1 /* 2 * Copyright Amazon.com Inc. 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/shenandoah/shenandoahCollectorPolicy.hpp" 27 #include "gc/shenandoah/shenandoahCollectionSetPreselector.hpp" 28 #include "gc/shenandoah/shenandoahFreeSet.hpp" 29 #include "gc/shenandoah/shenandoahGeneration.hpp" 30 #include "gc/shenandoah/shenandoahGenerationalHeap.inline.hpp" 31 #include "gc/shenandoah/shenandoahHeapRegionClosures.hpp" 32 #include "gc/shenandoah/shenandoahOldGeneration.hpp" 33 #include "gc/shenandoah/shenandoahReferenceProcessor.hpp" 34 #include "gc/shenandoah/shenandoahScanRemembered.inline.hpp" 35 #include "gc/shenandoah/shenandoahTaskqueue.inline.hpp" 36 #include "gc/shenandoah/shenandoahUtils.hpp" 37 #include "gc/shenandoah/shenandoahVerifier.hpp" 38 #include "gc/shenandoah/shenandoahYoungGeneration.hpp" 39 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp" 40 41 #include "utilities/quickSort.hpp" 42 43 template <bool PREPARE_FOR_CURRENT_CYCLE, bool FULL_GC = false> 44 class ShenandoahResetBitmapClosure final : public ShenandoahHeapRegionClosure { 45 private: 46 ShenandoahHeap* _heap; 47 ShenandoahMarkingContext* _ctx; 48 49 public: 50 explicit ShenandoahResetBitmapClosure() : 51 ShenandoahHeapRegionClosure(), _heap(ShenandoahHeap::heap()), _ctx(_heap->marking_context()) {} 52 53 void heap_region_do(ShenandoahHeapRegion* region) override { 54 assert(!_heap->is_uncommit_in_progress(), "Cannot uncommit bitmaps while resetting them."); 55 if (PREPARE_FOR_CURRENT_CYCLE) { 56 if (region->need_bitmap_reset() && _heap->is_bitmap_slice_committed(region)) { 57 _ctx->clear_bitmap(region); 58 } else { 59 region->set_needs_bitmap_reset(); 60 } 61 // Capture Top At Mark Start for this generation. 62 if (FULL_GC || region->is_active()) { 63 // Reset live data and set TAMS optimistically. We would recheck these under the pause 64 // anyway to capture any updates that happened since now. 65 _ctx->capture_top_at_mark_start(region); 66 region->clear_live_data(); 67 } 68 } else { 69 if (_heap->is_bitmap_slice_committed(region)) { 70 _ctx->clear_bitmap(region); 71 region->unset_needs_bitmap_reset(); 72 } else { 73 region->set_needs_bitmap_reset(); 74 } 75 } 76 } 77 78 bool is_thread_safe() override { return true; } 79 }; 80 81 // Copy the write-version of the card-table into the read-version, clearing the 82 // write-copy. 83 class ShenandoahMergeWriteTable: public ShenandoahHeapRegionClosure { 84 private: 85 ShenandoahScanRemembered* _scanner; 86 public: 87 ShenandoahMergeWriteTable(ShenandoahScanRemembered* scanner) : _scanner(scanner) {} 88 89 void heap_region_do(ShenandoahHeapRegion* r) override { 90 assert(r->is_old(), "Don't waste time doing this for non-old regions"); 91 _scanner->merge_write_table(r->bottom(), ShenandoahHeapRegion::region_size_words()); 92 } 93 94 bool is_thread_safe() override { 95 return true; 96 } 97 }; 98 99 // Add [TAMS, top) volume over young regions. Used to correct age 0 cohort census 100 // for adaptive tenuring when census is taken during marking. 101 // In non-product builds, for the purposes of verification, we also collect the total 102 // live objects in young regions as well. 103 class ShenandoahUpdateCensusZeroCohortClosure : public ShenandoahHeapRegionClosure { 104 private: 105 ShenandoahMarkingContext* const _ctx; 106 // Population size units are words (not bytes) 107 size_t _age0_pop; // running tally of age0 population size 108 size_t _total_pop; // total live population size 109 public: 110 explicit ShenandoahUpdateCensusZeroCohortClosure(ShenandoahMarkingContext* ctx) 111 : _ctx(ctx), _age0_pop(0), _total_pop(0) {} 112 113 void heap_region_do(ShenandoahHeapRegion* r) override { 114 if (_ctx != nullptr && r->is_active()) { 115 assert(r->is_young(), "Young regions only"); 116 HeapWord* tams = _ctx->top_at_mark_start(r); 117 HeapWord* top = r->top(); 118 if (top > tams) { 119 _age0_pop += pointer_delta(top, tams); 120 } 121 // TODO: check significance of _ctx != nullptr above, can that 122 // spoof _total_pop in some corner cases? 123 NOT_PRODUCT(_total_pop += r->get_live_data_words();) 124 } 125 } 126 127 size_t get_age0_population() const { return _age0_pop; } 128 size_t get_total_population() const { return _total_pop; } 129 }; 130 131 void ShenandoahGeneration::confirm_heuristics_mode() { 132 if (_heuristics->is_diagnostic() && !UnlockDiagnosticVMOptions) { 133 vm_exit_during_initialization( 134 err_msg("Heuristics \"%s\" is diagnostic, and must be enabled via -XX:+UnlockDiagnosticVMOptions.", 135 _heuristics->name())); 136 } 137 if (_heuristics->is_experimental() && !UnlockExperimentalVMOptions) { 138 vm_exit_during_initialization( 139 err_msg("Heuristics \"%s\" is experimental, and must be enabled via -XX:+UnlockExperimentalVMOptions.", 140 _heuristics->name())); 141 } 142 } 143 144 ShenandoahHeuristics* ShenandoahGeneration::initialize_heuristics(ShenandoahMode* gc_mode) { 145 _heuristics = gc_mode->initialize_heuristics(this); 146 _heuristics->set_guaranteed_gc_interval(ShenandoahGuaranteedGCInterval); 147 confirm_heuristics_mode(); 148 return _heuristics; 149 } 150 151 size_t ShenandoahGeneration::bytes_allocated_since_gc_start() const { 152 return Atomic::load(&_bytes_allocated_since_gc_start); 153 } 154 155 void ShenandoahGeneration::reset_bytes_allocated_since_gc_start() { 156 Atomic::store(&_bytes_allocated_since_gc_start, (size_t)0); 157 } 158 159 void ShenandoahGeneration::increase_allocated(size_t bytes) { 160 Atomic::add(&_bytes_allocated_since_gc_start, bytes, memory_order_relaxed); 161 } 162 163 void ShenandoahGeneration::set_evacuation_reserve(size_t new_val) { 164 _evacuation_reserve = new_val; 165 } 166 167 size_t ShenandoahGeneration::get_evacuation_reserve() const { 168 return _evacuation_reserve; 169 } 170 171 void ShenandoahGeneration::augment_evacuation_reserve(size_t increment) { 172 _evacuation_reserve += increment; 173 } 174 175 void ShenandoahGeneration::log_status(const char *msg) const { 176 typedef LogTarget(Info, gc, ergo) LogGcInfo; 177 178 if (!LogGcInfo::is_enabled()) { 179 return; 180 } 181 182 // Not under a lock here, so read each of these once to make sure 183 // byte size in proper unit and proper unit for byte size are consistent. 