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

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    1 /*-
    2  * Copyright (c) 1991 Regents of the University of California.
    3  * All rights reserved.
    4  * Copyright (c) 1994 John S. Dyson
    5  * All rights reserved.
    6  * Copyright (c) 1994 David Greenman
    7  * All rights reserved.
    8  * Copyright (c) 2005 Yahoo! Technologies Norway AS
    9  * All rights reserved.
   10  *
   11  * This code is derived from software contributed to Berkeley by
   12  * The Mach Operating System project at Carnegie-Mellon University.
   13  *
   14  * Redistribution and use in source and binary forms, with or without
   15  * modification, are permitted provided that the following conditions
   16  * are met:
   17  * 1. Redistributions of source code must retain the above copyright
   18  *    notice, this list of conditions and the following disclaimer.
   19  * 2. Redistributions in binary form must reproduce the above copyright
   20  *    notice, this list of conditions and the following disclaimer in the
   21  *    documentation and/or other materials provided with the distribution.
   22  * 3. All advertising materials mentioning features or use of this software
   23  *    must display the following acknowledgement:
   24  *      This product includes software developed by the University of
   25  *      California, Berkeley and its contributors.
   26  * 4. Neither the name of the University nor the names of its contributors
   27  *    may be used to endorse or promote products derived from this software
   28  *    without specific prior written permission.
   29  *
   30  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   31  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   32  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   33  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   34  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   35  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   36  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   37  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   38  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   39  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   40  * SUCH DAMAGE.
   41  *
   42  *      from: @(#)vm_pageout.c  7.4 (Berkeley) 5/7/91
   43  *
   44  *
   45  * Copyright (c) 1987, 1990 Carnegie-Mellon University.
   46  * All rights reserved.
   47  *
   48  * Authors: Avadis Tevanian, Jr., Michael Wayne Young
   49  *
   50  * Permission to use, copy, modify and distribute this software and
   51  * its documentation is hereby granted, provided that both the copyright
   52  * notice and this permission notice appear in all copies of the
   53  * software, derivative works or modified versions, and any portions
   54  * thereof, and that both notices appear in supporting documentation.
   55  *
   56  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
   57  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
   58  * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
   59  *
   60  * Carnegie Mellon requests users of this software to return to
   61  *
   62  *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
   63  *  School of Computer Science
   64  *  Carnegie Mellon University
   65  *  Pittsburgh PA 15213-3890
   66  *
   67  * any improvements or extensions that they make and grant Carnegie the
   68  * rights to redistribute these changes.
   69  */
   70 
   71 /*
   72  *      The proverbial page-out daemon.
   73  */
   74 
   75 #include <sys/cdefs.h>
   76 __FBSDID("$FreeBSD: releng/9.0/sys/vm/vm_pageout.c 225418 2011-09-06 10:30:11Z kib $");
   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/racct.h>
   90 #include <sys/resourcevar.h>
   91 #include <sys/sched.h>
   92 #include <sys/signalvar.h>
   93 #include <sys/vnode.h>
   94 #include <sys/vmmeter.h>
   95 #include <sys/sx.h>
   96 #include <sys/sysctl.h>
   97 
   98 #include <vm/vm.h>
   99 #include <vm/vm_param.h>
  100 #include <vm/vm_object.h>
  101 #include <vm/vm_page.h>
  102 #include <vm/vm_map.h>
  103 #include <vm/vm_pageout.h>
  104 #include <vm/vm_pager.h>
  105 #include <vm/swap_pager.h>
  106 #include <vm/vm_extern.h>
  107 #include <vm/uma.h>
  108 
  109 /*
  110  * System initialization
  111  */
  112 
  113 /* the kernel process "vm_pageout"*/
  114 static void vm_pageout(void);
  115 static int vm_pageout_clean(vm_page_t);
  116 static void vm_pageout_scan(int pass);
  117 
  118 struct proc *pageproc;
  119 
  120 static struct kproc_desc page_kp = {
  121         "pagedaemon",
  122         vm_pageout,
  123         &pageproc
  124 };
  125 SYSINIT(pagedaemon, SI_SUB_KTHREAD_PAGE, SI_ORDER_FIRST, kproc_start,
  126     &page_kp);
  127 
  128 #if !defined(NO_SWAPPING)
  129 /* the kernel process "vm_daemon"*/
  130 static void vm_daemon(void);
  131 static struct   proc *vmproc;
  132 
  133 static struct kproc_desc vm_kp = {
  134         "vmdaemon",
  135         vm_daemon,
  136         &vmproc
  137 };
  138 SYSINIT(vmdaemon, SI_SUB_KTHREAD_VM, SI_ORDER_FIRST, kproc_start, &vm_kp);
  139 #endif
  140 
  141 
  142 int vm_pages_needed;            /* Event on which pageout daemon sleeps */
  143 int vm_pageout_deficit;         /* Estimated number of pages deficit */
  144 int vm_pageout_pages_needed;    /* flag saying that the pageout daemon needs pages */
  145 
  146 #if !defined(NO_SWAPPING)
  147 static int vm_pageout_req_swapout;      /* XXX */
  148 static int vm_daemon_needed;
  149 static struct mtx vm_daemon_mtx;
  150 /* Allow for use by vm_pageout before vm_daemon is initialized. */
  151 MTX_SYSINIT(vm_daemon, &vm_daemon_mtx, "vm daemon", MTX_DEF);
  152 #endif
  153 static int vm_max_launder = 32;
  154 static int vm_pageout_stats_max=0, vm_pageout_stats_interval = 0;
  155 static int vm_pageout_full_stats_interval = 0;
  156 static int vm_pageout_algorithm=0;
  157 static int defer_swap_pageouts=0;
  158 static int disable_swap_pageouts=0;
  159 
  160 #if defined(NO_SWAPPING)
  161 static int vm_swap_enabled=0;
  162 static int vm_swap_idle_enabled=0;
  163 #else
  164 static int vm_swap_enabled=1;
  165 static int vm_swap_idle_enabled=0;
  166 #endif
  167 
  168 SYSCTL_INT(_vm, VM_PAGEOUT_ALGORITHM, pageout_algorithm,
  169         CTLFLAG_RW, &vm_pageout_algorithm, 0, "LRU page mgmt");
  170 
  171 SYSCTL_INT(_vm, OID_AUTO, max_launder,
  172         CTLFLAG_RW, &vm_max_launder, 0, "Limit dirty flushes in pageout");
  173 
  174 SYSCTL_INT(_vm, OID_AUTO, pageout_stats_max,
  175         CTLFLAG_RW, &vm_pageout_stats_max, 0, "Max pageout stats scan length");
  176 
  177 SYSCTL_INT(_vm, OID_AUTO, pageout_full_stats_interval,
  178         CTLFLAG_RW, &vm_pageout_full_stats_interval, 0, "Interval for full stats scan");
  179 
  180 SYSCTL_INT(_vm, OID_AUTO, pageout_stats_interval,
  181         CTLFLAG_RW, &vm_pageout_stats_interval, 0, "Interval for partial stats scan");
  182 
  183 #if defined(NO_SWAPPING)
  184 SYSCTL_INT(_vm, VM_SWAPPING_ENABLED, swap_enabled,
  185         CTLFLAG_RD, &vm_swap_enabled, 0, "Enable entire process swapout");
  186 SYSCTL_INT(_vm, OID_AUTO, swap_idle_enabled,
  187         CTLFLAG_RD, &vm_swap_idle_enabled, 0, "Allow swapout on idle criteria");
  188 #else
  189 SYSCTL_INT(_vm, VM_SWAPPING_ENABLED, swap_enabled,
  190         CTLFLAG_RW, &vm_swap_enabled, 0, "Enable entire process swapout");
  191 SYSCTL_INT(_vm, OID_AUTO, swap_idle_enabled,
  192         CTLFLAG_RW, &vm_swap_idle_enabled, 0, "Allow swapout on idle criteria");
  193 #endif
  194 
  195 SYSCTL_INT(_vm, OID_AUTO, defer_swapspace_pageouts,
  196         CTLFLAG_RW, &defer_swap_pageouts, 0, "Give preference to dirty pages in mem");
  197 
  198 SYSCTL_INT(_vm, OID_AUTO, disable_swapspace_pageouts,
  199         CTLFLAG_RW, &disable_swap_pageouts, 0, "Disallow swapout of dirty pages");
  200 
  201 static int pageout_lock_miss;
  202 SYSCTL_INT(_vm, OID_AUTO, pageout_lock_miss,
  203         CTLFLAG_RD, &pageout_lock_miss, 0, "vget() lock misses during pageout");
  204 
  205 #define VM_PAGEOUT_PAGE_COUNT 16
  206 int vm_pageout_page_count = VM_PAGEOUT_PAGE_COUNT;
  207 
  208 int vm_page_max_wired;          /* XXX max # of wired pages system-wide */
  209 SYSCTL_INT(_vm, OID_AUTO, max_wired,
  210         CTLFLAG_RW, &vm_page_max_wired, 0, "System-wide limit to wired page count");
  211 
  212 #if !defined(NO_SWAPPING)
  213 static void vm_pageout_map_deactivate_pages(vm_map_t, long);
  214 static void vm_pageout_object_deactivate_pages(pmap_t, vm_object_t, long);
  215 static void vm_req_vmdaemon(int req);
  216 #endif
  217 static void vm_pageout_page_stats(void);
  218 
  219 /*
  220  * Initialize a dummy page for marking the caller's place in the specified
  221  * paging queue.  In principle, this function only needs to set the flag
  222  * PG_MARKER.  Nonetheless, it sets the flag VPO_BUSY and initializes the hold
  223  * count to one as safety precautions.
