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

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Date:	Tue, 17 Apr 2012 08:17:53 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Glauber Costa <glommer@...allels.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	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, Frederic.

On Thu, Apr 12, 2012 at 06:59:27PM +0200, Frederic Weisbecker wrote:
> I want:
> 
> a) to prevent the forkbomb from going far enough to DDOS the machine
> b) to be able to kill that forkbomb once detected, in one go without race
> against concurrent forks.
> 
> I think a) can work just fine with kernel stack limiting. I also need
> to be notified about the fact we reached the limit. And b) should
> be feasible with the help of the cgroup freezer. 

kmem allocation fail after reaching the limit which in turn should
fail task creation.  Isn't that the same effect as the task_counter as
implemented?

> > Is there anything for which you need to know exactly the number of
> > processes?
> 
> No that's really about prevent/kill forkbomb as far as I'm concerned.

Hmm... so, accounting overhead aside, if the only purpose is
preventing the whole machine being brought down by a fork bomb, kmem
limiting is enough, right?

Thanks.

-- 
tejun
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