vmstat: mlocked pages statistics

Add NR_MLOCK zone page state, which provides a (conservative) count of
mlocked pages (actually, the number of mlocked pages moved off the LRU).

Reworked by lts to fit in with the modified mlock page support in the
Reclaim Scalability series.

[kosaki.motohiro@jp.fujitsu.com: fix incorrect Mlocked field of /proc/meminfo]
[lee.schermerhorn@hp.com: mlocked-pages: add event counting with statistics]
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 135840c..05b8050 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -45,6 +45,10 @@
 		UNEVICTABLE_PGCULLED,	/* culled to noreclaim list */
 		UNEVICTABLE_PGSCANNED,	/* scanned for reclaimability */
 		UNEVICTABLE_PGRESCUED,	/* rescued from noreclaim list */
+		UNEVICTABLE_PGMLOCKED,
+		UNEVICTABLE_PGMUNLOCKED,
+		UNEVICTABLE_PGCLEARED,	/* on COW, page truncate */
+		UNEVICTABLE_PGSTRANDED,	/* unable to isolate on unlock */
 #endif
 		NR_VM_EVENT_ITEMS
 };