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  *
    9  * This code is derived from software contributed to Berkeley by
   10  * The Mach Operating System project at Carnegie-Mellon University.
   11  *
   12  * Redistribution and use in source and binary forms, with or without
   13  * modification, are permitted provided that the following conditions
   14  * are met:
   15  * 1. Redistributions of source code must retain the above copyright
   16  *    notice, this list of conditions and the following disclaimer.
   17  * 2. Redistributions in binary form must reproduce the above copyright
   18  *    notice, this list of conditions and the following disclaimer in the
   19  *    documentation and/or other materials provided with the distribution.
   20  * 3. Neither the name of the University nor the names of its contributors
   21  *    may be used to endorse or promote products derived from this software
   22  *    without specific prior written permission.
   23  *
   24  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   25  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   26  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   27  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   28  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   29  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   30  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   31  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   32  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   33  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   34  * SUCH DAMAGE.
   35  *
   36  *      from: @(#)vm_pageout.c  7.4 (Berkeley) 5/7/91
   37  *
   38  *
   39  * Copyright (c) 1987, 1990 Carnegie-Mellon University.
   40  * All rights reserved.
   41  *
   42  * Authors: Avadis Tevanian, Jr., Michael Wayne Young
   43  *
   44  * Permission to use, copy, modify and distribute this software and
   45  * its documentation is hereby granted, provided that both the copyright
   46  * notice and this permission notice appear in all copies of the
   47  * software, derivative works or modified versions, and any portions
   48  * thereof, and that both notices appear in supporting documentation.
   49  *
   50  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
   51  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
   52  * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
   53  *
   54  * Carnegie Mellon requests users of this software to return to
   55  *
   56  *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
   57  *  School of Computer Science
   58  *  Carnegie Mellon University
   59  *  Pittsburgh PA 15213-3890
   60  *
   61  * any improvements or extensions that they make and grant Carnegie the
   62  * rights to redistribute these changes.
   63  *
   64  * $FreeBSD: src/sys/vm/vm_pageout.c,v 1.151.2.15 2002/12/29 18:21:04 dillon Exp $
   65  */
   66 
   67 /*
   68  *      The proverbial page-out daemon.
   69  */
   70 
   71 #include "opt_vm.h"
   72 #include <sys/param.h>
   73 #include <sys/systm.h>
   74 #include <sys/kernel.h>
   75 #include <sys/proc.h>
   76 #include <sys/kthread.h>
   77 #include <sys/resourcevar.h>
   78 #include <sys/signalvar.h>
   79 #include <sys/vnode.h>
   80 #include <sys/vmmeter.h>
   81 #include <sys/sysctl.h>
   82 
   83 #include <vm/vm.h>
   84 #include <vm/vm_param.h>
   85 #include <sys/lock.h>
   86 #include <vm/vm_object.h>
   87 #include <vm/vm_page.h>
   88 #include <vm/vm_map.h>
   89 #include <vm/vm_pageout.h>
   90 #include <vm/vm_pager.h>
   91 #include <vm/swap_pager.h>
   92 #include <vm/vm_extern.h>
   93 
   94 #include <sys/thread2.h>
   95 #include <sys/spinlock2.h>
   96 #include <vm/vm_page2.h>
   97 
   98 /*
   99  * System initialization
  100  */
  101 
  102 /* the kernel process "vm_pageout"*/
  103 static int vm_pageout_clean (vm_page_t);
  104 static int vm_pageout_free_page_calc (vm_size_t count);
  105 struct thread *pagethread;
  106 
  107 #if !defined(NO_SWAPPING)
  108 /* the kernel process "vm_daemon"*/
  109 static void vm_daemon (void);
  110 static struct   thread *vmthread;
  111 
  112 static struct kproc_desc vm_kp = {
  113         "vmdaemon",
  114         vm_daemon,
  115         &vmthread
  116 };
  117 SYSINIT(vmdaemon, SI_SUB_KTHREAD_VM, SI_ORDER_FIRST, kproc_start, &vm_kp)
  118 #endif
  119 
  120 int vm_pages_needed=0;          /* Event on which pageout daemon sleeps */
  121 int vm_pageout_deficit=0;       /* Estimated number of pages deficit */
  122 int vm_pageout_pages_needed=0;  /* pageout daemon needs pages */
  123 int vm_page_free_hysteresis = 16;
  124 
  125 #if !defined(NO_SWAPPING)
  126 static int vm_pageout_req_swapout;      /* XXX */
  127 static int vm_daemon_needed;
  128 #endif
  129 static int vm_max_launder = 4096;
  130 static int vm_pageout_stats_max=0, vm_pageout_stats_interval = 0;
  131 static int vm_pageout_full_stats_interval = 0;
  132 static int vm_pageout_stats_free_max=0, vm_pageout_algorithm=0;
  133 static int defer_swap_pageouts=0;
  134 static int disable_swap_pageouts=0;
  135 static u_int vm_anonmem_decline = ACT_DECLINE;
  136 static u_int vm_filemem_decline = ACT_DECLINE * 2;
  137 
  138 #if defined(NO_SWAPPING)
  139 static int vm_swap_enabled=0;
  140 static int vm_swap_idle_enabled=0;
  141 #else
  142 static int vm_swap_enabled=1;
  143 static int vm_swap_idle_enabled=0;
  144 #endif
  145 
  146 SYSCTL_UINT(_vm, VM_PAGEOUT_ALGORITHM, anonmem_decline,
  147         CTLFLAG_RW, &vm_anonmem_decline, 0, "active->inactive anon memory");
  148 
  149 SYSCTL_INT(_vm, VM_PAGEOUT_ALGORITHM, filemem_decline,
  150         CTLFLAG_RW, &vm_filemem_decline, 0, "active->inactive file cache");
  151 
  152 SYSCTL_INT(_vm, OID_AUTO, page_free_hysteresis,
  153         CTLFLAG_RW, &vm_page_free_hysteresis, 0,
  154         "Free more pages than the minimum required");
  155 
  156 SYSCTL_INT(_vm, OID_AUTO, max_launder,
  157         CTLFLAG_RW, &vm_max_launder, 0, "Limit dirty flushes in pageout");
  158 
  159 SYSCTL_INT(_vm, OID_AUTO, pageout_stats_max,
  160         CTLFLAG_RW, &vm_pageout_stats_max, 0, "Max pageout stats scan length");
  161 
  162 SYSCTL_INT(_vm, OID_AUTO, pageout_full_stats_interval,
  163         CTLFLAG_RW, &vm_pageout_full_stats_interval, 0, "Interval for full stats scan");
  164 
  165 SYSCTL_INT(_vm, OID_AUTO, pageout_stats_interval,
  166         CTLFLAG_RW, &vm_pageout_stats_interval, 0, "Interval for partial stats scan");
  167 
  168 SYSCTL_INT(_vm, OID_AUTO, pageout_stats_free_max,
  169         CTLFLAG_RW, &vm_pageout_stats_free_max, 0, "Not implemented");
  170 
  171 #if defined(NO_SWAPPING)
  172 SYSCTL_INT(_vm, VM_SWAPPING_ENABLED, swap_enabled,
  173         CTLFLAG_RD, &vm_swap_enabled, 0, "");
  174 SYSCTL_INT(_vm, OID_AUTO, swap_idle_enabled,
  175         CTLFLAG_RD, &vm_swap_idle_enabled, 0, "");
  176 #else
  177 SYSCTL_INT(_vm, VM_SWAPPING_ENABLED, swap_enabled,
  178         CTLFLAG_RW, &vm_swap_enabled, 0, "Enable entire process swapout");
  179 SYSCTL_INT(_vm, OID_AUTO, swap_idle_enabled,
  180         CTLFLAG_RW, &vm_swap_idle_enabled, 0, "Allow swapout on idle criteria");
  181 #endif
  182 
  183 SYSCTL_INT(_vm, OID_AUTO, defer_swapspace_pageouts,
  184         CTLFLAG_RW, &defer_swap_pageouts, 0, "Give preference to dirty pages in mem");
  185 
  186 SYSCTL_INT(_vm, OID_AUTO, disable_swapspace_pageouts,
  187         CTLFLAG_RW, &disable_swap_pageouts, 0, "Disallow swapout of dirty pages");
  188 
  189 static int pageout_lock_miss;
  190 SYSCTL_INT(_vm, OID_AUTO, pageout_lock_miss,
  191         CTLFLAG_RD, &pageout_lock_miss, 0, "vget() lock misses during pageout");
  192 
  193 int vm_page_max_wired;          /* XXX max # of wired pages system-wide */
  194 
  195 #if !defined(NO_SWAPPING)
  196 typedef void freeer_fcn_t (vm_map_t, vm_object_t, vm_pindex_t, int);
  197 static void vm_pageout_map_deactivate_pages (vm_map_t, vm_pindex_t);
  198 static freeer_fcn_t vm_pageout_object_deactivate_pages;
  199 static void vm_req_vmdaemon (void);
  200 #endif
  201 static void vm_pageout_page_stats(int q);
  202 
  203 static __inline int
  204 PQAVERAGE(int n)
  205 {
  206         if (n >= 0)
  207                 return((n + (PQ_L2_SIZE - 1)) / PQ_L2_SIZE + 1);
  208         else
  209                 return((n - (PQ_L2_SIZE - 1)) / PQ_L2_SIZE - 1);
  210 }
  211 
  212 /*
  213  * vm_pageout_clean:
  214  *
  215  * Clean the page and remove it from the laundry.  The page must not be
  216  * busy on-call.
  217  * 
  218  * We set the busy bit to cause potential page faults on this page to
  219  * block.  Note the careful timing, however, the busy bit isn't set till
  220  * late and we cannot do anything that will mess with the page.
  221  */
  222 static int
  223 vm_pageout_clean(vm_page_t m)
  224 {
  225         vm_object_t object;
  226         vm_page_t mc[BLIST_MAX_ALLOC];
  227         int error;
  228         int ib, is, page_base;
  229         vm_pindex_t pindex = m->pindex;
  230 
  231         object = m->object;
  232 
  233         /*
  234          * It doesn't cost us anything to pageout OBJT_DEFAULT or OBJT_SWAP
  235          * with the new swapper, but we could have serious problems paging
  236          * out other object types if there is insufficient memory.  
  237          *
  238          * Unfortunately, checking free memory here is far too late, so the
  239          * check has been moved up a procedural level.
  240          */
  241 
  242         /*
  243          * Don't mess with the page if it's busy, held, or special
  244          *
  245          * XXX do we really need to check hold_count here?  hold_count
  246          * isn't supposed to mess with vm_page ops except prevent the
  247          * page from being reused.
  248          */
  249         if (m->hold_count != 0 || (m->flags & PG_UNMANAGED)) {
  250                 vm_page_wakeup(m);
  251                 return 0;
  252         }
  253 
  254         /*
  255          * Place page in cluster.  Align cluster for optimal swap space
  256          * allocation (whether it is swap or not).  This is typically ~16-32
  257          * pages, which also tends to align the cluster to multiples of the
  258          * filesystem block size if backed by a filesystem.