  224  */ 
  225 static void
  226 vm_pageout_init_marker(vm_page_t marker, u_short queue)
  227 {
  228 
  229         bzero(marker, sizeof(*marker));
  230         marker->flags = PG_MARKER;
  231         marker->oflags = VPO_BUSY;
  232         marker->queue = queue;
  233         marker->hold_count = 1;
  234 }
  235 
  236 /*
  237  * vm_pageout_fallback_object_lock:
  238  * 
  239  * Lock vm object currently associated with `m'. VM_OBJECT_TRYLOCK is
  240  * known to have failed and page queue must be either PQ_ACTIVE or
  241  * PQ_INACTIVE.  To avoid lock order violation, unlock the page queues
  242  * while locking the vm object.  Use marker page to detect page queue
  243  * changes and maintain notion of next page on page queue.  Return
  244  * TRUE if no changes were detected, FALSE otherwise.  vm object is
  245  * locked on return.
  246  * 
  247  * This function depends on both the lock portion of struct vm_object
  248  * and normal struct vm_page being type stable.
  249  */
  250 boolean_t
  251 vm_pageout_fallback_object_lock(vm_page_t m, vm_page_t *next)
  252 {
  253         struct vm_page marker;
  254         boolean_t unchanged;
  255         u_short queue;
  256         vm_object_t object;
  257 
  258         queue = m->queue;
  259         vm_pageout_init_marker(&marker, queue);
  260         object = m->object;
  261         
  262         TAILQ_INSERT_AFTER(&vm_page_queues[queue].pl,
  263                            m, &marker, pageq);
  264         vm_page_unlock_queues();
  265         vm_page_unlock(m);
  266         VM_OBJECT_LOCK(object);
  267         vm_page_lock(m);
  268         vm_page_lock_queues();
  269 
  270         /* Page queue might have changed. */
  271         *next = TAILQ_NEXT(&marker, pageq);
  272         unchanged = (m->queue == queue &&
  273                      m->object == object &&
  274                      &marker == TAILQ_NEXT(m, pageq));
  275         TAILQ_REMOVE(&vm_page_queues[queue].pl,
  276                      &marker, pageq);
  277         return (unchanged);
  278 }
  279 
  280 /*
  281  * Lock the page while holding the page queue lock.  Use marker page
  282  * to detect page queue changes and maintain notion of next page on
  283  * page queue.  Return TRUE if no changes were detected, FALSE
  284  * otherwise.  The page is locked on return. The page queue lock might
  285  * be dropped and reacquired.
  286  *
  287  * This function depends on normal struct vm_page being type stable.
  288  */
  289 boolean_t
  290 vm_pageout_page_lock(vm_page_t m, vm_page_t *next)
  291 {
  292         struct vm_page marker;
  293         boolean_t unchanged;
  294         u_short queue;
  295 
  296         vm_page_lock_assert(m, MA_NOTOWNED);
  297         mtx_assert(&vm_page_queue_mtx, MA_OWNED);
  298 
  299         if (vm_page_trylock(m))
  300                 return (TRUE);
  301 
  302         queue = m->queue;
  303         vm_pageout_init_marker(&marker, queue);
  304 
  305         TAILQ_INSERT_AFTER(&vm_page_queues[queue].pl, m, &marker, pageq);
  306         vm_page_unlock_queues();
  307         vm_page_lock(m);
  308         vm_page_lock_queues();
  309 
  310         /* Page queue might have changed. */
  311         *next = TAILQ_NEXT(&marker, pageq);
  312         unchanged = (m->queue == queue && &marker == TAILQ_NEXT(m, pageq));
  313         TAILQ_REMOVE(&vm_page_queues[queue].pl, &marker, pageq);
  314         return (unchanged);
  315 }
  316 
  317 /*
  318  * vm_pageout_clean:
  319  *
  320  * Clean the page and remove it from the laundry.
  321  * 
  322  * We set the busy bit to cause potential page faults on this page to
  323  * block.  Note the careful timing, however, the busy bit isn't set till
  324  * late and we cannot do anything that will mess with the page.
  325  */
  326 static int
  327 vm_pageout_clean(vm_page_t m)
  328 {
  329         vm_object_t object;
  330         vm_page_t mc[2*vm_pageout_page_count], pb, ps;
  331         int pageout_count;
  332         int ib, is, page_base;
  333         vm_pindex_t pindex = m->pindex;
  334 
  335         vm_page_lock_assert(m, MA_OWNED);
  336         object = m->object;
  337         VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
  338 
  339         /*
  340          * It doesn't cost us anything to pageout OBJT_DEFAULT or OBJT_SWAP
  341          * with the new swapper, but we could have serious problems paging
  342          * out other object types if there is insufficient memory.  
  343          *
  344          * Unfortunately, checking free memory here is far too late, so the
  345          * check has been moved up a procedural level.
  346          */
  347 
  348         /*
  349          * Can't clean the page if it's busy or held.
  350          */
  351         KASSERT(m->busy == 0 && (m->oflags & VPO_BUSY) == 0,
  352             ("vm_pageout_clean: page %p is busy", m));
  353         KASSERT(m->hold_count == 0, ("vm_pageout_clean: page %p is held", m));
  354         vm_page_unlock(m);
  355 
  356         mc[vm_pageout_page_count] = pb = ps = m;
  357         pageout_count = 1;
  358         page_base = vm_pageout_page_count;
  359         ib = 1;
  360         is = 1;
  361 
  362         /*
  363          * Scan object for clusterable pages.
  364          *
  365          * We can cluster ONLY if: ->> the page is NOT
  366          * clean, wired, busy, held, or mapped into a
  367          * buffer, and one of the following:
  368          * 1) The page is inactive, or a seldom used
  369          *    active page.
  370          * -or-
  371          * 2) we force the issue.
  372          *
  373          * During heavy mmap/modification loads the pageout
  374          * daemon can really fragment the underlying file
  375          * due to flushing pages out of order and not trying
  376          * align the clusters (which leave sporatic out-of-order
  377          * holes).  To solve this problem we do the reverse scan
  378          * first and attempt to align our cluster, then do a 
  379          * forward scan if room remains.
  380          */
  381 more:
  382         while (ib && pageout_count < vm_pageout_page_count) {
  383                 vm_page_t p;
  384 
  385                 if (ib > pindex) {
  386                         ib = 0;
  387                         break;
  388                 }
  389 
  390                 if ((p = vm_page_prev(pb)) == NULL ||
  391                     (p->oflags & VPO_BUSY) != 0 || p->busy != 0) {
  392                         ib = 0;
  393                         break;
  394                 }
  395                 vm_page_lock(p);
  396                 vm_page_test_dirty(p);
  397                 if (p->dirty == 0 ||
  398                     p->queue != PQ_INACTIVE ||
  399                     p->hold_count != 0) {       /* may be undergoing I/O */
  400                         vm_page_unlock(p);
  401                         ib = 0;
  402                         break;
  403                 }
  404                 vm_page_unlock(p);
  405                 mc[--page_base] = pb = p;
  406                 ++pageout_count;
  407                 ++ib;
  408                 /*
  409                  * alignment boundry, stop here and switch directions.  Do
  410                  * not clear ib.
  411                  */
  412                 if ((pindex - (ib - 1)) % vm_pageout_page_count == 0)
  413                         break;
  414         }
  415 
  416         while (pageout_count < vm_pageout_page_count && 
  417             pindex + is < object->size) {
  418                 vm_page_t p;
  419 
  420                 if ((p = vm_page_next(ps)) == NULL ||
  421                     (p->oflags & VPO_BUSY) != 0 || p->busy != 0)
  422                         break;
  423                 vm_page_lock(p);
  424                 vm_page_test_dirty(p);
  425                 if (p->dirty == 0 ||
  426                     p->queue != PQ_INACTIVE ||
  427                     p->hold_count != 0) {       /* may be undergoing I/O */
  428                         vm_page_unlock(p);
  429                         break;
  430                 }
  431                 vm_page_unlock(p);
  432                 mc[page_base + pageout_count] = ps = p;
  433                 ++pageout_count;
  434                 ++is;
  435         }
  436 
  437         /*
  438          * If we exhausted our forward scan, continue with the reverse scan
  439          * when possible, even past a page boundry.  This catches boundry
  440          * conditions.
