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  24 
  25 #ifndef SHARE_GC_G1_G1COLLECTIONSET_HPP
  26 #define SHARE_GC_G1_G1COLLECTIONSET_HPP
  27 
  28 #include "utilities/debug.hpp"
  29 #include "utilities/globalDefinitions.hpp"
  30 
  31 class G1CollectedHeap;
  32 class G1CollectionSetCandidates;
  33 class G1CollectorState;
  34 class G1GCPhaseTimes;
  35 class G1ParScanThreadStateSet;
  36 class G1Policy;
  37 class G1SurvivorRegions;
  38 class HeapRegion;
  39 class HeapRegionClosure;
  40 
  41 // The collection set.
  42 //
  43 // The set of regions that are evacuated during an evacuation pause.
  44 //
  45 // At the end of a collection, before freeing the collection set, this set
  46 // contains all regions that were evacuated during this collection:
  47 //
  48 // - survivor regions from the last collection (if any)
  49 // - eden regions allocated by the mutator
  50 // - old gen regions evacuated during mixed gc
  51 //
  52 // This set is built incrementally at mutator time as regions are retired, and
  53 // if this had been a mixed gc, some additional (during gc) incrementally added
  54 // old regions from the collection set candidates built during the concurrent
  55 // cycle.
  56 //
  57 // A more detailed overview of how the collection set changes over time follows:
  58 //
  59 // 0) at the end of GC the survivor regions are added to this collection set.
  60 // 1) the mutator incrementally adds eden regions as they retire
  61 //
  62 // ----- gc starts
  63 //
  64 // 2) prepare (finalize) young regions of the collection set for collection
  65 //    - relabel the survivors as eden
  66 //    - finish up the incremental building that happened at mutator time
  67 //
  68 // iff this is a young-only collection:
  69 //
  70 // a3) evacuate the current collection set in one "initial evacuation" phase
  71 //
  72 // iff this is a mixed collection:
  73 //
  74 // b3) calculate the set of old gen regions we may be able to collect in this
  75 //     collection from the list of collection set candidates.
  76 //     - one part is added to the current collection set
  77 //     - the remainder regions are labeled as optional, and NOT yet added to the
  78 //     collection set.
  79 // b4) evacuate the current collection set in the "initial evacuation" phase
  80 // b5) evacuate the optional regions in the "optional evacuation" phase. This is
  81 //     done in increments (or rounds).
  82 //     b5-1) add a few of the optional regions to the current collection set
  83 //     b5-2) evacuate only these newly added optional regions. For this mechanism we
  84 //     reuse the incremental collection set building infrastructure (used also at
  85 //     mutator time).
  86 //     b5-3) repeat from b5-1 until the policy determines we are done
  87 //
  88 // all collections
  89 //
  90 // 6) free the collection set (contains all regions now; empties collection set
  91 //    afterwards)
  92 // 7) add survivors to this collection set
  93 //
  94 // ----- gc ends
  95 //
  96 // goto 1)
  97 //
  98 // Examples of how the collection set might look over time:
  99 //
 100 // Legend:
 101 // S = survivor, E = eden, O = old.
 102 // |xxxx| = increment (with increment markers), containing four regions
 103 //
 104 // |SSSS|                         ... after step 0), with four survivor regions
 105 // |SSSSEE|                       ... at step 1), after retiring two eden regions
 106 // |SSSSEEEE|                     ... after step 1), after retiring four eden regions
 107 // |EEEEEEEE|                     ... after step 2)
 108 //
 109 // iff this is a young-only collection
 110 //
 111 // EEEEEEEE||                      ... after step a3), after initial evacuation phase
 112 // ||                              ... after step 6)
 113 // |SS|                            ... after step 7), with two survivor regions
 114 //
 115 // iff this is a mixed collection
 116 //
 117 // |EEEEEEEEOOOO|                  ... after step b3), added four regions to be
 118 //                                     evacuated in the "initial evacuation" phase
 119 // EEEEEEEEOOOO||                  ... after step b4), incremental part is empty
 120 //                                     after evacuation
 121 // EEEEEEEEOOOO|OO|                ... after step b5.1), added two regions to be
 122 //                                     evacuated in the first round of the
 123 //                                     "optional evacuation" phase
 124 // EEEEEEEEOOOOOO|O|               ... after step b5.1), added one region to be
 125 //                                     evacuated in the second round of the
 126 //                                     "optional evacuation" phase
 127 // EEEEEEEEOOOOOOO||               ... after step b5), the complete collection set.
