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Message-ID: <20111110103803.GH3153@redhat.com> Date: Thu, 10 Nov 2011 11:38:03 +0100 From: Johannes Weiner <jweiner@...hat.com> To: Mel Gorman <mgorman@...e.de> Cc: Andrew Morton <akpm@...ux-foundation.org>, Jan Kara <jack@...e.cz>, Andy Isaacson <adi@...apodia.org>, Andrea Arcangeli <aarcange@...hat.com>, linux-kernel@...r.kernel.org, linux-mm@...ck.org Subject: Re: [PATCH] mm: Do not stall in synchronous compaction for THP allocations On Thu, Nov 10, 2011 at 10:06:16AM +0000, Mel Gorman wrote: > Occasionally during large file copies to slow storage, there are still > reports of user-visible stalls when THP is enabled. Reports on this > have been intermittent and not reliable to reproduce locally but; > > Andy Isaacson reported a problem copying to VFAT on SD Card > https://lkml.org/lkml/2011/11/7/2 > > In this case, it was stuck in munmap for betwen 20 and 60 > seconds in compaction. It is also possible that khugepaged > was holding mmap_sem on this process if CONFIG_NUMA was set. > > Johannes Weiner reported stalls on USB > https://lkml.org/lkml/2011/7/25/378 > > In this case, there is no stack trace but it looks like the > same problem. The USB stick may have been using NTFS as a > filesystem based on other work done related to writing back > to USB around the same time. Sorry, here is a trace from when I first recorded the problem: [171252.437688] firefox D 000000010a31e6b7 0 8502 1110 0x00000000 [171252.437691] ffff88001e91f8a8 0000000000000082 ffff880000000000 ffff88001e91ffd8 [171252.437693] ffff88001e91ffd8 0000000000004000 ffffffff8180b020 ffff8800456e4680 [171252.437696] ffff88001e91f7e8 ffffffff810cd4ed ffffea00028d4500 000000000000000e [171252.437699] Call Trace: [171252.437701] [<ffffffff810cd4ed>] ? __pagevec_free+0x2d/0x40 [171252.437703] [<ffffffff810d044c>] ? release_pages+0x24c/0x280 [171252.437705] [<ffffffff81099448>] ? ktime_get_ts+0xa8/0xe0 [171252.437707] [<ffffffff810c5040>] ? file_read_actor+0x170/0x170 [171252.437709] [<ffffffff8156ac8a>] io_schedule+0x8a/0xd0 [171252.437711] [<ffffffff810c5049>] sleep_on_page+0x9/0x10 [171252.437713] [<ffffffff8156b0f7>] __wait_on_bit+0x57/0x80 [171252.437715] [<ffffffff810c5630>] wait_on_page_bit+0x70/0x80 [171252.437718] [<ffffffff810916c0>] ? autoremove_wake_function+0x40/0x40 [171252.437720] [<ffffffff810f98a5>] migrate_pages+0x2a5/0x490 [171252.437722] [<ffffffff810f5940>] ? suitable_migration_target+0x50/0x50 [171252.437724] [<ffffffff810f6234>] compact_zone+0x4e4/0x770 [171252.437727] [<ffffffff810f65e0>] compact_zone_order+0x80/0xb0 [171252.437729] [<ffffffff810f66cd>] try_to_compact_pages+0xbd/0xf0 [171252.437731] [<ffffffff810cc608>] __alloc_pages_direct_compact+0xa8/0x180 [171252.437734] [<ffffffff810ccbdb>] __alloc_pages_nodemask+0x4fb/0x720 [171252.437736] [<ffffffff810fbfe3>] do_huge_pmd_wp_page+0x4c3/0x740 [171252.437738] [<ffffffff81094fff>] ? hrtimer_start_range_ns+0xf/0x20 [171252.437740] [<ffffffff810e3f9c>] handle_mm_fault+0x1bc/0x2f0 [171252.437743] [<ffffffff8102e6c6>] ? __switch_to+0x1e6/0x2c0 [171252.437745] [<ffffffff810511b2>] do_page_fault+0x132/0x430 [171252.437747] [<ffffffff810a4995>] ? sys_futex+0x105/0x1a0 [171252.437749] [<ffffffff8156cf9f>] page_fault+0x1f/0x30 It could have been vfat, I don't remember for sure. But I would think