  441          */
  442         if (ib && pageout_count < vm_pageout_page_count)
  443                 goto more;
  444 
  445         /*
  446          * we allow reads during pageouts...
  447          */
  448         return (vm_pageout_flush(&mc[page_base], pageout_count, 0, 0, NULL));
  449 }
  450 
  451 /*
  452  * vm_pageout_flush() - launder the given pages
  453  *
  454  *      The given pages are laundered.  Note that we setup for the start of
  455  *      I/O ( i.e. busy the page ), mark it read-only, and bump the object
  456  *      reference count all in here rather then in the parent.  If we want
  457  *      the parent to do more sophisticated things we may have to change
  458  *      the ordering.
  459  *
  460  *      Returned runlen is the count of pages between mreq and first
  461  *      page after mreq with status VM_PAGER_AGAIN.
  462  */
  463 int
  464 vm_pageout_flush(vm_page_t *mc, int count, int flags, int mreq, int *prunlen)
  465 {
  466         vm_object_t object = mc[0]->object;
  467         int pageout_status[count];
  468         int numpagedout = 0;
  469         int i, runlen;
  470 
  471         VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
  472         mtx_assert(&vm_page_queue_mtx, MA_NOTOWNED);
  473 
  474         /*
  475          * Initiate I/O.  Bump the vm_page_t->busy counter and
  476          * mark the pages read-only.
  477          *
  478          * We do not have to fixup the clean/dirty bits here... we can
  479          * allow the pager to do it after the I/O completes.
  480          *
  481          * NOTE! mc[i]->dirty may be partial or fragmented due to an
  482          * edge case with file fragments.
  483          */
  484         for (i = 0; i < count; i++) {
  485                 KASSERT(mc[i]->valid == VM_PAGE_BITS_ALL,
  486                     ("vm_pageout_flush: partially invalid page %p index %d/%d",
  487                         mc[i], i, count));
  488                 vm_page_io_start(mc[i]);
  489                 pmap_remove_write(mc[i]);
  490         }
  491         vm_object_pip_add(object, count);
  492 
  493         vm_pager_put_pages(object, mc, count, flags, pageout_status);
  494 
  495         runlen = count - mreq;
  496         for (i = 0; i < count; i++) {
  497                 vm_page_t mt = mc[i];
  498 
  499                 KASSERT(pageout_status[i] == VM_PAGER_PEND ||
  500                     (mt->aflags & PGA_WRITEABLE) == 0,
  501                     ("vm_pageout_flush: page %p is not write protected", mt));
  502                 switch (pageout_status[i]) {
  503                 case VM_PAGER_OK:
  504                 case VM_PAGER_PEND:
  505                         numpagedout++;
  506                         break;
  507                 case VM_PAGER_BAD:
  508                         /*
  509                          * Page outside of range of object. Right now we
  510                          * essentially lose the changes by pretending it
  511                          * worked.
  512                          */
  513                         vm_page_undirty(mt);
  514                         break;
  515                 case VM_PAGER_ERROR:
  516                 case VM_PAGER_FAIL:
  517                         /*
  518                          * If page couldn't be paged out, then reactivate the
  519                          * page so it doesn't clog the inactive list.  (We
  520                          * will try paging out it again later).
  521                          */
  522                         vm_page_lock(mt);
  523                         vm_page_activate(mt);
  524                         vm_page_unlock(mt);
  525                         break;
  526                 case VM_PAGER_AGAIN:
  527                         if (i >= mreq && i - mreq < runlen)
  528                                 runlen = i - mreq;
  529                         break;
  530                 }
  531 
  532                 /*
  533                  * If the operation is still going, leave the page busy to
  534                  * block all other accesses. Also, leave the paging in
  535                  * progress indicator set so that we don't attempt an object
  536                  * collapse.
  537                  */
  538                 if (pageout_status[i] != VM_PAGER_PEND) {
  539                         vm_object_pip_wakeup(object);
  540                         vm_page_io_finish(mt);
  541                         if (vm_page_count_severe()) {
  542                                 vm_page_lock(mt);
  543                                 vm_page_try_to_cache(mt);
  544                                 vm_page_unlock(mt);
  545                         }
  546                 }
  547         }
  548         if (prunlen != NULL)
  549                 *prunlen = runlen;
  550         return (numpagedout);
  551 }
  552 
  553 #if !defined(NO_SWAPPING)
  554 /*
  555  *      vm_pageout_object_deactivate_pages
  556  *
  557  *      Deactivate enough pages to satisfy the inactive target
  558  *      requirements.
  559  *
  560  *      The object and map must be locked.
  561  */
  562 static void
  563 vm_pageout_object_deactivate_pages(pmap_t pmap, vm_object_t first_object,
  564     long desired)
  565 {
  566         vm_object_t backing_object, object;
  567         vm_page_t p;
  568         int actcount, remove_mode;
  569 
  570         VM_OBJECT_LOCK_ASSERT(first_object, MA_OWNED);
  571         if (first_object->type == OBJT_DEVICE ||
  572             first_object->type == OBJT_SG)
  573                 return;
  574         for (object = first_object;; object = backing_object) {
  575                 if (pmap_resident_count(pmap) <= desired)
  576                         goto unlock_return;
  577                 VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
  578                 if (object->type == OBJT_PHYS || object->paging_in_progress)
  579                         goto unlock_return;
  580 
  581                 remove_mode = 0;
  582                 if (object->shadow_count > 1)
  583                         remove_mode = 1;
  584                 /*
  585                  * Scan the object's entire memory queue.
  586                  */
  587                 TAILQ_FOREACH(p, &object->memq, listq) {
  588                         if (pmap_resident_count(pmap) <= desired)
  589                                 goto unlock_return;
  590                         if ((p->oflags & VPO_BUSY) != 0 || p->busy != 0)
  591                                 continue;
  592                         PCPU_INC(cnt.v_pdpages);
  593                         vm_page_lock(p);
  594                         if (p->wire_count != 0 || p->hold_count != 0 ||
  595                             !pmap_page_exists_quick(pmap, p)) {
  596                                 vm_page_unlock(p);
  597                                 continue;
  598                         }
  599                         actcount = pmap_ts_referenced(p);
  600                         if ((p->aflags & PGA_REFERENCED) != 0) {
  601                                 if (actcount == 0)
  602                                         actcount = 1;
  603                                 vm_page_aflag_clear(p, PGA_REFERENCED);
  604                         }
  605                         if (p->queue != PQ_ACTIVE && actcount != 0) {
  606                                 vm_page_activate(p);
  607                                 p->act_count += actcount;
  608                         } else if (p->queue == PQ_ACTIVE) {
  609                                 if (actcount == 0) {
  610                                         p->act_count -= min(p->act_count,
  611                                             ACT_DECLINE);
  612                                         if (!remove_mode &&
  613                                             (vm_pageout_algorithm ||
  614                                             p->act_count == 0)) {
  615                                                 pmap_remove_all(p);
  616                                                 vm_page_deactivate(p);
  617                                         } else {
  618                                                 vm_page_lock_queues();
  619                                                 vm_page_requeue(p);
  620                                                 vm_page_unlock_queues();
  621                                         }
  622                                 } else {
  623                                         vm_page_activate(p);
  624                                         if (p->act_count < ACT_MAX -
  625                                             ACT_ADVANCE)
  626                                                 p->act_count += ACT_ADVANCE;
  627                                         vm_page_lock_queues();
  628                                         vm_page_requeue(p);
  629                                         vm_page_unlock_queues();
  630                                 }
  631                         } else if (p->queue == PQ_INACTIVE)
  632                                 pmap_remove_all(p);
  633                         vm_page_unlock(p);
  634                 }
  635                 if ((backing_object = object->backing_object) == NULL)
  636                         goto unlock_return;
  637                 VM_OBJECT_LOCK(backing_object);
  638                 if (object != first_object)
  639                         VM_OBJECT_UNLOCK(object);
  640         }
  641 unlock_return:
  642         if (object != first_object)
  643                 VM_OBJECT_UNLOCK(object);
  644 }
  645 
  646 /*
  647  * deactivate some number of pages in a map, try to do it fairly, but
  648  * that is really hard to do.
  649  */
  650 static void
  651 vm_pageout_map_deactivate_pages(map, desired)
  652         vm_map_t map;
  653         long desired;
  654 {
  655         vm_map_entry_t tmpe;
  656         vm_object_t obj, bigobj;
  657         int nothingwired;
  658 
  659         if (!vm_map_trylock(map))
  660                 return;
  661 
  662         bigobj = NULL;
  663         nothingwired = TRUE;
  664 
  665         /*
  666          * first, search out the biggest object, and try to free pages from
  667          * that.
