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("$FreeBSD$");
   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 /*
  109  * System initialization
  110  */
  111 
  112 /* the kernel process "vm_pageout"*/
  113 static void vm_pageout(void);
  114 static int vm_pageout_clean(vm_page_t);
  115 static void vm_pageout_scan(int pass);
  116 
  117 struct proc *pageproc;
  118 
  119 static struct kproc_desc page_kp = {
  120         "pagedaemon",
  121         vm_pageout,
  122         &pageproc
  123 };
  124 SYSINIT(pagedaemon, SI_SUB_KTHREAD_PAGE, SI_ORDER_FIRST, kproc_start,
  125     &page_kp);
  126 
  127 #if !defined(NO_SWAPPING)
  128 /* the kernel process "vm_daemon"*/
  129 static void vm_daemon(void);
  130 static struct   proc *vmproc;
  131 
  132 static struct kproc_desc vm_kp = {
  133         "vmdaemon",
  134         vm_daemon,
  135         &vmproc
  136 };
  137 SYSINIT(vmdaemon, SI_SUB_KTHREAD_VM, SI_ORDER_FIRST, kproc_start, &vm_kp);
  138 #endif
  139 
  140 
  141 int vm_pages_needed;            /* Event on which pageout daemon sleeps */
  142 int vm_pageout_deficit;         /* Estimated number of pages deficit */
  143 int vm_pageout_pages_needed;    /* flag saying that the pageout daemon needs pages */
  144 
  145 #if !defined(NO_SWAPPING)
  146 static int vm_pageout_req_swapout;      /* XXX */
  147 static int vm_daemon_needed;
  148 static struct mtx vm_daemon_mtx;
  149 /* Allow for use by vm_pageout before vm_daemon is initialized. */
  150 MTX_SYSINIT(vm_daemon, &vm_daemon_mtx, "vm daemon", MTX_DEF);
  151 #endif
  152 static int vm_max_launder = 32;
  153 static int vm_pageout_stats_max=0, vm_pageout_stats_interval = 0;
  154 static int vm_pageout_full_stats_interval = 0;
  155 static int vm_pageout_algorithm=0;
  156 static int defer_swap_pageouts=0;
  157 static int disable_swap_pageouts=0;
  158 
  159 #if defined(NO_SWAPPING)
  160 static int vm_swap_enabled=0;
  161 static int vm_swap_idle_enabled=0;
  162 #else
  163 static int vm_swap_enabled=1;
  164 static int vm_swap_idle_enabled=0;
  165 #endif
  166 
  167 SYSCTL_INT(_vm, VM_PAGEOUT_ALGORITHM, pageout_algorithm,
  168         CTLFLAG_RW, &vm_pageout_algorithm, 0, "LRU page mgmt");
  169 
  170 SYSCTL_INT(_vm, OID_AUTO, max_launder,
  171         CTLFLAG_RW, &vm_max_launder, 0, "Limit dirty flushes in pageout");
  172 
  173 SYSCTL_INT(_vm, OID_AUTO, pageout_stats_max,
  174         CTLFLAG_RW, &vm_pageout_stats_max, 0, "Max pageout stats scan length");
  175 
  176 SYSCTL_INT(_vm, OID_AUTO, pageout_full_stats_interval,
  177         CTLFLAG_RW, &vm_pageout_full_stats_interval, 0, "Interval for full stats scan");
  178 
  179 SYSCTL_INT(_vm, OID_AUTO, pageout_stats_interval,
  180         CTLFLAG_RW, &vm_pageout_stats_interval, 0, "Interval for partial stats scan");
  181 
  182 #if defined(NO_SWAPPING)
  183 SYSCTL_INT(_vm, VM_SWAPPING_ENABLED, swap_enabled,
  184         CTLFLAG_RD, &vm_swap_enabled, 0, "Enable entire process swapout");
  185 SYSCTL_INT(_vm, OID_AUTO, swap_idle_enabled,
  186         CTLFLAG_RD, &vm_swap_idle_enabled, 0, "Allow swapout on idle criteria");
  187 #else
  188 SYSCTL_INT(_vm, VM_SWAPPING_ENABLED, swap_enabled,
  189         CTLFLAG_RW, &vm_swap_enabled, 0, "Enable entire process swapout");
  190 SYSCTL_INT(_vm, OID_AUTO, swap_idle_enabled,
  191         CTLFLAG_RW, &vm_swap_idle_enabled, 0, "Allow swapout on idle criteria");
  192 #endif
  193 
  194 SYSCTL_INT(_vm, OID_AUTO, defer_swapspace_pageouts,
  195         CTLFLAG_RW, &defer_swap_pageouts, 0, "Give preference to dirty pages in mem");
  196 
  197 SYSCTL_INT(_vm, OID_AUTO, disable_swapspace_pageouts,
  198         CTLFLAG_RW, &disable_swap_pageouts, 0, "Disallow swapout of dirty pages");
  199 
  200 static int pageout_lock_miss;
  201 SYSCTL_INT(_vm, OID_AUTO, pageout_lock_miss,
  202         CTLFLAG_RD, &pageout_lock_miss, 0, "vget() lock misses during pageout");
  203 
  204 #define VM_PAGEOUT_PAGE_COUNT 16
  205 int vm_pageout_page_count = VM_PAGEOUT_PAGE_COUNT;
  206 
  207 int vm_page_max_wired;          /* XXX max # of wired pages system-wide */
  208 SYSCTL_INT(_vm, OID_AUTO, max_wired,
  209         CTLFLAG_RW, &vm_page_max_wired, 0, "System-wide limit to wired page count");
  210 
  211 #if !defined(NO_SWAPPING)
  212 static void vm_pageout_map_deactivate_pages(vm_map_t, long);
  213 static void vm_pageout_object_deactivate_pages(pmap_t, vm_object_t, long);
  214 static void vm_req_vmdaemon(int req);
  215 #endif
  216 static void vm_pageout_page_stats(void);
  217 
  218 /*
  219  * vm_pageout_fallback_object_lock:
  220  * 
  221  * Lock vm object currently associated with `m'. VM_OBJECT_TRYLOCK is
  222  * known to have failed and page queue must be either PQ_ACTIVE or
  223  * PQ_INACTIVE.  To avoid lock order violation, unlock the page queues
  224  * while locking the vm object.  Use marker page to detect page queue
  225  * changes and maintain notion of next page on page queue.  Return
  226  * TRUE if no changes were detected, FALSE otherwise.  vm object is
  227  * locked on return.
  228  * 
  229  * This function depends on both the lock portion of struct vm_object
  230  * and normal struct vm_page being type stable.
  231  */
  232 boolean_t
  233 vm_pageout_fallback_object_lock(vm_page_t m, vm_page_t *next)
  234 {
  235         struct vm_page marker;
  236         boolean_t unchanged;
  237         u_short queue;
  238         vm_object_t object;
  239 
  240         /*
  241          * Initialize our marker
  242          */
  243         bzero(&marker, sizeof(marker));
  244         marker.flags = PG_FICTITIOUS | PG_MARKER;
  245         marker.oflags = VPO_BUSY;
  246         marker.queue = m->queue;
  247         marker.wire_count = 1;
  248 
  249         queue = m->queue;
  250         object = m->object;
  251         
  252         TAILQ_INSERT_AFTER(&vm_page_queues[queue].pl,
  253                            m, &marker, pageq);
  254         vm_page_unlock_queues();
  255         VM_OBJECT_LOCK(object);
  256         vm_page_lock_queues();
  257 
  258         /* Page queue might have changed. */
  259         *next = TAILQ_NEXT(&marker, pageq);
  260         unchanged = (m->queue == queue &&
  261                      m->object == object &&
  262                      &marker == TAILQ_NEXT(m, pageq));
  263         TAILQ_REMOVE(&vm_page_queues[queue].pl,
  264                      &marker, pageq);
  265         return (unchanged);
  266 }
  267 
  268 /*
  269  * vm_pageout_clean:
  270  *
  271  * Clean the page and remove it from the laundry.
  272  * 
  273  * We set the busy bit to cause potential page faults on this page to
  274  * block.  Note the careful timing, however, the busy bit isn't set till
  275  * late and we cannot do anything that will mess with the page.
  276  */
  277 static int
  278 vm_pageout_clean(m)
  279         vm_page_t m;
  280 {
  281         vm_object_t object;
  282         vm_page_t mc[2*vm_pageout_page_count], pb, ps;
  283         int pageout_count;
  284         int ib, is, page_base;
  285         vm_pindex_t pindex = m->pindex;
  286 
  287         mtx_assert(&vm_page_queue_mtx, MA_OWNED);
  288         VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
  289 
  290         /*
  291          * It doesn't cost us anything to pageout OBJT_DEFAULT or OBJT_SWAP
  292          * with the new swapper, but we could have serious problems paging
  293          * out other object types if there is insufficient memory.  
  294          *
  295          * Unfortunately, checking free memory here is far too late, so the
  296          * check has been moved up a procedural level.
  297          */
  298 
  299         /*
  300          * Can't clean the page if it's busy or held.
  301          */
  302         if ((m->hold_count != 0) ||
  303             ((m->busy != 0) || (m->oflags & VPO_BUSY))) {
  304                 return 0;
  305         }
  306 
  307         mc[vm_pageout_page_count] = pb = ps = m;
  308         pageout_count = 1;
  309         page_base = vm_pageout_page_count;
  310         ib = 1;
  311         is = 1;
  312 
  313         /*
  314          * Scan object for clusterable pages.
  315          *
  316          * We can cluster ONLY if: ->> the page is NOT
  317          * clean, wired, busy, held, or mapped into a
  318          * buffer, and one of the following:
  319          * 1) The page is inactive, or a seldom used
  320          *    active page.
  321          * -or-
  322          * 2) we force the issue.
  323          *
  324          * During heavy mmap/modification loads the pageout
  325          * daemon can really fragment the underlying file
  326          * due to flushing pages out of order and not trying
  327          * align the clusters (which leave sporatic out-of-order
  328          * holes).  To solve this problem we do the reverse scan
  329          * first and attempt to align our cluster, then do a 
  330          * forward scan if room remains.
  331          */
  332         object = m->object;
  333 more:
  334         while (ib && pageout_count < vm_pageout_page_count) {
  335                 vm_page_t p;
  336 
  337                 if (ib > pindex) {
  338                         ib = 0;
  339                         break;
  340                 }
  341 
  342                 if ((p = vm_page_prev(pb)) == NULL ||
  343                     (p->oflags & VPO_BUSY) != 0 || p->busy != 0) {
  344                         ib = 0;
  345                         break;
  346                 }
  347                 vm_page_test_dirty(p);
  348                 if (p->dirty == 0 ||
  349                     p->queue != PQ_INACTIVE ||
  350                     p->hold_count != 0) {       /* may be undergoing I/O */
  351                         ib = 0;
  352                         break;
  353                 }
  354                 mc[--page_base] = pb = p;
  355                 ++pageout_count;
  356                 ++ib;
  357                 /*
  358                  * alignment boundry, stop here and switch directions.  Do
  359                  * not clear ib.
  360                  */
  361                 if ((pindex - (ib - 1)) % vm_pageout_page_count == 0)
  362                         break;
  363         }
  364 
  365         while (pageout_count < vm_pageout_page_count && 
  366             pindex + is < object->size) {
  367                 vm_page_t p;
  368 
  369                 if ((p = vm_page_next(ps)) == NULL ||
  370                     (p->oflags & VPO_BUSY) != 0 || p->busy != 0)
  371                         break;
  372                 vm_page_test_dirty(p);
  373                 if (p->dirty == 0 ||
  374                     p->queue != PQ_INACTIVE ||
  375                     p->hold_count != 0) {       /* may be undergoing I/O */
  376                         break;
  377                 }
  378                 mc[page_base + pageout_count] = ps = p;
  379                 ++pageout_count;
  380                 ++is;
  381         }
  382 
  383         /*
  384          * If we exhausted our forward scan, continue with the reverse scan
  385          * when possible, even past a page boundry.  This catches boundry
  386          * conditions.
  387          */
  388         if (ib && pageout_count < vm_pageout_page_count)
  389                 goto more;
  390 
  391         /*
  392          * we allow reads during pageouts...
  393          */
  394         return (vm_pageout_flush(&mc[page_base], pageout_count, 0, 0, NULL,
  395             NULL));
  396 }
  397 
  398 /*
  399  * vm_pageout_flush() - launder the given pages
  400  *
  401  *      The given pages are laundered.  Note that we setup for the start of
  402  *      I/O ( i.e. busy the page ), mark it read-only, and bump the object
  403  *      reference count all in here rather then in the parent.  If we want
  404  *      the parent to do more sophisticated things we may have to change
  405  *      the ordering.
  406  *
  407  *      Returned runlen is the count of pages between mreq and first
  408  *      page after mreq with status VM_PAGER_AGAIN.
  409  *      *eio is set to TRUE if pager returned VM_PAGER_ERROR or VM_PAGER_FAIL
  410  *      for any page in runlen set.
  411  */
  412 int
  413 vm_pageout_flush(vm_page_t *mc, int count, int flags, int mreq, int *prunlen,
  414     boolean_t *eio)
  415 {
  416         vm_object_t object = mc[0]->object;
  417         int pageout_status[count];
  418         int numpagedout = 0;
  419         int i, runlen;
  420 
  421         mtx_assert(&vm_page_queue_mtx, MA_OWNED);
  422         VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
  423         /*
  424          * Initiate I/O.  Bump the vm_page_t->busy counter and
  425          * mark the pages read-only.
  426          *
  427          * We do not have to fixup the clean/dirty bits here... we can
  428          * allow the pager to do it after the I/O completes.
  429          *
  430          * NOTE! mc[i]->dirty may be partial or fragmented due to an
  431          * edge case with file fragments.
  432          */
  433         for (i = 0; i < count; i++) {
  434                 KASSERT(mc[i]->valid == VM_PAGE_BITS_ALL,
  435                     ("vm_pageout_flush: partially invalid page %p index %d/%d",
  436                         mc[i], i, count));
  437                 vm_page_io_start(mc[i]);
  438                 pmap_remove_write(mc[i]);
  439         }
  440         vm_page_unlock_queues();
  441         vm_object_pip_add(object, count);
  442 
  443         vm_pager_put_pages(object, mc, count, flags, pageout_status);
  444 
  445         runlen = count - mreq;
  446         if (eio != NULL)
  447                 *eio = FALSE;
  448         vm_page_lock_queues();
  449         for (i = 0; i < count; i++) {
  450                 vm_page_t mt = mc[i];
  451 
  452                 KASSERT(pageout_status[i] == VM_PAGER_PEND ||
  453                     (mt->flags & PG_WRITEABLE) == 0,
  454                     ("vm_pageout_flush: page %p is not write protected", mt));
  455                 switch (pageout_status[i]) {
  456                 case VM_PAGER_OK:
  457                 case VM_PAGER_PEND:
  458                         numpagedout++;
  459                         break;
  460                 case VM_PAGER_BAD:
  461                         /*
  462                          * Page outside of range of object. Right now we
  463                          * essentially lose the changes by pretending it
  464                          * worked.
  465                          */
  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                         if (eio != NULL && i >= mreq && i - mreq < runlen)
  477                                 *eio = TRUE;
  478                         break;
  479                 case VM_PAGER_AGAIN:
  480                         if (i >= mreq && i - mreq < runlen)
  481                                 runlen = i - mreq;
  482                         break;
  483                 }
  484 
  485                 /*
  486                  * If the operation is still going, leave the page busy to
  487                  * block all other accesses. Also, leave the paging in
  488                  * progress indicator set so that we don't attempt an object
  489                  * collapse.
