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

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Message-ID: <47FEED67.1080006@linux.vnet.ibm.com>
Date:	Fri, 11 Apr 2008 10:17:35 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	Paul Menage <menage@...gle.com>,
	Pavel Emelianov <xemul@...nvz.org>,
	Hugh Dickins <hugh@...itas.com>,
	Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
	YAMAMOTO Takashi <yamamoto@...inux.co.jp>,
	linux-kernel@...r.kernel.org, taka@...inux.co.jp,
	linux-mm@...ck.org, David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [-mm] Add an owner to the mm_struct (v9)

KAMEZAWA Hiroyuki wrote:
> On Fri, 11 Apr 2008 09:57:06 +0530
> Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> 
>> KAMEZAWA Hiroyuki wrote:
>>> maybe I don't undestand correctlly...
>>>
>>> On Thu, 10 Apr 2008 14:46:02 +0530
>>> Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
>>>
>>>>  
>>>> +config MM_OWNER
>>>> +	bool
>>>> +
>>> no default is ok here  ? what value will this have if not selected ?
>>> I'm sorry if I misunderstand Kconfig.
>>>
>> The way this works is
>>
>> If I select memory resource controller, CONFIG_MM_OWNER is set to y, else it
>> does not even show up in the .config
>>
> ok, sorry for noise.
> 

No problem at all, please feel free to question anything.

>>>> +	/*
>>>> +	 * Search through everything else. We should not get
>>>> +	 * here often
>>>> +	 */
>>>> +	do_each_thread(g, c) {
>>>> +		if (c->mm == mm)
>>>> +			goto assign_new_owner;
>>>> +	} while_each_thread(g, c);
>>>> +
>>> Again, do_each_thread() is suitable here ?
>>> for_each_process() ?
>>>
>> do_each_thread(), while_each_thread() walks all processes and threads of those
>> processes in the system. It is a common pattern used in the kernel (see
>> try_to_freeze_tasks() or oom_kill_task() for example).
>>
> 
> What you want is finding a thread which has the "mm_struct". Why search all
> threads ? I think you only have to search processes(i.e. thread-group-leaders).
> 
> try_to_freeze_tasks()/oom_kill_task() have to chase all threads because
> it have to check flags in task_structs in a process.
> 

Good question. It is possible that clone() was called with CLONE_VM without
CLONE_THREAD. In which case we have threads sharing the VM without a thread
group leader. Please see zap_threads() for a similar search pattern.

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