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freebsd-dev/sys/vm/vm_pageout.c
Mark Johnston 27e29d103f Correct the description of vm_pageout_scan_inactive() after r334508. 
Reported by:	alc
2018-06-04 16:46:36 +00:00

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/*-
* SPDX-License-Identifier: (BSD-4-Clause AND MIT-CMU)
*
* Copyright (c) 1991 Regents of the University of California.
* All rights reserved.
* Copyright (c) 1994 John S. Dyson
* All rights reserved.
* Copyright (c) 1994 David Greenman
* All rights reserved.
* Copyright (c) 2005 Yahoo! Technologies Norway AS
* All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* The Mach Operating System project at Carnegie-Mellon University.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* from: @(#)vm_pageout.c 7.4 (Berkeley) 5/7/91
*
*
* Copyright (c) 1987, 1990 Carnegie-Mellon University.
* All rights reserved.
*
* Authors: Avadis Tevanian, Jr., Michael Wayne Young
*
* Permission to use, copy, modify and distribute this software and
* its documentation is hereby granted, provided that both the copyright
* notice and this permission notice appear in all copies of the
* software, derivative works or modified versions, and any portions
* thereof, and that both notices appear in supporting documentation.
*
* CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
* CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
* FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
*
* Carnegie Mellon requests users of this software to return to
*
* Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
* School of Computer Science
* Carnegie Mellon University
* Pittsburgh PA 15213-3890
*
* any improvements or extensions that they make and grant Carnegie the
* rights to redistribute these changes.
*/
/*
* The proverbial page-out daemon.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include "opt_vm.h"
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/eventhandler.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/kthread.h>
#include <sys/ktr.h>
#include <sys/mount.h>
#include <sys/racct.h>
#include <sys/resourcevar.h>
#include <sys/sched.h>
#include <sys/sdt.h>
#include <sys/signalvar.h>
#include <sys/smp.h>
#include <sys/time.h>
#include <sys/vnode.h>
#include <sys/vmmeter.h>
#include <sys/rwlock.h>
#include <sys/sx.h>
#include <sys/sysctl.h>
#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
#include <vm/vm_map.h>
#include <vm/vm_pageout.h>
#include <vm/vm_pager.h>
#include <vm/vm_phys.h>
#include <vm/vm_pagequeue.h>
#include <vm/swap_pager.h>
#include <vm/vm_extern.h>
#include <vm/uma.h>
/*
* System initialization
*/
/* the kernel process "vm_pageout"*/
static void vm_pageout(void);
static void vm_pageout_init(void);
static int vm_pageout_clean(vm_page_t m, int *numpagedout);
static int vm_pageout_cluster(vm_page_t m);
static void vm_pageout_mightbe_oom(struct vm_domain *vmd, int page_shortage,
int starting_page_shortage);
SYSINIT(pagedaemon_init, SI_SUB_KTHREAD_PAGE, SI_ORDER_FIRST, vm_pageout_init,
NULL);
struct proc *pageproc;
static struct kproc_desc page_kp = {
"pagedaemon",
vm_pageout,
&pageproc
};
SYSINIT(pagedaemon, SI_SUB_KTHREAD_PAGE, SI_ORDER_SECOND, kproc_start,
&page_kp);
SDT_PROVIDER_DEFINE(vm);
SDT_PROBE_DEFINE(vm, , , vm__lowmem_scan);
/* Pagedaemon activity rates, in subdivisions of one second. */
#define VM_LAUNDER_RATE 10
#define VM_INACT_SCAN_RATE 10
static int vm_pageout_oom_seq = 12;
static int vm_pageout_update_period;
static int disable_swap_pageouts;
static int lowmem_period = 10;
static time_t lowmem_uptime;
static int swapdev_enabled;
static int vm_panic_on_oom = 0;
SYSCTL_INT(_vm, OID_AUTO, panic_on_oom,
CTLFLAG_RWTUN, &vm_panic_on_oom, 0,
"panic on out of memory instead of killing the largest process");
SYSCTL_INT(_vm, OID_AUTO, pageout_update_period,
CTLFLAG_RWTUN, &vm_pageout_update_period, 0,
"Maximum active LRU update period");
SYSCTL_INT(_vm, OID_AUTO, lowmem_period, CTLFLAG_RWTUN, &lowmem_period, 0,
"Low memory callback period");
SYSCTL_INT(_vm, OID_AUTO, disable_swapspace_pageouts,
CTLFLAG_RWTUN, &disable_swap_pageouts, 0, "Disallow swapout of dirty pages");
static int pageout_lock_miss;
SYSCTL_INT(_vm, OID_AUTO, pageout_lock_miss,
CTLFLAG_RD, &pageout_lock_miss, 0, "vget() lock misses during pageout");
SYSCTL_INT(_vm, OID_AUTO, pageout_oom_seq,
CTLFLAG_RWTUN, &vm_pageout_oom_seq, 0,
"back-to-back calls to oom detector to start OOM");
static int act_scan_laundry_weight = 3;
SYSCTL_INT(_vm, OID_AUTO, act_scan_laundry_weight, CTLFLAG_RWTUN,
&act_scan_laundry_weight, 0,
"weight given to clean vs. dirty pages in active queue scans");
static u_int vm_background_launder_rate = 4096;
SYSCTL_UINT(_vm, OID_AUTO, background_launder_rate, CTLFLAG_RWTUN,
&vm_background_launder_rate, 0,
"background laundering rate, in kilobytes per second");
static u_int vm_background_launder_max = 20 * 1024;
SYSCTL_UINT(_vm, OID_AUTO, background_launder_max, CTLFLAG_RWTUN,
&vm_background_launder_max, 0, "background laundering cap, in kilobytes");
int vm_pageout_page_count = 32;
int vm_page_max_wired; /* XXX max # of wired pages system-wide */
SYSCTL_INT(_vm, OID_AUTO, max_wired,
CTLFLAG_RW, &vm_page_max_wired, 0, "System-wide limit to wired page count");
static u_int isqrt(u_int num);
static int vm_pageout_launder(struct vm_domain *vmd, int launder,
bool in_shortfall);
static void vm_pageout_laundry_worker(void *arg);
struct scan_state {
struct vm_batchqueue bq;
struct vm_pagequeue *pq;
vm_page_t marker;
int maxscan;
int scanned;
};
static void
vm_pageout_init_scan(struct scan_state *ss, struct vm_pagequeue *pq,
vm_page_t marker, vm_page_t after, int maxscan)
{
vm_pagequeue_assert_locked(pq);
KASSERT((marker->aflags & PGA_ENQUEUED) == 0,
("marker %p already enqueued", marker));
if (after == NULL)
TAILQ_INSERT_HEAD(&pq->pq_pl, marker, plinks.q);
else
TAILQ_INSERT_AFTER(&pq->pq_pl, after, marker, plinks.q);
vm_page_aflag_set(marker, PGA_ENQUEUED);
vm_batchqueue_init(&ss->bq);
ss->pq = pq;
ss->marker = marker;
ss->maxscan = maxscan;
ss->scanned = 0;
vm_pagequeue_unlock(pq);
}
static void
vm_pageout_end_scan(struct scan_state *ss)
{
struct vm_pagequeue *pq;
pq = ss->pq;
vm_pagequeue_assert_locked(pq);
KASSERT((ss->marker->aflags & PGA_ENQUEUED) != 0,
("marker %p not enqueued", ss->marker));
TAILQ_REMOVE(&pq->pq_pl, ss->marker, plinks.q);
vm_page_aflag_clear(ss->marker, PGA_ENQUEUED);
VM_CNT_ADD(v_pdpages, ss->scanned);
}
/*
* Add a small number of queued pages to a batch queue for later processing
* without the corresponding queue lock held. The caller must have enqueued a
* marker page at the desired start point for the scan. Pages will be
* physically dequeued if the caller so requests. Otherwise, the returned
* batch may contain marker pages, and it is up to the caller to handle them.
*
* When processing the batch queue, vm_page_queue() must be used to
* determine whether the page has been logically dequeued by another thread.
* Once this check is performed, the page lock guarantees that the page will
* not be disassociated from the queue.
