1 /* 2 * Copyright (c) 2001, 2016, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #include "precompiled.hpp" 26 #include "gc/g1/concurrentG1Refine.hpp" 27 #include "gc/g1/concurrentMarkThread.inline.hpp" 28 #include "gc/g1/g1Analytics.hpp" 29 #include "gc/g1/g1CollectedHeap.inline.hpp" 30 #include "gc/g1/g1CollectionSet.hpp" 31 #include "gc/g1/g1CollectorPolicy.hpp" 32 #include "gc/g1/g1ConcurrentMark.hpp" 33 #include "gc/g1/g1IHOPControl.hpp" 34 #include "gc/g1/g1GCPhaseTimes.hpp" 35 #include "gc/g1/g1YoungGenSizer.hpp" 36 #include "gc/g1/heapRegion.inline.hpp" 37 #include "gc/g1/heapRegionRemSet.hpp" 38 #include "gc/shared/gcPolicyCounters.hpp" 39 #include "runtime/arguments.hpp" 40 #include "runtime/java.hpp" 41 #include "runtime/mutexLocker.hpp" 42 #include "utilities/debug.hpp" 43 #include "utilities/pair.hpp" 44 45 G1CollectorPolicy::G1CollectorPolicy() : 46 _predictor(G1ConfidencePercent / 100.0), 47 _analytics(new G1Analytics(&_predictor)), 48 _pause_time_target_ms((double) MaxGCPauseMillis), 49 _rs_lengths_prediction(0), 50 _max_survivor_regions(0), 51 _survivors_age_table(true), 52 53 _bytes_allocated_in_old_since_last_gc(0), 54 _ihop_control(NULL), 55 _initial_mark_to_mixed() { 56 57 // SurvRateGroups below must be initialized after the predictor because they 58 // indirectly use it through this object passed to their constructor. 59 _short_lived_surv_rate_group = 60 new SurvRateGroup(&_predictor, "Short Lived", G1YoungSurvRateNumRegionsSummary); 61 _survivor_surv_rate_group = 62 new SurvRateGroup(&_predictor, "Survivor", G1YoungSurvRateNumRegionsSummary); 63 64 // Set up the region size and associated fields. Given that the 65 // policy is created before the heap, we have to set this up here, 66 // so it's done as soon as possible. 67 68 // It would have been natural to pass initial_heap_byte_size() and 69 // max_heap_byte_size() to setup_heap_region_size() but those have 70 // not been set up at this point since they should be aligned with 71 // the region size. So, there is a circular dependency here. We base 72 // the region size on the heap size, but the heap size should be 73 // aligned with the region size. To get around this we use the 74 // unaligned values for the heap. 75 HeapRegion::setup_heap_region_size(InitialHeapSize, MaxHeapSize); 76 HeapRegionRemSet::setup_remset_size(); 77 78 _phase_times = new G1GCPhaseTimes(ParallelGCThreads); 79 80 // Below, we might need to calculate the pause time target based on 81 // the pause interval. When we do so we are going to give G1 maximum 82 // flexibility and allow it to do pauses when it needs to. So, we'll 83 // arrange that the pause interval to be pause time target + 1 to 84 // ensure that a) the pause time target is maximized with respect to 85 // the pause interval and b) we maintain the invariant that pause 86 // time target < pause interval. If the user does not want this 87 // maximum flexibility, they will have to set the pause interval 88 // explicitly. 89 90 // First make sure that, if either parameter is set, its value is 91 // reasonable. 92 guarantee(MaxGCPauseMillis >= 1, "Range checking for MaxGCPauseMillis should guarantee that value is >= 1"); 93 94 // Then, if the pause time target parameter was not set, set it to 95 // the default value. 96 if (FLAG_IS_DEFAULT(MaxGCPauseMillis)) { 97 if (FLAG_IS_DEFAULT(GCPauseIntervalMillis)) { 98 // The default pause time target in G1 is 200ms 99 FLAG_SET_DEFAULT(MaxGCPauseMillis, 200); 100 } else { 101 // We do not allow the pause interval to be set without the 102 // pause time target 103 vm_exit_during_initialization("GCPauseIntervalMillis cannot be set " 104 "without setting MaxGCPauseMillis"); 105 } 106 } 107 108 // Then, if the interval parameter was not set, set it according to 109 // the pause time target (this will also deal with the case when the 110 // pause time target is the default value). 111 if (FLAG_IS_DEFAULT(GCPauseIntervalMillis)) { 112 FLAG_SET_DEFAULT(GCPauseIntervalMillis, MaxGCPauseMillis + 1); 113 } 114 guarantee(GCPauseIntervalMillis >= 1, "Constraint for GCPauseIntervalMillis should guarantee that value is >= 1"); 115 guarantee(GCPauseIntervalMillis > MaxGCPauseMillis, "Constraint for GCPauseIntervalMillis should guarantee that GCPauseIntervalMillis > MaxGCPauseMillis"); 116 117 double max_gc_time = (double) MaxGCPauseMillis / 1000.0; 118 double time_slice = (double) GCPauseIntervalMillis / 1000.0; 119 _mmu_tracker = new G1MMUTrackerQueue(time_slice, max_gc_time); 120 121 _tenuring_threshold = MaxTenuringThreshold; 122 123 124 guarantee(G1ReservePercent <= 50, "Range checking should not allow values over 50."); 125 _reserve_factor = (double) G1ReservePercent / 100.0; 126 // This will be set when the heap is expanded 127 // for the first time during initialization. 128 _reserve_regions = 0; 129 130 _ihop_control = create_ihop_control(); 131 } 132 133 G1CollectorPolicy::~G1CollectorPolicy() { 134 delete _ihop_control; 135 } 136 137 void G1CollectorPolicy::initialize_alignments() { 138 _space_alignment = HeapRegion::GrainBytes; 139 size_t card_table_alignment = CardTableRS::ct_max_alignment_constraint(); 140 size_t page_size = UseLargePages ? os::large_page_size() : os::vm_page_size(); 141 _heap_alignment = MAX3(card_table_alignment, _space_alignment, page_size); 142 } 143 144 G1CollectorState* G1CollectorPolicy::collector_state() const { return _g1->collector_state(); } 145 146 void G1CollectorPolicy::post_heap_initialize() { 147 uintx max_regions = G1CollectedHeap::heap()->max_regions(); 148 size_t max_young_size = (size_t)_young_gen_sizer->max_young_length(max_regions) * HeapRegion::GrainBytes; 149 if (max_young_size != MaxNewSize) { 150 FLAG_SET_ERGO(size_t, MaxNewSize, max_young_size); 151 } 152 } 153 154 void G1CollectorPolicy::initialize_flags() { 155 if (G1HeapRegionSize != HeapRegion::GrainBytes) { 156 FLAG_SET_ERGO(size_t, G1HeapRegionSize, HeapRegion::GrainBytes); 157 } 158 159 guarantee(SurvivorRatio >= 1, "Range checking for SurvivorRatio should guarantee that value is >= 1"); 160 161 CollectorPolicy::initialize_flags(); 162 _young_gen_sizer = new G1YoungGenSizer(); // Must be after call to initialize_flags 163 } 164 165 166 void G1CollectorPolicy::init() { 167 // Set aside an initial future to_space. 