cgroup: implement static_key based cgroup_subsys_enabled() and cgroup_subsys_on_dfl()

Whether a subsys is enabled and attached to the default hierarchy
seldom changes and may be tested in the hot paths.  This patch
implements static_key based cgroup_subsys_enabled() and
cgroup_subsys_on_dfl() tests.

The following patches will update the users and remove duplicate
mechanisms.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Zefan Li <lizefan@huawei.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index eb7ca55f72ef..c3a9f1eb4097 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -17,6 +17,7 @@
 #include <linux/fs.h>
 #include <linux/seq_file.h>
 #include <linux/kernfs.h>
+#include <linux/jump_label.h>
 
 #include <linux/cgroup-defs.h>
 
@@ -50,6 +51,26 @@ extern struct css_set init_css_set;
 #include <linux/cgroup_subsys.h>
 #undef SUBSYS
 
+#define SUBSYS(_x)                                                              \
+        extern struct static_key_true _x ## _cgrp_subsys_enabled_key;           \
+        extern struct static_key_true _x ## _cgrp_subsys_on_dfl_key;
+#include <linux/cgroup_subsys.h>
+#undef SUBSYS
+
+/**
+ * cgroup_subsys_enabled - fast test on whether a subsys is enabled
+ * @ss: subsystem in question
+ */
+#define cgroup_subsys_enabled(ss)                                               \
+        static_branch_likely(&ss ## _enabled_key)
+
+/**
+ * cgroup_subsys_on_dfl - fast test on whether a subsys is on default hierarchy
+ * @ss: subsystem in question
+ */
+#define cgroup_subsys_on_dfl(ss)                                                \
+        static_branch_likely(&ss ## _on_dfl_key)
+
 bool css_has_online_children(struct cgroup_subsys_state *css);
 struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss);
 struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgroup,