void add(long sizeInBytes, File reserveFile) {
      internalMap.computeIfAbsent(sizeInBytes, key -> new ConcurrentLinkedQueue<>()).add(reserveFile);
    }
Add a file of the specified file size to the reserve file map.
@param sizeInBytes the size of the reserve file
@param reserveFile the reserve file to add.
ambry-store/src/main/java/com/github/ambry/store/DiskSpaceAllocator.java