168 _g1 = G1CollectedHeap::heap(); 169 _collection_set = _g1->collection_set(); 170 _collection_set->set_policy(this); 171 172 assert(Heap_lock->owned_by_self(), "Locking discipline."); 173 174 initialize_gc_policy_counters(); 175 176 if (adaptive_young_list_length()) { 177 _young_list_fixed_length = 0; 178 } else { 179 _young_list_fixed_length = _young_gen_sizer->min_desired_young_length(); 180 } 181 _free_regions_at_end_of_collection = _g1->num_free_regions(); 182 183 update_young_list_max_and_target_length(); 184 // We may immediately start allocating regions and placing them on the 185 // collection set list. Initialize the per-collection set info 186 _collection_set->start_incremental_building(); 187 } 188 189 void G1CollectorPolicy::note_gc_start(uint num_active_workers) { 190 phase_times()->note_gc_start(num_active_workers); 191 } 192 193 // Create the jstat counters for the policy. 194 void G1CollectorPolicy::initialize_gc_policy_counters() { 195 _gc_policy_counters = new GCPolicyCounters("GarbageFirst", 1, 3); 196 } 197 198 bool G1CollectorPolicy::predict_will_fit(uint young_length, 199 double base_time_ms, 200 uint base_free_regions, 201 double target_pause_time_ms) const { 202 if (young_length >= base_free_regions) { 203 // end condition 1: not enough space for the young regions 204 return false; 205 } 206 207 double accum_surv_rate = accum_yg_surv_rate_pred((int) young_length - 1); 208 size_t bytes_to_copy = 209 (size_t) (accum_surv_rate * (double) HeapRegion::GrainBytes); 210 double copy_time_ms = _analytics->predict_object_copy_time_ms(bytes_to_copy, 211 collector_state()->during_concurrent_mark()); 212 double young_other_time_ms = _analytics->predict_young_other_time_ms(young_length); 213 double pause_time_ms = base_time_ms + copy_time_ms + young_other_time_ms; 214 if (pause_time_ms > target_pause_time_ms) { 215 // end condition 2: prediction is over the target pause time 216 return false; 217 } 218 219 size_t free_bytes = (base_free_regions - young_length) * HeapRegion::GrainBytes; 220 221 // When copying, we will likely need more bytes free than is live in the region. 222 // Add some safety margin to factor in the confidence of our guess, and the 223 // natural expected waste. 224 // (100.0 / G1ConfidencePercent) is a scale factor that expresses the uncertainty 225 // of the calculation: the lower the confidence, the more headroom. 226 // (100 + TargetPLABWastePct) represents the increase in expected bytes during 227 // copying due to anticipated waste in the PLABs. 228 double safety_factor = (100.0 / G1ConfidencePercent) * (100 + TargetPLABWastePct) / 100.0; 229 size_t expected_bytes_to_copy = (size_t)(safety_factor * bytes_to_copy); 230 231 if (expected_bytes_to_copy > free_bytes) { 232 // end condition 3: out-of-space 233 return false; 234 } 235 236 // success! 237 return true; 238 } 239 240 void G1CollectorPolicy::record_new_heap_size(uint new_number_of_regions) { 241 // re-calculate the necessary reserve 242 double reserve_regions_d = (double) new_number_of_regions * _reserve_factor; 243 // We use ceiling so that if reserve_regions_d is > 0.0 (but 244 // smaller than 1.0) we'll get 1. 245 _reserve_regions = (uint) ceil(reserve_regions_d); 246 247 _young_gen_sizer->heap_size_changed(new_number_of_regions); 248 249 _ihop_control->update_target_occupancy(new_number_of_regions * HeapRegion::GrainBytes); 250 } 251 252 uint G1CollectorPolicy::calculate_young_list_desired_min_length( 253 uint base_min_length) const { 254 uint desired_min_length = 0; 255 if (adaptive_young_list_length()) { 256 if (_analytics->num_alloc_rate_ms() > 3) { 257 double now_sec = os::elapsedTime(); 258 double when_ms = _mmu_tracker->when_max_gc_sec(now_sec) * 1000.0; 259 double alloc_rate_ms = _analytics->predict_alloc_rate_ms(); 260 desired_min_length = (uint) ceil(alloc_rate_ms * when_ms); 261 } else { 262 // otherwise we don't have enough info to make the prediction 263 } 264 } 265 desired_min_length += base_min_length; 266 // make sure we don't go below any user-defined minimum bound 267 return MAX2(_young_gen_sizer->min_desired_young_length(), desired_min_length); 268 } 269 270 uint G1CollectorPolicy::calculate_young_list_desired_max_length() const { 271 // Here, we might want to also take into account any additional 272 // constraints (i.e., user-defined minimum bound). Currently, we 273 // effectively don't set this bound. 274 return _young_gen_sizer->max_desired_young_length(); 275 } 276 277 uint G1CollectorPolicy::update_young_list_max_and_target_length() { 278 return update_young_list_max_and_target_length(_analytics->predict_rs_lengths()); 279 } 280 281 uint G1CollectorPolicy::update_young_list_max_and_target_length(size_t rs_lengths) { 282 uint unbounded_target_length = update_young_list_target_length(rs_lengths); 283 update_max_gc_locker_expansion(); 284 return unbounded_target_length; 285 } 286 287 uint G1CollectorPolicy::update_young_list_target_length(size_t rs_lengths) { 288 YoungTargetLengths young_lengths = young_list_target_lengths(rs_lengths); 289 _young_list_target_length = young_lengths.first; 290 return young_lengths.second; 291 } 292 293 G1CollectorPolicy::YoungTargetLengths G1CollectorPolicy::young_list_target_lengths(size_t rs_lengths) const { 294 YoungTargetLengths result; 295 296 // Calculate the absolute and desired min bounds first. 297 298 // This is how many young regions we already have (currently: the survivors). 299 const uint base_min_length = _g1->young_list()->survivor_length(); 300 uint desired_min_length = calculate_young_list_desired_min_length(base_min_length); 301 // This is the absolute minimum young length. Ensure that we 302 // will at least have one eden region available for allocation. 303 uint absolute_min_length = base_min_length + MAX2(_g1->young_list()->eden_length(), (uint)1); 304 // If we shrank the young list target it should not shrink below the current size. 305 desired_min_length = MAX2(desired_min_length, absolute_min_length); 306 // Calculate the absolute and desired max bounds. 307 308 uint desired_max_length = calculate_young_list_desired_max_length(); 309 310 uint young_list_target_length = 0; 311 if (adaptive_young_list_length()) { 312 if (collector_state()->gcs_are_young()) { 313 young_list_target_length = 314 calculate_young_list_target_length(rs_lengths, 315 base_min_length, 316 desired_min_length, 317 desired_max_length); 318 } else { 319 // Don't calculate anything and let the code below bound it to 320 // the desired_min_length, i.e., do the next GC as soon as 321 // possible to maximize how many old regions we can add to it. 322 } 323 } else { 324 // The user asked for a fixed young gen so we'll fix the young gen 325 // whether the next GC is young or mixed. 326 young_list_target_length = _young_list_fixed_length; 327 } 328 329 result.second = young_list_target_length; 330 331 // We will try our best not to "eat" into the reserve. 