1 /*
   2  * Copyright (c) 2016, 2018, 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/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/globalDefinitions.hpp"
  36 #include "utilities/quickSort.hpp"
  37 
  38 G1CollectorState* G1CollectionSet::collector_state() {
  39   return _g1h->collector_state();
  40 }
  41 
  42 G1GCPhaseTimes* G1CollectionSet::phase_times() {
  43   return _policy->phase_times();
  44 }
  45 
  46 CollectionSetChooser* G1CollectionSet::cset_chooser() {
  47   return _cset_chooser;
  48 }
  49 
  50 double G1CollectionSet::predict_region_elapsed_time_ms(HeapRegion* hr) {
  51   return _policy->predict_region_elapsed_time_ms(hr, collector_state()->in_young_only_phase());
  52 }
  53 
  54 G1CollectionSet::G1CollectionSet(G1CollectedHeap* g1h, G1Policy* policy) :
  55   _g1h(g1h),
  56   _policy(policy),
  57   _cset_chooser(new CollectionSetChooser()),
  58   _eden_region_length(0),
  59   _survivor_region_length(0),
  60   _old_region_length(0),
  61   _collection_set_regions(NULL),
  62   _collection_set_cur_length(0),
  63   _collection_set_max_length(0),
  64   _optional_regions(NULL),
  65   _optional_region_length(0),
  66   _optional_region_max_length(0),
  67   _bytes_used_before(0),
  68   _recorded_rs_lengths(0),
  69   _inc_build_state(Inactive),
  70   _inc_bytes_used_before(0),
  71   _inc_recorded_rs_lengths(0),
  72   _inc_recorded_rs_lengths_diffs(0),
  73   _inc_predicted_elapsed_time_ms(0.0),
  74   _inc_predicted_elapsed_time_ms_diffs(0.0) {
  75 }
  76 
  77 G1CollectionSet::~G1CollectionSet() {
  78   if (_collection_set_regions != NULL) {
  79     FREE_C_HEAP_ARRAY(uint, _collection_set_regions);
  80   }
  81   free_optional_regions();
  82   delete _cset_chooser;
  83 }
  84 
  85 void G1CollectionSet::init_region_lengths(uint eden_cset_region_length,
  86                                           uint survivor_cset_region_length) {
  87   assert_at_safepoint_on_vm_thread();
  88 
  89   _eden_region_length     = eden_cset_region_length;
  90   _survivor_region_length = survivor_cset_region_length;
  91 
  92   assert((size_t) young_region_length() == _collection_set_cur_length,
  93          "Young region length %u should match collection set length " SIZE_FORMAT, young_region_length(), _collection_set_cur_length);
  94 
  95   _old_region_length      = 0;
  96   _optional_region_length = 0;
  97 }
  98 
  99 void G1CollectionSet::initialize(uint max_region_length) {
 100   guarantee(_collection_set_regions == NULL, "Must only initialize once.");
 101   _collection_set_max_length = max_region_length;
 102   _collection_set_regions = NEW_C_HEAP_ARRAY(uint, max_region_length, mtGC);
 103 }
 104 
 105 void G1CollectionSet::initialize_optional(uint max_length) {
 106   assert(_optional_regions == NULL, "Already initialized");
 107   _optional_region_max_length = max_length;
 108   _optional_regions = NEW_C_HEAP_ARRAY(HeapRegion*, _optional_region_max_length, mtGC);
 109 }
 110 
 111 void G1CollectionSet::free_optional_regions() {
 112   _optional_region_length = 0;
 113   _optional_region_max_length = 0;
 114   if (_optional_regions != NULL) {
 115     FREE_C_HEAP_ARRAY(HeapRegion*, _optional_regions);
 116     _optional_regions = NULL;
 117   }
 118 }
 119 
 120 void G1CollectionSet::set_recorded_rs_lengths(size_t rs_lengths) {
 121   _recorded_rs_lengths = rs_lengths;
 122 }
 123 
 124 // Add the heap region at the head of the non-incremental collection set
 125 void G1CollectionSet::add_old_region(HeapRegion* hr) {
 126   assert_at_safepoint_on_vm_thread();
 127 
 128   assert(_inc_build_state == Active || hr->index_in_opt_cset() != G1OptionalCSet::InvalidCSetIndex,
 129          "Precondition, actively building cset or adding optional later on");
 130   assert(hr->is_old(), "the region should be old");
 131 
 132   assert(!hr->in_collection_set(), "should not already be in the CSet");
 133   _g1h->register_old_region_with_cset(hr);
 134 
 135   _collection_set_regions[_collection_set_cur_length++] = hr->hrm_index();
 136   assert(_collection_set_cur_length <= _collection_set_max_length, "Collection set now larger than maximum size.");
 137 
 138   _bytes_used_before += hr->used();
 139   size_t rs_length = hr->rem_set()->occupied();
 140   _recorded_rs_lengths += rs_length;
 141   _old_region_length += 1;
 142 
 143   log_trace(gc, cset)("Added old region %d to collection set", hr->hrm_index());
 144 }
 145 
 146 void G1CollectionSet::add_optional_region(HeapRegion* hr) {
 147   assert(!optional_is_full(), "Precondition, must have room left for this region");
 148   assert(hr->is_old(), "the region should be old");
 149   assert(!hr->in_collection_set(), "should not already be in the CSet");
 150 
 151   _g1h->register_optional_region_with_cset(hr);
 152 
 153   _optional_regions[_optional_region_length] = hr;
 154   uint index = _optional_region_length++;
 155   hr->set_index_in_opt_cset(index);
 156 
 157   log_trace(gc, cset)("Added region %d to optional collection set (%u)", hr->hrm_index(), _optional_region_length);
 158 }
 159 
 160 // Initialize the per-collection-set information
 161 void G1CollectionSet::start_incremental_building() {
 162   assert(_collection_set_cur_length == 0, "Collection set must be empty before starting a new collection set.");
 163   assert(_inc_build_state == Inactive, "Precondition");
 164 
 165   _inc_bytes_used_before = 0;
 166 
 167   _inc_recorded_rs_lengths = 0;
 168   _inc_recorded_rs_lengths_diffs = 0;
 169   _inc_predicted_elapsed_time_ms = 0.0;
 170   _inc_predicted_elapsed_time_ms_diffs = 0.0;
 171   _inc_build_state = Active;
 172 }
 173 
 174 void G1CollectionSet::finalize_incremental_building() {
 175   assert(_inc_build_state == Active, "Precondition");
 176   assert(SafepointSynchronize::is_at_safepoint(), "should be at a safepoint");
 177 
 178   // The two "main" fields, _inc_recorded_rs_lengths and
 179   // _inc_predicted_elapsed_time_ms, are updated by the thread
 180   // that adds a new region to the CSet. Further updates by the
 181   // concurrent refinement thread that samples the young RSet lengths
 182   // are accumulated in the *_diffs fields. Here we add the diffs to
 183   // the "main" fields.
 184 
 185   if (_inc_recorded_rs_lengths_diffs >= 0) {
 186     _inc_recorded_rs_lengths += _inc_recorded_rs_lengths_diffs;
 187   } else {
 188     // This is defensive. The diff should in theory be always positive
 189     // as RSets can only grow between GCs. However, given that we
 190     // sample their size concurrently with other threads updating them
 191     // it's possible that we might get the wrong size back, which
 192     // could make the calculations somewhat inaccurate.
 193     size_t diffs = (size_t) (-_inc_recorded_rs_lengths_diffs);
 194     if (_inc_recorded_rs_lengths >= diffs) {
 195       _inc_recorded_rs_lengths -= diffs;
 196     } else {
 197       _inc_recorded_rs_lengths = 0;
 198     }
 199   }
 200   _inc_predicted_elapsed_time_ms += _inc_predicted_elapsed_time_ms_diffs;
 201 
 202   _inc_recorded_rs_lengths_diffs = 0;
 203   _inc_predicted_elapsed_time_ms_diffs = 0.0;
 204 }
 205 
 206 void G1CollectionSet::clear() {
 207   assert_at_safepoint_on_vm_thread();
 208   _collection_set_cur_length = 0;
 209   _optional_region_length = 0;
 210 }
 211 
 212 void G1CollectionSet::iterate(HeapRegionClosure* cl) const {
 213   iterate_from(cl, 0, 1);
 214 }
 215 
 216 void G1CollectionSet::iterate_from(HeapRegionClosure* cl, uint worker_id, uint total_workers) const {
 217   size_t len = _collection_set_cur_length;
 218   OrderAccess::loadload();
 219   if (len == 0) {
 220     return;
 221   }
 222   size_t start_pos = (worker_id * len) / total_workers;
 223   size_t cur_pos = start_pos;
 224 
 225   do {
 226     HeapRegion* r = _g1h->region_at(_collection_set_regions[cur_pos]);
 227     bool result = cl->do_heap_region(r);
 228     if (result) {
 229       cl->set_incomplete();
 230       return;
 231     }
 232     cur_pos++;
 233     if (cur_pos == len) {
 234       cur_pos = 0;
 235     }
 236   } while (cur_pos != start_pos);
 237 }
 238 
 239 void G1CollectionSet::update_young_region_prediction(HeapRegion* hr,
 240                                                      size_t new_rs_length) {
 241   // Update the CSet information that is dependent on the new RS length
 242   assert(hr->is_young(), "Precondition");
 243   assert(!SafepointSynchronize::is_at_safepoint(), "should not be at a safepoint");
 244 
 245   // We could have updated _inc_recorded_rs_lengths and
 246   // _inc_predicted_elapsed_time_ms directly but we'd need to do
 247   // that atomically, as this code is executed by a concurrent
 248   // refinement thread, potentially concurrently with a mutator thread
 249   // allocating a new region and also updating the same fields. To
 250   // avoid the atomic operations we accumulate these updates on two
 251   // separate fields (*_diffs) and we'll just add them to the "main"
 252   // fields at the start of a GC.
 253 
 254   ssize_t old_rs_length = (ssize_t) hr->recorded_rs_length();
 255   ssize_t rs_lengths_diff = (ssize_t) new_rs_length - old_rs_length;
 256   _inc_recorded_rs_lengths_diffs += rs_lengths_diff;
 257 
 258   double old_elapsed_time_ms = hr->predicted_elapsed_time_ms();
 259   double new_region_elapsed_time_ms = predict_region_elapsed_time_ms(hr);
 260   double elapsed_ms_diff = new_region_elapsed_time_ms - old_elapsed_time_ms;
 261   _inc_predicted_elapsed_time_ms_diffs += elapsed_ms_diff;
 262 
 263   hr->set_recorded_rs_length(new_rs_length);
 264   hr->set_predicted_elapsed_time_ms(new_region_elapsed_time_ms);
 265 }
 266 
 267 void G1CollectionSet::add_young_region_common(HeapRegion* hr) {
 268   assert(hr->is_young(), "invariant");
 269   assert(_inc_build_state == Active, "Precondition");
 270 
 271   size_t collection_set_length = _collection_set_cur_length;
 272   assert(collection_set_length <= INT_MAX, "Collection set is too large with %d entries", (int)collection_set_length);
 273   hr->set_young_index_in_cset((int)collection_set_length);
 274 
 275   _collection_set_regions[collection_set_length] = hr->hrm_index();
 276   // Concurrent readers must observe the store of the value in the array before an
 277   // update to the length field.
 278   OrderAccess::storestore();
 279   _collection_set_cur_length++;
 280   assert(_collection_set_cur_length <= _collection_set_max_length, "Collection set larger than maximum allowed.");
 281 
 282   // This routine is used when:
 283   // * adding survivor regions to the incremental cset at the end of an
 284   //   evacuation pause or
 285   // * adding the current allocation region to the incremental cset
 286   //   when it is retired.
 287   // Therefore this routine may be called at a safepoint by the
 288   // VM thread, or in-between safepoints by mutator threads (when
 289   // retiring the current allocation region)
 290   // We need to clear and set the cached recorded/cached collection set
 291   // information in the heap region here (before the region gets added
 292   // to the collection set). An individual heap region's cached values
 293   // are calculated, aggregated with the policy collection set info,
 294   // and cached in the heap region here (initially) and (subsequently)
 295   // by the Young List sampling code.
 296   // Ignore calls to this due to retirement during full gc.
