mm: vmscan: consistent update to pgrefill

The vmstat pgrefill is useful together with pgscan and pgsteal stats to
measure the reclaim efficiency.  However vmstat's pgrefill is not updated
consistently at system level.  It gets updated for both global and memcg
reclaim however pgscan and pgsteal are updated for only global reclaim.
So, update pgrefill only for global reclaim.  If someone is interested in
the stats representing both system level as well as memcg level reclaim,
then consult the root memcg's memory.stat instead of /proc/vmstat.

Signed-off-by: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: Chris Down <chris@chrisdown.name>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Link: http://lkml.kernel.org/r/20200711011459.1159929-1-shakeelb@google.com


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>