The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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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 302089 2016-06-22 20:15:37Z kib $");
   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_pageout_deficit;         /* Estimated number of pages deficit */
  160 int vm_pageout_wakeup_thresh;
  161 static int vm_pageout_oom_seq = 12;
  162 bool vm_pageout_wanted;         /* Event on which pageout daemon sleeps */
  163 bool vm_pages_needed;           /* Are threads waiting for free pages? */
  164 
  165 #if !defined(NO_SWAPPING)
  166 static int vm_pageout_req_swapout;      /* XXX */
  167 static int vm_daemon_needed;
  168 static struct mtx vm_daemon_mtx;
  169 /* Allow for use by vm_pageout before vm_daemon is initialized. */
  170 MTX_SYSINIT(vm_daemon, &vm_daemon_mtx, "vm daemon", MTX_DEF);
  171 #endif
  172 static int vm_max_launder = 32;
  173 static int vm_pageout_update_period;
  174 static int defer_swap_pageouts;
  175 static int disable_swap_pageouts;
  176 static int lowmem_period = 10;
  177 static time_t lowmem_uptime;
  178 
  179 #if defined(NO_SWAPPING)
  180 static int vm_swap_enabled = 0;
  181 static int vm_swap_idle_enabled = 0;
  182 #else
  183 static int vm_swap_enabled = 1;
  184 static int vm_swap_idle_enabled = 0;
  185 #endif
  186 
  187 static int vm_panic_on_oom = 0;
  188 
  189 SYSCTL_INT(_vm, OID_AUTO, panic_on_oom,
  190         CTLFLAG_RWTUN, &vm_panic_on_oom, 0,
  191         "panic on out of memory instead of killing the largest process");
  192 
  193 SYSCTL_INT(_vm, OID_AUTO, pageout_wakeup_thresh,
  194         CTLFLAG_RW, &vm_pageout_wakeup_thresh, 0,
  195         "free page threshold for waking up the pageout daemon");
  196 
  197 SYSCTL_INT(_vm, OID_AUTO, max_launder,
  198         CTLFLAG_RW, &vm_max_launder, 0, "Limit dirty flushes in pageout");
  199 
  200 SYSCTL_INT(_vm, OID_AUTO, pageout_update_period,
  201         CTLFLAG_RW, &vm_pageout_update_period, 0,
  202         "Maximum active LRU update period");
  203   
  204 SYSCTL_INT(_vm, OID_AUTO, lowmem_period, CTLFLAG_RW, &lowmem_period, 0,
  205         "Low memory callback period");
  206 
  207 #if defined(NO_SWAPPING)
  208 SYSCTL_INT(_vm, VM_SWAPPING_ENABLED, swap_enabled,
  209         CTLFLAG_RD, &vm_swap_enabled, 0, "Enable entire process swapout");
  210 SYSCTL_INT(_vm, OID_AUTO, swap_idle_enabled,
  211         CTLFLAG_RD, &vm_swap_idle_enabled, 0, "Allow swapout on idle criteria");
  212 #else
  213 SYSCTL_INT(_vm, VM_SWAPPING_ENABLED, swap_enabled,
  214         CTLFLAG_RW, &vm_swap_enabled, 0, "Enable entire process swapout");
  215 SYSCTL_INT(_vm, OID_AUTO, swap_idle_enabled,
  216         CTLFLAG_RW, &vm_swap_idle_enabled, 0, "Allow swapout on idle criteria");
  217 #endif
  218 
  219 SYSCTL_INT(_vm, OID_AUTO, defer_swapspace_pageouts,
  220         CTLFLAG_RW, &defer_swap_pageouts, 0, "Give preference to dirty pages in mem");
  221 
  222 SYSCTL_INT(_vm, OID_AUTO, disable_swapspace_pageouts,
  223         CTLFLAG_RW, &disable_swap_pageouts, 0, "Disallow swapout of dirty pages");
  224 
  225 static int pageout_lock_miss;
  226 SYSCTL_INT(_vm, OID_AUTO, pageout_lock_miss,
  227         CTLFLAG_RD, &pageout_lock_miss, 0, "vget() lock misses during pageout");
  228 
  229 SYSCTL_INT(_vm, OID_AUTO, pageout_oom_seq,
  230         CTLFLAG_RW, &vm_pageout_oom_seq, 0,
  231         "back-to-back calls to oom detector to start OOM");
  232 
  233 #define VM_PAGEOUT_PAGE_COUNT 16
  234 int vm_pageout_page_count = VM_PAGEOUT_PAGE_COUNT;
  235 
  236 int vm_page_max_wired;          /* XXX max # of wired pages system-wide */
  237 SYSCTL_INT(_vm, OID_AUTO, max_wired,
  238         CTLFLAG_RW, &vm_page_max_wired, 0, "System-wide limit to wired page count");
  239 
  240 static boolean_t vm_pageout_fallback_object_lock(vm_page_t, vm_page_t *);
  241 #if !defined(NO_SWAPPING)
  242 static void vm_pageout_map_deactivate_pages(vm_map_t, long);
  243 static void vm_pageout_object_deactivate_pages(pmap_t, vm_object_t, long);
  244 static void vm_req_vmdaemon(int req);
  245 #endif
  246 static boolean_t vm_pageout_page_lock(vm_page_t, vm_page_t *);
  247 
  248 /*
  249  * Initialize a dummy page for marking the caller's place in the specified
  250  * paging queue.  In principle, this function only needs to set the flag
  251  * PG_MARKER.  Nonetheless, it wirte busies and initializes the hold count
  252  * to one as safety precautions.
  253  */ 
  254 static void
  255 vm_pageout_init_marker(vm_page_t marker, u_short queue)
  256 {
  257 
  258         bzero(marker, sizeof(*marker));
  259         marker->flags = PG_MARKER;
  260         marker->busy_lock = VPB_SINGLE_EXCLUSIVER;
  261         marker->queue = queue;
  262         marker->hold_count = 1;
  263 }
  264 
  265 /*
  266  * vm_pageout_fallback_object_lock:
  267  * 
  268  * Lock vm object currently associated with `m'. VM_OBJECT_TRYWLOCK is
  269  * known to have failed and page queue must be either PQ_ACTIVE or
  270  * PQ_INACTIVE.  To avoid lock order violation, unlock the page queues
  271  * while locking the vm object.  Use marker page to detect page queue
  272  * changes and maintain notion of next page on page queue.  Return
  273  * TRUE if no changes were detected, FALSE otherwise.  vm object is
  274  * locked on return.
  275  * 
  276  * This function depends on both the lock portion of struct vm_object
  277  * and normal struct vm_page being type stable.
  278  */
  279 static boolean_t
  280 vm_pageout_fallback_object_lock(vm_page_t m, vm_page_t *next)
  281 {
  282         struct vm_page marker;
  283         struct vm_pagequeue *pq;
  284         boolean_t unchanged;
  285         u_short queue;
  286         vm_object_t object;
  287 
  288         queue = m->queue;
  289         vm_pageout_init_marker(&marker, queue);
  290         pq = vm_page_pagequeue(m);
  291         object = m->object;
  292         
  293         TAILQ_INSERT_AFTER(&pq->pq_pl, m, &marker, plinks.q);
  294         vm_pagequeue_unlock(pq);
  295         vm_page_unlock(m);
  296         VM_OBJECT_WLOCK(object);
  297         vm_page_lock(m);
  298         vm_pagequeue_lock(pq);
  299 
  300         /*
  301          * The page's object might have changed, and/or the page might
  302          * have moved from its original position in the queue.  If the
  303          * page's object has changed, then the caller should abandon
  304          * processing the page because the wrong object lock was
  305          * acquired.  Use the marker's plinks.q, not the page's, to
  306          * determine if the page has been moved.  The state of the
  307          * page's plinks.q can be indeterminate; whereas, the marker's
  308          * plinks.q must be valid.
  309          */
  310         *next = TAILQ_NEXT(&marker, plinks.q);
  311         unchanged = m->object == object &&
  312             m == TAILQ_PREV(&marker, pglist, plinks.q);
  313         KASSERT(!unchanged || m->queue == queue,
  314             ("page %p queue %d %d", m, queue, m->queue));
  315         TAILQ_REMOVE(&pq->pq_pl, &marker, plinks.q);
  316         return (unchanged);
  317 }
  318 
  319 /*
  320  * Lock the page while holding the page queue lock.  Use marker page
  321  * to detect page queue changes and maintain notion of next page on
  322  * page queue.  Return TRUE if no changes were detected, FALSE
  323  * otherwise.  The page is locked on return. The page queue lock might
  324  * be dropped and reacquired.
  325  *
  326  * This function depends on normal struct vm_page being type stable.
