session_save_path() returns the path of the current directory used to save session data. If path is specified, the path to which data is saved will be changed. session_save_path() needs to be called before session_start() for that purpose.
Note: On some operating systems, you may want to specify a path on a filesystem that handles lots of small files efficiently. For example, on Linux, reiserfs may provide better performance than ext2fs.
See also the session.save_path configuration directive.