1 /* 2 * Copyright (c) 2001, 2020, 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/g1ConcurrentRefineStats.hpp" 35 #include "gc/g1/g1CollectionSetChooser.hpp" 36 #include "gc/g1/g1HeterogeneousHeapPolicy.hpp" 37 #include "gc/g1/g1HotCardCache.hpp" 38 #include "gc/g1/g1IHOPControl.hpp" 39 #include "gc/g1/g1GCPhaseTimes.hpp" 40 #include "gc/g1/g1Policy.hpp" 41 #include "gc/g1/g1SurvivorRegions.hpp" 42 #include "gc/g1/g1YoungGenSizer.hpp" 43 #include "gc/g1/heapRegion.inline.hpp" 44 #include "gc/g1/heapRegionRemSet.hpp" 45 #include "gc/shared/concurrentGCBreakpoints.hpp" 46 #include "gc/shared/gcPolicyCounters.hpp" 47 #include "logging/log.hpp" 48 #include "runtime/arguments.hpp" 49 #include "runtime/java.hpp" 50 #include "runtime/mutexLocker.hpp" 51 #include "utilities/debug.hpp" 52 #include "utilities/growableArray.hpp" 53 #include "utilities/pair.hpp" 54 55 G1Policy::G1Policy(STWGCTimer* gc_timer) : 56 _predictor(G1ConfidencePercent / 100.0), 57 _analytics(new G1Analytics(&_predictor)), 58 _remset_tracker(), 59 _mmu_tracker(new G1MMUTrackerQueue(GCPauseIntervalMillis / 1000.0, MaxGCPauseMillis / 1000.0)), 60 _old_gen_alloc_tracker(), 61 _ihop_control(create_ihop_control(&_old_gen_alloc_tracker, &_predictor)), 62 _policy_counters(new GCPolicyCounters("GarbageFirst", 1, 2)), 63 _full_collection_start_sec(0.0), 64 _young_list_target_length(0), 65 _young_list_fixed_length(0), 66 _young_list_max_length(0), 67 _eden_surv_rate_group(new G1SurvRateGroup()), 68 _survivor_surv_rate_group(new G1SurvRateGroup()), 69 _reserve_factor((double) G1ReservePercent / 100.0), 70 _reserve_regions(0), 71 _young_gen_sizer(G1YoungGenSizer::create_gen_sizer()), 72 _free_regions_at_end_of_collection(0), 73 _rs_length(0), 74 _rs_length_prediction(0), 75 _pending_cards_at_gc_start(0), 76 _concurrent_start_to_mixed(), 77 _collection_set(NULL), 78 _g1h(NULL), 79 _phase_times_timer(gc_timer), 80 _phase_times(NULL), 81 _mark_remark_start_sec(0), 82 _mark_cleanup_start_sec(0), 83 _tenuring_threshold(MaxTenuringThreshold), 84 _max_survivor_regions(0), 85 _survivors_age_table(true) 86 { 87 } 88 89 G1Policy::~G1Policy() { 90 delete _ihop_control; 91 delete _young_gen_sizer; 92 } 93 94 G1Policy* G1Policy::create_policy(STWGCTimer* gc_timer_stw) { 95 if (G1Arguments::is_heterogeneous_heap()) { 96 return new G1HeterogeneousHeapPolicy(gc_timer_stw); 97 } else { 98 return new G1Policy(gc_timer_stw); 99 } 100 } 101 102 G1CollectorState* G1Policy::collector_state() const { return _g1h->collector_state(); } 103 104 void G1Policy::init(G1CollectedHeap* g1h, G1CollectionSet* collection_set) { 105 _g1h = g1h; 106 _collection_set = collection_set; 107 108 assert(Heap_lock->owned_by_self(), "Locking discipline."); 109 110 if (!use_adaptive_young_list_length()) { 111 _young_list_fixed_length = _young_gen_sizer->min_desired_young_length(); 112 } 113 _young_gen_sizer->adjust_max_new_size(_g1h->max_expandable_regions()); 114 115 _free_regions_at_end_of_collection = _g1h->num_free_regions(); 116 117 update_young_list_max_and_target_length(); 118 // We may immediately start allocating regions and placing them on the 119 // collection set list. Initialize the per-collection set info 120 _collection_set->start_incremental_building(); 121 } 122 123 void G1Policy::note_gc_start() { 124 phase_times()->note_gc_start(); 125 } 126 127 class G1YoungLengthPredictor { 128 const double _base_time_ms; 129 const double _base_free_regions; 130 const double _target_pause_time_ms; 131 const G1Policy* const _policy; 132 133 public: 134 G1YoungLengthPredictor(double base_time_ms, 135 double base_free_regions, 136 double target_pause_time_ms, 137 const G1Policy* policy) : 138 _base_time_ms(base_time_ms), 139 _base_free_regions(base_free_regions), 140 _target_pause_time_ms(target_pause_time_ms), 141 _policy(policy) {} 142 143 bool will_fit(uint young_length) const { 144 if (young_length >= _base_free_regions) { 145 // end condition 1: not enough space for the young regions 146 return false; 147 } 148 149 size_t bytes_to_copy = 0; 150 const double copy_time_ms = _policy->predict_eden_copy_time_ms(young_length, &bytes_to_copy); 151 const double young_other_time_ms = _policy->analytics()->predict_young_other_time_ms(young_length); 152 const double pause_time_ms = _base_time_ms + copy_time_ms + young_other_time_ms; 153 if (pause_time_ms > _target_pause_time_ms) { 154 // end condition 2: prediction is over the target pause time 155 return false; 156 } 157 158 const size_t free_bytes = (_base_free_regions - young_length) * HeapRegion::GrainBytes; 159 160 // When copying, we will likely need more bytes free than is live in the region. 161 // Add some safety margin to factor in the confidence of our guess, and the 162 // natural expected waste. 163 // (100.0 / G1ConfidencePercent) is a scale factor that expresses the uncertainty 164 // of the calculation: the lower the confidence, the more headroom. 165 // (100 + TargetPLABWastePct) represents the increase in expected bytes during 166 // copying due to anticipated waste in the PLABs. 167 const double safety_factor = (100.0 / G1ConfidencePercent) * (100 + TargetPLABWastePct) / 100.0; 168 const size_t expected_bytes_to_copy = (size_t)(safety_factor * bytes_to_copy); 169 170 if (expected_bytes_to_copy > free_bytes) { 171 // end condition 3: out-of-space 172 return false; 173 } 174 175 // success! 176 return true; 177 } 178 }; 179 180 void G1Policy::record_new_heap_size(uint new_number_of_regions) { 181 // re-calculate the necessary reserve 182 double reserve_regions_d = (double) new_number_of_regions * _reserve_factor; 183 // We use ceiling so that if reserve_regions_d is > 0.0 (but 184 // smaller than 1.0) we'll get 1. 185 _reserve_regions = (uint) ceil(reserve_regions_d); 186 187 _young_gen_sizer->heap_size_changed(new_number_of_regions); 188 189 _ihop_control->update_target_occupancy(new_number_of_regions * HeapRegion::GrainBytes); 190 } 191 192 uint G1Policy::calculate_young_list_desired_min_length(uint base_min_length) const { 193 uint desired_min_length = 0; 194 if (use_adaptive_young_list_length()) { 195 if (_analytics->num_alloc_rate_ms() > 3) { 196 double now_sec = os::elapsedTime(); 197 double when_ms = _mmu_tracker->when_max_gc_sec(now_sec) * 1000.0; 198 double alloc_rate_ms = _analytics->predict_alloc_rate_ms(); 199 desired_min_length = (uint) ceil(alloc_rate_ms * when_ms); 200 } else { 201 // otherwise we don't have enough info to make the prediction 202 } 203 } 204 desired_min_length += base_min_length; 205 // make sure we don't go below any user-defined minimum bound 206 return MAX2(_young_gen_sizer->min_desired_young_length(), desired_min_length); 207 } 208 209 uint G1Policy::calculate_young_list_desired_max_length() const { 210 // Here, we might want to also take into account any additional 211 // constraints (i.e., user-defined minimum bound). Currently, we 212 // effectively don't set this bound. 213 return _young_gen_sizer->max_desired_young_length(); 214 } 215 216 uint G1Policy::update_young_list_max_and_target_length() { 217 return update_young_list_max_and_target_length(_analytics->predict_rs_length()); 218 } 219 220 uint G1Policy::update_young_list_max_and_target_length(size_t rs_length) { 221 uint unbounded_target_length = update_young_list_target_length(rs_length); 222 update_max_gc_locker_expansion(); 223 return unbounded_target_length; 224 } 225 226 uint G1Policy::update_young_list_target_length(size_t rs_length) { 227 YoungTargetLengths young_lengths = young_list_target_lengths(rs_length); 228 _young_list_target_length = young_lengths.first; 229 230 return young_lengths.second; 231 } 232 233 G1Policy::YoungTargetLengths G1Policy::young_list_target_lengths(size_t rs_length) const { 234 YoungTargetLengths result; 235 236 // Calculate the absolute and desired min bounds first. 