332 uint absolute_max_length = 0; 333 if (_free_regions_at_end_of_collection > _reserve_regions) { 334 absolute_max_length = _free_regions_at_end_of_collection - _reserve_regions; 335 } 336 if (desired_max_length > absolute_max_length) { 337 desired_max_length = absolute_max_length; 338 } 339 340 // Make sure we don't go over the desired max length, nor under the 341 // desired min length. In case they clash, desired_min_length wins 342 // which is why that test is second. 343 if (young_list_target_length > desired_max_length) { 344 young_list_target_length = desired_max_length; 345 } 346 if (young_list_target_length < desired_min_length) { 347 young_list_target_length = desired_min_length; 348 } 349 350 assert(young_list_target_length > base_min_length, 351 "we should be able to allocate at least one eden region"); 352 assert(young_list_target_length >= absolute_min_length, "post-condition"); 353 354 result.first = young_list_target_length; 355 return result; 356 } 357 358 uint 359 G1CollectorPolicy::calculate_young_list_target_length(size_t rs_lengths, 360 uint base_min_length, 361 uint desired_min_length, 362 uint desired_max_length) const { 363 assert(adaptive_young_list_length(), "pre-condition"); 364 assert(collector_state()->gcs_are_young(), "only call this for young GCs"); 365 366 // In case some edge-condition makes the desired max length too small... 367 if (desired_max_length <= desired_min_length) { 368 return desired_min_length; 369 } 370 371 // We'll adjust min_young_length and max_young_length not to include 372 // the already allocated young regions (i.e., so they reflect the 373 // min and max eden regions we'll allocate). The base_min_length 374 // will be reflected in the predictions by the 375 // survivor_regions_evac_time prediction. 376 assert(desired_min_length > base_min_length, "invariant"); 377 uint min_young_length = desired_min_length - base_min_length; 378 assert(desired_max_length > base_min_length, "invariant"); 379 uint max_young_length = desired_max_length - base_min_length; 380 381 double target_pause_time_ms = _mmu_tracker->max_gc_time() * 1000.0; 382 double survivor_regions_evac_time = predict_survivor_regions_evac_time(); 383 size_t pending_cards = _analytics->predict_pending_cards(); 384 size_t adj_rs_lengths = rs_lengths + _analytics->predict_rs_length_diff(); 385 size_t scanned_cards = _analytics->predict_card_num(adj_rs_lengths, /* gcs_are_young */ true); 386 double base_time_ms = 387 predict_base_elapsed_time_ms(pending_cards, scanned_cards) + 388 survivor_regions_evac_time; 389 uint available_free_regions = _free_regions_at_end_of_collection; 390 uint base_free_regions = 0; 391 if (available_free_regions > _reserve_regions) { 392 base_free_regions = available_free_regions - _reserve_regions; 393 } 394 395 // Here, we will make sure that the shortest young length that 396 // makes sense fits within the target pause time. 397 398 if (predict_will_fit(min_young_length, base_time_ms, 399 base_free_regions, target_pause_time_ms)) { 400 // The shortest young length will fit into the target pause time; 401 // we'll now check whether the absolute maximum number of young 402 // regions will fit in the target pause time. If not, we'll do 403 // a binary search between min_young_length and max_young_length. 404 if (predict_will_fit(max_young_length, base_time_ms, 405 base_free_regions, target_pause_time_ms)) { 406 // The maximum young length will fit into the target pause time. 407 // We are done so set min young length to the maximum length (as 408 // the result is assumed to be returned in min_young_length). 409 min_young_length = max_young_length; 410 } else { 411 // The maximum possible number of young regions will not fit within 412 // the target pause time so we'll search for the optimal 413 // length. The loop invariants are: 414 // 415 // min_young_length < max_young_length 416 // min_young_length is known to fit into the target pause time 417 // max_young_length is known not to fit into the target pause time 418 // 419 // Going into the loop we know the above hold as we've just 420 // checked them. Every time around the loop we check whether 421 // the middle value between min_young_length and 422 // max_young_length fits into the target pause time. If it 423 // does, it becomes the new min. If it doesn't, it becomes 424 // the new max. This way we maintain the loop invariants. 425 426 assert(min_young_length < max_young_length, "invariant"); 427 uint diff = (max_young_length - min_young_length) / 2; 428 while (diff > 0) { 429 uint young_length = min_young_length + diff; 430 if (predict_will_fit(young_length, base_time_ms, 431 base_free_regions, target_pause_time_ms)) { 432 min_young_length = young_length; 433 } else { 434 max_young_length = young_length; 435 } 436 assert(min_young_length < max_young_length, "invariant"); 437 diff = (max_young_length - min_young_length) / 2; 438 } 439 // The results is min_young_length which, according to the 440 // loop invariants, should fit within the target pause time. 441 442 // These are the post-conditions of the binary search above: 443 assert(min_young_length < max_young_length, 444 "otherwise we should have discovered that max_young_length " 445 "fits into the pause target and not done the binary search"); 446 assert(predict_will_fit(min_young_length, base_time_ms, 447 base_free_regions, target_pause_time_ms), 448 "min_young_length, the result of the binary search, should " 449 "fit into the pause target"); 450 assert(!predict_will_fit(min_young_length + 1, base_time_ms, 451 base_free_regions, target_pause_time_ms), 452 "min_young_length, the result of the binary search, should be " 453 "optimal, so no larger length should fit into the pause target"); 454 } 455 } else { 456 // Even the minimum length doesn't fit into the pause time 457 // target, return it as the result nevertheless. 458 } 459 return base_min_length + min_young_length; 460 } 461 462 double G1CollectorPolicy::predict_survivor_regions_evac_time() const { 463 double survivor_regions_evac_time = 0.0; 464 for (HeapRegion * r = _g1->young_list()->first_survivor_region(); 465 r != NULL && r != _g1->young_list()->last_survivor_region()->get_next_young_region(); 466 r = r->get_next_young_region()) { 467 survivor_regions_evac_time += predict_region_elapsed_time_ms(r, collector_state()->gcs_are_young()); 468 } 469 return survivor_regions_evac_time; 470 } 471 472 void G1CollectorPolicy::revise_young_list_target_length_if_necessary(size_t rs_lengths) { 473 guarantee( adaptive_young_list_length(), "should not call this otherwise" ); 474 475 if (rs_lengths > _rs_lengths_prediction) { 476 // add 10% to avoid having to recalculate often 477 size_t rs_lengths_prediction = rs_lengths * 1100 / 1000; 478 update_rs_lengths_prediction(rs_lengths_prediction); 479 480 update_young_list_max_and_target_length(rs_lengths_prediction); 