linux-kernel - Re: [PATCH v5 08/12] block: Introduce new bio

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Message-ID: <20120809013923.GH7262@moria.home.lan>
Date:	Wed, 8 Aug 2012 18:39:23 -0700
From:	Kent Overstreet <koverstreet@...gle.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, axboe@...nel.dk, agk@...hat.com,
	neilb@...e.de, drbd-dev@...ts.linbit.com, vgoyal@...hat.com,
	mpatocka@...hat.com, sage@...dream.net, yehuda@...newdream.net
Subject: Re: [PATCH v5 08/12] block: Introduce new bio_split()

On Wed, Aug 08, 2012 at 04:05:32PM -0700, Tejun Heo wrote:
> One more thing.
> 
> On Mon, Aug 06, 2012 at 03:08:37PM -0700, Kent Overstreet wrote:
> > +	if (bio_integrity(bio)) {
> > +		bio_integrity_clone(ret, bio, gfp, bs);
> > +		bio_integrity_trim(ret, 0, bio_sectors(ret));
> > +		bio_integrity_trim(bio, bio_sectors(ret), bio_sectors(bio));
> 
> Is this equivalent to bio_integrity_split() performance-wise?

Strictly speaking, no. But it has the advantage of being drastically
simpler - and the only one only worked for single page bios so I
would've had to come up with something new from scratch, and as
confusing as the integrity stuff is I wouldn't trust the result.

I'm skeptical that it's going to matter in practice given how much
iteration is done elsewhere in the course of processing a bio and given
that this stuff isn't used with high end SSDs...
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