1 /*
   2  * Copyright (c) 2016, 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.hpp"
  27 #include "gc/g1/g1CollectionSet.hpp"
  28 #include "gc/g1/g1CollectorState.hpp"
  29 #include "gc/g1/g1Policy.hpp"
  30 #include "gc/g1/heapRegion.inline.hpp"
  31 #include "gc/g1/heapRegionRemSet.hpp"
  32 #include "gc/g1/heapRegionSet.hpp"
  33 #include "logging/logStream.hpp"
  34 #include "utilities/debug.hpp"
  35 #include "utilities/quickSort.hpp"
  36 
  37 G1CollectorState* G1CollectionSet::collector_state() {
  38   return _g1->collector_state();
  39 }
  40 
  41 G1GCPhaseTimes* G1CollectionSet::phase_times() {
  42   return _policy->phase_times();
  43 }
  44 
  45 CollectionSetChooser* G1CollectionSet::cset_chooser() {
  46   return _cset_chooser;
  47 }
  48 
  49 double G1CollectionSet::predict_region_elapsed_time_ms(HeapRegion* hr) {
  50   return _policy->predict_region_elapsed_time_ms(hr, collector_state()->gcs_are_young());
  51 }
  52 
  53 G1CollectionSet::G1CollectionSet(G1CollectedHeap* g1h, G1Policy* policy) :
  54   _g1(g1h),
  55   _policy(policy),
  56   _cset_chooser(new CollectionSetChooser()),
  57   _eden_region_length(0),
  58   _survivor_region_length(0),
  59   _old_region_length(0),
  60   _bytes_used_before(0),
  61   _recorded_rs_lengths(0),
  62   _collection_set_regions(NULL),
  63   _collection_set_cur_length(0),
  64   _collection_set_max_length(0),
  65   // Incremental CSet attributes
  66   _inc_build_state(Inactive),
  67   _inc_bytes_used_before(0),
  68   _inc_recorded_rs_lengths(0),
  69   _inc_recorded_rs_lengths_diffs(0),
  70   _inc_predicted_elapsed_time_ms(0.0),
  71   _inc_predicted_elapsed_time_ms_diffs(0.0) {
  72 }
  73 
  74 G1CollectionSet::~G1CollectionSet() {
  75   if (_collection_set_regions != NULL) {
  76     FREE_C_HEAP_ARRAY(uint, _collection_set_regions);
  77   }
  78   delete _cset_chooser;
  79 }
  80 
  81 void G1CollectionSet::init_region_lengths(uint eden_cset_region_length,
  82                                           uint survivor_cset_region_length) {
  83   assert_at_safepoint(true);
  84 
  85   _eden_region_length     = eden_cset_region_length;
  86   _survivor_region_length = survivor_cset_region_length;
  87 
  88   assert((size_t) young_region_length() == _collection_set_cur_length,
  89          "Young region length %u should match collection set length " SIZE_FORMAT, young_region_length(), _collection_set_cur_length);
  90 
  91   _old_region_length      = 0;
  92 }
  93 
  94 void G1CollectionSet::initialize(uint max_region_length) {
  95   guarantee(_collection_set_regions == NULL, "Must only initialize once.");
  96   _collection_set_max_length = max_region_length;
  97   _collection_set_regions = NEW_C_HEAP_ARRAY(uint, max_region_length, mtGC);
  98 }
  99 
 100 void G1CollectionSet::set_recorded_rs_lengths(size_t rs_lengths) {
 101   _recorded_rs_lengths = rs_lengths;
 102 }
 103 
 104 // Add the heap region at the head of the non-incremental collection set
 105 void G1CollectionSet::add_old_region(HeapRegion* hr) {
 106   assert_at_safepoint(true);
 107 
 108   assert(_inc_build_state == Active, "Precondition");
 109   assert(hr->is_old(), "the region should be old");
 110 
 111   assert(!hr->in_collection_set(), "should not already be in the CSet");
 112   _g1->register_old_region_with_cset(hr);
 113 
 114   _collection_set_regions[_collection_set_cur_length++] = hr->hrm_index();
 115   assert(_collection_set_cur_length <= _collection_set_max_length, "Collection set now larger than maximum size.");
 116 
 117   _bytes_used_before += hr->used();
 118   size_t rs_length = hr->rem_set()->occupied();
 119   _recorded_rs_lengths += rs_length;
 120   _old_region_length += 1;
 121 }
 122 
 123 // Initialize the per-collection-set information
 124 void G1CollectionSet::start_incremental_building() {
