1 /*
   2  * Copyright (c) 2001, 2020, 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/g1ConcurrentRefineStats.hpp"
  35 #include "gc/g1/g1CollectionSetChooser.hpp"
  36 #include "gc/g1/g1HeterogeneousHeapPolicy.hpp"
  37 #include "gc/g1/g1HotCardCache.hpp"
  38 #include "gc/g1/g1IHOPControl.hpp"
  39 #include "gc/g1/g1GCPhaseTimes.hpp"
  40 #include "gc/g1/g1Policy.hpp"
  41 #include "gc/g1/g1SurvivorRegions.hpp"
  42 #include "gc/g1/g1YoungGenSizer.hpp"
  43 #include "gc/g1/heapRegion.inline.hpp"
  44 #include "gc/g1/heapRegionRemSet.hpp"
  45 #include "gc/shared/concurrentGCBreakpoints.hpp"
  46 #include "gc/shared/gcPolicyCounters.hpp"
  47 #include "logging/log.hpp"
  48 #include "runtime/arguments.hpp"
  49 #include "runtime/globals.hpp"
  50 #include "runtime/java.hpp"
  51 #include "runtime/mutexLocker.hpp"
  52 #include "utilities/debug.hpp"
  53 #include "utilities/growableArray.hpp"
  54 #include "utilities/pair.hpp"
  55 
  56 G1Policy::G1Policy(STWGCTimer* gc_timer) :
  57   _predictor(G1ConfidencePercent / 100.0),
  58   _analytics(new G1Analytics(&_predictor)),
  59   _remset_tracker(),
  60   _mmu_tracker(new G1MMUTrackerQueue(GCPauseIntervalMillis / 1000.0, MaxGCPauseMillis / 1000.0)),
  61   _ihop_control(create_ihop_control(&_predictor)),
  62   _policy_counters(new GCPolicyCounters("GarbageFirst", 1, 2)),
  63   _full_collection_start_sec(0.0),
  64   _young_list_desired_length(0),
  65   _young_list_target_length(0),
  66   _young_list_max_length(0),
  67   _eden_surv_rate_group(new G1SurvRateGroup()),
  68   _survivor_surv_rate_group(new G1SurvRateGroup()),
  69   _reserve_factor((double) G1ReservePercent / 100.0),
  70   _reserve_regions(0),
  71   _young_gen_sizer(G1YoungGenSizer::create_gen_sizer()),
  72   _free_regions_at_end_of_collection(0),
  73   _rs_length(0),
  74   _rs_length_prediction(0),
  75   _pending_cards_at_gc_start(0),
  76   _old_gen_alloc_tracker(),
  77   _initial_mark_to_mixed(),
  78   _collection_set(NULL),
  79   _g1h(NULL),
  80   _phase_times(new G1GCPhaseTimes(gc_timer, ParallelGCThreads)),
  81   _mark_remark_start_sec(0),
  82   _mark_cleanup_start_sec(0),
  83   _tenuring_threshold(MaxTenuringThreshold),
  84   _max_survivor_regions(0),
  85   _survivors_age_table(true)
  86 {
  87 }
  88 
  89 G1Policy::~G1Policy() {
  90   delete _ihop_control;
  91   delete _young_gen_sizer;
  92 }
  93 
  94 G1Policy* G1Policy::create_policy(STWGCTimer* gc_timer_stw) {
  95   if (G1Arguments::is_heterogeneous_heap()) {
  96     return new G1HeterogeneousHeapPolicy(gc_timer_stw);
  97   } else {
  98     return new G1Policy(gc_timer_stw);
  99   }
 100 }
 101 
 102 G1CollectorState* G1Policy::collector_state() const { return _g1h->collector_state(); }
 103 
 104 void G1Policy::init(G1CollectedHeap* g1h, G1CollectionSet* collection_set) {
 105   _g1h = g1h;
 106   _collection_set = collection_set;
 107 
 108   assert(Heap_lock->owned_by_self(), "Locking discipline.");
 109 
 110   _young_gen_sizer->adjust_max_new_size(_g1h->max_expandable_regions());
 111 
 112   _free_regions_at_end_of_collection = _g1h->num_free_regions();
 113 
 114   update_young_length_bounds();
 115   // We may immediately start allocating regions and placing them on the
 116   // collection set list. Initialize the per-collection set info
 117   _collection_set->start_incremental_building();
 118 }
 119 
 120 void G1Policy::note_gc_start() {
 121   phase_times()->note_gc_start();
 122 }
 123 
 124 class G1YoungLengthPredictor {
 125   const double _base_time_ms;
 126   const double _base_free_regions;
 127   const double _target_pause_time_ms;
 128   const G1Policy* const _policy;
 129 
 130  public:
 131   G1YoungLengthPredictor(double base_time_ms,
 132                          double base_free_regions,
 133                          double target_pause_time_ms,
 134                          const G1Policy* policy) :
 135     _base_time_ms(base_time_ms),
 136     _base_free_regions(base_free_regions),
 137     _target_pause_time_ms(target_pause_time_ms),
 138     _policy(policy) {}
 139 
 140   bool will_fit(uint young_length) const {
 141     if (young_length >= _base_free_regions) {
 142       // end condition 1: not enough space for the young regions
 143       return false;
 144     }
 145 
 146     size_t bytes_to_copy = 0;
 147     const double copy_time_ms = _policy->predict_eden_copy_time_ms(young_length, &bytes_to_copy);
 148     const double young_other_time_ms = _policy->analytics()->predict_young_other_time_ms(young_length);
 149     const double pause_time_ms = _base_time_ms + copy_time_ms + young_other_time_ms;
 150     if (pause_time_ms > _target_pause_time_ms) {
 151       // end condition 2: prediction is over the target pause time
 152       return false;
 153     }
 154 
 155     const size_t free_bytes = (_base_free_regions - young_length) * HeapRegion::GrainBytes;
 156 
 157     // When copying, we will likely need more bytes free than is live in the region.
 158     // Add some safety margin to factor in the confidence of our guess, and the
 159     // natural expected waste.
 160     // (100.0 / G1ConfidencePercent) is a scale factor that expresses the uncertainty
 161     // of the calculation: the lower the confidence, the more headroom.
 162     // (100 + TargetPLABWastePct) represents the increase in expected bytes during
 163     // copying due to anticipated waste in the PLABs.
 164     const double safety_factor = (100.0 / G1ConfidencePercent) * (100 + TargetPLABWastePct) / 100.0;
 165     const size_t expected_bytes_to_copy = (size_t)(safety_factor * bytes_to_copy);
 166 
 167     if (expected_bytes_to_copy > free_bytes) {
 168       // end condition 3: out-of-space
 169       return false;
 170     }
 171 
 172     // success!
 173     return true;
 174   }
 175 };
 176 
 177 void G1Policy::record_new_heap_size(uint new_number_of_regions) {
 178   // re-calculate the necessary reserve
 179   double reserve_regions_d = (double) new_number_of_regions * _reserve_factor;
 180   // We use ceiling so that if reserve_regions_d is > 0.0 (but
 181   // smaller than 1.0) we'll get 1.
 182   _reserve_regions = (uint) ceil(reserve_regions_d);
 183 
 184   _young_gen_sizer->heap_size_changed(new_number_of_regions);
 185 
 186   _ihop_control->update_target_occupancy(new_number_of_regions * HeapRegion::GrainBytes);
 187 }
 188 
 189 uint G1Policy::calculate_desired_eden_length_by_mmu() const {
 190   // One could argue that any useful eden length to keep any MMU would be 1, but
 191   // in theory this is possible. Other constraints enforce a minimum eden of 1
 192   // anyway.
 193   uint desired_min_length = 0;
 194   if (use_adaptive_young_list_length()) {
 195     double now_sec = os::elapsedTime();
 196     double when_ms = _mmu_tracker->when_max_gc_sec(now_sec) * 1000.0;
 197     double alloc_rate_ms = _analytics->predict_alloc_rate_ms();
 198     desired_min_length = (uint) ceil(alloc_rate_ms * when_ms);
 199   }
 200   return desired_min_length;
 201 }
 202 
 203 void G1Policy::update_young_length_bounds() {
 204   update_young_length_bounds(_analytics->predict_rs_length());
 205 }
 206 
 207 void G1Policy::update_young_length_bounds(size_t rs_length) {
 208   _young_list_desired_length = calculate_young_desired_length(rs_length);
 209   _young_list_target_length = calculate_young_target_length(_young_list_desired_length);
 210   _young_list_max_length = calculate_young_max_length(_young_list_target_length);
 211 
 212   log_debug(gc,ergo,heap)("Young list lengths: desired: %u, target: %u, max: %u",
 213                           _young_list_desired_length,
 214                           _young_list_target_length,
 215                           _young_list_max_length);
 216 }
 217 
 218 // Calculates desired young gen length. It is calculated from:
 219 //
 220 // - sizer min/max bounds on young gen
 221 // - pause time goal for whole young gen evacuation
 222 // - MMU goal influencing eden to make GCs spaced apart.
 223 // - a minimum one eden region length.
 224 //
 225 // We may enter with already allocated eden and survivor regions, that may be
 226 // higher than the maximum, or the above goals may result in a desired value
 227 // smaller than are already allocated.
 228 // The main reason is revising young length, with our without the GCLocker being
 229 // active.
