1 /*
   2  * Copyright (c) 2001, 2019, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  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).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "gc/g1/g1Analytics.hpp"
  27 #include "gc/g1/g1Arguments.hpp"
  28 #include "gc/g1/g1CollectedHeap.inline.hpp"
  29 #include "gc/g1/g1CollectionSet.hpp"
  30 #include "gc/g1/g1CollectionSetCandidates.hpp"
  31 #include "gc/g1/g1ConcurrentMark.hpp"
  32 #include "gc/g1/g1ConcurrentMarkThread.inline.hpp"
  33 #include "gc/g1/g1ConcurrentRefine.hpp"
  34 #include "gc/g1/g1CollectionSetChooser.hpp"
  35 #include "gc/g1/g1HeterogeneousHeapPolicy.hpp"
  36 #include "gc/g1/g1HotCardCache.hpp"
  37 #include "gc/g1/g1IHOPControl.hpp"
  38 #include "gc/g1/g1GCPhaseTimes.hpp"
  39 #include "gc/g1/g1Policy.hpp"
  40 #include "gc/g1/g1SurvivorRegions.hpp"
  41 #include "gc/g1/g1YoungGenSizer.hpp"
  42 #include "gc/g1/heapRegion.inline.hpp"
  43 #include "gc/g1/heapRegionRemSet.hpp"
  44 #include "gc/shared/gcPolicyCounters.hpp"
  45 #include "logging/logStream.hpp"
  46 #include "runtime/arguments.hpp"
  47 #include "runtime/java.hpp"
  48 #include "runtime/mutexLocker.hpp"
  49 #include "utilities/debug.hpp"
  50 #include "utilities/growableArray.hpp"
  51 #include "utilities/pair.hpp"
  52 
  53 G1Policy::G1Policy(STWGCTimer* gc_timer) :
  54   _predictor(G1ConfidencePercent / 100.0),
  55   _analytics(new G1Analytics(&_predictor)),
  56   _remset_tracker(),
  57   _mmu_tracker(new G1MMUTrackerQueue(GCPauseIntervalMillis / 1000.0, MaxGCPauseMillis / 1000.0)),
  58   _ihop_control(create_ihop_control(&_predictor)),
  59   _policy_counters(new GCPolicyCounters("GarbageFirst", 1, 2)),
  60   _full_collection_start_sec(0.0),
  61   _collection_pause_end_millis(os::javaTimeNanos() / NANOSECS_PER_MILLISEC),
  62   _young_list_target_length(0),
  63   _young_list_fixed_length(0),
  64   _young_list_max_length(0),
  65   _short_lived_surv_rate_group(new SurvRateGroup()),
  66   _survivor_surv_rate_group(new SurvRateGroup()),
  67   _reserve_factor((double) G1ReservePercent / 100.0),
  68   _reserve_regions(0),
  69   _young_gen_sizer(G1YoungGenSizer::create_gen_sizer()),
  70   _free_regions_at_end_of_collection(0),
  71   _rs_length(0),
  72   _rs_length_prediction(0),
  73   _pending_cards_at_gc_start(0),
  74   _pending_cards_at_prev_gc_end(0),
  75   _total_mutator_refined_cards(0),
  76   _total_concurrent_refined_cards(0),
  77   _total_concurrent_refinement_time(),
  78   _bytes_allocated_in_old_since_last_gc(0),
  79   _initial_mark_to_mixed(),
  80   _collection_set(NULL),
  81   _g1h(NULL),
  82   _phase_times(new G1GCPhaseTimes(gc_timer, ParallelGCThreads)),
  83   _mark_remark_start_sec(0),
  84   _mark_cleanup_start_sec(0),
  85   _tenuring_threshold(MaxTenuringThreshold),
  86   _max_survivor_regions(0),
  87   _survivors_age_table(true)
  88 {
  89 }
  90 
  91 G1Policy::~G1Policy() {
  92   delete _ihop_control;
  93   delete _young_gen_sizer;
  94 }
  95 
  96 G1Policy* G1Policy::create_policy(STWGCTimer* gc_timer_stw) {
  97   if (G1Arguments::is_heterogeneous_heap()) {
  98     return new G1HeterogeneousHeapPolicy(gc_timer_stw);
  99   } else {
 100     return new G1Policy(gc_timer_stw);
 101   }
 102 }
 103 
 104 G1CollectorState* G1Policy::collector_state() const { return _g1h->collector_state(); }
 105 
 106 void G1Policy::init(G1CollectedHeap* g1h, G1CollectionSet* collection_set) {
 107   _g1h = g1h;
 108   _collection_set = collection_set;
 109 
 110   assert(Heap_lock->owned_by_self(), "Locking discipline.");
 111 
 112   if (!use_adaptive_young_list_length()) {
 113     _young_list_fixed_length = _young_gen_sizer->min_desired_young_length();
 114   }
 115   _young_gen_sizer->adjust_max_new_size(_g1h->max_expandable_regions());
 116 
 117   _free_regions_at_end_of_collection = _g1h->num_free_regions();
 118 
 119   update_young_list_max_and_target_length();
 120   // We may immediately start allocating regions and placing them on the
 121   // collection set list. Initialize the per-collection set info
 122   _collection_set->start_incremental_building();
 123 }
 124 
 125 void G1Policy::note_gc_start() {
 126   phase_times()->note_gc_start();
 127 }
 128 
 129 class G1YoungLengthPredictor {
 130   const bool _during_cm;
 131   const double _base_time_ms;
 132   const double _base_free_regions;
 133   const double _target_pause_time_ms;
 134   const G1Policy* const _policy;
 135 
 136  public:
 137   G1YoungLengthPredictor(bool during_cm,
 138                          double base_time_ms,
 139                          double base_free_regions,
 140                          double target_pause_time_ms,
 141                          const G1Policy* policy) :
 142     _during_cm(during_cm),
 143     _base_time_ms(base_time_ms),
 144     _base_free_regions(base_free_regions),
 145     _target_pause_time_ms(target_pause_time_ms),
 146     _policy(policy) {}
 147 
 148   bool will_fit(uint young_length) const {
 149     if (young_length >= _base_free_regions) {
 150       // end condition 1: not enough space for the young regions
 151       return false;
 152     }
 153 
 154     const double accum_surv_rate = _policy->accum_yg_surv_rate_pred((int) young_length - 1);
 155     const size_t bytes_to_copy =
 156                  (size_t) (accum_surv_rate * (double) HeapRegion::GrainBytes);
 157     const double copy_time_ms =
 158       _policy->analytics()->predict_object_copy_time_ms(bytes_to_copy, _during_cm);
 159     const double young_other_time_ms = _policy->analytics()->predict_young_other_time_ms(young_length);
 160     const double pause_time_ms = _base_time_ms + copy_time_ms + young_other_time_ms;
 161     if (pause_time_ms > _target_pause_time_ms) {
 162       // end condition 2: prediction is over the target pause time
 163       return false;
 164     }
 165 
 166     const size_t free_bytes = (_base_free_regions - young_length) * HeapRegion::GrainBytes;
 167 
 168     // When copying, we will likely need more bytes free than is live in the region.
 169     // Add some safety margin to factor in the confidence of our guess, and the
 170     // natural expected waste.
 171     // (100.0 / G1ConfidencePercent) is a scale factor that expresses the uncertainty
 172     // of the calculation: the lower the confidence, the more headroom.
 173     // (100 + TargetPLABWastePct) represents the increase in expected bytes during
 174     // copying due to anticipated waste in the PLABs.
 175     const double safety_factor = (100.0 / G1ConfidencePercent) * (100 + TargetPLABWastePct) / 100.0;
 176     const size_t expected_bytes_to_copy = (size_t)(safety_factor * bytes_to_copy);
 177 
 178     if (expected_bytes_to_copy > free_bytes) {
 179       // end condition 3: out-of-space
 180       return false;
 181     }
 182 
 183     // success!
 184     return true;
 185   }
 186 };
 187 
 188 void G1Policy::record_new_heap_size(uint new_number_of_regions) {
 189   // re-calculate the necessary reserve
 190   double reserve_regions_d = (double) new_number_of_regions * _reserve_factor;
 191   // We use ceiling so that if reserve_regions_d is > 0.0 (but
 192   // smaller than 1.0) we'll get 1.