  668          */
  669         tmpe = map->header.next;
  670         while (tmpe != &map->header) {
  671                 if ((tmpe->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
  672                         obj = tmpe->object.vm_object;
  673                         if (obj != NULL && VM_OBJECT_TRYLOCK(obj)) {
  674                                 if (obj->shadow_count <= 1 &&
  675                                     (bigobj == NULL ||
  676                                      bigobj->resident_page_count < obj->resident_page_count)) {
  677                                         if (bigobj != NULL)
  678                                                 VM_OBJECT_UNLOCK(bigobj);
  679                                         bigobj = obj;
  680                                 } else
  681                                         VM_OBJECT_UNLOCK(obj);
  682                         }
  683                 }
  684                 if (tmpe->wired_count > 0)
  685                         nothingwired = FALSE;
  686                 tmpe = tmpe->next;
  687         }
  688 
  689         if (bigobj != NULL) {
  690                 vm_pageout_object_deactivate_pages(map->pmap, bigobj, desired);
  691                 VM_OBJECT_UNLOCK(bigobj);
  692         }
  693         /*
  694          * Next, hunt around for other pages to deactivate.  We actually
  695          * do this search sort of wrong -- .text first is not the best idea.
  696          */
  697         tmpe = map->header.next;
  698         while (tmpe != &map->header) {
  699                 if (pmap_resident_count(vm_map_pmap(map)) <= desired)
  700                         break;
  701                 if ((tmpe->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
  702                         obj = tmpe->object.vm_object;
  703                         if (obj != NULL) {
  704                                 VM_OBJECT_LOCK(obj);
  705                                 vm_pageout_object_deactivate_pages(map->pmap, obj, desired);
  706                                 VM_OBJECT_UNLOCK(obj);
  707                         }
  708                 }
  709                 tmpe = tmpe->next;
  710         }
  711 
  712         /*
  713          * Remove all mappings if a process is swapped out, this will free page
  714          * table pages.
  715          */
  716         if (desired == 0 && nothingwired) {
  717                 tmpe = map->header.next;
  718                 while (tmpe != &map->header) {
  719                         pmap_remove(vm_map_pmap(map), tmpe->start, tmpe->end);
  720                         tmpe = tmpe->next;
  721                 }
  722         }
  723         vm_map_unlock(map);
  724 }
  725 #endif          /* !defined(NO_SWAPPING) */
  726 
  727 /*
  728  *      vm_pageout_scan does the dirty work for the pageout daemon.
  729  */
  730 static void
  731 vm_pageout_scan(int pass)
  732 {
  733         vm_page_t m, next;
  734         struct vm_page marker;
  735         int page_shortage, maxscan, pcount;
  736         int addl_page_shortage, addl_page_shortage_init;
  737         vm_object_t object;
  738         int actcount;
  739         int vnodes_skipped = 0;
  740         int maxlaunder;
  741 
  742         /*
  743          * Decrease registered cache sizes.
  744          */
  745         EVENTHANDLER_INVOKE(vm_lowmem, 0);
  746         /*
  747          * We do this explicitly after the caches have been drained above.
  748          */
  749         uma_reclaim();
  750 
  751         addl_page_shortage_init = atomic_readandclear_int(&vm_pageout_deficit);
  752 
  753         /*
  754          * Calculate the number of pages we want to either free or move
  755          * to the cache.
  756          */
  757         page_shortage = vm_paging_target() + addl_page_shortage_init;
  758 
  759         vm_pageout_init_marker(&marker, PQ_INACTIVE);
  760 
  761         /*
  762          * Start scanning the inactive queue for pages we can move to the
  763          * cache or free.  The scan will stop when the target is reached or
  764          * we have scanned the entire inactive queue.  Note that m->act_count
  765          * is not used to form decisions for the inactive queue, only for the
  766          * active queue.
  767          *
  768          * maxlaunder limits the number of dirty pages we flush per scan.
  769          * For most systems a smaller value (16 or 32) is more robust under
  770          * extreme memory and disk pressure because any unnecessary writes
  771          * to disk can result in extreme performance degredation.  However,
  772          * systems with excessive dirty pages (especially when MAP_NOSYNC is
  773          * used) will die horribly with limited laundering.  If the pageout
  774          * daemon cannot clean enough pages in the first pass, we let it go
  775          * all out in succeeding passes.
  776          */
  777         if ((maxlaunder = vm_max_launder) <= 1)
  778                 maxlaunder = 1;
  779         if (pass)
  780                 maxlaunder = 10000;
  781         vm_page_lock_queues();
  782 rescan0:
  783         addl_page_shortage = addl_page_shortage_init;
  784         maxscan = cnt.v_inactive_count;
  785 
  786         for (m = TAILQ_FIRST(&vm_page_queues[PQ_INACTIVE].pl);
  787              m != NULL && maxscan-- > 0 && page_shortage > 0;
  788              m = next) {
  789 
  790                 cnt.v_pdpages++;
  791 
  792                 if (m->queue != PQ_INACTIVE)
  793                         goto rescan0;
  794 
  795                 next = TAILQ_NEXT(m, pageq);
  796 
  797                 /*
  798                  * skip marker pages
  799                  */
  800                 if (m->flags & PG_MARKER)
  801                         continue;
  802 
  803                 /*
  804                  * Lock the page.
  805                  */
  806                 if (!vm_pageout_page_lock(m, &next)) {
  807                         vm_page_unlock(m);
  808                         addl_page_shortage++;
  809                         continue;
  810                 }
  811 
  812                 /*
  813                  * A held page may be undergoing I/O, so skip it.
  814                  */
  815                 if (m->hold_count) {
  816                         vm_page_unlock(m);
  817                         vm_page_requeue(m);
  818                         addl_page_shortage++;
  819                         continue;
  820                 }
  821 
  822                 /*
  823                  * Don't mess with busy pages, keep in the front of the
  824                  * queue, most likely are being paged out.
  825                  */
  826                 object = m->object;
  827                 if (!VM_OBJECT_TRYLOCK(object) &&
  828                     (!vm_pageout_fallback_object_lock(m, &next) ||
  829                         m->hold_count != 0)) {
  830                         VM_OBJECT_UNLOCK(object);
  831                         vm_page_unlock(m);
  832                         addl_page_shortage++;
  833                         continue;
  834                 }
  835                 if (m->busy || (m->oflags & VPO_BUSY)) {
  836                         vm_page_unlock(m);
  837                         VM_OBJECT_UNLOCK(object);
  838                         addl_page_shortage++;
  839                         continue;
  840                 }
  841 
  842                 /*
  843                  * If the object is not being used, we ignore previous 
  844                  * references.
  845                  */
  846                 if (object->ref_count == 0) {
  847                         vm_page_aflag_clear(m, PGA_REFERENCED);
  848                         KASSERT(!pmap_page_is_mapped(m),
  849                             ("vm_pageout_scan: page %p is mapped", m));
  850 
  851                 /*
  852                  * Otherwise, if the page has been referenced while in the 
  853                  * inactive queue, we bump the "activation count" upwards, 
  854                  * making it less likely that the page will be added back to 
  855                  * the inactive queue prematurely again.  Here we check the 
  856                  * page tables (or emulated bits, if any), given the upper 
  857                  * level VM system not knowing anything about existing 
  858                  * references.
  859                  */
  860                 } else if (((m->aflags & PGA_REFERENCED) == 0) &&
  861                         (actcount = pmap_ts_referenced(m))) {
  862                         vm_page_activate(m);
  863                         vm_page_unlock(m);
  864                         m->act_count += actcount + ACT_ADVANCE;
  865                         VM_OBJECT_UNLOCK(object);
  866                         continue;
  867                 }
  868 
  869                 /*
  870                  * If the upper level VM system knows about any page 
  871                  * references, we activate the page.  We also set the 
  872                  * "activation count" higher than normal so that we will less 
  873                  * likely place pages back onto the inactive queue again.
  874                  */
  875                 if ((m->aflags & PGA_REFERENCED) != 0) {
  876                         vm_page_aflag_clear(m, PGA_REFERENCED);
  877                         actcount = pmap_ts_referenced(m);
  878                         vm_page_activate(m);
  879                         vm_page_unlock(m);
  880                         m->act_count += actcount + ACT_ADVANCE + 1;
  881                         VM_OBJECT_UNLOCK(object);
  882                         continue;
  883                 }
  884 
  885                 /*
  886                  * If the upper level VM system does not believe that the page
  887                  * is fully dirty, but it is mapped for write access, then we
  888                  * consult the pmap to see if the page's dirty status should
  889                  * be updated.
  890                  */
  891                 if (m->dirty != VM_PAGE_BITS_ALL &&
  892                     (m->aflags & PGA_WRITEABLE) != 0) {
  893                         /*
  894                          * Avoid a race condition: Unless write access is
  895                          * removed from the page, another processor could
  896                          * modify it before all access is removed by the call
  897                          * to vm_page_cache() below.  If vm_page_cache() finds
  898                          * that the page has been modified when it removes all
  899                          * access, it panics because it cannot cache dirty
  900                          * pages.  In principle, we could eliminate just write
  901                          * access here rather than all access.  In the expected
  902                          * case, when there are no last instant modifications
  903                          * to the page, removing all access will be cheaper
  904                          * overall.
