--- a/src/backend/storage/smgr/smgr.c
+++ b/src/backend/storage/smgr/smgr.c
@@ -742,14 +742,16 @@ smgrreadv(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
  * Compared to smgrreadv(), more responsibilities fall on the caller:
  * - Partial reads need to be handled by the caller re-issuing IO for the
  *   unread blocks
  * - smgr will ereport(LOG_SERVER_ONLY) some problems, but higher layers are
  *   responsible for pgaio_result_report() to mirror that news to the user (if
  *   the IO results in PGAIO_RS_WARNING) or abort the (sub)transaction (if
  *   PGAIO_RS_ERROR).
+ * - Under Valgrind, the "buffers" memory may or may not change status to
+ *   DEFINED, depending on io_method and concurrent activity.
  */
 void
 smgrstartreadv(PgAioHandle *ioh,