Date: Wed, 25 Mar 2009 17:24:41 +0100
From: Pierre Ossman <drzeus@drzeus.cx>
To: Jens Axboe <jens.axboe@oracle.com>
Cc: Manuel Lauss <mano@roarinelk.homelinux.net>, linux-kernel@vger.kernel.org
Subject: Re: MMC layer regression with single-block controllers
Message-ID: <20090325172441.26e32fe3@mjolnir.ossman.eu>
In-Reply-To: <20090325161425.GY27476@kernel.dk>
References: <20090323092802.GA30122@roarinelk.homelinux.net>
	<20090324210138.71029c2c@mjolnir.ossman.eu>
	<20090325104837.GA18389@roarinelk.homelinux.net>
	<20090325110401.GM27476@kernel.dk>
	<20090325123613.06404b17@mjolnir.ossman.eu>
	<20090325114248.GN27476@kernel.dk>
	<20090325165328.251daabb@mjolnir.ossman.eu>
	<20090325161425.GY27476@kernel.dk>
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On Wed, 25 Mar 2009 17:14:25 +0100
Jens Axboe <jens.axboe@oracle.com> wrote:

> On Wed, Mar 25 2009, Pierre Ossman wrote:
> >=20
> > The code was there previously, but it seemed a bit redundant to have
> > functionality like that in the block driver since we've already told
> > the block layer about the restrictions.
>=20
> You never saw the warnings? It's pretty clear that it does not support <
> PAGE_CACHE_SIZE blocks. It has always been so, I don't know why the
> subject says regression. I guess that is referring to a mmc layer
> regression?
>=20

Yes. The MMC code did all of this magic by itself previously and
assumed very little about the block layer.

> > The code was pretty simple. Basically it just cropped the sg list at
> > the correct place. Couldn't that be as easily done in the block layer?
>=20
> No, because if you do it transparently, then you have to keep partial
> state in the bio for completions. So it makes everything a lot more
> complex, I don't want to do that for something like this.
>=20

How is this different from the low level driver partially completing a
request, which is how it would have to be handled otherwise?

Rgds
--=20
     -- Pierre Ossman

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