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 time_t lowmem_uptime;
156 static int swapdev_enabled;
158 static int vm_panic_on_oom = 0;
160 SYSCTL_INT(_vm, OID_AUTO, panic_on_oom,
161 CTLFLAG_RWTUN, &vm_panic_on_oom, 0,
162 "panic on out of memory instead of killing the largest process");
164 SYSCTL_INT(_vm, OID_AUTO, pageout_update_period,
165 CTLFLAG_RWTUN, &vm_pageout_update_period, 0,
166 "Maximum active LRU update period");
168 SYSCTL_INT(_vm, OID_AUTO, lowmem_period, CTLFLAG_RWTUN, &lowmem_period, 0,
169 "Low memory callback period");
171 SYSCTL_INT(_vm, OID_AUTO, disable_swapspace_pageouts,
172 CTLFLAG_RWTUN, &disable_swap_pageouts, 0, "Disallow swapout of dirty pages");
174 static int pageout_lock_miss;
175 SYSCTL_INT(_vm, OID_AUTO, pageout_lock_miss,
176 CTLFLAG_RD, &pageout_lock_miss, 0, "vget() lock misses during pageout");
178 SYSCTL_INT(_vm, OID_AUTO, pageout_oom_seq,
179 CTLFLAG_RWTUN, &vm_pageout_oom_seq, 0,
180 "back-to-back calls to oom detector to start OOM");
182 static int act_scan_laundry_weight = 3;
183 SYSCTL_INT(_vm, OID_AUTO, act_scan_laundry_weight, CTLFLAG_RWTUN,
184 &act_scan_laundry_weight, 0,
185 "weight given to clean vs. dirty pages in active queue scans");
187 static u_int vm_background_launder_rate = 4096;
188 SYSCTL_UINT(_vm, OID_AUTO, background_launder_rate, CTLFLAG_RWTUN,
189 &vm_background_launder_rate, 0,
190 "background laundering rate, in kilobytes per second");
192 static u_int vm_background_launder_max = 20 * 1024;
193 SYSCTL_UINT(_vm, OID_AUTO, background_launder_max, CTLFLAG_RWTUN,
194 &vm_background_launder_max, 0, "background laundering cap, in kilobytes");
196 int vm_pageout_page_count = 32;
198 int vm_page_max_wired; /* XXX max # of wired pages system-wide */
199 SYSCTL_INT(_vm, OID_AUTO, max_wired,
200 CTLFLAG_RW, &vm_page_max_wired, 0, "System-wide limit to 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 VM_CNT_ADD(v_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;
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 = TAILQ_NEXT(m, plinks.q), ss->scanned++) {
281 if ((m->flags & PG_MARKER) == 0) {
282 KASSERT((m->aflags & PGA_ENQUEUED) != 0,
283 ("page %p not enqueued", m));
284 KASSERT((m->flags & PG_FICTITIOUS) == 0,
285 ("Fictitious page %p cannot be in page queue", m));
286 KASSERT((m->oflags & VPO_UNMANAGED) == 0,
287 ("Unmanaged page %p cannot be in page queue", m));
291 (void)vm_batchqueue_insert(&ss->bq, m);
293 TAILQ_REMOVE(&pq->pq_pl, m, plinks.q);
294 vm_page_aflag_clear(m, PGA_ENQUEUED);
297 TAILQ_REMOVE(&pq->pq_pl, marker, plinks.q);
298 if (__predict_true(m != NULL))
299 TAILQ_INSERT_BEFORE(m, marker, plinks.q);
301 TAILQ_INSERT_TAIL(&pq->pq_pl, marker, plinks.q);
303 vm_pagequeue_cnt_add(pq, -ss->bq.bq_cnt);
304 vm_pagequeue_unlock(pq);
307 /* Return the next page to be scanned, or NULL if the scan is complete. */
308 static __always_inline vm_page_t
309 vm_pageout_next(struct scan_state *ss, const bool dequeue)
312 if (ss->bq.bq_cnt == 0)
313 vm_pageout_collect_batch(ss, dequeue);
314 return (vm_batchqueue_pop(&ss->bq));
318 * Scan for pages at adjacent offsets within the given page's object that are
319 * eligible for laundering, form a cluster of these pages and the given page,
320 * and launder that cluster.
323 vm_pageout_cluster(vm_page_t m)
326 vm_page_t mc[2 * vm_pageout_page_count], p, pb, ps;
328 int ib, is, page_base, pageout_count;
330 vm_page_assert_locked(m);
332 VM_OBJECT_ASSERT_WLOCKED(object);
335 vm_page_assert_unbusied(m);
336 KASSERT(!vm_page_held(m), ("page %p is held", m));
338 pmap_remove_write(m);
341 mc[vm_pageout_page_count] = pb = ps = m;
343 page_base = vm_pageout_page_count;
348 * We can cluster only if the page is not clean, busy, or held, and
349 * the page is in the laundry queue.
351 * During heavy mmap/modification loads the pageout
352 * daemon can really fragment the underlying file
353 * due to flushing pages out of order and not trying to
354 * align the clusters (which leaves sporadic out-of-order
355 * holes). To solve this problem we do the reverse scan
356 * first and attempt to align our cluster, then do a
357 * forward scan if room remains.
360 while (ib != 0 && pageout_count < vm_pageout_page_count) {
365 if ((p = vm_page_prev(pb)) == NULL || vm_page_busied(p)) {
369 vm_page_test_dirty(p);
375 if (vm_page_held(p) || !vm_page_in_laundry(p)) {
380 pmap_remove_write(p);
382 mc[--page_base] = pb = p;
387 * We are at an alignment boundary. Stop here, and switch
388 * directions. Do not clear ib.
390 if ((pindex - (ib - 1)) % vm_pageout_page_count == 0)
393 while (pageout_count < vm_pageout_page_count &&
394 pindex + is < object->size) {
395 if ((p = vm_page_next(ps)) == NULL || vm_page_busied(p))
397 vm_page_test_dirty(p);
401 if (vm_page_held(p) || !vm_page_in_laundry(p)) {
405 pmap_remove_write(p);
407 mc[page_base + pageout_count] = ps = p;
413 * If we exhausted our forward scan, continue with the reverse scan
414 * when possible, even past an alignment boundary. This catches
415 * boundary conditions.
417 if (ib != 0 && pageout_count < vm_pageout_page_count)
420 return (vm_pageout_flush(&mc[page_base], pageout_count,
421 VM_PAGER_PUT_NOREUSE, 0, NULL, NULL));
425 * vm_pageout_flush() - launder the given pages
427 * The given pages are laundered. Note that we setup for the start of
428 * I/O ( i.e. busy the page ), mark it read-only, and bump the object
429 * reference count all in here rather then in the parent. If we want
430 * the parent to do more sophisticated things we may have to change
433 * Returned runlen is the count of pages between mreq and first
434 * page after mreq with status VM_PAGER_AGAIN.