 125   assert(_collection_set_cur_length == 0, "Collection set must be empty before starting a new collection set.");
 126   assert(_inc_build_state == Inactive, "Precondition");
 127 
 128   _inc_bytes_used_before = 0;
 129 
 130   _inc_recorded_rs_lengths = 0;
 131   _inc_recorded_rs_lengths_diffs = 0;
 132   _inc_predicted_elapsed_time_ms = 0.0;
 133   _inc_predicted_elapsed_time_ms_diffs = 0.0;
 134   _inc_build_state = Active;
 135 }
 136 
 137 void G1CollectionSet::finalize_incremental_building() {
 138   assert(_inc_build_state == Active, "Precondition");
 139   assert(SafepointSynchronize::is_at_safepoint(), "should be at a safepoint");
 140 
 141   // The two "main" fields, _inc_recorded_rs_lengths and
 142   // _inc_predicted_elapsed_time_ms, are updated by the thread
 143   // that adds a new region to the CSet. Further updates by the
 144   // concurrent refinement thread that samples the young RSet lengths
 145   // are accumulated in the *_diffs fields. Here we add the diffs to
 146   // the "main" fields.
 147 
 148   if (_inc_recorded_rs_lengths_diffs >= 0) {
 149     _inc_recorded_rs_lengths += _inc_recorded_rs_lengths_diffs;
 150   } else {
 151     // This is defensive. The diff should in theory be always positive
 152     // as RSets can only grow between GCs. However, given that we
 153     // sample their size concurrently with other threads updating them
 154     // it's possible that we might get the wrong size back, which
 155     // could make the calculations somewhat inaccurate.
 156     size_t diffs = (size_t) (-_inc_recorded_rs_lengths_diffs);
 157     if (_inc_recorded_rs_lengths >= diffs) {
 158       _inc_recorded_rs_lengths -= diffs;
 159     } else {
 160       _inc_recorded_rs_lengths = 0;
 161     }
 162   }
 163   _inc_predicted_elapsed_time_ms += _inc_predicted_elapsed_time_ms_diffs;
 164 
 165   _inc_recorded_rs_lengths_diffs = 0;
 166   _inc_predicted_elapsed_time_ms_diffs = 0.0;
 167 }
 168 
 169 void G1CollectionSet::clear() {
 170   assert_at_safepoint(true);
 171   _collection_set_cur_length = 0;
 172 }
 173 
 174 void G1CollectionSet::iterate(HeapRegionClosure* cl) const {
 175   iterate_from(cl, 0, 1);
 176 }
 177 
 178 void G1CollectionSet::iterate_from(HeapRegionClosure* cl, uint worker_id, uint total_workers) const {
 179   size_t len = _collection_set_cur_length;
 180   OrderAccess::loadload();
 181   if (len == 0) {
 182     return;
 183   }
 184   size_t start_pos = (worker_id * len) / total_workers;
 185   size_t cur_pos = start_pos;
 186 
 187   do {
 188     HeapRegion* r = G1CollectedHeap::heap()->region_at(_collection_set_regions[cur_pos]);
 189     bool result = cl->doHeapRegion(r);
 190     if (result) {
 191       cl->incomplete();
 192       return;
 193     }
 194     cur_pos++;
 195     if (cur_pos == len) {
 196       cur_pos = 0;
 197     }
 198   } while (cur_pos != start_pos);
 199 }
 200 
 201 void G1CollectionSet::update_young_region_prediction(HeapRegion* hr,
 202                                                      size_t new_rs_length) {
 203   // Update the CSet information that is dependent on the new RS length
 204   assert(hr->is_young(), "Precondition");
 205   assert(!SafepointSynchronize::is_at_safepoint(), "should not be at a safepoint");
 206 
 207   // We could have updated _inc_recorded_rs_lengths and
 208   // _inc_predicted_elapsed_time_ms directly but we'd need to do
 209   // that atomically, as this code is executed by a concurrent
 210   // refinement thread, potentially concurrently with a mutator thread
 211   // allocating a new region and also updating the same fields. To
 212   // avoid the atomic operations we accumulate these updates on two
 213   // separate fields (*_diffs) and we'll just add them to the "main"
 214   // fields at the start of a GC.