184 const size_t v_used = used(); 185 const size_t v_used_regions = used_regions_size(); 186 const size_t v_soft_max_capacity = ShenandoahHeap::heap()->soft_max_capacity(); 187 const size_t v_max_capacity = max_capacity(); 188 const size_t v_available = available(); 189 const size_t v_humongous_waste = get_humongous_waste(); 190 191 const LogGcInfo target; 192 LogStream ls(target); 193 ls.print("%s: ", msg); 194 if (_type != NON_GEN) { 195 ls.print("%s generation ", name()); 196 } 197 198 ls.print_cr("used: " PROPERFMT ", used regions: " PROPERFMT ", humongous waste: " PROPERFMT 199 ", soft capacity: " PROPERFMT ", max capacity: " PROPERFMT ", available: " PROPERFMT, 200 PROPERFMTARGS(v_used), PROPERFMTARGS(v_used_regions), PROPERFMTARGS(v_humongous_waste), 201 PROPERFMTARGS(v_soft_max_capacity), PROPERFMTARGS(v_max_capacity), PROPERFMTARGS(v_available)); 202 } 203 204 template <bool PREPARE_FOR_CURRENT_CYCLE, bool FULL_GC> 205 void ShenandoahGeneration::reset_mark_bitmap() { 206 ShenandoahHeap* heap = ShenandoahHeap::heap(); 207 heap->assert_gc_workers(heap->workers()->active_workers()); 208 209 set_mark_incomplete(); 210 211 ShenandoahResetBitmapClosure<PREPARE_FOR_CURRENT_CYCLE, FULL_GC> closure; 212 parallel_heap_region_iterate_free(&closure); 213 } 214 // Explicit specializations 215 template void ShenandoahGeneration::reset_mark_bitmap<true, false>(); 216 template void ShenandoahGeneration::reset_mark_bitmap<true, true>(); 217 template void ShenandoahGeneration::reset_mark_bitmap<false, false>(); 218 219 // Swap the read and write card table pointers prior to the next remset scan. 220 // This avoids the need to synchronize reads of the table by the GC workers 221 // doing remset scanning, on the one hand, with the dirtying of the table by 222 // mutators on the other. 223 void ShenandoahGeneration::swap_card_tables() { 224 // Must be sure that marking is complete before we swap remembered set. 225 ShenandoahGenerationalHeap* heap = ShenandoahGenerationalHeap::heap(); 226 heap->assert_gc_workers(heap->workers()->active_workers()); 227 shenandoah_assert_safepoint(); 228 229 ShenandoahOldGeneration* old_generation = heap->old_generation(); 230 old_generation->card_scan()->swap_card_tables(); 231 } 232 233 // Copy the write-version of the card-table into the read-version, clearing the 234 // write-version. The work is done at a safepoint and in parallel by the GC 235 // worker threads. 236 void ShenandoahGeneration::merge_write_table() { 237 // This should only happen for degenerated cycles 238 ShenandoahGenerationalHeap* heap = ShenandoahGenerationalHeap::heap(); 239 heap->assert_gc_workers(heap->workers()->active_workers()); 240 shenandoah_assert_safepoint(); 241 242 ShenandoahOldGeneration* old_generation = heap->old_generation(); 243 ShenandoahMergeWriteTable task(old_generation->card_scan()); 244 old_generation->parallel_heap_region_iterate(&task); 245 } 246 247 void ShenandoahGeneration::prepare_gc() { 248 reset_mark_bitmap<true>(); 249 } 250 251 void ShenandoahGeneration::parallel_heap_region_iterate_free(ShenandoahHeapRegionClosure* cl) { 252 ShenandoahHeap::heap()->parallel_heap_region_iterate(cl); 253 } 254 255 void ShenandoahGeneration::compute_evacuation_budgets(ShenandoahHeap* const heap) { 256 shenandoah_assert_generational(); 257 258 ShenandoahOldGeneration* const old_generation = heap->old_generation(); 259 ShenandoahYoungGeneration* const young_generation = heap->young_generation(); 260 261 // During initialization and phase changes, it is more likely that fewer objects die young and old-gen 262 // memory is not yet full (or is in the process of being replaced). During these times especially, it 263 // is beneficial to loan memory from old-gen to young-gen during the evacuation and update-refs phases 264 // of execution. 265 266 // Calculate EvacuationReserve before PromotionReserve. Evacuation is more critical than promotion. 267 // If we cannot evacuate old-gen, we will not be able to reclaim old-gen memory. Promotions are less 268 // critical. If we cannot promote, there may be degradation of young-gen memory because old objects 269 // accumulate there until they can be promoted. This increases the young-gen marking and evacuation work. 270 271 // First priority is to reclaim the easy garbage out of young-gen. 272 273 // maximum_young_evacuation_reserve is upper bound on memory to be evacuated out of young 274 const size_t maximum_young_evacuation_reserve = (young_generation->max_capacity() * ShenandoahEvacReserve) / 100; 275 const size_t young_evacuation_reserve = MIN2(maximum_young_evacuation_reserve, young_generation->available_with_reserve()); 276 277 // maximum_old_evacuation_reserve is an upper bound on memory evacuated from old and evacuated to old (promoted), 278 // clamped by the old generation space available. 279 // 280 // Here's the algebra. 281 // Let SOEP = ShenandoahOldEvacRatioPercent, 282 // OE = old evac, 283 // YE = young evac, and 284 // TE = total evac = OE + YE 285 // By definition: 286 // SOEP/100 = OE/TE 287 // = OE/(OE+YE) 288 // => SOEP/(100-SOEP) = OE/((OE+YE)-OE) // componendo-dividendo: If a/b = c/d, then a/(b-a) = c/(d-c) 289 // = OE/YE 290 // => OE = YE*SOEP/(100-SOEP) 291 292 // We have to be careful in the event that SOEP is set to 100 by the user. 293 assert(ShenandoahOldEvacRatioPercent <= 100, "Error"); 294 const size_t old_available = old_generation->available(); 295 const size_t maximum_old_evacuation_reserve = (ShenandoahOldEvacRatioPercent == 100) ? 296 old_available : MIN2((maximum_young_evacuation_reserve * ShenandoahOldEvacRatioPercent) / (100 - ShenandoahOldEvacRatioPercent), 297 old_available); 298 299 300 // Second priority is to reclaim garbage out of old-gen if there are old-gen collection candidates. Third priority 301 // is to promote as much as we have room to promote. However, if old-gen memory is in short supply, this means young 302 // GC is operating under "duress" and was unable to transfer the memory that we would normally expect. In this case, 303 // old-gen will refrain from compacting itself in order to allow a quicker young-gen cycle (by avoiding the update-refs 304 // through ALL of old-gen). If there is some memory available in old-gen, we will use this for promotions as promotions 305 // do not add to the update-refs burden of GC. 306 307 size_t old_evacuation_reserve, old_promo_reserve; 308 if (is_global()) { 309 // Global GC is typically triggered by user invocation of System.gc(), and typically indicates that there is lots 310 // of garbage to be reclaimed because we are starting a new phase of execution. Marking for global GC may take 311 // significantly longer than typical young marking because we must mark through all old objects. To expedite 312 // evacuation and update-refs, we give emphasis to reclaiming garbage first, wherever that garbage is found. 