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


[ source navigation ] [ diff markup ] [ identifier search ] [ freetext search ] [ file search ] [ list types ] [ track identifier ]

FreeBSD/Linux Kernel Cross Reference
sys/vm/vm_pageout.c

Version: -  FREEBSD  -  FREEBSD-13-STABLE  -  FREEBSD-13-0  -  FREEBSD-12-STABLE  -  FREEBSD-12-0  -  FREEBSD-11-STABLE  -  FREEBSD-11-0  -  FREEBSD-10-STABLE  -  FREEBSD-10-0  -  FREEBSD-9-STABLE  -  FREEBSD-9-0  -  FREEBSD-8-STABLE  -  FREEBSD-8-0  -  FREEBSD-7-STABLE  -  FREEBSD-7-0  -  FREEBSD-6-STABLE  -  FREEBSD-6-0  -  FREEBSD-5-STABLE  -  FREEBSD-5-0  -  FREEBSD-4-STABLE  -  FREEBSD-3-STABLE  -  FREEBSD22  -  l41  -  OPENBSD  -  linux-2.6  -  MK84  -  PLAN9  -  xnu-8792 
SearchContext: -  none  -  3  -  10 

    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("$FreeBSD$");
   77 
   78 #include "opt_vm.h"
   79 #include <sys/param.h>
   80 #include <sys/systm.h>
   81 #include <sys/kernel.h>
   82 #include <sys/eventhandler.h>
   83 #include <sys/lock.h>
   84 #include <sys/mutex.h>
   85 #include <sys/proc.h>
   86 #include <sys/kthread.h>
   87 #include <sys/ktr.h>
   88 #include <sys/mount.h>
   89 #include <sys/resourcevar.h>
   90 #include <sys/sched.h>
   91 #include <sys/signalvar.h>
   92 #include <sys/vnode.h>
   93 #include <sys/vmmeter.h>
   94 #include <sys/sx.h>
   95 #include <sys/sysctl.h>
   96 
   97 #include <vm/vm.h>
   98 #include <vm/vm_param.h>
   99 #include <vm/vm_object.h>
  100 #include <vm/vm_page.h>
  101 #include <vm/vm_map.h>
  102 #include <vm/vm_pageout.h>
  103 #include <vm/vm_pager.h>
  104 #include <vm/swap_pager.h>
  105 #include <vm/vm_extern.h>
  106 #include <vm/uma.h>
  107 
  108 #include <machine/mutex.h>
  109 
  110 /*
  111  * System initialization
  112  */
  113 
  114 /* the kernel process "vm_pageout"*/
  115 static void vm_pageout(void);
  116 static int vm_pageout_clean(vm_page_t);
  117 static void vm_pageout_scan(int pass);
  118 
  119 struct proc *pageproc;
  120 
  121 static struct kproc_desc page_kp = {
  122         "pagedaemon",
  123         vm_pageout,
  124         &pageproc
  125 };
  126 SYSINIT(pagedaemon, SI_SUB_KTHREAD_PAGE, SI_ORDER_FIRST, kproc_start,
  127     &page_kp);
  128 
  129 #if !defined(NO_SWAPPING)
  130 /* the kernel process "vm_daemon"*/
  131 static void vm_daemon(void);
  132 static struct   proc *vmproc;
  133 
  134 static struct kproc_desc vm_kp = {
  135         "vmdaemon",
  136         vm_daemon,
  137         &vmproc
  138 };
  139 SYSINIT(vmdaemon, SI_SUB_KTHREAD_VM, SI_ORDER_FIRST, kproc_start, &vm_kp);
  140 #endif
  141 
  142 
  143 int vm_pages_needed;            /* Event on which pageout daemon sleeps */
  144 int vm_pageout_deficit;         /* Estimated number of pages deficit */
  145 int vm_pageout_pages_needed;    /* flag saying that the pageout daemon needs pages */
  146 
  147 #if !defined(NO_SWAPPING)
  148 static int vm_pageout_req_swapout;      /* XXX */
  149 static int vm_daemon_needed;
  150 static struct mtx vm_daemon_mtx;
  151 /* Allow for use by vm_pageout before vm_daemon is initialized. */
  152 MTX_SYSINIT(vm_daemon, &vm_daemon_mtx, "vm daemon", MTX_DEF);
  153 #endif
  154 static int vm_max_launder = 32;
  155 static int vm_pageout_stats_max=0, vm_pageout_stats_interval = 0;
  156 static int vm_pageout_full_stats_interval = 0;
  157 static int vm_pageout_algorithm=0;
  158 static int defer_swap_pageouts=0;
  159 static int disable_swap_pageouts=0;
  160 
  161 #if defined(NO_SWAPPING)
  162 static int vm_swap_enabled=0;
  163 static int vm_swap_idle_enabled=0;
  164 #else
  165 static int vm_swap_enabled=1;
  166 static int vm_swap_idle_enabled=0;
  167 #endif
  168 
  169 SYSCTL_INT(_vm, VM_PAGEOUT_ALGORITHM, pageout_algorithm,
  170         CTLFLAG_RW, &vm_pageout_algorithm, 0, "LRU page mgmt");
  171 
  172 SYSCTL_INT(_vm, OID_AUTO, max_launder,
  173         CTLFLAG_RW, &vm_max_launder, 0, "Limit dirty flushes in pageout");
  174 
  175 SYSCTL_INT(_vm, OID_AUTO, pageout_stats_max,
  176         CTLFLAG_RW, &vm_pageout_stats_max, 0, "Max pageout stats scan length");
  177 
  178 SYSCTL_INT(_vm, OID_AUTO, pageout_full_stats_interval,
  179         CTLFLAG_RW, &vm_pageout_full_stats_interval, 0, "Interval for full stats scan");
  180 
  181 SYSCTL_INT(_vm, OID_AUTO, pageout_stats_interval,
  182         CTLFLAG_RW, &vm_pageout_stats_interval, 0, "Interval for partial stats scan");
  183 
  184 #if defined(NO_SWAPPING)
  185 SYSCTL_INT(_vm, VM_SWAPPING_ENABLED, swap_enabled,
  186         CTLFLAG_RD, &vm_swap_enabled, 0, "");
  187 SYSCTL_INT(_vm, OID_AUTO, swap_idle_enabled,
  188         CTLFLAG_RD, &vm_swap_idle_enabled, 0, "");
  189 #else
  190 SYSCTL_INT(_vm, VM_SWAPPING_ENABLED, swap_enabled,
  191         CTLFLAG_RW, &vm_swap_enabled, 0, "Enable entire process swapout");
  192 SYSCTL_INT(_vm, OID_AUTO, swap_idle_enabled,
  193         CTLFLAG_RW, &vm_swap_idle_enabled, 0, "Allow swapout on idle criteria");
  194 #endif
  195 
  196 SYSCTL_INT(_vm, OID_AUTO, defer_swapspace_pageouts,
  197         CTLFLAG_RW, &defer_swap_pageouts, 0, "Give preference to dirty pages in mem");
  198 
  199 SYSCTL_INT(_vm, OID_AUTO, disable_swapspace_pageouts,
  200         CTLFLAG_RW, &disable_swap_pageouts, 0, "Disallow swapout of dirty pages");
  201 
  202 static int pageout_lock_miss;
  203 SYSCTL_INT(_vm, OID_AUTO, pageout_lock_miss,
  204         CTLFLAG_RD, &pageout_lock_miss, 0, "vget() lock misses during pageout");
  205 
  206 #define VM_PAGEOUT_PAGE_COUNT 16
  207 int vm_pageout_page_count = VM_PAGEOUT_PAGE_COUNT;
  208 
  209 int vm_page_max_wired;          /* XXX max # of wired pages system-wide */
  210 SYSCTL_INT(_vm, OID_AUTO, max_wired,
  211         CTLFLAG_RW, &vm_page_max_wired, 0, "System-wide limit to wired page count");
  212 
  213 #if !defined(NO_SWAPPING)
  214 static void vm_pageout_map_deactivate_pages(vm_map_t, long);
  215 static void vm_pageout_object_deactivate_pages(pmap_t, vm_object_t, long);
  216 static void vm_req_vmdaemon(int req);
  217 #endif
  218 static void vm_pageout_page_stats(void);
  219 
  220 /*
  221  * vm_pageout_fallback_object_lock:
  222  * 
  223  * Lock vm object currently associated with `m'. VM_OBJECT_TRYLOCK is
  224  * known to have failed and page queue must be either PQ_ACTIVE or
  225  * PQ_INACTIVE.  To avoid lock order violation, unlock the page queues
  226  * while locking the vm object.  Use marker page to detect page queue
  227  * changes and maintain notion of next page on page queue.  Return
  228  * TRUE if no changes were detected, FALSE otherwise.  vm object is
  229  * locked on return.
