ext4: use bio layer instead of buffer layer in mpage_da_submit_io

Call the block I/O layer directly instad of going through the buffer
layer.  This should give us much better performance and scalability,
as well as lowering our CPU utilization when doing buffered writeback.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index a0e6230..a1e20c8 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -3202,7 +3202,7 @@
 		 * completed
 		 */
 		if (io)
-			io->flag = EXT4_IO_UNWRITTEN;
+			io->flag = EXT4_IO_END_UNWRITTEN;
 		else
 			ext4_set_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN);
 		if (ext4_should_dioread_nolock(inode))
@@ -3494,7 +3494,7 @@
 		 */
 		if ((flags & EXT4_GET_BLOCKS_PRE_IO)) {
 			if (io)
-				io->flag = EXT4_IO_UNWRITTEN;
+				io->flag = EXT4_IO_END_UNWRITTEN;
 			else
 				ext4_set_inode_state(inode,
 						     EXT4_STATE_DIO_UNWRITTEN);