2 * SPDX-License-Identifier: (BSD-4-Clause AND MIT-CMU)
4 * Copyright (c) 1991 Regents of the University of California.
6 * Copyright (c) 1994 John S. Dyson
8 * Copyright (c) 1994 David Greenman
10 * Copyright (c) 2005 Yahoo! Technologies Norway AS
11 * All rights reserved.
13 * This code is derived from software contributed to Berkeley by
14 * The Mach Operating System project at Carnegie-Mellon University.
16 * Redistribution and use in source and binary forms, with or without
17 * modification, are permitted provided that the following conditions
19 * 1. Redistributions of source code must retain the above copyright
20 * notice, this list of conditions and the following disclaimer.
21 * 2. Redistributions in binary form must reproduce the above copyright
22 * notice, this list of conditions and the following disclaimer in the
23 * documentation and/or other materials provided with the distribution.
24 * 3. All advertising materials mentioning features or use of this software
25 * must display the following acknowledgement:
26 * This product includes software developed by the University of
27 * California, Berkeley and its contributors.
28 * 4. Neither the name of the University nor the names of its contributors
29 * may be used to endorse or promote products derived from this software
30 * without specific prior written permission.
32 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
33 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
34 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
35 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
36 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
37 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
38 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
39 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
40 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
41 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
44 * from: @(#)vm_pageout.c 7.4 (Berkeley) 5/7/91
47 * Copyright (c) 1987, 1990 Carnegie-Mellon University.
48 * All rights reserved.
50 * Authors: Avadis Tevanian, Jr., Michael Wayne Young
52 * Permission to use, copy, modify and distribute this software and
53 * its documentation is hereby granted, provided that both the copyright
54 * notice and this permission notice appear in all copies of the
55 * software, derivative works or modified versions, and any portions
56 * thereof, and that both notices appear in supporting documentation.
58 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
59 * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
60 * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
62 * Carnegie Mellon requests users of this software to return to
64 * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
65 * School of Computer Science
66 * Carnegie Mellon University
67 * Pittsburgh PA 15213-3890
69 * any improvements or extensions that they make and grant Carnegie the
70 * rights to redistribute these changes.
74 * The proverbial page-out daemon.
77 #include <sys/cdefs.h>
78 __FBSDID("$FreeBSD$");
82 #include <sys/param.h>
83 #include <sys/systm.h>
84 #include <sys/kernel.h>
85 #include <sys/eventhandler.h>
87 #include <sys/mutex.h>
89 #include <sys/kthread.h>
91 #include <sys/mount.h>
92 #include <sys/racct.h>
93 #include <sys/resourcevar.h>
94 #include <sys/sched.h>
96 #include <sys/signalvar.h>
99 #include <sys/vnode.h>
100 #include <sys/vmmeter.h>
101 #include <sys/rwlock.h>
103 #include <sys/sysctl.h>
106 #include <vm/vm_param.h>
107 #include <vm/vm_object.h>
108 #include <vm/vm_page.h>
109 #include <vm/vm_map.h>
110 #include <vm/vm_pageout.h>
111 #include <vm/vm_pager.h>
112 #include <vm/vm_phys.h>
113 #include <vm/vm_pagequeue.h>
114 #include <vm/swap_pager.h>
115 #include <vm/vm_extern.h>
119 * System initialization
122 /* the kernel process "vm_pageout"*/
123 static void vm_pageout(void);
124 static void vm_pageout_init(void);
125 static int vm_pageout_clean(vm_page_t m, int *numpagedout);
126 static int vm_pageout_cluster(vm_page_t m);
127 static void vm_pageout_mightbe_oom(struct vm_domain *vmd, int page_shortage,
128 int starting_page_shortage);
130 SYSINIT(pagedaemon_init, SI_SUB_KTHREAD_PAGE, SI_ORDER_FIRST, vm_pageout_init,
133 struct proc *pageproc;
135 static struct kproc_desc page_kp = {
140 SYSINIT(pagedaemon, SI_SUB_KTHREAD_PAGE, SI_ORDER_SECOND, kproc_start,
143 SDT_PROVIDER_DEFINE(vm);
144 SDT_PROBE_DEFINE(vm, , , vm__lowmem_scan);
146 /* Pagedaemon activity rates, in subdivisions of one second. */
147 #define VM_LAUNDER_RATE 10
148 #define VM_INACT_SCAN_RATE 10
150 static int vm_pageout_oom_seq = 12;
152 static int vm_pageout_update_period;
153 static int disable_swap_pageouts;
154 static int lowmem_period = 10;
155 static int swapdev_enabled;
157 static int vm_panic_on_oom = 0;
159 SYSCTL_INT(_vm, OID_AUTO, panic_on_oom,
160 CTLFLAG_RWTUN, &vm_panic_on_oom, 0,
161 "panic on out of memory instead of killing the largest process");
163 SYSCTL_INT(_vm, OID_AUTO, pageout_update_period,
164 CTLFLAG_RWTUN, &vm_pageout_update_period, 0,
165 "Maximum active LRU update period");
167 SYSCTL_INT(_vm, OID_AUTO, lowmem_period, CTLFLAG_RWTUN, &lowmem_period, 0,
168 "Low memory callback period");
170 SYSCTL_INT(_vm, OID_AUTO, disable_swapspace_pageouts,
171 CTLFLAG_RWTUN, &disable_swap_pageouts, 0, "Disallow swapout of dirty pages");
173 static int pageout_lock_miss;
174 SYSCTL_INT(_vm, OID_AUTO, pageout_lock_miss,
175 CTLFLAG_RD, &pageout_lock_miss, 0, "vget() lock misses during pageout");
177 SYSCTL_INT(_vm, OID_AUTO, pageout_oom_seq,
178 CTLFLAG_RWTUN, &vm_pageout_oom_seq, 0,
179 "back-to-back calls to oom detector to start OOM");
181 static int act_scan_laundry_weight = 3;
182 SYSCTL_INT(_vm, OID_AUTO, act_scan_laundry_weight, CTLFLAG_RWTUN,
183 &act_scan_laundry_weight, 0,
184 "weight given to clean vs. dirty pages in active queue scans");
186 static u_int vm_background_launder_rate = 4096;
187 SYSCTL_UINT(_vm, OID_AUTO, background_launder_rate, CTLFLAG_RWTUN,
188 &vm_background_launder_rate, 0,
189 "background laundering rate, in kilobytes per second");
191 static u_int vm_background_launder_max = 20 * 1024;
192 SYSCTL_UINT(_vm, OID_AUTO, background_launder_max, CTLFLAG_RWTUN,
193 &vm_background_launder_max, 0, "background laundering cap, in kilobytes");
195 int vm_pageout_page_count = 32;
197 u_long vm_page_max_user_wired;
198 SYSCTL_ULONG(_vm, OID_AUTO, max_user_wired, CTLFLAG_RW,
199 &vm_page_max_user_wired, 0,
200 "system-wide limit to user-wired page count");
202 static u_int isqrt(u_int num);
203 static int vm_pageout_launder(struct vm_domain *vmd, int launder,
205 static void vm_pageout_laundry_worker(void *arg);
208 struct vm_batchqueue bq;
209 struct vm_pagequeue *pq;
216 vm_pageout_init_scan(struct scan_state *ss, struct vm_pagequeue *pq,
217 vm_page_t marker, vm_page_t after, int maxscan)
220 vm_pagequeue_assert_locked(pq);
221 KASSERT((marker->aflags & PGA_ENQUEUED) == 0,
222 ("marker %p already enqueued", marker));
225 TAILQ_INSERT_HEAD(&pq->pq_pl, marker, plinks.q);
227 TAILQ_INSERT_AFTER(&pq->pq_pl, after, marker, plinks.q);
228 vm_page_aflag_set(marker, PGA_ENQUEUED);
230 vm_batchqueue_init(&ss->bq);
233 ss->maxscan = maxscan;
235 vm_pagequeue_unlock(pq);
239 vm_pageout_end_scan(struct scan_state *ss)
241 struct vm_pagequeue *pq;
244 vm_pagequeue_assert_locked(pq);
245 KASSERT((ss->marker->aflags & PGA_ENQUEUED) != 0,
246 ("marker %p not enqueued", ss->marker));
248 TAILQ_REMOVE(&pq->pq_pl, ss->marker, plinks.q);
249 vm_page_aflag_clear(ss->marker, PGA_ENQUEUED);
250 pq->pq_pdpages += ss->scanned;
254 * Add a small number of queued pages to a batch queue for later processing
255 * without the corresponding queue lock held. The caller must have enqueued a
256 * marker page at the desired start point for the scan. Pages will be
257 * physically dequeued if the caller so requests. Otherwise, the returned
258 * batch may contain marker pages, and it is up to the caller to handle them.
