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/g1CollectorState.hpp"
  29 #include "gc/g1/g1ParScanThreadState.hpp"
  30 #include "gc/g1/g1Policy.hpp"
  31 #include "gc/g1/heapRegion.inline.hpp"
  32 #include "gc/g1/heapRegionRemSet.hpp"
  33 #include "gc/g1/heapRegionSet.hpp"
  34 #include "logging/logStream.hpp"
  35 #include "utilities/debug.hpp"
  36 #include "utilities/globalDefinitions.hpp"
  37 #include "utilities/quickSort.hpp"
  38 
  39 G1CollectorState* G1CollectionSet::collector_state() {
  40   return _g1h->collector_state();
  41 }
  42 
  43 G1GCPhaseTimes* G1CollectionSet::phase_times() {
  44   return _policy->phase_times();
  45 }
  46 
  47 double G1CollectionSet::predict_region_elapsed_time_ms(HeapRegion* hr) {
  48   return _policy->predict_region_elapsed_time_ms(hr, collector_state()->in_young_only_phase());
  49 }
  50 
  51 G1CollectionSet::G1CollectionSet(G1CollectedHeap* g1h, G1Policy* policy) :
  52   _g1h(g1h),
  53   _policy(policy),
  54   _candidates(NULL),
  55   _eden_region_length(0),
  56   _survivor_region_length(0),
  57   _old_region_length(0),
  58   _collection_set_regions(NULL),
  59   _collection_set_cur_length(0),
  60   _collection_set_max_length(0),
  61   _optional_regions(NULL),
  62   _optional_region_length(0),
  63   _optional_region_max_length(0),
  64   _bytes_used_before(0),
  65   _recorded_rs_lengths(0),
  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   free_optional_regions();
  79   clear_candidates();
  80 }
  81 
  82 void G1CollectionSet::init_region_lengths(uint eden_cset_region_length,
  83                                           uint survivor_cset_region_length) {
  84   assert_at_safepoint_on_vm_thread();
  85 
  86   _eden_region_length     = eden_cset_region_length;
  87   _survivor_region_length = survivor_cset_region_length;
  88 
  89   assert((size_t) young_region_length() == _collection_set_cur_length,
  90          "Young region length %u should match collection set length " SIZE_FORMAT, young_region_length(), _collection_set_cur_length);
  91 
  92   _old_region_length      = 0;
  93   _optional_region_length = 0;
  94 }
  95 
  96 void G1CollectionSet::initialize(uint max_region_length) {
  97   guarantee(_collection_set_regions == NULL, "Must only initialize once.");
  98   _collection_set_max_length = max_region_length;
  99   _collection_set_regions = NEW_C_HEAP_ARRAY(uint, max_region_length, mtGC);
 100 }
 101 
 102 void G1CollectionSet::initialize_optional(uint max_length) {
 103   assert(_optional_regions == NULL, "Already initialized");
 104   assert(_optional_region_length == 0, "Already initialized");
 105   assert(_optional_region_max_length == 0, "Already initialized");
 106   _optional_region_max_length = max_length;
 107   _optional_regions = NEW_C_HEAP_ARRAY(HeapRegion*, _optional_region_max_length, mtGC);
 108 }
 109 
 110 void G1CollectionSet::free_optional_regions() {
 111   _optional_region_length = 0;
 112   _optional_region_max_length = 0;
 113   if (_optional_regions != NULL) {
 114     FREE_C_HEAP_ARRAY(HeapRegion*, _optional_regions);
 115     _optional_regions = NULL;
 116   }
 117 }
 118 
 119 void G1CollectionSet::set_recorded_rs_lengths(size_t rs_lengths) {
 120   _recorded_rs_lengths = rs_lengths;
 121 }
 122 
 123 // Add the heap region at the head of the non-incremental collection set
 124 void G1CollectionSet::add_old_region(HeapRegion* hr) {
 125   assert_at_safepoint_on_vm_thread();
 126 
 127   assert(_inc_build_state == Active || hr->index_in_opt_cset() != G1OptionalCSet::InvalidCSetIndex,
 128          "Precondition, actively building cset or adding optional later on");
 129   assert(hr->is_old(), "the region should be old");
 130 
 131   assert(!hr->in_collection_set(), "should not already be in the CSet");
