Number of lstat and stat syscalls for each 'require'd file is doubled, because rb_realpath_internal is called from two places with the same arguments in require_internal; once for checking the realpaths cache, and once in load_iseq_eval when iseq is not found. Introduce rb_realpath_internal_cached function to reuse the realpath_map cache which memoizes rb_realpath_internal function, leading to less syscalls and increased startup performance depending on the cost of the syscalls in a particular environment.