Unlocks pages that were previously locked in memory by the Lock
    Pages in Memory ($LCKPAG) service. Locked pages are automatically
    unlocked and deleted at image exit.

    Format

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

    C Prototype

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

                      *retadr, unsigned int acmode);