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

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    1 /*-
    2  * Copyright (c) 1991 Regents of the University of California.
    3  * All rights reserved.
    4  * Copyright (c) 1994 John S. Dyson
    5  * All rights reserved.
    6  * Copyright (c) 1994 David Greenman
    7  * All rights reserved.
    8  * Copyright (c) 2005 Yahoo! Technologies Norway AS
    9  * All rights reserved.
   10  *
   11  * This code is derived from software contributed to Berkeley by
   12  * The Mach Operating System project at Carnegie-Mellon University.
   13  *
   14  * Redistribution and use in source and binary forms, with or without
   15  * modification, are permitted provided that the following conditions
   16  * are met:
   17  * 1. Redistributions of source code must retain the above copyright
   18  *    notice, this list of conditions and the following disclaimer.
   19  * 2. Redistributions in binary form must reproduce the above copyright
   20  *    notice, this list of conditions and the following disclaimer in the
   21  *    documentation and/or other materials provided with the distribution.
   22  * 3. All advertising materials mentioning features or use of this software
   23  *    must display the following acknowledgement:
   24  *      This product includes software developed by the University of
   25  *      California, Berkeley and its contributors.
   26  * 4. Neither the name of the University nor the names of its contributors
   27  *    may be used to endorse or promote products derived from this software
   28  *    without specific prior written permission.
   29  *
   30  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   31  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   32  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   33  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   34  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   35  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   36  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   37  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   38  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   39  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   40  * SUCH DAMAGE.
   41  *
   42  *      from: @(#)vm_pageout.c  7.4 (Berkeley) 5/7/91
   43  *
   44  *
   45  * Copyright (c) 1987, 1990 Carnegie-Mellon University.
   46  * All rights reserved.
   47  *
   48  * Authors: Avadis Tevanian, Jr., Michael Wayne Young
   49  *
   50  * Permission to use, copy, modify and distribute this software and
   51  * its documentation is hereby granted, provided that both the copyright
   52  * notice and this permission notice appear in all copies of the
   53  * software, derivative works or modified versions, and any portions
   54  * thereof, and that both notices appear in supporting documentation.
   55  *
   56  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
   57  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
   58  * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
   59  *
   60  * Carnegie Mellon requests users of this software to return to
   61  *
   62  *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
   63  *  School of Computer Science
   64  *  Carnegie Mellon University
   65  *  Pittsburgh PA 15213-3890
   66  *
   67  * any improvements or extensions that they make and grant Carnegie the
   68  * rights to redistribute these changes.
   69  */
   70 
   71 #include <sys/cdefs.h>
   72 __FBSDID("$FreeBSD: releng/11.2/sys/vm/vm_swapout.c 328122 2018-01-18 12:06:01Z kib $");
   73 
   74 #include "opt_kstack_pages.h"
   75 #include "opt_kstack_max_pages.h"
   76 #include "opt_vm.h"
   77 
   78 #include <sys/param.h>
   79 #include <sys/systm.h>
   80 #include <sys/limits.h>
   81 #include <sys/kernel.h>
   82 #include <sys/eventhandler.h>
   83 #include <sys/lock.h>
   84 #include <sys/mutex.h>
   85 #include <sys/proc.h>
   86 #include <sys/_kstack_cache.h>
   87 #include <sys/kthread.h>
   88 #include <sys/ktr.h>