  259          */
  260         page_base = pindex % BLIST_MAX_ALLOC;
  261         mc[page_base] = m;
  262         ib = page_base - 1;
  263         is = page_base + 1;
  264 
  265         /*
  266          * Scan object for clusterable pages.
  267          *
  268          * We can cluster ONLY if: ->> the page is NOT
  269          * clean, wired, busy, held, or mapped into a
  270          * buffer, and one of the following:
  271          * 1) The page is inactive, or a seldom used
  272          *    active page.
  273          * -or-
  274          * 2) we force the issue.
  275          *
  276          * During heavy mmap/modification loads the pageout
  277          * daemon can really fragment the underlying file
  278          * due to flushing pages out of order and not trying
  279          * align the clusters (which leave sporatic out-of-order
  280          * holes).  To solve this problem we do the reverse scan
  281          * first and attempt to align our cluster, then do a 
  282          * forward scan if room remains.
  283          */
  284 
  285         vm_object_hold(object);
  286         while (ib >= 0) {
  287                 vm_page_t p;
  288 
  289                 p = vm_page_lookup_busy_try(object, pindex - page_base + ib,
  290                                             TRUE, &error);
  291                 if (error || p == NULL)
  292                         break;
  293                 if ((p->queue - p->pc) == PQ_CACHE ||
  294                     (p->flags & PG_UNMANAGED)) {
  295                         vm_page_wakeup(p);
  296                         break;
  297                 }
  298                 vm_page_test_dirty(p);
  299                 if (((p->dirty & p->valid) == 0 &&
  300                      (p->flags & PG_NEED_COMMIT) == 0) ||
  301                     p->queue - p->pc != PQ_INACTIVE ||
  302                     p->wire_count != 0 ||       /* may be held by buf cache */
  303                     p->hold_count != 0) {       /* may be undergoing I/O */
  304                         vm_page_wakeup(p);
  305                         break;
  306                 }
  307                 mc[ib] = p;
  308                 --ib;
  309         }
  310         ++ib;   /* fixup */
  311 
  312         while (is < BLIST_MAX_ALLOC &&
  313                pindex - page_base + is < object->size) {
  314                 vm_page_t p;
  315 
  316                 p = vm_page_lookup_busy_try(object, pindex - page_base + is,
  317                                             TRUE, &error);
  318                 if (error || p == NULL)
  319                         break;
  320                 if (((p->queue - p->pc) == PQ_CACHE) ||
  321                     (p->flags & (PG_BUSY|PG_UNMANAGED)) || p->busy) {
  322                         vm_page_wakeup(p);
  323                         break;
  324                 }
  325                 vm_page_test_dirty(p);
  326                 if (((p->dirty & p->valid) == 0 &&
  327                      (p->flags & PG_NEED_COMMIT) == 0) ||
  328                     p->queue - p->pc != PQ_INACTIVE ||
  329                     p->wire_count != 0 ||       /* may be held by buf cache */
  330                     p->hold_count != 0) {       /* may be undergoing I/O */
  331                         vm_page_wakeup(p);
  332                         break;
  333                 }
  334                 mc[is] = p;
  335                 ++is;
  336         }
  337 
  338         vm_object_drop(object);
  339 
  340         /*
  341          * we allow reads during pageouts...
  342          */
  343         return vm_pageout_flush(&mc[ib], is - ib, 0);
  344 }
  345 
  346 /*
  347  * vm_pageout_flush() - launder the given pages
  348  *
  349  *      The given pages are laundered.  Note that we setup for the start of
  350  *      I/O ( i.e. busy the page ), mark it read-only, and bump the object
  351  *      reference count all in here rather then in the parent.  If we want
  352  *      the parent to do more sophisticated things we may have to change
  353  *      the ordering.
  354  *
  355  *      The pages in the array must be busied by the caller and will be
  356  *      unbusied by this function.
  357  */
  358 int
  359 vm_pageout_flush(vm_page_t *mc, int count, int flags)
  360 {
  361         vm_object_t object;
  362         int pageout_status[count];
  363         int numpagedout = 0;
  364         int i;
  365 
  366         /*
  367          * Initiate I/O.  Bump the vm_page_t->busy counter.
  368          */
  369         for (i = 0; i < count; i++) {
  370                 KASSERT(mc[i]->valid == VM_PAGE_BITS_ALL,
  371                         ("vm_pageout_flush page %p index %d/%d: partially "
  372                          "invalid page", mc[i], i, count));
  373                 vm_page_io_start(mc[i]);
  374         }
  375 
  376         /*
  377          * We must make the pages read-only.  This will also force the
  378          * modified bit in the related pmaps to be cleared.  The pager
  379          * cannot clear the bit for us since the I/O completion code
  380          * typically runs from an interrupt.  The act of making the page
  381          * read-only handles the case for us.
  382          *
  383          * Then we can unbusy the pages, we still hold a reference by virtue
  384          * of our soft-busy.
  385          */
  386         for (i = 0; i < count; i++) {
  387                 vm_page_protect(mc[i], VM_PROT_READ);
  388                 vm_page_wakeup(mc[i]);
  389         }
  390 
  391         object = mc[0]->object;
  392         vm_object_pip_add(object, count);
  393 
  394         vm_pager_put_pages(object, mc, count,
  395             (flags | ((object == &kernel_object) ? VM_PAGER_PUT_SYNC : 0)),
  396             pageout_status);
  397 
  398         for (i = 0; i < count; i++) {
  399                 vm_page_t mt = mc[i];
  400 
  401                 switch (pageout_status[i]) {
  402                 case VM_PAGER_OK:
  403                         numpagedout++;
  404                         break;
  405                 case VM_PAGER_PEND:
  406                         numpagedout++;
  407                         break;
  408                 case VM_PAGER_BAD:
  409                         /*
  410                          * Page outside of range of object. Right now we
  411                          * essentially lose the changes by pretending it
  412                          * worked.
  413                          */
  414                         vm_page_busy_wait(mt, FALSE, "pgbad");
  415                         pmap_clear_modify(mt);
  416                         vm_page_undirty(mt);
  417                         vm_page_wakeup(mt);
  418                         break;
  419                 case VM_PAGER_ERROR:
  420                 case VM_PAGER_FAIL:
  421                         /*
  422                          * A page typically cannot be paged out when we
  423                          * have run out of swap.  We leave the page
  424                          * marked inactive and will try to page it out
  425                          * again later.
  426                          *
  427                          * Starvation of the active page list is used to
  428                          * determine when the system is massively memory
  429                          * starved.
  430                          */
  431                         break;
  432                 case VM_PAGER_AGAIN:
  433                         break;
  434                 }
  435 
  436                 /*
  437                  * If the operation is still going, leave the page busy to
  438                  * block all other accesses. Also, leave the paging in
  439                  * progress indicator set so that we don't attempt an object
  440                  * collapse.
  441                  *
  442                  * For any pages which have completed synchronously, 
  443                  * deactivate the page if we are under a severe deficit.
  444                  * Do not try to enter them into the cache, though, they
  445                  * might still be read-heavy.
  446                  */
  447                 if (pageout_status[i] != VM_PAGER_PEND) {
  448                         vm_page_busy_wait(mt, FALSE, "pgouw");
  449                         if (vm_page_count_severe())
  450                                 vm_page_deactivate(mt);
  451 #if 0
  452                         if (!vm_page_count_severe() || !vm_page_try_to_cache(mt))
  453                                 vm_page_protect(mt, VM_PROT_READ);
  454 #endif
  455                         vm_page_io_finish(mt);
  456                         vm_page_wakeup(mt);
  457                         vm_object_pip_wakeup(object);
  458                 }
  459         }
  460         return numpagedout;
  461 }
  462 
  463 #if !defined(NO_SWAPPING)
  464 /*
  465  * deactivate enough pages to satisfy the inactive target
  466  * requirements or if vm_page_proc_limit is set, then
  467  * deactivate all of the pages in the object and its
  468  * backing_objects.
  469  *
  470  * The map must be locked.
  471  * The caller must hold the vm_object.
  472  */
  473 static int vm_pageout_object_deactivate_pages_callback(vm_page_t, void *);
  474 
  475 static void
  476 vm_pageout_object_deactivate_pages(vm_map_t map, vm_object_t object,
  477                                    vm_pindex_t desired, int map_remove_only)
  478 {
  479         struct rb_vm_page_scan_info info;
  480         vm_object_t lobject;
  481         vm_object_t tobject;
  482         int remove_mode;
  483 
  484         ASSERT_LWKT_TOKEN_HELD(vm_object_token(object));
  485         lobject = object;
  486 
  487         while (lobject) {
  488                 if (pmap_resident_count(vm_map_pmap(map)) <= desired)
  489                         break;
  490                 if (lobject->type == OBJT_DEVICE ||
  491                     lobject->type == OBJT_MGTDEVICE ||
  492                     lobject->type == OBJT_PHYS)
  493                         break;
  494                 if (lobject->paging_in_progress)
  495                         break;
  496 
  497                 remove_mode = map_remove_only;
  498                 if (lobject->shadow_count > 1)
  499                         remove_mode = 1;
  500 
  501                 /*
  502                  * scan the objects entire memory queue.  We hold the
  503                  * object's token so the scan should not race anything.
  504                  */
  505                 info.limit = remove_mode;
  506                 info.map = map;
  507                 info.desired = desired;
  508                 vm_page_rb_tree_RB_SCAN(&lobject->rb_memq, NULL,
  509                                 vm_pageout_object_deactivate_pages_callback,
  510                                 &info
  511                 );
  512                 while ((tobject = lobject->backing_object) != NULL) {
  513                         KKASSERT(tobject != object);
  514                         vm_object_hold(tobject);
  515                         if (tobject == lobject->backing_object)
  516                                 break;
  517                         vm_object_drop(tobject);
  518                 }
  519                 if (lobject != object) {
  520                         if (tobject)
  521                                 vm_object_lock_swap();
  522                         vm_object_drop(lobject);
  523                         /* leaves tobject locked & at top */
  524                 }
  525                 lobject = tobject;
  526         }
  527         if (lobject != object)
  528                 vm_object_drop(lobject);        /* NULL ok */
  529 }
  530 
  531 /*
  532  * The caller must hold the vm_object.
