1 /* 2 * Copyright (c) 2014, 2021, Red Hat, Inc. 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 27 #include "compiler/oopMap.hpp" 28 #include "gc/shared/gcTraceTime.inline.hpp" 29 #include "gc/shared/preservedMarks.inline.hpp" 30 #include "gc/shared/slidingForwarding.inline.hpp" 31 #include "gc/shared/tlab_globals.hpp" 32 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp" 33 #include "gc/shenandoah/shenandoahConcurrentGC.hpp" 34 #include "gc/shenandoah/shenandoahCollectionSet.hpp" 35 #include "gc/shenandoah/shenandoahFreeSet.hpp" 36 #include "gc/shenandoah/shenandoahFullGC.hpp" 37 #include "gc/shenandoah/shenandoahPhaseTimings.hpp" 38 #include "gc/shenandoah/shenandoahMark.inline.hpp" 39 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp" 40 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp" 41 #include "gc/shenandoah/shenandoahHeap.inline.hpp" 42 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp" 43 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp" 44 #include "gc/shenandoah/shenandoahMetrics.hpp" 45 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp" 46 #include "gc/shenandoah/shenandoahReferenceProcessor.hpp" 47 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp" 48 #include "gc/shenandoah/shenandoahSTWMark.hpp" 49 #include "gc/shenandoah/shenandoahUtils.hpp" 50 #include "gc/shenandoah/shenandoahVerifier.hpp" 51 #include "gc/shenandoah/shenandoahVMOperations.hpp" 52 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp" 53 #include "memory/metaspaceUtils.hpp" 54 #include "memory/universe.hpp" 55 #include "oops/compressedOops.inline.hpp" 56 #include "oops/oop.inline.hpp" 57 #include "runtime/biasedLocking.hpp" 58 #include "runtime/orderAccess.hpp" 59 #include "runtime/thread.hpp" 60 #include "runtime/vmThread.hpp" 61 #include "utilities/copy.hpp" 62 #include "utilities/events.hpp" 63 #include "utilities/growableArray.hpp" 64 #include "gc/shared/workgroup.hpp" 65 66 ShenandoahFullGC::ShenandoahFullGC() : 67 _gc_timer(ShenandoahHeap::heap()->gc_timer()), 68 _preserved_marks(new PreservedMarksSet(true)) {} 69 70 ShenandoahFullGC::~ShenandoahFullGC() { 71 delete _preserved_marks; 72 } 73 74 bool ShenandoahFullGC::collect(GCCause::Cause cause) { 75 vmop_entry_full(cause); 76 // Always success 77 return true; 78 } 79 80 void ShenandoahFullGC::vmop_entry_full(GCCause::Cause cause) { 81 ShenandoahHeap* const heap = ShenandoahHeap::heap(); 82 TraceCollectorStats tcs(heap->monitoring_support()->full_stw_collection_counters()); 83 ShenandoahTimingsTracker timing(ShenandoahPhaseTimings::full_gc_gross); 84 85 heap->try_inject_alloc_failure(); 86 VM_ShenandoahFullGC op(cause, this); 87 VMThread::execute(&op); 88 } 89 90 void ShenandoahFullGC::entry_full(GCCause::Cause cause) { 91 static const char* msg = "Pause Full"; 92 ShenandoahPausePhase gc_phase(msg, ShenandoahPhaseTimings::full_gc, true /* log_heap_usage */); 93 EventMark em("%s", msg); 94 95 ShenandoahWorkerScope scope(ShenandoahHeap::heap()->workers(), 96 ShenandoahWorkerPolicy::calc_workers_for_fullgc(), 97 "full gc"); 98 99 op_full(cause); 100 } 101 102 void ShenandoahFullGC::op_full(GCCause::Cause cause) { 103 ShenandoahMetricsSnapshot metrics; 104 metrics.snap_before(); 105 106 // Perform full GC 107 do_it(cause); 108 109 metrics.snap_after(); 110 111 if (metrics.is_good_progress()) { 112 ShenandoahHeap::heap()->notify_gc_progress(); 113 } else { 114 // Nothing to