QDirModel is not mentioned here:
http://developer.qt.nokia.com/doc/qt-4.8/qfilesystemmodel.html#caching-and-performance
but it is here:
http://doc.qt.nokia.com/4.8-snapshot/qfilesystemmodel.html#caching-and-performance
http://thread.gmane.org/gmane.comp.lib.qt.user/660