237 238 // This is how many young regions we already have (currently: the survivors). 239 const uint base_min_length = _g1h->survivor_regions_count(); 240 uint desired_min_length = calculate_young_list_desired_min_length(base_min_length); 241 // This is the absolute minimum young length. Ensure that we 242 // will at least have one eden region available for allocation. 243 uint absolute_min_length = base_min_length + MAX2(_g1h->eden_regions_count(), (uint)1); 244 // If we shrank the young list target it should not shrink below the current size. 245 desired_min_length = MAX2(desired_min_length, absolute_min_length); 246 // Calculate the absolute and desired max bounds. 247 248 uint desired_max_length = calculate_young_list_desired_max_length(); 249 250 uint young_list_target_length = 0; 251 if (use_adaptive_young_list_length()) { 252 if (collector_state()->in_young_only_phase()) { 253 young_list_target_length = 254 calculate_young_list_target_length(rs_length, 255 base_min_length, 256 desired_min_length, 257 desired_max_length); 258 } else { 259 // Don't calculate anything and let the code below bound it to 260 // the desired_min_length, i.e., do the next GC as soon as 261 // possible to maximize how many old regions we can add to it. 262 } 263 } else { 264 // The user asked for a fixed young gen so we'll fix the young gen 265 // whether the next GC is young or mixed. 266 young_list_target_length = _young_list_fixed_length; 267 } 268 269 result.second = young_list_target_length; 270 271 // We will try our best not to "eat" into the reserve. 272 uint absolute_max_length = 0; 273 if (_free_regions_at_end_of_collection > _reserve_regions) { 274 absolute_max_length = _free_regions_at_end_of_collection - _reserve_regions; 275 } 276 if (desired_max_length > absolute_max_length) { 277 desired_max_length = absolute_max_length; 278 } 279 280 // Make sure we don't go over the desired max length, nor under the 281 // desired min length. In case they clash, desired_min_length wins 282 // which is why that test is second. 283 if (young_list_target_length > desired_max_length) { 284 young_list_target_length = desired_max_length; 285 } 286 if (young_list_target_length < desired_min_length) { 287 young_list_target_length = desired_min_length; 288 } 289 290 assert(young_list_target_length > base_min_length, 291 "we should be able to allocate at least one eden region"); 292 assert(young_list_target_length >= absolute_min_length, "post-condition"); 293 294 result.first = young_list_target_length; 295 return result; 296 } 297 298 uint G1Policy::calculate_young_list_target_length(size_t rs_length, 299 uint base_min_length, 300 uint desired_min_length, 301 uint desired_max_length) const { 302 assert(use_adaptive_young_list_length(), "pre-condition"); 303 assert(collector_state()->in_young_only_phase(), "only call this for young GCs"); 304 305 // In case some edge-condition makes the desired max length too small... 306 if (desired_max_length <= desired_min_length) { 307 return desired_min_length; 308 } 309 310 // We'll adjust min_young_length and max_young_length not to include 311 // the already allocated young regions (i.e., so they reflect the 312 // min and max eden regions we'll allocate). The base_min_length 313 // will be reflected in the predictions by the 314 // survivor_regions_evac_time prediction. 315 assert(desired_min_length > base_min_length, "invariant"); 316 uint min_young_length = desired_min_length - base_min_length; 317 assert(desired_max_length > base_min_length, "invariant"); 318 uint max_young_length = desired_max_length - base_min_length; 319 320 const double target_pause_time_ms = _mmu_tracker->max_gc_time() * 1000.0; 321 const size_t pending_cards = _analytics->predict_pending_cards(); 322 const double base_time_ms = predict_base_elapsed_time_ms(pending_cards, rs_length); 323 const uint available_free_regions = _free_regions_at_end_of_collection; 324 const uint base_free_regions = 325 available_free_regions > _reserve_regions ? available_free_regions - _reserve_regions : 0; 326 327 // Here, we will make sure that the shortest young length that 328 // makes sense fits within the target pause time. 329 330 G1YoungLengthPredictor p(base_time_ms, 331 base_free_regions, 332 target_pause_time_ms, 333 this); 334 if (p.will_fit(min_young_length)) { 335 // The shortest young length will fit into the target pause time; 336 // we'll now check whether the absolute maximum number of young 337 // regions will fit in the target pause time. If not, we'll do 338 // a binary search between min_young_length and max_young_length. 339 if (p.will_fit(max_young_length)) { 340 // The maximum young length will fit into the target pause time. 341 // We are done so set min young length to the maximum length (as 342 // the result is assumed to be returned in min_young_length). 343 min_young_length = max_young_length; 344 } else { 345 // The maximum possible number of young regions will not fit within 346 // the target pause time so we'll search for the optimal 347 // length. The loop invariants are: 348 // 349 // min_young_length < max_young_length 350 // min_young_length is known to fit into the target pause time 351 // max_young_length is known not to fit into the target pause time 352 // 353 // Going into the loop we know the above hold as we've just 354 // checked them. Every time around the loop we check whether 355 // the middle value between min_young_length and 356 // max_young_length fits into the target pause time. If it 357 // does, it becomes the new min. If it doesn't, it becomes 358 // the new max. This way we maintain the loop invariants. 359 360 assert(min_young_length < max_young_length, "invariant"); 361 uint diff = (max_young_length - min_young_length) / 2; 362 while (diff > 0) { 363 uint young_length = min_young_length + diff; 364 if (p.will_fit(young_length)) { 365 min_young_length = young_length; 366 } else { 367 max_young_length = young_length; 368 } 369 assert(min_young_length < max_young_length, "invariant"); 370 diff = (max_young_length - min_young_length) / 2; 371 } 372 // The results is min_young_length which, according to the 373 // loop invariants, should fit within the target pause time. 374 375 // These are the post-conditions of the binary search above: 376 assert(min_young_length < max_young_length, 377 "otherwise we should have discovered that max_young_length " 378 "fits into the pause target and not done the binary search"); 379 assert(p.will_fit(min_young_length), 380 "min_young_length, the result of the binary search, should " 381 "fit into the pause target"); 382 assert(!p.will_fit(min_young_length + 1), 383 "min_young_length, the result of the binary search, should be " 384 "optimal, so no larger length should fit into the pause target"); 385 } 386 } else { 387 // Even the minimum length doesn't fit into the pause time 388 // target, return it as the result nevertheless. 389 } 390 return base_min_length + min_young_length; 391 } 392 393 double G1Policy::predict_survivor_regions_evac_time() const { 394 double survivor_regions_evac_time = 0.0; 395 const GrowableArray<HeapRegion*>* survivor_regions = _g1h->survivor()->regions(); 396 for (GrowableArrayIterator<HeapRegion*> it = survivor_regions->begin(); 397 it != survivor_regions->end(); 398 ++it) { 399 survivor_regions_evac_time += predict_region_total_time_ms(*it, collector_state()->in_young_only_phase()); 400 } 401 return survivor_regions_evac_time; 402 } 403 404 G1GCPhaseTimes* G1Policy::phase_times() const { 405 // Lazy allocation because it must follow initialization of all the 406 // OopStorage objects by various other subsystems. 