diff -r 0c4efb6eb4fa -r c16fe77e340a mercurial/copies.py
--- a/mercurial/copies.py	Tue Oct 08 04:28:23 2019 -0400
+++ b/mercurial/copies.py	Thu Oct 10 03:49:33 2019 +0200
@@ -162,7 +162,11 @@
 
 def _tracefile(fctx, am, basemf, limit):
     """return file context that is the ancestor of fctx present in ancestor
-    manifest am, stopping after the first ancestor lower than limit"""
+    manifest am
+
+    Note: we used to try and stop after a given limit, however checking if that
+    limit is reached turned out to be very expensive. we are better off
+    disabling that feature."""
 
     for f in fctx.ancestors():
         path = f.path()
@@ -170,8 +174,6 @@
             return path
         if basemf and basemf.get(path, None) == f.filenode():
             return path
-        if not f.isintroducedafter(limit):
-            return None
 
 
 def _dirstatecopies(repo, match=None):