 193   _reserve_regions = (uint) ceil(reserve_regions_d);
 194 
 195   _young_gen_sizer->heap_size_changed(new_number_of_regions);
 196 
 197   _ihop_control->update_target_occupancy(new_number_of_regions * HeapRegion::GrainBytes);
 198 }
 199 
 200 uint G1Policy::calculate_young_list_desired_min_length(uint base_min_length) const {
 201   uint desired_min_length = 0;
 202   if (use_adaptive_young_list_length()) {
 203     if (_analytics->num_alloc_rate_ms() > 3) {
 204       double now_sec = os::elapsedTime();
 205       double when_ms = _mmu_tracker->when_max_gc_sec(now_sec) * 1000.0;
 206       double alloc_rate_ms = _analytics->predict_alloc_rate_ms();
 207       desired_min_length = (uint) ceil(alloc_rate_ms * when_ms);
 208     } else {
 209       // otherwise we don't have enough info to make the prediction
 210     }
 211   }
 212   desired_min_length += base_min_length;
 213   // make sure we don't go below any user-defined minimum bound
 214   return MAX2(_young_gen_sizer->min_desired_young_length(), desired_min_length);
 215 }
 216 
 217 uint G1Policy::calculate_young_list_desired_max_length() const {
 218   // Here, we might want to also take into account any additional
 219   // constraints (i.e., user-defined minimum bound). Currently, we
 220   // effectively don't set this bound.
 221   return _young_gen_sizer->max_desired_young_length();
 222 }
 223 
 224 uint G1Policy::update_young_list_max_and_target_length() {
 225   return update_young_list_max_and_target_length(_analytics->predict_rs_length());
 226 }
 227 
 228 uint G1Policy::update_young_list_max_and_target_length(size_t rs_length) {
 229   uint unbounded_target_length = update_young_list_target_length(rs_length);
 230   update_max_gc_locker_expansion();
 231   return unbounded_target_length;
 232 }
 233 
 234 uint G1Policy::update_young_list_target_length(size_t rs_length) {
 235   YoungTargetLengths young_lengths = young_list_target_lengths(rs_length);
 236   _young_list_target_length = young_lengths.first;
 237 
 238   return young_lengths.second;
 239 }
 240 
 241 G1Policy::YoungTargetLengths G1Policy::young_list_target_lengths(size_t rs_length) const {
 242   YoungTargetLengths result;
 243 
 244   // Calculate the absolute and desired min bounds first.
 245 
 246   // This is how many young regions we already have (currently: the survivors).
 247   const uint base_min_length = _g1h->survivor_regions_count();
 248   uint desired_min_length = calculate_young_list_desired_min_length(base_min_length);
 249   // This is the absolute minimum young length. Ensure that we
 250   // will at least have one eden region available for allocation.
 251   uint absolute_min_length = base_min_length + MAX2(_g1h->eden_regions_count(), (uint)1);
 252   // If we shrank the young list target it should not shrink below the current size.
 253   desired_min_length = MAX2(desired_min_length, absolute_min_length);
 254   // Calculate the absolute and desired max bounds.
 255 
 256   uint desired_max_length = calculate_young_list_desired_max_length();
 257 
 258   uint young_list_target_length = 0;
 259   if (use_adaptive_young_list_length()) {
 260     if (collector_state()->in_young_only_phase()) {
 261       young_list_target_length =
 262                         calculate_young_list_target_length(rs_length,
 263                                                            base_min_length,
 264                                                            desired_min_length,
 265                                                            desired_max_length);
 266     } else {
 267       // Don't calculate anything and let the code below bound it to
 268       // the desired_min_length, i.e., do the next GC as soon as
 269       // possible to maximize how many old regions we can add to it.
 270     }
 271   } else {
 272     // The user asked for a fixed young gen so we'll fix the young gen
 273     // whether the next GC is young or mixed.
 274     young_list_target_length = _young_list_fixed_length;
 275   }
 276 
 277   result.second = young_list_target_length;
 278 
 279   // We will try our best not to "eat" into the reserve.
 280   uint absolute_max_length = 0;
 281   if (_free_regions_at_end_of_collection > _reserve_regions) {
 282     absolute_max_length = _free_regions_at_end_of_collection - _reserve_regions;
 283   }
 284   if (desired_max_length > absolute_max_length) {
 285     desired_max_length = absolute_max_length;
 286   }
 287 
 288   // Make sure we don't go over the desired max length, nor under the
 289   // desired min length. In case they clash, desired_min_length wins
 290   // which is why that test is second.
 291   if (young_list_target_length > desired_max_length) {
 292     young_list_target_length = desired_max_length;
 293   }
 294   if (young_list_target_length < desired_min_length) {
 295     young_list_target_length = desired_min_length;
 296   }
 297 
 298   assert(young_list_target_length > base_min_length,
 299          "we should be able to allocate at least one eden region");
 300   assert(young_list_target_length >= absolute_min_length, "post-condition");
 301 
 302   result.first = young_list_target_length;
 303   return result;
 304 }
 305 
 306 uint
 307 G1Policy::calculate_young_list_target_length(size_t rs_length,
 308                                                     uint base_min_length,
 309                                                     uint desired_min_length,
 310                                                     uint desired_max_length) const {
 311   assert(use_adaptive_young_list_length(), "pre-condition");
 312   assert(collector_state()->in_young_only_phase(), "only call this for young GCs");
 313 
 314   // In case some edge-condition makes the desired max length too small...
 315   if (desired_max_length <= desired_min_length) {
 316     return desired_min_length;
 317   }
 318 
 319   // We'll adjust min_young_length and max_young_length not to include
 320   // the already allocated young regions (i.e., so they reflect the
 321   // min and max eden regions we'll allocate). The base_min_length
 322   // will be reflected in the predictions by the
 323   // survivor_regions_evac_time prediction.
 324   assert(desired_min_length > base_min_length, "invariant");
 325   uint min_young_length = desired_min_length - base_min_length;
 326   assert(desired_max_length > base_min_length, "invariant");
 327   uint max_young_length = desired_max_length - base_min_length;
 328 
 329   const double target_pause_time_ms = _mmu_tracker->max_gc_time() * 1000.0;
 330   const double survivor_regions_evac_time = predict_survivor_regions_evac_time();
 331   const size_t pending_cards = _analytics->predict_pending_cards();
 332   const size_t scanned_cards = _analytics->predict_card_num(rs_length, true /* for_young_gc */);
 333   const double base_time_ms =
 334     predict_base_elapsed_time_ms(pending_cards, scanned_cards) +
 335     survivor_regions_evac_time;
 336   const uint available_free_regions = _free_regions_at_end_of_collection;
 337   const uint base_free_regions =
 338     available_free_regions > _reserve_regions ? available_free_regions - _reserve_regions : 0;
 339 
 340   // Here, we will make sure that the shortest young length that
 341   // makes sense fits within the target pause time.
 342 
 343   G1YoungLengthPredictor p(collector_state()->mark_or_rebuild_in_progress(),
 344                            base_time_ms,
 345                            base_free_regions,
 346                            target_pause_time_ms,
 347                            this);
 348   if (p.will_fit(min_young_length)) {
 349     // The shortest young length will fit into the target pause time;
 350     // we'll now check whether the absolute maximum number of young
 351     // regions will fit in the target pause time. If not, we'll do
 352     // a binary search between min_young_length and max_young_length.
 353     if (p.will_fit(max_young_length)) {
 354       // The maximum young length will fit into the target pause time.
 355       // We are done so set min young length to the maximum length (as
 356       // the result is assumed to be returned in min_young_length).
 357       min_young_length = max_young_length;
 358     } else {
 359       // The maximum possible number of young regions will not fit within
 360       // the target pause time so we'll search for the optimal
 361       // length. The loop invariants are:
 362       //
 363       // min_young_length < max_young_length
 364       // min_young_length is known to fit into the target pause time
 365       // max_young_length is known not to fit into the target pause time
 366       //
 367       // Going into the loop we know the above hold as we've just
 368       // checked them. Every time around the loop we check whether
 369       // the middle value between min_young_length and
 370       // max_young_length fits into the target pause time. If it
 371       // does, it becomes the new min. If it doesn't, it becomes
 372       // the new max. This way we maintain the loop invariants.
 373 
 374       assert(min_young_length < max_young_length, "invariant");
 375       uint diff = (max_young_length - min_young_length) / 2;
 376       while (diff > 0) {
 377         uint young_length = min_young_length + diff;
 378         if (p.will_fit(young_length)) {
 379           min_young_length = young_length;
 380         } else {
 381           max_young_length = young_length;
 382         }
 383         assert(min_young_length <  max_young_length, "invariant");
 384         diff = (max_young_length - min_young_length) / 2;
 385       }
 386       // The results is min_young_length which, according to the
 387       // loop invariants, should fit within the target pause time.
 388 
 389       // These are the post-conditions of the binary search above:
 390       assert(min_young_length < max_young_length,
 391              "otherwise we should have discovered that max_young_length "
 392              "fits into the pause target and not done the binary search");
 393       assert(p.will_fit(min_young_length),
 394              "min_young_length, the result of the binary search, should "
 395              "fit into the pause target");
 396       assert(!p.will_fit(min_young_length + 1),
 397              "min_young_length, the result of the binary search, should be "
 398              "optimal, so no larger length should fit into the pause target");
 399     }
 400   } else {
 401     // Even the minimum length doesn't fit into the pause time
 402     // target, return it as the result nevertheless.
