Set the split io size for the snapshot target.
--- diff/drivers/md/dm-snapshot.c	2003-11-26 10:18:32.000000000 +0000
+++ source/drivers/md/dm-snapshot.c	2003-11-26 10:19:11.000000000 +0000
@@ -527,6 +527,7 @@
 	}
 
 	ti->private = s;
+	ti->split_io = chunk_size;
 	return 0;
 
  bad6: