Take advantage of fstat calls clustering per directory if OS support it. util module implements two versions of statfiles function _statfiles calls lstat per file _statfiles_clustered takes advantage of optimizations in osutil.c, stats all files in directory at once when new directory is hit and caches the results util.statfiles dispatches to appropriate version during module loading The speedup on directory tree with 2k directories and 63k files is about factor of 1.8 (1.3s -> 0.8s for hg diff - hg startup overhead about .2s) At this point only Win32 now benefit from this patch. Rest of OSes use the non clustered implementation.