*/
static __always_inline void
vm_pageout_collect_batch(struct scan_state *ss, const bool dequeue)
{
struct vm_pagequeue *pq;
vm_page_t m, marker;
marker = ss->marker;
pq = ss->pq;
KASSERT((marker->aflags & PGA_ENQUEUED) != 0,
("marker %p not enqueued", ss->marker));
vm_pagequeue_lock(pq);
for (m = TAILQ_NEXT(marker, plinks.q); m != NULL &&
ss->scanned < ss->maxscan && ss->bq.bq_cnt < VM_BATCHQUEUE_SIZE;
m = TAILQ_NEXT(m, plinks.q), ss->scanned++) {
if ((m->flags & PG_MARKER) == 0) {
KASSERT((m->aflags & PGA_ENQUEUED) != 0,
("page %p not enqueued", m));
KASSERT((m->flags & PG_FICTITIOUS) == 0,
("Fictitious page %p cannot be in page queue", m));
KASSERT((m->oflags & VPO_UNMANAGED) == 0,
("Unmanaged page %p cannot be in page queue", m));
} else if (dequeue)
continue;
(void)vm_batchqueue_insert(&ss->bq, m);
if (dequeue) {
TAILQ_REMOVE(&pq->pq_pl, m, plinks.q);
vm_page_aflag_clear(m, PGA_ENQUEUED);
}
}
TAILQ_REMOVE(&pq->pq_pl, marker, plinks.q);
if (__predict_true(m != NULL))
TAILQ_INSERT_BEFORE(m, marker, plinks.q);
else
TAILQ_INSERT_TAIL(&pq->pq_pl, marker, plinks.q);
if (dequeue)
vm_pagequeue_cnt_add(pq, -ss->bq.bq_cnt);
vm_pagequeue_unlock(pq);
}
/* Return the next page to be scanned, or NULL if the scan is complete. */
static __always_inline vm_page_t
vm_pageout_next(struct scan_state *ss, const bool dequeue)
{
if (ss->bq.bq_cnt == 0)
vm_pageout_collect_batch(ss, dequeue);
return (vm_batchqueue_pop(&ss->bq));
}
/*
* Scan for pages at adjacent offsets within the given page's object that are
* eligible for laundering, form a cluster of these pages and the given page,
* and launder that cluster.
*/
static int
vm_pageout_cluster(vm_page_t m)
{
vm_object_t object;
vm_page_t mc[2 * vm_pageout_page_count], p, pb, ps;
vm_pindex_t pindex;
int ib, is, page_base, pageout_count;
vm_page_assert_locked(m);
object = m->object;
VM_OBJECT_ASSERT_WLOCKED(object);
pindex = m->pindex;
vm_page_assert_unbusied(m);
KASSERT(!vm_page_held(m), ("page %p is held", m));
pmap_remove_write(m);
vm_page_unlock(m);
mc[vm_pageout_page_count] = pb = ps = m;
pageout_count = 1;
page_base = vm_pageout_page_count;
ib = 1;
is = 1;
/*
* We can cluster only if the page is not clean, busy, or held, and
* the page is in the laundry queue.
*
* During heavy mmap/modification loads the pageout
* daemon can really fragment the underlying file
* due to flushing pages out of order and not trying to
* align the clusters (which leaves sporadic out-of-order
* holes). To solve this problem we do the reverse scan
* first and attempt to align our cluster, then do a
* forward scan if room remains.
*/
more:
while (ib != 0 && pageout_count < vm_pageout_page_count) {
if (ib > pindex) {
ib = 0;
break;
}
if ((p = vm_page_prev(pb)) == NULL || vm_page_busied(p)) {
ib = 0;
break;
}
vm_page_test_dirty(p);
if (p->dirty == 0) {
ib = 0;
break;
}
vm_page_lock(p);
if (vm_page_held(p) || !vm_page_in_laundry(p)) {
vm_page_unlock(p);
ib = 0;
break;
}
pmap_remove_write(p);
vm_page_unlock(p);
mc[--page_base] = pb = p;
++pageout_count;
++ib;
/*
* We are at an alignment boundary. Stop here, and switch
* directions. Do not clear ib.
*/
if ((pindex - (ib - 1)) % vm_pageout_page_count == 0)
break;
}
while (pageout_count < vm_pageout_page_count &&
pindex + is < object->size) {
if ((p = vm_page_next(ps)) == NULL || vm_page_busied(p))
break;
vm_page_test_dirty(p);
if (p->dirty == 0)
break;
vm_page_lock(p);
if (vm_page_held(p) || !vm_page_in_laundry(p)) {
vm_page_unlock(p);
break;
}
pmap_remove_write(p);
vm_page_unlock(p);
mc[page_base + pageout_count] = ps = p;
++pageout_count;
++is;
}
/*
* If we exhausted our forward scan, continue with the reverse scan
* when possible, even past an alignment boundary. This catches
* boundary conditions.
*/
if (ib != 0 && pageout_count < vm_pageout_page_count)
goto more;
return (vm_pageout_flush(&mc[page_base], pageout_count,
VM_PAGER_PUT_NOREUSE, 0, NULL, NULL));
}
/*
* vm_pageout_flush() - launder the given pages
*
* The given pages are laundered. Note that we setup for the start of
* I/O ( i.e. busy the page ), mark it read-only, and bump the object
* reference count all in here rather then in the parent. If we want
* the parent to do more sophisticated things we may have to change
* the ordering.
*
* Returned runlen is the count of pages between mreq and first
* page after mreq with status VM_PAGER_AGAIN.
* *eio is set to TRUE if pager returned VM_PAGER_ERROR or VM_PAGER_FAIL
* for any page in runlen set.
*/
int
vm_pageout_flush(vm_page_t *mc, int count, int flags, int mreq, int *prunlen,
boolean_t *eio)
{
vm_object_t object = mc[0]->object;
int pageout_status[count];
int numpagedout = 0;
int i, runlen;
VM_OBJECT_ASSERT_WLOCKED(object);
/*
* Initiate I/O. Mark the pages busy and verify that they're valid
* and read-only.
*
* We do not have to fixup the clean/dirty bits here... we can
* allow the pager to do it after the I/O completes.
*
* NOTE! mc[i]->dirty may be partial or fragmented due to an
* edge case with file fragments.
*/
for (i = 0; i < count; i++) {
KASSERT(mc[i]->valid == VM_PAGE_BITS_ALL,
("vm_pageout_flush: partially invalid page %p index %d/%d",
mc[i], i, count));
KASSERT((mc[i]->aflags & PGA_WRITEABLE) == 0,
("vm_pageout_flush: writeable page %p", mc[i]));
vm_page_sbusy(mc[i]);
}
vm_object_pip_add(object, count);
vm_pager_put_pages(object, mc, count, flags, pageout_status);
runlen = count - mreq;
if (eio != NULL)
*eio = FALSE;
for (i = 0; i < count; i++) {
vm_page_t mt = mc[i];
KASSERT(pageout_status[i] == VM_PAGER_PEND ||
!pmap_page_is_write_mapped(mt),
("vm_pageout_flush: page %p is not write protected", mt));
switch (pageout_status[i]) {
case VM_PAGER_OK:
vm_page_lock(mt);
if (vm_page_in_laundry(mt))
vm_page_deactivate_noreuse(mt);
vm_page_unlock(mt);
/* FALLTHROUGH */
case VM_PAGER_PEND:
numpagedout++;
break;
case VM_PAGER_BAD:
/*
* The page is outside the object's range. We pretend
* that the page out worked and clean the page, so the
* changes will be lost if the page is reclaimed by
* the page daemon.
*/
vm_page_undirty(mt);
vm_page_lock(mt);
if (vm_page_in_laundry(mt))
vm_page_deactivate_noreuse(mt);
vm_page_unlock(mt);
break;
case VM_PAGER_ERROR:
case VM_PAGER_FAIL:
/*
* If the page couldn't be paged out to swap because the
* pager wasn't able to find space, place the page in
* the PQ_UNSWAPPABLE holding queue. This is an
* optimization that prevents the page daemon from
* wasting CPU cycles on pages that cannot be reclaimed
* becase no swap device is configured.
