[PATCH] nogc: do disable gc for CPython

[Jun Wu]

# HG changeset patch
# User Jun Wu <quark at fb.com>
# Date 1495570793 25200
#      Tue May 23 13:19:53 2017 -0700
# Node ID 66dc3a3b4631507fed3ea7fd2fa3e3356ea820fe
# Parent  34e9b8b94f66db7ebe366f67cea7b64bd0ec6968
# Available At https://bitbucket.org/quark-zju/hg-draft
#              hg pull https://bitbucket.org/quark-zju/hg-draft -r 66dc3a3b4631
nogc: do disable gc for CPython

279cd8 makes util.nogc a no-op for Python >= 2.7. That's actually hurting
performance. For example, _fm1readmarkers takes 70ms with gc disabled, 190ms
with gc enabled.

This patch makes util.nogc effective for CPython and only a no-op for PyPy.

diff --git a/mercurial/util.py b/mercurial/util.py
--- a/mercurial/util.py
+++ b/mercurial/util.py
@@ -910,9 +910,5 @@ def nogc(func):
     into. As a workaround, disable GC while building complex (huge)
     containers.
-
-    This garbage collector issue have been fixed in 2.7.
     """
-    if sys.version_info >= (2, 7):
-        return func
     def wrapper(*args, **kwargs):
         gcenabled = gc.isenabled()
@@ -925,4 +921,9 @@ def nogc(func):
     return wrapper
 
+if pyplatform.python_implementation() != 'CPython':
+    # PyPy becomes slower with gc disabled
+    def nogc(func):
+        return func
+
 def pathto(root, n1, n2):
     '''return the relative path from one place to another.