2 * Copyright (c) 1991 Regents of the University of California.
4 * Copyright (c) 1994 John S. Dyson
6 * Copyright (c) 1994 David Greenman
8 * Copyright (c) 2005 Yahoo! Technologies Norway AS
11 * This code is derived from software contributed to Berkeley by
12 * The Mach Operating System project at Carnegie-Mellon University.
14 * Redistribution and use in source and binary forms, with or without
15 * modification, are permitted provided that the following conditions
17 * 1. Redistributions of source code must retain the above copyright
18 * notice, this list of conditions and the following disclaimer.
19 * 2. Redistributions in binary form must reproduce the above copyright
20 * notice, this list of conditions and the following disclaimer in the
21 * documentation and/or other materials provided with the distribution.
22 * 3. All advertising materials mentioning features or use of this software
23 * must display the following acknowledgement:
24 * This product includes software developed by the University of
25 * California, Berkeley and its contributors.
26 * 4. Neither the name of the University nor the names of its contributors
27 * may be used to endorse or promote products derived from this software
28 * without specific prior written permission.
30 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
31 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
32 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
33 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
34 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
35 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
36 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
37 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
38 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
39 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
42 * from: @(#)vm_pageout.c 7.4 (Berkeley) 5/7/91
45 * Copyright (c) 1987, 1990 Carnegie-Mellon University.
46 * All rights reserved.
48 * Authors: Avadis Tevanian, Jr., Michael Wayne Young
50 * Permission to use, copy, modify and distribute this software and
51 * its documentation is hereby granted, provided that both the copyright
52 * notice and this permission notice appear in all copies of the
53 * software, derivative works or modified versions, and any portions
54 * thereof, and that both notices appear in supporting documentation.
56 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
57 * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
58 * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
60 * Carnegie Mellon requests users of this software to return to
62 * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
63 * School of Computer Science
64 * Carnegie Mellon University
65 * Pittsburgh PA 15213-3890
67 * any improvements or extensions that they make and grant Carnegie the
68 * rights to redistribute these changes.
72 * The proverbial page-out daemon.
75 #include <sys/cdefs.h>
76 __FBSDID("$FreeBSD$");
79 #include <sys/param.h>
80 #include <sys/systm.h>
81 #include <sys/kernel.h>
82 #include <sys/eventhandler.h>
84 #include <sys/mutex.h>
86 #include <sys/kthread.h>
88 #include <sys/mount.h>
89 #include <sys/racct.h>
90 #include <sys/resourcevar.h>
91 #include <sys/sched.h>
92 #include <sys/signalvar.h>
93 #include <sys/vnode.h>
94 #include <sys/vmmeter.h>
96 #include <sys/sysctl.h>
99 #include <vm/vm_param.h>
100 #include <vm/vm_object.h>
101 #include <vm/vm_page.h>
102 #include <vm/vm_map.h>
103 #include <vm/vm_pageout.h>
104 #include <vm/vm_pager.h>
105 #include <vm/swap_pager.h>
106 #include <vm/vm_extern.h>
110 * System initialization
113 /* the kernel process "vm_pageout"*/
114 static void vm_pageout(void);
115 static int vm_pageout_clean(vm_page_t);
116 static void vm_pageout_scan(int pass);
118 struct proc *pageproc;
120 static struct kproc_desc page_kp = {
125 SYSINIT(pagedaemon, SI_SUB_KTHREAD_PAGE, SI_ORDER_FIRST, kproc_start,
128 #if !defined(NO_SWAPPING)
129 /* the kernel process "vm_daemon"*/
130 static void vm_daemon(void);
131 static struct proc *vmproc;
133 static struct kproc_desc vm_kp = {
138 SYSINIT(vmdaemon, SI_SUB_KTHREAD_VM, SI_ORDER_FIRST, kproc_start, &vm_kp);
142 int vm_pages_needed; /* Event on which pageout daemon sleeps */
143 int vm_pageout_deficit; /* Estimated number of pages deficit */
144 int vm_pageout_pages_needed; /* flag saying that the pageout daemon needs pages */
146 #if !defined(NO_SWAPPING)
147 static int vm_pageout_req_swapout; /* XXX */
148 static int vm_daemon_needed;
149 static struct mtx vm_daemon_mtx;
150 /* Allow for use by vm_pageout before vm_daemon is initialized. */
151 MTX_SYSINIT(vm_daemon, &vm_daemon_mtx, "vm daemon", MTX_DEF);
153 static int vm_max_launder = 32;
154 static int vm_pageout_stats_max=0, vm_pageout_stats_interval = 0;
155 static int vm_pageout_full_stats_interval = 0;
156 static int vm_pageout_algorithm=0;
157 static int defer_swap_pageouts=0;
158 static int disable_swap_pageouts=0;
160 #if defined(NO_SWAPPING)
161 static int vm_swap_enabled=0;
162 static int vm_swap_idle_enabled=0;
164 static int vm_swap_enabled=1;
165 static int vm_swap_idle_enabled=0;
168 SYSCTL_INT(_vm, VM_PAGEOUT_ALGORITHM, pageout_algorithm,
169 CTLFLAG_RW, &vm_pageout_algorithm, 0, "LRU page mgmt");
171 SYSCTL_INT(_vm, OID_AUTO, max_launder,
172 CTLFLAG_RW, &vm_max_launder, 0, "Limit dirty flushes in pageout");
174 SYSCTL_INT(_vm, OID_AUTO, pageout_stats_max,
175 CTLFLAG_RW, &vm_pageout_stats_max, 0, "Max pageout stats scan length");
