mm: only drain per-cpu pagevecs once per pagevec usage

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.net
Signed-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>

diff --git a/include/linux/pagevec.h b/include/linux/pagevec.h
index 4f56e0ad9d0003390b19541110b809689817b863..95c75c858d1fa21bca43ff7e6677fc3e472fbd3b 100644 (file)
--- a/include/linux/pagevec.h
+++ b/include/linux/pagevec.h
@@ -17,7 +17,8 @@ struct address_space;
 
 struct pagevec {
        unsigned long nr;
-       unsigned long cold;
+       bool cold;
+       bool drained;
        struct page *pages[PAGEVEC_SIZE];
 };
 
@@ -54,6 +55,7 @@ static inline void pagevec_init(struct pagevec *pvec, int cold)
 {
        pvec->nr = 0;
        pvec->cold = cold;
+       pvec->drained = false;
 }
 
 static inline void pagevec_reinit(struct pagevec *pvec)

diff --git a/mm/swap.c b/mm/swap.c
index 4edac536fe24cda7bb8e2fc4826ee7875fda9b38..3e564a95ee73fb9fee9f08fa655ed050d6879bbf 100644 (file)
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -833,7 +833,10 @@ EXPORT_SYMBOL(release_pages);
  */
 void __pagevec_release(struct pagevec *pvec)
 {
-       lru_add_drain();
+       if (!pvec->drained) {
+               lru_add_drain();
+               pvec->drained = true;
+       }
        release_pages(pvec->pages, pagevec_count(pvec), pvec->cold);
        pagevec_reinit(pvec);
 }