Re: [patch] mm, memcg: avoid unnecessary function call when memcg is disabled

While profiling numa/core v16 with cgroup_disable=memory on the command 
line, I noticed mem_cgroup_count_vm_event() still showed up as high as 
0.60% in perftop.

This occurs because the function is called extremely often even when memcg 
is disabled.

To fix this, inline the check for mem_cgroup_disabled() so we avoid the 
unnecessary function call if memcg is disabled.

...

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h

@@ -181,7 +181,14 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
 						gfp_t gfp_mask,
 						unsigned long *total_scanned);
 
-void mem_cgroup_count_vm_event(struct mm_struct *mm, enum vm_event_item idx);
+void __mem_cgroup_count_vm_event(struct mm_struct *mm, enum vm_event_item idx);
+static inline void mem_cgroup_count_vm_event(struct mm_struct *mm,
+					     enum vm_event_item idx)
+{
+	if (mem_cgroup_disabled() || !mm)
+		return;
+	__mem_cgroup_count_vm_event(mm, idx);
+}