 403   }
 404   return base_min_length + min_young_length;
 405 }
 406 
 407 double G1Policy::predict_survivor_regions_evac_time() const {
 408   double survivor_regions_evac_time = 0.0;
 409   const GrowableArray<HeapRegion*>* survivor_regions = _g1h->survivor()->regions();
 410 
 411   for (GrowableArrayIterator<HeapRegion*> it = survivor_regions->begin();
 412        it != survivor_regions->end();
 413        ++it) {
 414     survivor_regions_evac_time += predict_region_elapsed_time_ms(*it, collector_state()->in_young_only_phase());
 415   }
 416   return survivor_regions_evac_time;
 417 }
 418 
 419 void G1Policy::revise_young_list_target_length_if_necessary(size_t rs_length) {
 420   guarantee(use_adaptive_young_list_length(), "should not call this otherwise" );
 421 
 422   if (rs_length > _rs_length_prediction) {
 423     // add 10% to avoid having to recalculate often
 424     size_t rs_length_prediction = rs_length * 1100 / 1000;
 425     update_rs_length_prediction(rs_length_prediction);
 426 
 427     update_young_list_max_and_target_length(rs_length_prediction);
 428   }
 429 }
 430 
 431 void G1Policy::update_rs_length_prediction() {
 432   update_rs_length_prediction(_analytics->predict_rs_length());
 433 }
 434 
 435 void G1Policy::update_rs_length_prediction(size_t prediction) {
 436   if (collector_state()->in_young_only_phase() && use_adaptive_young_list_length()) {
 437     _rs_length_prediction = prediction;
 438   }
 439 }
 440 
 441 void G1Policy::record_full_collection_start() {
 442   _full_collection_start_sec = os::elapsedTime();
 443   // Release the future to-space so that it is available for compaction into.
 444   collector_state()->set_in_young_only_phase(false);
 445   collector_state()->set_in_full_gc(true);
 446   _collection_set->clear_candidates();
 447   record_concurrent_refinement_data(true /* is_full_collection */);
 448 }
 449 
 450 void G1Policy::record_full_collection_end() {
 451   // Consider this like a collection pause for the purposes of allocation
 452   // since last pause.
 453   double end_sec = os::elapsedTime();
 454   double full_gc_time_sec = end_sec - _full_collection_start_sec;
 455   double full_gc_time_ms = full_gc_time_sec * 1000.0;
 456 
 457   _analytics->update_recent_gc_times(end_sec, full_gc_time_ms);
 458 
 459   collector_state()->set_in_full_gc(false);
 460 
 461   // "Nuke" the heuristics that control the young/mixed GC
 462   // transitions and make sure we start with young GCs after the Full GC.
 463   collector_state()->set_in_young_only_phase(true);
 464   collector_state()->set_in_young_gc_before_mixed(false);
 465   collector_state()->set_initiate_conc_mark_if_possible(need_to_start_conc_mark("end of Full GC", 0));
 466   collector_state()->set_in_initial_mark_gc(false);
 467   collector_state()->set_mark_or_rebuild_in_progress(false);
 468   collector_state()->set_clearing_next_bitmap(false);
 469 
 470   _short_lived_surv_rate_group->start_adding_regions();
 471   // also call this on any additional surv rate groups
 472 
 473   _free_regions_at_end_of_collection = _g1h->num_free_regions();
 474   // Reset survivors SurvRateGroup.
 475   _survivor_surv_rate_group->reset();
 476   update_young_list_max_and_target_length();
 477   update_rs_length_prediction();
 478   _pending_cards_at_prev_gc_end = _g1h->pending_card_num();
 479 
 480   _bytes_allocated_in_old_since_last_gc = 0;
 481 
 482   record_pause(FullGC, _full_collection_start_sec, end_sec);
 483 }
 484 
 485 void G1Policy::record_concurrent_refinement_data(bool is_full_collection) {
 486   _pending_cards_at_gc_start = _g1h->pending_card_num();
 487 
 488   // Record info about concurrent refinement thread processing.
 489   G1ConcurrentRefine* cr = _g1h->concurrent_refine();
 490   G1ConcurrentRefine::RefinementStats cr_stats = cr->total_refinement_stats();
 491 
 492   Tickspan cr_time = cr_stats._time - _total_concurrent_refinement_time;
 493   _total_concurrent_refinement_time = cr_stats._time;
 494 
 495   size_t cr_cards = cr_stats._cards - _total_concurrent_refined_cards;
 496   _total_concurrent_refined_cards = cr_stats._cards;
 497 
 498   // Don't update rate if full collection.  We could be in an implicit full
 499   // collection after a non-full collection failure, in which case there
 500   // wasn't any mutator/cr-thread activity since last recording.  And if
 501   // we're in an explicit full collection, the time since the last GC can
 502   // be arbitrarily short, so not a very good sample.  Similarly, don't
 503   // update the rate if the current sample is empty or time is zero.
 504   if (!is_full_collection && (cr_cards > 0) && (cr_time > Tickspan())) {
 505     double rate = cr_cards / (cr_time.seconds() * MILLIUNITS);
 506     _analytics->report_concurrent_refine_rate_ms(rate);
 507   }
 508 
 509   // Record info about mutator thread processing.
 510   G1DirtyCardQueueSet& dcqs = G1BarrierSet::dirty_card_queue_set();
 511   size_t mut_total_cards = dcqs.total_mutator_refined_cards();
 512   size_t mut_cards = mut_total_cards - _total_mutator_refined_cards;
 513   _total_mutator_refined_cards = mut_total_cards;
 514 
 515   // Record mutator's card logging rate.
 516   // Don't update if full collection; see above.
 517   if (!is_full_collection) {
 518     size_t total_cards = _pending_cards_at_gc_start + cr_cards + mut_cards;
 519     assert(_pending_cards_at_prev_gc_end <= total_cards,
 520            "untracked cards: last pending: " SIZE_FORMAT
 521            ", pending: " SIZE_FORMAT ", conc refine: " SIZE_FORMAT
 522            ", mut refine:" SIZE_FORMAT,
 523            _pending_cards_at_prev_gc_end, _pending_cards_at_gc_start,
 524            cr_cards, mut_cards);
 525     size_t logged_cards = total_cards - _pending_cards_at_prev_gc_end;
 526     double logging_start_time = _analytics->prev_collection_pause_end_ms();
 527     double logging_end_time = Ticks::now().seconds() * MILLIUNITS;
 528     double logging_time = logging_end_time - logging_start_time;
 529     // Unlike above for conc-refine rate, here we should not require a
 530     // non-empty sample, since an application could go some time with only
 531     // young-gen or filtered out writes.  But we'll ignore unusually short
 532     // sample periods, as they may just pollute the predictions.
 533     if (logging_time > 1.0) {   // Require > 1ms sample time.
 534       _analytics->report_logged_cards_rate_ms(logged_cards / logging_time);
 535     }
 536   }
 537 }
 538 
 539 void G1Policy::record_collection_pause_start(double start_time_sec) {
 540   // We only need to do this here as the policy will only be applied
 541   // to the GC we're about to start. so, no point is calculating this
 542   // every time we calculate / recalculate the target young length.