do. Tell the allocation path that we have failed to make 115 // progress, and it can finally fail. 116 ShenandoahHeap::heap()->notify_gc_no_progress(); 117 } 118 } 119 120 void ShenandoahFullGC::do_it(GCCause::Cause gc_cause) { 121 ShenandoahHeap* heap = ShenandoahHeap::heap(); 122 123 if (ShenandoahVerify) { 124 heap->verifier()->verify_before_fullgc(); 125 } 126 127 if (VerifyBeforeGC) { 128 Universe::verify(); 129 } 130 131 // Degenerated GC may carry concurrent root flags when upgrading to 132 // full GC. We need to reset it before mutators resume. 133 heap->set_concurrent_strong_root_in_progress(false); 134 heap->set_concurrent_weak_root_in_progress(false); 135 136 heap->set_full_gc_in_progress(true); 137 138 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint"); 139 assert(Thread::current()->is_VM_thread(), "Do full GC only while world is stopped"); 140 141 { 142 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdump_pre); 143 heap->pre_full_gc_dump(_gc_timer); 144 } 145 146 { 147 ShenandoahGCPhase prepare_phase(ShenandoahPhaseTimings::full_gc_prepare); 148 // Full GC is supposed to recover from any GC state: 149 150 // a0. Remember if we have forwarded objects 151 bool has_forwarded_objects = heap->has_forwarded_objects(); 152 153 // a1. Cancel evacuation, if in progress 154 if (heap->is_evacuation_in_progress()) { 155 heap->set_evacuation_in_progress(false); 156 } 157 assert(!heap->is_evacuation_in_progress(), "sanity"); 158 159 // a2. Cancel update-refs, if in progress 160 if (heap->is_update_refs_in_progress()) { 161 heap->set_update_refs_in_progress(false); 162 } 163 assert(!heap->is_update_refs_in_progress(), "sanity"); 164 165 // b. Cancel concurrent mark, if in progress 166 if (heap->is_concurrent_mark_in_progress()) { 167 ShenandoahConcurrentGC::cancel(); 168 heap->set_concurrent_mark_in_progress(false); 169 } 170 assert(!heap->is_concurrent_mark_in_progress(), "sanity"); 171 172 // c. Update roots if this full GC is due to evac-oom, which may carry from-space pointers in roots. 173 if (has_forwarded_objects) { 174 update_roots(true /*full_gc*/); 175 } 176 177 // d. Reset the bitmaps for new marking 178 heap->reset_mark_bitmap(); 179 assert(heap->marking_context()->is_bitmap_clear(), "sanity"); 180 assert(!heap->marking_context()->is_complete(), "sanity"); 181 182 // e. Abandon reference discovery and clear all discovered references. 183 ShenandoahReferenceProcessor* rp = heap->ref_processor(); 184 rp->abandon_partial_discovery(); 185 186 // f. Sync pinned region status from the CP marks 187 heap->sync_pinned_region_status(); 188 189 // The rest of prologue: 190 BiasedLocking::preserve_marks(); 191 _preserved_marks->init(heap->workers()->active_workers()); 192 heap->forwarding()->clear(); 193 194 assert(heap->has_forwarded_objects() == has_forwarded_objects, "This should not change"); 195 } 196 197 if (UseTLAB) { 198 heap->gclabs_retire(ResizeTLAB); 199 heap->tlabs_retire(ResizeTLAB); 200 } 201 202 OrderAccess::fence(); 203 204 phase1_mark_heap(); 205 206 // Once marking is done, which may have fixed up forwarded objects, we can drop it. 207 // Coming out of Full GC, we would not have any forwarded objects. 208 // This also prevents resolves with fwdptr from kicking in while adjusting pointers in phase3. 209 heap->set_has_forwarded_objects(false); 210 211 heap->set_full_gc_move_in_progress(true); 212 213 // Setup workers for the rest 214 OrderAccess::fence(); 215 216 // Initialize worker slices 217 ShenandoahHeapRegionSet** worker_slices = NEW_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, heap->max_workers(), mtGC); 218 for (uint i = 0; i < heap->max_workers(); i++) { 219 worker_slices[i] = new ShenandoahHeapRegionSet(); 220 } 221 222 { 223 // The rest of code performs region moves, where region status is undefined 224 // until all phases run together. 225 ShenandoahHeapLocker lock(heap->lock()); 226 227 phase2_calculate_target_addresses(worker_slices); 228 229 OrderAccess::fence(); 230 231 phase3_update_references(); 232 233 phase4_compact_objects(worker_slices); 234 } 235 236 { 237 // Epilogue 238 _preserved_marks->restore(heap->workers()); 239 BiasedLocking::restore_marks(); 240 _preserved_marks->reclaim(); 241 } 242 243 // Resize metaspace 244 MetaspaceGC::compute_new_size(); 245 246 // Free worker slices 247 for (uint i = 0; i < heap->max_workers(); i++) { 248 delete worker_slices[i]; 249 } 250 FREE_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, worker_slices); 251 252 heap->set_full_gc_move_in_progress(false); 253 heap->set_full_gc_in_progress(false); 254 255 if (ShenandoahVerify) { 256 heap->verifier()->verify_after_fullgc(); 257 } 258 259 if (VerifyAfterGC) { 260 Universe::verify(); 261 } 262 263 { 264 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdump_post); 265 heap->post_full_gc_dump(_gc_timer); 266 } 267 } 268 269 class ShenandoahPrepareForMarkClosure: public ShenandoahHeapRegionClosure { 270 private: 271 ShenandoahMarkingContext* const _ctx; 272 273 public: 274 ShenandoahPrepareForMarkClosure() : _ctx(ShenandoahHeap::heap()->marking_context()) {} 275 276 void heap_region_do(ShenandoahHeapRegion *r) { 277 _ctx->capture_top_at_mark_start(r); 278 r->clear_live_data(); 279 } 280 }; 281 282 void ShenandoahFullGC::phase1_mark_heap() { 283 GCTraceTime(Info, gc, phases) time("Phase 1: Mark live objects", _gc_timer); 284 ShenandoahGCPhase mark_phase(ShenandoahPhaseTimings::full_gc_mark); 285 286 ShenandoahHeap* heap = ShenandoahHeap::heap(); 287 288 ShenandoahPrepareForMarkClosure cl; 289 heap->heap_region_iterate(&cl); 290 291 heap->set_unload_classes(heap->heuristics()->can_unload_classes()); 292 293 ShenandoahReferenceProcessor* rp = heap->ref_processor(); 294 // enable ("weak") refs discovery 295 rp->set_soft_reference_policy(true); // forcefully purge all soft references 296 297 ShenandoahSTWMark mark(true /*full_gc*/); 298 mark.mark(); 299 heap->parallel_cleaning(true /* full_gc */); 300 } 301 302 class ShenandoahPrepareForCompactionObjectClosure : public ObjectClosure { 303 private: 304 PreservedMarks* const _preserved_marks; 305 SlidingForwarding* const _forwarding; 306 ShenandoahHeap* const _heap; 307 GrowableArray<ShenandoahHeapRegion*>& _empty_regions; 308 int _empty_regions_pos; 309 ShenandoahHeapRegion* _to_region; 310 ShenandoahHeapRegion* _from_region; 311 HeapWord* _compact_point; 312 313 public: 314 ShenandoahPrepareForCompactionObjectClosure(PreservedMarks* preserved_marks, 315 GrowableArray<ShenandoahHeapRegion*>& empty_regions, 316 ShenandoahHeapRegion* to_region) : 317 _preserved_marks(preserved_marks), 318 _forwarding(ShenandoahHeap::heap()->forwarding()), 319 _heap(ShenandoahHeap::heap()), 320 _empty_regions(empty_regions), 321 _empty_regions_pos(0), 322 _to_region(to_region), 323 _from_region(NULL), 324 _compact_point(to_region->bottom()) {} 