  905                          */
  906                         if (pmap_is_modified(m))
  907                                 vm_page_dirty(m);
  908                         else if (m->dirty == 0)
  909                                 pmap_remove_all(m);
  910                 }
  911 
  912                 if (m->valid == 0) {
  913                         /*
  914                          * Invalid pages can be easily freed
  915                          */
  916                         vm_page_free(m);
  917                         cnt.v_dfree++;
  918                         --page_shortage;
  919                 } else if (m->dirty == 0) {
  920                         /*
  921                          * Clean pages can be placed onto the cache queue.
  922                          * This effectively frees them.
  923                          */
  924                         vm_page_cache(m);
  925                         --page_shortage;
  926                 } else if ((m->flags & PG_WINATCFLS) == 0 && pass == 0) {
  927                         /*
  928                          * Dirty pages need to be paged out, but flushing
  929                          * a page is extremely expensive verses freeing
  930                          * a clean page.  Rather then artificially limiting
  931                          * the number of pages we can flush, we instead give
  932                          * dirty pages extra priority on the inactive queue
  933                          * by forcing them to be cycled through the queue
  934                          * twice before being flushed, after which the
  935                          * (now clean) page will cycle through once more
  936                          * before being freed.  This significantly extends
  937                          * the thrash point for a heavily loaded machine.
  938                          */
  939                         m->flags |= PG_WINATCFLS;
  940                         vm_page_requeue(m);
  941                 } else if (maxlaunder > 0) {
  942                         /*
  943                          * We always want to try to flush some dirty pages if
  944                          * we encounter them, to keep the system stable.
  945                          * Normally this number is small, but under extreme
  946                          * pressure where there are insufficient clean pages
  947                          * on the inactive queue, we may have to go all out.
  948                          */
  949                         int swap_pageouts_ok, vfslocked = 0;
  950                         struct vnode *vp = NULL;
  951                         struct mount *mp = NULL;
  952 
  953                         if ((object->type != OBJT_SWAP) && (object->type != OBJT_DEFAULT)) {
  954                                 swap_pageouts_ok = 1;
  955                         } else {
  956                                 swap_pageouts_ok = !(defer_swap_pageouts || disable_swap_pageouts);
  957                                 swap_pageouts_ok |= (!disable_swap_pageouts && defer_swap_pageouts &&
  958                                 vm_page_count_min());
  959                                                                                 
  960                         }
  961 
  962                         /*
  963                          * We don't bother paging objects that are "dead".  
  964                          * Those objects are in a "rundown" state.
  965                          */
  966                         if (!swap_pageouts_ok || (object->flags & OBJ_DEAD)) {
  967                                 vm_page_unlock(m);
  968                                 VM_OBJECT_UNLOCK(object);
  969                                 vm_page_requeue(m);
  970                                 continue;
  971                         }
  972 
  973                         /*
  974                          * Following operations may unlock
  975                          * vm_page_queue_mtx, invalidating the 'next'
  976                          * pointer.  To prevent an inordinate number
  977                          * of restarts we use our marker to remember
  978                          * our place.
  979                          *
  980                          */
  981                         TAILQ_INSERT_AFTER(&vm_page_queues[PQ_INACTIVE].pl,
  982                                            m, &marker, pageq);
  983                         /*
  984                          * The object is already known NOT to be dead.   It
  985                          * is possible for the vget() to block the whole
  986                          * pageout daemon, but the new low-memory handling
  987                          * code should prevent it.
  988                          *
  989                          * The previous code skipped locked vnodes and, worse,
  990                          * reordered pages in the queue.  This results in
  991                          * completely non-deterministic operation and, on a
  992                          * busy system, can lead to extremely non-optimal
  993                          * pageouts.  For example, it can cause clean pages
  994                          * to be freed and dirty pages to be moved to the end
  995                          * of the queue.  Since dirty pages are also moved to
  996                          * the end of the queue once-cleaned, this gives
  997                          * way too large a weighting to defering the freeing
  998                          * of dirty pages.
  999                          *
 1000                          * We can't wait forever for the vnode lock, we might
 1001                          * deadlock due to a vn_read() getting stuck in
 1002                          * vm_wait while holding this vnode.  We skip the 
 1003                          * vnode if we can't get it in a reasonable amount
 1004                          * of time.
 1005                          */
 1006                         if (object->type == OBJT_VNODE) {
 1007                                 vm_page_unlock_queues();
 1008                                 vm_page_unlock(m);
 1009                                 vp = object->handle;
 1010                                 if (vp->v_type == VREG &&
 1011                                     vn_start_write(vp, &mp, V_NOWAIT) != 0) {
 1012                                         mp = NULL;
 1013                                         ++pageout_lock_miss;
 1014                                         if (object->flags & OBJ_MIGHTBEDIRTY)
 1015                                                 vnodes_skipped++;
 1016                                         vm_page_lock_queues();
 1017                                         goto unlock_and_continue;
 1018                                 }
 1019                                 KASSERT(mp != NULL,
 1020                                     ("vp %p with NULL v_mount", vp));
 1021                                 vm_object_reference_locked(object);
 1022                                 VM_OBJECT_UNLOCK(object);
 1023                                 vfslocked = VFS_LOCK_GIANT(vp->v_mount);
 1024                                 if (vget(vp, LK_EXCLUSIVE | LK_TIMELOCK,
 1025                                     curthread)) {
 1026                                         VM_OBJECT_LOCK(object);
 1027                                         vm_page_lock_queues();
 1028                                         ++pageout_lock_miss;
 1029                                         if (object->flags & OBJ_MIGHTBEDIRTY)
 1030                                                 vnodes_skipped++;
 1031                                         vp = NULL;
 1032                                         goto unlock_and_continue;
 1033                                 }
 1034                                 VM_OBJECT_LOCK(object);
 1035                                 vm_page_lock(m);
 1036                                 vm_page_lock_queues();
 1037                                 /*
 1038                                  * The page might have been moved to another
 1039                                  * queue during potential blocking in vget()
 1040                                  * above.  The page might have been freed and
 1041                                  * reused for another vnode.
 1042                                  */
 1043                                 if (m->queue != PQ_INACTIVE ||
 1044                                     m->object != object ||
 1045                                     TAILQ_NEXT(m, pageq) != &marker) {
 1046                                         vm_page_unlock(m);
 1047                                         if (object->flags & OBJ_MIGHTBEDIRTY)
 1048                                                 vnodes_skipped++;
 1049                                         goto unlock_and_continue;
 1050                                 }
 1051         
 1052                                 /*
 1053                                  * The page may have been busied during the
 1054                                  * blocking in vget().  We don't move the
 1055                                  * page back onto the end of the queue so that
 1056                                  * statistics are more correct if we don't.
 1057                                  */
 1058                                 if (m->busy || (m->oflags & VPO_BUSY)) {
 1059                                         vm_page_unlock(m);
 1060                                         goto unlock_and_continue;
 1061                                 }
 1062 
 1063                                 /*
 1064                                  * If the page has become held it might
 1065                                  * be undergoing I/O, so skip it
 1066                                  */
 1067                                 if (m->hold_count) {
 1068                                         vm_page_unlock(m);
 1069                                         vm_page_requeue(m);
 1070                                         if (object->flags & OBJ_MIGHTBEDIRTY)
 1071                                                 vnodes_skipped++;
 1072                                         goto unlock_and_continue;
 1073                                 }
 1074                         }
 1075 
 1076                         /*
 1077                          * If a page is dirty, then it is either being washed
 1078                          * (but not yet cleaned) or it is still in the
 1079                          * laundry.  If it is still in the laundry, then we
 1080                          * start the cleaning operation. 
 1081                          *
 1082                          * decrement page_shortage on success to account for
 1083                          * the (future) cleaned page.  Otherwise we could wind
 1084                          * up laundering or cleaning too many pages.
 1085                          */
 1086                         vm_page_unlock_queues();
 1087                         if (vm_pageout_clean(m) != 0) {
 1088                                 --page_shortage;
 1089                                 --maxlaunder;
 1090                         }
 1091                         vm_page_lock_queues();
 1092 unlock_and_continue:
 1093                         vm_page_lock_assert(m, MA_NOTOWNED);
 1094                         VM_OBJECT_UNLOCK(object);
 1095                         if (mp != NULL) {
 1096                                 vm_page_unlock_queues();
 1097                                 if (vp != NULL)
 1098                                         vput(vp);
 1099                                 VFS_UNLOCK_GIANT(vfslocked);
 1100                                 vm_object_deallocate(object);
 1101                                 vn_finished_write(mp);
 1102                                 vm_page_lock_queues();
 1103                         }
 1104                         next = TAILQ_NEXT(&marker, pageq);
 1105                         TAILQ_REMOVE(&vm_page_queues[PQ_INACTIVE].pl,
 1106                                      &marker, pageq);
 1107                         vm_page_lock_assert(m, MA_NOTOWNED);
 1108                         continue;
 1109                 }
 1110                 vm_page_unlock(m);
 1111                 VM_OBJECT_UNLOCK(object);
 1112         }
 1113 
 1114         /*
 1115          * Compute the number of pages we want to try to move from the
 1116          * active queue to the inactive queue.
