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Date: Thu, 3 Nov 2011 15:35:46 -0200
From: Glauber Costa <glommer@parallels.com>
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To: Paul Menage <paul@paulmenage.org>
CC: Frederic Weisbecker <fweisbec@gmail.com>,
        Glauber Costa <glommer@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Tim Hockin <thockin@hockin.org>, LKML <linux-kernel@vger.kernel.org>,
        Li Zefan <lizf@cn.fujitsu.com>, Johannes Weiner <hannes@cmpxchg.org>,
        Aditya Kali <adityakali@google.com>, Oleg Nesterov <oleg@redhat.com>,
        Kay Sievers <kay.sievers@vrfy.org>, Tejun Heo <tj@kernel.org>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Containers <containers@lists.linux-foundation.org>,
        Paul Turner <pjt@google.com>
Subject: Re: [PATCH 00/10] cgroups: Task counter subsystem v6
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On 11/03/2011 03:28 PM, Paul Menage wrote:
> On Thu, Nov 3, 2011 at 10:06 AM, Glauber Costa<glommer@parallels.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.