linux-kernel - Re: [PATCH 2/2] block: defer the use of inline biovecs for discard requests

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Date:	Mon, 28 Jun 2010 08:37:42 -0400
From:	Mike Snitzer <snitzer@...hat.com>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Christoph Hellwig <hch@....de>, dm-devel@...hat.com,
	James.Bottomley@...e.de, linux-kernel@...r.kernel.org,
	martin.petersen@...cle.com, akpm@...ux-foundation.org
Subject: Re: [PATCH 2/2] block: defer the use of inline biovecs for discard
 requests

On Mon, Jun 28 2010 at  8:34am -0400,
Jens Axboe <axboe@...nel.dk> wrote:

> On 2010-06-26 21:56, Mike Snitzer wrote:
> > Don't alloc discard bio with a biovec in blkdev_issue_discard.  Doing so
> > means bio_has_data() will not be true until the SCSI layer adds the
> > payload to the discard request via blk_add_request_payload.
> 
> Sorry, this looks horrible.

Your judgment isn't giving me much to work with... not sure where I go
with "horrible".

> What is the point of this?!

Enables discard requests with _not_ return true for bio_has_data().

> > bio_{enable,disable}_inline_vecs are not expected to be widely used so
> > they were exported using EXPORT_SYMBOL_GPL.
> 
> Never export anything that doesn't have an in-kernel modular user.

Yeap, v2 removed the exports.

> > This patch avoids the need for the following VM accounting fix for
> > discards: http://lkml.org/lkml/2010/6/23/361
> > NOTE: Jens, you said you applied Tao Ma's fix but I cannot see it in
> > your linux-2.6-block's for-next or for-2.6.36... as such I didn't revert
> > it in this patch.
> 
> It's in the for-linus branch, that is stuff headed for the current
> kernel.

OK.

Mike
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