linux-kernel - Re: [PATCHSET] block: remove ioc_*

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Message-ID: <20120320155118.GC17071@redhat.com>
Date:	Tue, 20 Mar 2012 11:51:18 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	axboe@...nel.dk, linux-kernel@...r.kernel.org, ctalbott@...gle.com,
	rni@...gle.com
Subject: Re: [PATCHSET] block: remove ioc_*_changed()

On Mon, Mar 19, 2012 at 03:10:55PM -0700, Tejun Heo wrote:
> Hello, guys.
> 
> The changed notification used by cfq is rather odd.  cfq caches the
> associated cfqqs per cic and uses the changed notification to expire
> those lookup caches.
> 
> The explicit notification mechanism might make sense if determining
> whether the current cache is up-to-date is difficult or expensive;
> however, that isn't the case here.  Determining whether ioprio or
> cgroup has changed is straight-forward and inexpensive.
> 
> This patchset updates cfq to so that it remembers the current ioprio
> and blkcg in the cic and determines whether cfqq's need to be reset
> without using the changed notification and drops the changed
> notification code.

Hi Tejun,

So this patch still breaks cic->cfqq association in asynchronous
manner, when new request comes in. So it will still not solve the
problem I reported where after doing IO a task changes cgroup and
tries to delete the old cgroup and hangs forever as cic->cfqq is still
holding a reference to cgroup?

Thanks
Vivek
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