Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934433Ab3DILSF (ORCPT ); Tue, 9 Apr 2013 07:18:05 -0400 Received: from cantor2.suse.de ([195.135.220.15]:50235 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1763315Ab3DILSB (ORCPT ); Tue, 9 Apr 2013 07:18:01 -0400 From: Mel Gorman To: Andrew Morton Cc: Jiri Slaby , Valdis Kletnieks , Rik van Riel , Zlatko Calusic , Johannes Weiner , dormando , Satoru Moriya , Michal Hocko , Linux-MM , LKML , Mel Gorman Subject: [PATCH 0/10] Reduce system disruption due to kswapd V2 Date: Tue, 9 Apr 2013 12:06:55 +0100 Message-Id: <1365505625-9460-1-git-send-email-mgorman@suse.de> X-Mailer: git-send-email 1.8.1.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 10009 Lines: 191 Posting V2 of this series got delayed due to trying to pin down an unrelated regression in 3.9-rc where interactive performance is shot to hell. That problem still has not been identified as it's resisting attempts to be reproducible by a script for the purposes of bisection. For those that looked at V1, the most important difference in this version is how patch 2 preserves the proportional scanning of anon/file LRUs. The series is against 3.9-rc6. Changelog since V1 o Rename ZONE_DIRTY to ZONE_TAIL_LRU_DIRTY (andi) o Reformat comment in shrink_page_list (andi) o Clarify some comments (dhillf) o Rework how the proportional scanning is preserved o Add PageReclaim check before kswapd starts writeback o Reset sc.nr_reclaimed on every full zone scan Kswapd and page reclaim behaviour has been screwy in one way or the other for a long time. Very broadly speaking it worked in the far past because machines were limited in memory so it did not have that many pages to scan and it stalled congestion_wait() frequently to prevent it going completely nuts. In recent times it has behaved very unsatisfactorily with some of the problems compounded by the removal of stall logic and the introduction of transparent hugepage support with high-order reclaims. There are many variations of bugs that are rooted in this area. One example is reports of a large copy operations or backup causing the machine to grind to a halt or applications pushed to swap. Sometimes in low memory situations a large percentage of memory suddenly gets reclaimed. In other cases an application starts and kswapd hits 100% CPU usage for prolonged periods of time and so on. There is now talk of introducing features like an extra free kbytes tunable to work around aspects of the problem instead of trying to deal with it. It's compounded by the problem that it can be very workload and machine specific. This series aims at addressing some of the worst of these problems without attempting to fundmentally alter how page reclaim works. Patches 1-2 limits the number of pages kswapd reclaims while still obeying the anon/file proportion of the LRUs it should be scanning. Patches 3-4 control how and when kswapd raises its scanning priority and deletes the scanning restart logic which is tricky to follow. Patch 5 notes that it is too easy for kswapd to reach priority 0 when scanning and then reclaim the world. Down with that sort of thing. Patch 6 notes that kswapd starts writeback based on scanning priority which is not necessarily related to dirty pages. It will have kswapd writeback pages if a number of unqueued dirty pages have been recently encountered at the tail of the LRU. Patch 7 notes that sometimes kswapd should stall waiting on IO to complete to reduce LRU churn and the likelihood that it'll reclaim young clean pages or push applications to swap. It will cause kswapd to block on IO if it detects that pages being reclaimed under writeback are recycling through the LRU before the IO completes. Patch 8 shrinks slab just once per priority scanned or if a zone is otherwise unreclaimable to avoid hammering slab when kswapd has to skip a large number of pages. Patches 9-10 are cosmetic but balance_pgdat() might be easier to follow. This was tested using memcached+memcachetest while some background IO was in progress as implemented by the parallel IO tests implement in MM Tests. memcachetest benchmarks how many operations/second memcached can service and it is run multiple times. It starts with no background IO and then re-runs the test with larger amounts of IO in the background to roughly simulate a large copy in progress. The expectation is that the IO should have little or no impact on memcachetest which is running entirely in memory. 