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Date: Mon, 1 Aug 2016 13:17:17 -0400
From: Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [PATCH] memcg: put soft limit reclaim out of way if the excess
 tree is empty
Message-ID: <20160801171717.GB8724@cmpxchg.org>
References: <1470045621-14335-1-git-send-email-mhocko@kernel.org>
 <20160801135757.GB19395@esperanza>
 <20160801141227.GI13544@dhcp22.suse.cz>
 <20160801150343.GA7603@cmpxchg.org>
 <20160801152454.GK13544@dhcp22.suse.cz>
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To: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>, Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>

On Mon, Aug 01, 2016 at 05:24:54PM +0200, Michal Hocko wrote:
> @@ -2564,7 +2559,13 @@ unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
>  		return 0;
>  
>  	mctz = soft_limit_tree_node(pgdat->node_id);
> -	if (soft_limit_tree_empty(mctz))
> +
> +	/*
> +	 * Do not even bother to check the largest node if the node

                                                               root

> +	 * is empty. Do it lockless to prevent lock bouncing. Races
> +	 * are acceptable as soft limit is best effort anyway.
> +	 */
> +	if (RB_EMPTY_ROOT(&mctz->rb_root))
>  		return 0;

Other than that, looks good. Please retain my

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

in version 2.

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