   89 #include <sys/mount.h>
   90 #include <sys/racct.h>
   91 #include <sys/resourcevar.h>
   92 #include <sys/sched.h>
   93 #include <sys/sdt.h>
   94 #include <sys/signalvar.h>
   95 #include <sys/smp.h>
   96 #include <sys/time.h>
   97 #include <sys/vnode.h>
   98 #include <sys/vmmeter.h>
   99 #include <sys/rwlock.h>
  100 #include <sys/sx.h>
  101 #include <sys/sysctl.h>
  102 
  103 #include <vm/vm.h>
  104 #include <vm/vm_param.h>
  105 #include <vm/vm_object.h>
  106 #include <vm/vm_page.h>
  107 #include <vm/vm_map.h>
  108 #include <vm/vm_pageout.h>
  109 #include <vm/vm_pager.h>
  110 #include <vm/vm_phys.h>
  111 #include <vm/swap_pager.h>
  112 #include <vm/vm_extern.h>
  113 #include <vm/uma.h>
  114 
  115 /* the kernel process "vm_daemon" */
  116 static void vm_daemon(void);
  117 static struct proc *vmproc;
  118 
  119 static struct kproc_desc vm_kp = {
  120         "vmdaemon",
  121         vm_daemon,
  122         &vmproc
  123 };
  124 SYSINIT(vmdaemon, SI_SUB_KTHREAD_VM, SI_ORDER_FIRST, kproc_start, &vm_kp);
  125 
  126 static int vm_swap_enabled = 1;
  127 static int vm_swap_idle_enabled = 0;
  128 
  129 SYSCTL_INT(_vm, VM_SWAPPING_ENABLED, swap_enabled, CTLFLAG_RW,
  130     &vm_swap_enabled, 0,
  131     "Enable entire process swapout");
  132 SYSCTL_INT(_vm, OID_AUTO, swap_idle_enabled, CTLFLAG_RW,
  133     &vm_swap_idle_enabled, 0,
  134     "Allow swapout on idle criteria");
  135 
  136 /*
  137  * Swap_idle_threshold1 is the guaranteed swapped in time for a process
  138  */
  139 static int swap_idle_threshold1 = 2;
  140 SYSCTL_INT(_vm, OID_AUTO, swap_idle_threshold1, CTLFLAG_RW,
  141     &swap_idle_threshold1, 0,
  142     "Guaranteed swapped in time for a process");
  143 
  144 /*
  145  * Swap_idle_threshold2 is the time that a process can be idle before
  146  * it will be swapped out, if idle swapping is enabled.
  147  */
  148 static int swap_idle_threshold2 = 10;
  149 SYSCTL_INT(_vm, OID_AUTO, swap_idle_threshold2, CTLFLAG_RW,
  150     &swap_idle_threshold2, 0,
  151     "Time before a process will be swapped out");
  152 
  153 static int vm_pageout_req_swapout;      /* XXX */
  154 static int vm_daemon_needed;
  155 static struct mtx vm_daemon_mtx;
  156 /* Allow for use by vm_pageout before vm_daemon is initialized. */
  157 MTX_SYSINIT(vm_daemon, &vm_daemon_mtx, "vm daemon", MTX_DEF);
  158 
  159 static void swapclear(struct proc *);
  160 static int swapout(struct proc *);
  161 static void vm_swapout_map_deactivate_pages(vm_map_t, long);
  162 static void vm_swapout_object_deactivate_pages(pmap_t, vm_object_t, long);
  163 static void swapout_procs(int action);
  164 static void vm_req_vmdaemon(int req);
  165 static void vm_thread_swapin(struct thread *td);
  166 static void vm_thread_swapout(struct thread *td);
  167 
  168 /*
  169  *      vm_swapout_object_deactivate_pages
  170  *
  171  *      Deactivate enough pages to satisfy the inactive target
  172  *      requirements.
  173  *
  174  *      The object and map must be locked.
  175  */
  176 static void
  177 vm_swapout_object_deactivate_pages(pmap_t pmap, vm_object_t first_object,
  178     long desired)
  179 {
  180         vm_object_t backing_object, object;
  181         vm_page_t p;
  182         int act_delta, remove_mode;
  183 
  184         VM_OBJECT_ASSERT_LOCKED(first_object);
  185         if ((first_object->flags & OBJ_FICTITIOUS) != 0)
  186                 return;
  187         for (object = first_object;; object = backing_object) {
  188                 if (pmap_resident_count(pmap) <= desired)
  189                         goto unlock_return;
  190                 VM_OBJECT_ASSERT_LOCKED(object);
  191                 if ((object->flags & OBJ_UNMANAGED) != 0 ||
  192                     object->paging_in_progress != 0)
  193                         goto unlock_return;
  194 
  195                 remove_mode = 0;
  196                 if (object->shadow_count > 1)
  197                         remove_mode = 1;
  198                 /*
  199                  * Scan the object's entire memory queue.
