From: Mel Gorman Subject: [PATCH 0/4] Reduce impact to overall system of SLUB using high-order allocations V2 Date: Fri, 13 May 2011 15:03:20 +0100 Message-ID: <1305295404-12129-1-git-send-email-mgorman@suse.de> Cc: James Bottomley , Colin King , Raghavendra D Prabhu , Jan Kara , Chris Mason , Christoph Lameter , Pekka Enberg , Rik van Riel , Johannes Weiner , linux-fsdevel , linux-mm , linux-kernel , linux-ext4 , Mel Gorman To: Andrew Morton Return-path: Sender: owner-linux-mm@kvack.org List-Id: linux-ext4.vger.kernel.org Changelog since V1 o kswapd should sleep if need_resched o Remove __GFP_REPEAT from GFP flags when speculatively using high orders so direct/compaction exits earlier o Remove __GFP_NORETRY for correctness o Correct logic in sleeping_prematurely o Leave SLUB using the default slub_max_order There are a few reports of people experiencing hangs when copying large amounts of data with kswapd using a large amount of CPU which appear to be due to recent reclaim changes. SLUB using high orders is the trigger but not the root cause as SLUB has been using high orders for a while. The following four patches aim to fix the problems in reclaim while reducing the cost for SLUB using those high orders. Patch 1 corrects logic introduced by commit [1741c877: mm: kswapd: keep kswapd awake for high-order allocations until a percentage of the node is balanced] to allow kswapd to go to sleep when balanced for high orders. Patch 2 prevents kswapd waking up in response to SLUBs speculative use of high orders. Patch 3 further reduces the cost by prevent SLUB entering direct compaction or reclaim paths on the grounds that falling back to order-0 should be cheaper. Patch 4 notes that even when kswapd is failing to keep up with allocation requests, it should still go to sleep when its quota has expired to prevent it spinning. My own data on this is not great. I haven't really been able to reproduce the same problem locally. The test case is simple. "download tar" wgets a large tar file and stores it locally. "unpack" is expanding it (15 times physical RAM in this case) and "delete source dirs" is the tarfile being deleted again. I also experimented with having the tar copied numerous times and into deeper directories to increase the size but the results were not particularly interesting so I left it as one tar. In the background, applications are being launched to time to vaguely simulate activity on the desktop and to measure how long it takes applications to start. Test server, 4 CPU threads, x86_64, 2G of RAM, no PREEMPT, no COMPACTION, X running LARGE COPY AND UNTAR vanilla fixprematurely kswapd-nowwake slub-noexstep kswapdsleep download tar 95 ( 0.00%) 94 ( 1.06%) 94 ( 1.06%) 94 ( 1.06%) 94 ( 1.06%) unpack tar 654 ( 0.00%) 649 ( 0.77%) 655 (-0.15%) 589 (11.04%) 598 ( 9.36%) copy source files 0 ( 0.00%) 0 ( 0.00%) 0 ( 0.00%) 0 ( 0.00%) 0 ( 0.00%) delete source dirs 327 ( 0.00%) 334 (-2.10%) 318 ( 2.83%) 325 ( 0.62%) 320 ( 2.19%) MMTests Statistics: duration User/Sys Time Running Test (seconds) 1139.7 1142.55 1149.78 1109.32 1113.26 Total Elapsed Time (seconds) 1341.59 1342.45 1324.90 1271.02 1247.35 MMTests Statistics: application launch evolution-wait30 mean 34.92 34.96 34.92 34.92 35.08 gnome-terminal-find mean 7.96 7.96 8.76 7.80 7.96 iceweasel-table mean 7.93 7.81 7.73 7.65 7.88 evolution-wait30 stddev 0.96 1.22 1.27 1.20 1.15 gnome-terminal-find stddev 3.02 3.09 3.51 2.99 3.02 iceweasel-table stddev 1.05 0.90 1.09 1.11 1.11 Having SLUB avoid expensive steps in reclaim improves performance by quite a bit with the overall test completing 1.5 minutes faster. Application launch times were not really affected but it's not something my test machine was suffering from in the first place so it's not really conclusive. The kswapd patches also did not appear to help but again, the test machine wasn't suffering that problem. These patches are against 2.6.39-rc7. Again, testing would be appreciated. Documentation/vm/slub.txt | 2 +- mm/page_alloc.c | 3 ++- mm/slub.c | 5 +++-- 3 files changed, 6 insertions(+), 4 deletions(-) mm/page_alloc.c | 3 ++- mm/slub.c | 3 ++- mm/vmscan.c | 6 +++++- 3 files changed, 9 insertions(+), 3 deletions(-) -- 1.7.3.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org