int getCount(long sizeInBytes) {
      Queue<File> reserveFilesForSize = internalMap.get(sizeInBytes);
      return reserveFilesForSize != null ? reserveFilesForSize.size() : 0;
    }
@param sizeInBytes the size of files of interest
@return the number of files in the map of size {@code sizeInBytes}
ambry-store/src/main/java/com/github/ambry/store/DiskSpaceAllocator.java