[RFC PATCH v3 4/9] mm/damon/ops-common: use probe-weighted score when probe weights are set

[Ravi Jonnalagadda]

When probe weights are configured (damon_has_probe_weights()), use
damon_probe_hits_wsum() for the frequency subscore in damon_hot_score()
instead of damon_nr_accesses_mvsum().  This routes hardware event counts
from a perf-event probe into the tiering decision.

When no probe weights are set the frequency subscore comes from
nr_accesses_mvsum, so page-table-only monitoring scores from the
page-table access rate.

Export damon_has_probe_weights() so ops-common.c can call it without a
static dependency on core.c internals.

Guard against integer overflow: clamp the probe-weighted subscore to
DAMON_MAX_SUBSCORE via min_t after the mult_frac scaling so a large
weighted-hit sum cannot overflow the subscore range.

Signed-off-by: Ravi Jonnalagadda <ravis.opensrc@xxxxxxxxx>
---
 include/linux/damon.h |  1 +
 mm/damon/core.c       |  2 +-
 mm/damon/ops-common.c | 21 ++++++++++++++++++---
 3 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 217299aa6c03..d7baa6a58d3d 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -1306,6 +1306,7 @@ unsigned int damon_probe_hits_mvsum(int probe_idx, struct damon_region *r,
 		struct damon_ctx *ctx);
 unsigned int damon_probe_hits_wsum(struct damon_region *r, bool last, bool mv,
 		struct damon_ctx *ctx);
+bool damon_has_probe_weights(struct damon_ctx *c);
 
 int damon_set_regions(struct damon_target *t, struct damon_addr_range *ranges,
 		unsigned int nr_ranges, unsigned long min_region_sz);
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 4fd1db12bc49..6a90cf465d40 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -351,7 +351,7 @@ static struct damon_probe *damon_nth_probe(int n, struct damon_ctx *ctx)
 	return NULL;
 }
 
-static bool damon_has_probe_weights(struct damon_ctx *c)
+bool damon_has_probe_weights(struct damon_ctx *c)
 {
 	struct damon_probe *p;
 
diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c
index 2f3bf86a221b..8cc6bc440153 100644
--- a/mm/damon/ops-common.c
+++ b/mm/damon/ops-common.c
@@ -172,9 +172,24 @@ int damon_hot_score(struct damon_ctx *c, struct damon_region *r,
 	unsigned int age_weight = s->quota.weight_age;
 	int hotness;
 
-	freq_subscore = mult_frac(damon_nr_accesses_mvsum(r, c),
-			DAMON_MAX_SUBSCORE,
-			damon_nr_samples_per_aggr(&c->attrs));
+	if (damon_has_probe_weights(c)) {
+		unsigned int wsum = damon_probe_hits_wsum(r, false, true, c);
+
+		/*
+		 * Route perf-event hardware event counts into the score.
+		 * Clamp to DAMON_MAX_SUBSCORE so a large weighted-hit sum
+		 * cannot overflow the subscore range.
+		 */
+		freq_subscore = min_t(int,
+				mult_frac(wsum, DAMON_MAX_SUBSCORE,
+					/* +1 guards divide-by-zero: samples-per-aggr can be 0 */
+					damon_nr_samples_per_aggr(&c->attrs) + 1),
+				DAMON_MAX_SUBSCORE);
+	} else {
+		freq_subscore = mult_frac(damon_nr_accesses_mvsum(r, c),
+				DAMON_MAX_SUBSCORE,
+				damon_nr_samples_per_aggr(&c->attrs));
+	}
 
 	age_in_sec = div_u64((u64)r->age * c->attrs.aggr_interval,
 			     USEC_PER_SEC);

-- 
Git-157)