 132   _g1h->register_old_region_with_cset(hr);
 133 
 134   _collection_set_regions[_collection_set_cur_length++] = hr->hrm_index();
 135   assert(_collection_set_cur_length <= _collection_set_max_length, "Collection set now larger than maximum size.");
 136 
 137   _bytes_used_before += hr->used();
 138   size_t rs_length = hr->rem_set()->occupied();
 139   _recorded_rs_lengths += rs_length;
 140   _old_region_length += 1;
 141 
 142   log_trace(gc, cset)("Added old region %d to collection set", hr->hrm_index());
 143 }
 144 
 145 void G1CollectionSet::add_optional_region(HeapRegion* hr) {
 146   assert(!optional_is_full(), "Precondition, must have room left for this region");
 147   assert(hr->is_old(), "the region should be old");
 148   assert(!hr->in_collection_set(), "should not already be in the CSet");
 149 
 150   _g1h->register_optional_region_with_cset(hr);
 151 
 152   _optional_regions[_optional_region_length] = hr;
 153   uint index = _optional_region_length++;
 154   hr->set_index_in_opt_cset(index);
 155 
 156   log_trace(gc, cset)("Added region %d to optional collection set (%u)", hr->hrm_index(), _optional_region_length);
 157 }
 158 
 159 // Initialize the per-collection-set information
 160 void G1CollectionSet::start_incremental_building() {
 161   assert(_collection_set_cur_length == 0, "Collection set must be empty before starting a new collection set.");
 162   assert(_inc_build_state == Inactive, "Precondition");
 163 
 164   _inc_bytes_used_before = 0;
 165 
 166   _inc_recorded_rs_lengths = 0;
 167   _inc_recorded_rs_lengths_diffs = 0;
 168   _inc_predicted_elapsed_time_ms = 0.0;
 169   _inc_predicted_elapsed_time_ms_diffs = 0.0;
 170   _inc_build_state = Active;
 171 }
 172 
 173 void G1CollectionSet::finalize_incremental_building() {
 174   assert(_inc_build_state == Active, "Precondition");
 175   assert(SafepointSynchronize::is_at_safepoint(), "should be at a safepoint");
 176 
 177   // The two "main" fields, _inc_recorded_rs_lengths and
 178   // _inc_predicted_elapsed_time_ms, are updated by the thread
 179   // that adds a new region to the CSet. Further updates by the
 180   // concurrent refinement thread that samples the young RSet lengths
 181   // are accumulated in the *_diffs fields. Here we add the diffs to
 182   // the "main" fields.
 183 
 184   if (_inc_recorded_rs_lengths_diffs >= 0) {
 185     _inc_recorded_rs_lengths += _inc_recorded_rs_lengths_diffs;
 186   } else {
 187     // This is defensive. The diff should in theory be always positive
 188     // as RSets can only grow between GCs. However, given that we
 189     // sample their size concurrently with other threads updating them
 190     // it's possible that we might get the wrong size back, which
 191     // could make the calculations somewhat inaccurate.
 192     size_t diffs = (size_t) (-_inc_recorded_rs_lengths_diffs);
 193     if (_inc_recorded_rs_lengths >= diffs) {
 194       _inc_recorded_rs_lengths -= diffs;
 195     } else {
 196       _inc_recorded_rs_lengths = 0;
 197     }
 198   }
 199   _inc_predicted_elapsed_time_ms += _inc_predicted_elapsed_time_ms_diffs;
 200 
 201   _inc_recorded_rs_lengths_diffs = 0;
 202   _inc_predicted_elapsed_time_ms_diffs = 0.0;
 203 }
 204 
 205 void G1CollectionSet::clear() {
 206   assert_at_safepoint_on_vm_thread();
 207   _collection_set_cur_length = 0;
 208   _optional_region_length = 0;
 209 }
 210 
 211 void G1CollectionSet::iterate(HeapRegionClosure* cl) const {
 212   iterate_from(cl, 0, 1);
 213 }
 214 
 215 void G1CollectionSet::iterate_from(HeapRegionClosure* cl, uint worker_id, uint total_workers) const {
 216   size_t len = _collection_set_cur_length;
 217   OrderAccess::loadload();
 218   if (len == 0) {
 219     return;