407 if (_phase_times == NULL) { 408 _phase_times = new G1GCPhaseTimes(_phase_times_timer, ParallelGCThreads); 409 } 410 return _phase_times; 411 } 412 413 void G1Policy::revise_young_list_target_length_if_necessary(size_t rs_length) { 414 guarantee(use_adaptive_young_list_length(), "should not call this otherwise" ); 415 416 if (rs_length > _rs_length_prediction) { 417 // add 10% to avoid having to recalculate often 418 size_t rs_length_prediction = rs_length * 1100 / 1000; 419 update_rs_length_prediction(rs_length_prediction); 420 421 update_young_list_max_and_target_length(rs_length_prediction); 422 } 423 } 424 425 void G1Policy::update_rs_length_prediction() { 426 update_rs_length_prediction(_analytics->predict_rs_length()); 427 } 428 429 void G1Policy::update_rs_length_prediction(size_t prediction) { 430 if (collector_state()->in_young_only_phase() && use_adaptive_young_list_length()) { 431 _rs_length_prediction = prediction; 432 } 433 } 434 435 void G1Policy::record_full_collection_start() { 436 _full_collection_start_sec = os::elapsedTime(); 437 // Release the future to-space so that it is available for compaction into. 438 collector_state()->set_in_young_only_phase(false); 439 collector_state()->set_in_full_gc(true); 440 _collection_set->clear_candidates(); 441 _pending_cards_at_gc_start = 0; 442 } 443 444 void G1Policy::record_full_collection_end() { 445 // Consider this like a collection pause for the purposes of allocation 446 // since last pause. 447 double end_sec = os::elapsedTime(); 448 double full_gc_time_sec = end_sec - _full_collection_start_sec; 449 double full_gc_time_ms = full_gc_time_sec * 1000.0; 450 451 _analytics->update_recent_gc_times(end_sec, full_gc_time_ms); 452 453 collector_state()->set_in_full_gc(false); 454 455 // "Nuke" the heuristics that control the young/mixed GC 456 // transitions and make sure we start with young GCs after the Full GC. 457 collector_state()->set_in_young_only_phase(true); 458 collector_state()->set_in_young_gc_before_mixed(false); 459 collector_state()->set_initiate_conc_mark_if_possible(need_to_start_conc_mark("end of Full GC", 0)); 460 collector_state()->set_in_concurrent_start_gc(false); 461 collector_state()->set_mark_or_rebuild_in_progress(false); 462 collector_state()->set_clearing_next_bitmap(false); 463 464 _eden_surv_rate_group->start_adding_regions(); 465 // also call this on any additional surv rate groups 466 467 _free_regions_at_end_of_collection = _g1h->num_free_regions(); 468 _survivor_surv_rate_group->reset(); 469 update_young_list_max_and_target_length(); 470 update_rs_length_prediction(); 471 472 _old_gen_alloc_tracker.reset_after_gc(_g1h->humongous_regions_count() * HeapRegion::GrainBytes); 473 474 record_pause(FullGC, _full_collection_start_sec, end_sec); 475 } 476 477 static void log_refinement_stats(const char* kind, const G1ConcurrentRefineStats& stats) { 478 log_debug(gc, refine, stats) 479 ("%s refinement: %.2fms, refined: " SIZE_FORMAT 480 ", precleaned: " SIZE_FORMAT ", dirtied: " SIZE_FORMAT, 481 kind, 482 stats.refinement_time().seconds() * MILLIUNITS, 483 stats.refined_cards(), 484 stats.precleaned_cards(), 485 stats.dirtied_cards()); 486 } 487 488 void G1Policy::record_concurrent_refinement_stats() { 489 G1DirtyCardQueueSet& dcqs = G1BarrierSet::dirty_card_queue_set(); 490 _pending_cards_at_gc_start = dcqs.num_cards(); 491 492 // Collect per-thread stats, mostly from mutator activity. 493 G1ConcurrentRefineStats mut_stats = dcqs.get_and_reset_refinement_stats(); 494 495 // Collect specialized concurrent refinement thread stats. 496 G1ConcurrentRefine* cr = _g1h->concurrent_refine(); 497 G1ConcurrentRefineStats cr_stats = cr->get_and_reset_refinement_stats(); 498 499 G1ConcurrentRefineStats total_stats = mut_stats + cr_stats; 500 501 log_refinement_stats("Mutator", mut_stats); 502 log_refinement_stats("Concurrent", cr_stats); 503 log_refinement_stats("Total", total_stats); 504 505 // Record the rate at which cards were refined. 506 // Don't update the rate if the current sample is empty or time is zero. 507 Tickspan refinement_time = total_stats.refinement_time(); 508 size_t refined_cards = total_stats.refined_cards(); 509 if ((refined_cards > 0) && (refinement_time > Tickspan())) { 510 double rate = refined_cards / (refinement_time.seconds() * MILLIUNITS); 511 _analytics->report_concurrent_refine_rate_ms(rate); 512 log_debug(gc, refine, stats)("Concurrent refinement rate: %.2f cards/ms", rate); 513 } 514 515 // Record mutator's card logging rate. 516 double mut_start_time = _analytics->prev_collection_pause_end_ms(); 517 double mut_end_time = phase_times()->cur_collection_start_sec() * MILLIUNITS; 518 double mut_time = mut_end_time - mut_start_time; 519 // Unlike above for conc-refine rate, here we should not require a 520 // non-empty sample, since an application could go some time with only 521 // young-gen or filtered out writes. But we'll ignore unusually short 522 // sample periods, as they may just pollute the predictions. 523 if (mut_time > 1.0) { // Require > 1ms sample time. 524 double dirtied_rate = total_stats.dirtied_cards() / mut_time; 525 _analytics->report_dirtied_cards_rate_ms(dirtied_rate); 526 log_debug(gc, refine, stats)("Generate dirty cards rate: %.2f cards/ms", dirtied_rate); 527 } 528 } 529 530 void G1Policy::record_collection_pause_start(double start_time_sec) { 531 // We only need to do this here as the policy will only be applied 532 // to the GC we're about to start. so, no point is calculating this 533 // every time we calculate / recalculate the target young length. 534 update_survivors_policy(); 535 536 assert(max_survivor_regions() + _g1h->num_used_regions() <= _g1h->max_regions(), 537 "Maximum survivor regions %u plus used regions %u exceeds max regions %u", 538 max_survivor_regions(), _g1h->num_used_regions(), _g1h->max_regions()); 539 assert_used_and_recalculate_used_equal(_g1h); 540 541 phase_times()->record_cur_collection_start_sec(start_time_sec); 542 543 record_concurrent_refinement_stats(); 544 545 _collection_set->reset_bytes_used_before(); 546 547 // do that for any other surv rate groups 548 _eden_surv_rate_group->stop_adding_regions(); 549 _survivors_age_table.clear(); 550 551 assert(_g1h->collection_set()->verify_young_ages(), "region age verification failed"); 552 } 553 554 void G1Policy::record_concurrent_mark_init_end(double mark_init_elapsed_time_ms) { 555 assert(!collector_state()->initiate_conc_mark_if_possible(), "we should have cleared it by now"); 556 collector_state()->set_in_concurrent_start_gc(false); 557 } 558 559 void G1Policy::record_concurrent_mark_remark_start() { 560 _mark_remark_start_sec = os::elapsedTime(); 561 } 562 563 void G1Policy::record_concurrent_mark_remark_end() { 564 double end_time_sec = os::elapsedTime(); 565 double elapsed_time_ms = (end_time_sec - _mark_remark_start_sec)*1000.0; 566 _analytics->report_concurrent_mark_remark_times_ms(elapsed_time_ms); 567 _analytics->append_prev_collection_pause_end_ms(elapsed_time_ms); 568 569 record_pause(Remark, _mark_remark_start_sec, end_time_sec); 570 } 571 572 void G1Policy::record_concurrent_mark_cleanup_start() { 573 _mark_cleanup_start_sec = os::elapsedTime(); 574 } 575 576 double G1Policy::average_time_ms(G1GCPhaseTimes::GCParPhases phase) const { 577 return phase_times()->average_time_ms(phase); 578 } 579 580 double G1Policy::young_other_time_ms() const { 581 return phase_times()->young_cset_choice_time_ms() + 582 phase_times()->average_time_ms(G1GCPhaseTimes::YoungFreeCSet); 583 } 584 585 double G1Policy::non_young_other_time_ms() const { 586 return phase_times()->non_young_cset_choice_time_ms() + 587 