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Date: Tue, 28 Apr 2015 23:32:00 -0700
Message-ID: <CAF1ivSb0OfbH8diZwep+ay-gYy3eV8yaY_RbdMjTs7Vp2t=WOg@mail.gmail.com>
Subject: Re: [PATCH 07/10] block: kill merge_bvec_fn() completely
From: Ming Lin <mlin@kernel.org>
To: lkml <linux-kernel@vger.kernel.org>, Christoph Hellwig <hch@lst.de>,
        Jens Axboe <axboe@kernel.dk>,
        Kent Overstreet <kent.overstreet@gmail.com>,
        Dongsu Park <dongsu.park@profitbricks.com>,
        Lars Ellenberg <drbd-dev@lists.linbit.com>, drbd-user@lists.linbit.com,
        Jiri Kosina <jkosina@suse.cz>, Yehuda Sadeh <yehuda@inktank.com>,
        Sage Weil <sage@inktank.com>, Alex Elder <elder@kernel.org>,
        ceph-devel@vger.kernel.org, Alasdair Kergon <agk@redhat.com>,
        Mike Snitzer <snitzer@redhat.com>, dm-devel@redhat.com,
        Neil Brown <neilb@suse.de>, linux-raid@vger.kernel.org,
        Christoph Hellwig <hch@infradead.org>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Dave Chinner <dchinner@redhat.com>,
        Wu Fengguang <fengguang.wu@intel.com>
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On Tue, Apr 28, 2015 at 10:31 AM, Alasdair G Kergon <agk@redhat.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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