Messages in this thread | | | Date | Tue, 24 May 2011 17:34:40 +0900 | Subject | Re: Unending loop in __alloc_pages_slowpath following OOM-kill; rfc: patch. | From | Minchan Kim <> |
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On Tue, May 24, 2011 at 1:54 PM, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote: >>>From 8bd3f16736548375238161d1bd85f7d7c381031f Mon Sep 17 00:00:00 2001 >> From: Minchan Kim <minchan.kim@gmail.com> >> Date: Sat, 21 May 2011 01:37:41 +0900 >> Subject: [PATCH] Prevent unending loop in __alloc_pages_slowpath >> >> From: Andrew Barry <abarry@cray.com> >> >> I believe I found a problem in __alloc_pages_slowpath, which allows a process to >> get stuck endlessly looping, even when lots of memory is available. >> >> Running an I/O and memory intensive stress-test I see a 0-order page allocation >> with __GFP_IO and __GFP_WAIT, running on a system with very little free memory. >> Right about the same time that the stress-test gets killed by the OOM-killer, >> the utility trying to allocate memory gets stuck in __alloc_pages_slowpath even >> though most of the systems memory was freed by the oom-kill of the stress-test. >> >> The utility ends up looping from the rebalance label down through the >> wait_iff_congested continiously. Because order=0, __alloc_pages_direct_compact >> skips the call to get_page_from_freelist. Because all of the reclaimable memory >> on the system has already been reclaimed, __alloc_pages_direct_reclaim skips the >> call to get_page_from_freelist. Since there is no __GFP_FS flag, the block with >> __alloc_pages_may_oom is skipped. The loop hits the wait_iff_congested, then >> jumps back to rebalance without ever trying to get_page_from_freelist. This loop >> repeats infinitely. >> >> The test case is pretty pathological. Running a mix of I/O stress-tests that do >> a lot of fork() and consume all of the system memory, I can pretty reliably hit >> this on 600 nodes, in about 12 hours. 32GB/node. >> >> Signed-off-by: Andrew Barry <abarry@cray.com> >> Reviewed-by: Minchan Kim <minchan.kim@gmail.com> >> Cc: Mel Gorman <mgorman@suse.de> >> --- >> mm/page_alloc.c | 2 +- >> 1 files changed, 1 insertions(+), 1 deletions(-) >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index 3f8bce2..e78b324 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -2064,6 +2064,7 @@ restart: >> first_zones_zonelist(zonelist, high_zoneidx, NULL, >> &preferred_zone); >> >> +rebalance: >> /* This is the last chance, in general, before the goto nopage. */ >> page = get_page_from_freelist(gfp_mask, nodemask, order, zonelist, >> high_zoneidx, alloc_flags & ~ALLOC_NO_WATERMARKS, >> @@ -2071,7 +2072,6 @@ restart: >> if (page) >> goto got_pg; >> >> -rebalance: >> /* Allocate without watermarks if the context allows */ >> if (alloc_flags & ALLOC_NO_WATERMARKS) { >> page = __alloc_pages_high_priority(gfp_mask, order, > > I'm sorry I missed this thread long time.
No problem. It would be better than not review.
> > In this case, I think we should call drain_all_pages(). then following > patch is better.
Strictly speaking, this problem isn't related to drain_all_pages. This problem caused by lru empty but I admit it could work well if your patch applied. So yours could help, too.
> However I also think your patch is valuable. because while the task is > sleeping in wait_iff_congested(), an another task may free some pages. > thus, rebalance path should try to get free pages. iow, you makes sense.
Yes. Off-topic. I would like to move cond_resched below get_page_from_freelist in __alloc_pages_direct_reclaim. Otherwise, it is likely we can be stolen pages to other processes. One more benefit is that if it's apparently OOM path(ie, did_some_progress = 0), we can reduce OOM kill latency due to remove unnecessary cond_resched.
> > So, I'd like to propose to merge both your and my patch.
Recently, there was discussion on drain_all_pages with Wu. He saw much overhead in 8-core system, AFAIR. I Cced Wu.
How about checking per-cpu before calling drain_all_pages() than unconditional calling? if (per_cpu_ptr(zone->pageset, smp_processor_id()) drain_all_pages();
Of course, It can miss other CPU free pages. But above routine assume local cpu direct reclaim is successful but it failed by per-cpu. So I think it works.
Thanks for good suggestion and Reviewed-by, KOSAKI. -- Kind regards, Minchan Kim -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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