From: KAMEZAWA Hiroyuki <redacted>

Current memory cgroup's code tends to assume page_size == PAGE_SIZE
and arrangement for THP is not enough yet.

This is one of fixes for supporing THP. This adds
mem_cgroup_check_margin() and checks whether there are required amount of
free resource after memory reclaim. By this, THP page allocation
can know whether it really succeeded or not and avoid infinite-loop
and hangup.

Total fixes for do_charge()/reclaim memory will follow this patch.

Signed-off-by: KAMEZAWA Hiroyuki <redacted>
---
 include/linux/res_counter.h |   11 +++++++++++
 mm/memcontrol.c             |   25 ++++++++++++++++++++++++-
 2 files changed, 35 insertions(+), 1 deletion(-)

Index: mmotm-0125/include/linux/res_counter.h
===================================================================

--- mmotm-0125.orig/include/linux/res_counter.h
+++ mmotm-0125/include/linux/res_counter.h

@@ -182,6 +182,17 @@ static inline bool res_counter_check_und
 	return ret;
 }
 
+static inline s64 res_counter_check_margin(struct res_counter *cnt)
+{
+	s64 ret;
+	unsigned long flags;
+
+	spin_lock_irqsave(&cnt->lock, flags);
+	ret = cnt->limit - cnt->usage;
+	spin_unlock_irqrestore(&cnt->lock, flags);
+	return ret;
+}

@@ -1853,7 +1869,14 @@ static int __mem_cgroup_do_charge(struct
 	 * Check the limit again to see if the reclaim reduced the
 	 * current usage of the cgroup before giving up
 	 */
-	if (ret || mem_cgroup_check_under_limit(mem_over_limit))
+	if (mem_cgroup_check_margin(mem_over_limit) >= csize)
+		return CHARGE_RETRY;
+
+	/*
+ 	 * If the charge size is a PAGE_SIZE, it's not hopeless while
+ 	 * we can reclaim a page.
+ 	 */
+	if (csize == PAGE_SIZE && ret)
 		return CHARGE_RETRY;