transferring bvecs over the network in drbd

[Christoph Hellwig]

On Thu, May 08, 2025 at 10:39:56AM +0200, Lars Ellenberg wrote:
> For async replication, we want to actually copy data into send buffer,
> we cannot have the network stack hold a reference to a page for which
> we signalled io completion already.
> 
> For sync replication we want to avoid additional data copy if possible,
> so try to use "zero copy sendpage".

I didn't even complain about having both variants :)

> 
> That's why we have two variants of what looks to be the same thing.
> 
> Why we do it that way: probably when we wrote that part,
> a better infrastructure was not available, or we were not aware of it.

Yes.  While the iov_iter and the bvec version of have been around
for a long time, drbd probably still predates them.

> Thanks for the pointers, we'll look into it.
> Using more efficient ways to do stuff sounds good.

thanks.  Note that now that ->sendpage has been replaced with the
MSG_SPLICE_PAGES flag you can actually share most code for both
variants as well.