mm: update_lru_size do the __mod_zone_page_state

Konstantin Khlebnikov pointed out (nearly four years ago, when lumpy
reclaim was removed) that lru_size can be updated by -nr_taken once per
call to isolate_lru_pages(), instead of page by page.

Update it inside isolate_lru_pages(), or at its two callsites? I chose
to update it at the callsites, rearranging and grouping the updates by
nr_taken and nr_scanned together in both.

With one exception, mem_cgroup_update_lru_size(,lru,) is then used where
__mod_zone_page_state(,NR_LRU_BASE+lru,) is used; and we shall be adding
some more calls in a future commit.  Make the code a little smaller and
simpler by incorporating stat update in lru_size update.

The exception was move_active_pages_to_lru(), which aggregated the
pgmoved stat update separately from the individual lru_size updates; but
I still think this a simplification worth making.

However, the __mod_zone_page_state is not peculiar to mem_cgroups: so
better use the name update_lru_size, calls mem_cgroup_update_lru_size
when CONFIG_MEMCG.

Signed-off-by: Hugh Dickins <[email protected]>
Cc: "Kirill A. Shutemov" <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Andres Lagar-Cavilla <[email protected]>
Cc: Yang Shi <[email protected]>
Cc: Ning Qu <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Konstantin Khlebnikov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/memcontrol.c

@@ -1035,6 +1035,8 @@ void mem_cgroup_update_lru_size(struct lruvec *lruvec, enum lru_list lru,
 	long size;
 	bool empty;
 
+	__update_lru_size(lruvec, lru, nr_pages);
+
 	if (mem_cgroup_disabled())
 		return;