memcg: simplify the way memory limits are checked

Since transparent huge pages, checking whether memory cgroups are below
their limits is no longer enough, but the actual amount of chargeable
space is important.

To not have more than one limit-checking interface, replace
memory_cgroup_check_under_limit() and memory_cgroup_check_margin() with a
single memory_cgroup_margin() that returns the chargeable space and leaves
the comparison to the callsite.

Soft limits are now checked the other way round, by using the already
existing function that returns the amount by which soft limits are
exceeded: res_counter_soft_limit_excess().

Also remove all the corresponding functions on the res_counter side that
are now no longer used.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 58 deletions

diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
index bf1f01b..c9d625c 100644
--- a/include/linux/res_counter.h
+++ b/include/linux/res_counter.h
@@ -129,20 +129,22 @@ 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(struct res_counter *counter, unsigned long val);
 
-static inline bool res_counter_limit_check_locked(struct res_counter *cnt)
-{
-	if (cnt->usage < cnt->limit)
-		return true;
-
-	return false;
-}
-
-static inline bool res_counter_soft_limit_check_locked(struct res_counter *cnt)
+/**
+ * res_counter_margin - calculate chargeable space of a counter
+ * @cnt: the counter
+ *
+ * Returns the difference between the hard limit and the current usage
+ * of resource counter @cnt.
+ */
+static inline unsigned long long res_counter_margin(struct res_counter *cnt)
 {
-	if (cnt->usage <= cnt->soft_limit)
-		return true;
+	unsigned long long margin;
+	unsigned long flags;
 
-	return false;
+	spin_lock_irqsave(&cnt->lock, flags);
+	margin = cnt->limit - cnt->usage;
+	spin_unlock_irqrestore(&cnt->lock, flags);
+	return margin;
 }
 
 /**
@@ -167,52 +169,6 @@ res_counter_soft_limit_excess(struct res_counter *cnt)
 	return excess;
 }
 
-/*
- * Helper function to detect if the cgroup is within it's limit or
- * not. It's currently called from cgroup_rss_prepare()
- */
-static inline bool res_counter_check_under_limit(struct res_counter *cnt)
-{
-	bool ret;
-	unsigned long flags;
-
-	spin_lock_irqsave(&cnt->lock, flags);
-	ret = res_counter_limit_check_locked(cnt);
-	spin_unlock_irqrestore(&cnt->lock, flags);
-	return ret;
-}
-
-/**
- * res_counter_check_margin - check if the counter allows charging
- * @cnt: the resource counter to check
- * @bytes: the number of bytes to check the remaining space against
- *
- * Returns a boolean value on whether the counter can be charged
- * @bytes or whether this would exceed the limit.
- */
-static inline bool res_counter_check_margin(struct res_counter *cnt,
-					    unsigned long bytes)
-{
-	bool ret;
-	unsigned long flags;
-
-	spin_lock_irqsave(&cnt->lock, flags);
-	ret = cnt->limit - cnt->usage >= bytes;
-	spin_unlock_irqrestore(&cnt->lock, flags);
-	return ret;
-}
-
-static inline bool res_counter_check_within_soft_limit(struct res_counter *cnt)
-{
-	bool ret;
-	unsigned long flags;
-
-	spin_lock_irqsave(&cnt->lock, flags);
-	ret = res_counter_soft_limit_check_locked(cnt);
-	spin_unlock_irqrestore(&cnt->lock, flags);
-	return ret;
-}
-
 static inline void res_counter_reset_max(struct res_counter *cnt)
 {
 	unsigned long flags;