260 * When processing the batch queue, vm_page_queue() must be used to
261 * determine whether the page has been logically dequeued by another thread.
262 * Once this check is performed, the page lock guarantees that the page will
263 * not be disassociated from the queue.
265 static __always_inline void
266 vm_pageout_collect_batch(struct scan_state *ss, const bool dequeue)
268 struct vm_pagequeue *pq;
269 vm_page_t m, marker, n;
274 KASSERT((marker->aflags & PGA_ENQUEUED) != 0,
275 ("marker %p not enqueued", ss->marker));
277 vm_pagequeue_lock(pq);
278 for (m = TAILQ_NEXT(marker, plinks.q); m != NULL &&
279 ss->scanned < ss->maxscan && ss->bq.bq_cnt < VM_BATCHQUEUE_SIZE;
280 m = n, ss->scanned++) {
281 n = TAILQ_NEXT(m, plinks.q);
282 if ((m->flags & PG_MARKER) == 0) {
283 KASSERT((m->aflags & PGA_ENQUEUED) != 0,
284 ("page %p not enqueued", m));
285 KASSERT((m->flags & PG_FICTITIOUS) == 0,
286 ("Fictitious page %p cannot be in page queue", m));
287 KASSERT((m->oflags & VPO_UNMANAGED) == 0,
288 ("Unmanaged page %p cannot be in page queue", m));
292 (void)vm_batchqueue_insert(&ss->bq, m);
294 TAILQ_REMOVE(&pq->pq_pl, m, plinks.q);
295 vm_page_aflag_clear(m, PGA_ENQUEUED);
298 TAILQ_REMOVE(&pq->pq_pl, marker, plinks.q);
299 if (__predict_true(m != NULL))
300 TAILQ_INSERT_BEFORE(m, marker, plinks.q);
302 TAILQ_INSERT_TAIL(&pq->pq_pl, marker, plinks.q);
304 vm_pagequeue_cnt_add(pq, -ss->bq.bq_cnt);
305 vm_pagequeue_unlock(pq);
309 * Return the next page to be scanned, or NULL if the scan is complete.
311 static __always_inline vm_page_t
312 vm_pageout_next(struct scan_state *ss, const bool dequeue)
315 if (ss->bq.bq_cnt == 0)
316 vm_pageout_collect_batch(ss, dequeue);
317 return (vm_batchqueue_pop(&ss->bq));
321 * Scan for pages at adjacent offsets within the given page's object that are
322 * eligible for laundering, form a cluster of these pages and the given page,
323 * and launder that cluster.
326 vm_pageout_cluster(vm_page_t m)
329 vm_page_t mc[2 * vm_pageout_page_count], p, pb, ps;
331 int ib, is, page_base, pageout_count;
334 VM_OBJECT_ASSERT_WLOCKED(object);
337 vm_page_assert_unbusied(m);
339 mc[vm_pageout_page_count] = pb = ps = m;
341 page_base = vm_pageout_page_count;
346 * We can cluster only if the page is not clean, busy, or held, and
347 * the page is in the laundry queue.
349 * During heavy mmap/modification loads the pageout
350 * daemon can really fragment the underlying file
351 * due to flushing pages out of order and not trying to
352 * align the clusters (which leaves sporadic out-of-order
353 * holes). To solve this problem we do the reverse scan
354 * first and attempt to align our cluster, then do a
355 * forward scan if room remains.
358 while (ib != 0 && pageout_count < vm_pageout_page_count) {
363 if ((p = vm_page_prev(pb)) == NULL || vm_page_busied(p) ||
368 vm_page_test_dirty(p);
374 if (!vm_page_in_laundry(p) || !vm_page_try_remove_write(p)) {
380 mc[--page_base] = pb = p;
385 * We are at an alignment boundary. Stop here, and switch
386 * directions. Do not clear ib.
388 if ((pindex - (ib - 1)) % vm_pageout_page_count == 0)
391 while (pageout_count < vm_pageout_page_count &&
392 pindex + is < object->size) {
393 if ((p = vm_page_next(ps)) == NULL || vm_page_busied(p) ||
396 vm_page_test_dirty(p);
400 if (!vm_page_in_laundry(p) || !vm_page_try_remove_write(p)) {
405 mc[page_base + pageout_count] = ps = p;
411 * If we exhausted our forward scan, continue with the reverse scan
412 * when possible, even past an alignment boundary. This catches
413 * boundary conditions.
415 if (ib != 0 && pageout_count < vm_pageout_page_count)
418 return (vm_pageout_flush(&mc[page_base], pageout_count,
419 VM_PAGER_PUT_NOREUSE, 0, NULL, NULL));
423 * vm_pageout_flush() - launder the given pages
425 * The given pages are laundered. Note that we setup for the start of
426 * I/O ( i.e. busy the page ), mark it read-only, and bump the object
427 * reference count all in here rather then in the parent. If we want
428 * the parent to do more sophisticated things we may have to change
431 * Returned runlen is the count of pages between mreq and first
432 * page after mreq with status VM_PAGER_AGAIN.
433 * *eio is set to TRUE if pager returned VM_PAGER_ERROR or VM_PAGER_FAIL
434 * for any page in runlen set.
437 vm_pageout_flush(vm_page_t *mc, int count, int flags, int mreq, int *prunlen,
440 vm_object_t object = mc[0]->object;
441 int pageout_status[count];
445 VM_OBJECT_ASSERT_WLOCKED(object);
448 * Initiate I/O. Mark the pages busy and verify that they're valid
451 * We do not have to fixup the clean/dirty bits here... we can
452 * allow the pager to do it after the I/O completes.
454 * NOTE! mc[i]->dirty may be partial or fragmented due to an
455 * edge case with file fragments.
457 for (i = 0; i < count; i++) {
458 KASSERT(mc[i]->valid == VM_PAGE_BITS_ALL,
459 ("vm_pageout_flush: partially invalid page %p index %d/%d",
461 KASSERT((mc[i]->aflags & PGA_WRITEABLE) == 0,
462 ("vm_pageout_flush: writeable page %p", mc[i]));
463 vm_page_sbusy(mc[i]);
465 vm_object_pip_add(object, count);
467 vm_pager_put_pages(object, mc, count, flags, pageout_status);
469 runlen = count - mreq;
472 for (i = 0; i < count; i++) {
473 vm_page_t mt = mc[i];
475 KASSERT(pageout_status[i] == VM_PAGER_PEND ||
476 !pmap_page_is_write_mapped(mt),
477 ("vm_pageout_flush: page %p is not write protected", mt));
478 switch (pageout_status[i]) {
481 if (vm_page_in_laundry(mt))
482 vm_page_deactivate_noreuse(mt);
490 * The page is outside the object's range. We pretend
491 * that the page out worked and clean the page, so the
492 * changes will be lost if the page is reclaimed by
497 if (vm_page_in_laundry(mt))
498 vm_page_deactivate_noreuse(mt);
504 * If the page couldn't be paged out to swap because the
505 * pager wasn't able to find space, place the page in
506 * the PQ_UNSWAPPABLE holding queue. This is an
507 * optimization that prevents the page daemon from
508 * wasting CPU cycles on pages that cannot be reclaimed
509 * becase no swap device is configured.
511 * Otherwise, reactivate the page so that it doesn't
512 * clog the laundry and inactive queues. (We will try
513 * paging it out again later.)