*
* Otherwise, reactivate the page so that it doesn't
* clog the laundry and inactive queues. (We will try
* paging it out again later.)
*/
vm_page_lock(mt);
if (object->type == OBJT_SWAP &&
pageout_status[i] == VM_PAGER_FAIL) {
vm_page_unswappable(mt);
numpagedout++;
} else
vm_page_activate(mt);
vm_page_unlock(mt);
if (eio != NULL && i >= mreq && i - mreq < runlen)
*eio = TRUE;
break;
case VM_PAGER_AGAIN:
if (i >= mreq && i - mreq < runlen)
runlen = i - mreq;
break;
}
/*
* If the operation is still going, leave the page busy to
* block all other accesses. Also, leave the paging in
* progress indicator set so that we don't attempt an object
* collapse.
*/
if (pageout_status[i] != VM_PAGER_PEND) {
vm_object_pip_wakeup(object);
vm_page_sunbusy(mt);
}
}
if (prunlen != NULL)
*prunlen = runlen;
return (numpagedout);
}
static void
vm_pageout_swapon(void *arg __unused, struct swdevt *sp __unused)
{
atomic_store_rel_int(&swapdev_enabled, 1);
}
static void
vm_pageout_swapoff(void *arg __unused, struct swdevt *sp __unused)
{
if (swap_pager_nswapdev() == 1)
atomic_store_rel_int(&swapdev_enabled, 0);
}
/*
* Attempt to acquire all of the necessary locks to launder a page and
* then call through the clustering layer to PUTPAGES. Wait a short
* time for a vnode lock.
*
* Requires the page and object lock on entry, releases both before return.
* Returns 0 on success and an errno otherwise.
*/
static int
vm_pageout_clean(vm_page_t m, int *numpagedout)
{
struct vnode *vp;
struct mount *mp;
vm_object_t object;
vm_pindex_t pindex;
int error, lockmode;
vm_page_assert_locked(m);
object = m->object;
VM_OBJECT_ASSERT_WLOCKED(object);
error = 0;
vp = NULL;
mp = NULL;
/*
* The object is already known NOT to be dead. It
* is possible for the vget() to block the whole
* pageout daemon, but the new low-memory handling
* code should prevent it.
*
* We can't wait forever for the vnode lock, we might
* deadlock due to a vn_read() getting stuck in
* vm_wait while holding this vnode. We skip the
* vnode if we can't get it in a reasonable amount
* of time.
*/
if (object->type == OBJT_VNODE) {
vm_page_unlock(m);
vp = object->handle;
if (vp->v_type == VREG &&
vn_start_write(vp, &mp, V_NOWAIT) != 0) {
mp = NULL;
error = EDEADLK;
goto unlock_all;
}
KASSERT(mp != NULL,
("vp %p with NULL v_mount", vp));
vm_object_reference_locked(object);
pindex = m->pindex;
VM_OBJECT_WUNLOCK(object);
lockmode = MNT_SHARED_WRITES(vp->v_mount) ?
LK_SHARED : LK_EXCLUSIVE;
if (vget(vp, lockmode | LK_TIMELOCK, curthread)) {
vp = NULL;
error = EDEADLK;
goto unlock_mp;
}
VM_OBJECT_WLOCK(object);
/*
* Ensure that the object and vnode were not disassociated
* while locks were dropped.
*/
if (vp->v_object != object) {
error = ENOENT;
goto unlock_all;
}
vm_page_lock(m);
/*
* While the object and page were unlocked, the page
* may have been:
* (1) moved to a different queue,
* (2) reallocated to a different object,
* (3) reallocated to a different offset, or
* (4) cleaned.
*/
if (!vm_page_in_laundry(m) || m->object != object ||
m->pindex != pindex || m->dirty == 0) {
vm_page_unlock(m);
error = ENXIO;
goto unlock_all;
}
/*
* The page may have been busied or referenced while the object
* and page locks were released.
*/
if (vm_page_busied(m) || vm_page_held(m)) {
vm_page_unlock(m);
error = EBUSY;
goto unlock_all;
}
}
/*
* If a page is dirty, then it is either being washed
* (but not yet cleaned) or it is still in the
* laundry. If it is still in the laundry, then we
* start the cleaning operation.
*/
if ((*numpagedout = vm_pageout_cluster(m)) == 0)
error = EIO;
unlock_all:
VM_OBJECT_WUNLOCK(object);
unlock_mp:
vm_page_lock_assert(m, MA_NOTOWNED);
if (mp != NULL) {
if (vp != NULL)
vput(vp);
vm_object_deallocate(object);
vn_finished_write(mp);
}
return (error);
}
/*
* Attempt to launder the specified number of pages.
*
* Returns the number of pages successfully laundered.
*/
static int
vm_pageout_launder(struct vm_domain *vmd, int launder, bool in_shortfall)
{
struct scan_state ss;
struct vm_pagequeue *pq;
struct mtx *mtx;
vm_object_t object;
vm_page_t m, marker;
int act_delta, error, numpagedout, queue, starting_target;
int vnodes_skipped;
bool obj_locked, pageout_ok;
mtx = NULL;
obj_locked = false;
object = NULL;
starting_target = launder;
vnodes_skipped = 0;
/*
* Scan the laundry queues for pages eligible to be laundered. We stop
* once the target number of dirty pages have been laundered, or once
* we've reached the end of the queue. A single iteration of this loop
* may cause more than one page to be laundered because of clustering.
*
* As an optimization, we avoid laundering from PQ_UNSWAPPABLE when no
* swap devices are configured.
*/
if (atomic_load_acq_int(&swapdev_enabled))
queue = PQ_UNSWAPPABLE;
else
queue = PQ_LAUNDRY;
scan:
marker = &vmd->vmd_markers[queue];
pq = &vmd->vmd_pagequeues[queue];
vm_pagequeue_lock(pq);
vm_pageout_init_scan(&ss, pq, marker, NULL, pq->pq_cnt);
while (launder > 0 && (m = vm_pageout_next(&ss, false)) != NULL) {
if (__predict_false((m->flags & PG_MARKER) != 0))
continue;
vm_page_change_lock(m, &mtx);
recheck:
/*
* The page may have been disassociated from the queue
* while locks were dropped.
*/
if (vm_page_queue(m) != queue)
continue;
/*
* A requeue was requested, so this page gets a second
* chance.
*/
if ((m->aflags & PGA_REQUEUE) != 0) {
vm_page_requeue(m);
continue;
}
/*
* Held pages are essentially stuck in the queue.
*
* Wired pages may not be freed. Complete their removal
* from the queue now to avoid needless revisits during
* future scans.
*/
if (m->hold_count != 0)
continue;
if (m->wire_count != 0) {
vm_page_dequeue_deferred(m);
continue;
}
if (object != m->object) {
if (obj_locked) {
VM_OBJECT_WUNLOCK(object);
obj_locked = false;
}
object = m->object;
}
if (!obj_locked) {
if (!VM_OBJECT_TRYWLOCK(object)) {
mtx_unlock(mtx);
/* Depends on type-stability. */
VM_OBJECT_WLOCK(object);
obj_locked = true;
mtx_lock(mtx);
goto recheck;
} else
obj_locked = true;
}
if (vm_page_busied(m))
continue;
/*
* Invalid pages can be easily freed. They cannot be
* mapped; vm_page_free() asserts this.
*/
if (m->valid == 0)
goto free_page;
/*
* If the page has been referenced and the object is not dead,
* reactivate or requeue the page depending on whether the
* object is mapped.
*/
if ((m->aflags & PGA_REFERENCED) != 0) {
vm_page_aflag_clear(m, PGA_REFERENCED);
act_delta = 1;
} else
act_delta = 0;
if (object->ref_count != 0)
act_delta += pmap_ts_referenced(m);
else {
KASSERT(!pmap_page_is_mapped(m),
("page %p is mapped", m));
}
if (act_delta != 0) {
if (object->ref_count != 0) {
VM_CNT_INC(v_reactivated);
vm_page_activate(m);
/*
* Increase the activation count if the page
* was referenced while in the laundry queue.