481 } 482 } 483 484 void G1CollectorPolicy::update_rs_lengths_prediction() { 485 update_rs_lengths_prediction(_analytics->predict_rs_lengths()); 486 } 487 488 void G1CollectorPolicy::update_rs_lengths_prediction(size_t prediction) { 489 if (collector_state()->gcs_are_young() && adaptive_young_list_length()) { 490 _rs_lengths_prediction = prediction; 491 } 492 } 493 494 #ifndef PRODUCT 495 bool G1CollectorPolicy::verify_young_ages() { 496 HeapRegion* head = _g1->young_list()->first_region(); 497 return 498 verify_young_ages(head, _short_lived_surv_rate_group); 499 // also call verify_young_ages on any additional surv rate groups 500 } 501 502 bool 503 G1CollectorPolicy::verify_young_ages(HeapRegion* head, 504 SurvRateGroup *surv_rate_group) { 505 guarantee( surv_rate_group != NULL, "pre-condition" ); 506 507 const char* name = surv_rate_group->name(); 508 bool ret = true; 509 int prev_age = -1; 510 511 for (HeapRegion* curr = head; 512 curr != NULL; 513 curr = curr->get_next_young_region()) { 514 SurvRateGroup* group = curr->surv_rate_group(); 515 if (group == NULL && !curr->is_survivor()) { 516 log_error(gc, verify)("## %s: encountered NULL surv_rate_group", name); 517 ret = false; 518 } 519 520 if (surv_rate_group == group) { 521 int age = curr->age_in_surv_rate_group(); 522 523 if (age < 0) { 524 log_error(gc, verify)("## %s: encountered negative age", name); 525 ret = false; 526 } 527 528 if (age <= prev_age) { 529 log_error(gc, verify)("## %s: region ages are not strictly increasing (%d, %d)", name, age, prev_age); 530 ret = false; 531 } 532 prev_age = age; 533 } 534 } 535 536 return ret; 537 } 538 #endif // PRODUCT 539 540 void G1CollectorPolicy::record_full_collection_start() { 541 _full_collection_start_sec = os::elapsedTime(); 542 // Release the future to-space so that it is available for compaction into. 543 collector_state()->set_full_collection(true); 544 } 545 546 void G1CollectorPolicy::record_full_collection_end() { 547 // Consider this like a collection pause for the purposes of allocation 548 // since last pause. 549 double end_sec = os::elapsedTime(); 550 double full_gc_time_sec = end_sec - _full_collection_start_sec; 551 double full_gc_time_ms = full_gc_time_sec * 1000.0; 552 553 _analytics->update_recent_gc_times(end_sec, full_gc_time_ms); 554 555 collector_state()->set_full_collection(false); 556 557 // "Nuke" the heuristics that control the young/mixed GC 558 // transitions and make sure we start with young GCs after the Full GC. 559 collector_state()->set_gcs_are_young(true); 560 collector_state()->set_last_young_gc(false); 561 collector_state()->set_initiate_conc_mark_if_possible(need_to_start_conc_mark("end of Full GC", 0)); 562 collector_state()->set_during_initial_mark_pause(false); 563 collector_state()->set_in_marking_window(false); 564 collector_state()->set_in_marking_window_im(false); 565 566 _short_lived_surv_rate_group->start_adding_regions(); 567 // also call this on any additional surv rate groups 568 569 _free_regions_at_end_of_collection = _g1->num_free_regions(); 570 // Reset survivors SurvRateGroup. 571 _survivor_surv_rate_group->reset(); 572 update_young_list_max_and_target_length(); 573 update_rs_lengths_prediction(); 574 cset_chooser()->clear(); 575 576 _bytes_allocated_in_old_since_last_gc = 0; 577 578 record_pause(FullGC, _full_collection_start_sec, end_sec); 579 } 580 581 void G1CollectorPolicy::record_collection_pause_start(double start_time_sec) { 582 // We only need to do this here as the policy will only be applied 583 // to the GC we're about to start. so, no point is calculating this 584 // every time we calculate / recalculate the target young length. 585 update_survivors_policy(); 586 587 assert(_g1->used() == _g1->recalculate_used(), 588 "sanity, used: " SIZE_FORMAT " recalculate_used: " SIZE_FORMAT, 589 _g1->used(), _g1->recalculate_used()); 590 591 phase_times()->record_cur_collection_start_sec(start_time_sec); 592 _pending_cards = _g1->pending_card_num(); 593 594 _collection_set->reset_bytes_used_before(); 595 _bytes_copied_during_gc = 0; 596 597 collector_state()->set_last_gc_was_young(false); 598 599 // do that for any other surv rate groups 600 _short_lived_surv_rate_group->stop_adding_regions(); 601 _survivors_age_table.clear(); 602 603 assert( verify_young_ages(), "region age verification" ); 604 } 605 606 void G1CollectorPolicy::record_concurrent_mark_init_end(double 607 mark_init_elapsed_time_ms) { 608 collector_state()->set_during_marking(true); 609 assert(!collector_state()->initiate_conc_mark_if_possible(), "we should have cleared it by now"); 610 collector_state()->set_during_initial_mark_pause(false); 611 } 612 613 void G1CollectorPolicy::record_concurrent_mark_remark_start() { 614 _mark_remark_start_sec = os::elapsedTime(); 615 collector_state()->set_during_marking(false); 616 } 617 618 void G1CollectorPolicy::record_concurrent_mark_remark_end() { 619 double end_time_sec = os::elapsedTime(); 620 double elapsed_time_ms = (end_time_sec - _mark_remark_start_sec)*1000.0; 621 _analytics->report_concurrent_mark_remark_times_ms(elapsed_time_ms); 622 _analytics->append_prev_collection_pause_end_ms(elapsed_time_ms); 623 624 record_pause(Remark, _mark_remark_start_sec, end_time_sec); 625 } 626 627 void G1CollectorPolicy::record_concurrent_mark_cleanup_start() { 628 _mark_cleanup_start_sec = os::elapsedTime(); 629 } 630 631 void G1CollectorPolicy::record_concurrent_mark_cleanup_completed() { 632 bool should_continue_with_reclaim = next_gc_should_be_mixed("request last young-only gc", 633 "skip last young-only gc"); 634 collector_state()->set_last_young_gc(should_continue_with_reclaim); 635 // We skip the marking phase. 636 if (!should_continue_with_reclaim) { 637 abort_time_to_mixed_tracking(); 638 } 639 collector_state()->set_in_marking_window(false); 640 } 641 642 double G1CollectorPolicy::average_time_ms(G1GCPhaseTimes::GCParPhases phase) const { 643 return phase_times()->average_time_ms(phase); 644 } 645 646 double G1CollectorPolicy::young_other_time_ms() const { 647 return phase_times()->young_cset_choice_time_ms() + 648 phase_times()->young_free_cset_time_ms(); 649 } 650 651 double G1CollectorPolicy::non_young_other_time_ms() const { 652 return phase_times()->non_young_cset_choice_time_ms() + 653 phase_times()->non_young_free_cset_time_ms(); 654 655 } 656 657 double G1CollectorPolicy::other_time_ms(double pause_time_ms) const { 658 return pause_time_ms - 659 average_time_ms(G1GCPhaseTimes::UpdateRS) - 660 average_time_ms(G1GCPhaseTimes::ScanRS) - 661 average_time_ms(G1GCPhaseTimes::ObjCopy) - 662 average_time_ms(G1GCPhaseTimes::Termination); 663 } 664 665 double G1CollectorPolicy::constant_other_time_ms(double