516 if (object->type == OBJT_SWAP &&
517 pageout_status[i] == VM_PAGER_FAIL) {
518 vm_page_unswappable(mt);
521 vm_page_activate(mt);
523 if (eio != NULL && i >= mreq && i - mreq < runlen)
527 if (i >= mreq && i - mreq < runlen)
533 * If the operation is still going, leave the page busy to
534 * block all other accesses. Also, leave the paging in
535 * progress indicator set so that we don't attempt an object
538 if (pageout_status[i] != VM_PAGER_PEND) {
539 vm_object_pip_wakeup(object);
545 return (numpagedout);
549 vm_pageout_swapon(void *arg __unused, struct swdevt *sp __unused)
552 atomic_store_rel_int(&swapdev_enabled, 1);
556 vm_pageout_swapoff(void *arg __unused, struct swdevt *sp __unused)
559 if (swap_pager_nswapdev() == 1)
560 atomic_store_rel_int(&swapdev_enabled, 0);
564 * Attempt to acquire all of the necessary locks to launder a page and
565 * then call through the clustering layer to PUTPAGES. Wait a short
566 * time for a vnode lock.
568 * Requires the page and object lock on entry, releases both before return.
569 * Returns 0 on success and an errno otherwise.
572 vm_pageout_clean(vm_page_t m, int *numpagedout)
580 vm_page_assert_locked(m);
582 VM_OBJECT_ASSERT_WLOCKED(object);
588 * The object is already known NOT to be dead. It
589 * is possible for the vget() to block the whole
590 * pageout daemon, but the new low-memory handling
591 * code should prevent it.
593 * We can't wait forever for the vnode lock, we might
594 * deadlock due to a vn_read() getting stuck in
595 * vm_wait while holding this vnode. We skip the
596 * vnode if we can't get it in a reasonable amount
599 if (object->type == OBJT_VNODE) {
602 if (vp->v_type == VREG &&
603 vn_start_write(vp, &mp, V_NOWAIT) != 0) {
609 ("vp %p with NULL v_mount", vp));
610 vm_object_reference_locked(object);
612 VM_OBJECT_WUNLOCK(object);
613 lockmode = MNT_SHARED_WRITES(vp->v_mount) ?
614 LK_SHARED : LK_EXCLUSIVE;
615 if (vget(vp, lockmode | LK_TIMELOCK, curthread)) {
620 VM_OBJECT_WLOCK(object);
623 * Ensure that the object and vnode were not disassociated
624 * while locks were dropped.
626 if (vp->v_object != object) {
633 * While the object and page were unlocked, the page
635 * (1) moved to a different queue,
636 * (2) reallocated to a different object,
637 * (3) reallocated to a different offset, or
640 if (!vm_page_in_laundry(m) || m->object != object ||
641 m->pindex != pindex || m->dirty == 0) {
648 * The page may have been busied while the object and page
649 * locks were released.
651 if (vm_page_busied(m)) {
659 * Remove all writeable mappings, failing if the page is wired.
661 if (!vm_page_try_remove_write(m)) {
669 * If a page is dirty, then it is either being washed
670 * (but not yet cleaned) or it is still in the
671 * laundry. If it is still in the laundry, then we
672 * start the cleaning operation.
674 if ((*numpagedout = vm_pageout_cluster(m)) == 0)
678 VM_OBJECT_WUNLOCK(object);
681 vm_page_lock_assert(m, MA_NOTOWNED);
685 vm_object_deallocate(object);
686 vn_finished_write(mp);
693 * Attempt to launder the specified number of pages.
695 * Returns the number of pages successfully laundered.
698 vm_pageout_launder(struct vm_domain *vmd, int launder, bool in_shortfall)
700 struct scan_state ss;
701 struct vm_pagequeue *pq;
705 int act_delta, error, numpagedout, queue, starting_target;
711 starting_target = launder;
715 * Scan the laundry queues for pages eligible to be laundered. We stop
716 * once the target number of dirty pages have been laundered, or once
717 * we've reached the end of the queue. A single iteration of this loop
718 * may cause more than one page to be laundered because of clustering.
720 * As an optimization, we avoid laundering from PQ_UNSWAPPABLE when no
721 * swap devices are configured.
723 if (atomic_load_acq_int(&swapdev_enabled))
724 queue = PQ_UNSWAPPABLE;
729 marker = &vmd->vmd_markers[queue];
730 pq = &vmd->vmd_pagequeues[queue];
731 vm_pagequeue_lock(pq);
732 vm_pageout_init_scan(&ss, pq, marker, NULL, pq->pq_cnt);
733 while (launder > 0 && (m = vm_pageout_next(&ss, false)) != NULL) {
734 if (__predict_false((m->flags & PG_MARKER) != 0))
737 vm_page_change_lock(m, &mtx);
741 * The page may have been disassociated from the queue
742 * or even freed while locks were dropped. We thus must be
743 * careful whenever modifying page state. Once the object lock
744 * has been acquired, we have a stable reference to the page.
746 if (vm_page_queue(m) != queue)
750 * A requeue was requested, so this page gets a second
753 if ((m->aflags & PGA_REQUEUE) != 0) {
754 vm_page_pqbatch_submit(m, queue);
759 * Wired pages may not be freed. Complete their removal
760 * from the queue now to avoid needless revisits during
761 * future scans. This check is racy and must be reverified once
762 * we hold the object lock and have verified that the page
765 if (vm_page_wired(m)) {
766 vm_page_dequeue_deferred(m);
770 if (object != m->object) {
772 VM_OBJECT_WUNLOCK(object);
775 * A page's object pointer may be set to NULL before
776 * the object lock is acquired.
778 object = (vm_object_t)atomic_load_ptr(&m->object);
779 if (object != NULL && !VM_OBJECT_TRYWLOCK(object)) {
781 /* Depends on type-stability. */
782 VM_OBJECT_WLOCK(object);
787 if (__predict_false(m->object == NULL))
789 * The page has been removed from its object.
792 KASSERT(m->object == object, ("page %p does not belong to %p",
795 if (vm_page_busied(m))
799 * Re-check for wirings now that we hold the object lock and
800 * have verified that the page is unbusied. If the page is
801 * mapped, it may still be wired by pmap lookups. The call to
802 * vm_page_try_remove_all() below atomically checks for such
803 * wirings and removes mappings. If the page is unmapped, the
804 * wire count is guaranteed not to increase.
806 if (__predict_false(vm_page_wired(m))) {
807 vm_page_dequeue_deferred(m);
812 * Invalid pages can be easily freed. They cannot be
813 * mapped; vm_page_free() asserts this.
819 * If the page has been referenced and the object is not dead,
820 * reactivate or requeue the page depending on whether the
823 * Test PGA_REFERENCED after calling pmap_ts_referenced() so
824 * that a reference from a concurrently destroyed mapping is
825 * observed here and now.
827 if (object->ref_count != 0)
828 act_delta = pmap_ts_referenced(m);
830 KASSERT(!pmap_page_is_mapped(m),
831 ("page %p is mapped", m));
834 if ((m->aflags & PGA_REFERENCED) != 0) {
835 vm_page_aflag_clear(m, PGA_REFERENCED);
838 if (act_delta != 0) {
839 if (object->ref_count != 0) {
840 VM_CNT_INC(v_reactivated);
844 * Increase the activation count if the page
845 * was referenced while in the laundry queue.
846 * This makes it less likely that the page will
847 * be returned prematurely to the inactive
850 m->act_count += act_delta + ACT_ADVANCE;
853 * If this was a background laundering, count
854 * activated pages towards our target. The
855 * purpose of background laundering is to ensure
856 * that pages are eventually cycled through the
857 * laundry queue, and an activation is a valid
863 } else if ((object->flags & OBJ_DEAD) == 0) {
870 * If the page appears to be clean at the machine-independent
871 * layer, then remove all of its mappings from the pmap in
872 * anticipation of freeing it. If, however, any of the page's
873 * mappings allow write access, then the page may still be
874 * modified until the last of those mappings are removed.
876 if (object->ref_count != 0) {
877 vm_page_test_dirty(m);
878 if (m->dirty == 0 && !vm_page_try_remove_all(m)) {
879 vm_page_dequeue_deferred(m);
885 * Clean pages are freed, and dirty pages are paged out unless
886 * they belong to a dead object. Requeueing dirty pages from
887 * dead objects is pointless, as they are being paged out and
888 * freed by the thread that destroyed the object.
