Brief freezes with -current as of early last week

After updating from -current built on 2004/04/27 to -current built on
2004/09/13, I'm seeing some annoying 'freezes'.  I'd not seen these with
the earlier -current.

To complicate matters, right around the time I did the update I also
switched from a configuration with two SCSI disks and an IDE disk, to a
configuration with two IDE disks (each SCSI disk, bought at the same
time, from the same supplier, died within 4 days of each other --
sheesh).

So, I guess what I might be seeing is plain old I/O contention --
although I'm surprised that it freezes the box.  According to
'atacontrol mode 0', both IDE devices are using UDMA100, which is the
maximum the motherboard (dual 1GHz PIII) supports).

The symptoms typically manifest themselves right after kicking off a
portupgrade command.  The system will (sort-of) freeze.  If I'm in X,
the mouse cursor stops responding, there's no response to the keyboard.
However, if I happen to have top(1) running in an xterm, the top(1)
display keeps updating.  This lasts (wall-clock) 10 to 15 seconds, and
then the system becomes responsive again.

I'm running a kernel built with SCHED_4BSD.  INVARIANTS,
INVARIANTS_SUPPORT, WITNESS, and WITNESS_SKIPSPIN are all commented out.
I don't have an /etc/malloc.conf symlink, so I'm using whatever the
-current defaults are (as a side note, where are those defaults
documented?)

Any thoughts, or recommendations to help tracking this down greatly
appreciated.

N
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