linux-kernel - Re: [patch 2/8] mm: memcg-aware global reclaim

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Message-ID: <20110609131203.GB3994@tiehlicka.suse.cz>
Date:	Thu, 9 Jun 2011 15:12:03 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Ying Han <yinghan@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>, Greg Thelen <gthelen@...gle.com>,
	Michel Lespinasse <walken@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 2/8] mm: memcg-aware global reclaim

On Wed 01-06-11 08:25:13, Johannes Weiner wrote:
[...]

Just a minor thing. I am really slow at reviewing these days due to
other work that has to be done...

> +struct mem_cgroup *mem_cgroup_hierarchy_walk(struct mem_cgroup *root,
> +					     struct mem_cgroup *prev)
> +{
> +	struct mem_cgroup *mem;

You want mem = NULL here because you might end up using it unitialized
AFAICS (css_get_next returns with NULL).

> +
> +	if (mem_cgroup_disabled())
> +		return NULL;
> +
> +	if (!root)
> +		root = root_mem_cgroup;
> +	/*
> +	 * Even without hierarchy explicitely enabled in the root
> +	 * memcg, it is the ultimate parent of all memcgs.
> +	 */
> +	if (!(root == root_mem_cgroup || root->use_hierarchy))
> +		return root;
> +	if (prev && prev != root)
> +		css_put(&prev->css);
> +	do {
> +		int id = root->last_scanned_child;
> +		struct cgroup_subsys_state *css;
> +
> +		rcu_read_lock();
> +		css = css_get_next(&mem_cgroup_subsys, id + 1, &root->css, &id);
> +		if (css && (css == &root->css || css_tryget(css)))
> +			mem = container_of(css, struct mem_cgroup, css);
> +		rcu_read_unlock();
> +		if (!css)
> +			id = 0;
> +		root->last_scanned_child = id;
> +	} while (!mem);
> +	return mem;

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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