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

[KOSAKI Motohiro]

(2011/05/24 13:54), KOSAKI Motohiro wrote:
>> >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>
>> ---
>>  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.
> 
> In this case, I think we should call drain_all_pages(). then following
> patch is better.
> 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.
> 
> So, I'd like to propose to merge both your and my patch.

I forgot to write important thing. Your patch looks good to me.
	Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>




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