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Date: Tue, 01 Apr 2008 13:43:03 +0530
From: Balbir Singh <balbir@linux.vnet.ibm.com>
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To: Paul Menage <menage@google.com>, YAMAMOTO Takashi <yamamoto@valinux.co.jp>
CC: balbir@linux.vnet.ibm.com, Pavel Emelianov <xemul@openvz.org>,
       Hugh Dickins <hugh@veritas.com>,
       Sudhir Kumar <skumar@linux.vnet.ibm.com>, lizf@cn.fujitsu.com,
       linux-kernel@vger.kernel.org, taka@valinux.co.jp, linux-mm@kvack.org,
       David Rientjes <rientjes@google.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Subject: Re: [RFC][-mm] Add an owner to the mm_struct (v3)
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Balbir Singh wrote:
> Paul Menage wrote:
>> On Mon, Mar 31, 2008 at 11:23 PM, Balbir Singh
>> <balbir@linux.vnet.ibm.com> wrote:
>>>  > Here we'll want to call vm_cgroup_update_mm_owner(), to adjust the
>>>  > accounting. (Or if in future we end up with more than a couple of
>>>  > subsystems that want notification at this time, we'll want to call
>>>  > cgroup_update_mm_owner() and have it call any interested subsystems.
>>>  >
>>>
>>>  I don't think we need to adjust accounting, since only mm->owner is changing and
>>>  not the cgroup to which the task/mm belongs. Do we really need to notify? I
>>>  don't want to do any notifications under task_lock().
>> It's possible but unlikely that the new owner is in a different cgroup.
> 
> Hmmm... that can never happen with thread groups, since mm->owner is
> p->group_leader and that never exits unless all threads are gone (it can
> explicitly change groups though). Without thread groups, the new owner can
> belong to a different cgroup, so we might need notification.
> 
> 

Thinking out aloud

If mm->owner changes and belongs to a different cgroup, we have a whole new
problem. We need to determine all tasks that share the mm and belong to a
particular cgroup, which changed since the new owner belongs to a different
cgroup and then update the charge.


-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL