xref: /freebsd/sys/vm/vm_pageout.c (revision 8a4217aacf57330755501a349d0ea662d4880386)
1 /*-
2  * SPDX-License-Identifier: BSD-4-Clause
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 		vm_page_lock(m);
651 		/*
652 		 * While the object and page were unlocked, the page
653 		 * may have been:
654 		 * (1) moved to a different queue,
655 		 * (2) reallocated to a different object,
656 		 * (3) reallocated to a different offset, or
657 		 * (4) cleaned.
658 		 */
659 		if (!vm_page_in_laundry(m) || m->object != object ||
660 		    m->pindex != pindex || m->dirty == 0) {
661 			vm_page_unlock(m);
662 			error = ENXIO;
663 			goto unlock_all;
664 		}
665 
666 		/*
667 		 * The page may have been busied or held while the object
668 		 * and page locks were released.
669 		 */
670 		if (vm_page_busied(m) || m->hold_count != 0) {
671 			vm_page_unlock(m);
672 			error = EBUSY;
673 			goto unlock_all;
674 		}
675 	}
676 
677 	/*
678 	 * If a page is dirty, then it is either being washed
679 	 * (but not yet cleaned) or it is still in the
680 	 * laundry.  If it is still in the laundry, then we
681 	 * start the cleaning operation.
682 	 */
683 	if ((*numpagedout = vm_pageout_cluster(m)) == 0)
684 		error = EIO;
685 
686 unlock_all:
687 	VM_OBJECT_WUNLOCK(object);
688 
689 unlock_mp:
690 	vm_page_lock_assert(m, MA_NOTOWNED);
691 	if (mp != NULL) {
692 		if (vp != NULL)
693 			vput(vp);
694 		vm_object_deallocate(object);
695 		vn_finished_write(mp);
696 	}
697 
698 	return (error);
699 }
700 
701 /*
702  * Attempt to launder the specified number of pages.
703  *
704  * Returns the number of pages successfully laundered.
705  */
706 static int
707 vm_pageout_launder(struct vm_domain *vmd, int launder, bool in_shortfall)
708 {
709 	struct vm_pagequeue *pq;
710 	vm_object_t object;
711 	vm_page_t m, next;
712 	int act_delta, error, maxscan, numpagedout, starting_target;
713 	int vnodes_skipped;
714 	bool pageout_ok, queue_locked;
715 
716 	starting_target = launder;
717 	vnodes_skipped = 0;
718 
719 	/*
720 	 * Scan the laundry queues for pages eligible to be laundered.  We stop
721 	 * once the target number of dirty pages have been laundered, or once
722 	 * we've reached the end of the queue.  A single iteration of this loop
723 	 * may cause more than one page to be laundered because of clustering.
724 	 *
725 	 * maxscan ensures that we don't re-examine requeued pages.  Any
726 	 * additional pages written as part of a cluster are subtracted from
727 	 * maxscan since they must be taken from the laundry queue.
728 	 *
729 	 * As an optimization, we avoid laundering from PQ_UNSWAPPABLE when no
730 	 * swap devices are configured.
731 	 */
732 	if (atomic_load_acq_int(&swapdev_enabled))
733 		pq = &vmd->vmd_pagequeues[PQ_UNSWAPPABLE];
734 	else
735 		pq = &vmd->vmd_pagequeues[PQ_LAUNDRY];
736 
737 scan:
738 	vm_pagequeue_lock(pq);
739 	maxscan = pq->pq_cnt;
740 	queue_locked = true;
741 	for (m = TAILQ_FIRST(&pq->pq_pl);
742 	    m != NULL && maxscan-- > 0 && launder > 0;
743 	    m = next) {
744 		vm_pagequeue_assert_locked(pq);
745 		KASSERT(queue_locked, ("unlocked laundry queue"));
746 		KASSERT(vm_page_in_laundry(m),
747 		    ("page %p has an inconsistent queue", m));
748 		next = TAILQ_NEXT(m, plinks.q);
749 		if ((m->flags & PG_MARKER) != 0)
750 			continue;
751 		KASSERT((m->flags & PG_FICTITIOUS) == 0,
752 		    ("PG_FICTITIOUS page %p cannot be in laundry queue", m));
753 		KASSERT((m->oflags & VPO_UNMANAGED) == 0,
754 		    ("VPO_UNMANAGED page %p cannot be in laundry queue", m));
755 		if (!vm_pageout_page_lock(m, &next) || m->hold_count != 0) {
756 			vm_page_unlock(m);
757 			continue;
758 		}
759 		object = m->object;
760 		if ((!VM_OBJECT_TRYWLOCK(object) &&
761 		    (!vm_pageout_fallback_object_lock(m, &next) ||
762 		    m->hold_count != 0)) || vm_page_busied(m)) {
763 			VM_OBJECT_WUNLOCK(object);
764 			vm_page_unlock(m);
765 			continue;
766 		}
767 
768 		/*
769 		 * Unlock the laundry queue, invalidating the 'next' pointer.
770 		 * Use a marker to remember our place in the laundry queue.
771 		 */
772 		TAILQ_INSERT_AFTER(&pq->pq_pl, m, &vmd->vmd_laundry_marker,
773 		    plinks.q);
774 		vm_pagequeue_unlock(pq);
775 		queue_locked = false;
776 
777 		/*
778 		 * Invalid pages can be easily freed.  They cannot be
779 		 * mapped; vm_page_free() asserts this.
780 		 */
781 		if (m->valid == 0)
782 			goto free_page;
783 
784 		/*
785 		 * If the page has been referenced and the object is not dead,
786 		 * reactivate or requeue the page depending on whether the
787 		 * object is mapped.
788 		 */
789 		if ((m->aflags & PGA_REFERENCED) != 0) {
790 			vm_page_aflag_clear(m, PGA_REFERENCED);
791 			act_delta = 1;
792 		} else
793 			act_delta = 0;
794 		if (object->ref_count != 0)
795 			act_delta += pmap_ts_referenced(m);
796 		else {
797 			KASSERT(!pmap_page_is_mapped(m),
798 			    ("page %p is mapped", m));
799 		}
800 		if (act_delta != 0) {
801 			if (object->ref_count != 0) {
802 				VM_CNT_INC(v_reactivated);
803 				vm_page_activate(m);
804 
805 				/*
806 				 * Increase the activation count if the page
807 				 * was referenced while in the laundry queue.
808 				 * This makes it less likely that the page will
809 				 * be returned prematurely to the inactive
810 				 * queue.
811  				 */
812 				m->act_count += act_delta + ACT_ADVANCE;
813 
814 				/*
815 				 * If this was a background laundering, count
816 				 * activated pages towards our target.  The
817 				 * purpose of background laundering is to ensure
818 				 * that pages are eventually cycled through the
819 				 * laundry queue, and an activation is a valid
820 				 * way out.
