[RFC PATCH 1/5] mm/damon/sysfs-schemes: implement DAMOS tried total bytes file

[SeongJae Park <sj@kernel.org>]

The tried_regions directory can be used for retrieving the monitoring
results snapshot for regions of specific access pattern, by setting the
scheme's action as 'stat' and the access pattern as required.  While the
interface provides every detail of the monitoring results, some use
cases including working set size monitoring requires only the total size
of the regions.  For such cases, users should read all the information
and calculate the total size of the regions.  However, it could incur
high overhead if the number of regions is high.  Add a file for
retrieving only the information, namely 'total_bytes' file.  It allows
users to get the total size by reading only the file.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs-schemes.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index 50cf89dcd898..6d3462eb31f2 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -117,6 +117,7 @@ struct damon_sysfs_scheme_regions {
 	struct kobject kobj;
 	struct list_head regions_list;
 	int nr_regions;
+	unsigned long total_bytes;
 };
 
 static struct damon_sysfs_scheme_regions *
@@ -128,9 +129,19 @@ damon_sysfs_scheme_regions_alloc(void)
 	regions->kobj = (struct kobject){};
 	INIT_LIST_HEAD(&regions->regions_list);
 	regions->nr_regions = 0;
+	regions->total_bytes = 0;
 	return regions;
 }
 
+static ssize_t total_bytes_show(struct kobject *kobj,
+		struct kobj_attribute *attr, char *buf)
+{
+	struct damon_sysfs_scheme_regions *regions = container_of(kobj,
+			struct damon_sysfs_scheme_regions, kobj);
+
+	return sysfs_emit(buf, "%lu\n", regions->total_bytes);
+}
+
 static void damon_sysfs_scheme_regions_rm_dirs(
 		struct damon_sysfs_scheme_regions *regions)
 {
@@ -148,7 +159,11 @@ static void damon_sysfs_scheme_regions_release(struct kobject *kobj)
 	kfree(container_of(kobj, struct damon_sysfs_scheme_regions, kobj));
 }
 
+static struct kobj_attribute damon_sysfs_scheme_regions_total_bytes_attr =
+		__ATTR_RO_MODE(total_bytes, 0400);
+
 static struct attribute *damon_sysfs_scheme_regions_attrs[] = {
+	&damon_sysfs_scheme_regions_total_bytes_attr.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(damon_sysfs_scheme_regions);
@@ -1648,6 +1663,7 @@ static int damon_sysfs_before_damos_apply(struct damon_ctx *ctx,
 		return 0;
 
 	sysfs_regions = sysfs_schemes->schemes_arr[schemes_idx]->tried_regions;
+	sysfs_regions->total_bytes += r->ar.end - r->ar.start;
 	region = damon_sysfs_scheme_region_alloc(r);
 	list_add_tail(&region->list, &sysfs_regions->regions_list);
 	sysfs_regions->nr_regions++;
@@ -1678,6 +1694,7 @@ int damon_sysfs_schemes_clear_regions(
 		sysfs_scheme = sysfs_schemes->schemes_arr[schemes_idx++];
 		damon_sysfs_scheme_regions_rm_dirs(
 				sysfs_scheme->tried_regions);
+		sysfs_scheme->tried_regions->total_bytes = 0;
 	}
 	return 0;
 }
-- 
2.25.1