diff -r 9695aca1a3a0 -r 9a3e88d4a030 mercurial/extensions.py
--- a/mercurial/extensions.py	Mon May 22 08:49:34 2017 -0700
+++ b/mercurial/extensions.py	Mon May 22 00:51:56 2017 -0700
@@ -179,8 +179,10 @@
                 raise
             extsetup() # old extsetup with no ui argument
 
-def loadall(ui):
+def loadall(ui, whitelist=None):
     result = ui.configitems("extensions")
+    if whitelist:
+        result = [(k, v) for (k, v) in result if k in whitelist]
     newindex = len(_order)
     for (name, path) in result:
         if path: