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

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Message-ID: <4C28987A.7000701@kernel.dk>
Date:	Mon, 28 Jun 2010 14:41:30 +0200
From:	Jens Axboe <axboe@...nel.dk>
To:	Mike Snitzer <snitzer@...hat.com>
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 2010-06-28 14:37, Mike Snitzer wrote:
> 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".

The horrible part is working around that issue by fiddling with the
assignment of the internal vec. THAT looks like a horrible solution
to that problem.

How about just adding a check to bio_has_data() for non-zero
bio->bi_vcnt?

-- 
Jens Axboe

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