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Date: Tue, 2 Apr 2013 18:20:56 +0400
From: Glauber Costa <glommer@parallels.com>
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To: Michal Hocko <mhocko@suse.cz>
CC: Li Zefan <lizefan@huawei.com>, Johannes Weiner <hannes@cmpxchg.org>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        LKML <linux-kernel@vger.kernel.org>, Cgroups <cgroups@vger.kernel.org>,
        <linux-mm@kvack.org>
Subject: Re: [PATCH] memcg: don't do cleanup manually if mem_cgroup_css_online()
 fails
References: <515A8A40.6020406@huawei.com> <20130402121600.GK24345@dhcp22.suse.cz> <20130402141646.GQ24345@dhcp22.suse.cz>
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On 04/02/2013 06:16 PM, Michal Hocko wrote:
>  mem_cgroup_css_online
>       memcg_init_kmem
>         mem_cgroup_get		# refcnt = 2
>           memcg_update_all_caches
>             memcg_update_cache_size	# fails with ENOMEM

Here is the thing: this one in kmem only happens for kmem enabled
memcgs. For those, we tend to do a get once, and put only when the last
kmem reference is gone.

For non-kmem memcgs, refcnt will be 1 here, and will be balanced out by
the mem_cgroup_put() in css_free.