xref: /freebsd/sys/vm/vm_pageout.c (revision f0408ed054ef74bbe52461a52efc647ed4739158)
1 /*-
2  * SPDX-License-Identifier: (BSD-4-Clause AND MIT-CMU)
3  *
4  * Copyright (c) 1991 Regents of the University of California.
5  * All rights reserved.
6  * Copyright (c) 1994 John S. Dyson
7  * All rights reserved.
8  * Copyright (c) 1994 David Greenman
9  * All rights reserved.
10  * Copyright (c) 2005 Yahoo! Technologies Norway AS
11  * All rights reserved.
12  *
13  * This code is derived from software contributed to Berkeley by
14  * The Mach Operating System project at Carnegie-Mellon University.
15  *
16  * Redistribution and use in source and binary forms, with or without
17  * modification, are permitted provided that the following conditions
18  * are met:
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.
31  *
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
42  * SUCH DAMAGE.
43  *
44  *	from: @(#)vm_pageout.c	7.4 (Berkeley) 5/7/91
45  *
46  *
47  * Copyright (c) 1987, 1990 Carnegie-Mellon University.
48  * All rights reserved.
49  *
50  * Authors: Avadis Tevanian, Jr., Michael Wayne Young
51  *
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.
57  *
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.
61  *
62  * Carnegie Mellon requests users of this software to return to
63  *
64  *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
65  *  School of Computer Science
66  *  Carnegie Mellon University
67  *  Pittsburgh PA 15213-3890
68  *
69  * any improvements or extensions that they make and grant Carnegie the
70  * rights to redistribute these changes.
71  */
72 
73 /*
74  *	The proverbial page-out daemon.
75  */
76 
77 #include <sys/cdefs.h>
78 __FBSDID("$FreeBSD$");
79 
80 #include "opt_vm.h"
81 
82 #include <sys/param.h>
83 #include <sys/systm.h>
84 #include <sys/kernel.h>
85 #include <sys/eventhandler.h>
86 #include <sys/lock.h>
87 #include <sys/mutex.h>
88 #include <sys/proc.h>
89 #include <sys/kthread.h>
90 #include <sys/ktr.h>
91 #include <sys/mount.h>
92 #include <sys/racct.h>
93 #include <sys/resourcevar.h>
94 #include <sys/sched.h>
95 #include <sys/sdt.h>
96 #include <sys/signalvar.h>
97 #include <sys/smp.h>
98 #include <sys/time.h>
99 #include <sys/vnode.h>
100 #include <sys/vmmeter.h>
101 #include <sys/rwlock.h>
102 #include <sys/sx.h>
103 #include <sys/sysctl.h>
104 
105 #include <vm/vm.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/swap_pager.h>
114 #include <vm/vm_extern.h>
115 #include <vm/uma.h>
116 
117 /*
118  * System initialization
119  */
120 
121 /* the kernel process "vm_pageout"*/
122 static void vm_pageout(void);
123 static void vm_pageout_init(void);
124 static int vm_pageout_clean(vm_page_t m, int *numpagedout);
125 static int vm_pageout_cluster(vm_page_t m);
126 static bool vm_pageout_scan(struct vm_domain *vmd, int pass);
127 static void vm_pageout_mightbe_oom(struct vm_domain *vmd, int page_shortage,
128     int starting_page_shortage);
129 
130 SYSINIT(pagedaemon_init, SI_SUB_KTHREAD_PAGE, SI_ORDER_FIRST, vm_pageout_init,
131     NULL);
132 
133 struct proc *pageproc;
134 
135 static struct kproc_desc page_kp = {
136 	"pagedaemon",
137 	vm_pageout,
138 	&pageproc
139 };
140 SYSINIT(pagedaemon, SI_SUB_KTHREAD_PAGE, SI_ORDER_SECOND, kproc_start,
141     &page_kp);
142 
143 SDT_PROVIDER_DEFINE(vm);
144 SDT_PROBE_DEFINE(vm, , , vm__lowmem_scan);
145 
146 /* Pagedaemon activity rates, in subdivisions of one second. */
147 #define	VM_LAUNDER_RATE		10
148 #define	VM_INACT_SCAN_RATE	2
149 
150 int vm_pageout_deficit;		/* Estimated number of pages deficit */
151 u_int vm_pageout_wakeup_thresh;
152 static int vm_pageout_oom_seq = 12;
153 bool vm_pageout_wanted;		/* Event on which pageout daemon sleeps */
154 bool vm_pages_needed;		/* Are threads waiting for free pages? */
155 
156 /* Pending request for dirty page laundering. */
157 static enum {
158 	VM_LAUNDRY_IDLE,
159 	VM_LAUNDRY_BACKGROUND,
160 	VM_LAUNDRY_SHORTFALL
161 } vm_laundry_request = VM_LAUNDRY_IDLE;
162 
163 static int vm_pageout_update_period;
164 static int disable_swap_pageouts;
165 static int lowmem_period = 10;
166 static time_t lowmem_uptime;
167 static int swapdev_enabled;
168 
169 static int vm_panic_on_oom = 0;
170 
171 SYSCTL_INT(_vm, OID_AUTO, panic_on_oom,
172 	CTLFLAG_RWTUN, &vm_panic_on_oom, 0,
173 	"panic on out of memory instead of killing the largest process");
174 
175 SYSCTL_INT(_vm, OID_AUTO, pageout_wakeup_thresh,
176 	CTLFLAG_RWTUN, &vm_pageout_wakeup_thresh, 0,
177 	"free page threshold for waking up the pageout daemon");
178 
179 SYSCTL_INT(_vm, OID_AUTO, pageout_update_period,
180 	CTLFLAG_RWTUN, &vm_pageout_update_period, 0,
181 	"Maximum active LRU update period");
182 
183 SYSCTL_INT(_vm, OID_AUTO, lowmem_period, CTLFLAG_RWTUN, &lowmem_period, 0,
184 	"Low memory callback period");
185 
186 SYSCTL_INT(_vm, OID_AUTO, disable_swapspace_pageouts,
187 	CTLFLAG_RWTUN, &disable_swap_pageouts, 0, "Disallow swapout of dirty pages");
188 
189 static int pageout_lock_miss;
190 SYSCTL_INT(_vm, OID_AUTO, pageout_lock_miss,
191 	CTLFLAG_RD, &pageout_lock_miss, 0, "vget() lock misses during pageout");
192 
193 SYSCTL_INT(_vm, OID_AUTO, pageout_oom_seq,
194 	CTLFLAG_RWTUN, &vm_pageout_oom_seq, 0,
195 	"back-to-back calls to oom detector to start OOM");
196 
197 static int act_scan_laundry_weight = 3;
198 SYSCTL_INT(_vm, OID_AUTO, act_scan_laundry_weight, CTLFLAG_RWTUN,
199     &act_scan_laundry_weight, 0,
200     "weight given to clean vs. dirty pages in active queue scans");
201 
202 static u_int vm_background_launder_target;
203 SYSCTL_UINT(_vm, OID_AUTO, background_launder_target, CTLFLAG_RWTUN,
204     &vm_background_launder_target, 0,
205     "background laundering target, in pages");
206 
207 static u_int vm_background_launder_rate = 4096;
208 SYSCTL_UINT(_vm, OID_AUTO, background_launder_rate, CTLFLAG_RWTUN,
209     &vm_background_launder_rate, 0,
210     "background laundering rate, in kilobytes per second");
211 
212 static u_int vm_background_launder_max = 20 * 1024;
213 SYSCTL_UINT(_vm, OID_AUTO, background_launder_max, CTLFLAG_RWTUN,
214     &vm_background_launder_max, 0, "background laundering cap, in kilobytes");
215 
216 int vm_pageout_page_count = 32;
217 
218 int vm_page_max_wired;		/* XXX max # of wired pages system-wide */
219 SYSCTL_INT(_vm, OID_AUTO, max_wired,
220 	CTLFLAG_RW, &vm_page_max_wired, 0, "System-wide limit to wired page count");
221 
222 static u_int isqrt(u_int num);
223 static boolean_t vm_pageout_fallback_object_lock(vm_page_t, vm_page_t *);
224 static int vm_pageout_launder(struct vm_domain *vmd, int launder,
225     bool in_shortfall);
226 static void vm_pageout_laundry_worker(void *arg);
227 static boolean_t vm_pageout_page_lock(vm_page_t, vm_page_t *);
228 
229 /*
230  * Initialize a dummy page for marking the caller's place in the specified
231  * paging queue.  In principle, this function only needs to set the flag
232  * PG_MARKER.  Nonetheless, it write busies and initializes the hold count
233  * to one as safety precautions.
234  */
235 static void
236 vm_pageout_init_marker(vm_page_t marker, u_short queue)
237 {
238 
239 	bzero(marker, sizeof(*marker));
240 	marker->flags = PG_MARKER;
241 	marker->busy_lock = VPB_SINGLE_EXCLUSIVER;
242 	marker->queue = queue;
243 	marker->hold_count = 1;
244 }
245 
246 /*
247  * vm_pageout_fallback_object_lock:
248  *
249  * Lock vm object currently associated with `m'. VM_OBJECT_TRYWLOCK is
250  * known to have failed and page queue must be either PQ_ACTIVE or
251  * PQ_INACTIVE.  To avoid lock order violation, unlock the page queue
252  * while locking the vm object.  Use marker page to detect page queue
253  * changes and maintain notion of next page on page queue.  Return
254  * TRUE if no changes were detected, FALSE otherwise.  vm object is
255  * locked on return.
256  *
257  * This function depends on both the lock portion of struct vm_object
258  * and normal struct vm_page being type stable.
259  */
260 static boolean_t
261 vm_pageout_fallback_object_lock(vm_page_t m, vm_page_t *next)
262 {
263 	struct vm_page marker;
264 	struct vm_pagequeue *pq;
265 	boolean_t unchanged;
266 	u_short queue;
267 	vm_object_t object;
268 
269 	queue = m->queue;
270 	vm_pageout_init_marker(&marker, queue);
271 	pq = vm_page_pagequeue(m);
272 	object = m->object;
273 
274 	TAILQ_INSERT_AFTER(&pq->pq_pl, m, &marker, plinks.q);
275 	vm_pagequeue_unlock(pq);
276 	vm_page_unlock(m);
277 	VM_OBJECT_WLOCK(object);
278 	vm_page_lock(m);
279 	vm_pagequeue_lock(pq);
280 
281 	/*
282 	 * The page's object might have changed, and/or the page might
283 	 * have moved from its original position in the queue.  If the
284 	 * page's object has changed, then the caller should abandon
285 	 * processing the page because the wrong object lock was
286 	 * acquired.  Use the marker's plinks.q, not the page's, to
287 	 * determine if the page has been moved.  The state of the
288 	 * page's plinks.q can be indeterminate; whereas, the marker's
289 	 * plinks.q must be valid.
290 	 */
291 	*next = TAILQ_NEXT(&marker, plinks.q);
292 	unchanged = m->object == object &&
293 	    m == TAILQ_PREV(&marker, pglist, plinks.q);
294 	KASSERT(!unchanged || m->queue == queue,
295 	    ("page %p queue %d %d", m, queue, m->queue));
296 	TAILQ_REMOVE(&pq->pq_pl, &marker, plinks.q);
297 	return (unchanged);
298 }
299 
300 /*
301  * Lock the page while holding the page queue lock.  Use marker page
302  * to detect page queue changes and maintain notion of next page on
303  * page queue.  Return TRUE if no changes were detected, FALSE
304  * otherwise.  The page is locked on return. The page queue lock might
305  * be dropped and reacquired.
306  *
307  * This function depends on normal struct vm_page being type stable.
308  */
309 static boolean_t
310 vm_pageout_page_lock(vm_page_t m, vm_page_t *next)
311 {
312 	struct vm_page marker;
313 	struct vm_pagequeue *pq;
314 	boolean_t unchanged;
315 	u_short queue;
316 
317 	vm_page_lock_assert(m, MA_NOTOWNED);
318 	if (vm_page_trylock(m))
319 		return (TRUE);
320 
321 	queue = m->queue;
322 	vm_pageout_init_marker(&marker, queue);
323 	pq = vm_page_pagequeue(m);
324 
325 	TAILQ_INSERT_AFTER(&pq->pq_pl, m, &marker, plinks.q);
326 	vm_pagequeue_unlock(pq);
327 	vm_page_lock(m);
328 	vm_pagequeue_lock(pq);
329 
330 	/* Page queue might have changed. */
331 	*next = TAILQ_NEXT(&marker, plinks.q);
332 	unchanged = m == TAILQ_PREV(&marker, pglist, plinks.q);
333 	KASSERT(!unchanged || m->queue == queue,
334 	    ("page %p queue %d %d", m, queue, m->queue));
335 	TAILQ_REMOVE(&pq->pq_pl, &marker, plinks.q);
336 	return (unchanged);
337 }
338 
339 /*
340  * Scan for pages at adjacent offsets within the given page's object that are
341  * eligible for laundering, form a cluster of these pages and the given page,
342  * and launder that cluster.
343  */
344 static int
345 vm_pageout_cluster(vm_page_t m)
346 {
347 	vm_object_t object;
348 	vm_page_t mc[2 * vm_pageout_page_count], p, pb, ps;
349 	vm_pindex_t pindex;
350 	int ib, is, page_base, pageout_count;
351 
352 	vm_page_assert_locked(m);
353 	object = m->object;
354 	VM_OBJECT_ASSERT_WLOCKED(object);
355 	pindex = m->pindex;
356 
357 	/*
358 	 * We can't clean the page if it is busy or held.
359 	 */
360 	vm_page_assert_unbusied(m);
361 	KASSERT(m->hold_count == 0, ("page %p is held", m));
362 
363 	pmap_remove_write(m);
364 	vm_page_unlock(m);
365 
366 	mc[vm_pageout_page_count] = pb = ps = m;
367 	pageout_count = 1;
368 	page_base = vm_pageout_page_count;
369 	ib = 1;
370 	is = 1;
371 
372 	/*
373 	 * We can cluster only if the page is not clean, busy, or held, and
374 	 * the page is in the laundry queue.
375 	 *
376 	 * During heavy mmap/modification loads the pageout
377 	 * daemon can really fragment the underlying file
378 	 * due to flushing pages out of order and not trying to
379 	 * align the clusters (which leaves sporadic out-of-order
380 	 * holes).  To solve this problem we do the reverse scan
381 	 * first and attempt to align our cluster, then do a
382 	 * forward scan if room remains.
383 	 */
384 more:
385 	while (ib != 0 && pageout_count < vm_pageout_page_count) {
386 		if (ib > pindex) {
387 			ib = 0;
388 			break;
389 		}
390 		if ((p = vm_page_prev(pb)) == NULL || vm_page_busied(p)) {
391 			ib = 0;
392 			break;
393 		}
394 		vm_page_test_dirty(p);
395 		if (p->dirty == 0) {
396 			ib = 0;
397 			break;
398 		}
399 		vm_page_lock(p);
400 		if (!vm_page_in_laundry(p) ||
401 		    p->hold_count != 0) {	/* may be undergoing I/O */
402 			vm_page_unlock(p);
403 			ib = 0;
404 			break;
405 		}
406 		pmap_remove_write(p);
407 		vm_page_unlock(p);
408 		mc[--page_base] = pb = p;
409 		++pageout_count;
410 		++ib;
411 
412 		/*
413 		 * We are at an alignment boundary.  Stop here, and switch
414 		 * directions.  Do not clear ib.
415 		 */
416 		if ((pindex - (ib - 1)) % vm_pageout_page_count == 0)
417 			break;
418 	}
419 	while (pageout_count < vm_pageout_page_count &&
420 	    pindex + is < object->size) {
421 		if ((p = vm_page_next(ps)) == NULL || vm_page_busied(p))
422 			break;
423 		vm_page_test_dirty(p);
424 		if (p->dirty == 0)
425 			break;
426 		vm_page_lock(p);
427 		if (!vm_page_in_laundry(p) ||
428 		    p->hold_count != 0) {	/* may be undergoing I/O */
429 			vm_page_unlock(p);
430 			break;
431 		}
432 		pmap_remove_write(p);
433 		vm_page_unlock(p);
434 		mc[page_base + pageout_count] = ps = p;
435 		++pageout_count;
436 		++is;
437 	}
438 
439 	/*
440 	 * If we exhausted our forward scan, continue with the reverse scan
441 	 * when possible, even past an alignment boundary.  This catches
442 	 * boundary conditions.
443 	 */
444 	if (ib != 0 && pageout_count < vm_pageout_page_count)
445 		goto more;
446 
447 	return (vm_pageout_flush(&mc[page_base], pageout_count,
448 	    VM_PAGER_PUT_NOREUSE, 0, NULL, NULL));
449 }
450 
451 /*
452  * vm_pageout_flush() - launder the given pages
453  *
454  *	The given pages are laundered.  Note that we setup for the start of
455  *	I/O ( i.e. busy the page ), mark it read-only, and bump the object
456  *	reference count all in here rather then in the parent.  If we want
457  *	the parent to do more sophisticated things we may have to change
458  *	the ordering.
459  *
460  *	Returned runlen is the count of pages between mreq and first
461  *	page after mreq with status VM_PAGER_AGAIN.
462  *	*eio is set to TRUE if pager returned VM_PAGER_ERROR or VM_PAGER_FAIL
463  *	for any page in runlen set.
464  */
465 int
466 vm_pageout_flush(vm_page_t *mc, int count, int flags, int mreq, int *prunlen,
467     boolean_t *eio)
468 {
469 	vm_object_t object = mc[0]->object;
470 	int pageout_status[count];
471 	int numpagedout = 0;
472 	int i, runlen;
473 
474 	VM_OBJECT_ASSERT_WLOCKED(object);
475 
476 	/*
477 	 * Initiate I/O.  Mark the pages busy and verify that they're valid
478 	 * and read-only.
479 	 *
480 	 * We do not have to fixup the clean/dirty bits here... we can
481 	 * allow the pager to do it after the I/O completes.
482 	 *
483 	 * NOTE! mc[i]->dirty may be partial or fragmented due to an
484 	 * edge case with file fragments.
485 	 */
486 	for (i = 0; i < count; i++) {
487 		KASSERT(mc[i]->valid == VM_PAGE_BITS_ALL,
488 		    ("vm_pageout_flush: partially invalid page %p index %d/%d",
489 			mc[i], i, count));
490 		KASSERT((mc[i]->aflags & PGA_WRITEABLE) == 0,
491 		    ("vm_pageout_flush: writeable page %p", mc[i]));
492 		vm_page_sbusy(mc[i]);
493 	}
494 	vm_object_pip_add(object, count);
495 
496 	vm_pager_put_pages(object, mc, count, flags, pageout_status);
497 
498 	runlen = count - mreq;
499 	if (eio != NULL)
500 		*eio = FALSE;
501 	for (i = 0; i < count; i++) {
502 		vm_page_t mt = mc[i];
503 
504 		KASSERT(pageout_status[i] == VM_PAGER_PEND ||
505 		    !pmap_page_is_write_mapped(mt),
506 		    ("vm_pageout_flush: page %p is not write protected", mt));
507 		switch (pageout_status[i]) {
508 		case VM_PAGER_OK:
509 			vm_page_lock(mt);
510 			if (vm_page_in_laundry(mt))
511 				vm_page_deactivate_noreuse(mt);
512 			vm_page_unlock(mt);
513 			/* FALLTHROUGH */
514 		case VM_PAGER_PEND:
515 			numpagedout++;
516 			break;
517 		case VM_PAGER_BAD:
518 			/*
519 			 * The page is outside the object's range.  We pretend
520 			 * that the page out worked and clean the page, so the
521 			 * changes will be lost if the page is reclaimed by
522 			 * the page daemon.