pause_time_ms) const { 666 return other_time_ms(pause_time_ms) - young_other_time_ms() - non_young_other_time_ms(); 667 } 668 669 CollectionSetChooser* G1CollectorPolicy::cset_chooser() const { 670 return _collection_set->cset_chooser(); 671 } 672 673 bool G1CollectorPolicy::about_to_start_mixed_phase() const { 674 return _g1->concurrent_mark()->cmThread()->during_cycle() || collector_state()->last_young_gc(); 675 } 676 677 bool G1CollectorPolicy::need_to_start_conc_mark(const char* source, size_t alloc_word_size) { 678 if (about_to_start_mixed_phase()) { 679 return false; 680 } 681 682 size_t marking_initiating_used_threshold = _ihop_control->get_conc_mark_start_threshold(); 683 684 size_t cur_used_bytes = _g1->non_young_capacity_bytes(); 685 size_t alloc_byte_size = alloc_word_size * HeapWordSize; 686 size_t marking_request_bytes = cur_used_bytes + alloc_byte_size; 687 688 bool result = false; 689 if (marking_request_bytes > marking_initiating_used_threshold) { 690 result = collector_state()->gcs_are_young() && !collector_state()->last_young_gc(); 691 log_debug(gc, ergo, ihop)("%s occupancy: " SIZE_FORMAT "B allocation request: " SIZE_FORMAT "B threshold: " SIZE_FORMAT "B (%1.2f) source: %s", 692 result ? "Request concurrent cycle initiation (occupancy higher than threshold)" : "Do not request concurrent cycle initiation (still doing mixed collections)", 693 cur_used_bytes, alloc_byte_size, marking_initiating_used_threshold, (double) marking_initiating_used_threshold / _g1->capacity() * 100, source); 694 } 695 696 return result; 697 } 698 699 // Anything below that is considered to be zero 700 #define MIN_TIMER_GRANULARITY 0.0000001 701 702 void G1CollectorPolicy::record_collection_pause_end(double pause_time_ms, size_t cards_scanned, size_t heap_used_bytes_before_gc) { 703 double end_time_sec = os::elapsedTime(); 704 705 size_t cur_used_bytes = _g1->used(); 706 assert(cur_used_bytes == _g1->recalculate_used(), "It should!"); 707 bool last_pause_included_initial_mark = false; 708 bool update_stats = !_g1->evacuation_failed(); 709 710 NOT_PRODUCT(_short_lived_surv_rate_group->print()); 711 712 record_pause(young_gc_pause_kind(), end_time_sec - pause_time_ms / 1000.0, end_time_sec); 713 714 last_pause_included_initial_mark = collector_state()->during_initial_mark_pause(); 715 if (last_pause_included_initial_mark) { 716 record_concurrent_mark_init_end(0.0); 717 } else { 718 maybe_start_marking(); 719 } 720 721 double app_time_ms = (phase_times()->cur_collection_start_sec() * 1000.0 - _analytics->prev_collection_pause_end_ms()); 722 if (app_time_ms < MIN_TIMER_GRANULARITY) { 723 // This usually happens due to the timer not having the required 724 // granularity. Some Linuxes are the usual culprits. 725 // We'll just set it to something (arbitrarily) small. 726 app_time_ms = 1.0; 727 } 728 729 if (update_stats) { 730 // We maintain the invariant that all objects allocated by mutator 731 // threads will be allocated out of eden regions. So, we can use 732 // the eden region number allocated since the previous GC to 733 // calculate the application's allocate rate. The only exception 734 // to that is humongous objects that are allocated separately. But 735 // given that humongous object allocations do not really affect 736 // either the pause's duration nor when the next pause will take 737 // place we can safely ignore them here. 738 uint regions_allocated = _collection_set->eden_region_length(); 739 double alloc_rate_ms = (double) regions_allocated / app_time_ms; 740 _analytics->report_alloc_rate_ms(alloc_rate_ms); 741 742 double interval_ms = 743 (end_time_sec - _analytics->last_known_gc_end_time_sec()) * 1000.0; 744 _analytics->update_recent_gc_times(end_time_sec, pause_time_ms); 745 _analytics->compute_pause_time_ratio(interval_ms, pause_time_ms); 746 } 747 748 bool new_in_marking_window = collector_state()->in_marking_window(); 749 bool new_in_marking_window_im = false; 750 if (last_pause_included_initial_mark) { 751 new_in_marking_window = true; 752 new_in_marking_window_im = true; 753 } 754 755 if (collector_state()->last_young_gc()) { 756 // This is supposed to to be the "last young GC" before we start 757 // doing mixed GCs. Here we decide whether to start mixed GCs or not. 758 assert(!last_pause_included_initial_mark, "The last young GC is not allowed to be an initial mark GC"); 759 760 if (next_gc_should_be_mixed("start mixed GCs", 761 "do not start mixed GCs")) { 762 collector_state()->set_gcs_are_young(false); 763 } else { 764 // We aborted the mixed GC phase early. 765 abort_time_to_mixed_tracking(); 766 } 767 768 collector_state()->set_last_young_gc(false); 769 } 770 771 if (!collector_state()->last_gc_was_young()) { 772 // This is a mixed GC. Here we decide whether to continue doing 773 // mixed GCs or not. 774 if (!next_gc_should_be_mixed("continue mixed GCs", 775 "do not continue mixed GCs")) { 776 collector_state()->set_gcs_are_young(true); 777 778 maybe_start_marking(); 779 } 780 } 781 782 _short_lived_surv_rate_group->start_adding_regions(); 783 // Do that for any other surv rate groups 784 785 double scan_hcc_time_ms = ConcurrentG1Refine::hot_card_cache_enabled() ? average_time_ms(G1GCPhaseTimes::ScanHCC) : 0.0; 786 787 if (update_stats) { 788 double cost_per_card_ms = 0.0; 789 if (_pending_cards > 0) { 790 cost_per_card_ms = (average_time_ms(G1GCPhaseTimes::UpdateRS) - scan_hcc_time_ms) / (double) _pending_cards; 791 _analytics->report_cost_per_card_ms(cost_per_card_ms); 792 } 793 _analytics->report_cost_scan_hcc(scan_hcc_time_ms); 794 795 double cost_per_entry_ms = 0.0; 796 if (cards_scanned > 10) { 797 cost_per_entry_ms = average_time_ms(G1GCPhaseTimes::ScanRS) / (double) cards_scanned; 798 _analytics->report_cost_per_entry_ms(cost_per_entry_ms, collector_state()->last_gc_was_young()); 799 } 800 801 if (_max_rs_lengths > 0) { 802 double cards_per_entry_ratio = 803 (double) cards_scanned / (double) _max_rs_lengths; 804 _analytics->report_cards_per_entry_ratio(cards_per_entry_ratio, collector_state()->last_gc_was_young()); 805 } 806 807 // This is defensive. For a while _max_rs_lengths could get 808 // smaller than _recorded_rs_lengths which was causing 809 // rs_length_diff to get very large and mess up the RSet length 810 // predictions. The reason was unsafe concurrent updates to the 811 // _inc_cset_recorded_rs_lengths field which the code below guards 812 // against (see CR 7118202). This bug has now been fixed (see CR 813 // 7119027). However, I'm still worried that 814 // _inc_cset_recorded_rs_lengths might still end up somewhat 815 // inaccurate. The concurrent refinement thread calculates an 816 // RSet's length concurrently with