages_needed = 0;
 1563                         wakeup(&vm_cnt.v_free_count);
 1564                 }
 1565                 if (vm_pages_needed) {
 1566                         /*
 1567                          * We're still not done.  Either vm_pages_needed was
 1568                          * set by another thread during the previous scan
 1569                          * (typically, this happens during a level 0 scan) or
 1570                          * vm_pages_needed was already set and the scan failed
 1571                          * to free enough pages.  If we haven't yet performed
 1572                          * a level >= 2 scan (unlimited dirty cleaning), then
 1573                          * upgrade the level and scan again now.  Otherwise,
 1574                          * sleep a bit and try again later.  While sleeping,
 1575                          * vm_pages_needed can be cleared.
 1576                          */
 1577                         if (domain->vmd_pass > 1)
 1578                                 msleep(&vm_pages_needed,
 1579                                     &vm_page_queue_free_mtx, PVM, "psleep",
 1580                                     hz / 2);
 1581                 } else {
 1582                         /*
 1583                          * Good enough, sleep until required to refresh
 1584                          * stats.
 1585                          */
 1586                         msleep(&vm_pages_needed, &vm_page_queue_free_mtx,
 1587                             PVM, "psleep", hz);
 1588                 }
 1589                 if (vm_pages_needed) {
 1590                         vm_cnt.v_pdwakeups++;
 1591                         domain->vmd_pass++;
 1592                 } else
 1593                         domain->vmd_pass = 0;
 1594                 mtx_unlock(&vm_page_queue_free_mtx);
 1595                 vm_pageout_scan(domain, domain->vmd_pass);
 1596         }
 1597 }
 1598 
 1599 /*
 1600  *      vm_pageout_init initialises basic pageout daemon settings.
 1601  */
 1602 static void
 1603 vm_pageout_init(void)
 1604 {
 1605         /*
 1606          * Initialize some paging parameters.
 1607          */
 1608         vm_cnt.v_interrupt_free_min = 2;
 1609         if (vm_cnt.v_page_count < 2000)
 1610                 vm_pageout_page_count = 8;
 1611 
 1612         /*
 1613          * v_free_reserved needs to include enough for the largest
 1614          * swap pager structures plus enough for any pv_entry structs
 1615          * when paging. 
 1616          */
 1617         if (vm_cnt.v_page_count > 1024)
 1618                 vm_cnt.v_free_min = 4 + (vm_cnt.v_page_count - 1024) / 200;
 1619         else
 1620                 vm_cnt.v_free_min = 4;
 1621         vm_cnt.v_pageout_free_min = (2*MAXBSIZE)/PAGE_SIZE +
 1622             vm_cnt.v_interrupt_free_min;
 1623         vm_cnt.v_free_reserved = vm_pageout_page_count +
 1624             vm_cnt.v_pageout_free_min + (vm_cnt.v_page_count / 768);
 1625         vm_cnt.v_free_severe = vm_cnt.v_free_min / 2;
 1626         vm_cnt.v_free_target = 4 * vm_cnt.v_free_min + vm_cnt.v_free_reserved;
 1627         vm_cnt.v_free_min += vm_cnt.v_free_reserved;
 1628         vm_cnt.v_free_severe += vm_cnt.v_free_reserved;
 1629         vm_cnt.v_inactive_target = (3 * vm_cnt.v_free_target) / 2;
 1630         if (vm_cnt.v_inactive_target > vm_cnt.v_free_count / 3)
 1631                 vm_cnt.v_inactive_target = vm_cnt.v_free_count / 3;
 1632 
 1633         /*
 1634          * Set the default wakeup threshold to be 10% above the minimum
 1635          * page limit.  This keeps the steady state out of shortfall.
 1636          */
 1637         vm_pageout_wakeup_thresh = (vm_cnt.v_free_min / 10) * 11;
 1638 
 1639         /*
 1640          * Set interval in seconds for active scan.  We want to visit each
 1641          * page at least once every ten minutes.  This is to prevent worst
 1642          * case paging behaviors with stale active LRU.
