mm: memcg: remove unneeded checks from uncharge_page()

mem_cgroup_uncharge_page() is only called on either freshly allocated
pages without page->mapping or on rmapped PageAnon() pages.  There is no
need to check for a page->mapping that is not an anon_vma.

Signed-off-by: Johannes Weiner <jweiner@redhat.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -3061,8 +3061,7 @@ void mem_cgroup_uncharge_page(struct page *page)
 	/* early check. */
 	if (page_mapped(page))
 		return;
-	if (page->mapping && !PageAnon(page))
-		return;
+	VM_BUG_ON(page->mapping && !PageAnon(page));
 	__mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_MAPPED);
 }