start adding the tag to iov_iter

For now, just use the same thing we pass to ->direct_IO() - it's all
iovec-based at the moment.  Pass it explicitly to iov_iter_init() and
account for kvec vs. iovec in there, by the same kludge NFS ->direct_IO()
uses.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/mm/page_io.c b/mm/page_io.c
index 0ed0644..313bfed 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -268,7 +268,7 @@
 		init_sync_kiocb(&kiocb, swap_file);
 		kiocb.ki_pos = page_file_offset(page);
 		kiocb.ki_nbytes = PAGE_SIZE;
-		iov_iter_init(&from, &iov, 1, PAGE_SIZE, 0);
+		iov_iter_init(&from, KERNEL_WRITE, &iov, 1, PAGE_SIZE);
 
 		set_page_writeback(page);
 		unlock_page(page);