313 // Global GC will adjust generation sizes to accommodate the collection set it chooses. 314 315 // Set old_promo_reserve to enforce that no regions are preselected for promotion. Such regions typically 316 // have relatively high memory utilization. We still call select_aged_regions() because this will prepare for 317 // promotions in place, if relevant. 318 old_promo_reserve = 0; 319 320 // Dedicate all available old memory to old_evacuation reserve. This may be small, because old-gen is only 321 // expanded based on an existing mixed evacuation workload at the end of the previous GC cycle. We'll expand 322 // the budget for evacuation of old during GLOBAL cset selection. 323 old_evacuation_reserve = maximum_old_evacuation_reserve; 324 } else if (old_generation->has_unprocessed_collection_candidates()) { 325 // We reserved all old-gen memory at end of previous GC to hold anticipated evacuations to old-gen. If this is 326 // mixed evacuation, reserve all of this memory for compaction of old-gen and do not promote. Prioritize compaction 327 // over promotion in order to defragment OLD so that it will be better prepared to efficiently receive promoted memory. 328 old_evacuation_reserve = maximum_old_evacuation_reserve; 329 old_promo_reserve = 0; 330 } else { 331 // Make all old-evacuation memory for promotion, but if we can't use it all for promotion, we'll allow some evacuation. 332 old_evacuation_reserve = 0; 333 old_promo_reserve = maximum_old_evacuation_reserve; 334 } 335 assert(old_evacuation_reserve <= old_available, "Error"); 336 337 // We see too many old-evacuation failures if we force ourselves to evacuate into regions that are not initially empty. 338 // So we limit the old-evacuation reserve to unfragmented memory. Even so, old-evacuation is free to fill in nooks and 339 // crannies within existing partially used regions and it generally tries to do so. 340 const size_t old_free_unfragmented = old_generation->free_unaffiliated_regions() * ShenandoahHeapRegion::region_size_bytes(); 341 if (old_evacuation_reserve > old_free_unfragmented) { 342 const size_t delta = old_evacuation_reserve - old_free_unfragmented; 343 old_evacuation_reserve -= delta; 344 // Let promo consume fragments of old-gen memory if not global 345 if (!is_global()) { 346 old_promo_reserve += delta; 347 } 348 } 349 350 // Preselect regions for promotion by evacuation (obtaining the live data to seed promoted_reserve), 351 // and identify regions that will promote in place. These use the tenuring threshold. 352 const size_t consumed_by_advance_promotion = select_aged_regions(old_promo_reserve); 353 assert(consumed_by_advance_promotion <= maximum_old_evacuation_reserve, "Cannot promote more than available old-gen memory"); 354 355 // Note that unused old_promo_reserve might not be entirely consumed_by_advance_promotion. Do not transfer this 356 // to old_evacuation_reserve because this memory is likely very fragmented, and we do not want to increase the likelihood 357 // of old evacuation failure. 358 young_generation->set_evacuation_reserve(young_evacuation_reserve); 359 old_generation->set_evacuation_reserve(old_evacuation_reserve); 360 old_generation->set_promoted_reserve(consumed_by_advance_promotion); 361 362 // There is no need to expand OLD because all memory used here was set aside at end of previous GC, except in the 363 // case of a GLOBAL gc. During choose_collection_set() of GLOBAL, old will be expanded on demand. 364 } 365 366 // Having chosen the collection set, adjust the budgets for generational mode based on its composition. Note 367 // that young_generation->available() now knows about recently discovered immediate garbage. 368 // 369 void ShenandoahGeneration::adjust_evacuation_budgets(ShenandoahHeap* const heap, ShenandoahCollectionSet* const collection_set) { 370 shenandoah_assert_generational(); 371 // We may find that old_evacuation_reserve and/or loaned_for_young_evacuation are not fully consumed, in which case we may 372 // be able to increase regions_available_to_loan 373 374 // The role of adjust_evacuation_budgets() is to compute the correct value of regions_available_to_loan and to make 375 // effective use of this memory, including the remnant memory within these regions that may result from rounding loan to 376 // integral number of regions. Excess memory that is available to be loaned is applied to an allocation supplement, 377 // which allows mutators to allocate memory beyond the current capacity of young-gen on the promise that the loan 378 // will be repaid as soon as we finish updating references for the recently evacuated collection set. 379 380 // We cannot recalculate regions_available_to_loan by simply dividing old_generation->available() by region_size_bytes 381 // because the available memory may be distributed between many partially occupied regions that are already holding old-gen 382 // objects. Memory in partially occupied regions is not "available" to be loaned. Note that an increase in old-gen 383 // available that results from a decrease in memory consumed by old evacuation is not necessarily available to be loaned 384 // to young-gen. 385 386 size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes(); 387 ShenandoahOldGeneration* const old_generation = heap->old_generation(); 388 ShenandoahYoungGeneration* const young_generation = heap->young_generation(); 389 390 size_t old_evacuated = collection_set->get_old_bytes_reserved_for_evacuation(); 391 size_t old_evacuated_committed = (size_t) (ShenandoahOldEvacWaste * double(old_evacuated)); 392 size_t old_evacuation_reserve = old_generation->get_evacuation_reserve(); 393 394 if (old_evacuated_committed > old_evacuation_reserve) { 395 // This should only happen due to round-off errors when enforcing ShenandoahOldEvacWaste 396 assert(old_evacuated_committed <= (33 * old_evacuation_reserve) / 32, 397 "Round-off errors should be less than 3.125%%, committed: " SIZE_FORMAT ", reserved: " SIZE_FORMAT, 398 old_evacuated_committed, old_evacuation_reserve); 399 old_evacuated_committed = old_evacuation_reserve; 400 // Leave old_evac_reserve as previously configured 401 } else if (old_evacuated_committed < old_evacuation_reserve) { 402 // This happens if the old-gen collection consumes less than full budget. 403 old_evacuation_reserve = old_evacuated_committed; 404 old_generation->set_evacuation_reserve(old_evacuation_reserve); 405 } 406 407 size_t young_advance_promoted = collection_set->get_young_bytes_to_be_promoted(); 408 size_t young_advance_promoted_reserve_used = (size_t) (ShenandoahPromoEvacWaste * double(young_advance_promoted)); 409 410 size_t young_evacuated = collection_set->get_young_bytes_reserved_for_evacuation(); 411 size_t young_evacuated_reserve_used = (size_t) (ShenandoahEvacWaste * double(young_evacuated)); 412 413 size_t total_young_available = young_generation->available_with_reserve(); 414 assert(young_evacuated_reserve_used <= total_young_available, "Cannot evacuate more than is available in young"); 415 young_generation->set_evacuation_reserve(young_evacuated_reserve_used); 416 417 size_t old_available = old_generation->available(); 418 // Now that we've established the collection set, we know how much memory is really required by old-gen for evacuation 419 // and promotion reserves. Try shrinking OLD now in case that gives us a bit more runway for mutator allocations during 420 // evac and update phases. 421 size_t old_consumed = old_evacuated_committed + young_advance_promoted_reserve_used; 422 423 if (old_available < old_consumed) { 424 // This can happen due to round-off errors when adding the results of truncated integer arithmetic. 425 // We've already truncated old_evacuated_committed. Truncate young_advance_promoted_reserve_used here. 426 assert(young_advance_promoted_reserve_used <= (33 * (old_available - old_evacuated_committed)) / 32, 427 "Round-off errors should be less than 3.125%%, committed: " SIZE_FORMAT ", reserved: " SIZE_FORMAT, 428 young_advance_promoted_reserve_used, old_available - old_evacuated_committed); 429 young_advance_promoted_reserve_used = old_available - old_evacuated_committed; 430 old_consumed = old_evacuated_committed + young_advance_promoted_reserve_used; 431 } 432 433 assert(old_available >= old_consumed, "Cannot consume (" SIZE_FORMAT ") more than is available (" SIZE_FORMAT ")", 434 old_consumed, old_available); 435 size_t excess_old = old_available - old_consumed; 436 size_t unaffiliated_old_regions = old_generation->free_unaffiliated_regions(); 437 size_t unaffiliated_old = unaffiliated_old_regions * region_size_bytes; 438 assert(old_available >= unaffiliated_old, "Unaffiliated old is a subset of old available"); 439 440 // Make sure old_evac_committed is unaffiliated 441 if (old_evacuated_committed > 0) { 442 if (unaffiliated_old > old_evacuated_committed) { 443 size_t giveaway = unaffiliated_old - old_evacuated_committed; 444 size_t giveaway_regions = giveaway / region_size_bytes; // round down 445 if (giveaway_regions > 0) { 446 excess_old = MIN2(excess_old, giveaway_regions * region_size_bytes); 447 } else { 448 excess_old = 0; 449 } 450 } else { 451 excess_old = 0; 452 } 453 } 454 455 // If we find that OLD has excess regions, give them back to YOUNG now to reduce likelihood we run out of allocation 456 // runway during evacuation and update-refs. 457 size_t regions_to_xfer = 0; 458 if (excess_old > unaffiliated_old) { 459 // we can give back unaffiliated_old (all of unaffiliated is excess) 460 if (unaffiliated_old_regions > 0) { 461 regions_to_xfer = unaffiliated_old_regions; 462 } 463 } else if (unaffiliated_old_regions > 0) { 464 // excess_old < unaffiliated old: we can give back MIN(excess_old/region_size_bytes, unaffiliated_old_regions) 465 size_t excess_regions = excess_old / region_size_bytes; 466 regions_to_xfer = MIN2(excess_regions, unaffiliated_old_regions); 467 } 468 469 if (regions_to_xfer > 0) { 470 bool result = ShenandoahGenerationalHeap::cast(heap)->generation_sizer()->transfer_to_young(regions_to_xfer); 471 assert(excess_old >= regions_to_xfer * region_size_bytes, 472 "Cannot transfer (" SIZE_FORMAT ", " SIZE_FORMAT ") more than excess old (" SIZE_FORMAT ")", 473 regions_to_xfer, region_size_bytes, excess_old); 474 excess_old -= regions_to_xfer * region_size_bytes; 475 log_debug(gc, ergo)("%s transferred " SIZE_FORMAT " excess regions to young before start of evacuation", 476 result? "Successfully": "Unsuccessfully", regions_to_xfer); 477 } 478 479 // Add in the excess_old memory to hold unanticipated promotions, if any. If there are more unanticipated 480 // promotions than fit in reserved memory, they will be deferred until a future GC pass. 481 size_t total_promotion_reserve = young_advance_promoted_reserve_used + excess_old; 482 old_generation->set_promoted_reserve(total_promotion_reserve); 483 old_generation->reset_promoted_expended(); 484 } 485 486 typedef struct { 487 ShenandoahHeapRegion* _region; 488 size_t _live_data; 489 } AgedRegionData; 490 491 static int compare_by_aged_live(AgedRegionData a, AgedRegionData b) { 492 if (a._live_data < b._live_data) 493 return -1; 494 else if (a._live_data > b._live_data) 495 return 1; 496 else return 0; 497 } 498 499 inline void assert_no_in_place_promotions() { 500 #ifdef ASSERT 501 class ShenandoahNoInPlacePromotions : public ShenandoahHeapRegionClosure { 502 public: 503 void heap_region_do(ShenandoahHeapRegion *r) override { 504 assert(r->get_top_before_promote() == nullptr, 505 "Region " SIZE_FORMAT " should not be ready for in-place promotion", r->index()); 506 } 507 } cl; 508 ShenandoahHeap::heap()->heap_region_iterate(&cl); 509 #endif 510 } 511 512 // Preselect for inclusion into the collection set regions whose age is at or above tenure age which contain more than 513 // ShenandoahOldGarbageThreshold amounts of garbage. We identify these regions by setting the appropriate entry of 514 // the collection set's preselected regions array to true. All entries are initialized to false before calling this 515 // function. 