linux-kernel - Re: [-mm] Add an owner to the mm

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Date:	Fri, 04 Apr 2008 13:58:12 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Paul Menage <menage@...gle.com>
CC:	Pavel Emelianov <xemul@...nvz.org>,
	Hugh Dickins <hugh@...itas.com>,
	Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
	YAMAMOTO Takashi <yamamoto@...inux.co.jp>, lizf@...fujitsu.com,
	linux-kernel@...r.kernel.org, taka@...inux.co.jp,
	linux-mm@...ck.org, David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [-mm] Add an owner to the mm_struct (v8)

Paul Menage wrote:
> On Fri, Apr 4, 2008 at 1:05 AM, Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
>>  After the thread group leader exits, it's moved to init_css_state by
>>  cgroup_exit(), thus all future charges from runnings threads would
>>  be redirected to the init_css_set's subsystem.
> 
> And its uncharges, which is more of the problem I was getting at
> earlier - surely when the mm is finally destroyed, all its virtual
> address space charges will be uncharged from the root cgroup rather
> than the correct cgroup, if we left the delayed group leader as the
> owner? Which is why I think the group leader optimization is unsafe.

It won't uncharge for the memory controller from the root cgroup since each page
 has the mem_cgroup information associated with it. For other controllers,
they'll need to monitor exit() callbacks to know when the leader is dead :( (sigh).

Not having the group leader optimization can introduce big overheads (consider
thousands of tasks, with the group leader being the first one to exit).

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