[PATCH v11 00/16] large atomic writes for xfs

John Garry
2025-05-04T09:00:13Z

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-based method.

The software-based 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 reflink CoW support.

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].

Catherine is currently working on further xfstests for this feature,
which we hope to share soon.

About 16/16, maybe it can be omitted as there is no strong demand to have
it included.

Based on bfecc4091e07 (xfs/next-rc, xfs/for-next) xfs: allow ro mounts
if rtdev or logdev are read-only

[0] https://lore.kernel.org/linux-xfs/20250310183946.932054-1-john.g.garry@oracle.com/

Differences to v10:
- add "xfs: only call xfs_setsize_buftarg once ..." by Darrick
- symbol renames in "xfs: ignore HW which cannot..." by Darrick

Differences to v9:
- rework "ignore HW which cannot .." patch by Darrick
- Ensure power-of-2 max always for unit min/max when no HW support

Differences to v8:
- Darrick reworked patch for mount option
- Darrick reworked patch to ignore HW
- Minor changes and cleanups from Darrick
- Rework some commit messages (Christoph)
- Pick up RB tags from Christoph (thanks!)

Differences to v7:
- Add patch for mp hw awu max and min
- Fixed for awu max mount option (Darrick)

Darrick J. Wong (5):
xfs: only call xfs_setsize_buftarg once per buffer target
xfs: add helpers to compute log item overhead
xfs: add helpers to compute transaction reservation for finishing
intent items
xfs: ignore HW which cannot atomic write a single block
xfs: allow sysadmins to specify a maximum atomic write limit at mount
time

John Garry (11):
fs: add atomic write unit max opt to statx
xfs: rename xfs_inode_can_atomicwrite() ->
xfs_inode_can_hw_atomic_write()
xfs: allow block allocator to take an alignment hint
xfs: refactor xfs_reflink_end_cow_extent()
xfs: refine atomic write size check in xfs_file_write_iter()
xfs: add xfs_atomic_write_cow_iomap_begin()
xfs: add large atomic writes checks in xfs_direct_write_iomap_begin()
xfs: commit CoW-based atomic writes atomically
xfs: add xfs_file_dio_write_atomic()
xfs: add xfs_calc_atomic_write_unit_max()
xfs: update atomic write limits

Documentation/admin-guide/xfs.rst | 11 +
block/bdev.c | 3 +-
fs/ext4/inode.c | 2 +-
fs/stat.c | 6 +-
fs/xfs/libxfs/xfs_bmap.c | 5 +
fs/xfs/libxfs/xfs_bmap.h | 6 +-
fs/xfs/libxfs/xfs_log_rlimit.c | 4 +
fs/xfs/libxfs/xfs_trans_resv.c | 343 +++++++++++++++++++++++++++---
fs/xfs/libxfs/xfs_trans_resv.h | 25 +++
fs/xfs/xfs_bmap_item.c | 10 +
fs/xfs/xfs_bmap_item.h | 3 +
fs/xfs/xfs_buf.c | 58 +++--
fs/xfs/xfs_buf.h | 9 +-
fs/xfs/xfs_buf_item.c | 19 ++
fs/xfs/xfs_buf_item.h | 3 +
fs/xfs/xfs_extfree_item.c | 10 +
fs/xfs/xfs_extfree_item.h | 3 +
fs/xfs/xfs_file.c | 87 +++++++-
fs/xfs/xfs_inode.h | 14 +-
fs/xfs/xfs_iomap.c | 190 ++++++++++++++++-
fs/xfs/xfs_iomap.h | 1 +
fs/xfs/xfs_iops.c | 76 ++++++-
fs/xfs/xfs_iops.h | 3 +
fs/xfs/xfs_log_cil.c | 4 +-
fs/xfs/xfs_log_priv.h | 13 ++
fs/xfs/xfs_mount.c | 159 ++++++++++++++
fs/xfs/xfs_mount.h | 17 ++
fs/xfs/xfs_refcount_item.c | 10 +
fs/xfs/xfs_refcount_item.h | 3 +
fs/xfs/xfs_reflink.c | 146 ++++++++++---
fs/xfs/xfs_reflink.h | 6 +
fs/xfs/xfs_rmap_item.c | 10 +
fs/xfs/xfs_rmap_item.h | 3 +
fs/xfs/xfs_super.c | 97 ++++++++-
fs/xfs/xfs_trace.h | 115 ++++++++++
include/linux/fs.h | 3 +-
include/linux/stat.h | 1 +
include/uapi/linux/stat.h | 8 +-
38 files changed, 1363 insertions(+), 123 deletions(-)

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2.31.1