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

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Message-ID: <CAFTL4hw3C4s6VS07pJzdBawv0ugKJJa+Vnb-Q_9FrWEq4=ka9Q@mail.gmail.com>
Date:	Wed, 18 Apr 2012 09:53:00 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Glauber Costa <glommer@...allels.com>, Tejun Heo <tj@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	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

2012/4/18 KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>:
> (2012/04/18 1:52), Glauber Costa wrote:
>
>>
>>>> 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....
>>>
>>
>> I personally think this is namespaces business, not cgroups.
>> If you have a process namespace, an interface that works to limit the
>> number of processes should keep working given the constraints you are
>> given.
>>
>> What doesn't make sense, is to create a *new* interface to limit
>> something that doesn't really need to be limited, just because you
>> limited a similar resource before.
>>
>
>
> Ok, limitiing forkbomb is unnecessary. ulimit+namespace should work.
> What we need is user-id namespace, isn't it ? If we have that, ulimit
> works enough fine, no overheads.

I have considered using NR_PROC rlimit on top of user namespaces to
fight forkbombs inside a container.
ie: one user namespace per container with its own rlimit.

But it doesn't work because we can have multiuser apps running in a
single container.
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