other CR threads updating it 817 // which might cause it to calculate the length incorrectly (if, 818 // say, it's in mid-coarsening). So I'll leave in the defensive 819 // conditional below just in case. 820 size_t rs_length_diff = 0; 821 size_t recorded_rs_lengths = _collection_set->recorded_rs_lengths(); 822 if (_max_rs_lengths > recorded_rs_lengths) { 823 rs_length_diff = _max_rs_lengths - recorded_rs_lengths; 824 } 825 _analytics->report_rs_length_diff((double) rs_length_diff); 826 827 size_t freed_bytes = heap_used_bytes_before_gc - cur_used_bytes; 828 size_t copied_bytes = _collection_set->bytes_used_before() - freed_bytes; 829 double cost_per_byte_ms = 0.0; 830 831 if (copied_bytes > 0) { 832 cost_per_byte_ms = average_time_ms(G1GCPhaseTimes::ObjCopy) / (double) copied_bytes; 833 _analytics->report_cost_per_byte_ms(cost_per_byte_ms, collector_state()->in_marking_window()); 834 } 835 836 if (_collection_set->young_region_length() > 0) { 837 _analytics->report_young_other_cost_per_region_ms(young_other_time_ms() / 838 _collection_set->young_region_length()); 839 } 840 841 if (_collection_set->old_region_length() > 0) { 842 _analytics->report_non_young_other_cost_per_region_ms(non_young_other_time_ms() / 843 _collection_set->old_region_length()); 844 } 845 846 _analytics->report_constant_other_time_ms(constant_other_time_ms(pause_time_ms)); 847 848 _analytics->report_pending_cards((double) _pending_cards); 849 _analytics->report_rs_lengths((double) _max_rs_lengths); 850 } 851 852 collector_state()->set_in_marking_window(new_in_marking_window); 853 collector_state()->set_in_marking_window_im(new_in_marking_window_im); 854 _free_regions_at_end_of_collection = _g1->num_free_regions(); 855 // IHOP control wants to know the expected young gen length if it were not 856 // restrained by the heap reserve. Using the actual length would make the 857 // prediction too small and the limit the young gen every time we get to the 858 // predicted target occupancy. 859 size_t last_unrestrained_young_length = update_young_list_max_and_target_length(); 860 update_rs_lengths_prediction(); 861 862 update_ihop_prediction(app_time_ms / 1000.0, 863 _bytes_allocated_in_old_since_last_gc, 864 last_unrestrained_young_length * HeapRegion::GrainBytes); 865 _bytes_allocated_in_old_since_last_gc = 0; 866 867 _ihop_control->send_trace_event(_g1->gc_tracer_stw()); 868 869 // Note that _mmu_tracker->max_gc_time() returns the time in seconds. 870 double update_rs_time_goal_ms = _mmu_tracker->max_gc_time() * MILLIUNITS * G1RSetUpdatingPauseTimePercent / 100.0; 871 872 if (update_rs_time_goal_ms < scan_hcc_time_ms) { 873 log_debug(gc, ergo, refine)("Adjust concurrent refinement thresholds (scanning the HCC expected to take longer than Update RS time goal)." 874 "Update RS time goal: %1.2fms Scan HCC time: %1.2fms", 875 update_rs_time_goal_ms, scan_hcc_time_ms); 876 877 update_rs_time_goal_ms = 0; 878 } else { 879 update_rs_time_goal_ms -= scan_hcc_time_ms; 880 } 881 _g1->concurrent_g1_refine()->adjust(average_time_ms(G1GCPhaseTimes::UpdateRS) - scan_hcc_time_ms, 882 phase_times()->sum_thread_work_items(G1GCPhaseTimes::UpdateRS), 883 update_rs_time_goal_ms); 884 885 cset_chooser()->verify(); 886 } 887 888 G1IHOPControl* G1CollectorPolicy::create_ihop_control() const { 889 if (G1UseAdaptiveIHOP) { 890 return new G1AdaptiveIHOPControl(InitiatingHeapOccupancyPercent, 891 &_predictor, 892 G1ReservePercent, 893 G1HeapWastePercent); 894 } else { 895 return new G1StaticIHOPControl(InitiatingHeapOccupancyPercent); 896 } 897 } 898 899 void G1CollectorPolicy::update_ihop_prediction(double mutator_time_s, 900 size_t mutator_alloc_bytes, 901 size_t young_gen_size) { 902 // Always try to update IHOP prediction. Even evacuation failures give information 903 // about e.g. whether to start IHOP earlier next time. 904 905 // Avoid using really small application times that might create samples with 906 // very high or very low values. They may be caused by e.g. back-to-back gcs. 907 double const min_valid_time = 1e-6; 908 909 bool report = false; 910 911 double marking_to_mixed_time = -1.0; 912 if (!collector_state()->last_gc_was_young() && _initial_mark_to_mixed.has_result()) { 913 marking_to_mixed_time = _initial_mark_to_mixed.last_marking_time(); 914 assert(marking_to_mixed_time > 0.0, 915 "Initial mark to mixed time must be larger than zero but is %.3f", 916 marking_to_mixed_time); 917 if (marking_to_mixed_time > min_valid_time) { 918 _ihop_control->update_marking_length(marking_to_mixed_time); 919 report = true; 920 } 921 } 922 923 // As an approximation for the young gc promotion rates during marking we use 924 // all of them. In many applications there are only a few if any young gcs during 925 // marking, which makes any prediction useless. This increases the accuracy of the 926 // prediction. 927 if (collector_state()->last_gc_was_young() && mutator_time_s > min_valid_time) { 928 _ihop_control->update_allocation_info(mutator_time_s, mutator_alloc_bytes, young_gen_size); 929 report = true; 930 } 931 932 if (report) { 933 report_ihop_statistics(); 934 } 935 } 936 937 void G1CollectorPolicy::report_ihop_statistics() { 938 _ihop_control->print(); 939 } 940 941 void G1CollectorPolicy::print_phases() { 942 phase_times()->print(); 943 } 944 945 double G1CollectorPolicy::predict_yg_surv_rate(int age, SurvRateGroup* surv_rate_group) const { 946 TruncatedSeq* seq = surv_rate_group->get_seq(age); 947 guarantee(seq->num() > 0, "There should be some young gen survivor samples available. Tried to access with age %d", age); 948 double pred = _predictor.get_new_prediction(seq); 949 if (pred > 1.0) { 950 pred = 1.0; 951 } 952 return pred; 953 } 954 955 double G1CollectorPolicy::predict_yg_surv_rate(int age) const { 956 return predict_yg_surv_rate(age, _short_lived_surv_rate_group); 957 } 958 959 double G1CollectorPolicy::accum_yg_surv_rate_pred(int age) const { 960 return _short_lived_surv_rate_group->accum_surv_rate_pred(age); 961 } 962 963 double G1CollectorPolicy::predict_base_elapsed_time_ms(size_t pending_cards, 964 size_t scanned_cards) const { 965 return 966 _analytics->predict_rs_update_time_ms(pending_cards) + 967 _analytics->predict_rs_scan_time_ms(scanned_cards, collector_state()->gcs_are_young()) + 968 _analytics->predict_constant_other_time_ms(); 969 } 970 971 double G1CollectorPolicy::predict_base_elapsed_time_ms(size_t pending_cards) const { 972 size_t rs_length = _analytics->predict_rs_lengths() + _analytics->predict_rs_length_diff(); 973 size_t card_num = _analytics->predict_card_num(rs_length, collector_state()->gcs_are_young()); 974 return predict_base_elapsed_time_ms(pending_cards, card_num); 975 } 976 977 