1 /*
   2  * Copyright (c) 2016, 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/g1CollectedHeap.inline.hpp"
  27 #include "gc/g1/g1CollectionSet.hpp"
  28 #include "gc/g1/g1CollectionSetCandidates.hpp"
  29 #include "gc/g1/g1CollectorState.hpp"
  30 #include "gc/g1/g1HotCardCache.hpp"
  31 #include "gc/g1/g1ParScanThreadState.hpp"
  32 #include "gc/g1/g1Policy.hpp"
  33 #include "gc/g1/heapRegion.inline.hpp"
  34 #include "gc/g1/heapRegionRemSet.hpp"
  35 #include "gc/g1/heapRegionSet.hpp"
  36 #include "logging/logStream.hpp"
  37 #include "utilities/debug.hpp"
  38 #include "utilities/globalDefinitions.hpp"
  39 #include "utilities/quickSort.hpp"
  40 
  41 G1CollectorState* G1CollectionSet::collector_state() const {
  42   return _g1h->collector_state();
  43 }
  44 
  45 G1GCPhaseTimes* G1CollectionSet::phase_times() {
  46   return _policy->phase_times();
  47 }
  48 
  49 double G1CollectionSet::predict_region_non_copy_time_ms(HeapRegion* hr) const {
  50   return _policy->predict_region_non_copy_time_ms(hr, collector_state()->in_young_only_phase());
  51 }
  52 
  53 G1CollectionSet::G1CollectionSet(G1CollectedHeap* g1h, G1Policy* policy) :
  54   _g1h(g1h),
  55   _policy(policy),
  56   _candidates(NULL),
  57   _eden_region_length(0),
  58   _survivor_region_length(0),
  59   _old_region_length(0),
  60   _collection_set_regions(NULL),
  61   _collection_set_cur_length(0),
  62   _collection_set_max_length(0),
  63   _num_optional_regions(0),
  64   _bytes_used_before(0),
  65   _recorded_rs_length(0),
  66   _inc_build_state(Inactive),
  67   _inc_part_start(0),
  68   _inc_collection_set_stats(NULL),
  69   _inc_bytes_used_before(0),
  70   _inc_recorded_rs_length(0),
  71   _inc_recorded_rs_length_diff(0),
  72   _inc_predicted_non_copy_time_ms(0.0),
  73   _inc_predicted_non_copy_time_ms_diff(0.0) {
  74 }
  75 
  76 G1CollectionSet::~G1CollectionSet() {
  77   FREE_C_HEAP_ARRAY(uint, _collection_set_regions);
  78   FREE_C_HEAP_ARRAY(IncCollectionSetRegionStat, _inc_collection_set_stats);
  79   free_optional_regions();
  80   clear_candidates();
  81 }
  82 
  83 void G1CollectionSet::init_region_lengths(uint eden_cset_region_length,
  84                                           uint survivor_cset_region_length) {
  85   assert_at_safepoint_on_vm_thread();
  86 
  87   _eden_region_length     = eden_cset_region_length;
  88   _survivor_region_length = survivor_cset_region_length;
  89 
  90   assert((size_t) young_region_length() == _collection_set_cur_length,
  91          "Young region length %u should match collection set length " SIZE_FORMAT, young_region_length(), _collection_set_cur_length);
  92 
  93   _old_region_length = 0;
  94   free_optional_regions();
  95 }
  96 
  97 void G1CollectionSet::initialize(uint max_region_length) {
  98   guarantee(_collection_set_regions == NULL, "Must only initialize once.");
  99   _collection_set_max_length = max_region_length;
 100   _collection_set_regions = NEW_C_HEAP_ARRAY(uint, max_region_length, mtGC);
 101   _inc_collection_set_stats = NEW_C_HEAP_ARRAY(IncCollectionSetRegionStat, max_region_length, mtGC);
 102 }
 103 
 104 void G1CollectionSet::free_optional_regions() {
 105   _num_optional_regions = 0;
 106 }
 107 
 108 void G1CollectionSet::clear_candidates() {
 109   delete _candidates;
 110   _candidates = NULL;
 111 }
 112 
 113 void G1CollectionSet::set_recorded_rs_length(size_t rs_length) {
 114   _recorded_rs_length = rs_length;
 115 }
 116 
 117 // Add the heap region at the head of the non-incremental collection set
 118 void G1CollectionSet::add_old_region(HeapRegion* hr) {
 119   assert_at_safepoint_on_vm_thread();
 120 
 121   assert(_inc_build_state == Active,
 122          "Precondition, actively building cset or adding optional later on");
