On Fri, Mar 18, 2011 at 01:05:15PM -0500, Alex Villac??s Lasso wrote: > El 18/03/11 06:13, Mel Gorman escribió: > > > >\o/ ... no wait, it's the other one - :( > > > >If you look at the stack traces though, all of them had called > >do_huge_pmd_anonymous_page() so while it looks similar to 12309, the trigger > >is new because it's THP triggering compaction that is causing the stalls > >rather than page reclaim doing direct writeback which was the culprit in > >the past. > > > >To confirm if this is the case, I'd be very interested in hearing if this > >problem persists in the following cases > > > >1. 2.6.38-rc8 with defrag disabled by > > echo never>/sys/kernel/mm/transparent_hugepage/defrag > > (this will stop THP allocations calling into compaction) > >2. 2.6.38-rc8 with THP disabled by > > echo never> > >/sys/kernel/mm/transparent_hugepage/enabled > > (if the problem still persists, then page reclaim is still a problem > > but we should still stop THP doing sync writes) > >3. 2.6.37 vanilla > > (in case this is a new regression introduced since then) > > > >Migration can do sync writes on dirty pages which is why it looks so similar > >to page reclaim but this can be controlled by the value of sync_migration > >passed into try_to_compact_pages(). If we find that option 1 above makes > >the regression go away or at least helps a lot, then a reasonable fix may > >be to never set sync_migration if __GFP_NO_KSWAPD which is always set for > >THP allocations. I've added Andrea to the cc to see what he thinks. > > > >Thanks for the report. > > > > I have just done tests 1 and 2 on 2.6.38 (final, not -rc8), and I > have verified that echoing "never" on either > /sys/kernel/mm/transparent_hugepage/defrag or > /sys/kernel/mm/transparent_hugepage/enabled does allow the file copy > to USB to proceed smoothly (copying 4GB of data). Just to verify, I > later wrote "always" to both files, and sure enough, some > applications stalled when I repeated the same file copy. So I have > at least a workaround for the issue. Given this evidence, will the > patch at comment #14 fix the issue for good? > Thanks for testing and reporting, it's very helpful. Based on that that report the patch should help. Can you test it to be absolutly sure please? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx 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: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>