435 * *eio is set to TRUE if pager returned VM_PAGER_ERROR or VM_PAGER_FAIL
436 * for any page in runlen set.
439 vm_pageout_flush(vm_page_t *mc, int count, int flags, int mreq, int *prunlen,
442 vm_object_t object = mc[0]->object;
443 int pageout_status[count];
447 VM_OBJECT_ASSERT_WLOCKED(object);
450 * Initiate I/O. Mark the pages busy and verify that they're valid
453 * We do not have to fixup the clean/dirty bits here... we can
454 * allow the pager to do it after the I/O completes.
456 * NOTE! mc[i]->dirty may be partial or fragmented due to an
457 * edge case with file fragments.
459 for (i = 0; i < count; i++) {
460 KASSERT(mc[i]->valid == VM_PAGE_BITS_ALL,
461 ("vm_pageout_flush: partially invalid page %p index %d/%d",
463 KASSERT((mc[i]->aflags & PGA_WRITEABLE) == 0,
464 ("vm_pageout_flush: writeable page %p", mc[i]));
465 vm_page_sbusy(mc[i]);
467 vm_object_pip_add(object, count);
469 vm_pager_put_pages(object, mc, count, flags, pageout_status);
471 runlen = count - mreq;
474 for (i = 0; i < count; i++) {
475 vm_page_t mt = mc[i];
477 KASSERT(pageout_status[i] == VM_PAGER_PEND ||
478 !pmap_page_is_write_mapped(mt),
479 ("vm_pageout_flush: page %p is not write protected", mt));
480 switch (pageout_status[i]) {
483 if (vm_page_in_laundry(mt))
484 vm_page_deactivate_noreuse(mt);
492 * The page is outside the object's range. We pretend
493 * that the page out worked and clean the page, so the
494 * changes will be lost if the page is reclaimed by
499 if (vm_page_in_laundry(mt))
500 vm_page_deactivate_noreuse(mt);
506 * If the page couldn't be paged out to swap because the
507 * pager wasn't able to find space, place the page in
508 * the PQ_UNSWAPPABLE holding queue. This is an
509 * optimization that prevents the page daemon from
510 * wasting CPU cycles on pages that cannot be reclaimed
511 * becase no swap device is configured.
513 * Otherwise, reactivate the page so that it doesn't
514 * clog the laundry and inactive queues. (We will try
515 * paging it out again later.)
518 if (object->type == OBJT_SWAP &&
519 pageout_status[i] == VM_PAGER_FAIL) {
520 vm_page_unswappable(mt);
523 vm_page_activate(mt);
525 if (eio != NULL && i >= mreq && i - mreq < runlen)
529 if (i >= mreq && i - mreq < runlen)
535 * If the operation is still going, leave the page busy to
536 * block all other accesses. Also, leave the paging in
537 * progress indicator set so that we don't attempt an object
540 if (pageout_status[i] != VM_PAGER_PEND) {
541 vm_object_pip_wakeup(object);
547 return (numpagedout);
551 vm_pageout_swapon(void *arg __unused, struct swdevt *sp __unused)
554 atomic_store_rel_int(&swapdev_enabled, 1);
558 vm_pageout_swapoff(void *arg __unused, struct swdevt *sp __unused)
561 if (swap_pager_nswapdev() == 1)
562 atomic_store_rel_int(&swapdev_enabled, 0);
566 * Attempt to acquire all of the necessary locks to launder a page and
567 * then call through the clustering layer to PUTPAGES. Wait a short
568 * time for a vnode lock.
570 * Requires the page and object lock on entry, releases both before return.
571 * Returns 0 on success and an errno otherwise.
574 vm_pageout_clean(vm_page_t m, int *numpagedout)
582 vm_page_assert_locked(m);
584 VM_OBJECT_ASSERT_WLOCKED(object);
590 * The object is already known NOT to be dead. It
591 * is possible for the vget() to block the whole
592 * pageout daemon, but the new low-memory handling
593 * code should prevent it.
595 * We can't wait forever for the vnode lock, we might
596 * deadlock due to a vn_read() getting stuck in
597 * vm_wait while holding this vnode. We skip the
598 * vnode if we can't get it in a reasonable amount
601 if (object->type == OBJT_VNODE) {
604 if (vp->v_type == VREG &&
605 vn_start_write(vp, &mp, V_NOWAIT) != 0) {
611 ("vp %p with NULL v_mount", vp));
612 vm_object_reference_locked(object);
614 VM_OBJECT_WUNLOCK(object);
615 lockmode = MNT_SHARED_WRITES(vp->v_mount) ?
616 LK_SHARED : LK_EXCLUSIVE;
617 if (vget(vp, lockmode | LK_TIMELOCK, curthread)) {
622 VM_OBJECT_WLOCK(object);
625 * Ensure that the object and vnode were not disassociated
626 * while locks were dropped.
628 if (vp->v_object != object) {
635 * While the object and page were unlocked, the page
637 * (1) moved to a different queue,
638 * (2) reallocated to a different object,
639 * (3) reallocated to a different offset, or
642 if (!vm_page_in_laundry(m) || m->object != object ||
643 m->pindex != pindex || m->dirty == 0) {
650 * The page may have been busied or referenced while the object
651 * and page locks were released.
653 if (vm_page_busied(m) || vm_page_held(m)) {
661 * If a page is dirty, then it is either being washed
662 * (but not yet cleaned) or it is still in the
663 * laundry. If it is still in the laundry, then we
664 * start the cleaning operation.
666 if ((*numpagedout = vm_pageout_cluster(m)) == 0)
670 VM_OBJECT_WUNLOCK(object);
673 vm_page_lock_assert(m, MA_NOTOWNED);
677 vm_object_deallocate(object);
678 vn_finished_write(mp);
685 * Attempt to launder the specified number of pages.
687 * Returns the number of pages successfully laundered.
690 vm_pageout_launder(struct vm_domain *vmd, int launder, bool in_shortfall)
692 struct scan_state ss;
693 struct vm_pagequeue *pq;
697 int act_delta, error, numpagedout, queue, starting_target;
699 bool obj_locked, pageout_ok;
704 starting_target = launder;
708 * Scan the laundry queues for pages eligible to be laundered. We stop
709 * once the target number of dirty pages have been laundered, or once
710 * we've reached the end of the queue. A single iteration of this loop
711 * may cause more than one page to be laundered because of clustering.
713 * As an optimization, we avoid laundering from PQ_UNSWAPPABLE when no
714 * swap devices are configured.