3.9.0-rc6 3.9.0-rc6 vanilla lessdisrupt-v2r11 Ops memcachetest-0M 11106.00 ( 0.00%) 10997.00 ( -0.98%) Ops memcachetest-749M 10960.00 ( 0.00%) 11032.00 ( 0.66%) Ops memcachetest-2498M 2588.00 ( 0.00%) 10948.00 (323.03%) Ops memcachetest-4246M 2401.00 ( 0.00%) 10960.00 (356.48%) Ops io-duration-0M 0.00 ( 0.00%) 0.00 ( 0.00%) Ops io-duration-749M 15.00 ( 0.00%) 8.00 ( 46.67%) Ops io-duration-2498M 112.00 ( 0.00%) 25.00 ( 77.68%) Ops io-duration-4246M 170.00 ( 0.00%) 45.00 ( 73.53%) Ops swaptotal-0M 0.00 ( 0.00%) 0.00 ( 0.00%) Ops swaptotal-749M 161678.00 ( 0.00%) 16.00 ( 99.99%) Ops swaptotal-2498M 471903.00 ( 0.00%) 192.00 ( 99.96%) Ops swaptotal-4246M 444010.00 ( 0.00%) 1323.00 ( 99.70%) Ops swapin-0M 0.00 ( 0.00%) 0.00 ( 0.00%) Ops swapin-749M 789.00 ( 0.00%) 0.00 ( 0.00%) Ops swapin-2498M 196496.00 ( 0.00%) 192.00 ( 99.90%) Ops swapin-4246M 168269.00 ( 0.00%) 154.00 ( 99.91%) Ops minorfaults-0M 1596126.00 ( 0.00%) 1521332.00 ( 4.69%) Ops minorfaults-749M 1766556.00 ( 0.00%) 1596350.00 ( 9.63%) Ops minorfaults-2498M 1661445.00 ( 0.00%) 1598762.00 ( 3.77%) Ops minorfaults-4246M 1628375.00 ( 0.00%) 1597624.00 ( 1.89%) Ops majorfaults-0M 9.00 ( 0.00%) 0.00 ( 0.00%) Ops majorfaults-749M 154.00 ( 0.00%) 101.00 ( 34.42%) Ops majorfaults-2498M 27214.00 ( 0.00%) 165.00 ( 99.39%) Ops majorfaults-4246M 23229.00 ( 0.00%) 114.00 ( 99.51%) Note how the vanilla kernels performance collapses when there is enough IO taking place in the background. This drop in performance is part of users complain of when they start backups. Note how the swapin and major fault figures indicate that processes were being pushed to swap prematurely. With the series applied, there is no noticable performance drop and while there is still some swap activity, it's tiny. 3.9.0-rc6 3.9.0-rc6 vanilla lessdisrupt-v2r11 Page Ins 9094288 346092 Page Outs 62897388 47599884 Swap Ins 2243749 19389 Swap Outs 3953966 142258 Direct pages scanned 0 2262897 Kswapd pages scanned 55530838 75725437 Kswapd pages reclaimed 6682620 1814689 Direct pages reclaimed 0 2187167 Kswapd efficiency 12% 2% Kswapd velocity 10537.501 14377.501 Direct efficiency 100% 96% Direct velocity 0.000 429.642 Percentage direct scans 0% 2% Page writes by reclaim 10835163 72419297 Page writes file 6881197 72277039 Page writes anon 3953966 142258 Page reclaim immediate 11463 8199 Page rescued immediate 0 0 Slabs scanned 38144 30592 Direct inode steals 0 0 Kswapd inode steals 11383 791 Kswapd skipped wait 0 0 THP fault alloc 10 111 THP collapse alloc 2782 1779 THP splits 10 27 THP fault fallback 0 5 THP collapse fail 0 21 Compaction stalls 0 89 Compaction success 0 53 Compaction failures 0 36 Page migrate success 0 37062 Page migrate failure 0 0 Compaction pages isolated 0 83481 Compaction migrate scanned 0 80830 Compaction free scanned 0 2660824 Compaction cost 0 40 NUMA PTE updates 0 0 NUMA hint faults 0 0 NUMA hint local faults 0 0 NUMA pages migrated 0 0 AutoNUMA cost 0 0 Note that while there is no noticeable performance drop and swap activity is massively reduced there are processes that direct reclaim as a consequence of the series due to kswapd not reclaiming the world. ftrace was not enabled for this particular test to avoid disruption but on a similar test with ftrace I found that the vast bulk of the direct reclaims were in the dd processes. The top direct reclaimers were; 11 ps-13204 12 top-13198 15 memcachetest-11712 20 gzip-3126 67 tclsh-3124 80 memcachetest-12924 191 flush-8:0-292 338 tee-3125 2184 dd-12135 10751 dd-13124 While processes did stall, it was mostly the "correct" processes that stalled. There is also still a risk that kswapd not reclaiming the world may mean that it stays awake balancing zones, does not stall on the appropriate events and continually scans pages it cannot reclaim consuming CPU. This will be visible as continued high CPU usage but in my own tests I only saw a single spike lasting less than a second and I did not observe any problems related to reclaim while running the series on my desktop. include/linux/mmzone.h | 17 ++ mm/vmscan.c | 449 ++++++++++++++++++++++++++++++------------------- 2 files changed, 293 insertions(+), 173 deletions(-) -- 1.8.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/