 220   }
 221   size_t start_pos = (worker_id * len) / total_workers;
 222   size_t cur_pos = start_pos;
 223 
 224   do {
 225     HeapRegion* r = _g1h->region_at(_collection_set_regions[cur_pos]);
 226     bool result = cl->do_heap_region(r);
 227     if (result) {
 228       cl->set_incomplete();
 229       return;
 230     }
 231     cur_pos++;
 232     if (cur_pos == len) {
 233       cur_pos = 0;
 234     }
 235   } while (cur_pos != start_pos);
 236 }
 237 
 238 void G1CollectionSet::update_young_region_prediction(HeapRegion* hr,
 239                                                      size_t new_rs_length) {
 240   // Update the CSet information that is dependent on the new RS length
 241   assert(hr->is_young(), "Precondition");
 242   assert(!SafepointSynchronize::is_at_safepoint(), "should not be at a safepoint");
 243 
 244   // We could have updated _inc_recorded_rs_lengths and
 245   // _inc_predicted_elapsed_time_ms directly but we'd need to do
 246   // that atomically, as this code is executed by a concurrent
 247   // refinement thread, potentially concurrently with a mutator thread
 248   // allocating a new region and also updating the same fields. To
 249   // avoid the atomic operations we accumulate these updates on two
 250   // separate fields (*_diffs) and we'll just add them to the "main"
 251   // fields at the start of a GC.
 252 
 253   ssize_t old_rs_length = (ssize_t) hr->recorded_rs_length();
 254   ssize_t rs_lengths_diff = (ssize_t) new_rs_length - old_rs_length;
 255   _inc_recorded_rs_lengths_diffs += rs_lengths_diff;
 256 
 257   double old_elapsed_time_ms = hr->predicted_elapsed_time_ms();
 258   double new_region_elapsed_time_ms = predict_region_elapsed_time_ms(hr);
 259   double elapsed_ms_diff = new_region_elapsed_time_ms - old_elapsed_time_ms;
 260   _inc_predicted_elapsed_time_ms_diffs += elapsed_ms_diff;
 261 
 262   hr->set_recorded_rs_length(new_rs_length);
 263   hr->set_predicted_elapsed_time_ms(new_region_elapsed_time_ms);
 264 }
 265 
 266 void G1CollectionSet::add_young_region_common(HeapRegion* hr) {
 267   assert(hr->is_young(), "invariant");
 268   assert(_inc_build_state == Active, "Precondition");
 269 
 270   size_t collection_set_length = _collection_set_cur_length;
 271   assert(collection_set_length <= INT_MAX, "Collection set is too large with %d entries", (int)collection_set_length);
 272   hr->set_young_index_in_cset((int)collection_set_length);
 273 
 274   _collection_set_regions[collection_set_length] = hr->hrm_index();
 275   // Concurrent readers must observe the store of the value in the array before an
 276   // update to the length field.
 277   OrderAccess::storestore();
 278   _collection_set_cur_length++;
 279   assert(_collection_set_cur_length <= _collection_set_max_length, "Collection set larger than maximum allowed.");
 280 
 281   // This routine is used when:
 282   // * adding survivor regions to the incremental cset at the end of an
 283   //   evacuation pause or
 284   // * adding the current allocation region to the incremental cset
 285   //   when it is retired.
 286   // Therefore this routine may be called at a safepoint by the
 287   // VM thread, or in-between safepoints by mutator threads (when
 288   // retiring the current allocation region)
 289   // We need to clear and set the cached recorded/cached collection set
 290   // information in the heap region here (before the region gets added
 291   // to the collection set). An individual heap region's cached values
 292   // are calculated, aggregated with the policy collection set info,
 293   // and cached in the heap region here (initially) and (subsequently)
 294   // by the Young List sampling code.
 295   // Ignore calls to this due to retirement during full gc.
