8234587: Rename the SurvRateGroup class to G1SurvRateGroup

Reviewed-by: kbarrett, sangheki

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

@@ -62,8 +62,8 @@ G1Policy::G1Policy(STWGCTimer* gc_timer) :
   _young_list_target_length(0),
   _young_list_fixed_length(0),
   _young_list_max_length(0),
-  _eden_surv_rate_group(new SurvRateGroup()),
-  _survivor_surv_rate_group(new SurvRateGroup()),
+  _eden_surv_rate_group(new G1SurvRateGroup()),
+  _survivor_surv_rate_group(new G1SurvRateGroup()),
   _reserve_factor((double) G1ReservePercent / 100.0),
   _reserve_regions(0),
   _young_gen_sizer(G1YoungGenSizer::create_gen_sizer()),
@@ -458,7 +458,6 @@ void G1Policy::record_full_collection_end() {
   // also call this on any additional surv rate groups
 
   _free_regions_at_end_of_collection = _g1h->num_free_regions();
-  // Reset survivors SurvRateGroup.
   _survivor_surv_rate_group->reset();
   update_young_list_max_and_target_length();
   update_rs_length_prediction();
@@ -1389,8 +1388,6 @@ void G1Policy::calculate_optional_collection_set_regions(G1CollectionSetCandidat
 }
 
 void G1Policy::transfer_survivors_to_cset(const G1SurvivorRegions* survivors) {
-
-  // Add survivor regions to SurvRateGroup.
   note_start_adding_survivor_regions();
 
   HeapRegion* last = NULL;

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

@@ -82,10 +82,10 @@ class G1Policy: public CHeapObj<mtGC> {
   // locker is active. This should be >= _young_list_target_length;
   uint _young_list_max_length;
 
-  // SurvRateGroups below must be initialized after the predictor because they
-  // indirectly use it through this object passed to their constructor.
-  SurvRateGroup* _eden_surv_rate_group;
-  SurvRateGroup* _survivor_surv_rate_group;
+  // The survivor rate groups below must be initialized after the predictor because they
+  // indirectly use it through the "this" object passed to their constructor.
+  G1SurvRateGroup* _eden_surv_rate_group;
+  G1SurvRateGroup* _survivor_surv_rate_group;
 
   double _reserve_factor;
   // This will be set when the heap is expanded

src/hotspot/share/gc/g1/g1SurvRateGroup.cpp

@@ -30,7 +30,7 @@
 #include "logging/log.hpp"
 #include "memory/allocation.hpp"
 
-SurvRateGroup::SurvRateGroup() :
+G1SurvRateGroup::G1SurvRateGroup() :
   _stats_arrays_length(0),
   _accum_surv_rate_pred(NULL),
   _last_pred(0.0),
@@ -40,7 +40,7 @@ SurvRateGroup::SurvRateGroup() :
   start_adding_regions();
 }
 
-void SurvRateGroup::reset() {
+void G1SurvRateGroup::reset() {
   _last_pred = 0.0;
   // the following will set up the arrays with length 1
   _num_added_regions = 1;
@@ -65,11 +65,11 @@ void SurvRateGroup::reset() {
   _num_added_regions = 0;
 }
 
-void SurvRateGroup::start_adding_regions() {
+void G1SurvRateGroup::start_adding_regions() {
   _num_added_regions = 0;
 }
 
-void SurvRateGroup::stop_adding_regions() {
+void G1SurvRateGroup::stop_adding_regions() {
   if (_num_added_regions > _stats_arrays_length) {
     _accum_surv_rate_pred = REALLOC_C_HEAP_ARRAY(double, _accum_surv_rate_pred, _num_added_regions, mtGC);
     _surv_rate_predictors = REALLOC_C_HEAP_ARRAY(TruncatedSeq*, _surv_rate_predictors, _num_added_regions, mtGC);
@@ -82,7 +82,7 @@ void SurvRateGroup::stop_adding_regions() {
   }
 }
 
-void SurvRateGroup::record_surviving_words(int age_in_group, size_t surv_words) {
+void G1SurvRateGroup::record_surviving_words(int age_in_group, size_t surv_words) {
   guarantee(0 <= age_in_group && (size_t)age_in_group < _num_added_regions,
             "age_in_group is %d not between 0 and " SIZE_FORMAT, age_in_group, _num_added_regions);
 
@@ -90,14 +90,14 @@ void SurvRateGroup::record_surviving_words(int age_in_group, size_t surv_words)
   _surv_rate_predictors[age_in_group]->add(surv_rate);
 }
 
-void SurvRateGroup::all_surviving_words_recorded(const G1Predictions& predictor, bool update_predictors) {
+void G1SurvRateGroup::all_surviving_words_recorded(const G1Predictions& predictor, bool update_predictors) {
   if (update_predictors) {
     fill_in_last_surv_rates();
   }
   finalize_predictions(predictor);
 }
 
-void SurvRateGroup::fill_in_last_surv_rates() {
+void G1SurvRateGroup::fill_in_last_surv_rates() {
   if (_num_added_regions > 0) { // conservative
     double surv_rate = _surv_rate_predictors[_num_added_regions-1]->last();
     for (size_t i = _num_added_regions; i < _stats_arrays_length; ++i) {
@@ -106,7 +106,7 @@ void SurvRateGroup::fill_in_last_surv_rates() {
   }
 }
 