  200                  */
  201                 TAILQ_FOREACH(p, &object->memq, listq) {
  202                         if (pmap_resident_count(pmap) <= desired)
  203                                 goto unlock_return;
  204                         if (should_yield())
  205                                 goto unlock_return;
  206                         if (vm_page_busied(p))
  207                                 continue;
  208                         PCPU_INC(cnt.v_pdpages);
  209                         vm_page_lock(p);
  210                         if (p->wire_count != 0 || p->hold_count != 0 ||
  211                             !pmap_page_exists_quick(pmap, p)) {
  212                                 vm_page_unlock(p);
  213                                 continue;
  214                         }
  215                         act_delta = pmap_ts_referenced(p);
  216                         if ((p->aflags & PGA_REFERENCED) != 0) {
  217                                 if (act_delta == 0)
  218                                         act_delta = 1;
  219                                 vm_page_aflag_clear(p, PGA_REFERENCED);
  220                         }
  221                         if (!vm_page_active(p) && act_delta != 0) {
  222                                 vm_page_activate(p);
  223                                 p->act_count += act_delta;
  224                         } else if (vm_page_active(p)) {
  225                                 if (act_delta == 0) {
  226                                         p->act_count -= min(p->act_count,
  227                                             ACT_DECLINE);
  228                                         if (!remove_mode && p->act_count == 0) {
  229                                                 pmap_remove_all(p);
  230                                                 vm_page_deactivate(p);
  231                                         } else
  232                                                 vm_page_requeue(p);
  233                                 } else {
  234                                         vm_page_activate(p);
  235                                         if (p->act_count < ACT_MAX -
  236                                             ACT_ADVANCE)
  237                                                 p->act_count += ACT_ADVANCE;
  238                                         vm_page_requeue(p);
  239                                 }
  240                         } else if (vm_page_inactive(p))
  241                                 pmap_remove_all(p);
  242                         vm_page_unlock(p);
  243                 }
  244                 if ((backing_object = object->backing_object) == NULL)
  245                         goto unlock_return;
  246                 VM_OBJECT_RLOCK(backing_object);
  247                 if (object != first_object)
  248                         VM_OBJECT_RUNLOCK(object);
  249         }
  250 unlock_return:
  251         if (object != first_object)
  252                 VM_OBJECT_RUNLOCK(object);
  253 }
  254 
  255 /*
  256  * deactivate some number of pages in a map, try to do it fairly, but
  257  * that is really hard to do.
  258  */
  259 static void
  260 vm_swapout_map_deactivate_pages(vm_map_t map, long desired)
  261 {
  262         vm_map_entry_t tmpe;
  263         vm_object_t obj, bigobj;
  264         int nothingwired;
  265 
  266         if (!vm_map_trylock_read(map))
  267                 return;
  268 
  269         bigobj = NULL;
  270         nothingwired = TRUE;
  271 
  272         /*
  273          * first, search out the biggest object, and try to free pages from
  274          * that.
  275          */
  276         tmpe = map->header.next;
  277         while (tmpe != &map->header) {
  278                 if ((tmpe->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
  279                         obj = tmpe->object.vm_object;
  280                         if (obj != NULL && VM_OBJECT_TRYRLOCK(obj)) {
  281                                 if (obj->shadow_count <= 1 &&
  282                                     (bigobj == NULL ||
  283                                      bigobj->resident_page_count <
  284                                      obj->resident_page_count)) {
  285                                         if (bigobj != NULL)
  286                                                 VM_OBJECT_RUNLOCK(bigobj);
  287                                         bigobj = obj;
  288                                 } else
  289                                         VM_OBJECT_RUNLOCK(obj);
  290                         }
  291                 }
  292                 if (tmpe->wired_count > 0)
  293                         nothingwired = FALSE;
  294                 tmpe = tmpe->next;
  295         }
  296 
  297         if (bigobj != NULL) {
  298                 vm_swapout_object_deactivate_pages(map->pmap, bigobj, desired);
  299                 VM_OBJECT_RUNLOCK(bigobj);
  300         }
  301         /*
  302          * Next, hunt around for other pages to deactivate.  We actually
  303          * do this search sort of wrong -- .text first is not the best idea.
  304          */
  305         tmpe = map->header.next;
  306         while (tmpe != &map->header) {
  307                 if (pmap_resident_count(vm_map_pmap(map)) <= desired)
  308                         break;
  309                 if ((tmpe->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
  310                         obj = tmpe->object.vm_object;
  311                         if (obj != NULL) {
  312                                 VM_OBJECT_RLOCK(obj);
  313                                 vm_swapout_object_deactivate_pages(map->pmap,
  314                                     obj, desired);
  315                                 VM_OBJECT_RUNLOCK(obj);
  316                         }
  317                 }
  318                 tmpe = tmpe->next;
  319         }
  320 
  321         /*
  322          * Remove all mappings if a process is swapped out, this will free page
  323          * table pages.
