Date: Mon, 8 Apr 2013 08:57:26 -0700
From: Tejun Heo <tj@kernel.org>
To: Michal Hocko <mhocko@suse.cz>
Cc: Li Zefan <lizefan@huawei.com>, Andrew Morton <akpm@linux-foundation.org>,
        Glauber Costa <glommer@parallels.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        LKML <linux-kernel@vger.kernel.org>, Cgroups <cgroups@vger.kernel.org>,
        linux-mm@kvack.org
Subject: Re: [PATCH 1/8] cgroup: implement cgroup_is_ancestor()
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References: <51627DA9.7020507@huawei.com>
 <51627DBB.5050005@huawei.com>
 <20130408144750.GK17178@dhcp22.suse.cz>
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Hello,

On Mon, Apr 08, 2013 at 04:47:50PM +0200, Michal Hocko wrote:
> On Mon 08-04-13 16:20:11, Li Zefan wrote:
> [...]
> > @@ -5299,6 +5300,26 @@ struct cgroup_subsys_state *cgroup_css_from_dir(struct file *f, int id)
> >  	return css ? css : ERR_PTR(-ENOENT);
> >  }
> >  
> > +/**
> > + * cgroup_is_ancestor - test "root" cgroup is an ancestor of "child"
> > + * @child: the cgroup to be tested.
> > + * @root: the cgroup supposed to be an ancestor of the child.
> > + *
> > + * Returns true if "root" is an ancestor of "child" in its hierarchy.
> > + */
> > +bool cgroup_is_ancestor(struct cgroup *child, struct cgroup *root)
> > +{
> > +	int depth = child->depth;
> 
> Is this functionality helpful for other controllers but memcg?
> css_is_ancestor is currently used only by memcg code AFAICS and we can
> get the same functionality easily by using something like:

It's a basic hierarchy operation.  I'd prefer it to be in cgroup and
in general let's try to avoid memcg-specific infrastructure.  It
doesn't seem to end well.

Thanks.

-- 
tejun
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