JDK-8236073 G1: Use SoftMaxHeapSize to guide GC heuristics

*** 106,116 ****
    // considered.
  
    double safe_total_heap_percentage = MIN2((double)(_heap_reserve_percent + _heap_waste_percent), 100.0);
  
    return (size_t)MIN2(
!     G1CollectedHeap::heap()->max_capacity() * (100.0 - safe_total_heap_percentage) / 100.0,
      _target_occupancy * (100.0 - _heap_waste_percent) / 100.0
      );
  }
  
  double G1AdaptiveIHOPControl::predict(TruncatedSeq const* seq) const {
--- 106,116 ----
    // considered.
  
    double safe_total_heap_percentage = MIN2((double)(_heap_reserve_percent + _heap_waste_percent), 100.0);
  
    return (size_t)MIN2(
!     G1CollectedHeap::heap()->soft_max_capacity() * (100.0 - safe_total_heap_percentage) / 100.0,
      _target_occupancy * (100.0 - _heap_waste_percent) / 100.0
      );
  }
  
  double G1AdaptiveIHOPControl::predict(TruncatedSeq const* seq) const {
*** 185,189 ****
--- 185,194 ----
                                            _last_unrestrained_young_size,
                                            predict(&_allocation_rate_s),
                                            predict(&_marking_times_s),
                                            have_enough_data_for_prediction());
  }
+ 
+ size_t G1AdaptiveIHOPControl::predict_unrestrained_buffer_size() const {
+   // Besides the young size, the promotion bytes of Prepare Mixed and 1st Mixed GC will be counted
+   return  _last_unrestrained_young_size + _last_allocated_bytes * 2;
+ }