On Mon, 2011-05-16 at 09:37 +0100, Mel Gorman wrote: > On Sat, May 14, 2011 at 10:34:33AM +0200, Colin Ian King wrote: > > On Fri, 2011-05-13 at 15:03 +0100, Mel Gorman wrote: > > > 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. > > > > These patches solve the problem for me. I've been soak testing the file > > copy test > > for 3.5 hours with nearly 400 test cycles and observed no lockups at all > > - rock solid. From my observations from the output from vmstat the > > system is behaving sanely. > > Thanks for finding a solution - much appreciated! > > > > Can you tell me if just patches 1 and 4 fix the problem please? It'd be good > to know if this was only a reclaim-related problem. Thanks. Hi Mel, Soak tested just patches 1 + 4 and works fine. Did 250 cycles for ~2 hours, no lockups, and the output from vmstat looked sane. Colin > -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