* This makes it less likely that the page will
* be returned prematurely to the inactive
* queue.
*/
m->act_count += act_delta + ACT_ADVANCE;
/*
* If this was a background laundering, count
* activated pages towards our target. The
* purpose of background laundering is to ensure
* that pages are eventually cycled through the
* laundry queue, and an activation is a valid
* way out.
*/
if (!in_shortfall)
launder--;
continue;
} else if ((object->flags & OBJ_DEAD) == 0) {
vm_page_requeue(m);
continue;
}
}
/*
* If the page appears to be clean at the machine-independent
* layer, then remove all of its mappings from the pmap in
* anticipation of freeing it. If, however, any of the page's
* mappings allow write access, then the page may still be
* modified until the last of those mappings are removed.
*/
if (object->ref_count != 0) {
vm_page_test_dirty(m);
if (m->dirty == 0)
pmap_remove_all(m);
}
/*
* Clean pages are freed, and dirty pages are paged out unless
* they belong to a dead object. Requeueing dirty pages from
* dead objects is pointless, as they are being paged out and
* freed by the thread that destroyed the object.
*/
if (m->dirty == 0) {
free_page:
vm_page_free(m);
VM_CNT_INC(v_dfree);
} else if ((object->flags & OBJ_DEAD) == 0) {
if (object->type != OBJT_SWAP &&
object->type != OBJT_DEFAULT)
pageout_ok = true;
else if (disable_swap_pageouts)
pageout_ok = false;
else
pageout_ok = true;
if (!pageout_ok) {
vm_page_requeue(m);
continue;
}
/*
* Form a cluster with adjacent, dirty pages from the
* same object, and page out that entire cluster.
*
* The adjacent, dirty pages must also be in the
* laundry. However, their mappings are not checked
* for new references. Consequently, a recently
* referenced page may be paged out. However, that
* page will not be prematurely reclaimed. After page
* out, the page will be placed in the inactive queue,
* where any new references will be detected and the
* page reactivated.
*/
error = vm_pageout_clean(m, &numpagedout);
if (error == 0) {
launder -= numpagedout;
ss.scanned += numpagedout;
} else if (error == EDEADLK) {
pageout_lock_miss++;
vnodes_skipped++;
}
mtx = NULL;
obj_locked = false;
}
}
if (mtx != NULL) {
mtx_unlock(mtx);
mtx = NULL;
}
if (obj_locked) {
VM_OBJECT_WUNLOCK(object);
obj_locked = false;
}
vm_pagequeue_lock(pq);
vm_pageout_end_scan(&ss);
vm_pagequeue_unlock(pq);
if (launder > 0 && queue == PQ_UNSWAPPABLE) {
queue = PQ_LAUNDRY;
goto scan;
}
/*
* Wakeup the sync daemon if we skipped a vnode in a writeable object
* and we didn't launder enough pages.
*/
if (vnodes_skipped > 0 && launder > 0)
(void)speedup_syncer();
return (starting_target - launder);
}
/*
* Compute the integer square root.
*/
static u_int
isqrt(u_int num)
{
u_int bit, root, tmp;
bit = 1u << ((NBBY * sizeof(u_int)) - 2);
while (bit > num)
bit >>= 2;
root = 0;
while (bit != 0) {
tmp = root + bit;
root >>= 1;
if (num >= tmp) {
num -= tmp;
root += bit;
}
bit >>= 2;
}
return (root);
}
/*
* Perform the work of the laundry thread: periodically wake up and determine
* whether any pages need to be laundered. If so, determine the number of pages
* that need to be laundered, and launder them.
*/
static void
vm_pageout_laundry_worker(void *arg)
{
struct vm_domain *vmd;
struct vm_pagequeue *pq;
uint64_t nclean, ndirty, nfreed;
int domain, last_target, launder, shortfall, shortfall_cycle, target;
bool in_shortfall;
domain = (uintptr_t)arg;
vmd = VM_DOMAIN(domain);
pq = &vmd->vmd_pagequeues[PQ_LAUNDRY];
KASSERT(vmd->vmd_segs != 0, ("domain without segments"));
shortfall = 0;
in_shortfall = false;
shortfall_cycle = 0;
target = 0;
nfreed = 0;
/*
* Calls to these handlers are serialized by the swap syscall lock.
*/
(void)EVENTHANDLER_REGISTER(swapon, vm_pageout_swapon, vmd,
EVENTHANDLER_PRI_ANY);
(void)EVENTHANDLER_REGISTER(swapoff, vm_pageout_swapoff, vmd,
EVENTHANDLER_PRI_ANY);
/*
* The pageout laundry worker is never done, so loop forever.
*/
for (;;) {
KASSERT(target >= 0, ("negative target %d", target));
KASSERT(shortfall_cycle >= 0,
("negative cycle %d", shortfall_cycle));
launder = 0;
/*
* First determine whether we need to launder pages to meet a
* shortage of free pages.
*/
if (shortfall > 0) {
in_shortfall = true;
shortfall_cycle = VM_LAUNDER_RATE / VM_INACT_SCAN_RATE;
target = shortfall;
} else if (!in_shortfall)
goto trybackground;
else if (shortfall_cycle == 0 || vm_laundry_target(vmd) <= 0) {
/*
* We recently entered shortfall and began laundering
* pages. If we have completed that laundering run
* (and we are no longer in shortfall) or we have met
* our laundry target through other activity, then we
* can stop laundering pages.
*/
in_shortfall = false;
target = 0;
goto trybackground;
}
launder = target / shortfall_cycle--;
goto dolaundry;
/*
* There's no immediate need to launder any pages; see if we
* meet the conditions to perform background laundering:
*
* 1. The ratio of dirty to clean inactive pages exceeds the
* background laundering threshold, or
* 2. we haven't yet reached the target of the current
* background laundering run.
*
* The background laundering threshold is not a constant.
* Instead, it is a slowly growing function of the number of
* clean pages freed by the page daemon since the last
* background laundering. Thus, as the ratio of dirty to
* clean inactive pages grows, the amount of memory pressure
* required to trigger laundering decreases. We ensure
* that the threshold is non-zero after an inactive queue
* scan, even if that scan failed to free a single clean page.
*/
trybackground:
nclean = vmd->vmd_free_count +
vmd->vmd_pagequeues[PQ_INACTIVE].pq_cnt;
ndirty = vmd->vmd_pagequeues[PQ_LAUNDRY].pq_cnt;
if (target == 0 && ndirty * isqrt(howmany(nfreed + 1,
vmd->vmd_free_target - vmd->vmd_free_min)) >= nclean) {
target = vmd->vmd_background_launder_target;
}
/*
* We have a non-zero background laundering target. If we've
* laundered up to our maximum without observing a page daemon
* request, just stop. This is a safety belt that ensures we
* don't launder an excessive amount if memory pressure is low
* and the ratio of dirty to clean pages is large. Otherwise,
* proceed at the background laundering rate.
*/
if (target > 0) {
if (nfreed > 0) {
nfreed = 0;
last_target = target;
} else if (last_target - target >=
vm_background_launder_max * PAGE_SIZE / 1024) {
target = 0;
}
launder = vm_background_launder_rate * PAGE_SIZE / 1024;
launder /= VM_LAUNDER_RATE;
if (launder > target)
launder = target;
}
dolaundry:
if (launder > 0) {
/*
* Because of I/O clustering, the number of laundered
* pages could exceed "target" by the maximum size of
* a cluster minus one.
*/
target -= min(vm_pageout_launder(vmd, launder,
in_shortfall), target);
pause("laundp", hz / VM_LAUNDER_RATE);
}
/*
* If we're not currently laundering pages and the page daemon
* hasn't posted a new request, sleep until the page daemon
* kicks us.
*/
vm_pagequeue_lock(pq);
if (target == 0 && vmd->vmd_laundry_request == VM_LAUNDRY_IDLE)
(void)mtx_sleep(&vmd->vmd_laundry_request,
vm_pagequeue_lockptr(pq), PVM, "launds", 0);
/*
* If the pagedaemon has indicated that it's in shortfall, start
* a shortfall laundering unless we're already in the middle of
* one. This may preempt a background laundering.