  230  * 
  231  * This function depends on both the lock portion of struct vm_object
  232  * and normal struct vm_page being type stable.
  233  */
  234 boolean_t
  235 vm_pageout_fallback_object_lock(vm_page_t m, vm_page_t *next)
  236 {
  237         struct vm_page marker;
  238         boolean_t unchanged;
  239         u_short queue;
  240         vm_object_t object;
  241 
  242         /*
  243          * Initialize our marker
  244          */
  245         bzero(&marker, sizeof(marker));
  246         marker.flags = PG_FICTITIOUS | PG_MARKER;
  247         marker.oflags = VPO_BUSY;
  248         marker.queue = m->queue;
  249         marker.wire_count = 1;
  250 
  251         queue = m->queue;
  252         object = m->object;
  253         
  254         TAILQ_INSERT_AFTER(&vm_page_queues[queue].pl,
  255                            m, &marker, pageq);
  256         vm_page_unlock_queues();
  257         VM_OBJECT_LOCK(object);
  258         vm_page_lock_queues();
  259 
  260         /* Page queue might have changed. */
  261         *next = TAILQ_NEXT(&marker, pageq);
  262         unchanged = (m->queue == queue &&
  263                      m->object == object &&
  264                      &marker == TAILQ_NEXT(m, pageq));
  265         TAILQ_REMOVE(&vm_page_queues[queue].pl,
  266                      &marker, pageq);
  267         return (unchanged);
  268 }
  269 
  270 /*
  271  * vm_pageout_clean:
  272  *
  273  * Clean the page and remove it from the laundry.
  274  * 
  275  * We set the busy bit to cause potential page faults on this page to
  276  * block.  Note the careful timing, however, the busy bit isn't set till
  277  * late and we cannot do anything that will mess with the page.
  278  */
  279 static int
  280 vm_pageout_clean(m)
  281         vm_page_t m;
  282 {
  283         vm_object_t object;
  284         vm_page_t mc[2*vm_pageout_page_count];
  285         int pageout_count;
  286         int ib, is, page_base;
  287         vm_pindex_t pindex = m->pindex;
  288 
  289         mtx_assert(&vm_page_queue_mtx, MA_OWNED);
  290         VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
  291 
  292         /*
  293          * It doesn't cost us anything to pageout OBJT_DEFAULT or OBJT_SWAP
  294          * with the new swapper, but we could have serious problems paging
  295          * out other object types if there is insufficient memory.  
  296          *
  297          * Unfortunately, checking free memory here is far too late, so the
  298          * check has been moved up a procedural level.
  299          */
  300 
  301         /*
  302          * Can't clean the page if it's busy or held.
  303          */
  304         if ((m->hold_count != 0) ||
  305             ((m->busy != 0) || (m->oflags & VPO_BUSY))) {
  306                 return 0;
  307         }
  308 
  309         mc[vm_pageout_page_count] = m;
  310         pageout_count = 1;
  311         page_base = vm_pageout_page_count;
  312         ib = 1;
  313         is = 1;
  314 
  315         /*
  316          * Scan object for clusterable pages.
  317          *
  318          * We can cluster ONLY if: ->> the page is NOT
  319          * clean, wired, busy, held, or mapped into a
  320          * buffer, and one of the following:
  321          * 1) The page is inactive, or a seldom used
  322          *    active page.
  323          * -or-
  324          * 2) we force the issue.
  325          *
  326          * During heavy mmap/modification loads the pageout
  327          * daemon can really fragment the underlying file
  328          * due to flushing pages out of order and not trying
  329          * align the clusters (which leave sporatic out-of-order
  330          * holes).  To solve this problem we do the reverse scan
  331          * first and attempt to align our cluster, then do a 
  332          * forward scan if room remains.
  333          */
  334         object = m->object;
  335 more:
  336         while (ib && pageout_count < vm_pageout_page_count) {
  337                 vm_page_t p;
  338 
  339                 if (ib > pindex) {
  340                         ib = 0;
  341                         break;
  342                 }
  343 
  344                 if ((p = vm_page_lookup(object, pindex - ib)) == NULL) {
  345                         ib = 0;
  346                         break;
  347                 }
  348                 if ((p->oflags & VPO_BUSY) || p->busy) {
  349                         ib = 0;
  350                         break;
  351                 }
  352                 vm_page_test_dirty(p);
  353                 if ((p->dirty & p->valid) == 0 ||
  354                     p->queue != PQ_INACTIVE ||
  355                     p->wire_count != 0 ||       /* may be held by buf cache */
  356                     p->hold_count != 0) {       /* may be undergoing I/O */
  357                         ib = 0;
  358                         break;
  359                 }
  360                 mc[--page_base] = p;
  361                 ++pageout_count;
  362                 ++ib;
  363                 /*
  364                  * alignment boundry, stop here and switch directions.  Do
  365                  * not clear ib.
  366                  */
  367                 if ((pindex - (ib - 1)) % vm_pageout_page_count == 0)
  368                         break;
  369         }
  370 
  371         while (pageout_count < vm_pageout_page_count && 
  372             pindex + is < object->size) {
  373                 vm_page_t p;
  374 
  375                 if ((p = vm_page_lookup(object, pindex + is)) == NULL)
  376                         break;
  377                 if ((p->oflags & VPO_BUSY) || p->busy) {
  378                         break;
  379                 }
  380                 vm_page_test_dirty(p);
  381                 if ((p->dirty & p->valid) == 0 ||
  382                     p->queue != PQ_INACTIVE ||
  383                     p->wire_count != 0 ||       /* may be held by buf cache */
  384                     p->hold_count != 0) {       /* may be undergoing I/O */
  385                         break;
  386                 }
  387                 mc[page_base + pageout_count] = p;
  388                 ++pageout_count;
  389                 ++is;
  390         }
  391 
  392         /*
  393          * If we exhausted our forward scan, continue with the reverse scan
  394          * when possible, even past a page boundry.  This catches boundry
  395          * conditions.
  396          */
  397         if (ib && pageout_count < vm_pageout_page_count)
  398                 goto more;
  399 
  400         /*
  401          * we allow reads during pageouts...
  402          */
  403         return (vm_pageout_flush(&mc[page_base], pageout_count, 0));
  404 }
  405 
  406 /*
  407  * vm_pageout_flush() - launder the given pages
  408  *
  409  *      The given pages are laundered.  Note that we setup for the start of
  410  *      I/O ( i.e. busy the page ), mark it read-only, and bump the object
  411  *      reference count all in here rather then in the parent.  If we want
  412  *      the parent to do more sophisticated things we may have to change
  413  *      the ordering.
  414  */
  415 int
  416 vm_pageout_flush(vm_page_t *mc, int count, int flags)
  417 {
  418         vm_object_t object = mc[0]->object;
  419         int pageout_status[count];
  420         int numpagedout = 0;
  421         int i;
  422 
  423         mtx_assert(&vm_page_queue_mtx, MA_OWNED);
  424         VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
  425         /*
  426          * Initiate I/O.  Bump the vm_page_t->busy counter and
  427          * mark the pages read-only.
  428          *
  429          * We do not have to fixup the clean/dirty bits here... we can
  430          * allow the pager to do it after the I/O completes.
  431          *
  432          * NOTE! mc[i]->dirty may be partial or fragmented due to an
  433          * edge case with file fragments.