523 			 */
524 			vm_page_undirty(mt);
525 			vm_page_lock(mt);
526 			if (vm_page_in_laundry(mt))
527 				vm_page_deactivate_noreuse(mt);
528 			vm_page_unlock(mt);
529 			break;
530 		case VM_PAGER_ERROR:
531 		case VM_PAGER_FAIL:
532 			/*
533 			 * If the page couldn't be paged out to swap because the
534 			 * pager wasn't able to find space, place the page in
535 			 * the PQ_UNSWAPPABLE holding queue.  This is an
536 			 * optimization that prevents the page daemon from
537 			 * wasting CPU cycles on pages that cannot be reclaimed
538 			 * becase no swap device is configured.
539 			 *
540 			 * Otherwise, reactivate the page so that it doesn't
541 			 * clog the laundry and inactive queues.  (We will try
542 			 * paging it out again later.)
543 			 */
544 			vm_page_lock(mt);
545 			if (object->type == OBJT_SWAP &&
546 			    pageout_status[i] == VM_PAGER_FAIL) {
547 				vm_page_unswappable(mt);
548 				numpagedout++;
549 			} else
550 				vm_page_activate(mt);
551 			vm_page_unlock(mt);
552 			if (eio != NULL && i >= mreq && i - mreq < runlen)
553 				*eio = TRUE;
554 			break;
555 		case VM_PAGER_AGAIN:
556 			if (i >= mreq && i - mreq < runlen)
557 				runlen = i - mreq;
558 			break;
559 		}
560 
561 		/*
562 		 * If the operation is still going, leave the page busy to
563 		 * block all other accesses. Also, leave the paging in
564 		 * progress indicator set so that we don't attempt an object
565 		 * collapse.
566 		 */
567 		if (pageout_status[i] != VM_PAGER_PEND) {
568 			vm_object_pip_wakeup(object);
569 			vm_page_sunbusy(mt);
570 		}
571 	}
572 	if (prunlen != NULL)
573 		*prunlen = runlen;
574 	return (numpagedout);
575 }
576 
577 static void
578 vm_pageout_swapon(void *arg __unused, struct swdevt *sp __unused)
579 {
580 
581 	atomic_store_rel_int(&swapdev_enabled, 1);
582 }
583 
584 static void
585 vm_pageout_swapoff(void *arg __unused, struct swdevt *sp __unused)
586 {
587 
588 	if (swap_pager_nswapdev() == 1)
589 		atomic_store_rel_int(&swapdev_enabled, 0);
590 }
591 
592 /*
593  * Attempt to acquire all of the necessary locks to launder a page and
594  * then call through the clustering layer to PUTPAGES.  Wait a short
595  * time for a vnode lock.
596  *
597  * Requires the page and object lock on entry, releases both before return.
598  * Returns 0 on success and an errno otherwise.
599  */
600 static int
601 vm_pageout_clean(vm_page_t m, int *numpagedout)
602 {
603 	struct vnode *vp;
604 	struct mount *mp;
605 	vm_object_t object;
606 	vm_pindex_t pindex;
607 	int error, lockmode;
608 
609 	vm_page_assert_locked(m);
610 	object = m->object;
611 	VM_OBJECT_ASSERT_WLOCKED(object);
612 	error = 0;
613 	vp = NULL;
614 	mp = NULL;
615 
616 	/*
617 	 * The object is already known NOT to be dead.   It
618 	 * is possible for the vget() to block the whole
619 	 * pageout daemon, but the new low-memory handling
620 	 * code should prevent it.
621 	 *
622 	 * We can't wait forever for the vnode lock, we might
623 	 * deadlock due to a vn_read() getting stuck in
624 	 * vm_wait while holding this vnode.  We skip the
625 	 * vnode if we can't get it in a reasonable amount
626 	 * of time.
627 	 */
628 	if (object->type == OBJT_VNODE) {
629 		vm_page_unlock(m);
630 		vp = object->handle;
631 		if (vp->v_type == VREG &&
632 		    vn_start_write(vp, &mp, V_NOWAIT) != 0) {
633 			mp = NULL;
634 			error = EDEADLK;
635 			goto unlock_all;
636 		}
637 		KASSERT(mp != NULL,
638 		    ("vp %p with NULL v_mount", vp));
639 		vm_object_reference_locked(object);
640 		pindex = m->pindex;
641 		VM_OBJECT_WUNLOCK(object);
642 		lockmode = MNT_SHARED_WRITES(vp->v_mount) ?
643 		    LK_SHARED : LK_EXCLUSIVE;
644 		if (vget(vp, lockmode | LK_TIMELOCK, curthread)) {
645 			vp = NULL;
646 			error = EDEADLK;
647 			goto unlock_mp;
648 		}
649 		VM_OBJECT_WLOCK(object);
650 
651 		/*
652 		 * Ensure that the object and vnode were not disassociated
653 		 * while locks were dropped.
654 		 */
655 		if (vp->v_object != object) {
656 			error = ENOENT;
657 			goto unlock_all;
658 		}
659 		vm_page_lock(m);
660 
661 		/*
662 		 * While the object and page were unlocked, the page
663 		 * may have been:
664 		 * (1) moved to a different queue,
665 		 * (2) reallocated to a different object,
666 		 * (3) reallocated to a different offset, or
667 		 * (4) cleaned.
668 		 */
669 		if (!vm_page_in_laundry(m) || m->object != object ||
670 		    m->pindex != pindex || m->dirty == 0) {
671 			vm_page_unlock(m);
672 			error = ENXIO;
673 			goto unlock_all;
674 		}
675 
676 		/*
677 		 * The page may have been busied or held while the object
678 		 * and page locks were released.
679 		 */
680 		if (vm_page_busied(m) || m->hold_count != 0) {
681 			vm_page_unlock(m);
682 			error = EBUSY;
683 			goto unlock_all;
684 		}
685 	}
686 
687 	/*
688 	 * If a page is dirty, then it is either being washed
689 	 * (but not yet cleaned) or it is still in the
690 	 * laundry.  If it is still in the laundry, then we
691 	 * start the cleaning operation.
692 	 */
693 	if ((*numpagedout = vm_pageout_cluster(m)) == 0)
694 		error = EIO;
695 
696 unlock_all:
697 	VM_OBJECT_WUNLOCK(object);
698 
699 unlock_mp:
700 	vm_page_lock_assert(m, MA_NOTOWNED);
701 	if (mp != NULL) {
702 		if (vp != NULL)
703 			vput(vp);
704 		vm_object_deallocate(object);
705 		vn_finished_write(mp);
706 	}
707 
708 	return (error);
709 }
710 
711 /*
712  * Attempt to launder the specified number of pages.
713  *
714  * Returns the number of pages successfully laundered.
715  */
716 static int
717 vm_pageout_launder(struct vm_domain *vmd, int launder, bool in_shortfall)
718 {
719 	struct vm_pagequeue *pq;
720 	vm_object_t object;
721 	vm_page_t m, next;
722 	int act_delta, error, maxscan, numpagedout, starting_target;
723 	int vnodes_skipped;
724 	bool pageout_ok, queue_locked;
725 
726 	starting_target = launder;
727 	vnodes_skipped = 0;
728 
729 	/*
730 	 * Scan the laundry queues for pages eligible to be laundered.  We stop
731 	 * once the target number of dirty pages have been laundered, or once
732 	 * we've reached the end of the queue.  A single iteration of this loop
733 	 * may cause more than one page to be laundered because of clustering.
734 	 *
735 	 * maxscan ensures that we don't re-examine requeued pages.  Any
736 	 * additional pages written as part of a cluster are subtracted from
737 	 * maxscan since they must be taken from the laundry queue.
738 	 *
739 	 * As an optimization, we avoid laundering from PQ_UNSWAPPABLE when no
740 	 * swap devices are configured.
741 	 */
742 	if (atomic_load_acq_int(&swapdev_enabled))
743 		pq = &vmd->vmd_pagequeues[PQ_UNSWAPPABLE];
744 	else
745 		pq = &vmd->vmd_pagequeues[PQ_LAUNDRY];
746 
747 scan:
748 	vm_pagequeue_lock(pq);
749 	maxscan = pq->pq_cnt;
750 	queue_locked = true;
751 	for (m = TAILQ_FIRST(&pq->pq_pl);
752 	    m != NULL && maxscan-- > 0 && launder > 0;
753 	    m = next) {
754 		vm_pagequeue_assert_locked(pq);
755 		KASSERT(queue_locked, ("unlocked laundry queue"));
756 		KASSERT(vm_page_in_laundry(m),
757 		    ("page %p has an inconsistent queue", m));
758 		next = TAILQ_NEXT(m, plinks.q);
759 		if ((m->flags & PG_MARKER) != 0)
760 			continue;
761 		KASSERT((m->flags & PG_FICTITIOUS) == 0,
762 		    ("PG_FICTITIOUS page %p cannot be in laundry queue", m));
763 		KASSERT((m->oflags & VPO_UNMANAGED) == 0,
764 		    ("VPO_UNMANAGED page %p cannot be in laundry queue", m));
765 		if (!vm_pageout_page_lock(m, &next) || m->hold_count != 0) {
766 			vm_page_unlock(m);
767 			continue;
768 		}
769 		object = m->object;
770 		if ((!VM_OBJECT_TRYWLOCK(object) &&
771 		    (!vm_pageout_fallback_object_lock(m, &next) ||
772 		    m->hold_count != 0)) || vm_page_busied(m)) {
773 			VM_OBJECT_WUNLOCK(object);
774 			vm_page_unlock(m);
775 			continue;
776 		}
777 
778 		/*
779 		 * Unlock the laundry queue, invalidating the 'next' pointer.