177 SYSCTL_INT(_vm, OID_AUTO, pageout_full_stats_interval,
178 CTLFLAG_RW, &vm_pageout_full_stats_interval, 0, "Interval for full stats scan");
180 SYSCTL_INT(_vm, OID_AUTO, pageout_stats_interval,
181 CTLFLAG_RW, &vm_pageout_stats_interval, 0, "Interval for partial stats scan");
183 #if defined(NO_SWAPPING)
184 SYSCTL_INT(_vm, VM_SWAPPING_ENABLED, swap_enabled,
185 CTLFLAG_RD, &vm_swap_enabled, 0, "Enable entire process swapout");
186 SYSCTL_INT(_vm, OID_AUTO, swap_idle_enabled,
187 CTLFLAG_RD, &vm_swap_idle_enabled, 0, "Allow swapout on idle criteria");
189 SYSCTL_INT(_vm, VM_SWAPPING_ENABLED, swap_enabled,
190 CTLFLAG_RW, &vm_swap_enabled, 0, "Enable entire process swapout");
191 SYSCTL_INT(_vm, OID_AUTO, swap_idle_enabled,
192 CTLFLAG_RW, &vm_swap_idle_enabled, 0, "Allow swapout on idle criteria");
195 SYSCTL_INT(_vm, OID_AUTO, defer_swapspace_pageouts,
196 CTLFLAG_RW, &defer_swap_pageouts, 0, "Give preference to dirty pages in mem");
198 SYSCTL_INT(_vm, OID_AUTO, disable_swapspace_pageouts,
199 CTLFLAG_RW, &disable_swap_pageouts, 0, "Disallow swapout of dirty pages");
201 static int pageout_lock_miss;
202 SYSCTL_INT(_vm, OID_AUTO, pageout_lock_miss,
203 CTLFLAG_RD, &pageout_lock_miss, 0, "vget() lock misses during pageout");
205 #define VM_PAGEOUT_PAGE_COUNT 16
206 int vm_pageout_page_count = VM_PAGEOUT_PAGE_COUNT;
208 int vm_page_max_wired; /* XXX max # of wired pages system-wide */
209 SYSCTL_INT(_vm, OID_AUTO, max_wired,
210 CTLFLAG_RW, &vm_page_max_wired, 0, "System-wide limit to wired page count");
212 #if !defined(NO_SWAPPING)
213 static void vm_pageout_map_deactivate_pages(vm_map_t, long);
214 static void vm_pageout_object_deactivate_pages(pmap_t, vm_object_t, long);
215 static void vm_req_vmdaemon(int req);
217 static void vm_pageout_page_stats(void);
220 * Initialize a dummy page for marking the caller's place in the specified
221 * paging queue. In principle, this function only needs to set the flag
222 * PG_MARKER. Nonetheless, it sets the flag VPO_BUSY and initializes the hold
223 * count to one as safety precautions.
226 vm_pageout_init_marker(vm_page_t marker, u_short queue)
229 bzero(marker, sizeof(*marker));
230 marker->flags = PG_MARKER;
231 marker->oflags = VPO_BUSY;
232 marker->queue = queue;
233 marker->hold_count = 1;
237 * vm_pageout_fallback_object_lock:
239 * Lock vm object currently associated with `m'. VM_OBJECT_TRYLOCK is
240 * known to have failed and page queue must be either PQ_ACTIVE or
241 * PQ_INACTIVE. To avoid lock order violation, unlock the page queues
242 * while locking the vm object. Use marker page to detect page queue
243 * changes and maintain notion of next page on page queue. Return
244 * TRUE if no changes were detected, FALSE otherwise. vm object is
247 * This function depends on both the lock portion of struct vm_object
248 * and normal struct vm_page being type stable.
251 vm_pageout_fallback_object_lock(vm_page_t m, vm_page_t *next)
253 struct vm_page marker;
259 vm_pageout_init_marker(&marker, queue);
262 TAILQ_INSERT_AFTER(&vm_page_queues[queue].pl,
264 vm_page_unlock_queues();
266 VM_OBJECT_LOCK(object);
268 vm_page_lock_queues();
270 /* Page queue might have changed. */
271 *next = TAILQ_NEXT(&marker, pageq);
272 unchanged = (m->queue == queue &&
273 m->object == object &&
274 &marker == TAILQ_NEXT(m, pageq));
275 TAILQ_REMOVE(&vm_page_queues[queue].pl,
281 * Lock the page while holding the page queue lock. Use marker page
282 * to detect page queue changes and maintain notion of next page on
283 * page queue. Return TRUE if no changes were detected, FALSE
284 * otherwise. The page is locked on return. The page queue lock might
285 * be dropped and reacquired.
287 * This function depends on normal struct vm_page being type stable.
290 vm_pageout_page_lock(vm_page_t m, vm_page_t *next)
292 struct vm_page marker;
296 vm_page_lock_assert(m, MA_NOTOWNED);
297 mtx_assert(&vm_page_queue_mtx, MA_OWNED);
299 if (vm_page_trylock(m))
303 vm_pageout_init_marker(&marker, queue);
305 TAILQ_INSERT_AFTER(&vm_page_queues[queue].pl, m, &marker, pageq);
306 vm_page_unlock_queues();
308 vm_page_lock_queues();
310 /* Page queue might have changed. */
311 *next = TAILQ_NEXT(&marker, pageq);
312 unchanged = (m->queue == queue && &marker == TAILQ_NEXT(m, pageq));
313 TAILQ_REMOVE(&vm_page_queues[queue].pl, &marker, pageq);
320 * Clean the page and remove it from the laundry.
322 * We set the busy bit to cause potential page faults on this page to
323 * block. Note the careful timing, however, the busy bit isn't set till
324 * late and we cannot do anything that will mess with the page.
327 vm_pageout_clean(vm_page_t m)
330 vm_page_t mc[2*vm_pageout_page_count], pb, ps;
332 int ib, is, page_base;
333 vm_pindex_t pindex = m->pindex;
335 vm_page_lock_assert(m, MA_OWNED);
337 VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
340 * It doesn't cost us anything to pageout OBJT_DEFAULT or OBJT_SWAP
341 * with the new swapper, but we could have serious problems paging
342 * out other object types if there is insufficient memory.
344 * Unfortunately, checking free memory here is far too late, so the
345 * check has been moved up a procedural level.
349 * Can't clean the page if it's busy or held.
351 KASSERT(m->busy == 0 && (m->oflags & VPO_BUSY) == 0,
352 ("vm_pageout_clean: page %p is busy", m));
353 KASSERT(m->hold_count == 0, ("vm_pageout_clean: page %p is held", m));
356 mc[vm_pageout_page_count] = pb = ps = m;
358 page_base = vm_pageout_page_count;
363 * Scan object for clusterable pages.
