diff -r c089a0947f3e -r f7459da77f23 mercurial/localrepo.py
--- a/mercurial/localrepo.py	Fri Feb 14 15:03:26 2020 +0100
+++ b/mercurial/localrepo.py	Tue Feb 11 11:18:52 2020 +0100
@@ -934,6 +934,8 @@
         options[b'rust.index'] = True
     if ui.configbool(b'experimental', b'exp-persistent-nodemap'):
         options[b'exp-persistent-nodemap'] = True
+    if ui.configbool(b'experimental', b'exp-persistent-nodemap.mmap'):
+        options[b'exp-persistent-nodemap.mmap'] = True
     if ui.configbool(b'devel', b'persistent-nodemap'):
         options[b'devel-force-nodemap'] = True