780 		 * Use a marker to remember our place in the laundry queue.
781 		 */
782 		TAILQ_INSERT_AFTER(&pq->pq_pl, m, &vmd->vmd_laundry_marker,
783 		    plinks.q);
784 		vm_pagequeue_unlock(pq);
785 		queue_locked = false;
786 
787 		/*
788 		 * Invalid pages can be easily freed.  They cannot be
789 		 * mapped; vm_page_free() asserts this.
790 		 */
791 		if (m->valid == 0)
792 			goto free_page;
793 
794 		/*
795 		 * If the page has been referenced and the object is not dead,
796 		 * reactivate or requeue the page depending on whether the
797 		 * object is mapped.
798 		 */
799 		if ((m->aflags & PGA_REFERENCED) != 0) {
800 			vm_page_aflag_clear(m, PGA_REFERENCED);
801 			act_delta = 1;
802 		} else
803 			act_delta = 0;
804 		if (object->ref_count != 0)
805 			act_delta += pmap_ts_referenced(m);
806 		else {
807 			KASSERT(!pmap_page_is_mapped(m),
808 			    ("page %p is mapped", m));
809 		}
810 		if (act_delta != 0) {
811 			if (object->ref_count != 0) {
812 				VM_CNT_INC(v_reactivated);
813 				vm_page_activate(m);
814 
815 				/*
816 				 * Increase the activation count if the page
817 				 * was referenced while in the laundry queue.
818 				 * This makes it less likely that the page will
819 				 * be returned prematurely to the inactive
820 				 * queue.
821  				 */
822 				m->act_count += act_delta + ACT_ADVANCE;
823 
824 				/*
825 				 * If this was a background laundering, count
826 				 * activated pages towards our target.  The
827 				 * purpose of background laundering is to ensure
828 				 * that pages are eventually cycled through the
829 				 * laundry queue, and an activation is a valid
830 				 * way out.
831 				 */
832 				if (!in_shortfall)
833 					launder--;
834 				goto drop_page;
835 			} else if ((object->flags & OBJ_DEAD) == 0)
836 				goto requeue_page;
837 		}
838 
839 		/*
840 		 * If the page appears to be clean at the machine-independent
841 		 * layer, then remove all of its mappings from the pmap in
842 		 * anticipation of freeing it.  If, however, any of the page's
843 		 * mappings allow write access, then the page may still be
844 		 * modified until the last of those mappings are removed.
845 		 */
846 		if (object->ref_count != 0) {
847 			vm_page_test_dirty(m);
848 			if (m->dirty == 0)
849 				pmap_remove_all(m);
850 		}
851 
852 		/*
853 		 * Clean pages are freed, and dirty pages are paged out unless
854 		 * they belong to a dead object.  Requeueing dirty pages from
855 		 * dead objects is pointless, as they are being paged out and
856 		 * freed by the thread that destroyed the object.
857 		 */
858 		if (m->dirty == 0) {
859 free_page:
860 			vm_page_free(m);
861 			VM_CNT_INC(v_dfree);
862 		} else if ((object->flags & OBJ_DEAD) == 0) {
863 			if (object->type != OBJT_SWAP &&
864 			    object->type != OBJT_DEFAULT)
865 				pageout_ok = true;
866 			else if (disable_swap_pageouts)
867 				pageout_ok = false;
868 			else
869 				pageout_ok = true;
870 			if (!pageout_ok) {
871 requeue_page:
872 				vm_pagequeue_lock(pq);
873 				queue_locked = true;
874 				vm_page_requeue_locked(m);
875 				goto drop_page;
876 			}
877 
878 			/*
879 			 * Form a cluster with adjacent, dirty pages from the
880 			 * same object, and page out that entire cluster.
881 			 *
882 			 * The adjacent, dirty pages must also be in the
883 			 * laundry.  However, their mappings are not checked
884 			 * for new references.  Consequently, a recently
885 			 * referenced page may be paged out.  However, that
886 			 * page will not be prematurely reclaimed.  After page
887 			 * out, the page will be placed in the inactive queue,
888 			 * where any new references will be detected and the
889 			 * page reactivated.
890 			 */
891 			error = vm_pageout_clean(m, &numpagedout);
892 			if (error == 0) {
893 				launder -= numpagedout;
894 				maxscan -= numpagedout - 1;
895 			} else if (error == EDEADLK) {
896 				pageout_lock_miss++;
897 				vnodes_skipped++;
898 			}
899 			goto relock_queue;
900 		}
901 drop_page:
902 		vm_page_unlock(m);
903 		VM_OBJECT_WUNLOCK(object);
904 relock_queue:
905 		if (!queue_locked) {
906 			vm_pagequeue_lock(pq);
907 			queue_locked = true;
908 		}
909 		next = TAILQ_NEXT(&vmd->vmd_laundry_marker, plinks.q);
910 		TAILQ_REMOVE(&pq->pq_pl, &vmd->vmd_laundry_marker, plinks.q);
911 	}
912 	vm_pagequeue_unlock(pq);
913 
914 	if (launder > 0 && pq == &vmd->vmd_pagequeues[PQ_UNSWAPPABLE]) {
915 		pq = &vmd->vmd_pagequeues[PQ_LAUNDRY];
916 		goto scan;
917 	}
918 
919 	/*
920 	 * Wakeup the sync daemon if we skipped a vnode in a writeable object
921 	 * and we didn't launder enough pages.
922 	 */
923 	if (vnodes_skipped > 0 && launder > 0)
924 		(void)speedup_syncer();
925 
926 	return (starting_target - launder);
927 }
928 
929 /*
930  * Compute the integer square root.
931  */
932 static u_int
933 isqrt(u_int num)
934 {
935 	u_int bit, root, tmp;
936 
937 	bit = 1u << ((NBBY * sizeof(u_int)) - 2);
938 	while (bit > num)
939 		bit >>= 2;
940 	root = 0;
941 	while (bit != 0) {
942 		tmp = root + bit;
943 		root >>= 1;
944 		if (num >= tmp) {
945 			num -= tmp;
946 			root += bit;
947 		}
948 		bit >>= 2;
949 	}
950 	return (root);
951 }
952 
953 /*
954  * Perform the work of the laundry thread: periodically wake up and determine
955  * whether any pages need to be laundered.  If so, determine the number of pages
956  * that need to be laundered, and launder them.
957  */
958 static void
959 vm_pageout_laundry_worker(void *arg)
960 {
961 	struct vm_domain *domain;
962 	struct vm_pagequeue *pq;
963 	uint64_t nclean, ndirty;
964 	u_int last_launder, wakeups;
965 	int domidx, last_target, launder, shortfall, shortfall_cycle, target;
966 	bool in_shortfall;
967 
968 	domidx = (uintptr_t)arg;
969 	domain = &vm_dom[domidx];
970 	pq = &domain->vmd_pagequeues[PQ_LAUNDRY];
971 	KASSERT(domain->vmd_segs != 0, ("domain without segments"));
972 	vm_pageout_init_marker(&domain->vmd_laundry_marker, PQ_LAUNDRY);
973 
974 	shortfall = 0;
975 	in_shortfall = false;
976 	shortfall_cycle = 0;
977 	target = 0;
978 	last_launder = 0;
979 
980 	/*
981 	 * Calls to these handlers are serialized by the swap syscall lock.
982 	 */
983 	(void)EVENTHANDLER_REGISTER(swapon, vm_pageout_swapon, domain,
984 	    EVENTHANDLER_PRI_ANY);
985 	(void)EVENTHANDLER_REGISTER(swapoff, vm_pageout_swapoff, domain,
986 	    EVENTHANDLER_PRI_ANY);
987 
988 	/*
989 	 * The pageout laundry worker is never done, so loop forever.
990 	 */
991 	for (;;) {
992 		KASSERT(target >= 0, ("negative target %d", target));
993 		KASSERT(shortfall_cycle >= 0,
994 		    ("negative cycle %d", shortfall_cycle));
995 		launder = 0;
996 		wakeups = VM_CNT_FETCH(v_pdwakeups);
997 
998 		/*
999 		 * First determine whether we need to launder pages to meet a
1000 		 * shortage of free pages.
1001 		 */
1002 		if (shortfall > 0) {
1003 			in_shortfall = true;
1004 			shortfall_cycle = VM_LAUNDER_RATE / VM_INACT_SCAN_RATE;
1005 			target = shortfall;
1006 		} else if (!in_shortfall)
1007 			goto trybackground;
1008 		else if (shortfall_cycle == 0 || vm_laundry_target() <= 0) {
1009 			/*
1010 			 * We recently entered shortfall and began laundering
1011 			 * pages.  If we have completed that laundering run
1012 			 * (and we are no longer in shortfall) or we have met
1013 			 * our laundry target through other activity, then we
1014 			 * can stop laundering pages.
