[PATCH v2 0/3] reduce reflink src inode lock contention

[Boris Burkov <boris@bur.io>]

We currently take the src and dst inode i_rwsem exclusive for the
entirety of a reflink which includes writing back all of both files and
walking all the src extents and duplicating them to dst. This results in
contention on those locks which I think can be reduced.

The basic strategy is:
1. try to do obvious easy src writeback outside the lock.
2. downgrade the src lock to shared where it is safe.

Boris Burkov (3):
  btrfs: pre-flush reflink source before taking inode locks
  btrfs: skip unlocked reflink source flush if the inode has writers
  btrfs: downgrade the reflink source inode lock for tree walking

 fs/btrfs/btrfs_inode.h |  6 ++++
 fs/btrfs/direct-io.c   |  7 ++++
 fs/btrfs/reflink.c     | 72 ++++++++++++++++++++++++++++++++++++++++--
 3 files changed, 83 insertions(+), 2 deletions(-)

-- 
2.55.0