linux-kernel - Re: [PATCH 3/9 v2] cgroup: implement generic child / descendant walk macros

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Message-ID: <509CC91D.4050207@huawei.com>
Date:	Fri, 9 Nov 2012 17:13:01 +0800
From:	Li Zefan <lizefan@...wei.com>
To:	Tejun Heo <tj@...nel.org>
CC:	<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 3/9 v2] cgroup: implement generic child / descendant walk
 macros

On 2012/11/9 1:59, Tejun Heo wrote:
> Currently, cgroup doesn't provide any generic helper for walking a
> given cgroup's children or descendants.  This patch adds the following
> three macros.
> 
> * cgroup_for_each_child() - walk immediate children of a cgroup.
> 
> * cgroup_for_each_descendant_pre() - visit all descendants of a cgroup
>   in pre-order tree traversal.
> 
> * cgroup_for_each_descendant_post() - visit all descendants of a
>   cgroup in post-order tree traversal.
> 
> All three only require the user to hold RCU read lock during
> traversal.  Verifying that each iterated cgroup is online is the
> responsibility of the user.  When used with proper synchronization,
> cgroup_for_each_descendant_pre() can be used to propagate state
> updates to descendants in reliable way.  See comments for details.
> 
> v2: s/config/state/ in commit message and comments per Michal.  More
>     documentation on synchronization rules.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujisu.com>
> Reviewed-by: Michal Hocko <mhocko@...e.cz>

I don't see anything wrong with the comment on cgroup_next_descendant_pre().

Acked-by: Li Zefan <lizefan@...wei.com>

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