diff -r 5dfa837d933e -r 82f3ee1a505f mercurial/upgrade_utils/actions.py
--- a/mercurial/upgrade_utils/actions.py	Wed Dec 30 16:11:24 2020 +0530
+++ b/mercurial/upgrade_utils/actions.py	Wed Dec 30 16:20:25 2020 +0530
@@ -12,6 +12,7 @@
     error,
     localrepo,
     requirements,
+    revlog,
     util,
 )
 
@@ -646,6 +647,17 @@
             i for i in all_optimizations if i not in self.upgrade_actions
         ]
 
+        # delta reuse mode of this upgrade operation
+        self.delta_reuse_mode = revlog.revlog.DELTAREUSEALWAYS
+        if b're-delta-all' in self._upgrade_actions_names:
+            self.delta_reuse_mode = revlog.revlog.DELTAREUSENEVER
+        elif b're-delta-parent' in self._upgrade_actions_names:
+            self.delta_reuse_mode = revlog.revlog.DELTAREUSESAMEREVS
+        elif b're-delta-multibase' in self._upgrade_actions_names:
+            self.delta_reuse_mode = revlog.revlog.DELTAREUSESAMEREVS
+        elif b're-delta-fulladd' in self._upgrade_actions_names:
+            self.delta_reuse_mode = revlog.revlog.DELTAREUSEFULLADD
+
     def _write_labeled(self, l, label):
         """
         Utility function to aid writing of a list under one label