linux-kernel - Re: [PATCH UPDATED 4/5] dm: implement REQ_FLUSH/FUA support for request-based dm

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Message-ID: <4C808BB8.6040005@ct.jp.nec.com>
Date:	Fri, 03 Sep 2010 14:46:32 +0900
From:	Kiyoshi Ueda <k-ueda@...jp.nec.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Mike Snitzer <snitzer@...hat.com>, jaxboe@...ionio.com,
	j-nomura@...jp.nec.com, jamie@...reable.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-raid@...r.kernel.org, hch@....de
Subject: Re: [PATCH UPDATED 4/5] dm: implement REQ_FLUSH/FUA support for request-based
 dm

Hi Tejun,

On 09/02/2010 10:22 PM +0900, Tejun Heo wrote:
> On 09/01/2010 09:15 AM, Kiyoshi Ueda wrote:
>>> @@ -2619,9 +2458,8 @@ int dm_suspend(struct mapped_device *md,
>>>  	up_write(&md->io_lock);
>>>
>>>  	/*
>>> -	 * Request-based dm uses md->wq for barrier (dm_rq_barrier_work) which
>>> -	 * can be kicked until md->queue is stopped.  So stop md->queue before
>>> -	 * flushing md->wq.
>>> +	 * Stop md->queue before flushing md->wq in case request-based
>>> +	 * dm defers requests to md->wq from md->queue.
>>>  	 */
>>>  	if (dm_request_based(md))
>>>  		stop_queue(md->queue);
>> 
>> Request-based dm doesn't use md->wq now, so you can just remove
>> the comment above.
> 
> I sure can remove it but md->wq already has most stuff necessary to
> process deferred requests and when someone starts using it, having the
> comment there about the rather delicate ordering would definitely be
> helpful, so I suggest keeping the comment.

OK, makes sense.

Thanks,
Kiyoshi Ueda
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