linux-kernel - Re: [PATCH v6 11/13] block: Rework bio_pair

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Message-ID: <yq1y5l5hvpw.fsf@sermon.lab.mkp.net>
Date:	Thu, 23 Aug 2012 22:25:47 -0400
From:	"Martin K. Petersen" <martin.petersen@...cle.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Kent Overstreet <koverstreet@...gle.com>,
	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, vgoyal@...hat.com, mpatocka@...hat.com,
	bharrosh@...asas.com, Jens Axboe <axboe@...nel.dk>,
	NeilBrown <neilb@...e.de>,
	Lars Ellenberg <lars.ellenberg@...bit.com>,
	Peter Osterlund <petero2@...ia.com>,
	Sage Weil <sage@...tank.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>
Subject: Re: [PATCH v6 11/13] block: Rework bio_pair_split()

>>>>> "Tejun" == Tejun Heo <tj@...nel.org> writes:

Tejun> I complained about this in the last posting and in the previous
Tejun> patch.  Please respond.  Martin, are you okay with these
Tejun> integrity changes?

I missed the first several iterations of all this while I was out on
vacation. I'll have to try to wrap my head around the new approach.

However, I'm not sure I like the overall approach of the new splitting.
Instead of all this cloning, slicing and dicing of bio_vecs I'd rather
we bit the bullet and had an offset + length for the vector inside each
bio. That way we could keep the bio_vec immutable and make clones more
lightweight since their vecs would always point to the parent. This also
makes it trivial to split I/Os in the stacking drivers and removes evils
in the partial completion code path. It would also allow to sever the
ties between "size of block range operated on" vs. bi_size which we need
for copy offload, discard, etc.

-- 
Martin K. Petersen	Oracle Linux Engineering
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