linux-kernel - Re: [PATCH] io-controller: implement per group request allocation limitation

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Date:	Tue, 14 Jul 2009 15:37:59 +0800
From:	Gui Jianfeng <guijianfeng@...fujitsu.com>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, dm-devel@...hat.com,
	jens.axboe@...cle.com, nauman@...gle.com, dpshah@...gle.com,
	lizf@...fujitsu.com, mikew@...gle.com, fchecconi@...il.com,
	paolo.valente@...more.it, ryov@...inux.co.jp,
	fernando@....ntt.co.jp, s-uchida@...jp.nec.com, taka@...inux.co.jp,
	jmoyer@...hat.com, dhaval@...ux.vnet.ibm.com,
	balbir@...ux.vnet.ibm.com, righi.andrea@...il.com,
	m-ikeda@...jp.nec.com, jbaron@...hat.com, agk@...hat.com,
	snitzer@...hat.com, akpm@...ux-foundation.org, peterz@...radead.org
Subject: Re: [PATCH] io-controller: implement per group request allocation
 limitation

Vivek Goyal wrote:
> On Fri, Jul 10, 2009 at 09:56:21AM +0800, Gui Jianfeng wrote:
>> Hi Vivek,
>>
>> This patch exports a cgroup based per group request limits interface.
>> and removes the global one. Now we can use this interface to perform
>> different request allocation limitation for different groups. 
>>
> 
> Thanks Gui. Few points come to mind.
> 
> - You seem to be making this as per cgroup limit on all devices. I guess
>   that different devices in the system can have different settings of
>   q->nr_requests and hence will probably want different per group limit.
>   So we might have to make it per cgroup per device limit.

  Yes, per cgroup per device limitation seems more reasonable. I'll see what
  i can do.

> 
> - There does not seem to be any checks for making sure that children
>   cgroups don't have more request descriptors allocated than parent group.

  Do we really need to make it hierarchical? IMHO, maintaining this limitation
  for cgroups independently is enough.

> 
> - I am re-thinking that what's the advantage of configuring request
>   descriptors also through cgroups. It does bring in additional complexity
>   with it and it should justfiy the advantages. Can you think of some?

  I'll try, but at least, this feature lets us be able to do more accurate
  limitation. :)

> 
>   Until and unless we can come up with some significant advantages, I will
>   prefer to continue to use per group limit through q->nr_group_requests
>   interface instead of cgroup. Once things stablize, we can revisit it and
>   see how this interface can be improved.

  I agree.

-- 
Regards
Gui Jianfeng

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