0 (disabled) or 1 (enabled)
Yes, but do not change this tunable dynamically. You can enable this parameter if it was originally disabled. Or, you can disable this parameter if it was originally enabled. However, enabling, disabling, and then enabling this parameter might lead to stale directory caches.
Directory caching has no known problems. However, if problems occur, then set dnlc_dir_enable to 0 to disable caching.