  533  */
  534 static int
  535 vm_pageout_object_deactivate_pages_callback(vm_page_t p, void *data)
  536 {
  537         struct rb_vm_page_scan_info *info = data;
  538         int actcount;
  539 
  540         if (pmap_resident_count(vm_map_pmap(info->map)) <= info->desired) {
  541                 return(-1);
  542         }
  543         mycpu->gd_cnt.v_pdpages++;
  544 
  545         if (vm_page_busy_try(p, TRUE))
  546                 return(0);
  547         if (p->wire_count || p->hold_count || (p->flags & PG_UNMANAGED)) {
  548                 vm_page_wakeup(p);
  549                 return(0);
  550         }
  551         if (!pmap_page_exists_quick(vm_map_pmap(info->map), p)) {
  552                 vm_page_wakeup(p);
  553                 return(0);
  554         }
  555 
  556         actcount = pmap_ts_referenced(p);
  557         if (actcount) {
  558                 vm_page_flag_set(p, PG_REFERENCED);
  559         } else if (p->flags & PG_REFERENCED) {
  560                 actcount = 1;
  561         }
  562 
  563         vm_page_and_queue_spin_lock(p);
  564         if (p->queue - p->pc != PQ_ACTIVE && (p->flags & PG_REFERENCED)) {
  565                 vm_page_and_queue_spin_unlock(p);
  566                 vm_page_activate(p);
  567                 p->act_count += actcount;
  568                 vm_page_flag_clear(p, PG_REFERENCED);
  569         } else if (p->queue - p->pc == PQ_ACTIVE) {
  570                 if ((p->flags & PG_REFERENCED) == 0) {
  571                         p->act_count -= min(p->act_count, ACT_DECLINE);
  572                         if (!info->limit &&
  573                             (vm_pageout_algorithm || (p->act_count == 0))) {
  574                                 vm_page_and_queue_spin_unlock(p);
  575                                 vm_page_protect(p, VM_PROT_NONE);
  576                                 vm_page_deactivate(p);
  577                         } else {
  578                                 TAILQ_REMOVE(&vm_page_queues[p->queue].pl,
  579                                              p, pageq);
  580                                 TAILQ_INSERT_TAIL(&vm_page_queues[p->queue].pl,
  581                                                   p, pageq);
  582                                 vm_page_and_queue_spin_unlock(p);
  583                         }
  584                 } else {
  585                         vm_page_and_queue_spin_unlock(p);
  586                         vm_page_activate(p);
  587                         vm_page_flag_clear(p, PG_REFERENCED);
  588 
  589                         vm_page_and_queue_spin_lock(p);
  590                         if (p->queue - p->pc == PQ_ACTIVE) {
  591                                 if (p->act_count < (ACT_MAX - ACT_ADVANCE))
  592                                         p->act_count += ACT_ADVANCE;
  593                                 TAILQ_REMOVE(&vm_page_queues[p->queue].pl,
  594                                              p, pageq);
  595                                 TAILQ_INSERT_TAIL(&vm_page_queues[p->queue].pl,
  596                                                   p, pageq);
  597                         }
  598                         vm_page_and_queue_spin_unlock(p);
  599                 }
  600         } else if (p->queue - p->pc == PQ_INACTIVE) {
  601                 vm_page_and_queue_spin_unlock(p);
  602                 vm_page_protect(p, VM_PROT_NONE);
  603         } else {
  604                 vm_page_and_queue_spin_unlock(p);
  605         }
  606         vm_page_wakeup(p);
  607         return(0);
  608 }
  609 
  610 /*
  611  * Deactivate some number of pages in a map, try to do it fairly, but
  612  * that is really hard to do.
  613  */
  614 static void
  615 vm_pageout_map_deactivate_pages(vm_map_t map, vm_pindex_t desired)
  616 {
  617         vm_map_entry_t tmpe;
  618         vm_object_t obj, bigobj;
  619         int nothingwired;
  620 
  621         if (lockmgr(&map->lock, LK_EXCLUSIVE | LK_NOWAIT)) {
  622                 return;
  623         }
  624 
  625         bigobj = NULL;
  626         nothingwired = TRUE;
  627 
  628         /*
  629          * first, search out the biggest object, and try to free pages from
  630          * that.
  631          */
  632         tmpe = map->header.next;
  633         while (tmpe != &map->header) {
  634                 switch(tmpe->maptype) {
  635                 case VM_MAPTYPE_NORMAL:
  636                 case VM_MAPTYPE_VPAGETABLE:
  637                         obj = tmpe->object.vm_object;
  638                         if ((obj != NULL) && (obj->shadow_count <= 1) &&
  639                                 ((bigobj == NULL) ||
  640                                  (bigobj->resident_page_count < obj->resident_page_count))) {
  641                                 bigobj = obj;
  642                         }
  643                         break;
  644                 default:
  645                         break;
  646                 }
  647                 if (tmpe->wired_count > 0)
  648                         nothingwired = FALSE;
  649                 tmpe = tmpe->next;
  650         }
  651 
  652         if (bigobj)  {
  653                 vm_object_hold(bigobj);
  654                 vm_pageout_object_deactivate_pages(map, bigobj, desired, 0);
  655                 vm_object_drop(bigobj);
  656         }
  657 
  658         /*
  659          * Next, hunt around for other pages to deactivate.  We actually
  660          * do this search sort of wrong -- .text first is not the best idea.
  661          */
  662         tmpe = map->header.next;
  663         while (tmpe != &map->header) {
  664                 if (pmap_resident_count(vm_map_pmap(map)) <= desired)
  665                         break;
  666                 switch(tmpe->maptype) {
  667                 case VM_MAPTYPE_NORMAL:
  668                 case VM_MAPTYPE_VPAGETABLE:
  669                         obj = tmpe->object.vm_object;
  670                         if (obj) {
  671                                 vm_object_hold(obj);
  672                                 vm_pageout_object_deactivate_pages(map, obj, desired, 0);
  673                                 vm_object_drop(obj);
  674                         }
  675                         break;
  676                 default:
  677                         break;
  678                 }
  679                 tmpe = tmpe->next;
  680         }
  681 
  682         /*
  683          * Remove all mappings if a process is swapped out, this will free page
  684          * table pages.
  685          */
  686         if (desired == 0 && nothingwired)
  687                 pmap_remove(vm_map_pmap(map),
  688                             VM_MIN_USER_ADDRESS, VM_MAX_USER_ADDRESS);
  689         vm_map_unlock(map);
  690 }
  691 #endif
  692 
  693 /*
  694  * Called when the pageout scan wants to free a page.  We no longer
  695  * try to cycle the vm_object here with a reference & dealloc, which can
  696  * cause a non-trivial object collapse in a critical path.
  697  *
  698  * It is unclear why we cycled the ref_count in the past, perhaps to try
  699  * to optimize shadow chain collapses but I don't quite see why it would
  700  * be necessary.  An OBJ_DEAD object should terminate any and all vm_pages
  701  * synchronously and not have to be kicked-start.
  702  */
  703 static void
  704 vm_pageout_page_free(vm_page_t m) 
  705 {
  706         vm_page_protect(m, VM_PROT_NONE);
  707         vm_page_free(m);
  708 }
  709 
  710 /*
  711  * vm_pageout_scan does the dirty work for the pageout daemon.
  712  */
  713 struct vm_pageout_scan_info {
  714         struct proc *bigproc;
  715         vm_offset_t bigsize;
  716 };
  717 
  718 static int vm_pageout_scan_callback(struct proc *p, void *data);
  719 
  720 static int
  721 vm_pageout_scan_inactive(int pass, int q, int avail_shortage,
  722                          int *vnodes_skippedp)
  723 {
  724         vm_page_t m;
  725         struct vm_page marker;
  726         struct vnode *vpfailed;         /* warning, allowed to be stale */
  727         int maxscan;
  728         int count;
  729         int delta = 0;
  730         vm_object_t object;
  731         int actcount;
  732         int maxlaunder;
  733 
  734         /*
  735          * Start scanning the inactive queue for pages we can move to the
  736          * cache or free.  The scan will stop when the target is reached or
  737          * we have scanned the entire inactive queue.  Note that m->act_count
  738          * is not used to form decisions for the inactive queue, only for the
  739          * active queue.
  740          *
  741          * maxlaunder limits the number of dirty pages we flush per scan.
  742          * For most systems a smaller value (16 or 32) is more robust under
  743          * extreme memory and disk pressure because any unnecessary writes
  744          * to disk can result in extreme performance degredation.  However,
  745          * systems with excessive dirty pages (especially when MAP_NOSYNC is
  746          * used) will die horribly with limited laundering.  If the pageout
  747          * daemon cannot clean enough pages in the first pass, we let it go
  748          * all out in succeeding passes.
  749          */
  750         if ((maxlaunder = vm_max_launder) <= 1)
  751                 maxlaunder = 1;
  752         if (pass)
  753                 maxlaunder = 10000;
  754 
  755         /*
  756          * Initialize our marker
  757          */
  758         bzero(&marker, sizeof(marker));
  759         marker.flags = PG_BUSY | PG_FICTITIOUS | PG_MARKER;
  760         marker.queue = PQ_INACTIVE + q;
  761         marker.pc = q;
  762         marker.wire_count = 1;
  763 
  764         /*
  765          * Inactive queue scan.
  766          *
  767          * NOTE: The vm_page must be spinlocked before the queue to avoid
  768          *       deadlocks, so it is easiest to simply iterate the loop
  769          *       with the queue unlocked at the top.
  770          */
  771         vpfailed = NULL;
  772 
  773         vm_page_queues_spin_lock(PQ_INACTIVE + q);
  774         TAILQ_INSERT_HEAD(&vm_page_queues[PQ_INACTIVE + q].pl, &marker, pageq);
  775         maxscan = vm_page_queues[PQ_INACTIVE + q].lcnt;
  776         vm_page_queues_spin_unlock(PQ_INACTIVE + q);
  777 
  778         while ((m = TAILQ_NEXT(&marker, pageq)) != NULL &&
  779                maxscan-- > 0 && avail_shortage - delta > 0)
  780         {
  781                 vm_page_and_queue_spin_lock(m);
  782                 if (m != TAILQ_NEXT(&marker, pageq)) {
  783                         vm_page_and_queue_spin_unlock(m);
  784                         ++maxscan;
  785                         continue;
  786                 }
  787                 KKASSERT(m->queue - m->pc == PQ_INACTIVE);
  788                 TAILQ_REMOVE(&vm_page_queues[PQ_INACTIVE + q].pl,
  789                              &marker, pageq);
  790                 TAILQ_INSERT_AFTER(&vm_page_queues[PQ_INACTIVE + q].pl, m,
  791                                    &marker, pageq);
  792                 mycpu->gd_cnt.v_pdpages++;
  793 
  794                 /*
  795                  * Skip marker pages
  796                  */
  797                 if (m->flags & PG_MARKER) {
  798                         vm_page_and_queue_spin_unlock(m);
  799                         continue;
  800                 }
  801 
  802                 /*
  803                  * Try to busy the page.  Don't mess with pages which are
  804                  * already busy or reorder them in the queue.
  805                  */
  806                 if (vm_page_busy_try(m, TRUE)) {
  807                         vm_page_and_queue_spin_unlock(m);
  808                         continue;
  809                 }
  810                 vm_page_and_queue_spin_unlock(m);
  811                 KKASSERT(m->queue - m->pc == PQ_INACTIVE);
  812 
  813                 lwkt_yield();
  814 
  815                 /*
  816                  * The page has been successfully busied and is now no
  817                  * longer spinlocked.  The queue is no longer spinlocked
  818                  * either.
  819                  */
  820 
  821                 /*
  822                  * It is possible for a page to be busied ad-hoc (e.g. the
  823                  * pmap_collect() code) and wired and race against the
  824                  * allocation of a new page.  vm_page_alloc() may be forced
  825                  * to deactivate the wired page in which case it winds up
  826                  * on the inactive queue and must be handled here.  We
  827                  * correct the problem simply by unqueuing the page.
