1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   6  * under the terms of the GNU General Public License version 2 only, as
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  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
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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 collection set is built incrementally: it starts off with the set of
  44 // survivor regions, and at mutator time G1 adds retired up eden regions to it.
  45 //
  46 // For non-mixed collections this is all the collection set consists of and its
  47 // regions are evacuated in one pass.
  48 //
  49 // For mixed collections we not only determine a few old gen regions for an initial
  50 // collection set, but also a set of optional collection set regions from the
  51 // collection set candidates.
  52 //
  53 // After evacuating the initial collection set, G1 incrementally selects more
  54 // regions from the optional collection set regions as time prediction permit.
  55 //
  56 // Support for incremental building is implemented by keeping an index into the
  57 // collection set set; during evacuation only the part from that index to the
  58 // end is used for evacuation.
  59 //
  60 // This results in having a single complete collection set of the evacuation phases
  61 // for cleaning up.
  62 class G1CollectionSet {
  63   G1CollectedHeap* _g1h;
  64   G1Policy* _policy;
  65 
  66   // All old gen collection set candidate regions for the current mixed phase.
  67   G1CollectionSetCandidates* _candidates;
  68 
  69   uint _eden_region_length;
  70   uint _survivor_region_length;
  71   uint _old_region_length;
  72 
  73   // The actual collection set as a set of region indices.
  74   // All entries in _collection_set_regions below _collection_set_cur_length are
  75   // assumed to be part of the collection set.
  76   // We assume that at any time there is at most only one writer and (one or more)
  77   // concurrent readers. This means we are good with using storestore and loadload
  78   // barriers on the writer and reader respectively only.
  79   uint* _collection_set_regions;
  80   volatile size_t _collection_set_cur_length;
  81   size_t _collection_set_max_length;
  82 
  83   // When doing mixed collections we can add old regions to the collection set, which
  84   // will be collected only if there is enough time. We call these optional regions.
  85   // This member records the current number of regions that are of that type that
  86   // correspond to the first x entries in the collection set candidates.
  87   uint _num_optional_regions;
  88 
  89   // The number of bytes in the collection set before the pause. Set from
  90   // the incrementally built collection set at the start of an evacuation
  91   // pause, and updated as more regions are added to the collection set.
  92   size_t _bytes_used_before;
  93 
  94   // The number of cards in the remembered set in the collection set. Set from
  95   // the incrementally built collection set at the start of an evacuation
  96   // pause, and updated as more regions are added to the collection set.
  97   size_t _recorded_rs_lengths;
  98 
  99   enum CSetBuildType {
 100     Active,             // We are actively building the collection set
 101     Inactive            // We are not actively building the collection set
 102   };
 103 
 104   CSetBuildType _inc_build_state;
 105   size_t _inc_part_start;
 106 
 107   // The associated information that is maintained while the incremental
 108   // collection set is being built with *young* regions. Used to populate
 109   // the recorded info for the evacuation pause.
 110 
 111   // The number of bytes in the incrementally built collection set.
 112   // Used to set _collection_set_bytes_used_before at the start of
 113   // an evacuation pause.
 114   size_t _inc_bytes_used_before;
 115 
 116   // The RSet lengths recorded for regions in the CSet. It is updated
 117   // by the thread that adds a new region to the CSet. We assume that
 118   // only one thread can be allocating a new CSet region (currently,
 119   // it does so after taking the Heap_lock) hence no need to
 120   // synchronize updates to this field.
 121   size_t _inc_recorded_rs_lengths;
 122 
 123   // A concurrent refinement thread periodically samples the young
 124   // region RSets and needs to update _inc_recorded_rs_lengths as
 125   // the RSets grow. Instead of having to synchronize updates to that
 126   // field we accumulate them in this field and add it to
 127   // _inc_recorded_rs_lengths_diffs at the start of a GC.
 128   ssize_t _inc_recorded_rs_lengths_diffs;
 129 
 130   // The predicted elapsed time it will take to collect the regions in
 131   // the CSet. This is updated by the thread that adds a new region to
 132   // the CSet. See the comment for _inc_recorded_rs_lengths about
 133   // MT-safety assumptions.
 134   double _inc_predicted_elapsed_time_ms;
 135 
 136   // See the comment for _inc_recorded_rs_lengths_diffs.
 137   double _inc_predicted_elapsed_time_ms_diffs;
 138 
 139   G1CollectorState* collector_state();
 140   G1GCPhaseTimes* phase_times();
 141 
 142   void verify_young_cset_indices() const NOT_DEBUG_RETURN;
 143 
 144   double predict_region_elapsed_time_ms(HeapRegion* hr);
 145 
 146   // Update the incremental collection set information when adding a region.
