G1CardLiveData::bm_word_t* G1CardLiveData::allocate_large_bitmap(size_t size_in_bits) {
  size_t size_in_words = BitMap::calc_size_in_words(size_in_bits);

  bm_word_t* map = MmapArrayAllocator<bm_word_t, mtGC>::allocate(size_in_words);

  return map;
}

void G1CardLiveData::free_large_bitmap(bm_word_t* bitmap, size_t size_in_bits) {
  MmapArrayAllocator<bm_word_t, mtGC>::free(bitmap, size_in_bits / BitsPerWord);
}

The calculation of the number of elements in free_large_bitmap() is different to the one of allocate_large_bitmap().

The calculation itself is correct, as size_in_bits is always word aligned for all callers.