On 11/08/2014 02:11 PM, P. Christeas wrote: > On Thursday 06 November 2014, Vlastimil Babka wrote: >>> On Wednesday 05 November 2014, Vlastimil Babka wrote: >>>> Can you please try the following patch? >>>> - compaction_defer_reset(zone, order, false); >> Oh and did I ask in this thread for /proc/zoneinfo yet? :) > > Using that same kernel[1], got again into a race, gathered a few more data. > > This time, I had 1x "urpmq" process [2] hung at 100% CPU , when "kwin" got > apparently blocked (100% CPU, too) trying to resize a GUI window. I suppose > the resizing operation would mean heavy memory alloc/free. > > The rest of the system was responsive, I could easily get a console, login, > gather the files.. Then, I have *killed* -9 the "urpmq" process, which solved > the race and my system is still alive! "kwin" is still running, returned to > regular CPU load. > > Attached is traces from SysRq+l (pressed a few times, wanted to "snapshot" the > stack) and /proc/zoneinfo + /proc/vmstat > > Bisection is not yet meaningful, IMHO, because I cannot be sure that "good" > points are really free from this issue. I'd estimate that each test would take > +3days, unless I really find a deterministic way to reproduce the issue . Hi, I think I finally found the cause by staring into the code... CCing people from all 4 separate threads I know about this issue. The problem with finding the cause was that the first report I got from Markus was about isolate_freepages_block() overhead, and later Norbert reported that reverting a patch for isolate_freepages* helped. But the problem seems to be that although the loop in isolate_migratepages exits because the scanners almost meet (they are within same pageblock), they don't truly meet, therefore compact_finished() decides to continue, but isolate_migratepages() exits immediately... boom! But indeed e14c720efdd7 made this situation possible, as free scaner pfn can now point to a middle of pageblock. So I hope the attached patch will fix the soft-lockup issues in compact_zone. Please apply on 3.18-rc3 or later without any other reverts, and test. It probably won't help Markus and his isolate_freepages_block() overhead though... Thanks, Vlastimil ------8<------ >From fbf8eb0bcd2897090312e23da6a31bad9cc6b337 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka <vbabka@xxxxxxx> Date: Sat, 8 Nov 2014 22:20:43 +0100 Subject: [PATCH] mm, compaction: prevent endless loop in migrate scanner --- mm/compaction.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index ec74cf0..1b7a1be 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1029,8 +1029,12 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone, } acct_isolated(zone, cc); - /* Record where migration scanner will be restarted */ - cc->migrate_pfn = low_pfn; + /* + * Record where migration scanner will be restarted. If we end up in + * the same pageblock as the free scanner, make the scanners fully + * meet so that compact_finished() terminates compaction. + */ + cc->migrate_pfn = (end_pfn <= cc->free_pfn) ? low_pfn : cc->free_pfn; return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE; } -- 2.1.2 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>