It's reasonably visible in low-memory systems.  I think someone explained
that the rule was something like "if a process which is partially paged
out exits and the parent process is also at least partially paged out,
the child process's pages are not reclaimed".  It was arcane.

Our system used to crash or need a reboot about every 3 days, with 8 megs
of memory, and comfortably goes for 2 weeks, with 16.  Symptom: swap
space runs out.

-s