325 326 void set_from_region(ShenandoahHeapRegion* from_region) { 327 _from_region = from_region; 328 } 329 330 void finish_region() { 331 assert(_to_region != NULL, "should not happen"); 332 _to_region->set_new_top(_compact_point); 333 } 334 335 bool is_compact_same_region() { 336 return _from_region == _to_region; 337 } 338 339 int empty_regions_pos() { 340 return _empty_regions_pos; 341 } 342 343 void do_object(oop p) { 344 assert(_from_region != NULL, "must set before work"); 345 assert(_heap->complete_marking_context()->is_marked(p), "must be marked"); 346 assert(!_heap->complete_marking_context()->allocated_after_mark_start(p), "must be truly marked"); 347 348 size_t obj_size = p->size(); 349 if (_compact_point + obj_size > _to_region->end()) { 350 finish_region(); 351 352 // Object doesn't fit. Pick next empty region and start compacting there. 353 ShenandoahHeapRegion* new_to_region; 354 if (_empty_regions_pos < _empty_regions.length()) { 355 new_to_region = _empty_regions.at(_empty_regions_pos); 356 _empty_regions_pos++; 357 } else { 358 // Out of empty region? Compact within the same region. 359 new_to_region = _from_region; 360 } 361 362 assert(new_to_region != _to_region, "must not reuse same to-region"); 363 assert(new_to_region != NULL, "must not be NULL"); 364 _to_region = new_to_region; 365 _compact_point = _to_region->bottom(); 366 } 367 368 // Object fits into current region, record new location: 369 assert(_compact_point + obj_size <= _to_region->end(), "must fit"); 370 shenandoah_assert_not_forwarded(NULL, p); 371 _preserved_marks->push_if_necessary(p, p->mark()); 372 _forwarding->forward_to(p, cast_to_oop(_compact_point)); 373 _compact_point += obj_size; 374 } 375 }; 376 377 class ShenandoahPrepareForCompactionTask : public AbstractGangTask { 378 private: 379 PreservedMarksSet* const _preserved_marks; 380 ShenandoahHeap* const _heap; 381 ShenandoahHeapRegionSet** const _worker_slices; 382 383 public: 384 ShenandoahPrepareForCompactionTask(PreservedMarksSet *preserved_marks, ShenandoahHeapRegionSet **worker_slices) : 385 AbstractGangTask("Shenandoah Prepare For Compaction"), 386 _preserved_marks(preserved_marks), 387 _heap(ShenandoahHeap::heap()), _worker_slices(worker_slices) { 388 } 389 390 static bool is_candidate_region(ShenandoahHeapRegion* r) { 391 // Empty region: get it into the slice to defragment the slice itself. 392 // We could have skipped this without violating correctness, but we really 393 // want to compact all live regions to the start of the heap, which sometimes 394 // means moving them into the fully empty regions. 395 if (r->is_empty()) return true; 396 397 // Can move the region, and this is not the humongous region. Humongous 398 // moves are special cased here, because their moves are handled separately. 399 return r->is_stw_move_allowed() && !r->is_humongous(); 400 } 401 402 void work(uint worker_id) { 403 ShenandoahParallelWorkerSession worker_session(worker_id); 404 ShenandoahHeapRegionSet* slice = _worker_slices[worker_id]; 405 ShenandoahHeapRegionSetIterator it(slice); 406 ShenandoahHeapRegion* from_region = it.next(); 407 // No work? 408 if (from_region == NULL) { 409 return; 410 } 411 412 // Sliding compaction. Walk all regions in the slice, and compact them. 413 // Remember empty regions and reuse them as needed. 