 543   update_survivors_policy();
 544 
 545   assert(max_survivor_regions() + _g1h->num_used_regions() <= _g1h->max_regions(),
 546          "Maximum survivor regions %u plus used regions %u exceeds max regions %u",
 547          max_survivor_regions(), _g1h->num_used_regions(), _g1h->max_regions());
 548   assert_used_and_recalculate_used_equal(_g1h);
 549 
 550   phase_times()->record_cur_collection_start_sec(start_time_sec);
 551 
 552   record_concurrent_refinement_data(false /* is_full_collection */);
 553 
 554   _collection_set->reset_bytes_used_before();
 555 
 556   // do that for any other surv rate groups
 557   _short_lived_surv_rate_group->stop_adding_regions();
 558   _survivors_age_table.clear();
 559 
 560   assert(_g1h->collection_set()->verify_young_ages(), "region age verification failed");
 561 }
 562 
 563 void G1Policy::record_concurrent_mark_init_end(double mark_init_elapsed_time_ms) {
 564   assert(!collector_state()->initiate_conc_mark_if_possible(), "we should have cleared it by now");
 565   collector_state()->set_in_initial_mark_gc(false);
 566 }
 567 
 568 void G1Policy::record_concurrent_mark_remark_start() {
 569   _mark_remark_start_sec = os::elapsedTime();
 570 }
 571 
 572 void G1Policy::record_concurrent_mark_remark_end() {
 573   double end_time_sec = os::elapsedTime();
 574   double elapsed_time_ms = (end_time_sec - _mark_remark_start_sec)*1000.0;
 575   _analytics->report_concurrent_mark_remark_times_ms(elapsed_time_ms);
 576   _analytics->append_prev_collection_pause_end_ms(elapsed_time_ms);
 577 
 578   record_pause(Remark, _mark_remark_start_sec, end_time_sec);
 579 }
 580 
 581 void G1Policy::record_concurrent_mark_cleanup_start() {
 582   _mark_cleanup_start_sec = os::elapsedTime();
 583 }
 584 
 585 double G1Policy::average_time_ms(G1GCPhaseTimes::GCParPhases phase) const {
 586   return phase_times()->average_time_ms(phase);
 587 }
 588 
 589 double G1Policy::young_other_time_ms() const {
 590   return phase_times()->young_cset_choice_time_ms() +
 591          phase_times()->average_time_ms(G1GCPhaseTimes::YoungFreeCSet);
 592 }
 593 
 594 double G1Policy::non_young_other_time_ms() const {
 595   return phase_times()->non_young_cset_choice_time_ms() +
 596          phase_times()->average_time_ms(G1GCPhaseTimes::NonYoungFreeCSet);
 597 }
 598 
 599 double G1Policy::other_time_ms(double pause_time_ms) const {
 600   return pause_time_ms - phase_times()->cur_collection_par_time_ms();
 601 }
 602 
 603 double G1Policy::constant_other_time_ms(double pause_time_ms) const {
 604   return other_time_ms(pause_time_ms) - phase_times()->total_free_cset_time_ms();
 605 }
 606 
 607 bool G1Policy::about_to_start_mixed_phase() const {
 608   return _g1h->concurrent_mark()->cm_thread()->during_cycle() || collector_state()->in_young_gc_before_mixed();
 609 }
 610 
 611 bool G1Policy::need_to_start_conc_mark(const char* source, size_t alloc_word_size) {
 612   if (about_to_start_mixed_phase()) {
 613     return false;
 614   }
 615 
 616   size_t marking_initiating_used_threshold = _ihop_control->get_conc_mark_start_threshold();
 617 
 618   size_t cur_used_bytes = _g1h->non_young_capacity_bytes();
 619   size_t alloc_byte_size = alloc_word_size * HeapWordSize;
 620   size_t marking_request_bytes = cur_used_bytes + alloc_byte_size;
 621 
 622   bool result = false;
 623   if (marking_request_bytes > marking_initiating_used_threshold) {
 624     result = collector_state()->in_young_only_phase() && !collector_state()->in_young_gc_before_mixed();
 625     log_debug(gc, ergo, ihop)("%s occupancy: " SIZE_FORMAT "B allocation request: " SIZE_FORMAT "B threshold: " SIZE_FORMAT "B (%1.2f) source: %s",
 626                               result ? "Request concurrent cycle initiation (occupancy higher than threshold)" : "Do not request concurrent cycle initiation (still doing mixed collections)",
 627                               cur_used_bytes, alloc_byte_size, marking_initiating_used_threshold, (double) marking_initiating_used_threshold / _g1h->capacity() * 100, source);
 628   }
 629 
 630   return result;
 631 }
 632 
 633 double G1Policy::logged_cards_processing_time() const {
 634   double all_cards_processing_time = average_time_ms(G1GCPhaseTimes::ScanHR) + average_time_ms(G1GCPhaseTimes::OptScanHR);
 635   size_t logged_dirty_cards = phase_times()->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards);
 636   size_t scan_heap_roots_cards = phase_times()->sum_thread_work_items(G1GCPhaseTimes::ScanHR, G1GCPhaseTimes::ScanHRScannedCards) +
 637                                  phase_times()->sum_thread_work_items(G1GCPhaseTimes::OptScanHR, G1GCPhaseTimes::ScanHRScannedCards);
 638   // This may happen if there are duplicate cards in different log buffers.
 639   if (logged_dirty_cards > scan_heap_roots_cards) {
 640     return all_cards_processing_time + average_time_ms(G1GCPhaseTimes::MergeLB);
 641   }
 642   return (all_cards_processing_time * logged_dirty_cards / scan_heap_roots_cards) + average_time_ms(G1GCPhaseTimes::MergeLB);
 643 }
 644 
 645 // Anything below that is considered to be zero
 646 #define MIN_TIMER_GRANULARITY 0.0000001
 647 
 648 void G1Policy::record_collection_pause_end(double pause_time_ms) {
 649   G1GCPhaseTimes* p = phase_times();
 650 
 651   double end_time_sec = os::elapsedTime();
 652 
 653   bool this_pause_included_initial_mark = false;
 654   bool this_pause_was_young_only = collector_state()->in_young_only_phase();
 655 
 656   bool update_stats = !_g1h->evacuation_failed();
 657 
 658   record_pause(young_gc_pause_kind(), end_time_sec - pause_time_ms / 1000.0, end_time_sec);
 659 
 660   _collection_pause_end_millis = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 661 
 662   this_pause_included_initial_mark = collector_state()->in_initial_mark_gc();
 663   if (this_pause_included_initial_mark) {
 664     record_concurrent_mark_init_end(0.0);
 665   } else {
 666     maybe_start_marking();
 667   }
 668 
 669   double app_time_ms = (phase_times()->cur_collection_start_sec() * 1000.0 - _analytics->prev_collection_pause_end_ms());
 670   if (app_time_ms < MIN_TIMER_GRANULARITY) {
 671     // This usually happens due to the timer not having the required
 672     // granularity. Some Linuxes are the usual culprits.
 673     // We'll just set it to something (arbitrarily) small.
 674     app_time_ms = 1.0;
 675   }
 676 
 677   if (update_stats) {
 678     // We maintain the invariant that all objects allocated by mutator
 679     // threads will be allocated out of eden regions. So, we can use
 680     // the eden region number allocated since the previous GC to
 681     // calculate the application's allocate rate. The only exception
 682     // to that is humongous objects that are allocated separately. But
 683     // given that humongous object allocations do not really affect
 684     // either the pause's duration nor when the next pause will take
 685     // place we can safely ignore them here.
 686     uint regions_allocated = _collection_set->eden_region_length();
 687     double alloc_rate_ms = (double) regions_allocated / app_time_ms;
 688     _analytics->report_alloc_rate_ms(alloc_rate_ms);
 689 
 690     double interval_ms =
 691       (end_time_sec - _analytics->last_known_gc_end_time_sec()) * 1000.0;
 692     _analytics->update_recent_gc_times(end_time_sec, pause_time_ms);
 693     _analytics->compute_pause_time_ratio(interval_ms, pause_time_ms);
 694   }
 695 
 696   if (collector_state()->in_young_gc_before_mixed()) {
 697     assert(!this_pause_included_initial_mark, "The young GC before mixed is not allowed to be an initial mark GC");
 698     // This has been the young GC before we start doing mixed GCs. We already
 699     // decided to start mixed GCs much earlier, so there is nothing to do except
 700     // advancing the state.
 701     collector_state()->set_in_young_only_phase(false);
 702     collector_state()->set_in_young_gc_before_mixed(false);
 703   } else if (!this_pause_was_young_only) {
 704     // This is a mixed GC. Here we decide whether to continue doing more
 705     // mixed GCs or not.
 706     if (!next_gc_should_be_mixed("continue mixed GCs",
 707                                  "do not continue mixed GCs")) {
 708       collector_state()->set_in_young_only_phase(true);
 709 
 710       clear_collection_set_candidates();
 711       maybe_start_marking();
 712     }
 713   }
 714 
 715   _short_lived_surv_rate_group->start_adding_regions();
 716   // Do that for any other surv rate groups
 717 
 718   double scan_hcc_time_ms = G1HotCardCache::default_use_cache() ? average_time_ms(G1GCPhaseTimes::MergeHCC) : 0.0;
 719 
 720   if (update_stats) {
 721     double cost_per_logged_card = 0.0;
 722     size_t const pending_logged_cards = p->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards);
 723     if (pending_logged_cards > 0) {
 724       cost_per_logged_card = logged_cards_processing_time() / pending_logged_cards;
 725       _analytics->report_cost_per_logged_card_ms(cost_per_logged_card);
 726     }
 727     _analytics->report_cost_scan_hcc(scan_hcc_time_ms);
 728 
 729     size_t const total_cards_scanned = p->sum_thread_work_items(G1GCPhaseTimes::ScanHR, G1GCPhaseTimes::ScanHRScannedCards) +
 730                                        p->sum_thread_work_items(G1GCPhaseTimes::OptScanHR, G1GCPhaseTimes::ScanHRScannedCards);
 731     size_t remset_cards_scanned = 0;
 732     // There might have been duplicate log buffer entries in the queues which could
 733     // increase this value beyond the cards scanned. In this case attribute all cards
 734     // to the log buffers.