821 				 */
822 				if (!in_shortfall)
823 					launder--;
824 				goto drop_page;
825 			} else if ((object->flags & OBJ_DEAD) == 0)
826 				goto requeue_page;
827 		}
828 
829 		/*
830 		 * If the page appears to be clean at the machine-independent
831 		 * layer, then remove all of its mappings from the pmap in
832 		 * anticipation of freeing it.  If, however, any of the page's
833 		 * mappings allow write access, then the page may still be
834 		 * modified until the last of those mappings are removed.
835 		 */
836 		if (object->ref_count != 0) {
837 			vm_page_test_dirty(m);
838 			if (m->dirty == 0)
839 				pmap_remove_all(m);
840 		}
841 
842 		/*
843 		 * Clean pages are freed, and dirty pages are paged out unless
844 		 * they belong to a dead object.  Requeueing dirty pages from
845 		 * dead objects is pointless, as they are being paged out and
846 		 * freed by the thread that destroyed the object.
847 		 */
848 		if (m->dirty == 0) {
849 free_page:
850 			vm_page_free(m);
851 			VM_CNT_INC(v_dfree);
852 		} else if ((object->flags & OBJ_DEAD) == 0) {
853 			if (object->type != OBJT_SWAP &&
854 			    object->type != OBJT_DEFAULT)
855 				pageout_ok = true;
856 			else if (disable_swap_pageouts)
857 				pageout_ok = false;
858 			else
859 				pageout_ok = true;
860 			if (!pageout_ok) {
861 requeue_page:
862 				vm_pagequeue_lock(pq);
863 				queue_locked = true;
864 				vm_page_requeue_locked(m);
865 				goto drop_page;
866 			}
867 
868 			/*
869 			 * Form a cluster with adjacent, dirty pages from the
870 			 * same object, and page out that entire cluster.
871 			 *
872 			 * The adjacent, dirty pages must also be in the
873 			 * laundry.  However, their mappings are not checked
874 			 * for new references.  Consequently, a recently
875 			 * referenced page may be paged out.  However, that
876 			 * page will not be prematurely reclaimed.  After page
877 			 * out, the page will be placed in the inactive queue,
878 			 * where any new references will be detected and the
879 			 * page reactivated.
880 			 */
881 			error = vm_pageout_clean(m, &numpagedout);
882 			if (error == 0) {
883 				launder -= numpagedout;
884 				maxscan -= numpagedout - 1;
885 			} else if (error == EDEADLK) {
886 				pageout_lock_miss++;
887 				vnodes_skipped++;
888 			}
889 			goto relock_queue;
890 		}
891 drop_page:
892 		vm_page_unlock(m);
893 		VM_OBJECT_WUNLOCK(object);
894 relock_queue:
895 		if (!queue_locked) {
896 			vm_pagequeue_lock(pq);
897 			queue_locked = true;
898 		}
899 		next = TAILQ_NEXT(&vmd->vmd_laundry_marker, plinks.q);
900 		TAILQ_REMOVE(&pq->pq_pl, &vmd->vmd_laundry_marker, plinks.q);
901 	}
902 	vm_pagequeue_unlock(pq);
903 
904 	if (launder > 0 && pq == &vmd->vmd_pagequeues[PQ_UNSWAPPABLE]) {
905 		pq = &vmd->vmd_pagequeues[PQ_LAUNDRY];
906 		goto scan;
907 	}
908 
909 	/*
910 	 * Wakeup the sync daemon if we skipped a vnode in a writeable object
911 	 * and we didn't launder enough pages.
912 	 */
913 	if (vnodes_skipped > 0 && launder > 0)
914 		(void)speedup_syncer();
915 
916 	return (starting_target - launder);
917 }
918 
919 /*
920  * Compute the integer square root.
921  */
922 static u_int
923 isqrt(u_int num)
924 {
925 	u_int bit, root, tmp;
926 
927 	bit = 1u << ((NBBY * sizeof(u_int)) - 2);
928 	while (bit > num)
929 		bit >>= 2;
930 	root = 0;
931 	while (bit != 0) {
932 		tmp = root + bit;
933 		root >>= 1;
934 		if (num >= tmp) {
935 			num -= tmp;
936 			root += bit;
937 		}
938 		bit >>= 2;
939 	}
940 	return (root);
941 }
942 
943 /*
944  * Perform the work of the laundry thread: periodically wake up and determine
945  * whether any pages need to be laundered.  If so, determine the number of pages
946  * that need to be laundered, and launder them.
947  */
948 static void
949 vm_pageout_laundry_worker(void *arg)
950 {
951 	struct vm_domain *domain;
952 	struct vm_pagequeue *pq;
953 	uint64_t nclean, ndirty;
954 	u_int last_launder, wakeups;
955 	int domidx, last_target, launder, shortfall, shortfall_cycle, target;
956 	bool in_shortfall;
957 
958 	domidx = (uintptr_t)arg;
959 	domain = &vm_dom[domidx];
960 	pq = &domain->vmd_pagequeues[PQ_LAUNDRY];
961 	KASSERT(domain->vmd_segs != 0, ("domain without segments"));
962 	vm_pageout_init_marker(&domain->vmd_laundry_marker, PQ_LAUNDRY);
963 
964 	shortfall = 0;
965 	in_shortfall = false;
966 	shortfall_cycle = 0;
967 	target = 0;
968 	last_launder = 0;
969 
970 	/*
971 	 * Calls to these handlers are serialized by the swap syscall lock.
972 	 */
973 	(void)EVENTHANDLER_REGISTER(swapon, vm_pageout_swapon, domain,
974 	    EVENTHANDLER_PRI_ANY);
975 	(void)EVENTHANDLER_REGISTER(swapoff, vm_pageout_swapoff, domain,
976 	    EVENTHANDLER_PRI_ANY);
977 
978 	/*
979 	 * The pageout laundry worker is never done, so loop forever.
980 	 */
981 	for (;;) {
982 		KASSERT(target >= 0, ("negative target %d", target));
983 		KASSERT(shortfall_cycle >= 0,
984 		    ("negative cycle %d", shortfall_cycle));
985 		launder = 0;
986 		wakeups = VM_CNT_FETCH(v_pdwakeups);
987 
988 		/*
989 		 * First determine whether we need to launder pages to meet a
990 		 * shortage of free pages.
