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Date: Mon, 14 May 2012 10:07:34 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
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To: Andrew Morton <akpm@linux-foundation.org>
CC: "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "cgroups@vger.kernel.org" <cgroups@vger.kernel.org>,
        Michal Hocko <mhocko@suse.cz>, Johannes Weiner <hannes@cmpxchg.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Han Ying <yinghan@google.com>, Glauber Costa <glommer@parallels.com>,
        Tejun Heo <tj@kernel.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Hiroyuki Kamezawa <kamezawa.hiroyuki@gmail.com>,
        Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 1/6] memcg: fix error code in hugetlb_force_memcg_empty()
References: <4FACDED0.3020400@jp.fujitsu.com> <4FACDFAE.5050808@jp.fujitsu.com> <20120511141754.e0719c26.akpm@linux-foundation.org>
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(2012/05/12 6:17), Andrew Morton wrote:

> On Fri, 11 May 2012 18:45:18 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> 
>> The conditions are handled as -EBUSY, _now_.
> 
> The changelog is poor.  I rewrote it to
> 
> : hugetlb_force_memcg_empty() incorrectly returns 0 (success) when the
> : cgroup is found to be busy.  Return -EBUSY instead.
> 
> But it still doesn't tell us the end-user-visible effects of the bug. 
> It should.
> 


Ah, sorry. How about this ?



The force_empty interface allows to make the memcg only when the cgroup
doesn't include any tasks.

	# echo 0 > /cgroup/xxxx/memory.force_empty

If cgroup isn't empty, force_empty does nothing and retruns -EBUSY in usual
memcg, memcontrol.c. But hugetlb implementation has inconsitency with
it and returns 0 and do nothing. Fix it to return -EBUSY.

Thanks,
-Kame