  490                  */
  491                 if (pageout_status[i] != VM_PAGER_PEND) {
  492                         vm_object_pip_wakeup(object);
  493                         vm_page_io_finish(mt);
  494                         if (vm_page_count_severe())
  495                                 vm_page_try_to_cache(mt);
  496                 }
  497         }
  498         if (prunlen != NULL)
  499                 *prunlen = runlen;
  500         return (numpagedout);
  501 }
  502 
  503 #if !defined(NO_SWAPPING)
  504 /*
  505  *      vm_pageout_object_deactivate_pages
  506  *
  507  *      deactivate enough pages to satisfy the inactive target
  508  *      requirements or if vm_page_proc_limit is set, then
  509  *      deactivate all of the pages in the object and its
  510  *      backing_objects.
  511  *
  512  *      The object and map must be locked.
  513  */
  514 static void
  515 vm_pageout_object_deactivate_pages(pmap, first_object, desired)
  516         pmap_t pmap;
  517         vm_object_t first_object;
  518         long desired;
  519 {
  520         vm_object_t backing_object, object;
  521         vm_page_t p, next;
  522         int actcount, rcount, remove_mode;
  523 
  524         VM_OBJECT_LOCK_ASSERT(first_object, MA_OWNED);
  525         if (first_object->type == OBJT_DEVICE ||
  526             first_object->type == OBJT_SG ||
  527             first_object->type == OBJT_PHYS)
  528                 return;
  529         for (object = first_object;; object = backing_object) {
  530                 if (pmap_resident_count(pmap) <= desired)
  531                         goto unlock_return;
  532                 if (object->paging_in_progress)
  533                         goto unlock_return;
  534 
  535                 remove_mode = 0;
  536                 if (object->shadow_count > 1)
  537                         remove_mode = 1;
  538                 /*
  539                  * scan the objects entire memory queue
  540                  */
  541                 rcount = object->resident_page_count;
  542                 p = TAILQ_FIRST(&object->memq);
  543                 vm_page_lock_queues();
  544                 while (p && (rcount-- > 0)) {
  545                         if (pmap_resident_count(pmap) <= desired) {
  546                                 vm_page_unlock_queues();
  547                                 goto unlock_return;
  548                         }
  549                         next = TAILQ_NEXT(p, listq);
  550                         cnt.v_pdpages++;
  551                         if (p->wire_count != 0 ||
  552                             p->hold_count != 0 ||
  553                             p->busy != 0 ||
  554                             (p->oflags & VPO_BUSY) ||
  555                             (p->flags & PG_UNMANAGED) ||
  556                             !pmap_page_exists_quick(pmap, p)) {
  557                                 p = next;
  558                                 continue;
  559                         }
  560                         actcount = pmap_ts_referenced(p);
  561                         if (actcount) {
  562                                 vm_page_flag_set(p, PG_REFERENCED);
  563                         } else if (p->flags & PG_REFERENCED) {
  564                                 actcount = 1;
  565                         }
  566                         if ((p->queue != PQ_ACTIVE) &&
  567                                 (p->flags & PG_REFERENCED)) {
  568                                 vm_page_activate(p);
  569                                 p->act_count += actcount;
  570                                 vm_page_flag_clear(p, PG_REFERENCED);
  571                         } else if (p->queue == PQ_ACTIVE) {
  572                                 if ((p->flags & PG_REFERENCED) == 0) {
  573                                         p->act_count -= min(p->act_count, ACT_DECLINE);
  574                                         if (!remove_mode && (vm_pageout_algorithm || (p->act_count == 0))) {
  575                                                 pmap_remove_all(p);
  576                                                 vm_page_deactivate(p);
  577                                         } else {
  578                                                 vm_page_requeue(p);
  579                                         }
  580                                 } else {
  581                                         vm_page_activate(p);
  582                                         vm_page_flag_clear(p, PG_REFERENCED);
  583                                         if (p->act_count < (ACT_MAX - ACT_ADVANCE))
  584                                                 p->act_count += ACT_ADVANCE;
  585                                         vm_page_requeue(p);
  586                                 }
  587                         } else if (p->queue == PQ_INACTIVE) {
  588                                 pmap_remove_all(p);
  589                         }
  590                         p = next;
  591                 }
  592                 vm_page_unlock_queues();
  593                 if ((backing_object = object->backing_object) == NULL)
  594                         goto unlock_return;
  595                 VM_OBJECT_LOCK(backing_object);
  596                 if (object != first_object)
  597                         VM_OBJECT_UNLOCK(object);
  598         }
  599 unlock_return:
  600         if (object != first_object)
  601                 VM_OBJECT_UNLOCK(object);
  602 }
  603 
  604 /*
  605  * deactivate some number of pages in a map, try to do it fairly, but
  606  * that is really hard to do.
  607  */
  608 static void
  609 vm_pageout_map_deactivate_pages(map, desired)
  610         vm_map_t map;
  611         long desired;
  612 {
  613         vm_map_entry_t tmpe;
  614         vm_object_t obj, bigobj;
  615         int nothingwired;
  616 
  617         if (!vm_map_trylock(map))
  618                 return;
  619 
  620         bigobj = NULL;
  621         nothingwired = TRUE;
  622 
  623         /*
  624          * first, search out the biggest object, and try to free pages from
  625          * that.
  626          */
  627         tmpe = map->header.next;
  628         while (tmpe != &map->header) {
  629                 if ((tmpe->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
  630                         obj = tmpe->object.vm_object;
  631                         if (obj != NULL && VM_OBJECT_TRYLOCK(obj)) {
  632                                 if (obj->shadow_count <= 1 &&
  633                                     (bigobj == NULL ||
  634                                      bigobj->resident_page_count < obj->resident_page_count)) {
  635                                         if (bigobj != NULL)
  636                                                 VM_OBJECT_UNLOCK(bigobj);
  637                                         bigobj = obj;
  638                                 } else
  639                                         VM_OBJECT_UNLOCK(obj);
  640                         }
  641                 }
  642                 if (tmpe->wired_count > 0)
  643                         nothingwired = FALSE;
  644                 tmpe = tmpe->next;
  645         }
  646 
  647         if (bigobj != NULL) {
  648                 vm_pageout_object_deactivate_pages(map->pmap, bigobj, desired);
  649                 VM_OBJECT_UNLOCK(bigobj);
  650         }
  651         /*
  652          * Next, hunt around for other pages to deactivate.  We actually
  653          * do this search sort of wrong -- .text first is not the best idea.
  654          */
  655         tmpe = map->header.next;
  656         while (tmpe != &map->header) {
  657                 if (pmap_resident_count(vm_map_pmap(map)) <= desired)
  658                         break;
  659                 if ((tmpe->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
  660                         obj = tmpe->object.vm_object;
  661                         if (obj != NULL) {
  662                                 VM_OBJECT_LOCK(obj);
  663                                 vm_pageout_object_deactivate_pages(map->pmap, obj, desired);
  664                                 VM_OBJECT_UNLOCK(obj);
  665                         }
  666                 }
  667                 tmpe = tmpe->next;
  668         }
  669 
  670         /*
  671          * Remove all mappings if a process is swapped out, this will free page
  672          * table pages.
  673          */
  674         if (desired == 0 && nothingwired) {
  675                 tmpe = map->header.next;
  676                 while (tmpe != &map->header) {
  677                         pmap_remove(vm_map_pmap(map), tmpe->start, tmpe->end);
  678                         tmpe = tmpe->next;
  679                 }
  680         }
  681         vm_map_unlock(map);
  682 }
  683 #endif          /* !defined(NO_SWAPPING) */
  684 
  685 /*
  686  *      vm_pageout_scan does the dirty work for the pageout daemon.