1015 			 */
1016 			in_shortfall = false;
1017 			target = 0;
1018 			goto trybackground;
1019 		}
1020 		last_launder = wakeups;
1021 		launder = target / shortfall_cycle--;
1022 		goto dolaundry;
1023 
1024 		/*
1025 		 * There's no immediate need to launder any pages; see if we
1026 		 * meet the conditions to perform background laundering:
1027 		 *
1028 		 * 1. The ratio of dirty to clean inactive pages exceeds the
1029 		 *    background laundering threshold and the pagedaemon has
1030 		 *    been woken up to reclaim pages since our last
1031 		 *    laundering, or
1032 		 * 2. we haven't yet reached the target of the current
1033 		 *    background laundering run.
1034 		 *
1035 		 * The background laundering threshold is not a constant.
1036 		 * Instead, it is a slowly growing function of the number of
1037 		 * page daemon wakeups since the last laundering.  Thus, as the
1038 		 * ratio of dirty to clean inactive pages grows, the amount of
1039 		 * memory pressure required to trigger laundering decreases.
1040 		 */
1041 trybackground:
1042 		nclean = vm_cnt.v_inactive_count + vm_cnt.v_free_count;
1043 		ndirty = vm_cnt.v_laundry_count;
1044 		if (target == 0 && wakeups != last_launder &&
1045 		    ndirty * isqrt(wakeups - last_launder) >= nclean) {
1046 			target = vm_background_launder_target;
1047 		}
1048 
1049 		/*
1050 		 * We have a non-zero background laundering target.  If we've
1051 		 * laundered up to our maximum without observing a page daemon
1052 		 * wakeup, 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.
1056 		 */
1057 		if (target > 0) {
1058 			if (wakeups != last_launder) {
1059 				last_launder = wakeups;
1060 				last_target = target;
1061 			} else if (last_target - target >=
1062 			    vm_background_launder_max * PAGE_SIZE / 1024) {
1063 				target = 0;
1064 			}
1065 			launder = vm_background_launder_rate * PAGE_SIZE / 1024;
1066 			launder /= VM_LAUNDER_RATE;
1067 			if (launder > target)
1068 				launder = target;
1069 		}
1070 
1071 dolaundry:
1072 		if (launder > 0) {
1073 			/*
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.
1077 			 */
1078 			target -= min(vm_pageout_launder(domain, launder,
1079 			    in_shortfall), target);
1080 			pause("laundp", hz / VM_LAUNDER_RATE);
1081 		}
1082 
1083 		/*
1084 		 * If we're not currently laundering pages and the page daemon
1085 		 * hasn't posted a new request, sleep until the page daemon
1086 		 * kicks us.
1087 		 */
1088 		vm_pagequeue_lock(pq);
1089 		if (target == 0 && vm_laundry_request == VM_LAUNDRY_IDLE)
1090 			(void)mtx_sleep(&vm_laundry_request,
1091 			    vm_pagequeue_lockptr(pq), PVM, "launds", 0);
1092 
1093 		/*
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.
1097 		 */
1098 		if (vm_laundry_request == VM_LAUNDRY_SHORTFALL &&
1099 		    (!in_shortfall || shortfall_cycle == 0)) {
1100 			shortfall = vm_laundry_target() + vm_pageout_deficit;
1101 			target = 0;
1102 		} else
1103 			shortfall = 0;
1104 
1105 		if (target == 0)
1106 			vm_laundry_request = VM_LAUNDRY_IDLE;
1107 		vm_pagequeue_unlock(pq);
1108 	}
1109 }
1110 
1111 /*
1112  *	vm_pageout_scan does the dirty work for the pageout daemon.
1113  *
1114  *	pass == 0: Update active LRU/deactivate pages
1115  *	pass >= 1: Free inactive pages
1116  *
1117  * Returns true if pass was zero or enough pages were freed by the inactive
1118  * queue scan to meet the target.
1119  */
1120 static bool
1121 vm_pageout_scan(struct vm_domain *vmd, int pass)
1122 {
1123 	vm_page_t m, next;
1124 	struct vm_pagequeue *pq;
1125 	vm_object_t object;
1126 	long min_scan;
1127 	int act_delta, addl_page_shortage, deficit, inactq_shortage, maxscan;
1128 	int page_shortage, scan_tick, scanned, starting_page_shortage;
1129 	boolean_t queue_locked;
1130 
1131 	/*
1132 	 * If we need to reclaim memory ask kernel caches to return
1133 	 * some.  We rate limit to avoid thrashing.
1134 	 */
1135 	if (vmd == &vm_dom[0] && pass > 0 &&
1136 	    (time_uptime - lowmem_uptime) >= lowmem_period) {
1137 		/*
1138 		 * Decrease registered cache sizes.
1139 		 */
1140 		SDT_PROBE0(vm, , , vm__lowmem_scan);
1141 		EVENTHANDLER_INVOKE(vm_lowmem, VM_LOW_PAGES);
1142 		/*
1143 		 * We do this explicitly after the caches have been
1144 		 * drained above.
1145 		 */
1146 		uma_reclaim();
1147 		lowmem_uptime = time_uptime;
1148 	}
1149 
1150 	/*
1151 	 * The addl_page_shortage is the number of temporarily
1152 	 * stuck pages in the inactive queue.  In other words, the
1153 	 * number of pages from the inactive count that should be
1154 	 * discounted in setting the target for the active queue scan.
1155 	 */
1156 	addl_page_shortage = 0;
1157 
1158 	/*
1159 	 * Calculate the number of pages that we want to free.  This number
1160 	 * can be negative if many pages are freed between the wakeup call to
1161 	 * the page daemon and this calculation.
1162 	 */
1163 	if (pass > 0) {
1164 		deficit = atomic_readandclear_int(&vm_pageout_deficit);
1165 		page_shortage = vm_paging_target() + deficit;
1166 	} else
1167 		page_shortage = deficit = 0;
1168 	starting_page_shortage = page_shortage;
1169 
1170 	/*
1171 	 * Start scanning the inactive queue for pages that we can free.  The
1172 	 * scan will stop when we reach the target or we have scanned the
1173 	 * entire queue.  (Note that m->act_count is not used to make
1174 	 * decisions for the inactive queue, only for the active queue.)
1175 	 */
1176 	pq = &vmd->vmd_pagequeues[PQ_INACTIVE];
1177 	maxscan = pq->pq_cnt;
1178 	vm_pagequeue_lock(pq);
1179 	queue_locked = TRUE;
1180 	for (m = TAILQ_FIRST(&pq->pq_pl);
1181 	     m != NULL && maxscan-- > 0 && page_shortage > 0;
1182 	     m = next) {
1183 		vm_pagequeue_assert_locked(pq);
1184 		KASSERT(queue_locked, ("unlocked inactive queue"));
1185 		KASSERT(vm_page_inactive(m), ("Inactive queue %p", m));
1186 
1187 		VM_CNT_INC(v_pdpages);
1188 		next = TAILQ_NEXT(m, plinks.q);
1189 
1190 		/*
1191 		 * skip marker pages
1192 		 */
1193 		if (m->flags & PG_MARKER)
1194 			continue;
1195 
1196 		KASSERT((m->flags & PG_FICTITIOUS) == 0,
1197 		    ("Fictitious page %p cannot be in inactive queue", m));
1198 		KASSERT((m->oflags & VPO_UNMANAGED) == 0,
1199 		    ("Unmanaged page %p cannot be in inactive queue", m));
1200 
1201 		/*
1202 		 * The page or object lock acquisitions fail if the
1203 		 * page was removed from the queue or moved to a
1204 		 * different position within the queue.  In either
1205 		 * case, addl_page_shortage should not be incremented.
1206 		 */
1207 		if (!vm_pageout_page_lock(m, &next))
1208 			goto unlock_page;
1209 		else if (m->hold_count != 0) {
1210 			/*
1211 			 * Held pages are essentially stuck in the
1212 			 * queue.  So, they ought to be discounted
1213 			 * from the inactive count.  See the
1214 			 * calculation of inactq_shortage before the
1215 			 * loop over the active queue below.
1216 			 */
1217 			addl_page_shortage++;
1218 			goto unlock_page;
1219 		}
1220 		object = m->object;
1221 		if (!VM_OBJECT_TRYWLOCK(object)) {
1222 			if (!vm_pageout_fallback_object_lock(m, &next))
1223 				goto unlock_object;
1224 			else if (m->hold_count != 0) {
1225 				addl_page_shortage++;
1226 				goto unlock_object;
1227 			}
1228 		}
1229 		if (vm_page_busied(m)) {
1230 			/*
1231 			 * Don't mess with busy pages.  Leave them at
1232 			 * the front of the queue.  Most likely, they
1233 			 * are being paged out and will leave the
1234 			 * queue shortly after the scan finishes.  So,
1235 			 * they ought to be discounted from the
1236 			 * inactive count.
1237 			 */
1238 			addl_page_shortage++;
1239 unlock_object:
1240 			VM_OBJECT_WUNLOCK(object);
1241 unlock_page:
1242 			vm_page_unlock(m);
1243 			continue;
1244 		}
1245 		KASSERT(m->hold_count == 0, ("Held page %p", m));
1246 
1247 		/*
1248 		 * Dequeue the inactive page and unlock the inactive page
1249 		 * queue, invalidating the 'next' pointer.  Dequeueing the
1250 		 * page here avoids a later reacquisition (and release) of
1251 		 * the inactive page queue lock when vm_page_activate(),
1252 		 * vm_page_free(), or vm_page_launder() is called.  Use a
1253 		 * marker to remember our place in the inactive queue.
1254 		 */
1255 		TAILQ_INSERT_AFTER(&pq->pq_pl, m, &vmd->vmd_marker, plinks.q);
1256 		vm_page_dequeue_locked(m);
1257 		vm_pagequeue_unlock(pq);
1258 		queue_locked = FALSE;
1259 
1260 		/*
1261 		 * Invalid pages can be easily freed. They cannot be
1262 		 * mapped, vm_page_free() asserts this.
