check_accesses() DAMON ops callback returns the maximum nr_accesses of
regions.  DAMON core uses it to calculate a reasonable region merge
threshold.  The core will need to adjust regions for not nr_accesses but
probe hits weighted sum in future.  For that, the core needs to know the
maximum weighted sum of the regions.  Update the protocol for the task.

Signed-off-by: SJ Park <sj@kernel.org>
---
 include/linux/damon.h | 5 ++++-
 mm/damon/core.c       | 2 +-
 mm/damon/paddr.c      | 4 +++-
 3 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index aee28b05acc6c..e7acd8e610a64 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -649,6 +649,8 @@ enum damon_ops_id {
  * @apply_probes should apply the data attribute probes to each region and
  * accordingly update the probe hits counter of the region.  It should also
  * set &damon_region->sampling_addr of each region if ``set_samples`` is true.
+ * It should also return maximum probe hits weighted sum of regions if
+ * ``return_max_wsum`` is true.
  * @get_scheme_score should return the priority score of a region for a scheme
  * as an integer in [0, &DAMOS_MAX_SCORE].
  * @apply_scheme is called from @kdamond when a region for user provided
@@ -666,7 +668,8 @@ struct damon_operations {
 	void (*update)(struct damon_ctx *context);
 	void (*prepare_access_checks)(struct damon_ctx *context);
 	unsigned int (*check_accesses)(struct damon_ctx *context);
-	void (*apply_probes)(struct damon_ctx *context, bool set_samples);
+	unsigned int (*apply_probes)(struct damon_ctx *context,
+			bool set_samples, bool return_max_wsum);
 	int (*get_scheme_score)(struct damon_ctx *context,
 			struct damon_region *r, struct damos *scheme);
 	unsigned long (*apply_scheme)(struct damon_ctx *context,
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 9fbea6204520b..9f6cdd810bd8a 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -3692,7 +3692,7 @@ static int kdamond_fn(void *data)
 		if (ctx->ops.check_accesses)
 			max_nr_accesses = ctx->ops.check_accesses(ctx);
 		if (ctx->ops.apply_probes)
-			ctx->ops.apply_probes(ctx, false);
+			ctx->ops.apply_probes(ctx, false, false);
 
 		if (time_after_eq(ctx->passed_sample_intervals,
 					next_aggregation_sis)) {
diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
index ff4fcca949660..3eba3564a31fc 100644
--- a/mm/damon/paddr.c
+++ b/mm/damon/paddr.c
@@ -166,7 +166,8 @@ static bool damon_pa_filter_pass(phys_addr_t pa, struct folio *folio,
 	return pass;
 }
 
-static void damon_pa_apply_probes(struct damon_ctx *ctx, bool set_samples)
+static unsigned int damon_pa_apply_probes(struct damon_ctx *ctx,
+		bool set_samples, bool return_max_wsum)
 {
 	struct damon_target *t;
 	struct damon_region *r;
@@ -194,6 +195,7 @@ static void damon_pa_apply_probes(struct damon_ctx *ctx, bool set_samples)
 				folio_put(folio);
 		}
 	}
+	return 0;
 }
 
 /*
-- 
2.47.3