[RFC PATCH v2.1 0/3] mm/damon/modules: detect and use fresh status

SeongJae Park
2026-04-18T22:28:13Z

DAMON modules including DAMON_RECLAIM, DAMON_LRU_SORT and DAMON_STAT
commonly expose the kdamond running status via their parameters. Under
certain scenarios including wrong user inputs and memory allocation
failures, those parameter values can be stale. It can confuse users.
For DAMON_RECLAIM and DAMON_LRU_SORT, it even makes the kdamond unable
to be restarted before the system reboot.

The problem comes from the fact that there are multiple events for the
status changes and it is difficult to follow up all the scenarios. Fix
the issue by detecting and using the status on demand, instead of using
a cached status that is difficult to be updated.

Patches 1-3 fix the bugs in DAMON_RECLAIM, DAMON_LRU_SORT and DAMON_STAT
in the order.

Changes from RFC v2
- rfc v2: https://lore.kernel.org/20260418014439.6353-1-sj@kernel.org
- Set kdamond_pid set callbacks.
- Support multiple enabled parameters setup on boot commandline.
- Acknowledge the third patch was discovered by Sashiko.
Changes from v2
- v2: https://lore.kernel.org/20260413185249.5921-1-aethernet65535@gmail.com
- Add RFC tag back, for sashiko review.
- Detect and use fresh status instead of trying to catch up all scenarios.
- Change Liew from the responsible author to a credit-deserved co-developer.
- Move authorship responsibility to SJ.
- Add DAMON_STAT fix.
- RFC of the fix was posted separately
(https://lore.kernel.org/20260416143857.76146-1-sj@kernel.org), and
only commit message wordsmithing is added in this version.
Changes from RFC
- rfc: https://lore.kernel.org/20260330164347.12772-1-aethernet65535@gmail.com
- Remove RFC tag.
- Remove 'damon_thread_status' structure and damon_update_thread_status()
(SJ pointed out this was too much extension of core API for a problem
that can be fixed more simply).
- Add a fallback in damon_{lru_sort, reclaim}_turn() 'N' path. If
damon_stop() fails but kdamond is not running, forcefully reset the
parameters.
- Reset 'enabled' and 'kdamond_pid' when damon_commit_ctx() fails in
damon_{lru_sort, reclaim}_apply_parameters() (kdamond will terminate
eventually in this case).

SeongJae Park (3):
mm/damon/reclaim: detect and use fresh enabled and kdamond_pid values
mm/damon/lru_sort: detect and use fresh enabled and kdamond_pid values
mm/damon/stat: detect and use fresh enabled value

mm/damon/lru_sort.c | 85 +++++++++++++++++++++++++++++----------------
mm/damon/reclaim.c | 85 +++++++++++++++++++++++++++++----------------
mm/damon/stat.c | 30 ++++++++++------
3 files changed, 130 insertions(+), 70 deletions(-)

base-commit: 710b7b26c423290803f447f5ed2fb264e91cda56
--
2.47.3