Following vm_lowmem event handler for dirhash

Hello, hope you're having a nice day,

Following 
http://lists.freebsd.org/pipermail/freebsd-current/2009-May/007367.html

 > It adds a vm_lowmem event handler to the dirhash code in UFS2
 > so that dirhashes will be deleted when the system is low on memory.
 From what I gather, this patch is in -CURRENT now; I've updated to 
-CURRENT 3 days ago (after using a snapshot from May) and my previously 
stable system threw a kernel panic yesterday. Panic happened during a 
benchmark on my ZFS pool (bonnie++ -s 32768) supposedly because of that 
exact patch (because ZFS is known to eat a lot of kmem and vm_lowmem was 
probably triggered). Alas, I don't have a dump available (because my 
system boots from a geom mirror and the swap space is there as well), so 
I only have the panic message: "dirhash: NULL hash on list".

My system is a Core2 Duo on a Q35 motherboard, using 2GB RAM and 4x 
500GB drives, of which 2 are in a GEOM_MIRROR and the other 2 are in a 
zpool.

fujibayashi_at_ameagari ~ % uname -a
FreeBSD ameagari.fujibayashi.jp 8.0-CURRENT FreeBSD 8.0-CURRENT #0: Tue 
Jun 16 21:50:53 JST 2009     
root_at_ameagari.fujibayashi.jp:/usr/obj/usr/src/sys/Ameagari  amd64

(Last line in /usr/src/UPDATING states "20090613".)

--
Kamigishi Rei
Systems Administrator
WIDE