public long getAllocatedSizeUnSync() {
   long sum = 0;
   for (PowerOfTwoAllocator a : sliceAllocators) {
     sum += a.occupied();
   }
   return sum;
 }
 public synchronized long getAllocatedSize() {
   long sum = 0;
   for (PowerOfTwoAllocator a : sliceAllocators) {
     sum += a.occupied();
   }
   return sum;
 }