*/
if (vmd->vmd_laundry_request == VM_LAUNDRY_SHORTFALL &&
(!in_shortfall || shortfall_cycle == 0)) {
shortfall = vm_laundry_target(vmd) +
vmd->vmd_pageout_deficit;
target = 0;
} else
shortfall = 0;
if (target == 0)
vmd->vmd_laundry_request = VM_LAUNDRY_IDLE;
nfreed += vmd->vmd_clean_pages_freed;
vmd->vmd_clean_pages_freed = 0;
vm_pagequeue_unlock(pq);
}
}
/*
* Compute the number of pages we want to try to move from the
* active queue to either the inactive or laundry queue.
*
* When scanning active pages during a shortage, we make clean pages
* count more heavily towards the page shortage than dirty pages.
* This is because dirty pages must be laundered before they can be
* reused and thus have less utility when attempting to quickly
* alleviate a free page shortage. However, this weighting also
* causes the scan to deactivate dirty pages more aggressively,
* improving the effectiveness of clustering.
*/
static int
vm_pageout_active_target(struct vm_domain *vmd)
{
int shortage;
shortage = vmd->vmd_inactive_target + vm_paging_target(vmd) -
(vmd->vmd_pagequeues[PQ_INACTIVE].pq_cnt +
vmd->vmd_pagequeues[PQ_LAUNDRY].pq_cnt / act_scan_laundry_weight);
shortage *= act_scan_laundry_weight;
return (shortage);
}
/*
* Scan the active queue. If there is no shortage of inactive pages, scan a
* small portion of the queue in order to maintain quasi-LRU.
*/
static void
vm_pageout_scan_active(struct vm_domain *vmd, int page_shortage)
{
struct scan_state ss;
struct mtx *mtx;
vm_page_t m, marker;
struct vm_pagequeue *pq;
long min_scan;
int act_delta, max_scan, scan_tick;
marker = &vmd->vmd_markers[PQ_ACTIVE];
pq = &vmd->vmd_pagequeues[PQ_ACTIVE];
vm_pagequeue_lock(pq);
/*
* If we're just idle polling attempt to visit every
* active page within 'update_period' seconds.
*/
scan_tick = ticks;
if (vm_pageout_update_period != 0) {
min_scan = pq->pq_cnt;
min_scan *= scan_tick - vmd->vmd_last_active_scan;
min_scan /= hz * vm_pageout_update_period;
} else
min_scan = 0;
if (min_scan > 0 || (page_shortage > 0 && pq->pq_cnt > 0))
vmd->vmd_last_active_scan = scan_tick;
/*
* Scan the active queue for pages that can be deactivated. Update
* the per-page activity counter and use it to identify deactivation
* candidates. Held pages may be deactivated.
*
* To avoid requeuing each page that remains in the active queue, we
* implement the CLOCK algorithm. To keep the implementation of the
* enqueue operation consistent for all page queues, we use two hands,
* represented by marker pages. Scans begin at the first hand, which
* precedes the second hand in the queue. When the two hands meet,
* they are moved back to the head and tail of the queue, respectively,
* and scanning resumes.
*/
max_scan = page_shortage > 0 ? pq->pq_cnt : min_scan;
mtx = NULL;
act_scan:
vm_pageout_init_scan(&ss, pq, marker, &vmd->vmd_clock[0], max_scan);
while ((m = vm_pageout_next(&ss, false)) != NULL) {
if (__predict_false(m == &vmd->vmd_clock[1])) {
vm_pagequeue_lock(pq);
TAILQ_REMOVE(&pq->pq_pl, &vmd->vmd_clock[0], plinks.q);
TAILQ_REMOVE(&pq->pq_pl, &vmd->vmd_clock[1], plinks.q);
TAILQ_INSERT_HEAD(&pq->pq_pl, &vmd->vmd_clock[0],
plinks.q);
TAILQ_INSERT_TAIL(&pq->pq_pl, &vmd->vmd_clock[1],
plinks.q);
max_scan -= ss.scanned;
vm_pageout_end_scan(&ss);
goto act_scan;
}
if (__predict_false((m->flags & PG_MARKER) != 0))
continue;
vm_page_change_lock(m, &mtx);
/*
* The page may have been disassociated from the queue
* while locks were dropped.
*/
if (vm_page_queue(m) != PQ_ACTIVE)
continue;
/*
* Wired pages are dequeued lazily.
*/
if (m->wire_count != 0) {
vm_page_dequeue_deferred(m);
continue;
}
/*
* Check to see "how much" the page has been used.
*/
if ((m->aflags & PGA_REFERENCED) != 0) {
vm_page_aflag_clear(m, PGA_REFERENCED);
act_delta = 1;
} else
act_delta = 0;
/*
* Perform an unsynchronized object ref count check. While
* the page lock ensures that the page is not reallocated to
* another object, in particular, one with unmanaged mappings
* that cannot support pmap_ts_referenced(), two races are,
* nonetheless, possible:
* 1) The count was transitioning to zero, but we saw a non-
* zero value. pmap_ts_referenced() will return zero
* because the page is not mapped.
* 2) The count was transitioning to one, but we saw zero.
* This race delays the detection of a new reference. At
* worst, we will deactivate and reactivate the page.
*/
if (m->object->ref_count != 0)
act_delta += pmap_ts_referenced(m);
/*
* Advance or decay the act_count based on recent usage.
*/
if (act_delta != 0) {
m->act_count += ACT_ADVANCE + act_delta;
if (m->act_count > ACT_MAX)
m->act_count = ACT_MAX;
} else
m->act_count -= min(m->act_count, ACT_DECLINE);
if (m->act_count == 0) {
/*
* When not short for inactive pages, let dirty pages go
* through the inactive queue before moving to the
* laundry queues. This gives them some extra time to
* be reactivated, potentially avoiding an expensive
* pageout. However, during a page shortage, the
* inactive queue is necessarily small, and so dirty
* pages would only spend a trivial amount of time in
* the inactive queue. Therefore, we might as well
* place them directly in the laundry queue to reduce
* queuing overhead.
*/
if (page_shortage <= 0)
vm_page_deactivate(m);
else {
/*
* Calling vm_page_test_dirty() here would
* require acquisition of the object's write
* lock. However, during a page shortage,
* directing dirty pages into the laundry
* queue is only an optimization and not a
* requirement. Therefore, we simply rely on
* the opportunistic updates to the page's
* dirty field by the pmap.
*/
if (m->dirty == 0) {
vm_page_deactivate(m);
page_shortage -=
act_scan_laundry_weight;
} else {
vm_page_launder(m);
page_shortage--;
}
}
}
}
if (mtx != NULL) {
mtx_unlock(mtx);
mtx = NULL;
}
vm_pagequeue_lock(pq);
TAILQ_REMOVE(&pq->pq_pl, &vmd->vmd_clock[0], plinks.q);
TAILQ_INSERT_AFTER(&pq->pq_pl, marker, &vmd->vmd_clock[0], plinks.q);
vm_pageout_end_scan(&ss);
vm_pagequeue_unlock(pq);
}
static int
vm_pageout_reinsert_inactive_page(struct scan_state *ss, vm_page_t m)
{
struct vm_domain *vmd;
if (m->queue != PQ_INACTIVE || (m->aflags & PGA_ENQUEUED) != 0)
return (0);
vm_page_aflag_set(m, PGA_ENQUEUED);
if ((m->aflags & PGA_REQUEUE_HEAD) != 0) {
vmd = vm_pagequeue_domain(m);
TAILQ_INSERT_BEFORE(&vmd->vmd_inacthead, m, plinks.q);
vm_page_aflag_clear(m, PGA_REQUEUE | PGA_REQUEUE_HEAD);
} else if ((m->aflags & PGA_REQUEUE) != 0) {
TAILQ_INSERT_TAIL(&ss->pq->pq_pl, m, plinks.q);
vm_page_aflag_clear(m, PGA_REQUEUE | PGA_REQUEUE_HEAD);
} else
TAILQ_INSERT_BEFORE(ss->marker, m, plinks.q);
return (1);
}
/*
* Re-add stuck pages to the inactive queue. We will examine them again
* during the next scan. If the queue state of a page has changed since
* it was physically removed from the page queue in
* vm_pageout_collect_batch(), don't do anything with that page.
