Re: [RFC PATCH 00/18] ceph, rbd: Collapse all the I/O types down to something iov_iter-based

[Xiubo Li <xiubli@redhat.com>]

On 8/4/23 21:13, David Howells wrote:
> Hi Ilya, Xiubo,
>
> [!] NOTE: This is a preview of a work in progress and doesn't yet fully
>      compile, let alone actually work!
>
> Here are some patches that (mostly) collapse the different I/O types
> (PAGES, PAGELIST, BVECS, BIO) down to a single one.  I added a new type,
> ceph_databuf, to make this easier.  The page list is attached to that as a
> bio_vec[] with an iov_iter, but could also be some other type supported by
> the iov_iter.  The iov_iter defines the data or buffer to be used.  I have
> an additional iov_iter type implemented that allows use of a straight
> folio[] or page[] instead of a bio_vec[] that I can deploy if that proves
> more useful.
>
> The conversion isn't quite complete:
>
>   (1) rbd is done; BVECS and BIO types are replaced with ceph_databuf.
>
>   (2) ceph_osd_linger_request::preply_pages needs switching over to a
>       ceph_databuf, but I haven't yet managed to work out how the pages that
>       handle_watch_notify() sticks in there come about.
>
>   (3) I haven't altered data transmission in net/ceph/messenger*.c yet.  The
>       aim is to reduce it to a single sendmsg() call for each ceph_msg_data
>       struct, using the iov_iter therein.
>
>   (4) The data reception routines in net/ceph/messenger*.c also need
>       modifying to pass each ceph_msg_data::iter to recvmsg() in turn.
>
>   (5) It might be possible to merge struct ceph_databuf into struct
>       ceph_msg_data and eliminate the former.
>
>   (6) fs/ceph/ still needs some work to clean up the use of page arrays.
>
>   (7) I would like to change front and middle buffers with a ceph_databuf,
>       vmapping them when we need to access them.
>
> I added a kmap_ceph_databuf_page() macro and used that to get a page and
> use kmap_local_page() on it to hide the bvec[] inside to make it easier to
> replace.
>
> Anyway, if anyone has any thoughts...
>
>
> I've pushed the patches here also:
>
> 	https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=iov-extract
>
> David
>
> David Howells (18):
>    iov_iter: Add function to see if buffer is all zeros
>    ceph: Rename alignment to offset
>    ceph: Add a new data container type, ceph_databuf
>    ceph: Convert ceph_mds_request::r_pagelist to a databuf
>    rbd: Use ceph_databuf for rbd_obj_read_sync()
>    ceph: Change ceph_osdc_call()'s reply to a ceph_databuf
>    ceph: Unexport osd_req_op_cls_request_data_pages()
>    ceph: Remove osd_req_op_cls_response_data_pages()

David,

I think the titles should be prefixed with "libceph: XXX" for the 
patches in net/ceph/ ?

Thanks

- Xiubo


>    ceph: Convert notify_id_pages to a ceph_databuf
>    rbd: Switch from using bvec_iter to iov_iter
>    ceph: Remove bvec and bio data container types
>    ceph: Convert some page arrays to ceph_databuf
>    ceph: Convert users of ceph_pagelist to ceph_databuf
>    ceph: Remove ceph_pagelist
>    ceph: Convert ceph_osdc_notify() reply to ceph_databuf
>    ceph: Remove CEPH_OS_DATA_TYPE_PAGES and its attendant helpers
>    ceph: Remove CEPH_MSG_DATA_PAGES and its helpers
>    ceph: Don't use data_pages
>
>   drivers/block/rbd.c             | 645 ++++++++++----------------------
>   fs/ceph/acl.c                   |  39 +-
>   fs/ceph/addr.c                  |  18 +-
>   fs/ceph/file.c                  | 157 ++++----
>   fs/ceph/inode.c                 |  85 ++---
>   fs/ceph/locks.c                 |  23 +-
>   fs/ceph/mds_client.c            | 134 ++++---
>   fs/ceph/mds_client.h            |   2 +-
>   fs/ceph/super.h                 |   8 +-
>   fs/ceph/xattr.c                 |  68 ++--
>   include/linux/ceph/databuf.h    |  65 ++++
>   include/linux/ceph/messenger.h  | 141 +------
>   include/linux/ceph/osd_client.h |  97 ++---
>   include/linux/ceph/pagelist.h   |  72 ----
>   include/linux/uio.h             |   1 +
>   lib/iov_iter.c                  |  22 ++
>   net/ceph/Makefile               |   5 +-
>   net/ceph/cls_lock_client.c      |  40 +-
>   net/ceph/databuf.c              | 149 ++++++++
>   net/ceph/messenger.c            | 376 +------------------
>   net/ceph/osd_client.c           | 430 +++++++--------------
>   net/ceph/pagelist.c             | 171 ---------
>   22 files changed, 876 insertions(+), 1872 deletions(-)
>   create mode 100644 include/linux/ceph/databuf.h
>   delete mode 100644 include/linux/ceph/pagelist.h
>   create mode 100644 net/ceph/databuf.c
>   delete mode 100644 net/ceph/pagelist.c
>