--- a/mercurial/revlogutils/deltas.py	Thu Nov 23 01:13:40 2023 +0100
+++ b/mercurial/revlogutils/deltas.py	Thu Nov 23 01:28:30 2023 +0100
@@ -776,6 +776,9 @@
                     tested.add(rev)
                     continue
                 # filter out delta base that will never produce good delta
+                #
+                # if the delta of that base is already bigger than the limit
+                # for the delta chain size, doing a delta is hopeless.
                 if deltas_limit < self.revlog.length(rev):
                     tested.add(rev)
                     continue