991 		 */
992 		if (shortfall > 0) {
993 			in_shortfall = true;
994 			shortfall_cycle = VM_LAUNDER_RATE / VM_INACT_SCAN_RATE;
995 			target = shortfall;
996 		} else if (!in_shortfall)
997 			goto trybackground;
998 		else if (shortfall_cycle == 0 || vm_laundry_target() <= 0) {
999 			/*
1000 			 * We recently entered shortfall and began laundering
1001 			 * pages.  If we have completed that laundering run
1002 			 * (and we are no longer in shortfall) or we have met
1003 			 * our laundry target through other activity, then we
1004 			 * can stop laundering pages.
1005 			 */
1006 			in_shortfall = false;
1007 			target = 0;
1008 			goto trybackground;
1009 		}
1010 		last_launder = wakeups;
1011 		launder = target / shortfall_cycle--;
1012 		goto dolaundry;
1013 
1014 		/*
1015 		 * There's no immediate need to launder any pages; see if we
1016 		 * meet the conditions to perform background laundering:
1017 		 *
1018 		 * 1. The ratio of dirty to clean inactive pages exceeds the
1019 		 *    background laundering threshold and the pagedaemon has
1020 		 *    been woken up to reclaim pages since our last
1021 		 *    laundering, or
1022 		 * 2. we haven't yet reached the target of the current
1023 		 *    background laundering run.
1024 		 *
1025 		 * The background laundering threshold is not a constant.
1026 		 * Instead, it is a slowly growing function of the number of
1027 		 * page daemon wakeups since the last laundering.  Thus, as the
1028 		 * ratio of dirty to clean inactive pages grows, the amount of
1029 		 * memory pressure required to trigger laundering decreases.
1030 		 */
1031 trybackground:
1032 		nclean = vm_cnt.v_inactive_count + vm_cnt.v_free_count;
1033 		ndirty = vm_cnt.v_laundry_count;
1034 		if (target == 0 && wakeups != last_launder &&
1035 		    ndirty * isqrt(wakeups - last_launder) >= nclean) {
1036 			target = vm_background_launder_target;
1037 		}
1038 
1039 		/*
1040 		 * We have a non-zero background laundering target.  If we've
1041 		 * laundered up to our maximum without observing a page daemon
1042 		 * wakeup, just stop.  This is a safety belt that ensures we
1043 		 * don't launder an excessive amount if memory pressure is low
1044 		 * and the ratio of dirty to clean pages is large.  Otherwise,
1045 		 * proceed at the background laundering rate.
1046 		 */
1047 		if (target > 0) {
1048 			if (wakeups != last_launder) {
1049 				last_launder = wakeups;
1050 				last_target = target;
1051 			} else if (last_target - target >=
1052 			    vm_background_launder_max * PAGE_SIZE / 1024) {
1053 				target = 0;
1054 			}
1055 			launder = vm_background_launder_rate * PAGE_SIZE / 1024;
1056 			launder /= VM_LAUNDER_RATE;
1057 			if (launder > target)
1058 				launder = target;
1059 		}
1060 
1061 dolaundry:
1062 		if (launder > 0) {
1063 			/*
1064 			 * Because of I/O clustering, the number of laundered
1065 			 * pages could exceed "target" by the maximum size of
1066 			 * a cluster minus one.
1067 			 */
1068 			target -= min(vm_pageout_launder(domain, launder,
1069 			    in_shortfall), target);
1070 			pause("laundp", hz / VM_LAUNDER_RATE);
1071 		}
1072 
1073 		/*
1074 		 * If we're not currently laundering pages and the page daemon
1075 		 * hasn't posted a new request, sleep until the page daemon
1076 		 * kicks us.
1077 		 */
1078 		vm_pagequeue_lock(pq);
1079 		if (target == 0 && vm_laundry_request == VM_LAUNDRY_IDLE)
1080 			(void)mtx_sleep(&vm_laundry_request,
1081 			    vm_pagequeue_lockptr(pq), PVM, "launds", 0);
1082 
1083 		/*
1084 		 * If the pagedaemon has indicated that it's in shortfall, start
1085 		 * a shortfall laundering unless we're already in the middle of
1086 		 * one.  This may preempt a background laundering.
1087 		 */
1088 		if (vm_laundry_request == VM_LAUNDRY_SHORTFALL &&
1089 		    (!in_shortfall || shortfall_cycle == 0)) {
1090 			shortfall = vm_laundry_target() + vm_pageout_deficit;
1091 			target = 0;
1092 		} else
1093 			shortfall = 0;
1094 
1095 		if (target == 0)
1096 			vm_laundry_request = VM_LAUNDRY_IDLE;
1097 		vm_pagequeue_unlock(pq);
1098 	}
1099 }
1100 
1101 /*
1102  *	vm_pageout_scan does the dirty work for the pageout daemon.
1103  *
1104  *	pass == 0: Update active LRU/deactivate pages
1105  *	pass >= 1: Free inactive pages
1106  *
1107  * Returns true if pass was zero or enough pages were freed by the inactive
1108  * queue scan to meet the target.
1109  */
1110 static bool
1111 vm_pageout_scan(struct vm_domain *vmd, int pass)
1112 {
1113 	vm_page_t m, next;
1114 	struct vm_pagequeue *pq;
1115 	vm_object_t object;
1116 	long min_scan;
1117 	int act_delta, addl_page_shortage, deficit, inactq_shortage, maxscan;
1118 	int page_shortage, scan_tick, scanned, starting_page_shortage;
1119 	boolean_t queue_locked;
1120 
1121 	/*
1122 	 * If we need to reclaim memory ask kernel caches to return
1123 	 * some.  We rate limit to avoid thrashing.
1124 	 */
1125 	if (vmd == &vm_dom[0] && pass > 0 &&
1126 	    (time_uptime - lowmem_uptime) >= lowmem_period) {
1127 		/*
1128 		 * Decrease registered cache sizes.
1129 		 */
1130 		SDT_PROBE0(vm, , , vm__lowmem_scan);
1131 		EVENTHANDLER_INVOKE(vm_lowmem, VM_LOW_PAGES);
1132 		/*
1133 		 * We do this explicitly after the caches have been
1134 		 * drained above.
1135 		 */
1136 		uma_reclaim();
1137 		lowmem_uptime = time_uptime;
1138 	}
1139 
1140 	/*
1141 	 * The addl_page_shortage is the number of temporarily
1142 	 * stuck pages in the inactive queue.  In other words, the
1143 	 * number of pages from the inactive count that should be
1144 	 * discounted in setting the target for the active queue scan.
1145 	 */
1146 	addl_page_shortage = 0;
1147 
1148 	/*
1149 	 * Calculate the number of pages that we want to free.  This number
1150 	 * can be negative if many pages are freed between the wakeup call to
1151 	 * the page daemon and this calculation.
