[PATCH v4 0/6] btrfs: subpage + zoned fixes

[Qu Wenruo <wqu@suse.com>]

[CHANGELOG]
v4:
- Rebased to the latest for-next branch
  Thankfully no conflicts at all.

- Include all the previous preparation patches
  It turns out I split the preparation into other series and even get
  myself confused.

- Use the correct commit message from my local branch
  It turns out Josef is totally correct, the problem I described in
  "btrfs: do no clera page dirty inside extent_write_locked_range()" is
  really confusing, it has direct IO involved and my local branch is
  already using a much better commit and I just forgot it.
 
v3:
- Use the minimal fsstress workload with trace_printk() output to
  explain the bug better

v2:
- Update the commit message for the first patch
  As there is something wrong with the ASCII art of the memory layout.

[REPO]
https://github.com/adam900710/linux/tree/subpage_delalloc

If running subpage with zoned devices (TCMU emulated HDD, 64K or 16K
page size with 4K sectorsize), btrfs can easily hitting various bugs:

- ASSERT()s related to submitting page range which has no OE coverage

- Various reserved space leakage and some OE never finished

This is caused by two major reasons:

- run_delalloc_cow() is not subpage compatible
  Thus we may try to submit pages which has no OE for it.

  This would be addressed by patch 1~4

- Some dirty range is not submitted thus OE would never finish
  This happens due to the mismatch that extent_write_locked_range() can
  clear the full page dirty, even if we're only submitting part of the 
  dirty ranges.

  Then later __extent_writepage_io() would refuse to submit a non-dirty
  page, and the check is only checking the full page dirty flag, not the
  subpage bitmaps.

  This would be addressed by patch 5~6.


Qu Wenruo (6):
  btrfs: make __extent_writepage_io() to write specified range only
  btrfs: lock subpage ranges in one go for writepage_delalloc()
  btrfs: subpage: introduce helpers to handle subpage delalloc locking
  btrfs: migrate writepage_delalloc() to use subpage helpers
  btrfs: do not clear page dirty inside extent_write_locked_range()
  btrfs: make extent_write_locked_range() to handle subpage writeback
    correctly

 fs/btrfs/extent_io.c | 105 +++++++++++++++++++++++++------
 fs/btrfs/subpage.c   | 144 +++++++++++++++++++++++++++++++++++++++++--
 fs/btrfs/subpage.h   |  10 ++-
 3 files changed, 233 insertions(+), 26 deletions(-)

-- 
2.45.0