 123   assert(hr->is_old(), "the region should be old");
 124 
 125   assert(!hr->in_collection_set(), "should not already be in the collection set");
 126   _g1h->register_old_region_with_region_attr(hr);
 127 
 128   _collection_set_regions[_collection_set_cur_length++] = hr->hrm_index();
 129   assert(_collection_set_cur_length <= _collection_set_max_length, "Collection set now larger than maximum size.");
 130 
 131   _bytes_used_before += hr->used();
 132   _recorded_rs_length += hr->rem_set()->occupied();
 133   _old_region_length++;
 134 
 135   _g1h->old_set_remove(hr);
 136 }
 137 
 138 void G1CollectionSet::add_optional_region(HeapRegion* hr) {
 139   assert(hr->is_old(), "the region should be old");
 140   assert(!hr->in_collection_set(), "should not already be in the CSet");
 141 
 142   _g1h->register_optional_region_with_region_attr(hr);
 143 
 144   hr->set_index_in_opt_cset(_num_optional_regions++);
 145 }
 146 
 147 void G1CollectionSet::start_incremental_building() {
 148   assert(_collection_set_cur_length == 0, "Collection set must be empty before starting a new collection set.");
 149   assert(_inc_build_state == Inactive, "Precondition");
 150 
 151   _inc_bytes_used_before = 0;
 152 
 153   _inc_recorded_rs_length = 0;
 154   _inc_recorded_rs_length_diff = 0;
 155   _inc_predicted_non_copy_time_ms = 0.0;
 156   _inc_predicted_non_copy_time_ms_diff = 0.0;
 157 
 158   update_incremental_marker();
 159 }
 160 
 161 void G1CollectionSet::finalize_incremental_building() {
 162   assert(_inc_build_state == Active, "Precondition");
 163   assert(SafepointSynchronize::is_at_safepoint(), "should be at a safepoint");
 164 
 165   // The two "main" fields, _inc_recorded_rs_length and
 166   // _inc_predicted_non_copy_time_ms, are updated by the thread
 167   // that adds a new region to the CSet. Further updates by the
 168   // concurrent refinement thread that samples the young RSet lengths
 169   // are accumulated in the *_diff fields. Here we add the diffs to
 170   // the "main" fields.
 171 
 172   _inc_recorded_rs_length += _inc_recorded_rs_length_diff;
 173   _inc_predicted_non_copy_time_ms += _inc_predicted_non_copy_time_ms_diff;
 174 
 175   _inc_recorded_rs_length_diff = 0;
 176   _inc_predicted_non_copy_time_ms_diff = 0.0;
 177 }
 178 
 179 void G1CollectionSet::clear() {
 180   assert_at_safepoint_on_vm_thread();
 181   _collection_set_cur_length = 0;
 182 }
 183 
 184 void G1CollectionSet::iterate(HeapRegionClosure* cl) const {
 185   size_t len = _collection_set_cur_length;
 186   OrderAccess::loadload();
 187 
 188   for (uint i = 0; i < len; i++) {
 189     HeapRegion* r = _g1h->region_at(_collection_set_regions[i]);
 190     bool result = cl->do_heap_region(r);
 191     if (result) {
 192       cl->set_incomplete();
 193       return;
 194     }
 195   }
 196 }
 197 
 198 void G1CollectionSet::iterate_optional(HeapRegionClosure* cl) const {
 199   assert_at_safepoint();
 200 
 201   for (uint i = 0; i < _num_optional_regions; i++) {
 202     HeapRegion* r = _candidates->at(i);
 203     bool result = cl->do_heap_region(r);
 204     guarantee(!result, "Must not cancel iteration");
 205   }
 206 }
 207 
 208 void G1CollectionSet::iterate_incremental_part_from(HeapRegionClosure* cl,
 209                                                     HeapRegionClaimer* hr_claimer,
 210                                                     uint worker_id,
 211                                                     uint total_workers) const {
 212   assert_at_safepoint();
 213 
 214   size_t len = increment_length();
 215   if (len == 0) {
 216     return;
 217   }
 218 
 219   size_t start_pos = (worker_id * len) / total_workers;
 220   size_t cur_pos = start_pos;
 221 
 222   do {
 223     uint region_idx = _collection_set_regions[cur_pos + _inc_part_start];
 224     if (hr_claimer == NULL || hr_claimer->claim_region(region_idx)) {
 225       HeapRegion* r = _g1h->region_at(region_idx);
 226       bool result = cl->do_heap_region(r);
 227       guarantee(!result, "Must not cancel iteration");
 228     }
 229 
 230     cur_pos++;
 231     if (cur_pos == len) {
 232       cur_pos = 0;
 233     }
 234   } while (cur_pos != start_pos);
 235 }
 236 
 237 void G1CollectionSet::update_young_region_prediction(HeapRegion* hr,
 238                                                      size_t new_rs_length) {
 239   // Update the CSet information that is dependent on the new RS length
 240   assert(hr->is_young(), "Precondition");
 241   assert(!SafepointSynchronize::is_at_safepoint(), "should not be at a safepoint");
 242 
 243   IncCollectionSetRegionStat* stat = &_inc_collection_set_stats[hr->hrm_index()];
 244   
 245   size_t old_rs_length = stat->_rs_length;
 246   assert(old_rs_length <= new_rs_length,
 247          "Remembered set sizes must increase (changed from " SIZE_FORMAT " to " SIZE_FORMAT " region %u type %s)",
 248          old_rs_length, new_rs_length, hr->hrm_index(), hr->get_short_type_str());
 249   size_t rs_length_diff = new_rs_length - old_rs_length;
 250   stat->_rs_length = new_rs_length;
 251   _inc_recorded_rs_length_diff += rs_length_diff;
 252 
 253   double old_non_copy_time = stat->_non_copy_time_ms;
 254   double new_non_copy_time = predict_region_non_copy_time_ms(hr);
 255   double non_copy_time_ms_diff = new_non_copy_time - old_non_copy_time;
 256   
 257   stat->_non_copy_time_ms = new_non_copy_time;
 258   _inc_predicted_non_copy_time_ms_diff += non_copy_time_ms_diff;
 259 }
 260 
 261 void G1CollectionSet::add_young_region_common(HeapRegion* hr) {
 262   assert(hr->is_young(), "invariant");
 263   assert(_inc_build_state == Active, "Precondition");
 264 
 265   // This routine is used when:
 266   // * adding survivor regions to the incremental cset at the end of an
 267   //   evacuation pause or
 268   // * adding the current allocation region to the incremental cset
 269   //   when it is retired.
 270   // Therefore this routine may be called at a safepoint by the
 271   // VM thread, or in-between safepoints by mutator threads (when
 272   // retiring the current allocation region)
 273   // We need to clear and set the cached recorded/cached collection set
 274   // information in the heap region here (before the region gets added
 275   // to the collection set). An individual heap region's cached values
 276   // are calculated, aggregated with the policy collection set info,
 277   // and cached in the heap region here (initially) and (subsequently)
 278   // by the Young List sampling code.
 279   // Ignore calls to this due to retirement during full gc.
 280 
 281   if (!_g1h->collector_state()->in_full_gc()) {
 282     size_t rs_length = hr->rem_set()->occupied();
 283     double non_copy_time = predict_region_non_copy_time_ms(hr);
 284 
 285     // Cache the values we have added to the aggregated information
 286     // in the heap region in case we have to remove this region from
 287     // the incremental collection set, or it is updated by the
 288     // rset sampling code
 289 
 290     IncCollectionSetRegionStat* stat = &_inc_collection_set_stats[hr->hrm_index()];
 291     stat->_rs_length = rs_length;
 292     stat->_non_copy_time_ms = non_copy_time;
 293 
 294     _inc_recorded_rs_length += rs_length;
 295     _inc_predicted_non_copy_time_ms += non_copy_time;
 296     _inc_bytes_used_before += hr->used();
 297   }
 298 
 299   assert(!hr->in_collection_set(), "invariant");
 300   _g1h->register_young_region_with_region_attr(hr);
 301 
 302   // We use UINT_MAX as "invalid" marker in verification.
