mm/damon/sysfs-schemes: implement tried_regions/<r>/probes/

Implement a sysfs directory for showing the per-region probe hit counts. 
It is named 'probes/' and located under the DAMOS tried region directory.

Link: https://lore.kernel.org/20260518234119.97569-16-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>

mm/damon/sysfs-schemes.c

@@ -10,6 +10,32 @@
 
 #include "sysfs-common.h"
 
+/*
+ * probes directory
+ */
+
+struct damos_sysfs_probes {
+	struct kobject kobj;
+};
+
+static struct damos_sysfs_probes *damos_sysfs_probes_alloc(void)
+{
+	return kzalloc_obj(struct damos_sysfs_probes);
+}
+
+static void damos_sysfs_probes_release(struct kobject *kobj)
+{
+	struct damos_sysfs_probes *probes = container_of(kobj,
+			struct damos_sysfs_probes, kobj);
+
+	kfree(probes);
+}
+
+static const struct kobj_type damos_sysfs_probes_ktype = {
+	.release = damos_sysfs_probes_release,
+	.sysfs_ops = &kobj_sysfs_ops,
+};
+
 /*
  * scheme region directory
  */
@@ -20,6 +46,7 @@ struct damon_sysfs_scheme_region {
 	unsigned int nr_accesses;
 	unsigned int age;
 	unsigned long sz_filter_passed;
+	struct damos_sysfs_probes *probes;
 	struct list_head list;
 };
 
@@ -34,10 +61,36 @@ static struct damon_sysfs_scheme_region *damon_sysfs_scheme_region_alloc(
 	sysfs_region->ar = region->ar;
 	sysfs_region->nr_accesses = region->nr_accesses_bp / 10000;
 	sysfs_region->age = region->age;
+	sysfs_region->probes = NULL;
 	INIT_LIST_HEAD(&sysfs_region->list);
 	return sysfs_region;
 }
 
+static int damos_sysfs_region_add_dirs(
+		struct damon_sysfs_scheme_region *region)
+{
+	struct damos_sysfs_probes *probes = damos_sysfs_probes_alloc();
+	int err;
+
+	if (!probes)
+		return -ENOMEM;
+	err = kobject_init_and_add(&probes->kobj, &damos_sysfs_probes_ktype,
+			&region->kobj, "probes");
+	if (err) {
+		kobject_put(&probes->kobj);
+		return err;
+	}
+
+	region->probes = probes;
+	return 0;
+}
+
+static void damos_sysfs_region_rm_dirs(
+		struct damon_sysfs_scheme_region *region)
+{
+	kobject_put(&region->probes->kobj);
+}
+
 static ssize_t start_show(struct kobject *kobj, struct kobj_attribute *attr,
 		char *buf)
 {
@@ -163,6 +216,7 @@ static void damon_sysfs_scheme_regions_rm_dirs(
 	struct damon_sysfs_scheme_region *r, *next;
 
 	list_for_each_entry_safe(r, next, &regions->regions_list, list) {
+		damos_sysfs_region_rm_dirs(r);
 		list_del(&r->list);
 		kobject_put(&r->kobj);
 		regions->nr_regions--;
@@ -2995,12 +3049,17 @@ void damos_sysfs_populate_region_dir(struct damon_sysfs_schemes *sysfs_schemes,
 	if (kobject_init_and_add(&region->kobj,
 				&damon_sysfs_scheme_region_ktype,
 				&sysfs_regions->kobj, "%d",
-				sysfs_regions->nr_regions)) {
+				sysfs_regions->nr_regions))
-		kobject_put(&region->kobj);
+		goto out;
-		return;
+	if (damos_sysfs_region_add_dirs(region))
-	}
+		goto out;
+
 	list_add_tail(&region->list, &sysfs_regions->regions_list);
 	sysfs_regions->nr_regions++;
+	return;
+
+out:
+	kobject_put(&region->kobj);
 }
 
 int damon_sysfs_schemes_clear_regions(