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

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Message-ID: <20100830191829.GB8458@redhat.com>
Date:	Mon, 30 Aug 2010 15:18:30 -0400
From:	Mike Snitzer <snitzer@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	jaxboe@...ionio.com, k-ueda@...jp.nec.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

On Mon, Aug 30 2010 at 11:45am -0400,
Tejun Heo <tj@...nel.org> wrote:

> This patch converts request-based dm to support the new REQ_FLUSH/FUA.
> 
> The original request-based flush implementation depended on
> request_queue blocking other requests while a barrier sequence is in
> progress, which is no longer true for the new REQ_FLUSH/FUA.
> 
> In general, request-based dm doesn't have infrastructure for cloning
> one source request to multiple targets, but the original flush
> implementation had a special mostly independent path which can issue
> flushes to multiple targets and sequence them.  However, the
> capability isn't currently in use and adds a lot of complexity.
> Moreoever, it's unlikely to be useful in its current form as it
> doesn't make sense to be able to send out flushes to multiple targets
> when write requests can't be.
> 
> This patch rips out special flush code path and deals handles
> REQ_FLUSH/FUA requests the same way as other requests.  The only
> special treatment is that REQ_FLUSH requests use the block address 0
> when finding target, which is enough for now.
> 
> * added BUG_ON(!dm_target_is_valid(ti)) in dm_request_fn() as
>   suggested by Mike Snitzer
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>

Looks good.

Acked-by: Mike Snitzer <snitzer@...hat.com>

Junichi and/or Kiyoshi,
Could you please review this patch and add your Acked-by if it is OK?
(Alasdair will want to see NEC's Ack to accept this patch).

Thanks,
Mike

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