@bpr never duplicated that problem, even on Ubuntu14. Things are fine on my MacAir, and on a Centos7 machine at work. But the Ubuntu14 machines at work have this strange behavior -- except they seem fine when my Nim program is run in serial mode.
Part of the problem was me. I had work-arounds in the the threadpool library which had a strange effect with araq's new code. Without those work-arounds, virtual memory is stable, but runtime is still horrible on the Ubuntu14 virtual machines. So I can't explain it, but I guess it's something with the set-up at work.