365 * We can cluster ONLY if: ->> the page is NOT
366 * clean, wired, busy, held, or mapped into a
367 * buffer, and one of the following:
368 * 1) The page is inactive, or a seldom used
371 * 2) we force the issue.
373 * During heavy mmap/modification loads the pageout
374 * daemon can really fragment the underlying file
375 * due to flushing pages out of order and not trying
376 * align the clusters (which leave sporatic out-of-order
377 * holes). To solve this problem we do the reverse scan
378 * first and attempt to align our cluster, then do a
379 * forward scan if room remains.
382 while (ib && pageout_count < vm_pageout_page_count) {
390 if ((p = vm_page_prev(pb)) == NULL ||
391 (p->oflags & VPO_BUSY) != 0 || p->busy != 0) {
396 vm_page_test_dirty(p);
398 p->queue != PQ_INACTIVE ||
399 p->hold_count != 0) { /* may be undergoing I/O */
405 mc[--page_base] = pb = p;
409 * alignment boundry, stop here and switch directions. Do
412 if ((pindex - (ib - 1)) % vm_pageout_page_count == 0)
416 while (pageout_count < vm_pageout_page_count &&
417 pindex + is < object->size) {
420 if ((p = vm_page_next(ps)) == NULL ||
421 (p->oflags & VPO_BUSY) != 0 || p->busy != 0)
424 vm_page_test_dirty(p);
426 p->queue != PQ_INACTIVE ||
427 p->hold_count != 0) { /* may be undergoing I/O */
432 mc[page_base + pageout_count] = ps = p;
438 * If we exhausted our forward scan, continue with the reverse scan
439 * when possible, even past a page boundry. This catches boundry
442 if (ib && pageout_count < vm_pageout_page_count)
446 * we allow reads during pageouts...
448 return (vm_pageout_flush(&mc[page_base], pageout_count, 0, 0, NULL,
453 * vm_pageout_flush() - launder the given pages
455 * The given pages are laundered. Note that we setup for the start of
456 * I/O ( i.e. busy the page ), mark it read-only, and bump the object
457 * reference count all in here rather then in the parent. If we want
458 * the parent to do more sophisticated things we may have to change
461 * Returned runlen is the count of pages between mreq and first
462 * page after mreq with status VM_PAGER_AGAIN.
463 * *eio is set to TRUE if pager returned VM_PAGER_ERROR or VM_PAGER_FAIL
464 * for any page in runlen set.
467 vm_pageout_flush(vm_page_t *mc, int count, int flags, int mreq, int *prunlen,
470 vm_object_t object = mc[0]->object;
471 int pageout_status[count];
475 VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
476 mtx_assert(&vm_page_queue_mtx, MA_NOTOWNED);
479 * Initiate I/O. Bump the vm_page_t->busy counter and
480 * mark the pages read-only.
482 * We do not have to fixup the clean/dirty bits here... we can
483 * allow the pager to do it after the I/O completes.
485 * NOTE! mc[i]->dirty may be partial or fragmented due to an
486 * edge case with file fragments.
488 for (i = 0; i < count; i++) {
489 KASSERT(mc[i]->valid == VM_PAGE_BITS_ALL,
490 ("vm_pageout_flush: partially invalid page %p index %d/%d",
492 vm_page_io_start(mc[i]);
493 pmap_remove_write(mc[i]);
495 vm_object_pip_add(object, count);
497 vm_pager_put_pages(object, mc, count, flags, pageout_status);
499 runlen = count - mreq;
502 for (i = 0; i < count; i++) {
503 vm_page_t mt = mc[i];
505 KASSERT(pageout_status[i] == VM_PAGER_PEND ||
506 (mt->aflags & PGA_WRITEABLE) == 0,
507 ("vm_pageout_flush: page %p is not write protected", mt));
508 switch (pageout_status[i]) {
515 * Page outside of range of object. Right now we
516 * essentially lose the changes by pretending it
524 * If page couldn't be paged out, then reactivate the
525 * page so it doesn't clog the inactive list. (We
526 * will try paging out it again later).
529 vm_page_activate(mt);
531 if (eio != NULL && i >= mreq && i - mreq < runlen)
535 if (i >= mreq && i - mreq < runlen)
541 * If the operation is still going, leave the page busy to
542 * block all other accesses. Also, leave the paging in
543 * progress indicator set so that we don't attempt an object
546 if (pageout_status[i] != VM_PAGER_PEND) {
547 vm_object_pip_wakeup(object);
548 vm_page_io_finish(mt);
549 if (vm_page_count_severe()) {
551 vm_page_try_to_cache(mt);
558 return (numpagedout);
561 #if !defined(NO_SWAPPING)
563 * vm_pageout_object_deactivate_pages
565 * Deactivate enough pages to satisfy the inactive target
568 * The object and map must be locked.
571 vm_pageout_object_deactivate_pages(pmap_t pmap, vm_object_t first_object,
574 vm_object_t backing_object, object;
576 int actcount, remove_mode;
578 VM_OBJECT_LOCK_ASSERT(first_object, MA_OWNED);
579 if (first_object->type == OBJT_DEVICE ||
580 first_object->type == OBJT_SG)
582 for (object = first_object;; object = backing_object) {
583 if (pmap_resident_count(pmap) <= desired)
585 VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
586 if (object->type == OBJT_PHYS || object->paging_in_progress)
590 if (object->shadow_count > 1)
593 * Scan the object's entire memory queue.