size_t G1CollectorPolicy::predict_bytes_to_copy(HeapRegion* hr) const { 978 size_t bytes_to_copy; 979 if (hr->is_marked()) 980 bytes_to_copy = hr->max_live_bytes(); 981 else { 982 assert(hr->is_young() && hr->age_in_surv_rate_group() != -1, "invariant"); 983 int age = hr->age_in_surv_rate_group(); 984 double yg_surv_rate = predict_yg_surv_rate(age, hr->surv_rate_group()); 985 bytes_to_copy = (size_t) (hr->used() * yg_surv_rate); 986 } 987 return bytes_to_copy; 988 } 989 990 double G1CollectorPolicy::predict_region_elapsed_time_ms(HeapRegion* hr, 991 bool for_young_gc) const { 992 size_t rs_length = hr->rem_set()->occupied(); 993 // Predicting the number of cards is based on which type of GC 994 // we're predicting for. 995 size_t card_num = _analytics->predict_card_num(rs_length, for_young_gc); 996 size_t bytes_to_copy = predict_bytes_to_copy(hr); 997 998 double region_elapsed_time_ms = 999 _analytics->predict_rs_scan_time_ms(card_num, collector_state()->gcs_are_young()) + 1000 _analytics->predict_object_copy_time_ms(bytes_to_copy, collector_state()->during_concurrent_mark()); 1001 1002 // The prediction of the "other" time for this region is based 1003 // upon the region type and NOT the GC type. 1004 if (hr->is_young()) { 1005 region_elapsed_time_ms += _analytics->predict_young_other_time_ms(1); 1006 } else { 1007 region_elapsed_time_ms += _analytics->predict_non_young_other_time_ms(1); 1008 } 1009 return region_elapsed_time_ms; 1010 } 1011 1012 1013 void G1CollectorPolicy::print_yg_surv_rate_info() const { 1014 #ifndef PRODUCT 1015 _short_lived_surv_rate_group->print_surv_rate_summary(); 1016 // add this call for any other surv rate groups 1017 #endif // PRODUCT 1018 } 1019 1020 bool G1CollectorPolicy::is_young_list_full() const { 1021 uint young_list_length = _g1->young_list()->length(); 1022 uint young_list_target_length = _young_list_target_length; 1023 return young_list_length >= young_list_target_length; 1024 } 1025 1026 bool G1CollectorPolicy::can_expand_young_list() const { 1027 uint young_list_length = _g1->young_list()->length(); 1028 uint young_list_max_length = _young_list_max_length; 1029 return young_list_length < young_list_max_length; 1030 } 1031 1032 bool G1CollectorPolicy::adaptive_young_list_length() const { 1033 return _young_gen_sizer->adaptive_young_list_length(); 1034 } 1035 1036 void G1CollectorPolicy::update_max_gc_locker_expansion() { 1037 uint expansion_region_num = 0; 1038 if (GCLockerEdenExpansionPercent > 0) { 1039 double perc = (double) GCLockerEdenExpansionPercent / 100.0; 1040 double expansion_region_num_d = perc * (double) _young_list_target_length; 1041 // We use ceiling so that if expansion_region_num_d is > 0.0 (but 1042 // less than 1.0) we'll get 1. 1043 expansion_region_num = (uint) ceil(expansion_region_num_d); 1044 } else { 1045 assert(expansion_region_num == 0, "sanity"); 1046 } 1047 _young_list_max_length = _young_list_target_length + expansion_region_num; 1048 assert(_young_list_target_length <= _young_list_max_length, "post-condition"); 1049 } 1050 1051 // Calculates survivor space parameters. 1052 void G1CollectorPolicy::update_survivors_policy() { 1053 double max_survivor_regions_d = 1054 (double) _young_list_target_length / (double) SurvivorRatio; 1055 // We use ceiling so that if max_survivor_regions_d is > 0.0 (but 1056 // smaller than 1.0) we'll get 1. 1057 _max_survivor_regions = (uint) ceil(max_survivor_regions_d); 1058 1059 _tenuring_threshold = _survivors_age_table.compute_tenuring_threshold( 1060 HeapRegion::GrainWords * _max_survivor_regions, counters()); 1061 } 1062 1063 bool G1CollectorPolicy::force_initial_mark_if_outside_cycle(GCCause::Cause gc_cause) { 1064 // We actually check whether we are marking here and not if we are in a 1065 // reclamation phase. This means that we will schedule a concurrent mark 1066 // even while we are still in the process of reclaiming memory. 1067 bool during_cycle = _g1->concurrent_mark()->cmThread()->during_cycle(); 1068 if (!during_cycle) { 1069 log_debug(gc, ergo)("Request concurrent cycle initiation (requested by GC cause). GC cause: %s", GCCause::to_string(gc_cause)); 1070 collector_state()->set_initiate_conc_mark_if_possible(true); 1071 return true; 1072 } else { 1073 log_debug(gc, ergo)("Do not request concurrent cycle initiation (concurrent cycle already in progress). GC cause: %s", GCCause::to_string(gc_cause)); 1074 return false; 1075 } 1076 } 1077 1078 void G1CollectorPolicy::initiate_conc_mark() { 1079 collector_state()->set_during_initial_mark_pause(true); 1080 collector_state()->set_initiate_conc_mark_if_possible(false); 1081 } 1082 1083 void G1CollectorPolicy::decide_on_conc_mark_initiation() { 1084 // We are about to decide on whether this pause will be an 1085 // initial-mark pause. 1086 1087 // First, collector_state()->during_initial_mark_pause() should not be already set. We 1088 // will set it here if we have to. However, it should be cleared by 1089 // the end of the pause (it's only set for the duration of an 1090 // initial-mark pause). 1091 assert(!collector_state()->during_initial_mark_pause(), "pre-condition"); 1092 1093 if (collector_state()->initiate_conc_mark_if_possible()) { 1094 // We had noticed on a previous pause that the heap occupancy has 1095 // gone over the initiating threshold and we should start a 1096 // concurrent marking cycle. So we might initiate one. 1097 1098 if (!about_to_start_mixed_phase() && collector_state()->gcs_are_young()) { 1099 // Initiate a new initial mark if there is no marking or reclamation going on. 1100 initiate_conc_mark(); 1101 log_debug(gc, ergo)("Initiate concurrent cycle (concurrent cycle initiation requested)"); 1102 } else if (_g1->is_user_requested_concurrent_full_gc(_g1->gc_cause())) { 1103 // Initiate a user requested initial mark. An initial mark must be young only 1104 // GC, so the collector state must be updated to reflect this. 1105 collector_state()->set_gcs_are_young(true); 1106 collector_state()->set_last_young_gc(false); 1107 1108 abort_time_to_mixed_tracking(); 1109 initiate_conc_mark(); 1110 log_debug(gc, ergo)("Initiate concurrent cycle (user requested concurrent cycle)"); 1111 } else { 1112 // The concurrent marking thread is still finishing up the 1113 // previous cycle. If we start one right now the two cycles 1114 // overlap. In particular, the concurrent marking thread might 1115 // be in the process of clearing the next marking bitmap (which 1116 // we will use for the next cycle if we start one). Starting a 1117 // cycle now will be bad given that parts of the marking 1118 // information might get cleared by the marking thread. And we 1119 // cannot wait for the marking thread to finish