716 if (atomic_load_acq_int(&swapdev_enabled))
717 queue = PQ_UNSWAPPABLE;
722 marker = &vmd->vmd_markers[queue];
723 pq = &vmd->vmd_pagequeues[queue];
724 vm_pagequeue_lock(pq);
725 vm_pageout_init_scan(&ss, pq, marker, NULL, pq->pq_cnt);
726 while (launder > 0 && (m = vm_pageout_next(&ss, false)) != NULL) {
727 if (__predict_false((m->flags & PG_MARKER) != 0))
730 vm_page_change_lock(m, &mtx);
734 * The page may have been disassociated from the queue
735 * while locks were dropped.
737 if (vm_page_queue(m) != queue)
741 * A requeue was requested, so this page gets a second
744 if ((m->aflags & PGA_REQUEUE) != 0) {
750 * Held pages are essentially stuck in the queue.
752 * Wired pages may not be freed. Complete their removal
753 * from the queue now to avoid needless revisits during
756 if (m->hold_count != 0)
758 if (m->wire_count != 0) {
759 vm_page_dequeue_deferred(m);
763 if (object != m->object) {
765 VM_OBJECT_WUNLOCK(object);
771 if (!VM_OBJECT_TRYWLOCK(object)) {
773 /* Depends on type-stability. */
774 VM_OBJECT_WLOCK(object);
782 if (vm_page_busied(m))
786 * Invalid pages can be easily freed. They cannot be
787 * mapped; vm_page_free() asserts this.
793 * If the page has been referenced and the object is not dead,
794 * reactivate or requeue the page depending on whether the
797 * Test PGA_REFERENCED after calling pmap_ts_referenced() so
798 * that a reference from a concurrently destroyed mapping is
799 * observed here and now.
801 if (object->ref_count != 0)
802 act_delta = pmap_ts_referenced(m);
804 KASSERT(!pmap_page_is_mapped(m),
805 ("page %p is mapped", m));
808 if ((m->aflags & PGA_REFERENCED) != 0) {
809 vm_page_aflag_clear(m, PGA_REFERENCED);
812 if (act_delta != 0) {
813 if (object->ref_count != 0) {
814 VM_CNT_INC(v_reactivated);
818 * Increase the activation count if the page
819 * was referenced while in the laundry queue.
820 * This makes it less likely that the page will
821 * be returned prematurely to the inactive
824 m->act_count += act_delta + ACT_ADVANCE;
827 * If this was a background laundering, count
828 * activated pages towards our target. The
829 * purpose of background laundering is to ensure
830 * that pages are eventually cycled through the
831 * laundry queue, and an activation is a valid
837 } else if ((object->flags & OBJ_DEAD) == 0) {
844 * If the page appears to be clean at the machine-independent
845 * layer, then remove all of its mappings from the pmap in
846 * anticipation of freeing it. If, however, any of the page's
847 * mappings allow write access, then the page may still be
848 * modified until the last of those mappings are removed.
850 if (object->ref_count != 0) {
851 vm_page_test_dirty(m);
857 * Clean pages are freed, and dirty pages are paged out unless
858 * they belong to a dead object. Requeueing dirty pages from
859 * dead objects is pointless, as they are being paged out and
860 * freed by the thread that destroyed the object.
866 } else if ((object->flags & OBJ_DEAD) == 0) {
867 if (object->type != OBJT_SWAP &&
868 object->type != OBJT_DEFAULT)
870 else if (disable_swap_pageouts)
880 * Form a cluster with adjacent, dirty pages from the
881 * same object, and page out that entire cluster.
883 * The adjacent, dirty pages must also be in the
884 * laundry. However, their mappings are not checked
885 * for new references. Consequently, a recently
886 * referenced page may be paged out. However, that
887 * page will not be prematurely reclaimed. After page
888 * out, the page will be placed in the inactive queue,
889 * where any new references will be detected and the
892 error = vm_pageout_clean(m, &numpagedout);
894 launder -= numpagedout;
895 ss.scanned += numpagedout;
896 } else if (error == EDEADLK) {
909 VM_OBJECT_WUNLOCK(object);
912 vm_pagequeue_lock(pq);
913 vm_pageout_end_scan(&ss);
914 vm_pagequeue_unlock(pq);
916 if (launder > 0 && queue == PQ_UNSWAPPABLE) {
922 * Wakeup the sync daemon if we skipped a vnode in a writeable object
923 * and we didn't launder enough pages.
925 if (vnodes_skipped > 0 && launder > 0)
926 (void)speedup_syncer();
928 return (starting_target - launder);
932 * Compute the integer square root.
937 u_int bit, root, tmp;
939 bit = 1u << ((NBBY * sizeof(u_int)) - 2);
956 * Perform the work of the laundry thread: periodically wake up and determine
957 * whether any pages need to be laundered. If so, determine the number of pages
958 * that need to be laundered, and launder them.
961 vm_pageout_laundry_worker(void *arg)
963 struct vm_domain *vmd;
964 struct vm_pagequeue *pq;
965 uint64_t nclean, ndirty, nfreed;
966 int domain, last_target, launder, shortfall, shortfall_cycle, target;
969 domain = (uintptr_t)arg;
970 vmd = VM_DOMAIN(domain);
971 pq = &vmd->vmd_pagequeues[PQ_LAUNDRY];
972 KASSERT(vmd->vmd_segs != 0, ("domain without segments"));
975 in_shortfall = false;
981 * Calls to these handlers are serialized by the swap syscall lock.
983 (void)EVENTHANDLER_REGISTER(swapon, vm_pageout_swapon, vmd,
984 EVENTHANDLER_PRI_ANY);
985 (void)EVENTHANDLER_REGISTER(swapoff, vm_pageout_swapoff, vmd,
986 EVENTHANDLER_PRI_ANY);
989 * The pageout laundry worker is never done, so loop forever.
992 KASSERT(target >= 0, ("negative target %d", target));
993 KASSERT(shortfall_cycle >= 0,
994 ("negative cycle %d", shortfall_cycle));
998 * First determine whether we need to launder pages to meet a
999 * shortage of free pages.
1001 if (shortfall > 0) {
1002 in_shortfall = true;
1003 shortfall_cycle = VM_LAUNDER_RATE / VM_INACT_SCAN_RATE;
1005 } else if (!in_shortfall)
1007 else if (shortfall_cycle == 0 || vm_laundry_target(vmd) <= 0) {
1009 * We recently entered shortfall and began laundering
1010 * pages. If we have completed that laundering run
1011 * (and we are no longer in shortfall) or we have met
1012 * our laundry target through other activity, then we
1013 * can stop laundering pages.
1015 in_shortfall = false;
1019 launder = target / shortfall_cycle--;
1023 * There's no immediate need to launder any pages; see if we
1024 * meet the conditions to perform background laundering:
1026 * 1. The ratio of dirty to clean inactive pages exceeds the
1027 * background laundering threshold, or
1028 * 2. we haven't yet reached the target of the current
1029 * background laundering run.
1031 * The background laundering threshold is not a constant.
