linux-kernel - Re: [RFC 2/5] memcg: rework mem_cgroup

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Message-ID: <20121113161442.GA18227@mtj.dyndns.org>
Date:	Tue, 13 Nov 2012 08:14:42 -0800
From:	Tejun Heo <htejun@...il.com>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Ying Han <yinghan@...gle.com>,
	Glauber Costa <glommer@...allels.com>
Subject: Re: [RFC 2/5] memcg: rework mem_cgroup_iter to use cgroup iterators

On Tue, Nov 13, 2012 at 04:30:36PM +0100, Michal Hocko wrote:
> @@ -1063,8 +1063,8 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
>  				   struct mem_cgroup *prev,
>  				   struct mem_cgroup_reclaim_cookie *reclaim)
>  {
> -	struct mem_cgroup *memcg = NULL;
> -	int id = 0;
> +	struct mem_cgroup *memcg = NULL,
> +			  *last_visited = NULL;

Nitpick but please don't do this.

> +		/*
> +		 * Root is not visited by cgroup iterators so it needs a special
> +		 * treatment.
> +		 */
> +		if (!last_visited) {
> +			css = &root->css;
> +		} else {
> +			struct cgroup *next_cgroup;
> +
> +			next_cgroup = cgroup_next_descendant_pre(
> +					last_visited->css.cgroup,
> +					root->css.cgroup);
> +			if (next_cgroup)
> +				css = cgroup_subsys_state(next_cgroup,
> +						mem_cgroup_subsys_id);

Hmmm... wouldn't it be better to move the reclaim logic into a
function and do the following?

	reclaim(root);
	for_each_descendent_pre()
		reclaim(descendant);

If this is a problem, I'd be happy to add a iterator which includes
the top node.  I'd prefer controllers not using the next functions
directly.

Thanks.

-- 
tejun
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