[v7,0/8] btrfs: remove buffer heads form superblock handling

Message

Johannes Thumshirn Feb. 12, 2020, 7:16 a.m. UTC

This patch series removes the use of buffer_heads from btrfs' super block read
and write paths. It also converts the integrity-checking code to only work
with pages and BIOs.

Compared to buffer heads, this gives us a leaner call path, as the
buffer_head code wraps around getting pages from the page-cache and adding
them to BIOs to submit.

Patches one to three are preparatory patches, the first one exports
btrfs_release_disk_super() as a commomn helper to release pages containig a
super block, the second removes the kmap() calls from block device mappings as
suggested by Christoph. The third one unexports btrfs_scratch_superblocks()

The fourth patch removes buffer_heads from superblock reading. The fifth
removes it from super_block writing and the subsequent patches remove the
buffer_heads from the integrity check code.

Due to a rebase error patch #3 of v5 got merged into the patch removing the
BHs form super-block reading, but in the end it isn't too bad this way either.

It's based on misc-next from Monday February 11
(23ba1a90f0571d91b55bdfef7f06f380a74e8475), and doesn't show any regressions
in xfstests to the baseline.

Changes to v6:
- Fixed build warning about unused result of write_one_page() (David)
- Unexport btrfs_scratch_superblocks()

Changes to v5:
- Rebase to newer misc-next
- Merge old patches 2 and 3
- Remove kmap()s of pages from block devices (both in new code as well as
  existing code)

Changes to v4:
- Ressurected Nikolay's patch exporting btrfs_release_disk_super()
- Incroporated feedback from Christoph

Changes to v3:
- Incroporated feedback from Christoph

Changes to v2:
- Removed patch #1 again
- Added Reviews from Josef
- Re-visited page locking, but not changes, it retains the same locking scheme
  the buffer_heads had
- Incroptorated comments from David regarding open-coding functions
- For more details see the idividual patches.

Changes to v1:
- Added patch #1
- Converted sb reading and integrity checking to use the page cache
- Added rationale behind the conversion to the commit messages.
- For more details see the idividual patches.


Johannes Thumshirn (7):
  btrfs: don't kmap() pages from block devices
  btrfs: unexport btrfs_scratch_superblocks
  btrfs: use the page-cache for super block reading
  btrfs: use BIOs instead of buffer_heads from superblock writeout
  btrfs: remove btrfsic_submit_bh()
  btrfs: remove buffer_heads from btrfsic_process_written_block()
  btrfs: remove buffer_heads form superblock mirror integrity checking

Nikolay Borisov (1):
  btrfs: Export btrfs_release_disk_super

 fs/btrfs/check-integrity.c | 215 +++++++++++--------------------------
 fs/btrfs/check-integrity.h |   2 -
 fs/btrfs/disk-io.c         | 191 ++++++++++++++++----------------
 fs/btrfs/disk-io.h         |   6 +-
 fs/btrfs/volumes.c         |  85 ++++++++-------
 fs/btrfs/volumes.h         |   4 +-
 6 files changed, 212 insertions(+), 291 deletions(-)