  687  */
  688 static void
  689 vm_pageout_scan(int pass)
  690 {
  691         vm_page_t m, next;
  692         struct vm_page marker;
  693         int page_shortage, maxscan, pcount;
  694         int addl_page_shortage, addl_page_shortage_init;
  695         vm_object_t object;
  696         int actcount;
  697         int vnodes_skipped = 0;
  698         int maxlaunder;
  699 
  700         /*
  701          * Decrease registered cache sizes.
  702          */
  703         EVENTHANDLER_INVOKE(vm_lowmem, 0);
  704         /*
  705          * We do this explicitly after the caches have been drained above.
  706          */
  707         uma_reclaim();
  708 
  709         addl_page_shortage_init = atomic_readandclear_int(&vm_pageout_deficit);
  710 
  711         /*
  712          * Calculate the number of pages we want to either free or move
  713          * to the cache.
  714          */
  715         page_shortage = vm_paging_target() + addl_page_shortage_init;
  716 
  717         /*
  718          * Initialize our marker
  719          */
  720         bzero(&marker, sizeof(marker));
  721         marker.flags = PG_FICTITIOUS | PG_MARKER;
  722         marker.oflags = VPO_BUSY;
  723         marker.queue = PQ_INACTIVE;
  724         marker.wire_count = 1;
  725 
  726         /*
  727          * Start scanning the inactive queue for pages we can move to the
  728          * cache or free.  The scan will stop when the target is reached or
  729          * we have scanned the entire inactive queue.  Note that m->act_count
  730          * is not used to form decisions for the inactive queue, only for the
  731          * active queue.
  732          *
  733          * maxlaunder limits the number of dirty pages we flush per scan.
  734          * For most systems a smaller value (16 or 32) is more robust under
  735          * extreme memory and disk pressure because any unnecessary writes
  736          * to disk can result in extreme performance degredation.  However,
  737          * systems with excessive dirty pages (especially when MAP_NOSYNC is
  738          * used) will die horribly with limited laundering.  If the pageout
  739          * daemon cannot clean enough pages in the first pass, we let it go
  740          * all out in succeeding passes.
  741          */
  742         if ((maxlaunder = vm_max_launder) <= 1)
  743                 maxlaunder = 1;
  744         if (pass)
  745                 maxlaunder = 10000;
  746         vm_page_lock_queues();
  747 rescan0:
  748         addl_page_shortage = addl_page_shortage_init;
  749         maxscan = cnt.v_inactive_count;
  750 
  751         for (m = TAILQ_FIRST(&vm_page_queues[PQ_INACTIVE].pl);
  752              m != NULL && maxscan-- > 0 && page_shortage > 0;
  753              m = next) {
  754 
  755                 cnt.v_pdpages++;
  756 
  757                 if (VM_PAGE_GETQUEUE(m) != PQ_INACTIVE) {
  758                         goto rescan0;
  759                 }
  760 
  761                 next = TAILQ_NEXT(m, pageq);
  762                 object = m->object;
  763 
  764                 /*
  765                  * skip marker pages
  766                  */
  767                 if (m->flags & PG_MARKER)
  768                         continue;
  769 
  770                 /*
  771                  * A held page may be undergoing I/O, so skip it.
  772                  */
  773                 if (m->hold_count) {
  774                         vm_page_requeue(m);
  775                         addl_page_shortage++;
  776                         continue;
  777                 }
  778                 /*
  779                  * Don't mess with busy pages, keep in the front of the
  780                  * queue, most likely are being paged out.
  781                  */
  782                 if (!VM_OBJECT_TRYLOCK(object) &&
  783                     (!vm_pageout_fallback_object_lock(m, &next) ||
  784                      m->hold_count != 0)) {
  785                         VM_OBJECT_UNLOCK(object);
  786                         addl_page_shortage++;
  787                         continue;
  788                 }
  789                 if (m->busy || (m->oflags & VPO_BUSY)) {
  790                         VM_OBJECT_UNLOCK(object);
  791                         addl_page_shortage++;
  792                         continue;
  793                 }
  794 
  795                 /*
  796                  * If the object is not being used, we ignore previous 
  797                  * references.
  798                  */
  799                 if (object->ref_count == 0) {
  800                         vm_page_flag_clear(m, PG_REFERENCED);
  801                         KASSERT(!pmap_page_is_mapped(m),
  802                             ("vm_pageout_scan: page %p is mapped", m));
  803 
  804                 /*
  805                  * Otherwise, if the page has been referenced while in the 
  806                  * inactive queue, we bump the "activation count" upwards, 
  807                  * making it less likely that the page will be added back to 
  808                  * the inactive queue prematurely again.  Here we check the 
  809                  * page tables (or emulated bits, if any), given the upper 
  810                  * level VM system not knowing anything about existing 
  811                  * references.
  812                  */
  813                 } else if (((m->flags & PG_REFERENCED) == 0) &&
  814                         (actcount = pmap_ts_referenced(m))) {
  815                         vm_page_activate(m);
  816                         VM_OBJECT_UNLOCK(object);
  817                         m->act_count += (actcount + ACT_ADVANCE);
  818                         continue;
  819                 }
  820 
  821                 /*
  822                  * If the upper level VM system knows about any page 
  823                  * references, we activate the page.  We also set the 
  824                  * "activation count" higher than normal so that we will less 
  825                  * likely place pages back onto the inactive queue again.
  826                  */
  827                 if ((m->flags & PG_REFERENCED) != 0) {
  828                         vm_page_flag_clear(m, PG_REFERENCED);
  829                         actcount = pmap_ts_referenced(m);
  830                         vm_page_activate(m);
  831                         VM_OBJECT_UNLOCK(object);
  832                         m->act_count += (actcount + ACT_ADVANCE + 1);
  833                         continue;
  834                 }
  835 
  836                 /*
  837                  * If the upper level VM system does not believe that the page
  838                  * is fully dirty, but it is mapped for write access, then we
  839                  * consult the pmap to see if the page's dirty status should
  840                  * be updated.
  841                  */
  842                 if (m->dirty != VM_PAGE_BITS_ALL &&
  843                     (m->flags & PG_WRITEABLE) != 0) {
  844                         /*
  845                          * Avoid a race condition: Unless write access is
  846                          * removed from the page, another processor could
  847                          * modify it before all access is removed by the call
  848                          * to vm_page_cache() below.  If vm_page_cache() finds
  849                          * that the page has been modified when it removes all
  850                          * access, it panics because it cannot cache dirty
  851                          * pages.  In principle, we could eliminate just write
  852                          * access here rather than all access.  In the expected
  853                          * case, when there are no last instant modifications
  854                          * to the page, removing all access will be cheaper
  855                          * overall.
  856                          */
  857                         if (pmap_is_modified(m))
  858                                 vm_page_dirty(m);
  859                         else if (m->dirty == 0)
  860                                 pmap_remove_all(m);
  861                 }
  862 
  863                 if (m->valid == 0) {
  864                         /*
  865                          * Invalid pages can be easily freed
  866                          */
  867                         vm_page_free(m);
  868                         cnt.v_dfree++;
  869                         --page_shortage;
  870                 } else if (m->dirty == 0) {
  871                         /*
  872                          * Clean pages can be placed onto the cache queue.
  873                          * This effectively frees them.
  874                          */
  875                         vm_page_cache(m);
  876                         --page_shortage;
  877                 } else if ((m->flags & PG_WINATCFLS) == 0 && pass == 0) {
  878                         /*
  879                          * Dirty pages need to be paged out, but flushing
  880                          * a page is extremely expensive verses freeing
  881                          * a clean page.  Rather then artificially limiting
  882                          * the number of pages we can flush, we instead give
  883                          * dirty pages extra priority on the inactive queue
  884                          * by forcing them to be cycled through the queue
  885                          * twice before being flushed, after which the
  886                          * (now clean) page will cycle through once more
  887                          * before being freed.  This significantly extends
  888                          * the thrash point for a heavily loaded machine.
