linux-kernel - Re: [PATCH 7/9] block: implement bio_associate

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Message-ID: <20120217225735.GP29414@google.com>
Date:	Fri, 17 Feb 2012 14:57:35 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Kent Overstreet <koverstreet@...gle.com>, axboe@...nel.dk,
	ctalbott@...gle.com, rni@...gle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/9] block: implement bio_associate_current()

Hey, Vivek.

On Fri, Feb 17, 2012 at 05:51:26PM -0500, Vivek Goyal wrote:
> Otherwise on every IO, we will end up comparing submitting tasks's
> cgroup and cic/cfqq's cgroup.

But how much is that different from checking CHANGED bit on each IO?
I mean, we can just do sth like cfqg->blkg->blkcg == bio_blkcg(bio).
It isn't expensive.

> Also this will create problems, if two threads sharing io context are
> in two different cgroups. We will frequently end up changing the
> association.

blkcg doesn't allow that anyway (it tries but is racy) and I actually
was thinking about sending a RFC patch to kill CLONE_IO.

Thanks.

-- 
tejun
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