516 // 517 // During the subsequent selection of the collection set, we give priority to these promotion set candidates. 518 // Without this prioritization, we found that the aged regions tend to be ignored because they typically have 519 // much less garbage and much more live data than the recently allocated "eden" regions. When aged regions are 520 // repeatedly excluded from the collection set, the amount of live memory within the young generation tends to 521 // accumulate and this has the undesirable side effect of causing young-generation collections to require much more 522 // CPU and wall-clock time. 523 // 524 // A second benefit of treating aged regions differently than other regions during collection set selection is 525 // that this allows us to more accurately budget memory to hold the results of evacuation. Memory for evacuation 526 // of aged regions must be reserved in the old generation. Memory for evacuation of all other regions must be 527 // reserved in the young generation. 528 size_t ShenandoahGeneration::select_aged_regions(size_t old_available) { 529 530 // There should be no regions configured for subsequent in-place-promotions carried over from the previous cycle. 531 assert_no_in_place_promotions(); 532 533 auto const heap = ShenandoahGenerationalHeap::heap(); 534 bool* const candidate_regions_for_promotion_by_copy = heap->collection_set()->preselected_regions(); 535 ShenandoahMarkingContext* const ctx = heap->marking_context(); 536 537 const size_t old_garbage_threshold = (ShenandoahHeapRegion::region_size_bytes() * ShenandoahOldGarbageThreshold) / 100; 538 539 size_t old_consumed = 0; 540 size_t promo_potential = 0; 541 size_t candidates = 0; 542 543 // Tracks the padding of space above top in regions eligible for promotion in place 544 size_t promote_in_place_pad = 0; 545 546 // Sort the promotion-eligible regions in order of increasing live-data-bytes so that we can first reclaim regions that require 547 // less evacuation effort. This prioritizes garbage first, expanding the allocation pool early before we reclaim regions that 548 // have more live data. 549 const size_t num_regions = heap->num_regions(); 550 551 ResourceMark rm; 552 AgedRegionData* sorted_regions = NEW_RESOURCE_ARRAY(AgedRegionData, num_regions); 553 554 for (size_t i = 0; i < num_regions; i++) { 555 ShenandoahHeapRegion* const r = heap->get_region(i); 556 if (r->is_empty() || !r->has_live() || !r->is_young() || !r->is_regular()) { 557 // skip over regions that aren't regular young with some live data 558 continue; 559 } 560 if (heap->is_tenurable(r)) { 561 if ((r->garbage() < old_garbage_threshold)) { 562 // This tenure-worthy region has too little garbage, so we do not want to expend the copying effort to 563 // reclaim the garbage; instead this region may be eligible for promotion-in-place to the 564 // old generation. 565 HeapWord* tams = ctx->top_at_mark_start(r); 566 HeapWord* original_top = r->top(); 567 if (!heap->is_concurrent_old_mark_in_progress() && tams == original_top) { 568 // No allocations from this region have been made during concurrent mark. It meets all the criteria 569 // for in-place-promotion. Though we only need the value of top when we fill the end of the region, 570 // we use this field to indicate that this region should be promoted in place during the evacuation 571 // phase. 572 r->save_top_before_promote(); 573 574 size_t remnant_size = r->free() / HeapWordSize; 575 if (remnant_size > ShenandoahHeap::min_fill_size()) { 576 ShenandoahHeap::fill_with_object(original_top, remnant_size); 577 // Fill the remnant memory within this region to assure no allocations prior to promote in place. Otherwise, 578 // newly allocated objects will not be parsable when promote in place tries to register them. Furthermore, any 579 // new allocations would not necessarily be eligible for promotion. This addresses both issues. 580 r->set_top(r->end()); 581 promote_in_place_pad += remnant_size * HeapWordSize; 582 } else { 583 // Since the remnant is so small that it cannot be filled, we don't have to worry about any accidental 584 // allocations occurring within this region before the region is promoted in place. 585 } 586 } 587 // Else, we do not promote this region (either in place or by copy) because it has received new allocations. 588 589 // During evacuation, we exclude from promotion regions for which age > tenure threshold, garbage < garbage-threshold, 590 // and get_top_before_promote() != tams 591 } else { 592 // Record this promotion-eligible candidate region. After sorting and selecting the best candidates below, 593 // we may still decide to exclude this promotion-eligible region from the current collection set. If this 594 // happens, we will consider this region as part of the anticipated promotion potential for the next GC 595 // pass; see further below. 596 sorted_regions[candidates]._region = r; 597 sorted_regions[candidates++]._live_data = r->get_live_data_bytes(); 598 } 599 } else { 600 // We only evacuate & promote objects from regular regions whose garbage() is above old-garbage-threshold. 601 // Objects in tenure-worthy regions with less garbage are promoted in place. These take a different path to 602 // old-gen. Regions excluded from promotion because their garbage content is too low (causing us to anticipate that 603 // the region would be promoted in place) may be eligible for evacuation promotion by the time promotion takes 604 // place during a subsequent GC pass because more garbage is found within the region between now and then. This 605 // should not happen if we are properly adapting the tenure age. The theory behind adaptive tenuring threshold 606 // is to choose the youngest age that demonstrates no "significant" further loss of population since the previous 607 // age. If not this, we expect the tenure age to demonstrate linear population decay for at least two population 608 // samples, whereas we expect to observe exponential population decay for ages younger than the tenure age. 609 // 610 // In the case that certain regions which were anticipated to be promoted in place need to be promoted by 611 // evacuation, it may be the case that there is not sufficient reserve within old-gen to hold evacuation of 612 // these regions. The likely outcome is that these regions will not be selected for evacuation or promotion 613 // in the current cycle and we will anticipate that they will be promoted in the next cycle. This will cause 614 // us to reserve more old-gen memory so that these objects can be promoted in the subsequent cycle. 615 if (heap->is_aging_cycle() && heap->age_census()->is_tenurable(r->age() + 1)) { 616 if (r->garbage() >= old_garbage_threshold) { 617 promo_potential += r->get_live_data_bytes(); 618 } 619 } 620 } 621 // Note that we keep going even if one region is excluded from selection. 622 // Subsequent regions may be selected if they have smaller live data. 623 } 624 // Sort in increasing order according to live data bytes. Note that candidates represents the number of regions 625 // that qualify to be promoted by evacuation. 626 if (candidates > 0) { 627 size_t selected_regions = 0; 628 size_t selected_live = 0; 629 QuickSort::sort<AgedRegionData>(sorted_regions, candidates, compare_by_aged_live, false); 630 for (size_t i = 0; i < candidates; i++) { 631 ShenandoahHeapRegion* const region = sorted_regions[i]._region; 632 size_t region_live_data = sorted_regions[i]._live_data; 633 size_t promotion_need = (size_t) (region_live_data * ShenandoahPromoEvacWaste); 634 if (old_consumed + promotion_need <= old_available) { 635 old_consumed += promotion_need; 636 candidate_regions_for_promotion_by_copy[region->index()] = true; 637 selected_regions++; 638 selected_live += region_live_data; 639 } else { 640 // We rejected this promotable region from the collection set because we had no room to hold its copy. 641 // Add this region to promo potential for next GC. 642 promo_potential += region_live_data; 643 assert(!candidate_regions_for_promotion_by_copy[region->index()], "Shouldn't be selected"); 644 } 645 // We keep going even if one region is excluded from selection because we need to accumulate all eligible 646 // regions that are not preselected into promo_potential 647 } 648 log_debug(gc)("Preselected " SIZE_FORMAT " regions containing " SIZE_FORMAT " live bytes," 649 " consuming: " SIZE_FORMAT " of budgeted: " SIZE_FORMAT, 650 selected_regions, selected_live, old_consumed, old_available); 651 } 652 653 heap->old_generation()->set_pad_for_promote_in_place(promote_in_place_pad); 654 heap->old_generation()->set_promotion_potential(promo_potential); 655 return old_consumed; 656 } 657 658 void ShenandoahGeneration::prepare_regions_and_collection_set(bool concurrent) { 659 ShenandoahHeap* heap = ShenandoahHeap::heap(); 660 ShenandoahCollectionSet* collection_set = heap->collection_set(); 661 bool is_generational = heap->mode()->is_generational(); 662 663 assert(!heap->is_full_gc_in_progress(), "Only for concurrent and degenerated GC"); 664 assert(!is_old(), "Only YOUNG and GLOBAL GC perform evacuations"); 665 { 666 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::final_update_region_states : 667 ShenandoahPhaseTimings::degen_gc_final_update_region_states); 668 ShenandoahFinalMarkUpdateRegionStateClosure cl(complete_marking_context()); 669 parallel_heap_region_iterate(&cl); 670 671 if (is_young()) { 672 // We always need to update the watermark for old regions. If there 673 // are mixed collections pending, we also need to synchronize the 674 // pinned status for old regions. Since we are already visiting every 675 // old region here, go ahead and sync the pin status too. 676 ShenandoahFinalMarkUpdateRegionStateClosure old_cl(nullptr); 677 heap->old_generation()->parallel_heap_region_iterate(&old_cl); 678 } 679 } 680 681 // Tally the census counts and compute the adaptive tenuring threshold 682 if (is_generational && ShenandoahGenerationalAdaptiveTenuring && !ShenandoahGenerationalCensusAtEvac) { 683 // Objects above TAMS weren't included in the age census. Since they were all 684 // allocated in this cycle they belong in the age 0 cohort. We walk over all 685 // young regions and sum the volume of objects between TAMS and top. 686 ShenandoahUpdateCensusZeroCohortClosure age0_cl(complete_marking_context()); 687 heap->young_generation()->heap_region_iterate(&age0_cl); 688 size_t age0_pop = age0_cl.get_age0_population(); 689 690 // Update the global census, including the missed age 0 cohort above, 691 // along with the census done during marking, and compute the tenuring threshold. 692 ShenandoahAgeCensus* census = ShenandoahGenerationalHeap::heap()->age_census(); 693 census->update_census(age0_pop); 694 #ifndef PRODUCT 695 size_t total_pop = age0_cl.get_total_population(); 696 size_t total_census = census->get_total(); 697 // Usually total_pop > total_census, but not by too much. 698 // We use integer division so anything up to just less than 2 is considered 699 // reasonable, and the "+1" is to avoid divide-by-zero. 700 assert((total_pop+1)/(total_census+1) == 1, "Extreme divergence: " 701 SIZE_FORMAT "/" SIZE_FORMAT, total_pop, total_census); 702 #endif 703 } 704 705 { 706 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::choose_cset : 707 ShenandoahPhaseTimings::degen_gc_choose_cset); 708 709 collection_set->clear(); 710 ShenandoahHeapLocker locker(heap->lock()); 711 if (is_generational) { 712 // Seed the collection set with resource area-allocated 713 // preselected regions, which are removed when we exit this scope. 714 ShenandoahCollectionSetPreselector preselector(collection_set, heap->num_regions()); 715 716 // Find the amount that will be promoted, regions that will be promoted in 717 // place, and preselect older regions that will be promoted by evacuation. 718 compute_evacuation_budgets(heap); 719 720 // Choose the collection set, including the regions preselected above for 721 // promotion into the old generation. 