  327  */
  328 static boolean_t
  329 vm_pageout_page_lock(vm_page_t m, vm_page_t *next)
  330 {
  331         struct vm_page marker;
  332         struct vm_pagequeue *pq;
  333         boolean_t unchanged;
  334         u_short queue;
  335 
  336         vm_page_lock_assert(m, MA_NOTOWNED);
  337         if (vm_page_trylock(m))
  338                 return (TRUE);
  339 
  340         queue = m->queue;
  341         vm_pageout_init_marker(&marker, queue);
  342         pq = vm_page_pagequeue(m);
  343 
  344         TAILQ_INSERT_AFTER(&pq->pq_pl, m, &marker, plinks.q);
  345         vm_pagequeue_unlock(pq);
  346         vm_page_lock(m);
  347         vm_pagequeue_lock(pq);
  348 
  349         /* Page queue might have changed. */
  350         *next = TAILQ_NEXT(&marker, plinks.q);
  351         unchanged = m == TAILQ_PREV(&marker, pglist, plinks.q);
  352         KASSERT(!unchanged || m->queue == queue,
  353             ("page %p queue %d %d", m, queue, m->queue));
  354         TAILQ_REMOVE(&pq->pq_pl, &marker, plinks.q);
  355         return (unchanged);
  356 }
  357 
  358 /*
  359  * vm_pageout_clean:
  360  *
  361  * Clean the page and remove it from the laundry.
  362  * 
  363  * We set the busy bit to cause potential page faults on this page to
  364  * block.  Note the careful timing, however, the busy bit isn't set till
  365  * late and we cannot do anything that will mess with the page.
  366  */
  367 static int
  368 vm_pageout_cluster(vm_page_t m)
  369 {
  370         vm_object_t object;
  371         vm_page_t mc[2*vm_pageout_page_count], pb, ps;
  372         int pageout_count;
  373         int ib, is, page_base;
  374         vm_pindex_t pindex = m->pindex;
  375 
  376         vm_page_lock_assert(m, MA_OWNED);
  377         object = m->object;
  378         VM_OBJECT_ASSERT_WLOCKED(object);
  379 
  380         /*
  381          * It doesn't cost us anything to pageout OBJT_DEFAULT or OBJT_SWAP
  382          * with the new swapper, but we could have serious problems paging
  383          * out other object types if there is insufficient memory.  
  384          *
  385          * Unfortunately, checking free memory here is far too late, so the
  386          * check has been moved up a procedural level.
  387          */
  388 
  389         /*
  390          * Can't clean the page if it's busy or held.
  391          */
  392         vm_page_assert_unbusied(m);
  393         KASSERT(m->hold_count == 0, ("vm_pageout_clean: page %p is held", m));
  394         vm_page_unlock(m);
  395 
  396         mc[vm_pageout_page_count] = pb = ps = m;
  397         pageout_count = 1;
  398         page_base = vm_pageout_page_count;
  399         ib = 1;
  400         is = 1;
  401 
  402         /*
  403          * Scan object for clusterable pages.
  404          *
  405          * We can cluster ONLY if: ->> the page is NOT
  406          * clean, wired, busy, held, or mapped into a
  407          * buffer, and one of the following:
  408          * 1) The page is inactive, or a seldom used
  409          *    active page.
  410          * -or-
  411          * 2) we force the issue.
  412          *
  413          * During heavy mmap/modification loads the pageout
  414          * daemon can really fragment the underlying file
  415          * due to flushing pages out of order and not trying
  416          * align the clusters (which leave sporatic out-of-order
  417          * holes).  To solve this problem we do the reverse scan
  418          * first and attempt to align our cluster, then do a 
  419          * forward scan if room remains.
  420          */
  421 more:
  422         while (ib && pageout_count < vm_pageout_page_count) {
  423                 vm_page_t p;
  424 
  425                 if (ib > pindex) {
  426                         ib = 0;
  427                         break;
  428                 }
  429 
  430                 if ((p = vm_page_prev(pb)) == NULL || vm_page_busied(p)) {
  431                         ib = 0;
  432                         break;
  433                 }
  434                 vm_page_test_dirty(p);
  435                 if (p->dirty == 0) {
  436                         ib = 0;
  437                         break;
  438                 }
  439                 vm_page_lock(p);
  440                 if (p->queue != PQ_INACTIVE ||
  441                     p->hold_count != 0) {       /* may be undergoing I/O */
  442                         vm_page_unlock(p);
  443                         ib = 0;
  444                         break;
  445                 }
  446                 vm_page_unlock(p);
  447                 mc[--page_base] = pb = p;
  448                 ++pageout_count;
  449                 ++ib;
  450                 /*
  451                  * alignment boundary, stop here and switch directions.  Do
  452                  * not clear ib.
  453                  */
  454                 if ((pindex - (ib - 1)) % vm_pageout_page_count == 0)
  455                         break;
  456         }
  457 
  458         while (pageout_count < vm_pageout_page_count && 
  459             pindex + is < object->size) {
  460                 vm_page_t p;
  461 
  462                 if ((p = vm_page_next(ps)) == NULL || vm_page_busied(p))
  463                         break;
  464                 vm_page_test_dirty(p);
  465                 if (p->dirty == 0)
  466                         break;
  467                 vm_page_lock(p);
  468                 if (p->queue != PQ_INACTIVE ||
  469                     p->hold_count != 0) {       /* may be undergoing I/O */
  470                         vm_page_unlock(p);
  471                         break;
  472                 }
  473                 vm_page_unlock(p);
  474                 mc[page_base + pageout_count] = ps = p;
  475                 ++pageout_count;
  476                 ++is;
  477         }
  478 
  479         /*
  480          * If we exhausted our forward scan, continue with the reverse scan
  481          * when possible, even past a page boundary.  This catches boundary
  482          * conditions.
  483          */
  484         if (ib && pageout_count < vm_pageout_page_count)
  485                 goto more;
  486 
  487         /*
  488          * we allow reads during pageouts...
  489          */
  490         return (vm_pageout_flush(&mc[page_base], pageout_count, 0, 0, NULL,
  491             NULL));
  492 }
  493 
  494 /*
  495  * vm_pageout_flush() - launder the given pages
  496  *
  497  *      The given pages are laundered.  Note that we setup for the start of
  498  *      I/O ( i.e. busy the page ), mark it read-only, and bump the object
  499  *      reference count all in here rather then in the parent.  If we want
  500  *      the parent to do more sophisticated things we may have to change
  501  *      the ordering.
  502  *
  503  *      Returned runlen is the count of pages between mreq and first
  504  *      page after mreq with status VM_PAGER_AGAIN.
  505  *      *eio is set to TRUE if pager returned VM_PAGER_ERROR or VM_PAGER_FAIL
  506  *      for any page in runlen set.
  507  */
  508 int
  509 vm_pageout_flush(vm_page_t *mc, int count, int flags, int mreq, int *prunlen,
  510     boolean_t *eio)
  511 {
  512         vm_object_t object = mc[0]->object;
  513         int pageout_status[count];
  514         int numpagedout = 0;
  515         int i, runlen;
  516 
  517         VM_OBJECT_ASSERT_WLOCKED(object);
  518 
  519         /*
  520          * Initiate I/O.  Bump the vm_page_t->busy counter and
  521          * mark the pages read-only.
  522          *
  523          * We do not have to fixup the clean/dirty bits here... we can
  524          * allow the pager to do it after the I/O completes.
  525          *
  526          * NOTE! mc[i]->dirty may be partial or fragmented due to an
  527          * edge case with file fragments.
  528          */
  529         for (i = 0; i < count; i++) {
  530                 KASSERT(mc[i]->valid == VM_PAGE_BITS_ALL,
  531                     ("vm_pageout_flush: partially invalid page %p index %d/%d",
  532                         mc[i], i, count));
  533                 vm_page_sbusy(mc[i]);
  534                 pmap_remove_write(mc[i]);
  535         }
  536         vm_object_pip_add(object, count);
  537 
  538         vm_pager_put_pages(object, mc, count, flags, pageout_status);
  539 
  540         runlen = count - mreq;
  541         if (eio != NULL)
  542                 *eio = FALSE;
  543         for (i = 0; i < count; i++) {
  544                 vm_page_t mt = mc[i];
  545 
  546                 KASSERT(pageout_status[i] == VM_PAGER_PEND ||
  547                     !pmap_page_is_write_mapped(mt),
  548                     ("vm_pageout_flush: page %p is not write protected", mt));
  549                 switch (pageout_status[i]) {
  550                 case VM_PAGER_OK:
  551                 case VM_PAGER_PEND:
  552                         numpagedout++;
  553                         break;
  554                 case VM_PAGER_BAD:
  555                         /*
  556                          * Page outside of range of object. Right now we
  557                          * essentially lose the changes by pretending it
  558                          * worked.
  559                          */
  560                         vm_page_undirty(mt);
  561                         break;
  562                 case VM_PAGER_ERROR:
  563                 case VM_PAGER_FAIL:
  564                         /*
  565                          * If page couldn't be paged out, then reactivate the
  566                          * page so it doesn't clog the inactive list.  (We
  567                          * will try paging out it again later).
  568                          */
  569                         vm_page_lock(mt);
  570                         vm_page_activate(mt);
  571                         vm_page_unlock(mt);
  572                         if (eio != NULL && i >= mreq && i - mreq < runlen)
  573                                 *eio = TRUE;
  574                         break;
  575                 case VM_PAGER_AGAIN:
  576                         if (i >= mreq && i - mreq < runlen)
  577                                 runlen = i - mreq;
  578                         break;
  579                 }
  580 
  581                 /*
  582                  * If the operation is still going, leave the page busy to
  583                  * block all other accesses. Also, leave the paging in
  584                  * progress indicator set so that we don't attempt an object
  585                  * collapse.
  586                  */
  587                 if (pageout_status[i] != VM_PAGER_PEND) {
  588                         vm_object_pip_wakeup(object);
  589                         vm_page_sunbusy(mt);
  590                 }
  591         }
  592         if (prunlen != NULL)
  593                 *prunlen = runlen;
  594         return (numpagedout);
  595 }
  596 
  597 #if !defined(NO_SWAPPING)
  598 /*
  599  *      vm_pageout_object_deactivate_pages
  600  *
  601  *      Deactivate enough pages to satisfy the inactive target
  602  *      requirements.
  603  *
  604  *      The object and map must be locked.
  605  */
  606 static void
  607 vm_pageout_object_deactivate_pages(pmap_t pmap, vm_object_t first_object,
  608     long desired)
  609 {
  610         vm_object_t backing_object, object;
  611         vm_page_t p;
  612         int act_delta, remove_mode;
  613 
  614         VM_OBJECT_ASSERT_LOCKED(first_object);
  615         if ((first_object->flags & OBJ_FICTITIOUS) != 0)
  616                 return;
  617         for (object = first_object;; object = backing_object) {
  618                 if (pmap_resident_count(pmap) <= desired)
  619                         goto unlock_return;
  620                 VM_OBJECT_ASSERT_LOCKED(object);
  621                 if ((object->flags & OBJ_UNMANAGED) != 0 ||
  622                     object->paging_in_progress != 0)
  623                         goto unlock_return;
  624 
  625                 remove_mode = 0;
  626                 if (object->shadow_count > 1)
  627                         remove_mode = 1;
  628                 /*
  629                  * Scan the object's entire memory queue.
  630                  */
  631                 TAILQ_FOREACH(p, &object->memq, listq) {
  632                         if (pmap_resident_count(pmap) <= desired)
  633                                 goto unlock_return;
  634                         if (vm_page_busied(p))
  635                                 continue;
  636                         PCPU_INC(cnt.v_pdpages);
  637                         vm_page_lock(p);
  638                         if (p->wire_count != 0 || p->hold_count != 0 ||
  639                             !pmap_page_exists_quick(pmap, p)) {
  640                                 vm_page_unlock(p);
  641                                 continue;
  642                         }
  643                         act_delta = pmap_ts_referenced(p);
  644                         if ((p->aflags & PGA_REFERENCED) != 0) {
  645                                 if (act_delta == 0)
  646                                         act_delta = 1;
  647                                 vm_page_aflag_clear(p, PGA_REFERENCED);
  648                         }
  649                         if (p->queue != PQ_ACTIVE && act_delta != 0) {
  650                                 vm_page_activate(p);
  651                                 p->act_count += act_delta;
  652                         } else if (p->queue == PQ_ACTIVE) {
  653                                 if (act_delta == 0) {
  654                                         p->act_count -= min(p->act_count,
  655                                             ACT_DECLINE);
  656                                         if (!remove_mode && p->act_count == 0) {
  657                                                 pmap_remove_all(p);
  658                                                 vm_page_deactivate(p);
  659                                         } else
  660                                                 vm_page_requeue(p);
  661                                 } else {
  662                                         vm_page_activate(p);
  663                                         if (p->act_count < ACT_MAX -
  664                                             ACT_ADVANCE)
  665                                                 p->act_count += ACT_ADVANCE;
  666                                         vm_page_requeue(p);
  667                                 }
  668                         } else if (p->queue == PQ_INACTIVE)
  669                                 pmap_remove_all(p);
  670                         vm_page_unlock(p);
  671                 }
  672                 if ((backing_object = object->backing_object) == NULL)
  673                         goto unlock_return;
  674                 VM_OBJECT_RLOCK(backing_object);
  675                 if (object != first_object)
  676                         VM_OBJECT_RUNLOCK(object);
  677         }
  678 unlock_return:
  679         if (object != first_object)
  680                 VM_OBJECT_RUNLOCK(object);
  681 }
  682 
  683 /*
  684  * deactivate some number of pages in a map, try to do it fairly, but
  685  * that is really hard to do.
  686  */
  687 static void
  688 vm_pageout_map_deactivate_pages(map, desired)
  689         vm_map_t map;
  690         long desired;
  691 {
  692         vm_map_entry_t tmpe;
  693         vm_object_t obj, bigobj;
  694         int nothingwired;
  695 
  696         if (!vm_map_trylock(map))
  697                 return;
  698 
  699         bigobj = NULL;
  700         nothingwired = TRUE;
  701 
  702         /*
  703          * first, search out the biggest object, and try to free pages from
  704          * that.
  705          */
  706         tmpe = map->header.next;
  707         while (tmpe != &map->header) {
  708                 if ((tmpe->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
  709                         obj = tmpe->object.vm_object;
  710                         if (obj != NULL && VM_OBJECT_TRYRLOCK(obj)) {
  711                                 if (obj->shadow_count <= 1 &&
  712                                     (bigobj == NULL ||
  713                                      bigobj->resident_page_count < obj->resident_page_count)) {
  714                                         if (bigobj != NULL)
  715                                                 VM_OBJECT_RUNLOCK(bigobj);
  716                                         bigobj = obj;
  717                                 } else
  718                                         VM_OBJECT_RUNLOCK(obj);
  719                         }
  720                 }
  721                 if (tmpe->wired_count > 0)
  722                         nothingwired = FALSE;
  723                 tmpe = tmpe->next;
  724         }
  725 
  726         if (bigobj != NULL) {
  727                 vm_pageout_object_deactivate_pages(map->pmap, bigobj, desired);
  728                 VM_OBJECT_RUNLOCK(bigobj);
  729         }
  730         /*
  731          * Next, hunt around for other pages to deactivate.  We actually
  732          * do this search sort of wrong -- .text first is not the best idea.
  733          */
  734         tmpe = map->header.next;
  735         while (tmpe != &map->header) {
  736                 if (pmap_resident_count(vm_map_pmap(map)) <= desired)
  737                         break;
  738                 if ((tmpe->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
  739                         obj = tmpe->object.vm_object;
  740                         if (obj != NULL) {
  741                                 VM_OBJECT_RLOCK(obj);
  742                                 vm_pageout_object_deactivate_pages(map->pmap, obj, desired);
  743                                 VM_OBJECT_RUNLOCK(obj);
  744                         }
  745                 }
  746                 tmpe = tmpe->next;
  747         }
  748 
  749         /*
  750          * Remove all mappings if a process is swapped out, this will free page
  751          * table pages.
  752          */
  753         if (desired == 0 && nothingwired) {
  754                 pmap_remove(vm_map_pmap(map), vm_map_min(map),
  755                     vm_map_max(map));
  756         }
  757 
  758         vm_map_unlock(map);
  759 }
  760 #endif          /* !defined(NO_SWAPPING) */
  761 
  762 /*
  763  * Attempt to acquire all of the necessary locks to launder a page and
  764  * then call through the clustering layer to PUTPAGES.  Wait a short
  765  * time for a vnode lock.
  766  *
  767  * Requires the page and object lock on entry, releases both before return.
  768  * Returns 0 on success and an errno otherwise.
  769  */
  770 static int
  771 vm_pageout_clean(vm_page_t m)
  772 {
  773         struct vnode *vp;
  774         struct mount *mp;
  775         vm_object_t object;
  776         vm_pindex_t pindex;
  777         int error, lockmode;
  778 
  779         vm_page_assert_locked(m);
  780         object = m->object;
  781         VM_OBJECT_ASSERT_WLOCKED(object);
  782         error = 0;
  783         vp = NULL;
  784         mp = NULL;
  785 
  786         /*
  787          * The object is already known NOT to be dead.   It
  788          * is possible for the vget() to block the whole
  789          * pageout daemon, but the new low-memory handling
  790          * code should prevent it.
  791          *
  792          * We can't wait forever for the vnode lock, we might
  793          * deadlock due to a vn_read() getting stuck in
  794          * vm_wait while holding this vnode.  We skip the 
  795          * vnode if we can't get it in a reasonable amount
  796          * of time.
