deletes the mappings for the specified address range,
and causes further references to addresses within the range
to generate invalid memory references.
Upon successful completion,
Otherwise, a value of \-1 is returned and
is set to indicate the error.
will fail if:
parameter was not page aligned,
specify a region that would extend beyond the end of the address space,
or some part of the region being unmapped is not part of the currently
valid address space.