boolean isAdjacent(long lowAddr, int lowSize, long highAddr) {
    return (lowAddr + lowSize) == highAddr;
  }
Returns true if the area if memory (starting at lowAddr and extending to lowAddr+lowSize) is
right before (i.e. adjacent) to highAddr.
geode-core/src/main/java/org/apache/geode/internal/offheap/FreeListManager.java