  797          */
  798         if (object->type == OBJT_VNODE) {
  799                 vm_page_unlock(m);
  800                 vp = object->handle;
  801                 if (vp->v_type == VREG &&
  802                     vn_start_write(vp, &mp, V_NOWAIT) != 0) {
  803                         mp = NULL;
  804                         error = EDEADLK;
  805                         goto unlock_all;
  806                 }
  807                 KASSERT(mp != NULL,
  808                     ("vp %p with NULL v_mount", vp));
  809                 vm_object_reference_locked(object);
  810                 pindex = m->pindex;
  811                 VM_OBJECT_WUNLOCK(object);
  812                 lockmode = MNT_SHARED_WRITES(vp->v_mount) ?
  813                     LK_SHARED : LK_EXCLUSIVE;
  814                 if (vget(vp, lockmode | LK_TIMELOCK, curthread)) {
  815                         vp = NULL;
  816                         error = EDEADLK;
  817                         goto unlock_mp;
  818                 }
  819                 VM_OBJECT_WLOCK(object);
  820                 vm_page_lock(m);
  821                 /*
  822                  * While the object and page were unlocked, the page
  823                  * may have been:
  824                  * (1) moved to a different queue,
  825                  * (2) reallocated to a different object,
  826                  * (3) reallocated to a different offset, or
  827                  * (4) cleaned.
  828                  */
  829                 if (m->queue != PQ_INACTIVE || m->object != object ||
  830                     m->pindex != pindex || m->dirty == 0) {
  831                         vm_page_unlock(m);
  832                         error = ENXIO;
  833                         goto unlock_all;
  834                 }
  835 
  836                 /*
  837                  * The page may have been busied or held while the object
  838                  * and page locks were released.
  839                  */
  840                 if (vm_page_busied(m) || m->hold_count != 0) {
  841                         vm_page_unlock(m);
  842                         error = EBUSY;
  843                         goto unlock_all;
  844                 }
  845         }
  846 
  847         /*
  848          * If a page is dirty, then it is either being washed
  849          * (but not yet cleaned) or it is still in the
  850          * laundry.  If it is still in the laundry, then we
  851          * start the cleaning operation. 
  852          */
  853         if (vm_pageout_cluster(m) == 0)
  854                 error = EIO;
  855 
  856 unlock_all:
  857         VM_OBJECT_WUNLOCK(object);
  858 
  859 unlock_mp:
  860         vm_page_lock_assert(m, MA_NOTOWNED);
  861         if (mp != NULL) {
  862                 if (vp != NULL)
  863                         vput(vp);
  864                 vm_object_deallocate(object);
  865                 vn_finished_write(mp);
  866         }
  867 
  868         return (error);
  869 }
  870 
  871 /*
  872  *      vm_pageout_scan does the dirty work for the pageout daemon.
  873  *
  874  *      pass 0 - Update active LRU/deactivate pages
  875  *      pass 1 - Move inactive to cache or free
  876  *      pass 2 - Launder dirty pages
  877  */
  878 static void
  879 vm_pageout_scan(struct vm_domain *vmd, int pass)
  880 {
  881         vm_page_t m, next;
  882         struct vm_pagequeue *pq;
  883         vm_object_t object;
  884         long min_scan;
  885         int act_delta, addl_page_shortage, deficit, error, maxlaunder, maxscan;
  886         int page_shortage, scan_tick, scanned, starting_page_shortage;
  887         int vnodes_skipped;
  888         boolean_t pageout_ok, queues_locked;
  889 
  890         /*
  891          * If we need to reclaim memory ask kernel caches to return
  892          * some.  We rate limit to avoid thrashing.
  893          */
  894         if (vmd == &vm_dom[0] && pass > 0 &&
  895             (time_uptime - lowmem_uptime) >= lowmem_period) {
  896                 /*
  897                  * Decrease registered cache sizes.
  898                  */
  899                 SDT_PROBE0(vm, , , vm__lowmem_scan);
  900                 EVENTHANDLER_INVOKE(vm_lowmem, 0);
  901                 /*
  902                  * We do this explicitly after the caches have been
  903                  * drained above.
  904                  */
  905                 uma_reclaim();
  906                 lowmem_uptime = time_uptime;
  907         }
  908 
  909         /*
  910          * The addl_page_shortage is the number of temporarily
  911          * stuck pages in the inactive queue.  In other words, the
  912          * number of pages from the inactive count that should be
  913          * discounted in setting the target for the active queue scan.
  914          */
  915         addl_page_shortage = 0;
  916 
  917         /*
  918          * Calculate the number of pages we want to either free or move
  919          * to the cache.
  920          */
  921         if (pass > 0) {
  922                 deficit = atomic_readandclear_int(&vm_pageout_deficit);
  923                 page_shortage = vm_paging_target() + deficit;
  924         } else
  925                 page_shortage = deficit = 0;
  926         starting_page_shortage = page_shortage;
  927 
  928         /*
  929          * maxlaunder limits the number of dirty pages we flush per scan.
  930          * For most systems a smaller value (16 or 32) is more robust under
  931          * extreme memory and disk pressure because any unnecessary writes
  932          * to disk can result in extreme performance degredation.  However,
  933          * systems with excessive dirty pages (especially when MAP_NOSYNC is
  934          * used) will die horribly with limited laundering.  If the pageout
  935          * daemon cannot clean enough pages in the first pass, we let it go
  936          * all out in succeeding passes.
  937          */
  938         if ((maxlaunder = vm_max_launder) <= 1)
  939                 maxlaunder = 1;
  940         if (pass > 1)
  941                 maxlaunder = 10000;
  942 
  943         vnodes_skipped = 0;
  944 
  945         /*
  946          * Start scanning the inactive queue for pages we can move to the
  947          * cache or free.  The scan will stop when the target is reached or
  948          * we have scanned the entire inactive queue.  Note that m->act_count
  949          * is not used to form decisions for the inactive queue, only for the
  950          * active queue.
  951          */
  952         pq = &vmd->vmd_pagequeues[PQ_INACTIVE];
  953         maxscan = pq->pq_cnt;
  954         vm_pagequeue_lock(pq);
  955         queues_locked = TRUE;
  956         for (m = TAILQ_FIRST(&pq->pq_pl);
  957              m != NULL && maxscan-- > 0 && page_shortage > 0;
  958              m = next) {
  959                 vm_pagequeue_assert_locked(pq);
  960                 KASSERT(queues_locked, ("unlocked queues"));
  961                 KASSERT(m->queue == PQ_INACTIVE, ("Inactive queue %p", m));
  962 
  963                 PCPU_INC(cnt.v_pdpages);
  964                 next = TAILQ_NEXT(m, plinks.q);
  965 
  966                 /*
  967                  * skip marker pages
  968                  */
  969                 if (m->flags & PG_MARKER)
  970                         continue;
  971 
  972                 KASSERT((m->flags & PG_FICTITIOUS) == 0,
  973                     ("Fictitious page %p cannot be in inactive queue", m));
  974                 KASSERT((m->oflags & VPO_UNMANAGED) == 0,
  975                     ("Unmanaged page %p cannot be in inactive queue", m));
  976 
  977                 /*
  978                  * The page or object lock acquisitions fail if the
  979                  * page was removed from the queue or moved to a
  980                  * different position within the queue.  In either
  981                  * case, addl_page_shortage should not be incremented.
  982                  */
  983                 if (!vm_pageout_page_lock(m, &next))
  984                         goto unlock_page;
  985                 else if (m->hold_count != 0) {
  986                         /*
  987                          * Held pages are essentially stuck in the
  988                          * queue.  So, they ought to be discounted
  989                          * from the inactive count.  See the
  990                          * calculation of the page_shortage for the
  991                          * loop over the active queue below.
  992                          */
  993                         addl_page_shortage++;
  994                         goto unlock_page;
  995                 }
  996                 object = m->object;
  997                 if (!VM_OBJECT_TRYWLOCK(object)) {
  998                         if (!vm_pageout_fallback_object_lock(m, &next))
  999                                 goto unlock_object;
 1000                         else if (m->hold_count != 0) {
 1001                                 addl_page_shortage++;
 1002                                 goto unlock_object;
 1003                         }
 1004                 }
 1005                 if (vm_page_busied(m)) {
 1006                         /*
 1007                          * Don't mess with busy pages.  Leave them at
 1008                          * the front of the queue.  Most likely, they
 1009                          * are being paged out and will leave the
 1010                          * queue shortly after the scan finishes.  So,
 1011                          * they ought to be discounted from the
 1012                          * inactive count.
 1013                          */
 1014                         addl_page_shortage++;
 1015 unlock_object:
 1016                         VM_OBJECT_WUNLOCK(object);
 1017 unlock_page:
 1018                         vm_page_unlock(m);
 1019                         continue;
 1020                 }
 1021                 KASSERT(m->hold_count == 0, ("Held page %p", m));
 1022 
 1023                 /*
 1024                  * We unlock the inactive page queue, invalidating the
 1025                  * 'next' pointer.  Use our marker to remember our
 1026                  * place.
