linux-kernel - Re: [-mm][PATCH 2/4] Enhance cgroup mm_owner_changed callback to add task information

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Date:	Tue, 06 May 2008 09:13:56 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	linux-mm@...ck.org, skumar@...ux.vnet.ibm.com,
	yamamoto@...inux.co.jp, menage@...gle.com, lizf@...fujitsu.com,
	linux-kernel@...r.kernel.org, rientjes@...gle.com,
	xemul@...nvz.org, kamezawa.hiroyu@...fujitsu.com
Subject: Re: [-mm][PATCH 2/4] Enhance cgroup mm_owner_changed callback to
 add task information

Andrew Morton wrote:
> On Sun, 04 May 2008 03:08:04 +0530
> Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> 
>>
>> This patch adds an additional field to the mm_owner callbacks. This field
>> is required to get to the mm that changed.
>>
>> Signed-off-by: Balbir Singh <balbir@...ux.vnet.ibm.com>
>> ---
>>
>>  include/linux/cgroup.h |    3 ++-
>>  kernel/cgroup.c        |    2 +-
>>  2 files changed, 3 insertions(+), 2 deletions(-)
>>
>> diff -puN kernel/cgroup.c~cgroup-add-task-to-mm--owner-callbacks kernel/cgroup.c
>> --- linux-2.6.25/kernel/cgroup.c~cgroup-add-task-to-mm--owner-callbacks	2008-05-04 02:53:05.000000000 +0530
>> +++ linux-2.6.25-balbir/kernel/cgroup.c	2008-05-04 02:53:05.000000000 +0530
>> @@ -2772,7 +2772,7 @@ void cgroup_mm_owner_callbacks(struct ta
>>  			if (oldcgrp == newcgrp)
>>  				continue;
>>  			if (ss->mm_owner_changed)
>> -				ss->mm_owner_changed(ss, oldcgrp, newcgrp);
>> +				ss->mm_owner_changed(ss, oldcgrp, newcgrp, new);
>>  		}
>>  	}
>>  }
>> diff -puN include/linux/cgroup.h~cgroup-add-task-to-mm--owner-callbacks include/linux/cgroup.h
>> --- linux-2.6.25/include/linux/cgroup.h~cgroup-add-task-to-mm--owner-callbacks	2008-05-04 02:53:05.000000000 +0530
>> +++ linux-2.6.25-balbir/include/linux/cgroup.h	2008-05-04 02:53:05.000000000 +0530
>> @@ -310,7 +310,8 @@ struct cgroup_subsys {
>>  	 */
>>  	void (*mm_owner_changed)(struct cgroup_subsys *ss,
>>  					struct cgroup *old,
>> -					struct cgroup *new);
>> +					struct cgroup *new,
>> +					struct task_struct *p);
> 
> If mm_owner_changed() had any documentation I'd suggest that it be updated.
> Sneaky.
> 

No, there's no documentation besides the comments. I'll go ahead and update
cgroups.txt with some documentation.

> The existing comment:
> 
> 	/*
> 	 * This routine is called with the task_lock of mm->owner held
> 	 */
> 	void (*mm_owner_changed)(struct cgroup_subsys *ss,
> 					struct cgroup *old,
> 					struct cgroup *new);
> 
> Is rather mysterious.  To what mm does it refer?

This callback is called when the mm->owner field that points to/owns a cgroup
changes as a result of the owner exiting.

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