diff --git a/hgext3rd/perftweaks.py b/hgext3rd/perftweaks.py
--- a/hgext3rd/perftweaks.py
+++ b/hgext3rd/perftweaks.py
@@ -26,12 +26,14 @@
     util,
 )
 from mercurial.extensions import wrapfunction
-from mercurial.node import bin, nullid, nullrev
+from mercurial.node import bin, hex, nullid, nullrev
 import errno
 import os
 
 testedwith = 'ships-with-fb-hgext'
 
+cachedirname = 'noderevsmap'
+
 def extsetup(ui):
     wrapfunction(tags, '_readtagcache', _readtagcache)
     wrapfunction(merge, '_checkcollision', _checkcollision)
@@ -66,7 +68,7 @@
 
 def reposetup(ui, repo):
     if repo.local() is not None:
-        _preloadrevs(repo)
+        _preloadrevmap(repo)
 
 def _readtagcache(orig, ui, repo):
     """Disables reading tags if the repo is known to not contain any."""
@@ -114,19 +116,19 @@
 def _branchmapwrite(orig, self, repo):
     result = orig(self, repo)
     if repo.ui.configbool('perftweaks', 'cachenoderevs', True):
-        revs = set()
+        revs = {}
         nodemap = repo.changelog.nodemap
         for branch, heads in self.iteritems():
-            revs.update(nodemap[n] for n in heads)
+            revs.update((nodemap[n], n) for n in heads)
         name = 'branchheads-%s' % repo.filtername
-        _savepreloadrevs(repo, name, revs)
+        _savenoderevmap(repo, name, revs)
 
     return result
 
 def _saveremotenames(orig, repo, remotepath, branches=None, bookmarks=None):
     result = orig(repo, remotepath, branches=branches, bookmarks=bookmarks)
     if repo.ui.configbool('perftweaks', 'cachenoderevs', True):
-        revs = set()
+        revs = {}
         nodemap = repo.changelog.nodemap
         if bookmarks:
             for b, n in bookmarks.iteritems():
@@ -135,28 +137,28 @@
                 # changelog yet. It filters them internally, but we need to as
                 # well.
                 if n in nodemap:
-                    revs.add(nodemap[n])
+                    revs[nodemap[n]] = n
         if branches:
             for branch, nodes in branches.iteritems():
                 for n in nodes:
                     if n in nodemap:
-                        revs.add(nodemap[n])
+                        revs[nodemap[n]] = n
 
         name = 'remotenames-%s' % remotepath
-        _savepreloadrevs(repo, name, revs)
+        _savenoderevmap(repo, name, revs)
 
     return result
 
 def _editphases(orig, self, repo, tr, *args):
     result = orig(self, repo, tr, *args)
     def _write(fp):
-        revs = set()
+        revs = {}
         nodemap = repo.changelog.nodemap
         for phase, roots in enumerate(self.phaseroots):
             for n in roots:
                 if n in nodemap:
-                    revs.add(nodemap[n])
-        _savepreloadrevs(repo, 'phaseroots', revs)
+                    revs[nodemap[n]] = n
+        _savenoderevmap(repo, 'phaseroots', revs)
 
     # We don't actually use the transaction file generator. It's just a hook so
     # we can write out at the same time as phases.
@@ -198,42 +200,37 @@
     return True
 
 def _cachefilename(name):
-    return 'noderevs/%s' % name
+    return '/'.join((cachedirname, name))
 
-def _preloadrevs(repo):
+def _preloadrevmap(repo):
     # Preloading the node-rev map for likely to be used revs saves 100ms on
     # every command. This is because normally to look up a node, hg has to scan
     # the changelog.i file backwards, potentially reading through hundreds of
     # thousands of entries and building a cache of them.  Looking up a rev
     # however is fast, because we know exactly what offset in the file to read.
     # Reading old commits is common, since the branchmap needs to to convert old
-    # branch heads from node to rev.
+    # branch heads from node to rev.  To avoid touching the older parts of the
+    # index file, we just prepopulate the node to rev map.
 
     if repo.ui.configbool('perftweaks', 'cachenoderevs', True):
-        repo = repo.unfiltered()
-        revs = set()
-        cachedir = repo.vfs.join('cache', 'noderevs')
+        cachedir = repo.vfs.join('cache', cachedirname)
         try:
+            nodemap = repo.changelog.nodemap
+            maxrev = len(repo.changelog)
             for cachefile in os.listdir(cachedir):
                 filename = _cachefilename(cachefile)
-                revs.update(int(r) for r in repo.cachevfs(filename))
-
-            getnode = repo.changelog.node
-            nodemap = repo.changelog.nodemap
-            for r in revs:
-                try:
-                    node = getnode(r)
-                    nodemap[node] = r
-                except (IndexError, ValueError):
-                    # Rev no longer exists or rev is out of range
-                    pass
+                for line in repo.cachevfs(filename):
+                    revstr, _, node = line.partition(':')
+                    rev = int(revstr)
+                    if rev < maxrev:
+                        nodemap[bin(node.strip())] = rev
         except EnvironmentError:
             # No permission to read? No big deal
             pass
 
-def _savepreloadrevs(repo, name, revs):
+def _savenoderevmap(repo, name, revs):
     if repo.ui.configbool('perftweaks', 'cachenoderevs', True):
-        cachedir = repo.vfs.join('cache', 'noderevs')
+        cachedir = repo.vfs.join('cache', cachedirname)
         try:
             repo.vfs.mkdir(cachedir)
         except OSError as ex:
@@ -246,7 +243,8 @@
         try:
             filename = _cachefilename(name)
             f = repo.cachevfs.open(filename, mode='w+', atomictemp=True)
-            f.write('\n'.join(str(r) for r in revs))
+            for r, n in revs.iteritems():
+                f.write('%s:%s\n' % (r, hex(n)))
             f.close()
         except EnvironmentError:
             # No permission to write? No big deal
diff --git a/tests/test-perftweaks.t b/tests/test-perftweaks.t
--- a/tests/test-perftweaks.t
+++ b/tests/test-perftweaks.t
@@ -113,7 +113,7 @@
   $ cd repo
   $ touch a
   $ hg commit -qAm a
-  $ ls -la .hg/cache/noderevs/
+  $ ls -la .hg/cache/noderevsmap/
   total * (glob)
   drwxrw[sx]r-x.? [0-9]+ .* \. (re)
   drwxrw[sx]r-x.? [0-9]+ .* \.\. (re)