vmscan: fix it to take care of nodemask

try_to_free_pages() is used for the direct reclaim of up to
SWAP_CLUSTER_MAX pages when watermarks are low.  The caller to
alloc_pages_nodemask() can specify a nodemask of nodes that are allowed to
be used but this is not passed to try_to_free_pages().  This can lead to
unnecessary reclaim of pages that are unusable by the caller and int the
worst case lead to allocation failure as progress was not been make where
it is needed.

This patch passes the nodemask used for alloc_pages_nodemask() to
try_to_free_pages().

Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.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>
diff --git a/fs/buffer.c b/fs/buffer.c
index 0c14f8d..c77b848 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -290,7 +290,7 @@
 						&zone);
 		if (zone)
 			try_to_free_pages(node_zonelist(nid, GFP_NOFS), 0,
-						GFP_NOFS);
+						GFP_NOFS, NULL);
 	}
 }