 296 
 297   if (!_g1h->collector_state()->in_full_gc()) {
 298     size_t rs_length = hr->rem_set()->occupied();
 299     double region_elapsed_time_ms = predict_region_elapsed_time_ms(hr);
 300 
 301     // Cache the values we have added to the aggregated information
 302     // in the heap region in case we have to remove this region from
 303     // the incremental collection set, or it is updated by the
 304     // rset sampling code
 305     hr->set_recorded_rs_length(rs_length);
 306     hr->set_predicted_elapsed_time_ms(region_elapsed_time_ms);
 307 
 308     _inc_recorded_rs_lengths += rs_length;
 309     _inc_predicted_elapsed_time_ms += region_elapsed_time_ms;
 310     _inc_bytes_used_before += hr->used();
 311   }
 312 
 313   assert(!hr->in_collection_set(), "invariant");
 314   _g1h->register_young_region_with_cset(hr);
 315 }
 316 
 317 void G1CollectionSet::add_survivor_regions(HeapRegion* hr) {
 318   assert(hr->is_survivor(), "Must only add survivor regions, but is %s", hr->get_type_str());
 319   add_young_region_common(hr);
 320 }
 321 
 322 void G1CollectionSet::add_eden_region(HeapRegion* hr) {
 323   assert(hr->is_eden(), "Must only add eden regions, but is %s", hr->get_type_str());
 324   add_young_region_common(hr);
 325 }
 326 
 327 #ifndef PRODUCT
 328 class G1VerifyYoungAgesClosure : public HeapRegionClosure {
 329 public:
 330   bool _valid;
 331 public:
 332   G1VerifyYoungAgesClosure() : HeapRegionClosure(), _valid(true) { }
 333 
 334   virtual bool do_heap_region(HeapRegion* r) {
 335     guarantee(r->is_young(), "Region must be young but is %s", r->get_type_str());
 336 
 337     SurvRateGroup* group = r->surv_rate_group();
 338 
 339     if (group == NULL) {
 340       log_error(gc, verify)("## encountered NULL surv_rate_group in young region");
 341       _valid = false;
 342     }
 343 
 344     if (r->age_in_surv_rate_group() < 0) {
 345       log_error(gc, verify)("## encountered negative age in young region");
 346       _valid = false;
 347     }
 348 
 349     return false;
 350   }
 351 
 352   bool valid() const { return _valid; }
 353 };
 354 
 355 bool G1CollectionSet::verify_young_ages() {
 356   assert_at_safepoint_on_vm_thread();
 357 
 358   G1VerifyYoungAgesClosure cl;
 359   iterate(&cl);
 360 
 361   if (!cl.valid()) {
 362     LogStreamHandle(Error, gc, verify) log;
 363     print(&log);
 364   }
 365 
 366   return cl.valid();
 367 }
 368 
 369 class G1PrintCollectionSetDetailClosure : public HeapRegionClosure {
 370   outputStream* _st;
 371 public:
 372   G1PrintCollectionSetDetailClosure(outputStream* st) : HeapRegionClosure(), _st(st) { }
 373 
 374   virtual bool do_heap_region(HeapRegion* r) {
 375     assert(r->in_collection_set(), "Region %u should be in collection set", r->hrm_index());
 376     _st->print_cr("  " HR_FORMAT ", P: " PTR_FORMAT "N: " PTR_FORMAT ", age: %4d",
 377                   HR_FORMAT_PARAMS(r),
 378                   p2i(r->prev_top_at_mark_start()),
 379                   p2i(r->next_top_at_mark_start()),
 380                   r->age_in_surv_rate_group_cond());
 381     return false;
 382   }
 383 };
 384 
 385 void G1CollectionSet::print(outputStream* st) {
 386   st->print_cr("\nCollection_set:");
 387 
 388   G1PrintCollectionSetDetailClosure cl(st);
 389   iterate(&cl);
 390 }
 391 #endif // !PRODUCT
 392 
 393 double G1CollectionSet::finalize_young_part(double target_pause_time_ms, G1SurvivorRegions* survivors) {
 394   double young_start_time_sec = os::elapsedTime();
 395 
 396   finalize_incremental_building();
 397 
 398   guarantee(target_pause_time_ms > 0.0,
 399             "target_pause_time_ms = %1.6lf should be positive", target_pause_time_ms);
 400 
 401   size_t pending_cards = _policy->pending_cards();
 402   double base_time_ms = _policy->predict_base_elapsed_time_ms(pending_cards);
 403   double time_remaining_ms = MAX2(target_pause_time_ms - base_time_ms, 0.0);
 404 
 405   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",
 406                             pending_cards, base_time_ms, time_remaining_ms, target_pause_time_ms);
 407 
 408   // The young list is laid with the survivor regions from the previous
 409   // pause are appended to the RHS of the young list, i.e.