 215 
 216   ssize_t old_rs_length = (ssize_t) hr->recorded_rs_length();
 217   ssize_t rs_lengths_diff = (ssize_t) new_rs_length - old_rs_length;
 218   _inc_recorded_rs_lengths_diffs += rs_lengths_diff;
 219 
 220   double old_elapsed_time_ms = hr->predicted_elapsed_time_ms();
 221   double new_region_elapsed_time_ms = predict_region_elapsed_time_ms(hr);
 222   double elapsed_ms_diff = new_region_elapsed_time_ms - old_elapsed_time_ms;
 223   _inc_predicted_elapsed_time_ms_diffs += elapsed_ms_diff;
 224 
 225   hr->set_recorded_rs_length(new_rs_length);
 226   hr->set_predicted_elapsed_time_ms(new_region_elapsed_time_ms);
 227 }
 228 
 229 void G1CollectionSet::add_young_region_common(HeapRegion* hr) {
 230   assert(hr->is_young(), "invariant");
 231   assert(_inc_build_state == Active, "Precondition");
 232 
 233   size_t collection_set_length = _collection_set_cur_length;
 234   assert(collection_set_length <= INT_MAX, "Collection set is too large with %d entries", (int)collection_set_length);
 235   hr->set_young_index_in_cset((int)collection_set_length);
 236 
 237   _collection_set_regions[collection_set_length] = hr->hrm_index();
 238   // Concurrent readers must observe the store of the value in the array before an
 239   // update to the length field.
 240   OrderAccess::storestore();
 241   _collection_set_cur_length++;
 242   assert(_collection_set_cur_length <= _collection_set_max_length, "Collection set larger than maximum allowed.");
 243 
 244   // This routine is used when:
 245   // * adding survivor regions to the incremental cset at the end of an
 246   //   evacuation pause or
 247   // * adding the current allocation region to the incremental cset
 248   //   when it is retired.
 249   // Therefore this routine may be called at a safepoint by the
 250   // VM thread, or in-between safepoints by mutator threads (when
 251   // retiring the current allocation region)
 252   // We need to clear and set the cached recorded/cached collection set
 253   // information in the heap region here (before the region gets added
 254   // to the collection set). An individual heap region's cached values
 255   // are calculated, aggregated with the policy collection set info,
 256   // and cached in the heap region here (initially) and (subsequently)
 257   // by the Young List sampling code.
 258 
 259   size_t rs_length = hr->rem_set()->occupied();
 260   double region_elapsed_time_ms = predict_region_elapsed_time_ms(hr);
 261 
 262   // Cache the values we have added to the aggregated information
 263   // in the heap region in case we have to remove this region from
 264   // the incremental collection set, or it is updated by the
 265   // rset sampling code
 266   hr->set_recorded_rs_length(rs_length);
 267   hr->set_predicted_elapsed_time_ms(region_elapsed_time_ms);
 268 
 269   size_t used_bytes = hr->used();
 270   _inc_recorded_rs_lengths += rs_length;
 271   _inc_predicted_elapsed_time_ms += region_elapsed_time_ms;
 272   _inc_bytes_used_before += used_bytes;
 273 
 274   assert(!hr->in_collection_set(), "invariant");
 275   _g1->register_young_region_with_cset(hr);
 276 }
 277 
 278 void G1CollectionSet::add_survivor_regions(HeapRegion* hr) {
 279   assert(hr->is_survivor(), "Must only add survivor regions, but is %s", hr->get_type_str());
 280   add_young_region_common(hr);
 281 }
 282 
 283 void G1CollectionSet::add_eden_region(HeapRegion* hr) {
 284   assert(hr->is_eden(), "Must only add eden regions, but is %s", hr->get_type_str());
 285   add_young_region_common(hr);