the problem depends only on the duration of PageWriteback being set. > Internally in SUSE, I received a bug report related to stalls in firefox > when using Java and Flash heavily while copying from NFS > to VFAT on USB. It has not been confirmed to be the same problem > but if it looks like a duck and quacks like a duck..... > > In the past, commit [11bc82d6: mm: compaction: Use async migration for > __GFP_NO_KSWAPD and enforce no writeback] forced that sync compaction > would never be used for THP allocations. This was reverted in commit > [c6a140bf: mm/compaction: reverse the change that forbade sync > migraton with __GFP_NO_KSWAPD] on the grounds that it was uncertain > it was beneficial. > > While user-visible stalls do not happen for me when writing to USB, > I setup a test running postmark while short-lived processes created > anonymous mapping. The objective was to exercise the paths that > allocate transparent huge pages. I then logged when processes were > stalled for more than 1 second, recorded a stack strace and did some > analysis to aggregate unique "stall events" which revealed > > Time stalled in this event: 47369 ms > Event count: 20 > usemem sleep_on_page 3690 ms > usemem sleep_on_page 2148 ms > usemem sleep_on_page 1534 ms > usemem sleep_on_page 1518 ms > usemem sleep_on_page 1225 ms > usemem sleep_on_page 2205 ms > usemem sleep_on_page 2399 ms > usemem sleep_on_page 2398 ms > usemem sleep_on_page 3760 ms > usemem sleep_on_page 1861 ms > usemem sleep_on_page 2948 ms > usemem sleep_on_page 1515 ms > usemem sleep_on_page 1386 ms > usemem sleep_on_page 1882 ms > usemem sleep_on_page 1850 ms > usemem sleep_on_page 3715 ms > usemem sleep_on_page 3716 ms > usemem sleep_on_page 4846 ms > usemem sleep_on_page 1306 ms > usemem sleep_on_page 1467 ms > [<ffffffff810ef30c>] wait_on_page_bit+0x6c/0x80 > [<ffffffff8113de9f>] unmap_and_move+0x1bf/0x360 > [<ffffffff8113e0e2>] migrate_pages+0xa2/0x1b0 > [<ffffffff81134273>] compact_zone+0x1f3/0x2f0 > [<ffffffff811345d8>] compact_zone_order+0xa8/0xf0 > [<ffffffff811346ff>] try_to_compact_pages+0xdf/0x110 > [<ffffffff810f773a>] __alloc_pages_direct_compact+0xda/0x1a0 > [<ffffffff810f7d5d>] __alloc_pages_slowpath+0x55d/0x7a0 > [<ffffffff810f8151>] __alloc_pages_nodemask+0x1b1/0x1c0 > [<ffffffff811331db>] alloc_pages_vma+0x9b/0x160 > [<ffffffff81142bb0>] do_huge_pmd_anonymous_page+0x160/0x270 > [<ffffffff814410a7>] do_page_fault+0x207/0x4c0 > [<ffffffff8143dde5>] page_fault+0x25/0x30 > > The stall times are approximate at best but the estimates represent 25% > of the worst stalls and even if the estimates are off by a factor of > 10, it's severe. > > This patch once again prevents sync migration for transparent > hugepage allocations as it is preferable to fail a THP allocation > than stall. It was suggested that __GFP_NORETRY be used instead of > __GFP_NO_KSWAPD. This would look less like a special case but would > still cause compaction to run at least once with sync compaction. > > If accepted, this is a -stable candidate. > > Reported-by: Andy Isaacson <adi@...apodia.org> > Reported-by: Johannes Weiner <hannes@...xchg.org> > Signed-off-by: Mel Gorman <mgorman@...e.de> Tested-by: Johannes Weiner <jweiner@...hat.com> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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