  434          */
  435         for (i = 0; i < count; i++) {
  436                 KASSERT(mc[i]->valid == VM_PAGE_BITS_ALL,
  437                     ("vm_pageout_flush: partially invalid page %p index %d/%d",
  438                         mc[i], i, count));
  439                 vm_page_io_start(mc[i]);
  440                 pmap_remove_write(mc[i]);
  441         }
  442         vm_page_unlock_queues();
  443         vm_object_pip_add(object, count);
  444 
  445         vm_pager_put_pages(object, mc, count, flags, pageout_status);
  446 
  447         vm_page_lock_queues();
  448         for (i = 0; i < count; i++) {
  449                 vm_page_t mt = mc[i];
  450 
  451                 KASSERT(pageout_status[i] == VM_PAGER_PEND ||
  452                     (mt->flags & PG_WRITEABLE) == 0,
  453                     ("vm_pageout_flush: page %p is not write protected", mt));
  454                 switch (pageout_status[i]) {
  455                 case VM_PAGER_OK:
  456                 case VM_PAGER_PEND:
  457                         numpagedout++;
  458                         break;
  459                 case VM_PAGER_BAD:
  460                         /*
  461                          * Page outside of range of object. Right now we
  462                          * essentially lose the changes by pretending it
  463                          * worked.
  464                          */
  465                         pmap_clear_modify(mt);
  466                         vm_page_undirty(mt);
  467                         break;
  468                 case VM_PAGER_ERROR:
  469                 case VM_PAGER_FAIL:
  470                         /*
  471                          * If page couldn't be paged out, then reactivate the
  472                          * page so it doesn't clog the inactive list.  (We
  473                          * will try paging out it again later).
  474                          */
  475                         vm_page_activate(mt);
  476                         break;
  477                 case VM_PAGER_AGAIN:
  478                         break;
  479                 }
  480 
  481                 /*
  482                  * If the operation is still going, leave the page busy to
  483                  * block all other accesses. Also, leave the paging in
  484                  * progress indicator set so that we don't attempt an object
  485                  * collapse.
  486                  */
  487                 if (pageout_status[i] != VM_PAGER_PEND) {
  488                         vm_object_pip_wakeup(object);
  489                         vm_page_io_finish(mt);
  490                         if (vm_page_count_severe())
  491                                 vm_page_try_to_cache(mt);
  492                 }
  493         }
  494         return numpagedout;
  495 }
  496 
  497 #if !defined(NO_SWAPPING)
  498 /*
  499  *      vm_pageout_object_deactivate_pages
  500  *
  501  *      deactivate enough pages to satisfy the inactive target
  502  *      requirements or if vm_page_proc_limit is set, then
  503  *      deactivate all of the pages in the object and its
  504  *      backing_objects.
  505  *
  506  *      The object and map must be locked.
  507  */
  508 static void
  509 vm_pageout_object_deactivate_pages(pmap, first_object, desired)
  510         pmap_t pmap;
  511         vm_object_t first_object;
  512         long desired;
  513 {
  514         vm_object_t backing_object, object;
  515         vm_page_t p, next;
  516         int actcount, rcount, remove_mode;
  517 
  518         VM_OBJECT_LOCK_ASSERT(first_object, MA_OWNED);
  519         if (first_object->type == OBJT_DEVICE || first_object->type == OBJT_PHYS)
  520                 return;
  521         for (object = first_object;; object = backing_object) {
  522                 if (pmap_resident_count(pmap) <= desired)
  523                         goto unlock_return;
  524                 if (object->paging_in_progress)
  525                         goto unlock_return;
  526 
  527                 remove_mode = 0;
  528                 if (object->shadow_count > 1)
  529                         remove_mode = 1;
  530                 /*
  531                  * scan the objects entire memory queue
  532                  */
  533                 rcount = object->resident_page_count;
  534                 p = TAILQ_FIRST(&object->memq);
  535                 vm_page_lock_queues();
  536                 while (p && (rcount-- > 0)) {
  537                         if (pmap_resident_count(pmap) <= desired) {
  538                                 vm_page_unlock_queues();
  539                                 goto unlock_return;
  540                         }
  541                         next = TAILQ_NEXT(p, listq);
  542                         cnt.v_pdpages++;
  543                         if (p->wire_count != 0 ||
  544                             p->hold_count != 0 ||
  545                             p->busy != 0 ||
  546                             (p->oflags & VPO_BUSY) ||
  547                             (p->flags & PG_UNMANAGED) ||
  548                             !pmap_page_exists_quick(pmap, p)) {
  549                                 p = next;
  550                                 continue;
  551                         }
  552                         actcount = pmap_ts_referenced(p);
  553                         if (actcount) {
  554                                 vm_page_flag_set(p, PG_REFERENCED);
  555                         } else if (p->flags & PG_REFERENCED) {
  556                                 actcount = 1;
  557                         }
  558                         if ((p->queue != PQ_ACTIVE) &&
  559                                 (p->flags & PG_REFERENCED)) {
  560                                 vm_page_activate(p);
  561                                 p->act_count += actcount;
  562                                 vm_page_flag_clear(p, PG_REFERENCED);
  563                         } else if (p->queue == PQ_ACTIVE) {
  564                                 if ((p->flags & PG_REFERENCED) == 0) {
  565                                         p->act_count -= min(p->act_count, ACT_DECLINE);
  566                                         if (!remove_mode && (vm_pageout_algorithm || (p->act_count == 0))) {
  567                                                 pmap_remove_all(p);
  568                                                 vm_page_deactivate(p);
  569                                         } else {
  570                                                 vm_pageq_requeue(p);
  571                                         }
  572                                 } else {
  573                                         vm_page_activate(p);
  574                                         vm_page_flag_clear(p, PG_REFERENCED);
  575                                         if (p->act_count < (ACT_MAX - ACT_ADVANCE))
  576                                                 p->act_count += ACT_ADVANCE;
  577                                         vm_pageq_requeue(p);
  578                                 }
  579                         } else if (p->queue == PQ_INACTIVE) {
  580                                 pmap_remove_all(p);
  581                         }
  582                         p = next;
  583                 }
  584                 vm_page_unlock_queues();
  585                 if ((backing_object = object->backing_object) == NULL)
  586                         goto unlock_return;
  587                 VM_OBJECT_LOCK(backing_object);
  588                 if (object != first_object)
  589                         VM_OBJECT_UNLOCK(object);
  590         }
  591 unlock_return:
  592         if (object != first_object)
  593                 VM_OBJECT_UNLOCK(object);
  594 }
  595 
  596 /*
  597  * deactivate some number of pages in a map, try to do it fairly, but
  598  * that is really hard to do.
  599  */
  600 static void
  601 vm_pageout_map_deactivate_pages(map, desired)
  602         vm_map_t map;
  603         long desired;
  604 {
  605         vm_map_entry_t tmpe;
  606         vm_object_t obj, bigobj;
  607         int nothingwired;
  608 
  609         if (!vm_map_trylock(map))
  610                 return;
  611 
  612         bigobj = NULL;
  613         nothingwired = TRUE;
  614 
  615         /*
  616          * first, search out the biggest object, and try to free pages from
  617          * that.
  618          */
  619         tmpe = map->header.next;
  620         while (tmpe != &map->header) {
  621                 if ((tmpe->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
  622                         obj = tmpe->object.vm_object;
  623                         if (obj != NULL && VM_OBJECT_TRYLOCK(obj)) {
  624                                 if (obj->shadow_count <= 1 &&
  625                                     (bigobj == NULL ||
  626                                      bigobj->resident_page_count < obj->resident_page_count)) {
  627                                         if (bigobj != NULL)
  628                                                 VM_OBJECT_UNLOCK(bigobj);
  629                                         bigobj = obj;
  630                                 } else
  631                                         VM_OBJECT_UNLOCK(obj);
  632                         }
  633                 }
  634                 if (tmpe->wired_count > 0)
  635                         nothingwired = FALSE;
  636                 tmpe = tmpe->next;
  637         }
  638 
  639         if (bigobj != NULL) {
  640                 vm_pageout_object_deactivate_pages(map->pmap, bigobj, desired);
  641                 VM_OBJECT_UNLOCK(bigobj);
  642         }
  643         /*
  644          * Next, hunt around for other pages to deactivate.  We actually
  645          * do this search sort of wrong -- .text first is not the best idea.
