When a pagevec is initialised on the stack, it is generally used
multiple times over a range of pages, looking up entries and then
releasing them.  On each pagevec_release, the per-cpu deferred LRU
pagevecs are drained on the grounds the page being released may be on
those queues and the pages may be cache hot.  In many cases only the
first drain is necessary as it's unlikely that the range of pages being
walked is racing against LRU addition.  Even if there is such a race,
the impact is marginal where as constantly redraining the lru pagevecs
costs.

This patch ensures that pagevec is only drained once in a given
lifecycle without increasing the cache footprint of the pagevec
structure.  Only sparsetruncate tiny is shown here as large files have
many exceptional entries and calls pagecache_release less frequently.

sparsetruncate (tiny)
                              4.14.0-rc4             4.14.0-rc4
                        batchshadow-v1r1          onedrain-v1r1
Min          Time      141.00 (   0.00%)      141.00 (   0.00%)
1st-qrtle    Time      142.00 (   0.00%)      142.00 (   0.00%)
2nd-qrtle    Time      142.00 (   0.00%)      142.00 (   0.00%)
3rd-qrtle    Time      143.00 (   0.00%)      143.00 (   0.00%)
Max-90%      Time      144.00 (   0.00%)      144.00 (   0.00%)
Max-95%      Time      146.00 (   0.00%)      145.00 (   0.68%)
Max-99%      Time      198.00 (   0.00%)      194.00 (   2.02%)
Max          Time      254.00 (   0.00%)      208.00 (  18.11%)
Amean        Time      145.12 (   0.00%)      144.30 (   0.56%)
Stddev       Time       12.74 (   0.00%)        9.62 (  24.49%)
Coeff        Time        8.78 (   0.00%)        6.67 (  24.06%)
Best99%Amean Time      144.29 (   0.00%)      143.82 (   0.32%)
Best95%Amean Time      142.68 (   0.00%)      142.31 (   0.26%)
Best90%Amean Time      142.52 (   0.00%)      142.19 (   0.24%)
Best75%Amean Time      142.26 (   0.00%)      141.98 (   0.20%)
Best50%Amean Time      141.90 (   0.00%)      141.71 (   0.13%)
Best25%Amean Time      141.80 (   0.00%)      141.43 (   0.26%)

The impact on bonnie is marginal and within the noise because a
significant percentage of the file being truncated has been reclaimed
and consists of shadow entries which reduce the hotness of the
pagevec_release path.

Link: http://lkml.kernel.org/r/20171018075952.10627-5-mgorman@techsingularity.netSigned-off-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>