 410   //   [Newly Young Regions ++ Survivors from last pause].
 411 
 412   uint survivor_region_length = survivors->length();
 413   uint eden_region_length = _g1h->eden_regions_count();
 414   init_region_lengths(eden_region_length, survivor_region_length);
 415 
 416   verify_young_cset_indices();
 417 
 418   // Clear the fields that point to the survivor list - they are all young now.
 419   survivors->convert_to_eden();
 420 
 421   _bytes_used_before = _inc_bytes_used_before;
 422   time_remaining_ms = MAX2(time_remaining_ms - _inc_predicted_elapsed_time_ms, 0.0);
 423 
 424   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",
 425                             eden_region_length, survivor_region_length, _inc_predicted_elapsed_time_ms, target_pause_time_ms);
 426 
 427   // The number of recorded young regions is the incremental
 428   // collection set's current size
 429   set_recorded_rs_lengths(_inc_recorded_rs_lengths);
 430 
 431   double young_end_time_sec = os::elapsedTime();
 432   phase_times()->record_young_cset_choice_time_ms((young_end_time_sec - young_start_time_sec) * 1000.0);
 433 
 434   return time_remaining_ms;
 435 }
 436 
 437 void G1CollectionSet::add_as_old(HeapRegion* hr) {
 438   candidates()->pop_front(); // already have region via peek()
 439   _g1h->old_set_remove(hr);
 440   add_old_region(hr);
 441 }
 442 
 443 void G1CollectionSet::add_as_optional(HeapRegion* hr) {
 444   assert(_optional_regions != NULL, "Must not be called before array is allocated");
 445   candidates()->pop_front(); // already have region via peek()
 446   _g1h->old_set_remove(hr);
 447   add_optional_region(hr);
 448 }
 449 
 450 bool G1CollectionSet::optional_is_full() {
 451   assert(_optional_region_length <= _optional_region_max_length, "Invariant");
 452   return _optional_region_length == _optional_region_max_length;
 453 }
 454 
 455 void G1CollectionSet::clear_optional_region(const HeapRegion* hr) {
 456   assert(_optional_regions != NULL, "Must not be called before array is allocated");
 457   uint index = hr->index_in_opt_cset();
 458   _optional_regions[index] = NULL;
 459 }
 460 
 461 static int compare_region_idx(const uint a, const uint b) {
 462   if (a > b) {
 463     return 1;
 464   } else if (a == b) {
 465     return 0;
 466   } else {
 467     return -1;
 468   }
 469 }
 470 
 471 void G1CollectionSet::finalize_old_part(double time_remaining_ms) {
 472   double non_young_start_time_sec = os::elapsedTime();
 473   double predicted_old_time_ms = 0.0;
 474   double predicted_optional_time_ms = 0.0;
 475   double optional_threshold_ms = time_remaining_ms * _policy->optional_prediction_fraction();
 476   uint expensive_region_num = 0;
 477 
 478   if (collector_state()->in_mixed_phase()) {
 479     candidates()->verify();
 480     const uint min_old_cset_length = _policy->calc_min_old_cset_length();
 481     const uint max_old_cset_length = MAX2(min_old_cset_length, _policy->calc_max_old_cset_length());
 482     bool check_time_remaining = _policy->adaptive_young_list_length();
 483 
 484     initialize_optional(max_old_cset_length - min_old_cset_length);
 485     log_debug(gc, ergo, cset)("Start adding old regions for mixed gc. min %u regions, max %u regions, "
 486                               "time remaining %1.2fms, optional threshold %1.2fms",
 487                               min_old_cset_length, max_old_cset_length, time_remaining_ms, optional_threshold_ms);
 488 
 489     HeapRegion* hr = candidates()->peek_front();
 490     while (hr != NULL) {
 491       if (old_region_length() + optional_region_length() >= max_old_cset_length) {
 492         // Added maximum number of old regions to the CSet.
 493         log_debug(gc, ergo, cset)("Finish adding old regions to CSet (old CSet region num reached max). "
 494                                   "old %u regions, optional %u regions",
 495                                   old_region_length(), optional_region_length());
 496         break;
 497       }
 498 
 499       // Stop adding regions if the remaining reclaimable space is
 500       // not above G1HeapWastePercent.
