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@xxxxxxxxxx>
---
include/linux/cgroup.h | 21 +++++++++++++++++++++
kernel/cgroup.c | 27 ++++++++++++++++++++++++++-
2 files changed, 47 insertions(+), 1 deletion(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index eb7ca55..c3a9f1e 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,
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 2cf0f79..3619389 100644
--- 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);
--
2.4.3
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