[PATCH v3 0/4] btrfs: reduce btrfs_get_extent() calls for buffered write path

[Qu Wenruo <wqu@suse.com>]

[CHANGELOG]
v3:
- Use @cur_len for btrfs_get_extent() in the last patch
  And remove the hole related comment.
  This should not cause any behavior change.

  The @len parameter for btrfs_get_extent() is only going to cause a
  difference when the range is completely a hole (e.g. beyond EOF).

  For our writeback routine, there should be an extent map for us thus
  it's no different passing @cur_len or sectorsize.

  I think this @len parameter of btrfs_get_extent() is causing
  unnecessary complexity, and want to remove it completely. But that
  will be a new series.

v2:
- Fix a potential bug where OEs beyond EOF are not truncated properly
  This replace the original patch to extract the code into a helper.

- Replace more for_each_set_bit() with for_each_set_bitrange()

- Fix several copy-n-pasted incorrect range inside submit_range()


Although btrfs has bs < ps support for a long time, and the larger data
folios support is also going to be graduate from experimental features
soon, the write path is still iterating each fs block and call
btrfs_get_extent() on each fs block.

What makes the situation worse is that, for the write path we do not
have any cached extent map, meaning even with large folios and we got a
continuous range that can be submitted in one go, we still call
btrfs_get_extent() many times and get the same range extent map again
and again.

This series will reduce the duplicated btrfs_get_extent() calls by only
call it once for each range, other than for each fs block.

The first one is a potential bug inspired by Boris' review.
Patch 2~3 are minor cleanups.
Patch 4 is the core of the optimization.

Although I don't expect there will be much difference in the real world though.


Qu Wenruo (4):
  btrfs: make sure all ordered extents beyond EOF is properly truncated
  btrfs: integrate the error handling of submit_one_sector()
  btrfs: replace for_each_set_bit() with for_each_set_bitmap()
  btrfs: reduce extent map lookup during writes

 fs/btrfs/extent_io.c    | 230 ++++++++++++++++++++--------------------
 fs/btrfs/ordered-data.c |  38 +++++++
 fs/btrfs/ordered-data.h |   2 +
 3 files changed, 156 insertions(+), 114 deletions(-)

-- 
2.52.0