[PATCH 1/9] Remove parent field in cpuacct cgroup

[Glauber Costa <glommer@parallels.com>]

cgroup already has parent pointers, so we  don't need to define our
own.

Signed-off-by: Glauber Costa <glommer@parallels.com>
---
 kernel/sched.c |   18 ++++++++++++------
 1 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index ccacdbd..4cde3eb 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -9096,7 +9096,6 @@ struct cpuacct {
 	/* cpuusage holds pointer to a u64-type object on every cpu */
 	u64 __percpu *cpuusage;
 	struct percpu_counter cpustat[CPUACCT_STAT_NSTATS];
-	struct cpuacct *parent;
 };
 
 struct cgroup_subsys cpuacct_subsys;
@@ -9115,6 +9114,16 @@ static inline struct cpuacct *task_ca(struct task_struct *tsk)
 			    struct cpuacct, css);
 }
 
+static inline struct cpuacct *parent_ca(struct cpuacct *ca)
+{
+	struct cpuacct *parent = NULL;
+	struct cgroup *cgrp = ca->css.cgroup;
+	if (cgrp->parent)
+		parent = container_of(cgroup_subsys_state(cgrp->parent, cpuacct_subsys_id),
+				    struct cpuacct, css);
+	return parent;
+}
+
 /* create a new cpu accounting group */
 static struct cgroup_subsys_state *cpuacct_create(
 	struct cgroup_subsys *ss, struct cgroup *cgrp)
@@ -9133,9 +9142,6 @@ static struct cgroup_subsys_state *cpuacct_create(
 		if (percpu_counter_init(&ca->cpustat[i], 0))
 			goto out_free_counters;
 
-	if (cgrp->parent)
-		ca->parent = cgroup_ca(cgrp->parent);
-
 	return &ca->css;
 
 out_free_counters:
@@ -9302,7 +9308,7 @@ static void cpuacct_charge(struct task_struct *tsk, u64 cputime)
 
 	ca = task_ca(tsk);
 
-	for (; ca; ca = ca->parent) {
+	for (; ca; ca = parent_ca(ca)) {
 		u64 *cpuusage = per_cpu_ptr(ca->cpuusage, cpu);
 		*cpuusage += cputime;
 	}
@@ -9344,7 +9350,7 @@ static void cpuacct_update_stats(struct task_struct *tsk,
 
 	do {
 		__percpu_counter_add(&ca->cpustat[idx], val, batch);
-		ca = ca->parent;
+		ca = parent_ca(ca);
 	} while (ca);
 	rcu_read_unlock();
 }
-- 
1.7.6