linux-kernel - Re: [PATCH] cfq-iosched: Reduce linked group count upon group destruction

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Date:	Tue, 2 Aug 2011 09:24:40 +0200
From:	Jens Axboe <jaxboe@...ionio.com>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	"Israel G. Lugo" <israel.lugo@...osys.com>
Subject: Re: [PATCH] cfq-iosched: Reduce linked group count upon group  destruction

On 2011-08-01 20:47, Vivek Goyal wrote:
> CFQ keeps track of number of groups which are linked on blkcg->blkg_list.
> This is useful to avoid races between queue exit and cgroup exit code
> paths. So if at the request queue exit time linked group count is not
> zero, that means there are some group out there which is yet to be
> deleted under rcu read period and queue exit code should wait for
> on rcu period.
> 
> In my previous patch I forgot to decrease the number of group count.
> So in current form, we nr_blkcg_linked_grps is always non-zero and
> we will always wait one rcu period (if BLK_CGROUP=y). The side effect
> of this is that it can increase boot time. I am surprised, nobody
> complained so far.

Thanks Vivek, applied.

-- 
Jens Axboe

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