894 } else if ((object->flags & OBJ_DEAD) == 0) {
895 if (object->type != OBJT_SWAP &&
896 object->type != OBJT_DEFAULT)
898 else if (disable_swap_pageouts)
908 * Form a cluster with adjacent, dirty pages from the
909 * same object, and page out that entire cluster.
911 * The adjacent, dirty pages must also be in the
912 * laundry. However, their mappings are not checked
913 * for new references. Consequently, a recently
914 * referenced page may be paged out. However, that
915 * page will not be prematurely reclaimed. After page
916 * out, the page will be placed in the inactive queue,
917 * where any new references will be detected and the
920 error = vm_pageout_clean(m, &numpagedout);
922 launder -= numpagedout;
923 ss.scanned += numpagedout;
924 } else if (error == EDEADLK) {
936 if (object != NULL) {
937 VM_OBJECT_WUNLOCK(object);
940 vm_pagequeue_lock(pq);
941 vm_pageout_end_scan(&ss);
942 vm_pagequeue_unlock(pq);
944 if (launder > 0 && queue == PQ_UNSWAPPABLE) {
950 * Wakeup the sync daemon if we skipped a vnode in a writeable object
951 * and we didn't launder enough pages.
953 if (vnodes_skipped > 0 && launder > 0)
954 (void)speedup_syncer();
956 return (starting_target - launder);
960 * Compute the integer square root.
965 u_int bit, root, tmp;
967 bit = num != 0 ? (1u << ((fls(num) - 1) & ~1)) : 0;
982 * Perform the work of the laundry thread: periodically wake up and determine
983 * whether any pages need to be laundered. If so, determine the number of pages
984 * that need to be laundered, and launder them.
987 vm_pageout_laundry_worker(void *arg)
989 struct vm_domain *vmd;
990 struct vm_pagequeue *pq;
991 uint64_t nclean, ndirty, nfreed;
992 int domain, last_target, launder, shortfall, shortfall_cycle, target;
995 domain = (uintptr_t)arg;
996 vmd = VM_DOMAIN(domain);
997 pq = &vmd->vmd_pagequeues[PQ_LAUNDRY];
998 KASSERT(vmd->vmd_segs != 0, ("domain without segments"));
1001 in_shortfall = false;
1002 shortfall_cycle = 0;
1003 last_target = target = 0;
1007 * Calls to these handlers are serialized by the swap syscall lock.
1009 (void)EVENTHANDLER_REGISTER(swapon, vm_pageout_swapon, vmd,
1010 EVENTHANDLER_PRI_ANY);
1011 (void)EVENTHANDLER_REGISTER(swapoff, vm_pageout_swapoff, vmd,
1012 EVENTHANDLER_PRI_ANY);
1015 * The pageout laundry worker is never done, so loop forever.
1018 KASSERT(target >= 0, ("negative target %d", target));
1019 KASSERT(shortfall_cycle >= 0,
1020 ("negative cycle %d", shortfall_cycle));
1024 * First determine whether we need to launder pages to meet a
1025 * shortage of free pages.
1027 if (shortfall > 0) {
1028 in_shortfall = true;
1029 shortfall_cycle = VM_LAUNDER_RATE / VM_INACT_SCAN_RATE;
1031 } else if (!in_shortfall)
1033 else if (shortfall_cycle == 0 || vm_laundry_target(vmd) <= 0) {
1035 * We recently entered shortfall and began laundering
1036 * pages. If we have completed that laundering run
1037 * (and we are no longer in shortfall) or we have met
1038 * our laundry target through other activity, then we
1039 * can stop laundering pages.
1041 in_shortfall = false;
1045 launder = target / shortfall_cycle--;
1049 * There's no immediate need to launder any pages; see if we
1050 * meet the conditions to perform background laundering:
1052 * 1. The ratio of dirty to clean inactive pages exceeds the
1053 * background laundering threshold, or
1054 * 2. we haven't yet reached the target of the current
1055 * background laundering run.
1057 * The background laundering threshold is not a constant.
1058 * Instead, it is a slowly growing function of the number of
1059 * clean pages freed by the page daemon since the last
1060 * background laundering. Thus, as the ratio of dirty to
1061 * clean inactive pages grows, the amount of memory pressure
1062 * required to trigger laundering decreases. We ensure
1063 * that the threshold is non-zero after an inactive queue
1064 * scan, even if that scan failed to free a single clean page.
1067 nclean = vmd->vmd_free_count +
1068 vmd->vmd_pagequeues[PQ_INACTIVE].pq_cnt;
1069 ndirty = vmd->vmd_pagequeues[PQ_LAUNDRY].pq_cnt;
1070 if (target == 0 && ndirty * isqrt(howmany(nfreed + 1,
1071 vmd->vmd_free_target - vmd->vmd_free_min)) >= nclean) {
1072 target = vmd->vmd_background_launder_target;
1076 * We have a non-zero background laundering target. If we've
1077 * laundered up to our maximum without observing a page daemon
1078 * request, just stop. This is a safety belt that ensures we
1079 * don't launder an excessive amount if memory pressure is low
1080 * and the ratio of dirty to clean pages is large. Otherwise,
1081 * proceed at the background laundering rate.
1086 last_target = target;
1087 } else if (last_target - target >=
1088 vm_background_launder_max * PAGE_SIZE / 1024) {
1091 launder = vm_background_launder_rate * PAGE_SIZE / 1024;
1092 launder /= VM_LAUNDER_RATE;
1093 if (launder > target)
1100 * Because of I/O clustering, the number of laundered
1101 * pages could exceed "target" by the maximum size of
1102 * a cluster minus one.
1104 target -= min(vm_pageout_launder(vmd, launder,
1105 in_shortfall), target);
1106 pause("laundp", hz / VM_LAUNDER_RATE);
1110 * If we're not currently laundering pages and the page daemon
1111 * hasn't posted a new request, sleep until the page daemon
1114 vm_pagequeue_lock(pq);
1115 if (target == 0 && vmd->vmd_laundry_request == VM_LAUNDRY_IDLE)
1116 (void)mtx_sleep(&vmd->vmd_laundry_request,
1117 vm_pagequeue_lockptr(pq), PVM, "launds", 0);
1120 * If the pagedaemon has indicated that it's in shortfall, start
1121 * a shortfall laundering unless we're already in the middle of
1122 * one. This may preempt a background laundering.
1124 if (vmd->vmd_laundry_request == VM_LAUNDRY_SHORTFALL &&
1125 (!in_shortfall || shortfall_cycle == 0)) {
1126 shortfall = vm_laundry_target(vmd) +
1127 vmd->vmd_pageout_deficit;
1133 vmd->vmd_laundry_request = VM_LAUNDRY_IDLE;
1134 nfreed += vmd->vmd_clean_pages_freed;
1135 vmd->vmd_clean_pages_freed = 0;
1136 vm_pagequeue_unlock(pq);
1141 * Compute the number of pages we want to try to move from the
1142 * active queue to either the inactive or laundry queue.
1144 * When scanning active pages during a shortage, we make clean pages
1145 * count more heavily towards the page shortage than dirty pages.
1146 * This is because dirty pages must be laundered before they can be
1147 * reused and thus have less utility when attempting to quickly
1148 * alleviate a free page shortage. However, this weighting also
1149 * causes the scan to deactivate dirty pages more aggressively,
1150 * improving the effectiveness of clustering.
1153 vm_pageout_active_target(struct vm_domain *vmd)
1157 shortage = vmd->vmd_inactive_target + vm_paging_target(vmd) -
1158 (vmd->vmd_pagequeues[PQ_INACTIVE].pq_cnt +
1159 vmd->vmd_pagequeues[PQ_LAUNDRY].pq_cnt / act_scan_laundry_weight);
1160 shortage *= act_scan_laundry_weight;
1165 * Scan the active queue. If there is no shortage of inactive pages, scan a
1166 * small portion of the queue in order to maintain quasi-LRU.
1169 vm_pageout_scan_active(struct vm_domain *vmd, int page_shortage)
1171 struct scan_state ss;
1174 vm_page_t m, marker;
1175 struct vm_pagequeue *pq;
1177 int act_delta, max_scan, scan_tick;
1179 marker = &vmd->vmd_markers[PQ_ACTIVE];
1180 pq = &vmd->vmd_pagequeues[PQ_ACTIVE];
1181 vm_pagequeue_lock(pq);
1184 * If we're just idle polling attempt to visit every
1185 * active page within 'update_period' seconds.