 735     if (pending_logged_cards <= total_cards_scanned) {
 736       remset_cards_scanned = total_cards_scanned - pending_logged_cards;
 737     }
 738 
 739     double cost_per_remset_card_ms = 0.0;
 740     if (remset_cards_scanned > 10) {
 741       double avg_time_remset_scan = ((average_time_ms(G1GCPhaseTimes::ScanHR) + average_time_ms(G1GCPhaseTimes::OptScanHR)) *
 742                                      remset_cards_scanned / total_cards_scanned) +
 743                                      average_time_ms(G1GCPhaseTimes::MergeER) +
 744                                      average_time_ms(G1GCPhaseTimes::MergeRS) +
 745                                      average_time_ms(G1GCPhaseTimes::OptMergeRS);
 746 
 747       cost_per_remset_card_ms = avg_time_remset_scan / remset_cards_scanned;
 748       _analytics->report_cost_per_remset_card_ms(cost_per_remset_card_ms, this_pause_was_young_only);
 749     }
 750 
 751     if (_rs_length > 0) {
 752       double cards_per_entry_ratio =
 753         (double) remset_cards_scanned / (double) _rs_length;
 754       _analytics->report_cards_per_entry_ratio(cards_per_entry_ratio, this_pause_was_young_only);
 755     }
 756 
 757     // This is defensive. For a while _rs_length could get
 758     // smaller than _recorded_rs_length which was causing
 759     // rs_length_diff to get very large and mess up the RSet length
 760     // predictions. The reason was unsafe concurrent updates to the
 761     // _inc_cset_recorded_rs_length field which the code below guards
 762     // against (see CR 7118202). This bug has now been fixed (see CR
 763     // 7119027). However, I'm still worried that
 764     // _inc_cset_recorded_rs_length might still end up somewhat
 765     // inaccurate. The concurrent refinement thread calculates an
 766     // RSet's length concurrently with other CR threads updating it
 767     // which might cause it to calculate the length incorrectly (if,
 768     // say, it's in mid-coarsening). So I'll leave in the defensive
 769     // conditional below just in case.
 770     size_t rs_length_diff = 0;
 771     size_t recorded_rs_length = _collection_set->recorded_rs_length();
 772     if (_rs_length > recorded_rs_length) {
 773       rs_length_diff = _rs_length - recorded_rs_length;
 774     }
 775     _analytics->report_rs_length_diff((double) rs_length_diff);
 776 
 777     size_t copied_bytes = p->sum_thread_work_items(G1GCPhaseTimes::MergePSS, G1GCPhaseTimes::MergePSSCopiedBytes);
 778 
 779     if (copied_bytes > 0) {
 780       double cost_per_byte_ms = (average_time_ms(G1GCPhaseTimes::ObjCopy) + average_time_ms(G1GCPhaseTimes::OptObjCopy)) / copied_bytes;
 781       _analytics->report_cost_per_byte_ms(cost_per_byte_ms, collector_state()->mark_or_rebuild_in_progress());
 782     }
 783 
 784     if (_collection_set->young_region_length() > 0) {
 785       _analytics->report_young_other_cost_per_region_ms(young_other_time_ms() /
 786                                                         _collection_set->young_region_length());
 787     }
 788 
 789     if (_collection_set->old_region_length() > 0) {
 790       _analytics->report_non_young_other_cost_per_region_ms(non_young_other_time_ms() /
 791                                                             _collection_set->old_region_length());
 792     }
 793 
 794     _analytics->report_constant_other_time_ms(constant_other_time_ms(pause_time_ms));
 795 
 796     // Do not update RS lengths and the number of pending cards with information from mixed gc:
 797     // these are is wildly different to during young only gc and mess up young gen sizing right
 798     // after the mixed gc phase.
 799     // During mixed gc we do not use them for young gen sizing.
 800     if (this_pause_was_young_only) {
 801       _analytics->report_pending_cards((double) _pending_cards_at_gc_start);
 802       _analytics->report_rs_length((double) _rs_length);
 803     }
 804   }
 805 
 806   assert(!(this_pause_included_initial_mark && collector_state()->mark_or_rebuild_in_progress()),
 807          "If the last pause has been an initial mark, we should not have been in the marking window");
 808   if (this_pause_included_initial_mark) {
 809     collector_state()->set_mark_or_rebuild_in_progress(true);
 810   }
 811 
 812   _free_regions_at_end_of_collection = _g1h->num_free_regions();
 813 
 814   update_rs_length_prediction();
 815 
 816   // Do not update dynamic IHOP due to G1 periodic collection as it is highly likely
 817   // that in this case we are not running in a "normal" operating mode.
 818   if (_g1h->gc_cause() != GCCause::_g1_periodic_collection) {
 819     // IHOP control wants to know the expected young gen length if it were not
 820     // restrained by the heap reserve. Using the actual length would make the
 821     // prediction too small and the limit the young gen every time we get to the
 822     // predicted target occupancy.
 823     size_t last_unrestrained_young_length = update_young_list_max_and_target_length();
 824 
 825     update_ihop_prediction(app_time_ms / 1000.0,
 826                            _bytes_allocated_in_old_since_last_gc,
 827                            last_unrestrained_young_length * HeapRegion::GrainBytes,
 828                            this_pause_was_young_only);
 829     _bytes_allocated_in_old_since_last_gc = 0;
 830 
 831     _ihop_control->send_trace_event(_g1h->gc_tracer_stw());
 832   } else {
 833     // Any garbage collection triggered as periodic collection resets the time-to-mixed
 834     // measurement. Periodic collection typically means that the application is "inactive", i.e.
 835     // the marking threads may have received an uncharacterisic amount of cpu time
 836     // for completing the marking, i.e. are faster than expected.
 837     // This skews the predicted marking length towards smaller values which might cause
 838     // the mark start being too late.
 839     _initial_mark_to_mixed.reset();
 840   }
 841 
 842   // Note that _mmu_tracker->max_gc_time() returns the time in seconds.
 843   double scan_logged_cards_time_goal_ms = _mmu_tracker->max_gc_time() * MILLIUNITS * G1RSetUpdatingPauseTimePercent / 100.0;
 844 
 845   if (scan_logged_cards_time_goal_ms < scan_hcc_time_ms) {
 846     log_debug(gc, ergo, refine)("Adjust concurrent refinement thresholds (scanning the HCC expected to take longer than Update RS time goal)."
 847                                 "Logged Cards Scan time goal: %1.2fms Scan HCC time: %1.2fms",
 848                                 scan_logged_cards_time_goal_ms, scan_hcc_time_ms);
 849 
 850     scan_logged_cards_time_goal_ms = 0;
 851   } else {
 852     scan_logged_cards_time_goal_ms -= scan_hcc_time_ms;
 853   }
 854 
 855   _pending_cards_at_prev_gc_end = _g1h->pending_card_num();
 856   double const logged_cards_time = logged_cards_processing_time();
 857 
 858   log_debug(gc, ergo, refine)("Concurrent refinement times: Logged Cards Scan time goal: %1.2fms Logged Cards Scan time: %1.2fms HCC time: %1.2fms",
 859                               scan_logged_cards_time_goal_ms, logged_cards_time, scan_hcc_time_ms);
 860 
 861   _g1h->concurrent_refine()->adjust(logged_cards_time,
 862                                     phase_times()->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards),
 863                                     scan_logged_cards_time_goal_ms);
 864 }
 865 
 866 G1IHOPControl* G1Policy::create_ihop_control(const G1Predictions* predictor){
 867   if (G1UseAdaptiveIHOP) {
 868     return new G1AdaptiveIHOPControl(InitiatingHeapOccupancyPercent,
 869                                      predictor,
 870                                      G1ReservePercent,
 871                                      G1HeapWastePercent);
 872   } else {
 873     return new G1StaticIHOPControl(InitiatingHeapOccupancyPercent);
 874   }
 875 }
 876 
 877 void G1Policy::update_ihop_prediction(double mutator_time_s,
 878                                       size_t mutator_alloc_bytes,
 879                                       size_t young_gen_size,
 880                                       bool this_gc_was_young_only) {
 881   // Always try to update IHOP prediction. Even evacuation failures give information
 882   // about e.g. whether to start IHOP earlier next time.
 883 
 884   // Avoid using really small application times that might create samples with
 885   // very high or very low values. They may be caused by e.g. back-to-back gcs.
