Task Control Groups: shared cgroup subsystem group arrays

Replace the struct css_set embedded in task_struct with a pointer; all tasks
that have the same set of memberships across all hierarchies will share a
css_set object, and will be linked via their css_sets field to the "tasks"
list_head in the css_set.

Assuming that many tasks share the same cgroup assignments, this reduces
overall space usage and keeps the size of the task_struct down (three pointers
added to task_struct compared to a non-cgroups kernel, no matter how many
subsystems are registered).

[akpm@linux-foundation.org: fix a printk]
[akpm@linux-foundation.org: build fix]
Signed-off-by: Paul Menage <menage@google.com>
Cc: Serge E. Hallyn <serue@us.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Dave Hansen <haveblue@us.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Paul Jackson <pj@sgi.com>
Cc: Kirill Korotaev <dev@openvz.org>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>
Cc: Serge E. Hallyn <serue@us.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Dave Hansen <haveblue@us.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Paul Jackson <pj@sgi.com>
Cc: Kirill Korotaev <dev@openvz.org>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 29 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index af2ed4bae67..1aa1cfa63b3 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -894,34 +894,6 @@ struct sched_entity {
 #endif
 };
 
-#ifdef CONFIG_CGROUPS
-
-#define SUBSYS(_x) _x ## _subsys_id,
-enum cgroup_subsys_id {
-#include <linux/cgroup_subsys.h>
-        CGROUP_SUBSYS_COUNT
-};
-#undef SUBSYS
-
-/* A css_set is a structure holding pointers to a set of
- * cgroup_subsys_state objects.
- */
-
-struct css_set {
-
-        /* Set of subsystem states, one for each subsystem. NULL for
-         * subsystems that aren't part of this hierarchy. These
-         * pointers reduce the number of dereferences required to get
-         * from a task to its state for a given cgroup, but result
-         * in increased space usage if tasks are in wildly different
-         * groupings across different hierarchies. This array is
-         * immutable after creation */
-        struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];
-
-};
-
-#endif /* CONFIG_CGROUPS */
-
 struct task_struct {
         volatile long state;    /* -1 unrunnable, 0 runnable, >0 stopped */
         void *stack;
@@ -1159,7 +1131,10 @@ struct task_struct {
         int cpuset_mem_spread_rotor;
 #endif
 #ifdef CONFIG_CGROUPS
-        struct css_set cgroups;
+        /* Control Group info protected by css_set_lock */
+        struct css_set *cgroups;
+        /* cg_list protected by css_set_lock and tsk->alloc_lock */
+        struct list_head cg_list;
 #endif
 #ifdef CONFIG_FUTEX
         struct robust_list_head __user *robust_list;