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 24 
 25 #ifndef SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHOLDHEURISTICS_HPP
 26 #define SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHOLDHEURISTICS_HPP
 27 
 28 
 29 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
 30 #include "gc/shenandoah/shenandoahGenerationalHeap.hpp"
 31 
 32 class ShenandoahCollectionSet;
 33 class ShenandoahHeapRegion;
 34 class ShenandoahOldGeneration;
 35 
 36 /*
 37  * This heuristic is responsible for choosing a set of candidates for inclusion
 38  * in mixed collections. These candidates are chosen when marking of the old
 39  * generation is complete. Note that this list of candidates may live through
 40  * several mixed collections.
 41  *
 42  * This heuristic is also responsible for triggering old collections. It has its
 43  * own collection of triggers to decide whether to start an old collection. It does
 44  * _not_ use any of the functionality from the adaptive heuristics for triggers.
 45  * It also does not use any of the functionality from the heuristics base classes
 46  * to choose the collection set. For these reasons, it does not extend from
 47  * ShenandoahGenerationalHeuristics.
 48  */
 49 class ShenandoahOldHeuristics : public ShenandoahHeuristics {
 50 
 51 private:
 52 
 53   static uint NOT_FOUND;
 54 
 55   ShenandoahGenerationalHeap* _heap;
 56   ShenandoahOldGeneration* _old_gen;
 57 
 58   // After final marking of the old generation, this heuristic will select
 59   // a set of candidate regions to be included in subsequent mixed collections.
 60   // The regions are sorted into a `_region_data` array (declared in base
 61   // class) in decreasing order of garbage. The heuristic will give priority
 62   // to regions containing more garbage.
 63 
 64   // The following members are used to keep track of which candidate regions
 65   // have yet to be added to a mixed collection. There is also some special
 66   // handling for pinned regions, described further below.
 67 
 68   // Pinned regions may not be included in the collection set. Any old regions
 69   // which were pinned at the time when old regions were added to the mixed
 70   // collection will have been skipped. These regions are still contain garbage,
 71   // so we want to include them at the start of the list of candidates for the
 72   // _next_ mixed collection cycle. This variable is the index of the _first_
 73   // old region which is pinned when the mixed collection set is formed.
 74   uint _first_pinned_candidate;
 75 
 76   // This is the index of the last region which is above the garbage threshold.
 77   // No regions after this will be considered for inclusion in a mixed collection
 78   // set.
 79   uint _last_old_collection_candidate;
 80 
 81   // This index points to the first candidate in line to be added to the mixed
 82   // collection set. It is updated as regions are added to the collection set.
 83   uint _next_old_collection_candidate;
 84 
 85   // This is the last index in the array of old regions which were active at
 86   // the end of old final mark.
 87   uint _last_old_region;
 88 
 89   // How much live data must be evacuated from within the unprocessed mixed evacuation candidates?
 90   size_t _live_bytes_in_unprocessed_candidates;
 91 
 92   // Keep a pointer to our generation that we can use without down casting a protected member from the base class.
 93   ShenandoahOldGeneration* _old_generation;
 94 
 95   // Flags are set when promotion failure is detected (by gc thread), and cleared when
 96   // old generation collection begins (by control thread).  Flags are set and cleared at safepoints.
 97   bool _cannot_expand_trigger;
 98   bool _fragmentation_trigger;
 99   bool _growth_trigger;
100 
101   // Motivation for a fragmentation_trigger
102   double _fragmentation_density;
103   size_t _fragmentation_first_old_region;
104   size_t _fragmentation_last_old_region;
105 
106   // Compare by live is used to prioritize compaction of old-gen regions.  With old-gen compaction, the goal is
107   // to tightly pack long-lived objects into available regions.  In most cases, there has not been an accumulation
108   // of garbage within old-gen regions.  The more likely opportunity will be to combine multiple sparsely populated
109   // old-gen regions which may have been promoted in place into a smaller number of densely packed old-gen regions.
