I just upgraded the kernel of an i386 box from
NetBSD 1.6ZH (QUARTZ) #380: Tue Jan 20 11:50:29 GMT 2004
to
NetBSD 1.6ZI (QUARTZ) #382: Tue Feb  3 16:49:50 GMT 2004

and it is now so slow as to be practically unusable (eg overnight small
database dump took 1h10m instead of 10m, I can watch the delay in the
characters appearing - it is as if I were on a slow modem rather than
on a keyboard plugged in the back).

It has 2Gb memory, the idea being that the database can essentially sit
in the file cache.

I tried doubling bufmem_hiwater to
  vm.bufmem_hiwater = 643891200
and increasing filemax to
  vm.filemax = 80
but that didn't achieve much.
It already had
  kern.maxvnodes = 262144

Memory: 1115M Act, 558M Inact, 3708K Wired, 17M Exec, 1543M File, 1172K Free
Swap: 397M Total, 397M Free
   10 root     -18    0     0K  315M pgdaemon   8:35  4.98%  4.98% [pagedaemon]
is in at number 3 in top and
   11 root      18    0     0K  315M syncer    20:55  0.88%  0.88% [ioflush]
is not far behind.

The filesystems are mounted with softdeps, and the kernel does not have
NEW_BUFQ_STRATEGY defined.

Any options other than returning to netbsd.old?

Cheers,

Patrick