cgroup: Add misc cgroup controller

The Miscellaneous cgroup provides the resource limiting and tracking
mechanism for the scalar resources which cannot be abstracted like the
other cgroup resources. Controller is enabled by the CONFIG_CGROUP_MISC
config option.

A resource can be added to the controller via enum misc_res_type{} in
the include/linux/misc_cgroup.h file and the corresponding name via
misc_res_name[] in the kernel/cgroup/misc.c file. Provider of the
resource must set its capacity prior to using the resource by calling
misc_cg_set_capacity().

Once a capacity is set then the resource usage can be updated using
charge and uncharge APIs. All of the APIs to interact with misc
controller are in include/linux/misc_cgroup.h.

Miscellaneous controller provides 3 interface files. If two misc
resources (res_a and res_b) are registered then:

misc.capacity
A read-only flat-keyed file shown only in the root cgroup.  It shows
miscellaneous scalar resources available on the platform along with
their quantities::

    $ cat misc.capacity
    res_a 50
    res_b 10

misc.current
A read-only flat-keyed file shown in the non-root cgroups.  It shows
the current usage of the resources in the cgroup and its children::

    $ cat misc.current
    res_a 3
    res_b 0

misc.max
A read-write flat-keyed file shown in the non root cgroups. Allowed
maximum usage of the resources in the cgroup and its children.::

    $ cat misc.max
    res_a max
    res_b 4

Limit can be set by::

    # echo res_a 1 > misc.max

Limit can be set to max by::

    # echo res_a max > misc.max

Limits can be set more than the capacity value in the misc.capacity
file.

Signed-off-by: Vipin Sharma <vipinsh@google.com>
Reviewed-by: David Rientjes <rientjes@google.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

2 files changed, 130 insertions, 0 deletions

diff --git a/include/linux/cgroup_subsys.h b/include/linux/cgroup_subsys.h
index acb77dcff3b4..445235487230 100644
--- a/include/linux/cgroup_subsys.h
+++ b/include/linux/cgroup_subsys.h
@@ -61,6 +61,10 @@ SUBSYS(pids)
 SUBSYS(rdma)
 #endif
 
+#if IS_ENABLED(CONFIG_CGROUP_MISC)
+SUBSYS(misc)
+#endif
+
 /*
  * The following subsystems are not supported on the default hierarchy.
  */
diff --git a/include/linux/misc_cgroup.h b/include/linux/misc_cgroup.h
new file mode 100644
index 000000000000..1195d36558b4
--- /dev/null
+++ b/include/linux/misc_cgroup.h
@@ -0,0 +1,126 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Miscellaneous cgroup controller.
+ *
+ * Copyright 2020 Google LLC
+ * Author: Vipin Sharma <vipinsh@google.com>
+ */
+#ifndef _MISC_CGROUP_H_
+#define _MISC_CGROUP_H_
+
+/**
+ * Types of misc cgroup entries supported by the host.
+ */
+enum misc_res_type {
+	MISC_CG_RES_TYPES
+};
+
+struct misc_cg;
+
+#ifdef CONFIG_CGROUP_MISC
+
+#include <linux/cgroup.h>
+
+/**
+ * struct misc_res: Per cgroup per misc type resource
+ * @max: Maximum limit on the resource.
+ * @usage: Current usage of the resource.
+ * @failed: True if charged failed for the resource in a cgroup.
+ */
+struct misc_res {
+	unsigned long max;
+	atomic_long_t usage;
+	bool failed;
+};
+
+/**
+ * struct misc_cg - Miscellaneous controller's cgroup structure.
+ * @css: cgroup subsys state object.
+ * @res: Array of misc resources usage in the cgroup.
+ */
+struct misc_cg {
+	struct cgroup_subsys_state css;
+	struct misc_res res[MISC_CG_RES_TYPES];
+};
+
+unsigned long misc_cg_res_total_usage(enum misc_res_type type);
+int misc_cg_set_capacity(enum misc_res_type type, unsigned long capacity);
+int misc_cg_try_charge(enum misc_res_type type, struct misc_cg *cg,
+		       unsigned long amount);
+void misc_cg_uncharge(enum misc_res_type type, struct misc_cg *cg,
+		      unsigned long amount);
+
+/**
+ * css_misc() - Get misc cgroup from the css.
+ * @css: cgroup subsys state object.
+ *
+ * Context: Any context.
+ * Return:
+ * * %NULL - If @css is null.
+ * * struct misc_cg* - misc cgroup pointer of the passed css.
+ */
+static inline struct misc_cg *css_misc(struct cgroup_subsys_state *css)
+{
+	return css ? container_of(css, struct misc_cg, css) : NULL;
+}
+
+/*
+ * get_current_misc_cg() - Find and get the misc cgroup of the current task.
+ *
+ * Returned cgroup has its ref count increased by 1. Caller must call
+ * put_misc_cg() to return the reference.
+ *
+ * Return: Misc cgroup to which the current task belongs to.
+ */
+static inline struct misc_cg *get_current_misc_cg(void)
+{
+	return css_misc(task_get_css(current, misc_cgrp_id));
+}
+
+/*
+ * put_misc_cg() - Put the misc cgroup and reduce its ref count.
+ * @cg - cgroup to put.
+ */
+static inline void put_misc_cg(struct misc_cg *cg)
+{
+	if (cg)
+		css_put(&cg->css);
+}
+
+#else /* !CONFIG_CGROUP_MISC */
+
+unsigned long misc_cg_res_total_usage(enum misc_res_type type)
+{
+	return 0;
+}
+
+static inline int misc_cg_set_capacity(enum misc_res_type type,
+				       unsigned long capacity)
+{
+	return 0;
+}
+
+static inline int misc_cg_try_charge(enum misc_res_type type,
+				     struct misc_cg *cg,
+				     unsigned long amount)
+{
+	return 0;
+}
+
+static inline void misc_cg_uncharge(enum misc_res_type type,
+				    struct misc_cg *cg,
+				    unsigned long amount)
+{
+}
+
+static inline struct misc_cg *get_current_misc_cg(void)
+{
+	return NULL;
+}
+
+static inline void put_misc_cg(struct misc_cg *cg)
+{
+}
+
+#endif /* CONFIG_CGROUP_MISC */
+#endif /* _MISC_CGROUP_H_ */