Message-ID: <50349A01.5020906@parallels.com>
Date: Wed, 22 Aug 2012 12:36:17 +0400
From: Glauber Costa <glommer@parallels.com>
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To: Michal Hocko <mhocko@suse.cz>
CC: <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
        <cgroups@vger.kernel.org>, <devel@openvz.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        <kamezawa.hiroyu@jp.fujitsu.com>, Christoph Lameter <cl@linux.com>,
        David Rientjes <rientjes@google.com>,
        Pekka Enberg <penberg@kernel.org>,
        Pekka Enberg <penberg@cs.helsinki.fi>,
        Suleiman Souhlal <suleiman@google.com>
Subject: Re: [PATCH v2 10/11] memcg: allow a memcg with kmem charges to be
 destructed.
References: <1344517279-30646-1-git-send-email-glommer@parallels.com> <1344517279-30646-11-git-send-email-glommer@parallels.com> <20120821082259.GB19797@dhcp22.suse.cz>
In-Reply-To: <20120821082259.GB19797@dhcp22.suse.cz>
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On 08/21/2012 12:22 PM, Michal Hocko wrote:
> On Thu 09-08-12 17:01:18, Glauber Costa wrote:
>> Because the ultimate goal of the kmem tracking in memcg is to track slab
>> pages as well, we can't guarantee that we'll always be able to point a
>> page to a particular process, and migrate the charges along with it -
>> since in the common case, a page will contain data belonging to multiple
>> processes.
>>
>> Because of that, when we destroy a memcg, we only make sure the
>> destruction will succeed by discounting the kmem charges from the user
>> charges when we try to empty the cgroup.
> 
> This changes the semantic of memory.force_empty file because the usage
> should be 0 on success but it will show kmem usage in fact now. I guess
> it is inevitable with u+k accounting so you should be explicit about
> that and also update the documentation.
aaand, it's done.

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