quoted

quoted

     struct bio_vec bvec;
     struct msghdr msg = { .msg_flags = MSG_SPLICE_PAGES | ... };

     ..

     bvec_set_virt
     iov_iter_bvec
     sock_sendmsg

is a frequent pattern. Does it make sense to define a wrapper? Same 
for bvec_set_page.

I dunno.  I'm trying to move towards aggregating multiple pages in a bvec
before calling sendmsg if possible rather than doing it one page at a 
time,
but it's easier and more obvious in some places than others.

That would be great to do, but nvme needs to calculate a data digest
and doing that in a separate scan of the payload is not very cache
friendly...

There is also the fact that the payload may be sent in portions 
asynchronously driven by how the controller wants to accept them,
so there is some complexity there.

But worth looking at for sure.

The patch looks good to me, taking it to run some tests
(from sendpage-3-frag branch in your kernel.org tree correct?)

For now, you can add:
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>

Patches seem to hold up.
Tested-by: Sagi Grimberg <sagi@grimberg.me>

However if possible, can you please split nvme/host and nvme/target
changes? We try to separate host side and target side changes in the
same patch.