 286 }
 287 
 288 #ifndef PRODUCT
 289 class G1VerifyYoungAgesClosure : public HeapRegionClosure {
 290 public:
 291   bool _valid;
 292 public:
 293   G1VerifyYoungAgesClosure() : HeapRegionClosure(), _valid(true) { }
 294 
 295   virtual bool doHeapRegion(HeapRegion* r) {
 296     guarantee(r->is_young(), "Region must be young but is %s", r->get_type_str());
 297 
 298     SurvRateGroup* group = r->surv_rate_group();
 299 
 300     if (group == NULL) {
 301       log_error(gc, verify)("## encountered NULL surv_rate_group in young region");
 302       _valid = false;
 303     }
 304 
 305     if (r->age_in_surv_rate_group() < 0) {
 306       log_error(gc, verify)("## encountered negative age in young region");
 307       _valid = false;
 308     }
 309 
 310     return false;
 311   }
 312 
 313   bool valid() const { return _valid; }
 314 };
 315 
 316 bool G1CollectionSet::verify_young_ages() {
 317   assert_at_safepoint(true);
 318 
 319   G1VerifyYoungAgesClosure cl;
 320   iterate(&cl);
 321 
 322   if (!cl.valid()) {
 323     LogStreamHandle(Error, gc, verify) log;
 324     print(&log);
 325   }
 326 
 327   return cl.valid();
 328 }
 329 
 330 class G1PrintCollectionSetClosure : public HeapRegionClosure {
 331   outputStream* _st;
 332 public:
 333   G1PrintCollectionSetClosure(outputStream* st) : HeapRegionClosure(), _st(st) { }
 334 
 335   virtual bool doHeapRegion(HeapRegion* r) {
 336     assert(r->in_collection_set(), "Region %u should be in collection set", r->hrm_index());
 337     _st->print_cr("  " HR_FORMAT ", P: " PTR_FORMAT "N: " PTR_FORMAT ", age: %4d",
 338                   HR_FORMAT_PARAMS(r),
 339                   p2i(r->prev_top_at_mark_start()),
 340                   p2i(r->next_top_at_mark_start()),
 341                   r->age_in_surv_rate_group_cond());
 342     return false;
 343   }
 344 };
 345 
 346 void G1CollectionSet::print(outputStream* st) {
 347   st->print_cr("\nCollection_set:");
 348 
 349   G1PrintCollectionSetClosure cl(st);
 350   iterate(&cl);
 351 }
 352 #endif // !PRODUCT
 353 
 354 double G1CollectionSet::finalize_young_part(double target_pause_time_ms, G1SurvivorRegions* survivors) {
 355   double young_start_time_sec = os::elapsedTime();
 356 
 357   finalize_incremental_building();
 358 
 359   guarantee(target_pause_time_ms > 0.0,
 360             "target_pause_time_ms = %1.6lf should be positive", target_pause_time_ms);
 361 
 362   size_t pending_cards = _policy->pending_cards();
 363   double base_time_ms = _policy->predict_base_elapsed_time_ms(pending_cards);
 364   double time_remaining_ms = MAX2(target_pause_time_ms - base_time_ms, 0.0);
 365 
 366   log_trace(gc, ergo, cset)("Start choosing CSet. pending cards: " SIZE_FORMAT " predicted base time: %1.2fms remaining time: %1.2fms target pause time: %1.2fms",
 367                             pending_cards, base_time_ms, time_remaining_ms, target_pause_time_ms);
 368 
 369   collector_state()->set_last_gc_was_young(collector_state()->gcs_are_young());
 370 
 371   // The young list is laid with the survivor regions from the previous
 372   // pause are appended to the RHS of the young list, i.e.
 373   //   [Newly Young Regions ++ Survivors from last pause].
 374 
 375   uint survivor_region_length = survivors->length();
 376   uint eden_region_length = _g1->eden_regions_count();
 377   init_region_lengths(eden_region_length, survivor_region_length);
 378 
 379   verify_young_cset_indices();
 380 
 381   // Clear the fields that point to the survivor list - they are all young now.
