diff -r a0f2641ddd61 -r 875d2af8cb4e mercurial/configitems.py
--- a/mercurial/configitems.py	Sat Dec 01 15:57:27 2018 +0100
+++ b/mercurial/configitems.py	Fri Nov 23 06:07:33 2018 +0100
@@ -544,9 +544,6 @@
 coreconfigitem('experimental', 'mergetempdirprefix',
     default=None,
 )
-coreconfigitem('experimental', 'mmapindexthreshold',
-    default=None,
-)
 coreconfigitem('experimental', 'narrow',
     default=False,
 )
@@ -978,6 +975,10 @@
 coreconfigitem('push', 'pushvars.server',
     default=False,
 )
+coreconfigitem('storage', 'mmap-threshold',
+    default=None,
+    alias=[('experimental', 'mmapindexthreshold')],
+)
 coreconfigitem('storage', 'new-repo-backend',
     default='revlogv1',
 )