1152 	 */
1153 	if (pass > 0) {
1154 		deficit = atomic_readandclear_int(&vm_pageout_deficit);
1155 		page_shortage = vm_paging_target() + deficit;
1156 	} else
1157 		page_shortage = deficit = 0;
1158 	starting_page_shortage = page_shortage;
1159 
1160 	/*
1161 	 * Start scanning the inactive queue for pages that we can free.  The
1162 	 * scan will stop when we reach the target or we have scanned the
1163 	 * entire queue.  (Note that m->act_count is not used to make
1164 	 * decisions for the inactive queue, only for the active queue.)
1165 	 */
1166 	pq = &vmd->vmd_pagequeues[PQ_INACTIVE];
1167 	maxscan = pq->pq_cnt;
1168 	vm_pagequeue_lock(pq);
1169 	queue_locked = TRUE;
1170 	for (m = TAILQ_FIRST(&pq->pq_pl);
1171 	     m != NULL && maxscan-- > 0 && page_shortage > 0;
1172 	     m = next) {
1173 		vm_pagequeue_assert_locked(pq);
1174 		KASSERT(queue_locked, ("unlocked inactive queue"));
1175 		KASSERT(vm_page_inactive(m), ("Inactive queue %p", m));
1176 
1177 		VM_CNT_INC(v_pdpages);
1178 		next = TAILQ_NEXT(m, plinks.q);
1179 
1180 		/*
1181 		 * skip marker pages
1182 		 */
1183 		if (m->flags & PG_MARKER)
1184 			continue;
1185 
1186 		KASSERT((m->flags & PG_FICTITIOUS) == 0,
1187 		    ("Fictitious page %p cannot be in inactive queue", m));
1188 		KASSERT((m->oflags & VPO_UNMANAGED) == 0,
1189 		    ("Unmanaged page %p cannot be in inactive queue", m));
1190 
1191 		/*
1192 		 * The page or object lock acquisitions fail if the
1193 		 * page was removed from the queue or moved to a
1194 		 * different position within the queue.  In either
1195 		 * case, addl_page_shortage should not be incremented.
1196 		 */
1197 		if (!vm_pageout_page_lock(m, &next))
1198 			goto unlock_page;
1199 		else if (m->hold_count != 0) {
1200 			/*
1201 			 * Held pages are essentially stuck in the
1202 			 * queue.  So, they ought to be discounted
1203 			 * from the inactive count.  See the
1204 			 * calculation of inactq_shortage before the
1205 			 * loop over the active queue below.
1206 			 */
1207 			addl_page_shortage++;
1208 			goto unlock_page;
1209 		}
1210 		object = m->object;
1211 		if (!VM_OBJECT_TRYWLOCK(object)) {
1212 			if (!vm_pageout_fallback_object_lock(m, &next))
1213 				goto unlock_object;
1214 			else if (m->hold_count != 0) {
1215 				addl_page_shortage++;
1216 				goto unlock_object;
1217 			}
1218 		}
1219 		if (vm_page_busied(m)) {
1220 			/*
1221 			 * Don't mess with busy pages.  Leave them at
1222 			 * the front of the queue.  Most likely, they
1223 			 * are being paged out and will leave the
1224 			 * queue shortly after the scan finishes.  So,
1225 			 * they ought to be discounted from the
1226 			 * inactive count.
1227 			 */
1228 			addl_page_shortage++;
1229 unlock_object:
1230 			VM_OBJECT_WUNLOCK(object);
1231 unlock_page:
1232 			vm_page_unlock(m);
1233 			continue;
1234 		}
1235 		KASSERT(m->hold_count == 0, ("Held page %p", m));
1236 
1237 		/*
1238 		 * Dequeue the inactive page and unlock the inactive page
1239 		 * queue, invalidating the 'next' pointer.  Dequeueing the
1240 		 * page here avoids a later reacquisition (and release) of
1241 		 * the inactive page queue lock when vm_page_activate(),
1242 		 * vm_page_free(), or vm_page_launder() is called.  Use a
1243 		 * marker to remember our place in the inactive queue.
1244 		 */
1245 		TAILQ_INSERT_AFTER(&pq->pq_pl, m, &vmd->vmd_marker, plinks.q);
1246 		vm_page_dequeue_locked(m);
1247 		vm_pagequeue_unlock(pq);
1248 		queue_locked = FALSE;
1249 
1250 		/*
1251 		 * Invalid pages can be easily freed. They cannot be
1252 		 * mapped, vm_page_free() asserts this.
1253 		 */
1254 		if (m->valid == 0)
1255 			goto free_page;
1256 
1257 		/*
1258 		 * If the page has been referenced and the object is not dead,
1259 		 * reactivate or requeue the page depending on whether the
1260 		 * object is mapped.
1261 		 */
1262 		if ((m->aflags & PGA_REFERENCED) != 0) {
1263 			vm_page_aflag_clear(m, PGA_REFERENCED);
1264 			act_delta = 1;
1265 		} else
1266 			act_delta = 0;
1267 		if (object->ref_count != 0) {
1268 			act_delta += pmap_ts_referenced(m);
1269 		} else {
1270 			KASSERT(!pmap_page_is_mapped(m),
1271 			    ("vm_pageout_scan: page %p is mapped", m));
1272 		}
1273 		if (act_delta != 0) {
1274 			if (object->ref_count != 0) {
1275 				VM_CNT_INC(v_reactivated);
1276 				vm_page_activate(m);
1277 
1278 				/*
1279 				 * Increase the activation count if the page
1280 				 * was referenced while in the inactive queue.
1281 				 * This makes it less likely that the page will
1282 				 * be returned prematurely to the inactive
1283 				 * queue.
1284  				 */
1285 				m->act_count += act_delta + ACT_ADVANCE;
1286 				goto drop_page;
1287 			} else if ((object->flags & OBJ_DEAD) == 0) {
1288 				vm_pagequeue_lock(pq);
1289 				queue_locked = TRUE;
1290 				m->queue = PQ_INACTIVE;
1291 				TAILQ_INSERT_TAIL(&pq->pq_pl, m, plinks.q);
1292 				vm_pagequeue_cnt_inc(pq);
1293 				goto drop_page;
1294 			}
1295 		}
1296 
1297 		/*
1298 		 * If the page appears to be clean at the machine-independent
1299 		 * layer, then remove all of its mappings from the pmap in
1300 		 * anticipation of freeing it.  If, however, any of the page's
1301 		 * mappings allow write access, then the page may still be
1302 		 * modified until the last of those mappings are removed.
1303 		 */
1304 		if (object->ref_count != 0) {
1305 			vm_page_test_dirty(m);
1306 			if (m->dirty == 0)
1307 				pmap_remove_all(m);
1308 		}
1309 
1310 		/*
1311 		 * Clean pages can be freed, but dirty pages must be sent back
1312 		 * to the laundry, unless they belong to a dead object.
