swap: clean-up #ifdef in page_mapping()

PageSwapCache() is always false when !CONFIG_SWAP, so compiler
properly discard related code. Therefore, we don't need #ifdef explicitly.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
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>

include/linux/swap.h

@@ -447,6 +447,7 @@ mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout)
 
 #else /* CONFIG_SWAP */
 
+#define swap_address_space(entry)		(NULL)
 #define get_nr_swap_pages()			0L
 #define total_swap_pages			0L
 #define total_swapcache_pages()			0UL

mm/util.c

@@ -388,15 +388,12 @@ struct address_space *page_mapping(struct page *page)
 	struct address_space *mapping = page->mapping;
 
 	VM_BUG_ON(PageSlab(page));
-#ifdef CONFIG_SWAP
 	if (unlikely(PageSwapCache(page))) {
 		swp_entry_t entry;
 
 		entry.val = page_private(page);
 		mapping = swap_address_space(entry);
-	} else
-#endif
-	if ((unsigned long)mapping & PAGE_MAPPING_ANON)
+	} else if ((unsigned long)mapping & PAGE_MAPPING_ANON)
 		mapping = NULL;
 	return mapping;
 }