[PATCH v2 00/12] io-uring/btrfs: support async buffered writes

[Stefan Roesch <shr@fb.com>]

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:
  For fio the following results have been obtained with a queue depth of
  1 and 4k block size (runtime 600 secs):

                 sequential writes:
                 without patch           with patch      libaio     psync
  iops:              55k                    134k          117K       148K
  bw:               221MB/s                 538MB/s       469MB/s    592MB/s
  clat:           15286ns                    82ns         994ns     6340ns


For an io depth of 1, 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. To achieve the
same or better performance with the exisiting code an io depth of 4 is required.
Increasing the iodepth further does not lead to improvements.


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:

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: btrfs: plumb NOWAIT through the write path
  btrfs: make balance_dirty_pages nowait compatible
  btrfs: add assert to search functions
  btrfs: enable nowait async buffered writes

 fs/btrfs/block-group.c    |   2 +-
 fs/btrfs/ctree.c          |  48 ++++++++++++++-
 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, 239 insertions(+), 59 deletions(-)


base-commit: 53e99dcff61e1523ec1c3628b2d564ba15d32eb7
-- 
2.30.2