1263 		 */
1264 		if (m->valid == 0)
1265 			goto free_page;
1266 
1267 		/*
1268 		 * If the page has been referenced and the object is not dead,
1269 		 * reactivate or requeue the page depending on whether the
1270 		 * object is mapped.
1271 		 */
1272 		if ((m->aflags & PGA_REFERENCED) != 0) {
1273 			vm_page_aflag_clear(m, PGA_REFERENCED);
1274 			act_delta = 1;
1275 		} else
1276 			act_delta = 0;
1277 		if (object->ref_count != 0) {
1278 			act_delta += pmap_ts_referenced(m);
1279 		} else {
1280 			KASSERT(!pmap_page_is_mapped(m),
1281 			    ("vm_pageout_scan: page %p is mapped", m));
1282 		}
1283 		if (act_delta != 0) {
1284 			if (object->ref_count != 0) {
1285 				VM_CNT_INC(v_reactivated);
1286 				vm_page_activate(m);
1287 
1288 				/*
1289 				 * Increase the activation count if the page
1290 				 * was referenced while in the inactive queue.
1291 				 * This makes it less likely that the page will
1292 				 * be returned prematurely to the inactive
1293 				 * queue.
1294  				 */
1295 				m->act_count += act_delta + ACT_ADVANCE;
1296 				goto drop_page;
1297 			} else if ((object->flags & OBJ_DEAD) == 0) {
1298 				vm_pagequeue_lock(pq);
1299 				queue_locked = TRUE;
1300 				m->queue = PQ_INACTIVE;
1301 				TAILQ_INSERT_TAIL(&pq->pq_pl, m, plinks.q);
1302 				vm_pagequeue_cnt_inc(pq);
1303 				goto drop_page;
1304 			}
1305 		}
1306 
1307 		/*
1308 		 * If the page appears to be clean at the machine-independent
1309 		 * layer, then remove all of its mappings from the pmap in
1310 		 * anticipation of freeing it.  If, however, any of the page's
1311 		 * mappings allow write access, then the page may still be
1312 		 * modified until the last of those mappings are removed.
1313 		 */
1314 		if (object->ref_count != 0) {
1315 			vm_page_test_dirty(m);
1316 			if (m->dirty == 0)
1317 				pmap_remove_all(m);
1318 		}
1319 
1320 		/*
1321 		 * Clean pages can be freed, but dirty pages must be sent back
1322 		 * to the laundry, unless they belong to a dead object.
1323 		 * Requeueing dirty pages from dead objects is pointless, as
1324 		 * they are being paged out and freed by the thread that
1325 		 * destroyed the object.
1326 		 */
1327 		if (m->dirty == 0) {
1328 free_page:
1329 			vm_page_free(m);
1330 			VM_CNT_INC(v_dfree);
1331 			--page_shortage;
1332 		} else if ((object->flags & OBJ_DEAD) == 0)
1333 			vm_page_launder(m);
1334 drop_page:
1335 		vm_page_unlock(m);
1336 		VM_OBJECT_WUNLOCK(object);
1337 		if (!queue_locked) {
1338 			vm_pagequeue_lock(pq);
1339 			queue_locked = TRUE;
1340 		}
1341 		next = TAILQ_NEXT(&vmd->vmd_marker, plinks.q);
1342 		TAILQ_REMOVE(&pq->pq_pl, &vmd->vmd_marker, plinks.q);
1343 	}
1344 	vm_pagequeue_unlock(pq);
1345 
1346 	/*
1347 	 * Wake up the laundry thread so that it can perform any needed
1348 	 * laundering.  If we didn't meet our target, we're in shortfall and
1349 	 * need to launder more aggressively.  If PQ_LAUNDRY is empty and no
1350 	 * swap devices are configured, the laundry thread has no work to do, so
1351 	 * don't bother waking it up.
1352 	 */
1353 	if (vm_laundry_request == VM_LAUNDRY_IDLE &&
1354 	    starting_page_shortage > 0) {
1355 		pq = &vm_dom[0].vmd_pagequeues[PQ_LAUNDRY];
1356 		vm_pagequeue_lock(pq);
1357 		if (pq->pq_cnt > 0 || atomic_load_acq_int(&swapdev_enabled)) {
1358 			if (page_shortage > 0) {
1359 				vm_laundry_request = VM_LAUNDRY_SHORTFALL;
1360 				VM_CNT_INC(v_pdshortfalls);
1361 			} else if (vm_laundry_request != VM_LAUNDRY_SHORTFALL)
1362 				vm_laundry_request = VM_LAUNDRY_BACKGROUND;
1363 			wakeup(&vm_laundry_request);
1364 		}
1365 		vm_pagequeue_unlock(pq);
1366 	}
1367 
1368 	/*
1369 	 * Wakeup the swapout daemon if we didn't free the targeted number of
1370 	 * pages.
1371 	 */
1372 	if (page_shortage > 0)
1373 		vm_swapout_run();
1374 
1375 	/*
1376 	 * If the inactive queue scan fails repeatedly to meet its
1377 	 * target, kill the largest process.
1378 	 */
1379 	vm_pageout_mightbe_oom(vmd, page_shortage, starting_page_shortage);
1380 
1381 	/*
1382 	 * Compute the number of pages we want to try to move from the
1383 	 * active queue to either the inactive or laundry queue.
1384 	 *
1385 	 * When scanning active pages, we make clean pages count more heavily
1386 	 * towards the page shortage than dirty pages.  This is because dirty
1387 	 * pages must be laundered before they can be reused and thus have less
1388 	 * utility when attempting to quickly alleviate a shortage.  However,
1389 	 * this weighting also causes the scan to deactivate dirty pages more
1390 	 * more aggressively, improving the effectiveness of clustering and
1391 	 * ensuring that they can eventually be reused.
1392 	 */
1393 	inactq_shortage = vm_cnt.v_inactive_target - (vm_cnt.v_inactive_count +
1394 	    vm_cnt.v_laundry_count / act_scan_laundry_weight) +
1395 	    vm_paging_target() + deficit + addl_page_shortage;
1396 	page_shortage *= act_scan_laundry_weight;
1397 
1398 	pq = &vmd->vmd_pagequeues[PQ_ACTIVE];
1399 	vm_pagequeue_lock(pq);
1400 	maxscan = pq->pq_cnt;
1401 
1402 	/*
1403 	 * If we're just idle polling attempt to visit every
1404 	 * active page within 'update_period' seconds.
1405 	 */
1406 	scan_tick = ticks;
1407 	if (vm_pageout_update_period != 0) {
1408 		min_scan = pq->pq_cnt;
1409 		min_scan *= scan_tick - vmd->vmd_last_active_scan;
1410 		min_scan /= hz * vm_pageout_update_period;
1411 	} else
1412 		min_scan = 0;
1413 	if (min_scan > 0 || (inactq_shortage > 0 && maxscan > 0))
1414 		vmd->vmd_last_active_scan = scan_tick;
1415 
1416 	/*
1417 	 * Scan the active queue for pages that can be deactivated.  Update
1418 	 * the per-page activity counter and use it to identify deactivation
1419 	 * candidates.  Held pages may be deactivated.
1420 	 */
1421 	for (m = TAILQ_FIRST(&pq->pq_pl), scanned = 0; m != NULL && (scanned <
1422 	    min_scan || (inactq_shortage > 0 && scanned < maxscan)); m = next,
1423 	    scanned++) {
1424 		KASSERT(m->queue == PQ_ACTIVE,
1425 		    ("vm_pageout_scan: page %p isn't active", m));
1426 		next = TAILQ_NEXT(m, plinks.q);
1427 		if ((m->flags & PG_MARKER) != 0)
1428 			continue;
1429 		KASSERT((m->flags & PG_FICTITIOUS) == 0,
1430 		    ("Fictitious page %p cannot be in active queue", m));
1431 		KASSERT((m->oflags & VPO_UNMANAGED) == 0,
1432 		    ("Unmanaged page %p cannot be in active queue", m));
1433 		if (!vm_pageout_page_lock(m, &next)) {
1434 			vm_page_unlock(m);
1435 			continue;
1436 		}
1437 
1438 		/*
1439 		 * The count for page daemon pages is updated after checking
1440 		 * the page for eligibility.
1441 		 */
1442 		VM_CNT_INC(v_pdpages);
1443 
1444 		/*
1445 		 * Check to see "how much" the page has been used.
1446 		 */
1447 		if ((m->aflags & PGA_REFERENCED) != 0) {
1448 			vm_page_aflag_clear(m, PGA_REFERENCED);
1449 			act_delta = 1;
1450 		} else
1451 			act_delta = 0;
1452 
1453 		/*
1454 		 * Perform an unsynchronized object ref count check.  While
1455 		 * the page lock ensures that the page is not reallocated to
1456 		 * another object, in particular, one with unmanaged mappings
1457 		 * that cannot support pmap_ts_referenced(), two races are,
1458 		 * nonetheless, possible:
1459 		 * 1) The count was transitioning to zero, but we saw a non-
1460 		 *    zero value.  pmap_ts_referenced() will return zero
1461 		 *    because the page is not mapped.
1462 		 * 2) The count was transitioning to one, but we saw zero.
1463 		 *    This race delays the detection of a new reference.  At
1464 		 *    worst, we will deactivate and reactivate the page.
1465 		 */
1466 		if (m->object->ref_count != 0)
1467 			act_delta += pmap_ts_referenced(m);
1468 
1469 		/*
1470 		 * Advance or decay the act_count based on recent usage.
