Recently I ran into a maze around mbinit().  It calls two
pool_init()s, one for mbpool and another for mclpool.  The two pools
are prepared distictly.  The latter is bound with dedicated memory
allocators, mclpool_alloc() and mclpool_free().

NetBSD/alpha and NetBSD/mips (and probably NetBSD/sh3) leave mb_map
global variable to have NULL.  For such the ports the invocation of
mclpool_alloc() callback would bring NULL pointer reference in
uvm_km_kmemalloc().  This is what I experienced with my own
DECstation kernel.   My Q is the reason why the two pools are managed
differently and the correct solution for my trouble.

Tohru Nishimura