  324          */
  325         if (desired == 0 && nothingwired) {
  326                 pmap_remove(vm_map_pmap(map), vm_map_min(map),
  327                     vm_map_max(map));
  328         }
  329 
  330         vm_map_unlock_read(map);
  331 }
  332 
  333 /*
  334  * Swap out requests
  335  */
  336 #define VM_SWAP_NORMAL 1
  337 #define VM_SWAP_IDLE 2
  338 
  339 void
  340 vm_swapout_run(void)
  341 {
  342 
  343         if (vm_swap_enabled)
  344                 vm_req_vmdaemon(VM_SWAP_NORMAL);
  345 }
  346 
  347 /*
  348  * Idle process swapout -- run once per second when pagedaemons are
  349  * reclaiming pages.
  350  */
  351 void
  352 vm_swapout_run_idle(void)
  353 {
  354         static long lsec;
  355 
  356         if (!vm_swap_idle_enabled || time_second == lsec)
  357                 return;
  358         vm_req_vmdaemon(VM_SWAP_IDLE);
  359         lsec = time_second;
  360 }
  361 
  362 static void
  363 vm_req_vmdaemon(int req)
  364 {
  365         static int lastrun = 0;
  366 
  367         mtx_lock(&vm_daemon_mtx);
  368         vm_pageout_req_swapout |= req;
  369         if ((ticks > (lastrun + hz)) || (ticks < lastrun)) {
  370                 wakeup(&vm_daemon_needed);
  371                 lastrun = ticks;
  372         }
  373         mtx_unlock(&vm_daemon_mtx);
  374 }
  375 
  376 static void
  377 vm_daemon(void)
  378 {
  379         struct rlimit rsslim;
  380         struct proc *p;
  381         struct thread *td;
  382         struct vmspace *vm;
  383         int breakout, swapout_flags, tryagain, attempts;
  384 #ifdef RACCT
  385         uint64_t rsize, ravailable;
  386 #endif
  387 
  388         while (TRUE) {
  389                 mtx_lock(&vm_daemon_mtx);
  390                 msleep(&vm_daemon_needed, &vm_daemon_mtx, PPAUSE, "psleep",
  391 #ifdef RACCT
  392                     racct_enable ? hz : 0
  393 #else
  394                     0
  395 #endif
  396                 );
  397                 swapout_flags = vm_pageout_req_swapout;
  398                 vm_pageout_req_swapout = 0;
  399                 mtx_unlock(&vm_daemon_mtx);
  400                 if (swapout_flags)
  401                         swapout_procs(swapout_flags);
  402 
  403                 /*
  404                  * scan the processes for exceeding their rlimits or if
  405                  * process is swapped out -- deactivate pages
  406                  */
  407                 tryagain = 0;
  408                 attempts = 0;
  409 again:
  410                 attempts++;
  411                 sx_slock(&allproc_lock);
  412                 FOREACH_PROC_IN_SYSTEM(p) {
  413                         vm_pindex_t limit, size;
  414 
  415                         /*
  416                          * if this is a system process or if we have already
  417                          * looked at this process, skip it.
  418                          */
  419                         PROC_LOCK(p);
  420                         if (p->p_state != PRS_NORMAL ||
  421                             p->p_flag & (P_INEXEC | P_SYSTEM | P_WEXIT)) {
  422                                 PROC_UNLOCK(p);
  423                                 continue;
  424                         }
  425                         /*
  426                          * if the process is in a non-running type state,
  427                          * don't touch it.
  428                          */
  429                         breakout = 0;
  430                         FOREACH_THREAD_IN_PROC(p, td) {
  431                                 thread_lock(td);
  432                                 if (!TD_ON_RUNQ(td) &&
  433                                     !TD_IS_RUNNING(td) &&
  434                                     !TD_IS_SLEEPING(td) &&
  435                                     !TD_IS_SUSPENDED(td)) {
  436                                         thread_unlock(td);
  437                                         breakout = 1;
  438                                         break;
  439                                 }
  440                                 thread_unlock(td);
  441                         }
  442                         if (breakout) {
  443                                 PROC_UNLOCK(p);
  444                                 continue;
  445                         }
  446                         /*
  447                          * get a limit
  448                          */
  449                         lim_rlimit_proc(p, RLIMIT_RSS, &rsslim);
  450                         limit = OFF_TO_IDX(
  451                             qmin(rsslim.rlim_cur, rsslim.rlim_max));
  452 
  453                         /*
  454                          * let processes that are swapped out really be
  455                          * swapped out set the limit to nothing (will force a
  456                          * swap-out.)
