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Date: Fri, 28 Mar 2008 04:04:17 -0700
From: "Paul Menage" <menage@google.com>
To: balbir@linux.vnet.ibm.com
Subject: Re: [-mm] Add an owner to the mm_struct (v2)
Cc: "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@jp.fujitsu.com>,
       "Pavel Emelianov" <xemul@openvz.org>, "Hugh Dickins" <hugh@veritas.com>,
       "Sudhir Kumar" <skumar@linux.vnet.ibm.com>,
       "YAMAMOTO Takashi" <yamamoto@valinux.co.jp>, 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>
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On Fri, Mar 28, 2008 at 3:52 AM, Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
>  > How about changing this css_get()/css_put() from accounting against mm_struct
>  > to accouting against task_struct ?
>  > It seems simpler way after this mm->owner change.
>
>  But the reason why we account the mem_cgroup is that we don't want the
>  mem_cgroup to be deleted. I hope you meant mem_cgroup instead of mm_struct.
>

If there are any tasks in the cgroup then the cgroup can't be deleted,
and hence the mem_cgroup is safe.

css_get()/css_put() is only needed when you have a reference from a
non-task object that needs to keep the mem_cgroup alive, which is no
longer the case for mm_struct once we have mm->owner.

Paul