[PATCH v3 00/12] io-uring/btrfs: support async buffered writes

Stefan Roesch
2022-09-12T19:28:11Z

This patch series adds support for async buffered writes when using both
btrfs and io-uring. Currently io-uring only supports buffered writes (for btrfs)
in the slow path, by processing them in the io workers. With this patch series
it is now possible to support buffered writes in the fast path. To be able to use
the fast path, the required pages must be in the page cache, the required locks
in btrfs can be granted immediately and no additional blocks need to be read
form disk.

This patch series makes use of the changes that have been introduced by a
previous patch series: "io-uring/xfs: support async buffered writes"

Performance results:

The new patch improves throughput by over two times (compared to the exiting
behavior, where buffered writes are processed by an io-worker process) and also
the latency is considerably reduced. Detailled results are part of the changelog
of the first commit.

BTRFS changes:
-Add option for NOWAIT IOCB's to tell that searches do not wait on locks. This
adds the nowait option to btrfs_path.
-For NOWAIT buffered writes on PREALLOC or NOCOW extents tell can_nocow_extent()
that we don't want to wait on any locks or metadata IO.
-Support no_flush reservations for nowait buffered writes.
-Add btrfs_try_lock_ordered_range() function.
-Add nowait flag to btrfs_check_nocow_lock() to use it in write code path.
-Add nowait parameter to prepare_pages() function.
-Plumb nowait through the write code path.
-Enable nowait buffered writes.

Testing:
This patch has been tested with xfstests, fsx, fio. xfstests shows no new
diffs compared to running without the patch series.

Changes:

V3:
- Updated changelog of "btrfs: implement a nowait option for tree searches"
to say -EAGAIN.
- Use bool return value in signature of btrfs_try_lock_ordered_range
- Renamed variable tmp to can_nocow in btrfs_buffered_write
- Fixed coding style in get_prepare_fgp_flags
- Set pages[i] to NULL in error code path of lock_and_cleanup_extent_if_need()
- Added const in definition of "bool nowait"
- Removed unlikely from btrfs_buffered_write
- Rephrased changelog for "btrfs: add assert to search functions" and used
asserts instead of warnings
- Explained why enocded writes are not supported in the changelog
- Moved performance results to changelog of first commit

V2:
- Replace EWOULDBLOCK with EAGAIN. In Version 1 it was not used consistently
- Export function balance_dirty_pages_ratelimited_flags()
- Add asserts/warnings for search functions when nowait is set, but we don't
expect that they are invoked with nowait set.

Josef Bacik (5):
btrfs: implement a nowait option for tree searches
btrfs: make can_nocow_extent nowait compatible
btrfs: add the ability to use NO_FLUSH for data reservations
btrfs: add btrfs_try_lock_ordered_range
btrfs: make btrfs_check_nocow_lock nowait compatible

Stefan Roesch (7):
mm: export balance_dirty_pages_ratelimited_flags()
btrfs: make prepare_pages nowait compatible
btrfs: make lock_and_cleanup_extent_if_need nowait compatible
btrfs: plumb NOWAIT through the write path
btrfs: make balance_dirty_pages nowait compatible
btrfs: assert nowait mode is not used for some btree search functions
btrfs: enable nowait async buffered writes

fs/btrfs/block-group.c | 2 +-
fs/btrfs/ctree.c | 43 ++++++++++++-
fs/btrfs/ctree.h | 8 ++-
fs/btrfs/delalloc-space.c | 13 +++-
fs/btrfs/delalloc-space.h | 3 +-
fs/btrfs/extent-tree.c | 5 ++
fs/btrfs/file-item.c | 4 +-
fs/btrfs/file.c | 124 ++++++++++++++++++++++++++++----------
fs/btrfs/inode.c | 22 ++++---
fs/btrfs/locking.c | 23 +++++++
fs/btrfs/locking.h | 1 +
fs/btrfs/ordered-data.c | 28 +++++++++
fs/btrfs/ordered-data.h | 1 +
fs/btrfs/relocation.c | 2 +-
fs/btrfs/scrub.c | 4 +-
fs/btrfs/space-info.c | 3 +-
fs/btrfs/tree-log.c | 6 +-
mm/page-writeback.c | 1 +
18 files changed, 234 insertions(+), 59 deletions(-)

base-commit: 80e78fcce86de0288793a0ef0f6acf37656ee4cf
--
2.30.2