The munmap function unmaps a mapped file or shared memory region.

    The addr and len arguments specify the address and length, in
    bytes, respectively, of the region to be unmapped.

    The len argument must be a multiple of the page size as returned
    by sysconf(_SC_PAGE_SIZE); otherwise, the length of the region is
    rounded up to the next multiple of the page size.

    The result of using an address that lies in an unmapped region
    and not in any subsequently mapped region is undefined.

    See also sysconf.