[RFC PATCH 13/18] mm/damon/sysfs-schemes: implement schemes/tried_regions directory

[SeongJae Park <sj@kernel.org>]

For deep level investigation of DAMON and efficient query-like
monitoring results reading, DAMON kernel API (include/linux/damon.h)
users can use 'before_damos_apply' DAMON callback.  However, DAMON sysfs
interface users don't have such option.  Add a directory, namely
'tried_regions', under each scheme directory to use it as the interface
for the purpose.  That is, users will be able to signal DAMON to fill
the directory with the regions that corresponding scheme has tried to be
applied.  By setting the access pattern of the scheme, users could do the
efficient query-like monitoring.  Note that this commit is implementing
only the directory but the data filling.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs-schemes.c | 57 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index 7ea4bcce90cb..f9714ac62565 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -9,6 +9,36 @@
 
 #include "sysfs-common.h"
 
+/*
+ * scheme regions directory
+ */
+
+struct damon_sysfs_scheme_regions {
+	struct kobject kobj;
+};
+
+static struct damon_sysfs_scheme_regions *
+damon_sysfs_scheme_regions_alloc(void)
+{
+	return kzalloc(sizeof(struct damon_sysfs_scheme_regions), GFP_KERNEL);
+}
+
+static void damon_sysfs_scheme_regions_release(struct kobject *kobj)
+{
+	kfree(container_of(kobj, struct damon_sysfs_scheme_regions, kobj));
+}
+
+static struct attribute *damon_sysfs_scheme_regions_attrs[] = {
+	NULL,
+};
+ATTRIBUTE_GROUPS(damon_sysfs_scheme_regions);
+
+static struct kobj_type damon_sysfs_scheme_regions_ktype = {
+	.release = damon_sysfs_scheme_regions_release,
+	.sysfs_ops = &kobj_sysfs_ops,
+	.default_groups = damon_sysfs_scheme_regions_groups,
+};
+
 /*
  * schemes/stats directory
  */
@@ -635,6 +665,7 @@ struct damon_sysfs_scheme {
 	struct damon_sysfs_quotas *quotas;
 	struct damon_sysfs_watermarks *watermarks;
 	struct damon_sysfs_stats *stats;
+	struct damon_sysfs_scheme_regions *tried_regions;
 };
 
 /* This should match with enum damos_action */
@@ -743,6 +774,25 @@ static int damon_sysfs_scheme_set_stats(struct damon_sysfs_scheme *scheme)
 	return err;
 }
 
+static int damon_sysfs_scheme_set_tried_regions(
+		struct damon_sysfs_scheme *scheme)
+{
+	struct damon_sysfs_scheme_regions *tried_regions =
+		damon_sysfs_scheme_regions_alloc();
+	int err;
+
+	if (!tried_regions)
+		return -ENOMEM;
+	err = kobject_init_and_add(&tried_regions->kobj,
+			&damon_sysfs_scheme_regions_ktype, &scheme->kobj,
+			"tried_regions");
+	if (err)
+		kobject_put(&tried_regions->kobj);
+	else
+		scheme->tried_regions = tried_regions;
+	return err;
+}
+
 static int damon_sysfs_scheme_add_dirs(struct damon_sysfs_scheme *scheme)
 {
 	int err;
@@ -759,8 +809,14 @@ static int damon_sysfs_scheme_add_dirs(struct damon_sysfs_scheme *scheme)
 	err = damon_sysfs_scheme_set_stats(scheme);
 	if (err)
 		goto put_watermarks_quotas_access_pattern_out;
+	err = damon_sysfs_scheme_set_tried_regions(scheme);
+	if (err)
+		goto put_tried_regions_out;
 	return 0;
 
+put_tried_regions_out:
+	kobject_put(&scheme->tried_regions->kobj);
+	scheme->tried_regions = NULL;
 put_watermarks_quotas_access_pattern_out:
 	kobject_put(&scheme->watermarks->kobj);
 	scheme->watermarks = NULL;
@@ -781,6 +837,7 @@ static void damon_sysfs_scheme_rm_dirs(struct damon_sysfs_scheme *scheme)
 	kobject_put(&scheme->quotas->kobj);
 	kobject_put(&scheme->watermarks->kobj);
 	kobject_put(&scheme->stats->kobj);
+	kobject_put(&scheme->tried_regions->kobj);
 }
 
 static ssize_t action_show(struct kobject *kobj, struct kobj_attribute *attr,
-- 
2.25.1