 1643          */
 1644         if (vm_pageout_update_period == 0)
 1645                 vm_pageout_update_period = 600;
 1646 
 1647         /* XXX does not really belong here */
 1648         if (vm_page_max_wired == 0)
 1649                 vm_page_max_wired = vm_cnt.v_free_count / 3;
 1650 }
 1651 
 1652 /*
 1653  *     vm_pageout is the high level pageout daemon.
 1654  */
 1655 static void
 1656 vm_pageout(void)
 1657 {
 1658         int error;
 1659 #if MAXMEMDOM > 1
 1660         int i;
 1661 #endif
 1662 
 1663         swap_pager_swap_init();
 1664 #if MAXMEMDOM > 1
 1665         for (i = 1; i < vm_ndomains; i++) {
 1666                 error = kthread_add(vm_pageout_worker, (void *)(uintptr_t)i,
 1667                     curproc, NULL, 0, 0, "dom%d", i);
 1668                 if (error != 0) {
 1669                         panic("starting pageout for domain %d, error %d\n",
 1670                             i, error);
 1671                 }
 1672         }
 1673 #endif
 1674         error = kthread_add(uma_reclaim_worker, NULL, curproc, NULL,
 1675             0, 0, "uma");
 1676         if (error != 0)
 1677                 panic("starting uma_reclaim helper, error %d\n", error);
 1678         vm_pageout_worker((void *)(uintptr_t)0);
 1679 }
 1680 
 1681 /*
 1682  * Unless the free page queue lock is held by the caller, this function
 1683  * should be regarded as advisory.  Specifically, the caller should
 1684  * not msleep() on &vm_cnt.v_free_count following this function unless
 1685  * the free page queue lock is held until the msleep() is performed.
 1686  */
 1687 void
 1688 pagedaemon_wakeup(void)
 1689 {
 1690 
 1691         if (!vm_pages_needed && curthread->td_proc != pageproc) {
 1692                 vm_pages_needed = 1;
 1693                 wakeup(&vm_pages_needed);
 1694         }
 1695 }
 1696 
 1697 #if !defined(NO_SWAPPING)
 1698 static void
 1699 vm_req_vmdaemon(int req)
 1700 {
 1701         static int lastrun = 0;
 1702 
 1703         mtx_lock(&vm_daemon_mtx);
 1704         vm_pageout_req_swapout |= req;
 1705         if ((ticks > (lastrun + hz)) || (ticks < lastrun)) {
 1706                 wakeup(&vm_daemon_needed);
 1707                 lastrun = ticks;
 1708         }
 1709         mtx_unlock(&vm_daemon_mtx);
 1710 }
 1711 
 1712 static void
 1713 vm_daemon(void)
 1714 {
 1715         struct rlimit rsslim;
 1716         struct proc *p;
 1717         struct thread *td;
 1718         struct vmspace *vm;
 1719         int breakout, swapout_flags, tryagain, attempts;
 1720 #ifdef RACCT
 1721         uint64_t rsize, ravailable;
 1722 #endif
 1723 
 1724         while (TRUE) {
 1725                 mtx_lock(&vm_daemon_mtx);
 1726                 msleep(&vm_daemon_needed, &vm_daemon_mtx, PPAUSE, "psleep",
 1727 #ifdef RACCT
 1728                     racct_enable ? hz : 0
 1729 #else
 1730                     0
 1731 #endif
 1732                 );
 1733                 swapout_flags = vm_pageout_req_swapout;
 1734                 vm_pageout_req_swapout = 0;
 1735                 mtx_unlock(&vm_daemon_mtx);
 1736                 if (swapout_flags)
 1737                         swapout_procs(swapout_flags);
 1738 
 1739                 /*
 1740                  * scan the processes for exceeding their rlimits or if
 1741                  * process is swapped out -- deactivate pages
 1742                  */
 1743                 tryagain = 0;
 1744                 attempts = 0;
 1745 again:
 1746                 attempts++;
 1747                 sx_slock(&allproc_lock);
 1748                 FOREACH_PROC_IN_SYSTEM(p) {
 1749                         vm_pindex_t limit, size;
 1750 
 1751                         /*
 1752                          * if this is a system process or if we have already
 1753                          * looked at this process, skip it.