  828                  */
  829                 if (m->wire_count) {
  830                         vm_page_unqueue_nowakeup(m);
  831                         vm_page_wakeup(m);
  832                         kprintf("WARNING: pagedaemon: wired page on "
  833                                 "inactive queue %p\n", m);
  834                         continue;
  835                 }
  836 
  837                 /*
  838                  * A held page may be undergoing I/O, so skip it.
  839                  */
  840                 if (m->hold_count) {
  841                         vm_page_and_queue_spin_lock(m);
  842                         if (m->queue - m->pc == PQ_INACTIVE) {
  843                                 TAILQ_REMOVE(
  844                                         &vm_page_queues[PQ_INACTIVE + q].pl,
  845                                         m, pageq);
  846                                 TAILQ_INSERT_TAIL(
  847                                         &vm_page_queues[PQ_INACTIVE + q].pl,
  848                                         m, pageq);
  849                                 ++vm_swapcache_inactive_heuristic;
  850                         }
  851                         vm_page_and_queue_spin_unlock(m);
  852                         vm_page_wakeup(m);
  853                         continue;
  854                 }
  855 
  856                 if (m->object == NULL || m->object->ref_count == 0) {
  857                         /*
  858                          * If the object is not being used, we ignore previous 
  859                          * references.
  860                          */
  861                         vm_page_flag_clear(m, PG_REFERENCED);
  862                         pmap_clear_reference(m);
  863                         /* fall through to end */
  864                 } else if (((m->flags & PG_REFERENCED) == 0) &&
  865                             (actcount = pmap_ts_referenced(m))) {
  866                         /*
  867                          * Otherwise, if the page has been referenced while 
  868                          * in the inactive queue, we bump the "activation
  869                          * count" upwards, making it less likely that the
  870                          * page will be added back to the inactive queue
  871                          * prematurely again.  Here we check the page tables
  872                          * (or emulated bits, if any), given the upper level
  873                          * VM system not knowing anything about existing 
  874                          * references.
  875                          */
  876                         vm_page_activate(m);
  877                         m->act_count += (actcount + ACT_ADVANCE);
  878                         vm_page_wakeup(m);
  879                         continue;
  880                 }
  881 
  882                 /*
  883                  * (m) is still busied.
  884                  *
  885                  * If the upper level VM system knows about any page 
  886                  * references, we activate the page.  We also set the 
  887                  * "activation count" higher than normal so that we will less 
  888                  * likely place pages back onto the inactive queue again.
  889                  */
  890                 if ((m->flags & PG_REFERENCED) != 0) {
  891                         vm_page_flag_clear(m, PG_REFERENCED);
  892                         actcount = pmap_ts_referenced(m);
  893                         vm_page_activate(m);
  894                         m->act_count += (actcount + ACT_ADVANCE + 1);
  895                         vm_page_wakeup(m);
  896                         continue;
  897                 }
  898 
  899                 /*
  900                  * If the upper level VM system doesn't know anything about 
  901                  * the page being dirty, we have to check for it again.  As 
  902                  * far as the VM code knows, any partially dirty pages are 
  903                  * fully dirty.
  904                  *
  905                  * Pages marked PG_WRITEABLE may be mapped into the user
  906                  * address space of a process running on another cpu.  A
  907                  * user process (without holding the MP lock) running on
  908                  * another cpu may be able to touch the page while we are
  909                  * trying to remove it.  vm_page_cache() will handle this
  910                  * case for us.
  911                  */
  912                 if (m->dirty == 0) {
  913                         vm_page_test_dirty(m);
  914                 } else {
  915                         vm_page_dirty(m);
  916                 }
  917 
  918                 if (m->valid == 0 && (m->flags & PG_NEED_COMMIT) == 0) {
  919                         /*
  920                          * Invalid pages can be easily freed
  921                          */
  922                         vm_pageout_page_free(m);
  923                         mycpu->gd_cnt.v_dfree++;
  924                         ++delta;
  925                 } else if (m->dirty == 0 && (m->flags & PG_NEED_COMMIT) == 0) {
  926                         /*
  927                          * Clean pages can be placed onto the cache queue.
  928                          * This effectively frees them.
  929                          */
  930                         vm_page_cache(m);
  931                         ++delta;
  932                 } else if ((m->flags & PG_WINATCFLS) == 0 && pass == 0) {
  933                         /*
  934                          * Dirty pages need to be paged out, but flushing
  935                          * a page is extremely expensive verses freeing
  936                          * a clean page.  Rather then artificially limiting
  937                          * the number of pages we can flush, we instead give
  938                          * dirty pages extra priority on the inactive queue
  939                          * by forcing them to be cycled through the queue
  940                          * twice before being flushed, after which the 
  941                          * (now clean) page will cycle through once more
  942                          * before being freed.  This significantly extends
  943                          * the thrash point for a heavily loaded machine.
  944                          */
  945                         vm_page_flag_set(m, PG_WINATCFLS);
  946                         vm_page_and_queue_spin_lock(m);
  947                         if (m->queue - m->pc == PQ_INACTIVE) {
  948                                 TAILQ_REMOVE(
  949                                         &vm_page_queues[PQ_INACTIVE + q].pl,
  950                                         m, pageq);
  951                                 TAILQ_INSERT_TAIL(
  952                                         &vm_page_queues[PQ_INACTIVE + q].pl,
  953                                         m, pageq);
  954                                 ++vm_swapcache_inactive_heuristic;
  955                         }
  956                         vm_page_and_queue_spin_unlock(m);
  957                         vm_page_wakeup(m);
  958                 } else if (maxlaunder > 0) {
  959                         /*
  960                          * We always want to try to flush some dirty pages if
  961                          * we encounter them, to keep the system stable.
  962                          * Normally this number is small, but under extreme
  963                          * pressure where there are insufficient clean pages
  964                          * on the inactive queue, we may have to go all out.
  965                          */
  966                         int swap_pageouts_ok;
  967                         struct vnode *vp = NULL;
  968 
  969                         swap_pageouts_ok = 0;
  970                         object = m->object;
  971                         if (object &&
  972                             (object->type != OBJT_SWAP) && 
  973                             (object->type != OBJT_DEFAULT)) {
  974                                 swap_pageouts_ok = 1;
  975                         } else {
  976                                 swap_pageouts_ok = !(defer_swap_pageouts || disable_swap_pageouts);
  977                                 swap_pageouts_ok |= (!disable_swap_pageouts && defer_swap_pageouts &&
  978                                 vm_page_count_min(0));
  979                                                                                 
  980                         }
  981 
  982                         /*
  983                          * We don't bother paging objects that are "dead".  
  984                          * Those objects are in a "rundown" state.
  985                          */
  986                         if (!swap_pageouts_ok || 
  987                             (object == NULL) ||
  988                             (object->flags & OBJ_DEAD)) {
  989                                 vm_page_and_queue_spin_lock(m);
  990                                 if (m->queue - m->pc == PQ_INACTIVE) {
  991                                         TAILQ_REMOVE(
  992                                             &vm_page_queues[PQ_INACTIVE + q].pl,
  993                                             m, pageq);
  994                                         TAILQ_INSERT_TAIL(
  995                                             &vm_page_queues[PQ_INACTIVE + q].pl,
  996                                             m, pageq);
  997                                         ++vm_swapcache_inactive_heuristic;
  998                                 }
  999                                 vm_page_and_queue_spin_unlock(m);
 1000                                 vm_page_wakeup(m);
 1001                                 continue;
 1002                         }
 1003 
 1004                         /*
 1005                          * (m) is still busied.
 1006                          *
 1007                          * The object is already known NOT to be dead.   It
 1008                          * is possible for the vget() to block the whole
 1009                          * pageout daemon, but the new low-memory handling
 1010                          * code should prevent it.
 1011                          *
 1012                          * The previous code skipped locked vnodes and, worse,
 1013                          * reordered pages in the queue.  This results in
 1014                          * completely non-deterministic operation because,
 1015                          * quite often, a vm_fault has initiated an I/O and
 1016                          * is holding a locked vnode at just the point where
 1017                          * the pageout daemon is woken up.
 1018                          *
 1019                          * We can't wait forever for the vnode lock, we might
 1020                          * deadlock due to a vn_read() getting stuck in
 1021                          * vm_wait while holding this vnode.  We skip the 
 1022                          * vnode if we can't get it in a reasonable amount
 1023                          * of time.
 1024                          *
 1025                          * vpfailed is used to (try to) avoid the case where
 1026                          * a large number of pages are associated with a
 1027                          * locked vnode, which could cause the pageout daemon
 1028                          * to stall for an excessive amount of time.
 1029                          */
 1030                         if (object->type == OBJT_VNODE) {
 1031                                 int flags;
 1032 
 1033                                 vp = object->handle;
 1034                                 flags = LK_EXCLUSIVE;
 1035                                 if (vp == vpfailed)
 1036                                         flags |= LK_NOWAIT;
 1037                                 else
 1038                                         flags |= LK_TIMELOCK;
 1039                                 vm_page_hold(m);
 1040                                 vm_page_wakeup(m);
 1041 
 1042                                 /*
 1043                                  * We have unbusied (m) temporarily so we can
 1044                                  * acquire the vp lock without deadlocking.
 1045                                  * (m) is held to prevent destruction.
 1046                                  */
 1047                                 if (vget(vp, flags) != 0) {
 1048                                         vpfailed = vp;
 1049                                         ++pageout_lock_miss;
 1050                                         if (object->flags & OBJ_MIGHTBEDIRTY)
 1051                                                     ++*vnodes_skippedp;
 1052                                         vm_page_unhold(m);
 1053                                         continue;
 1054                                 }
 1055 
 1056                                 /*
 1057                                  * The page might have been moved to another
 1058                                  * queue during potential blocking in vget()
 1059                                  * above.  The page might have been freed and
 1060                                  * reused for another vnode.  The object might
 1061                                  * have been reused for another vnode.
 1062                                  */
 1063                                 if (m->queue - m->pc != PQ_INACTIVE ||
 1064                                     m->object != object ||
 1065                                     object->handle != vp) {
 1066                                         if (object->flags & OBJ_MIGHTBEDIRTY)
 1067                                                 ++*vnodes_skippedp;
 1068                                         vput(vp);
 1069                                         vm_page_unhold(m);
 1070                                         continue;
 1071                                 }
 1072         
 1073                                 /*
 1074                                  * The page may have been busied during the
 1075                                  * blocking in vput();  We don't move the
 1076                                  * page back onto the end of the queue so that
 1077                                  * statistics are more correct if we don't.
 1078                                  */
 1079                                 if (vm_page_busy_try(m, TRUE)) {
 1080                                         vput(vp);
 1081                                         vm_page_unhold(m);
 1082                                         continue;
 1083                                 }
 1084                                 vm_page_unhold(m);
 1085 
 1086                                 /*
 1087                                  * (m) is busied again
 1088                                  *
 1089                                  * We own the busy bit and remove our hold
 1090                                  * bit.  If the page is still held it
 1091                                  * might be undergoing I/O, so skip it.
