linux-kernel - Re: [PATCH 00/10] cgroups: Task counter subsystem v6

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Message-ID: <4EB2D0F2.40309@parallels.com>
Date:	Thu, 3 Nov 2011 15:35:46 -0200
From:	Glauber Costa <glommer@...allels.com>
To:	Paul Menage <paul@...lmenage.org>
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	Glauber Costa <glommer@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tim Hockin <thockin@...kin.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Li Zefan <lizf@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Aditya Kali <adityakali@...gle.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Kay Sievers <kay.sievers@...y.org>, Tejun Heo <tj@...nel.org>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Containers <containers@...ts.linux-foundation.org>,
	Paul Turner <pjt@...gle.com>
Subject: Re: [PATCH 00/10] cgroups: Task counter subsystem v6

On 11/03/2011 03:28 PM, Paul Menage wrote:
> On Thu, Nov 3, 2011 at 10:06 AM, Glauber Costa<glommer@...allels.com>  wrote:
>> Sorry if I wasn't clear: It removes the need to walk multiple independent
>> hierarchies. The walk is done only once.
>
> You're talking about at fork time, and the concern is the cache
> footprint involved in walking up the parent pointer chain?

Yes, we can say this is my main concern.

> Isn't that an argument against multiple hierarchies (which is a
> decision for the admin), rather than against more subsystem
> flexibility?

Not always it is a decision for the admin. In most cases, it is a 
constraint of the problem. For containers - take lxc as an example,
the most reasonable thing to do is to grab all cgroups subsystems 
available, and contain them.

> If multiple subsystems on the same hierarchy each need to
> walk up the pointer chain on the same event, then after the first
> subsystem has done so the chain will be in cache for any subsequent
> walks from other subsystems.
No, it won't. Precisely because different subsystems have completely
independent pointer chains.

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