phase_times()->average_time_ms(G1GCPhaseTimes::NonYoungFreeCSet); 588 } 589 590 double G1Policy::other_time_ms(double pause_time_ms) const { 591 return pause_time_ms - phase_times()->cur_collection_par_time_ms(); 592 } 593 594 double G1Policy::constant_other_time_ms(double pause_time_ms) const { 595 return other_time_ms(pause_time_ms) - phase_times()->total_free_cset_time_ms() - phase_times()->total_rebuild_freelist_time_ms(); 596 } 597 598 bool G1Policy::about_to_start_mixed_phase() const { 599 return _g1h->concurrent_mark()->cm_thread()->during_cycle() || collector_state()->in_young_gc_before_mixed(); 600 } 601 602 bool G1Policy::need_to_start_conc_mark(const char* source, size_t alloc_word_size) { 603 if (about_to_start_mixed_phase()) { 604 return false; 605 } 606 607 size_t marking_initiating_used_threshold = _ihop_control->get_conc_mark_start_threshold(); 608 609 size_t cur_used_bytes = _g1h->non_young_capacity_bytes(); 610 size_t alloc_byte_size = alloc_word_size * HeapWordSize; 611 size_t marking_request_bytes = cur_used_bytes + alloc_byte_size; 612 613 bool result = false; 614 if (marking_request_bytes > marking_initiating_used_threshold) { 615 result = collector_state()->in_young_only_phase() && !collector_state()->in_young_gc_before_mixed(); 616 log_debug(gc, ergo, ihop)("%s occupancy: " SIZE_FORMAT "B allocation request: " SIZE_FORMAT "B threshold: " SIZE_FORMAT "B (%1.2f) source: %s", 617 result ? "Request concurrent cycle initiation (occupancy higher than threshold)" : "Do not request concurrent cycle initiation (still doing mixed collections)", 618 cur_used_bytes, alloc_byte_size, marking_initiating_used_threshold, (double) marking_initiating_used_threshold / _g1h->capacity() * 100, source); 619 } 620 621 return result; 622 } 623 624 double G1Policy::logged_cards_processing_time() const { 625 double all_cards_processing_time = average_time_ms(G1GCPhaseTimes::ScanHR) + average_time_ms(G1GCPhaseTimes::OptScanHR); 626 size_t logged_dirty_cards = phase_times()->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards); 627 size_t scan_heap_roots_cards = phase_times()->sum_thread_work_items(G1GCPhaseTimes::ScanHR, G1GCPhaseTimes::ScanHRScannedCards) + 628 phase_times()->sum_thread_work_items(G1GCPhaseTimes::OptScanHR, G1GCPhaseTimes::ScanHRScannedCards); 629 // This may happen if there are duplicate cards in different log buffers. 630 if (logged_dirty_cards > scan_heap_roots_cards) { 631 return all_cards_processing_time + average_time_ms(G1GCPhaseTimes::MergeLB); 632 } 633 return (all_cards_processing_time * logged_dirty_cards / scan_heap_roots_cards) + average_time_ms(G1GCPhaseTimes::MergeLB); 634 } 635 636 // Anything below that is considered to be zero 637 #define MIN_TIMER_GRANULARITY 0.0000001 638 639 void G1Policy::record_collection_pause_end(double pause_time_ms) { 640 G1GCPhaseTimes* p = phase_times(); 641 642 double end_time_sec = os::elapsedTime(); 643 644 PauseKind this_pause = young_gc_pause_kind(); 645 646 bool update_stats = !_g1h->evacuation_failed(); 647 648 record_pause(this_pause, end_time_sec - pause_time_ms / 1000.0, end_time_sec); 649 650 if (is_concurrent_start_pause(this_pause)) { 651 record_concurrent_mark_init_end(0.0); 652 } else { 653 maybe_start_marking(); 654 } 655 656 double app_time_ms = (phase_times()->cur_collection_start_sec() * 1000.0 - _analytics->prev_collection_pause_end_ms()); 657 if (app_time_ms < MIN_TIMER_GRANULARITY) { 658 // This usually happens due to the timer not having the required 659 // granularity. Some Linuxes are the usual culprits. 660 // We'll just set it to something (arbitrarily) small. 661 app_time_ms = 1.0; 662 } 663 664 if (update_stats) { 665 // We maintain the invariant that all objects allocated by mutator 666 // threads will be allocated out of eden regions. So, we can use 667 // the eden region number allocated since the previous GC to 668 // calculate the application's allocate rate. The only exception 669 // to that is humongous objects that are allocated separately. But 670 // given that humongous object allocations do not really affect 671 // either the pause's duration nor when the next pause will take 672 // place we can safely ignore them here. 673 uint regions_allocated = _collection_set->eden_region_length(); 674 double alloc_rate_ms = (double) regions_allocated / app_time_ms; 675 _analytics->report_alloc_rate_ms(alloc_rate_ms); 676 677 _analytics->compute_pause_time_ratios(end_time_sec, pause_time_ms); 678 _analytics->update_recent_gc_times(end_time_sec, pause_time_ms); 679 } 680 681 if (is_last_young_pause(this_pause)) { 682 assert(!is_concurrent_start_pause(this_pause), 683 "The young GC before mixed is not allowed to be concurrent start 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 (is_mixed_pause(this_pause)) { 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 } else { 700 assert(is_young_only_pause(this_pause), "must be"); 701 } 702 703 _eden_surv_rate_group->start_adding_regions(); 704 705 double merge_hcc_time_ms = average_time_ms(G1GCPhaseTimes::MergeHCC); 706 if (update_stats) { 707 size_t const total_log_buffer_cards = p->sum_thread_work_items(G1GCPhaseTimes::MergeHCC, G1GCPhaseTimes::MergeHCCDirtyCards) + 708 p->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards); 709 // Update prediction for card merge; MergeRSDirtyCards includes the cards from the Eager Reclaim phase. 710 size_t const total_cards_merged = p->sum_thread_work_items(G1GCPhaseTimes::MergeRS, G1GCPhaseTimes::MergeRSDirtyCards) + 711 p->sum_thread_work_items(G1GCPhaseTimes::OptMergeRS, G1GCPhaseTimes::MergeRSDirtyCards) + 712 total_log_buffer_cards; 713 714 // The threshold for the number of cards in a given sampling which we consider 715 // large enough so that the impact from setup and other costs is negligible. 716 size_t const CardsNumSamplingThreshold = 10; 717 718 if (total_cards_merged > CardsNumSamplingThreshold) { 719 double avg_time_merge_cards = average_time_ms(G1GCPhaseTimes::MergeER) + 720 average_time_ms(G1GCPhaseTimes::MergeRS) + 721 average_time_ms(G1GCPhaseTimes::MergeHCC) + 722 average_time_ms(G1GCPhaseTimes::MergeLB) + 723 average_time_ms(G1GCPhaseTimes::OptMergeRS); 724 _analytics->report_cost_per_card_merge_ms(avg_time_merge_cards / total_cards_merged, 725 is_young_only_pause(this_pause)); 726 } 727 728 // Update prediction for card scan 729 size_t const total_cards_scanned = p->sum_thread_work_items(G1GCPhaseTimes::ScanHR, G1GCPhaseTimes::ScanHRScannedCards) + 730 p->sum_thread_work_items(G1GCPhaseTimes::OptScanHR, G1GCPhaseTimes::ScanHRScannedCards); 731 732 if (total_cards_scanned > CardsNumSamplingThreshold) { 733 double avg_time_dirty_card_scan = average_time_ms(G1GCPhaseTimes::ScanHR) + 734 average_time_ms(G1GCPhaseTimes::OptScanHR); 735 736 _analytics->report_cost_per_card_scan_ms(avg_time_dirty_card_scan / total_cards_scanned, 737 is_young_only_pause(this_pause)); 738 } 739 740 // Update prediction for the ratio between cards from the remembered 741 // sets and actually scanned cards from the remembered sets. 742 // Cards from the remembered sets are all cards not duplicated by cards from 743 // the logs. 744 // Due to duplicates in the log buffers, the number of actually scanned cards 745 // can be smaller than the cards in the log buffers. 