 1092                                  */
 1093                                 if (m->hold_count) {
 1094                                         vm_page_and_queue_spin_lock(m);
 1095                                         if (m->queue - m->pc == PQ_INACTIVE) {
 1096                                                 TAILQ_REMOVE(&vm_page_queues[PQ_INACTIVE + q].pl, m, pageq);
 1097                                                 TAILQ_INSERT_TAIL(&vm_page_queues[PQ_INACTIVE + q].pl, m, pageq);
 1098                                                 ++vm_swapcache_inactive_heuristic;
 1099                                         }
 1100                                         vm_page_and_queue_spin_unlock(m);
 1101                                         if (object->flags & OBJ_MIGHTBEDIRTY)
 1102                                                 ++*vnodes_skippedp;
 1103                                         vm_page_wakeup(m);
 1104                                         vput(vp);
 1105                                         continue;
 1106                                 }
 1107                                 /* (m) is left busied as we fall through */
 1108                         }
 1109 
 1110                         /*
 1111                          * page is busy and not held here.
 1112                          *
 1113                          * If a page is dirty, then it is either being washed
 1114                          * (but not yet cleaned) or it is still in the
 1115                          * laundry.  If it is still in the laundry, then we
 1116                          * start the cleaning operation. 
 1117                          *
 1118                          * decrement inactive_shortage on success to account
 1119                          * for the (future) cleaned page.  Otherwise we
 1120                          * could wind up laundering or cleaning too many
 1121                          * pages.
 1122                          */
 1123                         count = vm_pageout_clean(m);
 1124                         delta += count;
 1125                         maxlaunder -= count;
 1126 
 1127                         /*
 1128                          * Clean ate busy, page no longer accessible
 1129                          */
 1130                         if (vp != NULL)
 1131                                 vput(vp);
 1132                 } else {
 1133                         vm_page_wakeup(m);
 1134                 }
 1135 
 1136                 /*
 1137                  * Systems with a ton of memory can wind up with huge
 1138                  * deactivation counts.  Because the inactive scan is
 1139                  * doing a lot of flushing, the combination can result
 1140                  * in excessive paging even in situations where other
 1141                  * unrelated threads free up sufficient VM.
 1142                  *
 1143                  * To deal with this we abort the nominal active->inactive
 1144                  * scan before we hit the inactive target when free+cache
 1145                  * levels have already reached their target.
 1146                  *
 1147                  * Note that nominally the inactive scan is not freeing or
 1148                  * caching pages, it is deactivating active pages, so it
 1149                  * will not by itself cause the abort condition.
 1150                  */
 1151                 if (vm_paging_target() < 0)
 1152                         break;
 1153         }
 1154         vm_page_queues_spin_lock(PQ_INACTIVE + q);
 1155         TAILQ_REMOVE(&vm_page_queues[PQ_INACTIVE + q].pl, &marker, pageq);
 1156         vm_page_queues_spin_unlock(PQ_INACTIVE + q);
 1157 
 1158         return (delta);
 1159 }
 1160 
 1161 static int
 1162 vm_pageout_scan_active(int pass, int q,
 1163                        int avail_shortage, int inactive_shortage,
 1164                        int *recycle_countp)
 1165 {
 1166         struct vm_page marker;
 1167         vm_page_t m;
 1168         int actcount;
 1169         int delta = 0;
 1170         int maxscan;
 1171 
 1172         /*
 1173          * We want to move pages from the active queue to the inactive
 1174          * queue to get the inactive queue to the inactive target.  If
 1175          * we still have a page shortage from above we try to directly free
 1176          * clean pages instead of moving them.
 1177          *
 1178          * If we do still have a shortage we keep track of the number of
 1179          * pages we free or cache (recycle_count) as a measure of thrashing
 1180          * between the active and inactive queues.
 1181          *
 1182          * If we were able to completely satisfy the free+cache targets
 1183          * from the inactive pool we limit the number of pages we move
 1184          * from the active pool to the inactive pool to 2x the pages we
 1185          * had removed from the inactive pool (with a minimum of 1/5 the
 1186          * inactive target).  If we were not able to completely satisfy
 1187          * the free+cache targets we go for the whole target aggressively.
 1188          *
 1189          * NOTE: Both variables can end up negative.
 1190          * NOTE: We are still in a critical section.
 1191          */
 1192 
 1193         bzero(&marker, sizeof(marker));
 1194         marker.flags = PG_BUSY | PG_FICTITIOUS | PG_MARKER;
 1195         marker.queue = PQ_ACTIVE + q;
 1196         marker.pc = q;
 1197         marker.wire_count = 1;
 1198 
 1199         vm_page_queues_spin_lock(PQ_ACTIVE + q);
 1200         TAILQ_INSERT_HEAD(&vm_page_queues[PQ_ACTIVE + q].pl, &marker, pageq);
 1201         maxscan = vm_page_queues[PQ_ACTIVE + q].lcnt;
 1202         vm_page_queues_spin_unlock(PQ_ACTIVE + q);
 1203 
 1204         while ((m = TAILQ_NEXT(&marker, pageq)) != NULL &&
 1205                maxscan-- > 0 && (avail_shortage - delta > 0 ||
 1206                                 inactive_shortage > 0))
 1207         {
 1208                 vm_page_and_queue_spin_lock(m);
 1209                 if (m != TAILQ_NEXT(&marker, pageq)) {
 1210                         vm_page_and_queue_spin_unlock(m);
 1211                         ++maxscan;
 1212                         continue;
 1213                 }
 1214                 KKASSERT(m->queue - m->pc == PQ_ACTIVE);
 1215                 TAILQ_REMOVE(&vm_page_queues[PQ_ACTIVE + q].pl,
 1216                              &marker, pageq);
 1217                 TAILQ_INSERT_AFTER(&vm_page_queues[PQ_ACTIVE + q].pl, m,
 1218                                    &marker, pageq);
 1219 
 1220                 /*
 1221                  * Skip marker pages
 1222                  */
 1223                 if (m->flags & PG_MARKER) {
 1224                         vm_page_and_queue_spin_unlock(m);
 1225                         continue;
 1226                 }
 1227 
 1228                 /*
 1229                  * Try to busy the page.  Don't mess with pages which are
 1230                  * already busy or reorder them in the queue.
 1231                  */
 1232                 if (vm_page_busy_try(m, TRUE)) {
 1233                         vm_page_and_queue_spin_unlock(m);
 1234                         continue;
 1235                 }
 1236 
 1237                 /*
 1238                  * Don't deactivate pages that are held, even if we can
 1239                  * busy them.  (XXX why not?)
 1240                  */
 1241                 if (m->hold_count != 0) {
 1242                         TAILQ_REMOVE(&vm_page_queues[PQ_ACTIVE + q].pl,
 1243                                      m, pageq);
 1244                         TAILQ_INSERT_TAIL(&vm_page_queues[PQ_ACTIVE + q].pl,
 1245                                           m, pageq);
 1246                         vm_page_and_queue_spin_unlock(m);
 1247                         vm_page_wakeup(m);
 1248                         continue;
 1249                 }
 1250                 vm_page_and_queue_spin_unlock(m);
 1251                 lwkt_yield();
 1252 
 1253                 /*
 1254                  * The page has been successfully busied and the page and
 1255                  * queue are no longer locked.
 1256                  */
 1257 
 1258                 /*
 1259                  * The count for pagedaemon pages is done after checking the
 1260                  * page for eligibility...
 1261                  */
 1262                 mycpu->gd_cnt.v_pdpages++;
 1263 
 1264                 /*
 1265                  * Check to see "how much" the page has been used and clear
 1266                  * the tracking access bits.  If the object has no references
 1267                  * don't bother paying the expense.
 1268                  */
 1269                 actcount = 0;
 1270                 if (m->object && m->object->ref_count != 0) {
 1271                         if (m->flags & PG_REFERENCED)
 1272                                 ++actcount;
 1273                         actcount += pmap_ts_referenced(m);
 1274                         if (actcount) {
 1275                                 m->act_count += ACT_ADVANCE + actcount;
 1276                                 if (m->act_count > ACT_MAX)
 1277                                         m->act_count = ACT_MAX;
 1278                         }
 1279                 }
 1280                 vm_page_flag_clear(m, PG_REFERENCED);
 1281 
 1282                 /*
 1283                  * actcount is only valid if the object ref_count is non-zero.
 1284                  * If the page does not have an object, actcount will be zero.
 1285                  */
 1286                 if (actcount && m->object->ref_count != 0) {
 1287                         vm_page_and_queue_spin_lock(m);
 1288                         if (m->queue - m->pc == PQ_ACTIVE) {
 1289                                 TAILQ_REMOVE(
 1290                                         &vm_page_queues[PQ_ACTIVE + q].pl,
 1291                                         m, pageq);
 1292                                 TAILQ_INSERT_TAIL(
 1293                                         &vm_page_queues[PQ_ACTIVE + q].pl,
 1294                                         m, pageq);
 1295                         }
 1296                         vm_page_and_queue_spin_unlock(m);
 1297                         vm_page_wakeup(m);
 1298                 } else {
 1299                         switch(m->object->type) {
 1300                         case OBJT_DEFAULT:
 1301                         case OBJT_SWAP:
 1302                                 m->act_count -= min(m->act_count,
 1303                                                     vm_anonmem_decline);
 1304                                 break;
 1305                         default:
 1306                                 m->act_count -= min(m->act_count,
 1307                                                     vm_filemem_decline);
 1308                                 break;
 1309                         }
 1310                         if (vm_pageout_algorithm ||
 1311                             (m->object == NULL) ||
 1312                             (m->object && (m->object->ref_count == 0)) ||
 1313                             m->act_count < pass + 1
 1314                         ) {
 1315                                 /*
 1316                                  * Deactivate the page.  If we had a
 1317                                  * shortage from our inactive scan try to
 1318                                  * free (cache) the page instead.
 1319                                  *
 1320                                  * Don't just blindly cache the page if
 1321                                  * we do not have a shortage from the
 1322                                  * inactive scan, that could lead to
 1323                                  * gigabytes being moved.
 1324                                  */
 1325                                 --inactive_shortage;
 1326                                 if (avail_shortage - delta > 0 ||
 1327                                     (m->object && (m->object->ref_count == 0)))
 1328                                 {
 1329                                         if (avail_shortage - delta > 0)
 1330                                                 ++*recycle_countp;
 1331                                         vm_page_protect(m, VM_PROT_NONE);
 1332                                         if (m->dirty == 0 &&
 1333                                             (m->flags & PG_NEED_COMMIT) == 0 &&
 1334                                             avail_shortage - delta > 0) {
 1335                                                 vm_page_cache(m);
 1336                                         } else {
 1337                                                 vm_page_deactivate(m);
 1338                                                 vm_page_wakeup(m);
 1339                                         }
 1340                                 } else {
 1341                                         vm_page_deactivate(m);
 1342                                         vm_page_wakeup(m);
 1343                                 }
 1344                                 ++delta;
 1345                         } else {
 1346                                 vm_page_and_queue_spin_lock(m);
 1347                                 if (m->queue - m->pc == PQ_ACTIVE) {
 1348                                         TAILQ_REMOVE(
 1349                                             &vm_page_queues[PQ_ACTIVE + q].pl,
 1350                                             m, pageq);
 1351                                         TAILQ_INSERT_TAIL(
 1352                                             &vm_page_queues[PQ_ACTIVE + q].pl,
 1353                                             m, pageq);
 1354                                 }
 1355                                 vm_page_and_queue_spin_unlock(m);
 1356                                 vm_page_wakeup(m);
 1357                         }
 1358                 }
 1359         }
 1360 
 1361         /*
 1362          * Clean out our local marker.