 147   void add_young_region_common(HeapRegion* hr);
 148 
 149   // Add old region "hr" to the collection set.
 150   void add_old_region(HeapRegion* hr);
 151 
 152   // Add old region "hr" to optional collection set.
 153   void add_optional_region(HeapRegion* hr);
 154 
 155   void move_candidates_to_collection_set(uint num_regions);
 156 
 157   // Choose a new collection set.  Marks the chosen regions as being
 158   // "in_collection_set".
 159   double finalize_young_part(double target_pause_time_ms, G1SurvivorRegions* survivors);
 160   // Perform any final calculations on the incremental collection set fields
 161   // before we can use them.
 162   void finalize_young_increment();
 163 
 164   void finalize_old_part(double time_remaining_ms);
 165 public:
 166   G1CollectionSet(G1CollectedHeap* g1h, G1Policy* policy);
 167   ~G1CollectionSet();
 168 
 169   // Initializes the collection set giving the maximum possible length of the collection set.
 170   void initialize(uint max_region_length);
 171   void initialize_optional(uint max_length);
 172   void free_optional_regions();
 173 
 174   void clear_candidates();
 175 
 176   void set_candidates(G1CollectionSetCandidates* candidates) {
 177     assert(_candidates == NULL, "Trying to replace collection set candidates.");
 178     _candidates = candidates;
 179   }
 180   G1CollectionSetCandidates* candidates() { return _candidates; }
 181 
 182   void init_region_lengths(uint eden_cset_region_length,
 183                            uint survivor_cset_region_length);
 184 
 185   void set_recorded_rs_lengths(size_t rs_lengths);
 186 
 187   uint region_length() const       { return young_region_length() +
 188                                             old_region_length(); }
 189   uint young_region_length() const { return eden_region_length() +
 190                                             survivor_region_length(); }
 191 
 192   uint eden_region_length() const     { return _eden_region_length;     }
 193   uint survivor_region_length() const { return _survivor_region_length; }
 194   uint old_region_length() const      { return _old_region_length;      }
 195   uint optional_region_length() const { return _num_optional_regions; }
 196 
 197   // Reset the contents of the collection set.
 198   void clear();
 199 
 200   // Incremental collection set support
 201 
 202   // Initialize incremental collection set info.
 203   void start_incremental_building();
 204   // Start a new collection set increment.
 205   void update_incremental_marker() { _inc_build_state = Active; _inc_part_start = _collection_set_cur_length; }
 206   // Stop adding regions to the current collection set increment.
 207   void stop_incremental_building() { _inc_build_state = Inactive; }
 208 
 209   // Iterate over the current collection set increment applying the given HeapRegionClosure
 210   // from a starting position determined by the given worker id.
 211   void iterate_incremental_part_from(HeapRegionClosure* cl, uint worker_id, uint total_workers) const;
 212 
 213   // Iterate over the entire collection set (all increments calculated so far), applying
 214   // the given HeapRegionClosure on all of them.
 215   void iterate(HeapRegionClosure* cl) const;
 216 
 217   void iterate_optional(HeapRegionClosure* cl) const;
 218 
 219   size_t recorded_rs_lengths() { return _recorded_rs_lengths; }
 220 
 221   size_t bytes_used_before() const {
 222     return _bytes_used_before;
 223   }
 224 
 225   void reset_bytes_used_before() {
 226     _bytes_used_before = 0;
 227   }
 228 
 229   // Finalize the initial (first) collection set consisting of all young regions and a
 230   // few old gen regions.
 231   void finalize_initial_collection_set(double target_pause_time_ms, G1SurvivorRegions* survivor);
 232   // Finalize the next collection set from the set of available optional old gen regions.
 233   bool finalize_optional_for_evacuation(double remaining_pause_time);
 234   // Abandon (clean up) optional collection set regions that were not evacuated in this
 235   // pause.
 236   void abandon_optional_collection_set(G1ParScanThreadStateSet* pss);
 237 
 238   // Update information about hr in the aggregated information for
 239   // the incrementally built collection set.
 240   void update_young_region_prediction(HeapRegion* hr, size_t new_rs_length);
 241 
 242   // Add eden region to the collection set.
 243   void add_eden_region(HeapRegion* hr);
 244 
 245   // Add survivor region to the collection set.
 246   void add_survivor_regions(HeapRegion* hr);
 247 
 248 #ifndef PRODUCT
 249   bool verify_young_ages();
 250 
 251   void print(outputStream* st);
 252 #endif // !PRODUCT
 253 };
 254 
 255 #endif // SHARE_GC_G1_G1COLLECTIONSET_HPP