 382   survivors->convert_to_eden();
 383 
 384   _bytes_used_before = _inc_bytes_used_before;
 385   time_remaining_ms = MAX2(time_remaining_ms - _inc_predicted_elapsed_time_ms, 0.0);
 386 
 387   log_trace(gc, ergo, cset)("Add young regions to CSet. eden: %u regions, survivors: %u regions, predicted young region time: %1.2fms, target pause time: %1.2fms",
 388                             eden_region_length, survivor_region_length, _inc_predicted_elapsed_time_ms, target_pause_time_ms);
 389 
 390   // The number of recorded young regions is the incremental
 391   // collection set's current size
 392   set_recorded_rs_lengths(_inc_recorded_rs_lengths);
 393 
 394   double young_end_time_sec = os::elapsedTime();
 395   phase_times()->record_young_cset_choice_time_ms((young_end_time_sec - young_start_time_sec) * 1000.0);
 396 
 397   return time_remaining_ms;
 398 }
 399 
 400 static int compare_region_idx(const uint a, const uint b) {
 401   if (a > b) {
 402     return 1;
 403   } else if (a == b) {
 404     return 0;
 405   } else {
 406     return -1;
 407   }
 408 }
 409 
 410 void G1CollectionSet::finalize_old_part(double time_remaining_ms) {
 411   double non_young_start_time_sec = os::elapsedTime();
 412   double predicted_old_time_ms = 0.0;
 413 
 414   if (!collector_state()->gcs_are_young()) {
 415     cset_chooser()->verify();
 416     const uint min_old_cset_length = _policy->calc_min_old_cset_length();
 417     const uint max_old_cset_length = _policy->calc_max_old_cset_length();
 418 
 419     uint expensive_region_num = 0;
 420     bool check_time_remaining = _policy->adaptive_young_list_length();
 421 
 422     HeapRegion* hr = cset_chooser()->peek();
 423     while (hr != NULL) {
 424       if (old_region_length() >= max_old_cset_length) {
 425         // Added maximum number of old regions to the CSet.
 426         log_debug(gc, ergo, cset)("Finish adding old regions to CSet (old CSet region num reached max). old %u regions, max %u regions",
 427                                   old_region_length(), max_old_cset_length);
 428         break;
 429       }
 430 
 431       // Stop adding regions if the remaining reclaimable space is
 432       // not above G1HeapWastePercent.
 433       size_t reclaimable_bytes = cset_chooser()->remaining_reclaimable_bytes();
 434       double reclaimable_perc = _policy->reclaimable_bytes_perc(reclaimable_bytes);
 435       double threshold = (double) G1HeapWastePercent;
 436       if (reclaimable_perc <= threshold) {
 437         // We've added enough old regions that the amount of uncollected
 438         // reclaimable space is at or below the waste threshold. Stop
 439         // adding old regions to the CSet.
 440         log_debug(gc, ergo, cset)("Finish adding old regions to CSet (reclaimable percentage not over threshold). "
 441                                   "old %u regions, max %u regions, reclaimable: " SIZE_FORMAT "B (%1.2f%%) threshold: " UINTX_FORMAT "%%",
 442                                   old_region_length(), max_old_cset_length, reclaimable_bytes, reclaimable_perc, G1HeapWastePercent);
 443         break;
 444       }
 445 
 446       double predicted_time_ms = predict_region_elapsed_time_ms(hr);
 447       if (check_time_remaining) {
 448         if (predicted_time_ms > time_remaining_ms) {
 449           // Too expensive for the current CSet.
 450 
 451           if (old_region_length() >= min_old_cset_length) {
 452             // We have added the minimum number of old regions to the CSet,
 453             // we are done with this CSet.
 454             log_debug(gc, ergo, cset)("Finish adding old regions to CSet (predicted time is too high). "
 455                                       "predicted time: %1.2fms, remaining time: %1.2fms old %u regions, min %u regions",
 456                                       predicted_time_ms, time_remaining_ms, old_region_length(), min_old_cset_length);
 457             break;
 458           }
 459 
 460           // We'll add it anyway given that we haven't reached the
 461           // minimum number of old regions.