1032 * Instead, it is a slowly growing function of the number of
1033 * clean pages freed by the page daemon since the last
1034 * background laundering. Thus, as the ratio of dirty to
1035 * clean inactive pages grows, the amount of memory pressure
1036 * required to trigger laundering decreases. We ensure
1037 * that the threshold is non-zero after an inactive queue
1038 * scan, even if that scan failed to free a single clean page.
1041 nclean = vmd->vmd_free_count +
1042 vmd->vmd_pagequeues[PQ_INACTIVE].pq_cnt;
1043 ndirty = vmd->vmd_pagequeues[PQ_LAUNDRY].pq_cnt;
1044 if (target == 0 && ndirty * isqrt(howmany(nfreed + 1,
1045 vmd->vmd_free_target - vmd->vmd_free_min)) >= nclean) {
1046 target = vmd->vmd_background_launder_target;
1050 * We have a non-zero background laundering target. If we've
1051 * laundered up to our maximum without observing a page daemon
1052 * request, just stop. This is a safety belt that ensures we
1053 * don't launder an excessive amount if memory pressure is low
1054 * and the ratio of dirty to clean pages is large. Otherwise,
1055 * proceed at the background laundering rate.
1060 last_target = target;
1061 } else if (last_target - target >=
1062 vm_background_launder_max * PAGE_SIZE / 1024) {
1065 launder = vm_background_launder_rate * PAGE_SIZE / 1024;
1066 launder /= VM_LAUNDER_RATE;
1067 if (launder > target)
1074 * Because of I/O clustering, the number of laundered
1075 * pages could exceed "target" by the maximum size of
1076 * a cluster minus one.
1078 target -= min(vm_pageout_launder(vmd, launder,
1079 in_shortfall), target);
1080 pause("laundp", hz / VM_LAUNDER_RATE);
1084 * If we're not currently laundering pages and the page daemon
1085 * hasn't posted a new request, sleep until the page daemon
1088 vm_pagequeue_lock(pq);
1089 if (target == 0 && vmd->vmd_laundry_request == VM_LAUNDRY_IDLE)
1090 (void)mtx_sleep(&vmd->vmd_laundry_request,
1091 vm_pagequeue_lockptr(pq), PVM, "launds", 0);
1094 * If the pagedaemon has indicated that it's in shortfall, start
1095 * a shortfall laundering unless we're already in the middle of
1096 * one. This may preempt a background laundering.
1098 if (vmd->vmd_laundry_request == VM_LAUNDRY_SHORTFALL &&
1099 (!in_shortfall || shortfall_cycle == 0)) {
1100 shortfall = vm_laundry_target(vmd) +
1101 vmd->vmd_pageout_deficit;
1107 vmd->vmd_laundry_request = VM_LAUNDRY_IDLE;
1108 nfreed += vmd->vmd_clean_pages_freed;
1109 vmd->vmd_clean_pages_freed = 0;
1110 vm_pagequeue_unlock(pq);
1115 * Compute the number of pages we want to try to move from the
1116 * active queue to either the inactive or laundry queue.
1118 * When scanning active pages during a shortage, we make clean pages
1119 * count more heavily towards the page shortage than dirty pages.
1120 * This is because dirty pages must be laundered before they can be
1121 * reused and thus have less utility when attempting to quickly
1122 * alleviate a free page shortage. However, this weighting also
1123 * causes the scan to deactivate dirty pages more aggressively,
1124 * improving the effectiveness of clustering.
1127 vm_pageout_active_target(struct vm_domain *vmd)
1131 shortage = vmd->vmd_inactive_target + vm_paging_target(vmd) -
1132 (vmd->vmd_pagequeues[PQ_INACTIVE].pq_cnt +
1133 vmd->vmd_pagequeues[PQ_LAUNDRY].pq_cnt / act_scan_laundry_weight);
1134 shortage *= act_scan_laundry_weight;
1139 * Scan the active queue. If there is no shortage of inactive pages, scan a
1140 * small portion of the queue in order to maintain quasi-LRU.
1143 vm_pageout_scan_active(struct vm_domain *vmd, int page_shortage)
1145 struct scan_state ss;
1147 vm_page_t m, marker;
1148 struct vm_pagequeue *pq;
1150 int act_delta, max_scan, scan_tick;
1152 marker = &vmd->vmd_markers[PQ_ACTIVE];
1153 pq = &vmd->vmd_pagequeues[PQ_ACTIVE];
1154 vm_pagequeue_lock(pq);
1157 * If we're just idle polling attempt to visit every
1158 * active page within 'update_period' seconds.
1161 if (vm_pageout_update_period != 0) {
1162 min_scan = pq->pq_cnt;
1163 min_scan *= scan_tick - vmd->vmd_last_active_scan;
1164 min_scan /= hz * vm_pageout_update_period;
1167 if (min_scan > 0 || (page_shortage > 0 && pq->pq_cnt > 0))
1168 vmd->vmd_last_active_scan = scan_tick;
1171 * Scan the active queue for pages that can be deactivated. Update
1172 * the per-page activity counter and use it to identify deactivation
1173 * candidates. Held pages may be deactivated.
1175 * To avoid requeuing each page that remains in the active queue, we
1176 * implement the CLOCK algorithm. To keep the implementation of the
1177 * enqueue operation consistent for all page queues, we use two hands,
1178 * represented by marker pages. Scans begin at the first hand, which
1179 * precedes the second hand in the queue. When the two hands meet,
1180 * they are moved back to the head and tail of the queue, respectively,
1181 * and scanning resumes.
1183 max_scan = page_shortage > 0 ? pq->pq_cnt : min_scan;
1186 vm_pageout_init_scan(&ss, pq, marker, &vmd->vmd_clock[0], max_scan);
1187 while ((m = vm_pageout_next(&ss, false)) != NULL) {
1188 if (__predict_false(m == &vmd->vmd_clock[1])) {
1189 vm_pagequeue_lock(pq);
1190 TAILQ_REMOVE(&pq->pq_pl, &vmd->vmd_clock[0], plinks.q);
1191 TAILQ_REMOVE(&pq->pq_pl, &vmd->vmd_clock[1], plinks.q);
1192 TAILQ_INSERT_HEAD(&pq->pq_pl, &vmd->vmd_clock[0],
1194 TAILQ_INSERT_TAIL(&pq->pq_pl, &vmd->vmd_clock[1],
1196 max_scan -= ss.scanned;
1197 vm_pageout_end_scan(&ss);
1200 if (__predict_false((m->flags & PG_MARKER) != 0))
1203 vm_page_change_lock(m, &mtx);
1206 * The page may have been disassociated from the queue
1207 * while locks were dropped.
1209 if (vm_page_queue(m) != PQ_ACTIVE)
1213 * Wired pages are dequeued lazily.
1215 if (m->wire_count != 0) {
1216 vm_page_dequeue_deferred(m);
1221 * Check to see "how much" the page has been used.