  889                          */
  890                         vm_page_flag_set(m, PG_WINATCFLS);
  891                         vm_page_requeue(m);
  892                 } else if (maxlaunder > 0) {
  893                         /*
  894                          * We always want to try to flush some dirty pages if
  895                          * we encounter them, to keep the system stable.
  896                          * Normally this number is small, but under extreme
  897                          * pressure where there are insufficient clean pages
  898                          * on the inactive queue, we may have to go all out.
  899                          */
  900                         int swap_pageouts_ok, vfslocked = 0;
  901                         struct vnode *vp = NULL;
  902                         struct mount *mp = NULL;
  903 
  904                         if ((object->type != OBJT_SWAP) && (object->type != OBJT_DEFAULT)) {
  905                                 swap_pageouts_ok = 1;
  906                         } else {
  907                                 swap_pageouts_ok = !(defer_swap_pageouts || disable_swap_pageouts);
  908                                 swap_pageouts_ok |= (!disable_swap_pageouts && defer_swap_pageouts &&
  909                                 vm_page_count_min());
  910                                                                                 
  911                         }
  912 
  913                         /*
  914                          * We don't bother paging objects that are "dead".  
  915                          * Those objects are in a "rundown" state.
  916                          */
  917                         if (!swap_pageouts_ok || (object->flags & OBJ_DEAD)) {
  918                                 VM_OBJECT_UNLOCK(object);
  919                                 vm_page_requeue(m);
  920                                 continue;
  921                         }
  922 
  923                         /*
  924                          * Following operations may unlock
  925                          * vm_page_queue_mtx, invalidating the 'next'
  926                          * pointer.  To prevent an inordinate number
  927                          * of restarts we use our marker to remember
  928                          * our place.
  929                          *
  930                          */
  931                         TAILQ_INSERT_AFTER(&vm_page_queues[PQ_INACTIVE].pl,
  932                                            m, &marker, pageq);
  933                         /*
  934                          * The object is already known NOT to be dead.   It
  935                          * is possible for the vget() to block the whole
  936                          * pageout daemon, but the new low-memory handling
  937                          * code should prevent it.
  938                          *
  939                          * The previous code skipped locked vnodes and, worse,
  940                          * reordered pages in the queue.  This results in
  941                          * completely non-deterministic operation and, on a
  942                          * busy system, can lead to extremely non-optimal
  943                          * pageouts.  For example, it can cause clean pages
  944                          * to be freed and dirty pages to be moved to the end
  945                          * of the queue.  Since dirty pages are also moved to
  946                          * the end of the queue once-cleaned, this gives
  947                          * way too large a weighting to defering the freeing
  948                          * of dirty pages.
  949                          *
  950                          * We can't wait forever for the vnode lock, we might
  951                          * deadlock due to a vn_read() getting stuck in
  952                          * vm_wait while holding this vnode.  We skip the 
  953                          * vnode if we can't get it in a reasonable amount
  954                          * of time.
  955                          */
  956                         if (object->type == OBJT_VNODE) {
  957                                 vp = object->handle;
  958                                 if (vp->v_type == VREG &&
  959                                     vn_start_write(vp, &mp, V_NOWAIT) != 0) {
  960                                         mp = NULL;
  961                                         ++pageout_lock_miss;
  962                                         if (object->flags & OBJ_MIGHTBEDIRTY)
  963                                                 vnodes_skipped++;
  964                                         goto unlock_and_continue;
  965                                 }
  966                                 KASSERT(mp != NULL,
  967                                     ("vp %p with NULL v_mount", vp));
  968                                 vm_page_unlock_queues();
  969                                 vm_object_reference_locked(object);
  970                                 VM_OBJECT_UNLOCK(object);
  971                                 vfslocked = VFS_LOCK_GIANT(vp->v_mount);
  972                                 if (vget(vp, LK_EXCLUSIVE | LK_TIMELOCK,
  973                                     curthread)) {
  974                                         VM_OBJECT_LOCK(object);
  975                                         vm_page_lock_queues();
  976                                         ++pageout_lock_miss;
  977                                         if (object->flags & OBJ_MIGHTBEDIRTY)
  978                                                 vnodes_skipped++;
  979                                         vp = NULL;
  980                                         goto unlock_and_continue;
  981                                 }
  982                                 VM_OBJECT_LOCK(object);
  983                                 vm_page_lock_queues();
  984                                 /*
  985                                  * The page might have been moved to another
  986                                  * queue during potential blocking in vget()
  987                                  * above.  The page might have been freed and
  988                                  * reused for another vnode.
  989                                  */
  990                                 if (VM_PAGE_GETQUEUE(m) != PQ_INACTIVE ||
  991                                     m->object != object ||
  992                                     TAILQ_NEXT(m, pageq) != &marker) {
  993                                         if (object->flags & OBJ_MIGHTBEDIRTY)
  994                                                 vnodes_skipped++;
  995                                         goto unlock_and_continue;
  996                                 }
  997         
  998                                 /*
  999                                  * The page may have been busied during the
 1000                                  * blocking in vget().  We don't move the
 1001                                  * page back onto the end of the queue so that
 1002                                  * statistics are more correct if we don't.
 1003                                  */
 1004                                 if (m->busy || (m->oflags & VPO_BUSY)) {
 1005                                         goto unlock_and_continue;
 1006                                 }
 1007 
 1008                                 /*
 1009                                  * If the page has become held it might
 1010                                  * be undergoing I/O, so skip it
 1011                                  */
 1012                                 if (m->hold_count) {
 1013                                         vm_page_requeue(m);
 1014                                         if (object->flags & OBJ_MIGHTBEDIRTY)
 1015                                                 vnodes_skipped++;
 1016                                         goto unlock_and_continue;
 1017                                 }
 1018                         }
 1019 
 1020                         /*
 1021                          * If a page is dirty, then it is either being washed
 1022                          * (but not yet cleaned) or it is still in the
 1023                          * laundry.  If it is still in the laundry, then we
 1024                          * start the cleaning operation. 
 1025                          *
 1026                          * decrement page_shortage on success to account for
 1027                          * the (future) cleaned page.  Otherwise we could wind
 1028                          * up laundering or cleaning too many pages.
 1029                          */
 1030                         if (vm_pageout_clean(m) != 0) {
 1031                                 --page_shortage;
 1032                                 --maxlaunder;
 1033                         }
 1034 unlock_and_continue:
 1035                         VM_OBJECT_UNLOCK(object);
 1036                         if (mp != NULL) {
 1037                                 vm_page_unlock_queues();
 1038                                 if (vp != NULL)
 1039                                         vput(vp);
 1040                                 VFS_UNLOCK_GIANT(vfslocked);
 1041                                 vm_object_deallocate(object);
 1042                                 vn_finished_write(mp);
 1043                                 vm_page_lock_queues();
 1044                         }
 1045                         next = TAILQ_NEXT(&marker, pageq);
 1046                         TAILQ_REMOVE(&vm_page_queues[PQ_INACTIVE].pl,
 1047                                      &marker, pageq);
 1048                         continue;
 1049                 }
 1050                 VM_OBJECT_UNLOCK(object);
 1051         }
 1052 
 1053         /*
 1054          * Compute the number of pages we want to try to move from the
 1055          * active queue to the inactive queue.
 1056          */
 1057         page_shortage = vm_paging_target() +
 1058                 cnt.v_inactive_target - cnt.v_inactive_count;
 1059         page_shortage += addl_page_shortage;
 1060 
 1061         /*
 1062          * Scan the active queue for things we can deactivate. We nominally
 1063          * track the per-page activity counter and use it to locate
 1064          * deactivation candidates.