 501       size_t reclaimable_bytes = candidates()->remaining_reclaimable_bytes();
 502       double reclaimable_percent = _policy->reclaimable_bytes_percent(reclaimable_bytes);
 503       double threshold = (double) G1HeapWastePercent;
 504       if (reclaimable_percent <= threshold) {
 505         // We've added enough old regions that the amount of uncollected
 506         // reclaimable space is at or below the waste threshold. Stop
 507         // adding old regions to the CSet.
 508         log_debug(gc, ergo, cset)("Finish adding old regions to CSet (reclaimable percentage not over threshold). "
 509                                   "reclaimable: " SIZE_FORMAT "%s (%1.2f%%) threshold: " UINTX_FORMAT "%%",
 510                                   byte_size_in_proper_unit(reclaimable_bytes), proper_unit_for_byte_size(reclaimable_bytes),
 511                                   reclaimable_percent, G1HeapWastePercent);
 512         break;
 513       }
 514 
 515       double predicted_time_ms = predict_region_elapsed_time_ms(hr);
 516       time_remaining_ms = MAX2(time_remaining_ms - predicted_time_ms, 0.0);
 517       // Add regions to old set until we reach minimum amount
 518       if (old_region_length() < min_old_cset_length) {
 519         predicted_old_time_ms += predicted_time_ms;
 520         add_as_old(hr);
 521         // Record the number of regions added when no time remaining
 522         if (time_remaining_ms == 0.0) {
 523           expensive_region_num++;
 524         }
 525       } else {
 526         // In the non-auto-tuning case, we'll finish adding regions
 527         // to the CSet if we reach the minimum.
 528         if (!check_time_remaining) {
 529           log_debug(gc, ergo, cset)("Finish adding old regions to CSet (old CSet region num reached min).");
 530           break;
 531         }
 532         // Keep adding regions to old set until we reach optional threshold
 533         if (time_remaining_ms > optional_threshold_ms) {
 534           predicted_old_time_ms += predicted_time_ms;
 535           add_as_old(hr);
 536         } else if (time_remaining_ms > 0) {
 537           // Keep adding optional regions until time is up
 538           if (!optional_is_full()) {
 539             predicted_optional_time_ms += predicted_time_ms;
 540             add_as_optional(hr);
 541           } else {
 542             log_debug(gc, ergo, cset)("Finish adding old regions to CSet (optional set full).");
 543             break;
 544           }
 545         } else {
 546           log_debug(gc, ergo, cset)("Finish adding old regions to CSet (predicted time is too high).");
 547           break;
 548         }
 549       }
 550       hr = candidates()->peek_front();
 551     }
 552     if (hr == NULL) {
 553       log_debug(gc, ergo, cset)("Finish adding old regions to CSet (candidate old regions not available)");
 554     }
 555 
 556     candidates()->verify();
 557   }
 558 
 559   stop_incremental_building();
 560 
 561   log_debug(gc, ergo, cset)("Finish choosing CSet regions old: %u, optional: %u, "
 562                             "predicted old time: %1.2fms, predicted optional time: %1.2fms, time remaining: %1.2f",
 563                             old_region_length(), optional_region_length(),
 564                             predicted_old_time_ms, predicted_optional_time_ms, time_remaining_ms);
 565   if (expensive_region_num > 0) {
 566     log_debug(gc, ergo, cset)("CSet contains %u old regions that were added although the predicted time was too high.",
 567                               expensive_region_num);
 568   }
 569 
 570   double non_young_end_time_sec = os::elapsedTime();
 571   phase_times()->record_non_young_cset_choice_time_ms((non_young_end_time_sec - non_young_start_time_sec) * 1000.0);
 572 
 573   QuickSort::sort(_collection_set_regions, _collection_set_cur_length, compare_region_idx, true);
 574 }
 575 
 576 HeapRegion* G1OptionalCSet::region_at(uint index) {
 577   return _cset->optional_region_at(index);
 578 }
 579 
 580 void G1OptionalCSet::prepare_evacuation(double time_limit) {
 581   assert(_current_index == _current_limit, "Before prepare no regions should be ready for evac");
 582 
 583   uint prepared_regions = 0;
 584   double prediction_ms = 0;
 585 
 586   _prepare_failed = true;
 587   for (uint i = _current_index; i < _cset->optional_region_length(); i++) {
 588     HeapRegion* hr = region_at(i);
 589     prediction_ms += _cset->predict_region_elapsed_time_ms(hr);
 590     if (prediction_ms > time_limit) {
 591       log_debug(gc, cset)("Prepared %u regions for optional evacuation. Predicted time: %.3fms", prepared_regions, prediction_ms);
 592       return;
 593     }
 594 
 595     // This region will be included in the next optional evacuation.