1313 		 * Requeueing dirty pages from dead objects is pointless, as
1314 		 * they are being paged out and freed by the thread that
1315 		 * destroyed the object.
1316 		 */
1317 		if (m->dirty == 0) {
1318 free_page:
1319 			vm_page_free(m);
1320 			VM_CNT_INC(v_dfree);
1321 			--page_shortage;
1322 		} else if ((object->flags & OBJ_DEAD) == 0)
1323 			vm_page_launder(m);
1324 drop_page:
1325 		vm_page_unlock(m);
1326 		VM_OBJECT_WUNLOCK(object);
1327 		if (!queue_locked) {
1328 			vm_pagequeue_lock(pq);
1329 			queue_locked = TRUE;
1330 		}
1331 		next = TAILQ_NEXT(&vmd->vmd_marker, plinks.q);
1332 		TAILQ_REMOVE(&pq->pq_pl, &vmd->vmd_marker, plinks.q);
1333 	}
1334 	vm_pagequeue_unlock(pq);
1335 
1336 	/*
1337 	 * Wake up the laundry thread so that it can perform any needed
1338 	 * laundering.  If we didn't meet our target, we're in shortfall and
1339 	 * need to launder more aggressively.  If PQ_LAUNDRY is empty and no
1340 	 * swap devices are configured, the laundry thread has no work to do, so
1341 	 * don't bother waking it up.
1342 	 */
1343 	if (vm_laundry_request == VM_LAUNDRY_IDLE &&
1344 	    starting_page_shortage > 0) {
1345 		pq = &vm_dom[0].vmd_pagequeues[PQ_LAUNDRY];
1346 		vm_pagequeue_lock(pq);
1347 		if (pq->pq_cnt > 0 || atomic_load_acq_int(&swapdev_enabled)) {
1348 			if (page_shortage > 0) {
1349 				vm_laundry_request = VM_LAUNDRY_SHORTFALL;
1350 				VM_CNT_INC(v_pdshortfalls);
1351 			} else if (vm_laundry_request != VM_LAUNDRY_SHORTFALL)
1352 				vm_laundry_request = VM_LAUNDRY_BACKGROUND;
1353 			wakeup(&vm_laundry_request);
1354 		}
1355 		vm_pagequeue_unlock(pq);
1356 	}
1357 
1358 	/*
1359 	 * Wakeup the swapout daemon if we didn't free the targeted number of
1360 	 * pages.
1361 	 */
1362 	if (page_shortage > 0)
1363 		vm_swapout_run();
1364 
1365 	/*
1366 	 * If the inactive queue scan fails repeatedly to meet its
1367 	 * target, kill the largest process.
1368 	 */
1369 	vm_pageout_mightbe_oom(vmd, page_shortage, starting_page_shortage);
1370 
1371 	/*
1372 	 * Compute the number of pages we want to try to move from the
1373 	 * active queue to either the inactive or laundry queue.
1374 	 *
1375 	 * When scanning active pages, we make clean pages count more heavily
1376 	 * towards the page shortage than dirty pages.  This is because dirty
1377 	 * pages must be laundered before they can be reused and thus have less
1378 	 * utility when attempting to quickly alleviate a shortage.  However,
1379 	 * this weighting also causes the scan to deactivate dirty pages more
1380 	 * more aggressively, improving the effectiveness of clustering and
1381 	 * ensuring that they can eventually be reused.
1382 	 */
1383 	inactq_shortage = vm_cnt.v_inactive_target - (vm_cnt.v_inactive_count +
1384 	    vm_cnt.v_laundry_count / act_scan_laundry_weight) +
1385 	    vm_paging_target() + deficit + addl_page_shortage;
1386 	page_shortage *= act_scan_laundry_weight;
1387 
1388 	pq = &vmd->vmd_pagequeues[PQ_ACTIVE];
1389 	vm_pagequeue_lock(pq);
1390 	maxscan = pq->pq_cnt;
1391 
1392 	/*
1393 	 * If we're just idle polling attempt to visit every
1394 	 * active page within 'update_period' seconds.
1395 	 */
1396 	scan_tick = ticks;
1397 	if (vm_pageout_update_period != 0) {
1398 		min_scan = pq->pq_cnt;
1399 		min_scan *= scan_tick - vmd->vmd_last_active_scan;
1400 		min_scan /= hz * vm_pageout_update_period;
1401 	} else
1402 		min_scan = 0;
1403 	if (min_scan > 0 || (inactq_shortage > 0 && maxscan > 0))
1404 		vmd->vmd_last_active_scan = scan_tick;
1405 
1406 	/*
1407 	 * Scan the active queue for pages that can be deactivated.  Update
1408 	 * the per-page activity counter and use it to identify deactivation
1409 	 * candidates.  Held pages may be deactivated.
1410 	 */
1411 	for (m = TAILQ_FIRST(&pq->pq_pl), scanned = 0; m != NULL && (scanned <
1412 	    min_scan || (inactq_shortage > 0 && scanned < maxscan)); m = next,
1413 	    scanned++) {
1414 		KASSERT(m->queue == PQ_ACTIVE,
1415 		    ("vm_pageout_scan: page %p isn't active", m));
1416 		next = TAILQ_NEXT(m, plinks.q);
1417 		if ((m->flags & PG_MARKER) != 0)
1418 			continue;
1419 		KASSERT((m->flags & PG_FICTITIOUS) == 0,
1420 		    ("Fictitious page %p cannot be in active queue", m));
1421 		KASSERT((m->oflags & VPO_UNMANAGED) == 0,
1422 		    ("Unmanaged page %p cannot be in active queue", m));
1423 		if (!vm_pageout_page_lock(m, &next)) {
1424 			vm_page_unlock(m);
1425 			continue;
1426 		}
1427 
1428 		/*
1429 		 * The count for page daemon pages is updated after checking
1430 		 * the page for eligibility.
1431 		 */
1432 		VM_CNT_INC(v_pdpages);
1433 
1434 		/*
1435 		 * Check to see "how much" the page has been used.
1436 		 */
1437 		if ((m->aflags & PGA_REFERENCED) != 0) {
1438 			vm_page_aflag_clear(m, PGA_REFERENCED);
1439 			act_delta = 1;
1440 		} else
1441 			act_delta = 0;
1442 
1443 		/*
1444 		 * Perform an unsynchronized object ref count check.  While
1445 		 * the page lock ensures that the page is not reallocated to
1446 		 * another object, in particular, one with unmanaged mappings
1447 		 * that cannot support pmap_ts_referenced(), two races are,
1448 		 * nonetheless, possible:
1449 		 * 1) The count was transitioning to zero, but we saw a non-
1450 		 *    zero value.  pmap_ts_referenced() will return zero
1451 		 *    because the page is not mapped.