  646          */
  647         tmpe = map->header.next;
  648         while (tmpe != &map->header) {
  649                 if (pmap_resident_count(vm_map_pmap(map)) <= desired)
  650                         break;
  651                 if ((tmpe->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
  652                         obj = tmpe->object.vm_object;
  653                         if (obj != NULL) {
  654                                 VM_OBJECT_LOCK(obj);
  655                                 vm_pageout_object_deactivate_pages(map->pmap, obj, desired);
  656                                 VM_OBJECT_UNLOCK(obj);
  657                         }
  658                 }
  659                 tmpe = tmpe->next;
  660         }
  661 
  662         /*
  663          * Remove all mappings if a process is swapped out, this will free page
  664          * table pages.
  665          */
  666         if (desired == 0 && nothingwired) {
  667                 pmap_remove(vm_map_pmap(map), vm_map_min(map),
  668                     vm_map_max(map));
  669         }
  670         vm_map_unlock(map);
  671 }
  672 #endif          /* !defined(NO_SWAPPING) */
  673 
  674 /*
  675  *      vm_pageout_scan does the dirty work for the pageout daemon.
  676  */
  677 static void
  678 vm_pageout_scan(int pass)
  679 {
  680         vm_page_t m, next;
  681         struct vm_page marker;
  682         int page_shortage, maxscan, pcount;
  683         int addl_page_shortage, addl_page_shortage_init;
  684         struct proc *p, *bigproc;
  685         struct thread *td;
  686         vm_offset_t size, bigsize;
  687         vm_object_t object;
  688         int actcount;
  689         int vnodes_skipped = 0;
  690         int maxlaunder;
  691 
  692         /*
  693          * Decrease registered cache sizes.
  694          */
  695         EVENTHANDLER_INVOKE(vm_lowmem, 0);
  696         /*
  697          * We do this explicitly after the caches have been drained above.
  698          */
  699         uma_reclaim();
  700 
  701         addl_page_shortage_init = atomic_readandclear_int(&vm_pageout_deficit);
  702 
  703         /*
  704          * Calculate the number of pages we want to either free or move
  705          * to the cache.
  706          */
  707         page_shortage = vm_paging_target() + addl_page_shortage_init;
  708 
  709         /*
  710          * Initialize our marker
  711          */
  712         bzero(&marker, sizeof(marker));
  713         marker.flags = PG_FICTITIOUS | PG_MARKER;
  714         marker.oflags = VPO_BUSY;
  715         marker.queue = PQ_INACTIVE;
  716         marker.wire_count = 1;
  717 
  718         /*
  719          * Start scanning the inactive queue for pages we can move to the
  720          * cache or free.  The scan will stop when the target is reached or
  721          * we have scanned the entire inactive queue.  Note that m->act_count
  722          * is not used to form decisions for the inactive queue, only for the
  723          * active queue.
  724          *
  725          * maxlaunder limits the number of dirty pages we flush per scan.
  726          * For most systems a smaller value (16 or 32) is more robust under
  727          * extreme memory and disk pressure because any unnecessary writes
  728          * to disk can result in extreme performance degredation.  However,
  729          * systems with excessive dirty pages (especially when MAP_NOSYNC is
  730          * used) will die horribly with limited laundering.  If the pageout
  731          * daemon cannot clean enough pages in the first pass, we let it go
  732          * all out in succeeding passes.
  733          */
  734         if ((maxlaunder = vm_max_launder) <= 1)
  735                 maxlaunder = 1;
  736         if (pass)
  737                 maxlaunder = 10000;
  738         vm_page_lock_queues();
  739 rescan0:
  740         addl_page_shortage = addl_page_shortage_init;
  741         maxscan = cnt.v_inactive_count;
  742 
  743         for (m = TAILQ_FIRST(&vm_page_queues[PQ_INACTIVE].pl);
  744              m != NULL && maxscan-- > 0 && page_shortage > 0;
  745              m = next) {
  746 
  747                 cnt.v_pdpages++;
  748 
  749                 if (VM_PAGE_GETQUEUE(m) != PQ_INACTIVE) {
  750                         goto rescan0;
  751                 }
  752 
  753                 next = TAILQ_NEXT(m, pageq);
  754                 object = m->object;
  755 
  756                 /*
  757                  * skip marker pages
  758                  */
  759                 if (m->flags & PG_MARKER)
  760                         continue;
  761 
  762                 /*
  763                  * A held page may be undergoing I/O, so skip it.
  764                  */
  765                 if (m->hold_count) {
  766                         vm_pageq_requeue(m);
  767                         addl_page_shortage++;
  768                         continue;
  769                 }
  770                 /*
  771                  * Don't mess with busy pages, keep in the front of the
  772                  * queue, most likely are being paged out.
  773                  */
  774                 if (!VM_OBJECT_TRYLOCK(object) &&
  775                     (!vm_pageout_fallback_object_lock(m, &next) ||
  776                      m->hold_count != 0)) {
  777                         VM_OBJECT_UNLOCK(object);
  778                         addl_page_shortage++;
  779                         continue;
  780                 }
  781                 if (m->busy || (m->oflags & VPO_BUSY)) {
  782                         VM_OBJECT_UNLOCK(object);
  783                         addl_page_shortage++;
  784                         continue;
  785                 }
  786 
  787                 /*
  788                  * If the object is not being used, we ignore previous 
  789                  * references.
  790                  */
  791                 if (object->ref_count == 0) {
  792                         vm_page_flag_clear(m, PG_REFERENCED);
  793                         pmap_clear_reference(m);
  794 
  795                 /*
  796                  * Otherwise, if the page has been referenced while in the 
  797                  * inactive queue, we bump the "activation count" upwards, 
  798                  * making it less likely that the page will be added back to 
  799                  * the inactive queue prematurely again.  Here we check the 
  800                  * page tables (or emulated bits, if any), given the upper 
  801                  * level VM system not knowing anything about existing 
  802                  * references.
  803                  */
  804                 } else if (((m->flags & PG_REFERENCED) == 0) &&
  805                         (actcount = pmap_ts_referenced(m))) {
  806                         vm_page_activate(m);
  807                         VM_OBJECT_UNLOCK(object);
  808                         m->act_count += (actcount + ACT_ADVANCE);
  809                         continue;
  810                 }
  811 
  812                 /*
  813                  * If the upper level VM system knows about any page 
  814                  * references, we activate the page.  We also set the 
  815                  * "activation count" higher than normal so that we will less 
  816                  * likely place pages back onto the inactive queue again.
  817                  */
  818                 if ((m->flags & PG_REFERENCED) != 0) {
  819                         vm_page_flag_clear(m, PG_REFERENCED);
  820                         actcount = pmap_ts_referenced(m);
  821                         vm_page_activate(m);
  822                         VM_OBJECT_UNLOCK(object);
  823                         m->act_count += (actcount + ACT_ADVANCE + 1);
  824                         continue;
  825                 }
  826 
  827                 /*
  828                  * If the upper level VM system doesn't know anything about 
  829                  * the page being dirty, we have to check for it again.  As 
  830                  * far as the VM code knows, any partially dirty pages are 
  831                  * fully dirty.
  832                  */
  833                 if (m->dirty == 0 && !pmap_is_modified(m)) {
  834                         /*
  835                          * Avoid a race condition: Unless write access is
  836                          * removed from the page, another processor could
  837                          * modify it before all access is removed by the call
  838                          * to vm_page_cache() below.  If vm_page_cache() finds
  839                          * that the page has been modified when it removes all
  840                          * access, it panics because it cannot cache dirty
  841                          * pages.  In principle, we could eliminate just write
  842                          * access here rather than all access.  In the expected
  843                          * case, when there are no last instant modifications
  844                          * to the page, removing all access will be cheaper
  845                          * overall.
