Messages in this thread | | | Subject | Re: [PATCH v2 5/5] mm, compaction: adapt isolation_suitable flushing to kcompactd | From | Vlastimil Babka <> | Date | Tue, 1 Mar 2016 15:44:21 +0100 |
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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
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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@suse.cz>
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