595 TAILQ_FOREACH(p, &object->memq, listq) {
596 if (pmap_resident_count(pmap) <= desired)
598 if ((p->oflags & VPO_BUSY) != 0 || p->busy != 0)
600 PCPU_INC(cnt.v_pdpages);
602 if (p->wire_count != 0 || p->hold_count != 0 ||
603 !pmap_page_exists_quick(pmap, p)) {
607 actcount = pmap_ts_referenced(p);
608 if ((p->aflags & PGA_REFERENCED) != 0) {
611 vm_page_aflag_clear(p, PGA_REFERENCED);
613 if (p->queue != PQ_ACTIVE && actcount != 0) {
615 p->act_count += actcount;
616 } else if (p->queue == PQ_ACTIVE) {
618 p->act_count -= min(p->act_count,
621 (vm_pageout_algorithm ||
622 p->act_count == 0)) {
624 vm_page_deactivate(p);
626 vm_page_lock_queues();
628 vm_page_unlock_queues();
632 if (p->act_count < ACT_MAX -
634 p->act_count += ACT_ADVANCE;
635 vm_page_lock_queues();
637 vm_page_unlock_queues();
639 } else if (p->queue == PQ_INACTIVE)
643 if ((backing_object = object->backing_object) == NULL)
645 VM_OBJECT_LOCK(backing_object);
646 if (object != first_object)
647 VM_OBJECT_UNLOCK(object);
650 if (object != first_object)
651 VM_OBJECT_UNLOCK(object);
655 * deactivate some number of pages in a map, try to do it fairly, but
656 * that is really hard to do.
659 vm_pageout_map_deactivate_pages(map, desired)
664 vm_object_t obj, bigobj;
667 if (!vm_map_trylock(map))
674 * first, search out the biggest object, and try to free pages from
677 tmpe = map->header.next;
678 while (tmpe != &map->header) {
679 if ((tmpe->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
680 obj = tmpe->object.vm_object;
681 if (obj != NULL && VM_OBJECT_TRYLOCK(obj)) {
682 if (obj->shadow_count <= 1 &&
684 bigobj->resident_page_count < obj->resident_page_count)) {
686 VM_OBJECT_UNLOCK(bigobj);
689 VM_OBJECT_UNLOCK(obj);
692 if (tmpe->wired_count > 0)
693 nothingwired = FALSE;
697 if (bigobj != NULL) {
698 vm_pageout_object_deactivate_pages(map->pmap, bigobj, desired);
699 VM_OBJECT_UNLOCK(bigobj);
702 * Next, hunt around for other pages to deactivate. We actually
703 * do this search sort of wrong -- .text first is not the best idea.
705 tmpe = map->header.next;
706 while (tmpe != &map->header) {
707 if (pmap_resident_count(vm_map_pmap(map)) <= desired)
709 if ((tmpe->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
710 obj = tmpe->object.vm_object;
713 vm_pageout_object_deactivate_pages(map->pmap, obj, desired);
714 VM_OBJECT_UNLOCK(obj);
721 * Remove all mappings if a process is swapped out, this will free page
724 if (desired == 0 && nothingwired) {
725 pmap_remove(vm_map_pmap(map), vm_map_min(map),
730 #endif /* !defined(NO_SWAPPING) */
733 * vm_pageout_scan does the dirty work for the pageout daemon.
736 vm_pageout_scan(int pass)
739 struct vm_page marker;
740 int page_shortage, maxscan, pcount;
741 int addl_page_shortage, addl_page_shortage_init;
744 int vnodes_skipped = 0;
748 * Decrease registered cache sizes.
750 EVENTHANDLER_INVOKE(vm_lowmem, 0);
752 * We do this explicitly after the caches have been drained above.
756 addl_page_shortage_init = atomic_readandclear_int(&vm_pageout_deficit);
759 * Calculate the number of pages we want to either free or move
762 page_shortage = vm_paging_target() + addl_page_shortage_init;
764 vm_pageout_init_marker(&marker, PQ_INACTIVE);
767 * Start scanning the inactive queue for pages we can move to the
768 * cache or free. The scan will stop when the target is reached or
769 * we have scanned the entire inactive queue. Note that m->act_count
770 * is not used to form decisions for the inactive queue, only for the
773 * maxlaunder limits the number of dirty pages we flush per scan.
774 * For most systems a smaller value (16 or 32) is more robust under
775 * extreme memory and disk pressure because any unnecessary writes
776 * to disk can result in extreme performance degredation. However,
777 * systems with excessive dirty pages (especially when MAP_NOSYNC is
778 * used) will die horribly with limited laundering. If the pageout
779 * daemon cannot clean enough pages in the first pass, we let it go
780 * all out in succeeding passes.
782 if ((maxlaunder = vm_max_launder) <= 1)
786 vm_page_lock_queues();
788 addl_page_shortage = addl_page_shortage_init;
789 maxscan = cnt.v_inactive_count;
791 for (m = TAILQ_FIRST(&vm_page_queues[PQ_INACTIVE].pl);
792 m != NULL && maxscan-- > 0 && page_shortage > 0;
797 if (m->queue != PQ_INACTIVE)
800 next = TAILQ_NEXT(m, pageq);
805 if (m->flags & PG_MARKER)
811 if (!vm_pageout_page_lock(m, &next)) {
813 addl_page_shortage++;
818 * A held page may be undergoing I/O, so skip it.
823 addl_page_shortage++;
828 * Don't mess with busy pages, keep in the front of the
829 * queue, most likely are being paged out.
832 if (!VM_OBJECT_TRYLOCK(object) &&
833 (!vm_pageout_fallback_object_lock(m, &next) ||
834 m->hold_count != 0)) {
835 VM_OBJECT_UNLOCK(object);
837 addl_page_shortage++;
840 if (m->busy || (m->oflags & VPO_BUSY)) {
842 VM_OBJECT_UNLOCK(object);
843 addl_page_shortage++;
848 * If the object is not being used, we ignore previous
851 if (object->ref_count == 0) {
852 vm_page_aflag_clear(m, PGA_REFERENCED);
853 KASSERT(!pmap_page_is_mapped(m),
854 ("vm_pageout_scan: page %p is mapped", m));
857 * Otherwise, if the page has been referenced while in the
858 * inactive queue, we bump the "activation count" upwards,
859 * making it less likely that the page will be added back to
860 * the inactive queue prematurely again. Here we check the
861 * page tables (or emulated bits, if any), given the upper
862 * level VM system not knowing anything about existing
865 } else if (((m->aflags & PGA_REFERENCED) == 0) &&
866 (actcount = pmap_ts_referenced(m))) {
869 m->act_count += actcount + ACT_ADVANCE;
870 VM_OBJECT_UNLOCK(object);
875 * If the upper level VM system knows about any page
876 * references, we activate the page. We also set the
877 * "activation count" higher than normal so that we will less
878 * likely place pages back onto the inactive queue again.
