linux-kernel - Re: memcg creates an unkillable task in 3.11-rc2

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Date:	Mon, 9 Sep 2013 10:31:47 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Li Zefan <lizefan@...wei.com>, Tejun Heo <tj@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	cgroups@...r.kernel.org, containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, kent.overstreet@...il.com,
	Glauber Costa <glommer@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: memcg creates an unkillable task in 3.11-rc2

On Fri 06-09-13 11:09:21, Eric W. Biederman wrote:
> Michal Hocko <mhocko@...e.cz> writes:
> 
> > It seems that this one fell though the cracks?
> 
> Not completely, but it happened just as I was doing my initial triage of
> memcg problems and I haven't quite made it back to this.

OK. I am primarily asking because I am not sure I understood whether the
proposed patch helped or not. It should as per my last email but it is
possible that I have missed something...

> I have an even nastier memcg hang (without yet an easy reproducer).
> During mkdir ext3 can add a page to the page cache with the ext3 journal
> transaction lock held.  Normally that isn't a problem but freezing there
> stops all writes to that filesystem, and the world stops.
> 
> It looks like the only way to avoid that kind of scenario is to move the
> the memcg sleep to the edge of userspace, like we do with signals and a
> few other things so we can be guaranteed not to increase lock hold
> times, when it is avoidable.  I think I saw some similar comments about
> the slab limiting.

Johannes has patches that move memcg oom out of any locks already: 
https://lkml.org/lkml/2013/8/3/81. There is some development going on
there and I guess he will post v3 soon but that sounds it might help
with what you describe above.

Thanks!
-- 
Michal Hocko
SUSE Labs
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