linux-kernel - Re: [RFD] cgroup: about multiple hierarchies

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Message-ID: <20120223173348.GD22536@google.com>
Date:	Thu, 23 Feb 2012 09:33:48 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kay Sievers <kay.sievers@...y.org>,
	Lennart Poettering <lennart@...ttering.net>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFD] cgroup: about multiple hierarchies

Hello, Li.

On Thu, Feb 23, 2012 at 04:22:26PM +0800, Li Zefan wrote:
> > The following is a "best practices" document on using cgroups.
> > 
> >   http://www.freedesktop.org/wiki/Software/systemd/PaxControlGroups
> > 
> > To me, it seems to demonstrate the rather ugly situation that the
> > current cgroup is providing.  Everyone should tip-toe around cgroup
> > hierarchies and nobody has full knowledge or control over them.
> > e.g. base system management (e.g. systemd) can't use freezer or task
> > counter as someone else might want to use it for different hierarchy
> > layout.
> > 
> 
> This issue still exists if we allow a single hierarchy only, right?
> Different cgroup users/applications have to struggle not to step
> on each other's toe.

Oh sure, having single hierarchy doesn't solve that problem but makes
it clear that there's single representation that kernel understands
and deals with.  I think the problem now is that kernel tries to
multiplex multiple users.  Unfortunately, it does that half-way and
badly and I think the nature of the problem doesn't really allow
proper muxed interface at kernel layer.  So, I'm suggesting to let go
of the broken pretense and just have a single unified interfce and let
userland deal with resource allocation policies.

Thanks.

-- 
tejun
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