G1: Use SoftMaxHeapSize to guide GC heuristics

*** 677,686 ****
--- 677,689 ----
        (end_time_sec - _analytics->last_known_gc_end_time_sec()) * 1000.0;
      _analytics->update_recent_gc_times(end_time_sec, pause_time_ms);
      _analytics->compute_pause_time_ratio(interval_ms, pause_time_ms);
    }
  
+   if (collector_state()->finish_of_mixed_gc()) {
+     collector_state()->set_finish_of_mixed_gc(false);
+   }
    if (collector_state()->in_young_gc_before_mixed()) {
      assert(!this_pause_included_initial_mark, "The young GC before mixed is not allowed to be an initial mark GC");
      // This has been the young GC before we start doing mixed GCs. We already
      // decided to start mixed GCs much earlier, so there is nothing to do except
      // advancing the state.
*** 690,699 ****
--- 693,703 ----
      // This is a mixed GC. Here we decide whether to continue doing more
      // mixed GCs or not.
      if (!next_gc_should_be_mixed("continue mixed GCs",
                                   "do not continue mixed GCs")) {
        collector_state()->set_in_young_only_phase(true);
+       collector_state()->set_finish_of_mixed_gc(true);
  
        clear_collection_set_candidates();
        maybe_start_marking();
      }
    }
*** 1409,1413 ****
--- 1413,1424 ----
    // Don't clear the survivor list handles until the start of
    // the next evacuation pause - we need it in order to re-tag
    // the survivor regions from this evacuation pause as 'young'
    // at the start of the next.
  }
+ 
+ size_t G1Policy::minimum_desired_bytes_after_concurrent_mark(size_t used_bytes) {
+   size_t minimum_desired_buffer_size = _ihop_control->predict_unstrained_buffer_size();
+   return minimum_desired_buffer_size != 0 ?
+            minimum_desired_buffer_size : _young_list_max_length * HeapRegion::GrainBytes
+          + _reserve_regions * HeapRegion::GrainBytes + used_bytes;
+ }