the cycle as it 1120 // periodically yields while clearing the next marking bitmap 1121 // and, if it's in a yield point, it's waiting for us to 1122 // finish. So, at this point we will not start a cycle and we'll 1123 // let the concurrent marking thread complete the last one. 1124 log_debug(gc, ergo)("Do not initiate concurrent cycle (concurrent cycle already in progress)"); 1125 } 1126 } 1127 } 1128 1129 void G1CollectorPolicy::record_concurrent_mark_cleanup_end() { 1130 cset_chooser()->rebuild(_g1->workers(), _g1->num_regions()); 1131 1132 double end_sec = os::elapsedTime(); 1133 double elapsed_time_ms = (end_sec - _mark_cleanup_start_sec) * 1000.0; 1134 _analytics->report_concurrent_mark_cleanup_times_ms(elapsed_time_ms); 1135 _analytics->append_prev_collection_pause_end_ms(elapsed_time_ms); 1136 1137 record_pause(Cleanup, _mark_cleanup_start_sec, end_sec); 1138 } 1139 1140 double G1CollectorPolicy::reclaimable_bytes_perc(size_t reclaimable_bytes) const { 1141 // Returns the given amount of reclaimable bytes (that represents 1142 // the amount of reclaimable space still to be collected) as a 1143 // percentage of the current heap capacity. 1144 size_t capacity_bytes = _g1->capacity(); 1145 return (double) reclaimable_bytes * 100.0 / (double) capacity_bytes; 1146 } 1147 1148 void G1CollectorPolicy::maybe_start_marking() { 1149 if (need_to_start_conc_mark("end of GC")) { 1150 // Note: this might have already been set, if during the last 1151 // pause we decided to start a cycle but at the beginning of 1152 // this pause we decided to postpone it. That's OK. 1153 collector_state()->set_initiate_conc_mark_if_possible(true); 1154 } 1155 } 1156 1157 G1CollectorPolicy::PauseKind G1CollectorPolicy::young_gc_pause_kind() const { 1158 assert(!collector_state()->full_collection(), "must be"); 1159 if (collector_state()->during_initial_mark_pause()) { 1160 assert(collector_state()->last_gc_was_young(), "must be"); 1161 assert(!collector_state()->last_young_gc(), "must be"); 1162 return InitialMarkGC; 1163 } else if (collector_state()->last_young_gc()) { 1164 assert(!collector_state()->during_initial_mark_pause(), "must be"); 1165 assert(collector_state()->last_gc_was_young(), "must be"); 1166 return LastYoungGC; 1167 } else if (!collector_state()->last_gc_was_young()) { 1168 assert(!collector_state()->during_initial_mark_pause(), "must be"); 1169 assert(!collector_state()->last_young_gc(), "must be"); 1170 return MixedGC; 1171 } else { 1172 assert(collector_state()->last_gc_was_young(), "must be"); 1173 assert(!collector_state()->during_initial_mark_pause(), "must be"); 1174 assert(!collector_state()->last_young_gc(), "must be"); 1175 return YoungOnlyGC; 1176 } 1177 } 1178 1179 void G1CollectorPolicy::record_pause(PauseKind kind, double start, double end) { 1180 // Manage the MMU tracker. For some reason it ignores Full GCs. 1181 if (kind != FullGC) { 1182 _mmu_tracker->add_pause(start, end); 1183 } 1184 // Manage the mutator time tracking from initial mark to first mixed gc. 1185 switch (kind) { 1186 case FullGC: 1187 abort_time_to_mixed_tracking(); 1188 break; 1189 case Cleanup: 1190 case Remark: 1191 case YoungOnlyGC: 1192 case LastYoungGC: 1193 _initial_mark_to_mixed.add_pause(end - start); 1194 break; 1195 case InitialMarkGC: 1196 _initial_mark_to_mixed.record_initial_mark_end(end); 1197 break; 1198 case MixedGC: 1199 _initial_mark_to_mixed.record_mixed_gc_start(start); 1200 break; 1201 default: 1202 ShouldNotReachHere(); 1203 } 1204 } 1205 1206 void G1CollectorPolicy::abort_time_to_mixed_tracking() { 1207 _initial_mark_to_mixed.reset(); 1208 } 1209 1210 bool G1CollectorPolicy::next_gc_should_be_mixed(const char* true_action_str, 1211 const char* false_action_str) const { 1212 if (cset_chooser()->is_empty()) { 1213 log_debug(gc, ergo)("%s (candidate old regions not available)", false_action_str); 1214 return false; 1215 } 1216 1217 // Is the amount of uncollected reclaimable space above G1HeapWastePercent? 1218 size_t reclaimable_bytes = cset_chooser()->remaining_reclaimable_bytes(); 1219 double reclaimable_perc = reclaimable_bytes_perc(reclaimable_bytes); 1220 double threshold = (double) G1HeapWastePercent; 1221 if (reclaimable_perc <= threshold) { 1222 log_debug(gc, ergo)("%s (reclaimable percentage not over threshold). candidate old regions: %u reclaimable: " SIZE_FORMAT " (%1.2f) threshold: " UINTX_FORMAT, 1223 false_action_str, cset_chooser()->remaining_regions(), reclaimable_bytes, reclaimable_perc, G1HeapWastePercent); 1224 return false; 1225 } 1226 log_debug(gc, ergo)("%s (candidate old regions available). candidate old regions: %u reclaimable: " SIZE_FORMAT " (%1.2f) threshold: " UINTX_FORMAT, 1227 true_action_str, cset_chooser()->remaining_regions(), reclaimable_bytes, reclaimable_perc, G1HeapWastePercent); 1228 return true; 1229 } 1230 1231 uint G1CollectorPolicy::calc_min_old_cset_length() const { 1232 // The min old CSet region bound is based on the maximum desired 1233 // number of mixed GCs after a cycle. I.e., even if some old regions 1234 // look expensive, we should add them to the CSet anyway to make 1235 // sure we go through the available old regions in no more than the 1236 // maximum desired number of mixed GCs. 1237 // 1238 // The calculation is based on the number of marked regions we added 1239 // to the CSet chooser in the first place, not how many remain, so 1240 // that the result is the same during all mixed GCs that follow a cycle. 1241 1242 const size_t region_num = (size_t) cset_chooser()->length(); 1243 const size_t gc_num = (size_t) MAX2(G1MixedGCCountTarget, (uintx) 1); 1244 size_t result = region_num / gc_num; 1245 // emulate ceiling 1246 if (result * gc_num < region_num) { 1247 result += 1; 1248 } 1249 return (uint) result; 1250 } 1251 1252 uint G1CollectorPolicy::calc_max_old_cset_length() const { 1253 // The max old CSet region bound is based on the threshold expressed 1254 // as a percentage of the heap size. I.e., it should bound the 1255 // number of old regions added to the CSet irrespective of how many 1256 // of them are available. 1257 1258 const G1CollectedHeap* g1h = G1CollectedHeap::heap(); 1259 const size_t region_num = g1h->num_regions(); 1260 const size_t perc = (size_t) G1OldCSetRegionThresholdPercent; 1261 size_t result = region_num * perc / 100; 1262 // emulate ceiling 1263 if (100 * result < region_num * perc) { 1264 result += 1; 1265 } 1266 return (uint) result; 1267 } 1268 1269 void G1CollectorPolicy::finalize_collection_set(double target_pause_time_ms) { 1270 double time_remaining_ms = _collection_set->finalize_young_part(target_pause_time_ms); 1271 _collection_set->finalize_old_part(time_remaining_ms); 1272 }