Unresponsive after dtrace

[Wes Morgan]

I know this has been reported already, but I want to give a "me too". 
After installing a new world and kernel from the tree yesterday afternoon, 
I let my system run all night. This morning everything was extremely 
sluggish and unresponsive. According to top, which I thankfully left 
running, processes were going in and out of "*kmem_" (obviously 
truncated). CPU usage was 80+% system and load averages were around 5.4. 
The only changes I made to my system besides upgrading were to include the 
options KDB, DDB and STACK in my kernel for zfs functionality. 
Unfortunately, I cannot try without those options since my root is zfs. 
Booting a kernel from 8/20 works fine.