page_daemon problem

Hi,

today my laptop started hanging. after investigating on the console, i
could isolate this problem:

whatever i do, the load keeps growing and the machine stops responding a
few minutes(sometimes 10 or 20) after booting with this message:

swap_pager: indefinite wait buffer: device: ad0s1b, blkno: 352, size
4096.

when running top before the hang, it shows page_daemon taking all CPU.
right before the first "swap_pager" message, top stops refreshing, then
"swap_pager" message keeps appearing every 20 seconds approx. i can't do
anything (keyboard doesn't respond, nor acpi power switch) but switching
off the machine.

KERNEL, dmesg can be found at:
www.deep-ocean.net/~olive/freebsd/syrenna/

my last cvsup && world is:

FreeBSD syrenna.deep-ocean.local 5.1-CURRENT FreeBSD 5.1-CURRENT #5: Fri
Jun 27 21:32:09 CEST 2003    
root_at_syrenna.deep-ocean.local:/usr/obj/usr/src/sys/SYRENNA  i386

do you have any hints or advice on how to avoid this problem ? how can i
investigate further in order to provide more efficient info for you ?

regards,

Olivier