[PATCH 0/2] md/raid5: reduce resync/recovery dispatch overhead

[Hiroshi Nishida <nishidafmly@gmail.com>]

Two changes to how resync/recovery submits work, reducing per-stripe
overhead on the rebuild path.  Neither adds memory.

  1/2 submits a window of stripes per raid5_sync_request() call instead
      of one at a time.  On a rebuild this reduces the number of
      raid5_sync_request() invocations by ~30x (a call-count measurement,
      not a throughput figure) and bounds the per-stripe jiffy-sleep that
      otherwise throttles progress when the stripe cache is under
      pressure.

  2/2 reserves a small amount of stripe cache for user I/O during a
      rebuild, so foreground I/O is not starved by the resync stream.  A
      pure rebuild with no competing I/O is unchanged.

Both touch only the resync/recovery path and are independent of the other
md patches I'm sending separately.

Hiroshi Nishida (2):
  md/raid5: submit a window of stripes during resync/recovery
  md/raid5: reserve stripe cache for user I/O during rebuild

 drivers/md/raid5.c | 68 +++++++++++++++++++++++++++++++++++++---------
 drivers/md/raid5.h |  2 ++
 2 files changed, 57 insertions(+), 13 deletions(-)


base-commit: 55b77337bdd088c77461588e5ec094421b89911b
-- 
2.43.0