1 /* 2 * Copyright (c) 2001, 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/g1Analytics.hpp" 27 #include "gc/g1/g1Arguments.hpp" 28 #include "gc/g1/g1CollectedHeap.inline.hpp" 29 #include "gc/g1/g1CollectionSet.hpp" 30 #include "gc/g1/g1CollectionSetCandidates.hpp" 31 #include "gc/g1/g1ConcurrentMark.hpp" 32 #include "gc/g1/g1ConcurrentMarkThread.inline.hpp" 33 #include "gc/g1/g1ConcurrentRefine.hpp" 34 #include "gc/g1/g1CollectionSetChooser.hpp" 35 #include "gc/g1/g1HeterogeneousHeapPolicy.hpp" 36 #include "gc/g1/g1HotCardCache.hpp" 37 #include "gc/g1/g1IHOPControl.hpp" 38 #include "gc/g1/g1GCPhaseTimes.hpp" 39 #include "gc/g1/g1Policy.hpp" 40 #include "gc/g1/g1SurvivorRegions.hpp" 41 #include "gc/g1/g1YoungGenSizer.hpp" 42 #include "gc/g1/heapRegion.inline.hpp" 43 #include "gc/g1/heapRegionRemSet.hpp" 44 #include "gc/shared/gcPolicyCounters.hpp" 45 #include "logging/logStream.hpp" 46 #include "runtime/arguments.hpp" 47 #include "runtime/java.hpp" 48 #include "runtime/mutexLocker.hpp" 49 #include "utilities/debug.hpp" 50 #include "utilities/growableArray.hpp" 51 #include "utilities/pair.hpp" 52 53 G1Policy::G1Policy(STWGCTimer* gc_timer) : 54 _predictor(G1ConfidencePercent / 100.0), 55 _analytics(new G1Analytics(&_predictor)), 56 _remset_tracker(), 57 _mmu_tracker(new G1MMUTrackerQueue(GCPauseIntervalMillis / 1000.0, MaxGCPauseMillis / 1000.0)), 58 _ihop_control(create_ihop_control(&_predictor)), 59 _policy_counters(new GCPolicyCounters("GarbageFirst", 1, 2)), 60 _full_collection_start_sec(0.0), 61 _collection_pause_end_millis(os::javaTimeNanos() / NANOSECS_PER_MILLISEC), 62 _young_list_target_length(0), 63 _young_list_fixed_length(0), 64 _young_list_max_length(0), 65 _eden_surv_rate_group(new G1SurvRateGroup()), 66 _survivor_surv_rate_group(new G1SurvRateGroup()), 67 _reserve_factor((double) G1ReservePercent / 100.0), 68 _reserve_regions(0), 69 _young_gen_sizer(G1YoungGenSizer::create_gen_sizer()), 70 _free_regions_at_end_of_collection(0), 71 _rs_length(0), 72 _rs_length_prediction(0), 73 _pending_cards_at_gc_start(0), 74 _pending_cards_at_prev_gc_end(0), 75 _total_mutator_refined_cards(0), 76 _total_concurrent_refined_cards(0), 77 _total_concurrent_refinement_time(), 78 _bytes_allocated_in_old_since_last_gc(0), 79 _initial_mark_to_mixed(), 80 _collection_set(NULL), 81 _g1h(NULL), 82 _phase_times(new G1GCPhaseTimes(gc_timer, ParallelGCThreads)), 83 _mark_remark_start_sec(0), 84 _mark_cleanup_start_sec(0), 85 _tenuring_threshold(MaxTenuringThreshold), 86 _max_survivor_regions(0), 87 _survivors_age_table(true) 88 { 89 } 90 91 G1Policy::~G1Policy() { 92 delete _ihop_control; 93 delete _young_gen_sizer; 94 } 95 96 G1Policy* G1Policy::create_policy(STWGCTimer* gc_timer_stw) { 97 if (G1Arguments::is_heterogeneous_heap()) { 98 return new G1HeterogeneousHeapPolicy(gc_timer_stw); 99 } else { 100 return new G1Policy(gc_timer_stw); 101 } 102 } 103 104 G1CollectorState* G1Policy::collector_state() const { return _g1h->collector_state(); } 105 106 void G1Policy::init(G1CollectedHeap* g1h, G1CollectionSet* collection_set) { 107 _g1h = g1h; 108 _collection_set = collection_set; 109 110 assert(Heap_lock->owned_by_self(), "Locking discipline."); 111 112 if (!use_adaptive_young_list_length()) { 113 _young_list_fixed_length = _young_gen_sizer->min_desired_young_length(); 114 } 115 _young_gen_sizer->adjust_max_new_size(_g1h->max_expandable_regions()); 116 117 _free_regions_at_end_of_collection = _g1h->num_free_regions(); 118 119 update_young_list_max_and_target_length(); 120 // We may immediately start allocating regions and placing them on the 121 // collection set list. Initialize the per-collection set info 122 _collection_set->start_incremental_building(); 123 } 124 125 void G1Policy::note_gc_start() { 126 phase_times()->note_gc_start(); 127 } 128 129 class G1YoungLengthPredictor { 130 const double _base_time_ms; 131 const double _base_free_regions; 132 const double _target_pause_time_ms; 133 const G1Policy* const _policy; 134 135 public: 136 G1YoungLengthPredictor(double base_time_ms, 137 double base_free_regions, 138 double target_pause_time_ms, 139 const G1Policy* policy) : 140 _base_time_ms(base_time_ms), 141 _base_free_regions(base_free_regions), 142 _target_pause_time_ms(target_pause_time_ms), 143 _policy(policy) {} 144 145 bool will_fit(uint young_length) const { 146 if (young_length >= _base_free_regions) { 147 // end condition 1: not enough space for the young regions 148 return false; 149 } 150 151 size_t bytes_to_copy = 0; 152 const double copy_time_ms = _policy->predict_eden_copy_time_ms(young_length, &bytes_to_copy); 153 const double young_other_time_ms = _policy->analytics()->predict_young_other_time_ms(young_length); 154 const double pause_time_ms = _base_time_ms + copy_time_ms + young_other_time_ms; 155 if (pause_time_ms > _target_pause_time_ms) { 156 // end condition 2: prediction is over the target pause time 157 return false; 158 } 159 160 const size_t free_bytes = (_base_free_regions - young_length) * HeapRegion::GrainBytes; 161 162 // When copying, we will likely need more bytes free than is live in the region. 163 // Add some safety margin to factor in the confidence of our guess, and the 164 // natural expected waste. 165 // (100.0 / G1ConfidencePercent) is a scale factor that expresses the uncertainty 166 // of the calculation: the lower the confidence, the more headroom. 167 // (100 + TargetPLABWastePct) represents the increase in expected bytes during 168 // copying due to anticipated waste in the PLABs. 169 const double safety_factor = (100.0 / G1ConfidencePercent) * (100 + TargetPLABWastePct) / 100.0; 170 const size_t expected_bytes_to_copy = (size_t)(safety_factor * bytes_to_copy); 171 172 if (expected_bytes_to_copy > free_bytes) { 173 // end condition 3: out-of-space 174 return false; 175 } 176 177 // success! 178 return true; 179 } 180 }; 181 182 void G1Policy::record_new_heap_size(uint new_number_of_regions) { 183 // re-calculate the necessary reserve 184 double reserve_regions_d = (double) new_number_of_regions * _reserve_factor; 185 // We use ceiling so that if reserve_regions_d is > 0.0 (but 186 // smaller than 1.0) we'll get 1. 187 _reserve_regions = (uint) ceil(reserve_regions_d); 188 189 _young_gen_sizer->heap_size_changed(new_number_of_regions); 190 191 _ihop_control->update_target_occupancy(new_number_of_regions * HeapRegion::GrainBytes); 192 } 193 194 uint G1Policy::calculate_young_list_desired_min_length(uint base_min_length) const { 195 uint desired_min_length = 0; 196 if (use_adaptive_young_list_length()) { 197 if (_analytics->num_alloc_rate_ms() > 3) { 198 double now_sec = os::elapsedTime(); 199 double when_ms = _mmu_tracker->when_max_gc_sec(now_sec) * 1000.0; 200 double alloc_rate_ms = _analytics->predict_alloc_rate_ms(); 201 desired_min_length = (uint) ceil(alloc_rate_ms * when_ms); 202 } else { 203 // otherwise we don't have enough info to make the prediction 204 } 205 } 206 desired_min_length += base_min_length; 207 // make sure we don't go below any user-defined minimum bound 208 return MAX2(_young_gen_sizer->min_desired_young_length(), desired_min_length); 209 } 210 211 uint G1Policy::calculate_young_list_desired_max_length() const { 212 // Here, we might want to also take into account any additional 213 // constraints (i.e., user-defined minimum bound). Currently, we 214 // effectively don't set this bound. 215 return _young_gen_sizer->max_desired_young_length(); 216 } 217 218 uint G1Policy::update_young_list_max_and_target_length() { 219 return update_young_list_max_and_target_length(_analytics->predict_rs_length()); 220 } 221 222 uint G1Policy::update_young_list_max_and_target_length(size_t rs_length) { 223 uint unbounded_target_length = update_young_list_target_length(rs_length); 224 update_max_gc_locker_expansion(); 225 return unbounded_target_length; 226 } 227 228 uint G1Policy::update_young_list_target_length(size_t rs_length) { 229 YoungTargetLengths young_lengths = young_list_target_lengths(rs_length); 230 _young_list_target_length = young_lengths.first; 231 232 return young_lengths.second; 233 } 234 235 G1Policy::YoungTargetLengths G1Policy::young_list_target_lengths(size_t rs_length) const { 236 YoungTargetLengths result; 237 238 // Calculate the absolute and desired min bounds first. 239 240 // This is how many young regions we already have (currently: the survivors). 241 const uint base_min_length = _g1h->survivor_regions_count(); 242 uint desired_min_length = calculate_young_list_desired_min_length(base_min_length); 243 // This is the absolute minimum young length. Ensure that we 244 // will at least have one eden region available for allocation. 245 uint absolute_min_length = base_min_length + MAX2(_g1h->eden_regions_count(), (uint)1); 246 // If we shrank the young list target it should not shrink below the current size. 247 desired_min_length = MAX2(desired_min_length, absolute_min_length); 248 // Calculate the absolute and desired max bounds. 249 250 uint desired_max_length = calculate_young_list_desired_max_length(); 251 252 uint young_list_target_length = 0; 253 if (use_adaptive_young_list_length()) { 254 if (collector_state()->in_young_only_phase()) { 255 young_list_target_length = 256 calculate_young_list_target_length(rs_length, 257 base_min_length, 258 desired_min_length, 259 desired_max_length); 260 } else { 261 // Don't calculate anything and let the code below bound it to 262 // the desired_min_length, i.e., do the next GC as soon as 263 // possible to maximize how many old regions we can add to it. 264 } 265 } else { 266 // The user asked for a fixed young gen so we'll fix the young gen 267 // whether the next GC is young or mixed. 268 young_list_target_length = _young_list_fixed_length; 269 } 270 271 result.second = young_list_target_length; 272 273 // We will try our best not to "eat" into the reserve. 274 uint absolute_max_length = 0; 275 if (_free_regions_at_end_of_collection > _reserve_regions) { 276 absolute_max_length = _free_regions_at_end_of_collection - _reserve_regions; 277 } 278 if (desired_max_length > absolute_max_length) { 279 desired_max_length = absolute_max_length; 280 } 281 282 // Make sure we don't go over the desired max length, nor under the 283 // desired min length. In case they clash, desired_min_length wins 284 // which is why that test is second. 285 if (young_list_target_length > desired_max_length) { 286 young_list_target_length = desired_max_length; 287 } 288 if (young_list_target_length < desired_min_length) { 289 young_list_target_length = desired_min_length; 290 } 291 292 assert(young_list_target_length > base_min_length, 293 "we should be able to allocate at least one eden region"); 294 assert(young_list_target_length >= absolute_min_length, "post-condition"); 295 296 result.first = young_list_target_length; 297 return result; 298 } 299 300 uint G1Policy::calculate_young_list_target_length(size_t rs_length, 301 uint base_min_length, 302 uint desired_min_length, 303 uint desired_max_length) const { 304 assert(use_adaptive_young_list_length(), "pre-condition"); 305 assert(collector_state()->in_young_only_phase(), "only call this for young GCs"); 306 307 // In case some edge-condition makes the desired max length too small... 308 if (desired_max_length <= desired_min_length) { 309 return desired_min_length; 310 } 311 312 // We'll adjust min_young_length and max_young_length not to include 313 // the already allocated young regions (i.e., so they reflect the 314 // min and max eden regions we'll allocate). The base_min_length 315 // will be reflected in the predictions by the 316 // survivor_regions_evac_time prediction. 317 assert(desired_min_length > base_min_length, "invariant"); 318 uint min_young_length = desired_min_length - base_min_length; 319 assert(desired_max_length > base_min_length, "invariant"); 320 uint max_young_length = desired_max_length - base_min_length; 321 322 const double target_pause_time_ms = _mmu_tracker->max_gc_time() * 1000.0; 323 const size_t pending_cards = _analytics->predict_pending_cards(); 324 const double base_time_ms = predict_base_elapsed_time_ms(pending_cards, rs_length); 325 const uint available_free_regions = _free_regions_at_end_of_collection; 326 const uint base_free_regions = 327 available_free_regions > _reserve_regions ? available_free_regions - _reserve_regions : 0; 328 329 // Here, we will make sure that the shortest young length that 330 // makes sense fits within the target pause time. 331 332 G1YoungLengthPredictor p(base_time_ms, 333 base_free_regions, 334 target_pause_time_ms, 335 this); 336 if (p.will_fit(min_young_length)) { 337 // The shortest young length will fit into the target pause time; 338 // we'll now check whether the absolute maximum number of young 339 // regions will fit in the target pause time. If not, we'll do 340 // a binary search between min_young_length and max_young_length. 341 if (p.will_fit(max_young_length)) { 342 // The maximum young length will fit into the target pause time. 343 // We are done so set min young length to the maximum length (as 344 // the result is assumed to be returned in min_young_length). 345 min_young_length = max_young_length; 346 } else { 347 // The maximum possible number of young regions will not fit within 348 // the target pause time so we'll search for the optimal 349 // length. The loop invariants are: 350 // 351 // min_young_length < max_young_length 352 // min_young_length is known to fit into the target pause time 353 // max_young_length is known not to fit into the target pause time 354 // 355 // Going into the loop we know the above hold as we've just 356 // checked them. Every time around the loop we check whether 357 // the middle value between min_young_length and 358 // max_young_length fits into the target pause time. If it 359 // does, it becomes the new min. If it doesn't, it becomes 360 // the new max. This way we maintain the loop invariants. 361 362 assert(min_young_length < max_young_length, "invariant"); 363 uint diff = (max_young_length - min_young_length) / 2; 364 while (diff > 0) { 365 uint young_length = min_young_length + diff; 366 if (p.will_fit(young_length)) { 367 min_young_length = young_length; 368 } else { 369 max_young_length = young_length; 370 } 371 assert(min_young_length < max_young_length, "invariant"); 372 diff = (max_young_length - min_young_length) / 2; 373 } 374 // The results is min_young_length which, according to the 375 // loop invariants, should fit within the target pause time. 376 377 // These are the post-conditions of the binary search above: 378 assert(min_young_length < max_young_length, 379 "otherwise we should have discovered that max_young_length " 380 "fits into the pause target and not done the binary search"); 381 assert(p.will_fit(min_young_length), 382 "min_young_length, the result of the binary search, should " 383 "fit into the pause target"); 384 assert(!p.will_fit(min_young_length + 1), 385 "min_young_length, the result of the binary search, should be " 386 "optimal, so no larger length should fit into the pause target"); 387 } 388 } else { 389 // Even the minimum length doesn't fit into the pause time 390 // target, return it as the result nevertheless. 391 } 392 return base_min_length + min_young_length; 393 } 394 395 double G1Policy::predict_survivor_regions_evac_time() const { 396 double survivor_regions_evac_time = 0.0; 397 const GrowableArray<HeapRegion*>* survivor_regions = _g1h->survivor()->regions(); 398 for (GrowableArrayIterator<HeapRegion*> it = survivor_regions->begin(); 399 it != survivor_regions->end(); 400 ++it) { 401 survivor_regions_evac_time += predict_region_total_time_ms(*it, collector_state()->in_young_only_phase()); 402 } 403 return survivor_regions_evac_time; 404 } 405 406 void G1Policy::revise_young_list_target_length_if_necessary(size_t rs_length) { 407 guarantee(use_adaptive_young_list_length(), "should not call this otherwise" ); 408 409 if (rs_length > _rs_length_prediction) { 410 // add 10% to avoid having to recalculate often 411 size_t rs_length_prediction = rs_length * 1100 / 1000; 412 update_rs_length_prediction(rs_length_prediction); 413 414 update_young_list_max_and_target_length(rs_length_prediction); 415 } 416 } 417 418 void G1Policy::update_rs_length_prediction() { 419 update_rs_length_prediction(_analytics->predict_rs_length()); 420 } 421 422 void G1Policy::update_rs_length_prediction(size_t prediction) { 423 if (collector_state()->in_young_only_phase() && use_adaptive_young_list_length()) { 424 _rs_length_prediction = prediction; 425 } 426 } 427 428 void G1Policy::record_full_collection_start() { 429 _full_collection_start_sec = os::elapsedTime(); 430 // Release the future to-space so that it is available for compaction into. 431 collector_state()->set_in_young_only_phase(false); 432 collector_state()->set_in_full_gc(true); 433 _collection_set->clear_candidates(); 434 record_concurrent_refinement_data(true /* is_full_collection */); 435 } 436 437 void G1Policy::record_full_collection_end() { 438 // Consider this like a collection pause for the purposes of allocation 439 // since last pause. 440 double end_sec = os::elapsedTime(); 441 double full_gc_time_sec = end_sec - _full_collection_start_sec; 442 double full_gc_time_ms = full_gc_time_sec * 1000.0; 443 444 _analytics->update_recent_gc_times(end_sec, full_gc_time_ms); 445 446 collector_state()->set_in_full_gc(false); 447 448 // "Nuke" the heuristics that control the young/mixed GC 449 // transitions and make sure we start with young GCs after the Full GC. 450 collector_state()->set_in_young_only_phase(true); 451 collector_state()->set_in_young_gc_before_mixed(false); 452 collector_state()->set_initiate_conc_mark_if_possible(need_to_start_conc_mark("end of Full GC", 0)); 453 collector_state()->set_in_initial_mark_gc(false); 454 collector_state()->set_mark_or_rebuild_in_progress(false); 455 collector_state()->set_clearing_next_bitmap(false); 456 457 _eden_surv_rate_group->start_adding_regions(); 458 // also call this on any additional surv rate groups 459 460 _free_regions_at_end_of_collection = _g1h->num_free_regions(); 461 _survivor_surv_rate_group->reset(); 462 update_young_list_max_and_target_length(); 463 update_rs_length_prediction(); 464 _pending_cards_at_prev_gc_end = _g1h->pending_card_num(); 465 466 _bytes_allocated_in_old_since_last_gc = 0; 467 468 record_pause(FullGC, _full_collection_start_sec, end_sec); 469 } 470 471 void G1Policy::record_concurrent_refinement_data(bool is_full_collection) { 472 _pending_cards_at_gc_start = _g1h->pending_card_num(); 473 474 // Record info about concurrent refinement thread processing. 475 G1ConcurrentRefine* cr = _g1h->concurrent_refine(); 476 G1ConcurrentRefine::RefinementStats cr_stats = cr->total_refinement_stats(); 477 478 Tickspan cr_time = cr_stats._time - _total_concurrent_refinement_time; 479 _total_concurrent_refinement_time = cr_stats._time; 480 481 size_t cr_cards = cr_stats._cards - _total_concurrent_refined_cards; 482 _total_concurrent_refined_cards = cr_stats._cards; 483 484 // Don't update rate if full collection. We could be in an implicit full 485 // collection after a non-full collection failure, in which case there 486 // wasn't any mutator/cr-thread activity since last recording. And if 487 // we're in an explicit full collection, the time since the last GC can 488 // be arbitrarily short, so not a very good sample. Similarly, don't 489 // update the rate if the current sample is empty or time is zero. 490 if (!is_full_collection && (cr_cards > 0) && (cr_time > Tickspan())) { 491 double rate = cr_cards / (cr_time.seconds() * MILLIUNITS); 492 _analytics->report_concurrent_refine_rate_ms(rate); 493 } 494 495 // Record info about mutator thread processing. 496 G1DirtyCardQueueSet& dcqs = G1BarrierSet::dirty_card_queue_set(); 497 size_t mut_total_cards = dcqs.total_mutator_refined_cards(); 498 size_t mut_cards = mut_total_cards - _total_mutator_refined_cards; 499 _total_mutator_refined_cards = mut_total_cards; 500 501 // Record mutator's card logging rate. 502 // Don't update if full collection; see above. 503 if (!is_full_collection) { 504 size_t total_cards = _pending_cards_at_gc_start + cr_cards + mut_cards; 505 assert(_pending_cards_at_prev_gc_end <= total_cards, 506 "untracked cards: last pending: " SIZE_FORMAT 507 ", pending: " SIZE_FORMAT ", conc refine: " SIZE_FORMAT 508 ", mut refine:" SIZE_FORMAT, 509 _pending_cards_at_prev_gc_end, _pending_cards_at_gc_start, 510 cr_cards, mut_cards); 511 size_t logged_cards = total_cards - _pending_cards_at_prev_gc_end; 512 double logging_start_time = _analytics->prev_collection_pause_end_ms(); 513 double logging_end_time = Ticks::now().seconds() * MILLIUNITS; 514 double logging_time = logging_end_time - logging_start_time; 515 // Unlike above for conc-refine rate, here we should not require a 516 // non-empty sample, since an application could go some time with only 517 // young-gen or filtered out writes. But we'll ignore unusually short 518 // sample periods, as they may just pollute the predictions. 519 if (logging_time > 1.0) { // Require > 1ms sample time. 520 _analytics->report_logged_cards_rate_ms(logged_cards / logging_time); 521 } 522 } 523 } 524 525 void G1Policy::record_collection_pause_start(double start_time_sec) { 526 // We only need to do this here as the policy will only be applied 527 // to the GC we're about to start. so, no point is calculating this 528 // every time we calculate / recalculate the target young length. 529 update_survivors_policy(); 530 531 assert(max_survivor_regions() + _g1h->num_used_regions() <= _g1h->max_regions(), 532 "Maximum survivor regions %u plus used regions %u exceeds max regions %u", 533 max_survivor_regions(), _g1h->num_used_regions(), _g1h->max_regions()); 534 assert_used_and_recalculate_used_equal(_g1h); 535 536 phase_times()->record_cur_collection_start_sec(start_time_sec); 537 538 record_concurrent_refinement_data(false /* is_full_collection */); 539 540 _collection_set->reset_bytes_used_before(); 541 542 // do that for any other surv rate groups 543 _eden_surv_rate_group->stop_adding_regions(); 544 _survivors_age_table.clear(); 545 546 assert(_g1h->collection_set()->verify_young_ages(), "region age verification failed"); 547 } 548 549 void G1Policy::record_concurrent_mark_init_end(double mark_init_elapsed_time_ms) { 550 assert(!collector_state()->initiate_conc_mark_if_possible(), "we should have cleared it by now"); 551 collector_state()->set_in_initial_mark_gc(false); 552 } 553 554 void G1Policy::record_concurrent_mark_remark_start() { 555 _mark_remark_start_sec = os::elapsedTime(); 556 } 557 558 void G1Policy::record_concurrent_mark_remark_end() { 559 double end_time_sec = os::elapsedTime(); 560 double elapsed_time_ms = (end_time_sec - _mark_remark_start_sec)*1000.0; 561 _analytics->report_concurrent_mark_remark_times_ms(elapsed_time_ms); 562 _analytics->append_prev_collection_pause_end_ms(elapsed_time_ms); 563 564 record_pause(Remark, _mark_remark_start_sec, end_time_sec); 565 } 566 567 void G1Policy::record_concurrent_mark_cleanup_start() { 568 _mark_cleanup_start_sec = os::elapsedTime(); 569 } 570 571 double G1Policy::average_time_ms(G1GCPhaseTimes::GCParPhases phase) const { 572 return phase_times()->average_time_ms(phase); 573 } 574 575 double G1Policy::young_other_time_ms() const { 576 return phase_times()->young_cset_choice_time_ms() + 577 phase_times()->average_time_ms(G1GCPhaseTimes::YoungFreeCSet); 578 } 579 580 double G1Policy::non_young_other_time_ms() const { 581 return phase_times()->non_young_cset_choice_time_ms() + 582 phase_times()->average_time_ms(G1GCPhaseTimes::NonYoungFreeCSet); 583 } 584 585 double G1Policy::other_time_ms(double pause_time_ms) const { 586 return pause_time_ms - phase_times()->cur_collection_par_time_ms(); 587 } 588 589 double G1Policy::constant_other_time_ms(double pause_time_ms) const { 590 return other_time_ms(pause_time_ms) - phase_times()->total_free_cset_time_ms() - phase_times()->total_rebuild_freelist_time_ms(); 591 } 592 593 bool G1Policy::about_to_start_mixed_phase() const { 594 return _g1h->concurrent_mark()->cm_thread()->during_cycle() || collector_state()->in_young_gc_before_mixed(); 595 } 596 597 bool G1Policy::need_to_start_conc_mark(const char* source, size_t alloc_word_size) { 598 if (about_to_start_mixed_phase()) { 599 return false; 600 } 601 602 size_t marking_initiating_used_threshold = _ihop_control->get_conc_mark_start_threshold(); 603 604 size_t cur_used_bytes = _g1h->non_young_capacity_bytes(); 605 size_t alloc_byte_size = alloc_word_size * HeapWordSize; 606 size_t marking_request_bytes = cur_used_bytes + alloc_byte_size; 607 608 bool result = false; 609 if (marking_request_bytes > marking_initiating_used_threshold) { 610 result = collector_state()->in_young_only_phase() && !collector_state()->in_young_gc_before_mixed(); 611 log_debug(gc, ergo, ihop)("%s occupancy: " SIZE_FORMAT "B allocation request: " SIZE_FORMAT "B threshold: " SIZE_FORMAT "B (%1.2f) source: %s", 612 result ? "Request concurrent cycle initiation (occupancy higher than threshold)" : "Do not request concurrent cycle initiation (still doing mixed collections)", 613 cur_used_bytes, alloc_byte_size, marking_initiating_used_threshold, (double) marking_initiating_used_threshold / _g1h->capacity() * 100, source); 614 } 615 616 return result; 617 } 618 619 double G1Policy::logged_cards_processing_time() const { 620 double all_cards_processing_time = average_time_ms(G1GCPhaseTimes::ScanHR) + average_time_ms(G1GCPhaseTimes::OptScanHR); 621 size_t logged_dirty_cards = phase_times()->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards); 622 size_t scan_heap_roots_cards = phase_times()->sum_thread_work_items(G1GCPhaseTimes::ScanHR, G1GCPhaseTimes::ScanHRScannedCards) + 623 phase_times()->sum_thread_work_items(G1GCPhaseTimes::OptScanHR, G1GCPhaseTimes::ScanHRScannedCards); 624 // This may happen if there are duplicate cards in different log buffers. 625 if (logged_dirty_cards > scan_heap_roots_cards) { 626 return all_cards_processing_time + average_time_ms(G1GCPhaseTimes::MergeLB); 627 } 628 return (all_cards_processing_time * logged_dirty_cards / scan_heap_roots_cards) + average_time_ms(G1GCPhaseTimes::MergeLB); 629 } 630 631 // Anything below that is considered to be zero 632 #define MIN_TIMER_GRANULARITY 0.0000001 633 634 void G1Policy::record_collection_pause_end(double pause_time_ms) { 635 G1GCPhaseTimes* p = phase_times(); 636 637 double end_time_sec = os::elapsedTime(); 638 639 bool this_pause_included_initial_mark = false; 640 bool this_pause_was_young_only = collector_state()->in_young_only_phase(); 641 642 bool update_stats = !_g1h->evacuation_failed(); 643 644 record_pause(young_gc_pause_kind(), end_time_sec - pause_time_ms / 1000.0, end_time_sec); 645 646 _collection_pause_end_millis = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 647 648 this_pause_included_initial_mark = collector_state()->in_initial_mark_gc(); 649 if (this_pause_included_initial_mark) { 650 record_concurrent_mark_init_end(0.0); 651 } else { 652 maybe_start_marking(); 653 } 654 655 double app_time_ms = (phase_times()->cur_collection_start_sec() * 1000.0 - _analytics->prev_collection_pause_end_ms()); 656 if (app_time_ms < MIN_TIMER_GRANULARITY) { 657 // This usually happens due to the timer not having the required 658 // granularity. Some Linuxes are the usual culprits. 659 // We'll just set it to something (arbitrarily) small. 660 app_time_ms = 1.0; 661 } 662 663 if (update_stats) { 664 // We maintain the invariant that all objects allocated by mutator 665 // threads will be allocated out of eden regions. So, we can use 666 // the eden region number allocated since the previous GC to 667 // calculate the application's allocate rate. The only exception 668 // to that is humongous objects that are allocated separately. But 669 // given that humongous object allocations do not really affect 670 // either the pause's duration nor when the next pause will take 671 // place we can safely ignore them here. 672 uint regions_allocated = _collection_set->eden_region_length(); 673 double alloc_rate_ms = (double) regions_allocated / app_time_ms; 674 _analytics->report_alloc_rate_ms(alloc_rate_ms); 675 676 double interval_ms = 677 (end_time_sec - _analytics->last_known_gc_end_time_sec()) * 1000.0; 678 _analytics->update_recent_gc_times(end_time_sec, pause_time_ms); 679 _analytics->compute_pause_time_ratio(interval_ms, pause_time_ms); 680 } 681 682 if (collector_state()->in_young_gc_before_mixed()) { 683 assert(!this_pause_included_initial_mark, "The young GC before mixed is not allowed to be an initial mark GC"); 684 // This has been the young GC before we start doing mixed GCs. We already 685 // decided to start mixed GCs much earlier, so there is nothing to do except 686 // advancing the state. 687 collector_state()->set_in_young_only_phase(false); 688 collector_state()->set_in_young_gc_before_mixed(false); 689 } else if (!this_pause_was_young_only) { 690 // This is a mixed GC. Here we decide whether to continue doing more 691 // mixed GCs or not. 692 if (!next_gc_should_be_mixed("continue mixed GCs", 693 "do not continue mixed GCs")) { 694 collector_state()->set_in_young_only_phase(true); 695 696 clear_collection_set_candidates(); 697 maybe_start_marking(); 698 } 699 } 700 701 _eden_surv_rate_group->start_adding_regions(); 702 703 double merge_hcc_time_ms = average_time_ms(G1GCPhaseTimes::MergeHCC); 704 if (update_stats) { 705 size_t const total_log_buffer_cards = p->sum_thread_work_items(G1GCPhaseTimes::MergeHCC, G1GCPhaseTimes::MergeHCCDirtyCards) + 706 p->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards); 707 // Update prediction for card merge; MergeRSDirtyCards includes the cards from the Eager Reclaim phase. 708 size_t const total_cards_merged = p->sum_thread_work_items(G1GCPhaseTimes::MergeRS, G1GCPhaseTimes::MergeRSDirtyCards) + 709 p->sum_thread_work_items(G1GCPhaseTimes::OptMergeRS, G1GCPhaseTimes::MergeRSDirtyCards) + 710 total_log_buffer_cards; 711 712 // The threshold for the number of cards in a given sampling which we consider 713 // large enough so that the impact from setup and other costs is negligible. 