 1363          */
 1364         vm_page_queues_spin_lock(PQ_ACTIVE + q);
 1365         TAILQ_REMOVE(&vm_page_queues[PQ_ACTIVE + q].pl, &marker, pageq);
 1366         vm_page_queues_spin_unlock(PQ_ACTIVE + q);
 1367 
 1368         return (delta);
 1369 }
 1370 
 1371 /*
 1372  * The number of actually free pages can drop down to v_free_reserved,
 1373  * we try to build the free count back above v_free_min.  Note that
 1374  * vm_paging_needed() also returns TRUE if v_free_count is not at
 1375  * least v_free_min so that is the minimum we must build the free
 1376  * count to.
 1377  *
 1378  * We use a slightly higher target to improve hysteresis,
 1379  * ((v_free_target + v_free_min) / 2).  Since v_free_target
 1380  * is usually the same as v_cache_min this maintains about
 1381  * half the pages in the free queue as are in the cache queue,
 1382  * providing pretty good pipelining for pageout operation.
 1383  *
 1384  * The system operator can manipulate vm.v_cache_min and
 1385  * vm.v_free_target to tune the pageout demon.  Be sure
 1386  * to keep vm.v_free_min < vm.v_free_target.
 1387  *
 1388  * Note that the original paging target is to get at least
 1389  * (free_min + cache_min) into (free + cache).  The slightly
 1390  * higher target will shift additional pages from cache to free
 1391  * without effecting the original paging target in order to
 1392  * maintain better hysteresis and not have the free count always
 1393  * be dead-on v_free_min.
 1394  *
 1395  * NOTE: we are still in a critical section.
 1396  *
 1397  * Pages moved from PQ_CACHE to totally free are not counted in the
 1398  * pages_freed counter.
 1399  */
 1400 static void
 1401 vm_pageout_scan_cache(int avail_shortage, int vnodes_skipped, int recycle_count)
 1402 {
 1403         struct vm_pageout_scan_info info;
 1404         vm_page_t m;
 1405 
 1406         while (vmstats.v_free_count <
 1407                (vmstats.v_free_min + vmstats.v_free_target) / 2) {
 1408                 /*
 1409                  * This steals some code from vm/vm_page.c
 1410                  */
 1411                 static int cache_rover = 0;
 1412 
 1413                 m = vm_page_list_find(PQ_CACHE, cache_rover & PQ_L2_MASK, FALSE);
 1414                 if (m == NULL)
 1415                         break;
 1416                 /* page is returned removed from its queue and spinlocked */
 1417                 if (vm_page_busy_try(m, TRUE)) {
 1418                         vm_page_deactivate_locked(m);
 1419                         vm_page_spin_unlock(m);
 1420                         continue;
 1421                 }
 1422                 vm_page_spin_unlock(m);
 1423                 pagedaemon_wakeup();
 1424                 lwkt_yield();
 1425 
 1426                 /*
 1427                  * Page has been successfully busied and it and its queue
 1428                  * is no longer spinlocked.
 1429                  */
 1430                 if ((m->flags & (PG_UNMANAGED | PG_NEED_COMMIT)) ||
 1431                     m->hold_count ||
 1432                     m->wire_count) {
 1433                         vm_page_deactivate(m);
 1434                         vm_page_wakeup(m);
 1435                         continue;
 1436                 }
 1437                 KKASSERT((m->flags & PG_MAPPED) == 0);
 1438                 KKASSERT(m->dirty == 0);
 1439                 cache_rover += PQ_PRIME2;
 1440                 vm_pageout_page_free(m);
 1441                 mycpu->gd_cnt.v_dfree++;
 1442         }
 1443 
 1444 #if !defined(NO_SWAPPING)
 1445         /*
 1446          * Idle process swapout -- run once per second.
 1447          */
 1448         if (vm_swap_idle_enabled) {
 1449                 static time_t lsec;
 1450                 if (time_uptime != lsec) {
 1451                         vm_pageout_req_swapout |= VM_SWAP_IDLE;
 1452                         vm_req_vmdaemon();
 1453                         lsec = time_uptime;
 1454                 }
 1455         }
 1456 #endif
 1457                 
 1458         /*
 1459          * If we didn't get enough free pages, and we have skipped a vnode
 1460          * in a writeable object, wakeup the sync daemon.  And kick swapout
 1461          * if we did not get enough free pages.
 1462          */
 1463         if (vm_paging_target() > 0) {
 1464                 if (vnodes_skipped && vm_page_count_min(0))
 1465                         speedup_syncer(NULL);
 1466 #if !defined(NO_SWAPPING)
 1467                 if (vm_swap_enabled && vm_page_count_target()) {
 1468                         vm_req_vmdaemon();
 1469                         vm_pageout_req_swapout |= VM_SWAP_NORMAL;
 1470                 }
 1471 #endif
 1472         }
 1473 
 1474         /*
 1475          * Handle catastrophic conditions.  Under good conditions we should
 1476          * be at the target, well beyond our minimum.  If we could not even
 1477          * reach our minimum the system is under heavy stress.
 1478          *
 1479          * Determine whether we have run out of memory.  This occurs when
 1480          * swap_pager_full is TRUE and the only pages left in the page
 1481          * queues are dirty.  We will still likely have page shortages.
 1482          *
 1483          * - swap_pager_full is set if insufficient swap was
 1484          *   available to satisfy a requested pageout.
 1485          *
 1486          * - the inactive queue is bloated (4 x size of active queue),
 1487          *   meaning it is unable to get rid of dirty pages and.
 1488          *
 1489          * - vm_page_count_min() without counting pages recycled from the
 1490          *   active queue (recycle_count) means we could not recover
 1491          *   enough pages to meet bare minimum needs.  This test only
 1492          *   works if the inactive queue is bloated.
 1493          *
 1494          * - due to a positive avail_shortage we shifted the remaining
 1495          *   dirty pages from the active queue to the inactive queue
 1496          *   trying to find clean ones to free.
 1497          */
 1498         if (swap_pager_full && vm_page_count_min(recycle_count))
 1499                 kprintf("Warning: system low on memory+swap!\n");
 1500         if (swap_pager_full && vm_page_count_min(recycle_count) &&
 1501             vmstats.v_inactive_count > vmstats.v_active_count * 4 &&
 1502             avail_shortage > 0) {
 1503                 /*
 1504                  * Kill something.
 1505                  */
 1506                 info.bigproc = NULL;
 1507                 info.bigsize = 0;
 1508                 allproc_scan(vm_pageout_scan_callback, &info);
 1509                 if (info.bigproc != NULL) {
 1510                         killproc(info.bigproc, "out of swap space");
 1511                         info.bigproc->p_nice = PRIO_MIN;
 1512                         info.bigproc->p_usched->resetpriority(
 1513                                 FIRST_LWP_IN_PROC(info.bigproc));
 1514                         wakeup(&vmstats.v_free_count);
 1515                         PRELE(info.bigproc);
 1516                 }
 1517         }
 1518 }
 1519 
 1520 static int
 1521 vm_pageout_scan_callback(struct proc *p, void *data)
 1522 {
 1523         struct vm_pageout_scan_info *info = data;
 1524         vm_offset_t size;
 1525 
 1526         /*
 1527          * Never kill system processes or init.  If we have configured swap
 1528          * then try to avoid killing low-numbered pids.
 1529          */
 1530         if ((p->p_flags & P_SYSTEM) || (p->p_pid == 1) ||
 1531             ((p->p_pid < 48) && (vm_swap_size != 0))) {
 1532                 return (0);
 1533         }
 1534 
 1535         lwkt_gettoken(&p->p_token);
 1536 
 1537         /*
 1538          * if the process is in a non-running type state,
 1539          * don't touch it.
 1540          */
 1541         if (p->p_stat != SACTIVE && p->p_stat != SSTOP) {
 1542                 lwkt_reltoken(&p->p_token);
 1543                 return (0);
 1544         }
 1545 
 1546         /*
 1547          * Get the approximate process size.  Note that anonymous pages
 1548          * with backing swap will be counted twice, but there should not
 1549          * be too many such pages due to the stress the VM system is
 1550          * under at this point.
 1551          */
 1552         size = vmspace_anonymous_count(p->p_vmspace) +
 1553                 vmspace_swap_count(p->p_vmspace);
 1554 
 1555         /*
 1556          * If the this process is bigger than the biggest one
 1557          * remember it.
 1558          */
 1559         if (info->bigsize < size) {
 1560                 if (info->bigproc)
 1561                         PRELE(info->bigproc);
 1562                 PHOLD(p);
 1563                 info->bigproc = p;
 1564                 info->bigsize = size;
 1565         }
 1566         lwkt_reltoken(&p->p_token);
 1567         lwkt_yield();
 1568 
 1569         return(0);
 1570 }
 1571 
 1572 /*
 1573  * This routine tries to maintain the pseudo LRU active queue,
 1574  * so that during long periods of time where there is no paging,
 1575  * that some statistic accumulation still occurs.  This code
 1576  * helps the situation where paging just starts to occur.
