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

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Message-ID: <87ob85kejy.fsf@xmission.com>
Date:	Fri, 06 Sep 2013 11:09:21 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Michal Hocko <mhocko@...e.cz>
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

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.

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.

Eric
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