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From:   David Howells <dhowells@redhat.com>
To:     Ilya Dryomov <idryomov@gmail.com>, Xiubo Li <xiubli@redhat.com>
Cc:     David Howells <dhowells@redhat.com>,
        Jeff Layton <jlayton@kernel.org>,
        Dongsheng Yang <dongsheng.yang@easystack.cn>,
        ceph-devel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [RFC PATCH 00/18] ceph, rbd: Collapse all the I/O types down to something iov_iter-based
Date:   Fri,  4 Aug 2023 14:13:09 +0100
Message-ID: <20230804131327.2574082-1-dhowells@redhat.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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()
  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