From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [patch 1/2]block: handle merged discard request
Date: Mon, 20 Aug 2012 09:58:54 -0400
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To: Mike Snitzer <snitzer@redhat.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>, Christoph Hellwig <hch@infradead.org>, Shaohua Li <shli@kernel.org>, Vivek Goyal <vgoyal@redhat.com>, axboe@kernel.dk, linux-kernel@vger.kernel.org, neilb@suse.de, linux-scsi@vger.kernel.org

On Mon, Aug 20, 2012 at 09:57:39AM -0400, Mike Snitzer wrote:
> But I haven't put my finger on _why_ a discard bio has bio->bi_io_vec
> (but given my use of DM, bio comes from bio_alloc_bioset, and DM passes
> original bio->bi_max_vecs for nr_iovecs).

TRIM has a payload and we cheay by preallocation a data page for it.