1188 if (vm_pageout_update_period != 0) {
1189 min_scan = pq->pq_cnt;
1190 min_scan *= scan_tick - vmd->vmd_last_active_scan;
1191 min_scan /= hz * vm_pageout_update_period;
1194 if (min_scan > 0 || (page_shortage > 0 && pq->pq_cnt > 0))
1195 vmd->vmd_last_active_scan = scan_tick;
1198 * Scan the active queue for pages that can be deactivated. Update
1199 * the per-page activity counter and use it to identify deactivation
1200 * candidates. Held pages may be deactivated.
1202 * To avoid requeuing each page that remains in the active queue, we
1203 * implement the CLOCK algorithm. To keep the implementation of the
1204 * enqueue operation consistent for all page queues, we use two hands,
1205 * represented by marker pages. Scans begin at the first hand, which
1206 * precedes the second hand in the queue. When the two hands meet,
1207 * they are moved back to the head and tail of the queue, respectively,
1208 * and scanning resumes.
1210 max_scan = page_shortage > 0 ? pq->pq_cnt : min_scan;
1213 vm_pageout_init_scan(&ss, pq, marker, &vmd->vmd_clock[0], max_scan);
1214 while ((m = vm_pageout_next(&ss, false)) != NULL) {
1215 if (__predict_false(m == &vmd->vmd_clock[1])) {
1216 vm_pagequeue_lock(pq);
1217 TAILQ_REMOVE(&pq->pq_pl, &vmd->vmd_clock[0], plinks.q);
1218 TAILQ_REMOVE(&pq->pq_pl, &vmd->vmd_clock[1], plinks.q);
1219 TAILQ_INSERT_HEAD(&pq->pq_pl, &vmd->vmd_clock[0],
1221 TAILQ_INSERT_TAIL(&pq->pq_pl, &vmd->vmd_clock[1],
1223 max_scan -= ss.scanned;
1224 vm_pageout_end_scan(&ss);
1227 if (__predict_false((m->flags & PG_MARKER) != 0))
1230 vm_page_change_lock(m, &mtx);
1233 * The page may have been disassociated from the queue
1234 * or even freed while locks were dropped. We thus must be
1235 * careful whenever modifying page state. Once the object lock
1236 * has been acquired, we have a stable reference to the page.
1238 if (vm_page_queue(m) != PQ_ACTIVE)
1242 * Wired pages are dequeued lazily.
1244 if (vm_page_wired(m)) {
1245 vm_page_dequeue_deferred(m);
1250 * A page's object pointer may be set to NULL before
1251 * the object lock is acquired.
1253 object = (vm_object_t)atomic_load_ptr(&m->object);
1254 if (__predict_false(object == NULL))
1256 * The page has been removed from its object.
1261 * Check to see "how much" the page has been used.
1263 * Test PGA_REFERENCED after calling pmap_ts_referenced() so
1264 * that a reference from a concurrently destroyed mapping is
1265 * observed here and now.
1267 * Perform an unsynchronized object ref count check. While
1268 * the page lock ensures that the page is not reallocated to
1269 * another object, in particular, one with unmanaged mappings
1270 * that cannot support pmap_ts_referenced(), two races are,
1271 * nonetheless, possible:
1272 * 1) The count was transitioning to zero, but we saw a non-
1273 * zero value. pmap_ts_referenced() will return zero
1274 * because the page is not mapped.
1275 * 2) The count was transitioning to one, but we saw zero.
1276 * This race delays the detection of a new reference. At
1277 * worst, we will deactivate and reactivate the page.
1279 if (object->ref_count != 0)
1280 act_delta = pmap_ts_referenced(m);
1283 if ((m->aflags & PGA_REFERENCED) != 0) {
1284 vm_page_aflag_clear(m, PGA_REFERENCED);
1289 * Advance or decay the act_count based on recent usage.
1291 if (act_delta != 0) {
1292 m->act_count += ACT_ADVANCE + act_delta;
1293 if (m->act_count > ACT_MAX)
1294 m->act_count = ACT_MAX;
1296 m->act_count -= min(m->act_count, ACT_DECLINE);
1298 if (m->act_count == 0) {
1300 * When not short for inactive pages, let dirty pages go
1301 * through the inactive queue before moving to the
1302 * laundry queues. This gives them some extra time to
1303 * be reactivated, potentially avoiding an expensive
1304 * pageout. However, during a page shortage, the
1305 * inactive queue is necessarily small, and so dirty
1306 * pages would only spend a trivial amount of time in
1307 * the inactive queue. Therefore, we might as well
1308 * place them directly in the laundry queue to reduce
1311 if (page_shortage <= 0) {
1312 vm_page_swapqueue(m, PQ_ACTIVE, PQ_INACTIVE);
1315 * Calling vm_page_test_dirty() here would
1316 * require acquisition of the object's write
1317 * lock. However, during a page shortage,
1318 * directing dirty pages into the laundry
1319 * queue is only an optimization and not a
1320 * requirement. Therefore, we simply rely on
1321 * the opportunistic updates to the page's
1322 * dirty field by the pmap.
1324 if (m->dirty == 0) {
1325 vm_page_swapqueue(m, PQ_ACTIVE,
1328 act_scan_laundry_weight;
1330 vm_page_swapqueue(m, PQ_ACTIVE,
1341 vm_pagequeue_lock(pq);
1342 TAILQ_REMOVE(&pq->pq_pl, &vmd->vmd_clock[0], plinks.q);
1343 TAILQ_INSERT_AFTER(&pq->pq_pl, marker, &vmd->vmd_clock[0], plinks.q);
1344 vm_pageout_end_scan(&ss);
1345 vm_pagequeue_unlock(pq);
1349 vm_pageout_reinsert_inactive_page(struct scan_state *ss, vm_page_t m)
1351 struct vm_domain *vmd;
1353 if (m->queue != PQ_INACTIVE || (m->aflags & PGA_ENQUEUED) != 0)
1355 vm_page_aflag_set(m, PGA_ENQUEUED);
1356 if ((m->aflags & PGA_REQUEUE_HEAD) != 0) {
1357 vmd = vm_pagequeue_domain(m);
1358 TAILQ_INSERT_BEFORE(&vmd->vmd_inacthead, m, plinks.q);
1359 vm_page_aflag_clear(m, PGA_REQUEUE | PGA_REQUEUE_HEAD);
1360 } else if ((m->aflags & PGA_REQUEUE) != 0) {
1361 TAILQ_INSERT_TAIL(&ss->pq->pq_pl, m, plinks.q);
1362 vm_page_aflag_clear(m, PGA_REQUEUE | PGA_REQUEUE_HEAD);
1364 TAILQ_INSERT_BEFORE(ss->marker, m, plinks.q);
1369 * Re-add stuck pages to the inactive queue. We will examine them again
1370 * during the next scan. If the queue state of a page has changed since
1371 * it was physically removed from the page queue in
1372 * vm_pageout_collect_batch(), don't do anything with that page.
1375 vm_pageout_reinsert_inactive(struct scan_state *ss, struct vm_batchqueue *bq,
1378 struct vm_pagequeue *pq;
1385 if (vm_batchqueue_insert(bq, m))
1387 vm_pagequeue_lock(pq);
1388 delta += vm_pageout_reinsert_inactive_page(ss, m);
1390 vm_pagequeue_lock(pq);
1391 while ((m = vm_batchqueue_pop(bq)) != NULL)
1392 delta += vm_pageout_reinsert_inactive_page(ss, m);
1393 vm_pagequeue_cnt_add(pq, delta);
1394 vm_pagequeue_unlock(pq);
1395 vm_batchqueue_init(bq);
1399 * Attempt to reclaim the requested number of pages from the inactive queue.
1400 * Returns true if the shortage was addressed.
1403 vm_pageout_scan_inactive(struct vm_domain *vmd, int shortage,
1406 struct scan_state ss;
1407 struct vm_batchqueue rq;
1409 vm_page_t m, marker;
1410 struct vm_pagequeue *pq;
1412 int act_delta, addl_page_shortage, deficit, page_shortage;
1413 int starting_page_shortage;
1416 * The addl_page_shortage is an estimate of the number of temporarily
1417 * stuck pages in the inactive queue. In other words, the
1418 * number of pages from the inactive count that should be
1419 * discounted in setting the target for the active queue scan.
