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Date: Tue, 1 Mar 2016 15:44:21 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org,
Andrea Arcangeli <aarcange@...hat.com>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Rik van Riel <riel@...hat.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Mel Gorman <mgorman@...hsingularity.net>,
David Rientjes <rientjes@...gle.com>,
Michal Hocko <mhocko@...e.com>,
Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH v2 5/5] mm, compaction: adapt isolation_suitable flushing
to kcompactd
For consistency with previous patch's updated changelog, here's similar update
for this one:
http://ozlabs.org/~akpm/mmots/broken-out/mm-compaction-adapt-isolation_suitable-flushing-to-kcompactd.patch
----8<----
Compaction maintains a pageblock_skip bitmap to record pageblocks where
isolation recently failed. This bitmap can be reset by three ways:
1) direct compaction is restarting after going through the full deferred cycle
2) kswapd goes to sleep, and some other direct compaction has previously
finished scanning the whole zone and set zone->compact_blockskip_flush.
Note that a successful direct compaction clears this flag.
3) compaction was invoked manually via trigger in /proc
The case 2) is somewhat fuzzy to begin with, but after introducing kcompactd we
should update it. The check for direct compaction in 1), and to set the flush
flag in 2) use current_is_kswapd(), which doesn't work for kcompactd. Thus,
this patch adds bool direct_compaction to compact_control to use in 2). For
the case 1) we remove the check completely - unlike the former kswapd
compaction, kcompactd does use the deferred compaction functionality, so
flushing tied to restarting from deferred compaction makes sense here.
Note that when kswapd goes to sleep, kcompactd is woken up, so it will see the
flushed pageblock_skip bits. This is different from when the former kswapd
compaction observed the bits and I believe it makes more sense. Kcompactd can
afford to be more thorough than a direct compaction trying to limit allocation
latency, or kswapd whose primary goal is to reclaim.
To sum up, after this patch, the pageblock_skip flushing makes intuitively
more sense for kcompactd. Practially, the differences are minimal.
Stress-highalloc With order-9 allocations without direct reclaim/compaction:
stress-highalloc
4.5-rc1+before 4.5-rc1+after
-nodirect -nodirect
Success 1 Min 3.00 ( 0.00%) 5.00 (-66.67%)
Success 1 Mean 4.00 ( 0.00%) 6.20 (-55.00%)
Success 1 Max 6.00 ( 0.00%) 7.00 (-16.67%)
Success 2 Min 3.00 ( 0.00%) 5.00 (-66.67%)
Success 2 Mean 4.20 ( 0.00%) 6.40 (-52.38%)
Success 2 Max 6.00 ( 0.00%) 7.00 (-16.67%)
Success 3 Min 63.00 ( 0.00%) 62.00 ( 1.59%)
Success 3 Mean 64.60 ( 0.00%) 63.80 ( 1.24%)
Success 3 Max 67.00 ( 0.00%) 65.00 ( 2.99%)
User 3088.82 3181.09
System 1142.01 1158.25
Elapsed 1780.91 1799.37
4.5-rc1+before 4.5-rc1+after
-nodirect -nodirect
Direct pages scanned 31429 32797
Kswapd pages scanned 2185293 2202613
Kswapd pages reclaimed 2134389 2143524
Direct pages reclaimed 31234 32545
Percentage direct scans 1% 1%
THP fault alloc 614 612
THP collapse alloc 324 316
THP splits 0 0
THP fault fallback 730 778
THP collapse fail 14 16
Compaction stalls 959 1007
Compaction success 69 67
Compaction failures 890 939
Page migrate success 662054 721374
Page migrate failure 32846 23469
Compaction pages isolated 1370326 1479924
Compaction migrate scanned 7025772 8812554
Compaction free scanned 73302642 84327916
Compaction cost 762 838
With direct reclaim/compaction:
stress-highalloc
4.5-rc1+before 4.5-rc1+after
-direct -direct
Success 1 Min 6.00 ( 0.00%) 9.00 (-50.00%)
Success 1 Mean 8.40 ( 0.00%) 10.00 (-19.05%)
Success 1 Max 13.00 ( 0.00%) 11.00 ( 15.38%)
Success 2 Min 6.00 ( 0.00%) 9.00 (-50.00%)
Success 2 Mean 8.60 ( 0.00%) 10.00 (-16.28%)
Success 2 Max 12.00 ( 0.00%) 11.00 ( 8.33%)
Success 3 Min 75.00 ( 0.00%) 74.00 ( 1.33%)
Success 3 Mean 75.60 ( 0.00%) 75.20 ( 0.53%)
Success 3 Max 76.00 ( 0.00%) 76.00 ( 0.00%)
User 3258.62 3246.04
System 1177.92 1172.29
Elapsed 1837.02 1836.76
4.5-rc1+before 4.5-rc1+after
-direct -direct
Direct pages scanned 108854 120966
Kswapd pages scanned 2131589 2135012
Kswapd pages reclaimed 2090937 2108388
Direct pages reclaimed 108699 120577
Percentage direct scans 4% 5%
THP fault alloc 567 652
THP collapse alloc 326 354
THP splits 0 0
THP fault fallback 805 793
THP collapse fail 18 16
Compaction stalls 2070 2025
Compaction success 527 518
Compaction failures 1543 1507
Page migrate success 2423657 2360608
Page migrate failure 28790 40852
Compaction pages isolated 4916017 4802025
Compaction migrate scanned 19370264 21750613
Compaction free scanned 360662356 344372001
Compaction cost 2745 2694
Singed-off-by: Vlastimil Babka <vbabka@...e.cz>
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