svn commit: r306706 - head/sys/vm
Alan Cox
alc at FreeBSD.org
Wed Oct 5 16:15:28 UTC 2016
Author: alc
Date: Wed Oct 5 16:15:26 2016
New Revision: 306706
URL: https://svnweb.freebsd.org/changeset/base/306706
Log:
Change vm_pageout_scan() to return a value indicating whether the free page
target was met.
Previously, vm_pageout_worker() itself checked the length of the free page
queues to determine whether vm_pageout_scan(pass >= 1)'s inactive queue scan
freed enough pages to meet the free page target. Specifically,
vm_pageout_worker() used vm_paging_needed(). The trouble with
vm_paging_needed() is that it compares the length of the free page queues to
the wakeup threshold for the page daemon, which is much lower than the free
page target. Consequently, vm_pageout_worker() could conclude that the
inactive queue scan succeeded in meeting its free page target when in fact
it did not; and rather than immediately triggering an all-out laundering
pass over the inactive queue, vm_pageout_worker() would go back to sleep
waiting for the free page count to fall below the page daemon wakeup
threshold again, at which point it will perform another limited (pass == 1)
scan over the inactive queue.
Changing vm_pageout_worker() to use vm_page_count_target() instead of
vm_paging_needed() won't work because any page allocations that happen
concurrently with the inactive queue scan will result in the free page count
being below the target at the end of a successful scan. Instead, having
vm_pageout_scan() return a value indicating success or failure is the most
straightforward fix.
Reviewed by: kib, markj
MFC after: 3 weeks
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D8111
Modified:
head/sys/vm/vm_pageout.c
Modified: head/sys/vm/vm_pageout.c
==============================================================================
--- head/sys/vm/vm_pageout.c Wed Oct 5 14:00:05 2016 (r306705)
+++ head/sys/vm/vm_pageout.c Wed Oct 5 16:15:26 2016 (r306706)
@@ -121,7 +121,7 @@ static void vm_pageout(void);
static void vm_pageout_init(void);
static int vm_pageout_clean(vm_page_t m);
static int vm_pageout_cluster(vm_page_t m);
-static void vm_pageout_scan(struct vm_domain *vmd, int pass);
+static bool vm_pageout_scan(struct vm_domain *vmd, int pass);
static void vm_pageout_mightbe_oom(struct vm_domain *vmd, int page_shortage,
int starting_page_shortage);
@@ -845,17 +845,20 @@ unlock_mp:
* pass 0 - Update active LRU/deactivate pages
* pass 1 - Free inactive pages
* pass 2 - Launder dirty pages
+ *
+ * Returns true if pass was zero or enough pages were freed by the inactive
+ * queue scan to meet the target.
*/
-static void
+static bool
vm_pageout_scan(struct vm_domain *vmd, int pass)
{
vm_page_t m, next;
struct vm_pagequeue *pq;
vm_object_t object;
long min_scan;
- int act_delta, addl_page_shortage, deficit, error, maxlaunder, maxscan;
- int page_shortage, scan_tick, scanned, starting_page_shortage;
- int vnodes_skipped;
+ int act_delta, addl_page_shortage, deficit, error, inactq_shortage;
+ int maxlaunder, maxscan, page_shortage, scan_tick, scanned;
+ int starting_page_shortage, vnodes_skipped;
boolean_t pageout_ok, queue_locked;
/*
@@ -886,7 +889,9 @@ vm_pageout_scan(struct vm_domain *vmd, i
addl_page_shortage = 0;
/*
- * Calculate the number of pages that we want to free.
+ * Calculate the number of pages that we want to free. This number
+ * can be negative if many pages are freed between the wakeup call to
+ * the page daemon and this calculation.
*/
if (pass > 0) {
deficit = atomic_readandclear_int(&vm_pageout_deficit);
@@ -956,7 +961,7 @@ vm_pageout_scan(struct vm_domain *vmd, i
* Held pages are essentially stuck in the
* queue. So, they ought to be discounted
* from the inactive count. See the
- * calculation of the page_shortage for the
+ * calculation of inactq_shortage before the
* loop over the active queue below.
*/
addl_page_shortage++;
@@ -1164,7 +1169,7 @@ relock_queue:
* Compute the number of pages we want to try to move from the
* active queue to the inactive queue.
*/
- page_shortage = vm_cnt.v_inactive_target - vm_cnt.v_inactive_count +
+ inactq_shortage = vm_cnt.v_inactive_target - vm_cnt.v_inactive_count +
vm_paging_target() + deficit + addl_page_shortage;
pq = &vmd->vmd_pagequeues[PQ_ACTIVE];
@@ -1182,7 +1187,7 @@ relock_queue:
min_scan /= hz * vm_pageout_update_period;
} else
min_scan = 0;
- if (min_scan > 0 || (page_shortage > 0 && maxscan > 0))
+ if (min_scan > 0 || (inactq_shortage > 0 && maxscan > 0))
vmd->vmd_last_active_scan = scan_tick;
/*
@@ -1191,7 +1196,7 @@ relock_queue:
* candidates. Held pages may be deactivated.
*/
for (m = TAILQ_FIRST(&pq->pq_pl), scanned = 0; m != NULL && (scanned <
- min_scan || (page_shortage > 0 && scanned < maxscan)); m = next,
+ min_scan || (inactq_shortage > 0 && scanned < maxscan)); m = next,
scanned++) {
KASSERT(m->queue == PQ_ACTIVE,
("vm_pageout_scan: page %p isn't active", m));
@@ -1256,7 +1261,7 @@ relock_queue:
/* Dequeue to avoid later lock recursion. */
vm_page_dequeue_locked(m);
vm_page_deactivate(m);
- page_shortage--;
+ inactq_shortage--;
} else
vm_page_requeue_locked(m);
vm_page_unlock(m);
@@ -1275,6 +1280,7 @@ relock_queue:
}
}
#endif
+ return (page_shortage <= 0);
}
static int vm_pageout_oom_vote;
@@ -1504,9 +1510,11 @@ vm_pageout_worker(void *arg)
{
struct vm_domain *domain;
int domidx;
+ bool target_met;
domidx = (uintptr_t)arg;
domain = &vm_dom[domidx];
+ target_met = true;
/*
* XXXKIB It could be useful to bind pageout daemon threads to
@@ -1545,11 +1553,11 @@ vm_pageout_worker(void *arg)
}
/*
- * Do not clear vm_pageout_wanted until we reach our target.
- * Otherwise, we may be awakened over and over again, wasting
- * CPU time.
+ * Do not clear vm_pageout_wanted until we reach our free page
+ * target. Otherwise, we may be awakened over and over again,
+ * wasting CPU time.
*/
- if (vm_pageout_wanted && !vm_paging_needed())
+ if (vm_pageout_wanted && target_met)
vm_pageout_wanted = false;
/*
@@ -1584,7 +1592,7 @@ vm_pageout_worker(void *arg)
domain->vmd_pass = 0;
}
- vm_pageout_scan(domain, domain->vmd_pass);
+ target_met = vm_pageout_scan(domain, domain->vmd_pass);
}
}
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