414 ResourceMark rm; 415 416 GrowableArray<ShenandoahHeapRegion*> empty_regions((int)_heap->num_regions()); 417 418 ShenandoahPrepareForCompactionObjectClosure cl(_preserved_marks->get(worker_id), empty_regions, from_region); 419 420 while (from_region != NULL) { 421 assert(is_candidate_region(from_region), "Sanity"); 422 423 cl.set_from_region(from_region); 424 if (from_region->has_live()) { 425 _heap->marked_object_iterate(from_region, &cl); 426 } 427 428 // Compacted the region to somewhere else? From-region is empty then. 429 if (!cl.is_compact_same_region()) { 430 empty_regions.append(from_region); 431 } 432 from_region = it.next(); 433 } 434 cl.finish_region(); 435 436 // Mark all remaining regions as empty 437 for (int pos = cl.empty_regions_pos(); pos < empty_regions.length(); ++pos) { 438 ShenandoahHeapRegion* r = empty_regions.at(pos); 439 r->set_new_top(r->bottom()); 440 } 441 } 442 }; 443 444 void ShenandoahFullGC::calculate_target_humongous_objects() { 445 ShenandoahHeap* heap = ShenandoahHeap::heap(); 446 SlidingForwarding* forwarding = heap->forwarding(); 447 448 // Compute the new addresses for humongous objects. We need to do this after addresses 449 // for regular objects are calculated, and we know what regions in heap suffix are 450 // available for humongous moves. 451 // 452 // Scan the heap backwards, because we are compacting humongous regions towards the end. 453 // Maintain the contiguous compaction window in [to_begin; to_end), so that we can slide 454 // humongous start there. 455 // 456 // The complication is potential non-movable regions during the scan. If such region is 457 // detected, then sliding restarts towards that non-movable region. 458 459 size_t to_begin = heap->num_regions(); 460 size_t to_end = heap->num_regions(); 461 462 for (size_t c = heap->num_regions(); c > 0; c--) { 463 ShenandoahHeapRegion *r = heap->get_region(c - 1); 464 if (r->is_humongous_continuation() || (r->new_top() == r->bottom())) { 465 // To-region candidate: record this, and continue scan 466 to_begin = r->index(); 467 continue; 468 } 469 470 if (r->is_humongous_start() && r->is_stw_move_allowed()) { 471 // From-region candidate: movable humongous region 472 oop old_obj = cast_to_oop(r->bottom()); 473 size_t words_size = old_obj->size(); 474 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize); 475 476 size_t start = to_end - num_regions; 477 478 if (start >= to_begin && start != r->index()) { 479 // Fits into current window, and the move is non-trivial. Record the move then, and continue scan. 480 _preserved_marks->get(0)->push_if_necessary(old_obj, old_obj->mark()); 481 forwarding->forward_to(old_obj, cast_to_oop(heap->get_region(start)->bottom())); 482 to_end = start; 483 continue; 484 } 485 } 486 487 // Failed to fit. Scan starting from current region. 488 to_begin = r->index(); 489 to_end = r->index(); 490 } 491 } 492 493 class ShenandoahEnsureHeapActiveClosure: public ShenandoahHeapRegionClosure { 494 private: 495 ShenandoahHeap* const _heap; 496 497 public: 498 ShenandoahEnsureHeapActiveClosure() : _heap(ShenandoahHeap::heap()) {} 499 void heap_region_do(ShenandoahHeapRegion* r) { 500 if (r->is_trash()) { 501 r->recycle(); 502 } 503 if (r->is_cset()) { 504 r->make_regular_bypass(); 505 } 506 if (r->is_empty_uncommitted()) { 507 r->make_committed_bypass(); 508 } 509 assert (r->is_committed(), "only committed regions in heap now, see region " SIZE_FORMAT, r->index()); 510 511 // Record current region