writeback: send work item to queue_io, move_expired_inodes

Instead of sending ->older_than_this to queue_io() and
move_expired_inodes(), send the entire wb_writeback_work
structure.  There are other fields of a work item that are
useful in these routines and in tracepoints.

Acked-by: Jan Kara <jack@suse.cz>
Signed-off-by: Curt Wohlgemuth <curtw@google.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 6401cd7..c510296 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -251,7 +251,7 @@
  */
 static int move_expired_inodes(struct list_head *delaying_queue,
 			       struct list_head *dispatch_queue,
-			       unsigned long *older_than_this)
+			       struct wb_writeback_work *work)
 {
 	LIST_HEAD(tmp);
 	struct list_head *pos, *node;
@@ -262,8 +262,8 @@
 
 	while (!list_empty(delaying_queue)) {
 		inode = wb_inode(delaying_queue->prev);
-		if (older_than_this &&
-		    inode_dirtied_after(inode, *older_than_this))
+		if (work->older_than_this &&
+		    inode_dirtied_after(inode, *work->older_than_this))
 			break;
 		if (sb && sb != inode->i_sb)
 			do_sb_sort = 1;
@@ -302,13 +302,13 @@
  *                                           |
  *                                           +--> dequeue for IO
  */
-static void queue_io(struct bdi_writeback *wb, unsigned long *older_than_this)
+static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work)
 {
 	int moved;
 	assert_spin_locked(&wb->list_lock);
 	list_splice_init(&wb->b_more_io, &wb->b_io);
-	moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, older_than_this);
-	trace_writeback_queue_io(wb, older_than_this, moved);
+	moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, work);
+	trace_writeback_queue_io(wb, work, moved);
 }
 
 static int write_inode(struct inode *inode, struct writeback_control *wbc)
@@ -651,7 +651,7 @@
 
 	spin_lock(&wb->list_lock);
 	if (list_empty(&wb->b_io))
-		queue_io(wb, NULL);
+		queue_io(wb, &work);
 	__writeback_inodes_wb(wb, &work);
 	spin_unlock(&wb->list_lock);
 
@@ -745,7 +745,7 @@
 
 		trace_writeback_start(wb->bdi, work);
 		if (list_empty(&wb->b_io))
-			queue_io(wb, work->older_than_this);
+			queue_io(wb, work);
 		if (work->sb)
 			progress = writeback_sb_inodes(work->sb, wb, work);
 		else