Function mi_os_claim_huge_pages

3rd/mimalloc-2.0.9/src/os.c:1244–1267

Claim an aligned address range for huge pages

// Claim an aligned address range for huge pages
static uint8_t* mi_os_claim_huge_pages(size_t pages, size_t* total_size) {
  if (total_size != NULL) *total_size = 0;
  const size_t size = pages * MI_HUGE_OS_PAGE_SIZE;

  uintptr_t start = 0;
  uintptr_t end = 0;
  uintptr_t huge_start = mi_atomic_load_relaxed(&mi_huge_start);
  do {
    start = huge_start;
    if (start == 0) {
      // Initialize the start address after the 32TiB area
      start = ((uintptr_t)32 << 40);  // 32TiB virtual start address
#if (MI_SECURE>0 || MI_DEBUG==0)      // security: randomize start of huge pages unless in debug mode
      uintptr_t r = _mi_heap_random_next(mi_get_default_heap());
      start = start + ((uintptr_t)MI_HUGE_OS_PAGE_SIZE * ((r>>17) & 0x0FFF));  // (randomly 12bits)*1GiB == between 0 to 4TiB
#endif
    }
    end = start + size;
    mi_assert_internal(end % MI_SEGMENT_SIZE == 0);
  } while (!mi_atomic_cas_strong_acq_rel(&mi_huge_start, &huge_start, end));

  if (total_size != NULL) *total_size = size;
  return (uint8_t*)start;
}
#else
static uint8_t* mi_os_claim_huge_pages(size_t pages, size_t* total_size) {
  MI_UNUSED(pages);