From e48982734ea0500d1eba4f9d96195acc5406cad6 Mon Sep 17 00:00:00 2001 From: Michal Hocko Date: Tue, 29 May 2012 15:06:45 -0700 Subject: [PATCH] mm: consider all swapped back pages in used-once logic Commit 645747462435 ("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. The customer's workload is shmem backed database (80% of RAM) and they are measuring transactions/s with an IO in the background (20%). Transactions touch more or less random rows in the table. The transaction rate fell by a factor of 3 (in the worst case) because of commit 64574746. This patch restores the previous numbers. Signed-off-by: Michal Hocko Acked-by: Johannes Weiner Cc: Mel Gorman Cc: Minchan Kim Cc: KAMEZAWA Hiroyuki Reviewed-by: Rik van Riel Cc: [2.6.34+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/vmscan.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 44f04364a304..67a4fd4792de 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -657,7 +657,7 @@ 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