 886   double const min_valid_time = 1e-6;
 887 
 888   bool report = false;
 889 
 890   double marking_to_mixed_time = -1.0;
 891   if (!this_gc_was_young_only && _initial_mark_to_mixed.has_result()) {
 892     marking_to_mixed_time = _initial_mark_to_mixed.last_marking_time();
 893     assert(marking_to_mixed_time > 0.0,
 894            "Initial mark to mixed time must be larger than zero but is %.3f",
 895            marking_to_mixed_time);
 896     if (marking_to_mixed_time > min_valid_time) {
 897       _ihop_control->update_marking_length(marking_to_mixed_time);
 898       report = true;
 899     }
 900   }
 901 
 902   // As an approximation for the young gc promotion rates during marking we use
 903   // all of them. In many applications there are only a few if any young gcs during
 904   // marking, which makes any prediction useless. This increases the accuracy of the
 905   // prediction.
 906   if (this_gc_was_young_only && mutator_time_s > min_valid_time) {
 907     _ihop_control->update_allocation_info(mutator_time_s, mutator_alloc_bytes, young_gen_size);
 908     report = true;
 909   }
 910 
 911   if (report) {
 912     report_ihop_statistics();
 913   }
 914 }
 915 
 916 void G1Policy::report_ihop_statistics() {
 917   _ihop_control->print();
 918 }
 919 
 920 void G1Policy::print_phases() {
 921   phase_times()->print();
 922 }
 923 
 924 double G1Policy::predict_yg_surv_rate(int age, SurvRateGroup* surv_rate_group) const {
 925   TruncatedSeq* seq = surv_rate_group->get_seq(age);
 926   guarantee(seq->num() > 0, "There should be some young gen survivor samples available. Tried to access with age %d", age);
 927   double pred = _predictor.get_new_prediction(seq);
 928   if (pred > 1.0) {
 929     pred = 1.0;
 930   }
 931   return pred;
 932 }
 933 
 934 double G1Policy::accum_yg_surv_rate_pred(int age) const {
 935   return _short_lived_surv_rate_group->accum_surv_rate_pred(age);
 936 }
 937 
 938 double G1Policy::predict_base_elapsed_time_ms(size_t pending_cards,
 939                                               size_t scanned_cards) const {
 940   return
 941     _analytics->predict_rs_update_time_ms(pending_cards) +
 942     _analytics->predict_rs_scan_time_ms(scanned_cards, collector_state()->in_young_only_phase()) +
 943     _analytics->predict_constant_other_time_ms();
 944 }
 945 
 946 double G1Policy::predict_base_elapsed_time_ms(size_t pending_cards) const {
 947   size_t rs_length = _analytics->predict_rs_length();
 948   size_t card_num = _analytics->predict_card_num(rs_length, collector_state()->in_young_only_phase());
 949   return predict_base_elapsed_time_ms(pending_cards, card_num);
 950 }
 951 
 952 size_t G1Policy::predict_bytes_to_copy(HeapRegion* hr) const {
 953   size_t bytes_to_copy;
 954   if (!hr->is_young()) {
 955     bytes_to_copy = hr->max_live_bytes();
 956   } else {
 957     assert(hr->age_in_surv_rate_group() != -1, "invariant");
 958     int age = hr->age_in_surv_rate_group();
 959     double yg_surv_rate = predict_yg_surv_rate(age, hr->surv_rate_group());
 960     bytes_to_copy = (size_t) (hr->used() * yg_surv_rate);
 961   }
 962   return bytes_to_copy;
 963 }
 964 
 965 double G1Policy::predict_region_elapsed_time_ms(HeapRegion* hr,
 966                                                 bool for_young_gc) const {
 967   size_t rs_length = hr->rem_set()->occupied();
 968   // Predicting the number of cards is based on which type of GC
 969   // we're predicting for.
 970   size_t card_num = _analytics->predict_card_num(rs_length, for_young_gc);
 971   size_t bytes_to_copy = predict_bytes_to_copy(hr);
 972 
 973   double region_elapsed_time_ms =
 974     _analytics->predict_rs_scan_time_ms(card_num, collector_state()->in_young_only_phase()) +
 975     _analytics->predict_object_copy_time_ms(bytes_to_copy, collector_state()->mark_or_rebuild_in_progress());
 976 
 977   // The prediction of the "other" time for this region is based
 978   // upon the region type and NOT the GC type.
 979   if (hr->is_young()) {
 980     region_elapsed_time_ms += _analytics->predict_young_other_time_ms(1);
 981   } else {
 982     region_elapsed_time_ms += _analytics->predict_non_young_other_time_ms(1);
 983   }
 984   return region_elapsed_time_ms;
 985 }
 986 
 987 bool G1Policy::should_allocate_mutator_region() const {
 988   uint young_list_length = _g1h->young_regions_count();
 989   uint young_list_target_length = _young_list_target_length;
 990   return young_list_length < young_list_target_length;
 991 }
 992 
 993 bool G1Policy::can_expand_young_list() const {
 994   uint young_list_length = _g1h->young_regions_count();
 995   uint young_list_max_length = _young_list_max_length;
 996   return young_list_length < young_list_max_length;
 997 }
 998 
 999 bool G1Policy::use_adaptive_young_list_length() const {
1000   return _young_gen_sizer->use_adaptive_young_list_length();
1001 }
1002 
1003 size_t G1Policy::desired_survivor_size(uint max_regions) const {
1004   size_t const survivor_capacity = HeapRegion::GrainWords * max_regions;
1005   return (size_t)((((double)survivor_capacity) * TargetSurvivorRatio) / 100);
1006 }
1007 
1008 void G1Policy::print_age_table() {
1009   _survivors_age_table.print_age_table(_tenuring_threshold);
1010 }
1011 
1012 void G1Policy::update_max_gc_locker_expansion() {
1013   uint expansion_region_num = 0;
1014   if (GCLockerEdenExpansionPercent > 0) {
1015     double perc = (double) GCLockerEdenExpansionPercent / 100.0;
1016     double expansion_region_num_d = perc * (double) _young_list_target_length;
1017     // We use ceiling so that if expansion_region_num_d is > 0.0 (but
1018     // less than 1.0) we'll get 1.
1019     expansion_region_num = (uint) ceil(expansion_region_num_d);
1020   } else {
1021     assert(expansion_region_num == 0, "sanity");
1022   }
1023   _young_list_max_length = _young_list_target_length + expansion_region_num;
1024   assert(_young_list_target_length <= _young_list_max_length, "post-condition");
1025 }
1026 
1027 // Calculates survivor space parameters.
1028 void G1Policy::update_survivors_policy() {
1029   double max_survivor_regions_d =
1030                  (double) _young_list_target_length / (double) SurvivorRatio;
1031 
1032   // Calculate desired survivor size based on desired max survivor regions (unconstrained
1033   // by remaining heap). Otherwise we may cause undesired promotions as we are
1034   // already getting close to end of the heap, impacting performance even more.
1035   uint const desired_max_survivor_regions = ceil(max_survivor_regions_d);
1036   size_t const survivor_size = desired_survivor_size(desired_max_survivor_regions);
1037 
1038   _tenuring_threshold = _survivors_age_table.compute_tenuring_threshold(survivor_size);
1039   if (UsePerfData) {
1040     _policy_counters->tenuring_threshold()->set_value(_tenuring_threshold);
1041     _policy_counters->desired_survivor_size()->set_value(survivor_size * oopSize);
1042   }
1043   // The real maximum survivor size is bounded by the number of regions that can
1044   // be allocated into.
1045   _max_survivor_regions = MIN2(desired_max_survivor_regions,
1046                                _g1h->num_free_or_available_regions());
1047 }
1048 
1049 bool G1Policy::force_initial_mark_if_outside_cycle(GCCause::Cause gc_cause) {
1050   // We actually check whether we are marking here and not if we are in a
1051   // reclamation phase. This means that we will schedule a concurrent mark
1052   // even while we are still in the process of reclaiming memory.
1053   bool during_cycle = _g1h->concurrent_mark()->cm_thread()->during_cycle();
1054   if (!during_cycle) {
1055     log_debug(gc, ergo)("Request concurrent cycle initiation (requested by GC cause). GC cause: %s", GCCause::to_string(gc_cause));
1056     collector_state()->set_initiate_conc_mark_if_possible(true);
1057     return true;
1058   } else {
1059     log_debug(gc, ergo)("Do not request concurrent cycle initiation (concurrent cycle already in progress). GC cause: %s", GCCause::to_string(gc_cause));
1060     return false;
1061   }
1062 }
1063 
1064 void G1Policy::initiate_conc_mark() {
1065   collector_state()->set_in_initial_mark_gc(true);
1066   collector_state()->set_initiate_conc_mark_if_possible(false);
1067 }
1068 
1069 void G1Policy::decide_on_conc_mark_initiation() {
1070   // We are about to decide on whether this pause will be an
1071   // initial-mark pause.
1072 
1073   // First, collector_state()->in_initial_mark_gc() should not be already set. We
1074   // will set it here if we have to. However, it should be cleared by
1075   // the end of the pause (it's only set for the duration of an
1076   // initial-mark pause).