880 if ((m->aflags & PGA_REFERENCED) != 0) {
881 vm_page_aflag_clear(m, PGA_REFERENCED);
882 actcount = pmap_ts_referenced(m);
885 m->act_count += actcount + ACT_ADVANCE + 1;
886 VM_OBJECT_UNLOCK(object);
891 * If the upper level VM system does not believe that the page
892 * is fully dirty, but it is mapped for write access, then we
893 * consult the pmap to see if the page's dirty status should
896 if (m->dirty != VM_PAGE_BITS_ALL &&
897 (m->aflags & PGA_WRITEABLE) != 0) {
899 * Avoid a race condition: Unless write access is
900 * removed from the page, another processor could
901 * modify it before all access is removed by the call
902 * to vm_page_cache() below. If vm_page_cache() finds
903 * that the page has been modified when it removes all
904 * access, it panics because it cannot cache dirty
905 * pages. In principle, we could eliminate just write
906 * access here rather than all access. In the expected
907 * case, when there are no last instant modifications
908 * to the page, removing all access will be cheaper
911 if (pmap_is_modified(m))
913 else if (m->dirty == 0)
919 * Invalid pages can be easily freed
924 } else if (m->dirty == 0) {
926 * Clean pages can be placed onto the cache queue.
927 * This effectively frees them.
931 } else if ((m->flags & PG_WINATCFLS) == 0 && pass == 0) {
933 * Dirty pages need to be paged out, but flushing
934 * a page is extremely expensive verses freeing
935 * a clean page. Rather then artificially limiting
936 * the number of pages we can flush, we instead give
937 * dirty pages extra priority on the inactive queue
938 * by forcing them to be cycled through the queue
939 * twice before being flushed, after which the
940 * (now clean) page will cycle through once more
941 * before being freed. This significantly extends
942 * the thrash point for a heavily loaded machine.
944 m->flags |= PG_WINATCFLS;
946 } else if (maxlaunder > 0) {
948 * We always want to try to flush some dirty pages if
949 * we encounter them, to keep the system stable.
950 * Normally this number is small, but under extreme
951 * pressure where there are insufficient clean pages
952 * on the inactive queue, we may have to go all out.
954 int swap_pageouts_ok, vfslocked = 0;
955 struct vnode *vp = NULL;
956 struct mount *mp = NULL;
958 if ((object->type != OBJT_SWAP) && (object->type != OBJT_DEFAULT)) {
959 swap_pageouts_ok = 1;
961 swap_pageouts_ok = !(defer_swap_pageouts || disable_swap_pageouts);
962 swap_pageouts_ok |= (!disable_swap_pageouts && defer_swap_pageouts &&
963 vm_page_count_min());
968 * We don't bother paging objects that are "dead".
969 * Those objects are in a "rundown" state.
971 if (!swap_pageouts_ok || (object->flags & OBJ_DEAD)) {
973 VM_OBJECT_UNLOCK(object);
979 * Following operations may unlock
980 * vm_page_queue_mtx, invalidating the 'next'
981 * pointer. To prevent an inordinate number
982 * of restarts we use our marker to remember
986 TAILQ_INSERT_AFTER(&vm_page_queues[PQ_INACTIVE].pl,
989 * The object is already known NOT to be dead. It
990 * is possible for the vget() to block the whole
991 * pageout daemon, but the new low-memory handling
992 * code should prevent it.
994 * The previous code skipped locked vnodes and, worse,
995 * reordered pages in the queue. This results in
996 * completely non-deterministic operation and, on a
997 * busy system, can lead to extremely non-optimal
998 * pageouts. For example, it can cause clean pages
999 * to be freed and dirty pages to be moved to the end
1000 * of the queue. Since dirty pages are also moved to
1001 * the end of the queue once-cleaned, this gives
1002 * way too large a weighting to defering the freeing
1005 * We can't wait forever for the vnode lock, we might
1006 * deadlock due to a vn_read() getting stuck in
1007 * vm_wait while holding this vnode. We skip the
1008 * vnode if we can't get it in a reasonable amount
1011 if (object->type == OBJT_VNODE) {
1012 vm_page_unlock_queues();
1014 vp = object->handle;
1015 if (vp->v_type == VREG &&
1016 vn_start_write(vp, &mp, V_NOWAIT) != 0) {
1018 ++pageout_lock_miss;
1019 if (object->flags & OBJ_MIGHTBEDIRTY)
1021 vm_page_lock_queues();
1022 goto unlock_and_continue;
1025 ("vp %p with NULL v_mount", vp));
1026 vm_object_reference_locked(object);
1027 VM_OBJECT_UNLOCK(object);
1028 vfslocked = VFS_LOCK_GIANT(vp->v_mount);
1029 if (vget(vp, LK_EXCLUSIVE | LK_TIMELOCK,
1031 VM_OBJECT_LOCK(object);
1032 vm_page_lock_queues();
1033 ++pageout_lock_miss;
1034 if (object->flags & OBJ_MIGHTBEDIRTY)
1037 goto unlock_and_continue;
1039 VM_OBJECT_LOCK(object);
1041 vm_page_lock_queues();
1043 * The page might have been moved to another
1044 * queue during potential blocking in vget()
1045 * above. The page might have been freed and
1046 * reused for another vnode.
1048 if (m->queue != PQ_INACTIVE ||
1049 m->object != object ||
1050 TAILQ_NEXT(m, pageq) != &marker) {
1052 if (object->flags & OBJ_MIGHTBEDIRTY)
1054 goto unlock_and_continue;
1058 * The page may have been busied during the
1059 * blocking in vget(). We don't move the
1060 * page back onto the end of the queue so that
1061 * statistics are more correct if we don't.
1063 if (m->busy || (m->oflags & VPO_BUSY)) {
1065 goto unlock_and_continue;
1069 * If the page has become held it might
1070 * be undergoing I/O, so skip it
1072 if (m->hold_count) {
1075 if (object->flags & OBJ_MIGHTBEDIRTY)
1077 goto unlock_and_continue;
1082 * If a page is dirty, then it is either being washed
1083 * (but not yet cleaned) or it is still in the
1084 * laundry. If it is still in the laundry, then we
1085 * start the cleaning operation.
