diff -r 3cfcbb219496 -r 059c99af141d mercurial/configitems.py
--- a/mercurial/configitems.py	Tue Apr 14 04:08:46 2020 +0200
+++ b/mercurial/configitems.py	Tue Apr 14 03:20:21 2020 +0200
@@ -663,9 +663,6 @@
     b'experimental', b'rust.index', default=False,
 )
 coreconfigitem(
-    b'experimental', b'exp-persistent-nodemap.mmap', default=True,
-)
-coreconfigitem(
     b'experimental', b'exp-persistent-nodemap.mode', default=b'compat',
 )
 coreconfigitem(
@@ -1082,6 +1079,10 @@
     default=True,
     alias=[(b'format', b'aggressivemergedeltas')],
 )
+# experimental as long as rust is experimental (or a C version is implemented)
+coreconfigitem(
+    b'storage', b'revlog.nodemap.mmap', default=True, experimental=True
+)
 coreconfigitem(
     b'storage', b'revlog.reuse-external-delta', default=True,
 )