722 _heuristics->choose_collection_set(collection_set); 723 if (!collection_set->is_empty()) { 724 // only make use of evacuation budgets when we are evacuating 725 adjust_evacuation_budgets(heap, collection_set); 726 } 727 728 if (is_global()) { 729 // We have just chosen a collection set for a global cycle. The mark bitmap covering old regions is complete, so 730 // the remembered set scan can use that to avoid walking into garbage. When the next old mark begins, we will 731 // use the mark bitmap to make the old regions parsable by coalescing and filling any unmarked objects. Thus, 732 // we prepare for old collections by remembering which regions are old at this time. Note that any objects 733 // promoted into old regions will be above TAMS, and so will be considered marked. However, free regions that 734 // become old after this point will not be covered correctly by the mark bitmap, so we must be careful not to 735 // coalesce those regions. Only the old regions which are not part of the collection set at this point are 736 // eligible for coalescing. As implemented now, this has the side effect of possibly initiating mixed-evacuations 737 // after a global cycle for old regions that were not included in this collection set. 738 heap->old_generation()->prepare_for_mixed_collections_after_global_gc(); 739 } 740 } else { 741 _heuristics->choose_collection_set(collection_set); 742 } 743 } 744 745 746 { 747 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::final_rebuild_freeset : 748 ShenandoahPhaseTimings::degen_gc_final_rebuild_freeset); 749 ShenandoahHeapLocker locker(heap->lock()); 750 size_t young_cset_regions, old_cset_regions; 751 752 // We are preparing for evacuation. At this time, we ignore cset region tallies. 753 size_t first_old, last_old, num_old; 754 heap->free_set()->prepare_to_rebuild(young_cset_regions, old_cset_regions, first_old, last_old, num_old); 755 // Free set construction uses reserve quantities, because they are known to be valid here 756 heap->free_set()->finish_rebuild(young_cset_regions, old_cset_regions, num_old, true); 757 } 758 } 759 760 bool ShenandoahGeneration::is_bitmap_clear() { 761 ShenandoahHeap* heap = ShenandoahHeap::heap(); 762 ShenandoahMarkingContext* context = heap->marking_context(); 763 const size_t num_regions = heap->num_regions(); 764 for (size_t idx = 0; idx < num_regions; idx++) { 765 ShenandoahHeapRegion* r = heap->get_region(idx); 766 if (contains(r) && r->is_affiliated()) { 767 if (heap->is_bitmap_slice_committed(r) && (context->top_at_mark_start(r) > r->bottom()) && 768 !context->is_bitmap_range_within_region_clear(r->bottom(), r->end())) { 769 return false; 770 } 771 } 772 } 773 return true; 774 } 775 776 void ShenandoahGeneration::set_mark_complete() { 777 _is_marking_complete.set(); 778 } 779 780 void ShenandoahGeneration::set_mark_incomplete() { 781 _is_marking_complete.unset(); 782 } 783 784 ShenandoahMarkingContext* ShenandoahGeneration::complete_marking_context() { 785 assert(is_mark_complete(), "Marking must be completed."); 786 return ShenandoahHeap::heap()->marking_context(); 787 } 788 789 void ShenandoahGeneration::cancel_marking() { 790 log_info(gc)("Cancel marking: %s", name()); 791 if (is_concurrent_mark_in_progress()) { 792 set_mark_incomplete(); 793 } 794 _task_queues->clear(); 795 ref_processor()->abandon_partial_discovery(); 796 set_concurrent_mark_in_progress(false); 797 } 798 799 ShenandoahGeneration::ShenandoahGeneration(ShenandoahGenerationType type, 800 uint max_workers, 801 size_t max_capacity) : 802 _type(type), 803 _task_queues(new ShenandoahObjToScanQueueSet(max_workers)), 804 _ref_processor(new ShenandoahReferenceProcessor(MAX2(max_workers, 1U))), 805 _affiliated_region_count(0), _humongous_waste(0), _evacuation_reserve(0), 806 _used(0), _bytes_allocated_since_gc_start(0), 807 _max_capacity(max_capacity), 808 _heuristics(nullptr) 809 { 810 _is_marking_complete.set(); 811 assert(max_workers > 0, "At least one queue"); 812 for (uint i = 0; i < max_workers; ++i) { 813 ShenandoahObjToScanQueue* task_queue = new ShenandoahObjToScanQueue(); 814 _task_queues->register_queue(i, task_queue); 815 } 816 } 817 818 ShenandoahGeneration::~ShenandoahGeneration() { 819 for (uint i = 0; i < _task_queues->size(); ++i) { 820 ShenandoahObjToScanQueue* q = _task_queues->queue(i); 821 delete q; 822 } 823 delete _task_queues; 824 } 825 826 void ShenandoahGeneration::reserve_task_queues(uint workers) { 827 _task_queues->reserve(workers); 828 } 829 830 ShenandoahObjToScanQueueSet* ShenandoahGeneration::old_gen_task_queues() const { 831 return nullptr; 832 } 833 834 void ShenandoahGeneration::scan_remembered_set(bool is_concurrent) { 835 assert(is_young(), "Should only scan remembered set for young generation."); 836 837 ShenandoahGenerationalHeap* const heap = ShenandoahGenerationalHeap::heap(); 838 uint nworkers = heap->workers()->active_workers(); 839 reserve_task_queues(nworkers); 840 841 ShenandoahReferenceProcessor* rp = ref_processor(); 842 ShenandoahRegionChunkIterator work_list(nworkers); 843 ShenandoahScanRememberedTask task(task_queues(), old_gen_task_queues(), rp, &work_list, is_concurrent); 844 heap->assert_gc_workers(nworkers); 845 heap->workers()->run_task(&task); 846 if (ShenandoahEnableCardStats) { 847 ShenandoahScanRemembered* scanner = heap->old_generation()->card_scan(); 848 assert(scanner != nullptr, "Not generational"); 849 scanner->log_card_stats(nworkers, CARD_STAT_SCAN_RS); 850 } 851 } 852 853 size_t ShenandoahGeneration::increment_affiliated_region_count() { 854 shenandoah_assert_heaplocked_or_safepoint(); 855 // During full gc, multiple GC worker threads may change region affiliations without a lock. No lock is enforced 856 // on read and write of _affiliated_region_count. At the end of full gc, a single thread overwrites the count with 857 // a coherent value. 858 return Atomic::add(&_affiliated_region_count, (size_t) 1); 859 } 860 861 size_t ShenandoahGeneration::decrement_affiliated_region_count() { 862 shenandoah_assert_heaplocked_or_safepoint(); 863 // During full gc, multiple GC worker threads may change region affiliations without a lock. No lock is enforced 864 // on read and write of _affiliated_region_count. At the end of full gc, a single thread overwrites the count with 865 // a coherent value. 