 596     prepare_to_evacuate_optional_region(hr);
 597     prepared_regions++;
 598     _current_limit++;
 599     _prepare_failed = false;
 600   }
 601 
 602   log_debug(gc, cset)("Prepared all %u regions for optional evacuation. Predicted time: %.3fms",
 603                       prepared_regions, prediction_ms);
 604 }
 605 
 606 bool G1OptionalCSet::prepare_failed() {
 607   return _prepare_failed;
 608 }
 609 
 610 void G1OptionalCSet::complete_evacuation() {
 611   _evacuation_failed = false;
 612   for (uint i = _current_index; i < _current_limit; i++) {
 613     HeapRegion* hr = region_at(i);
 614     _cset->clear_optional_region(hr);
 615     if (hr->evacuation_failed()){
 616       _evacuation_failed = true;
 617     }
 618   }
 619   _current_index = _current_limit;
 620 }
 621 
 622 bool G1OptionalCSet::evacuation_failed() {
 623   return _evacuation_failed;
 624 }
 625 
 626 G1OptionalCSet::~G1OptionalCSet() {
 627   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 628   while (!is_empty()) {
 629     // We want to return regions not evacuated to the collection set candidates
 630     // in reverse order to maintain the old order.
 631     HeapRegion* hr = _cset->remove_last_optional_region();
 632     assert(hr != NULL, "Should be valid region left");
 633     _pset->record_unused_optional_region(hr);
 634     g1h->old_set_add(hr);
 635     g1h->clear_in_cset(hr);
 636     hr->set_index_in_opt_cset(InvalidCSetIndex);
 637     _cset->candidates()->push_front(hr);
 638   }
 639   _cset->free_optional_regions();
 640 }
 641 
 642 uint G1OptionalCSet::size() {
 643   return _cset->optional_region_length() - _current_index;
 644 }
 645 
 646 bool G1OptionalCSet::is_empty() {
 647   return size() == 0;
 648 }
 649 
 650 void G1OptionalCSet::prepare_to_evacuate_optional_region(HeapRegion* hr) {
 651   log_trace(gc, cset)("Adding region %u for optional evacuation", hr->hrm_index());
 652   G1CollectedHeap::heap()->clear_in_cset(hr);
 653   _cset->add_old_region(hr);
 654 }
 655 
 656 #ifdef ASSERT
 657 class G1VerifyYoungCSetIndicesClosure : public HeapRegionClosure {
 658 private:
 659   size_t _young_length;
 660   int* _heap_region_indices;
 661 public:
 662   G1VerifyYoungCSetIndicesClosure(size_t young_length) : HeapRegionClosure(), _young_length(young_length) {
 663     _heap_region_indices = NEW_C_HEAP_ARRAY(int, young_length, mtGC);
 664     for (size_t i = 0; i < young_length; i++) {
 665       _heap_region_indices[i] = -1;
 666     }
 667   }
 668   ~G1VerifyYoungCSetIndicesClosure() {
 669     FREE_C_HEAP_ARRAY(int, _heap_region_indices);
 670   }
 671 
 672   virtual bool do_heap_region(HeapRegion* r) {
 673     const int idx = r->young_index_in_cset();
 674 
 675     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());
 676     assert((size_t)idx < _young_length, "Young cset index too large for region %u", r->hrm_index());
 677 
 678     assert(_heap_region_indices[idx] == -1,
 679            "Index %d used by multiple regions, first use by region %u, second by region %u",
 680            idx, _heap_region_indices[idx], r->hrm_index());
 681 
 682     _heap_region_indices[idx] = r->hrm_index();
 683 
 684     return false;
 685   }
 686 };
 687 
 688 void G1CollectionSet::verify_young_cset_indices() const {
 689   assert_at_safepoint_on_vm_thread();
 690 
 691   G1VerifyYoungCSetIndicesClosure cl(_collection_set_cur_length);
 692   iterate(&cl);
 693 }
 694 #endif