 230 //
 231 uint G1Policy::calculate_young_desired_length(size_t rs_length) const {
 232   uint min_young_length_by_sizer = _young_gen_sizer->min_desired_young_length();
 233   uint max_young_length_by_sizer = _young_gen_sizer->max_desired_young_length();
 234 
 235   assert(min_young_length_by_sizer >= 1, "invariant");
 236   assert(max_young_length_by_sizer >= min_young_length_by_sizer, "invariant");
 237 
 238   // Absolute minimum eden length.
 239   // Enforcing a minimum eden length helps at startup when the predictors are not
 240   // yet trained on the application to avoid unnecessary (but very short) full gcs
 241   // on very small (initial) heaps.
 242   uint const MinDesiredEdenLength = 1;
 243 
 244   // Calculate the absolute and desired min bounds first.
 245 
 246   // This is how many survivor regions we already have.
 247   const uint survivor_length = _g1h->survivor_regions_count();
 248   // Size of the already allocated young gen.
 249   const uint allocated_young_length = _g1h->young_regions_count();
 250   // This is the absolute minimum young length that we can return. Ensure that we
 251   // don't go below any user-defined minimum bound; but we might have already
 252   // allocated more than that for reasons. In this case, use that.
 253   uint absolute_min_young_length = MAX2(allocated_young_length, min_young_length_by_sizer);
 254   // Calculate the absolute max bounds. After evac failure or when revising the
 255   // young length we might have exceeded absolute min length or absolute_max_length,
 256   // so adjust the result accordingly.
 257   uint absolute_max_young_length = MAX2(max_young_length_by_sizer, absolute_min_young_length);
 258 
 259   uint desired_eden_length_by_mmu = 0;
 260   uint desired_eden_length_by_pause = 0;
 261   uint desired_eden_length_before_mixed = 0;
 262 
 263   uint desired_young_length = 0;
 264   if (use_adaptive_young_list_length()) {
 265     desired_eden_length_by_mmu = calculate_desired_eden_length_by_mmu();
 266 
 267     const size_t pending_cards = _analytics->predict_pending_cards();
 268     double survivor_base_time_ms = predict_base_elapsed_time_ms(pending_cards, rs_length);
 269 
 270     if (!next_gc_should_be_mixed(NULL, NULL)) {
 271       desired_eden_length_by_pause =
 272         calculate_desired_eden_length_by_pause(survivor_base_time_ms,
 273                                                absolute_min_young_length - survivor_length,
 274                                                absolute_max_young_length - survivor_length);
 275     } else {
 276       desired_eden_length_before_mixed =
 277         calculate_desired_eden_length_before_mixed(survivor_base_time_ms,
 278                                                    absolute_min_young_length - survivor_length,
 279                                                    absolute_max_young_length - survivor_length);
 280     }
 281     // Above either sets desired_eden_length_by_pause or desired_eden_length_before_mixed,
 282     // the other is zero. Use the one that has been set below.
 283     uint desired_eden_length = MAX2(desired_eden_length_by_pause,
 284                                     desired_eden_length_before_mixed);
 285 
 286     // Finally incorporate MMU concerns; assume that it overrides the pause time
 287     // goal, as the default value has been chosen to effectively disable it.
 288     // Also request at least one eden region, see above for reasons.
 289     desired_eden_length = MAX3(desired_eden_length,
 290                                desired_eden_length_by_mmu,
 291                                MinDesiredEdenLength);
 292 
 293     desired_young_length = desired_eden_length + survivor_length;
 294   } else {
 295     // The user asked for a fixed young gen so we'll fix the young gen
 296     // whether the next GC is young or mixed.
 297     desired_young_length = min_young_length_by_sizer;
 298   }
 299   // Clamp to absolute min/max after we determined desired lengths.
 300   desired_young_length = clamp(desired_young_length, absolute_min_young_length, absolute_max_young_length);
 301 
 302   log_trace(gc, ergo, heap)("Young desired length %u "
 303                             "survivor length %u "
 304                             "allocated young length %u "
 305                             "absolute min young length %u "
 306                             "absolute max young length %u "
 307                             "desired eden length by mmu %u "
 308                             "desired eden length by pause %u "
 309                             "desired eden length before mixed %u"
 310                             "desired eden length by default %u",
 311                             desired_young_length, survivor_length,
 312                             allocated_young_length, absolute_min_young_length,
 313                             absolute_max_young_length, desired_eden_length_by_mmu,
 314                             desired_eden_length_by_pause,
 315                             desired_eden_length_before_mixed,
 316                             MinDesiredEdenLength);
 317 
 318   assert(desired_young_length >= allocated_young_length, "must be");
 319   return desired_young_length;
 320 }
 321 
 322 // Limit the desired (wished) young length by current free regions. If the request
 323 // can be satisfied without using up reserve regions, do so, otherwise eat into
 324 // the reserve, giving away at most what the heap sizer allows.
 325 uint G1Policy::calculate_young_target_length(uint desired_young_length) const {
 326   uint allocated_young_length = _g1h->young_regions_count();
 327 
 328   uint receiving_additional_eden;
 329   if (allocated_young_length >= desired_young_length) {
 330     // Already used up all we actually want (may happen as G1 revises the
 331     // young list length concurrently, or caused by gclocker). Do not allow more,
 332     // potentially resulting in GC.
 333     receiving_additional_eden = 0;
 334     log_trace(gc, ergo, heap)("Young target length: Already used up desired young %u allocated %u",
 335                               desired_young_length,
 336                               allocated_young_length);
 337   } else {
 338     // Now look at how many free regions are there currently, and the heap reserve.
 339     // We will try our best not to "eat" into the reserve as long as we can. If we
 340     // do, we at most eat the sizer's minimum regions into the reserve or half the
 341     // reserve rounded up (if possible; this is an arbitrary value).
 342 
 343     uint max_to_eat_into_reserve = MIN2(_young_gen_sizer->min_desired_young_length(),
 344                                         (_reserve_regions + 1) / 2);
 345 
 346     log_trace(gc, ergo, heap)("Young target length: Common "
 347                               "free regions at end of collection %u "
 348                               "desired young length %u "
 349                               "reserve region %u "
 350                               "max to eat into reserve %u",
 351                               _free_regions_at_end_of_collection,
 352                               desired_young_length,
 353                               _reserve_regions,
 354                               max_to_eat_into_reserve);
 355 
 356     if (_free_regions_at_end_of_collection <= _reserve_regions) {
 357       // Fully eat (or already eating) into the reserve, hand back at most absolute_min_length regions.
 358       uint receiving_young = MIN3(_free_regions_at_end_of_collection,
 359                                   desired_young_length,
 360                                   max_to_eat_into_reserve);
 361       // We could already have allocated more regions than what we could get
 362       // above.
 363       receiving_additional_eden = allocated_young_length < receiving_young ?
 364                                   receiving_young - allocated_young_length : 0;
 365 
 366       log_trace(gc, ergo, heap)("Young target length: Fully eat into reserve "
 367                                 "receiving young %u receiving additional eden %u",
 368                                 receiving_young,
 369                                 receiving_additional_eden);
 370     } else if (_free_regions_at_end_of_collection < (desired_young_length + _reserve_regions)) {
 371       // Partially eat into the reserve, at most max_to_eat_into_reserve regions.
 372       uint free_outside_reserve = _free_regions_at_end_of_collection - _reserve_regions;
 373       assert(free_outside_reserve < desired_young_length,
 374              "must be %u %u",
 375              free_outside_reserve, desired_young_length);
 376 
 377       uint receiving_within_reserve = MIN2(desired_young_length - free_outside_reserve,
 378                                            max_to_eat_into_reserve);
 379       uint receiving_young = free_outside_reserve + receiving_within_reserve;
 380       // Again, we could have already allocated more than we could get.
 381       receiving_additional_eden = allocated_young_length < receiving_young ?
 382                                   receiving_young - allocated_young_length : 0;
 383 
 384       log_trace(gc, ergo, heap)("Young target length: Partially eat into reserve "
 385                                 "free outside reserve %u "
 386                                 "receiving within reserve %u "
 387                                 "receiving young %u "
 388                                 "receiving additional eden %u",
 389                                 free_outside_reserve, receiving_within_reserve,
 390                                 receiving_young, receiving_additional_eden);
 391     } else {
 392       // No need to use the reserve.
 393       receiving_additional_eden = desired_young_length - allocated_young_length;
 394       log_trace(gc, ergo, heap)("Young target length: No need to use reserve "
 395                                 "receiving additional eden %u",
 396                                 receiving_additional_eden);
 397     }
 398   }
 399 
 400   uint target_young_length = allocated_young_length + receiving_additional_eden;
 401 
 402   assert(target_young_length >= allocated_young_length, "must be");
 403 
 404   log_trace(gc, ergo, heap)("Young target length: "
 405                             "young target length %u "
 406                             "allocated young length %u "
 407                             "received additional eden %u",
 408                             target_young_length, allocated_young_length,
 409                             receiving_additional_eden);
 410   return target_young_length;
 411 }
 412 
 413 uint G1Policy::calculate_desired_eden_length_by_pause(double base_time_ms,
 414                                                       uint min_eden_length,
 415                                                       uint max_eden_length) const {
 416   assert(use_adaptive_young_list_length(), "pre-condition");
 417 
 418   assert(min_eden_length <= max_eden_length, "must be %u %u", min_eden_length, max_eden_length);
 419 
 420   // Here, we will make sure that the shortest young length that
 421   // makes sense fits within the target pause time.
