armv7, silent hang, low swap, high priorities

An old (v 1.1) Pi2 running armv7 -current often hangs during buildworld.

It doesn't respond to enter-tilda-control-B and has to be powercycled.
Once rebooted, buildworld can be restarted and makes further progress,
sometimes to completion. Swap was configured in two partitions, one
on microSD and one on mechanical hard disk, thus both over-provisioned 
and wildly unequal in speed. Root is on the mechanical disk. 

An orphan top window surprised me by reporting very high priorities
in the 130 range but swap usage was relatively low, less than 100MB.
That seemed an odd combination. Usually priorities that high are
associated with severe memory pressure. Could the mismatched swap
speeds have confused the scheduler? There were no console warnings. 

The machine was fully loaded with a -j4 buildworld, so the fact of 
the hang isn't hugely surprising. The top display, at
http://www.zefox.net/~fbsd/rpi2/crashes/20241219/top_display
seemed internally inconsitent.  Does it surprise anybody else? 

I've since removed the microSD swap, leaving only the mechanical disk
swap, to see if that changes the hang behavior. 

Thanks for reading,

bob prohaska