1087 * decrement page_shortage on success to account for
1088 * the (future) cleaned page. Otherwise we could wind
1089 * up laundering or cleaning too many pages.
1091 vm_page_unlock_queues();
1092 if (vm_pageout_clean(m) != 0) {
1096 vm_page_lock_queues();
1097 unlock_and_continue:
1098 vm_page_lock_assert(m, MA_NOTOWNED);
1099 VM_OBJECT_UNLOCK(object);
1101 vm_page_unlock_queues();
1104 VFS_UNLOCK_GIANT(vfslocked);
1105 vm_object_deallocate(object);
1106 vn_finished_write(mp);
1107 vm_page_lock_queues();
1109 next = TAILQ_NEXT(&marker, pageq);
1110 TAILQ_REMOVE(&vm_page_queues[PQ_INACTIVE].pl,
1112 vm_page_lock_assert(m, MA_NOTOWNED);
1116 VM_OBJECT_UNLOCK(object);
1120 * Compute the number of pages we want to try to move from the
1121 * active queue to the inactive queue.
1123 page_shortage = vm_paging_target() +
1124 cnt.v_inactive_target - cnt.v_inactive_count;
1125 page_shortage += addl_page_shortage;
1128 * Scan the active queue for things we can deactivate. We nominally
1129 * track the per-page activity counter and use it to locate
1130 * deactivation candidates.
1132 pcount = cnt.v_active_count;
1133 m = TAILQ_FIRST(&vm_page_queues[PQ_ACTIVE].pl);
1134 mtx_assert(&vm_page_queue_mtx, MA_OWNED);
1136 while ((m != NULL) && (pcount-- > 0) && (page_shortage > 0)) {
1138 KASSERT(m->queue == PQ_ACTIVE,
1139 ("vm_pageout_scan: page %p isn't active", m));
1141 next = TAILQ_NEXT(m, pageq);
1142 if ((m->flags & PG_MARKER) != 0) {
1146 if (!vm_pageout_page_lock(m, &next)) {
1152 if (!VM_OBJECT_TRYLOCK(object) &&
1153 !vm_pageout_fallback_object_lock(m, &next)) {
1154 VM_OBJECT_UNLOCK(object);
1161 * Don't deactivate pages that are busy.
1163 if ((m->busy != 0) ||
1164 (m->oflags & VPO_BUSY) ||
1165 (m->hold_count != 0)) {
1167 VM_OBJECT_UNLOCK(object);
1174 * The count for pagedaemon pages is done after checking the
1175 * page for eligibility...
1180 * Check to see "how much" the page has been used.
1183 if (object->ref_count != 0) {
1184 if (m->aflags & PGA_REFERENCED) {
1187 actcount += pmap_ts_referenced(m);
1189 m->act_count += ACT_ADVANCE + actcount;
1190 if (m->act_count > ACT_MAX)
1191 m->act_count = ACT_MAX;
1196 * Since we have "tested" this bit, we need to clear it now.
1198 vm_page_aflag_clear(m, PGA_REFERENCED);
1201 * Only if an object is currently being used, do we use the
1202 * page activation count stats.
1204 if (actcount && (object->ref_count != 0)) {
1207 m->act_count -= min(m->act_count, ACT_DECLINE);
1208 if (vm_pageout_algorithm ||
1209 object->ref_count == 0 ||
1210 m->act_count == 0) {
1212 if (object->ref_count == 0) {
1213 KASSERT(!pmap_page_is_mapped(m),
1214 ("vm_pageout_scan: page %p is mapped", m));
1218 vm_page_deactivate(m);
1220 vm_page_deactivate(m);
1227 VM_OBJECT_UNLOCK(object);
1230 vm_page_unlock_queues();
1231 #if !defined(NO_SWAPPING)
1233 * Idle process swapout -- run once per second.
1235 if (vm_swap_idle_enabled) {
1237 if (time_second != lsec) {
1238 vm_req_vmdaemon(VM_SWAP_IDLE);
1245 * If we didn't get enough free pages, and we have skipped a vnode
1246 * in a writeable object, wakeup the sync daemon. And kick swapout
1247 * if we did not get enough free pages.
1249 if (vm_paging_target() > 0) {
1250 if (vnodes_skipped && vm_page_count_min())
1251 (void) speedup_syncer();
1252 #if !defined(NO_SWAPPING)
1253 if (vm_swap_enabled && vm_page_count_target())
1254 vm_req_vmdaemon(VM_SWAP_NORMAL);
1259 * If we are critically low on one of RAM or swap and low on
1260 * the other, kill the largest process. However, we avoid
1261 * doing this on the first pass in order to give ourselves a
1262 * chance to flush out dirty vnode-backed pages and to allow
1263 * active pages to be moved to the inactive queue and reclaimed.
1266 ((swap_pager_avail < 64 && vm_page_count_min()) ||
1267 (swap_pager_full && vm_paging_target() > 0)))
1268 vm_pageout_oom(VM_OOM_MEM);
1273 vm_pageout_oom(int shortage)
1275 struct proc *p, *bigproc;
1276 vm_offset_t size, bigsize;
1281 * We keep the process bigproc locked once we find it to keep anyone
1282 * from messing with it; however, there is a possibility of
1283 * deadlock if process B is bigproc and one of it's child processes
1284 * attempts to propagate a signal to B while we are waiting for A's
1285 * lock while walking this list. To avoid this, we don't block on
1286 * the process lock but just skip a process if it is already locked.
1290 sx_slock(&allproc_lock);
1291 FOREACH_PROC_IN_SYSTEM(p) {
1294 if (PROC_TRYLOCK(p) == 0)
1297 * If this is a system, protected or killed process, skip it.
1299 if (p->p_state != PRS_NORMAL ||
1300 (p->p_flag & (P_INEXEC | P_PROTECTED | P_SYSTEM)) ||
1301 (p->p_pid == 1) || P_KILLED(p) ||
1302 ((p->p_pid < 48) && (swap_pager_avail != 0))) {
1307 * If the process is in a non-running type state,
1308 * don't touch it. Check all the threads individually.
