diff -r 97ebdb192b00 -r 6493f0a567c2 mercurial/localrepo.py
--- a/mercurial/localrepo.py	Sun Apr 05 18:32:46 2020 +0200
+++ b/mercurial/localrepo.py	Tue Apr 14 02:45:05 2020 +0200
@@ -937,6 +937,8 @@
         options[b'exp-persistent-nodemap'] = True
     if ui.configbool(b'experimental', b'exp-persistent-nodemap.mmap'):
         options[b'exp-persistent-nodemap.mmap'] = True
+    epnm = ui.config(b'experimental', b'exp-persistent-nodemap.mode')
+    options[b'exp-persistent-nodemap.mode'] = epnm
     if ui.configbool(b'devel', b'persistent-nodemap'):
         options[b'devel-force-nodemap'] = True