mm/damon: avoid applying DAMOS action to same entity multiple times

'paddr' DAMON operations set can apply a DAMOS scheme's action to a large
folio multiple times in single DAMOS-regions-walk if the folio is laid on
multiple DAMON regions.  Add a field for DAMOS scheme object that can be
used by the underlying ops to know what was the last entity that the
scheme's action has applied.  The core layer unsets the field when each
DAMOS-regions-walk is done for the given scheme.  And update 'paddr' ops
to use the infrastructure to avoid the problem.

Link: https://lkml.kernel.org/r/20250207212033.45269-3-sj@kernel.org
Fixes: 57223ac29584 ("mm/damon/paddr: support the pageout scheme")
Signed-off-by: SeongJae Park <sj@kernel.org>
Reported-by: Usama Arif <usamaarif642@gmail.com>
Closes: https://lore.kernel.org/20250203225604.44742-3-usamaarif642@gmail.com
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/include/linux/damon.h b/include/linux/damon.h
index c9074d569596..b4d37d9b9221 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -432,6 +432,7 @@ struct damos_access_pattern {
  * @wmarks:		Watermarks for automated (in)activation of this scheme.
  * @target_nid:		Destination node if @action is "migrate_{hot,cold}".
  * @filters:		Additional set of &struct damos_filter for &action.
+ * @last_applied:	Last @action applied ops-managing entity.
  * @stat:		Statistics of this scheme.
  * @list:		List head for siblings.
  *
@@ -454,6 +455,15 @@ struct damos_access_pattern {
  * implementation could check pages of the region and skip &action to respect
  * &filters
  *
+ * The minimum entity that @action can be applied depends on the underlying
+ * &struct damon_operations.  Since it may not be aligned with the core layer
+ * abstract, namely &struct damon_region, &struct damon_operations could apply
+ * @action to same entity multiple times.  Large folios that underlying on
+ * multiple &struct damon region objects could be such examples.  The &struct
+ * damon_operations can use @last_applied to avoid that.  DAMOS core logic
+ * unsets @last_applied when each regions walking for applying the scheme is
+ * finished.
+ *
  * After applying the &action to each region, &stat_count and &stat_sz is
  * updated to reflect the number of regions and total size of regions that the
  * &action is applied.
@@ -482,6 +492,7 @@ struct damos {
 		int target_nid;
 	};
 	struct list_head filters;
+	void *last_applied;
 	struct damos_stat stat;
 	struct list_head list;
 };