 297 
 298   if (!_g1h->collector_state()->in_full_gc()) {
 299     size_t rs_length = hr->rem_set()->occupied();
 300     double region_elapsed_time_ms = predict_region_elapsed_time_ms(hr);
 301 
 302     // Cache the values we have added to the aggregated information
 303     // in the heap region in case we have to remove this region from
 304     // the incremental collection set, or it is updated by the
 305     // rset sampling code
 306     hr->set_recorded_rs_length(rs_length);
 307     hr->set_predicted_elapsed_time_ms(region_elapsed_time_ms);
 308 
 309     _inc_recorded_rs_lengths += rs_length;
 310     _inc_predicted_elapsed_time_ms += region_elapsed_time_ms;
 311     _inc_bytes_used_before += hr->used();
 312   }
 313 
 314   assert(!hr->in_collection_set(), "invariant");
 315   _g1h->register_young_region_with_cset(hr);
 316 }
 317 
 318 void G1CollectionSet::add_survivor_regions(HeapRegion* hr) {
 319   assert(hr->is_survivor(), "Must only add survivor regions, but is %s", hr->get_type_str());
 320   add_young_region_common(hr);
 321 }
 322 
 323 void G1CollectionSet::add_eden_region(HeapRegion* hr) {
 324   assert(hr->is_eden(), "Must only add eden regions, but is %s", hr->get_type_str());
 325   add_young_region_common(hr);
 326 }
 327 
 328 #ifndef PRODUCT
 329 class G1VerifyYoungAgesClosure : public HeapRegionClosure {
 330 public:
 331   bool _valid;
 332 public:
 333   G1VerifyYoungAgesClosure() : HeapRegionClosure(), _valid(true) { }
 334 
 335   virtual bool do_heap_region(HeapRegion* r) {
 336     guarantee(r->is_young(), "Region must be young but is %s", r->get_type_str());
 337 
 338     SurvRateGroup* group = r->surv_rate_group();
 339 
 340     if (group == NULL) {
 341       log_error(gc, verify)("## encountered NULL surv_rate_group in young region");
 342       _valid = false;
 343     }
 344 
 345     if (r->age_in_surv_rate_group() < 0) {
 346       log_error(gc, verify)("## encountered negative age in young region");
 347       _valid = false;
 348     }
 349 
 350     return false;
 351   }
 352 
 353   bool valid() const { return _valid; }
 354 };
 355 
 356 bool G1CollectionSet::verify_young_ages() {
 357   assert_at_safepoint_on_vm_thread();
 358 
 359   G1VerifyYoungAgesClosure cl;
 360   iterate(&cl);
 361 
 362   if (!cl.valid()) {
 363     LogStreamHandle(Error, gc, verify) log;
 364     print(&log);
 365   }
 366 
 367   return cl.valid();
 368 }
 369 
 370 class G1PrintCollectionSetDetailClosure : public HeapRegionClosure {
 371   outputStream* _st;
 372 public:
 373   G1PrintCollectionSetDetailClosure(outputStream* st) : HeapRegionClosure(), _st(st) { }
 374 
 375   virtual bool do_heap_region(HeapRegion* r) {
 376     assert(r->in_collection_set(), "Region %u should be in collection set", r->hrm_index());
 377     _st->print_cr("  " HR_FORMAT ", P: " PTR_FORMAT "N: " PTR_FORMAT ", age: %4d",
 378                   HR_FORMAT_PARAMS(r),
 379                   p2i(r->prev_top_at_mark_start()),
 380                   p2i(r->next_top_at_mark_start()),
 381                   r->age_in_surv_rate_group_cond());
 382     return false;
 383   }
 384 };
 385 
 386 void G1CollectionSet::print(outputStream* st) {
 387   st->print_cr("\nCollection_set:");
 388 
 389   G1PrintCollectionSetDetailClosure cl(st);
 390   iterate(&cl);
 391 }
 392 #endif // !PRODUCT
 393 
 394 double G1CollectionSet::finalize_young_part(double target_pause_time_ms, G1SurvivorRegions* survivors) {
 395   double young_start_time_sec = os::elapsedTime();
 396 
 397   finalize_incremental_building();
 398 
 399   guarantee(target_pause_time_ms > 0.0,
 400             "target_pause_time_ms = %1.6lf should be positive", target_pause_time_ms);
 401 
 402   size_t pending_cards = _policy->pending_cards();
 403   double base_time_ms = _policy->predict_base_elapsed_time_ms(pending_cards);
 404   double time_remaining_ms = MAX2(target_pause_time_ms - base_time_ms, 0.0);
 405 
 406   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",
 407                             pending_cards, base_time_ms, time_remaining_ms, target_pause_time_ms);
 408 
 409   // The young list is laid with the survivor regions from the previous
 410   // pause are appended to the RHS of the young list, i.e.
 411   //   [Newly Young Regions ++ Survivors from last pause].
