Messages in this thread | | | Date | Thu, 27 Mar 2014 16:41:45 -0400 | From | Rik van Riel <> | Subject | Re: [PATCH] mm: Only force scan in reclaim when none of the LRUs are big enough. |
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On 03/15/2014 11:36 PM, Hugh Dickins wrote: > From: Suleiman Souhlal <suleiman@google.com> > > 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 <suleiman@google.com> > Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Rik van Riel <riel@redhat.com>
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