  846                          */
  847                         if ((m->flags & PG_WRITEABLE) != 0)
  848                                 pmap_remove_all(m);
  849                 } else {
  850                         vm_page_dirty(m);
  851                 }
  852 
  853                 if (m->valid == 0) {
  854                         /*
  855                          * Invalid pages can be easily freed
  856                          */
  857                         vm_page_free(m);
  858                         cnt.v_dfree++;
  859                         --page_shortage;
  860                 } else if (m->dirty == 0) {
  861                         /*
  862                          * Clean pages can be placed onto the cache queue.
  863                          * This effectively frees them.
  864                          */
  865                         vm_page_cache(m);
  866                         --page_shortage;
  867                 } else if ((m->flags & PG_WINATCFLS) == 0 && pass == 0) {
  868                         /*
  869                          * Dirty pages need to be paged out, but flushing
  870                          * a page is extremely expensive verses freeing
  871                          * a clean page.  Rather then artificially limiting
  872                          * the number of pages we can flush, we instead give
  873                          * dirty pages extra priority on the inactive queue
  874                          * by forcing them to be cycled through the queue
  875                          * twice before being flushed, after which the
  876                          * (now clean) page will cycle through once more
  877                          * before being freed.  This significantly extends
  878                          * the thrash point for a heavily loaded machine.
  879                          */
  880                         vm_page_flag_set(m, PG_WINATCFLS);
  881                         vm_pageq_requeue(m);
  882                 } else if (maxlaunder > 0) {
  883                         /*
  884                          * We always want to try to flush some dirty pages if
  885                          * we encounter them, to keep the system stable.
  886                          * Normally this number is small, but under extreme
  887                          * pressure where there are insufficient clean pages
  888                          * on the inactive queue, we may have to go all out.
  889                          */
  890                         int swap_pageouts_ok, vfslocked = 0;
  891                         struct vnode *vp = NULL;
  892                         struct mount *mp = NULL;
  893 
  894                         if ((object->type != OBJT_SWAP) && (object->type != OBJT_DEFAULT)) {
  895                                 swap_pageouts_ok = 1;
  896                         } else {
  897                                 swap_pageouts_ok = !(defer_swap_pageouts || disable_swap_pageouts);
  898                                 swap_pageouts_ok |= (!disable_swap_pageouts && defer_swap_pageouts &&
  899                                 vm_page_count_min());
  900                                                                                 
  901                         }
  902 
  903                         /*
  904                          * We don't bother paging objects that are "dead".  
  905                          * Those objects are in a "rundown" state.
  906                          */
  907                         if (!swap_pageouts_ok || (object->flags & OBJ_DEAD)) {
  908                                 VM_OBJECT_UNLOCK(object);
  909                                 vm_pageq_requeue(m);
  910                                 continue;
  911                         }
  912 
  913                         /*
  914                          * Following operations may unlock
  915                          * vm_page_queue_mtx, invalidating the 'next'
  916                          * pointer.  To prevent an inordinate number
  917                          * of restarts we use our marker to remember
  918                          * our place.
  919                          *
  920                          */
  921                         TAILQ_INSERT_AFTER(&vm_page_queues[PQ_INACTIVE].pl,
  922                                            m, &marker, pageq);
  923                         /*
  924                          * The object is already known NOT to be dead.   It
  925                          * is possible for the vget() to block the whole
  926                          * pageout daemon, but the new low-memory handling
  927                          * code should prevent it.
  928                          *
  929                          * The previous code skipped locked vnodes and, worse,
  930                          * reordered pages in the queue.  This results in
  931                          * completely non-deterministic operation and, on a
  932                          * busy system, can lead to extremely non-optimal
  933                          * pageouts.  For example, it can cause clean pages
  934                          * to be freed and dirty pages to be moved to the end
  935                          * of the queue.  Since dirty pages are also moved to
  936                          * the end of the queue once-cleaned, this gives
  937                          * way too large a weighting to defering the freeing
  938                          * of dirty pages.
  939                          *
  940                          * We can't wait forever for the vnode lock, we might
  941                          * deadlock due to a vn_read() getting stuck in
  942                          * vm_wait while holding this vnode.  We skip the 
  943                          * vnode if we can't get it in a reasonable amount
  944                          * of time.
  945                          */
  946                         if (object->type == OBJT_VNODE) {
  947                                 vp = object->handle;
  948                                 if (vp->v_type == VREG &&
  949                                     vn_start_write(vp, &mp, V_NOWAIT) != 0) {
  950                                         mp = NULL;
  951                                         ++pageout_lock_miss;
  952                                         if (object->flags & OBJ_MIGHTBEDIRTY)
  953                                                 vnodes_skipped++;
  954                                         goto unlock_and_continue;
  955                                 }
  956                                 vm_page_unlock_queues();
  957                                 vm_object_reference_locked(object);
  958                                 VM_OBJECT_UNLOCK(object);
  959                                 vfslocked = VFS_LOCK_GIANT(vp->v_mount);
  960                                 if (vget(vp, LK_EXCLUSIVE | LK_TIMELOCK,
  961                                     curthread)) {
  962                                         VM_OBJECT_LOCK(object);
  963                                         vm_page_lock_queues();
  964                                         ++pageout_lock_miss;
  965                                         if (object->flags & OBJ_MIGHTBEDIRTY)
  966                                                 vnodes_skipped++;
  967                                         vp = NULL;
  968                                         goto unlock_and_continue;
  969                                 }
  970                                 VM_OBJECT_LOCK(object);
  971                                 vm_page_lock_queues();
  972                                 /*
  973                                  * The page might have been moved to another
  974                                  * queue during potential blocking in vget()
  975                                  * above.  The page might have been freed and
  976                                  * reused for another vnode.
  977                                  */
  978                                 if (VM_PAGE_GETQUEUE(m) != PQ_INACTIVE ||
  979                                     m->object != object ||
  980                                     TAILQ_NEXT(m, pageq) != &marker) {
  981                                         if (object->flags & OBJ_MIGHTBEDIRTY)
  982                                                 vnodes_skipped++;
  983                                         goto unlock_and_continue;
  984                                 }
  985         
  986                                 /*
  987                                  * The page may have been busied during the
  988                                  * blocking in vget().  We don't move the
  989                                  * page back onto the end of the queue so that
  990                                  * statistics are more correct if we don't.
  991                                  */
  992                                 if (m->busy || (m->oflags & VPO_BUSY)) {
  993                                         goto unlock_and_continue;
  994                                 }
  995 
  996                                 /*
  997                                  * If the page has become held it might
  998                                  * be undergoing I/O, so skip it
  999                                  */
 1000                                 if (m->hold_count) {
 1001                                         vm_pageq_requeue(m);
 1002                                         if (object->flags & OBJ_MIGHTBEDIRTY)
 1003                                                 vnodes_skipped++;
 1004                                         goto unlock_and_continue;
 1005                                 }
 1006                         }
 1007 
 1008                         /*
 1009                          * If a page is dirty, then it is either being washed
 1010                          * (but not yet cleaned) or it is still in the
 1011                          * laundry.  If it is still in the laundry, then we
 1012                          * start the cleaning operation. 
 1013                          *
 1014                          * decrement page_shortage on success to account for
 1015                          * the (future) cleaned page.  Otherwise we could wind
 1016                          * up laundering or cleaning too many pages.
 1017                          */
 1018                         if (vm_pageout_clean(m) != 0) {
 1019                                 --page_shortage;
 1020                                 --maxlaunder;
 1021                         }
 1022 unlock_and_continue:
 1023                         VM_OBJECT_UNLOCK(object);
 1024                         if (mp != NULL) {
 1025                                 vm_page_unlock_queues();
 1026                                 if (vp != NULL)
 1027                                         vput(vp);
 1028                                 VFS_UNLOCK_GIANT(vfslocked);
 1029                                 vm_object_deallocate(object);
 1030                                 vn_finished_write(mp);
 1031                                 vm_page_lock_queues();
 1032                         }
 1033                         next = TAILQ_NEXT(&marker, pageq);
 1034                         TAILQ_REMOVE(&vm_page_queues[PQ_INACTIVE].pl,
 1035                                      &marker, pageq);
 1036                         continue;
 1037                 }
 1038                 VM_OBJECT_UNLOCK(object);
 1039         }
 1040 
 1041         /*
 1042          * Compute the number of pages we want to try to move from the
 1043          * active queue to the inactive queue.
