mm: memcg: remove mem_cgroup_move_account_page_stat()

It used to disable preemption and run sanity checks but now it's only
taking a number out of one percpu counter and putting it into another.
Do this directly in the callsite and save the indirection.
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -3744,16 +3744,6 @@ void mem_cgroup_split_huge_fixup(struct page *head)
 }
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
-static void mem_cgroup_move_account_page_stat(struct mem_cgroup *from,
-					      struct mem_cgroup *to,
-					      unsigned int nr_pages,
-					      enum mem_cgroup_stat_index idx)
-{
-	/* Update stat data for mem_cgroup */
-	__this_cpu_sub(from->stat->count[idx], nr_pages);
-	__this_cpu_add(to->stat->count[idx], nr_pages);
-}
-
 /**
  * mem_cgroup_move_account - move account of the page
  * @page: the page
@@ -3799,13 +3789,19 @@ static int mem_cgroup_move_account(struct page *page,
 
 	move_lock_mem_cgroup(from, &flags);
 
-	if (!anon && page_mapped(page))
-		mem_cgroup_move_account_page_stat(from, to, nr_pages,
-			MEM_CGROUP_STAT_FILE_MAPPED);
+	if (!anon && page_mapped(page)) {
+		__this_cpu_sub(from->stat->count[MEM_CGROUP_STAT_FILE_MAPPED],
+			       nr_pages);
+		__this_cpu_add(to->stat->count[MEM_CGROUP_STAT_FILE_MAPPED],
+			       nr_pages);
+	}
 
-	if (PageWriteback(page))
-		mem_cgroup_move_account_page_stat(from, to, nr_pages,
-			MEM_CGROUP_STAT_WRITEBACK);
+	if (PageWriteback(page)) {
+		__this_cpu_sub(from->stat->count[MEM_CGROUP_STAT_WRITEBACK],
+			       nr_pages);
+		__this_cpu_add(to->stat->count[MEM_CGROUP_STAT_WRITEBACK],
+			       nr_pages);
+	}
 
 	mem_cgroup_charge_statistics(from, page, anon, -nr_pages);