1452 		 * 2) The count was transitioning to one, but we saw zero.
1453 		 *    This race delays the detection of a new reference.  At
1454 		 *    worst, we will deactivate and reactivate the page.
1455 		 */
1456 		if (m->object->ref_count != 0)
1457 			act_delta += pmap_ts_referenced(m);
1458 
1459 		/*
1460 		 * Advance or decay the act_count based on recent usage.
1461 		 */
1462 		if (act_delta != 0) {
1463 			m->act_count += ACT_ADVANCE + act_delta;
1464 			if (m->act_count > ACT_MAX)
1465 				m->act_count = ACT_MAX;
1466 		} else
1467 			m->act_count -= min(m->act_count, ACT_DECLINE);
1468 
1469 		/*
1470 		 * Move this page to the tail of the active, inactive or laundry
1471 		 * queue depending on usage.
1472 		 */
1473 		if (m->act_count == 0) {
1474 			/* Dequeue to avoid later lock recursion. */
1475 			vm_page_dequeue_locked(m);
1476 
1477 			/*
1478 			 * When not short for inactive pages, let dirty pages go
1479 			 * through the inactive queue before moving to the
1480 			 * laundry queues.  This gives them some extra time to
1481 			 * be reactivated, potentially avoiding an expensive
1482 			 * pageout.  During a page shortage, the inactive queue
1483 			 * is necessarily small, so we may move dirty pages
1484 			 * directly to the laundry queue.
1485 			 */
1486 			if (inactq_shortage <= 0)
1487 				vm_page_deactivate(m);
1488 			else {
1489 				/*
1490 				 * Calling vm_page_test_dirty() here would
1491 				 * require acquisition of the object's write
1492 				 * lock.  However, during a page shortage,
1493 				 * directing dirty pages into the laundry
1494 				 * queue is only an optimization and not a
1495 				 * requirement.  Therefore, we simply rely on
1496 				 * the opportunistic updates to the page's
1497 				 * dirty field by the pmap.
1498 				 */
1499 				if (m->dirty == 0) {
1500 					vm_page_deactivate(m);
1501 					inactq_shortage -=
1502 					    act_scan_laundry_weight;
1503 				} else {
1504 					vm_page_launder(m);
1505 					inactq_shortage--;
1506 				}
1507 			}
1508 		} else
1509 			vm_page_requeue_locked(m);
1510 		vm_page_unlock(m);
1511 	}
1512 	vm_pagequeue_unlock(pq);
1513 	if (pass > 0)
1514 		vm_swapout_run_idle();
1515 	return (page_shortage <= 0);
1516 }
1517 
1518 static int vm_pageout_oom_vote;
1519 
1520 /*
1521  * The pagedaemon threads randlomly select one to perform the
1522  * OOM.  Trying to kill processes before all pagedaemons
1523  * failed to reach free target is premature.
1524  */
1525 static void
1526 vm_pageout_mightbe_oom(struct vm_domain *vmd, int page_shortage,
1527     int starting_page_shortage)
1528 {
1529 	int old_vote;
1530 
1531 	if (starting_page_shortage <= 0 || starting_page_shortage !=
1532 	    page_shortage)
1533 		vmd->vmd_oom_seq = 0;
1534 	else
1535 		vmd->vmd_oom_seq++;
1536 	if (vmd->vmd_oom_seq < vm_pageout_oom_seq) {
1537 		if (vmd->vmd_oom) {
1538 			vmd->vmd_oom = FALSE;
1539 			atomic_subtract_int(&vm_pageout_oom_vote, 1);
1540 		}
1541 		return;
1542 	}
1543 
1544 	/*
1545 	 * Do not follow the call sequence until OOM condition is
1546 	 * cleared.
1547 	 */
1548 	vmd->vmd_oom_seq = 0;
1549 
1550 	if (vmd->vmd_oom)
1551 		return;
1552 
1553 	vmd->vmd_oom = TRUE;
1554 	old_vote = atomic_fetchadd_int(&vm_pageout_oom_vote, 1);
1555 	if (old_vote != vm_ndomains - 1)
1556 		return;
1557 
1558 	/*
1559 	 * The current pagedaemon thread is the last in the quorum to
1560 	 * start OOM.  Initiate the selection and signaling of the
1561 	 * victim.
1562 	 */
1563 	vm_pageout_oom(VM_OOM_MEM);
1564 
1565 	/*
1566 	 * After one round of OOM terror, recall our vote.  On the
1567 	 * next pass, current pagedaemon would vote again if the low
1568 	 * memory condition is still there, due to vmd_oom being
1569 	 * false.
1570 	 */
1571 	vmd->vmd_oom = FALSE;
1572 	atomic_subtract_int(&vm_pageout_oom_vote, 1);
1573 }
1574 
1575 /*
1576  * The OOM killer is the page daemon's action of last resort when
1577  * memory allocation requests have been stalled for a prolonged period
1578  * of time because it cannot reclaim memory.  This function computes
1579  * the approximate number of physical pages that could be reclaimed if
1580  * the specified address space is destroyed.
1581  *
1582  * Private, anonymous memory owned by the address space is the
1583  * principal resource that we expect to recover after an OOM kill.
1584  * Since the physical pages mapped by the address space's COW entries
1585  * are typically shared pages, they are unlikely to be released and so
1586  * they are not counted.
1587  *
1588  * To get to the point where the page daemon runs the OOM killer, its
1589  * efforts to write-back vnode-backed pages may have stalled.  This
1590  * could be caused by a memory allocation deadlock in the write path
1591  * that might be resolved by an OOM kill.  Therefore, physical pages
1592  * belonging to vnode-backed objects are counted, because they might
1593  * be freed without being written out first if the address space holds
1594  * the last reference to an unlinked vnode.
1595  *
1596  * Similarly, physical pages belonging to OBJT_PHYS objects are
1597  * counted because the address space might hold the last reference to
1598  * the object.
