From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ming Lei <ming.lei@redhat.com>
Date: Wed, 21 Nov 2018 13:04:00 +0800
Subject: [Cluster-devel] [PATCH V10 09/19] block: introduce bio_bvecs()
In-Reply-To: <7378bf49-5a7e-5622-d4d1-808ba37ce656@grimberg.me>
References: <20181115085306.9910-10-ming.lei@redhat.com>
	<20181116134541.GH3165@lst.de>
	<002fe56b-25e4-573e-c09b-bb12c3e8d25a@grimberg.me>
	<20181120161651.GB2629@lst.de>
	<53526aae-fb9b-ee38-0a01-e5899e2d4e4d@grimberg.me>
	<20181121005902.GA31748@ming.t460p>
	<2d9bee7a-f010-dcf4-1184-094101058584@grimberg.me>
	<20181121034415.GA8408@ming.t460p>
	<2a47d336-c19b-6bf4-c247-d7382871eeea@grimberg.me>
	<7378bf49-5a7e-5622-d4d1-808ba37ce656@grimberg.me>
Message-ID: <20181121050359.GA31915@ming.t460p>
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On Tue, Nov 20, 2018 at 08:42:04PM -0800, Sagi Grimberg wrote:
> 
> > > Yeah, that is the most common example, given merge is enabled
> > > in most of cases. If the driver or device doesn't care merge,
> > > you can disable it and always get single bio request, then the
> > > bio's bvec table can be reused for send().
> > 
> > Does bvec_iter span bvecs with your patches? I didn't see that change?
> 
> Wait, I see that the bvec is still a single array per bio. When you said
> a table I thought you meant a 2-dimentional array...

I mean a new 1-d table A has to be created for multiple bios in one rq,
and build it in the following way

           rq_for_each_bvec(tmp, rq, rq_iter)
                    *A = tmp;

Then you can pass A to iov_iter_bvec() & send().

Given it is over TCP, I guess it should be doable for you to preallocate one
256-bvec table in one page for each request, then sets the max segment size as
(unsigned int)-1, and max segment number as 256, the preallocated table
should work anytime.


Thanks,
Ming