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Date: Sat, 24 Sep 2011 10:40:53 -0300
From: Glauber Costa <glommer@parallels.com>
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To: Balbir Singh <bsingharora@gmail.com>
CC: Greg Thelen <gthelen@google.com>, <linux-kernel@vger.kernel.org>,
        <paul@paulmenage.org>, <lizf@cn.fujitsu.com>,
        <kamezawa.hiroyu@jp.fujitsu.com>, <ebiederm@xmission.com>,
        <davem@davemloft.net>, <netdev@vger.kernel.org>, <linux-mm@kvack.org>,
        <kirill@shutemov.name>
Subject: Re: [PATCH v3 2/7] socket: initial cgroup code.
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On 09/22/2011 12:09 PM, Balbir Singh wrote:
> On Thu, Sep 22, 2011 at 11:30 AM, Greg Thelen<gthelen@google.com>  wrote:
>> On Wed, Sep 21, 2011 at 11:59 AM, Glauber Costa<glommer@parallels.com>  wrote:
>>> Right now I am working under the assumption that tasks are long lived inside
>>> the cgroup. Migration potentially introduces some nasty locking problems in
>>> the mem_schedule path.
>>>
>>> Also, unless I am missing something, the memcg already has the policy of
>>> not carrying charges around, probably because of this very same complexity.
>>>
>>> True that at least it won't EBUSY you... But I think this is at least a way
>>> to guarantee that the cgroup under our nose won't disappear in the middle of
>>> our allocations.
>>
>> Here's the memcg user page behavior using the same pattern:
>>
>> 1. user page P is allocate by task T in memcg M1
>> 2. T is moved to memcg M2.  The P charge is left behind still charged
>> to M1 if memory.move_charge_at_immigrate=0; or the charge is moved to
>> M2 if memory.move_charge_at_immigrate=1.
>> 3. rmdir M1 will try to reclaim P (if P was left in M1).  If unable to
>> reclaim, then P is recharged to parent(M1).
>>
>
> We also have some magic in page_referenced() to remove pages
> referenced from different containers. What we do is try not to
> penalize a cgroup if another cgroup is referencing this page and the
> page under consideration is being reclaimed from the cgroup that
> touched it.
>
> Balbir Singh
Btw:

This has the same problem we'll face for any kmem related memory in the 
cgroup: We can't just force reclaim to make the cgroup empty...