746 const size_t from_rs_length_cards = (total_cards_scanned > total_log_buffer_cards) ? total_cards_scanned - total_log_buffer_cards : 0; 747 double merge_to_scan_ratio = 0.0; 748 if (total_cards_scanned > 0) { 749 merge_to_scan_ratio = (double) from_rs_length_cards / total_cards_scanned; 750 } 751 _analytics->report_card_merge_to_scan_ratio(merge_to_scan_ratio, 752 is_young_only_pause(this_pause)); 753 754 const size_t recorded_rs_length = _collection_set->recorded_rs_length(); 755 const size_t rs_length_diff = _rs_length > recorded_rs_length ? _rs_length - recorded_rs_length : 0; 756 _analytics->report_rs_length_diff(rs_length_diff); 757 758 // Update prediction for copy cost per byte 759 size_t copied_bytes = p->sum_thread_work_items(G1GCPhaseTimes::MergePSS, G1GCPhaseTimes::MergePSSCopiedBytes); 760 761 if (copied_bytes > 0) { 762 double cost_per_byte_ms = (average_time_ms(G1GCPhaseTimes::ObjCopy) + average_time_ms(G1GCPhaseTimes::OptObjCopy)) / copied_bytes; 763 _analytics->report_cost_per_byte_ms(cost_per_byte_ms, collector_state()->mark_or_rebuild_in_progress()); 764 } 765 766 if (_collection_set->young_region_length() > 0) { 767 _analytics->report_young_other_cost_per_region_ms(young_other_time_ms() / 768 _collection_set->young_region_length()); 769 } 770 771 if (_collection_set->old_region_length() > 0) { 772 _analytics->report_non_young_other_cost_per_region_ms(non_young_other_time_ms() / 773 _collection_set->old_region_length()); 774 } 775 776 _analytics->report_constant_other_time_ms(constant_other_time_ms(pause_time_ms)); 777 778 // Do not update RS lengths and the number of pending cards with information from mixed gc: 779 // these are is wildly different to during young only gc and mess up young gen sizing right 780 // after the mixed gc phase. 781 // During mixed gc we do not use them for young gen sizing. 782 if (is_young_only_pause(this_pause)) { 783 _analytics->report_pending_cards((double) _pending_cards_at_gc_start); 784 _analytics->report_rs_length((double) _rs_length); 785 } 786 } 787 788 assert(!(is_concurrent_start_pause(this_pause) && collector_state()->mark_or_rebuild_in_progress()), 789 "If the last pause has been concurrent start, we should not have been in the marking window"); 790 if (is_concurrent_start_pause(this_pause)) { 791 collector_state()->set_mark_or_rebuild_in_progress(true); 792 } 793 794 _free_regions_at_end_of_collection = _g1h->num_free_regions(); 795 796 update_rs_length_prediction(); 797 798 // Do not update dynamic IHOP due to G1 periodic collection as it is highly likely 799 // that in this case we are not running in a "normal" operating mode. 800 if (_g1h->gc_cause() != GCCause::_g1_periodic_collection) { 801 // IHOP control wants to know the expected young gen length if it were not 802 // restrained by the heap reserve. Using the actual length would make the 803 // prediction too small and the limit the young gen every time we get to the 804 // predicted target occupancy. 805 size_t last_unrestrained_young_length = update_young_list_max_and_target_length(); 806 807 _old_gen_alloc_tracker.reset_after_gc(_g1h->humongous_regions_count() * HeapRegion::GrainBytes); 808 update_ihop_prediction(app_time_ms / 1000.0, 809 last_unrestrained_young_length * HeapRegion::GrainBytes, 810 is_young_only_pause(this_pause)); 811 812 _ihop_control->send_trace_event(_g1h->gc_tracer_stw()); 813 } else { 814 // Any garbage collection triggered as periodic collection resets the time-to-mixed 815 // measurement. Periodic collection typically means that the application is "inactive", i.e. 816 // the marking threads may have received an uncharacterisic amount of cpu time 817 // for completing the marking, i.e. are faster than expected. 818 // This skews the predicted marking length towards smaller values which might cause 819 // the mark start being too late. 820 _concurrent_start_to_mixed.reset(); 821 } 822 823 // Note that _mmu_tracker->max_gc_time() returns the time in seconds. 824 double scan_logged_cards_time_goal_ms = _mmu_tracker->max_gc_time() * MILLIUNITS * G1RSetUpdatingPauseTimePercent / 100.0; 825 826 if (scan_logged_cards_time_goal_ms < merge_hcc_time_ms) { 827 log_debug(gc, ergo, refine)("Adjust concurrent refinement thresholds (scanning the HCC expected to take longer than Update RS time goal)." 828 "Logged Cards Scan time goal: %1.2fms Scan HCC time: %1.2fms", 829 scan_logged_cards_time_goal_ms, merge_hcc_time_ms); 830 831 scan_logged_cards_time_goal_ms = 0; 832 } else { 833 scan_logged_cards_time_goal_ms -= merge_hcc_time_ms; 834 } 835 836 double const logged_cards_time = logged_cards_processing_time(); 837 838 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", 839 scan_logged_cards_time_goal_ms, logged_cards_time, merge_hcc_time_ms); 840 841 _g1h->concurrent_refine()->adjust(logged_cards_time, 842 phase_times()->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards), 843 scan_logged_cards_time_goal_ms); 844 } 845 846 G1IHOPControl* G1Policy::create_ihop_control(const G1OldGenAllocationTracker* old_gen_alloc_tracker, 847 const G1Predictions* predictor) { 848 if (G1UseAdaptiveIHOP) { 849 return new G1AdaptiveIHOPControl(InitiatingHeapOccupancyPercent, 850 old_gen_alloc_tracker, 851 predictor, 852 G1ReservePercent, 853 G1HeapWastePercent); 854 } else { 855 return new G1StaticIHOPControl(InitiatingHeapOccupancyPercent, old_gen_alloc_tracker); 856 } 857 } 858 859 void G1Policy::update_ihop_prediction(double mutator_time_s, 860 size_t young_gen_size, 861 bool this_gc_was_young_only) { 862 // Always try to update IHOP prediction. Even evacuation failures give information 863 // about e.g. whether to start IHOP earlier next time. 864 865 // Avoid using really small application times that might create samples with 866 // very high or very low values. They may be caused by e.g. back-to-back gcs. 867 double const min_valid_time = 1e-6; 868 869 bool report = false; 870 871 double marking_to_mixed_time = -1.0; 872 if (!this_gc_was_young_only && _concurrent_start_to_mixed.has_result()) { 873 marking_to_mixed_time = _concurrent_start_to_mixed.last_marking_time(); 874 assert(marking_to_mixed_time > 0.0, 875 "Concurrent start to mixed time must be larger than zero but is %.3f", 876 marking_to_mixed_time); 877 if (marking_to_mixed_time > min_valid_time) { 878 _ihop_control->update_marking_length(marking_to_mixed_time); 879 report = true; 880 } 881 } 882 883 // As an approximation for the young gc promotion rates during marking we use 884 // all of them. In many applications there are only a few if any young gcs during 885 // marking, which makes any prediction useless. This increases the accuracy of the 886 // prediction. 887 if (this_gc_was_young_only && mutator_time_s > min_valid_time) { 888 _ihop_control->update_allocation_info(mutator_time_s, young_gen_size); 889 report = true; 890 } 891 892 if (report) { 893 report_ihop_statistics(); 894 } 895 } 896 897 void G1Policy::report_ihop_statistics() { 898 _ihop_control->print(); 899 } 900 901 void G1Policy::print_phases() { 902 phase_times()->print(); 903 } 904 905 double G1Policy::predict_base_elapsed_time_ms(size_t pending_cards, 906 size_t rs_length) const { 907 size_t effective_scanned_cards = _analytics->predict_scan_card_num(rs_length, collector_state()->in_young_only_phase()); 908 return 909 _analytics->predict_card_merge_time_ms(pending_cards + rs_length, collector_state()->in_young_only_phase()) + 910 _analytics->predict_card_scan_time_ms(effective_scanned_cards, collector_state()->in_young_only_phase()) + 911 _analytics->predict_constant_other_time_ms() + 912 predict_survivor_regions_evac_time(); 913 } 914 915 double G1Policy::predict_base_elapsed_time_ms(size_t pending_cards) const { 916 size_t rs_length = _analytics->predict_rs_length(); 917 return predict_base_elapsed_time_ms(pending_cards, rs_length); 918 } 919 920 size_t G1Policy::predict_bytes_to_copy(HeapRegion* hr) const { 921 size_t bytes_to_copy; 922 if (!hr->is_young()) { 923 bytes_to_copy = hr->max_live_bytes(); 924 } else { 925 bytes_to_copy = (size_t) (hr->used() * hr->surv_rate_prediction(_predictor)); 926 } 927 return