[PATCH 5 of 5] manifest: increase lrucache from 3 to 4

[Durham Goode]

# HG changeset patch
# User Durham Goode <durham at fb.com>
# Date 1384216512 28800
#      Mon Nov 11 16:35:12 2013 -0800
# Node ID 8df5693d385b21487fc08c98456219d07074d950
# Parent  bd7f7d542d7417d2784b577d3e9a7a55476e5f54
manifest: increase lrucache from 3 to 4

During a commit amend there are 4 manifests being handled:

- original commit
- temporary commit
- amended commit
- merge base

This causes a manifest cache miss which hurts perf on large repos. On a large
repo, this fix causes amend to go from 5.3 seconds to 4.8 seconds.

diff --git a/mercurial/manifest.py b/mercurial/manifest.py
--- a/mercurial/manifest.py
+++ b/mercurial/manifest.py
@@ -31,7 +31,7 @@
 class manifest(revlog.revlog):
     def __init__(self, opener):
         # we expect to deal with not more than three revs at a time in merge
-        self._mancache = util.lrucachedict(3)
+        self._mancache = util.lrucachedict(4)
         revlog.revlog.__init__(self, opener, "00manifest.i")
 
     def parse(self, lines):