1599  */
1600 static long
1601 vm_pageout_oom_pagecount(struct vmspace *vmspace)
1602 {
1603 	vm_map_t map;
1604 	vm_map_entry_t entry;
1605 	vm_object_t obj;
1606 	long res;
1607 
1608 	map = &vmspace->vm_map;
1609 	KASSERT(!map->system_map, ("system map"));
1610 	sx_assert(&map->lock, SA_LOCKED);
1611 	res = 0;
1612 	for (entry = map->header.next; entry != &map->header;
1613 	    entry = entry->next) {
1614 		if ((entry->eflags & MAP_ENTRY_IS_SUB_MAP) != 0)
1615 			continue;
1616 		obj = entry->object.vm_object;
1617 		if (obj == NULL)
1618 			continue;
1619 		if ((entry->eflags & MAP_ENTRY_NEEDS_COPY) != 0 &&
1620 		    obj->ref_count != 1)
1621 			continue;
1622 		switch (obj->type) {
1623 		case OBJT_DEFAULT:
1624 		case OBJT_SWAP:
1625 		case OBJT_PHYS:
1626 		case OBJT_VNODE:
1627 			res += obj->resident_page_count;
1628 			break;
1629 		}
1630 	}
1631 	return (res);
1632 }
1633 
1634 void
1635 vm_pageout_oom(int shortage)
1636 {
1637 	struct proc *p, *bigproc;
1638 	vm_offset_t size, bigsize;
1639 	struct thread *td;
1640 	struct vmspace *vm;
1641 	bool breakout;
1642 
1643 	/*
1644 	 * We keep the process bigproc locked once we find it to keep anyone
1645 	 * from messing with it; however, there is a possibility of
1646 	 * deadlock if process B is bigproc and one of its child processes
1647 	 * attempts to propagate a signal to B while we are waiting for A's
1648 	 * lock while walking this list.  To avoid this, we don't block on
1649 	 * the process lock but just skip a process if it is already locked.
1650 	 */
1651 	bigproc = NULL;
1652 	bigsize = 0;
1653 	sx_slock(&allproc_lock);
1654 	FOREACH_PROC_IN_SYSTEM(p) {
1655 		PROC_LOCK(p);
1656 
1657 		/*
1658 		 * If this is a system, protected or killed process, skip it.
1659 		 */
1660 		if (p->p_state != PRS_NORMAL || (p->p_flag & (P_INEXEC |
1661 		    P_PROTECTED | P_SYSTEM | P_WEXIT)) != 0 ||
1662 		    p->p_pid == 1 || P_KILLED(p) ||
1663 		    (p->p_pid < 48 && swap_pager_avail != 0)) {
1664 			PROC_UNLOCK(p);
1665 			continue;
1666 		}
1667 		/*
1668 		 * If the process is in a non-running type state,
1669 		 * don't touch it.  Check all the threads individually.
1670 		 */
1671 		breakout = false;
1672 		FOREACH_THREAD_IN_PROC(p, td) {
1673 			thread_lock(td);
1674 			if (!TD_ON_RUNQ(td) &&
1675 			    !TD_IS_RUNNING(td) &&
1676 			    !TD_IS_SLEEPING(td) &&
1677 			    !TD_IS_SUSPENDED(td) &&
1678 			    !TD_IS_SWAPPED(td)) {
1679 				thread_unlock(td);
1680 				breakout = true;
1681 				break;
1682 			}
1683 			thread_unlock(td);
1684 		}
1685 		if (breakout) {
1686 			PROC_UNLOCK(p);
1687 			continue;
1688 		}
1689 		/*
1690 		 * get the process size
1691 		 */
1692 		vm = vmspace_acquire_ref(p);
1693 		if (vm == NULL) {
1694 			PROC_UNLOCK(p);
1695 			continue;
1696 		}
1697 		_PHOLD_LITE(p);
1698 		PROC_UNLOCK(p);
1699 		sx_sunlock(&allproc_lock);
1700 		if (!vm_map_trylock_read(&vm->vm_map)) {
1701 			vmspace_free(vm);
1702 			sx_slock(&allproc_lock);
1703 			PRELE(p);
1704 			continue;
1705 		}
1706 		size = vmspace_swap_count(vm);
1707 		if (shortage == VM_OOM_MEM)
1708 			size += vm_pageout_oom_pagecount(vm);
1709 		vm_map_unlock_read(&vm->vm_map);
1710 		vmspace_free(vm);
1711 		sx_slock(&allproc_lock);
1712 
1713 		/*
1714 		 * If this process is bigger than the biggest one,
1715 		 * remember it.
1716 		 */
1717 		if (size > bigsize) {
1718 			if (bigproc != NULL)
1719 				PRELE(bigproc);
1720 			bigproc = p;
1721 			bigsize = size;
1722 		} else {
1723 			PRELE(p);
1724 		}
1725 	}
1726 	sx_sunlock(&allproc_lock);
1727 	if (bigproc != NULL) {
1728 		if (vm_panic_on_oom != 0)
1729 			panic("out of swap space");
1730 		PROC_LOCK(bigproc);
1731 		killproc(bigproc, "out of swap space");
1732 		sched_nice(bigproc, PRIO_MIN);
1733 		_PRELE(bigproc);
1734 		PROC_UNLOCK(bigproc);
1735 		wakeup(&vm_cnt.v_free_count);
1736 	}
1737 }
1738 
1739 static void
1740 vm_pageout_worker(void *arg)
1741 {
1742 	struct vm_domain *domain;
1743 	int domidx, pass;
1744 	bool target_met;
1745 
1746 	domidx = (uintptr_t)arg;
1747 	domain = &vm_dom[domidx];
1748 	pass = 0;
1749 	target_met = true;
1750 
1751 	/*
1752 	 * XXXKIB It could be useful to bind pageout daemon threads to
1753 	 * the cores belonging to the domain, from which vm_page_array
1754 	 * is allocated.
1755 	 */
1756 
1757 	KASSERT(domain->vmd_segs != 0, ("domain without segments"));
1758 	domain->vmd_last_active_scan = ticks;
1759 	vm_pageout_init_marker(&domain->vmd_marker, PQ_INACTIVE);
1760 	vm_pageout_init_marker(&domain->vmd_inacthead, PQ_INACTIVE);
1761 	TAILQ_INSERT_HEAD(&domain->vmd_pagequeues[PQ_INACTIVE].pq_pl,
1762 	    &domain->vmd_inacthead, plinks.q);
1763 
1764 	/*
1765 	 * The pageout daemon worker is never done, so loop forever.
1766 	 */
1767 	while (TRUE) {
1768 		mtx_lock(&vm_page_queue_free_mtx);
1769 
1770 		/*
1771 		 * Generally, after a level >= 1 scan, if there are enough
1772 		 * free pages to wakeup the waiters, then they are already
1773 		 * awake.  A call to vm_page_free() during the scan awakened
1774 		 * them.  However, in the following case, this wakeup serves
1775 		 * to bound the amount of time that a thread might wait.
1776 		 * Suppose a thread's call to vm_page_alloc() fails, but
1777 		 * before that thread calls VM_WAIT, enough pages are freed by
1778 		 * other threads to alleviate the free page shortage.  The
1779 		 * thread will, nonetheless, wait until another page is freed
1780 		 * or this wakeup is performed.