 1065          */
 1066         pcount = cnt.v_active_count;
 1067         m = TAILQ_FIRST(&vm_page_queues[PQ_ACTIVE].pl);
 1068 
 1069         while ((m != NULL) && (pcount-- > 0) && (page_shortage > 0)) {
 1070 
 1071                 KASSERT(VM_PAGE_INQUEUE2(m, PQ_ACTIVE),
 1072                     ("vm_pageout_scan: page %p isn't active", m));
 1073 
 1074                 next = TAILQ_NEXT(m, pageq);
 1075                 object = m->object;
 1076                 if ((m->flags & PG_MARKER) != 0) {
 1077                         m = next;
 1078                         continue;
 1079                 }
 1080                 if (!VM_OBJECT_TRYLOCK(object) &&
 1081                     !vm_pageout_fallback_object_lock(m, &next)) {
 1082                         VM_OBJECT_UNLOCK(object);
 1083                         m = next;
 1084                         continue;
 1085                 }
 1086 
 1087                 /*
 1088                  * Don't deactivate pages that are busy.
 1089                  */
 1090                 if ((m->busy != 0) ||
 1091                     (m->oflags & VPO_BUSY) ||
 1092                     (m->hold_count != 0)) {
 1093                         VM_OBJECT_UNLOCK(object);
 1094                         vm_page_requeue(m);
 1095                         m = next;
 1096                         continue;
 1097                 }
 1098 
 1099                 /*
 1100                  * The count for pagedaemon pages is done after checking the
 1101                  * page for eligibility...
 1102                  */
 1103                 cnt.v_pdpages++;
 1104 
 1105                 /*
 1106                  * Check to see "how much" the page has been used.
 1107                  */
 1108                 actcount = 0;
 1109                 if (object->ref_count != 0) {
 1110                         if (m->flags & PG_REFERENCED) {
 1111                                 actcount += 1;
 1112                         }
 1113                         actcount += pmap_ts_referenced(m);
 1114                         if (actcount) {
 1115                                 m->act_count += ACT_ADVANCE + actcount;
 1116                                 if (m->act_count > ACT_MAX)
 1117                                         m->act_count = ACT_MAX;
 1118                         }
 1119                 }
 1120 
 1121                 /*
 1122                  * Since we have "tested" this bit, we need to clear it now.
 1123                  */
 1124                 vm_page_flag_clear(m, PG_REFERENCED);
 1125 
 1126                 /*
 1127                  * Only if an object is currently being used, do we use the
 1128                  * page activation count stats.
 1129                  */
 1130                 if (actcount && (object->ref_count != 0)) {
 1131                         vm_page_requeue(m);
 1132                 } else {
 1133                         m->act_count -= min(m->act_count, ACT_DECLINE);
 1134                         if (vm_pageout_algorithm ||
 1135                             object->ref_count == 0 ||
 1136                             m->act_count == 0) {
 1137                                 page_shortage--;
 1138                                 if (object->ref_count == 0) {
 1139                                         pmap_remove_all(m);
 1140                                         if (m->dirty == 0)
 1141                                                 vm_page_cache(m);
 1142                                         else
 1143                                                 vm_page_deactivate(m);
 1144                                 } else {
 1145                                         vm_page_deactivate(m);
 1146                                 }
 1147                         } else {
 1148                                 vm_page_requeue(m);
 1149                         }
 1150                 }
 1151                 VM_OBJECT_UNLOCK(object);
 1152                 m = next;
 1153         }
 1154         vm_page_unlock_queues();
 1155 #if !defined(NO_SWAPPING)
 1156         /*
 1157          * Idle process swapout -- run once per second.
 1158          */
 1159         if (vm_swap_idle_enabled) {
 1160                 static long lsec;
 1161                 if (time_second != lsec) {
 1162                         vm_req_vmdaemon(VM_SWAP_IDLE);
 1163                         lsec = time_second;
 1164                 }
 1165         }
 1166 #endif
 1167                 
 1168         /*
 1169          * If we didn't get enough free pages, and we have skipped a vnode
 1170          * in a writeable object, wakeup the sync daemon.  And kick swapout
 1171          * if we did not get enough free pages.
 1172          */
 1173         if (vm_paging_target() > 0) {
 1174                 if (vnodes_skipped && vm_page_count_min())
 1175                         (void) speedup_syncer();
 1176 #if !defined(NO_SWAPPING)
 1177                 if (vm_swap_enabled && vm_page_count_target())
 1178                         vm_req_vmdaemon(VM_SWAP_NORMAL);
 1179 #endif
 1180         }
 1181 
 1182         /*
 1183          * If we are critically low on one of RAM or swap and low on
 1184          * the other, kill the largest process.  However, we avoid
 1185          * doing this on the first pass in order to give ourselves a
 1186          * chance to flush out dirty vnode-backed pages and to allow
 1187          * active pages to be moved to the inactive queue and reclaimed.
 1188          */
 1189         if (pass != 0 &&
 1190             ((swap_pager_avail < 64 && vm_page_count_min()) ||
 1191              (swap_pager_full && vm_paging_target() > 0)))
 1192                 vm_pageout_oom(VM_OOM_MEM);
 1193 }
 1194 
 1195 
 1196 void
 1197 vm_pageout_oom(int shortage)
 1198 {
 1199         struct proc *p, *bigproc;
 1200         vm_offset_t size, bigsize;
 1201         struct thread *td;
 1202         struct vmspace *vm;
 1203 
 1204         /*
 1205          * We keep the process bigproc locked once we find it to keep anyone
 1206          * from messing with it; however, there is a possibility of
 1207          * deadlock if process B is bigproc and one of it's child processes
 1208          * attempts to propagate a signal to B while we are waiting for A's
 1209          * lock while walking this list.  To avoid this, we don't block on
 1210          * the process lock but just skip a process if it is already locked.
 1211          */
 1212         bigproc = NULL;
 1213         bigsize = 0;
 1214         sx_slock(&allproc_lock);
 1215         FOREACH_PROC_IN_SYSTEM(p) {
 1216                 int breakout;
 1217 
 1218                 if (PROC_TRYLOCK(p) == 0)
 1219                         continue;
 1220                 /*
 1221                  * If this is a system, protected or killed process, skip it.
 1222                  */
 1223                 if (p->p_state != PRS_NORMAL ||
 1224                     (p->p_flag & (P_INEXEC | P_PROTECTED | P_SYSTEM)) ||
 1225                     (p->p_pid == 1) || P_KILLED(p) ||
 1226                     ((p->p_pid < 48) && (swap_pager_avail != 0))) {
 1227                         PROC_UNLOCK(p);
 1228                         continue;
 1229                 }
 1230                 /*
 1231                  * If the process is in a non-running type state,
 1232                  * don't touch it.  Check all the threads individually.
 1233                  */
 1234                 breakout = 0;
 1235                 FOREACH_THREAD_IN_PROC(p, td) {
 1236                         thread_lock(td);
 1237                         if (!TD_ON_RUNQ(td) &&
 1238                             !TD_IS_RUNNING(td) &&
 1239                             !TD_IS_SLEEPING(td)) {
 1240                                 thread_unlock(td);
 1241                                 breakout = 1;
 1242                                 break;
 1243                         }
 1244                         thread_unlock(td);
 1245                 }
 1246                 if (breakout) {
 1247                         PROC_UNLOCK(p);
 1248                         continue;
 1249                 }
 1250                 /*
 1251                  * get the process size
 1252                  */
 1253                 vm = vmspace_acquire_ref(p);
 1254                 if (vm == NULL) {
 1255                         PROC_UNLOCK(p);
 1256                         continue;
 1257                 }
 1258                 if (!vm_map_trylock_read(&vm->vm_map)) {
 1259                         vmspace_free(vm);
 1260                         PROC_UNLOCK(p);
 1261                         continue;
 1262                 }
 1263                 size = vmspace_swap_count(vm);
 1264                 vm_map_unlock_read(&vm->vm_map);
 1265                 if (shortage == VM_OOM_MEM)
 1266                         size += vmspace_resident_count(vm);
 1267                 vmspace_free(vm);
 1268                 /*
 1269                  * if the this process is bigger than the biggest one
 1270                  * remember it.