occupancy: this communicates empty regions are free 512 // to the rest of Full GC code. 513 r->set_new_top(r->top()); 514 } 515 }; 516 517 class ShenandoahTrashImmediateGarbageClosure: public ShenandoahHeapRegionClosure { 518 private: 519 ShenandoahHeap* const _heap; 520 ShenandoahMarkingContext* const _ctx; 521 522 public: 523 ShenandoahTrashImmediateGarbageClosure() : 524 _heap(ShenandoahHeap::heap()), 525 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {} 526 527 void heap_region_do(ShenandoahHeapRegion* r) { 528 if (r->is_humongous_start()) { 529 oop humongous_obj = cast_to_oop(r->bottom()); 530 if (!_ctx->is_marked(humongous_obj)) { 531 assert(!r->has_live(), 532 "Region " SIZE_FORMAT " is not marked, should not have live", r->index()); 533 _heap->trash_humongous_region_at(r); 534 } else { 535 assert(r->has_live(), 536 "Region " SIZE_FORMAT " should have live", r->index()); 537 } 538 } else if (r->is_humongous_continuation()) { 539 // If we hit continuation, the non-live humongous starts should have been trashed already 540 assert(r->humongous_start_region()->has_live(), 541 "Region " SIZE_FORMAT " should have live", r->index()); 542 } else if (r->is_regular()) { 543 if (!r->has_live()) { 544 r->make_trash_immediate(); 545 } 546 } 547 } 548 }; 549 550 void ShenandoahFullGC::distribute_slices(ShenandoahHeapRegionSet** worker_slices) { 551 ShenandoahHeap* heap = ShenandoahHeap::heap(); 552 553 uint n_workers = heap->workers()->active_workers(); 554 size_t n_regions = heap->num_regions(); 555 556 // What we want to accomplish: have the dense prefix of data, while still balancing 557 // out the parallel work. 558 // 559 // Assuming the amount of work is driven by the live data that needs moving, we can slice 560 // the entire heap into equal-live-sized prefix slices, and compact into them. So, each 561 // thread takes all regions in its prefix subset, and then it takes some regions from 562 // the tail. 563 // 564 // Tail region selection becomes interesting. 565 // 566 // First, we want to distribute the regions fairly between the workers, and those regions 567 // might have different amount of live data. So, until we sure no workers need live data, 568 // we need to only take what the worker needs. 569 // 570 // Second, since we slide everything to the left in each slice, the most busy regions 571 // would be the ones on the left. Which means we want to have all workers have their after-tail 572 // regions as close to the left as possible. 573 // 574 // The easiest way to do this is to distribute after-tail regions in round-robin between 575 // workers that still need live data. 576 // 577 // Consider parallel workers A, B, C, then the target slice layout would be: 578 // 579 // AAAAAAAABBBBBBBBCCCCCCCC|ABCABCABCABCABCABCABCABABABABABABABABABABAAAAA 580 // 581 // (.....dense-prefix.....) (.....................tail...................) 582 // [all regions fully live] [left-most regions are fuller that right-most] 583 // 584 585 // Compute how much live data is there. This would approximate the size of dense prefix 586 // we target to create. 