1471 		 */
1472 		if (act_delta != 0) {
1473 			m->act_count += ACT_ADVANCE + act_delta;
1474 			if (m->act_count > ACT_MAX)
1475 				m->act_count = ACT_MAX;
1476 		} else
1477 			m->act_count -= min(m->act_count, ACT_DECLINE);
1478 
1479 		/*
1480 		 * Move this page to the tail of the active, inactive or laundry
1481 		 * queue depending on usage.
1482 		 */
1483 		if (m->act_count == 0) {
1484 			/* Dequeue to avoid later lock recursion. */
1485 			vm_page_dequeue_locked(m);
1486 
1487 			/*
1488 			 * When not short for inactive pages, let dirty pages go
1489 			 * through the inactive queue before moving to the
1490 			 * laundry queues.  This gives them some extra time to
1491 			 * be reactivated, potentially avoiding an expensive
1492 			 * pageout.  During a page shortage, the inactive queue
1493 			 * is necessarily small, so we may move dirty pages
1494 			 * directly to the laundry queue.
1495 			 */
1496 			if (inactq_shortage <= 0)
1497 				vm_page_deactivate(m);
1498 			else {
1499 				/*
1500 				 * Calling vm_page_test_dirty() here would
1501 				 * require acquisition of the object's write
1502 				 * lock.  However, during a page shortage,
1503 				 * directing dirty pages into the laundry
1504 				 * queue is only an optimization and not a
1505 				 * requirement.  Therefore, we simply rely on
1506 				 * the opportunistic updates to the page's
1507 				 * dirty field by the pmap.
1508 				 */
1509 				if (m->dirty == 0) {
1510 					vm_page_deactivate(m);
1511 					inactq_shortage -=
1512 					    act_scan_laundry_weight;
1513 				} else {
1514 					vm_page_launder(m);
1515 					inactq_shortage--;
1516 				}
1517 			}
1518 		} else
1519 			vm_page_requeue_locked(m);
1520 		vm_page_unlock(m);
1521 	}
1522 	vm_pagequeue_unlock(pq);
1523 	if (pass > 0)
1524 		vm_swapout_run_idle();
1525 	return (page_shortage <= 0);
1526 }
1527 
1528 static int vm_pageout_oom_vote;
1529 
1530 /*
1531  * The pagedaemon threads randlomly select one to perform the
1532  * OOM.  Trying to kill processes before all pagedaemons
1533  * failed to reach free target is premature.
1534  */
1535 static void
1536 vm_pageout_mightbe_oom(struct vm_domain *vmd, int page_shortage,
1537     int starting_page_shortage)
1538 {
1539 	int old_vote;
1540 
1541 	if (starting_page_shortage <= 0 || starting_page_shortage !=
1542 	    page_shortage)
1543 		vmd->vmd_oom_seq = 0;
1544 	else
1545 		vmd->vmd_oom_seq++;
1546 	if (vmd->vmd_oom_seq < vm_pageout_oom_seq) {
1547 		if (vmd->vmd_oom) {
1548 			vmd->vmd_oom = FALSE;
1549 			atomic_subtract_int(&vm_pageout_oom_vote, 1);
1550 		}
1551 		return;
1552 	}
1553 
1554 	/*
1555 	 * Do not follow the call sequence until OOM condition is
1556 	 * cleared.
1557 	 */
1558 	vmd->vmd_oom_seq = 0;
1559 
1560 	if (vmd->vmd_oom)
1561 		return;
1562 
1563 	vmd->vmd_oom = TRUE;
1564 	old_vote = atomic_fetchadd_int(&vm_pageout_oom_vote, 1);
1565 	if (old_vote != vm_ndomains - 1)
1566 		return;
1567 
1568 	/*
1569 	 * The current pagedaemon thread is the last in the quorum to
1570 	 * start OOM.  Initiate the selection and signaling of the
1571 	 * victim.
1572 	 */
1573 	vm_pageout_oom(VM_OOM_MEM);
1574 
1575 	/*
1576 	 * After one round of OOM terror, recall our vote.  On the
1577 	 * next pass, current pagedaemon would vote again if the low
1578 	 * memory condition is still there, due to vmd_oom being
1579 	 * false.
1580 	 */
1581 	vmd->vmd_oom = FALSE;
1582 	atomic_subtract_int(&vm_pageout_oom_vote, 1);
1583 }
1584 
1585 /*
1586  * The OOM killer is the page daemon's action of last resort when
1587  * memory allocation requests have been stalled for a prolonged period
1588  * of time because it cannot reclaim memory.  This function computes
1589  * the approximate number of physical pages that could be reclaimed if
1590  * the specified address space is destroyed.
1591  *
1592  * Private, anonymous memory owned by the address space is the
1593  * principal resource that we expect to recover after an OOM kill.
1594  * Since the physical pages mapped by the address space's COW entries
1595  * are typically shared pages, they are unlikely to be released and so
1596  * they are not counted.
1597  *
1598  * To get to the point where the page daemon runs the OOM killer, its
1599  * efforts to write-back vnode-backed pages may have stalled.  This
1600  * could be caused by a memory allocation deadlock in the write path
1601  * that might be resolved by an OOM kill.  Therefore, physical pages
1602  * belonging to vnode-backed objects are counted, because they might
1603  * be freed without being written out first if the address space holds
1604  * the last reference to an unlinked vnode.
1605  *
1606  * Similarly, physical pages belonging to OBJT_PHYS objects are
1607  * counted because the address space might hold the last reference to
1608  * the object.
1609  */
1610 static long
1611 vm_pageout_oom_pagecount(struct vmspace *vmspace)
1612 {
1613 	vm_map_t map;
1614 	vm_map_entry_t entry;
1615 	vm_object_t obj;
1616 	long res;
1617 
1618 	map = &vmspace->vm_map;
1619 	KASSERT(!map->system_map, ("system map"));
1620 	sx_assert(&map->lock, SA_LOCKED);
1621 	res = 0;
1622 	for (entry = map->header.next; entry != &map->header;
1623 	    entry = entry->next) {
1624 		if ((entry->eflags & MAP_ENTRY_IS_SUB_MAP) != 0)
1625 			continue;
1626 		obj = entry->object.vm_object;
1627 		if (obj == NULL)
1628 			continue;
1629 		if ((entry->eflags & MAP_ENTRY_NEEDS_COPY) != 0 &&
1630 		    obj->ref_count != 1)
1631 			continue;
1632 		switch (obj->type) {
1633 		case OBJT_DEFAULT:
1634 		case OBJT_SWAP:
1635 		case OBJT_PHYS:
1636 		case OBJT_VNODE:
1637 			res += obj->resident_page_count;
1638 			break;
1639 		}
1640 	}
1641 	return (res);
1642 }
1643 
1644 void
1645 vm_pageout_oom(int shortage)
1646 {
1647 	struct proc *p, *bigproc;
1648 	vm_offset_t size, bigsize;
1649 	struct thread *td;
1650 	struct vmspace *vm;
1651 	bool breakout;
1652 
1653 	/*
1654 	 * We keep the process bigproc locked once we find it to keep anyone
1655 	 * from messing with it; however, there is a possibility of
1656 	 * deadlock if process B is bigproc and one of its child processes
1657 	 * attempts to propagate a signal to B while we are waiting for A's
1658 	 * lock while walking this list.  To avoid this, we don't block on
1659 	 * the process lock but just skip a process if it is already locked.
1660 	 */
1661 	bigproc = NULL;
1662 	bigsize = 0;
1663 	sx_slock(&allproc_lock);
1664 	FOREACH_PROC_IN_SYSTEM(p) {
1665 		PROC_LOCK(p);
1666 
1667 		/*
1668 		 * If this is a system, protected or killed process, skip it.
1669 		 */
1670 		if (p->p_state != PRS_NORMAL || (p->p_flag & (P_INEXEC |
1671 		    P_PROTECTED | P_SYSTEM | P_WEXIT)) != 0 ||
1672 		    p->p_pid == 1 || P_KILLED(p) ||
1673 		    (p->p_pid < 48 && swap_pager_avail != 0)) {
1674 			PROC_UNLOCK(p);
1675 			continue;
1676 		}
1677 		/*
1678 		 * If the process is in a non-running type state,
1679 		 * don't touch it.  Check all the threads individually.
1680 		 */
1681 		breakout = false;
1682 		FOREACH_THREAD_IN_PROC(p, td) {
1683 			thread_lock(td);
1684 			if (!TD_ON_RUNQ(td) &&
1685 			    !TD_IS_RUNNING(td) &&
1686 			    !TD_IS_SLEEPING(td) &&
1687 			    !TD_IS_SUSPENDED(td) &&
1688 			    !TD_IS_SWAPPED(td)) {
1689 				thread_unlock(td);
1690 				breakout = true;
1691 				break;
1692 			}
1693 			thread_unlock(td);
1694 		}
1695 		if (breakout) {
1696 			PROC_UNLOCK(p);
1697 			continue;
1698 		}
1699 		/*
1700 		 * get the process size
1701 		 */
1702 		vm = vmspace_acquire_ref(p);
1703 		if (vm == NULL) {
1704 			PROC_UNLOCK(p);
1705 			continue;
1706 		}
1707 		_PHOLD_LITE(p);
1708 		PROC_UNLOCK(p);
1709 		sx_sunlock(&allproc_lock);
1710 		if (!vm_map_trylock_read(&vm->vm_map)) {
1711 			vmspace_free(vm);
1712 			sx_slock(&allproc_lock);
1713 			PRELE(p);
1714 			continue;
1715 		}
1716 		size = vmspace_swap_count(vm);
1717 		if (shortage == VM_OOM_MEM)
1718 			size += vm_pageout_oom_pagecount(vm);
1719 		vm_map_unlock_read(&vm->vm_map);
1720 		vmspace_free(vm);
1721 		sx_slock(&allproc_lock);
1722 
1723 		/*
1724 		 * If this process is bigger than the biggest one,
1725 		 * remember it.