 1044          */
 1045         page_shortage = vm_paging_target() +
 1046                 cnt.v_inactive_target - cnt.v_inactive_count;
 1047         page_shortage += addl_page_shortage;
 1048 
 1049         /*
 1050          * Scan the active queue for things we can deactivate. We nominally
 1051          * track the per-page activity counter and use it to locate
 1052          * deactivation candidates.
 1053          */
 1054         pcount = cnt.v_active_count;
 1055         m = TAILQ_FIRST(&vm_page_queues[PQ_ACTIVE].pl);
 1056 
 1057         while ((m != NULL) && (pcount-- > 0) && (page_shortage > 0)) {
 1058 
 1059                 KASSERT(VM_PAGE_INQUEUE2(m, PQ_ACTIVE),
 1060                     ("vm_pageout_scan: page %p isn't active", m));
 1061 
 1062                 next = TAILQ_NEXT(m, pageq);
 1063                 object = m->object;
 1064                 if ((m->flags & PG_MARKER) != 0) {
 1065                         m = next;
 1066                         continue;
 1067                 }
 1068                 if (!VM_OBJECT_TRYLOCK(object) &&
 1069                     !vm_pageout_fallback_object_lock(m, &next)) {
 1070                         VM_OBJECT_UNLOCK(object);
 1071                         m = next;
 1072                         continue;
 1073                 }
 1074 
 1075                 /*
 1076                  * Don't deactivate pages that are busy.
 1077                  */
 1078                 if ((m->busy != 0) ||
 1079                     (m->oflags & VPO_BUSY) ||
 1080                     (m->hold_count != 0)) {
 1081                         VM_OBJECT_UNLOCK(object);
 1082                         vm_pageq_requeue(m);
 1083                         m = next;
 1084                         continue;
 1085                 }
 1086 
 1087                 /*
 1088                  * The count for pagedaemon pages is done after checking the
 1089                  * page for eligibility...
 1090                  */
 1091                 cnt.v_pdpages++;
 1092 
 1093                 /*
 1094                  * Check to see "how much" the page has been used.
 1095                  */
 1096                 actcount = 0;
 1097                 if (object->ref_count != 0) {
 1098                         if (m->flags & PG_REFERENCED) {
 1099                                 actcount += 1;
 1100                         }
 1101                         actcount += pmap_ts_referenced(m);
 1102                         if (actcount) {
 1103                                 m->act_count += ACT_ADVANCE + actcount;
 1104                                 if (m->act_count > ACT_MAX)
 1105                                         m->act_count = ACT_MAX;
 1106                         }
 1107                 }
 1108 
 1109                 /*
 1110                  * Since we have "tested" this bit, we need to clear it now.
 1111                  */
 1112                 vm_page_flag_clear(m, PG_REFERENCED);
 1113 
 1114                 /*
 1115                  * Only if an object is currently being used, do we use the
 1116                  * page activation count stats.
 1117                  */
 1118                 if (actcount && (object->ref_count != 0)) {
 1119                         vm_pageq_requeue(m);
 1120                 } else {
 1121                         m->act_count -= min(m->act_count, ACT_DECLINE);
 1122                         if (vm_pageout_algorithm ||
 1123                             object->ref_count == 0 ||
 1124                             m->act_count == 0) {
 1125                                 page_shortage--;
 1126                                 if (object->ref_count == 0) {
 1127                                         pmap_remove_all(m);
 1128                                         if (m->dirty == 0)
 1129                                                 vm_page_cache(m);
 1130                                         else
 1131                                                 vm_page_deactivate(m);
 1132                                 } else {
 1133                                         vm_page_deactivate(m);
 1134                                 }
 1135                         } else {
 1136                                 vm_pageq_requeue(m);
 1137                         }
 1138                 }
 1139                 VM_OBJECT_UNLOCK(object);
 1140                 m = next;
 1141         }
 1142         vm_page_unlock_queues();
 1143 #if !defined(NO_SWAPPING)
 1144         /*
 1145          * Idle process swapout -- run once per second.
 1146          */
 1147         if (vm_swap_idle_enabled) {
 1148                 static long lsec;
 1149                 if (time_second != lsec) {
 1150                         vm_req_vmdaemon(VM_SWAP_IDLE);
 1151                         lsec = time_second;
 1152                 }
 1153         }
 1154 #endif
 1155                 
 1156         /*
 1157          * If we didn't get enough free pages, and we have skipped a vnode
 1158          * in a writeable object, wakeup the sync daemon.  And kick swapout
 1159          * if we did not get enough free pages.
 1160          */
 1161         if (vm_paging_target() > 0) {
 1162                 if (vnodes_skipped && vm_page_count_min())
 1163                         (void) speedup_syncer();
 1164 #if !defined(NO_SWAPPING)
 1165                 if (vm_swap_enabled && vm_page_count_target())
 1166                         vm_req_vmdaemon(VM_SWAP_NORMAL);
 1167 #endif
 1168         }
 1169 
 1170         /*
 1171          * If we are critically low on one of RAM or swap and low on
 1172          * the other, kill the largest process.  However, we avoid
 1173          * doing this on the first pass in order to give ourselves a
 1174          * chance to flush out dirty vnode-backed pages and to allow
 1175          * active pages to be moved to the inactive queue and reclaimed.
 1176          *
 1177          * We keep the process bigproc locked once we find it to keep anyone
 1178          * from messing with it; however, there is a possibility of
 1179          * deadlock if process B is bigproc and one of it's child processes
 1180          * attempts to propagate a signal to B while we are waiting for A's
 1181          * lock while walking this list.  To avoid this, we don't block on
 1182          * the process lock but just skip a process if it is already locked.
 1183          */
 1184         if (pass != 0 &&
 1185             ((swap_pager_avail < 64 && vm_page_count_min()) ||
 1186              (swap_pager_full && vm_paging_target() > 0))) {
 1187                 bigproc = NULL;
 1188                 bigsize = 0;
 1189                 sx_slock(&allproc_lock);
 1190                 FOREACH_PROC_IN_SYSTEM(p) {
 1191                         int breakout;
 1192 
 1193                         if (PROC_TRYLOCK(p) == 0)
 1194                                 continue;
 1195                         /*
 1196                          * If this is a system or protected process, skip it.
 1197                          */
 1198                         if ((p->p_flag & P_SYSTEM) || (p->p_pid == 1) ||
 1199                             (p->p_flag & P_PROTECTED) ||
 1200                             ((p->p_pid < 48) && (swap_pager_avail != 0))) {
 1201                                 PROC_UNLOCK(p);
 1202                                 continue;
 1203                         }
 1204                         /*
 1205                          * If the process is in a non-running type state,
 1206                          * don't touch it.  Check all the threads individually.
 1207                          */
 1208                         PROC_SLOCK(p);
 1209                         breakout = 0;
 1210                         FOREACH_THREAD_IN_PROC(p, td) {
 1211                                 thread_lock(td);
 1212                                 if (!TD_ON_RUNQ(td) &&
 1213                                     !TD_IS_RUNNING(td) &&
 1214                                     !TD_IS_SLEEPING(td)) {
 1215                                         thread_unlock(td);
 1216                                         breakout = 1;
 1217                                         break;
 1218                                 }
 1219                                 thread_unlock(td);
 1220                         }
 1221                         PROC_SUNLOCK(p);
 1222                         if (breakout) {
 1223                                 PROC_UNLOCK(p);
 1224                                 continue;
 1225                         }
 1226                         /*
 1227                          * get the process size
 1228                          */
 1229                         if (!vm_map_trylock_read(&p->p_vmspace->vm_map)) {
 1230                                 PROC_UNLOCK(p);
 1231                                 continue;
 1232                         }
 1233                         size = vmspace_swap_count(p->p_vmspace);
 1234                         vm_map_unlock_read(&p->p_vmspace->vm_map);
 1235                         size += vmspace_resident_count(p->p_vmspace);
 1236                         /*
 1237                          * if the this process is bigger than the biggest one
 1238                          * remember it.