 303   assert(_collection_set_cur_length < (UINT_MAX - 1),
 304          "Collection set is too large with " SIZE_FORMAT " entries", _collection_set_cur_length);
 305   hr->set_young_index_in_cset((uint)_collection_set_cur_length + 1);
 306 
 307   _collection_set_regions[_collection_set_cur_length] = hr->hrm_index();
 308   // Concurrent readers must observe the store of the value in the array before an
 309   // update to the length field.
 310   OrderAccess::storestore();
 311   _collection_set_cur_length++;
 312   assert(_collection_set_cur_length <= _collection_set_max_length, "Collection set larger than maximum allowed.");
 313 }
 314 
 315 void G1CollectionSet::add_survivor_regions(HeapRegion* hr) {
 316   assert(hr->is_survivor(), "Must only add survivor regions, but is %s", hr->get_type_str());
 317   add_young_region_common(hr);
 318 }
 319 
 320 void G1CollectionSet::add_eden_region(HeapRegion* hr) {
 321   assert(hr->is_eden(), "Must only add eden regions, but is %s", hr->get_type_str());
 322   add_young_region_common(hr);
 323 }
 324 
 325 #ifndef PRODUCT
 326 class G1VerifyYoungAgesClosure : public HeapRegionClosure {
 327 public:
 328   bool _valid;
 329 
 330   G1VerifyYoungAgesClosure() : HeapRegionClosure(), _valid(true) { }
 331 
 332   virtual bool do_heap_region(HeapRegion* r) {
 333     guarantee(r->is_young(), "Region must be young but is %s", r->get_type_str());
 334 
 335     if (!r->has_surv_rate_group()) {
 336       log_error(gc, verify)("## encountered young region without surv_rate_group");
 337       _valid = false;
 338     }
 339 
 340     if (!r->has_valid_age_in_surv_rate()) {
 341       log_error(gc, verify)("## encountered invalid age in young region");
 342       _valid = false;
 343     }
 344 
 345     return false;
 346   }
 347 
 348   bool valid() const { return _valid; }
 349 };
 350 
 351 bool G1CollectionSet::verify_young_ages() {
 352   assert_at_safepoint_on_vm_thread();
 353 
 354   G1VerifyYoungAgesClosure cl;
 355   iterate(&cl);
 356 
 357   if (!cl.valid()) {
 358     LogStreamHandle(Error, gc, verify) log;
 359     print(&log);
 360   }
 361 
 362   return cl.valid();
 363 }
 364 
 365 class G1PrintCollectionSetDetailClosure : public HeapRegionClosure {
 366   outputStream* _st;
 367 public:
 368   G1PrintCollectionSetDetailClosure(outputStream* st) : HeapRegionClosure(), _st(st) { }
 369 
 370   virtual bool do_heap_region(HeapRegion* r) {
 371     assert(r->in_collection_set(), "Region %u should be in collection set", r->hrm_index());
 372     _st->print_cr("  " HR_FORMAT ", P: " PTR_FORMAT "N: " PTR_FORMAT ", age: %4d",
 373                   HR_FORMAT_PARAMS(r),
 374                   p2i(r->prev_top_at_mark_start()),
 375                   p2i(r->next_top_at_mark_start()),
 376                   r->has_surv_rate_group() ? r->age_in_surv_rate_group() : -1);
 377     return false;
 378   }
 379 };
 380 
 381 void G1CollectionSet::print(outputStream* st) {
 382   st->print_cr("\nCollection_set:");
 383 
 384   G1PrintCollectionSetDetailClosure cl(st);
 385   iterate(&cl);
 386 }
 387 #endif // !PRODUCT
 388 
 389 double G1CollectionSet::finalize_young_part(double target_pause_time_ms, G1SurvivorRegions* survivors) {
 390   Ticks start_time = Ticks::now();
 391 
 392   finalize_incremental_building();
 393 
 394   guarantee(target_pause_time_ms > 0.0,
 395             "target_pause_time_ms = %1.6lf should be positive", target_pause_time_ms);
 396 
 397   size_t pending_cards = _policy->pending_cards_at_gc_start() + _g1h->hot_card_cache()->num_entries();
 398 
 399   log_trace(gc, ergo, cset)("Start choosing CSet. Pending cards: " SIZE_FORMAT " target pause time: %1.2fms",
 400                             pending_cards, target_pause_time_ms);
 401 
 402   // The young list is laid with the survivor regions from the previous
 403   // pause are appended to the RHS of the young list, i.e.