 1577  */
 1578 static void
 1579 vm_pageout_page_stats(int q)
 1580 {
 1581         static int fullintervalcount = 0;
 1582         struct vm_page marker;
 1583         vm_page_t m;
 1584         int pcount, tpcount;            /* Number of pages to check */
 1585         int page_shortage;
 1586 
 1587         page_shortage = (vmstats.v_inactive_target + vmstats.v_cache_max +
 1588                          vmstats.v_free_min) -
 1589                         (vmstats.v_free_count + vmstats.v_inactive_count +
 1590                          vmstats.v_cache_count);
 1591 
 1592         if (page_shortage <= 0)
 1593                 return;
 1594 
 1595         pcount = vm_page_queues[PQ_ACTIVE + q].lcnt;
 1596         fullintervalcount += vm_pageout_stats_interval;
 1597         if (fullintervalcount < vm_pageout_full_stats_interval) {
 1598                 tpcount = (vm_pageout_stats_max * pcount) /
 1599                           vmstats.v_page_count + 1;
 1600                 if (pcount > tpcount)
 1601                         pcount = tpcount;
 1602         } else {
 1603                 fullintervalcount = 0;
 1604         }
 1605 
 1606         bzero(&marker, sizeof(marker));
 1607         marker.flags = PG_BUSY | PG_FICTITIOUS | PG_MARKER;
 1608         marker.queue = PQ_ACTIVE + q;
 1609         marker.pc = q;
 1610         marker.wire_count = 1;
 1611 
 1612         vm_page_queues_spin_lock(PQ_ACTIVE + q);
 1613         TAILQ_INSERT_HEAD(&vm_page_queues[PQ_ACTIVE + q].pl, &marker, pageq);
 1614         vm_page_queues_spin_unlock(PQ_ACTIVE + q);
 1615 
 1616         while ((m = TAILQ_NEXT(&marker, pageq)) != NULL &&
 1617                pcount-- > 0)
 1618         {
 1619                 int actcount;
 1620 
 1621                 vm_page_and_queue_spin_lock(m);
 1622                 if (m != TAILQ_NEXT(&marker, pageq)) {
 1623                         vm_page_and_queue_spin_unlock(m);
 1624                         ++pcount;
 1625                         continue;
 1626                 }
 1627                 KKASSERT(m->queue - m->pc == PQ_ACTIVE);
 1628                 TAILQ_REMOVE(&vm_page_queues[PQ_ACTIVE + q].pl, &marker, pageq);
 1629                 TAILQ_INSERT_AFTER(&vm_page_queues[PQ_ACTIVE + q].pl, m,
 1630                                    &marker, pageq);
 1631 
 1632                 /*
 1633                  * Ignore markers
 1634                  */
 1635                 if (m->flags & PG_MARKER) {
 1636                         vm_page_and_queue_spin_unlock(m);
 1637                         continue;
 1638                 }
 1639 
 1640                 /*
 1641                  * Ignore pages we can't busy
 1642                  */
 1643                 if (vm_page_busy_try(m, TRUE)) {
 1644                         vm_page_and_queue_spin_unlock(m);
 1645                         continue;
 1646                 }
 1647                 vm_page_and_queue_spin_unlock(m);
 1648                 KKASSERT(m->queue - m->pc == PQ_ACTIVE);
 1649 
 1650                 /*
 1651                  * We now have a safely busied page, the page and queue
 1652                  * spinlocks have been released.
 1653                  *
 1654                  * Ignore held pages
 1655                  */
 1656                 if (m->hold_count) {
 1657                         vm_page_wakeup(m);
 1658                         continue;
 1659                 }
 1660 
 1661                 /*
 1662                  * Calculate activity
 1663                  */
 1664                 actcount = 0;
 1665                 if (m->flags & PG_REFERENCED) {
 1666                         vm_page_flag_clear(m, PG_REFERENCED);
 1667                         actcount += 1;
 1668                 }
 1669                 actcount += pmap_ts_referenced(m);
 1670 
 1671                 /*
 1672                  * Update act_count and move page to end of queue.
 1673                  */
 1674                 if (actcount) {
 1675                         m->act_count += ACT_ADVANCE + actcount;
 1676                         if (m->act_count > ACT_MAX)
 1677                                 m->act_count = ACT_MAX;
 1678                         vm_page_and_queue_spin_lock(m);
 1679                         if (m->queue - m->pc == PQ_ACTIVE) {
 1680                                 TAILQ_REMOVE(
 1681                                         &vm_page_queues[PQ_ACTIVE + q].pl,
 1682                                         m, pageq);
 1683                                 TAILQ_INSERT_TAIL(
 1684                                         &vm_page_queues[PQ_ACTIVE + q].pl,
 1685                                         m, pageq);
 1686                         }
 1687                         vm_page_and_queue_spin_unlock(m);
 1688                         vm_page_wakeup(m);
 1689                         continue;
 1690                 }
 1691 
 1692                 if (m->act_count == 0) {
 1693                         /*
 1694                          * We turn off page access, so that we have
 1695                          * more accurate RSS stats.  We don't do this
 1696                          * in the normal page deactivation when the
 1697                          * system is loaded VM wise, because the
 1698                          * cost of the large number of page protect
 1699                          * operations would be higher than the value
 1700                          * of doing the operation.
 1701                          *
 1702                          * We use the marker to save our place so
 1703                          * we can release the spin lock.  both (m)
 1704                          * and (next) will be invalid.
 1705                          */
 1706                         vm_page_protect(m, VM_PROT_NONE);
 1707                         vm_page_deactivate(m);
 1708                 } else {
 1709                         m->act_count -= min(m->act_count, ACT_DECLINE);
 1710                         vm_page_and_queue_spin_lock(m);
 1711                         if (m->queue - m->pc == PQ_ACTIVE) {
 1712                                 TAILQ_REMOVE(
 1713                                         &vm_page_queues[PQ_ACTIVE + q].pl,
 1714                                         m, pageq);
 1715                                 TAILQ_INSERT_TAIL(
 1716                                         &vm_page_queues[PQ_ACTIVE + q].pl,
 1717                                         m, pageq);
 1718                         }
 1719                         vm_page_and_queue_spin_unlock(m);
 1720                 }
 1721                 vm_page_wakeup(m);
 1722         }
 1723 
 1724         /*
 1725          * Remove our local marker
 1726          */
 1727         vm_page_queues_spin_lock(PQ_ACTIVE + q);
 1728         TAILQ_REMOVE(&vm_page_queues[PQ_ACTIVE + q].pl, &marker, pageq);
 1729         vm_page_queues_spin_unlock(PQ_ACTIVE + q);
 1730 }
 1731 
 1732 static int
 1733 vm_pageout_free_page_calc(vm_size_t count)
 1734 {
 1735         if (count < vmstats.v_page_count)
 1736                  return 0;
 1737         /*
 1738          * free_reserved needs to include enough for the largest swap pager
 1739          * structures plus enough for any pv_entry structs when paging.
 1740          *
 1741          * v_free_min           normal allocations
 1742          * v_free_reserved      system allocations
 1743          * v_pageout_free_min   allocations by pageout daemon
 1744          * v_interrupt_free_min low level allocations (e.g swap structures)
 1745          */
 1746         if (vmstats.v_page_count > 1024)
 1747                 vmstats.v_free_min = 64 + (vmstats.v_page_count - 1024) / 200;
 1748         else
 1749                 vmstats.v_free_min = 64;
 1750         vmstats.v_free_reserved = vmstats.v_free_min * 4 / 8 + 7;
 1751         vmstats.v_free_severe = vmstats.v_free_min * 4 / 8 + 0;
 1752         vmstats.v_pageout_free_min = vmstats.v_free_min * 2 / 8 + 7;
 1753         vmstats.v_interrupt_free_min = vmstats.v_free_min * 1 / 8 + 7;
 1754 
 1755         return 1;
 1756 }
 1757 
 1758 
 1759 /*
 1760  * vm_pageout is the high level pageout daemon.
 1761  *
 1762  * No requirements.
 1763  */
 1764 static void
 1765 vm_pageout_thread(void)
 1766 {
 1767         int pass;
 1768         int q;
 1769         int q1iterator = 0;
 1770         int q2iterator = 0;
 1771 
 1772         /*
 1773          * Initialize some paging parameters.
 1774          */
 1775         curthread->td_flags |= TDF_SYSTHREAD;
 1776 
 1777         vm_pageout_free_page_calc(vmstats.v_page_count);
 1778 
 1779         /*
 1780          * v_free_target and v_cache_min control pageout hysteresis.  Note
 1781          * that these are more a measure of the VM cache queue hysteresis
 1782          * then the VM free queue.  Specifically, v_free_target is the
 1783          * high water mark (free+cache pages).
 1784          *
 1785          * v_free_reserved + v_cache_min (mostly means v_cache_min) is the
 1786          * low water mark, while v_free_min is the stop.  v_cache_min must
 1787          * be big enough to handle memory needs while the pageout daemon
 1788          * is signalled and run to free more pages.
 1789          */
 1790         if (vmstats.v_free_count > 6144)
 1791                 vmstats.v_free_target = 4 * vmstats.v_free_min + vmstats.v_free_reserved;
 1792         else
 1793                 vmstats.v_free_target = 2 * vmstats.v_free_min + vmstats.v_free_reserved;
 1794 
 1795         /*
 1796          * NOTE: With the new buffer cache b_act_count we want the default
 1797          *       inactive target to be a percentage of available memory.
 1798          *
 1799          *       The inactive target essentially determines the minimum
 1800          *       number of 'temporary' pages capable of caching one-time-use
 1801          *       files when the VM system is otherwise full of pages
 1802          *       belonging to multi-time-use files or active program data.
 1803          *
 1804          * NOTE: The inactive target is aggressively persued only if the
 1805          *       inactive queue becomes too small.  If the inactive queue
 1806          *       is large enough to satisfy page movement to free+cache
 1807          *       then it is repopulated more slowly from the active queue.
 1808          *       This allows a general inactive_target default to be set.
 1809          *
 1810          *       There is an issue here for processes which sit mostly idle
 1811          *       'overnight', such as sshd, tcsh, and X.  Any movement from
 1812          *       the active queue will eventually cause such pages to
 1813          *       recycle eventually causing a lot of paging in the morning.
 1814          *       To reduce the incidence of this pages cycled out of the
 1815          *       buffer cache are moved directly to the inactive queue if
 1816          *       they were only used once or twice.
 1817          *
 1818          *       The vfs.vm_cycle_point sysctl can be used to adjust this.
 1819          *       Increasing the value (up to 64) increases the number of
 1820          *       buffer recyclements which go directly to the inactive queue.
 1821          */
 1822         if (vmstats.v_free_count > 2048) {
 1823                 vmstats.v_cache_min = vmstats.v_free_target;
 1824                 vmstats.v_cache_max = 2 * vmstats.v_cache_min;
 1825         } else {
 1826                 vmstats.v_cache_min = 0;
 1827                 vmstats.v_cache_max = 0;
 1828         }
 1829         vmstats.v_inactive_target = vmstats.v_free_count / 4;
 1830 
 1831         /* XXX does not really belong here */
 1832         if (vm_page_max_wired == 0)
 1833                 vm_page_max_wired = vmstats.v_free_count / 3;
 1834 
 1835         if (vm_pageout_stats_max == 0)
 1836                 vm_pageout_stats_max = vmstats.v_free_target;
 1837 
 1838         /*
 1839          * Set interval in seconds for stats scan.
 1840          */
 1841         if (vm_pageout_stats_interval == 0)
 1842                 vm_pageout_stats_interval = 5;
 1843         if (vm_pageout_full_stats_interval == 0)
 1844                 vm_pageout_full_stats_interval = vm_pageout_stats_interval * 4;
 1845         
 1846 
 1847         /*
 1848          * Set maximum free per pass
 1849          */
 1850         if (vm_pageout_stats_free_max == 0)
 1851                 vm_pageout_stats_free_max = 5;
 1852 
 1853         swap_pager_swap_init();
 1854         pass = 0;
 1855 
 1856         /*
 1857          * The pageout daemon is never done, so loop forever.
 1858          */
 1859         while (TRUE) {
 1860                 int error;
 1861                 int avail_shortage;
 1862                 int inactive_shortage;
 1863                 int vnodes_skipped = 0;
 1864                 int recycle_count = 0;
 1865                 int tmp;
 1866 
 1867                 /*
 1868                  * Wait for an action request.  If we timeout check to
 1869                  * see if paging is needed (in case the normal wakeup
 1870                  * code raced us).
