mm,page_owner: filter out stacks by a threshold

We want to be able to filter out the stacks based on a threshold we can
can tune.  By writing to 'count_threshold' file, we can adjust the
threshold value.

Link: https://lkml.kernel.org/r/20240215215907.20121-7-osalvador@suse.deSigned-off-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page_owner.c

@@ -846,6 +846,8 @@ static void *stack_next(struct seq_file *m, void *v, loff_t *ppos)
 	return stack;
 }
 
+static unsigned long page_owner_stack_threshold;
+
 static int stack_print(struct seq_file *m, void *v)
 {
 	int i, stack_count;
@@ -858,7 +860,8 @@ static int stack_print(struct seq_file *m, void *v)
 	entries = stack_record->entries;
 	stack_count = refcount_read(&stack_record->count) - 1;
 
-	if (!nr_entries || nr_entries < 0 || stack_count < 1)
+	if (!nr_entries || nr_entries < 0 || stack_count < 1 ||
+	    stack_count < page_owner_stack_threshold)
 		return 0;
 
 	for (i = 0; i < nr_entries; i++)
@@ -891,6 +894,22 @@ static const struct file_operations page_owner_stack_operations = {
 	.release	= seq_release,
 };
 
+static int page_owner_threshold_get(void *data, u64 *val)
+{
+	*val = READ_ONCE(page_owner_stack_threshold);
+	return 0;
+}
+
+static int page_owner_threshold_set(void *data, u64 val)
+{
+	WRITE_ONCE(page_owner_stack_threshold, val);
+	return 0;
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(proc_page_owner_threshold, &page_owner_threshold_get,
+			&page_owner_threshold_set, "%llu");
+
+
 static int __init pageowner_init(void)
 {
 	struct dentry *dir;
@@ -905,6 +924,8 @@ static int __init pageowner_init(void)
 	dir = debugfs_create_dir("page_owner_stacks", NULL);
 	debugfs_create_file("show_stacks", 0400, dir, NULL,
 			    &page_owner_stack_operations);
+	debugfs_create_file("count_threshold", 0600, dir, NULL,
+			    &proc_page_owner_threshold);
 
 	return 0;
 }