*/
static void
vm_pageout_reinsert_inactive(struct scan_state *ss, struct vm_batchqueue *bq,
vm_page_t m)
{
struct vm_pagequeue *pq;
int delta;
delta = 0;
pq = ss->pq;
if (m != NULL) {
if (vm_batchqueue_insert(bq, m))
return;
vm_pagequeue_lock(pq);
delta += vm_pageout_reinsert_inactive_page(ss, m);
} else
vm_pagequeue_lock(pq);
while ((m = vm_batchqueue_pop(bq)) != NULL)
delta += vm_pageout_reinsert_inactive_page(ss, m);
vm_pagequeue_cnt_add(pq, delta);
vm_pagequeue_unlock(pq);
vm_batchqueue_init(bq);
}
/*
* Attempt to reclaim the requested number of pages from the inactive queue.
* Returns true if the shortage was addressed.
*/
static int
vm_pageout_scan_inactive(struct vm_domain *vmd, int shortage,
int *addl_shortage)
{
struct scan_state ss;
struct vm_batchqueue rq;
struct mtx *mtx;
vm_page_t m, marker;
struct vm_pagequeue *pq;
vm_object_t object;
int act_delta, addl_page_shortage, deficit, page_shortage;
int starting_page_shortage;
bool obj_locked;
/*
* The addl_page_shortage is an estimate of the number of temporarily
* stuck pages in the inactive queue. In other words, the
* number of pages from the inactive count that should be
* discounted in setting the target for the active queue scan.
*/
addl_page_shortage = 0;
/*
* vmd_pageout_deficit counts the number of pages requested in
* allocations that failed because of a free page shortage. We assume
* that the allocations will be reattempted and thus include the deficit
* in our scan target.
*/
deficit = atomic_readandclear_int(&vmd->vmd_pageout_deficit);
starting_page_shortage = page_shortage = shortage + deficit;
mtx = NULL;
obj_locked = false;
object = NULL;
vm_batchqueue_init(&rq);
/*
* Start scanning the inactive queue for pages that we can free. The
* scan will stop when we reach the target or we have scanned the
* entire queue. (Note that m->act_count is not used to make
* decisions for the inactive queue, only for the active queue.)
*/
marker = &vmd->vmd_markers[PQ_INACTIVE];
pq = &vmd->vmd_pagequeues[PQ_INACTIVE];
vm_pagequeue_lock(pq);
vm_pageout_init_scan(&ss, pq, marker, NULL, pq->pq_cnt);
while (page_shortage > 0 && (m = vm_pageout_next(&ss, true)) != NULL) {
KASSERT((m->flags & PG_MARKER) == 0,
("marker page %p was dequeued", m));
vm_page_change_lock(m, &mtx);
recheck:
/*
* The page may have been disassociated from the queue
* while locks were dropped.
*/
if (vm_page_queue(m) != PQ_INACTIVE) {
addl_page_shortage++;
continue;
}
/*
* The page was re-enqueued after the page queue lock was
* dropped, or a requeue was requested. This page gets a second
* chance.
*/
if ((m->aflags & (PGA_ENQUEUED | PGA_REQUEUE |
PGA_REQUEUE_HEAD)) != 0)
goto reinsert;
/*
* Held pages are essentially stuck in the queue. So,
* they ought to be discounted from the inactive count.
* See the description of addl_page_shortage above.
*
* Wired pages may not be freed. Complete their removal
* from the queue now to avoid needless revisits during
* future scans.
*/
if (m->hold_count != 0) {
addl_page_shortage++;
goto reinsert;
}
if (m->wire_count != 0) {
vm_page_dequeue_deferred(m);
continue;
}
if (object != m->object) {
if (obj_locked) {
VM_OBJECT_WUNLOCK(object);
obj_locked = false;
}
object = m->object;
}
if (!obj_locked) {
if (!VM_OBJECT_TRYWLOCK(object)) {
mtx_unlock(mtx);
/* Depends on type-stability. */
VM_OBJECT_WLOCK(object);
obj_locked = true;
mtx_lock(mtx);
goto recheck;
} else
obj_locked = true;
}
if (vm_page_busied(m)) {
/*
* Don't mess with busy pages. Leave them at
* the front of the queue. Most likely, they
* are being paged out and will leave the
* queue shortly after the scan finishes. So,
* they ought to be discounted from the
* inactive count.
*/
addl_page_shortage++;
goto reinsert;
}
/*
* Invalid pages can be easily freed. They cannot be
* mapped, vm_page_free() asserts this.
*/
if (m->valid == 0)
goto free_page;
/*
* If the page has been referenced and the object is not dead,
* reactivate or requeue the page depending on whether the
* object is mapped.
*/
if ((m->aflags & PGA_REFERENCED) != 0) {
vm_page_aflag_clear(m, PGA_REFERENCED);
act_delta = 1;
} else
act_delta = 0;
if (object->ref_count != 0) {
act_delta += pmap_ts_referenced(m);
} else {
KASSERT(!pmap_page_is_mapped(m),
("page %p is mapped", m));
}
if (act_delta != 0) {
if (object->ref_count != 0) {
VM_CNT_INC(v_reactivated);
vm_page_activate(m);
/*
* Increase the activation count if the page
* was referenced while in the inactive queue.
* This makes it less likely that the page will
* be returned prematurely to the inactive
* queue.
*/
m->act_count += act_delta + ACT_ADVANCE;
continue;
} else if ((object->flags & OBJ_DEAD) == 0) {
vm_page_aflag_set(m, PGA_REQUEUE);
goto reinsert;
}
}
/*
* If the page appears to be clean at the machine-independent
* layer, then remove all of its mappings from the pmap in
* anticipation of freeing it. If, however, any of the page's
* mappings allow write access, then the page may still be
* modified until the last of those mappings are removed.
*/
if (object->ref_count != 0) {
vm_page_test_dirty(m);
if (m->dirty == 0)
pmap_remove_all(m);
}
/*
* Clean pages can be freed, but dirty pages must be sent back
* to the laundry, unless they belong to a dead object.
* Requeueing dirty pages from dead objects is pointless, as
* they are being paged out and freed by the thread that
* destroyed the object.
*/
if (m->dirty == 0) {
free_page:
/*
* Because we dequeued the page and have already
* checked for concurrent dequeue and enqueue
* requests, we can safely disassociate the page
* from the inactive queue.
*/
KASSERT((m->aflags & PGA_QUEUE_STATE_MASK) == 0,
("page %p has queue state", m));
m->queue = PQ_NONE;
vm_page_free(m);
page_shortage--;
} else if ((object->flags & OBJ_DEAD) == 0)
vm_page_launder(m);
continue;
reinsert:
vm_pageout_reinsert_inactive(&ss, &rq, m);
}
if (mtx != NULL) {
mtx_unlock(mtx);
mtx = NULL;
}
if (obj_locked) {
VM_OBJECT_WUNLOCK(object);
obj_locked = false;
}
vm_pageout_reinsert_inactive(&ss, &rq, NULL);
vm_pageout_reinsert_inactive(&ss, &ss.bq, NULL);
vm_pagequeue_lock(pq);
vm_pageout_end_scan(&ss);
vm_pagequeue_unlock(pq);
VM_CNT_ADD(v_dfree, starting_page_shortage - page_shortage);
/*
* Wake up the laundry thread so that it can perform any needed
* laundering. If we didn't meet our target, we're in shortfall and
* need to launder more aggressively. If PQ_LAUNDRY is empty and no
* swap devices are configured, the laundry thread has no work to do, so
* don't bother waking it up.
*
* The laundry thread uses the number of inactive queue scans elapsed
* since the last laundering to determine whether to launder again, so
* keep count.