1077   assert(!collector_state()->in_initial_mark_gc(), "pre-condition");
1078 
1079   if (collector_state()->initiate_conc_mark_if_possible()) {
1080     // We had noticed on a previous pause that the heap occupancy has
1081     // gone over the initiating threshold and we should start a
1082     // concurrent marking cycle. So we might initiate one.
1083 
1084     if (!about_to_start_mixed_phase() && collector_state()->in_young_only_phase()) {
1085       // Initiate a new initial mark if there is no marking or reclamation going on.
1086       initiate_conc_mark();
1087       log_debug(gc, ergo)("Initiate concurrent cycle (concurrent cycle initiation requested)");
1088     } else if (_g1h->is_user_requested_concurrent_full_gc(_g1h->gc_cause())) {
1089       // Initiate a user requested initial mark. An initial mark must be young only
1090       // GC, so the collector state must be updated to reflect this.
1091       collector_state()->set_in_young_only_phase(true);
1092       collector_state()->set_in_young_gc_before_mixed(false);
1093 
1094       // We might have ended up coming here about to start a mixed phase with a collection set
1095       // active. The following remark might change the change the "evacuation efficiency" of
1096       // the regions in this set, leading to failing asserts later.
1097       // Since the concurrent cycle will recreate the collection set anyway, simply drop it here.
1098       clear_collection_set_candidates();
1099       abort_time_to_mixed_tracking();
1100       initiate_conc_mark();
1101       log_debug(gc, ergo)("Initiate concurrent cycle (user requested concurrent cycle)");
1102     } else {
1103       // The concurrent marking thread is still finishing up the
1104       // previous cycle. If we start one right now the two cycles
1105       // overlap. In particular, the concurrent marking thread might
1106       // be in the process of clearing the next marking bitmap (which
1107       // we will use for the next cycle if we start one). Starting a
1108       // cycle now will be bad given that parts of the marking
1109       // information might get cleared by the marking thread. And we
1110       // cannot wait for the marking thread to finish the cycle as it
1111       // periodically yields while clearing the next marking bitmap
1112       // and, if it's in a yield point, it's waiting for us to
1113       // finish. So, at this point we will not start a cycle and we'll
1114       // let the concurrent marking thread complete the last one.
1115       log_debug(gc, ergo)("Do not initiate concurrent cycle (concurrent cycle already in progress)");
1116     }
1117   }
1118 }
1119 
1120 void G1Policy::record_concurrent_mark_cleanup_end() {
1121   G1CollectionSetCandidates* candidates = G1CollectionSetChooser::build(_g1h->workers(), _g1h->num_regions());
1122   _collection_set->set_candidates(candidates);
1123 
1124   bool mixed_gc_pending = next_gc_should_be_mixed("request mixed gcs", "request young-only gcs");
1125   if (!mixed_gc_pending) {
1126     clear_collection_set_candidates();
1127     abort_time_to_mixed_tracking();
1128   }
1129   collector_state()->set_in_young_gc_before_mixed(mixed_gc_pending);
1130   collector_state()->set_mark_or_rebuild_in_progress(false);
1131 
1132   double end_sec = os::elapsedTime();
1133   double elapsed_time_ms = (end_sec - _mark_cleanup_start_sec) * 1000.0;
1134   _analytics->report_concurrent_mark_cleanup_times_ms(elapsed_time_ms);
1135   _analytics->append_prev_collection_pause_end_ms(elapsed_time_ms);
1136 
1137   record_pause(Cleanup, _mark_cleanup_start_sec, end_sec);
1138 }
1139 
1140 double G1Policy::reclaimable_bytes_percent(size_t reclaimable_bytes) const {
1141   return percent_of(reclaimable_bytes, _g1h->capacity());
1142 }
1143 
1144 class G1ClearCollectionSetCandidateRemSets : public HeapRegionClosure {
1145   virtual bool do_heap_region(HeapRegion* r) {
1146     r->rem_set()->clear_locked(true /* only_cardset */);
1147     return false;
1148   }
1149 };
1150 
1151 void G1Policy::clear_collection_set_candidates() {
1152   // Clear remembered sets of remaining candidate regions and the actual candidate
1153   // set.
1154   G1ClearCollectionSetCandidateRemSets cl;
1155   _collection_set->candidates()->iterate(&cl);
1156   _collection_set->clear_candidates();
1157 }
1158 
1159 void G1Policy::maybe_start_marking() {
1160   if (need_to_start_conc_mark("end of GC")) {
1161     // Note: this might have already been set, if during the last
1162     // pause we decided to start a cycle but at the beginning of
1163     // this pause we decided to postpone it. That's OK.
1164     collector_state()->set_initiate_conc_mark_if_possible(true);
1165   }
1166 }
1167 
1168 G1Policy::PauseKind G1Policy::young_gc_pause_kind() const {
1169   assert(!collector_state()->in_full_gc(), "must be");
1170   if (collector_state()->in_initial_mark_gc()) {
1171     assert(!collector_state()->in_young_gc_before_mixed(), "must be");
1172     return InitialMarkGC;
1173   } else if (collector_state()->in_young_gc_before_mixed()) {
1174     assert(!collector_state()->in_initial_mark_gc(), "must be");
1175     return LastYoungGC;
1176   } else if (collector_state()->in_mixed_phase()) {
1177     assert(!collector_state()->in_initial_mark_gc(), "must be");
1178     assert(!collector_state()->in_young_gc_before_mixed(), "must be");
1179     return MixedGC;
1180   } else {
1181     assert(!collector_state()->in_initial_mark_gc(), "must be");
1182     assert(!collector_state()->in_young_gc_before_mixed(), "must be");
1183     return YoungOnlyGC;
1184   }
1185 }
1186 
1187 void G1Policy::record_pause(PauseKind kind, double start, double end) {
1188   // Manage the MMU tracker. For some reason it ignores Full GCs.
1189   if (kind != FullGC) {
1190     _mmu_tracker->add_pause(start, end);
1191   }
1192   // Manage the mutator time tracking from initial mark to first mixed gc.
1193   switch (kind) {
1194     case FullGC:
1195       abort_time_to_mixed_tracking();
1196       break;
1197     case Cleanup:
1198     case Remark:
1199     case YoungOnlyGC:
1200     case LastYoungGC:
1201       _initial_mark_to_mixed.add_pause(end - start);
1202       break;
1203     case InitialMarkGC:
1204       if (_g1h->gc_cause() != GCCause::_g1_periodic_collection) {
1205         _initial_mark_to_mixed.record_initial_mark_end(end);
1206       }
1207       break;
1208     case MixedGC:
1209       _initial_mark_to_mixed.record_mixed_gc_start(start);
1210       break;
1211     default:
1212       ShouldNotReachHere();
1213   }
1214 }
1215 
1216 void G1Policy::abort_time_to_mixed_tracking() {
1217   _initial_mark_to_mixed.reset();
1218 }
1219 
1220 bool G1Policy::next_gc_should_be_mixed(const char* true_action_str,
1221                                        const char* false_action_str) const {
1222   G1CollectionSetCandidates* candidates = _collection_set->candidates();
1223 
1224   if (candidates->is_empty()) {
1225     log_debug(gc, ergo)("%s (candidate old regions not available)", false_action_str);
1226     return false;
1227   }
1228 
1229   // Is the amount of uncollected reclaimable space above G1HeapWastePercent?
1230   size_t reclaimable_bytes = candidates->remaining_reclaimable_bytes();
1231   double reclaimable_percent = reclaimable_bytes_percent(reclaimable_bytes);
1232   double threshold = (double) G1HeapWastePercent;
1233   if (reclaimable_percent <= threshold) {
1234     log_debug(gc, ergo)("%s (reclaimable percentage not over threshold). candidate old regions: %u reclaimable: " SIZE_FORMAT " (%1.2f) threshold: " UINTX_FORMAT,
1235                         false_action_str, candidates->num_remaining(), reclaimable_bytes, reclaimable_percent, G1HeapWastePercent);
1236     return false;
1237   }
1238   log_debug(gc, ergo)("%s (candidate old regions available). candidate old regions: %u reclaimable: " SIZE_FORMAT " (%1.2f) threshold: " UINTX_FORMAT,
1239                       true_action_str, candidates->num_remaining(), reclaimable_bytes, reclaimable_percent, G1HeapWastePercent);
1240   return true;
1241 }
1242 
1243 uint G1Policy::calc_min_old_cset_length() const {
1244   // The min old CSet region bound is based on the maximum desired
1245   // number of mixed GCs after a cycle. I.e., even if some old regions
1246   // look expensive, we should add them to the CSet anyway to make
1247   // sure we go through the available old regions in no more than the
1248   // maximum desired number of mixed GCs.
