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Subject[PATCH] mm: consider all swapped back pages in used-once logic
Date
[64574746 vmscan: detect mapped file pages used only once] made mapped pages
have another round in inactive list because they might be just short
lived and so we could consider them again next time. This heuristic
helps to reduce pressure on the active list with a streaming IO
worklods.
This patch fixes a regression introduced by this commit for heavy shmem
based workloads because unlike Anon pages, which are excluded from this
heuristic because they are usually long lived, shmem pages are handled
as a regular page cache.
This doesn't work quite well, unfortunately, if the workload is mostly
backed by shmem (in memory database sitting on 80% of memory) with a
streaming IO in the background (backup - up to 20% of memory). Anon
inactive list is full of (dirty) shmem pages when watermarks are
hit. Shmem pages are kept in the inactive list (they are referenced)
in the first round and it is hard to reclaim anything else so we reach
lower scanning priorities very quickly which leads to an excessive swap
out.

Let's fix this by excluding all swap backed pages (they tend to be long
lived wrt. the regular page cache anyway) from used-once heuristic and
rather activate them if they are referenced.

CC: Johannes Weiner <hannes@cmpxchg.org>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Mel Gorman <mel@csn.ul.ie>
CC: Minchan Kim <minchan@kernel.org>
CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
CC: Rik van Riel <riel@redhat.com>
CC: stable [2.6.34+]
Signed-off-by: Michal Hocko <mhocko@suse.cz>
---
mm/vmscan.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 33dc256..0932dc2 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -722,7 +722,7 @@ static enum page_references page_check_references(struct page *page,
return PAGEREF_RECLAIM;

if (referenced_ptes) {
- if (PageAnon(page))
+ if (PageSwapBacked(page))
return PAGEREF_ACTIVATE;
/*
* All mapped pages start out with page table
--
1.7.10


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