 422 
 423   G1YoungLengthPredictor p(base_time_ms,
 424                            _free_regions_at_end_of_collection,
 425                            _mmu_tracker->max_gc_time() * 1000.0,
 426                            this);
 427   if (p.will_fit(min_eden_length)) {
 428     // The shortest young length will fit into the target pause time;
 429     // we'll now check whether the absolute maximum number of young
 430     // regions will fit in the target pause time. If not, we'll do
 431     // a binary search between min_young_length and max_young_length.
 432     if (p.will_fit(max_eden_length)) {
 433       // The maximum young length will fit into the target pause time.
 434       // We are done so set min young length to the maximum length (as
 435       // the result is assumed to be returned in min_young_length).
 436       min_eden_length = max_eden_length;
 437     } else {
 438       // The maximum possible number of young regions will not fit within
 439       // the target pause time so we'll search for the optimal
 440       // length. The loop invariants are:
 441       //
 442       // min_young_length < max_young_length
 443       // min_young_length is known to fit into the target pause time
 444       // max_young_length is known not to fit into the target pause time
 445       //
 446       // Going into the loop we know the above hold as we've just
 447       // checked them. Every time around the loop we check whether
 448       // the middle value between min_young_length and
 449       // max_young_length fits into the target pause time. If it
 450       // does, it becomes the new min. If it doesn't, it becomes
 451       // the new max. This way we maintain the loop invariants.
 452 
 453       assert(min_eden_length < max_eden_length, "invariant");
 454       uint diff = (max_eden_length - min_eden_length) / 2;
 455       while (diff > 0) {
 456         uint eden_length = min_eden_length + diff;
 457         if (p.will_fit(eden_length)) {
 458           min_eden_length = eden_length;
 459         } else {
 460           max_eden_length = eden_length;
 461         }
 462         assert(min_eden_length <  max_eden_length, "invariant");
 463         diff = (max_eden_length - min_eden_length) / 2;
 464       }
 465       // The results is min_young_length which, according to the
 466       // loop invariants, should fit within the target pause time.
 467 
 468       // These are the post-conditions of the binary search above:
 469       assert(min_eden_length < max_eden_length,
 470              "otherwise we should have discovered that max_eden_length "
 471              "fits into the pause target and not done the binary search");
 472       assert(p.will_fit(min_eden_length),
 473              "min_eden_length, the result of the binary search, should "
 474              "fit into the pause target");
 475       assert(!p.will_fit(min_eden_length + 1),
 476              "min_eden_length, the result of the binary search, should be "
 477              "optimal, so no larger length should fit into the pause target");
 478     }
 479   } else {
 480     // Even the minimum length doesn't fit into the pause time
 481     // target, return it as the result nevertheless.
 482   }
 483   return min_eden_length;
 484 }
 485 
 486 uint G1Policy::calculate_desired_eden_length_before_mixed(double survivor_base_time_ms,
 487                                                           uint min_eden_length,
 488                                                           uint max_eden_length) const {
 489   G1CollectionSetCandidates* candidates = _collection_set->candidates();
 490 
 491   uint min_old_regions_end = MIN2(candidates->cur_idx() + calc_min_old_cset_length(), candidates->num_regions());
 492   double predicted_region_evac_time_ms = survivor_base_time_ms;
 493   for (uint i = candidates->cur_idx(); i < min_old_regions_end; i++) {
 494     HeapRegion* r = candidates->at(i);
 495     predicted_region_evac_time_ms += predict_region_total_time_ms(r, false);
 496   }
 497   uint desired_eden_length_by_min_cset_length =
 498      calculate_desired_eden_length_by_pause(predicted_region_evac_time_ms,
 499                                             min_eden_length,
 500                                             max_eden_length);
 501 
 502   return desired_eden_length_by_min_cset_length;
 503 }
 504 
 505 double G1Policy::predict_survivor_regions_evac_time() const {
 506   double survivor_regions_evac_time = 0.0;
 507   const GrowableArray<HeapRegion*>* survivor_regions = _g1h->survivor()->regions();
 508   for (GrowableArrayIterator<HeapRegion*> it = survivor_regions->begin();
 509        it != survivor_regions->end();
 510        ++it) {
 511     survivor_regions_evac_time += predict_region_total_time_ms(*it, collector_state()->in_young_only_phase());
 512   }
 513   return survivor_regions_evac_time;
 514 }
 515 
 516 void G1Policy::revise_young_list_target_length_if_necessary(size_t rs_length) {
 517   guarantee(use_adaptive_young_list_length(), "should not call this otherwise" );
 518 
 519   if (rs_length > _rs_length_prediction) {
 520     // add 10% to avoid having to recalculate often
 521     size_t rs_length_prediction = rs_length * 1100 / 1000;
 522     update_rs_length_prediction(rs_length_prediction);
 523     update_young_length_bounds(rs_length_prediction);
 524   }
 525 }
 526 
 527 void G1Policy::update_rs_length_prediction() {
 528   update_rs_length_prediction(_analytics->predict_rs_length());
 529 }
 530 
 531 void G1Policy::update_rs_length_prediction(size_t prediction) {
 532   if (collector_state()->in_young_only_phase() && use_adaptive_young_list_length()) {
 533     _rs_length_prediction = prediction;
 534   }
 535 }
 536 
 537 void G1Policy::record_full_collection_start() {
 538   _full_collection_start_sec = os::elapsedTime();
 539   // Release the future to-space so that it is available for compaction into.
 540   collector_state()->set_in_young_only_phase(false);
 541   collector_state()->set_in_full_gc(true);
 542   _collection_set->clear_candidates();
 543   _pending_cards_at_gc_start = 0;
 544 }
 545 
 546 void G1Policy::record_full_collection_end() {
 547   // Consider this like a collection pause for the purposes of allocation
 548   // since last pause.
 549   double end_sec = os::elapsedTime();
 550   double full_gc_time_sec = end_sec - _full_collection_start_sec;
 551   double full_gc_time_ms = full_gc_time_sec * 1000.0;
 552 
 553   _analytics->update_recent_gc_times(end_sec, full_gc_time_ms);
 554 
 555   collector_state()->set_in_full_gc(false);
 556 
 557   // "Nuke" the heuristics that control the young/mixed GC
 558   // transitions and make sure we start with young GCs after the Full GC.
 559   collector_state()->set_in_young_only_phase(true);
 560   collector_state()->set_in_young_gc_before_mixed(false);
 561   collector_state()->set_initiate_conc_mark_if_possible(need_to_start_conc_mark("end of Full GC", 0));
 562   collector_state()->set_in_initial_mark_gc(false);
 563   collector_state()->set_mark_or_rebuild_in_progress(false);
 564   collector_state()->set_clearing_next_bitmap(false);
 565 
 566   _eden_surv_rate_group->start_adding_regions();
 567   // also call this on any additional surv rate groups
 568 
 569   _free_regions_at_end_of_collection = _g1h->num_free_regions();
 570   _survivor_surv_rate_group->reset();
 571   update_young_length_bounds();
 572   update_rs_length_prediction();
 573 
 574   _old_gen_alloc_tracker.reset_after_full_gc();
 575 
 576   record_pause(FullGC, _full_collection_start_sec, end_sec);
 577 }
 578 
 579 static void log_refinement_stats(const char* kind, const G1ConcurrentRefineStats& stats) {
 580   log_debug(gc, refine, stats)
 581            ("%s refinement: %.2fms, refined: " SIZE_FORMAT
 582             ", precleaned: " SIZE_FORMAT ", dirtied: " SIZE_FORMAT,
 583             kind,
 584             stats.refinement_time().seconds() * MILLIUNITS,
 585             stats.refined_cards(),
 586             stats.precleaned_cards(),
 587             stats.dirtied_cards());
 588 }
 589 
 590 void G1Policy::record_concurrent_refinement_stats() {
 591   G1DirtyCardQueueSet& dcqs = G1BarrierSet::dirty_card_queue_set();
 592   _pending_cards_at_gc_start = dcqs.num_cards();
 593 
 594   // Collect per-thread stats, mostly from mutator activity.
 595   G1ConcurrentRefineStats mut_stats = dcqs.get_and_reset_refinement_stats();
 596 
 597   // Collect specialized concurrent refinement thread stats.
 598   G1ConcurrentRefine* cr = _g1h->concurrent_refine();
 599   G1ConcurrentRefineStats cr_stats = cr->get_and_reset_refinement_stats();
 600 
 601   G1ConcurrentRefineStats total_stats = mut_stats + cr_stats;
 602 
 603   log_refinement_stats("Mutator", mut_stats);
 604   log_refinement_stats("Concurrent", cr_stats);
 605   log_refinement_stats("Total", total_stats);
 606 
 607   // Record the rate at which cards were refined.
 608   // Don't update the rate if the current sample is empty or time is zero.
 609   Tickspan refinement_time = total_stats.refinement_time();
 610   size_t refined_cards = total_stats.refined_cards();
 611   if ((refined_cards > 0) && (refinement_time > Tickspan())) {
 612     double rate = refined_cards / (refinement_time.seconds() * MILLIUNITS);
 613     _analytics->report_concurrent_refine_rate_ms(rate);
 614     log_debug(gc, refine, stats)("Concurrent refinement rate: %.2f cards/ms", rate);
 615   }
 616 
 617   // Record mutator's card logging rate.