1421 addl_page_shortage = 0;
1424 * vmd_pageout_deficit counts the number of pages requested in
1425 * allocations that failed because of a free page shortage. We assume
1426 * that the allocations will be reattempted and thus include the deficit
1427 * in our scan target.
1429 deficit = atomic_readandclear_int(&vmd->vmd_pageout_deficit);
1430 starting_page_shortage = page_shortage = shortage + deficit;
1434 vm_batchqueue_init(&rq);
1437 * Start scanning the inactive queue for pages that we can free. The
1438 * scan will stop when we reach the target or we have scanned the
1439 * entire queue. (Note that m->act_count is not used to make
1440 * decisions for the inactive queue, only for the active queue.)
1442 marker = &vmd->vmd_markers[PQ_INACTIVE];
1443 pq = &vmd->vmd_pagequeues[PQ_INACTIVE];
1444 vm_pagequeue_lock(pq);
1445 vm_pageout_init_scan(&ss, pq, marker, NULL, pq->pq_cnt);
1446 while (page_shortage > 0 && (m = vm_pageout_next(&ss, true)) != NULL) {
1447 KASSERT((m->flags & PG_MARKER) == 0,
1448 ("marker page %p was dequeued", m));
1450 vm_page_change_lock(m, &mtx);
1454 * The page may have been disassociated from the queue
1455 * or even freed while locks were dropped. We thus must be
1456 * careful whenever modifying page state. Once the object lock
1457 * has been acquired, we have a stable reference to the page.
1459 if (vm_page_queue(m) != PQ_INACTIVE) {
1460 addl_page_shortage++;
1465 * The page was re-enqueued after the page queue lock was
1466 * dropped, or a requeue was requested. This page gets a second
1469 if ((m->aflags & (PGA_ENQUEUED | PGA_REQUEUE |
1470 PGA_REQUEUE_HEAD)) != 0)
1474 * Wired pages may not be freed. Complete their removal
1475 * from the queue now to avoid needless revisits during
1476 * future scans. This check is racy and must be reverified once
1477 * we hold the object lock and have verified that the page
1480 if (vm_page_wired(m)) {
1481 vm_page_dequeue_deferred(m);
1485 if (object != m->object) {
1487 VM_OBJECT_WUNLOCK(object);
1490 * A page's object pointer may be set to NULL before
1491 * the object lock is acquired.
1493 object = (vm_object_t)atomic_load_ptr(&m->object);
1494 if (object != NULL && !VM_OBJECT_TRYWLOCK(object)) {
1496 /* Depends on type-stability. */
1497 VM_OBJECT_WLOCK(object);
1502 if (__predict_false(m->object == NULL))
1504 * The page has been removed from its object.
1507 KASSERT(m->object == object, ("page %p does not belong to %p",
1510 if (vm_page_busied(m)) {
1512 * Don't mess with busy pages. Leave them at
1513 * the front of the queue. Most likely, they
1514 * are being paged out and will leave the
1515 * queue shortly after the scan finishes. So,
1516 * they ought to be discounted from the
1519 addl_page_shortage++;
1524 * Re-check for wirings now that we hold the object lock and
1525 * have verified that the page is unbusied. If the page is
1526 * mapped, it may still be wired by pmap lookups. The call to
1527 * vm_page_try_remove_all() below atomically checks for such
1528 * wirings and removes mappings. If the page is unmapped, the
1529 * wire count is guaranteed not to increase.
1531 if (__predict_false(vm_page_wired(m))) {
1532 vm_page_dequeue_deferred(m);
1537 * Invalid pages can be easily freed. They cannot be
1538 * mapped, vm_page_free() asserts this.
1544 * If the page has been referenced and the object is not dead,
1545 * reactivate or requeue the page depending on whether the
1548 * Test PGA_REFERENCED after calling pmap_ts_referenced() so
1549 * that a reference from a concurrently destroyed mapping is
1550 * observed here and now.
1552 if (object->ref_count != 0)
1553 act_delta = pmap_ts_referenced(m);
1555 KASSERT(!pmap_page_is_mapped(m),
1556 ("page %p is mapped", m));
1559 if ((m->aflags & PGA_REFERENCED) != 0) {
1560 vm_page_aflag_clear(m, PGA_REFERENCED);
1563 if (act_delta != 0) {
1564 if (object->ref_count != 0) {
1565 VM_CNT_INC(v_reactivated);
1566 vm_page_activate(m);
1569 * Increase the activation count if the page
1570 * was referenced while in the inactive queue.
1571 * This makes it less likely that the page will
1572 * be returned prematurely to the inactive
1575 m->act_count += act_delta + ACT_ADVANCE;
1577 } else if ((object->flags & OBJ_DEAD) == 0) {
1578 vm_page_aflag_set(m, PGA_REQUEUE);
1584 * If the page appears to be clean at the machine-independent
1585 * layer, then remove all of its mappings from the pmap in
1586 * anticipation of freeing it. If, however, any of the page's
1587 * mappings allow write access, then the page may still be
1588 * modified until the last of those mappings are removed.
1590 if (object->ref_count != 0) {
1591 vm_page_test_dirty(m);
1592 if (m->dirty == 0 && !vm_page_try_remove_all(m)) {
1593 vm_page_dequeue_deferred(m);
1599 * Clean pages can be freed, but dirty pages must be sent back
1600 * to the laundry, unless they belong to a dead object.
1601 * Requeueing dirty pages from dead objects is pointless, as
1602 * they are being paged out and freed by the thread that
1603 * destroyed the object.
1605 if (m->dirty == 0) {
1608 * Because we dequeued the page and have already
1609 * checked for concurrent dequeue and enqueue
1610 * requests, we can safely disassociate the page
1611 * from the inactive queue.
1613 KASSERT((m->aflags & PGA_QUEUE_STATE_MASK) == 0,
1614 ("page %p has queue state", m));
1618 } else if ((object->flags & OBJ_DEAD) == 0)
1622 vm_pageout_reinsert_inactive(&ss, &rq, m);
1627 VM_OBJECT_WUNLOCK(object);
1628 vm_pageout_reinsert_inactive(&ss, &rq, NULL);
1629 vm_pageout_reinsert_inactive(&ss, &ss.bq, NULL);
1630 vm_pagequeue_lock(pq);
1631 vm_pageout_end_scan(&ss);
1632 vm_pagequeue_unlock(pq);
1634 VM_CNT_ADD(v_dfree, starting_page_shortage - page_shortage);
1637 * Wake up the laundry thread so that it can perform any needed
1638 * laundering. If we didn't meet our target, we're in shortfall and
1639 * need to launder more aggressively. If PQ_LAUNDRY is empty and no
1640 * swap devices are configured, the laundry thread has no work to do, so
1641 * don't bother waking it up.
1643 * The laundry thread uses the number of inactive queue scans elapsed
1644 * since the last laundering to determine whether to launder again, so
1647 if (starting_page_shortage > 0) {
1648 pq = &vmd->vmd_pagequeues[PQ_LAUNDRY];
1649 vm_pagequeue_lock(pq);
1650 if (vmd->vmd_laundry_request == VM_LAUNDRY_IDLE &&
1651 (pq->pq_cnt > 0 || atomic_load_acq_int(&swapdev_enabled))) {
1652 if (page_shortage > 0) {
1653 vmd->vmd_laundry_request = VM_LAUNDRY_SHORTFALL;
1654 VM_CNT_INC(v_pdshortfalls);
1655 } else if (vmd->vmd_laundry_request !=
1656 VM_LAUNDRY_SHORTFALL)
1657 vmd->vmd_laundry_request =
1658 VM_LAUNDRY_BACKGROUND;
1659 wakeup(&vmd->vmd_laundry_request);
1661 vmd->vmd_clean_pages_freed +=
1662 starting_page_shortage - page_shortage;
1663 vm_pagequeue_unlock(pq);
1667 * Wakeup the swapout daemon if we didn't free the targeted number of
1670 if (page_shortage > 0)
1674 * If the inactive queue scan fails repeatedly to meet its
1675 * target, kill the largest process.
