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>

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index eb7ca55..c3a9f1e 100644 (file)
--- 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,

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 2cf0f79..3619389 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -139,6 +139,27 @@ static const char *cgroup_subsys_name[] = {
 };
 #undef SUBSYS
 
+/* array of static_keys for cgroup_subsys_enabled() and cgroup_subsys_on_dfl() */
+#define SUBSYS(_x)                                                             \
+       DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_enabled_key);                 \
+       DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_on_dfl_key);                  \
+       EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_enabled_key);                      \
+       EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_on_dfl_key);
+#include <linux/cgroup_subsys.h>
+#undef SUBSYS
+
+#define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_enabled_key,
+static struct static_key_true *cgroup_subsys_enabled_key[] = {
+#include <linux/cgroup_subsys.h>
+};
+#undef SUBSYS
+
+#define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_on_dfl_key,
+static struct static_key_true *cgroup_subsys_on_dfl_key[] = {
+#include <linux/cgroup_subsys.h>
+};
+#undef SUBSYS
+
 /*
  * The default hierarchy, reserved for the subsystems that are otherwise
  * unattached - it never has more than a single cgroup, and all tasks are
@@ -1319,9 +1340,12 @@ static int rebind_subsystems(struct cgroup_root *dst_root,
 
                /* default hierarchy doesn't enable controllers by default */
                dst_root->subsys_mask |= 1 << ssid;
-               if (dst_root != &cgrp_dfl_root) {
+               if (dst_root == &cgrp_dfl_root) {
+                       static_branch_enable(cgroup_subsys_on_dfl_key[ssid]);
+               } else {
                        dst_root->cgrp.subtree_control |= 1 << ssid;
                        cgroup_refresh_child_subsys_mask(&dst_root->cgrp);
+                       static_branch_disable(cgroup_subsys_on_dfl_key[ssid]);
                }
 
                if (ss->bind)
@@ -5483,6 +5507,7 @@ static int __init cgroup_disable(char *str)
                            strcmp(token, ss->legacy_name))
                                continue;
 
+                       static_branch_disable(cgroup_subsys_enabled_key[i]);
                        ss->disabled = 1;
                        printk(KERN_INFO "Disabling %s control group subsystem\n",
                               ss->name);