linux-kernel - Re: [PATCH 06/10] cgroup: convert memcg controller to the new cftype interface

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Message-ID: <20120319161507.GD11069@google.com>
Date:	Mon, 19 Mar 2012 09:15:07 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Glauber Costa <glommer@...allels.com>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	lizf@...fujitsu.com, containers@...ts.linux-foundation.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	fweisbec@...il.com, rni@...gle.com, ctalbott@...gle.com,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Balbir Singh <bsingharora@...il.com>,
	Hugh Dickins <hughd@...gle.com>,
	Greg Thelen <gthelen@...gle.com>
Subject: Re: [PATCH 06/10] cgroup: convert memcg controller to the new
 cftype interface

Hey,

On Mon, Mar 19, 2012 at 02:43:14PM +0400, Glauber Costa wrote:
> I am still in the middle of the review. Is it possible to dynamically
> register entries? (right now, I mean)

Before the patchset, no.  After the patchset, yes.

> If yes - which seems to be a bit of the point of the exercise, so it
> should be totally okay from my PoV. I have that call in populate because
> which files will be created depends on which protocols you have registered.
> 
> The trick here, is that doesn't need to happen at all cgroup creations.
> But it can't happen at root's either, because this is quite fragile:
> some protocols may only be registered after root memcg is created.

Yeah, it can happen anytime but it shouldn't be called from ->create()
or other callbacks which are invoked under cgroup_mutex.  We can
provide an alternative interface or other locking trickery to avoid
this, but I don't think I'll take that path unless there are very
strong rationale.

Thanks.

-- 
tejun
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