*/
if (starting_page_shortage > 0) {
pq = &vmd->vmd_pagequeues[PQ_LAUNDRY];
vm_pagequeue_lock(pq);
if (vmd->vmd_laundry_request == VM_LAUNDRY_IDLE &&
(pq->pq_cnt > 0 || atomic_load_acq_int(&swapdev_enabled))) {
if (page_shortage > 0) {
vmd->vmd_laundry_request = VM_LAUNDRY_SHORTFALL;
VM_CNT_INC(v_pdshortfalls);
} else if (vmd->vmd_laundry_request !=
VM_LAUNDRY_SHORTFALL)
vmd->vmd_laundry_request =
VM_LAUNDRY_BACKGROUND;
wakeup(&vmd->vmd_laundry_request);
}
vmd->vmd_clean_pages_freed +=
starting_page_shortage - page_shortage;
vm_pagequeue_unlock(pq);
}
/*
* Wakeup the swapout daemon if we didn't free the targeted number of
* pages.
*/
if (page_shortage > 0)
vm_swapout_run();
/*
* If the inactive queue scan fails repeatedly to meet its
* target, kill the largest process.
*/
vm_pageout_mightbe_oom(vmd, page_shortage, starting_page_shortage);
/*
* Reclaim pages by swapping out idle processes, if configured to do so.
*/
vm_swapout_run_idle();
/*
* See the description of addl_page_shortage above.
*/
*addl_shortage = addl_page_shortage + deficit;
return (page_shortage <= 0);
}
static int vm_pageout_oom_vote;
/*
* The pagedaemon threads randlomly select one to perform the
* OOM. Trying to kill processes before all pagedaemons
* failed to reach free target is premature.
*/
static void
vm_pageout_mightbe_oom(struct vm_domain *vmd, int page_shortage,
int starting_page_shortage)
{
int old_vote;
if (starting_page_shortage <= 0 || starting_page_shortage !=
page_shortage)
vmd->vmd_oom_seq = 0;
else
vmd->vmd_oom_seq++;
if (vmd->vmd_oom_seq < vm_pageout_oom_seq) {
if (vmd->vmd_oom) {
vmd->vmd_oom = FALSE;
atomic_subtract_int(&vm_pageout_oom_vote, 1);
}
return;
}
/*
* Do not follow the call sequence until OOM condition is
* cleared.
*/
vmd->vmd_oom_seq = 0;
if (vmd->vmd_oom)
return;
vmd->vmd_oom = TRUE;
old_vote = atomic_fetchadd_int(&vm_pageout_oom_vote, 1);
if (old_vote != vm_ndomains - 1)
return;
/*
* The current pagedaemon thread is the last in the quorum to
* start OOM. Initiate the selection and signaling of the
* victim.
*/
vm_pageout_oom(VM_OOM_MEM);
/*
* After one round of OOM terror, recall our vote. On the
* next pass, current pagedaemon would vote again if the low
* memory condition is still there, due to vmd_oom being
* false.
*/
vmd->vmd_oom = FALSE;
atomic_subtract_int(&vm_pageout_oom_vote, 1);
}
/*
* The OOM killer is the page daemon's action of last resort when
* memory allocation requests have been stalled for a prolonged period
* of time because it cannot reclaim memory. This function computes
* the approximate number of physical pages that could be reclaimed if
* the specified address space is destroyed.
*
* Private, anonymous memory owned by the address space is the
* principal resource that we expect to recover after an OOM kill.
* Since the physical pages mapped by the address space's COW entries
* are typically shared pages, they are unlikely to be released and so
* they are not counted.
*
* To get to the point where the page daemon runs the OOM killer, its
* efforts to write-back vnode-backed pages may have stalled. This
* could be caused by a memory allocation deadlock in the write path
* that might be resolved by an OOM kill. Therefore, physical pages
* belonging to vnode-backed objects are counted, because they might
* be freed without being written out first if the address space holds
* the last reference to an unlinked vnode.
*
* Similarly, physical pages belonging to OBJT_PHYS objects are
* counted because the address space might hold the last reference to
* the object.
*/
static long
vm_pageout_oom_pagecount(struct vmspace *vmspace)
{
vm_map_t map;
vm_map_entry_t entry;
vm_object_t obj;
long res;
map = &vmspace->vm_map;
KASSERT(!map->system_map, ("system map"));
sx_assert(&map->lock, SA_LOCKED);
res = 0;
for (entry = map->header.next; entry != &map->header;
entry = entry->next) {
if ((entry->eflags & MAP_ENTRY_IS_SUB_MAP) != 0)
continue;
obj = entry->object.vm_object;
if (obj == NULL)
continue;
if ((entry->eflags & MAP_ENTRY_NEEDS_COPY) != 0 &&
obj->ref_count != 1)
continue;
switch (obj->type) {
case OBJT_DEFAULT:
case OBJT_SWAP:
case OBJT_PHYS:
case OBJT_VNODE:
res += obj->resident_page_count;
break;
}
}
return (res);
}
void
vm_pageout_oom(int shortage)
{
struct proc *p, *bigproc;
vm_offset_t size, bigsize;
struct thread *td;
struct vmspace *vm;
bool breakout;
/*
* We keep the process bigproc locked once we find it to keep anyone
* from messing with it; however, there is a possibility of
* deadlock if process B is bigproc and one of its child processes
* attempts to propagate a signal to B while we are waiting for A's
* lock while walking this list. To avoid this, we don't block on
* the process lock but just skip a process if it is already locked.
*/
bigproc = NULL;
bigsize = 0;
sx_slock(&allproc_lock);
FOREACH_PROC_IN_SYSTEM(p) {
PROC_LOCK(p);
/*
* If this is a system, protected or killed process, skip it.
*/
if (p->p_state != PRS_NORMAL || (p->p_flag & (P_INEXEC |
P_PROTECTED | P_SYSTEM | P_WEXIT)) != 0 ||
p->p_pid == 1 || P_KILLED(p) ||
(p->p_pid < 48 && swap_pager_avail != 0)) {
PROC_UNLOCK(p);
continue;
}
/*
* If the process is in a non-running type state,
* don't touch it. Check all the threads individually.
*/
breakout = false;
FOREACH_THREAD_IN_PROC(p, td) {
thread_lock(td);
if (!TD_ON_RUNQ(td) &&
!TD_IS_RUNNING(td) &&
!TD_IS_SLEEPING(td) &&
!TD_IS_SUSPENDED(td) &&
!TD_IS_SWAPPED(td)) {
thread_unlock(td);
breakout = true;
break;
}
thread_unlock(td);
}
if (breakout) {
PROC_UNLOCK(p);
continue;
}
/*
* get the process size
*/
vm = vmspace_acquire_ref(p);
if (vm == NULL) {
PROC_UNLOCK(p);
continue;
}
_PHOLD_LITE(p);
PROC_UNLOCK(p);
sx_sunlock(&allproc_lock);
if (!vm_map_trylock_read(&vm->vm_map)) {
vmspace_free(vm);
sx_slock(&allproc_lock);
PRELE(p);
continue;
}
size = vmspace_swap_count(vm);
if (shortage == VM_OOM_MEM)
size += vm_pageout_oom_pagecount(vm);
vm_map_unlock_read(&vm->vm_map);
vmspace_free(vm);
sx_slock(&allproc_lock);
/*
* If this process is bigger than the biggest one,
* remember it.
*/
if (size > bigsize) {
if (bigproc != NULL)
PRELE(bigproc);
bigproc = p;
bigsize = size;
} else {
PRELE(p);
}
}
sx_sunlock(&allproc_lock);
if (bigproc != NULL) {
if (vm_panic_on_oom != 0)
panic("out of swap space");
PROC_LOCK(bigproc);
killproc(bigproc, "out of swap space");
sched_nice(bigproc, PRIO_MIN);
_PRELE(bigproc);
PROC_UNLOCK(bigproc);
}
}
static void
vm_pageout_lowmem(struct vm_domain *vmd)
{
if (vmd == VM_DOMAIN(0) &&
time_uptime - lowmem_uptime >= lowmem_period) {
/*
* Decrease registered cache sizes.
*/
SDT_PROBE0(vm, , , vm__lowmem_scan);
EVENTHANDLER_INVOKE(vm_lowmem, VM_LOW_PAGES);
/*
* We do this explicitly after the caches have been
* drained above.