bytes_to_copy; 928 } 929 930 double G1Policy::predict_eden_copy_time_ms(uint count, size_t* bytes_to_copy) const { 931 if (count == 0) { 932 return 0.0; 933 } 934 size_t const expected_bytes = _eden_surv_rate_group->accum_surv_rate_pred(count) * HeapRegion::GrainBytes; 935 if (bytes_to_copy != NULL) { 936 *bytes_to_copy = expected_bytes; 937 } 938 return _analytics->predict_object_copy_time_ms(expected_bytes, collector_state()->mark_or_rebuild_in_progress()); 939 } 940 941 double G1Policy::predict_region_copy_time_ms(HeapRegion* hr) const { 942 size_t const bytes_to_copy = predict_bytes_to_copy(hr); 943 return _analytics->predict_object_copy_time_ms(bytes_to_copy, collector_state()->mark_or_rebuild_in_progress()); 944 } 945 946 double G1Policy::predict_region_non_copy_time_ms(HeapRegion* hr, 947 bool for_young_gc) const { 948 size_t rs_length = hr->rem_set()->occupied(); 949 size_t scan_card_num = _analytics->predict_scan_card_num(rs_length, for_young_gc); 950 951 double region_elapsed_time_ms = 952 _analytics->predict_card_merge_time_ms(rs_length, collector_state()->in_young_only_phase()) + 953 _analytics->predict_card_scan_time_ms(scan_card_num, collector_state()->in_young_only_phase()); 954 955 // The prediction of the "other" time for this region is based 956 // upon the region type and NOT the GC type. 957 if (hr->is_young()) { 958 region_elapsed_time_ms += _analytics->predict_young_other_time_ms(1); 959 } else { 960 region_elapsed_time_ms += _analytics->predict_non_young_other_time_ms(1); 961 } 962 return region_elapsed_time_ms; 963 } 964 965 double G1Policy::predict_region_total_time_ms(HeapRegion* hr, bool for_young_gc) const { 966 return predict_region_non_copy_time_ms(hr, for_young_gc) + predict_region_copy_time_ms(hr); 967 } 968 969 bool G1Policy::should_allocate_mutator_region() const { 970 uint young_list_length = _g1h->young_regions_count(); 971 uint young_list_target_length = _young_list_target_length; 972 return young_list_length < young_list_target_length; 973 } 974 975 bool G1Policy::can_expand_young_list() const { 976 uint young_list_length = _g1h->young_regions_count(); 977 uint young_list_max_length = _young_list_max_length; 978 return young_list_length < young_list_max_length; 979 } 980 981 bool G1Policy::use_adaptive_young_list_length() const { 982 return _young_gen_sizer->use_adaptive_young_list_length(); 983 } 984 985 size_t G1Policy::desired_survivor_size(uint max_regions) const { 986 size_t const survivor_capacity = HeapRegion::GrainWords * max_regions; 987 return (size_t)((((double)survivor_capacity) * TargetSurvivorRatio) / 100); 988 } 989 990 void G1Policy::print_age_table() { 991 _survivors_age_table.print_age_table(_tenuring_threshold); 992 } 993 994 void G1Policy::update_max_gc_locker_expansion() { 995 uint expansion_region_num = 0; 996 if (GCLockerEdenExpansionPercent > 0) { 997 double perc = (double) GCLockerEdenExpansionPercent / 100.0; 998 double expansion_region_num_d = perc * (double) _young_list_target_length; 999 // We use ceiling so that if expansion_region_num_d is > 0.0 (but 1000 // less than 1.0) we'll get 1. 1001 expansion_region_num = (uint) ceil(expansion_region_num_d); 1002 } else { 1003 assert(expansion_region_num == 0, "sanity"); 1004 } 1005 _young_list_max_length = _young_list_target_length + expansion_region_num; 1006 assert(_young_list_target_length <= _young_list_max_length, "post-condition"); 1007 } 1008 1009 // Calculates survivor space parameters. 1010 void G1Policy::update_survivors_policy() { 1011 double max_survivor_regions_d = 1012 (double) _young_list_target_length / (double) SurvivorRatio; 1013 1014 // Calculate desired survivor size based on desired max survivor regions (unconstrained 1015 // by remaining heap). Otherwise we may cause undesired promotions as we are 1016 // already getting close to end of the heap, impacting performance even more. 1017 uint const desired_max_survivor_regions = ceil(max_survivor_regions_d); 1018 size_t const survivor_size = desired_survivor_size(desired_max_survivor_regions); 1019 1020 _tenuring_threshold = _survivors_age_table.compute_tenuring_threshold(survivor_size); 1021 if (UsePerfData) { 1022 _policy_counters->tenuring_threshold()->set_value(_tenuring_threshold); 1023 _policy_counters->desired_survivor_size()->set_value(survivor_size * oopSize); 1024 } 1025 // The real maximum survivor size is bounded by the number of regions that can 1026 // be allocated into. 1027 _max_survivor_regions = MIN2(desired_max_survivor_regions, 1028 _g1h->num_free_or_available_regions()); 1029 } 1030 1031 bool G1Policy::force_concurrent_start_if_outside_cycle(GCCause::Cause gc_cause) { 1032 // We actually check whether we are marking here and not if we are in a 1033 // reclamation phase. This means that we will schedule a concurrent mark 1034 // even while we are still in the process of reclaiming memory. 1035 bool during_cycle = _g1h->concurrent_mark()->cm_thread()->during_cycle(); 1036 if (!during_cycle) { 1037 log_debug(gc, ergo)("Request concurrent cycle initiation (requested by GC cause). " 1038 "GC cause: %s", 1039 GCCause::to_string(gc_cause)); 1040 collector_state()->set_initiate_conc_mark_if_possible(true); 1041 return true; 1042 } else { 1043 log_debug(gc, ergo)("Do not request concurrent cycle initiation " 1044 "(concurrent cycle already in progress). GC cause: %s", 1045 GCCause::to_string(gc_cause)); 1046 return false; 1047 } 1048 } 1049 1050 void G1Policy::initiate_conc_mark() { 1051 collector_state()->set_in_concurrent_start_gc(true); 1052 collector_state()->set_initiate_conc_mark_if_possible(false); 1053 } 1054 1055 void G1Policy::decide_on_conc_mark_initiation() { 1056 // We are about to decide on whether this pause will be a 1057 // concurrent start pause. 1058 1059 // First, collector_state()->in_concurrent_start_gc() should not be already set. We 1060 // will set it here if we have to. However, it should be cleared by 1061 // the end of the pause (it's only set for the duration of a 1062 // concurrent start pause). 1063 assert(!collector_state()->in_concurrent_start_gc(), "pre-condition"); 1064 1065 if (collector_state()->initiate_conc_mark_if_possible()) { 1066 // We had noticed on a previous pause that the heap occupancy has 1067 // gone over the initiating threshold and we should start a 1068 // concurrent marking cycle. Or we've been explicitly requested 1069 // to start a concurrent marking cycle. Either way, we initiate 1070 // one if not inhibited for some reason. 1071 1072 GCCause::Cause cause = _g1h->gc_cause(); 1073 if ((cause != GCCause::_wb_breakpoint) && 1074 ConcurrentGCBreakpoints::is_controlled()) { 1075 log_debug(gc, ergo)("Do not initiate concurrent cycle (whitebox controlled)"); 1076 } else if (!about_to_start_mixed_phase() && collector_state()->in_young_only_phase()) { 1077 // Initiate a new concurrent start if there is no marking or reclamation going on. 1078 initiate_conc_mark(); 1079 log_debug(gc, ergo)("Initiate concurrent cycle (concurrent cycle initiation requested)"); 1080 } else if (_g1h->is_user_requested_concurrent_full_gc(cause) || 1081 (cause == GCCause::_wb_breakpoint)) { 1082 // Initiate a user requested concurrent start or run to a breakpoint. 1083 // A concurrent start must be young only GC, so the collector state 1084 // must be updated to reflect this. 1085 collector_state()->set_in_young_only_phase(true); 1086 collector_state()->set_in_young_gc_before_mixed(false); 1087 1088 // We might have ended up coming here about to start a mixed phase with a collection set 1089 // active. The following remark might change the change the "evacuation efficiency" of 1090 // the regions in this set, leading to failing asserts later. 