587 size_t total_live = 0; 588 for (size_t idx = 0; idx < n_regions; idx++) { 589 ShenandoahHeapRegion *r = heap->get_region(idx); 590 if (ShenandoahPrepareForCompactionTask::is_candidate_region(r)) { 591 total_live += r->get_live_data_words(); 592 } 593 } 594 595 // Estimate the size for the dense prefix. Note that we specifically count only the 596 // "full" regions, so there would be some non-full regions in the slice tail. 597 size_t live_per_worker = total_live / n_workers; 598 size_t prefix_regions_per_worker = live_per_worker / ShenandoahHeapRegion::region_size_words(); 599 size_t prefix_regions_total = prefix_regions_per_worker * n_workers; 600 prefix_regions_total = MIN2(prefix_regions_total, n_regions); 601 assert(prefix_regions_total <= n_regions, "Sanity"); 602 603 // There might be non-candidate regions in the prefix. To compute where the tail actually 604 // ends up being, we need to account those as well. 605 size_t prefix_end = prefix_regions_total; 606 for (size_t idx = 0; idx < prefix_regions_total; idx++) { 607 ShenandoahHeapRegion *r = heap->get_region(idx); 608 if (!ShenandoahPrepareForCompactionTask::is_candidate_region(r)) { 609 prefix_end++; 610 } 611 } 612 prefix_end = MIN2(prefix_end, n_regions); 613 assert(prefix_end <= n_regions, "Sanity"); 614 615 // Distribute prefix regions per worker: each thread definitely gets its own same-sized 616 // subset of dense prefix. 617 size_t prefix_idx = 0; 618 619 size_t* live = NEW_C_HEAP_ARRAY(size_t, n_workers, mtGC); 620 621 for (size_t wid = 0; wid < n_workers; wid++) { 622 ShenandoahHeapRegionSet* slice = worker_slices[wid]; 623 624 live[wid] = 0; 625 size_t regs = 0; 626 627 // Add all prefix regions for this worker 628 while (prefix_idx < prefix_end && regs < prefix_regions_per_worker) { 629 ShenandoahHeapRegion *r = heap->get_region(prefix_idx); 630 if (ShenandoahPrepareForCompactionTask::is_candidate_region(r)) { 631 slice->add_region(r); 632 live[wid] += r->get_live_data_words(); 633 regs++; 634 } 635 prefix_idx++; 636 } 637 } 638 639 // Distribute the tail among workers in round-robin fashion. 640 size_t wid = n_workers - 1; 641 642 for (size_t tail_idx = prefix_end; tail_idx < n_regions; tail_idx++) { 643 ShenandoahHeapRegion *r = heap->get_region(tail_idx); 644 if (ShenandoahPrepareForCompactionTask::is_candidate_region(r)) { 645 assert(wid < n_workers, "Sanity"); 646 647 size_t live_region = r->get_live_data_words(); 648 649 // Select next worker that still needs live data. 650 size_t old_wid = wid; 651 do { 652 wid++; 653 if (wid == n_workers) wid = 0; 654 } while (live[wid] + live_region >= live_per_worker && old_wid != wid); 655 656 if (old_wid == wid) { 657 // Circled back to the same worker? This means liveness data was 658 // miscalculated. Bump the live_per_worker limit so that 659 // everyone gets a piece of the leftover work. 660 live_per_worker += ShenandoahHeapRegion::region_size_words(); 661 } 662 663 worker_slices[wid]->add_region(r); 664 live[wid] += live_region; 665 } 666 } 667 668 FREE_C_HEAP_ARRAY(size_t, live); 669 670 #ifdef ASSERT 671 ResourceBitMap map(n_regions); 672 for (size_t wid = 0; wid < n_workers; wid++) { 673 ShenandoahHeapRegionSetIterator it(worker_slices[wid]); 674 ShenandoahHeapRegion* r = it.next(); 675 while (r != NULL) { 676 size_t idx = r->index(); 677 assert(ShenandoahPrepareForCompactionTask::is_candidate_region(r), "Sanity: " SIZE_FORMAT, idx); 678 assert(!map.at(idx), "No region distributed twice: " SIZE_FORMAT, idx); 679 map.at_put(idx, true); 680 r = it.next(); 681 } 682 } 683 684 for (size_t rid = 0; rid < n_regions; rid++) { 685 bool is_candidate = ShenandoahPrepareForCompactionTask::is_candidate_region(heap->get_region(rid)); 686 bool