  457                          */
  458                         if ((p->p_flag & P_INMEM) == 0)
  459                                 limit = 0;      /* XXX */
  460                         vm = vmspace_acquire_ref(p);
  461                         _PHOLD_LITE(p);
  462                         PROC_UNLOCK(p);
  463                         if (vm == NULL) {
  464                                 PRELE(p);
  465                                 continue;
  466                         }
  467                         sx_sunlock(&allproc_lock);
  468 
  469                         size = vmspace_resident_count(vm);
  470                         if (size >= limit) {
  471                                 vm_swapout_map_deactivate_pages(
  472                                     &vm->vm_map, limit);
  473                                 size = vmspace_resident_count(vm);
  474                         }
  475 #ifdef RACCT
  476                         if (racct_enable) {
  477                                 rsize = IDX_TO_OFF(size);
  478                                 PROC_LOCK(p);
  479                                 if (p->p_state == PRS_NORMAL)
  480                                         racct_set(p, RACCT_RSS, rsize);
  481                                 ravailable = racct_get_available(p, RACCT_RSS);
  482                                 PROC_UNLOCK(p);
  483                                 if (rsize > ravailable) {
  484                                         /*
  485                                          * Don't be overly aggressive; this
  486                                          * might be an innocent process,
  487                                          * and the limit could've been exceeded
  488                                          * by some memory hog.  Don't try
  489                                          * to deactivate more than 1/4th
  490                                          * of process' resident set size.
  491                                          */
  492                                         if (attempts <= 8) {
  493                                                 if (ravailable < rsize -
  494                                                     (rsize / 4)) {
  495                                                         ravailable = rsize -
  496                                                             (rsize / 4);
  497                                                 }
  498                                         }
  499                                         vm_swapout_map_deactivate_pages(
  500                                             &vm->vm_map,
  501                                             OFF_TO_IDX(ravailable));
  502                                         /* Update RSS usage after paging out. */
  503                                         size = vmspace_resident_count(vm);
  504                                         rsize = IDX_TO_OFF(size);
  505                                         PROC_LOCK(p);
  506                                         if (p->p_state == PRS_NORMAL)
  507                                                 racct_set(p, RACCT_RSS, rsize);
  508                                         PROC_UNLOCK(p);
  509                                         if (rsize > ravailable)
  510                                                 tryagain = 1;
  511                                 }
  512                         }
  513 #endif
  514                         vmspace_free(vm);
  515                         sx_slock(&allproc_lock);
  516                         PRELE(p);
  517                 }
  518                 sx_sunlock(&allproc_lock);
  519                 if (tryagain != 0 && attempts <= 10) {
  520                         maybe_yield();
  521                         goto again;
  522                 }
  523         }
  524 }
  525 
  526 /*
  527  * Allow a thread's kernel stack to be paged out.
  528  */
  529 static void
  530 vm_thread_swapout(struct thread *td)
  531 {
  532         vm_object_t ksobj;
  533         vm_page_t m;
  534         int i, pages;
  535 
  536         cpu_thread_swapout(td);
  537         pages = td->td_kstack_pages;
  538         ksobj = td->td_kstack_obj;
  539         pmap_qremove(td->td_kstack, pages);
  540         VM_OBJECT_WLOCK(ksobj);
  541         for (i = 0; i < pages; i++) {
  542                 m = vm_page_lookup(ksobj, i);
  543                 if (m == NULL)
  544                         panic("vm_thread_swapout: kstack already missing?");
  545                 vm_page_dirty(m);
  546                 vm_page_lock(m);
  547                 vm_page_unwire(m, PQ_INACTIVE);
  548                 vm_page_unlock(m);
  549         }
  550         VM_OBJECT_WUNLOCK(ksobj);
  551 }
  552 
  553 /*
  554  * Bring the kernel stack for a specified thread back in.