1091 // Since the concurrent cycle will recreate the collection set anyway, simply drop it here. 1092 clear_collection_set_candidates(); 1093 abort_time_to_mixed_tracking(); 1094 initiate_conc_mark(); 1095 log_debug(gc, ergo)("Initiate concurrent cycle (%s requested concurrent cycle)", 1096 (cause == GCCause::_wb_breakpoint) ? "run_to breakpoint" : "user"); 1097 } else { 1098 // The concurrent marking thread is still finishing up the 1099 // previous cycle. If we start one right now the two cycles 1100 // overlap. In particular, the concurrent marking thread might 1101 // be in the process of clearing the next marking bitmap (which 1102 // we will use for the next cycle if we start one). Starting a 1103 // cycle now will be bad given that parts of the marking 1104 // information might get cleared by the marking thread. And we 1105 // cannot wait for the marking thread to finish the cycle as it 1106 // periodically yields while clearing the next marking bitmap 1107 // and, if it's in a yield point, it's waiting for us to 1108 // finish. So, at this point we will not start a cycle and we'll 1109 // let the concurrent marking thread complete the last one. 1110 log_debug(gc, ergo)("Do not initiate concurrent cycle (concurrent cycle already in progress)"); 1111 } 1112 } 1113 } 1114 1115 void G1Policy::record_concurrent_mark_cleanup_end() { 1116 G1CollectionSetCandidates* candidates = G1CollectionSetChooser::build(_g1h->workers(), _g1h->num_regions()); 1117 _collection_set->set_candidates(candidates); 1118 1119 bool mixed_gc_pending = next_gc_should_be_mixed("request mixed gcs", "request young-only gcs"); 1120 if (!mixed_gc_pending) { 1121 clear_collection_set_candidates(); 1122 abort_time_to_mixed_tracking(); 1123 } 1124 collector_state()->set_in_young_gc_before_mixed(mixed_gc_pending); 1125 collector_state()->set_mark_or_rebuild_in_progress(false); 1126 1127 double end_sec = os::elapsedTime(); 1128 double elapsed_time_ms = (end_sec - _mark_cleanup_start_sec) * 1000.0; 1129 _analytics->report_concurrent_mark_cleanup_times_ms(elapsed_time_ms); 1130 _analytics->append_prev_collection_pause_end_ms(elapsed_time_ms); 1131 1132 record_pause(Cleanup, _mark_cleanup_start_sec, end_sec); 1133 } 1134 1135 double G1Policy::reclaimable_bytes_percent(size_t reclaimable_bytes) const { 1136 return percent_of(reclaimable_bytes, _g1h->capacity()); 1137 } 1138 1139 class G1ClearCollectionSetCandidateRemSets : public HeapRegionClosure { 1140 virtual bool do_heap_region(HeapRegion* r) { 1141 r->rem_set()->clear_locked(true /* only_cardset */); 1142 return false; 1143 } 1144 }; 1145 1146 void G1Policy::clear_collection_set_candidates() { 1147 // Clear remembered sets of remaining candidate regions and the actual candidate 1148 // set. 1149 G1ClearCollectionSetCandidateRemSets cl; 1150 _collection_set->candidates()->iterate(&cl); 1151 _collection_set->clear_candidates(); 1152 } 1153 1154 void G1Policy::maybe_start_marking() { 1155 if (need_to_start_conc_mark("end of GC")) { 1156 // Note: this might have already been set, if during the last 1157 // pause we decided to start a cycle but at the beginning of 1158 // this pause we decided to postpone it. That's OK. 1159 collector_state()->set_initiate_conc_mark_if_possible(true); 1160 } 1161 } 1162 1163 bool G1Policy::is_young_only_pause(PauseKind kind) { 1164 assert(kind != FullGC, "must be"); 1165 assert(kind != Remark, "must be"); 1166 assert(kind != Cleanup, "must be"); 1167 return kind == ConcurrentStartGC || kind == LastYoungGC || kind == YoungOnlyGC; 1168 } 1169 1170 bool G1Policy::is_mixed_pause(PauseKind kind) { 1171 assert(kind != FullGC, "must be"); 1172 assert(kind != Remark, "must be"); 1173 assert(kind != Cleanup, "must be"); 1174 return kind == MixedGC; 1175 } 1176 1177 bool G1Policy::is_last_young_pause(PauseKind kind) { 1178 return kind == LastYoungGC; 1179 } 1180 1181 bool G1Policy::is_concurrent_start_pause(PauseKind kind) { 1182 return kind == ConcurrentStartGC; 1183 } 1184 1185 G1Policy::PauseKind G1Policy::young_gc_pause_kind() const { 1186 assert(!collector_state()->in_full_gc(), "must be"); 1187 if (collector_state()->in_concurrent_start_gc()) { 1188 assert(!collector_state()->in_young_gc_before_mixed(), "must be"); 1189 return ConcurrentStartGC; 1190 } else if (collector_state()->in_young_gc_before_mixed()) { 1191 assert(!collector_state()->in_concurrent_start_gc(), "must be"); 1192 return LastYoungGC; 1193 } else if (collector_state()->in_mixed_phase()) { 1194 assert(!collector_state()->in_concurrent_start_gc(), "must be"); 1195 assert(!collector_state()->in_young_gc_before_mixed(), "must be"); 1196 return MixedGC; 1197 } else { 1198 assert(!collector_state()->in_concurrent_start_gc(), "must be"); 1199 assert(!collector_state()->in_young_gc_before_mixed(), "must be"); 1200 return YoungOnlyGC; 1201 } 1202 } 1203 1204 void G1Policy::record_pause(PauseKind kind, double start, double end) { 1205 // Manage the MMU tracker. For some reason it ignores Full GCs. 1206 if (kind != FullGC) { 1207 _mmu_tracker->add_pause(start, end); 1208 } 1209 // Manage the mutator time tracking from concurrent start to first mixed gc. 1210 switch (kind) { 1211 case FullGC: 1212 abort_time_to_mixed_tracking(); 1213 break; 1214 case Cleanup: 1215 case Remark: 1216 case YoungOnlyGC: 1217 case LastYoungGC: 1218 _concurrent_start_to_mixed.add_pause(end - start); 1219 break; 1220 case ConcurrentStartGC: 1221 if (_g1h->gc_cause() != GCCause::_g1_periodic_collection) { 1222 _concurrent_start_to_mixed.record_concurrent_start_end(end); 1223 } 1224 break; 1225 case MixedGC: 1226 _concurrent_start_to_mixed.record_mixed_gc_start(start); 1227 break; 1228 default: 1229 ShouldNotReachHere(); 1230 } 1231 } 1232 1233 void G1Policy::abort_time_to_mixed_tracking() { 1234 _concurrent_start_to_mixed.reset(); 1235 } 1236 1237 bool G1Policy::next_gc_should_be_mixed(const char* true_action_str, 1238 const char* false_action_str) const { 1239 G1CollectionSetCandidates* candidates = _collection_set->candidates(); 1240 1241 if (candidates->is_empty()) { 1242 log_debug(gc, ergo)("%s (candidate old regions not available)", false_action_str); 1243 return false; 1244 } 1245 1246 // Is the amount of uncollected reclaimable space above G1HeapWastePercent? 1247 size_t reclaimable_bytes = candidates->remaining_reclaimable_bytes(); 1248 double reclaimable_percent = reclaimable_bytes_percent(reclaimable_bytes); 1249 double threshold = (double) G1HeapWastePercent; 1250 if (reclaimable_percent <= threshold) { 1251 log_debug(gc, ergo)("%s (reclaimable percentage not over threshold). candidate old regions: %u reclaimable: " SIZE_FORMAT " (%1.2f) threshold: " UINTX_FORMAT, 1252 false_action_str, candidates->num_remaining(), reclaimable_bytes, reclaimable_percent, G1HeapWastePercent); 1253 return false; 1254 } 1255 log_debug(gc, ergo)("%s (candidate old regions available). candidate old regions: %u reclaimable: " SIZE_FORMAT " (%1.2f) threshold: " UINTX_FORMAT, 1256 true_action_str, candidates->num_remaining(), reclaimable_bytes, reclaimable_percent, G1HeapWastePercent); 1257 return true; 1258 } 1259 1260 uint G1Policy::calc_min_old_cset_length() const { 1261 // The min old CSet region bound is based on the maximum desired 1262 // number of mixed GCs after a cycle. I.e., even if some old regions 1263 // look expensive, we should add them to the CSet anyway to make 1264 // sure we go through the available old regions in no more than the 1265 // maximum desired number of mixed GCs. 1266 // 1267 // The calculation is based on the number of marked regions we added 1268 // to the CSet candidates in the first place, not how many remain, so 1269 // that the result is the same during all mixed GCs that follow a cycle. 