-----Original Message-----
From: Darrick J. Wong <djwong@kernel.org>
Sent: Tuesday, May 11, 2021 11:57 AM
Subject: Re: [PATCH v5 0/7] fsdax,xfs: Add reflink&dedupe support for fsdax

On Tue, May 11, 2021 at 11:09:26AM +0800, Shiyang Ruan wrote:

quoted

This patchset is attempt to add CoW support for fsdax, and take XFS,
which has both reflink and fsdax feature, as an example.

Slightly off topic, but I noticed all my pmem disappeared once I rolled forward to
5.13-rc1.  Am I the only lucky one?  Qemu 4.2, with fake memory devices
backed by tmpfs files -- info qtree says they're there, but the kernel doesn't show
anything in /proc/iomem.

I have the same situation on 5.13-rc1 too. (Qemu 5.2.0, fake memory device backed by files)
I tested this code in v5.12-rc8 and then rebased it to v5.13-rc1...  It's my bad for not testing again.


--
Thanks,
Ruan Shiyang.

--D

quoted

Changes from V4:
 - Fix the mistake of breaking dax layout for two inodes
 - Add CONFIG_FS_DAX judgement for fsdax code in remap_range.c
 - Fix other small problems and mistakes

Changes from V3:
 - Take out the first 3 patches as a cleanup patchset[1], which has been
    sent yesterday.
 - Fix usage of code in dax_iomap_cow_copy()
 - Add comments for macro definitions
 - Fix other code style problems and mistakes

One of the key mechanism need to be implemented in fsdax is CoW.  Copy
the data from srcmap before we actually write data to the destance
iomap.  And we just copy range in which data won't be changed.

Another mechanism is range comparison.  In page cache case, readpage()
is used to load data on disk to page cache in order to be able to
compare data.  In fsdax case, readpage() does not work.  So, we need
another compare data with direct access support.

With the two mechanisms implemented in fsdax, we are able to make
reflink and fsdax work together in XFS.

Some of the patches are picked up from Goldwyn's patchset.  I made
some changes to adapt to this patchset.


(Rebased on v5.13-rc1 and patchset[1])
[1]: https://lkml.org/lkml/2021/4/22/575

Shiyang Ruan (7):
  fsdax: Introduce dax_iomap_cow_copy()
  fsdax: Replace mmap entry in case of CoW
  fsdax: Add dax_iomap_cow_copy() for dax_iomap_zero
  iomap: Introduce iomap_apply2() for operations on two files
  fsdax: Dedup file range to use a compare function
  fs/xfs: Handle CoW for fsdax write() path
  fs/xfs: Add dax dedupe support

 fs/dax.c               | 206

+++++++++++++++++++++++++++++++++++------

quoted

 fs/iomap/apply.c       |  52 +++++++++++
 fs/iomap/buffered-io.c |   2 +-
 fs/remap_range.c       |  57 ++++++++++--
 fs/xfs/xfs_bmap_util.c |   3 +-
 fs/xfs/xfs_file.c      |  11 +--
 fs/xfs/xfs_inode.c     |  66 ++++++++++++-
 fs/xfs/xfs_inode.h     |   1 +
 fs/xfs/xfs_iomap.c     |  61 +++++++++++-
 fs/xfs/xfs_iomap.h     |   4 +
 fs/xfs/xfs_iops.c      |   7 +-
 fs/xfs/xfs_reflink.c   |  15 +--
 include/linux/dax.h    |   7 +-
 include/linux/fs.h     |  12 ++-
 include/linux/iomap.h  |   7 +-
 15 files changed, 449 insertions(+), 62 deletions(-)

--
2.31.1