linux-kernel - Re: [PATCH] mm: skip zombie in OOM-killer

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Message-ID: <alpine.DEB.2.00.1103061400170.23737@chino.kir.corp.google.com>
Date:	Sun, 6 Mar 2011 14:03:39 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
cc:	Andrey Vagin <avagin@...nvz.org>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: skip zombie in OOM-killer

On Sun, 6 Mar 2011, KOSAKI Motohiro wrote:

> > When we check that task has flag TIF_MEMDIE, we forgot check that
> > it has mm. A task may be zombie and a parent may wait a memor.
> > 
> > v2: Check that task doesn't have mm one time and skip it immediately
> > 
> > Signed-off-by: Andrey Vagin <avagin@...nvz.org>
> 
> This seems incorrect. Do you have a reprodusable testcasae?
> Your patch only care thread group leader state, but current code
> care all thread in the process. Please look at oom_badness() and 
> find_lock_task_mm(). 
> 

That's all irrelevant, the test for TIF_MEMDIE specifically makes the oom 
killer a complete no-op when an eligible task is found to have been oom 
killed to prevent needlessly killing additional tasks.  oom_badness() and 
find_lock_task_mm() have nothing to do with that check to return 
ERR_PTR(-1UL) from select_bad_process().

Andrey is patching the case where an eligible TIF_MEMDIE process is found 
but it has already detached its ->mm.  In combination with the patch 
posted to linux-mm, oom: prevent unnecessary oom kills or kernel panics, 
which makes select_bad_process() iterate over all threads, it is an 
effective solution.

Thanks.
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