-void SurvRateGroup::finalize_predictions(const G1Predictions& predictor) {
+void G1SurvRateGroup::finalize_predictions(const G1Predictions& predictor) {
   double accum = 0.0;
   double pred = 0.0;
   for (size_t i = 0; i < _stats_arrays_length; ++i) {

src/hotspot/share/gc/g1/g1SurvRateGroup.hpp

@@ -28,13 +28,33 @@
 #include "gc/g1/g1Predictions.hpp"
 #include "utilities/numberSeq.hpp"
 
-class SurvRateGroup : public CHeapObj<mtGC> {
+// A survivor rate group tracks survival ratios of objects allocated in the
+// heap regions associated to a set of regions (a "space", i.e. eden or survivor)
+// on a time basis to predict future survival rates of regions of the same "age".
+//
+// Every time a new heap region associated with a survivor rate group is retired
+// (i.e. the time basis), it gets associated the next "age" entry in that group.
+//
+// During garbage collection G1 keeps track how much of total data is copied out
+// of a heap region (i.e. survives), to update the survivor rate predictor of that age.
+//
+// This information is used to predict, given a particular age of a heap region,
+// how much of its contents will likely survive to determine young generation sizes.
+//
+// The age index associated with a heap region is incremented from 0 (retired first)
+// to N (retired just before the GC).
+//
+// To avoid copying around data all the time when the total amount of regions in
+// a survivor rate group changes, this class organizes the arrays containing the
+// predictors in reverse chronological order as returned by age_in_group(). I.e.
+// index 0 contains the rate information for the region retired most recently.
+class G1SurvRateGroup : public CHeapObj<mtGC> {
   size_t  _stats_arrays_length;
   double* _accum_surv_rate_pred;
   double  _last_pred;
   TruncatedSeq** _surv_rate_predictors;
 
-  size_t _num_added_regions;   // The number of regions in this SurvRateGroup
+  size_t _num_added_regions;   // The number of regions in this survivor rate group.
 
   void fill_in_last_surv_rates();
   void finalize_predictions(const G1Predictions& predictor);
@@ -43,7 +63,7 @@ public:
   static const int InvalidAgeIndex = -1;
   static bool is_valid_age_index(int age) { return age >= 0; }
 
-  SurvRateGroup();
+  G1SurvRateGroup();
   void reset();
   void start_adding_regions();
   void stop_adding_regions();

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

@@ -252,7 +252,7 @@ HeapRegion::HeapRegion(uint hrm_index,
   _prev_top_at_mark_start(NULL), _next_top_at_mark_start(NULL),
   _prev_marked_bytes(0), _next_marked_bytes(0),
   _young_index_in_cset(-1),
-  _surv_rate_group(NULL), _age_index(SurvRateGroup::InvalidAgeIndex), _gc_efficiency(0.0),
+  _surv_rate_group(NULL), _age_index(G1SurvRateGroup::InvalidAgeIndex), _gc_efficiency(0.0),
   _node_index(G1NUMA::UnknownNodeIndex)
 {
   assert(Universe::on_page_boundary(mr.start()) && Universe::on_page_boundary(mr.end()),

src/hotspot/share/gc/g1/heapRegion.hpp

@@ -246,7 +246,7 @@ private:
 
   // Data for young region survivor prediction.
   uint  _young_index_in_cset;
-  SurvRateGroup* _surv_rate_group;
+  G1SurvRateGroup* _surv_rate_group;
   int  _age_index;
 
   // Cached attributes used in the collection set policy information
@@ -544,7 +544,7 @@ public:
 
   double surv_rate_prediction(G1Predictions const& predictor) const;
 
-  void install_surv_rate_group(SurvRateGroup* surv_rate_group);
+  void install_surv_rate_group(G1SurvRateGroup* surv_rate_group);
   void uninstall_surv_rate_group();
 
   void record_surv_words_in_group(size_t words_survived);

src/hotspot/share/gc/g1/heapRegion.inline.hpp

@@ -378,7 +378,7 @@ inline int HeapRegion::age_in_surv_rate_group() const {
 }
 
 inline bool HeapRegion::has_valid_age_in_surv_rate() const {
-  return SurvRateGroup::is_valid_age_index(_age_index);
+  return G1SurvRateGroup::is_valid_age_index(_age_index);
 }
 
 inline bool HeapRegion::has_surv_rate_group() const {
@@ -390,7 +390,7 @@ inline double HeapRegion::surv_rate_prediction(G1Predictions const& predictor) c
   return _surv_rate_group->surv_rate_pred(predictor, age_in_surv_rate_group());
 }
 
-inline void HeapRegion::install_surv_rate_group(SurvRateGroup* surv_rate_group) {
+inline void HeapRegion::install_surv_rate_group(G1SurvRateGroup* surv_rate_group) {
   assert(surv_rate_group != NULL, "pre-condition");
   assert(!has_surv_rate_group(), "pre-condition");
   assert(is_young(), "pre-condition");
@@ -405,7 +405,7 @@ inline void HeapRegion::uninstall_surv_rate_group() {
     assert(is_young(), "pre-condition");
 
     _surv_rate_group = NULL;
-    _age_index = SurvRateGroup::InvalidAgeIndex;
+    _age_index = G1SurvRateGroup::InvalidAgeIndex;
   } else {
     assert(!has_valid_age_in_surv_rate(), "pre-condition");
   }