866 auto affiliated_region_count = Atomic::sub(&_affiliated_region_count, (size_t) 1); 867 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() || 868 (used() + _humongous_waste <= affiliated_region_count * ShenandoahHeapRegion::region_size_bytes()), 869 "used + humongous cannot exceed regions"); 870 return affiliated_region_count; 871 } 872 873 size_t ShenandoahGeneration::decrement_affiliated_region_count_without_lock() { 874 return Atomic::sub(&_affiliated_region_count, (size_t) 1); 875 } 876 877 size_t ShenandoahGeneration::increase_affiliated_region_count(size_t delta) { 878 shenandoah_assert_heaplocked_or_safepoint(); 879 return Atomic::add(&_affiliated_region_count, delta); 880 } 881 882 size_t ShenandoahGeneration::decrease_affiliated_region_count(size_t delta) { 883 shenandoah_assert_heaplocked_or_safepoint(); 884 assert(Atomic::load(&_affiliated_region_count) >= delta, "Affiliated region count cannot be negative"); 885 886 auto const affiliated_region_count = Atomic::sub(&_affiliated_region_count, delta); 887 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() || 888 (_used + _humongous_waste <= affiliated_region_count * ShenandoahHeapRegion::region_size_bytes()), 889 "used + humongous cannot exceed regions"); 890 return affiliated_region_count; 891 } 892 893 void ShenandoahGeneration::establish_usage(size_t num_regions, size_t num_bytes, size_t humongous_waste) { 894 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint"); 895 Atomic::store(&_affiliated_region_count, num_regions); 896 Atomic::store(&_used, num_bytes); 897 _humongous_waste = humongous_waste; 898 } 899 900 void ShenandoahGeneration::increase_used(size_t bytes) { 901 Atomic::add(&_used, bytes); 902 } 903 904 void ShenandoahGeneration::increase_humongous_waste(size_t bytes) { 905 if (bytes > 0) { 906 Atomic::add(&_humongous_waste, bytes); 907 } 908 } 909 910 void ShenandoahGeneration::decrease_humongous_waste(size_t bytes) { 911 if (bytes > 0) { 912 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() || (_humongous_waste >= bytes), 913 "Waste (" SIZE_FORMAT ") cannot be negative (after subtracting " SIZE_FORMAT ")", _humongous_waste, bytes); 914 Atomic::sub(&_humongous_waste, bytes); 915 } 916 } 917 918 void ShenandoahGeneration::decrease_used(size_t bytes) { 919 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() || 920 (_used >= bytes), "cannot reduce bytes used by generation below zero"); 921 Atomic::sub(&_used, bytes); 922 } 923 924 size_t ShenandoahGeneration::used_regions() const { 925 return Atomic::load(&_affiliated_region_count); 926 } 927 928 size_t ShenandoahGeneration::free_unaffiliated_regions() const { 929 size_t result = max_capacity() / ShenandoahHeapRegion::region_size_bytes(); 930 auto const used_regions = this->used_regions(); 931 if (used_regions > result) { 932 result = 0; 933 } else { 934 result -= used_regions; 935 } 936 return result; 937 } 938 939 size_t ShenandoahGeneration::used_regions_size() const { 940 return used_regions() * ShenandoahHeapRegion::region_size_bytes(); 941 } 942 943 size_t ShenandoahGeneration::available() const { 944 return available(max_capacity()); 945 } 946 947 // For ShenandoahYoungGeneration, Include the young available that may have been reserved for the Collector. 948 size_t ShenandoahGeneration::available_with_reserve() const { 949 return available(max_capacity()); 950 } 951 952 size_t ShenandoahGeneration::soft_available() const { 953 return available(ShenandoahHeap::heap()->soft_max_capacity()); 954 } 955 956 size_t ShenandoahGeneration::available(size_t capacity) const { 957 size_t in_use = used() + get_humongous_waste(); 958 return in_use > capacity ? 0 : capacity - in_use; 959 } 960 961 size_t ShenandoahGeneration::increase_capacity(size_t increment) { 962 shenandoah_assert_heaplocked_or_safepoint(); 963 964 // We do not enforce that new capacity >= heap->max_size_for(this). The maximum generation size is treated as a rule of thumb 965 // which may be violated during certain transitions, such as when we are forcing transfers for the purpose of promoting regions 966 // in place. 967 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() || 968 (_max_capacity + increment <= ShenandoahHeap::heap()->max_capacity()), "Generation cannot be larger than heap size"); 969 assert(increment % ShenandoahHeapRegion::region_size_bytes() == 0, "Generation capacity must be multiple of region size"); 970 _max_capacity += increment; 971 972 // This detects arithmetic wraparound on _used 973 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() || 974 (used_regions_size() >= used()), 975 "Affiliated regions must hold more than what is currently used"); 976 return _max_capacity; 977 } 978 979 size_t ShenandoahGeneration::set_capacity(size_t byte_size) { 980 shenandoah_assert_heaplocked_or_safepoint(); 981 _max_capacity = byte_size; 982 return _max_capacity; 983 } 984 985 size_t ShenandoahGeneration::decrease_capacity(size_t decrement) { 986 shenandoah_assert_heaplocked_or_safepoint(); 987 988 // We do not enforce that new capacity >= heap->min_size_for(this). The minimum generation size is treated as a rule of thumb 989 // which may be violated during certain transitions, such as when we are forcing transfers for the purpose of promoting regions 990 // in place. 991 assert(decrement % ShenandoahHeapRegion::region_size_bytes() == 0, "Generation capacity must be multiple of region size"); 992 assert(_max_capacity >= decrement, "Generation capacity cannot be negative"); 993 994 _max_capacity -= decrement; 995 996 // This detects arithmetic wraparound on _used 997 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() || 998 (used_regions_size() >= used()), 999 "Affiliated regions must hold more than what is currently used"); 1000 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() || 1001 (_used <= _max_capacity), "Cannot use more than capacity"); 1002 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() || 1003 (used_regions_size() <= _max_capacity), 1004 "Cannot use more than capacity"); 1005 return _max_capacity; 1006 } 1007 1008 void ShenandoahGeneration::record_success_concurrent(bool abbreviated) { 1009 heuristics()->record_success_concurrent(); 1010 ShenandoahHeap::heap()->shenandoah_policy()->record_success_concurrent(is_young(), abbreviated); 1011 }