  555  */
  556 static void
  557 vm_thread_swapin(struct thread *td)
  558 {
  559         vm_object_t ksobj;
  560         vm_page_t ma[KSTACK_MAX_PAGES];
  561         int a, count, i, j, pages, rv;
  562 
  563         pages = td->td_kstack_pages;
  564         ksobj = td->td_kstack_obj;
  565         VM_OBJECT_WLOCK(ksobj);
  566         (void)vm_page_grab_pages(ksobj, 0, VM_ALLOC_NORMAL | VM_ALLOC_WIRED, ma,
  567             pages);
  568         for (i = 0; i < pages;) {
  569                 vm_page_assert_xbusied(ma[i]);
  570                 if (ma[i]->valid == VM_PAGE_BITS_ALL) {
  571                         vm_page_xunbusy(ma[i]);
  572                         i++;
  573                         continue;
  574                 }
  575                 vm_object_pip_add(ksobj, 1);
  576                 for (j = i + 1; j < pages; j++)
  577                         if (ma[j]->valid == VM_PAGE_BITS_ALL)
  578                                 break;
  579                 rv = vm_pager_has_page(ksobj, ma[i]->pindex, NULL, &a);
  580                 KASSERT(rv == 1, ("%s: missing page %p", __func__, ma[i]));
  581                 count = min(a + 1, j - i);
  582                 rv = vm_pager_get_pages(ksobj, ma + i, count, NULL, NULL);
  583                 KASSERT(rv == VM_PAGER_OK, ("%s: cannot get kstack for proc %d",
  584                     __func__, td->td_proc->p_pid));
  585                 vm_object_pip_wakeup(ksobj);
  586                 for (j = i; j < i + count; j++)
  587                         vm_page_xunbusy(ma[j]);
  588                 i += count;
  589         }
  590         VM_OBJECT_WUNLOCK(ksobj);
  591         pmap_qenter(td->td_kstack, ma, pages);
  592         cpu_thread_swapin(td);
  593 }
  594 
  595 void
  596 faultin(struct proc *p)
  597 {
  598         struct thread *td;
  599 
  600         PROC_LOCK_ASSERT(p, MA_OWNED);
  601         /*
  602          * If another process is swapping in this process,
  603          * just wait until it finishes.
  604          */
  605         if (p->p_flag & P_SWAPPINGIN) {
  606                 while (p->p_flag & P_SWAPPINGIN)
  607                         msleep(&p->p_flag, &p->p_mtx, PVM, "faultin", 0);
  608                 return;
  609         }
  610         if ((p->p_flag & P_INMEM) == 0) {
  611                 /*
  612                  * Don't let another thread swap process p out while we are
  613                  * busy swapping it in.
  614                  */
  615                 ++p->p_lock;
  616                 p->p_flag |= P_SWAPPINGIN;
  617                 PROC_UNLOCK(p);
  618 
  619                 /*
  620                  * We hold no lock here because the list of threads
  621                  * can not change while all threads in the process are
  622                  * swapped out.
  623                  */
  624                 FOREACH_THREAD_IN_PROC(p, td)
  625                         vm_thread_swapin(td);
  626                 PROC_LOCK(p);
  627                 swapclear(p);
  628                 p->p_swtick = ticks;
  629 
  630                 wakeup(&p->p_flag);
  631 
  632                 /* Allow other threads to swap p out now. */
  633                 --p->p_lock;
  634         }
  635 }
  636 
  637 /*
  638  * This swapin algorithm attempts to swap-in processes only if there
  639  * is enough space for them.  Of course, if a process waits for a long
  640  * time, it will be swapped in anyway.
  641  */
  642 void
  643 swapper(void)
  644 {
  645         struct proc *p, *pp;
  646         struct thread *td;
  647         int ppri, pri, slptime, swtime;
  648 
  649 loop:
  650         if (vm_page_count_min()) {
  651                 VM_WAIT;
  652                 goto loop;
  653         }
  654 
  655         pp = NULL;
  656         ppri = INT_MIN;
  657         sx_slock(&allproc_lock);
  658         FOREACH_PROC_IN_SYSTEM(p) {
  659                 PROC_LOCK(p);
  660                 if (p->p_state == PRS_NEW ||
  661                     p->p_flag & (P_SWAPPINGOUT | P_SWAPPINGIN | P_INMEM)) {
  662                         PROC_UNLOCK(p);
  663                         continue;
  664                 }
  665                 swtime = (ticks - p->p_swtick) / hz;
  666                 FOREACH_THREAD_IN_PROC(p, td) {
  667                         /*
  668                          * An otherwise runnable thread of a process
  669                          * swapped out has only the TDI_SWAPPED bit set.
