[PATCH] splice: call handle_ra_miss() on failure to lookup page

Notify the readahead logic of the missing page. Suggested by
Oleg Nesterov.
Signed-off-by: Jens Axboe <axboe@suse.de>

fs/splice.c

@@ -301,6 +301,12 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
 		 */
 		page = find_get_page(mapping, index);
 		if (!page) {
+			/*
+			 * Make sure the read-ahead engine is notified
+			 * about this failure.
+			 */
+			handle_ra_miss(mapping, &in->f_ra, index);
+
 			/*
 			 * page didn't exist, allocate one.
 			 */