1223 * Test PGA_REFERENCED after calling pmap_ts_referenced() so
1224 * that a reference from a concurrently destroyed mapping is
1225 * observed here and now.
1227 * Perform an unsynchronized object ref count check. While
1228 * the page lock ensures that the page is not reallocated to
1229 * another object, in particular, one with unmanaged mappings
1230 * that cannot support pmap_ts_referenced(), two races are,
1231 * nonetheless, possible:
1232 * 1) The count was transitioning to zero, but we saw a non-
1233 * zero value. pmap_ts_referenced() will return zero
1234 * because the page is not mapped.
1235 * 2) The count was transitioning to one, but we saw zero.
1236 * This race delays the detection of a new reference. At
1237 * worst, we will deactivate and reactivate the page.
1239 if (m->object->ref_count != 0)
1240 act_delta = pmap_ts_referenced(m);
1243 if ((m->aflags & PGA_REFERENCED) != 0) {
1244 vm_page_aflag_clear(m, PGA_REFERENCED);
1249 * Advance or decay the act_count based on recent usage.
1251 if (act_delta != 0) {
1252 m->act_count += ACT_ADVANCE + act_delta;
1253 if (m->act_count > ACT_MAX)
1254 m->act_count = ACT_MAX;
1256 m->act_count -= min(m->act_count, ACT_DECLINE);
1258 if (m->act_count == 0) {
1260 * When not short for inactive pages, let dirty pages go
1261 * through the inactive queue before moving to the
1262 * laundry queues. This gives them some extra time to
1263 * be reactivated, potentially avoiding an expensive
1264 * pageout. However, during a page shortage, the
1265 * inactive queue is necessarily small, and so dirty
1266 * pages would only spend a trivial amount of time in
1267 * the inactive queue. Therefore, we might as well
1268 * place them directly in the laundry queue to reduce
1271 if (page_shortage <= 0)
1272 vm_page_deactivate(m);
1275 * Calling vm_page_test_dirty() here would
1276 * require acquisition of the object's write
1277 * lock. However, during a page shortage,
1278 * directing dirty pages into the laundry
1279 * queue is only an optimization and not a
1280 * requirement. Therefore, we simply rely on
1281 * the opportunistic updates to the page's
1282 * dirty field by the pmap.
1284 if (m->dirty == 0) {
1285 vm_page_deactivate(m);
1287 act_scan_laundry_weight;
1299 vm_pagequeue_lock(pq);
1300 TAILQ_REMOVE(&pq->pq_pl, &vmd->vmd_clock[0], plinks.q);
1301 TAILQ_INSERT_AFTER(&pq->pq_pl, marker, &vmd->vmd_clock[0], plinks.q);
1302 vm_pageout_end_scan(&ss);
1303 vm_pagequeue_unlock(pq);
1307 vm_pageout_reinsert_inactive_page(struct scan_state *ss, vm_page_t m)
1309 struct vm_domain *vmd;
1311 if (m->queue != PQ_INACTIVE || (m->aflags & PGA_ENQUEUED) != 0)
1313 vm_page_aflag_set(m, PGA_ENQUEUED);
1314 if ((m->aflags & PGA_REQUEUE_HEAD) != 0) {
1315 vmd = vm_pagequeue_domain(m);
1316 TAILQ_INSERT_BEFORE(&vmd->vmd_inacthead, m, plinks.q);
1317 vm_page_aflag_clear(m, PGA_REQUEUE | PGA_REQUEUE_HEAD);
1318 } else if ((m->aflags & PGA_REQUEUE) != 0) {
1319 TAILQ_INSERT_TAIL(&ss->pq->pq_pl, m, plinks.q);
1320 vm_page_aflag_clear(m, PGA_REQUEUE | PGA_REQUEUE_HEAD);
1322 TAILQ_INSERT_BEFORE(ss->marker, m, plinks.q);
1327 * Re-add stuck pages to the inactive queue. We will examine them again
1328 * during the next scan. If the queue state of a page has changed since
1329 * it was physically removed from the page queue in
1330 * vm_pageout_collect_batch(), don't do anything with that page.
1333 vm_pageout_reinsert_inactive(struct scan_state *ss, struct vm_batchqueue *bq,
1336 struct vm_pagequeue *pq;
1343 if (vm_batchqueue_insert(bq, m))
1345 vm_pagequeue_lock(pq);
1346 delta += vm_pageout_reinsert_inactive_page(ss, m);
1348 vm_pagequeue_lock(pq);
1349 while ((m = vm_batchqueue_pop(bq)) != NULL)
1350 delta += vm_pageout_reinsert_inactive_page(ss, m);
1351 vm_pagequeue_cnt_add(pq, delta);
1352 vm_pagequeue_unlock(pq);
1353 vm_batchqueue_init(bq);
1357 * Attempt to reclaim the requested number of pages from the inactive queue.
1358 * Returns true if the shortage was addressed.
1361 vm_pageout_scan_inactive(struct vm_domain *vmd, int shortage,
1364 struct scan_state ss;
1365 struct vm_batchqueue rq;
1367 vm_page_t m, marker;
1368 struct vm_pagequeue *pq;
1370 int act_delta, addl_page_shortage, deficit, page_shortage;
1371 int starting_page_shortage;
1375 * The addl_page_shortage is an estimate of the number of temporarily
1376 * stuck pages in the inactive queue. In other words, the
1377 * number of pages from the inactive count that should be
1378 * discounted in setting the target for the active queue scan.
1380 addl_page_shortage = 0;
1383 * vmd_pageout_deficit counts the number of pages requested in
1384 * allocations that failed because of a free page shortage. We assume
1385 * that the allocations will be reattempted and thus include the deficit
1386 * in our scan target.
1388 deficit = atomic_readandclear_int(&vmd->vmd_pageout_deficit);
1389 starting_page_shortage = page_shortage = shortage + deficit;
1394 vm_batchqueue_init(&rq);
1397 * Start scanning the inactive queue for pages that we can free. The
1398 * scan will stop when we reach the target or we have scanned the
1399 * entire queue. (Note that m->act_count is not used to make
1400 * decisions for the inactive queue, only for the active queue.)
1402 marker = &vmd->vmd_markers[PQ_INACTIVE];
1403 pq = &vmd->vmd_pagequeues[PQ_INACTIVE];
1404 vm_pagequeue_lock(pq);
1405 vm_pageout_init_scan(&ss, pq, marker, NULL, pq->pq_cnt);
1406 while (page_shortage > 0 && (m = vm_pageout_next(&ss, true)) != NULL) {
1407 KASSERT((m->flags & PG_MARKER) == 0,
1408 ("marker page %p was dequeued", m));
1410 vm_page_change_lock(m, &mtx);
1414 * The page may have been disassociated from the queue
1415 * while locks were dropped.
1417 if (vm_page_queue(m) != PQ_INACTIVE) {
1418 addl_page_shortage++;
1423 * The page was re-enqueued after the page queue lock was
1424 * dropped, or a requeue was requested. This page gets a second
1427 if ((m->aflags & (PGA_ENQUEUED | PGA_REQUEUE |
1428 PGA_REQUEUE_HEAD)) != 0)
1432 * Held pages are essentially stuck in the queue. So,
1433 * they ought to be discounted from the inactive count.
1434 * See the description of addl_page_shortage above.
1436 * Wired pages may not be freed. Complete their removal
1437 * from the queue now to avoid needless revisits during
1440 if (m->hold_count != 0) {
1441 addl_page_shortage++;
1444 if (m->wire_count != 0) {
1445 vm_page_dequeue_deferred(m);
1449 if (object != m->object) {
1451 VM_OBJECT_WUNLOCK(object);
1457 if (!VM_OBJECT_TRYWLOCK(object)) {
1459 /* Depends on type-stability. */
1460 VM_OBJECT_WLOCK(object);
1468 if (vm_page_busied(m)) {
1470 * Don't mess with busy pages. Leave them at
1471 * the front of the queue. Most likely, they
1472 * are being paged out and will leave the
1473 * queue shortly after the scan finishes. So,
1474 * they ought to be discounted from the
1477 addl_page_shortage++;
1482 * Invalid pages can be easily freed. They cannot be
1483 * mapped, vm_page_free() asserts this.
1489 * If the page has been referenced and the object is not dead,
1490 * reactivate or requeue the page depending on whether the
1493 * Test PGA_REFERENCED after calling pmap_ts_referenced() so
1494 * that a reference from a concurrently destroyed mapping is
1495 * observed here and now.
1497 if (object->ref_count != 0)
1498 act_delta = pmap_ts_referenced(m);
1500 KASSERT(!pmap_page_is_mapped(m),
1501 ("page %p is mapped", m));
1504 if ((m->aflags & PGA_REFERENCED) != 0) {
1505 vm_page_aflag_clear(m, PGA_REFERENCED);
1508 if (act_delta != 0) {
1509 if (object->ref_count != 0) {
1510 VM_CNT_INC(v_reactivated);
1511 vm_page_activate(m);
1514 * Increase the activation count if the page
1515 * was referenced while in the inactive queue.
1516 * This makes it less likely that the page will
1517 * be returned prematurely to the inactive
1520 m->act_count += act_delta + ACT_ADVANCE;
1522 } else if ((object->flags & OBJ_DEAD) == 0) {
1523 vm_page_aflag_set(m, PGA_REQUEUE);
1529 * If the page appears to be clean at the machine-independent
1530 * layer, then remove all of its mappings from the pmap in
1531 * anticipation of freeing it. If, however, any of the page's
1532 * mappings allow write access, then the page may still be
1533 * modified until the last of those mappings are removed.
1535 if (object->ref_count != 0) {
1536 vm_page_test_dirty(m);
1542 * Clean pages can be freed, but dirty pages must be sent back
1543 * to the laundry, unless they belong to a dead object.
1544 * Requeueing dirty pages from dead objects is pointless, as
1545 * they are being paged out and freed by the thread that
1546 * destroyed the object.
1548 if (m->dirty == 0) {
1551 * Because we dequeued the page and have already
1552 * checked for concurrent dequeue and enqueue
1553 * requests, we can safely disassociate the page
1554 * from the inactive queue.
1556 KASSERT((m->aflags & PGA_QUEUE_STATE_MASK) == 0,
1557 ("page %p has queue state", m));
1561 } else if ((object->flags & OBJ_DEAD) == 0)
1565 vm_pageout_reinsert_inactive(&ss, &rq, m);
1572 VM_OBJECT_WUNLOCK(object);
1575 vm_pageout_reinsert_inactive(&ss, &rq, NULL);
1576 vm_pageout_reinsert_inactive(&ss, &ss.bq, NULL);
1577 vm_pagequeue_lock(pq);
1578 vm_pageout_end_scan(&ss);
1579 vm_pagequeue_unlock(pq);
1581 VM_CNT_ADD(v_dfree, starting_page_shortage - page_shortage);
1584 * Wake up the laundry thread so that it can perform any needed
1585 * laundering. If we didn't meet our target, we're in shortfall and
1586 * need to launder more aggressively. If PQ_LAUNDRY is empty and no
1587 * swap devices are configured, the laundry thread has no work to do, so
1588 * don't bother waking it up.
1590 * The laundry thread uses the number of inactive queue scans elapsed
1591 * since the last laundering to determine whether to launder again, so
1594 if (starting_page_shortage > 0) {
1595 pq = &vmd->vmd_pagequeues[PQ_LAUNDRY];
1596 vm_pagequeue_lock(pq);
1597 if (vmd->vmd_laundry_request == VM_LAUNDRY_IDLE &&
1598 (pq->pq_cnt > 0 || atomic_load_acq_int(&swapdev_enabled))) {
1599 if (page_shortage > 0) {
1600 vmd->vmd_laundry_request = VM_LAUNDRY_SHORTFALL;
1601 VM_CNT_INC(v_pdshortfalls);
1602 } else if (vmd->vmd_laundry_request !=
1603 VM_LAUNDRY_SHORTFALL)
1604 vmd->vmd_laundry_request =
1605 VM_LAUNDRY_BACKGROUND;
1606 wakeup(&vmd->vmd_laundry_request);
1608 vmd->vmd_clean_pages_freed +=
1609 starting_page_shortage - page_shortage;
1610 vm_pagequeue_unlock(pq);
1614 * Wakeup the swapout daemon if we didn't free the targeted number of
1617 if (page_shortage > 0)
1621 * If the inactive queue scan fails repeatedly to meet its
1622 * target, kill the largest process.
1624 vm_pageout_mightbe_oom(vmd, page_shortage, starting_page_shortage);
1627 * Reclaim pages by swapping out idle processes, if configured to do so.
1629 vm_swapout_run_idle();
1632 * See the description of addl_page_shortage above.
1634 *addl_shortage = addl_page_shortage + deficit;
1636 return (page_shortage <= 0);
1639 static int vm_pageout_oom_vote;
1642 * The pagedaemon threads randlomly select one to perform the
1643 * OOM. Trying to kill processes before all pagedaemons
1644 * failed to reach free target is premature.
