[PATCH v3 0/2] mm/swap: skip empty clusters in the swapoff scan

[Youngjun Park <youngjun.park@lge.com>]

find_next_to_unuse() walks a swap device one offset at a time.  Slot
state now lives in a per cluster swap table, so patch 2 dismisses an
empty cluster with one counter read instead of SWAPFILE_CLUSTER table
reads.

Patch 1 is an unrelated one line comment fix noticed on the way.

A debug test confirmed the skip path runs, and swapoff completed
under load with no DEBUG_VM or lockdep splats.

Changes in v3:
- 2/2: clamp the scan end with min_t() so it stops at si->max, rather
  than running into the masked tail of the last cluster, which drops the
  need to explain why walking that tail was safe (Barry)
- 2/2: compute ci_off only where it is used
- 1/2, 2/2: pick up Barry's Reviewed-by
- Rebased on mm-new
- Link to v2: https://lore.kernel.org/r/20260805141146.127776-1-youngjun.park@lge.com

Changes in v2:
- 1/2: reword the comment to "array, one entry per cluster", dropping
  the redundant "on every device" (Barry)
- 1/2: pick up Kairui's Acked-by
- 2/2: drop the min(), the swap table is always SWAPFILE_CLUSTER entries
  and swapon() masks the tail past si->max as bad (Kairui)
- 2/2: mark the unlocked ci->count read with READ_ONCE() for KCSAN
  instead of cluster_is_empty(), whose other callers hold ci->lock
  (Kairui)
- 2/2: expand the commit message to cover both of the above
- Rebased on mm-new
- Link to v1: https://lore.kernel.org/r/20260728155907.391820-1-youngjun.park@lge.com

Youngjun Park (2):
  mm/swap: fix stale comment on swap_info_struct::cluster_info
  mm/swap: scan by cluster in find_next_to_unuse()

 include/linux/swap.h |  2 +-
 mm/swapfile.c        | 43 ++++++++++++++++++++++++++++++-------------
 2 files changed, 31 insertions(+), 14 deletions(-)


base-commit: 1fb556c523f6c18b43b1f52fb366f61c9963ce06
-- 
2.48.1