linux-kernel - Re: [PATCH 07/10] block: kill merge_bvec

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Message-ID: <CAF1ivSb0OfbH8diZwep+ay-gYy3eV8yaY_RbdMjTs7Vp2t=WOg@mail.gmail.com>
Date:	Tue, 28 Apr 2015 23:32:00 -0700
From:	Ming Lin <mlin@...nel.org>
To:	lkml <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
	Kent Overstreet <kent.overstreet@...il.com>,
	Dongsu Park <dongsu.park@...fitbricks.com>,
	Lars Ellenberg <drbd-dev@...ts.linbit.com>,
	drbd-user@...ts.linbit.com, Jiri Kosina <jkosina@...e.cz>,
	Yehuda Sadeh <yehuda@...tank.com>,
	Sage Weil <sage@...tank.com>, Alex Elder <elder@...nel.org>,
	ceph-devel@...r.kernel.org, Alasdair Kergon <agk@...hat.com>,
	Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com,
	Neil Brown <neilb@...e.de>, linux-raid@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Dave Chinner <dchinner@...hat.com>,
	Wu Fengguang <fengguang.wu@...el.com>
Subject: Re: [PATCH 07/10] block: kill merge_bvec_fn() completely

On Tue, Apr 28, 2015 at 10:31 AM, Alasdair G Kergon <agk@...hat.com> wrote:
> On Mon, Apr 27, 2015 at 11:48:34PM -0700, Ming Lin wrote:
>> As generic_make_request() is now able to handle arbitrarily sized bios,
>> it's no longer necessary for each individual block driver to define its
>> own ->merge_bvec_fn() callback. Remove every invocation completely.
>
> merge_bvec_fn is also about telling the code building up bios what optimum
> maximum size to use.
>
> Have you got some test data to demonstrate that we won't find some situations
> where performance is now lost by code building up bios that are far too big
> and are always going to have to be split up later?

Not yet.
Fengguang will help to run some tests.

Thanks.

>
> Alasdair
>
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