private RegularFile createBlockCache(int maxCachedBlockCount) {
    // This file is just for holding blocks so things like the creation time don't matter
    return new RegularFile(
        -1,
        SystemFileTimeSource.INSTANCE.now(),
        this,
        new byte[Math.min(maxCachedBlockCount, 8192)][],
        0,
        0);
  }
Returns the nearest multiple of {@code blockSize} that is <= {@code size}.
jimfs/src/main/java/com/google/common/jimfs/HeapDisk.java