[PATCH V10 09/19] block: introduce bio_bvecs()

[Ming Lei]

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