 462           expensive_region_num += 1;
 463         }
 464       } else {
 465         if (old_region_length() >= min_old_cset_length) {
 466           // In the non-auto-tuning case, we'll finish adding regions
 467           // to the CSet if we reach the minimum.
 468 
 469           log_debug(gc, ergo, cset)("Finish adding old regions to CSet (old CSet region num reached min). old %u regions, min %u regions",
 470                                     old_region_length(), min_old_cset_length);
 471           break;
 472         }
 473       }
 474 
 475       // We will add this region to the CSet.
 476       time_remaining_ms = MAX2(time_remaining_ms - predicted_time_ms, 0.0);
 477       predicted_old_time_ms += predicted_time_ms;
 478       cset_chooser()->pop(); // already have region via peek()
 479       _g1->old_set_remove(hr);
 480       add_old_region(hr);
 481 
 482       hr = cset_chooser()->peek();
 483     }
 484     if (hr == NULL) {
 485       log_debug(gc, ergo, cset)("Finish adding old regions to CSet (candidate old regions not available)");
 486     }
 487 
 488     if (expensive_region_num > 0) {
 489       // We print the information once here at the end, predicated on
 490       // whether we added any apparently expensive regions or not, to
 491       // avoid generating output per region.
 492       log_debug(gc, ergo, cset)("Added expensive regions to CSet (old CSet region num not reached min)."
 493                                 "old: %u regions, expensive: %u regions, min: %u regions, remaining time: %1.2fms",
 494                                 old_region_length(), expensive_region_num, min_old_cset_length, time_remaining_ms);
 495     }
 496 
 497     cset_chooser()->verify();
 498   }
 499 
 500   stop_incremental_building();
 501 
 502   log_debug(gc, ergo, cset)("Finish choosing CSet. old: %u regions, predicted old region time: %1.2fms, time remaining: %1.2f",
 503                             old_region_length(), predicted_old_time_ms, time_remaining_ms);
 504 
 505   double non_young_end_time_sec = os::elapsedTime();
 506   phase_times()->record_non_young_cset_choice_time_ms((non_young_end_time_sec - non_young_start_time_sec) * 1000.0);
 507 
 508   QuickSort::sort<uint>(_collection_set_regions, (int)_collection_set_cur_length, compare_region_idx, true);
 509 }
 510 
 511 #ifdef ASSERT
 512 class G1VerifyYoungCSetIndicesClosure : public HeapRegionClosure {
 513 private:
 514   size_t _young_length;
 515   int* _heap_region_indices;
 516 public:
 517   G1VerifyYoungCSetIndicesClosure(size_t young_length) : HeapRegionClosure(), _young_length(young_length) {
 518     _heap_region_indices = NEW_C_HEAP_ARRAY(int, young_length, mtGC);
 519     for (size_t i = 0; i < young_length; i++) {
 520       _heap_region_indices[i] = -1;
 521     }
 522   }
 523   ~G1VerifyYoungCSetIndicesClosure() {
 524     FREE_C_HEAP_ARRAY(int, _heap_region_indices);
 525   }
 526 
 527   virtual bool doHeapRegion(HeapRegion* r) {
 528     const int idx = r->young_index_in_cset();
 529 
 530     assert(idx > -1, "Young index must be set for all regions in the incremental collection set but is not for region %u.", r->hrm_index());
 531     assert((size_t)idx < _young_length, "Young cset index too large for region %u", r->hrm_index());
 532 
 533     assert(_heap_region_indices[idx] == -1,
 534            "Index %d used by multiple regions, first use by region %u, second by region %u",
 535            idx, _heap_region_indices[idx], r->hrm_index());
 536 
 537     _heap_region_indices[idx] = r->hrm_index();
 538 
 539     return false;
 540   }
 541 };
 542 
 543 void G1CollectionSet::verify_young_cset_indices() const {
 544   assert_at_safepoint(true);
 545 
 546   G1VerifyYoungCSetIndicesClosure cl(_collection_set_cur_length);
 547   iterate(&cl);
 548 }
 549 #endif