 1271                  */
 1272                 if (size > bigsize) {
 1273                         if (bigproc != NULL)
 1274                                 PROC_UNLOCK(bigproc);
 1275                         bigproc = p;
 1276                         bigsize = size;
 1277                 } else
 1278                         PROC_UNLOCK(p);
 1279         }
 1280         sx_sunlock(&allproc_lock);
 1281         if (bigproc != NULL) {
 1282                 killproc(bigproc, "out of swap space");
 1283                 sched_nice(bigproc, PRIO_MIN);
 1284                 PROC_UNLOCK(bigproc);
 1285                 wakeup(&cnt.v_free_count);
 1286         }
 1287 }
 1288 
 1289 /*
 1290  * This routine tries to maintain the pseudo LRU active queue,
 1291  * so that during long periods of time where there is no paging,
 1292  * that some statistic accumulation still occurs.  This code
 1293  * helps the situation where paging just starts to occur.
 1294  */
 1295 static void
 1296 vm_pageout_page_stats()
 1297 {
 1298         vm_object_t object;
 1299         vm_page_t m,next;
 1300         int pcount,tpcount;             /* Number of pages to check */
 1301         static int fullintervalcount = 0;
 1302         int page_shortage;
 1303 
 1304         mtx_assert(&vm_page_queue_mtx, MA_OWNED);
 1305         page_shortage = 
 1306             (cnt.v_inactive_target + cnt.v_cache_max + cnt.v_free_min) -
 1307             (cnt.v_free_count + cnt.v_inactive_count + cnt.v_cache_count);
 1308 
 1309         if (page_shortage <= 0)
 1310                 return;
 1311 
 1312         pcount = cnt.v_active_count;
 1313         fullintervalcount += vm_pageout_stats_interval;
 1314         if (fullintervalcount < vm_pageout_full_stats_interval) {
 1315                 tpcount = (int64_t)vm_pageout_stats_max * cnt.v_active_count /
 1316                     cnt.v_page_count;
 1317                 if (pcount > tpcount)
 1318                         pcount = tpcount;
 1319         } else {
 1320                 fullintervalcount = 0;
 1321         }
 1322 
 1323         m = TAILQ_FIRST(&vm_page_queues[PQ_ACTIVE].pl);
 1324         while ((m != NULL) && (pcount-- > 0)) {
 1325                 int actcount;
 1326 
 1327                 KASSERT(VM_PAGE_INQUEUE2(m, PQ_ACTIVE),
 1328                     ("vm_pageout_page_stats: page %p isn't active", m));
 1329 
 1330                 next = TAILQ_NEXT(m, pageq);
 1331                 object = m->object;
 1332 
 1333                 if ((m->flags & PG_MARKER) != 0) {
 1334                         m = next;
 1335                         continue;
 1336                 }
 1337                 if (!VM_OBJECT_TRYLOCK(object) &&
 1338                     !vm_pageout_fallback_object_lock(m, &next)) {
 1339                         VM_OBJECT_UNLOCK(object);
 1340                         m = next;
 1341                         continue;
 1342                 }
 1343 
 1344                 /*
 1345                  * Don't deactivate pages that are busy.
 1346                  */
 1347                 if ((m->busy != 0) ||
 1348                     (m->oflags & VPO_BUSY) ||
 1349                     (m->hold_count != 0)) {
 1350                         VM_OBJECT_UNLOCK(object);
 1351                         vm_page_requeue(m);
 1352                         m = next;
 1353                         continue;
 1354                 }
 1355 
 1356                 actcount = 0;
 1357                 if (m->flags & PG_REFERENCED) {
 1358                         vm_page_flag_clear(m, PG_REFERENCED);
 1359                         actcount += 1;
 1360                 }
 1361 
 1362                 actcount += pmap_ts_referenced(m);
 1363                 if (actcount) {
 1364                         m->act_count += ACT_ADVANCE + actcount;
 1365                         if (m->act_count > ACT_MAX)
 1366                                 m->act_count = ACT_MAX;
 1367                         vm_page_requeue(m);
 1368                 } else {
 1369                         if (m->act_count == 0) {
 1370                                 /*
 1371                                  * We turn off page access, so that we have
 1372                                  * more accurate RSS stats.  We don't do this
 1373                                  * in the normal page deactivation when the
 1374                                  * system is loaded VM wise, because the
 1375                                  * cost of the large number of page protect
 1376                                  * operations would be higher than the value
 1377                                  * of doing the operation.
 1378                                  */
 1379                                 pmap_remove_all(m);
 1380                                 vm_page_deactivate(m);
 1381                         } else {
 1382                                 m->act_count -= min(m->act_count, ACT_DECLINE);
 1383                                 vm_page_requeue(m);
 1384                         }
 1385                 }
 1386                 VM_OBJECT_UNLOCK(object);
 1387                 m = next;
 1388         }
 1389 }
 1390 
 1391 /*
 1392  *      vm_pageout is the high level pageout daemon.
 1393  */
 1394 static void
 1395 vm_pageout()
 1396 {
 1397         int error, pass;
 1398 
 1399         /*
 1400          * Initialize some paging parameters.
 1401          */
 1402         cnt.v_interrupt_free_min = 2;
 1403         if (cnt.v_page_count < 2000)
 1404                 vm_pageout_page_count = 8;
 1405 
 1406         /*
 1407          * v_free_reserved needs to include enough for the largest
 1408          * swap pager structures plus enough for any pv_entry structs
 1409          * when paging. 
 1410          */
 1411         if (cnt.v_page_count > 1024)
 1412                 cnt.v_free_min = 4 + (cnt.v_page_count - 1024) / 200;
 1413         else
 1414                 cnt.v_free_min = 4;
 1415         cnt.v_pageout_free_min = (2*MAXBSIZE)/PAGE_SIZE +
 1416             cnt.v_interrupt_free_min;
 1417         cnt.v_free_reserved = vm_pageout_page_count +
 1418             cnt.v_pageout_free_min + (cnt.v_page_count / 768);
 1419         cnt.v_free_severe = cnt.v_free_min / 2;
 1420         cnt.v_free_min += cnt.v_free_reserved;
 1421         cnt.v_free_severe += cnt.v_free_reserved;
 1422 
 1423         /*
 1424          * v_free_target and v_cache_min control pageout hysteresis.  Note
 1425          * that these are more a measure of the VM cache queue hysteresis
 1426          * then the VM free queue.  Specifically, v_free_target is the
 1427          * high water mark (free+cache pages).
 1428          *
 1429          * v_free_reserved + v_cache_min (mostly means v_cache_min) is the
 1430          * low water mark, while v_free_min is the stop.  v_cache_min must
 1431          * be big enough to handle memory needs while the pageout daemon
 1432          * is signalled and run to free more pages.
 1433          */
 1434         if (cnt.v_free_count > 6144)
 1435                 cnt.v_free_target = 4 * cnt.v_free_min + cnt.v_free_reserved;
 1436         else
 1437                 cnt.v_free_target = 2 * cnt.v_free_min + cnt.v_free_reserved;
 1438 
 1439         if (cnt.v_free_count > 2048) {
 1440                 cnt.v_cache_min = cnt.v_free_target;
 1441                 cnt.v_cache_max = 2 * cnt.v_cache_min;
 1442                 cnt.v_inactive_target = (3 * cnt.v_free_target) / 2;
 1443         } else {
 1444                 cnt.v_cache_min = 0;
 1445                 cnt.v_cache_max = 0;
 1446                 cnt.v_inactive_target = cnt.v_free_count / 4;
 1447         }
 1448         if (cnt.v_inactive_target > cnt.v_free_count / 3)
 1449                 cnt.v_inactive_target = cnt.v_free_count / 3;
 1450 
 1451         /* XXX does not really belong here */
 1452         if (vm_page_max_wired == 0)
 1453                 vm_page_max_wired = cnt.v_free_count / 3;
 1454 
 1455         if (vm_pageout_stats_max == 0)
 1456                 vm_pageout_stats_max = cnt.v_free_target;
 1457 
 1458         /*
 1459          * Set interval in seconds for stats scan.
