On 05/17/2012 05:13 AM, Michal Hocko wrote:
[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@xxxxxxxxxxx> CC: Andrew Morton<akpm@xxxxxxxxxxxxxxxxxxxx> CC: Mel Gorman<mel@xxxxxxxxx> CC: Minchan Kim<minchan@xxxxxxxxxx> CC: KAMEZAWA Hiroyuki<kamezawa.hiroyu@xxxxxxxxxxxxxx> CC: Rik van Riel<riel@xxxxxxxxxx> CC: stable [2.6.34+] Signed-off-by: Michal Hocko<mhocko@xxxxxxx>
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