linux-kernel - Re: [PATCH 1/4] cfq-iosced: Remove the check for same cfq group from allow

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Date:	Thu, 17 Dec 2009 17:26:03 +0800
From:	Gui Jianfeng <guijianfeng@...fujitsu.com>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	linux-kernel@...r.kernel.org, jens.axboe@...cle.com,
	nauman@...gle.com, lizf@...fujitsu.com, ryov@...inux.co.jp,
	fernando@....ntt.co.jp, taka@...inux.co.jp, jmoyer@...hat.com,
	m-ikeda@...jp.nec.com, czoccolo@...il.com, Alan.Brunelle@...com
Subject: Re: [PATCH 1/4] cfq-iosced: Remove the check for same cfq group from
 allow_merge

Vivek Goyal wrote:
> o allow_merge() already checks if submitting task is pointing to same cfqq
>   as rq has been queued in. If everything is fine, we should not be having
>   a task in one cgroup and having a pointer to cfqq in other cgroup.
> 
>   Well I guess in some situations it can happen and that is, when a random
>   IO queue has been moved into root cgroup for group_isolation=0. In
>   this case, tasks's cgroup/group is different from where actually cfqq is,
>   but this is intentional and in this case merging should be allowed.
> 
>   The second situation is where due to close cooperator patches, multiple
>   processes can be sharing a cfqq. If everything implemented right, we should
>   not end up in a situation where tasks from different processes in different
>   groups are sharing the same cfqq as we allow merging of cooperating queues
>   only if they are in same group.
> 
> Signed-off-by: Vivek Goyal <vgoyal@...hat.com>

Reviewed-by: Gui Jianfeng <guijianfeng@...fujitsu.com>

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