  670                          */
  671                         thread_lock(td);
  672                         if (td->td_inhibitors == TDI_SWAPPED) {
  673                                 slptime = (ticks - td->td_slptick) / hz;
  674                                 pri = swtime + slptime;
  675                                 if ((td->td_flags & TDF_SWAPINREQ) == 0)
  676                                         pri -= p->p_nice * 8;
  677                                 /*
  678                                  * if this thread is higher priority
  679                                  * and there is enough space, then select
  680                                  * this process instead of the previous
  681                                  * selection.
  682                                  */
  683                                 if (pri > ppri) {
  684                                         pp = p;
  685                                         ppri = pri;
  686                                 }
  687                         }
  688                         thread_unlock(td);
  689                 }
  690                 PROC_UNLOCK(p);
  691         }
  692         sx_sunlock(&allproc_lock);
  693 
  694         /*
  695          * Nothing to do, back to sleep.
  696          */
  697         if ((p = pp) == NULL) {
  698                 tsleep(&proc0, PVM, "swapin", MAXSLP * hz / 2);
  699                 goto loop;
  700         }
  701         PROC_LOCK(p);
  702 
  703         /*
  704          * Another process may be bringing or may have already
  705          * brought this process in while we traverse all threads.
  706          * Or, this process may even be being swapped out again.
  707          */
  708         if (p->p_flag & (P_INMEM | P_SWAPPINGOUT | P_SWAPPINGIN)) {
  709                 PROC_UNLOCK(p);
  710                 goto loop;
  711         }
  712 
  713         /*
  714          * We would like to bring someone in.
  715          */
  716         faultin(p);
  717         PROC_UNLOCK(p);
  718         goto loop;
  719 }
  720 
  721 /*
  722  * First, if any processes have been sleeping or stopped for at least
  723  * "swap_idle_threshold1" seconds, they are swapped out.  If, however,
  724  * no such processes exist, then the longest-sleeping or stopped
  725  * process is swapped out.  Finally, and only as a last resort, if
  726  * there are no sleeping or stopped processes, the longest-resident
  727  * process is swapped out.
  728  */
  729 static void
  730 swapout_procs(int action)
  731 {
  732         struct proc *p;
  733         struct thread *td;
  734         int slptime;
  735         bool didswap, doswap;
  736 
  737         MPASS((action & (VM_SWAP_NORMAL | VM_SWAP_IDLE)) != 0);
  738 
  739         didswap = false;
  740         sx_slock(&allproc_lock);
  741         FOREACH_PROC_IN_SYSTEM(p) {
  742                 /*
  743                  * Filter out not yet fully constructed processes.  Do
  744                  * not swap out held processes.  Avoid processes which
  745                  * are system, exiting, execing, traced, already swapped
  746                  * out or are in the process of being swapped in or out.
  747                  */
  748                 PROC_LOCK(p);
  749                 if (p->p_state != PRS_NORMAL || p->p_lock != 0 || (p->p_flag &
  750                     (P_SYSTEM | P_WEXIT | P_INEXEC | P_STOPPED_SINGLE |
  751                     P_TRACED | P_SWAPPINGOUT | P_SWAPPINGIN | P_INMEM)) !=
  752                     P_INMEM) {
  753                         PROC_UNLOCK(p);
  754                         continue;
  755                 }
  756 
  757                 /*
  758                  * Further consideration of this process for swap out
  759                  * requires iterating over its threads.  We release
  760                  * allproc_lock here so that process creation and
  761                  * destruction are not blocked while we iterate.
  762                  *
  763                  * To later reacquire allproc_lock and resume
  764                  * iteration over the allproc list, we will first have
  765                  * to release the lock on the process.  We place a
  766                  * hold on the process so that it remains in the
  767                  * allproc list while it is unlocked.
  768                  */
  769                 _PHOLD_LITE(p);
  770                 sx_sunlock(&allproc_lock);
  771 
  772                 /*
  773                  * Do not swapout a realtime process.
  774                  * Guarantee swap_idle_threshold1 time in memory.
