[PATCH RFC 0/9] btrfs: zoned: fixes for garbage collection under preassure

[Johannes Thumshirn <jth@kernel.org>]

From: Johannes Thumshirn <johannes.thumshirn@wdc.com>

A few weeks ago Damien started benchmarking zoned BTRFS and zoned XFS
garbage collection on SMR and ZNS drives. 

One of these benchmarks was filling the FS to 75% and then subsequientially
overwriting the files again.

One thing that came out of these trials, is that BTRFS on ZNS devices did
not finish the overwrite phase because it prematurely ran out of space.

Once I tried reclaiming earlier (patch 9/9) I've seen haning task because
of extremely high lock contention on serveral locks. The patches 2 to 6
either remove these locks, or in case of the space-info lock remove
unneeded lock contentiom.

Patches 7 and 8 lower the log level of reclaim messages, because with the
automatic reclaim BTRFS has these days there is a lot of log spamming.

Pathch 8 triggers removal of unused block groups on allocation failure, I
opted for making it non zoned specific as I think even regular filesystems
can benefit from this.. The first patch from Naohiro is also needed so we
don't prematurely finish metadata block groups on zoned devices.

Reasons for RFC, there are a lot of locking changes involved in this
series. As much as I'm comfortable with running fio workloads and fstests,
I really prefere more eyes. Especially Filipe always is a good reviewer of
locking related changes and Boris for reclaiming. The series is probably
not the final solution either but only forward progress, but I don't want
to be running into the wrong direction.

This series also includes a previously sent series of me titled "btrfs:
zoned: reduce lock contention in zoned extent allocator" and can be found
here:
https://lore.kernel.org/linux-btrfs/20250624093710.18685-1-jth@kernel.org/

Johannes Thumshirn (8):
  btrfs: zoned: get rid of relocation_bg_lock
  btrfs: zoned: get rid of treelog_bg_lock
  btrfs: zoned: don't hold space_info lock on zoned allocation
  btrfs: remove delalloc_root_mutex
  btrfs: remove btrfs_root's delalloc_mutex
  btrfs: lower auto-reclaim message log level
  btrfs: lower log level of relocation messages
  btrfs: remove unused bgs on allocation failure

Naohiro Aota (1):
  btrfs: zoned: do not select metadata BG as finish target

 fs/btrfs/block-group.c |  2 +-
 fs/btrfs/block-group.h | 11 ++++++
 fs/btrfs/ctree.h       |  1 -
 fs/btrfs/disk-io.c     |  4 ---
 fs/btrfs/extent-tree.c | 81 ++++++++++++++----------------------------
 fs/btrfs/fs.h          |  8 +----
 fs/btrfs/inode.c       |  4 ---
 fs/btrfs/relocation.c  |  4 +--
 fs/btrfs/zoned.c       | 19 +++++-----
 fs/btrfs/zoned.h       |  7 ++--
 10 files changed, 55 insertions(+), 86 deletions(-)

-- 
2.49.0