mm: remove SWAP_MLOCK in ttu

ttu doesn't need to return SWAP_MLOCK.  Instead, just return SWAP_FAIL
because it means the page is not-swappable so it should move to another
LRU list(active or unevictable).  putback friends will move it to right
list depending on the page's LRU flag.

Link: http://lkml.kernel.org/r/1489555493-14659-6-git-send-email-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/rmap.c

@@ -1329,7 +1329,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 					 */
 					mlock_vma_page(page);
 				}
-				ret = SWAP_MLOCK;
+				ret = SWAP_FAIL;
 				page_vma_mapped_walk_done(&pvmw);
 				break;
 			}
@@ -1506,7 +1506,6 @@ static int page_mapcount_is_zero(struct page *page)
  * SWAP_SUCCESS	- we succeeded in removing all mappings
  * SWAP_AGAIN	- we missed a mapping, try again later
  * SWAP_FAIL	- the page is unswappable
- * SWAP_MLOCK	- page is mlocked.
  */
 int try_to_unmap(struct page *page, enum ttu_flags flags)
 {