Function mi_win_virtual_alloc

3rd/mimalloc-2.0.9/src/os.c:430–463

}

static void* mi_win_virtual_alloc(void* addr, size_t size, size_t try_alignment, DWORD flags, bool large_only, bool allow_large, bool* is_large) {
  mi_assert_internal(!(large_only && !allow_large));
  static _Atomic(size_t) large_page_try_ok; // = 0;
  void* p = NULL;
  // Try to allocate large OS pages (2MiB) if allowed or required.
  if ((large_only || use_large_os_page(size, try_alignment))
      && allow_large && (flags&MEM_COMMIT)!=0 && (flags&MEM_RESERVE)!=0) {
    size_t try_ok = mi_atomic_load_acquire(&large_page_try_ok);
    if (!large_only && try_ok > 0) {
      // if a large page allocation fails, it seems the calls to VirtualAlloc get very expensive.
      // therefore, once a large page allocation failed, we don't try again for `large_page_try_ok` times.
      mi_atomic_cas_strong_acq_rel(&large_page_try_ok, &try_ok, try_ok - 1);
    }
    else {
      // large OS pages must always reserve and commit.
      *is_large = true;
      p = mi_win_virtual_allocx(addr, size, try_alignment, flags | MEM_LARGE_PAGES);
      if (large_only) return p;
      // fall back to non-large page allocation on error (`p == NULL`).
      if (p == NULL) {
        mi_atomic_store_release(&large_page_try_ok,10UL);  // on error, don't try again for the next N allocations
      }
    }
  }
  // Fall back to regular page allocation
  if (p == NULL) {
    *is_large = ((flags&MEM_LARGE_PAGES) != 0);
    p = mi_win_virtual_allocx(addr, size, try_alignment, flags);
  }
  if (p == NULL) {
    _mi_warning_message("unable to allocate OS memory (%zu bytes, error code: 0x%x, address: %p, alignment: %zu, flags: 0x%x, large only: %d, allow large: %d)\n", size, GetLastError(), addr, try_alignment, flags, large_only, allow_large);
  }
  return p;
}

/* -----------------------------------------------------------
  Raw allocation using `sbrk` or `wasm_memory_grow`