From mboxrd@z Thu Jan  1 00:00:00 1970
From: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
Subject: Re: [PATCH] memcg: don't do cleanup manually if mem_cgroup_css_online()
 fails
Date: Tue, 2 Apr 2013 18:20:56 +0400
Message-ID: <515AE948.1000704@parallels.com>
References: <515A8A40.6020406@huawei.com> <20130402121600.GK24345@dhcp22.suse.cz> <20130402141646.GQ24345@dhcp22.suse.cz>
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To: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
Cc: Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>, Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, KAMEZAWA Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>, LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Cgroups <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org

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.