enforce mem limits or support vmem

5.15: adda/mem'mgt/enforce limits or support vmem:
. how to handle the situation where
a process may use too much memory ?
how do we set limits ?
. if a subprogram has a large job,
it might get a warning exception
and its exception handler for that
wants to offer to OS some reassurance:
just like it should be telling user how far along the job is,
each subprogram needs to declare a
max memory usage intention,
or know of the default max,
or handle the max'd-mem.exception
with a percentage of work done .

. another strategy for avoiding memory limits
is to implement our own virtual memory,
so that unused local heaps can be stored ....
. the c heap provides only a finite virtual memory:
each process may have a 4gb vmem limit .
. so, we need to get around this limit
by using files to store our memory;
then we only need to keep an eye on harddisk limits .