linux-kernel - Re: [PATCH] oom: Make coredump interruptible

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Date:	Sun, 13 Jun 2010 20:24:51 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	kosaki.motohiro@...fujitsu.com, Roland McGrath <roland@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH] oom: Make coredump interruptible

Sorry for the delay.

> On 06/04, Oleg Nesterov wrote:
> >
> > On 06/04, KOSAKI Motohiro wrote:
> > >
> > > In multi threaded OOM case, we have two problematic routine, coredump
> > > and vmscan. Roland's idea can only solve the former.
> > >
> > > But I also interest vmscan quickly exit if OOM received.
> >
> > Yes, agreed. See another email from me, MMF_ flags looks "obviously
> > useful" to me.
> 
> Well. But somehow we forgot about the !coredumping case... Suppose
> that select_bad_process() chooses the process P to kill and we have
> other processes (not sub-threads) which share the same ->mm.

Ah, yes. I think you are correct.


> In that case I am not sure we should blindly set MMF_OOMKILL. Suppose
> that we kill P and after that the "out-of-memory" condition goes away.
> But its ->mm still has MMF_OOMKILL set, and it is used. Who/when will
> clear this flag?
> 
> Perhaps something like below makes sense for now.

Probably, this works. at least I don't find any problems.
But umm... Do you mean we can't implement per-process oom flags?

example,
	1) back to implement signal->oom_victim
	   because We are using SIGKILL for OOM and struct signal
	   naturally represent signal target.
	2) mm->nr_oom_killed_task
	   just avoid simple flag. instead counting number of tasks of
	   oom-killed.

I think both avoid your explained problem. Am I missing something?

But, again, I have no objection to your patch. because I really hope to
fix coredump vs oom issue.



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