What are the ramifications of increasing NGROUPS?

[Karl Kleinpaste]

I have a small research project in mind which will require the
possibility for much larger NGROUPS values on my systems than seem
typical.  Currently, I am looking at Suns, HPs, Pyramids, and Encore
MultiMaxen (Umax, not Mach) for this; the Suns and Multimax have
NGROUPS #defined as 8, whereas the HPs and Pyramids use 20.

I am inclined to send NGROUPS up quite a ways, possibly to 100 or
higher.  If one assumes that I have all sources to everything required
(not yet a true statement; but by the time I get around to doing
something about this, it should be), am I doing the necessary and
sufficient thing by merely editing <sys/param.h> and recompiling The
World?  Can I get away with recompiling just the kernel and
/bin/login?

I have never examined the implementation of BSD's multiple groups
concept closely; this is my first serious approach to this area.

--Karl