1311 FOREACH_THREAD_IN_PROC(p, td) {
1313 if (!TD_ON_RUNQ(td) &&
1314 !TD_IS_RUNNING(td) &&
1315 !TD_IS_SLEEPING(td) &&
1316 !TD_IS_SUSPENDED(td)) {
1328 * get the process size
1330 vm = vmspace_acquire_ref(p);
1335 if (!vm_map_trylock_read(&vm->vm_map)) {
1340 size = vmspace_swap_count(vm);
1341 vm_map_unlock_read(&vm->vm_map);
1342 if (shortage == VM_OOM_MEM)
1343 size += vmspace_resident_count(vm);
1346 * if the this process is bigger than the biggest one
1349 if (size > bigsize) {
1350 if (bigproc != NULL)
1351 PROC_UNLOCK(bigproc);
1357 sx_sunlock(&allproc_lock);
1358 if (bigproc != NULL) {
1359 killproc(bigproc, "out of swap space");
1360 sched_nice(bigproc, PRIO_MIN);
1361 PROC_UNLOCK(bigproc);
1362 wakeup(&cnt.v_free_count);
1367 * This routine tries to maintain the pseudo LRU active queue,
1368 * so that during long periods of time where there is no paging,
1369 * that some statistic accumulation still occurs. This code
1370 * helps the situation where paging just starts to occur.
1373 vm_pageout_page_stats()
1377 int pcount,tpcount; /* Number of pages to check */
1378 static int fullintervalcount = 0;
1382 (cnt.v_inactive_target + cnt.v_cache_max + cnt.v_free_min) -
1383 (cnt.v_free_count + cnt.v_inactive_count + cnt.v_cache_count);
1385 if (page_shortage <= 0)
1388 vm_page_lock_queues();
1389 pcount = cnt.v_active_count;
1390 fullintervalcount += vm_pageout_stats_interval;
1391 if (fullintervalcount < vm_pageout_full_stats_interval) {
1392 tpcount = (int64_t)vm_pageout_stats_max * cnt.v_active_count /
1394 if (pcount > tpcount)
1397 fullintervalcount = 0;
1400 m = TAILQ_FIRST(&vm_page_queues[PQ_ACTIVE].pl);
1401 while ((m != NULL) && (pcount-- > 0)) {
1404 KASSERT(m->queue == PQ_ACTIVE,
1405 ("vm_pageout_page_stats: page %p isn't active", m));
1407 next = TAILQ_NEXT(m, pageq);
1408 if ((m->flags & PG_MARKER) != 0) {
1412 vm_page_lock_assert(m, MA_NOTOWNED);
1413 if (!vm_pageout_page_lock(m, &next)) {
1419 if (!VM_OBJECT_TRYLOCK(object) &&
1420 !vm_pageout_fallback_object_lock(m, &next)) {
1421 VM_OBJECT_UNLOCK(object);
1428 * Don't deactivate pages that are busy.
1430 if ((m->busy != 0) ||
1431 (m->oflags & VPO_BUSY) ||
1432 (m->hold_count != 0)) {
1434 VM_OBJECT_UNLOCK(object);
1441 if (m->aflags & PGA_REFERENCED) {
1442 vm_page_aflag_clear(m, PGA_REFERENCED);
1446 actcount += pmap_ts_referenced(m);
1448 m->act_count += ACT_ADVANCE + actcount;
1449 if (m->act_count > ACT_MAX)
1450 m->act_count = ACT_MAX;
1453 if (m->act_count == 0) {
1455 * We turn off page access, so that we have
1456 * more accurate RSS stats. We don't do this
1457 * in the normal page deactivation when the
1458 * system is loaded VM wise, because the
1459 * cost of the large number of page protect
1460 * operations would be higher than the value
1461 * of doing the operation.
1464 vm_page_deactivate(m);
1466 m->act_count -= min(m->act_count, ACT_DECLINE);
1471 VM_OBJECT_UNLOCK(object);
1474 vm_page_unlock_queues();
1478 * vm_pageout is the high level pageout daemon.
1486 * Initialize some paging parameters.
1488 cnt.v_interrupt_free_min = 2;
1489 if (cnt.v_page_count < 2000)
1490 vm_pageout_page_count = 8;
1493 * v_free_reserved needs to include enough for the largest
1494 * swap pager structures plus enough for any pv_entry structs
1497 if (cnt.v_page_count > 1024)
1498 cnt.v_free_min = 4 + (cnt.v_page_count - 1024) / 200;
1501 cnt.v_pageout_free_min = (2*MAXBSIZE)/PAGE_SIZE +
1502 cnt.v_interrupt_free_min;
1503 cnt.v_free_reserved = vm_pageout_page_count +
1504 cnt.v_pageout_free_min + (cnt.v_page_count / 768);
1505 cnt.v_free_severe = cnt.v_free_min / 2;
1506 cnt.v_free_min += cnt.v_free_reserved;
1507 cnt.v_free_severe += cnt.v_free_reserved;
1510 * v_free_target and v_cache_min control pageout hysteresis. Note
1511 * that these are more a measure of the VM cache queue hysteresis
1512 * then the VM free queue. Specifically, v_free_target is the
1513 * high water mark (free+cache pages).
1515 * v_free_reserved + v_cache_min (mostly means v_cache_min) is the
1516 * low water mark, while v_free_min is the stop. v_cache_min must
1517 * be big enough to handle memory needs while the pageout daemon
1518 * is signalled and run to free more pages.
1520 if (cnt.v_free_count > 6144)
1521 cnt.v_free_target = 4 * cnt.v_free_min + cnt.v_free_reserved;
1523 cnt.v_free_target = 2 * cnt.v_free_min + cnt.v_free_reserved;
1525 if (cnt.v_free_count > 2048) {
1526 cnt.v_cache_min = cnt.v_free_target;
1527 cnt.v_cache_max = 2 * cnt.v_cache_min;
1528 cnt.v_inactive_target = (3 * cnt.v_free_target) / 2;
1530 cnt.v_cache_min = 0;
1531 cnt.v_cache_max = 0;
1532 cnt.v_inactive_target = cnt.v_free_count / 4;
1534 if (cnt.v_inactive_target > cnt.v_free_count / 3)
1535 cnt.v_inactive_target = cnt.v_free_count / 3;
1537 /* XXX does not really belong here */
1538 if (vm_page_max_wired == 0)
1539 vm_page_max_wired = cnt.v_free_count / 3;
1541 if (vm_pageout_stats_max == 0)
1542 vm_pageout_stats_max = cnt.v_free_target;
1545 * Set interval in seconds for stats scan.