714 size_t const CardsNumSamplingThreshold = 10; 715 716 if (total_cards_merged > CardsNumSamplingThreshold) { 717 double avg_time_merge_cards = average_time_ms(G1GCPhaseTimes::MergeER) + 718 average_time_ms(G1GCPhaseTimes::MergeRS) + 719 average_time_ms(G1GCPhaseTimes::MergeHCC) + 720 average_time_ms(G1GCPhaseTimes::MergeLB) + 721 average_time_ms(G1GCPhaseTimes::OptMergeRS); 722 _analytics->report_cost_per_card_merge_ms(avg_time_merge_cards / total_cards_merged, this_pause_was_young_only); 723 } 724 725 // Update prediction for card scan 726 size_t const total_cards_scanned = p->sum_thread_work_items(G1GCPhaseTimes::ScanHR, G1GCPhaseTimes::ScanHRScannedCards) + 727 p->sum_thread_work_items(G1GCPhaseTimes::OptScanHR, G1GCPhaseTimes::ScanHRScannedCards); 728 729 if (total_cards_scanned > CardsNumSamplingThreshold) { 730 double avg_time_dirty_card_scan = average_time_ms(G1GCPhaseTimes::ScanHR) + 731 average_time_ms(G1GCPhaseTimes::OptScanHR); 732 733 _analytics->report_cost_per_card_scan_ms(avg_time_dirty_card_scan / total_cards_scanned, this_pause_was_young_only); 734 } 735 736 // Update prediction for the ratio between cards from the remembered 737 // sets and actually scanned cards from the remembered sets. 738 // Cards from the remembered sets are all cards not duplicated by cards from 739 // the logs. 740 // Due to duplicates in the log buffers, the number of actually scanned cards 741 // can be smaller than the cards in the log buffers. 742 const size_t from_rs_length_cards = (total_cards_scanned > total_log_buffer_cards) ? total_cards_scanned - total_log_buffer_cards : 0; 743 double merge_to_scan_ratio = 0.0; 744 if (total_cards_scanned > 0) { 745 merge_to_scan_ratio = (double) from_rs_length_cards / total_cards_scanned; 746 } 747 _analytics->report_card_merge_to_scan_ratio(merge_to_scan_ratio, this_pause_was_young_only); 748 749 const size_t recorded_rs_length = _collection_set->recorded_rs_length(); 750 const size_t rs_length_diff = _rs_length > recorded_rs_length ? _rs_length - recorded_rs_length : 0; 751 _analytics->report_rs_length_diff(rs_length_diff); 752 753 // Update prediction for copy cost per byte 754 size_t copied_bytes = p->sum_thread_work_items(G1GCPhaseTimes::MergePSS, G1GCPhaseTimes::MergePSSCopiedBytes); 755 756 if (copied_bytes > 0) { 757 double cost_per_byte_ms = (average_time_ms(G1GCPhaseTimes::ObjCopy) + average_time_ms(G1GCPhaseTimes::OptObjCopy)) / copied_bytes; 758 _analytics->report_cost_per_byte_ms(cost_per_byte_ms, collector_state()->mark_or_rebuild_in_progress()); 759 } 760 761 if (_collection_set->young_region_length() > 0) { 762 _analytics->report_young_other_cost_per_region_ms(young_other_time_ms() / 763 _collection_set->young_region_length()); 764 } 765 766 if (_collection_set->old_region_length() > 0) { 767 _analytics->report_non_young_other_cost_per_region_ms(non_young_other_time_ms() / 768 _collection_set->old_region_length()); 769 } 770 771 _analytics->report_constant_other_time_ms(constant_other_time_ms(pause_time_ms)); 772 773 // Do not update RS lengths and the number of pending cards with information from mixed gc: 774 // these are is wildly different to during young only gc and mess up young gen sizing right 775 // after the mixed gc phase. 776 // During mixed gc we do not use them for young gen sizing. 777 if (this_pause_was_young_only) { 778 _analytics->report_pending_cards((double) _pending_cards_at_gc_start); 779 _analytics->report_rs_length((double) _rs_length); 780 } 781 } 782 783 assert(!(this_pause_included_initial_mark && collector_state()->mark_or_rebuild_in_progress()), 784 "If the last pause has been an initial mark, we should not have been in the marking window"); 785 if (this_pause_included_initial_mark) { 786 collector_state()->set_mark_or_rebuild_in_progress(true); 787 } 788 789 _free_regions_at_end_of_collection = _g1h->num_free_regions(); 790 791 update_rs_length_prediction(); 792 793 // Do not update dynamic IHOP due to G1 periodic collection as it is highly likely 794 // that in this case we are not running in a "normal" operating mode. 795 if (_g1h->gc_cause() != GCCause::_g1_periodic_collection) { 796 // IHOP control wants to know the expected young gen length if it were not 797 // restrained by the heap reserve. Using the actual length would make the 798 // prediction too small and the limit the young gen every time we get to the 799 // predicted target occupancy. 800 size_t last_unrestrained_young_length = update_young_list_max_and_target_length(); 801 802 update_ihop_prediction(app_time_ms / 1000.0, 803 _bytes_allocated_in_old_since_last_gc, 804 last_unrestrained_young_length * HeapRegion::GrainBytes, 805 this_pause_was_young_only); 806 _bytes_allocated_in_old_since_last_gc = 0; 807 808 _ihop_control->send_trace_event(_g1h->gc_tracer_stw()); 809 } else { 810 // Any garbage collection triggered as periodic collection resets the time-to-mixed 811 // measurement. Periodic collection typically means that the application is "inactive", i.e. 812 // the marking threads may have received an uncharacterisic amount of cpu time 813 // for completing the marking, i.e. are faster than expected. 814 // This skews the predicted marking length towards smaller values which might cause 815 // the mark start being too late. 816 _initial_mark_to_mixed.reset(); 817 } 818 819 // Note that _mmu_tracker->max_gc_time() returns the time in seconds. 820 double scan_logged_cards_time_goal_ms = _mmu_tracker->max_gc_time() * MILLIUNITS * G1RSetUpdatingPauseTimePercent / 100.0; 821 822 if (scan_logged_cards_time_goal_ms < merge_hcc_time_ms) { 823 log_debug(gc, ergo, refine)("Adjust concurrent refinement thresholds (scanning the HCC expected to take longer than Update RS time goal)." 824 "Logged Cards Scan time goal: %1.2fms Scan HCC time: %1.2fms", 825 scan_logged_cards_time_goal_ms, merge_hcc_time_ms); 826 827 scan_logged_cards_time_goal_ms = 0; 828 } else { 829 scan_logged_cards_time_goal_ms -= merge_hcc_time_ms; 830 } 831 832 _pending_cards_at_prev_gc_end = _g1h->pending_card_num(); 833 double const logged_cards_time = logged_cards_processing_time(); 834 835 log_debug(gc, ergo, refine)("Concurrent refinement times: Logged Cards Scan time goal: %1.2fms Logged Cards Scan time: %1.2fms HCC time: %1.2fms", 836 scan_logged_cards_time_goal_ms, logged_cards_time, merge_hcc_time_ms); 837 838 _g1h->concurrent_refine()->adjust(logged_cards_time, 839 phase_times()->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards), 840 scan_logged_cards_time_goal_ms); 841 } 842 843 G1IHOPControl* G1Policy::create_ihop_control(const G1Predictions* predictor){ 844 if (G1UseAdaptiveIHOP) { 845 return new G1AdaptiveIHOPControl(InitiatingHeapOccupancyPercent, 846 predictor, 847 G1ReservePercent, 848 G1HeapWastePercent); 849 } else { 850 return new G1StaticIHOPControl(InitiatingHeapOccupancyPercent); 851 } 852 } 853 854 void G1Policy::update_ihop_prediction(double mutator_time_s, 855 size_t mutator_alloc_bytes, 856 size_t young_gen_size, 857 bool this_gc_was_young_only) { 858 // Always try to update IHOP prediction. Even evacuation failures give information 859 // about e.g. whether to start IHOP earlier next time. 860 861 // Avoid using really small application times that might create samples with 862 // very high or very low values. They may be caused by e.g. back-to-back gcs. 863 double const min_valid_time = 1e-6; 864 865 bool report = false; 866 867 double marking_to_mixed_time = -1.0; 868 if (!this_gc_was_young_only && _initial_mark_to_mixed.has_result()) { 869 marking_to_mixed_time = _initial_mark_to_mixed.last_marking_time(); 870 assert(marking_to_mixed_time > 0.0, 871 "Initial mark to mixed time must be larger than zero but is %.3f", 872 marking_to_mixed_time); 873 if (marking_to_mixed_time > min_valid_time) { 874 _ihop_control->update_marking_length(marking_to_mixed_time); 875 report = true; 876 } 877 } 878 879 // As an approximation for the young gc promotion rates during marking we use 880 // all of them. In many applications there are only a few if any young gcs during 881 // marking, which makes any prediction useless. This increases the accuracy of the 882 // prediction. 