Re: [PATCH 0/2] ceph: add new iov_iter type and use it for reads

[Jeff Layton <jlayton@kernel.org>]

On Thu, 2022-06-09 at 15:34 -0400, Jeff Layton wrote:
> This patchset was inspired by some earlier work that David Howells did
> to add a similar type.
> 
> Currently, we take an iov_iter from the netfs layer, turn that into an
> array of pages, and then pass that to the messenger which eventually
> turns that back into an iov_iter before handing it back to the socket.
> 
> This patchset adds a new ceph_msg_data_type that uses an iov_iter
> directly instead of requiring an array of pages or bvecs. This allows
> us to avoid an extra allocation in the buffered read path, and should
> make it easier to plumb in write helpers later.
> 
> For now, this is still just a slow, stupid implementation that hands
> the socket layer a page at a time like the existing messenger does. It
> doesn't yet attempt to pass through the iov_iter directly.
> 
> I have some patches that pass the cursor's iov_iter directly to the
> socket in the receive path, but it requires some infrastructure that's
> not in mainline yet (iov_iter_scan(), for instance). It should be
> possible to something similar in the send path as well.
> 
> Jeff Layton (2):
>   libceph: add new iov_iter-based ceph_msg_data_type and
>     ceph_osd_data_type
>   ceph: use osd_req_op_extent_osd_iter for netfs reads
> 
>  fs/ceph/addr.c                  | 18 +---------
>  include/linux/ceph/messenger.h  |  5 +++
>  include/linux/ceph/osd_client.h |  4 +++
>  net/ceph/messenger.c            | 64 +++++++++++++++++++++++++++++++++
>  net/ceph/osd_client.c           | 27 ++++++++++++++
>  5 files changed, 101 insertions(+), 17 deletions(-)
> 

I've had these sitting in testing branch for a bit and they seem to work
just fine. Unfortunately though, Al mentioned on IRC that he was
planning to change iov_iter_get_pages to auto-advance the iterator,
which will require a redesign of the first patch. I'm going to drop this
series from the testing branch for now.

Thanks,
-- 
Jeff Layton <jlayton@kernel.org>