1249   //
1250   // The calculation is based on the number of marked regions we added
1251   // to the CSet candidates in the first place, not how many remain, so
1252   // that the result is the same during all mixed GCs that follow a cycle.
1253 
1254   const size_t region_num = _collection_set->candidates()->num_regions();
1255   const size_t gc_num = (size_t) MAX2(G1MixedGCCountTarget, (uintx) 1);
1256   size_t result = region_num / gc_num;
1257   // emulate ceiling
1258   if (result * gc_num < region_num) {
1259     result += 1;
1260   }
1261   return (uint) result;
1262 }
1263 
1264 uint G1Policy::calc_max_old_cset_length() const {
1265   // The max old CSet region bound is based on the threshold expressed
1266   // as a percentage of the heap size. I.e., it should bound the
1267   // number of old regions added to the CSet irrespective of how many
1268   // of them are available.
1269 
1270   const G1CollectedHeap* g1h = G1CollectedHeap::heap();
1271   const size_t region_num = g1h->num_regions();
1272   const size_t perc = (size_t) G1OldCSetRegionThresholdPercent;
1273   size_t result = region_num * perc / 100;
1274   // emulate ceiling
1275   if (100 * result < region_num * perc) {
1276     result += 1;
1277   }
1278   return (uint) result;
1279 }
1280 
1281 void G1Policy::calculate_old_collection_set_regions(G1CollectionSetCandidates* candidates,
1282                                                     double time_remaining_ms,
1283                                                     uint& num_initial_regions,
1284                                                     uint& num_optional_regions) {
1285   assert(candidates != NULL, "Must be");
1286 
1287   num_initial_regions = 0;
1288   num_optional_regions = 0;
1289   uint num_expensive_regions = 0;
1290 
1291   double predicted_old_time_ms = 0.0;
1292   double predicted_initial_time_ms = 0.0;
1293   double predicted_optional_time_ms = 0.0;
1294 
1295   double optional_threshold_ms = time_remaining_ms * optional_prediction_fraction();
1296 
1297   const uint min_old_cset_length = calc_min_old_cset_length();
1298   const uint max_old_cset_length = MAX2(min_old_cset_length, calc_max_old_cset_length());
1299   const uint max_optional_regions = max_old_cset_length - min_old_cset_length;
1300   bool check_time_remaining = use_adaptive_young_list_length();
1301 
1302   uint candidate_idx = candidates->cur_idx();
1303 
1304   log_debug(gc, ergo, cset)("Start adding old regions to collection set. Min %u regions, max %u regions, "
1305                             "time remaining %1.2fms, optional threshold %1.2fms",
1306                             min_old_cset_length, max_old_cset_length, time_remaining_ms, optional_threshold_ms);
1307 
1308   HeapRegion* hr = candidates->at(candidate_idx);
1309   while (hr != NULL) {
1310     if (num_initial_regions + num_optional_regions >= max_old_cset_length) {
1311       // Added maximum number of old regions to the CSet.
1312       log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Maximum number of regions). "
1313                                 "Initial %u regions, optional %u regions",
1314                                 num_initial_regions, num_optional_regions);
1315       break;
1316     }
1317 
1318     // Stop adding regions if the remaining reclaimable space is
1319     // not above G1HeapWastePercent.
1320     size_t reclaimable_bytes = candidates->remaining_reclaimable_bytes();
1321     double reclaimable_percent = reclaimable_bytes_percent(reclaimable_bytes);
1322     double threshold = (double) G1HeapWastePercent;
1323     if (reclaimable_percent <= threshold) {
1324       // We've added enough old regions that the amount of uncollected
1325       // reclaimable space is at or below the waste threshold. Stop
1326       // adding old regions to the CSet.
1327       log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Reclaimable percentage below threshold). "
1328                                 "Reclaimable: " SIZE_FORMAT "%s (%1.2f%%) threshold: " UINTX_FORMAT "%%",
1329                                 byte_size_in_proper_unit(reclaimable_bytes), proper_unit_for_byte_size(reclaimable_bytes),
1330                                 reclaimable_percent, G1HeapWastePercent);
1331       break;
1332     }
1333 
1334     double predicted_time_ms = predict_region_elapsed_time_ms(hr, false);
1335     time_remaining_ms = MAX2(time_remaining_ms - predicted_time_ms, 0.0);
1336     // Add regions to old set until we reach the minimum amount
1337     if (num_initial_regions < min_old_cset_length) {
1338       predicted_old_time_ms += predicted_time_ms;
1339       num_initial_regions++;
1340       // Record the number of regions added with no time remaining
1341       if (time_remaining_ms == 0.0) {
1342         num_expensive_regions++;
1343       }
1344     } else if (!check_time_remaining) {
1345       // In the non-auto-tuning case, we'll finish adding regions
1346       // to the CSet if we reach the minimum.
1347       log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Region amount reached min).");
1348       break;
1349     } else {
1350       // Keep adding regions to old set until we reach the optional threshold
1351       if (time_remaining_ms > optional_threshold_ms) {
1352         predicted_old_time_ms += predicted_time_ms;
1353         num_initial_regions++;
1354       } else if (time_remaining_ms > 0) {
1355         // Keep adding optional regions until time is up.
1356         assert(num_optional_regions < max_optional_regions, "Should not be possible.");
1357         predicted_optional_time_ms += predicted_time_ms;
1358         num_optional_regions++;
1359       } else {
1360         log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Predicted time too high).");
1361         break;
1362       }
1363     }
1364     hr = candidates->at(++candidate_idx);
1365   }
1366   if (hr == NULL) {
1367     log_debug(gc, ergo, cset)("Old candidate collection set empty.");
1368   }
1369 
1370   if (num_expensive_regions > 0) {
1371     log_debug(gc, ergo, cset)("Added %u initial old regions to collection set although the predicted time was too high.",
1372                               num_expensive_regions);
1373   }
1374 
1375   log_debug(gc, ergo, cset)("Finish choosing collection set old regions. Initial: %u, optional: %u, "
1376                             "predicted old time: %1.2fms, predicted optional time: %1.2fms, time remaining: %1.2f",
1377                             num_initial_regions, num_optional_regions,
1378                             predicted_initial_time_ms, predicted_optional_time_ms, time_remaining_ms);
1379 }
1380 
1381 void G1Policy::calculate_optional_collection_set_regions(G1CollectionSetCandidates* candidates,
1382                                                          uint const max_optional_regions,
1383                                                          double time_remaining_ms,
1384                                                          uint& num_optional_regions) {
1385   assert(_g1h->collector_state()->in_mixed_phase(), "Should only be called in mixed phase");
1386 
1387   num_optional_regions = 0;
1388   double prediction_ms = 0;
1389   uint candidate_idx = candidates->cur_idx();
1390 
1391   HeapRegion* r = candidates->at(candidate_idx);
1392   while (num_optional_regions < max_optional_regions) {
1393     assert(r != NULL, "Region must exist");
1394     prediction_ms += predict_region_elapsed_time_ms(r, false);
1395 
1396     if (prediction_ms > time_remaining_ms) {
1397       log_debug(gc, ergo, cset)("Prediction %.3fms for region %u does not fit remaining time: %.3fms.",
1398                                 prediction_ms, r->hrm_index(), time_remaining_ms);
1399       break;
1400     }
1401     // This region will be included in the next optional evacuation.
1402 
1403     time_remaining_ms -= prediction_ms;
1404     num_optional_regions++;
1405     r = candidates->at(++candidate_idx);
1406   }
1407 
1408   log_debug(gc, ergo, cset)("Prepared %u regions out of %u for optional evacuation. Predicted time: %.3fms",
1409                             num_optional_regions, max_optional_regions, prediction_ms);
1410 }
1411 
1412 void G1Policy::transfer_survivors_to_cset(const G1SurvivorRegions* survivors) {
1413 
1414   // Add survivor regions to SurvRateGroup.
1415   note_start_adding_survivor_regions();
1416   finished_recalculating_age_indexes(true /* is_survivors */);
1417 
1418   HeapRegion* last = NULL;
1419   for (GrowableArrayIterator<HeapRegion*> it = survivors->regions()->begin();
1420        it != survivors->regions()->end();
1421        ++it) {
1422     HeapRegion* curr = *it;
1423     set_region_survivor(curr);
1424 
1425     // The region is a non-empty survivor so let's add it to
1426     // the incremental collection set for the next evacuation
1427     // pause.
1428     _collection_set->add_survivor_regions(curr);
1429 
1430     last = curr;
1431   }
1432   note_stop_adding_survivor_regions();
1433 
1434   // Don't clear the survivor list handles until the start of
1435   // the next evacuation pause - we need it in order to re-tag
1436   // the survivor regions from this evacuation pause as 'young'
1437   // at the start of the next.
1438 
1439   finished_recalculating_age_indexes(false /* is_survivors */);
1440 }