Re: Unending loop in __alloc_pages_slowpath following OOM-kill; rfc:patch.

[Mel Gorman]

On Sat, May 21, 2011 at 01:49:24AM +0900, Minchan Kim wrote:
> <SNIP>
> 
> From 8bd3f16736548375238161d1bd85f7d7c381031f Mon Sep 17 00:00:00 2001
> From: Minchan Kim <minchan.kim@xxxxxxxxx>
> Date: Sat, 21 May 2011 01:37:41 +0900
> Subject: [PATCH] Prevent unending loop in __alloc_pages_slowpath
> 
> From: Andrew Barry <abarry@xxxxxxxx>
> 
> 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@xxxxxxxx>
> Reviewed-by: Minchan Kim <minchan.kim@xxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>

Acked-by: Mel Gorman <mgorman@xxxxxxx>

-- 
Mel Gorman
SUSE Labs
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