[PATCH] mm/memcontrol: make the local VM stats consistent with total stats

[Yafang Shao <laoar.shao@gmail.com>]

After commit 815744d75152 ("mm: memcontrol: don't batch updates of local VM stats and events"),
the local VM stats is not consistent with total VM stats.

Bellow is one example on my server (with 8 CPUs),
	inactive_file 3567570944
	total_inactive_file 3568029696

We can find that the deviation is very great, that is because the 'val' in
__mod_memcg_state() is in pages while the effective value
in memcg_stat_show() is in bytes.
So the maximum of this deviation between local VM stats and total VM
stats can be (32 * number_of_cpu * PAGE_SIZE), that may be an unacceptable
great value.

We should make the local VM stats consistent with the total stats.
Although the deviation between local VM events and total events are not
great, I think we'd better make them consistent with each other as well.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Yafang Shao <shaoyafang@didiglobal.com>
---
 mm/memcontrol.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ba9138a..a9448c3 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -691,12 +691,12 @@ void __mod_memcg_state(struct mem_cgroup *memcg, int idx, int val)
 	if (mem_cgroup_disabled())
 		return;
 
-	__this_cpu_add(memcg->vmstats_local->stat[idx], val);
 
 	x = val + __this_cpu_read(memcg->vmstats_percpu->stat[idx]);
 	if (unlikely(abs(x) > MEMCG_CHARGE_BATCH)) {
 		struct mem_cgroup *mi;
 
+		__this_cpu_add(memcg->vmstats_local->stat[idx], x);
 		for (mi = memcg; mi; mi = parent_mem_cgroup(mi))
 			atomic_long_add(x, &mi->vmstats[idx]);
 		x = 0;
@@ -773,12 +773,12 @@ void __count_memcg_events(struct mem_cgroup *memcg, enum vm_event_item idx,
 	if (mem_cgroup_disabled())
 		return;
 
-	__this_cpu_add(memcg->vmstats_local->events[idx], count);
 
 	x = count + __this_cpu_read(memcg->vmstats_percpu->events[idx]);
 	if (unlikely(x > MEMCG_CHARGE_BATCH)) {
 		struct mem_cgroup *mi;
 
+		__this_cpu_add(memcg->vmstats_local->events[idx], x);
 		for (mi = memcg; mi; mi = parent_mem_cgroup(mi))
 			atomic_long_add(x, &mi->vmevents[idx]);
 		x = 0;
-- 
1.8.3.1