 1754                          */
 1755                         PROC_LOCK(p);
 1756                         if (p->p_state != PRS_NORMAL ||
 1757                             p->p_flag & (P_INEXEC | P_SYSTEM | P_WEXIT)) {
 1758                                 PROC_UNLOCK(p);
 1759                                 continue;
 1760                         }
 1761                         /*
 1762                          * if the process is in a non-running type state,
 1763                          * don't touch it.
 1764                          */
 1765                         breakout = 0;
 1766                         FOREACH_THREAD_IN_PROC(p, td) {
 1767                                 thread_lock(td);
 1768                                 if (!TD_ON_RUNQ(td) &&
 1769                                     !TD_IS_RUNNING(td) &&
 1770                                     !TD_IS_SLEEPING(td) &&
 1771                                     !TD_IS_SUSPENDED(td)) {
 1772                                         thread_unlock(td);
 1773                                         breakout = 1;
 1774                                         break;
 1775                                 }
 1776                                 thread_unlock(td);
 1777                         }
 1778                         if (breakout) {
 1779                                 PROC_UNLOCK(p);
 1780                                 continue;
 1781                         }
 1782                         /*
 1783                          * get a limit
 1784                          */
 1785                         lim_rlimit_proc(p, RLIMIT_RSS, &rsslim);
 1786                         limit = OFF_TO_IDX(
 1787                             qmin(rsslim.rlim_cur, rsslim.rlim_max));
 1788 
 1789                         /*
 1790                          * let processes that are swapped out really be
 1791                          * swapped out set the limit to nothing (will force a
 1792                          * swap-out.)
 1793                          */
 1794                         if ((p->p_flag & P_INMEM) == 0)
 1795                                 limit = 0;      /* XXX */
 1796                         vm = vmspace_acquire_ref(p);
 1797                         PROC_UNLOCK(p);
 1798                         if (vm == NULL)
 1799                                 continue;
 1800 
 1801                         size = vmspace_resident_count(vm);
 1802                         if (size >= limit) {
 1803                                 vm_pageout_map_deactivate_pages(
 1804                                     &vm->vm_map, limit);
 1805                         }
 1806 #ifdef RACCT
 1807                         if (racct_enable) {
 1808                                 rsize = IDX_TO_OFF(size);
 1809                                 PROC_LOCK(p);
 1810                                 racct_set(p, RACCT_RSS, rsize);
 1811                                 ravailable = racct_get_available(p, RACCT_RSS);
 1812                                 PROC_UNLOCK(p);
 1813                                 if (rsize > ravailable) {
 1814                                         /*
 1815                                          * Don't be overly aggressive; this
 1816                                          * might be an innocent process,
 1817                                          * and the limit could've been exceeded
 1818                                          * by some memory hog.  Don't try
 1819                                          * to deactivate more than 1/4th
 1820                                          * of process' resident set size.
 1821                                          */
 1822                                         if (attempts <= 8) {
 1823                                                 if (ravailable < rsize -
 1824                                                     (rsize / 4)) {
 1825                                                         ravailable = rsize -
 1826                                                             (rsize / 4);
 1827                                                 }
 1828                                         }
 1829                                         vm_pageout_map_deactivate_pages(
 1830                                             &vm->vm_map,
 1831                                             OFF_TO_IDX(ravailable));
 1832                                         /* Update RSS usage after paging out. */
 1833                                         size = vmspace_resident_count(vm);
 1834                                         rsize = IDX_TO_OFF(size);
 1835                                         PROC_LOCK(p);
 1836                                         racct_set(p, RACCT_RSS, rsize);
 1837                                         PROC_UNLOCK(p);
 1838                                         if (rsize > ravailable)
 1839                                                 tryagain = 1;
 1840                                 }
 1841                         }
 1842 #endif
 1843                         vmspace_free(vm);
 1844                 }
 1845                 sx_sunlock(&allproc_lock);
 1846                 if (tryagain != 0 && attempts <= 10)
 1847                         goto again;
 1848         }
 1849 }
 1850 #endif                  /* !defined(NO_SWAPPING) */

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