mm: clean up page_remove_rmap()

page_remove_rmap() has multiple PageAnon() tests and it has deep nesting.
Clean this up.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: Wu Fengguang <fengguang.wu@intel.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/rmap.c

@@ -739,7 +739,10 @@ void page_dup_rmap(struct page *page, struct vm_area_struct *vma, unsigned long
  */
 void page_remove_rmap(struct page *page)
 {
-	if (atomic_add_negative(-1, &page->_mapcount)) {
+	/* page still mapped by someone else? */
+	if (!atomic_add_negative(-1, &page->_mapcount))
+		return;
+
 	/*
 	 * Now that the last pte has gone, s390 must transfer dirty
 	 * flag from storage key to struct page.  We can usually skip
@@ -747,15 +750,16 @@ void page_remove_rmap(struct page *page)
 	 * not if it's in swapcache - there might be another pte slot
 	 * containing the swap entry, but page not yet written to swap.
 	 */
-		if ((!PageAnon(page) || PageSwapCache(page)) &&
-		    page_test_dirty(page)) {
+	if ((!PageAnon(page) || PageSwapCache(page)) && page_test_dirty(page)) {
 		page_clear_dirty(page);
 		set_page_dirty(page);
 	}
-		if (PageAnon(page))
+	if (PageAnon(page)) {
 		mem_cgroup_uncharge_page(page);
-		__dec_zone_page_state(page,
-			PageAnon(page) ? NR_ANON_PAGES : NR_FILE_MAPPED);
+		__dec_zone_page_state(page, NR_ANON_PAGES);
+	} else {
+		__dec_zone_page_state(page, NR_FILE_MAPPED);
+	}
 	mem_cgroup_update_mapped_file_stat(page, -1);
 	/*
 	 * It would be tidy to reset the PageAnon mapping here,
@@ -766,7 +770,6 @@ void page_remove_rmap(struct page *page)
 	 * Leaving it set also helps swapoff to reinstate ptes
 	 * faster for those pages still in swapcache.
 	 */
-	}
 }
 
 /*