1270 1271 const size_t region_num = _collection_set->candidates()->num_regions(); 1272 const size_t gc_num = (size_t) MAX2(G1MixedGCCountTarget, (uintx) 1); 1273 size_t result = region_num / gc_num; 1274 // emulate ceiling 1275 if (result * gc_num < region_num) { 1276 result += 1; 1277 } 1278 return (uint) result; 1279 } 1280 1281 uint G1Policy::calc_max_old_cset_length() const { 1282 // The max old CSet region bound is based on the threshold expressed 1283 // as a percentage of the heap size. I.e., it should bound the 1284 // number of old regions added to the CSet irrespective of how many 1285 // of them are available. 1286 1287 const G1CollectedHeap* g1h = G1CollectedHeap::heap(); 1288 const size_t region_num = g1h->num_regions(); 1289 const size_t perc = (size_t) G1OldCSetRegionThresholdPercent; 1290 size_t result = region_num * perc / 100; 1291 // emulate ceiling 1292 if (100 * result < region_num * perc) { 1293 result += 1; 1294 } 1295 return (uint) result; 1296 } 1297 1298 void G1Policy::calculate_old_collection_set_regions(G1CollectionSetCandidates* candidates, 1299 double time_remaining_ms, 1300 uint& num_initial_regions, 1301 uint& num_optional_regions) { 1302 assert(candidates != NULL, "Must be"); 1303 1304 num_initial_regions = 0; 1305 num_optional_regions = 0; 1306 uint num_expensive_regions = 0; 1307 1308 double predicted_old_time_ms = 0.0; 1309 double predicted_initial_time_ms = 0.0; 1310 double predicted_optional_time_ms = 0.0; 1311 1312 double optional_threshold_ms = time_remaining_ms * optional_prediction_fraction(); 1313 1314 const uint min_old_cset_length = calc_min_old_cset_length(); 1315 const uint max_old_cset_length = MAX2(min_old_cset_length, calc_max_old_cset_length()); 1316 const uint max_optional_regions = max_old_cset_length - min_old_cset_length; 1317 bool check_time_remaining = use_adaptive_young_list_length(); 1318 1319 uint candidate_idx = candidates->cur_idx(); 1320 1321 log_debug(gc, ergo, cset)("Start adding old regions to collection set. Min %u regions, max %u regions, " 1322 "time remaining %1.2fms, optional threshold %1.2fms", 1323 min_old_cset_length, max_old_cset_length, time_remaining_ms, optional_threshold_ms); 1324 1325 HeapRegion* hr = candidates->at(candidate_idx); 1326 while (hr != NULL) { 1327 if (num_initial_regions + num_optional_regions >= max_old_cset_length) { 1328 // Added maximum number of old regions to the CSet. 1329 log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Maximum number of regions). " 1330 "Initial %u regions, optional %u regions", 1331 num_initial_regions, num_optional_regions); 1332 break; 1333 } 1334 1335 // Stop adding regions if the remaining reclaimable space is 1336 // not above G1HeapWastePercent. 1337 size_t reclaimable_bytes = candidates->remaining_reclaimable_bytes(); 1338 double reclaimable_percent = reclaimable_bytes_percent(reclaimable_bytes); 1339 double threshold = (double) G1HeapWastePercent; 1340 if (reclaimable_percent <= threshold) { 1341 // We've added enough old regions that the amount of uncollected 1342 // reclaimable space is at or below the waste threshold. Stop 1343 // adding old regions to the CSet. 1344 log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Reclaimable percentage below threshold). " 1345 "Reclaimable: " SIZE_FORMAT "%s (%1.2f%%) threshold: " UINTX_FORMAT "%%", 1346 byte_size_in_proper_unit(reclaimable_bytes), proper_unit_for_byte_size(reclaimable_bytes), 1347 reclaimable_percent, G1HeapWastePercent); 1348 break; 1349 } 1350 1351 double predicted_time_ms = predict_region_total_time_ms(hr, false); 1352 time_remaining_ms = MAX2(time_remaining_ms - predicted_time_ms, 0.0); 1353 // Add regions to old set until we reach the minimum amount 1354 if (num_initial_regions < min_old_cset_length) { 1355 predicted_old_time_ms += predicted_time_ms; 1356 num_initial_regions++; 1357 // Record the number of regions added with no time remaining 1358 if (time_remaining_ms == 0.0) { 1359 num_expensive_regions++; 1360 } 1361 } else if (!check_time_remaining) { 1362 // In the non-auto-tuning case, we'll finish adding regions 1363 // to the CSet if we reach the minimum. 1364 log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Region amount reached min)."); 1365 break; 1366 } else { 1367 // Keep adding regions to old set until we reach the optional threshold 1368 if (time_remaining_ms > optional_threshold_ms) { 1369 predicted_old_time_ms += predicted_time_ms; 1370 num_initial_regions++; 1371 } else if (time_remaining_ms > 0) { 1372 // Keep adding optional regions until time is up. 1373 assert(num_optional_regions < max_optional_regions, "Should not be possible."); 1374 predicted_optional_time_ms += predicted_time_ms; 1375 num_optional_regions++; 1376 } else { 1377 log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Predicted time too high)."); 1378 break; 1379 } 1380 } 1381 hr = candidates->at(++candidate_idx); 1382 } 1383 if (hr == NULL) { 1384 log_debug(gc, ergo, cset)("Old candidate collection set empty."); 1385 } 1386 1387 if (num_expensive_regions > 0) { 1388 log_debug(gc, ergo, cset)("Added %u initial old regions to collection set although the predicted time was too high.", 1389 num_expensive_regions); 1390 } 1391 1392 log_debug(gc, ergo, cset)("Finish choosing collection set old regions. Initial: %u, optional: %u, " 1393 "predicted old time: %1.2fms, predicted optional time: %1.2fms, time remaining: %1.2f", 1394 num_initial_regions, num_optional_regions, 1395 predicted_initial_time_ms, predicted_optional_time_ms, time_remaining_ms); 1396 } 1397 1398 void G1Policy::calculate_optional_collection_set_regions(G1CollectionSetCandidates* candidates, 1399 uint const max_optional_regions, 1400 double time_remaining_ms, 1401 uint& num_optional_regions) { 1402 assert(_g1h->collector_state()->in_mixed_phase(), "Should only be called in mixed phase"); 1403 1404 num_optional_regions = 0; 1405 double prediction_ms = 0; 1406 uint candidate_idx = candidates->cur_idx(); 1407 1408 HeapRegion* r = candidates->at(candidate_idx); 1409 while (num_optional_regions < max_optional_regions) { 1410 assert(r != NULL, "Region must exist"); 1411 prediction_ms += predict_region_total_time_ms(r, false); 1412 1413 if (prediction_ms > time_remaining_ms) { 1414 log_debug(gc, ergo, cset)("Prediction %.3fms for region %u does not fit remaining time: %.3fms.", 1415 prediction_ms, r->hrm_index(), time_remaining_ms); 1416 break; 1417 } 1418 // This region will be included in the next optional evacuation. 1419 1420 time_remaining_ms -= prediction_ms; 1421 num_optional_regions++; 1422 r = candidates->at(++candidate_idx); 1423 } 1424 1425 log_debug(gc, ergo, cset)("Prepared %u regions out of %u for optional evacuation. Predicted time: %.3fms", 1426 num_optional_regions, max_optional_regions, prediction_ms); 1427 } 1428 1429 void G1Policy::transfer_survivors_to_cset(const G1SurvivorRegions* survivors) { 1430 note_start_adding_survivor_regions(); 1431 1432 HeapRegion* last = NULL; 1433 for (GrowableArrayIterator<HeapRegion*> it = survivors->regions()->begin(); 1434 it != survivors->regions()->end(); 1435 ++it) { 1436 HeapRegion* curr = *it; 1437 set_region_survivor(curr); 1438 1439 // The region is a non-empty survivor so let's add it to 1440 // the incremental collection set for the next evacuation 1441 // pause. 1442 _collection_set->add_survivor_regions(curr); 1443 1444 last = curr; 1445 } 1446 note_stop_adding_survivor_regions(); 1447 1448 // Don't clear the survivor list handles until the start of 1449 // the next evacuation pause - we need it in order to re-tag 1450 // the survivor regions from this evacuation pause as 'young' 1451 // at the start of the next. 1452 }