linux-kernel - Re: [PATCH 7/7] cgroups: Update documentation for bindable subsystems

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Message-ID: <AANLkTinbtLkF=haFeDkzecEWv_FE9jG4TefiptSnZcPi@mail.gmail.com>
Date:	Thu, 28 Oct 2010 17:13:36 -0700
From:	Paul Menage <menage@...gle.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	"akpm >> Andrew Morton" <akpm@...ux-foundation.org>,
	Stephane Eranian <eranian@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	containers@...ts.linux-foundation.org
Subject: Re: [PATCH 7/7] cgroups: Update documentation for bindable subsystems

>
>  Called when a cgroup subsystem is rebound to a different hierarchy
> -and root cgroup. Currently this will only involve movement between
> -the default hierarchy (which never has sub-cgroups) and a hierarchy
> -that is being created/destroyed (and hence has no sub-cgroups).
> +and root cgroup. For some subsystems this will only involve movement
> +between the default hierarchy (which never has sub-cgroups) and a
> +hierarchy that is being created/destroyed (and hence has no sub-cgroups).
> +For some other subsystems this can involve movement between the default
> +hierarchy and a mounted hierarchy which may have sub-cgroups in it.

This is a bit vague. How about:

For non-bindable subsystems, this will  only involve movement
between the default hierarchy (which never has sub-cgroups) and a
hierarchy that is being created/destroyed (and hence has no sub-cgroups).

For binadable subsystems, this may also involve movement between the
default hierarchy and a mounted hierarchy that's populated with
sub-cgroups.

Also, the docs should mention that a cgroup setting the can_bind flag
has to be able to support side-effect free movement of a task into any
just-created cgroup, and into the root cgroup at any time. i.e. it's
not suitable for any subsystem where can_attach() might return false
for the root cgroup or a newly-created cgroup, or attach() might have
side-effects for those same cases.

Actually, perhaps we should forbid the combination of having both an
attach() callback and can_bind=true ?

Also, post_clone() doesn't get called when creating the css hierarchy
during binding.

Paul
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