linux-kernel - Re: [PATCH 1/7] Make DISCARD_BARRIER and DISCARD

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Date:	Thu, 3 Sep 2009 11:56:18 -0600
From:	Matthew Wilcox <matthew@....cx>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Christoph Hellwig <hch@...radead.org>, linux-scsi@...r.kernel.org,
	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org,
	liml@....ca, jens.axboe@...cle.com,
	Matthew Wilcox <willy@...ux.intel.com>
Subject: Re: [PATCH 1/7] Make DISCARD_BARRIER and DISCARD_NOBARRIER writes
	instead of reads

On Thu, Sep 03, 2009 at 06:52:20PM +0100, David Woodhouse wrote:
> On Sat, 2009-08-29 at 19:03 -0400, Christoph Hellwig wrote:
> > 
> > The commands are conceptually writes, and in the case of IDE and SCSI
> > commands actually are writes.  They were only reads because we thought
> > that would interact better with the elevators.  Now the elevators know
> > about discard requests, that advantage no longer exists.
> 
> Can you drop the final sentence of that? It isn't true, and I never said
> it.

No, but you wouldn't give me a changelog entry, so I had to make
something up.

> s/.  Now.*/, but that isn't necessary, and making them writes makes it
> easier for the low-level IDE and SCSI code to cope with the fact that
> the command has to be sent with a payload./

Thanks.

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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