 1871                  */
 1872                 if (vm_pages_needed == 0) {
 1873                         error = tsleep(&vm_pages_needed,
 1874                                        0, "psleep",
 1875                                        vm_pageout_stats_interval * hz);
 1876                         if (error &&
 1877                             vm_paging_needed() == 0 &&
 1878                             vm_pages_needed == 0) {
 1879                                 for (q = 0; q < PQ_L2_SIZE; ++q)
 1880                                         vm_pageout_page_stats(q);
 1881                                 continue;
 1882                         }
 1883                         vm_pages_needed = 1;
 1884                 }
 1885 
 1886                 mycpu->gd_cnt.v_pdwakeups++;
 1887 
 1888                 /*
 1889                  * Do whatever cleanup that the pmap code can.
 1890                  */
 1891                 pmap_collect();
 1892 
 1893                 /*
 1894                  * Scan for pageout.  Try to avoid thrashing the system
 1895                  * with activity.
 1896                  *
 1897                  * Calculate our target for the number of free+cache pages we
 1898                  * want to get to.  This is higher then the number that causes
 1899                  * allocations to stall (severe) in order to provide hysteresis,
 1900                  * and if we don't make it all the way but get to the minimum
 1901                  * we're happy.  Goose it a bit if there are multipler
 1902                  * requests for memory.
 1903                  */
 1904                 avail_shortage = vm_paging_target() + vm_pageout_deficit;
 1905                 vm_pageout_deficit = 0;
 1906 
 1907                 if (avail_shortage > 0) {
 1908                         for (q = 0; q < PQ_L2_SIZE; ++q) {
 1909                                 avail_shortage -=
 1910                                         vm_pageout_scan_inactive(
 1911                                             pass,
 1912                                             (q + q1iterator) & PQ_L2_MASK,
 1913                                             PQAVERAGE(avail_shortage),
 1914                                             &vnodes_skipped);
 1915                                 if (avail_shortage <= 0)
 1916                                         break;
 1917                         }
 1918                         q1iterator = q + 1;
 1919                 }
 1920 
 1921                 /*
 1922                  * Figure out how many active pages we must deactivate.  If
 1923                  * we were able to reach our target with just the inactive
 1924                  * scan above we limit the number of active pages we
 1925                  * deactivate to reduce unnecessary work.
 1926                  */
 1927                 inactive_shortage = vmstats.v_inactive_target -
 1928                                     vmstats.v_inactive_count;
 1929 
 1930                 /*
 1931                  * If we were unable to free sufficient inactive pages to
 1932                  * satisfy the free/cache queue requirements then simply
 1933                  * reaching the inactive target may not be good enough.
 1934                  * Try to deactivate pages in excess of the target based
 1935                  * on the shortfall.
 1936                  *
 1937                  * However to prevent thrashing the VM system do not
 1938                  * deactivate more than an additional 1/10 the inactive
 1939                  * target's worth of active pages.
 1940                  */
 1941                 if (avail_shortage > 0) {
 1942                         tmp = avail_shortage * 2;
 1943                         if (tmp > vmstats.v_inactive_target / 10)
 1944                                 tmp = vmstats.v_inactive_target / 10;
 1945                         inactive_shortage += tmp;
 1946                 }
 1947 
 1948                 /*
 1949                  * Only trigger on inactive shortage.  Triggering on
 1950                  * avail_shortage can starve the active queue with
 1951                  * unnecessary active->inactive transitions and destroy
 1952                  * performance.
 1953                  */
 1954                 if (/*avail_shortage > 0 ||*/ inactive_shortage > 0) {
 1955                         int delta;
 1956 
 1957                         for (q = 0; q < PQ_L2_SIZE; ++q) {
 1958                                 delta = vm_pageout_scan_active(
 1959                                                 pass,
 1960                                                 (q + q2iterator) & PQ_L2_MASK,
 1961                                                 PQAVERAGE(avail_shortage),
 1962                                                 PQAVERAGE(inactive_shortage),
 1963                                                 &recycle_count);
 1964                                 inactive_shortage -= delta;
 1965                                 avail_shortage -= delta;
 1966                                 if (inactive_shortage <= 0 &&
 1967                                     avail_shortage <= 0) {
 1968                                         break;
 1969                                 }
 1970                         }
 1971                         q2iterator = q + 1;
 1972                 }
 1973 
 1974                 /*
 1975                  * Finally free enough cache pages to meet our free page
 1976                  * requirement and take more drastic measures if we are
 1977                  * still in trouble.
 1978                  */
 1979                 vm_pageout_scan_cache(avail_shortage, vnodes_skipped,
 1980                                       recycle_count);
 1981 
 1982                 /*
 1983                  * Wait for more work.
 1984                  */
 1985                 if (avail_shortage > 0) {
 1986                         ++pass;
 1987                         if (swap_pager_full) {
 1988                                 /*
 1989                                  * Running out of memory, catastrophic back-off
 1990                                  * to one-second intervals.
 1991                                  */
 1992                                 tsleep(&vm_pages_needed, 0, "pdelay", hz);
 1993                         } else if (pass < 10 && vm_pages_needed > 1) {
 1994                                 /*
 1995                                  * Normal operation, additional processes
 1996                                  * have already kicked us.  Retry immediately.
 1997                                  */
 1998                         } else if (pass < 10) {
 1999                                 /*
 2000                                  * Normal operation, fewer processes.  Delay
 2001                                  * a bit but allow wakeups.
 2002                                  */
 2003                                 vm_pages_needed = 0;
 2004                                 tsleep(&vm_pages_needed, 0, "pdelay", hz / 10);
 2005                                 vm_pages_needed = 1;
 2006                         } else {
 2007                                 /*
 2008                                  * We've taken too many passes, forced delay.
 2009                                  */
 2010                                 tsleep(&vm_pages_needed, 0, "pdelay", hz / 10);
 2011                         }
 2012                 } else if (vm_pages_needed) {
 2013                         /*
 2014                          * Interlocked wakeup of waiters (non-optional).
 2015                          *
 2016                          * Similar to vm_page_free_wakeup() in vm_page.c,
 2017                          * wake
 2018                          */
 2019                         pass = 0;
 2020                         if (!vm_page_count_min(vm_page_free_hysteresis) ||
 2021                             !vm_page_count_target()) {
 2022                                 vm_pages_needed = 0;
 2023                                 wakeup(&vmstats.v_free_count);
 2024                         }
 2025                 } else {
 2026                         pass = 0;
 2027                 }
 2028         }
 2029 }
 2030 
 2031 static struct kproc_desc page_kp = {
 2032         "pagedaemon",
 2033         vm_pageout_thread,
 2034         &pagethread
 2035 };
 2036 SYSINIT(pagedaemon, SI_SUB_KTHREAD_PAGE, SI_ORDER_FIRST, kproc_start, &page_kp)
 2037 
 2038 
 2039 /*
 2040  * Called after allocating a page out of the cache or free queue
 2041  * to possibly wake the pagedaemon up to replentish our supply.
 2042  *
 2043  * We try to generate some hysteresis by waking the pagedaemon up
 2044  * when our free+cache pages go below the free_min+cache_min level.
 2045  * The pagedaemon tries to get the count back up to at least the
 2046  * minimum, and through to the target level if possible.
 2047  *
 2048  * If the pagedaemon is already active bump vm_pages_needed as a hint
 2049  * that there are even more requests pending.
 2050  *
 2051  * SMP races ok?
 2052  * No requirements.
 2053  */
 2054 void
 2055 pagedaemon_wakeup(void)
 2056 {
 2057         if (vm_paging_needed() && curthread != pagethread) {
 2058                 if (vm_pages_needed == 0) {
 2059                         vm_pages_needed = 1;    /* SMP race ok */
 2060                         wakeup(&vm_pages_needed);
 2061                 } else if (vm_page_count_min(0)) {
 2062                         ++vm_pages_needed;      /* SMP race ok */
 2063                 }
 2064         }
 2065 }
 2066 
 2067 #if !defined(NO_SWAPPING)
 2068 
 2069 /*
 2070  * SMP races ok?
 2071  * No requirements.
 2072  */
 2073 static void
 2074 vm_req_vmdaemon(void)
 2075 {
 2076         static int lastrun = 0;
 2077 
 2078         if ((ticks > (lastrun + hz)) || (ticks < lastrun)) {
 2079                 wakeup(&vm_daemon_needed);
 2080                 lastrun = ticks;
 2081         }
 2082 }
 2083 
 2084 static int vm_daemon_callback(struct proc *p, void *data __unused);
 2085 
 2086 /*
 2087  * No requirements.
 2088  */
 2089 static void
 2090 vm_daemon(void)
 2091 {
 2092         /*
 2093          * XXX vm_daemon_needed specific token?
 2094          */
 2095         while (TRUE) {
 2096                 tsleep(&vm_daemon_needed, 0, "psleep", 0);
 2097                 if (vm_pageout_req_swapout) {
 2098                         swapout_procs(vm_pageout_req_swapout);
 2099                         vm_pageout_req_swapout = 0;
 2100                 }
 2101                 /*
 2102                  * scan the processes for exceeding their rlimits or if
 2103                  * process is swapped out -- deactivate pages
 2104                  */
 2105                 allproc_scan(vm_daemon_callback, NULL);
 2106         }
 2107 }
 2108 
 2109 static int
 2110 vm_daemon_callback(struct proc *p, void *data __unused)
 2111 {
 2112         struct vmspace *vm;
 2113         vm_pindex_t limit, size;
 2114 
 2115         /*
 2116          * if this is a system process or if we have already
 2117          * looked at this process, skip it.
 2118          */
 2119         lwkt_gettoken(&p->p_token);
 2120 
 2121         if (p->p_flags & (P_SYSTEM | P_WEXIT)) {
 2122                 lwkt_reltoken(&p->p_token);
 2123                 return (0);
 2124         }
 2125 
 2126         /*
 2127          * if the process is in a non-running type state,
 2128          * don't touch it.
 2129          */
 2130         if (p->p_stat != SACTIVE && p->p_stat != SSTOP) {
 2131                 lwkt_reltoken(&p->p_token);
 2132                 return (0);
 2133         }
 2134 
 2135         /*
 2136          * get a limit
 2137          */
 2138         limit = OFF_TO_IDX(qmin(p->p_rlimit[RLIMIT_RSS].rlim_cur,
 2139                                 p->p_rlimit[RLIMIT_RSS].rlim_max));
 2140 
 2141         /*
 2142          * let processes that are swapped out really be
 2143          * swapped out.  Set the limit to nothing to get as
 2144          * many pages out to swap as possible.
 2145          */
 2146         if (p->p_flags & P_SWAPPEDOUT)
 2147                 limit = 0;
 2148 
 2149         vm = p->p_vmspace;
 2150         vmspace_hold(vm);
 2151         size = vmspace_resident_count(vm);
 2152         if (limit >= 0 && size >= limit) {
 2153                 vm_pageout_map_deactivate_pages(&vm->vm_map, limit);
 2154         }
 2155         vmspace_drop(vm);
 2156 
 2157         lwkt_reltoken(&p->p_token);
 2158 
 2159         return (0);
 2160 }
 2161 
 2162 #endif

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