 1239                          */
 1240                         if (size > bigsize) {
 1241                                 if (bigproc != NULL)
 1242                                         PROC_UNLOCK(bigproc);
 1243                                 bigproc = p;
 1244                                 bigsize = size;
 1245                         } else
 1246                                 PROC_UNLOCK(p);
 1247                 }
 1248                 sx_sunlock(&allproc_lock);
 1249                 if (bigproc != NULL) {
 1250                         killproc(bigproc, "out of swap space");
 1251                         PROC_SLOCK(bigproc);
 1252                         sched_nice(bigproc, PRIO_MIN);
 1253                         PROC_SUNLOCK(bigproc);
 1254                         PROC_UNLOCK(bigproc);
 1255                         wakeup(&cnt.v_free_count);
 1256                 }
 1257         }
 1258 }
 1259 
 1260 /*
 1261  * This routine tries to maintain the pseudo LRU active queue,
 1262  * so that during long periods of time where there is no paging,
 1263  * that some statistic accumulation still occurs.  This code
 1264  * helps the situation where paging just starts to occur.
 1265  */
 1266 static void
 1267 vm_pageout_page_stats()
 1268 {
 1269         vm_object_t object;
 1270         vm_page_t m,next;
 1271         int pcount,tpcount;             /* Number of pages to check */
 1272         static int fullintervalcount = 0;
 1273         int page_shortage;
 1274 
 1275         mtx_assert(&vm_page_queue_mtx, MA_OWNED);
 1276         page_shortage = 
 1277             (cnt.v_inactive_target + cnt.v_cache_max + cnt.v_free_min) -
 1278             (cnt.v_free_count + cnt.v_inactive_count + cnt.v_cache_count);
 1279 
 1280         if (page_shortage <= 0)
 1281                 return;
 1282 
 1283         pcount = cnt.v_active_count;
 1284         fullintervalcount += vm_pageout_stats_interval;
 1285         if (fullintervalcount < vm_pageout_full_stats_interval) {
 1286                 tpcount = (int64_t)vm_pageout_stats_max * cnt.v_active_count /
 1287                     cnt.v_page_count;
 1288                 if (pcount > tpcount)
 1289                         pcount = tpcount;
 1290         } else {
 1291                 fullintervalcount = 0;
 1292         }
 1293 
 1294         m = TAILQ_FIRST(&vm_page_queues[PQ_ACTIVE].pl);
 1295         while ((m != NULL) && (pcount-- > 0)) {
 1296                 int actcount;
 1297 
 1298                 KASSERT(VM_PAGE_INQUEUE2(m, PQ_ACTIVE),
 1299                     ("vm_pageout_page_stats: page %p isn't active", m));
 1300 
 1301                 next = TAILQ_NEXT(m, pageq);
 1302                 object = m->object;
 1303 
 1304                 if ((m->flags & PG_MARKER) != 0) {
 1305                         m = next;
 1306                         continue;
 1307                 }
 1308                 if (!VM_OBJECT_TRYLOCK(object) &&
 1309                     !vm_pageout_fallback_object_lock(m, &next)) {
 1310                         VM_OBJECT_UNLOCK(object);
 1311                         m = next;
 1312                         continue;
 1313                 }
 1314 
 1315                 /*
 1316                  * Don't deactivate pages that are busy.
 1317                  */
 1318                 if ((m->busy != 0) ||
 1319                     (m->oflags & VPO_BUSY) ||
 1320                     (m->hold_count != 0)) {
 1321                         VM_OBJECT_UNLOCK(object);
 1322                         vm_pageq_requeue(m);
 1323                         m = next;
 1324                         continue;
 1325                 }
 1326 
 1327                 actcount = 0;
 1328                 if (m->flags & PG_REFERENCED) {
 1329                         vm_page_flag_clear(m, PG_REFERENCED);
 1330                         actcount += 1;
 1331                 }
 1332 
 1333                 actcount += pmap_ts_referenced(m);
 1334                 if (actcount) {
 1335                         m->act_count += ACT_ADVANCE + actcount;
 1336                         if (m->act_count > ACT_MAX)
 1337                                 m->act_count = ACT_MAX;
 1338                         vm_pageq_requeue(m);
 1339                 } else {
 1340                         if (m->act_count == 0) {
 1341                                 /*
 1342                                  * We turn off page access, so that we have
 1343                                  * more accurate RSS stats.  We don't do this
 1344                                  * in the normal page deactivation when the
 1345                                  * system is loaded VM wise, because the
 1346                                  * cost of the large number of page protect
 1347                                  * operations would be higher than the value
 1348                                  * of doing the operation.
 1349                                  */
 1350                                 pmap_remove_all(m);
 1351                                 vm_page_deactivate(m);
 1352                         } else {
 1353                                 m->act_count -= min(m->act_count, ACT_DECLINE);
 1354                                 vm_pageq_requeue(m);
 1355                         }
 1356                 }
 1357                 VM_OBJECT_UNLOCK(object);
 1358                 m = next;
 1359         }
 1360 }
 1361 
 1362 /*
 1363  *      vm_pageout is the high level pageout daemon.
 1364  */
 1365 static void
 1366 vm_pageout()
 1367 {
 1368         int error, pass;
 1369 
 1370         /*
 1371          * Initialize some paging parameters.
 1372          */
 1373         cnt.v_interrupt_free_min = 2;
 1374         if (cnt.v_page_count < 2000)
 1375                 vm_pageout_page_count = 8;
 1376 
 1377         /*
 1378          * v_free_reserved needs to include enough for the largest
 1379          * swap pager structures plus enough for any pv_entry structs
 1380          * when paging. 
 1381          */
 1382         if (cnt.v_page_count > 1024)
 1383                 cnt.v_free_min = 4 + (cnt.v_page_count - 1024) / 200;
 1384         else
 1385                 cnt.v_free_min = 4;
 1386         cnt.v_pageout_free_min = (2*MAXBSIZE)/PAGE_SIZE +
 1387             cnt.v_interrupt_free_min;
 1388         cnt.v_free_reserved = vm_pageout_page_count +
 1389             cnt.v_pageout_free_min + (cnt.v_page_count / 768);
 1390         cnt.v_free_severe = cnt.v_free_min / 2;
 1391         cnt.v_free_min += cnt.v_free_reserved;
 1392         cnt.v_free_severe += cnt.v_free_reserved;
 1393 
 1394         /*
 1395          * v_free_target and v_cache_min control pageout hysteresis.  Note
 1396          * that these are more a measure of the VM cache queue hysteresis
 1397          * then the VM free queue.  Specifically, v_free_target is the
 1398          * high water mark (free+cache pages).
 1399          *
 1400          * v_free_reserved + v_cache_min (mostly means v_cache_min) is the
 1401          * low water mark, while v_free_min is the stop.  v_cache_min must
 1402          * be big enough to handle memory needs while the pageout daemon
 1403          * is signalled and run to free more pages.
 1404          */
 1405         if (cnt.v_free_count > 6144)
 1406                 cnt.v_free_target = 4 * cnt.v_free_min + cnt.v_free_reserved;
 1407         else
 1408                 cnt.v_free_target = 2 * cnt.v_free_min + cnt.v_free_reserved;
 1409 
 1410         if (cnt.v_free_count > 2048) {
 1411                 cnt.v_cache_min = cnt.v_free_target;
 1412                 cnt.v_cache_max = 2 * cnt.v_cache_min;
 1413                 cnt.v_inactive_target = (3 * cnt.v_free_target) / 2;
 1414         } else {
 1415                 cnt.v_cache_min = 0;
 1416                 cnt.v_cache_max = 0;
 1417                 cnt.v_inactive_target = cnt.v_free_count / 4;
 1418         }
 1419         if (cnt.v_inactive_target > cnt.v_free_count / 3)
 1420                 cnt.v_inactive_target = cnt.v_free_count / 3;
 1421 
 1422         /* XXX does not really belong here */
 1423         if (vm_page_max_wired == 0)
 1424                 vm_page_max_wired = cnt.v_free_count / 3;
 1425 
 1426         if (vm_pageout_stats_max == 0)
 1427                 vm_pageout_stats_max = cnt.v_free_target;
 1428 
 1429         /*
 1430          * Set interval in seconds for stats scan.
