> >   Rebooting with the same kernel as before?  Hm, sounds like something
> >    not being properly initialised, perhaps. What if you reboot a few more
> >    times and try each time?

After a reboot, the problem is not recurring.  Last time, it was pretty much
immediate.  (However, the out-of-swap-space condition which sparked the
previous reboot could plausibly have been due to nanosleeping processes
accumulating, and in that case my system had been up for a few months.)