linux-kernel - Re: [RFD] Merge task counter into memcg

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Message-ID: <20120417154117.GE32402@google.com>
Date:	Tue, 17 Apr 2012 08:41:17 -0700
From:	Tejun Heo <tj@...nel.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	Glauber Costa <glommer@...allels.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Walsh <dwalsh@...hat.com>,
	"Daniel P. Berrange" <berrange@...hat.com>,
	Li Zefan <lizf@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Cgroups <cgroups@...r.kernel.org>,
	Containers <containers@...ts.linux-foundation.org>
Subject: Re: [RFD] Merge task counter into memcg

Hello, KAMEZAWA.

On Fri, Apr 13, 2012 at 10:42:24AM +0900, KAMEZAWA Hiroyuki wrote:
> > So, there's spectrum of solutions between merging task counter and
> > just directing everyone to kmem without distinguishing task resource
> > at all, and at the moment voices in my head are succeeding at making
> > cases for both directions.  What do you guys think about the above two
> > issues?
> 
> 
> To be honest, I doubt that task counter is unnecessary...memcg can catch
> oom situation well. I often test 'make -j' under memcg.

Heh, the double negation is confusing me.  Were you trying to say that
task_counter is necessary or was it the other way around?

> To the questions
> *   It sounds like a 'ulimit' cgroup. How about overwriting
>     ulimit values via cgroup ? (sounds joke?) Then, overhead will be small but
>     I'm not sure it can be hierarchical and doesn't break userland.
> 
>     If people wants to limit the number of tasks, I think interface should provide it
>     in the unit of objects. Then, I'm ok to have other subsystem for counting something.
>     fork-bomb's memory overhead can be prevent by memcg. What memcg cannot handle
>     is ulimit. If forkbomb exhausts all ulimit/tasks, the user cannot login.
>     So, having task-limit cgroup subsys for a sandbox will make sense in some situation.
> 
> In short, I don't think it's better to have task-counting and fd-counting in memcg.
> It's kmem, but it's more than that, I think.
> Please provide subsys like ulimit.

So, you think that while kmem would be enough to prevent fork-bombs,
it would still make sense to limit in more traditional ways
(ie. ulimit style object limits).  Hmmm....

Thanks.

-- 
tejun
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