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

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Date:	Thu, 03 Apr 2008 12:13:00 +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>, 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>
Subject: Re: [-mm] Add an owner to the mm_struct (v5)

KAMEZAWA Hiroyuki wrote:
> just nitpicks ;)
> 
> On Thu, 03 Apr 2008 11:29:01 +0530
> Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> 
>>  #define mm_match_cgroup(mm, cgroup)	\
>> -	((cgroup) == rcu_dereference((mm)->mem_cgroup))
>> +	((cgroup) == mem_cgroup_from_task((mm)->owner))
>>  
> 
> After this patch, above should be 
> ==
> #define mm_match_cgroup_css(mm, css, subsys_id)
> 	((css) == task_subsys_state((mm)->owner, subsys_id) 
> ==
> This generic macro may be good for your purpose.
> 

When we call mm_match_cgroup_*, we don't want to dereference mem_cont->css to
get the css, hence we abstract it away. This is called from mm/rmap.c

> 
>>  #endif
>> diff -puN init/Kconfig~memory-controller-add-mm-owner init/Kconfig
>> --- linux-2.6.25-rc8/init/Kconfig~memory-controller-add-mm-owner	2008-04-03 10:08:23.000000000 +0530
>> +++ linux-2.6.25-rc8-balbir/init/Kconfig	2008-04-03 10:08:23.000000000 +0530
>> @@ -371,9 +371,21 @@ config RESOURCE_COUNTERS
>>            infrastructure that works with cgroups
>>  	depends on CGROUPS
>>  
>> +config MM_OWNER
>> +	bool "Enable ownership of mm structure"
>> +	help
>> +	  This option enables mm_struct's to have an owner. The advantage
>> +	  of this approach is that it allows for several independent memory
>> +	  based cgorup controllers to co-exist independently without too
>> +	  much space overhead
> 	 Above is an explanation for this patch.
> 	  More simple text is better... How about
> 	 ==
> 	  This is necessary for some cgroup subsystem related to memory management.
> 	 ==

Yes, but several other developers have also asked for it. revoke*, swap
namespaces, etc will use it. I wanted to have a common definition.

>> +
>> +	  This feature adds fork/exit overhead. So enable this only if
>> +	  you need resource controllers
>> +
> 
> 
>>  config CGROUP_MEM_RES_CTLR
>>  	bool "Memory Resource Controller for Control Groups"
>>  	depends on CGROUPS && RESOURCE_COUNTERS
>> +	select MM_OWNER
> 
> I don't like "select"....this should be
> 	depends on CGROUPS && RESOURCE_COUNTERS && MM_OWNER
> 

I discussed this will Paul and I think select is better. The user might ignore
to enable MM_OWNER and wonder why memory controller or other features are not
getting enabled.

> Thanks,
> -Kame

Thanks for the review

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