[PATCH 5/7] cgroups: Ability to stop res charge propagation on bounded ancestor

[Frederic Weisbecker <fweisbec@gmail.com>]

Moving a task from a cgroup to another may require to substract
its resource charge from the old cgroup and add it to the new one.

For this to happen, the uncharge/charge propagation can just stop
when we reach the common ancestor for the two cgroups. Further
the performance reasons, we also want to avoid to temporarily
overload the common ancestors with a non-accurate resource
counter usage if we charge first the new cgroup and uncharge the
old one thereafter. This is going to be a requirement for the coming
max number of task subsystem.

To solve this, provide a pair of new API that can charge/uncharge
a resource counter until we reach a given ancestor.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Menage <menage@google.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Aditya Kali <adityakali@google.com>
---
 include/linux/res_counter.h |    6 ++++++
 kernel/res_counter.c        |   23 ++++++++++++++++++-----
 2 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
index 109d118..8c421ac 100644
--- a/include/linux/res_counter.h
+++ b/include/linux/res_counter.h
@@ -117,6 +117,10 @@ void res_counter_init(struct res_counter *counter, struct res_counter *parent);
 
 int __must_check res_counter_charge_locked(struct res_counter *counter,
 		unsigned long val);
+int __must_check res_counter_charge_until(struct res_counter *counter,
+					  struct res_counter *limit,
+					  unsigned long val,
+					  struct res_counter **limit_fail_at);
 int __must_check res_counter_charge(struct res_counter *counter,
 		unsigned long val, struct res_counter **limit_fail_at);
 
@@ -131,6 +135,8 @@ int __must_check res_counter_charge(struct res_counter *counter,
  */
 
 void res_counter_uncharge_locked(struct res_counter *counter, unsigned long val);
+void res_counter_uncharge_until(struct res_counter *counter, struct res_counter *limit,
+				unsigned long val);
 void res_counter_uncharge(struct res_counter *counter, unsigned long val);
 
 /**
diff --git a/kernel/res_counter.c b/kernel/res_counter.c
index 8cb0362..39f2513 100644
--- a/kernel/res_counter.c
+++ b/kernel/res_counter.c
@@ -35,8 +35,9 @@ int res_counter_charge_locked(struct res_counter *counter, unsigned long val)
 	return 0;
 }
 
-int res_counter_charge(struct res_counter *counter, unsigned long val,
-			struct res_counter **limit_fail_at)
+int res_counter_charge_until(struct res_counter *counter,
+			     struct res_counter *limit, unsigned long val,
+			     struct res_counter **limit_fail_at)
 {
 	int ret;
 	unsigned long flags;
@@ -44,7 +45,7 @@ int res_counter_charge(struct res_counter *counter, unsigned long val,
 
 	*limit_fail_at = NULL;
 	local_irq_save(flags);
-	for (c = counter; c != NULL; c = c->parent) {
+	for (c = counter; c != limit; c = c->parent) {
 		spin_lock(&c->lock);
 		ret = res_counter_charge_locked(c, val);
 		spin_unlock(&c->lock);
@@ -66,6 +67,12 @@ done:
 	return ret;
 }
 
+int res_counter_charge(struct res_counter *counter, unsigned long val,
+			struct res_counter **limit_fail_at)
+{
+	return res_counter_charge_until(counter, NULL, val, limit_fail_at);
+}
+
 void res_counter_uncharge_locked(struct res_counter *counter, unsigned long val)
 {
 	if (WARN_ON(counter->usage < val))
@@ -74,13 +81,15 @@ void res_counter_uncharge_locked(struct res_counter *counter, unsigned long val)
 	counter->usage -= val;
 }
 
-void res_counter_uncharge(struct res_counter *counter, unsigned long val)
+void res_counter_uncharge_until(struct res_counter *counter,
+				struct res_counter *limit,
+				unsigned long val)
 {
 	unsigned long flags;
 	struct res_counter *c;
 
 	local_irq_save(flags);
-	for (c = counter; c != NULL; c = c->parent) {
+	for (c = counter; c != limit; c = c->parent) {
 		spin_lock(&c->lock);
 		res_counter_uncharge_locked(c, val);
 		spin_unlock(&c->lock);
@@ -88,6 +97,10 @@ void res_counter_uncharge(struct res_counter *counter, unsigned long val)
 	local_irq_restore(flags);
 }
 
+void res_counter_uncharge(struct res_counter *counter, unsigned long val)
+{
+	res_counter_uncharge_until(counter, NULL, val);
+}
 
 static inline unsigned long long *
 res_counter_member(struct res_counter *counter, int member)
-- 
1.7.5.4