linux-kernel - Re: [PATCH 1/9] cgroup: add cgroup_subsys->post

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Date:	Mon, 5 Nov 2012 14:42:19 +0100
From:	Glauber Costa <glommer@...allels.com>
To:	Tejun Heo <tj@...nel.org>
CC:	<lizefan@...wei.com>, <mhocko@...e.cz>, <rjw@...k.pl>,
	<containers@...ts.linux-foundation.org>, <cgroups@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>,
	<fweisbec@...il.com>
Subject: Re: [PATCH 1/9] cgroup: add cgroup_subsys->post_create()

On 11/03/2012 09:38 AM, Tejun Heo wrote:
> Currently, there's no way for a controller to find out whether a new
> cgroup finished all ->create() allocatinos successfully and is
> considered "live" by cgroup.
> 
> This becomes a problem later when we add generic descendants walking
> to cgroup which can be used by controllers as controllers don't have a
> synchronization point where it can synchronize against new cgroups
> appearing in such walks.
> 
> This patch adds ->post_create().  It's called after all ->create()
> succeeded and the cgroup is linked into the generic cgroup hierarchy.
> This plays the counterpart of ->pre_destroy().
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Glauber Costa <glommer@...allels.com>

Tejun, If we do it this way, we end up with two callbacks that are
called after create: post_clone and post_create. I myself prefer the
approach I took, that convert post_clone into post_create, and would
prefer if you would pick that up.

For me, post_clone is totally a glitch that should not exist. Merging
this with post_create gives the following semantics:

* A while after cgroup creation, you will get a callback. In that
callback, you do whatever initialization you may need that you could not
in create. Why is reacting to a flag being set any different?

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