 1117          */
 1118         page_shortage = vm_paging_target() +
 1119                 cnt.v_inactive_target - cnt.v_inactive_count;
 1120         page_shortage += addl_page_shortage;
 1121 
 1122         /*
 1123          * Scan the active queue for things we can deactivate. We nominally
 1124          * track the per-page activity counter and use it to locate
 1125          * deactivation candidates.
 1126          */
 1127         pcount = cnt.v_active_count;
 1128         m = TAILQ_FIRST(&vm_page_queues[PQ_ACTIVE].pl);
 1129         mtx_assert(&vm_page_queue_mtx, MA_OWNED);
 1130 
 1131         while ((m != NULL) && (pcount-- > 0) && (page_shortage > 0)) {
 1132 
 1133                 KASSERT(m->queue == PQ_ACTIVE,
 1134                     ("vm_pageout_scan: page %p isn't active", m));
 1135 
 1136                 next = TAILQ_NEXT(m, pageq);
 1137                 if ((m->flags & PG_MARKER) != 0) {
 1138                         m = next;
 1139                         continue;
 1140                 }
 1141                 if (!vm_pageout_page_lock(m, &next)) {
 1142                         vm_page_unlock(m);
 1143                         m = next;
 1144                         continue;
 1145                 }
 1146                 object = m->object;
 1147                 if (!VM_OBJECT_TRYLOCK(object) &&
 1148                     !vm_pageout_fallback_object_lock(m, &next)) {
 1149                         VM_OBJECT_UNLOCK(object);
 1150                         vm_page_unlock(m);
 1151                         m = next;
 1152                         continue;
 1153                 }
 1154 
 1155                 /*
 1156                  * Don't deactivate pages that are busy.
 1157                  */
 1158                 if ((m->busy != 0) ||
 1159                     (m->oflags & VPO_BUSY) ||
 1160                     (m->hold_count != 0)) {
 1161                         vm_page_unlock(m);
 1162                         VM_OBJECT_UNLOCK(object);
 1163                         vm_page_requeue(m);
 1164                         m = next;
 1165                         continue;
 1166                 }
 1167 
 1168                 /*
 1169                  * The count for pagedaemon pages is done after checking the
 1170                  * page for eligibility...
 1171                  */
 1172                 cnt.v_pdpages++;
 1173 
 1174                 /*
 1175                  * Check to see "how much" the page has been used.
 1176                  */
 1177                 actcount = 0;
 1178                 if (object->ref_count != 0) {
 1179                         if (m->aflags & PGA_REFERENCED) {
 1180                                 actcount += 1;
 1181                         }
 1182                         actcount += pmap_ts_referenced(m);
 1183                         if (actcount) {
 1184                                 m->act_count += ACT_ADVANCE + actcount;
 1185                                 if (m->act_count > ACT_MAX)
 1186                                         m->act_count = ACT_MAX;
 1187                         }
 1188                 }
 1189 
 1190                 /*
 1191                  * Since we have "tested" this bit, we need to clear it now.
 1192                  */
 1193                 vm_page_aflag_clear(m, PGA_REFERENCED);
 1194 
 1195                 /*
 1196                  * Only if an object is currently being used, do we use the
 1197                  * page activation count stats.
 1198                  */
 1199                 if (actcount && (object->ref_count != 0)) {
 1200                         vm_page_requeue(m);
 1201                 } else {
 1202                         m->act_count -= min(m->act_count, ACT_DECLINE);
 1203                         if (vm_pageout_algorithm ||
 1204                             object->ref_count == 0 ||
 1205                             m->act_count == 0) {
 1206                                 page_shortage--;
 1207                                 if (object->ref_count == 0) {
 1208                                         KASSERT(!pmap_page_is_mapped(m),
 1209                                     ("vm_pageout_scan: page %p is mapped", m));
 1210                                         if (m->dirty == 0)
 1211                                                 vm_page_cache(m);
 1212                                         else
 1213                                                 vm_page_deactivate(m);
 1214                                 } else {
 1215                                         vm_page_deactivate(m);
 1216                                 }
 1217                         } else {
 1218                                 vm_page_requeue(m);
 1219                         }
 1220                 }
 1221                 vm_page_unlock(m);
 1222                 VM_OBJECT_UNLOCK(object);
 1223                 m = next;
 1224         }
 1225         vm_page_unlock_queues();
 1226 #if !defined(NO_SWAPPING)
 1227         /*
 1228          * Idle process swapout -- run once per second.
 1229          */
 1230         if (vm_swap_idle_enabled) {
 1231                 static long lsec;
 1232                 if (time_second != lsec) {
 1233                         vm_req_vmdaemon(VM_SWAP_IDLE);
 1234                         lsec = time_second;
 1235                 }
 1236         }
 1237 #endif
 1238                 
 1239         /*
 1240          * If we didn't get enough free pages, and we have skipped a vnode
 1241          * in a writeable object, wakeup the sync daemon.  And kick swapout
 1242          * if we did not get enough free pages.
 1243          */
 1244         if (vm_paging_target() > 0) {
 1245                 if (vnodes_skipped && vm_page_count_min())
 1246                         (void) speedup_syncer();
 1247 #if !defined(NO_SWAPPING)
 1248                 if (vm_swap_enabled && vm_page_count_target())
 1249                         vm_req_vmdaemon(VM_SWAP_NORMAL);
 1250 #endif
 1251         }
 1252 
 1253         /*
 1254          * If we are critically low on one of RAM or swap and low on
 1255          * the other, kill the largest process.  However, we avoid
 1256          * doing this on the first pass in order to give ourselves a
 1257          * chance to flush out dirty vnode-backed pages and to allow
 1258          * active pages to be moved to the inactive queue and reclaimed.
 1259          */
 1260         if (pass != 0 &&
 1261             ((swap_pager_avail < 64 && vm_page_count_min()) ||
 1262              (swap_pager_full && vm_paging_target() > 0)))
 1263                 vm_pageout_oom(VM_OOM_MEM);
 1264 }
 1265 
 1266 
 1267 void
 1268 vm_pageout_oom(int shortage)
 1269 {
 1270         struct proc *p, *bigproc;
 1271         vm_offset_t size, bigsize;
 1272         struct thread *td;
 1273         struct vmspace *vm;
 1274 
 1275         /*
 1276          * We keep the process bigproc locked once we find it to keep anyone
 1277          * from messing with it; however, there is a possibility of
 1278          * deadlock if process B is bigproc and one of it's child processes
 1279          * attempts to propagate a signal to B while we are waiting for A's
 1280          * lock while walking this list.  To avoid this, we don't block on
 1281          * the process lock but just skip a process if it is already locked.
 1282          */
 1283         bigproc = NULL;
 1284         bigsize = 0;
 1285         sx_slock(&allproc_lock);
 1286         FOREACH_PROC_IN_SYSTEM(p) {
 1287                 int breakout;
 1288 
 1289                 if (PROC_TRYLOCK(p) == 0)
 1290                         continue;
 1291                 /*
 1292                  * If this is a system, protected or killed process, skip it.
 1293                  */
 1294                 if (p->p_state != PRS_NORMAL ||
 1295                     (p->p_flag & (P_INEXEC | P_PROTECTED | P_SYSTEM)) ||
 1296                     (p->p_pid == 1) || P_KILLED(p) ||
 1297                     ((p->p_pid < 48) && (swap_pager_avail != 0))) {
 1298                         PROC_UNLOCK(p);
 1299                         continue;
 1300                 }
 1301                 /*
 1302                  * If the process is in a non-running type state,
 1303                  * don't touch it.  Check all the threads individually.
 1304                  */
 1305                 breakout = 0;
 1306                 FOREACH_THREAD_IN_PROC(p, td) {
 1307                         thread_lock(td);
 1308                         if (!TD_ON_RUNQ(td) &&
 1309                             !TD_IS_RUNNING(td) &&
 1310                             !TD_IS_SLEEPING(td) &&
 1311                             !TD_IS_SUSPENDED(td)) {
 1312                                 thread_unlock(td);
 1313                                 breakout = 1;
 1314                                 break;
 1315                         }
 1316                         thread_unlock(td);
 1317                 }
 1318                 if (breakout) {
 1319                         PROC_UNLOCK(p);
 1320                         continue;
 1321                 }
 1322                 /*
 1323                  * get the process size
 1324                  */
 1325                 vm = vmspace_acquire_ref(p);
 1326                 if (vm == NULL) {
 1327                         PROC_UNLOCK(p);
 1328                         continue;
 1329                 }
 1330                 if (!vm_map_trylock_read(&vm->vm_map)) {
 1331                         vmspace_free(vm);
 1332                         PROC_UNLOCK(p);
 1333                         continue;
 1334                 }
 1335                 size = vmspace_swap_count(vm);
 1336                 vm_map_unlock_read(&vm->vm_map);
 1337                 if (shortage == VM_OOM_MEM)
 1338                         size += vmspace_resident_count(vm);
 1339                 vmspace_free(vm);
 1340                 /*
 1341                  * if the this process is bigger than the biggest one
 1342                  * remember it.