1677 vm_pageout_mightbe_oom(vmd, page_shortage, starting_page_shortage);
1680 * Reclaim pages by swapping out idle processes, if configured to do so.
1682 vm_swapout_run_idle();
1685 * See the description of addl_page_shortage above.
1687 *addl_shortage = addl_page_shortage + deficit;
1689 return (page_shortage <= 0);
1692 static int vm_pageout_oom_vote;
1695 * The pagedaemon threads randlomly select one to perform the
1696 * OOM. Trying to kill processes before all pagedaemons
1697 * failed to reach free target is premature.
1700 vm_pageout_mightbe_oom(struct vm_domain *vmd, int page_shortage,
1701 int starting_page_shortage)
1705 if (starting_page_shortage <= 0 || starting_page_shortage !=
1707 vmd->vmd_oom_seq = 0;
1710 if (vmd->vmd_oom_seq < vm_pageout_oom_seq) {
1712 vmd->vmd_oom = FALSE;
1713 atomic_subtract_int(&vm_pageout_oom_vote, 1);
1719 * Do not follow the call sequence until OOM condition is
1722 vmd->vmd_oom_seq = 0;
1727 vmd->vmd_oom = TRUE;
1728 old_vote = atomic_fetchadd_int(&vm_pageout_oom_vote, 1);
1729 if (old_vote != vm_ndomains - 1)
1733 * The current pagedaemon thread is the last in the quorum to
1734 * start OOM. Initiate the selection and signaling of the
1737 vm_pageout_oom(VM_OOM_MEM);
1740 * After one round of OOM terror, recall our vote. On the
1741 * next pass, current pagedaemon would vote again if the low
1742 * memory condition is still there, due to vmd_oom being
1745 vmd->vmd_oom = FALSE;
1746 atomic_subtract_int(&vm_pageout_oom_vote, 1);
1750 * The OOM killer is the page daemon's action of last resort when
1751 * memory allocation requests have been stalled for a prolonged period
1752 * of time because it cannot reclaim memory. This function computes
1753 * the approximate number of physical pages that could be reclaimed if
1754 * the specified address space is destroyed.
1756 * Private, anonymous memory owned by the address space is the
1757 * principal resource that we expect to recover after an OOM kill.
1758 * Since the physical pages mapped by the address space's COW entries
1759 * are typically shared pages, they are unlikely to be released and so
1760 * they are not counted.
1762 * To get to the point where the page daemon runs the OOM killer, its
1763 * efforts to write-back vnode-backed pages may have stalled. This
1764 * could be caused by a memory allocation deadlock in the write path
1765 * that might be resolved by an OOM kill. Therefore, physical pages
1766 * belonging to vnode-backed objects are counted, because they might
1767 * be freed without being written out first if the address space holds
1768 * the last reference to an unlinked vnode.
1770 * Similarly, physical pages belonging to OBJT_PHYS objects are
1771 * counted because the address space might hold the last reference to
1775 vm_pageout_oom_pagecount(struct vmspace *vmspace)
1778 vm_map_entry_t entry;
1782 map = &vmspace->vm_map;
1783 KASSERT(!map->system_map, ("system map"));
1784 sx_assert(&map->lock, SA_LOCKED);
1786 for (entry = map->header.next; entry != &map->header;
1787 entry = entry->next) {
1788 if ((entry->eflags & MAP_ENTRY_IS_SUB_MAP) != 0)
1790 obj = entry->object.vm_object;
1793 if ((entry->eflags & MAP_ENTRY_NEEDS_COPY) != 0 &&
1794 obj->ref_count != 1)
1796 switch (obj->type) {
1801 res += obj->resident_page_count;
1808 static int vm_oom_ratelim_last;
1809 static int vm_oom_pf_secs = 10;
1810 SYSCTL_INT(_vm, OID_AUTO, oom_pf_secs, CTLFLAG_RWTUN, &vm_oom_pf_secs, 0,
1812 static struct mtx vm_oom_ratelim_mtx;
1815 vm_pageout_oom(int shortage)
1817 struct proc *p, *bigproc;
1818 vm_offset_t size, bigsize;
1825 * For OOM requests originating from vm_fault(), there is a high
1826 * chance that a single large process faults simultaneously in
1827 * several threads. Also, on an active system running many
1828 * processes of middle-size, like buildworld, all of them
1829 * could fault almost simultaneously as well.
1831 * To avoid killing too many processes, rate-limit OOMs
1832 * initiated by vm_fault() time-outs on the waits for free
1835 mtx_lock(&vm_oom_ratelim_mtx);
1837 if (shortage == VM_OOM_MEM_PF &&
1838 (u_int)(now - vm_oom_ratelim_last) < hz * vm_oom_pf_secs) {
1839 mtx_unlock(&vm_oom_ratelim_mtx);
1842 vm_oom_ratelim_last = now;
1843 mtx_unlock(&vm_oom_ratelim_mtx);
1846 * We keep the process bigproc locked once we find it to keep anyone
1847 * from messing with it; however, there is a possibility of
1848 * deadlock if process B is bigproc and one of its child processes
1849 * attempts to propagate a signal to B while we are waiting for A's
1850 * lock while walking this list. To avoid this, we don't block on
1851 * the process lock but just skip a process if it is already locked.
1855 sx_slock(&allproc_lock);
1856 FOREACH_PROC_IN_SYSTEM(p) {
1860 * If this is a system, protected or killed process, skip it.
1862 if (p->p_state != PRS_NORMAL || (p->p_flag & (P_INEXEC |
1863 P_PROTECTED | P_SYSTEM | P_WEXIT)) != 0 ||
1864 p->p_pid == 1 || P_KILLED(p) ||
1865 (p->p_pid < 48 && swap_pager_avail != 0)) {
1870 * If the process is in a non-running type state,
1871 * don't touch it. Check all the threads individually.
1874 FOREACH_THREAD_IN_PROC(p, td) {
1876 if (!TD_ON_RUNQ(td) &&
1877 !TD_IS_RUNNING(td) &&
1878 !TD_IS_SLEEPING(td) &&
1879 !TD_IS_SUSPENDED(td) &&
1880 !TD_IS_SWAPPED(td)) {
1892 * get the process size
1894 vm = vmspace_acquire_ref(p);
1901 sx_sunlock(&allproc_lock);
1902 if (!vm_map_trylock_read(&vm->vm_map)) {
1904 sx_slock(&allproc_lock);
1908 size = vmspace_swap_count(vm);
1909 if (shortage == VM_OOM_MEM || shortage == VM_OOM_MEM_PF)
1910 size += vm_pageout_oom_pagecount(vm);
1911 vm_map_unlock_read(&vm->vm_map);
1913 sx_slock(&allproc_lock);
1916 * If this process is bigger than the biggest one,
1919 if (size > bigsize) {
1920 if (bigproc != NULL)
1928 sx_sunlock(&allproc_lock);
1929 if (bigproc != NULL) {
1930 if (vm_panic_on_oom != 0)
1931 panic("out of swap space");
1933 killproc(bigproc, "out of swap space");
1934 sched_nice(bigproc, PRIO_MIN);
1936 PROC_UNLOCK(bigproc);
1941 vm_pageout_lowmem(void)
1943 static int lowmem_ticks = 0;
1946 last = atomic_load_int(&lowmem_ticks);
1947 while ((u_int)(ticks - last) / hz >= lowmem_period) {
1948 if (atomic_fcmpset_int(&lowmem_ticks, &last, ticks) == 0)
1952 * Decrease registered cache sizes.
1954 SDT_PROBE0(vm, , , vm__lowmem_scan);
1955 EVENTHANDLER_INVOKE(vm_lowmem, VM_LOW_PAGES);
1958 * We do this explicitly after the caches have been
1959 * drained above. If we have a severe page shortage on
1960 * our hands, completely drain all UMA zones. Otherwise,
1961 * just prune the caches.
1963 uma_reclaim(vm_page_count_min() ? UMA_RECLAIM_DRAIN_CPU :
1971 vm_pageout_worker(void *arg)
1973 struct vm_domain *vmd;
1975 int addl_shortage, domain, shortage;
1978 domain = (uintptr_t)arg;
1979 vmd = VM_DOMAIN(domain);
1984 * XXXKIB It could be useful to bind pageout daemon threads to
1985 * the cores belonging to the domain, from which vm_page_array
1989 KASSERT(vmd->vmd_segs != 0, ("domain without segments"));
1990 vmd->vmd_last_active_scan = ticks;
1993 * The pageout daemon worker is never done, so loop forever.