*/
uma_reclaim();
lowmem_uptime = time_uptime;
}
}
static void
vm_pageout_worker(void *arg)
{
struct vm_domain *vmd;
int addl_shortage, domain, shortage;
bool target_met;
domain = (uintptr_t)arg;
vmd = VM_DOMAIN(domain);
shortage = 0;
target_met = true;
/*
* XXXKIB It could be useful to bind pageout daemon threads to
* the cores belonging to the domain, from which vm_page_array
* is allocated.
*/
KASSERT(vmd->vmd_segs != 0, ("domain without segments"));
vmd->vmd_last_active_scan = ticks;
/*
* The pageout daemon worker is never done, so loop forever.
*/
while (TRUE) {
vm_domain_pageout_lock(vmd);
/*
* We need to clear wanted before we check the limits. This
* prevents races with wakers who will check wanted after they
* reach the limit.
*/
atomic_store_int(&vmd->vmd_pageout_wanted, 0);
/*
* Might the page daemon need to run again?
*/
if (vm_paging_needed(vmd, vmd->vmd_free_count)) {
/*
* Yes. If the scan failed to produce enough free
* pages, sleep uninterruptibly for some time in the
* hope that the laundry thread will clean some pages.
*/
vm_domain_pageout_unlock(vmd);
if (!target_met)
pause("pwait", hz / VM_INACT_SCAN_RATE);
} else {
/*
* No, sleep until the next wakeup or until pages
* need to have their reference stats updated.
*/
if (mtx_sleep(&vmd->vmd_pageout_wanted,
vm_domain_pageout_lockptr(vmd), PDROP | PVM,
"psleep", hz / VM_INACT_SCAN_RATE) == 0)
VM_CNT_INC(v_pdwakeups);
}
/* Prevent spurious wakeups by ensuring that wanted is set. */
atomic_store_int(&vmd->vmd_pageout_wanted, 1);
/*
* Use the controller to calculate how many pages to free in
* this interval, and scan the inactive queue.
*/
shortage = pidctrl_daemon(&vmd->vmd_pid, vmd->vmd_free_count);
if (shortage > 0) {
vm_pageout_lowmem(vmd);
target_met = vm_pageout_scan_inactive(vmd, shortage,
&addl_shortage);
} else
addl_shortage = 0;
/*
* Scan the active queue. A positive value for shortage
* indicates that we must aggressively deactivate pages to avoid
* a shortfall.
*/
shortage = vm_pageout_active_target(vmd) + addl_shortage;
vm_pageout_scan_active(vmd, shortage);
}
}
/*
* vm_pageout_init initialises basic pageout daemon settings.
*/
static void
vm_pageout_init_domain(int domain)
{
struct vm_domain *vmd;
struct sysctl_oid *oid;
vmd = VM_DOMAIN(domain);
vmd->vmd_interrupt_free_min = 2;
/*
* v_free_reserved needs to include enough for the largest
* swap pager structures plus enough for any pv_entry structs
* when paging.
*/
if (vmd->vmd_page_count > 1024)
vmd->vmd_free_min = 4 + (vmd->vmd_page_count - 1024) / 200;
else
vmd->vmd_free_min = 4;
vmd->vmd_pageout_free_min = (2*MAXBSIZE)/PAGE_SIZE +
vmd->vmd_interrupt_free_min;
vmd->vmd_free_reserved = vm_pageout_page_count +
vmd->vmd_pageout_free_min + (vmd->vmd_page_count / 768);
vmd->vmd_free_severe = vmd->vmd_free_min / 2;
vmd->vmd_free_target = 4 * vmd->vmd_free_min + vmd->vmd_free_reserved;
vmd->vmd_free_min += vmd->vmd_free_reserved;
vmd->vmd_free_severe += vmd->vmd_free_reserved;
vmd->vmd_inactive_target = (3 * vmd->vmd_free_target) / 2;
if (vmd->vmd_inactive_target > vmd->vmd_free_count / 3)
vmd->vmd_inactive_target = vmd->vmd_free_count / 3;
/*
* Set the default wakeup threshold to be 10% below the paging
* target. This keeps the steady state out of shortfall.
*/
vmd->vmd_pageout_wakeup_thresh = (vmd->vmd_free_target / 10) * 9;
/*
* Target amount of memory to move out of the laundry queue during a
* background laundering. This is proportional to the amount of system
* memory.
*/
vmd->vmd_background_launder_target = (vmd->vmd_free_target -
vmd->vmd_free_min) / 10;
/* Initialize the pageout daemon pid controller. */
pidctrl_init(&vmd->vmd_pid, hz / VM_INACT_SCAN_RATE,
vmd->vmd_free_target, PIDCTRL_BOUND,
PIDCTRL_KPD, PIDCTRL_KID, PIDCTRL_KDD);
oid = SYSCTL_ADD_NODE(NULL, SYSCTL_CHILDREN(vmd->vmd_oid), OID_AUTO,
"pidctrl", CTLFLAG_RD, NULL, "");
pidctrl_init_sysctl(&vmd->vmd_pid, SYSCTL_CHILDREN(oid));
}
static void
vm_pageout_init(void)
{
u_int freecount;
int i;
/*
* Initialize some paging parameters.
*/
if (vm_cnt.v_page_count < 2000)
vm_pageout_page_count = 8;
freecount = 0;
for (i = 0; i < vm_ndomains; i++) {
struct vm_domain *vmd;
vm_pageout_init_domain(i);
vmd = VM_DOMAIN(i);
vm_cnt.v_free_reserved += vmd->vmd_free_reserved;
vm_cnt.v_free_target += vmd->vmd_free_target;
vm_cnt.v_free_min += vmd->vmd_free_min;
vm_cnt.v_inactive_target += vmd->vmd_inactive_target;
vm_cnt.v_pageout_free_min += vmd->vmd_pageout_free_min;
vm_cnt.v_interrupt_free_min += vmd->vmd_interrupt_free_min;
vm_cnt.v_free_severe += vmd->vmd_free_severe;
freecount += vmd->vmd_free_count;
}
/*
* Set interval in seconds for active scan. We want to visit each
* page at least once every ten minutes. This is to prevent worst
* case paging behaviors with stale active LRU.
*/
if (vm_pageout_update_period == 0)
vm_pageout_update_period = 600;
if (vm_page_max_wired == 0)
vm_page_max_wired = freecount / 3;
}
/*
* vm_pageout is the high level pageout daemon.
*/
static void
vm_pageout(void)
{
int error;
int i;
swap_pager_swap_init();
snprintf(curthread->td_name, sizeof(curthread->td_name), "dom0");
error = kthread_add(vm_pageout_laundry_worker, NULL, curproc, NULL,
0, 0, "laundry: dom0");
if (error != 0)
panic("starting laundry for domain 0, error %d", error);
for (i = 1; i < vm_ndomains; i++) {
error = kthread_add(vm_pageout_worker, (void *)(uintptr_t)i,
curproc, NULL, 0, 0, "dom%d", i);
if (error != 0) {
panic("starting pageout for domain %d, error %d\n",
i, error);
}
error = kthread_add(vm_pageout_laundry_worker,
(void *)(uintptr_t)i, curproc, NULL, 0, 0,
"laundry: dom%d", i);
if (error != 0)
panic("starting laundry for domain %d, error %d",
i, error);
}
error = kthread_add(uma_reclaim_worker, NULL, curproc, NULL,
0, 0, "uma");
if (error != 0)
panic("starting uma_reclaim helper, error %d\n", error);
vm_pageout_worker((void *)(uintptr_t)0);
}
/*
* Perform an advisory wakeup of the page daemon.
*/
void
pagedaemon_wakeup(int domain)
{
struct vm_domain *vmd;
vmd = VM_DOMAIN(domain);
vm_domain_pageout_assert_unlocked(vmd);
if (curproc == pageproc)
return;
if (atomic_fetchadd_int(&vmd->vmd_pageout_wanted, 1) == 0) {
vm_domain_pageout_lock(vmd);
atomic_store_int(&vmd->vmd_pageout_wanted, 1);
wakeup(&vmd->vmd_pageout_wanted);
vm_domain_pageout_unlock(vmd);
}
}
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