 128 // ||                              ... after step b6)
 129 // |SSS|                           ... after step 7), with three survivor regions
 130 //
 131 class G1CollectionSet {
 132   G1CollectedHeap* _g1h;
 133   G1Policy* _policy;
 134 
 135   // All old gen collection set candidate regions for the current mixed phase.
 136   G1CollectionSetCandidates* _candidates;
 137 
 138   uint _eden_region_length;
 139   uint _survivor_region_length;
 140   uint _old_region_length;
 141 
 142   // The actual collection set as a set of region indices.
 143   // All entries in _collection_set_regions below _collection_set_cur_length are
 144   // assumed to be part of the collection set.
 145   // We assume that at any time there is at most only one writer and (one or more)
 146   // concurrent readers. This means we are good with using storestore and loadload
 147   // barriers on the writer and reader respectively only.
 148   uint* _collection_set_regions;
 149   volatile size_t _collection_set_cur_length;
 150   size_t _collection_set_max_length;
 151 
 152   // When doing mixed collections we can add old regions to the collection set, which
 153   // will be collected only if there is enough time. We call these optional regions.
 154   // This member records the current number of regions that are of that type that
 155   // correspond to the first x entries in the collection set candidates.
 156   uint _num_optional_regions;
 157 
 158   // The number of bytes in the collection set before the pause. Set from
 159   // the incrementally built collection set at the start of an evacuation
 160   // pause, and updated as more regions are added to the collection set.
 161   size_t _bytes_used_before;
 162 
 163   // The number of cards in the remembered set in the collection set. Set from
 164   // the incrementally built collection set at the start of an evacuation
 165   // pause, and updated as more regions are added to the collection set.
 166   size_t _recorded_rs_lengths;
 167 
 168   enum CSetBuildType {
 169     Active,             // We are actively building the collection set
 170     Inactive            // We are not actively building the collection set
 171   };
 172 
 173   CSetBuildType _inc_build_state;
 174   size_t _inc_part_start;
 175 
 176   // The associated information that is maintained while the incremental
 177   // collection set is being built with *young* regions. Used to populate
 178   // the recorded info for the evacuation pause.
 179 
 180   // The number of bytes in the incrementally built collection set.
 181   // Used to set _collection_set_bytes_used_before at the start of
 182   // an evacuation pause.
 183   size_t _inc_bytes_used_before;
 184 
 185   // The RSet lengths recorded for regions in the CSet. It is updated
 186   // by the thread that adds a new region to the CSet. We assume that
 187   // only one thread can be allocating a new CSet region (currently,
 188   // it does so after taking the Heap_lock) hence no need to
 189   // synchronize updates to this field.
 190   size_t _inc_recorded_rs_lengths;
 191 
 192   // A concurrent refinement thread periodically samples the young
 193   // region RSets and needs to update _inc_recorded_rs_lengths as
 194   // the RSets grow. Instead of having to synchronize updates to that
 195   // field we accumulate them in this field and add it to
 196   // _inc_recorded_rs_lengths_diffs at the start of a GC.
 197   ssize_t _inc_recorded_rs_lengths_diffs;
 198 
 199   // The predicted elapsed time it will take to collect the regions in
 200   // the CSet. This is updated by the thread that adds a new region to
 201   // the CSet. See the comment for _inc_recorded_rs_lengths about
 202   // MT-safety assumptions.
 203   double _inc_predicted_elapsed_time_ms;
 204 
 205   // See the comment for _inc_recorded_rs_lengths_diffs.
 206   double _inc_predicted_elapsed_time_ms_diffs;
 207 
 208   void set_recorded_rs_lengths(size_t rs_lengths);
 209 
 210   G1CollectorState* collector_state();
 211   G1GCPhaseTimes* phase_times();
 212 
 213   void verify_young_cset_indices() const NOT_DEBUG_RETURN;
 214 
 215   double predict_region_elapsed_time_ms(HeapRegion* hr);
 216 
 217   // Update the incremental collection set information when adding a region.
 218   void add_young_region_common(HeapRegion* hr);
 219 
 220   // Add old region "hr" to the collection set.
 221   void add_old_region(HeapRegion* hr);
 222   void free_optional_regions();
 223 
 224   // Add old region "hr" to optional collection set.
 225   void add_optional_region(HeapRegion* hr);
 226 
 227   void move_candidates_to_collection_set(uint num_regions);
 228 
 229   // Finalize the young part of the initial collection set. Relabel survivor regions
 230   // as Eden and calculate a prediction on how long the evacuation of all young regions
 231   // will take.
 232   double finalize_young_part(double target_pause_time_ms, G1SurvivorRegions* survivors);
 233   // Perform any final calculations on the incremental collection set fields before we
 234   // can use them.
 235   void finalize_incremental_building();
 236 
 237   // Select the old regions of the initial collection set and determine how many optional
 238   // regions we might be able to evacuate in this pause.
 239   void finalize_old_part(double time_remaining_ms);
 240 public:
 241   G1CollectionSet(G1CollectedHeap* g1h, G1Policy* policy);
 242   ~G1CollectionSet();
 243 
 244   // Initializes the collection set giving the maximum possible length of the collection set.
 245   void initialize(uint max_region_length);
 246 
 247   void clear_candidates();
 248 
 249   void set_candidates(G1CollectionSetCandidates* candidates) {
 250     assert(_candidates == NULL, "Trying to replace collection set candidates.");
 251     _candidates = candidates;
 252   }
 253   G1CollectionSetCandidates* candidates() { return _candidates; }
 254 
 255   void init_region_lengths(uint eden_cset_region_length,
 256                            uint survivor_cset_region_length);
 257 
 258   uint region_length() const       { return young_region_length() +
 259                                             old_region_length(); }
 260   uint young_region_length() const { return eden_region_length() +
 261                                             survivor_region_length(); }
 262 
 263   uint eden_region_length() const     { return _eden_region_length;     }
 264   uint survivor_region_length() const { return _survivor_region_length; }
 265   uint old_region_length() const      { return _old_region_length;      }
 266   uint optional_region_length() const { return _num_optional_regions; }
 267 
 268   // Reset the contents of the collection set.
 269   void clear();
 270 
 271   // Incremental collection set support
 272 
 273   // Initialize incremental collection set info.
 274   void start_incremental_building();
 275   // Start a new collection set increment.
 276   void update_incremental_marker() { _inc_build_state = Active; _inc_part_start = _collection_set_cur_length; }
 277   // Stop adding regions to the current collection set increment.
 278   void stop_incremental_building() { _inc_build_state = Inactive; }
 279 
 280   // Iterate over the current collection set increment applying the given HeapRegionClosure
 281   // from a starting position determined by the given worker id.
 282   void iterate_incremental_part_from(HeapRegionClosure* cl, uint worker_id, uint total_workers) const;
 283 
 284   // Iterate over the entire collection set (all increments calculated so far), applying
 285   // the given HeapRegionClosure on all of them.
 286   void iterate(HeapRegionClosure* cl) const;
 287 
 288   void iterate_optional(HeapRegionClosure* cl) const;
 289 
 290   size_t recorded_rs_lengths() { return _recorded_rs_lengths; }
 291 
 292   size_t bytes_used_before() const {
 293     return _bytes_used_before;
 294   }
 295 
 296   void reset_bytes_used_before() {
 297     _bytes_used_before = 0;
 298   }
 299 
 300   // Finalize the initial collection set consisting of all young regions potentially a
 301   // few old gen regions.
 302   void finalize_initial_collection_set(double target_pause_time_ms, G1SurvivorRegions* survivor);
 303   // Finalize the next collection set from the set of available optional old gen regions.
 304   bool finalize_optional_for_evacuation(double remaining_pause_time);
 305   // Abandon (clean up) optional collection set regions that were not evacuated in this
 306   // pause.
 307   void abandon_optional_collection_set(G1ParScanThreadStateSet* pss);
 308 
 309   // Update information about hr in the aggregated information for
 310   // the incrementally built collection set.
 311   void update_young_region_prediction(HeapRegion* hr, size_t new_rs_length);
 312 
 313   // Add eden region to the collection set.
 314   void add_eden_region(HeapRegion* hr);
 315 
 316   // Add survivor region to the collection set.
 317   void add_survivor_regions(HeapRegion* hr);
 318 
 319 #ifndef PRODUCT
 320   bool verify_young_ages();
 321 
 322   void print(outputStream* st);
 323 #endif // !PRODUCT
 324 };
 325 
 326 #endif // SHARE_GC_G1_G1COLLECTIONSET_HPP