linux-kernel - Re: [RFC 0/5] forced comounts for cgroups.

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Date:	Wed, 05 Sep 2012 11:26:49 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Glauber Costa <glommer@...allels.com>
Cc:	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org, linux-mm@...ck.org, davej@...hat.com,
	ben@...adent.org.uk, pjt@...gle.com, lennart@...ttering.net,
	kay.sievers@...y.org
Subject: Re: [RFC 0/5] forced comounts for cgroups.

On Wed, 2012-09-05 at 13:12 +0400, Glauber Costa wrote:
> On 09/05/2012 01:11 PM, Tejun Heo wrote:
> > Hello, Peter.
> > 
> > On Wed, Sep 05, 2012 at 11:06:33AM +0200, Peter Zijlstra wrote:
> >> *confused* I always thought that was exactly what you meant with unified
> >> hierarchy.
> > 
> > No, I never counted out differing granularity.
> > 
> 
> Can you elaborate on which interface do you envision to make it work?
> They will clearly be mounted in the same hierarchy, or as said
> alternatively, comounted.
> 
> If you can turn them on/off on a per-subtree basis, which interface
> exactly do you propose for that?

I wouldn't, screw that. That would result in the exact same problem
we're trying to fix. I want a single hierarchy walk, that's expensive
enough.

> Would a pair of cgroup core files like available_controllers and
> current_controllers are a lot of drivers do, suffice?

No.. its not a 'feature' I care to support for 'my' controllers.

I simply don't want to have to do two (or more) hierarchy walks for
accounting on every schedule event, all that pointer chasing is stupidly
expensive.
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