#include <sys/mman.h>

mmap in use

  // the -1 could be a file descriptor instead                           here
  //                                        PROT_EXEC also                **
  void * vsbase = mmap(NULL, orig_size, PROT_READ | PROT_WRITE, MAP_ANON, -1, 0);
  if (vsbase == MAP_FAILED)
  { perror("memory::allocate: mmap failed");
    exit(1); }

  long long int ibase = (long long int) vsbase; 
  if (ibase & (sizeof(cons_cell) - 1) != 0)
  { fprintf(stderr, "Warning: base address %016llX not properly aligned\n", vsbase);
    ibase = (ibase + sizeof(cons_cell) - 1) & ~ (sizeof(cons_cell) - 1);
    num_cells -= 1; }
  cells = (cons_cell *) ibase;
  printf("cells = %lld\n", cells);

  for (ulli i = 0; i < num_cells; i += 1)
    cells[i].cdr = (ulli) (cells + i + 1);
  cells[num_cells - 1].cdr = 0;
  first_free = cells;
  printf("allocate, first_free = %lld\n", first_free); }    

giving it back

  int r = munmap(vsbase, orig_size);
  if (r < 0)
    ... error ...

also

  madvise(vsbase, orig_size, behaviour);

  behaviour is one of
    MADV_RANDOM        no prefetch
    MADV_SEQUENTIAL    deprioritise previous page
    MADV_WILLNEED      increase priority
    MADV_DONTNEED      opposite
    and others