mm/damon: implement a new DAMOS filter type for active pages

Patch series "mm/damon: introduce DAMOS filter type for active pages".

The memory reclaim algorithm categorizes pages into active and inactive
lists, separately for file and anon pages.  The system's performance
relies heavily on the (relative and absolute) accuracy of this
categorization.

This patch series add a new DAMOS filter for pages' activeness, giving us
visibility into the access frequency of the pages on each list.  This
insight can help us diagnose issues with the active-inactive balancing
dynamics, and make decisions to optimize reclaim efficiency and memory
utilization.

For instance, we might decide to enable DAMON_LRU_SORT, if we find that
there are pages on the active list that are infrequently accessed, or less
frequently accessed than pages on the inactive list.


This patch (of 2):

Implement a DAMOS filter type for active pages on DAMON kernel API, and
add support of it from the physical address space DAMON operations set
(paddr).

Link: https://lkml.kernel.org/r/20250318183029.2062917-1-nphamcs@gmail.com
Link: https://lkml.kernel.org/r/20250318183029.2062917-2-nphamcs@gmail.com
Signed-off-by: Nhat Pham <nphamcs@gmail.com>
Suggested-by: SeongJae Park <sj@kernel.org>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/damon.h

@@ -334,6 +334,7 @@ struct damos_stat {
 /**
  * enum damos_filter_type - Type of memory for &struct damos_filter
  * @DAMOS_FILTER_TYPE_ANON:	Anonymous pages.
+ * @DAMOS_FILTER_TYPE_ACTIVE:	Active pages.
  * @DAMOS_FILTER_TYPE_MEMCG:	Specific memcg's pages.
  * @DAMOS_FILTER_TYPE_YOUNG:	Recently accessed pages.
  * @DAMOS_FILTER_TYPE_HUGEPAGE_SIZE:	Page is part of a hugepage.
@@ -355,6 +356,7 @@ struct damos_stat {
  */
 enum damos_filter_type {
 	DAMOS_FILTER_TYPE_ANON,
+	DAMOS_FILTER_TYPE_ACTIVE,
 	DAMOS_FILTER_TYPE_MEMCG,
 	DAMOS_FILTER_TYPE_YOUNG,
 	DAMOS_FILTER_TYPE_HUGEPAGE_SIZE,

mm/damon/paddr.c

@@ -217,6 +217,9 @@ static bool damos_pa_filter_match(struct damos_filter *filter,
 	case DAMOS_FILTER_TYPE_ANON:
 		matched = folio_test_anon(folio);
 		break;
+	case DAMOS_FILTER_TYPE_ACTIVE:
+		matched = folio_test_active(folio);
+		break;
 	case DAMOS_FILTER_TYPE_MEMCG:
 		rcu_read_lock();
 		memcg = folio_memcg_check(folio);

mm/damon/sysfs-schemes.c

@@ -344,6 +344,7 @@ static struct damon_sysfs_scheme_filter *damon_sysfs_scheme_filter_alloc(
 /* Should match with enum damos_filter_type */
 static const char * const damon_sysfs_scheme_filter_type_strs[] = {
 	"anon",
+	"active",
 	"memcg",
 	"young",
 	"hugepage_size",