 618   double mut_start_time = _analytics->prev_collection_pause_end_ms();
 619   double mut_end_time = phase_times()->cur_collection_start_sec() * MILLIUNITS;
 620   double mut_time = mut_end_time - mut_start_time;
 621   // Unlike above for conc-refine rate, here we should not require a
 622   // non-empty sample, since an application could go some time with only
 623   // young-gen or filtered out writes.  But we'll ignore unusually short
 624   // sample periods, as they may just pollute the predictions.
 625   if (mut_time > 1.0) {   // Require > 1ms sample time.
 626     double dirtied_rate = total_stats.dirtied_cards() / mut_time;
 627     _analytics->report_dirtied_cards_rate_ms(dirtied_rate);
 628     log_debug(gc, refine, stats)("Generate dirty cards rate: %.2f cards/ms", dirtied_rate);
 629   }
 630 }
 631 
 632 void G1Policy::record_collection_pause_start(double start_time_sec) {
 633   // We only need to do this here as the policy will only be applied
 634   // to the GC we're about to start. so, no point is calculating this
 635   // every time we calculate / recalculate the target young length.
 636   update_survivors_policy();
 637 
 638   assert(max_survivor_regions() + _g1h->num_used_regions() <= _g1h->max_regions(),
 639          "Maximum survivor regions %u plus used regions %u exceeds max regions %u",
 640          max_survivor_regions(), _g1h->num_used_regions(), _g1h->max_regions());
 641   assert_used_and_recalculate_used_equal(_g1h);
 642 
 643   phase_times()->record_cur_collection_start_sec(start_time_sec);
 644 
 645   record_concurrent_refinement_stats();
 646 
 647   _collection_set->reset_bytes_used_before();
 648 
 649   // do that for any other surv rate groups
 650   _eden_surv_rate_group->stop_adding_regions();
 651   _survivors_age_table.clear();
 652 
 653   assert(_g1h->collection_set()->verify_young_ages(), "region age verification failed");
 654 }
 655 
 656 void G1Policy::record_concurrent_mark_init_end(double mark_init_elapsed_time_ms) {
 657   assert(!collector_state()->initiate_conc_mark_if_possible(), "we should have cleared it by now");
 658   collector_state()->set_in_initial_mark_gc(false);
 659 }
 660 
 661 void G1Policy::record_concurrent_mark_remark_start() {
 662   _mark_remark_start_sec = os::elapsedTime();
 663 }
 664 
 665 void G1Policy::record_concurrent_mark_remark_end() {
 666   double end_time_sec = os::elapsedTime();
 667   double elapsed_time_ms = (end_time_sec - _mark_remark_start_sec)*1000.0;
 668   _analytics->report_concurrent_mark_remark_times_ms(elapsed_time_ms);
 669   _analytics->append_prev_collection_pause_end_ms(elapsed_time_ms);
 670 
 671   record_pause(Remark, _mark_remark_start_sec, end_time_sec);
 672 }
 673 
 674 void G1Policy::record_concurrent_mark_cleanup_start() {
 675   _mark_cleanup_start_sec = os::elapsedTime();
 676 }
 677 
 678 double G1Policy::average_time_ms(G1GCPhaseTimes::GCParPhases phase) const {
 679   return phase_times()->average_time_ms(phase);
 680 }
 681 
 682 double G1Policy::young_other_time_ms() const {
 683   return phase_times()->young_cset_choice_time_ms() +
 684          phase_times()->average_time_ms(G1GCPhaseTimes::YoungFreeCSet);
 685 }
 686 
 687 double G1Policy::non_young_other_time_ms() const {
 688   return phase_times()->non_young_cset_choice_time_ms() +
 689          phase_times()->average_time_ms(G1GCPhaseTimes::NonYoungFreeCSet);
 690 }
 691 
 692 double G1Policy::other_time_ms(double pause_time_ms) const {
 693   return pause_time_ms - phase_times()->cur_collection_par_time_ms();
 694 }
 695 
 696 double G1Policy::constant_other_time_ms(double pause_time_ms) const {
 697   return other_time_ms(pause_time_ms) - phase_times()->total_free_cset_time_ms() - phase_times()->total_rebuild_freelist_time_ms();
 698 }
 699 
 700 bool G1Policy::about_to_start_mixed_phase() const {
 701   return _g1h->concurrent_mark()->cm_thread()->during_cycle() || collector_state()->in_young_gc_before_mixed();
 702 }
 703 
 704 bool G1Policy::need_to_start_conc_mark(const char* source, size_t alloc_word_size) {
 705   if (about_to_start_mixed_phase()) {
 706     return false;
 707   }
 708 
 709   size_t marking_initiating_used_threshold = _ihop_control->get_conc_mark_start_threshold();
 710 
 711   size_t cur_used_bytes = _g1h->non_young_capacity_bytes();
 712   size_t alloc_byte_size = alloc_word_size * HeapWordSize;
 713   size_t marking_request_bytes = cur_used_bytes + alloc_byte_size;
 714 
 715   bool result = false;
 716   if (marking_request_bytes > marking_initiating_used_threshold) {
 717     result = collector_state()->in_young_only_phase() && !collector_state()->in_young_gc_before_mixed();
 718     log_debug(gc, ergo, ihop)("%s occupancy: " SIZE_FORMAT "B allocation request: " SIZE_FORMAT "B threshold: " SIZE_FORMAT "B (%1.2f) source: %s",
 719                               result ? "Request concurrent cycle initiation (occupancy higher than threshold)" : "Do not request concurrent cycle initiation (still doing mixed collections)",
 720                               cur_used_bytes, alloc_byte_size, marking_initiating_used_threshold, (double) marking_initiating_used_threshold / _g1h->capacity() * 100, source);
 721   }
 722 
 723   return result;
 724 }
 725 
 726 double G1Policy::logged_cards_processing_time() const {
 727   double all_cards_processing_time = average_time_ms(G1GCPhaseTimes::ScanHR) + average_time_ms(G1GCPhaseTimes::OptScanHR);
 728   size_t logged_dirty_cards = phase_times()->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards);
 729   size_t scan_heap_roots_cards = phase_times()->sum_thread_work_items(G1GCPhaseTimes::ScanHR, G1GCPhaseTimes::ScanHRScannedCards) +
 730                                  phase_times()->sum_thread_work_items(G1GCPhaseTimes::OptScanHR, G1GCPhaseTimes::ScanHRScannedCards);
 731   // This may happen if there are duplicate cards in different log buffers.
 732   if (logged_dirty_cards > scan_heap_roots_cards) {
 733     return all_cards_processing_time + average_time_ms(G1GCPhaseTimes::MergeLB);
 734   }
 735   return (all_cards_processing_time * logged_dirty_cards / scan_heap_roots_cards) + average_time_ms(G1GCPhaseTimes::MergeLB);
 736 }
 737 
 738 // Anything below that is considered to be zero
 739 #define MIN_TIMER_GRANULARITY 0.0000001
 740 
 741 void G1Policy::record_collection_pause_end(double pause_time_ms) {
 742   G1GCPhaseTimes* p = phase_times();
 743 
 744   double end_time_sec = os::elapsedTime();
 745 
 746   bool this_pause_included_initial_mark = false;
 747   bool this_pause_was_young_only = collector_state()->in_young_only_phase();
 748 
 749   bool update_stats = !_g1h->evacuation_failed();
 750 
 751   record_pause(young_gc_pause_kind(), end_time_sec - pause_time_ms / 1000.0, end_time_sec);
 752 
 753   this_pause_included_initial_mark = collector_state()->in_initial_mark_gc();
 754   if (this_pause_included_initial_mark) {
 755     record_concurrent_mark_init_end(0.0);
 756   } else {
 757     maybe_start_marking();
 758   }
 759 
 760   double app_time_ms = (phase_times()->cur_collection_start_sec() * 1000.0 - _analytics->prev_collection_pause_end_ms());
 761   if (app_time_ms < MIN_TIMER_GRANULARITY) {
 762     // This usually happens due to the timer not having the required
 763     // granularity. Some Linuxes are the usual culprits.
 764     // We'll just set it to something (arbitrarily) small.
 765     app_time_ms = 1.0;
 766   }
 767 
 768   if (update_stats) {
 769     // We maintain the invariant that all objects allocated by mutator
 770     // threads will be allocated out of eden regions. So, we can use
 771     // the eden region number allocated since the previous GC to
 772     // calculate the application's allocate rate. The only exception
 773     // to that is humongous objects that are allocated separately. But
 774     // given that humongous object allocations do not really affect
 775     // either the pause's duration nor when the next pause will take
 776     // place we can safely ignore them here.
 777     uint regions_allocated = _collection_set->eden_region_length();
 778     double alloc_rate_ms = (double) regions_allocated / app_time_ms;
 779     _analytics->report_alloc_rate_ms(alloc_rate_ms);
 780 
 781     _analytics->compute_pause_time_ratios(end_time_sec, pause_time_ms);
 782     _analytics->update_recent_gc_times(end_time_sec, pause_time_ms);
 783   }
 784 
 785   if (collector_state()->in_young_gc_before_mixed()) {
 786     assert(!this_pause_included_initial_mark, "The young GC before mixed is not allowed to be an initial mark GC");
 787     // This has been the young GC before we start doing mixed GCs. We already
 788     // decided to start mixed GCs much earlier, so there is nothing to do except
 789     // advancing the state.
