diff --git a/mm/readahead.c b/mm/readahead.c
index aa1aa23..033bc13 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -547,5 +547,17 @@
 
 	/* do read-ahead */
 	ondemand_readahead(mapping, ra, filp, true, offset, req_size);
+
+#ifdef CONFIG_BLOCK
+	/*
+	 * Normally the current page is !uptodate and lock_page() will be
+	 * immediately called to implicitly unplug the device. However this
+	 * is not always true for RAID conifgurations, where data arrives
+	 * not strictly in their submission order. In this case we need to
+	 * explicitly kick off the IO.
+	 */
+	if (PageUptodate(page))
+		blk_run_backing_dev(mapping->backing_dev_info, NULL);
+#endif
 }
 EXPORT_SYMBOL_GPL(page_cache_async_readahead);