883 if (this_gc_was_young_only && mutator_time_s > min_valid_time) { 884 _ihop_control->update_allocation_info(mutator_time_s, mutator_alloc_bytes, young_gen_size); 885 report = true; 886 } 887 888 if (report) { 889 report_ihop_statistics(); 890 } 891 } 892 893 void G1Policy::report_ihop_statistics() { 894 _ihop_control->print(); 895 } 896 897 void G1Policy::print_phases() { 898 phase_times()->print(); 899 } 900 901 double G1Policy::predict_base_elapsed_time_ms(size_t pending_cards, 902 size_t rs_length) const { 903 size_t effective_scanned_cards = _analytics->predict_scan_card_num(rs_length, collector_state()->in_young_only_phase()); 904 return 905 _analytics->predict_card_merge_time_ms(pending_cards + rs_length, collector_state()->in_young_only_phase()) + 906 _analytics->predict_card_scan_time_ms(effective_scanned_cards, collector_state()->in_young_only_phase()) + 907 _analytics->predict_constant_other_time_ms() + 908 predict_survivor_regions_evac_time(); 909 } 910 911 double G1Policy::predict_base_elapsed_time_ms(size_t pending_cards) const { 912 size_t rs_length = _analytics->predict_rs_length(); 913 return predict_base_elapsed_time_ms(pending_cards, rs_length); 914 } 915 916 size_t G1Policy::predict_bytes_to_copy(HeapRegion* hr) const { 917 size_t bytes_to_copy; 918 if (!hr->is_young()) { 919 bytes_to_copy = hr->max_live_bytes(); 920 } else { 921 bytes_to_copy = (size_t) (hr->used() * hr->surv_rate_prediction(_predictor)); 922 } 923 return bytes_to_copy; 924 } 925 926 double G1Policy::predict_eden_copy_time_ms(uint count, size_t* bytes_to_copy) const { 927 if (count == 0) { 928 return 0.0; 929 } 930 size_t const expected_bytes = _eden_surv_rate_group->accum_surv_rate_pred(count) * HeapRegion::GrainBytes; 931 if (bytes_to_copy != NULL) { 932 *bytes_to_copy = expected_bytes; 933 } 934 return _analytics->predict_object_copy_time_ms(expected_bytes, collector_state()->mark_or_rebuild_in_progress()); 935 } 936 937 double G1Policy::predict_region_copy_time_ms(HeapRegion* hr) const { 938 size_t const bytes_to_copy = predict_bytes_to_copy(hr); 939 return _analytics->predict_object_copy_time_ms(bytes_to_copy, collector_state()->mark_or_rebuild_in_progress()); 940 } 941 942 double G1Policy::predict_region_non_copy_time_ms(HeapRegion* hr, 943 bool for_young_gc) const { 944 size_t rs_length = hr->rem_set()->occupied(); 945 size_t scan_card_num = _analytics->predict_scan_card_num(rs_length, for_young_gc); 946 947 double region_elapsed_time_ms = 948 _analytics->predict_card_merge_time_ms(rs_length, collector_state()->in_young_only_phase()) + 949 _analytics->predict_card_scan_time_ms(scan_card_num, collector_state()->in_young_only_phase()); 950 951 // The prediction of the "other" time for this region is based 952 // upon the region type and NOT the GC type. 953 if (hr->is_young()) { 954 region_elapsed_time_ms += _analytics->predict_young_other_time_ms(1); 955 } else { 956 region_elapsed_time_ms += _analytics->predict_non_young_other_time_ms(1); 957 } 958 return region_elapsed_time_ms; 959 } 960 961 double G1Policy::predict_region_total_time_ms(HeapRegion* hr, bool for_young_gc) const { 962 return predict_region_non_copy_time_ms(hr, for_young_gc) + predict_region_copy_time_ms(hr); 963 } 964 965 bool G1Policy::should_allocate_mutator_region() const { 966 uint young_list_length = _g1h->young_regions_count(); 967 uint young_list_target_length = _young_list_target_length; 968 return young_list_length < young_list_target_length; 969 } 970 971 bool G1Policy::can_expand_young_list() const { 972 uint young_list_length = _g1h->young_regions_count(); 973 uint young_list_max_length = _young_list_max_length; 974 return young_list_length < young_list_max_length; 975 } 976 977 bool G1Policy::use_adaptive_young_list_length() const { 978 return _young_gen_sizer->use_adaptive_young_list_length(); 979 } 980 981 size_t G1Policy::desired_survivor_size(uint max_regions) const { 982 size_t const survivor_capacity = HeapRegion::GrainWords * max_regions; 983 return (size_t)((((double)survivor_capacity) * TargetSurvivorRatio) / 100); 984 } 985 986 void G1Policy::print_age_table() { 987 _survivors_age_table.print_age_table(_tenuring_threshold); 988 } 989 990 void G1Policy::update_max_gc_locker_expansion() { 991 uint expansion_region_num = 0; 992 if (GCLockerEdenExpansionPercent > 0) { 993 double perc = (double) GCLockerEdenExpansionPercent / 100.0; 994 double expansion_region_num_d = perc * (double) _young_list_target_length; 995 // We use ceiling so that if expansion_region_num_d is > 0.0 (but 996 // less than 1.0) we'll get 1. 997 expansion_region_num = (uint) ceil(expansion_region_num_d); 998 } else { 999 assert(expansion_region_num == 0, "sanity"); 1000 } 1001 _young_list_max_length = _young_list_target_length + expansion_region_num; 1002 assert(_young_list_target_length <= _young_list_max_length, "post-condition"); 1003 } 1004 1005 // Calculates survivor space parameters. 1006 void G1Policy::update_survivors_policy() { 1007 double max_survivor_regions_d = 1008 (double) _young_list_target_length / (double) SurvivorRatio; 1009 1010 // Calculate desired survivor size based on desired max survivor regions (unconstrained 1011 // by remaining heap). Otherwise we may cause undesired promotions as we are 1012 // already getting close to end of the heap, impacting performance even more. 1013 uint const desired_max_survivor_regions = ceil(max_survivor_regions_d); 1014 size_t const survivor_size = desired_survivor_size(desired_max_survivor_regions); 1015 1016 _tenuring_threshold = _survivors_age_table.compute_tenuring_threshold(survivor_size); 1017 if (UsePerfData) { 1018 _policy_counters->tenuring_threshold()->set_value(_tenuring_threshold); 1019 _policy_counters->desired_survivor_size()->set_value(survivor_size * oopSize); 1020 } 1021 // The real maximum survivor size is bounded by the number of regions that can 1022 // be allocated into. 1023 _max_survivor_regions = MIN2(desired_max_survivor_regions, 1024 _g1h->num_free_or_available_regions()); 1025 } 1026 1027 bool G1Policy::force_initial_mark_if_outside_cycle(GCCause::Cause gc_cause) { 1028 // We actually check whether we are marking here and not if we are in a 1029 // reclamation phase. This means that we will schedule a concurrent mark 1030 // even while we are still in the process of reclaiming memory. 1031 bool during_cycle = _g1h->concurrent_mark()->cm_thread()->during_cycle(); 1032 if (!during_cycle) { 1033 log_debug(gc, ergo)("Request concurrent cycle initiation (requested by GC cause). GC cause: %s", GCCause::to_string(gc_cause)); 1034 collector_state()->set_initiate_conc_mark_if_possible(true); 1035 return true; 1036 } else { 1037 log_debug(gc, ergo)("Do not request concurrent cycle initiation (concurrent cycle already in progress). GC cause: %s", GCCause::to_string(gc_cause)); 1038 return false; 1039 } 1040 } 1041 1042 void G1Policy::initiate_conc_mark() { 1043 collector_state()->set_in_initial_mark_gc(true); 1044 collector_state()->set_initiate_conc_mark_if_possible(false); 1045 } 1046 1047 void G1Policy::decide_on_conc_mark_initiation() { 1048 // We are about to decide on whether this pause will be an 1049 // initial-mark pause. 1050 1051 // First, collector_state()->in_initial_mark_gc() should not be already set. We 1052 // will set it here if we have to. However, it should be cleared by 1053 // the end of the pause (it's only set for the duration of an 1054 // initial-mark pause). 