1726 		 */
1727 		if (size > bigsize) {
1728 			if (bigproc != NULL)
1729 				PRELE(bigproc);
1730 			bigproc = p;
1731 			bigsize = size;
1732 		} else {
1733 			PRELE(p);
1734 		}
1735 	}
1736 	sx_sunlock(&allproc_lock);
1737 	if (bigproc != NULL) {
1738 		if (vm_panic_on_oom != 0)
1739 			panic("out of swap space");
1740 		PROC_LOCK(bigproc);
1741 		killproc(bigproc, "out of swap space");
1742 		sched_nice(bigproc, PRIO_MIN);
1743 		_PRELE(bigproc);
1744 		PROC_UNLOCK(bigproc);
1745 		wakeup(&vm_cnt.v_free_count);
1746 	}
1747 }
1748 
1749 static void
1750 vm_pageout_worker(void *arg)
1751 {
1752 	struct vm_domain *domain;
1753 	int domidx, pass;
1754 	bool target_met;
1755 
1756 	domidx = (uintptr_t)arg;
1757 	domain = &vm_dom[domidx];
1758 	pass = 0;
1759 	target_met = true;
1760 
1761 	/*
1762 	 * XXXKIB It could be useful to bind pageout daemon threads to
1763 	 * the cores belonging to the domain, from which vm_page_array
1764 	 * is allocated.
1765 	 */
1766 
1767 	KASSERT(domain->vmd_segs != 0, ("domain without segments"));
1768 	domain->vmd_last_active_scan = ticks;
1769 	vm_pageout_init_marker(&domain->vmd_marker, PQ_INACTIVE);
1770 	vm_pageout_init_marker(&domain->vmd_inacthead, PQ_INACTIVE);
1771 	TAILQ_INSERT_HEAD(&domain->vmd_pagequeues[PQ_INACTIVE].pq_pl,
1772 	    &domain->vmd_inacthead, plinks.q);
1773 
1774 	/*
1775 	 * The pageout daemon worker is never done, so loop forever.
1776 	 */
1777 	while (TRUE) {
1778 		mtx_lock(&vm_page_queue_free_mtx);
1779 
1780 		/*
1781 		 * Generally, after a level >= 1 scan, if there are enough
1782 		 * free pages to wakeup the waiters, then they are already
1783 		 * awake.  A call to vm_page_free() during the scan awakened
1784 		 * them.  However, in the following case, this wakeup serves
1785 		 * to bound the amount of time that a thread might wait.
1786 		 * Suppose a thread's call to vm_page_alloc() fails, but
1787 		 * before that thread calls VM_WAIT, enough pages are freed by
1788 		 * other threads to alleviate the free page shortage.  The
1789 		 * thread will, nonetheless, wait until another page is freed
1790 		 * or this wakeup is performed.
1791 		 */
1792 		if (vm_pages_needed && !vm_page_count_min()) {
1793 			vm_pages_needed = false;
1794 			wakeup(&vm_cnt.v_free_count);
1795 		}
1796 
1797 		/*
1798 		 * Do not clear vm_pageout_wanted until we reach our free page
1799 		 * target.  Otherwise, we may be awakened over and over again,
1800 		 * wasting CPU time.
1801 		 */
1802 		if (vm_pageout_wanted && target_met)
1803 			vm_pageout_wanted = false;
1804 
1805 		/*
1806 		 * Might the page daemon receive a wakeup call?
1807 		 */
1808 		if (vm_pageout_wanted) {
1809 			/*
1810 			 * No.  Either vm_pageout_wanted was set by another
1811 			 * thread during the previous scan, which must have
1812 			 * been a level 0 scan, or vm_pageout_wanted was
1813 			 * already set and the scan failed to free enough
1814 			 * pages.  If we haven't yet performed a level >= 1
1815 			 * (page reclamation) scan, then increase the level
1816 			 * and scan again now.  Otherwise, sleep a bit and
1817 			 * try again later.
1818 			 */
1819 			mtx_unlock(&vm_page_queue_free_mtx);
1820 			if (pass >= 1)
1821 				pause("pwait", hz / VM_INACT_SCAN_RATE);
1822 			pass++;
1823 		} else {
1824 			/*
1825 			 * Yes.  Sleep until pages need to be reclaimed or
1826 			 * have their reference stats updated.
1827 			 */
1828 			if (mtx_sleep(&vm_pageout_wanted,
1829 			    &vm_page_queue_free_mtx, PDROP | PVM, "psleep",
1830 			    hz) == 0) {
1831 				VM_CNT_INC(v_pdwakeups);
1832 				pass = 1;
1833 			} else
1834 				pass = 0;
1835 		}
1836 
1837 		target_met = vm_pageout_scan(domain, pass);
1838 	}
1839 }
1840 
1841 /*
1842  *	vm_pageout_init initialises basic pageout daemon settings.
1843  */
1844 static void
1845 vm_pageout_init(void)
1846 {
1847 	/*
1848 	 * Initialize some paging parameters.
1849 	 */
1850 	vm_cnt.v_interrupt_free_min = 2;
1851 	if (vm_cnt.v_page_count < 2000)
1852 		vm_pageout_page_count = 8;
1853 
1854 	/*
1855 	 * v_free_reserved needs to include enough for the largest
1856 	 * swap pager structures plus enough for any pv_entry structs
1857 	 * when paging.
1858 	 */
1859 	if (vm_cnt.v_page_count > 1024)
1860 		vm_cnt.v_free_min = 4 + (vm_cnt.v_page_count - 1024) / 200;
1861 	else
1862 		vm_cnt.v_free_min = 4;
1863 	vm_cnt.v_pageout_free_min = (2*MAXBSIZE)/PAGE_SIZE +
1864 	    vm_cnt.v_interrupt_free_min;
1865 	vm_cnt.v_free_reserved = vm_pageout_page_count +
1866 	    vm_cnt.v_pageout_free_min + (vm_cnt.v_page_count / 768);
1867 	vm_cnt.v_free_severe = vm_cnt.v_free_min / 2;
1868 	vm_cnt.v_free_target = 4 * vm_cnt.v_free_min + vm_cnt.v_free_reserved;
1869 	vm_cnt.v_free_min += vm_cnt.v_free_reserved;
1870 	vm_cnt.v_free_severe += vm_cnt.v_free_reserved;
1871 	vm_cnt.v_inactive_target = (3 * vm_cnt.v_free_target) / 2;
1872 	if (vm_cnt.v_inactive_target > vm_cnt.v_free_count / 3)
1873 		vm_cnt.v_inactive_target = vm_cnt.v_free_count / 3;
1874 
1875 	/*
1876 	 * Set the default wakeup threshold to be 10% above the minimum
1877 	 * page limit.  This keeps the steady state out of shortfall.
1878 	 */
1879 	vm_pageout_wakeup_thresh = (vm_cnt.v_free_min / 10) * 11;
1880 
1881 	/*
1882 	 * Set interval in seconds for active scan.  We want to visit each
1883 	 * page at least once every ten minutes.  This is to prevent worst
1884 	 * case paging behaviors with stale active LRU.
1885 	 */
1886 	if (vm_pageout_update_period == 0)
1887 		vm_pageout_update_period = 600;
1888 
1889 	/* XXX does not really belong here */
1890 	if (vm_page_max_wired == 0)
1891 		vm_page_max_wired = vm_cnt.v_free_count / 3;
1892 
1893 	/*
1894 	 * Target amount of memory to move out of the laundry queue during a
1895 	 * background laundering.  This is proportional to the amount of system
1896 	 * memory.
1897 	 */
1898 	vm_background_launder_target = (vm_cnt.v_free_target -
1899 	    vm_cnt.v_free_min) / 10;
1900 }
1901 
1902 /*
1903  *     vm_pageout is the high level pageout daemon.
1904  */
1905 static void
1906 vm_pageout(void)
1907 {
1908 	int error;
1909 #ifdef VM_NUMA_ALLOC
1910 	int i;
1911 #endif
1912 
1913 	swap_pager_swap_init();
1914 	error = kthread_add(vm_pageout_laundry_worker, NULL, curproc, NULL,
1915 	    0, 0, "laundry: dom0");
1916 	if (error != 0)
1917 		panic("starting laundry for domain 0, error %d", error);
1918 #ifdef VM_NUMA_ALLOC
1919 	for (i = 1; i < vm_ndomains; i++) {
1920 		error = kthread_add(vm_pageout_worker, (void *)(uintptr_t)i,
1921 		    curproc, NULL, 0, 0, "dom%d", i);
1922 		if (error != 0) {
1923 			panic("starting pageout for domain %d, error %d\n",
1924 			    i, error);
1925 		}
1926 	}
1927 #endif
1928 	error = kthread_add(uma_reclaim_worker, NULL, curproc, NULL,
1929 	    0, 0, "uma");
1930 	if (error != 0)
1931 		panic("starting uma_reclaim helper, error %d\n", error);
1932 	vm_pageout_worker((void *)(uintptr_t)0);
1933 }
1934 
1935 /*
1936  * Unless the free page queue lock is held by the caller, this function
1937  * should be regarded as advisory.  Specifically, the caller should
1938  * not msleep() on &vm_cnt.v_free_count following this function unless
1939  * the free page queue lock is held until the msleep() is performed.
1940  */
1941 void
1942 pagedaemon_wakeup(void)
1943 {
1944 
1945 	if (!vm_pageout_wanted && curthread->td_proc != pageproc) {
1946 		vm_pageout_wanted = true;
1947 		wakeup(&vm_pageout_wanted);
1948 	}
1949 }
1950