1996 vm_domain_pageout_lock(vmd);
1999 * We need to clear wanted before we check the limits. This
2000 * prevents races with wakers who will check wanted after they
2003 atomic_store_int(&vmd->vmd_pageout_wanted, 0);
2006 * Might the page daemon need to run again?
2008 if (vm_paging_needed(vmd, vmd->vmd_free_count)) {
2010 * Yes. If the scan failed to produce enough free
2011 * pages, sleep uninterruptibly for some time in the
2012 * hope that the laundry thread will clean some pages.
2014 vm_domain_pageout_unlock(vmd);
2016 pause("pwait", hz / VM_INACT_SCAN_RATE);
2019 * No, sleep until the next wakeup or until pages
2020 * need to have their reference stats updated.
2022 if (mtx_sleep(&vmd->vmd_pageout_wanted,
2023 vm_domain_pageout_lockptr(vmd), PDROP | PVM,
2024 "psleep", hz / VM_INACT_SCAN_RATE) == 0)
2025 VM_CNT_INC(v_pdwakeups);
2028 /* Prevent spurious wakeups by ensuring that wanted is set. */
2029 atomic_store_int(&vmd->vmd_pageout_wanted, 1);
2032 * Use the controller to calculate how many pages to free in
2033 * this interval, and scan the inactive queue. If the lowmem
2034 * handlers appear to have freed up some pages, subtract the
2035 * difference from the inactive queue scan target.
2037 shortage = pidctrl_daemon(&vmd->vmd_pid, vmd->vmd_free_count);
2039 ofree = vmd->vmd_free_count;
2040 if (vm_pageout_lowmem() && vmd->vmd_free_count > ofree)
2041 shortage -= min(vmd->vmd_free_count - ofree,
2043 target_met = vm_pageout_scan_inactive(vmd, shortage,
2049 * Scan the active queue. A positive value for shortage
2050 * indicates that we must aggressively deactivate pages to avoid
2053 shortage = vm_pageout_active_target(vmd) + addl_shortage;
2054 vm_pageout_scan_active(vmd, shortage);
2059 * vm_pageout_init initialises basic pageout daemon settings.
2062 vm_pageout_init_domain(int domain)
2064 struct vm_domain *vmd;
2065 struct sysctl_oid *oid;
2067 vmd = VM_DOMAIN(domain);
2068 vmd->vmd_interrupt_free_min = 2;
2071 * v_free_reserved needs to include enough for the largest
2072 * swap pager structures plus enough for any pv_entry structs
2075 if (vmd->vmd_page_count > 1024)
2076 vmd->vmd_free_min = 4 + (vmd->vmd_page_count - 1024) / 200;
2078 vmd->vmd_free_min = 4;
2079 vmd->vmd_pageout_free_min = 2 * MAXBSIZE / PAGE_SIZE +
2080 vmd->vmd_interrupt_free_min;
2081 vmd->vmd_free_reserved = vm_pageout_page_count +
2082 vmd->vmd_pageout_free_min + (vmd->vmd_page_count / 768);
2083 vmd->vmd_free_severe = vmd->vmd_free_min / 2;
2084 vmd->vmd_free_target = 4 * vmd->vmd_free_min + vmd->vmd_free_reserved;
2085 vmd->vmd_free_min += vmd->vmd_free_reserved;
2086 vmd->vmd_free_severe += vmd->vmd_free_reserved;
2087 vmd->vmd_inactive_target = (3 * vmd->vmd_free_target) / 2;
2088 if (vmd->vmd_inactive_target > vmd->vmd_free_count / 3)
2089 vmd->vmd_inactive_target = vmd->vmd_free_count / 3;
2092 * Set the default wakeup threshold to be 10% below the paging
2093 * target. This keeps the steady state out of shortfall.
2095 vmd->vmd_pageout_wakeup_thresh = (vmd->vmd_free_target / 10) * 9;
2098 * Target amount of memory to move out of the laundry queue during a
2099 * background laundering. This is proportional to the amount of system
2102 vmd->vmd_background_launder_target = (vmd->vmd_free_target -
2103 vmd->vmd_free_min) / 10;
2105 /* Initialize the pageout daemon pid controller. */
2106 pidctrl_init(&vmd->vmd_pid, hz / VM_INACT_SCAN_RATE,
2107 vmd->vmd_free_target, PIDCTRL_BOUND,
2108 PIDCTRL_KPD, PIDCTRL_KID, PIDCTRL_KDD);
2109 oid = SYSCTL_ADD_NODE(NULL, SYSCTL_CHILDREN(vmd->vmd_oid), OID_AUTO,
2110 "pidctrl", CTLFLAG_RD, NULL, "");
2111 pidctrl_init_sysctl(&vmd->vmd_pid, SYSCTL_CHILDREN(oid));
2115 vm_pageout_init(void)
2121 * Initialize some paging parameters.
2123 if (vm_cnt.v_page_count < 2000)
2124 vm_pageout_page_count = 8;
2127 for (i = 0; i < vm_ndomains; i++) {
2128 struct vm_domain *vmd;
2130 vm_pageout_init_domain(i);
2132 vm_cnt.v_free_reserved += vmd->vmd_free_reserved;
2133 vm_cnt.v_free_target += vmd->vmd_free_target;
2134 vm_cnt.v_free_min += vmd->vmd_free_min;
2135 vm_cnt.v_inactive_target += vmd->vmd_inactive_target;
2136 vm_cnt.v_pageout_free_min += vmd->vmd_pageout_free_min;
2137 vm_cnt.v_interrupt_free_min += vmd->vmd_interrupt_free_min;
2138 vm_cnt.v_free_severe += vmd->vmd_free_severe;
2139 freecount += vmd->vmd_free_count;
2143 * Set interval in seconds for active scan. We want to visit each
2144 * page at least once every ten minutes. This is to prevent worst
2145 * case paging behaviors with stale active LRU.
2147 if (vm_pageout_update_period == 0)
2148 vm_pageout_update_period = 600;
2150 if (vm_page_max_user_wired == 0)
2151 vm_page_max_user_wired = freecount / 3;
2155 * vm_pageout is the high level pageout daemon.
2162 int error, first, i;
2167 mtx_init(&vm_oom_ratelim_mtx, "vmoomr", NULL, MTX_DEF);
2168 swap_pager_swap_init();
2169 for (first = -1, i = 0; i < vm_ndomains; i++) {
2170 if (VM_DOMAIN_EMPTY(i)) {
2172 printf("domain %d empty; skipping pageout\n",
2179 error = kthread_add(vm_pageout_worker,
2180 (void *)(uintptr_t)i, p, NULL, 0, 0, "dom%d", i);
2182 panic("starting pageout for domain %d: %d\n",
2185 error = kthread_add(vm_pageout_laundry_worker,
2186 (void *)(uintptr_t)i, p, NULL, 0, 0, "laundry: dom%d", i);
2188 panic("starting laundry for domain %d: %d", i, error);
2190 error = kthread_add(uma_reclaim_worker, NULL, p, NULL, 0, 0, "uma");
2192 panic("starting uma_reclaim helper, error %d\n", error);
2194 snprintf(td->td_name, sizeof(td->td_name), "dom%d", first);
2195 vm_pageout_worker((void *)(uintptr_t)first);
2199 * Perform an advisory wakeup of the page daemon.
2202 pagedaemon_wakeup(int domain)
2204 struct vm_domain *vmd;
2206 vmd = VM_DOMAIN(domain);
2207 vm_domain_pageout_assert_unlocked(vmd);
2208 if (curproc == pageproc)
2211 if (atomic_fetchadd_int(&vmd->vmd_pageout_wanted, 1) == 0) {
2212 vm_domain_pageout_lock(vmd);
2213 atomic_store_int(&vmd->vmd_pageout_wanted, 1);
2214 wakeup(&vmd->vmd_pageout_wanted);
2215 vm_domain_pageout_unlock(vmd);