 412 
 413   uint survivor_region_length = survivors->length();
 414   uint eden_region_length = _g1h->eden_regions_count();
 415   init_region_lengths(eden_region_length, survivor_region_length);
 416 
 417   verify_young_cset_indices();
 418 
 419   // Clear the fields that point to the survivor list - they are all young now.
 420   survivors->convert_to_eden();
 421 
 422   _bytes_used_before = _inc_bytes_used_before;
 423   time_remaining_ms = MAX2(time_remaining_ms - _inc_predicted_elapsed_time_ms, 0.0);
 424 
 425   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",
 426                             eden_region_length, survivor_region_length, _inc_predicted_elapsed_time_ms, target_pause_time_ms);
 427 
 428   // The number of recorded young regions is the incremental
 429   // collection set's current size
 430   set_recorded_rs_lengths(_inc_recorded_rs_lengths);
 431 
 432   double young_end_time_sec = os::elapsedTime();
 433   phase_times()->record_young_cset_choice_time_ms((young_end_time_sec - young_start_time_sec) * 1000.0);
 434 
 435   return time_remaining_ms;
 436 }
 437 
 438 void G1CollectionSet::add_as_old(HeapRegion* hr) {
 439   cset_chooser()->pop(); // already have region via peek()
 440   _g1h->old_set_remove(hr);
 441   add_old_region(hr);
 442 }
 443 
 444 void G1CollectionSet::add_as_optional(HeapRegion* hr) {
 445   assert(_optional_regions != NULL, "Must not be called before array is allocated");
 446   cset_chooser()->pop(); // already have region via peek()
 447   _g1h->old_set_remove(hr);
 448   add_optional_region(hr);
 449 }
 450 
 451 bool G1CollectionSet::optional_is_full() {
 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     cset_chooser()->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 = cset_chooser()->peek();
 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 = cset_chooser()->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 = cset_chooser()->peek();
 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     cset_chooser()->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
 630     // chooser 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     g1h->old_set_add(hr);
 634     g1h->clear_in_cset(hr);
 635     hr->set_index_in_opt_cset(InvalidCSetIndex);
 636     _cset->cset_chooser()->push(hr);
 637   }
 638   _cset->free_optional_regions();
 639 }
 640 
 641 uint G1OptionalCSet::size() {
 642   return _cset->optional_region_length() - _current_index;
 643 }
 644 
 645 bool G1OptionalCSet::is_empty() {
 646   return size() == 0;
 647 }
 648 
 649 void G1OptionalCSet::prepare_to_evacuate_optional_region(HeapRegion* hr) {
 650   log_trace(gc, cset)("Adding region %u for optional evacuation", hr->hrm_index());
 651   G1CollectedHeap::heap()->clear_in_cset(hr);
 652   _cset->add_old_region(hr);
 653 }
 654 
 655 #ifdef ASSERT
 656 class G1VerifyYoungCSetIndicesClosure : public HeapRegionClosure {
 657 private:
 658   size_t _young_length;
 659   int* _heap_region_indices;
 660 public:
 661   G1VerifyYoungCSetIndicesClosure(size_t young_length) : HeapRegionClosure(), _young_length(young_length) {
 662     _heap_region_indices = NEW_C_HEAP_ARRAY(int, young_length, mtGC);
 663     for (size_t i = 0; i < young_length; i++) {
 664       _heap_region_indices[i] = -1;
 665     }
 666   }
 667   ~G1VerifyYoungCSetIndicesClosure() {
 668     FREE_C_HEAP_ARRAY(int, _heap_region_indices);
 669   }
 670 
 671   virtual bool do_heap_region(HeapRegion* r) {
 672     const int idx = r->young_index_in_cset();
 673 
 674     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());
 675     assert((size_t)idx < _young_length, "Young cset index too large for region %u", r->hrm_index());
 676 
 677     assert(_heap_region_indices[idx] == -1,
 678            "Index %d used by multiple regions, first use by region %u, second by region %u",
 679            idx, _heap_region_indices[idx], r->hrm_index());
 680 
 681     _heap_region_indices[idx] = r->hrm_index();
 682 
 683     return false;
 684   }
 685 };
 686 
 687 void G1CollectionSet::verify_young_cset_indices() const {
 688   assert_at_safepoint_on_vm_thread();
 689 
 690   G1VerifyYoungCSetIndicesClosure cl(_collection_set_cur_length);
 691   iterate(&cl);
 692 }
 693 #endif