 790     collector_state()->set_in_young_only_phase(false);
 791     collector_state()->set_in_young_gc_before_mixed(false);
 792   } else if (!this_pause_was_young_only) {
 793     // This is a mixed GC. Here we decide whether to continue doing more
 794     // mixed GCs or not.
 795     if (!next_gc_should_be_mixed("continue mixed GCs",
 796                                  "do not continue mixed GCs")) {
 797       collector_state()->set_in_young_only_phase(true);
 798 
 799       clear_collection_set_candidates();
 800       maybe_start_marking();
 801     }
 802   }
 803 
 804   _eden_surv_rate_group->start_adding_regions();
 805 
 806   double merge_hcc_time_ms = average_time_ms(G1GCPhaseTimes::MergeHCC);
 807   if (update_stats) {
 808     size_t const total_log_buffer_cards = p->sum_thread_work_items(G1GCPhaseTimes::MergeHCC, G1GCPhaseTimes::MergeHCCDirtyCards) +
 809                                           p->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards);
 810     // Update prediction for card merge; MergeRSDirtyCards includes the cards from the Eager Reclaim phase.
 811     size_t const total_cards_merged = p->sum_thread_work_items(G1GCPhaseTimes::MergeRS, G1GCPhaseTimes::MergeRSDirtyCards) +
 812                                       p->sum_thread_work_items(G1GCPhaseTimes::OptMergeRS, G1GCPhaseTimes::MergeRSDirtyCards) +
 813                                       total_log_buffer_cards;
 814 
 815     // The threshold for the number of cards in a given sampling which we consider
 816     // large enough so that the impact from setup and other costs is negligible.
 817     size_t const CardsNumSamplingThreshold = 10;
 818 
 819     if (total_cards_merged > CardsNumSamplingThreshold) {
 820       double avg_time_merge_cards = average_time_ms(G1GCPhaseTimes::MergeER) +
 821                                     average_time_ms(G1GCPhaseTimes::MergeRS) +
 822                                     average_time_ms(G1GCPhaseTimes::MergeHCC) +
 823                                     average_time_ms(G1GCPhaseTimes::MergeLB) +
 824                                     average_time_ms(G1GCPhaseTimes::OptMergeRS);
 825       _analytics->report_cost_per_card_merge_ms(avg_time_merge_cards / total_cards_merged, this_pause_was_young_only);
 826     }
 827 
 828     // Update prediction for card scan
 829     size_t const total_cards_scanned = p->sum_thread_work_items(G1GCPhaseTimes::ScanHR, G1GCPhaseTimes::ScanHRScannedCards) +
 830                                        p->sum_thread_work_items(G1GCPhaseTimes::OptScanHR, G1GCPhaseTimes::ScanHRScannedCards);
 831 
 832     if (total_cards_scanned > CardsNumSamplingThreshold) {
 833       double avg_time_dirty_card_scan = average_time_ms(G1GCPhaseTimes::ScanHR) +
 834                                         average_time_ms(G1GCPhaseTimes::OptScanHR);
 835 
 836       _analytics->report_cost_per_card_scan_ms(avg_time_dirty_card_scan / total_cards_scanned, this_pause_was_young_only);
 837     }
 838 
 839     // Update prediction for the ratio between cards from the remembered
 840     // sets and actually scanned cards from the remembered sets.
 841     // Cards from the remembered sets are all cards not duplicated by cards from
 842     // the logs.
 843     // Due to duplicates in the log buffers, the number of actually scanned cards
 844     // can be smaller than the cards in the log buffers.
 845     const size_t from_rs_length_cards = (total_cards_scanned > total_log_buffer_cards) ? total_cards_scanned - total_log_buffer_cards : 0;
 846     double merge_to_scan_ratio = 0.0;
 847     if (total_cards_scanned > 0) {
 848       merge_to_scan_ratio = (double) from_rs_length_cards / total_cards_scanned;
 849     }
 850     _analytics->report_card_merge_to_scan_ratio(merge_to_scan_ratio, this_pause_was_young_only);
 851 
 852     const size_t recorded_rs_length = _collection_set->recorded_rs_length();
 853     const size_t rs_length_diff = _rs_length > recorded_rs_length ? _rs_length - recorded_rs_length : 0;
 854     _analytics->report_rs_length_diff(rs_length_diff);
 855 
 856     // Update prediction for copy cost per byte
 857     size_t copied_bytes = p->sum_thread_work_items(G1GCPhaseTimes::MergePSS, G1GCPhaseTimes::MergePSSCopiedBytes);
 858 
 859     if (copied_bytes > 0) {
 860       double cost_per_byte_ms = (average_time_ms(G1GCPhaseTimes::ObjCopy) + average_time_ms(G1GCPhaseTimes::OptObjCopy)) / copied_bytes;
 861       _analytics->report_cost_per_byte_ms(cost_per_byte_ms, collector_state()->mark_or_rebuild_in_progress());
 862     }
 863 
 864     if (_collection_set->young_region_length() > 0) {
 865       _analytics->report_young_other_cost_per_region_ms(young_other_time_ms() /
 866                                                         _collection_set->young_region_length());
 867     }
 868 
 869     if (_collection_set->old_region_length() > 0) {
 870       _analytics->report_non_young_other_cost_per_region_ms(non_young_other_time_ms() /
 871                                                             _collection_set->old_region_length());
 872     }
 873 
 874     _analytics->report_constant_other_time_ms(constant_other_time_ms(pause_time_ms));
 875 
 876     // Do not update RS lengths and the number of pending cards with information from mixed gc:
 877     // these are is wildly different to during young only gc and mess up young gen sizing right
 878     // after the mixed gc phase.
 879     // During mixed gc we do not use them for young gen sizing.
 880     if (this_pause_was_young_only) {
 881       _analytics->report_pending_cards((double) _pending_cards_at_gc_start);
 882       _analytics->report_rs_length((double) _rs_length);
 883     }
 884   }
 885 
 886   assert(!(this_pause_included_initial_mark && collector_state()->mark_or_rebuild_in_progress()),
 887          "If the last pause has been an initial mark, we should not have been in the marking window");
 888   if (this_pause_included_initial_mark) {
 889     collector_state()->set_mark_or_rebuild_in_progress(true);
 890   }
 891 
 892   _free_regions_at_end_of_collection = _g1h->num_free_regions();
 893 
 894   update_rs_length_prediction();
 895 
 896   // Do not update dynamic IHOP due to G1 periodic collection as it is highly likely
 897   // that in this case we are not running in a "normal" operating mode.
 898   if (_g1h->gc_cause() != GCCause::_g1_periodic_collection) {
 899     update_young_length_bounds();
 900 
 901     _old_gen_alloc_tracker.reset_after_young_gc(app_time_ms / 1000.0);
 902     update_ihop_prediction(_old_gen_alloc_tracker.last_cycle_duration(),
 903                            _old_gen_alloc_tracker.last_cycle_old_bytes(),
 904                            this_pause_was_young_only);
 905 
 906     _ihop_control->send_trace_event(_g1h->gc_tracer_stw());
 907   } else {
 908     // Any garbage collection triggered as periodic collection resets the time-to-mixed
 909     // measurement. Periodic collection typically means that the application is "inactive", i.e.
 910     // the marking threads may have received an uncharacterisic amount of cpu time
 911     // for completing the marking, i.e. are faster than expected.
 912     // This skews the predicted marking length towards smaller values which might cause
 913     // the mark start being too late.
 914     _initial_mark_to_mixed.reset();
 915   }
 916 
 917   // Note that _mmu_tracker->max_gc_time() returns the time in seconds.
 918   double scan_logged_cards_time_goal_ms = _mmu_tracker->max_gc_time() * MILLIUNITS * G1RSetUpdatingPauseTimePercent / 100.0;
 919 
 920   if (scan_logged_cards_time_goal_ms < merge_hcc_time_ms) {
 921     log_debug(gc, ergo, refine)("Adjust concurrent refinement thresholds (scanning the HCC expected to take longer than Update RS time goal)."
 922                                 "Logged Cards Scan time goal: %1.2fms Scan HCC time: %1.2fms",
 923                                 scan_logged_cards_time_goal_ms, merge_hcc_time_ms);
 924 
 925     scan_logged_cards_time_goal_ms = 0;
 926   } else {
 927     scan_logged_cards_time_goal_ms -= merge_hcc_time_ms;
 928   }
 929 
 930   double const logged_cards_time = logged_cards_processing_time();
 931 
 932   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",
 933                               scan_logged_cards_time_goal_ms, logged_cards_time, merge_hcc_time_ms);
 934 
 935   _g1h->concurrent_refine()->adjust(logged_cards_time,
 936                                     phase_times()->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards),
 937                                     scan_logged_cards_time_goal_ms);
 938 }
 939 
 940 G1IHOPControl* G1Policy::create_ihop_control(const G1Predictions* predictor){
 941   if (G1UseAdaptiveIHOP) {
 942     return new G1AdaptiveIHOPControl(InitiatingHeapOccupancyPercent,
 943                                      predictor,
 944                                      G1ReservePercent,
 945                                      G1HeapWastePercent);
 946   } else {
 947     return new G1StaticIHOPControl(InitiatingHeapOccupancyPercent);
 948   }
 949 }
 950 
 951 void G1Policy::update_ihop_prediction(double mutator_time_s,
 952                                       size_t mutator_alloc_bytes,
 953                                       bool this_gc_was_young_only) {
 954   // Always try to update IHOP prediction. Even evacuation failures give information
 955   // about e.g. whether to start IHOP earlier next time.
 956 
 957   // Avoid using really small application times that might create samples with
 958   // very high or very low values. They may be caused by e.g. back-to-back gcs.
 959   double const min_valid_time = 1e-6;
 960 
 961   bool report = false;
 962 
 963   double marking_to_mixed_time = -1.0;
 964   if (!this_gc_was_young_only && _initial_mark_to_mixed.has_result()) {
 965     marking_to_mixed_time = _initial_mark_to_mixed.last_marking_time();
 966     assert(marking_to_mixed_time > 0.0,
 967            "Initial mark to mixed time must be larger than zero but is %.3f",
 968            marking_to_mixed_time);
 969     if (marking_to_mixed_time > min_valid_time) {
 970       _ihop_control->update_marking_length(marking_to_mixed_time);
 971       report = true;
 972     }
 973   }
 974 
 975   // As an approximation for the young gc promotion rates during marking we use
 976   // all of them. In many applications there are only a few if any young gcs during
 977   // marking, which makes any prediction useless. This increases the accuracy of the
 978   // prediction.
 979   if (this_gc_was_young_only && mutator_time_s > min_valid_time) {
 980     // IHOP control wants to know the expected young gen length if it were not
 981     // restrained by the heap reserve. Using the actual length would make the
 982     // prediction too small and the limit the young gen every time we get to the
 983     // predicted target occupancy.
 984     uint young_gen_size = young_list_desired_length() * HeapRegion::GrainBytes;
 985     _ihop_control->update_allocation_info(mutator_time_s, mutator_alloc_bytes, young_gen_size);
 986     report = true;
 987   }
 988 
 989   if (report) {
 990     report_ihop_statistics();
 991   }
 992 }
 993 
 994 void G1Policy::report_ihop_statistics() {
 995   _ihop_control->print();
 996 }
 997 
 998 void G1Policy::print_phases() {
 999   phase_times()->print();
1000 }
1001 
1002 double G1Policy::predict_base_elapsed_time_ms(size_t pending_cards,
1003                                               size_t rs_length) const {
1004   size_t effective_scanned_cards = _analytics->predict_scan_card_num(rs_length, collector_state()->in_young_only_phase());
1005   return
1006     _analytics->predict_card_merge_time_ms(pending_cards + rs_length, collector_state()->in_young_only_phase()) +
1007     _analytics->predict_card_scan_time_ms(effective_scanned_cards, collector_state()->in_young_only_phase()) +
1008     _analytics->predict_constant_other_time_ms() +
1009     predict_survivor_regions_evac_time();
1010 }
1011 
1012 double G1Policy::predict_base_elapsed_time_ms(size_t pending_cards) const {
1013   size_t rs_length = _analytics->predict_rs_length();
1014   return predict_base_elapsed_time_ms(pending_cards, rs_length);
1015 }
1016 
1017 size_t G1Policy::predict_bytes_to_copy(HeapRegion* hr) const {
1018   size_t bytes_to_copy;
1019   if (!hr->is_young()) {
1020     bytes_to_copy = hr->max_live_bytes();
1021   } else {
1022     bytes_to_copy = (size_t) (hr->used() * hr->surv_rate_prediction(_predictor));
1023   }
1024   return bytes_to_copy;
1025 }
1026 
1027 double G1Policy::predict_eden_copy_time_ms(uint count, size_t* bytes_to_copy) const {
1028   if (count == 0) {
1029     return 0.0;
1030   }
1031   size_t const expected_bytes = _eden_surv_rate_group->accum_surv_rate_pred(count) * HeapRegion::GrainBytes;
1032   if (bytes_to_copy != NULL) {
1033     *bytes_to_copy = expected_bytes;
1034   }
1035   return _analytics->predict_object_copy_time_ms(expected_bytes, collector_state()->mark_or_rebuild_in_progress());
1036 }
1037 
1038 double G1Policy::predict_region_copy_time_ms(HeapRegion* hr) const {
1039   size_t const bytes_to_copy = predict_bytes_to_copy(hr);
1040   return _analytics->predict_object_copy_time_ms(bytes_to_copy, collector_state()->mark_or_rebuild_in_progress());
1041 }
1042 
1043 double G1Policy::predict_region_non_copy_time_ms(HeapRegion* hr,
1044                                                  bool for_young_gc) const {
1045   size_t rs_length = hr->rem_set()->occupied();
1046   size_t scan_card_num = _analytics->predict_scan_card_num(rs_length, for_young_gc);
1047 
1048   double region_elapsed_time_ms =
1049     _analytics->predict_card_merge_time_ms(rs_length, collector_state()->in_young_only_phase()) +
1050     _analytics->predict_card_scan_time_ms(scan_card_num, collector_state()->in_young_only_phase());
1051 
1052   // The prediction of the "other" time for this region is based
1053   // upon the region type and NOT the GC type.
1054   if (hr->is_young()) {
1055     region_elapsed_time_ms += _analytics->predict_young_other_time_ms(1);
1056   } else {
1057     region_elapsed_time_ms += _analytics->predict_non_young_other_time_ms(1);
1058   }
1059   return region_elapsed_time_ms;
1060 }
1061 
1062 double G1Policy::predict_region_total_time_ms(HeapRegion* hr, bool for_young_gc) const {
1063   return predict_region_non_copy_time_ms(hr, for_young_gc) + predict_region_copy_time_ms(hr);
1064 }
1065 
1066 bool G1Policy::should_allocate_mutator_region() const {
1067   uint young_list_length = _g1h->young_regions_count();
1068   uint young_list_target_length = _young_list_target_length;
1069   return young_list_length < young_list_target_length;
1070 }
1071 
1072 bool G1Policy::can_expand_young_list() const {
1073   uint young_list_length = _g1h->young_regions_count();
1074   uint young_list_max_length = _young_list_max_length;
1075   return young_list_length < young_list_max_length;
1076 }
1077 
1078 bool G1Policy::use_adaptive_young_list_length() const {
1079   return _young_gen_sizer->use_adaptive_young_list_length();
1080 }
1081 
1082 size_t G1Policy::desired_survivor_size(uint max_regions) const {
1083   size_t const survivor_capacity = HeapRegion::GrainWords * max_regions;
1084   return (size_t)((((double)survivor_capacity) * TargetSurvivorRatio) / 100);
1085 }
1086 
1087 void G1Policy::print_age_table() {
1088   _survivors_age_table.print_age_table(_tenuring_threshold);
1089 }
1090 
1091 uint G1Policy::calculate_young_max_length(uint target_young_length) const {
1092   uint expansion_region_num = 0;
1093   if (GCLockerEdenExpansionPercent > 0) {
1094     double perc = (double) GCLockerEdenExpansionPercent / 100.0;
1095     double expansion_region_num_d = perc * (double) _young_list_target_length;
1096     // We use ceiling so that if expansion_region_num_d is > 0.0 (but
1097     // less than 1.0) we'll get 1.
1098     expansion_region_num = (uint) ceil(expansion_region_num_d);
1099   } else {
1100     assert(expansion_region_num == 0, "sanity");
1101   }
1102   uint max_length = target_young_length + expansion_region_num;
1103   assert(target_young_length <= max_length, "post-condition");
1104   return max_length;
1105 }
1106 
1107 // Calculates survivor space parameters.
1108 void G1Policy::update_survivors_policy() {
1109   double max_survivor_regions_d =
1110                  (double) _young_list_target_length / (double) SurvivorRatio;
1111 
1112   // Calculate desired survivor size based on desired max survivor regions (unconstrained
1113   // by remaining heap). Otherwise we may cause undesired promotions as we are
1114   // already getting close to end of the heap, impacting performance even more.
1115   uint const desired_max_survivor_regions = ceil(max_survivor_regions_d);
1116   size_t const survivor_size = desired_survivor_size(desired_max_survivor_regions);
1117 
1118   _tenuring_threshold = _survivors_age_table.compute_tenuring_threshold(survivor_size);
1119   if (UsePerfData) {
1120     _policy_counters->tenuring_threshold()->set_value(_tenuring_threshold);
1121     _policy_counters->desired_survivor_size()->set_value(survivor_size * oopSize);
1122   }
1123   // The real maximum survivor size is bounded by the number of regions that can
1124   // be allocated into.
1125   _max_survivor_regions = MIN2(desired_max_survivor_regions,
1126                                _g1h->num_free_or_available_regions());
1127 }
1128 
1129 bool G1Policy::force_initial_mark_if_outside_cycle(GCCause::Cause gc_cause) {
1130   // We actually check whether we are marking here and not if we are in a
1131   // reclamation phase. This means that we will schedule a concurrent mark
1132   // even while we are still in the process of reclaiming memory.
1133   bool during_cycle = _g1h->concurrent_mark()->cm_thread()->during_cycle();
1134   if (!during_cycle) {
1135     log_debug(gc, ergo)("Request concurrent cycle initiation (requested by GC cause). GC cause: %s", GCCause::to_string(gc_cause));
1136     collector_state()->set_initiate_conc_mark_if_possible(true);
1137     return true;
1138   } else {
1139     log_debug(gc, ergo)("Do not request concurrent cycle initiation (concurrent cycle already in progress). GC cause: %s", GCCause::to_string(gc_cause));
1140     return false;
1141   }
1142 }
1143 
1144 void G1Policy::initiate_conc_mark() {
1145   collector_state()->set_in_initial_mark_gc(true);
1146   collector_state()->set_initiate_conc_mark_if_possible(false);
1147 }
1148 
1149 void G1Policy::decide_on_conc_mark_initiation() {
1150   // We are about to decide on whether this pause will be an
1151   // initial-mark pause.
1152 
1153   // First, collector_state()->in_initial_mark_gc() should not be already set. We
1154   // will set it here if we have to. However, it should be cleared by
1155   // the end of the pause (it's only set for the duration of an
1156   // initial-mark pause).
1157   assert(!collector_state()->in_initial_mark_gc(), "pre-condition");
1158 
1159   if (collector_state()->initiate_conc_mark_if_possible()) {
1160     // We had noticed on a previous pause that the heap occupancy has
1161     // gone over the initiating threshold and we should start a
1162     // concurrent marking cycle.  Or we've been explicitly requested
1163     // to start a concurrent marking cycle.  Either way, we initiate
1164     // one if not inhibited for some reason.
1165 
1166     GCCause::Cause cause = _g1h->gc_cause();
1167     if ((cause != GCCause::_wb_breakpoint) &&
1168         ConcurrentGCBreakpoints::is_controlled()) {
1169       log_debug(gc, ergo)("Do not initiate concurrent cycle (whitebox controlled)");
1170     } else if (!about_to_start_mixed_phase() && collector_state()->in_young_only_phase()) {
1171       // Initiate a new initial mark if there is no marking or reclamation going on.
1172       initiate_conc_mark();
1173       log_debug(gc, ergo)("Initiate concurrent cycle (concurrent cycle initiation requested)");
1174     } else if (_g1h->is_user_requested_concurrent_full_gc(cause) ||
1175                (cause == GCCause::_wb_breakpoint)) {
1176       // Initiate a user requested initial mark or run_to a breakpoint.
1177       // An initial mark must be young only GC, so the collector state
1178       // must be updated to reflect this.
1179       collector_state()->set_in_young_only_phase(true);
1180       collector_state()->set_in_young_gc_before_mixed(false);
1181 
1182       // We might have ended up coming here about to start a mixed phase with a collection set
1183       // active. The following remark might change the change the "evacuation efficiency" of
1184       // the regions in this set, leading to failing asserts later.
1185       // Since the concurrent cycle will recreate the collection set anyway, simply drop it here.
1186       clear_collection_set_candidates();
1187       abort_time_to_mixed_tracking();
1188       initiate_conc_mark();
1189       log_debug(gc, ergo)("Initiate concurrent cycle (%s requested concurrent cycle)",
1190                           (cause == GCCause::_wb_breakpoint) ? "run_to breakpoint" : "user");
1191     } else {
1192       // The concurrent marking thread is still finishing up the
1193       // previous cycle. If we start one right now the two cycles
1194       // overlap. In particular, the concurrent marking thread might
1195       // be in the process of clearing the next marking bitmap (which
1196       // we will use for the next cycle if we start one). Starting a
1197       // cycle now will be bad given that parts of the marking
1198       // information might get cleared by the marking thread. And we
1199       // cannot wait for the marking thread to finish the cycle as it
1200       // periodically yields while clearing the next marking bitmap
1201       // and, if it's in a yield point, it's waiting for us to
1202       // finish. So, at this point we will not start a cycle and we'll
1203       // let the concurrent marking thread complete the last one.
1204       log_debug(gc, ergo)("Do not initiate concurrent cycle (concurrent cycle already in progress)");
1205     }
1206   }
1207 }
1208 
1209 void G1Policy::record_concurrent_mark_cleanup_end() {
1210   G1CollectionSetCandidates* candidates = G1CollectionSetChooser::build(_g1h->workers(), _g1h->num_regions());
1211   _collection_set->set_candidates(candidates);
1212 
1213   bool mixed_gc_pending = next_gc_should_be_mixed("request mixed gcs", "request young-only gcs");
1214   if (!mixed_gc_pending) {
1215     clear_collection_set_candidates();
1216     abort_time_to_mixed_tracking();
1217   }
1218   collector_state()->set_in_young_gc_before_mixed(mixed_gc_pending);
1219   collector_state()->set_mark_or_rebuild_in_progress(false);
1220 
1221   double end_sec = os::elapsedTime();
1222   double elapsed_time_ms = (end_sec - _mark_cleanup_start_sec) * 1000.0;
1223   _analytics->report_concurrent_mark_cleanup_times_ms(elapsed_time_ms);
1224   _analytics->append_prev_collection_pause_end_ms(elapsed_time_ms);
1225 
1226   record_pause(Cleanup, _mark_cleanup_start_sec, end_sec);
1227 }
1228 
1229 double G1Policy::reclaimable_bytes_percent(size_t reclaimable_bytes) const {
1230   return percent_of(reclaimable_bytes, _g1h->capacity());
1231 }
1232 
1233 class G1ClearCollectionSetCandidateRemSets : public HeapRegionClosure {
1234   virtual bool do_heap_region(HeapRegion* r) {
1235     r->rem_set()->clear_locked(true /* only_cardset */);
1236     return false;
1237   }
1238 };
1239 
1240 void G1Policy::clear_collection_set_candidates() {
1241   // Clear remembered sets of remaining candidate regions and the actual candidate
1242   // set.
1243   G1ClearCollectionSetCandidateRemSets cl;
1244   _collection_set->candidates()->iterate(&cl);
1245   _collection_set->clear_candidates();
1246 }
1247 
1248 void G1Policy::maybe_start_marking() {
1249   if (need_to_start_conc_mark("end of GC")) {
1250     // Note: this might have already been set, if during the last
1251     // pause we decided to start a cycle but at the beginning of
1252     // this pause we decided to postpone it. That's OK.
1253     collector_state()->set_initiate_conc_mark_if_possible(true);
1254   }
1255 }
1256 
1257 G1Policy::PauseKind G1Policy::young_gc_pause_kind() const {
1258   assert(!collector_state()->in_full_gc(), "must be");
1259   if (collector_state()->in_initial_mark_gc()) {
1260     assert(!collector_state()->in_young_gc_before_mixed(), "must be");
1261     return InitialMarkGC;
1262   } else if (collector_state()->in_young_gc_before_mixed()) {
1263     assert(!collector_state()->in_initial_mark_gc(), "must be");
1264     return LastYoungGC;
1265   } else if (collector_state()->in_mixed_phase()) {
1266     assert(!collector_state()->in_initial_mark_gc(), "must be");
1267     assert(!collector_state()->in_young_gc_before_mixed(), "must be");
1268     return MixedGC;
1269   } else {
1270     assert(!collector_state()->in_initial_mark_gc(), "must be");
1271     assert(!collector_state()->in_young_gc_before_mixed(), "must be");
1272     return YoungOnlyGC;
1273   }
1274 }
1275 
1276 void G1Policy::record_pause(PauseKind kind, double start, double end) {
1277   // Manage the MMU tracker. For some reason it ignores Full GCs.
1278   if (kind != FullGC) {
1279     _mmu_tracker->add_pause(start, end);
1280   }
1281   // Manage the mutator time tracking from initial mark to first mixed gc.
1282   switch (kind) {
1283     case FullGC:
1284       abort_time_to_mixed_tracking();
1285       break;
1286     case Cleanup:
1287     case Remark:
1288     case YoungOnlyGC:
1289     case LastYoungGC:
1290       _initial_mark_to_mixed.add_pause(end - start);
1291       break;
1292     case InitialMarkGC:
1293       if (_g1h->gc_cause() != GCCause::_g1_periodic_collection) {
1294         _initial_mark_to_mixed.record_initial_mark_end(end);
1295       }
1296       break;
1297     case MixedGC:
1298       _initial_mark_to_mixed.record_mixed_gc_start(start);
1299       break;
1300     default:
1301       ShouldNotReachHere();
1302   }
1303 }
1304 
1305 void G1Policy::abort_time_to_mixed_tracking() {
1306   _initial_mark_to_mixed.reset();
1307 }
1308 
1309 bool G1Policy::next_gc_should_be_mixed(const char* true_action_str,
1310                                        const char* false_action_str) const {
1311   G1CollectionSetCandidates* candidates = _collection_set->candidates();
1312 
1313   if (candidates == NULL || candidates->is_empty()) {
1314     if (false_action_str != NULL) {
1315       log_debug(gc, ergo)("%s (candidate old regions not available)", false_action_str);
1316     }
1317     return false;
1318   }
1319 
1320   // Is the amount of uncollected reclaimable space above G1HeapWastePercent?