1055 assert(!collector_state()->in_initial_mark_gc(), "pre-condition"); 1056 1057 if (collector_state()->initiate_conc_mark_if_possible()) { 1058 // We had noticed on a previous pause that the heap occupancy has 1059 // gone over the initiating threshold and we should start a 1060 // concurrent marking cycle. So we might initiate one. 1061 1062 if (!about_to_start_mixed_phase() && collector_state()->in_young_only_phase()) { 1063 // Initiate a new initial mark if there is no marking or reclamation going on. 1064 initiate_conc_mark(); 1065 log_debug(gc, ergo)("Initiate concurrent cycle (concurrent cycle initiation requested)"); 1066 } else if (_g1h->is_user_requested_concurrent_full_gc(_g1h->gc_cause())) { 1067 // Initiate a user requested initial mark. An initial mark must be young only 1068 // GC, so the collector state must be updated to reflect this. 1069 collector_state()->set_in_young_only_phase(true); 1070 collector_state()->set_in_young_gc_before_mixed(false); 1071 1072 // We might have ended up coming here about to start a mixed phase with a collection set 1073 // active. The following remark might change the change the "evacuation efficiency" of 1074 // the regions in this set, leading to failing asserts later. 1075 // Since the concurrent cycle will recreate the collection set anyway, simply drop it here. 1076 clear_collection_set_candidates(); 1077 abort_time_to_mixed_tracking(); 1078 initiate_conc_mark(); 1079 log_debug(gc, ergo)("Initiate concurrent cycle (user requested concurrent cycle)"); 1080 } else { 1081 // The concurrent marking thread is still finishing up the 1082 // previous cycle. If we start one right now the two cycles 1083 // overlap. In particular, the concurrent marking thread might 1084 // be in the process of clearing the next marking bitmap (which 1085 // we will use for the next cycle if we start one). Starting a 1086 // cycle now will be bad given that parts of the marking 1087 // information might get cleared by the marking thread. And we 1088 // cannot wait for the marking thread to finish the cycle as it 1089 // periodically yields while clearing the next marking bitmap 1090 // and, if it's in a yield point, it's waiting for us to 1091 // finish. So, at this point we will not start a cycle and we'll 1092 // let the concurrent marking thread complete the last one. 1093 log_debug(gc, ergo)("Do not initiate concurrent cycle (concurrent cycle already in progress)"); 1094 } 1095 } 1096 } 1097 1098 void G1Policy::record_concurrent_mark_cleanup_end() { 1099 G1CollectionSetCandidates* candidates = G1CollectionSetChooser::build(_g1h->workers(), _g1h->num_regions()); 1100 _collection_set->set_candidates(candidates); 1101 1102 bool mixed_gc_pending = next_gc_should_be_mixed("request mixed gcs", "request young-only gcs"); 1103 if (!mixed_gc_pending) { 1104 clear_collection_set_candidates(); 1105 abort_time_to_mixed_tracking(); 1106 } 1107 collector_state()->set_in_young_gc_before_mixed(mixed_gc_pending); 1108 collector_state()->set_mark_or_rebuild_in_progress(false); 1109 1110 double end_sec = os::elapsedTime(); 1111 double elapsed_time_ms = (end_sec - _mark_cleanup_start_sec) * 1000.0; 1112 _analytics->report_concurrent_mark_cleanup_times_ms(elapsed_time_ms); 1113 _analytics->append_prev_collection_pause_end_ms(elapsed_time_ms); 1114 1115 record_pause(Cleanup, _mark_cleanup_start_sec, end_sec); 1116 } 1117 1118 double G1Policy::reclaimable_bytes_percent(size_t reclaimable_bytes) const { 1119 return percent_of(reclaimable_bytes, _g1h->capacity()); 1120 } 1121 1122 class G1ClearCollectionSetCandidateRemSets : public HeapRegionClosure { 1123 virtual bool do_heap_region(HeapRegion* r) { 1124 r->rem_set()->clear_locked(true /* only_cardset */); 1125 return false; 1126 } 1127 }; 1128 1129 void G1Policy::clear_collection_set_candidates() { 1130 // Clear remembered sets of remaining candidate regions and the actual candidate 1131 // set. 1132 G1ClearCollectionSetCandidateRemSets cl; 1133 _collection_set->candidates()->iterate(&cl); 1134 _collection_set->clear_candidates(); 1135 } 1136 1137 void G1Policy::maybe_start_marking() { 1138 if (need_to_start_conc_mark("end of GC")) { 1139 // Note: this might have already been set, if during the last 1140 // pause we decided to start a cycle but at the beginning of 1141 // this pause we decided to postpone it. That's OK. 1142 collector_state()->set_initiate_conc_mark_if_possible(true); 1143 } 1144 } 1145 1146 G1Policy::PauseKind G1Policy::young_gc_pause_kind() const { 1147 assert(!collector_state()->in_full_gc(), "must be"); 1148 if (collector_state()->in_initial_mark_gc()) { 1149 assert(!collector_state()->in_young_gc_before_mixed(), "must be"); 1150 return InitialMarkGC; 1151 } else if (collector_state()->in_young_gc_before_mixed()) { 1152 assert(!collector_state()->in_initial_mark_gc(), "must be"); 1153 return LastYoungGC; 1154 } else if (collector_state()->in_mixed_phase()) { 1155 assert(!collector_state()->in_initial_mark_gc(), "must be"); 1156 assert(!collector_state()->in_young_gc_before_mixed(), "must be"); 1157 return MixedGC; 1158 } else { 1159 assert(!collector_state()->in_initial_mark_gc(), "must be"); 1160 assert(!collector_state()->in_young_gc_before_mixed(), "must be"); 1161 return YoungOnlyGC; 1162 } 1163 } 1164 1165 void G1Policy::record_pause(PauseKind kind, double start, double end) { 1166 // Manage the MMU tracker. For some reason it ignores Full GCs. 1167 if (kind != FullGC) { 1168 _mmu_tracker->add_pause(start, end); 1169 } 1170 // Manage the mutator time tracking from initial mark to first mixed gc. 1171 switch (kind) { 1172 case FullGC: 1173 abort_time_to_mixed_tracking(); 1174 break; 1175 case Cleanup: 1176 case Remark: 1177 case YoungOnlyGC: 1178 case LastYoungGC: 1179 _initial_mark_to_mixed.add_pause(end - start); 1180 break; 1181 case InitialMarkGC: 1182 if (_g1h->gc_cause() != GCCause::_g1_periodic_collection) { 1183 _initial_mark_to_mixed.record_initial_mark_end(end); 1184 } 1185 break; 1186 case MixedGC: 1187 _initial_mark_to_mixed.record_mixed_gc_start(start); 1188 break; 1189 default: 1190 ShouldNotReachHere(); 1191 } 1192 } 1193 1194 void G1Policy::abort_time_to_mixed_tracking() { 1195 _initial_mark_to_mixed.reset(); 1196 } 1197 1198 bool G1Policy::next_gc_should_be_mixed(const char* true_action_str, 1199 const char* false_action_str) const { 1200 G1CollectionSetCandidates* candidates = _collection_set->candidates(); 1201 1202 if (candidates->is_empty()) { 1203 log_debug(gc, ergo)("%s (candidate old regions not available)", false_action_str); 1204 return false; 1205 } 1206 1207 // Is the amount of uncollected reclaimable space above G1HeapWastePercent? 1208 size_t reclaimable_bytes = candidates->remaining_reclaimable_bytes(); 1209 double reclaimable_percent = reclaimable_bytes_percent(reclaimable_bytes); 1210 double threshold = (double) G1HeapWastePercent; 1211 if (reclaimable_percent <= threshold) { 1212 log_debug(gc, ergo)("%s (reclaimable percentage not over threshold). candidate old regions: %u reclaimable: " SIZE_FORMAT " (%1.2f) threshold: " UINTX_FORMAT, 1213 false_action_str, candidates->num_remaining(), reclaimable_bytes, reclaimable_percent, G1HeapWastePercent); 1214 return false; 1215 } 1216 log_debug(gc, ergo)("%s (candidate old regions available). candidate old regions: %u reclaimable: " SIZE_FORMAT " (%1.2f) threshold: " UINTX_FORMAT, 1217 true_action_str, candidates->num_remaining(), reclaimable_bytes, reclaimable_percent, G1HeapWastePercent); 1218 return true; 1219 } 1220 1221 uint G1Policy::calc_min_old_cset_length() const { 1222 // The min old CSet region bound is based on the maximum desired 1223 // number of mixed GCs after a cycle. I.e., even if some old regions 1224 // look expensive, we should add them to the CSet anyway to make 1225 // sure we go through the available old regions in no more than the 1226 // maximum desired number of mixed GCs. 1227 // 1228 // The calculation is based on the number of marked regions we added 1229 // to the CSet candidates in the first place, not how many remain, so 1230 // that the result is the same during all mixed GCs that follow a cycle. 