 1027                  */
 1028                 TAILQ_INSERT_AFTER(&pq->pq_pl, m, &vmd->vmd_marker, plinks.q);
 1029                 vm_pagequeue_unlock(pq);
 1030                 queues_locked = FALSE;
 1031 
 1032                 /*
 1033                  * Invalid pages can be easily freed. They cannot be
 1034                  * mapped, vm_page_free() asserts this.
 1035                  */
 1036                 if (m->valid == 0)
 1037                         goto free_page;
 1038 
 1039                 /*
 1040                  * If the page has been referenced and the object is not dead,
 1041                  * reactivate or requeue the page depending on whether the
 1042                  * object is mapped.
 1043                  */
 1044                 if ((m->aflags & PGA_REFERENCED) != 0) {
 1045                         vm_page_aflag_clear(m, PGA_REFERENCED);
 1046                         act_delta = 1;
 1047                 } else
 1048                         act_delta = 0;
 1049                 if (object->ref_count != 0) {
 1050                         act_delta += pmap_ts_referenced(m);
 1051                 } else {
 1052                         KASSERT(!pmap_page_is_mapped(m),
 1053                             ("vm_pageout_scan: page %p is mapped", m));
 1054                 }
 1055                 if (act_delta != 0) {
 1056                         if (object->ref_count != 0) {
 1057                                 vm_page_activate(m);
 1058 
 1059                                 /*
 1060                                  * Increase the activation count if the page
 1061                                  * was referenced while in the inactive queue.
 1062                                  * This makes it less likely that the page will
 1063                                  * be returned prematurely to the inactive
 1064                                  * queue.
 1065                                  */
 1066                                 m->act_count += act_delta + ACT_ADVANCE;
 1067                                 goto drop_page;
 1068                         } else if ((object->flags & OBJ_DEAD) == 0)
 1069                                 goto requeue_page;
 1070                 }
 1071 
 1072                 /*
 1073                  * If the page appears to be clean at the machine-independent
 1074                  * layer, then remove all of its mappings from the pmap in
 1075                  * anticipation of placing it onto the cache queue.  If,
 1076                  * however, any of the page's mappings allow write access,
 1077                  * then the page may still be modified until the last of those
 1078                  * mappings are removed.
 1079                  */
 1080                 if (object->ref_count != 0) {
 1081                         vm_page_test_dirty(m);
 1082                         if (m->dirty == 0)
 1083                                 pmap_remove_all(m);
 1084                 }
 1085 
 1086                 if (m->dirty == 0) {
 1087                         /*
 1088                          * Clean pages can be freed.
 1089                          */
 1090 free_page:
 1091                         vm_page_free(m);
 1092                         PCPU_INC(cnt.v_dfree);
 1093                         --page_shortage;
 1094                 } else if ((object->flags & OBJ_DEAD) != 0) {
 1095                         /*
 1096                          * Leave dirty pages from dead objects at the front of
 1097                          * the queue.  They are being paged out and freed by
 1098                          * the thread that destroyed the object.  They will
 1099                          * leave the queue shortly after the scan finishes, so 
 1100                          * they should be discounted from the inactive count.
 1101                          */
 1102                         addl_page_shortage++;
 1103                 } else if ((m->flags & PG_WINATCFLS) == 0 && pass < 2) {
 1104                         /*
 1105                          * Dirty pages need to be paged out, but flushing
 1106                          * a page is extremely expensive versus freeing
 1107                          * a clean page.  Rather then artificially limiting
 1108                          * the number of pages we can flush, we instead give
 1109                          * dirty pages extra priority on the inactive queue
 1110                          * by forcing them to be cycled through the queue
 1111                          * twice before being flushed, after which the
 1112                          * (now clean) page will cycle through once more
 1113                          * before being freed.  This significantly extends
 1114                          * the thrash point for a heavily loaded machine.
 1115                          */
 1116                         m->flags |= PG_WINATCFLS;
 1117 requeue_page:
 1118                         vm_pagequeue_lock(pq);
 1119                         queues_locked = TRUE;
 1120                         vm_page_requeue_locked(m);
 1121                 } else if (maxlaunder > 0) {
 1122                         /*
 1123                          * We always want to try to flush some dirty pages if
 1124                          * we encounter them, to keep the system stable.
 1125                          * Normally this number is small, but under extreme
 1126                          * pressure where there are insufficient clean pages
 1127                          * on the inactive queue, we may have to go all out.
 1128                          */
 1129 
 1130                         if (object->type != OBJT_SWAP &&
 1131                             object->type != OBJT_DEFAULT)
 1132                                 pageout_ok = TRUE;
 1133                         else if (disable_swap_pageouts)
 1134                                 pageout_ok = FALSE;
 1135                         else if (defer_swap_pageouts)
 1136                                 pageout_ok = vm_page_count_min();
 1137                         else
 1138                                 pageout_ok = TRUE;
 1139                         if (!pageout_ok)
 1140                                 goto requeue_page;
 1141                         error = vm_pageout_clean(m);
 1142                         /*
 1143                          * Decrement page_shortage on success to account for
 1144                          * the (future) cleaned page.  Otherwise we could wind
 1145                          * up laundering or cleaning too many pages.
 1146                          */
 1147                         if (error == 0) {
 1148                                 page_shortage--;
 1149                                 maxlaunder--;
 1150                         } else if (error == EDEADLK) {
 1151                                 pageout_lock_miss++;
 1152                                 vnodes_skipped++;
 1153                         } else if (error == EBUSY) {
 1154                                 addl_page_shortage++;
 1155                         }
 1156                         vm_page_lock_assert(m, MA_NOTOWNED);
 1157                         goto relock_queues;
 1158                 }
 1159 drop_page:
 1160                 vm_page_unlock(m);
 1161                 VM_OBJECT_WUNLOCK(object);
 1162 relock_queues:
 1163                 if (!queues_locked) {
 1164                         vm_pagequeue_lock(pq);
 1165                         queues_locked = TRUE;
 1166                 }
 1167                 next = TAILQ_NEXT(&vmd->vmd_marker, plinks.q);
 1168                 TAILQ_REMOVE(&pq->pq_pl, &vmd->vmd_marker, plinks.q);
 1169         }
 1170         vm_pagequeue_unlock(pq);
 1171 
 1172 #if !defined(NO_SWAPPING)
 1173         /*
 1174          * Wakeup the swapout daemon if we didn't cache or free the targeted
 1175          * number of pages. 
 1176          */
 1177         if (vm_swap_enabled && page_shortage > 0)
 1178                 vm_req_vmdaemon(VM_SWAP_NORMAL);
 1179 #endif
 1180 
 1181         /*
 1182          * Wakeup the sync daemon if we skipped a vnode in a writeable object
 1183          * and we didn't cache or free enough pages.
 1184          */
 1185         if (vnodes_skipped > 0 && page_shortage > vm_cnt.v_free_target -
 1186             vm_cnt.v_free_min)
 1187                 (void)speedup_syncer();
 1188 
 1189         /*
 1190          * If the inactive queue scan fails repeatedly to meet its
 1191          * target, kill the largest process.
 1192          */
 1193         vm_pageout_mightbe_oom(vmd, page_shortage, starting_page_shortage);
 1194 
 1195         /*
 1196          * Compute the number of pages we want to try to move from the
 1197          * active queue to the inactive queue.
 1198          */
 1199         page_shortage = vm_cnt.v_inactive_target - vm_cnt.v_inactive_count +
 1200             vm_paging_target() + deficit + addl_page_shortage;
 1201 
 1202         pq = &vmd->vmd_pagequeues[PQ_ACTIVE];
 1203         vm_pagequeue_lock(pq);
 1204         maxscan = pq->pq_cnt;
 1205 
 1206         /*
 1207          * If we're just idle polling attempt to visit every
 1208          * active page within 'update_period' seconds.
 1209          */
 1210         scan_tick = ticks;
 1211         if (vm_pageout_update_period != 0) {
 1212                 min_scan = pq->pq_cnt;
 1213                 min_scan *= scan_tick - vmd->vmd_last_active_scan;
 1214                 min_scan /= hz * vm_pageout_update_period;
 1215         } else
 1216                 min_scan = 0;
 1217         if (min_scan > 0 || (page_shortage > 0 && maxscan > 0))
 1218                 vmd->vmd_last_active_scan = scan_tick;
 1219 
 1220         /*
 1221          * Scan the active queue for pages that can be deactivated.  Update
 1222          * the per-page activity counter and use it to identify deactivation
 1223          * candidates.
