# \[RFC PATCH v3 18/28\] mm/damon: trace probe\_hits

- From: SeongJae Park \<sj@kernel.org\>
- Date: 2026-05-16 18:37:31 
- List: linux-trace-kernel
- Page: https://ratatoskr.run/linux-trace-kernel/2026/05/9013231
- Thread: https://ratatoskr.run/damon/2026/05/9013219/t.md

```text
Introduce a new tracepoint for exposing the per-region per-probe
positive sample count via tracefs.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/trace/events/damon.h | 38 ++++++++++++++++++++++++++++++++++++
 mm/damon/core.c              |  9 +++++++++
 2 files changed, 47 insertions(+)

diff --git a/include/trace/events/damon.h b/include/trace/events/damon.h
index 24fc402ab3c85..2fd914895c405 100644
--- a/include/trace/events/damon.h
+++ b/include/trace/events/damon.h
@@ -130,6 +130,44 @@ TRACE_EVENT(damon_monitor_intervals_tune,
 	TP_printk("sample_us=%lu", __entry->sample_us)
 );
 
+TRACE_EVENT_CONDITION(damon_region_aggregated,
+
+	TP_PROTO(unsigned int target_id, struct damon_region *r,
+		unsigned int nr_regions, unsigned int nr_probes),
+
+	TP_ARGS(target_id, r, nr_regions, nr_probes),
+
+	TP_CONDITION(nr_probes > 0),
+
+	TP_STRUCT__entry(
+		__field(unsigned long, target_id)
+		__field(unsigned long, start)
+		__field(unsigned long, end)
+		__field(unsigned int, nr_regions)
+		__field(unsigned int, nr_accesses)
+		__field(unsigned int, age)
+		__dynamic_array(unsigned char, probe_hits, nr_probes)
+	),
+
+	TP_fast_assign(
+		__entry->target_id = target_id;
+		__entry->start = r->ar.start;
+		__entry->end = r->ar.end;
+		__entry->nr_regions = nr_regions;
+		__entry->nr_accesses = r->nr_accesses;
+		__entry->age = r->age;
+		memcpy(__get_dynamic_array(probe_hits), r->probe_hits,
+			sizeof(*r->probe_hits) * nr_probes);
+	),
+
+	TP_printk("target_id=%lu nr_regions=%u %lu-%lu: %u %u probe_hits=%s",
+			__entry->target_id, __entry->nr_regions,
+			__entry->start, __entry->end,
+			__entry->nr_accesses, __entry->age,
+			__print_hex(__get_dynamic_array(probe_hits),
+				__get_dynamic_array_len(probe_hits)))
+);
+
 TRACE_EVENT(damon_aggregated,
 
 	TP_PROTO(unsigned int target_id, struct damon_region *r,
diff --git a/mm/damon/core.c b/mm/damon/core.c
index dde3c8d8fef89..11b513eb077fe 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -1881,6 +1881,13 @@ static void kdamond_reset_aggregated(struct damon_ctx *c)
 {
 	struct damon_target *t;
 	unsigned int ti = 0;	/* target's index */
+	unsigned int nr_probes = 0;
+	struct damon_probe *probe;
+
+	if (trace_damon_region_aggregated_enabled()) {
+		damon_for_each_probe(probe, c)
+			nr_probes++;
+	}
 
 	damon_for_each_target(t, c) {
 		struct damon_region *r;
@@ -1889,6 +1896,8 @@ static void kdamond_reset_aggregated(struct damon_ctx *c)
 			int i;
 
 			trace_damon_aggregated(ti, r, damon_nr_regions(t));
+			trace_damon_region_aggregated(ti, r,
+					damon_nr_regions(t), nr_probes);
 			damon_warn_fix_nr_accesses_corruption(r);
 			r->last_nr_accesses = r->nr_accesses;
 			r->nr_accesses = 0;
-- 
2.47.3
```