1547 if (vm_pageout_stats_interval == 0)
1548 vm_pageout_stats_interval = 5;
1549 if (vm_pageout_full_stats_interval == 0)
1550 vm_pageout_full_stats_interval = vm_pageout_stats_interval * 4;
1552 swap_pager_swap_init();
1555 * The pageout daemon is never done, so loop forever.
1559 * If we have enough free memory, wakeup waiters. Do
1560 * not clear vm_pages_needed until we reach our target,
1561 * otherwise we may be woken up over and over again and
1562 * waste a lot of cpu.
1564 mtx_lock(&vm_page_queue_free_mtx);
1565 if (vm_pages_needed && !vm_page_count_min()) {
1566 if (!vm_paging_needed())
1567 vm_pages_needed = 0;
1568 wakeup(&cnt.v_free_count);
1570 if (vm_pages_needed) {
1572 * Still not done, take a second pass without waiting
1573 * (unlimited dirty cleaning), otherwise sleep a bit
1578 msleep(&vm_pages_needed,
1579 &vm_page_queue_free_mtx, PVM, "psleep",
1583 * Good enough, sleep & handle stats. Prime the pass
1590 error = msleep(&vm_pages_needed,
1591 &vm_page_queue_free_mtx, PVM, "psleep",
1592 vm_pageout_stats_interval * hz);
1593 if (error && !vm_pages_needed) {
1594 mtx_unlock(&vm_page_queue_free_mtx);
1596 vm_pageout_page_stats();
1600 if (vm_pages_needed)
1602 mtx_unlock(&vm_page_queue_free_mtx);
1603 vm_pageout_scan(pass);
1608 * Unless the free page queue lock is held by the caller, this function
1609 * should be regarded as advisory. Specifically, the caller should
1610 * not msleep() on &cnt.v_free_count following this function unless
1611 * the free page queue lock is held until the msleep() is performed.
1617 if (!vm_pages_needed && curthread->td_proc != pageproc) {
1618 vm_pages_needed = 1;
1619 wakeup(&vm_pages_needed);
1623 #if !defined(NO_SWAPPING)
1625 vm_req_vmdaemon(int req)
1627 static int lastrun = 0;
1629 mtx_lock(&vm_daemon_mtx);
1630 vm_pageout_req_swapout |= req;
1631 if ((ticks > (lastrun + hz)) || (ticks < lastrun)) {
1632 wakeup(&vm_daemon_needed);
1635 mtx_unlock(&vm_daemon_mtx);
1641 struct rlimit rsslim;
1645 int breakout, swapout_flags, tryagain, attempts;
1647 uint64_t rsize, ravailable;
1651 mtx_lock(&vm_daemon_mtx);
1653 msleep(&vm_daemon_needed, &vm_daemon_mtx, PPAUSE, "psleep", hz);
1655 msleep(&vm_daemon_needed, &vm_daemon_mtx, PPAUSE, "psleep", 0);
1657 swapout_flags = vm_pageout_req_swapout;
1658 vm_pageout_req_swapout = 0;
1659 mtx_unlock(&vm_daemon_mtx);
1661 swapout_procs(swapout_flags);
1664 * scan the processes for exceeding their rlimits or if
1665 * process is swapped out -- deactivate pages
1671 sx_slock(&allproc_lock);
1672 FOREACH_PROC_IN_SYSTEM(p) {
1673 vm_pindex_t limit, size;
1676 * if this is a system process or if we have already
1677 * looked at this process, skip it.
1680 if (p->p_state != PRS_NORMAL ||
1681 p->p_flag & (P_INEXEC | P_SYSTEM | P_WEXIT)) {
1686 * if the process is in a non-running type state,
1690 FOREACH_THREAD_IN_PROC(p, td) {
1692 if (!TD_ON_RUNQ(td) &&
1693 !TD_IS_RUNNING(td) &&
1694 !TD_IS_SLEEPING(td) &&
1695 !TD_IS_SUSPENDED(td)) {
1709 lim_rlimit(p, RLIMIT_RSS, &rsslim);
1711 qmin(rsslim.rlim_cur, rsslim.rlim_max));
1714 * let processes that are swapped out really be
1715 * swapped out set the limit to nothing (will force a
1718 if ((p->p_flag & P_INMEM) == 0)
1719 limit = 0; /* XXX */
1720 vm = vmspace_acquire_ref(p);
1725 size = vmspace_resident_count(vm);
1726 if (limit >= 0 && size >= limit) {
1727 vm_pageout_map_deactivate_pages(
1728 &vm->vm_map, limit);
1731 rsize = IDX_TO_OFF(size);
1733 racct_set(p, RACCT_RSS, rsize);
1734 ravailable = racct_get_available(p, RACCT_RSS);
1736 if (rsize > ravailable) {
1738 * Don't be overly aggressive; this might be
1739 * an innocent process, and the limit could've
1740 * been exceeded by some memory hog. Don't
1741 * try to deactivate more than 1/4th of process'
1742 * resident set size.
1744 if (attempts <= 8) {
1745 if (ravailable < rsize - (rsize / 4))
1746 ravailable = rsize - (rsize / 4);
1748 vm_pageout_map_deactivate_pages(
1749 &vm->vm_map, OFF_TO_IDX(ravailable));
1750 /* Update RSS usage after paging out. */
1751 size = vmspace_resident_count(vm);
1752 rsize = IDX_TO_OFF(size);
1754 racct_set(p, RACCT_RSS, rsize);
1756 if (rsize > ravailable)
1762 sx_sunlock(&allproc_lock);
1763 if (tryagain != 0 && attempts <= 10)
1767 #endif /* !defined(NO_SWAPPING) */