1781 		 */
1782 		if (vm_pages_needed && !vm_page_count_min()) {
1783 			vm_pages_needed = false;
1784 			wakeup(&vm_cnt.v_free_count);
1785 		}
1786 
1787 		/*
1788 		 * Do not clear vm_pageout_wanted until we reach our free page
1789 		 * target.  Otherwise, we may be awakened over and over again,
1790 		 * wasting CPU time.
1791 		 */
1792 		if (vm_pageout_wanted && target_met)
1793 			vm_pageout_wanted = false;
1794 
1795 		/*
1796 		 * Might the page daemon receive a wakeup call?
1797 		 */
1798 		if (vm_pageout_wanted) {
1799 			/*
1800 			 * No.  Either vm_pageout_wanted was set by another
1801 			 * thread during the previous scan, which must have
1802 			 * been a level 0 scan, or vm_pageout_wanted was
1803 			 * already set and the scan failed to free enough
1804 			 * pages.  If we haven't yet performed a level >= 1
1805 			 * (page reclamation) scan, then increase the level
1806 			 * and scan again now.  Otherwise, sleep a bit and
1807 			 * try again later.
1808 			 */
1809 			mtx_unlock(&vm_page_queue_free_mtx);
1810 			if (pass >= 1)
1811 				pause("psleep", hz / VM_INACT_SCAN_RATE);
1812 			pass++;
1813 		} else {
1814 			/*
1815 			 * Yes.  Sleep until pages need to be reclaimed or
1816 			 * have their reference stats updated.
1817 			 */
1818 			if (mtx_sleep(&vm_pageout_wanted,
1819 			    &vm_page_queue_free_mtx, PDROP | PVM, "psleep",
1820 			    hz) == 0) {
1821 				VM_CNT_INC(v_pdwakeups);
1822 				pass = 1;
1823 			} else
1824 				pass = 0;
1825 		}
1826 
1827 		target_met = vm_pageout_scan(domain, pass);
1828 	}
1829 }
1830 
1831 /*
1832  *	vm_pageout_init initialises basic pageout daemon settings.
1833  */
1834 static void
1835 vm_pageout_init(void)
1836 {
1837 	/*
1838 	 * Initialize some paging parameters.
1839 	 */
1840 	vm_cnt.v_interrupt_free_min = 2;
1841 	if (vm_cnt.v_page_count < 2000)
1842 		vm_pageout_page_count = 8;
1843 
1844 	/*
1845 	 * v_free_reserved needs to include enough for the largest
1846 	 * swap pager structures plus enough for any pv_entry structs
1847 	 * when paging.
1848 	 */
1849 	if (vm_cnt.v_page_count > 1024)
1850 		vm_cnt.v_free_min = 4 + (vm_cnt.v_page_count - 1024) / 200;
1851 	else
1852 		vm_cnt.v_free_min = 4;
1853 	vm_cnt.v_pageout_free_min = (2*MAXBSIZE)/PAGE_SIZE +
1854 	    vm_cnt.v_interrupt_free_min;
1855 	vm_cnt.v_free_reserved = vm_pageout_page_count +
1856 	    vm_cnt.v_pageout_free_min + (vm_cnt.v_page_count / 768);
1857 	vm_cnt.v_free_severe = vm_cnt.v_free_min / 2;
1858 	vm_cnt.v_free_target = 4 * vm_cnt.v_free_min + vm_cnt.v_free_reserved;
1859 	vm_cnt.v_free_min += vm_cnt.v_free_reserved;
1860 	vm_cnt.v_free_severe += vm_cnt.v_free_reserved;
1861 	vm_cnt.v_inactive_target = (3 * vm_cnt.v_free_target) / 2;
1862 	if (vm_cnt.v_inactive_target > vm_cnt.v_free_count / 3)
1863 		vm_cnt.v_inactive_target = vm_cnt.v_free_count / 3;
1864 
1865 	/*
1866 	 * Set the default wakeup threshold to be 10% above the minimum
1867 	 * page limit.  This keeps the steady state out of shortfall.
1868 	 */
1869 	vm_pageout_wakeup_thresh = (vm_cnt.v_free_min / 10) * 11;
1870 
1871 	/*
1872 	 * Set interval in seconds for active scan.  We want to visit each
1873 	 * page at least once every ten minutes.  This is to prevent worst
1874 	 * case paging behaviors with stale active LRU.
1875 	 */
1876 	if (vm_pageout_update_period == 0)
1877 		vm_pageout_update_period = 600;
1878 
1879 	/* XXX does not really belong here */
1880 	if (vm_page_max_wired == 0)
1881 		vm_page_max_wired = vm_cnt.v_free_count / 3;
1882 
1883 	/*
1884 	 * Target amount of memory to move out of the laundry queue during a
1885 	 * background laundering.  This is proportional to the amount of system
1886 	 * memory.
1887 	 */
1888 	vm_background_launder_target = (vm_cnt.v_free_target -
1889 	    vm_cnt.v_free_min) / 10;
1890 }
1891 
1892 /*
1893  *     vm_pageout is the high level pageout daemon.
1894  */
1895 static void
1896 vm_pageout(void)
1897 {
1898 	int error;
1899 #ifdef VM_NUMA_ALLOC
1900 	int i;
1901 #endif
1902 
1903 	swap_pager_swap_init();
1904 	error = kthread_add(vm_pageout_laundry_worker, NULL, curproc, NULL,
1905 	    0, 0, "laundry: dom0");
1906 	if (error != 0)
1907 		panic("starting laundry for domain 0, error %d", error);
1908 #ifdef VM_NUMA_ALLOC
1909 	for (i = 1; i < vm_ndomains; i++) {
1910 		error = kthread_add(vm_pageout_worker, (void *)(uintptr_t)i,
1911 		    curproc, NULL, 0, 0, "dom%d", i);
1912 		if (error != 0) {
1913 			panic("starting pageout for domain %d, error %d\n",
1914 			    i, error);
1915 		}
1916 	}
1917 #endif
1918 	error = kthread_add(uma_reclaim_worker, NULL, curproc, NULL,
1919 	    0, 0, "uma");
1920 	if (error != 0)
1921 		panic("starting uma_reclaim helper, error %d\n", error);
1922 	vm_pageout_worker((void *)(uintptr_t)0);
1923 }
1924 
1925 /*
1926  * Unless the free page queue lock is held by the caller, this function
1927  * should be regarded as advisory.  Specifically, the caller should
1928  * not msleep() on &vm_cnt.v_free_count following this function unless
1929  * the free page queue lock is held until the msleep() is performed.
1930  */
1931 void
1932 pagedaemon_wakeup(void)
1933 {
1934 
1935 	if (!vm_pageout_wanted && curthread->td_proc != pageproc) {
1936 		vm_pageout_wanted = true;
1937 		wakeup(&vm_pageout_wanted);
1938 	}
1939 }
1940