110   // This improves subsequent allocation efficiency and reduces the likelihood of allocation failure (including
111   // humongous allocation failure) due to fragmentation of the available old-gen allocation pool
112   static int compare_by_live(RegionData a, RegionData b);
113 
114   static int compare_by_index(RegionData a, RegionData b);
115 
116   inline void trigger_old_is_fragmented(double density, size_t first_old_index, size_t last_old_index) {
117     _fragmentation_trigger = true;
118     _fragmentation_density = density;
119     _fragmentation_first_old_region = first_old_index;
120     _fragmentation_last_old_region = last_old_index;
121   }
122   inline void trigger_old_has_grown() { _growth_trigger = true; }
123 
124   void trigger_collection_if_fragmented(size_t first_old_region, size_t last_old_region, size_t old_region_count, size_t num_regions);
125   void trigger_collection_if_overgrown();
126 
127  protected:
128   void choose_collection_set_from_regiondata(ShenandoahCollectionSet* set, RegionData* data, size_t data_size, size_t free) override;
129 
130 public:
131   explicit ShenandoahOldHeuristics(ShenandoahOldGeneration* generation, ShenandoahGenerationalHeap* gen_heap);
132 
133   // Prepare for evacuation of old-gen regions by capturing the mark results of a recently completed concurrent mark pass.
134   void prepare_for_old_collections();
135 
136   // Return true iff the collection set is primed with at least one old-gen region.
137   bool prime_collection_set(ShenandoahCollectionSet* set);
138 
139   // How many old-collection candidates have not yet been processed?
140   uint unprocessed_old_collection_candidates() const;
141 
142   // How much live memory must be evacuated from within old-collection candidates that have not yet been processed?
143   size_t unprocessed_old_collection_candidates_live_memory() const;
144 
145   void set_unprocessed_old_collection_candidates_live_memory(size_t initial_live);
146 
147   void decrease_unprocessed_old_collection_candidates_live_memory(size_t evacuated_live);
148 
149   // How many old or hidden collection candidates have not yet been processed?
150   uint last_old_collection_candidate_index() const;
151 
152   // Return the next old-collection candidate in order of decreasing amounts of garbage.  (We process most-garbage regions
153   // first.)  This does not consume the candidate.  If the candidate is selected for inclusion in a collection set, then
154   // the candidate is consumed by invoking consume_old_collection_candidate().
155   ShenandoahHeapRegion* next_old_collection_candidate();
156 
157   // Adjust internal state to reflect that one fewer old-collection candidate remains to be processed.
158   void consume_old_collection_candidate();
159 
160   // Fill in buffer with all the old-collection regions that were identified at the end of the most recent old-gen
161   // mark to require their unmarked objects to be coalesced and filled.  The buffer array must have at least
162   // last_old_region_index() entries, or memory may be corrupted when this function overwrites the
163   // end of the array.
164   unsigned int get_coalesce_and_fill_candidates(ShenandoahHeapRegion** buffer);
165 
166   // True if there are old regions that need to be filled.
167   bool has_coalesce_and_fill_candidates() const { return coalesce_and_fill_candidates_count() > 0; }
168 
169   // Return the number of old regions that need to be filled.
170   size_t coalesce_and_fill_candidates_count() const { return _last_old_region - _next_old_collection_candidate; }
171 
172   // If a GLOBAL gc occurs, it will collect the entire heap which invalidates any collection candidates being
173   // held by this heuristic for supplying mixed collections.
174   void abandon_collection_candidates();
175 
176   void trigger_cannot_expand() { _cannot_expand_trigger = true; };
177 
178   inline void get_fragmentation_trigger_reason_for_log_message(double &density, size_t &first_index, size_t &last_index) {
179     density = _fragmentation_density;
180     first_index = _fragmentation_first_old_region;
181     last_index = _fragmentation_last_old_region;
182   }
183 
184   void clear_triggers();
185 
186   void trigger_maybe(size_t first_old_region, size_t last_old_region, size_t old_region_count, size_t num_regions);
187 
188   void record_cycle_end() override;
189 
190   bool should_start_gc() override;
191 
192   void record_success_concurrent(bool abbreviated) override;
193 
194   void record_success_degenerated() override;
195 
196   void record_success_full() override;
197 
198   const char* name() override;
199 
200   bool is_diagnostic() override;
201 
202   bool is_experimental() override;
203 
204 private:
205   void slide_pinned_regions_to_front();
206   bool all_candidates_are_pinned();
207 };
208 
209 #endif // SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHOLDHEURISTICS_HPP