 404   //   [Newly Young Regions ++ Survivors from last pause].
 405 
 406   uint eden_region_length = _g1h->eden_regions_count();
 407   uint survivor_region_length = survivors->length();
 408   init_region_lengths(eden_region_length, survivor_region_length);
 409 
 410   verify_young_cset_indices();
 411 
 412   // Clear the fields that point to the survivor list - they are all young now.
 413   survivors->convert_to_eden();
 414 
 415   _bytes_used_before = _inc_bytes_used_before;
 416 
 417   // The number of recorded young regions is the incremental
 418   // collection set's current size
 419   set_recorded_rs_length(_inc_recorded_rs_length);
 420 
 421   double predicted_base_time_ms = _policy->predict_base_elapsed_time_ms(pending_cards);
 422   double predicted_eden_time = _inc_predicted_non_copy_time_ms + _policy->predict_eden_copy_time_ms(eden_region_length);
 423   double remaining_time_ms = MAX2(target_pause_time_ms - (predicted_base_time_ms + predicted_eden_time), 0.0);
 424 
 425   log_trace(gc, ergo, cset)("Added young regions to CSet. Eden: %u regions, Survivors: %u regions, "
 426                             "predicted eden time: %1.2fms, predicted base time: %1.2fms, target pause time: %1.2fms, remaining time: %1.2fms",
 427                             eden_region_length, survivor_region_length,
 428                             predicted_eden_time, predicted_base_time_ms, target_pause_time_ms, remaining_time_ms);
 429 
 430   phase_times()->record_young_cset_choice_time_ms((Ticks::now() - start_time).seconds() * 1000.0);
 431 
 432   return remaining_time_ms;
 433 }
 434 
 435 static int compare_region_idx(const uint a, const uint b) {
 436   if (a > b) {
 437     return 1;
 438   } else if (a == b) {
 439     return 0;
 440   } else {
 441     return -1;
 442   }
 443 }
 444 
 445 void G1CollectionSet::finalize_old_part(double time_remaining_ms) {
 446   double non_young_start_time_sec = os::elapsedTime();
 447 
 448   if (collector_state()->in_mixed_phase()) {
 449     candidates()->verify();
 450 
 451     uint num_initial_old_regions;
 452     uint num_optional_old_regions;
 453 
 454     _policy->calculate_old_collection_set_regions(candidates(),
 455                                                   time_remaining_ms,
 456                                                   num_initial_old_regions,
 457                                                   num_optional_old_regions);
 458 
 459     // Prepare initial old regions.
 460     move_candidates_to_collection_set(num_initial_old_regions);
 461 
 462     // Prepare optional old regions for evacuation.
 463     uint candidate_idx = candidates()->cur_idx();
 464     for (uint i = 0; i < num_optional_old_regions; i++) {
 465       add_optional_region(candidates()->at(candidate_idx + i));
 466     }
 467 
 468     candidates()->verify();
 469   }
 470 
 471   stop_incremental_building();
 472 
 473   double non_young_end_time_sec = os::elapsedTime();
 474   phase_times()->record_non_young_cset_choice_time_ms((non_young_end_time_sec - non_young_start_time_sec) * 1000.0);
 475 
 476   QuickSort::sort(_collection_set_regions, _collection_set_cur_length, compare_region_idx, true);
 477 }
 478 
 479 void G1CollectionSet::move_candidates_to_collection_set(uint num_old_candidate_regions) {
 480   if (num_old_candidate_regions == 0) {
 481     return;
 482   }
 483   uint candidate_idx = candidates()->cur_idx();
 484   for (uint i = 0; i < num_old_candidate_regions; i++) {
 485     HeapRegion* r = candidates()->at(candidate_idx + i);
 486     // This potentially optional candidate region is going to be an actual collection
 487     // set region. Clear cset marker.