1231 1232 const size_t region_num = _collection_set->candidates()->num_regions(); 1233 const size_t gc_num = (size_t) MAX2(G1MixedGCCountTarget, (uintx) 1); 1234 size_t result = region_num / gc_num; 1235 // emulate ceiling 1236 if (result * gc_num < region_num) { 1237 result += 1; 1238 } 1239 return (uint) result; 1240 } 1241 1242 uint G1Policy::calc_max_old_cset_length() const { 1243 // The max old CSet region bound is based on the threshold expressed 1244 // as a percentage of the heap size. I.e., it should bound the 1245 // number of old regions added to the CSet irrespective of how many 1246 // of them are available. 1247 1248 const G1CollectedHeap* g1h = G1CollectedHeap::heap(); 1249 const size_t region_num = g1h->num_regions(); 1250 const size_t perc = (size_t) G1OldCSetRegionThresholdPercent; 1251 size_t result = region_num * perc / 100; 1252 // emulate ceiling 1253 if (100 * result < region_num * perc) { 1254 result += 1; 1255 } 1256 return (uint) result; 1257 } 1258 1259 void G1Policy::calculate_old_collection_set_regions(G1CollectionSetCandidates* candidates, 1260 double time_remaining_ms, 1261 uint& num_initial_regions, 1262 uint& num_optional_regions) { 1263 assert(candidates != NULL, "Must be"); 1264 1265 num_initial_regions = 0; 1266 num_optional_regions = 0; 1267 uint num_expensive_regions = 0; 1268 1269 double predicted_old_time_ms = 0.0; 1270 double predicted_initial_time_ms = 0.0; 1271 double predicted_optional_time_ms = 0.0; 1272 1273 double optional_threshold_ms = time_remaining_ms * optional_prediction_fraction(); 1274 1275 const uint min_old_cset_length = calc_min_old_cset_length(); 1276 const uint max_old_cset_length = MAX2(min_old_cset_length, calc_max_old_cset_length()); 1277 const uint max_optional_regions = max_old_cset_length - min_old_cset_length; 1278 bool check_time_remaining = use_adaptive_young_list_length(); 1279 1280 uint candidate_idx = candidates->cur_idx(); 1281 1282 log_debug(gc, ergo, cset)("Start adding old regions to collection set. Min %u regions, max %u regions, " 1283 "time remaining %1.2fms, optional threshold %1.2fms", 1284 min_old_cset_length, max_old_cset_length, time_remaining_ms, optional_threshold_ms); 1285 1286 HeapRegion* hr = candidates->at(candidate_idx); 1287 while (hr != NULL) { 1288 if (num_initial_regions + num_optional_regions >= max_old_cset_length) { 1289 // Added maximum number of old regions to the CSet. 1290 log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Maximum number of regions). " 1291 "Initial %u regions, optional %u regions", 1292 num_initial_regions, num_optional_regions); 1293 break; 1294 } 1295 1296 // Stop adding regions if the remaining reclaimable space is 1297 // not above G1HeapWastePercent. 1298 size_t reclaimable_bytes = candidates->remaining_reclaimable_bytes(); 1299 double reclaimable_percent = reclaimable_bytes_percent(reclaimable_bytes); 1300 double threshold = (double) G1HeapWastePercent; 1301 if (reclaimable_percent <= threshold) { 1302 // We've added enough old regions that the amount of uncollected 1303 // reclaimable space is at or below the waste threshold. Stop 1304 // adding old regions to the CSet. 1305 log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Reclaimable percentage below threshold). " 1306 "Reclaimable: " SIZE_FORMAT "%s (%1.2f%%) threshold: " UINTX_FORMAT "%%", 1307 byte_size_in_proper_unit(reclaimable_bytes), proper_unit_for_byte_size(reclaimable_bytes), 1308 reclaimable_percent, G1HeapWastePercent); 1309 break; 1310 } 1311 1312 double predicted_time_ms = predict_region_total_time_ms(hr, false); 1313 time_remaining_ms = MAX2(time_remaining_ms - predicted_time_ms, 0.0); 1314 // Add regions to old set until we reach the minimum amount 1315 if (num_initial_regions < min_old_cset_length) { 1316 predicted_old_time_ms += predicted_time_ms; 1317 num_initial_regions++; 1318 // Record the number of regions added with no time remaining 1319 if (time_remaining_ms == 0.0) { 1320 num_expensive_regions++; 1321 } 1322 } else if (!check_time_remaining) { 1323 // In the non-auto-tuning case, we'll finish adding regions 1324 // to the CSet if we reach the minimum. 1325 log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Region amount reached min)."); 1326 break; 1327 } else { 1328 // Keep adding regions to old set until we reach the optional threshold 1329 if (time_remaining_ms > optional_threshold_ms) { 1330 predicted_old_time_ms += predicted_time_ms; 1331 num_initial_regions++; 1332 } else if (time_remaining_ms > 0) { 1333 // Keep adding optional regions until time is up. 1334 assert(num_optional_regions < max_optional_regions, "Should not be possible."); 1335 predicted_optional_time_ms += predicted_time_ms; 1336 num_optional_regions++; 1337 } else { 1338 log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Predicted time too high)."); 1339 break; 1340 } 1341 } 1342 hr = candidates->at(++candidate_idx); 1343 } 1344 if (hr == NULL) { 1345 log_debug(gc, ergo, cset)("Old candidate collection set empty."); 1346 } 1347 1348 if (num_expensive_regions > 0) { 1349 log_debug(gc, ergo, cset)("Added %u initial old regions to collection set although the predicted time was too high.", 1350 num_expensive_regions); 1351 } 1352 1353 log_debug(gc, ergo, cset)("Finish choosing collection set old regions. Initial: %u, optional: %u, " 1354 "predicted old time: %1.2fms, predicted optional time: %1.2fms, time remaining: %1.2f", 1355 num_initial_regions, num_optional_regions, 1356 predicted_initial_time_ms, predicted_optional_time_ms, time_remaining_ms); 1357 } 1358 1359 void G1Policy::calculate_optional_collection_set_regions(G1CollectionSetCandidates* candidates, 1360 uint const max_optional_regions, 1361 double time_remaining_ms, 1362 uint& num_optional_regions) { 1363 assert(_g1h->collector_state()->in_mixed_phase(), "Should only be called in mixed phase"); 1364 1365 num_optional_regions = 0; 1366 double prediction_ms = 0; 1367 uint candidate_idx = candidates->cur_idx(); 1368 1369 HeapRegion* r = candidates->at(candidate_idx); 1370 while (num_optional_regions < max_optional_regions) { 1371 assert(r != NULL, "Region must exist"); 1372 prediction_ms += predict_region_total_time_ms(r, false); 1373 1374 if (prediction_ms > time_remaining_ms) { 1375 log_debug(gc, ergo, cset)("Prediction %.3fms for region %u does not fit remaining time: %.3fms.", 1376 prediction_ms, r->hrm_index(), time_remaining_ms); 1377 break; 1378 } 1379 // This region will be included in the next optional evacuation. 1380 1381 time_remaining_ms -= prediction_ms; 1382 num_optional_regions++; 1383 r = candidates->at(++candidate_idx); 1384 } 1385 1386 log_debug(gc, ergo, cset)("Prepared %u regions out of %u for optional evacuation. Predicted time: %.3fms", 1387 num_optional_regions, max_optional_regions, prediction_ms); 1388 } 1389 1390 void G1Policy::transfer_survivors_to_cset(const G1SurvivorRegions* survivors) { 1391 note_start_adding_survivor_regions(); 1392 1393 HeapRegion* last = NULL; 1394 for (GrowableArrayIterator<HeapRegion*> it = survivors->regions()->begin(); 1395 it != survivors->regions()->end(); 1396 ++it) { 1397 HeapRegion* curr = *it; 1398 set_region_survivor(curr); 1399 1400 // The region is a non-empty survivor so let's add it to 1401 // the incremental collection set for the next evacuation 1402 // pause. 1403 _collection_set->add_survivor_regions(curr); 1404 1405 last = curr; 1406 } 1407 note_stop_adding_survivor_regions(); 1408 1409 // Don't clear the survivor list handles until the start of 1410 // the next evacuation pause - we need it in order to re-tag 1411 // the survivor regions from this evacuation pause as 'young' 1412 // at the start of the next. 1413 }