1647 vm_pageout_mightbe_oom(struct vm_domain *vmd, int page_shortage,
1648 int starting_page_shortage)
1652 if (starting_page_shortage <= 0 || starting_page_shortage !=
1654 vmd->vmd_oom_seq = 0;
1657 if (vmd->vmd_oom_seq < vm_pageout_oom_seq) {
1659 vmd->vmd_oom = FALSE;
1660 atomic_subtract_int(&vm_pageout_oom_vote, 1);
1666 * Do not follow the call sequence until OOM condition is
1669 vmd->vmd_oom_seq = 0;
1674 vmd->vmd_oom = TRUE;
1675 old_vote = atomic_fetchadd_int(&vm_pageout_oom_vote, 1);
1676 if (old_vote != vm_ndomains - 1)
1680 * The current pagedaemon thread is the last in the quorum to
1681 * start OOM. Initiate the selection and signaling of the
1684 vm_pageout_oom(VM_OOM_MEM);
1687 * After one round of OOM terror, recall our vote. On the
1688 * next pass, current pagedaemon would vote again if the low
1689 * memory condition is still there, due to vmd_oom being
1692 vmd->vmd_oom = FALSE;
1693 atomic_subtract_int(&vm_pageout_oom_vote, 1);
1697 * The OOM killer is the page daemon's action of last resort when
1698 * memory allocation requests have been stalled for a prolonged period
1699 * of time because it cannot reclaim memory. This function computes
1700 * the approximate number of physical pages that could be reclaimed if
1701 * the specified address space is destroyed.
1703 * Private, anonymous memory owned by the address space is the
1704 * principal resource that we expect to recover after an OOM kill.
1705 * Since the physical pages mapped by the address space's COW entries
1706 * are typically shared pages, they are unlikely to be released and so
1707 * they are not counted.
1709 * To get to the point where the page daemon runs the OOM killer, its
1710 * efforts to write-back vnode-backed pages may have stalled. This
1711 * could be caused by a memory allocation deadlock in the write path
1712 * that might be resolved by an OOM kill. Therefore, physical pages
1713 * belonging to vnode-backed objects are counted, because they might
1714 * be freed without being written out first if the address space holds
1715 * the last reference to an unlinked vnode.
1717 * Similarly, physical pages belonging to OBJT_PHYS objects are
1718 * counted because the address space might hold the last reference to
1722 vm_pageout_oom_pagecount(struct vmspace *vmspace)
1725 vm_map_entry_t entry;
1729 map = &vmspace->vm_map;
1730 KASSERT(!map->system_map, ("system map"));
1731 sx_assert(&map->lock, SA_LOCKED);
1733 for (entry = map->header.next; entry != &map->header;
1734 entry = entry->next) {
1735 if ((entry->eflags & MAP_ENTRY_IS_SUB_MAP) != 0)
1737 obj = entry->object.vm_object;
1740 if ((entry->eflags & MAP_ENTRY_NEEDS_COPY) != 0 &&
1741 obj->ref_count != 1)
1743 switch (obj->type) {
1748 res += obj->resident_page_count;
1756 vm_pageout_oom(int shortage)
1758 struct proc *p, *bigproc;
1759 vm_offset_t size, bigsize;
1765 * We keep the process bigproc locked once we find it to keep anyone
1766 * from messing with it; however, there is a possibility of
1767 * deadlock if process B is bigproc and one of its child processes
1768 * attempts to propagate a signal to B while we are waiting for A's
1769 * lock while walking this list. To avoid this, we don't block on
1770 * the process lock but just skip a process if it is already locked.
1774 sx_slock(&allproc_lock);
1775 FOREACH_PROC_IN_SYSTEM(p) {
1779 * If this is a system, protected or killed process, skip it.
1781 if (p->p_state != PRS_NORMAL || (p->p_flag & (P_INEXEC |
1782 P_PROTECTED | P_SYSTEM | P_WEXIT)) != 0 ||
1783 p->p_pid == 1 || P_KILLED(p) ||
1784 (p->p_pid < 48 && swap_pager_avail != 0)) {
1789 * If the process is in a non-running type state,
1790 * don't touch it. Check all the threads individually.
1793 FOREACH_THREAD_IN_PROC(p, td) {
1795 if (!TD_ON_RUNQ(td) &&
1796 !TD_IS_RUNNING(td) &&
1797 !TD_IS_SLEEPING(td) &&
1798 !TD_IS_SUSPENDED(td) &&
1799 !TD_IS_SWAPPED(td)) {
1811 * get the process size
1813 vm = vmspace_acquire_ref(p);
1820 sx_sunlock(&allproc_lock);
1821 if (!vm_map_trylock_read(&vm->vm_map)) {
1823 sx_slock(&allproc_lock);
1827 size = vmspace_swap_count(vm);
1828 if (shortage == VM_OOM_MEM)
1829 size += vm_pageout_oom_pagecount(vm);
1830 vm_map_unlock_read(&vm->vm_map);
1832 sx_slock(&allproc_lock);
1835 * If this process is bigger than the biggest one,
1838 if (size > bigsize) {
1839 if (bigproc != NULL)
1847 sx_sunlock(&allproc_lock);
1848 if (bigproc != NULL) {
1849 if (vm_panic_on_oom != 0)
1850 panic("out of swap space");
1852 killproc(bigproc, "out of swap space");
1853 sched_nice(bigproc, PRIO_MIN);
1855 PROC_UNLOCK(bigproc);
1860 vm_pageout_lowmem(struct vm_domain *vmd)
1863 if (vmd == VM_DOMAIN(0) &&
1864 time_uptime - lowmem_uptime >= lowmem_period) {
1866 * Decrease registered cache sizes.
1868 SDT_PROBE0(vm, , , vm__lowmem_scan);
1869 EVENTHANDLER_INVOKE(vm_lowmem, VM_LOW_PAGES);
1872 * We do this explicitly after the caches have been
1876 lowmem_uptime = time_uptime;
1881 vm_pageout_worker(void *arg)
1883 struct vm_domain *vmd;
1884 int addl_shortage, domain, shortage;
1887 domain = (uintptr_t)arg;
1888 vmd = VM_DOMAIN(domain);
1893 * XXXKIB It could be useful to bind pageout daemon threads to
1894 * the cores belonging to the domain, from which vm_page_array
1898 KASSERT(vmd->vmd_segs != 0, ("domain without segments"));
1899 vmd->vmd_last_active_scan = ticks;
1902 * The pageout daemon worker is never done, so loop forever.
1905 vm_domain_pageout_lock(vmd);
1908 * We need to clear wanted before we check the limits. This
1909 * prevents races with wakers who will check wanted after they
1912 atomic_store_int(&vmd->vmd_pageout_wanted, 0);
1915 * Might the page daemon need to run again?
1917 if (vm_paging_needed(vmd, vmd->vmd_free_count)) {
1919 * Yes. If the scan failed to produce enough free
1920 * pages, sleep uninterruptibly for some time in the
1921 * hope that the laundry thread will clean some pages.
1923 vm_domain_pageout_unlock(vmd);
1925 pause("pwait", hz / VM_INACT_SCAN_RATE);
1928 * No, sleep until the next wakeup or until pages
1929 * need to have their reference stats updated.