 1431          */
 1432         if (vm_pageout_stats_interval == 0)
 1433                 vm_pageout_stats_interval = 5;
 1434         if (vm_pageout_full_stats_interval == 0)
 1435                 vm_pageout_full_stats_interval = vm_pageout_stats_interval * 4;
 1436 
 1437         swap_pager_swap_init();
 1438         pass = 0;
 1439         /*
 1440          * The pageout daemon is never done, so loop forever.
 1441          */
 1442         while (TRUE) {
 1443                 /*
 1444                  * If we have enough free memory, wakeup waiters.  Do
 1445                  * not clear vm_pages_needed until we reach our target,
 1446                  * otherwise we may be woken up over and over again and
 1447                  * waste a lot of cpu.
 1448                  */
 1449                 mtx_lock(&vm_page_queue_free_mtx);
 1450                 if (vm_pages_needed && !vm_page_count_min()) {
 1451                         if (!vm_paging_needed())
 1452                                 vm_pages_needed = 0;
 1453                         wakeup(&cnt.v_free_count);
 1454                 }
 1455                 if (vm_pages_needed) {
 1456                         /*
 1457                          * Still not done, take a second pass without waiting
 1458                          * (unlimited dirty cleaning), otherwise sleep a bit
 1459                          * and try again.
 1460                          */
 1461                         ++pass;
 1462                         if (pass > 1)
 1463                                 msleep(&vm_pages_needed,
 1464                                     &vm_page_queue_free_mtx, PVM, "psleep",
 1465                                     hz / 2);
 1466                 } else {
 1467                         /*
 1468                          * Good enough, sleep & handle stats.  Prime the pass
 1469                          * for the next run.
 1470                          */
 1471                         if (pass > 1)
 1472                                 pass = 1;
 1473                         else
 1474                                 pass = 0;
 1475                         error = msleep(&vm_pages_needed,
 1476                             &vm_page_queue_free_mtx, PVM, "psleep",
 1477                             vm_pageout_stats_interval * hz);
 1478                         if (error && !vm_pages_needed) {
 1479                                 mtx_unlock(&vm_page_queue_free_mtx);
 1480                                 pass = 0;
 1481                                 vm_page_lock_queues();
 1482                                 vm_pageout_page_stats();
 1483                                 vm_page_unlock_queues();
 1484                                 continue;
 1485                         }
 1486                 }
 1487                 if (vm_pages_needed)
 1488                         cnt.v_pdwakeups++;
 1489                 mtx_unlock(&vm_page_queue_free_mtx);
 1490                 vm_pageout_scan(pass);
 1491         }
 1492 }
 1493 
 1494 /*
 1495  * Unless the free page queue lock is held by the caller, this function
 1496  * should be regarded as advisory.  Specifically, the caller should
 1497  * not msleep() on &cnt.v_free_count following this function unless
 1498  * the free page queue lock is held until the msleep() is performed.
 1499  */
 1500 void
 1501 pagedaemon_wakeup()
 1502 {
 1503 
 1504         if (!vm_pages_needed && curthread->td_proc != pageproc) {
 1505                 vm_pages_needed = 1;
 1506                 wakeup(&vm_pages_needed);
 1507         }
 1508 }
 1509 
 1510 #if !defined(NO_SWAPPING)
 1511 static void
 1512 vm_req_vmdaemon(int req)
 1513 {
 1514         static int lastrun = 0;
 1515 
 1516         mtx_lock(&vm_daemon_mtx);
 1517         vm_pageout_req_swapout |= req;
 1518         if ((ticks > (lastrun + hz)) || (ticks < lastrun)) {
 1519                 wakeup(&vm_daemon_needed);
 1520                 lastrun = ticks;
 1521         }
 1522         mtx_unlock(&vm_daemon_mtx);
 1523 }
 1524 
 1525 static void
 1526 vm_daemon()
 1527 {
 1528         struct rlimit rsslim;
 1529         struct proc *p;
 1530         struct thread *td;
 1531         int breakout, swapout_flags;
 1532 
 1533         while (TRUE) {
 1534                 mtx_lock(&vm_daemon_mtx);
 1535                 msleep(&vm_daemon_needed, &vm_daemon_mtx, PPAUSE, "psleep", 0);
 1536                 swapout_flags = vm_pageout_req_swapout;
 1537                 vm_pageout_req_swapout = 0;
 1538                 mtx_unlock(&vm_daemon_mtx);
 1539                 if (swapout_flags)
 1540                         swapout_procs(swapout_flags);
 1541 
 1542                 /*
 1543                  * scan the processes for exceeding their rlimits or if
 1544                  * process is swapped out -- deactivate pages
 1545                  */
 1546                 sx_slock(&allproc_lock);
 1547                 FOREACH_PROC_IN_SYSTEM(p) {
 1548                         vm_pindex_t limit, size;
 1549 
 1550                         /*
 1551                          * if this is a system process or if we have already
 1552                          * looked at this process, skip it.
 1553                          */
 1554                         PROC_LOCK(p);
 1555                         if (p->p_flag & (P_SYSTEM | P_WEXIT)) {
 1556                                 PROC_UNLOCK(p);
 1557                                 continue;
 1558                         }
 1559                         /*
 1560                          * if the process is in a non-running type state,
 1561                          * don't touch it.
 1562                          */
 1563                         PROC_SLOCK(p);
 1564                         breakout = 0;
 1565                         FOREACH_THREAD_IN_PROC(p, td) {
 1566                                 thread_lock(td);
 1567                                 if (!TD_ON_RUNQ(td) &&
 1568                                     !TD_IS_RUNNING(td) &&
 1569                                     !TD_IS_SLEEPING(td)) {
 1570                                         thread_unlock(td);
 1571                                         breakout = 1;
 1572                                         break;
 1573                                 }
 1574                                 thread_unlock(td);
 1575                         }
 1576                         PROC_SUNLOCK(p);
 1577                         if (breakout) {
 1578                                 PROC_UNLOCK(p);
 1579                                 continue;
 1580                         }
 1581                         /*
 1582                          * get a limit
 1583                          */
 1584                         lim_rlimit(p, RLIMIT_RSS, &rsslim);
 1585                         limit = OFF_TO_IDX(
 1586                             qmin(rsslim.rlim_cur, rsslim.rlim_max));
 1587 
 1588                         /*
 1589                          * let processes that are swapped out really be
 1590                          * swapped out set the limit to nothing (will force a
 1591                          * swap-out.)
 1592                          */
 1593                         if ((p->p_flag & P_INMEM) == 0)
 1594                                 limit = 0;      /* XXX */
 1595                         PROC_UNLOCK(p);
 1596 
 1597                         size = vmspace_resident_count(p->p_vmspace);
 1598                         if (limit >= 0 && size >= limit) {
 1599                                 vm_pageout_map_deactivate_pages(
 1600                                     &p->p_vmspace->vm_map, limit);
 1601                         }
 1602                 }
 1603                 sx_sunlock(&allproc_lock);
 1604         }
 1605 }
 1606 #endif                  /* !defined(NO_SWAPPING) */

Cache object: 2cc917a0fd141821b161d0bb680f8c8a


[ source navigation ] [ diff markup ] [ identifier search ] [ freetext search ] [ file search ] [ list types ] [ track identifier ]


This page is part of the FreeBSD/Linux Linux Kernel Cross-Reference, and was automatically generated using a modified version of the LXR engine.