Locks a page or range of pages in memory. The specified virtual
    pages are forced into the working set and then locked in memory.
    A locked page is not swapped out of memory if the working set of
    the process is swapped out. These pages are not candidates for
    page replacement and in this sense are locked in the working set
    as well.

    Format

      SYS$LCKPAG  inadr ,[retadr] ,[acmode]

    C Prototype

      int sys$lckpag  (struct _va_range *inadr, struct _va_range

                      *retadr, unsigned int acmode);