1931 if (mtx_sleep(&vmd->vmd_pageout_wanted,
1932 vm_domain_pageout_lockptr(vmd), PDROP | PVM,
1933 "psleep", hz / VM_INACT_SCAN_RATE) == 0)
1934 VM_CNT_INC(v_pdwakeups);
1937 /* Prevent spurious wakeups by ensuring that wanted is set. */
1938 atomic_store_int(&vmd->vmd_pageout_wanted, 1);
1941 * Use the controller to calculate how many pages to free in
1942 * this interval, and scan the inactive queue.
1944 shortage = pidctrl_daemon(&vmd->vmd_pid, vmd->vmd_free_count);
1946 vm_pageout_lowmem(vmd);
1947 target_met = vm_pageout_scan_inactive(vmd, shortage,
1953 * Scan the active queue. A positive value for shortage
1954 * indicates that we must aggressively deactivate pages to avoid
1957 shortage = vm_pageout_active_target(vmd) + addl_shortage;
1958 vm_pageout_scan_active(vmd, shortage);
1963 * vm_pageout_init initialises basic pageout daemon settings.
1966 vm_pageout_init_domain(int domain)
1968 struct vm_domain *vmd;
1969 struct sysctl_oid *oid;
1971 vmd = VM_DOMAIN(domain);
1972 vmd->vmd_interrupt_free_min = 2;
1975 * v_free_reserved needs to include enough for the largest
1976 * swap pager structures plus enough for any pv_entry structs
1979 if (vmd->vmd_page_count > 1024)
1980 vmd->vmd_free_min = 4 + (vmd->vmd_page_count - 1024) / 200;
1982 vmd->vmd_free_min = 4;
1983 vmd->vmd_pageout_free_min = (2*MAXBSIZE)/PAGE_SIZE +
1984 vmd->vmd_interrupt_free_min;
1985 vmd->vmd_free_reserved = vm_pageout_page_count +
1986 vmd->vmd_pageout_free_min + (vmd->vmd_page_count / 768);
1987 vmd->vmd_free_severe = vmd->vmd_free_min / 2;
1988 vmd->vmd_free_target = 4 * vmd->vmd_free_min + vmd->vmd_free_reserved;
1989 vmd->vmd_free_min += vmd->vmd_free_reserved;
1990 vmd->vmd_free_severe += vmd->vmd_free_reserved;
1991 vmd->vmd_inactive_target = (3 * vmd->vmd_free_target) / 2;
1992 if (vmd->vmd_inactive_target > vmd->vmd_free_count / 3)
1993 vmd->vmd_inactive_target = vmd->vmd_free_count / 3;
1996 * Set the default wakeup threshold to be 10% below the paging
1997 * target. This keeps the steady state out of shortfall.
1999 vmd->vmd_pageout_wakeup_thresh = (vmd->vmd_free_target / 10) * 9;
2002 * Target amount of memory to move out of the laundry queue during a
2003 * background laundering. This is proportional to the amount of system
2006 vmd->vmd_background_launder_target = (vmd->vmd_free_target -
2007 vmd->vmd_free_min) / 10;
2009 /* Initialize the pageout daemon pid controller. */
2010 pidctrl_init(&vmd->vmd_pid, hz / VM_INACT_SCAN_RATE,
2011 vmd->vmd_free_target, PIDCTRL_BOUND,
2012 PIDCTRL_KPD, PIDCTRL_KID, PIDCTRL_KDD);
2013 oid = SYSCTL_ADD_NODE(NULL, SYSCTL_CHILDREN(vmd->vmd_oid), OID_AUTO,
2014 "pidctrl", CTLFLAG_RD, NULL, "");
2015 pidctrl_init_sysctl(&vmd->vmd_pid, SYSCTL_CHILDREN(oid));
2019 vm_pageout_init(void)
2025 * Initialize some paging parameters.
2027 if (vm_cnt.v_page_count < 2000)
2028 vm_pageout_page_count = 8;
2031 for (i = 0; i < vm_ndomains; i++) {
2032 struct vm_domain *vmd;
2034 vm_pageout_init_domain(i);
2036 vm_cnt.v_free_reserved += vmd->vmd_free_reserved;
2037 vm_cnt.v_free_target += vmd->vmd_free_target;
2038 vm_cnt.v_free_min += vmd->vmd_free_min;
2039 vm_cnt.v_inactive_target += vmd->vmd_inactive_target;
2040 vm_cnt.v_pageout_free_min += vmd->vmd_pageout_free_min;
2041 vm_cnt.v_interrupt_free_min += vmd->vmd_interrupt_free_min;
2042 vm_cnt.v_free_severe += vmd->vmd_free_severe;
2043 freecount += vmd->vmd_free_count;
2047 * Set interval in seconds for active scan. We want to visit each
2048 * page at least once every ten minutes. This is to prevent worst
2049 * case paging behaviors with stale active LRU.
2051 if (vm_pageout_update_period == 0)
2052 vm_pageout_update_period = 600;
2054 if (vm_page_max_wired == 0)
2055 vm_page_max_wired = freecount / 3;
2059 * vm_pageout is the high level pageout daemon.
2067 swap_pager_swap_init();
2068 snprintf(curthread->td_name, sizeof(curthread->td_name), "dom0");
2069 error = kthread_add(vm_pageout_laundry_worker, NULL, curproc, NULL,
2070 0, 0, "laundry: dom0");
2072 panic("starting laundry for domain 0, error %d", error);
2073 for (i = 1; i < vm_ndomains; i++) {
2074 error = kthread_add(vm_pageout_worker, (void *)(uintptr_t)i,
2075 curproc, NULL, 0, 0, "dom%d", i);
2077 panic("starting pageout for domain %d, error %d\n",
2080 error = kthread_add(vm_pageout_laundry_worker,
2081 (void *)(uintptr_t)i, curproc, NULL, 0, 0,
2082 "laundry: dom%d", i);
2084 panic("starting laundry for domain %d, error %d",
2087 error = kthread_add(uma_reclaim_worker, NULL, curproc, NULL,
2090 panic("starting uma_reclaim helper, error %d\n", error);
2091 vm_pageout_worker((void *)(uintptr_t)0);
2095 * Perform an advisory wakeup of the page daemon.
2098 pagedaemon_wakeup(int domain)
2100 struct vm_domain *vmd;
2102 vmd = VM_DOMAIN(domain);
2103 vm_domain_pageout_assert_unlocked(vmd);
2104 if (curproc == pageproc)
2107 if (atomic_fetchadd_int(&vmd->vmd_pageout_wanted, 1) == 0) {
2108 vm_domain_pageout_lock(vmd);
2109 atomic_store_int(&vmd->vmd_pageout_wanted, 1);
2110 wakeup(&vmd->vmd_pageout_wanted);
2111 vm_domain_pageout_unlock(vmd);