 1343                  */
 1344                 if (size > bigsize) {
 1345                         if (bigproc != NULL)
 1346                                 PROC_UNLOCK(bigproc);
 1347                         bigproc = p;
 1348                         bigsize = size;
 1349                 } else
 1350                         PROC_UNLOCK(p);
 1351         }
 1352         sx_sunlock(&allproc_lock);
 1353         if (bigproc != NULL) {
 1354                 killproc(bigproc, "out of swap space");
 1355                 sched_nice(bigproc, PRIO_MIN);
 1356                 PROC_UNLOCK(bigproc);
 1357                 wakeup(&cnt.v_free_count);
 1358         }
 1359 }
 1360 
 1361 /*
 1362  * This routine tries to maintain the pseudo LRU active queue,
 1363  * so that during long periods of time where there is no paging,
 1364  * that some statistic accumulation still occurs.  This code
 1365  * helps the situation where paging just starts to occur.
 1366  */
 1367 static void
 1368 vm_pageout_page_stats()
 1369 {
 1370         vm_object_t object;
 1371         vm_page_t m,next;
 1372         int pcount,tpcount;             /* Number of pages to check */
 1373         static int fullintervalcount = 0;
 1374         int page_shortage;
 1375 
 1376         page_shortage = 
 1377             (cnt.v_inactive_target + cnt.v_cache_max + cnt.v_free_min) -
 1378             (cnt.v_free_count + cnt.v_inactive_count + cnt.v_cache_count);
 1379 
 1380         if (page_shortage <= 0)
 1381                 return;
 1382 
 1383         vm_page_lock_queues();
 1384         pcount = cnt.v_active_count;
 1385         fullintervalcount += vm_pageout_stats_interval;
 1386         if (fullintervalcount < vm_pageout_full_stats_interval) {
 1387                 tpcount = (int64_t)vm_pageout_stats_max * cnt.v_active_count /
 1388                     cnt.v_page_count;
 1389                 if (pcount > tpcount)
 1390                         pcount = tpcount;
 1391         } else {
 1392                 fullintervalcount = 0;
 1393         }
 1394 
 1395         m = TAILQ_FIRST(&vm_page_queues[PQ_ACTIVE].pl);
 1396         while ((m != NULL) && (pcount-- > 0)) {
 1397                 int actcount;
 1398 
 1399                 KASSERT(m->queue == PQ_ACTIVE,
 1400                     ("vm_pageout_page_stats: page %p isn't active", m));
 1401 
 1402                 next = TAILQ_NEXT(m, pageq);
 1403                 if ((m->flags & PG_MARKER) != 0) {
 1404                         m = next;
 1405                         continue;
 1406                 }
 1407                 vm_page_lock_assert(m, MA_NOTOWNED);
 1408                 if (!vm_pageout_page_lock(m, &next)) {
 1409                         vm_page_unlock(m);
 1410                         m = next;
 1411                         continue;
 1412                 }
 1413                 object = m->object;
 1414                 if (!VM_OBJECT_TRYLOCK(object) &&
 1415                     !vm_pageout_fallback_object_lock(m, &next)) {
 1416                         VM_OBJECT_UNLOCK(object);
 1417                         vm_page_unlock(m);
 1418                         m = next;
 1419                         continue;
 1420                 }
 1421 
 1422                 /*
 1423                  * Don't deactivate pages that are busy.
 1424                  */
 1425                 if ((m->busy != 0) ||
 1426                     (m->oflags & VPO_BUSY) ||
 1427                     (m->hold_count != 0)) {
 1428                         vm_page_unlock(m);
 1429                         VM_OBJECT_UNLOCK(object);
 1430                         vm_page_requeue(m);
 1431                         m = next;
 1432                         continue;
 1433                 }
 1434 
 1435                 actcount = 0;
 1436                 if (m->aflags & PGA_REFERENCED) {
 1437                         vm_page_aflag_clear(m, PGA_REFERENCED);
 1438                         actcount += 1;
 1439                 }
 1440 
 1441                 actcount += pmap_ts_referenced(m);
 1442                 if (actcount) {
 1443                         m->act_count += ACT_ADVANCE + actcount;
 1444                         if (m->act_count > ACT_MAX)
 1445                                 m->act_count = ACT_MAX;
 1446                         vm_page_requeue(m);
 1447                 } else {
 1448                         if (m->act_count == 0) {
 1449                                 /*
 1450                                  * We turn off page access, so that we have
 1451                                  * more accurate RSS stats.  We don't do this
 1452                                  * in the normal page deactivation when the
 1453                                  * system is loaded VM wise, because the
 1454                                  * cost of the large number of page protect
 1455                                  * operations would be higher than the value
 1456                                  * of doing the operation.
 1457                                  */
 1458                                 pmap_remove_all(m);
 1459                                 vm_page_deactivate(m);
 1460                         } else {
 1461                                 m->act_count -= min(m->act_count, ACT_DECLINE);
 1462                                 vm_page_requeue(m);
 1463                         }
 1464                 }
 1465                 vm_page_unlock(m);
 1466                 VM_OBJECT_UNLOCK(object);
 1467                 m = next;
 1468         }
 1469         vm_page_unlock_queues();
 1470 }
 1471 
 1472 /*
 1473  *      vm_pageout is the high level pageout daemon.
 1474  */
 1475 static void
 1476 vm_pageout()
 1477 {
 1478         int error, pass;
 1479 
 1480         /*
 1481          * Initialize some paging parameters.
 1482          */
 1483         cnt.v_interrupt_free_min = 2;
 1484         if (cnt.v_page_count < 2000)
 1485                 vm_pageout_page_count = 8;
 1486 
 1487         /*
 1488          * v_free_reserved needs to include enough for the largest
 1489          * swap pager structures plus enough for any pv_entry structs
 1490          * when paging. 
 1491          */
 1492         if (cnt.v_page_count > 1024)
 1493                 cnt.v_free_min = 4 + (cnt.v_page_count - 1024) / 200;
 1494         else
 1495                 cnt.v_free_min = 4;
 1496         cnt.v_pageout_free_min = (2*MAXBSIZE)/PAGE_SIZE +
 1497             cnt.v_interrupt_free_min;
 1498         cnt.v_free_reserved = vm_pageout_page_count +
 1499             cnt.v_pageout_free_min + (cnt.v_page_count / 768);
 1500         cnt.v_free_severe = cnt.v_free_min / 2;
 1501         cnt.v_free_min += cnt.v_free_reserved;
 1502         cnt.v_free_severe += cnt.v_free_reserved;
 1503 
 1504         /*
 1505          * v_free_target and v_cache_min control pageout hysteresis.  Note
 1506          * that these are more a measure of the VM cache queue hysteresis
 1507          * then the VM free queue.  Specifically, v_free_target is the
 1508          * high water mark (free+cache pages).
 1509          *
 1510          * v_free_reserved + v_cache_min (mostly means v_cache_min) is the
 1511          * low water mark, while v_free_min is the stop.  v_cache_min must
 1512          * be big enough to handle memory needs while the pageout daemon
 1513          * is signalled and run to free more pages.
 1514          */
 1515         if (cnt.v_free_count > 6144)
 1516                 cnt.v_free_target = 4 * cnt.v_free_min + cnt.v_free_reserved;
 1517         else
 1518                 cnt.v_free_target = 2 * cnt.v_free_min + cnt.v_free_reserved;
 1519 
 1520         if (cnt.v_free_count > 2048) {
 1521                 cnt.v_cache_min = cnt.v_free_target;
 1522                 cnt.v_cache_max = 2 * cnt.v_cache_min;
 1523                 cnt.v_inactive_target = (3 * cnt.v_free_target) / 2;
 1524         } else {
 1525                 cnt.v_cache_min = 0;
 1526                 cnt.v_cache_max = 0;
 1527                 cnt.v_inactive_target = cnt.v_free_count / 4;
 1528         }
 1529         if (cnt.v_inactive_target > cnt.v_free_count / 3)
 1530                 cnt.v_inactive_target = cnt.v_free_count / 3;
 1531 
 1532         /* XXX does not really belong here */
 1533         if (vm_page_max_wired == 0)
 1534                 vm_page_max_wired = cnt.v_free_count / 3;
 1535 
 1536         if (vm_pageout_stats_max == 0)
 1537                 vm_pageout_stats_max = cnt.v_free_target;
 1538 
 1539         /*
 1540          * Set interval in seconds for stats scan.