1321   size_t reclaimable_bytes = candidates->remaining_reclaimable_bytes();
1322   double reclaimable_percent = reclaimable_bytes_percent(reclaimable_bytes);
1323   double threshold = (double) G1HeapWastePercent;
1324   if (reclaimable_percent <= threshold) {
1325     if (false_action_str != NULL) {
1326       log_debug(gc, ergo)("%s (reclaimable percentage not over threshold). candidate old regions: %u reclaimable: " SIZE_FORMAT " (%1.2f) threshold: " UINTX_FORMAT,
1327                           false_action_str, candidates->num_remaining(), reclaimable_bytes, reclaimable_percent, G1HeapWastePercent);
1328     }
1329     return false;
1330   }
1331   if (true_action_str != NULL) {
1332     log_debug(gc, ergo)("%s (candidate old regions available). candidate old regions: %u reclaimable: " SIZE_FORMAT " (%1.2f) threshold: " UINTX_FORMAT,
1333                         true_action_str, candidates->num_remaining(), reclaimable_bytes, reclaimable_percent, G1HeapWastePercent);
1334   }
1335   return true;
1336 }
1337 
1338 uint G1Policy::calc_min_old_cset_length() const {
1339   // The min old CSet region bound is based on the maximum desired
1340   // number of mixed GCs after a cycle. I.e., even if some old regions
1341   // look expensive, we should add them to the CSet anyway to make
1342   // sure we go through the available old regions in no more than the
1343   // maximum desired number of mixed GCs.
1344   //
1345   // The calculation is based on the number of marked regions we added
1346   // to the CSet candidates in the first place, not how many remain, so
1347   // that the result is the same during all mixed GCs that follow a cycle.
1348 
1349   const size_t region_num = _collection_set->candidates()->num_regions();
1350   const size_t gc_num = (size_t) MAX2(G1MixedGCCountTarget, (uintx) 1);
1351   size_t result = region_num / gc_num;
1352   // emulate ceiling
1353   if (result * gc_num < region_num) {
1354     result += 1;
1355   }
1356   return (uint) result;
1357 }
1358 
1359 uint G1Policy::calc_max_old_cset_length() const {
1360   // The max old CSet region bound is based on the threshold expressed
1361   // as a percentage of the heap size. I.e., it should bound the
1362   // number of old regions added to the CSet irrespective of how many
1363   // of them are available.
1364 
1365   const G1CollectedHeap* g1h = G1CollectedHeap::heap();
1366   const size_t region_num = g1h->num_regions();
1367   const size_t perc = (size_t) G1OldCSetRegionThresholdPercent;
1368   size_t result = region_num * perc / 100;
1369   // emulate ceiling
1370   if (100 * result < region_num * perc) {
1371     result += 1;
1372   }
1373   return (uint) result;
1374 }
1375 
1376 void G1Policy::calculate_old_collection_set_regions(G1CollectionSetCandidates* candidates,
1377                                                     double time_remaining_ms,
1378                                                     uint& num_initial_regions,
1379                                                     uint& num_optional_regions) {
1380   assert(candidates != NULL, "Must be");
1381 
1382   num_initial_regions = 0;
1383   num_optional_regions = 0;
1384   uint num_expensive_regions = 0;
1385 
1386   double predicted_old_time_ms = 0.0;
1387   double predicted_initial_time_ms = 0.0;
1388   double predicted_optional_time_ms = 0.0;
1389 
1390   double optional_threshold_ms = time_remaining_ms * optional_prediction_fraction();
1391 
1392   const uint min_old_cset_length = calc_min_old_cset_length();
1393   const uint max_old_cset_length = MAX2(min_old_cset_length, calc_max_old_cset_length());
1394   const uint max_optional_regions = max_old_cset_length - min_old_cset_length;
1395   bool check_time_remaining = use_adaptive_young_list_length();
1396 
1397   uint candidate_idx = candidates->cur_idx();
1398 
1399   log_debug(gc, ergo, cset)("Start adding old regions to collection set. Min %u regions, max %u regions, "
1400                             "time remaining %1.2fms, optional threshold %1.2fms",
1401                             min_old_cset_length, max_old_cset_length, time_remaining_ms, optional_threshold_ms);
1402 
1403   HeapRegion* hr = candidates->at(candidate_idx);
1404   while (hr != NULL) {
1405     if (num_initial_regions + num_optional_regions >= max_old_cset_length) {
1406       // Added maximum number of old regions to the CSet.
1407       log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Maximum number of regions). "
1408                                 "Initial %u regions, optional %u regions",
1409                                 num_initial_regions, num_optional_regions);
1410       break;
1411     }
1412 
1413     // Stop adding regions if the remaining reclaimable space is
1414     // not above G1HeapWastePercent.
1415     size_t reclaimable_bytes = candidates->remaining_reclaimable_bytes();
1416     double reclaimable_percent = reclaimable_bytes_percent(reclaimable_bytes);
1417     double threshold = (double) G1HeapWastePercent;
1418     if (reclaimable_percent <= threshold) {
1419       // We've added enough old regions that the amount of uncollected
1420       // reclaimable space is at or below the waste threshold. Stop
1421       // adding old regions to the CSet.
1422       log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Reclaimable percentage below threshold). "
1423                                 "Reclaimable: " SIZE_FORMAT "%s (%1.2f%%) threshold: " UINTX_FORMAT "%%",
1424                                 byte_size_in_proper_unit(reclaimable_bytes), proper_unit_for_byte_size(reclaimable_bytes),
1425                                 reclaimable_percent, G1HeapWastePercent);
1426       break;
1427     }
1428 
1429     double predicted_time_ms = predict_region_total_time_ms(hr, false);
1430     time_remaining_ms = MAX2(time_remaining_ms - predicted_time_ms, 0.0);
1431     // Add regions to old set until we reach the minimum amount
1432     if (num_initial_regions < min_old_cset_length) {
1433       predicted_old_time_ms += predicted_time_ms;
1434       num_initial_regions++;
1435       // Record the number of regions added with no time remaining
1436       if (time_remaining_ms == 0.0) {
1437         num_expensive_regions++;
1438       }
1439     } else if (!check_time_remaining) {
1440       // In the non-auto-tuning case, we'll finish adding regions
1441       // to the CSet if we reach the minimum.
1442       log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Region amount reached min).");
1443       break;
1444     } else {
1445       // Keep adding regions to old set until we reach the optional threshold
1446       if (time_remaining_ms > optional_threshold_ms) {
1447         predicted_old_time_ms += predicted_time_ms;
1448         num_initial_regions++;
1449       } else if (time_remaining_ms > 0) {
1450         // Keep adding optional regions until time is up.
1451         assert(num_optional_regions < max_optional_regions, "Should not be possible.");
1452         predicted_optional_time_ms += predicted_time_ms;
1453         num_optional_regions++;
1454       } else {
1455         log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Predicted time too high).");
1456         break;
1457       }
1458     }
1459     hr = candidates->at(++candidate_idx);
1460   }
1461   if (hr == NULL) {
1462     log_debug(gc, ergo, cset)("Old candidate collection set empty.");
1463   }
1464 
1465   if (num_expensive_regions > 0) {
1466     log_debug(gc, ergo, cset)("Added %u initial old regions to collection set although the predicted time was too high.",
1467                               num_expensive_regions);
1468   }
1469 
1470   log_debug(gc, ergo, cset)("Finish choosing collection set old regions. Initial: %u, optional: %u, "
1471                             "predicted old time: %1.2fms, predicted optional time: %1.2fms, time remaining: %1.2f",
1472                             num_initial_regions, num_optional_regions,
1473                             predicted_initial_time_ms, predicted_optional_time_ms, time_remaining_ms);
1474 }
1475 
1476 void G1Policy::calculate_optional_collection_set_regions(G1CollectionSetCandidates* candidates,
1477                                                          uint const max_optional_regions,
1478                                                          double time_remaining_ms,
1479                                                          uint& num_optional_regions) {
1480   assert(_g1h->collector_state()->in_mixed_phase(), "Should only be called in mixed phase");
1481 
1482   num_optional_regions = 0;
1483   double prediction_ms = 0;
1484   uint candidate_idx = candidates->cur_idx();
1485 
1486   HeapRegion* r = candidates->at(candidate_idx);
1487   while (num_optional_regions < max_optional_regions) {
1488     assert(r != NULL, "Region must exist");
1489     prediction_ms += predict_region_total_time_ms(r, false);
1490 
1491     if (prediction_ms > time_remaining_ms) {
1492       log_debug(gc, ergo, cset)("Prediction %.3fms for region %u does not fit remaining time: %.3fms.",
1493                                 prediction_ms, r->hrm_index(), time_remaining_ms);
1494       break;
1495     }
1496     // This region will be included in the next optional evacuation.
1497 
1498     time_remaining_ms -= prediction_ms;
1499     num_optional_regions++;
1500     r = candidates->at(++candidate_idx);
1501   }
1502 
1503   log_debug(gc, ergo, cset)("Prepared %u regions out of %u for optional evacuation. Predicted time: %.3fms",
1504                             num_optional_regions, max_optional_regions, prediction_ms);
1505 }
1506 
1507 void G1Policy::transfer_survivors_to_cset(const G1SurvivorRegions* survivors) {
1508   note_start_adding_survivor_regions();
1509 
1510   HeapRegion* last = NULL;
1511   for (GrowableArrayIterator<HeapRegion*> it = survivors->regions()->begin();
1512        it != survivors->regions()->end();
1513        ++it) {
1514     HeapRegion* curr = *it;
1515     set_region_survivor(curr);
1516 
1517     // The region is a non-empty survivor so let's add it to
1518     // the incremental collection set for the next evacuation
1519     // pause.
1520     _collection_set->add_survivor_regions(curr);
1521 
1522     last = curr;
1523   }
1524   note_stop_adding_survivor_regions();
1525 
1526   // Don't clear the survivor list handles until the start of
1527   // the next evacuation pause - we need it in order to re-tag
1528   // the survivor regions from this evacuation pause as 'young'
1529   // at the start of the next.
1530 }