Re: [PATCH 3/8] mm, truncate: Remove all exceptional entries from pagevec under one lock

Johannes Weiner
2017-10-12T19:45:47Z

On Thu, Oct 12, 2017 at 10:30:58AM +0100, Mel Gorman wrote:
> During truncate each entry in a pagevec is checked to see if it is an
> exceptional entry and if so, the shadow entry is cleaned up. This is
> potentially expensive as multiple entries for a mapping locks/unlocks the
> tree lock. This batches the operation such that any exceptional entries
> removed from a pagevec only acquire the mapping tree lock once. The corner
> case where this is more expensive is where there is only one exceptional
> entry but this is unlikely due to temporal locality and how it affects
> LRU ordering. Note that for truncations of small files created recently,
> this patch should show no gain because it only batches the handling of
> exceptional entries.
>
> sparsetruncate (large)
> 4.14.0-rc4 4.14.0-rc4
> pickhelper-v1r1 batchshadow-v1r1
> Min Time 38.00 ( 0.00%) 27.00 ( 28.95%)
> 1st-qrtle Time 40.00 ( 0.00%) 28.00 ( 30.00%)
> 2nd-qrtle Time 44.00 ( 0.00%) 41.00 ( 6.82%)
> 3rd-qrtle Time 146.00 ( 0.00%) 147.00 ( -0.68%)
> Max-90% Time 153.00 ( 0.00%) 153.00 ( 0.00%)
> Max-95% Time 155.00 ( 0.00%) 156.00 ( -0.65%)
> Max-99% Time 181.00 ( 0.00%) 171.00 ( 5.52%)
> Amean Time 93.04 ( 0.00%) 88.43 ( 4.96%)
> Best99%Amean Time 92.08 ( 0.00%) 86.13 ( 6.46%)
> Best95%Amean Time 89.19 ( 0.00%) 83.13 ( 6.80%)
> Best90%Amean Time 85.60 ( 0.00%) 79.15 ( 7.53%)
> Best75%Amean Time 72.95 ( 0.00%) 65.09 ( 10.78%)
> Best50%Amean Time 39.86 ( 0.00%) 28.20 ( 29.25%)
> Best25%Amean Time 39.44 ( 0.00%) 27.70 ( 29.77%)
>
> bonnie
> 4.14.0-rc4 4.14.0-rc4
> pickhelper-v1r1 batchshadow-v1r1
> Hmean SeqCreate ops 71.92 ( 0.00%) 76.78 ( 6.76%)
> Hmean SeqCreate read 42.42 ( 0.00%) 45.01 ( 6.10%)
> Hmean SeqCreate del 26519.88 ( 0.00%) 27191.87 ( 2.53%)
> Hmean RandCreate ops 71.92 ( 0.00%) 76.95 ( 7.00%)
> Hmean RandCreate read 44.44 ( 0.00%) 49.23 ( 10.78%)
> Hmean RandCreate del 24948.62 ( 0.00%) 24764.97 ( -0.74%)
>
> Truncation of a large number of files shows a substantial gain with 99% of files
> being trruncated 6.46% faster. bonnie shows a modest gain of 2.53%
>
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>