[wahern]

The red-black tree implementation typically used in *BSD development, <sys/tree.h>, is an intrusive data structure; tree nodes are embedded within the object you must dereference for key comparison. There's no need to optimize fanout because you've entirely removed that extra indirection.

As a general purpose data structure implementation for systems development, <sys/tree.h> is quite nice. However, for any particular task you can always optimize the data structure, or choose an entirely different data structure, to better fit the problem. Which is perhaps why the Linux kernel has so many different tree and hash implementations.