This parameter has no effect on NFS or ZFS file systems.
0 to MAXUINT (no maximum)
Yes, this parameter can be changed at any time.
If performance problems occur with caching small directories, then increase dnlc_dir_min_size. Note that individual file systems might have their own range limits for caching directories. For instance, UFS limits directories to a minimum of ufs_min_dir_cache bytes (approximately 1024 entries), assuming 16 bytes per entry.