Now that I know this is an i386 specific thing (somewhat ;)..

I set NKPDE to 32 in ..i386/include/pmap.h, but it didn't seem to help
(or maybe I'm asking for too much).  Anyway, the command that crashes the
system is

 dd if=/dev/rsd1e of=/dev/null bs=4194304 count=100

This happens on a P120 with 32 MB RAM, two 1-gig SCSI disks and one 1-gig
IDE disk.  bs=2MB works ok.

Any ideas?

  -jm

P.S. Completely unrelated, my Turbo TC-400 serial card driver seems to
     work.  I haven't run any extensive tests so far.  The driver is
     based on the ast driver (both cards have 4 serial ports).  If anyone
     wants to test the driver, please e-mail to jmarin@jmp.fi.  Thanks.