linux-kernel - Re: [PATCH 1/2] blktrace: treat flush as barrier

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Message-ID: <4DE4C4D7.9060107@fusionio.com>
Date:	Tue, 31 May 2011 12:37:11 +0200
From:	Jens Axboe <jaxboe@...ionio.com>
To:	Namhyung Kim <namhyung@...il.com>
CC:	Christoph Hellwig <hch@...radead.org>,
	Mike Snitzer <snitzer@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH 1/2] blktrace: treat flush as barrier

On 2011-05-28 04:09, Namhyung Kim wrote:
> 2011-05-27 (금), 16:27 -0400, Christoph Hellwig:
>> On Fri, May 27, 2011 at 10:17:09PM +0200, Jens Axboe wrote:
>>> Agree on Christophs comments, we should not pretend they are the same
>>> (since they are not). Since flush is a request on its own, F works
>>> nicely. For FUA it's associated with a write, so F should work there too
>>> indicating Write Fua (and easily humanly parsed as that, or Write
>>> Flush). WU would look confusing.
>>
>> REQ_FLUSH can also be set on a write bio, it only gets split at the
>> request level.  And even there we're at least pondering allowing it
>> to stay as part of the write for some paravirtualized storage protocols.
>>
> 
> Hi,
> 
> AFAIK FLUSH always precedes WRITE and then followed by FUA, so how about
> using the same F for both of them and distinguishing by position?
> 
>  - WRITE:            W
>  - WRITE_FLUSH:      FW
>  - WRITE_FUA:        WF
>  - WRITE_FLUSH_FUA:  FWF

That looks fine. 'U' would be an illogical choice.

-- 
Jens Axboe

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