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Date: Mon, 1 Aug 2016 16:12:28 +0200
From: Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH] memcg: put soft limit reclaim out of way if the excess
 tree is empty
Message-ID: <20160801141227.GI13544@dhcp22.suse.cz>
References: <1470045621-14335-1-git-send-email-mhocko@kernel.org>
 <20160801135757.GB19395@esperanza>
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Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Johannes Weiner <hannes@cmpxchg.org>, linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>

On Mon 01-08-16 16:57:57, Vladimir Davydov wrote:
> On Mon, Aug 01, 2016 at 12:00:21PM +0200, Michal Hocko wrote:
> ...
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index c265212bec8c..eb7e39c2d948 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -2543,6 +2543,11 @@ static int mem_cgroup_resize_memsw_limit(struct mem_cgroup *memcg,
> >  	return ret;
> >  }
> >  
> > +static inline bool soft_limit_tree_empty(struct mem_cgroup_tree_per_node *mctz)
> > +{
> > +	return rb_last(&mctz->rb_root) == NULL;
> > +}
> > +
> 
> I don't think traversing rb tree as rb_last() does w/o holding the lock
> is a good idea. Why is RB_EMPTY_ROOT() insufficient here?

Of course it is not. Dohh, forgot to refresh the patch! Sorry about
that.

Updated patch.
---