  775                  * If the system is under memory stress, or if we are
  776                  * swapping idle processes >= swap_idle_threshold2,
  777                  * then swap the process out.
  778                  */
  779                 doswap = true;
  780                 FOREACH_THREAD_IN_PROC(p, td) {
  781                         thread_lock(td);
  782                         slptime = (ticks - td->td_slptick) / hz;
  783                         if (PRI_IS_REALTIME(td->td_pri_class) ||
  784                             slptime < swap_idle_threshold1 ||
  785                             !thread_safetoswapout(td) ||
  786                             ((action & VM_SWAP_NORMAL) == 0 &&
  787                             slptime < swap_idle_threshold2))
  788                                 doswap = false;
  789                         thread_unlock(td);
  790                         if (!doswap)
  791                                 break;
  792                 }
  793                 if (doswap && swapout(p) == 0)
  794                         didswap = true;
  795 
  796                 PROC_UNLOCK(p);
  797                 sx_slock(&allproc_lock);
  798                 PRELE(p);
  799         }
  800         sx_sunlock(&allproc_lock);
  801 
  802         /*
  803          * If we swapped something out, and another process needed memory,
  804          * then wakeup the sched process.
  805          */
  806         if (didswap)
  807                 wakeup(&proc0);
  808 }
  809 
  810 static void
  811 swapclear(struct proc *p)
  812 {
  813         struct thread *td;
  814 
  815         PROC_LOCK_ASSERT(p, MA_OWNED);
  816 
  817         FOREACH_THREAD_IN_PROC(p, td) {
  818                 thread_lock(td);
  819                 td->td_flags |= TDF_INMEM;
  820                 td->td_flags &= ~TDF_SWAPINREQ;
  821                 TD_CLR_SWAPPED(td);
  822                 if (TD_CAN_RUN(td))
  823                         if (setrunnable(td)) {
  824 #ifdef INVARIANTS
  825                                 /*
  826                                  * XXX: We just cleared TDI_SWAPPED
  827                                  * above and set TDF_INMEM, so this
  828                                  * should never happen.
  829                                  */
  830                                 panic("not waking up swapper");
  831 #endif
  832                         }
  833                 thread_unlock(td);
  834         }
  835         p->p_flag &= ~(P_SWAPPINGIN | P_SWAPPINGOUT);
  836         p->p_flag |= P_INMEM;
  837 }
  838 
  839 static int
  840 swapout(struct proc *p)
  841 {
  842         struct thread *td;
  843 
  844         PROC_LOCK_ASSERT(p, MA_OWNED);
  845 
  846         /*
  847          * The states of this process and its threads may have changed
  848          * by now.  Assuming that there is only one pageout daemon thread,
  849          * this process should still be in memory.
  850          */
  851         KASSERT((p->p_flag & (P_INMEM | P_SWAPPINGOUT | P_SWAPPINGIN)) ==
  852             P_INMEM, ("swapout: lost a swapout race?"));
  853 
  854         /*
  855          * Remember the resident count.
  856          */
  857         p->p_vmspace->vm_swrss = vmspace_resident_count(p->p_vmspace);
  858 
  859         /*
  860          * Check and mark all threads before we proceed.
  861          */
  862         p->p_flag &= ~P_INMEM;
  863         p->p_flag |= P_SWAPPINGOUT;
  864         FOREACH_THREAD_IN_PROC(p, td) {
  865                 thread_lock(td);
  866                 if (!thread_safetoswapout(td)) {
  867                         thread_unlock(td);
  868                         swapclear(p);
  869                         return (EBUSY);
  870                 }
  871                 td->td_flags &= ~TDF_INMEM;
  872                 TD_SET_SWAPPED(td);
  873                 thread_unlock(td);
  874         }
  875         td = FIRST_THREAD_IN_PROC(p);
  876         ++td->td_ru.ru_nswap;
  877         PROC_UNLOCK(p);
  878 
  879         /*
  880          * This list is stable because all threads are now prevented from
  881          * running.  The list is only modified in the context of a running
  882          * thread in this process.
  883          */
  884         FOREACH_THREAD_IN_PROC(p, td)
  885                 vm_thread_swapout(td);
  886 
  887         PROC_LOCK(p);
  888         p->p_flag &= ~P_SWAPPINGOUT;
  889         p->p_swtick = ticks;
  890         return (0);
  891 }

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