xfs: bump up nr_to_write in xfs_vm_writepage

VM calculation for nr_to_write seems off.  Bump it way
up, this gets simple streaming writes zippy again.
To be reviewed again after Jens' writeback changes.
Signed-off-by: NChristoph Hellwig <hch@infradead.org>
Signed-off-by: NEric Sandeen <sandeen@sandeen.net>
Cc: Chris Mason <chris.mason@oracle.com>
Reviewed-by: NFelix Blyakher <felixb@sgi.com>
Signed-off-by: NFelix Blyakher <felixb@sgi.com>

fs/xfs/linux-2.6/xfs_aops.c

@@ -1268,6 +1268,14 @@ xfs_vm_writepage(
 	if (!page_has_buffers(page))
 		create_empty_buffers(page, 1 << inode->i_blkbits, 0);
 
+
+	/*
+	 *  VM calculation for nr_to_write seems off.  Bump it way
+	 *  up, this gets simple streaming writes zippy again.
+	 *  To be reviewed again after Jens' writeback changes.
+	 */
+	wbc->nr_to_write *= 4;
+
 	/*
 	 * Convert delayed allocate, unwritten or unmapped space
 	 * to real space and flush out to disk.