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

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Message-Id: <20110308102147.7E96.A69D9226@jp.fujitsu.com>
Date:	Tue,  8 Mar 2011 10:24:52 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Andrew Vagin <avagin@...il.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	David Rientjes <rientjes@...gle.com>,
	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

> 2011/3/7 David Rientjes <rientjes@...gle.com>:
> > 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.
> 
> Probably you said about the first version of my patch.
> This version is incorrect because of
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=dd8e8f405ca386c7ce7cbb996ccd985d283b0e03
> 
> but my first patch is correct and it has a simple reproducer(I
> attached it). You can execute it and your kernel hangs up, because the
> parent doesn't wait children, but the one child (zombie) will have
> flag TIF_MEMDIE, oom_killer will kill nobody
> 
> 
> The link on the first patch:
> http://groups.google.com/group/linux.kernel/browse_thread/thread/b9c6ddf34d1671ab/2941e1877ca4f626?lnk=raot&pli=1

OK. I can ack this.
TIF_MEMDIE  mean the process have been receive SIGKILL therefore we can assume it
as per process flag.



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