We've just spent almost a month chasing kernel memory corruption problems
on one of the TNF build servers.  These manifested as panics all over the
kernel, particularly in the networking code, where a pointer within a
datastructure (usually a pool-allocated structure) had been overwritten
with garbage -- upon examination, usually part of some other datastructure.

Removing UFS_DIRHASH from our kernel configuration made the problem go
away.  Though it is possible that there is an underlying problem of some
kind in one of the allocators that is simply particularly badly exposed
by UFS_DIRHASH, it seems more likely that there is a problem (which we
haven't found yet) in UFS_DIRHASH itself.  The code has a history of
similar problems on FreeBSD which seem to have ended only when the entire
kernel synchronization scheme in FreeBSD was reworked in FreeBSD 5.

I strongly recommend not using UFS_DIRHASH.

-- 
  Thor Lancelot Simon	                                     tls@rek.tjls.com

  "We cannot usually in social life pursue a single value or a single moral
   aim, untroubled by the need to compromise with others."      - H.L.A. Hart