> 
> this is basically a result of the Mach vm object design.   memory objects
> (files, devices, and in this case anonymous memory) have no idea how
> much of their range is mapped and how much us unmapped.   for files
> this isn't a problem because we can just write out (or toss) unused pages
> to backing store and be done with it.   but anonymous memory is backed
> by swap, thus we have to write it out to swap.    if you keep doing this
> sort of thing swap will eventually fill up.
> 
> 
> if this is indeed the problem, i'd like to use it as a practical example
> for my writeup on the uvm stuff.
> 
Fixed in FreeBSD-current.  Minor work-around fix for now.  It'll be a
few days before I determine that this is sufficient for all cases.  Tested
with your example, no problems.

John