linux-kernel - Re: can't oom-kill zap the victim's memory?

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Message-ID: <561639F7.3080504@suse.cz>
Date:	Thu, 8 Oct 2015 11:40:07 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	mhocko@...nel.org, torvalds@...ux-foundation.org,
	rientjes@...gle.com, oleg@...hat.com, kwalker@...hat.com,
	cl@...ux.com, akpm@...ux-foundation.org, hannes@...xchg.org,
	vdavydov@...allels.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, skozina@...hat.com
Subject: Re: can't oom-kill zap the victim's memory?

On 10/07/2015 12:43 PM, Tetsuo Handa wrote:
> Vlastimil Babka wrote:
>> On 5.10.2015 16:44, Michal Hocko wrote:
>>> So I can see basically only few ways out of this deadlock situation.
>>> Either we face the reality and allow small allocations (withtout
>>> __GFP_NOFAIL) to fail after all attempts to reclaim memory have failed
>>> (so after even OOM killer hasn't made any progress).
>>
>> Note that small allocations already *can* fail if they are done in the context
>> of a task selected as OOM victim (i.e. TIF_MEMDIE). And yeah I've seen a case
>> when they failed in a code that "handled" the allocation failure with a
>> BUG_ON(!page).
>>
> Did You hit a race described below?

I don't know, I don't even have direct evidence of TIF_MEMDIE being set, 
but OOMs were happening all over the place, and I haven't found another 
reason why the allocation would not be too-small-to-fail otherwise.

> http://lkml.kernel.org/r/201508272249.HDH81838.FtQOLMFFOVSJOH@I-love.SAKURA.ne.jp
>
> Where was the BUG_ON(!page) ? Maybe it is a candidate for adding __GFP_NOFAIL.

Yes, I suggested so:
http://marc.info/?l=linux-kernel&m=144181523115244&w=2

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