linux-kernel - Re: [PATCH 1/8] cgroup: implement cgroup_is

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Message-ID: <20130408155726.GG3021@htj.dyndns.org>
Date:	Mon, 8 Apr 2013 08:57:26 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Li Zefan <lizefan@...wei.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Glauber Costa <glommer@...allels.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Cgroups <cgroups@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH 1/8] cgroup: implement cgroup_is_ancestor()

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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