 1541          */
 1542         if (vm_pageout_stats_interval == 0)
 1543                 vm_pageout_stats_interval = 5;
 1544         if (vm_pageout_full_stats_interval == 0)
 1545                 vm_pageout_full_stats_interval = vm_pageout_stats_interval * 4;
 1546 
 1547         swap_pager_swap_init();
 1548         pass = 0;
 1549         /*
 1550          * The pageout daemon is never done, so loop forever.
 1551          */
 1552         while (TRUE) {
 1553                 /*
 1554                  * If we have enough free memory, wakeup waiters.  Do
 1555                  * not clear vm_pages_needed until we reach our target,
 1556                  * otherwise we may be woken up over and over again and
 1557                  * waste a lot of cpu.
 1558                  */
 1559                 mtx_lock(&vm_page_queue_free_mtx);
 1560                 if (vm_pages_needed && !vm_page_count_min()) {
 1561                         if (!vm_paging_needed())
 1562                                 vm_pages_needed = 0;
 1563                         wakeup(&cnt.v_free_count);
 1564                 }
 1565                 if (vm_pages_needed) {
 1566                         /*
 1567                          * Still not done, take a second pass without waiting
 1568                          * (unlimited dirty cleaning), otherwise sleep a bit
 1569                          * and try again.
 1570                          */
 1571                         ++pass;
 1572                         if (pass > 1)
 1573                                 msleep(&vm_pages_needed,
 1574                                     &vm_page_queue_free_mtx, PVM, "psleep",
 1575                                     hz / 2);
 1576                 } else {
 1577                         /*
 1578                          * Good enough, sleep & handle stats.  Prime the pass
 1579                          * for the next run.
 1580                          */
 1581                         if (pass > 1)
 1582                                 pass = 1;
 1583                         else
 1584                                 pass = 0;
 1585                         error = msleep(&vm_pages_needed,
 1586                             &vm_page_queue_free_mtx, PVM, "psleep",
 1587                             vm_pageout_stats_interval * hz);
 1588                         if (error && !vm_pages_needed) {
 1589                                 mtx_unlock(&vm_page_queue_free_mtx);
 1590                                 pass = 0;
 1591                                 vm_pageout_page_stats();
 1592                                 continue;
 1593                         }
 1594                 }
 1595                 if (vm_pages_needed)
 1596                         cnt.v_pdwakeups++;
 1597                 mtx_unlock(&vm_page_queue_free_mtx);
 1598                 vm_pageout_scan(pass);
 1599         }
 1600 }
 1601 
 1602 /*
 1603  * Unless the free page queue lock is held by the caller, this function
 1604  * should be regarded as advisory.  Specifically, the caller should
 1605  * not msleep() on &cnt.v_free_count following this function unless
 1606  * the free page queue lock is held until the msleep() is performed.
 1607  */
 1608 void
 1609 pagedaemon_wakeup()
 1610 {
 1611 
 1612         if (!vm_pages_needed && curthread->td_proc != pageproc) {
 1613                 vm_pages_needed = 1;
 1614                 wakeup(&vm_pages_needed);
 1615         }
 1616 }
 1617 
 1618 #if !defined(NO_SWAPPING)
 1619 static void
 1620 vm_req_vmdaemon(int req)
 1621 {
 1622         static int lastrun = 0;
 1623 
 1624         mtx_lock(&vm_daemon_mtx);
 1625         vm_pageout_req_swapout |= req;
 1626         if ((ticks > (lastrun + hz)) || (ticks < lastrun)) {
 1627                 wakeup(&vm_daemon_needed);
 1628                 lastrun = ticks;
 1629         }
 1630         mtx_unlock(&vm_daemon_mtx);
 1631 }
 1632 
 1633 static void
 1634 vm_daemon()
 1635 {
 1636         struct rlimit rsslim;
 1637         struct proc *p;
 1638         struct thread *td;
 1639         struct vmspace *vm;
 1640         int breakout, swapout_flags, tryagain, attempts;
 1641 #ifdef RACCT
 1642         uint64_t rsize, ravailable;
 1643 #endif
 1644 
 1645         while (TRUE) {
 1646                 mtx_lock(&vm_daemon_mtx);
 1647 #ifdef RACCT
 1648                 msleep(&vm_daemon_needed, &vm_daemon_mtx, PPAUSE, "psleep", hz);
 1649 #else
 1650                 msleep(&vm_daemon_needed, &vm_daemon_mtx, PPAUSE, "psleep", 0);
 1651 #endif
 1652                 swapout_flags = vm_pageout_req_swapout;
 1653                 vm_pageout_req_swapout = 0;
 1654                 mtx_unlock(&vm_daemon_mtx);
 1655                 if (swapout_flags)
 1656                         swapout_procs(swapout_flags);
 1657 
 1658                 /*
 1659                  * scan the processes for exceeding their rlimits or if
 1660                  * process is swapped out -- deactivate pages
 1661                  */
 1662                 tryagain = 0;
 1663                 attempts = 0;
 1664 again:
 1665                 attempts++;
 1666                 sx_slock(&allproc_lock);
 1667                 FOREACH_PROC_IN_SYSTEM(p) {
 1668                         vm_pindex_t limit, size;
 1669 
 1670                         /*
 1671                          * if this is a system process or if we have already
 1672                          * looked at this process, skip it.
 1673                          */
 1674                         PROC_LOCK(p);
 1675                         if (p->p_state != PRS_NORMAL ||
 1676                             p->p_flag & (P_INEXEC | P_SYSTEM | P_WEXIT)) {
 1677                                 PROC_UNLOCK(p);
 1678                                 continue;
 1679                         }
 1680                         /*
 1681                          * if the process is in a non-running type state,
 1682                          * don't touch it.
 1683                          */
 1684                         breakout = 0;
 1685                         FOREACH_THREAD_IN_PROC(p, td) {
 1686                                 thread_lock(td);
 1687                                 if (!TD_ON_RUNQ(td) &&
 1688                                     !TD_IS_RUNNING(td) &&
 1689                                     !TD_IS_SLEEPING(td) &&
 1690                                     !TD_IS_SUSPENDED(td)) {
 1691                                         thread_unlock(td);
 1692                                         breakout = 1;
 1693                                         break;
 1694                                 }
 1695                                 thread_unlock(td);
 1696                         }
 1697                         if (breakout) {
 1698                                 PROC_UNLOCK(p);
 1699                                 continue;
 1700                         }
 1701                         /*
 1702                          * get a limit
 1703                          */
 1704                         lim_rlimit(p, RLIMIT_RSS, &rsslim);
 1705                         limit = OFF_TO_IDX(
 1706                             qmin(rsslim.rlim_cur, rsslim.rlim_max));
 1707 
 1708                         /*
 1709                          * let processes that are swapped out really be
 1710                          * swapped out set the limit to nothing (will force a
 1711                          * swap-out.)
 1712                          */
 1713                         if ((p->p_flag & P_INMEM) == 0)
 1714                                 limit = 0;      /* XXX */
 1715                         vm = vmspace_acquire_ref(p);
 1716                         PROC_UNLOCK(p);
 1717                         if (vm == NULL)
 1718                                 continue;
 1719 
 1720                         size = vmspace_resident_count(vm);
 1721                         if (limit >= 0 && size >= limit) {
 1722                                 vm_pageout_map_deactivate_pages(
 1723                                     &vm->vm_map, limit);
 1724                         }
 1725 #ifdef RACCT
 1726                         rsize = IDX_TO_OFF(size);
 1727                         PROC_LOCK(p);
 1728                         racct_set(p, RACCT_RSS, rsize);
 1729                         ravailable = racct_get_available(p, RACCT_RSS);
 1730                         PROC_UNLOCK(p);
 1731                         if (rsize > ravailable) {
 1732                                 /*
 1733                                  * Don't be overly aggressive; this might be
 1734                                  * an innocent process, and the limit could've
 1735                                  * been exceeded by some memory hog.  Don't
 1736                                  * try to deactivate more than 1/4th of process'
 1737                                  * resident set size.
 1738                                  */
 1739                                 if (attempts <= 8) {
 1740                                         if (ravailable < rsize - (rsize / 4))
 1741                                                 ravailable = rsize - (rsize / 4);
 1742                                 }
 1743                                 vm_pageout_map_deactivate_pages(
 1744                                     &vm->vm_map, OFF_TO_IDX(ravailable));
 1745                                 /* Update RSS usage after paging out. */
 1746                                 size = vmspace_resident_count(vm);
 1747                                 rsize = IDX_TO_OFF(size);
 1748                                 PROC_LOCK(p);
 1749                                 racct_set(p, RACCT_RSS, rsize);
 1750                                 PROC_UNLOCK(p);
 1751                                 if (rsize > ravailable)
 1752                                         tryagain = 1;
 1753                         }
 1754 #endif
 1755                         vmspace_free(vm);
 1756                 }
 1757                 sx_sunlock(&allproc_lock);
 1758                 if (tryagain != 0 && attempts <= 10)
 1759                         goto again;
 1760         }
 1761 }
 1762 #endif                  /* !defined(NO_SWAPPING) */

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