[v4,00/12] large atomic writes for xfs with CoW

Message

John Garry March 3, 2025, 5:11 p.m. UTC

Currently atomic write support for xfs is limited to writing a single
block as we have no way to guarantee alignment and that the write covers
a single extent.

This series introduces a method to issue atomic writes via a software
emulated method.

The software emulated method is used as a fallback for when attempting to
issue an atomic write over misaligned or multiple extents.

For XFS, this support is based on CoW.

The basic idea of this CoW method is to alloc a range in the CoW fork,
write the data, and atomically update the mapping.

Initial mysql performance testing has shown this method to perform ok.
However, there we are only using 16K atomic writes (and 4K block size),
so typically - and thankfully - this software fallback method won't be
used often.

For other FSes which want large atomics writes and don't support CoW, I
think that they can follow the example in [0].

Based on 0a1fd78080c8 (xfs/xfs-6.15-merge) Merge branch
'vfs-6.15.iomap' of
git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs into
xfs-6.15-merge

[0] https://lore.kernel.org/linux-xfs/[e-mail]/

Differences to v3:
- Error !reflink in xfs_atomic_write_sw_iomap_begin() (Darrick)
- Fix unused variable (kbuild bot)
- Add RB tags from Darrick (Thanks!)

Differences to v2:
(all from Darrick)
- Add dedicated function for xfs iomap sw-based atomic write
- Don't ignore xfs_reflink_end_atomic_cow() -> xfs_trans_commit() return
  value
- Pass flags for reflink alloc functions
- Rename IOMAP_ATOMIC_COW -> IOMAP_ATOMIC_SW
- Coding style corrections and comment improvements
- Add RB tags (thanks!)

Differences to RFC:
- Rework CoW alloc method
- Rename IOMAP_ATOMIC -> IOMAP_ATOMIC_HW
- Rework transaction commit func args
- Chaneg resblks size for transaction commit
- Rename BMAPI extszhint align flag

John Garry (11):
  xfs: Pass flags to xfs_reflink_allocate_cow()
  iomap: Rename IOMAP_ATOMIC -> IOMAP_ATOMIC_HW
  xfs: Switch atomic write size check in xfs_file_write_iter()
  xfs: Refactor xfs_reflink_end_cow_extent()
  iomap: Support SW-based atomic writes
  xfs: Reflink CoW-based atomic write support
  xfs: Iomap SW-based atomic write support
  xfs: Add xfs_file_dio_write_atomic()
  xfs: Commit CoW-based atomic writes atomically
  xfs: Update atomic write max size
  xfs: Allow block allocator to take an alignment hint

Ritesh Harjani (IBM) (1):
  iomap: Lift blocksize restriction on atomic writes

 .../filesystems/iomap/operations.rst          |  20 ++-
 fs/ext4/inode.c                               |   2 +-
 fs/iomap/direct-io.c                          |  20 +--
 fs/iomap/trace.h                              |   2 +-
 fs/xfs/libxfs/xfs_bmap.c                      |   7 +-
 fs/xfs/libxfs/xfs_bmap.h                      |   6 +-
 fs/xfs/xfs_file.c                             |  59 ++++++-
 fs/xfs/xfs_iomap.c                            | 144 ++++++++++++++++-
 fs/xfs/xfs_iomap.h                            |   1 +
 fs/xfs/xfs_iops.c                             |  31 +++-
 fs/xfs/xfs_iops.h                             |   2 +
 fs/xfs/xfs_mount.c                            |  28 ++++
 fs/xfs/xfs_mount.h                            |   1 +
 fs/xfs/xfs_reflink.c                          | 145 +++++++++++++-----
 fs/xfs/xfs_reflink.h                          |  11 +-
 include/linux/iomap.h                         |   8 +-
 16 files changed, 415 insertions(+), 72 deletions(-)

Comments

Christian Brauner March 6, 2025, 8:47 a.m. UTC | #1

On Mon, 03 Mar 2025 17:11:08 +0000, John Garry wrote:
> Currently atomic write support for xfs is limited to writing a single
> block as we have no way to guarantee alignment and that the write covers
> a single extent.
> 
> This series introduces a method to issue atomic writes via a software
> emulated method.
> 
> [...]

Applied to the vfs-6.15.iomap branch of the vfs/vfs.git tree.
Patches in the vfs-6.15.iomap branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs-6.15.iomap

[02/12] iomap: Rename IOMAP_ATOMIC -> IOMAP_ATOMIC_HW
        https://git.kernel.org/vfs/vfs/c/af97c9498b28
[05/12] iomap: Support SW-based atomic writes
        https://git.kernel.org/vfs/vfs/c/e5708b92d9bf
[06/12] iomap: Lift blocksize restriction on atomic writes
        https://git.kernel.org/vfs/vfs/c/2ebcf55ea0c6