long getFreeFragmentMemory() {
    long result = 0;
    for (Fragment f : fragmentList) {
      int freeSpace = f.freeSpace();
      if (freeSpace >= OffHeapStoredObject.MIN_CHUNK_SIZE) {
        result += freeSpace;
      }
    }
    return result;
  }
If addr is in the free space of a fragment then return that fragment; otherwise return null.
geode-core/src/main/java/org/apache/geode/internal/offheap/FreeListManager.java