 1224          */
 1225         for (m = TAILQ_FIRST(&pq->pq_pl), scanned = 0; m != NULL && (scanned <
 1226             min_scan || (page_shortage > 0 && scanned < maxscan)); m = next,
 1227             scanned++) {
 1228 
 1229                 KASSERT(m->queue == PQ_ACTIVE,
 1230                     ("vm_pageout_scan: page %p isn't active", m));
 1231 
 1232                 next = TAILQ_NEXT(m, plinks.q);
 1233                 if ((m->flags & PG_MARKER) != 0)
 1234                         continue;
 1235                 KASSERT((m->flags & PG_FICTITIOUS) == 0,
 1236                     ("Fictitious page %p cannot be in active queue", m));
 1237                 KASSERT((m->oflags & VPO_UNMANAGED) == 0,
 1238                     ("Unmanaged page %p cannot be in active queue", m));
 1239                 if (!vm_pageout_page_lock(m, &next)) {
 1240                         vm_page_unlock(m);
 1241                         continue;
 1242                 }
 1243 
 1244                 /*
 1245                  * The count for pagedaemon pages is done after checking the
 1246                  * page for eligibility...
 1247                  */
 1248                 PCPU_INC(cnt.v_pdpages);
 1249 
 1250                 /*
 1251                  * Check to see "how much" the page has been used.
 1252                  */
 1253                 if ((m->aflags & PGA_REFERENCED) != 0) {
 1254                         vm_page_aflag_clear(m, PGA_REFERENCED);
 1255                         act_delta = 1;
 1256                 } else
 1257                         act_delta = 0;
 1258 
 1259                 /*
 1260                  * Unlocked object ref count check.  Two races are possible.
 1261                  * 1) The ref was transitioning to zero and we saw non-zero,
 1262                  *    the pmap bits will be checked unnecessarily.
 1263                  * 2) The ref was transitioning to one and we saw zero. 
 1264                  *    The page lock prevents a new reference to this page so
 1265                  *    we need not check the reference bits.
 1266                  */
 1267                 if (m->object->ref_count != 0)
 1268                         act_delta += pmap_ts_referenced(m);
 1269 
 1270                 /*
 1271                  * Advance or decay the act_count based on recent usage.
 1272                  */
 1273                 if (act_delta != 0) {
 1274                         m->act_count += ACT_ADVANCE + act_delta;
 1275                         if (m->act_count > ACT_MAX)
 1276                                 m->act_count = ACT_MAX;
 1277                 } else
 1278                         m->act_count -= min(m->act_count, ACT_DECLINE);
 1279 
 1280                 /*
 1281                  * Move this page to the tail of the active or inactive
 1282                  * queue depending on usage.
 1283                  */
 1284                 if (m->act_count == 0) {
 1285                         /* Dequeue to avoid later lock recursion. */
 1286                         vm_page_dequeue_locked(m);
 1287                         vm_page_deactivate(m);
 1288                         page_shortage--;
 1289                 } else
 1290                         vm_page_requeue_locked(m);
 1291                 vm_page_unlock(m);
 1292         }
 1293         vm_pagequeue_unlock(pq);
 1294 #if !defined(NO_SWAPPING)
 1295         /*
 1296          * Idle process swapout -- run once per second.
 1297          */
 1298         if (vm_swap_idle_enabled) {
 1299                 static long lsec;
 1300                 if (time_second != lsec) {
 1301                         vm_req_vmdaemon(VM_SWAP_IDLE);
 1302                         lsec = time_second;
 1303                 }
 1304         }
 1305 #endif
 1306 }
 1307 
 1308 static int vm_pageout_oom_vote;
 1309 
 1310 /*
 1311  * The pagedaemon threads randlomly select one to perform the
 1312  * OOM.  Trying to kill processes before all pagedaemons
 1313  * failed to reach free target is premature.
 1314  */
 1315 static void
 1316 vm_pageout_mightbe_oom(struct vm_domain *vmd, int page_shortage,
 1317     int starting_page_shortage)
 1318 {
 1319         int old_vote;
 1320 
 1321         if (starting_page_shortage <= 0 || starting_page_shortage !=
 1322             page_shortage)
 1323                 vmd->vmd_oom_seq = 0;
 1324         else
 1325                 vmd->vmd_oom_seq++;
 1326         if (vmd->vmd_oom_seq < vm_pageout_oom_seq) {
 1327                 if (vmd->vmd_oom) {
 1328                         vmd->vmd_oom = FALSE;
 1329                         atomic_subtract_int(&vm_pageout_oom_vote, 1);
 1330                 }
 1331                 return;
 1332         }
 1333 
 1334         /*
 1335          * Do not follow the call sequence until OOM condition is
 1336          * cleared.
 1337          */
 1338         vmd->vmd_oom_seq = 0;
 1339 
 1340         if (vmd->vmd_oom)
 1341                 return;
 1342 
 1343         vmd->vmd_oom = TRUE;
 1344         old_vote = atomic_fetchadd_int(&vm_pageout_oom_vote, 1);
 1345         if (old_vote != vm_ndomains - 1)
 1346                 return;
 1347 
 1348         /*
 1349          * The current pagedaemon thread is the last in the quorum to
 1350          * start OOM.  Initiate the selection and signaling of the
 1351          * victim.
 1352          */
 1353         vm_pageout_oom(VM_OOM_MEM);
 1354 
 1355         /*
 1356          * After one round of OOM terror, recall our vote.  On the
 1357          * next pass, current pagedaemon would vote again if the low
 1358          * memory condition is still there, due to vmd_oom being
 1359          * false.
 1360          */
 1361         vmd->vmd_oom = FALSE;
 1362         atomic_subtract_int(&vm_pageout_oom_vote, 1);
 1363 }
 1364 
 1365 /*
 1366  * The OOM killer is the page daemon's action of last resort when
 1367  * memory allocation requests have been stalled for a prolonged period
 1368  * of time because it cannot reclaim memory.  This function computes
 1369  * the approximate number of physical pages that could be reclaimed if
 1370  * the specified address space is destroyed.
 1371  *
 1372  * Private, anonymous memory owned by the address space is the
 1373  * principal resource that we expect to recover after an OOM kill.
 1374  * Since the physical pages mapped by the address space's COW entries
 1375  * are typically shared pages, they are unlikely to be released and so
 1376  * they are not counted.
 1377  *
 1378  * To get to the point where the page daemon runs the OOM killer, its
 1379  * efforts to write-back vnode-backed pages may have stalled.  This
 1380  * could be caused by a memory allocation deadlock in the write path
 1381  * that might be resolved by an OOM kill.  Therefore, physical pages
 1382  * belonging to vnode-backed objects are counted, because they might
 1383  * be freed without being written out first if the address space holds
 1384  * the last reference to an unlinked vnode.
 1385  *
 1386  * Similarly, physical pages belonging to OBJT_PHYS objects are
 1387  * counted because the address space might hold the last reference to
 1388  * the object.
 1389  */
 1390 static long
 1391 vm_pageout_oom_pagecount(struct vmspace *vmspace)
 1392 {
 1393         vm_map_t map;
 1394         vm_map_entry_t entry;
 1395         vm_object_t obj;
 1396         long res;
 1397 
 1398         map = &vmspace->vm_map;
 1399         KASSERT(!map->system_map, ("system map"));
 1400         sx_assert(&map->lock, SA_LOCKED);
 1401         res = 0;
 1402         for (entry = map->header.next; entry != &map->header;
 1403             entry = entry->next) {
 1404                 if ((entry->eflags & MAP_ENTRY_IS_SUB_MAP) != 0)
 1405                         continue;
 1406                 obj = entry->object.vm_object;
 1407                 if (obj == NULL)
 1408                         continue;
 1409                 if ((entry->eflags & MAP_ENTRY_NEEDS_COPY) != 0 &&
 1410                     obj->ref_count != 1)
 1411                         continue;
 1412                 switch (obj->type) {
 1413                 case OBJT_DEFAULT:
 1414                 case OBJT_SWAP:
 1415                 case OBJT_PHYS:
 1416                 case OBJT_VNODE:
 1417                         res += obj->resident_page_count;
 1418                         break;
 1419                 }
 1420         }
 1421         return (res);
 1422 }
 1423 
 1424 void
 1425 vm_pageout_oom(int shortage)
 1426 {
 1427         struct proc *p, *bigproc;
 1428         vm_offset_t size, bigsize;
 1429         struct thread *td;
 1430         struct vmspace *vm;
 1431 
 1432         /*
 1433          * We keep the process bigproc locked once we find it to keep anyone
 1434          * from messing with it; however, there is a possibility of
 1435          * deadlock if process B is bigproc and one of it's child processes
 1436          * attempts to propagate a signal to B while we are waiting for A's
 1437          * lock while walking this list.  To avoid this, we don't block on
 1438          * the process lock but just skip a process if it is already locked.
 1439          */
 1440         bigproc = NULL;
 1441         bigsize = 0;
 1442         sx_slock(&allproc_lock);
 1443         FOREACH_PROC_IN_SYSTEM(p) {
 1444                 int breakout;
 1445 
 1446                 PROC_LOCK(p);
 1447 
 1448                 /*
 1449                  * If this is a system, protected or killed process, skip it.
