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src/hotspot/share/gc/shenandoah/heuristics/shenandoahHeuristics.hpp

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@@ -1,7 +1,8 @@
  /*
   * Copyright (c) 2018, 2019, Red Hat, Inc. All rights reserved.
+  * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.

@@ -24,15 +25,14 @@
  
  #ifndef SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHHEURISTICS_HPP
  #define SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHHEURISTICS_HPP
  
  #include "gc/shenandoah/heuristics/shenandoahSpaceInfo.hpp"
- #include "gc/shenandoah/shenandoahHeap.hpp"
- #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
  #include "gc/shenandoah/shenandoahSharedVariables.hpp"
  #include "memory/allocation.hpp"
  #include "runtime/globals_extension.hpp"
+ #include "utilities/numberSeq.hpp"
  
  #define SHENANDOAH_ERGO_DISABLE_FLAG(name)                                  \
    do {                                                                      \
      if (FLAG_IS_DEFAULT(name) && (name)) {                                  \
        log_info(gc)("Heuristics ergonomically sets -XX:-" #name);            \

@@ -68,32 +68,55 @@
    static const intx Concurrent_Adjust   = -1; // recover from penalties
    static const intx Degenerated_Penalty = 10; // how much to penalize average GC duration history on Degenerated GC
    static const intx Full_Penalty        = 20; // how much to penalize average GC duration history on Full GC
  
  protected:
+   static const uint Moving_Average_Samples = 10; // Number of samples to store in moving averages
+ 
    typedef struct {
      ShenandoahHeapRegion* _region;
-     size_t _garbage;
+     union {
+       size_t _garbage;          // Not used by old-gen heuristics.
+       size_t _live_data;        // Only used for old-gen heuristics, which prioritizes retention of _live_data over garbage reclaim
+     } _u;
    } RegionData;
  
    // Source of information about the memory space managed by this heuristic
    ShenandoahSpaceInfo* _space_info;
  
+   // Depending on generation mode, region data represents the results of the relevant
+   // most recently completed marking pass:
+   //   - in GLOBAL mode, global marking pass
+   //   - in OLD mode,    old-gen marking pass
+   //   - in YOUNG mode,  young-gen marking pass
+   //
+   // Note that there is some redundancy represented in region data because
+   // each instance is an array large enough to hold all regions. However,
+   // any region in young-gen is not in old-gen. And any time we are
+   // making use of the GLOBAL data, there is no need to maintain the
+   // YOUNG or OLD data. Consider this redundancy of data structure to
+   // have negligible cost unless proven otherwise.
    RegionData* _region_data;
  
+   size_t _guaranteed_gc_interval;
+ 
    double _cycle_start;
    double _last_cycle_end;
  
    size_t _gc_times_learned;
    intx _gc_time_penalties;
-   TruncatedSeq* _gc_time_history;
+   TruncatedSeq* _gc_cycle_time_history;
  
    // There may be many threads that contend to set this flag
    ShenandoahSharedFlag _metaspace_oom;
  
    static int compare_by_garbage(RegionData a, RegionData b);
  
+   // TODO: We need to enhance this API to give visibility to accompanying old-gen evacuation effort.
+   // In the case that the old-gen evacuation effort is small or zero, the young-gen heuristics
+   // should feel free to dedicate increased efforts to young-gen evacuation.
+ 
    virtual void choose_collection_set_from_regiondata(ShenandoahCollectionSet* set,
                                                       RegionData* data, size_t data_size,
                                                       size_t free) = 0;
  
    void adjust_penalty(intx step);

@@ -104,19 +127,23 @@
  
    void record_metaspace_oom()     { _metaspace_oom.set(); }
    void clear_metaspace_oom()      { _metaspace_oom.unset(); }
    bool has_metaspace_oom() const  { return _metaspace_oom.is_set(); }
  
+   void set_guaranteed_gc_interval(size_t guaranteed_gc_interval) {
+     _guaranteed_gc_interval = guaranteed_gc_interval;
+   }
+ 
    virtual void record_cycle_start();
  
    virtual void record_cycle_end();
  
    virtual bool should_start_gc();
  
    virtual bool should_degenerate_cycle();
  
-   virtual void record_success_concurrent();
+   virtual void record_success_concurrent(bool abbreviated);
  
    virtual void record_success_degenerated();
  
    virtual void record_success_full();
  

@@ -125,16 +152,19 @@
    virtual void record_requested_gc();
  
    virtual void choose_collection_set(ShenandoahCollectionSet* collection_set);
  
    virtual bool can_unload_classes();
+ 
+   // This indicates whether or not the current cycle should unload classes.
+   // It does NOT indicate that a cycle should be started.
    virtual bool should_unload_classes();
  
    virtual const char* name() = 0;
    virtual bool is_diagnostic() = 0;
    virtual bool is_experimental() = 0;
    virtual void initialize();
  
-   double time_since_last_gc() const;
+   double elapsed_cycle_time() const;
  };
  
  #endif // SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHHEURISTICS_HPP
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