diff --git a/mm/readahead.c b/mm/readahead.c
index 7b05082c89ea2..770f8ecf7ef06 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -146,6 +146,17 @@ file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping)
 }
 EXPORT_SYMBOL_GPL(file_ra_state_init);
 
+/**
+ * read_pages() - Start IO for a contiguous range of allocated folios in the
+ *                page cache.
+ * @rac: Readahead control.
+ *
+ * When read_pages() returns, it is guaranteed that all of the folios will have
+ * been processed or removed so that ``readahead_count(rac) == 0``. However,
+ * that does not imply that ``readahead_index(rac)`` will be updated to point
+ * to the end of the originally requested range because, for example, the
+ * filesystem may expand the range upwards.
+ */
 static void read_pages(struct readahead_control *rac)
 {
 	const struct address_space_operations *aops = rac->mapping->a_ops;