>> So, after several hours top still shows >500MB.  Will it ever go back
>> down to the level reported by vm-parameters [1,2 or 3]?
>
> I'm not sure.  It all depends on the useMmap variable in the linux vm.  If
> it is non-zero then a cursory reading of the source says that yes, the
> memory should be returned.

It appears Igor is right.  Even if I just do:

Y:=String new: 550000000.

and then:

Y:=nil

nothing I do other than rebooting the image seems to recover that
memory for other processes.  But rebooting the image is not an option
for a 24x7 server.

I hope this can be fixed because it really neuters Squeak's ability to
outshine other systems by its flexibility.