 1460          */
 1461         if (vm_pageout_stats_interval == 0)
 1462                 vm_pageout_stats_interval = 5;
 1463         if (vm_pageout_full_stats_interval == 0)
 1464                 vm_pageout_full_stats_interval = vm_pageout_stats_interval * 4;
 1465 
 1466         swap_pager_swap_init();
 1467         pass = 0;
 1468         /*
 1469          * The pageout daemon is never done, so loop forever.
 1470          */
 1471         while (TRUE) {
 1472                 /*
 1473                  * If we have enough free memory, wakeup waiters.  Do
 1474                  * not clear vm_pages_needed until we reach our target,
 1475                  * otherwise we may be woken up over and over again and
 1476                  * waste a lot of cpu.
 1477                  */
 1478                 mtx_lock(&vm_page_queue_free_mtx);
 1479                 if (vm_pages_needed && !vm_page_count_min()) {
 1480                         if (!vm_paging_needed())
 1481                                 vm_pages_needed = 0;
 1482                         wakeup(&cnt.v_free_count);
 1483                 }
 1484                 if (vm_pages_needed) {
 1485                         /*
 1486                          * Still not done, take a second pass without waiting
 1487                          * (unlimited dirty cleaning), otherwise sleep a bit
 1488                          * and try again.
 1489                          */
 1490                         ++pass;
 1491                         if (pass > 1)
 1492                                 msleep(&vm_pages_needed,
 1493                                     &vm_page_queue_free_mtx, PVM, "psleep",
 1494                                     hz / 2);
 1495                 } else {
 1496                         /*
 1497                          * Good enough, sleep & handle stats.  Prime the pass
 1498                          * for the next run.
 1499                          */
 1500                         if (pass > 1)
 1501                                 pass = 1;
 1502                         else
 1503                                 pass = 0;
 1504                         error = msleep(&vm_pages_needed,
 1505                             &vm_page_queue_free_mtx, PVM, "psleep",
 1506                             vm_pageout_stats_interval * hz);
 1507                         if (error && !vm_pages_needed) {
 1508                                 mtx_unlock(&vm_page_queue_free_mtx);
 1509                                 pass = 0;
 1510                                 vm_page_lock_queues();
 1511                                 vm_pageout_page_stats();
 1512                                 vm_page_unlock_queues();
 1513                                 continue;
 1514                         }
 1515                 }
 1516                 if (vm_pages_needed)
 1517                         cnt.v_pdwakeups++;
 1518                 mtx_unlock(&vm_page_queue_free_mtx);
 1519                 vm_pageout_scan(pass);
 1520         }
 1521 }
 1522 
 1523 /*
 1524  * Unless the free page queue lock is held by the caller, this function
 1525  * should be regarded as advisory.  Specifically, the caller should
 1526  * not msleep() on &cnt.v_free_count following this function unless
 1527  * the free page queue lock is held until the msleep() is performed.
 1528  */
 1529 void
 1530 pagedaemon_wakeup()
 1531 {
 1532 
 1533         if (!vm_pages_needed && curthread->td_proc != pageproc) {
 1534                 vm_pages_needed = 1;
 1535                 wakeup(&vm_pages_needed);
 1536         }
 1537 }
 1538 
 1539 #if !defined(NO_SWAPPING)
 1540 static void
 1541 vm_req_vmdaemon(int req)
 1542 {
 1543         static int lastrun = 0;
 1544 
 1545         mtx_lock(&vm_daemon_mtx);
 1546         vm_pageout_req_swapout |= req;
 1547         if ((ticks > (lastrun + hz)) || (ticks < lastrun)) {
 1548                 wakeup(&vm_daemon_needed);
 1549                 lastrun = ticks;
 1550         }
 1551         mtx_unlock(&vm_daemon_mtx);
 1552 }
 1553 
 1554 static void
 1555 vm_daemon()
 1556 {
 1557         struct rlimit rsslim;
 1558         struct proc *p;
 1559         struct thread *td;
 1560         struct vmspace *vm;
 1561         int breakout, swapout_flags;
 1562 
 1563         while (TRUE) {
 1564                 mtx_lock(&vm_daemon_mtx);
 1565                 msleep(&vm_daemon_needed, &vm_daemon_mtx, PPAUSE, "psleep", 0);
 1566                 swapout_flags = vm_pageout_req_swapout;
 1567                 vm_pageout_req_swapout = 0;
 1568                 mtx_unlock(&vm_daemon_mtx);
 1569                 if (swapout_flags)
 1570                         swapout_procs(swapout_flags);
 1571 
 1572                 /*
 1573                  * scan the processes for exceeding their rlimits or if
 1574                  * process is swapped out -- deactivate pages
 1575                  */
 1576                 sx_slock(&allproc_lock);
 1577                 FOREACH_PROC_IN_SYSTEM(p) {
 1578                         vm_pindex_t limit, size;
 1579 
 1580                         /*
 1581                          * if this is a system process or if we have already
 1582                          * looked at this process, skip it.
 1583                          */
 1584                         PROC_LOCK(p);
 1585                         if (p->p_state != PRS_NORMAL ||
 1586                             p->p_flag & (P_INEXEC | P_SYSTEM | P_WEXIT)) {
 1587                                 PROC_UNLOCK(p);
 1588                                 continue;
 1589                         }
 1590                         /*
 1591                          * if the process is in a non-running type state,
 1592                          * don't touch it.
 1593                          */
 1594                         breakout = 0;
 1595                         FOREACH_THREAD_IN_PROC(p, td) {
 1596                                 thread_lock(td);
 1597                                 if (!TD_ON_RUNQ(td) &&
 1598                                     !TD_IS_RUNNING(td) &&
 1599                                     !TD_IS_SLEEPING(td)) {
 1600                                         thread_unlock(td);
 1601                                         breakout = 1;
 1602                                         break;
 1603                                 }
 1604                                 thread_unlock(td);
 1605                         }
 1606                         if (breakout) {
 1607                                 PROC_UNLOCK(p);
 1608                                 continue;
 1609                         }
 1610                         /*
 1611                          * get a limit
 1612                          */
 1613                         lim_rlimit(p, RLIMIT_RSS, &rsslim);
 1614                         limit = OFF_TO_IDX(
 1615                             qmin(rsslim.rlim_cur, rsslim.rlim_max));
 1616 
 1617                         /*
 1618                          * let processes that are swapped out really be
 1619                          * swapped out set the limit to nothing (will force a
 1620                          * swap-out.)
 1621                          */
 1622                         if ((p->p_flag & P_INMEM) == 0)
 1623                                 limit = 0;      /* XXX */
 1624                         vm = vmspace_acquire_ref(p);
 1625                         PROC_UNLOCK(p);
 1626                         if (vm == NULL)
 1627                                 continue;
 1628 
 1629                         size = vmspace_resident_count(vm);
 1630                         if (limit >= 0 && size >= limit) {
 1631                                 vm_pageout_map_deactivate_pages(
 1632                                     &vm->vm_map, limit);
 1633                         }
 1634                         vmspace_free(vm);
 1635                 }
 1636                 sx_sunlock(&allproc_lock);
 1637         }
 1638 }
 1639 #endif                  /* !defined(NO_SWAPPING) */

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