 1450                  */
 1451                 if (p->p_state != PRS_NORMAL || (p->p_flag & (P_INEXEC |
 1452                     P_PROTECTED | P_SYSTEM | P_WEXIT)) != 0 ||
 1453                     p->p_pid == 1 || P_KILLED(p) ||
 1454                     (p->p_pid < 48 && swap_pager_avail != 0)) {
 1455                         PROC_UNLOCK(p);
 1456                         continue;
 1457                 }
 1458                 /*
 1459                  * If the process is in a non-running type state,
 1460                  * don't touch it.  Check all the threads individually.
 1461                  */
 1462                 breakout = 0;
 1463                 FOREACH_THREAD_IN_PROC(p, td) {
 1464                         thread_lock(td);
 1465                         if (!TD_ON_RUNQ(td) &&
 1466                             !TD_IS_RUNNING(td) &&
 1467                             !TD_IS_SLEEPING(td) &&
 1468                             !TD_IS_SUSPENDED(td) &&
 1469                             !TD_IS_SWAPPED(td)) {
 1470                                 thread_unlock(td);
 1471                                 breakout = 1;
 1472                                 break;
 1473                         }
 1474                         thread_unlock(td);
 1475                 }
 1476                 if (breakout) {
 1477                         PROC_UNLOCK(p);
 1478                         continue;
 1479                 }
 1480                 /*
 1481                  * get the process size
 1482                  */
 1483                 vm = vmspace_acquire_ref(p);
 1484                 if (vm == NULL) {
 1485                         PROC_UNLOCK(p);
 1486                         continue;
 1487                 }
 1488                 _PHOLD_LITE(p);
 1489                 PROC_UNLOCK(p);
 1490                 sx_sunlock(&allproc_lock);
 1491                 if (!vm_map_trylock_read(&vm->vm_map)) {
 1492                         vmspace_free(vm);
 1493                         sx_slock(&allproc_lock);
 1494                         PRELE(p);
 1495                         continue;
 1496                 }
 1497                 size = vmspace_swap_count(vm);
 1498                 if (shortage == VM_OOM_MEM)
 1499                         size += vm_pageout_oom_pagecount(vm);
 1500                 vm_map_unlock_read(&vm->vm_map);
 1501                 vmspace_free(vm);
 1502                 sx_slock(&allproc_lock);
 1503 
 1504                 /*
 1505                  * If this process is bigger than the biggest one,
 1506                  * remember it.
 1507                  */
 1508                 if (size > bigsize) {
 1509                         if (bigproc != NULL)
 1510                                 PRELE(bigproc);
 1511                         bigproc = p;
 1512                         bigsize = size;
 1513                 } else {
 1514                         PRELE(p);
 1515                 }
 1516         }
 1517         sx_sunlock(&allproc_lock);
 1518         if (bigproc != NULL) {
 1519                 if (vm_panic_on_oom != 0)
 1520                         panic("out of swap space");
 1521                 PROC_LOCK(bigproc);
 1522                 killproc(bigproc, "out of swap space");
 1523                 sched_nice(bigproc, PRIO_MIN);
 1524                 _PRELE(bigproc);
 1525                 PROC_UNLOCK(bigproc);
 1526                 wakeup(&vm_cnt.v_free_count);
 1527         }
 1528 }
 1529 
 1530 static void
 1531 vm_pageout_worker(void *arg)
 1532 {
 1533         struct vm_domain *domain;
 1534         int domidx;
 1535 
 1536         domidx = (uintptr_t)arg;
 1537         domain = &vm_dom[domidx];
 1538 
 1539         /*
 1540          * XXXKIB It could be useful to bind pageout daemon threads to
 1541          * the cores belonging to the domain, from which vm_page_array
 1542          * is allocated.
 1543          */
 1544 
 1545         KASSERT(domain->vmd_segs != 0, ("domain without segments"));
 1546         domain->vmd_last_active_scan = ticks;
 1547         vm_pageout_init_marker(&domain->vmd_marker, PQ_INACTIVE);
 1548         vm_pageout_init_marker(&domain->vmd_inacthead, PQ_INACTIVE);
 1549         TAILQ_INSERT_HEAD(&domain->vmd_pagequeues[PQ_INACTIVE].pq_pl,
 1550             &domain->vmd_inacthead, plinks.q);
 1551 
 1552         /*
 1553          * The pageout daemon worker is never done, so loop forever.
 1554          */
 1555         while (TRUE) {
 1556                 mtx_lock(&vm_page_queue_free_mtx);
 1557 
 1558                 /*
 1559                  * Generally, after a level >= 1 scan, if there are enough
 1560                  * free pages to wakeup the waiters, then they are already
 1561                  * awake.  A call to vm_page_free() during the scan awakened
 1562                  * them.  However, in the following case, this wakeup serves
 1563                  * to bound the amount of time that a thread might wait.
 1564                  * Suppose a thread's call to vm_page_alloc() fails, but
 1565                  * before that thread calls VM_WAIT, enough pages are freed by
 1566                  * other threads to alleviate the free page shortage.  The
 1567                  * thread will, nonetheless, wait until another page is freed
 1568                  * or this wakeup is performed.
 1569                  */
 1570                 if (vm_pages_needed && !vm_page_count_min()) {
 1571                         vm_pages_needed = false;
 1572                         wakeup(&vm_cnt.v_free_count);
 1573                 }
 1574 
 1575                 /*
 1576                  * Do not clear vm_pageout_wanted until we reach our target.
 1577                  * Otherwise, we may be awakened over and over again, wasting
 1578                  * CPU time.
 1579                  */
 1580                 if (vm_pageout_wanted && !vm_paging_needed())
 1581                         vm_pageout_wanted = false;
 1582 
 1583                 /*
 1584                  * Might the page daemon receive a wakeup call?
 1585                  */
 1586                 if (vm_pageout_wanted) {
 1587                         /*
 1588                          * No.  Either vm_pageout_wanted was set by another
 1589                          * thread during the previous scan, which must have
 1590                          * been a level 0 scan, or vm_pageout_wanted was
 1591                          * already set and the scan failed to free enough
 1592                          * pages.  If we haven't yet performed a level >= 2
 1593                          * scan (unlimited dirty cleaning), then upgrade the
 1594                          * level and scan again now.  Otherwise, sleep a bit
 1595                          * and try again later.
 1596                          */
 1597                         mtx_unlock(&vm_page_queue_free_mtx);
 1598                         if (domain->vmd_pass > 1)
 1599                                 pause("psleep", hz / 2);
 1600                         domain->vmd_pass++;
 1601                 } else {
 1602                         /*
 1603                          * Yes.  Sleep until pages need to be reclaimed or
 1604                          * have their reference stats updated.
 1605                          */
 1606                         if (mtx_sleep(&vm_pageout_wanted,
 1607                             &vm_page_queue_free_mtx, PDROP | PVM, "psleep",
 1608                             hz) == 0) {
 1609                                 PCPU_INC(cnt.v_pdwakeups);
 1610                                 domain->vmd_pass = 1;
 1611                         } else
 1612                                 domain->vmd_pass = 0;
 1613                 }
 1614 
 1615                 vm_pageout_scan(domain, domain->vmd_pass);
 1616         }
 1617 }
 1618 
 1619 /*
 1620  *      vm_pageout_init initialises basic pageout daemon settings.
 1621  */
 1622 static void
 1623 vm_pageout_init(void)
 1624 {
 1625         /*
 1626          * Initialize some paging parameters.
 1627          */
 1628         vm_cnt.v_interrupt_free_min = 2;
 1629         if (vm_cnt.v_page_count < 2000)
 1630                 vm_pageout_page_count = 8;
 1631 
 1632         /*
 1633          * v_free_reserved needs to include enough for the largest
 1634          * swap pager structures plus enough for any pv_entry structs
 1635          * when paging. 
 1636          */
 1637         if (vm_cnt.v_page_count > 1024)
 1638                 vm_cnt.v_free_min = 4 + (vm_cnt.v_page_count - 1024) / 200;
 1639         else
 1640                 vm_cnt.v_free_min = 4;
 1641         vm_cnt.v_pageout_free_min = (2*MAXBSIZE)/PAGE_SIZE +
 1642             vm_cnt.v_interrupt_free_min;
 1643         vm_cnt.v_free_reserved = vm_pageout_page_count +
 1644             vm_cnt.v_pageout_free_min + (vm_cnt.v_page_count / 768);
 1645         vm_cnt.v_free_severe = vm_cnt.v_free_min / 2;
 1646         vm_cnt.v_free_target = 4 * vm_cnt.v_free_min + vm_cnt.v_free_reserved;
 1647         vm_cnt.v_free_min += vm_cnt.v_free_reserved;
 1648         vm_cnt.v_free_severe += vm_cnt.v_free_reserved;
 1649         vm_cnt.v_inactive_target = (3 * vm_cnt.v_free_target) / 2;
 1650         if (vm_cnt.v_inactive_target > vm_cnt.v_free_count / 3)
 1651                 vm_cnt.v_inactive_target = vm_cnt.v_free_count / 3;
 1652 
 1653         /*
 1654          * Set the default wakeup threshold to be 10% above the minimum
 1655          * page limit.  This keeps the steady state out of shortfall.
