From: Suleiman Souhlal Date: Wed, 4 Jun 2014 23:06:44 +0000 (-0700) Subject: mm: only force scan in reclaim when none of the LRUs are big enough. X-Git-Tag: omap-for-v3.16/fixes-against-rc1~56^2~16^2~225 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6f04f48dc9c0433e2bb687f5f7f7af1aba97b04d;p=pandora-kernel.git mm: only force scan in reclaim when none of the LRUs are big enough. Prior to this change, we would decide whether to force scan a LRU during reclaim if that LRU itself was too small for the current priority. However, this can lead to the file LRU getting force scanned even if there are a lot of anonymous pages we can reclaim, leading to hot file pages getting needlessly reclaimed. To address this, we instead only force scan when none of the reclaimable LRUs are big enough. Gives huge improvements with zswap. For example, when doing -j20 kernel build in a 500MB container with zswap enabled, runtime (in seconds) is greatly reduced: x without this change + with this change N Min Max Median Avg Stddev x 5 700.997 790.076 763.928 754.05 39.59493 + 5 141.634 197.899 155.706 161.9 21.270224 Difference at 95.0% confidence -592.15 +/- 46.3521 -78.5293% +/- 6.14709% (Student's t, pooled s = 31.7819) Should also give some improvements in regular (non-zswap) swap cases. Yes, hughd found significant speedup using regular swap, with several memcgs under pressure; and it should also be effective in the non-memcg case, whenever one or another zone LRU is forced too small. Signed-off-by: Suleiman Souhlal Signed-off-by: Hugh Dickins Cc: Suleiman Souhlal Cc: Mel Gorman Acked-by: Rik van Riel Acked-by: Rafael Aquini Cc: Michal Hocko Cc: Yuanhan Liu Cc: Seth Jennings Cc: Bob Liu Cc: Minchan Kim Cc: Luigi Semenzato Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Reading git-diff-tree failed