From: SeongJae Park <sj@kernel.org>
Date: Mon, 18 May 2026 23:40:53 +0000 (-0700)
Subject: mm/damon/core: introduce damon_region->probe_hits
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=57c6332f2548d94f137f51bd18111e4316fd1ba4;p=thirdparty%2Fkernel%2Flinux.git

mm/damon/core: introduce damon_region->probe_hits

Add an array for the per-region per-probe positive samples count.  For
simple and efficient implementation, add a limit to the number of data
probes and set the array to support only the limited number of counters.

Link: https://lore.kernel.org/20260518234119.97569-6-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/include/linux/damon.h b/include/linux/damon.h
index f8b679dd944d..3a30af119ac6 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -17,6 +17,8 @@
 
 /* Minimal region size.  Every damon_region is aligned by this. */
 #define DAMON_MIN_REGION_SZ	PAGE_SIZE
+/* Maximum number of monitoring probes. */
+#define DAMON_MAX_PROBES	(4)
 /* Max priority score for DAMON-based operation schemes */
 #define DAMOS_MAX_SCORE		(99)
 
@@ -47,6 +49,7 @@ struct damon_size_range {
  * @nr_accesses:	Access frequency of this region.
  * @nr_accesses_bp:	@nr_accesses in basis point (0.01%) that updated for
  *			each sampling interval.
+ * @probe_hits:		Number of probe-positive region samples.
  * @list:		List head for siblings.
  * @age:		Age of this region.
  *
@@ -75,6 +78,7 @@ struct damon_region {
 	unsigned long sampling_addr;
 	unsigned int nr_accesses;
 	unsigned int nr_accesses_bp;
+	unsigned char probe_hits[DAMON_MAX_PROBES];
 	struct list_head list;
 
 	unsigned int age;
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 240cae1420c1..0f6b3b66d1de 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -229,6 +229,7 @@ static void damon_verify_new_region(unsigned long start, unsigned long end)
 struct damon_region *damon_new_region(unsigned long start, unsigned long end)
 {
 	struct damon_region *region;
+	int i;
 
 	damon_verify_new_region(start, end);
 	region = kmem_cache_alloc(damon_region_cache, GFP_KERNEL);
@@ -239,6 +240,8 @@ struct damon_region *damon_new_region(unsigned long start, unsigned long end)
 	region->ar.end = end;
 	region->nr_accesses = 0;
 	region->nr_accesses_bp = 0;
+	for (i = 0; i < DAMON_MAX_PROBES; i++)
+		region->probe_hits[i] = 0;
 	INIT_LIST_HEAD(&region->list);
 
 	region->age = 0;
@@ -2980,12 +2983,17 @@ static void damon_merge_two_regions(struct damon_target *t,
 		struct damon_region *l, struct damon_region *r)
 {
 	unsigned long sz_l = damon_sz_region(l), sz_r = damon_sz_region(r);
+	int i;
 
 	l->nr_accesses = (l->nr_accesses * sz_l + r->nr_accesses * sz_r) /
 			(sz_l + sz_r);
 	l->nr_accesses_bp = l->nr_accesses * 10000;
 	l->age = (l->age * sz_l + r->age * sz_r) / (sz_l + sz_r);
 	l->ar.end = r->ar.end;
+	/* todo: do this for only installed probes */
+	for (i = 0; i < DAMON_MAX_PROBES; i++)
+		l->probe_hits[i] = (l->probe_hits[i] * sz_l + r->probe_hits[i]
+				* sz_r) / (sz_l + sz_r);
 	damon_verify_merge_two_regions(l, r);
 	damon_destroy_region(r, t);
 }
@@ -3108,6 +3116,8 @@ static void damon_split_region_at(struct damon_target *t,
 	new->last_nr_accesses = r->last_nr_accesses;
 	new->nr_accesses_bp = r->nr_accesses_bp;
 	new->nr_accesses = r->nr_accesses;
+	/* todo: do this for only installed probes */
+	memcpy(new->probe_hits, r->probe_hits, sizeof(r->probe_hits));
 
 	damon_insert_region(new, r, damon_next_region(r), t);
 }