 1656          */
 1657         vm_pageout_wakeup_thresh = (vm_cnt.v_free_min / 10) * 11;
 1658 
 1659         /*
 1660          * Set interval in seconds for active scan.  We want to visit each
 1661          * page at least once every ten minutes.  This is to prevent worst
 1662          * case paging behaviors with stale active LRU.
 1663          */
 1664         if (vm_pageout_update_period == 0)
 1665                 vm_pageout_update_period = 600;
 1666 
 1667         /* XXX does not really belong here */
 1668         if (vm_page_max_wired == 0)
 1669                 vm_page_max_wired = vm_cnt.v_free_count / 3;
 1670 }
 1671 
 1672 /*
 1673  *     vm_pageout is the high level pageout daemon.
 1674  */
 1675 static void
 1676 vm_pageout(void)
 1677 {
 1678         int error;
 1679 #ifdef VM_NUMA_ALLOC
 1680         int i;
 1681 #endif
 1682 
 1683         swap_pager_swap_init();
 1684 #ifdef VM_NUMA_ALLOC
 1685         for (i = 1; i < vm_ndomains; i++) {
 1686                 error = kthread_add(vm_pageout_worker, (void *)(uintptr_t)i,
 1687                     curproc, NULL, 0, 0, "dom%d", i);
 1688                 if (error != 0) {
 1689                         panic("starting pageout for domain %d, error %d\n",
 1690                             i, error);
 1691                 }
 1692         }
 1693 #endif
 1694         error = kthread_add(uma_reclaim_worker, NULL, curproc, NULL,
 1695             0, 0, "uma");
 1696         if (error != 0)
 1697                 panic("starting uma_reclaim helper, error %d\n", error);
 1698         vm_pageout_worker((void *)(uintptr_t)0);
 1699 }
 1700 
 1701 /*
 1702  * Unless the free page queue lock is held by the caller, this function
 1703  * should be regarded as advisory.  Specifically, the caller should
 1704  * not msleep() on &vm_cnt.v_free_count following this function unless
 1705  * the free page queue lock is held until the msleep() is performed.
 1706  */
 1707 void
 1708 pagedaemon_wakeup(void)
 1709 {
 1710 
 1711         if (!vm_pageout_wanted && curthread->td_proc != pageproc) {
 1712                 vm_pageout_wanted = true;
 1713                 wakeup(&vm_pageout_wanted);
 1714         }
 1715 }
 1716 
 1717 #if !defined(NO_SWAPPING)
 1718 static void
 1719 vm_req_vmdaemon(int req)
 1720 {
 1721         static int lastrun = 0;
 1722 
 1723         mtx_lock(&vm_daemon_mtx);
 1724         vm_pageout_req_swapout |= req;
 1725         if ((ticks > (lastrun + hz)) || (ticks < lastrun)) {
 1726                 wakeup(&vm_daemon_needed);
 1727                 lastrun = ticks;
 1728         }
 1729         mtx_unlock(&vm_daemon_mtx);
 1730 }
 1731 
 1732 static void
 1733 vm_daemon(void)
 1734 {
 1735         struct rlimit rsslim;
 1736         struct proc *p;
 1737         struct thread *td;
 1738         struct vmspace *vm;
 1739         int breakout, swapout_flags, tryagain, attempts;
 1740 #ifdef RACCT
 1741         uint64_t rsize, ravailable;
 1742 #endif
 1743 
 1744         while (TRUE) {
 1745                 mtx_lock(&vm_daemon_mtx);
 1746                 msleep(&vm_daemon_needed, &vm_daemon_mtx, PPAUSE, "psleep",
 1747 #ifdef RACCT
 1748                     racct_enable ? hz : 0
 1749 #else
 1750                     0
 1751 #endif
 1752                 );
 1753                 swapout_flags = vm_pageout_req_swapout;
 1754                 vm_pageout_req_swapout = 0;
 1755                 mtx_unlock(&vm_daemon_mtx);
 1756                 if (swapout_flags)
 1757                         swapout_procs(swapout_flags);
 1758 
 1759                 /*
 1760                  * scan the processes for exceeding their rlimits or if
 1761                  * process is swapped out -- deactivate pages
 1762                  */
 1763                 tryagain = 0;
 1764                 attempts = 0;
 1765 again:
 1766                 attempts++;
 1767                 sx_slock(&allproc_lock);
 1768                 FOREACH_PROC_IN_SYSTEM(p) {
 1769                         vm_pindex_t limit, size;
 1770 
 1771                         /*
 1772                          * if this is a system process or if we have already
 1773                          * looked at this process, skip it.
 1774                          */
 1775                         PROC_LOCK(p);
 1776                         if (p->p_state != PRS_NORMAL ||
 1777                             p->p_flag & (P_INEXEC | P_SYSTEM | P_WEXIT)) {
 1778                                 PROC_UNLOCK(p);
 1779                                 continue;
 1780                         }
 1781                         /*
 1782                          * if the process is in a non-running type state,
 1783                          * don't touch it.
 1784                          */
 1785                         breakout = 0;
 1786                         FOREACH_THREAD_IN_PROC(p, td) {
 1787                                 thread_lock(td);
 1788                                 if (!TD_ON_RUNQ(td) &&
 1789                                     !TD_IS_RUNNING(td) &&
 1790                                     !TD_IS_SLEEPING(td) &&
 1791                                     !TD_IS_SUSPENDED(td)) {
 1792                                         thread_unlock(td);
 1793                                         breakout = 1;
 1794                                         break;
 1795                                 }
 1796                                 thread_unlock(td);
 1797                         }
 1798                         if (breakout) {
 1799                                 PROC_UNLOCK(p);
 1800                                 continue;
 1801                         }
 1802                         /*
 1803                          * get a limit
 1804                          */
 1805                         lim_rlimit_proc(p, RLIMIT_RSS, &rsslim);
 1806                         limit = OFF_TO_IDX(
 1807                             qmin(rsslim.rlim_cur, rsslim.rlim_max));
 1808 
 1809                         /*
 1810                          * let processes that are swapped out really be
 1811                          * swapped out set the limit to nothing (will force a
 1812                          * swap-out.)
 1813                          */
 1814                         if ((p->p_flag & P_INMEM) == 0)
 1815                                 limit = 0;      /* XXX */
 1816                         vm = vmspace_acquire_ref(p);
 1817                         _PHOLD_LITE(p);
 1818                         PROC_UNLOCK(p);
 1819                         if (vm == NULL) {
 1820                                 PRELE(p);
 1821                                 continue;
 1822                         }
 1823                         sx_sunlock(&allproc_lock);
 1824 
 1825                         size = vmspace_resident_count(vm);
 1826                         if (size >= limit) {
 1827                                 vm_pageout_map_deactivate_pages(
 1828                                     &vm->vm_map, limit);
 1829                         }
 1830 #ifdef RACCT
 1831                         if (racct_enable) {
 1832                                 rsize = IDX_TO_OFF(size);
 1833                                 PROC_LOCK(p);
 1834                                 racct_set(p, RACCT_RSS, rsize);
 1835                                 ravailable = racct_get_available(p, RACCT_RSS);
 1836                                 PROC_UNLOCK(p);
 1837                                 if (rsize > ravailable) {
 1838                                         /*
 1839                                          * Don't be overly aggressive; this
 1840                                          * might be an innocent process,
 1841                                          * and the limit could've been exceeded
 1842                                          * by some memory hog.  Don't try
 1843                                          * to deactivate more than 1/4th
 1844                                          * of process' resident set size.
 1845                                          */
 1846                                         if (attempts <= 8) {
 1847                                                 if (ravailable < rsize -
 1848                                                     (rsize / 4)) {
 1849                                                         ravailable = rsize -
 1850                                                             (rsize / 4);
 1851                                                 }
 1852                                         }
 1853                                         vm_pageout_map_deactivate_pages(
 1854                                             &vm->vm_map,
 1855                                             OFF_TO_IDX(ravailable));
 1856                                         /* Update RSS usage after paging out. */
 1857                                         size = vmspace_resident_count(vm);
 1858                                         rsize = IDX_TO_OFF(size);
 1859                                         PROC_LOCK(p);
 1860                                         racct_set(p, RACCT_RSS, rsize);
 1861                                         PROC_UNLOCK(p);
 1862                                         if (rsize > ravailable)
 1863                                                 tryagain = 1;
 1864                                 }
 1865                         }
 1866 #endif
 1867                         vmspace_free(vm);
 1868                         sx_slock(&allproc_lock);
 1869                         PRELE(p);
 1870                 }
 1871                 sx_sunlock(&allproc_lock);
 1872                 if (tryagain != 0 && attempts <= 10)
 1873                         goto again;
 1874         }
 1875 }
 1876 #endif                  /* !defined(NO_SWAPPING) */

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