src/hotspot/share/gc/g1/g1Policy.cpp

rev 52448 : JDK-8212657: Implementation of JDK-8204089 Promptly Return Unused Committed Memory from G1
Summary: Issue optional, default enabled, concurrent cycles when the VM is idle to reclaim unused internal and Java heap memory.
Reviewed-by:
Contributed-by: Rodrigo Bruno <rbruno@gsd.inesc-id.pt>, Ruslan Synytsky <rs@jelastic.com>, Thomas Schatzl <thomas.schatzl@oracle.com>

*** 712,735 ****
    if (this_pause_included_initial_mark) {
      collector_state()->set_mark_or_rebuild_in_progress(true);
    }
  
    _free_regions_at_end_of_collection = _g1h->num_free_regions();
    // IHOP control wants to know the expected young gen length if it were not
    // restrained by the heap reserve. Using the actual length would make the
    // prediction too small and the limit the young gen every time we get to the
    // predicted target occupancy.
    size_t last_unrestrained_young_length = update_young_list_max_and_target_length();
-   update_rs_lengths_prediction();
  
    update_ihop_prediction(app_time_ms / 1000.0,
                           _bytes_allocated_in_old_since_last_gc,
                           last_unrestrained_young_length * HeapRegion::GrainBytes,
                           this_pause_was_young_only);
    _bytes_allocated_in_old_since_last_gc = 0;
  
    _ihop_control->send_trace_event(_g1h->gc_tracer_stw());
  
    // Note that _mmu_tracker->max_gc_time() returns the time in seconds.
    double update_rs_time_goal_ms = _mmu_tracker->max_gc_time() * MILLIUNITS * G1RSetUpdatingPauseTimePercent / 100.0;
  
    if (update_rs_time_goal_ms < scan_hcc_time_ms) {
--- 712,749 ----
    if (this_pause_included_initial_mark) {
      collector_state()->set_mark_or_rebuild_in_progress(true);
    }
  
    _free_regions_at_end_of_collection = _g1h->num_free_regions();
+ 
+   update_rs_lengths_prediction();
+ 
+   // Do not update dynamic IHOP due to G1 periodic collection as it is highly likely
+   // that in this case we are not running in a "normal" operating mode.
+   if (_g1h->gc_cause() != GCCause::_g1_periodic_collection) {
      // IHOP control wants to know the expected young gen length if it were not
      // restrained by the heap reserve. Using the actual length would make the
      // prediction too small and the limit the young gen every time we get to the
      // predicted target occupancy.
      size_t last_unrestrained_young_length = update_young_list_max_and_target_length();
  
      update_ihop_prediction(app_time_ms / 1000.0,
                             _bytes_allocated_in_old_since_last_gc,
                             last_unrestrained_young_length * HeapRegion::GrainBytes,
                             this_pause_was_young_only);
      _bytes_allocated_in_old_since_last_gc = 0;
  
      _ihop_control->send_trace_event(_g1h->gc_tracer_stw());
+   } else {
+     // Any garbage collection triggered as periodic collection resets the time-to-mixed
+     // measurement. Periodic collection typically means that the application is "inactive", i.e.
+     // the marking threads may have received an uncharacterisic amount of cpu time
+     // for completing the marking, i.e. are faster than expected.
+     // This skews the predicted marking length towards smaller values which might cause
+     // the mark start being too late.
+     _initial_mark_to_mixed.reset();
+   }
  
    // Note that _mmu_tracker->max_gc_time() returns the time in seconds.
    double update_rs_time_goal_ms = _mmu_tracker->max_gc_time() * MILLIUNITS * G1RSetUpdatingPauseTimePercent / 100.0;
  
    if (update_rs_time_goal_ms < scan_hcc_time_ms) {
*** 1076,1086 ****
--- 1090,1102 ----
      case YoungOnlyGC:
      case LastYoungGC:
        _initial_mark_to_mixed.add_pause(end - start);
        break;
      case InitialMarkGC:
+       if (_g1h->gc_cause() != GCCause::_g1_periodic_collection) {
          _initial_mark_to_mixed.record_initial_mark_end(end);
+       }
        break;
      case MixedGC:
        _initial_mark_to_mixed.record_mixed_gc_start(start);
        break;
      default: