mm/damon/sysfs-schemes: implement schemes/tried_regions directory

For efficient and simple query-like DAMON monitoring results readings and
deep level investigations of DAMOS, 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.  Note that this commit is
implementing only the directory but the data filling.

After the data filling change is made, 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.

Link: https://lkml.kernel.org/r/20221101220328.95765-3-sj@kernel.orgSigned-off-by: SeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

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,