 488     _g1h->clear_region_attr(r);
 489     add_old_region(r);
 490   }
 491   candidates()->remove(num_old_candidate_regions);
 492 
 493   candidates()->verify();
 494 }
 495 
 496 void G1CollectionSet::finalize_initial_collection_set(double target_pause_time_ms, G1SurvivorRegions* survivor) {
 497   double time_remaining_ms = finalize_young_part(target_pause_time_ms, survivor);
 498   finalize_old_part(time_remaining_ms);
 499 }
 500 
 501 bool G1CollectionSet::finalize_optional_for_evacuation(double remaining_pause_time) {
 502   update_incremental_marker();
 503 
 504   uint num_selected_regions;
 505   _policy->calculate_optional_collection_set_regions(candidates(),
 506                                                      _num_optional_regions,
 507                                                      remaining_pause_time,
 508                                                      num_selected_regions);
 509 
 510   move_candidates_to_collection_set(num_selected_regions);
 511 
 512   _num_optional_regions -= num_selected_regions;
 513 
 514   stop_incremental_building();
 515 
 516   _g1h->verify_region_attr_remset_update();
 517 
 518   return num_selected_regions > 0;
 519 }
 520 
 521 void G1CollectionSet::abandon_optional_collection_set(G1ParScanThreadStateSet* pss) {
 522   for (uint i = 0; i < _num_optional_regions; i++) {
 523     HeapRegion* r = candidates()->at(candidates()->cur_idx() + i);
 524     pss->record_unused_optional_region(r);
 525     // Clear collection set marker and make sure that the remembered set information
 526     // is correct as we still need it later.
 527     _g1h->clear_region_attr(r);
 528     _g1h->register_region_with_region_attr(r);
 529     r->clear_index_in_opt_cset();
 530   }
 531   free_optional_regions();
 532 
 533   _g1h->verify_region_attr_remset_update();
 534 }
 535 
 536 #ifdef ASSERT
 537 class G1VerifyYoungCSetIndicesClosure : public HeapRegionClosure {
 538 private:
 539   size_t _young_length;
 540   uint* _heap_region_indices;
 541 public:
 542   G1VerifyYoungCSetIndicesClosure(size_t young_length) : HeapRegionClosure(), _young_length(young_length) {
 543     _heap_region_indices = NEW_C_HEAP_ARRAY(uint, young_length + 1, mtGC);
 544     for (size_t i = 0; i < young_length + 1; i++) {
 545       _heap_region_indices[i] = UINT_MAX;
 546     }
 547   }
 548   ~G1VerifyYoungCSetIndicesClosure() {
 549     FREE_C_HEAP_ARRAY(int, _heap_region_indices);
 550   }
 551 
 552   virtual bool do_heap_region(HeapRegion* r) {
 553     const uint idx = r->young_index_in_cset();
 554 
 555     assert(idx > 0, "Young index must be set for all regions in the incremental collection set but is not for region %u.", r->hrm_index());
 556     assert(idx <= _young_length, "Young cset index %u too large for region %u", idx, r->hrm_index());
 557 
 558     assert(_heap_region_indices[idx] == UINT_MAX,
 559            "Index %d used by multiple regions, first use by region %u, second by region %u",
 560            idx, _heap_region_indices[idx], r->hrm_index());
 561 
 562     _heap_region_indices[idx] = r->hrm_index();
 563 
 564     return false;
 565   }
 566 };
 567 
 568 void G1CollectionSet::verify_young_cset_indices() const {
 569   assert_at_safepoint_on_vm_thread();
 570 
 571   G1VerifyYoungCSetIndicesClosure cl(_collection_set_cur_length);
 572   iterate(&cl);
 573 }
 574 #endif