[PATCH] memcg: fix event counting breakage by recent THP update

[KAMEZAWA Hiroyuki]

Thanks to Johannes for catching this.
And sorry for my patch, I'd like to consinder some debug check..
=
Changes in commit e401f1761c0b01966e36e41e2c385d455a7b44ee
adds nr_pages to support multiple page size in memory_cgroup_charge_statistics.

But counting the number of event nees abs(nr_pages) for increasing
counters. This patch fixes event counting.

Reported-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
 mm/memcontrol.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Index: mmotm-0125/mm/memcontrol.c
===================================================================
--- mmotm-0125.orig/mm/memcontrol.c
+++ mmotm-0125/mm/memcontrol.c
@@ -612,8 +612,10 @@ static void mem_cgroup_charge_statistics
 	/* pagein of a big page is an event. So, ignore page size */
 	if (nr_pages > 0)
 		__this_cpu_inc(mem->stat->count[MEM_CGROUP_STAT_PGPGIN_COUNT]);
-	else
+	else {
 		__this_cpu_inc(mem->stat->count[MEM_CGROUP_STAT_PGPGOUT_COUNT]);
+		nr_pages = -nr_pages; /* for event */
+	}
 
 	__this_cpu_add(mem->stat->count[MEM_CGROUP_EVENTS], nr_pages);
 

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