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authorJohannes Weiner <hannes@cmpxchg.org>2014-05-06 12:50:07 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-05-06 13:04:59 -0700
commit623762517e2370be3b3f95f4fe08d6c063a49b06 (patch)
tree94d42e42a3b1eb693ba387b6b297351ef6b03ed2
parent6b6751f7feba68d8f5c72b72cc69a1c5a625529c (diff)
revert "mm: vmscan: do not swap anon pages just because free+file is low"
This reverts commit 0bf1457f0cfc ("mm: vmscan: do not swap anon pages just because free+file is low") because it introduced a regression in mostly-anonymous workloads, where reclaim would become ineffective and trap every allocating task in direct reclaim. The problem is that there is a runaway feedback loop in the scan balance between file and anon, where the balance tips heavily towards a tiny thrashing file LRU and anonymous pages are no longer being looked at. The commit in question removed the safe guard that would detect such situations and respond with forced anonymous reclaim. This commit was part of a series to fix premature swapping in loads with relatively little cache, and while it made a small difference, the cure is obviously worse than the disease. Revert it. Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Reported-by: Christian Borntraeger <borntraeger@de.ibm.com> Acked-by: Christian Borntraeger <borntraeger@de.ibm.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Rik van Riel <riel@redhat.com> Cc: <stable@kernel.org> [3.12+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/vmscan.c18
1 files changed, 18 insertions, 0 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3f56c8deb3c0..32c661d66a45 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1916,6 +1916,24 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
get_lru_size(lruvec, LRU_INACTIVE_FILE);
/*
+ * Prevent the reclaimer from falling into the cache trap: as
+ * cache pages start out inactive, every cache fault will tip
+ * the scan balance towards the file LRU. And as the file LRU
+ * shrinks, so does the window for rotation from references.
+ * This means we have a runaway feedback loop where a tiny
+ * thrashing file LRU becomes infinitely more attractive than
+ * anon pages. Try to detect this based on file LRU size.
+ */
+ if (global_reclaim(sc)) {
+ unsigned long free = zone_page_state(zone, NR_FREE_PAGES);
+
+ if (unlikely(file + free <= high_wmark_pages(zone))) {
+ scan_balance = SCAN_ANON;
+ goto out;
+ }
+ }
+
+ /*
* There is enough inactive page cache, do not reclaim
* anything from the anonymous working set right now.
*/