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Date: Tue, 28 Apr 2015 18:31:37 +0100
From: Alasdair G Kergon <agk@redhat.com>
To: Ming Lin <mlin@kernel.org>
Message-ID: <20150428173137.GC12975@agk-dp.fab.redhat.com>
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Cc: Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@infradead.org>,
	Alex Elder <elder@kernel.org>, Sage Weil <sage@inktank.com>,
	Mike Snitzer <snitzer@redhat.com>, Neil Brown <neilb@suse.de>,
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	Yehuda Sadeh <yehuda@inktank.com>, linux-raid@vger.kernel.org,
	dm-devel@redhat.com, Alasdair Kergon <agk@redhat.com>,
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	Kent Overstreet <kent.overstreet@gmail.com>, drbd-user@lists.linbit.com,
	Lars Ellenberg <drbd-dev@lists.linbit.com>
Subject: Re: [Drbd-dev] [PATCH 07/10] block: kill merge_bvec_fn() completely
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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?

Alasdair