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

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Date:	Sat, 28 May 2011 11:09:41 +0900
From:	Namhyung Kim <namhyung@...il.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Jens Axboe <jaxboe@...ionio.com>,
	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

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

Or using lower-case 'f' for FUA?

Thanks.


-- 
Regards,
Namhyung Kim


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