mm/zsmalloc: drop pool->lock from zs_free on 64-bit systems

Browse source

With class_idx encoded in obj, zs_free() can locate the size_class without
holding pool->lock on 64-bit systems.  Page migration also takes
class->lock and only rewrites the PFN field of obj, so:

  1. read obj locklessly,
  2. lock the size_class derived from obj's class_idx,
  3. re-read obj under class->lock to get a stable PFN.

This eliminates the rwlock read-side cacheline bouncing between zs_free()
and migration/compaction on multi-core systems.

Annotate handle_to_obj()/record_obj() with READ_ONCE()/WRITE_ONCE() to
prevent load/store tearing on the lockless read path and silence KCSAN
data race reports.

When ZS_OBJ_CLASS_BITS == 0 (32-bit, or 64-bit with obj too narrow to hold
class_idx), zs_free() keeps pool->lock.

[akpm@linux-foundation.org: build fix]
[akpm@linux-foundation.org: fix obj_to_class_idx() warning yet again]
[baohua@kernel.org: update the comment about pool lock]
  Link: https://lore.kernel.org/20260725035733.53241-1-baohua@kernel.org
Link: https://lore.kernel.org/20260626015003.2965881-3-haowenchao22@gmail.com
Signed-off-by: Wenchao Hao <haowenchao@xiaomi.com>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Xueyuan Chen <xueyuan.chen21@gmail.com>
Cc: kernel test robot <lkp@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

...

This commit is contained in:

Wenchao Hao 2026-06-26 09:50:01 +08:00 • committed by Andrew Morton

parent 9909b088b1

commit 59e88952a8

1 changed files with 73 additions and 25 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

98

mm/zsmalloc.c

View file