is_distributed = map.at(rid); 687 assert(is_distributed || !is_candidate, "All candidates are distributed: " SIZE_FORMAT, rid); 688 } 689 #endif 690 } 691 692 void ShenandoahFullGC::phase2_calculate_target_addresses(ShenandoahHeapRegionSet** worker_slices) { 693 GCTraceTime(Info, gc, phases) time("Phase 2: Compute new object addresses", _gc_timer); 694 ShenandoahGCPhase calculate_address_phase(ShenandoahPhaseTimings::full_gc_calculate_addresses); 695 696 ShenandoahHeap* heap = ShenandoahHeap::heap(); 697 698 // About to figure out which regions can be compacted, make sure pinning status 699 // had been updated in GC prologue. 700 heap->assert_pinned_region_status(); 701 702 { 703 // Trash the immediately collectible regions before computing addresses 704 ShenandoahTrashImmediateGarbageClosure tigcl; 705 heap->heap_region_iterate(&tigcl); 706 707 // Make sure regions are in good state: committed, active, clean. 708 // This is needed because we are potentially sliding the data through them. 709 ShenandoahEnsureHeapActiveClosure ecl; 710 heap->heap_region_iterate(&ecl); 711 } 712 713 // Compute the new addresses for regular objects 714 { 715 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_regular); 716 717 distribute_slices(worker_slices); 718 719 ShenandoahPrepareForCompactionTask task(_preserved_marks, worker_slices); 720 heap->workers()->run_task(&task); 721 } 722 723 // Compute the new addresses for humongous objects 724 { 725 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_humong); 726 calculate_target_humongous_objects(); 727 } 728 } 729 730 class ShenandoahAdjustPointersClosure : public MetadataVisitingOopIterateClosure { 731 private: 732 ShenandoahHeap* const _heap; 733 const SlidingForwarding* const _forwarding; 734 ShenandoahMarkingContext* const _ctx; 735 736 template <class T> 737 inline void do_oop_work(T* p) { 738 T o = RawAccess<>::oop_load(p); 739 if (!CompressedOops::is_null(o)) { 740 oop obj = CompressedOops::decode_not_null(o); 741 assert(_ctx->is_marked(obj), "must be marked"); 742 if (obj->is_forwarded()) { 743 oop forw = _forwarding->forwardee(obj); 744 RawAccess<IS_NOT_NULL>::oop_store(p, forw); 745 } 746 } 747 } 748 749 public: 750 ShenandoahAdjustPointersClosure() : 751 _heap(ShenandoahHeap::heap()), 752 _forwarding(_heap->forwarding()), 753 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {} 754 755 void do_oop(oop* p) { do_oop_work(p); } 756 void do_oop(narrowOop* p) { do_oop_work(p); } 757 }; 758 759 class ShenandoahAdjustPointersObjectClosure : public ObjectClosure { 760 private: 761 ShenandoahHeap* const _heap; 762 ShenandoahAdjustPointersClosure _cl; 763 764 public: 765 ShenandoahAdjustPointersObjectClosure() : 766 _heap(ShenandoahHeap::heap()) { 767 } 768 void do_object(oop p) { 769 assert(_heap->complete_marking_context()->is_marked(p), "must be marked"); 770 p->oop_iterate(&_cl); 771 } 772 }; 773 774 class ShenandoahAdjustPointersTask : public AbstractGangTask { 775 private: 776 ShenandoahHeap* const _heap; 777 ShenandoahRegionIterator _regions; 778 779 public: 780 ShenandoahAdjustPointersTask() : 781 AbstractGangTask("Shenandoah Adjust Pointers"), 782 _heap(ShenandoahHeap::heap()) { 783 } 784 785 void work(uint worker_id) { 786 ShenandoahParallelWorkerSession worker_session(worker_id); 787 ShenandoahAdjustPointersObjectClosure obj_cl; 788 ShenandoahHeapRegion* r = _regions.next(); 789 while (r != NULL) { 790 if (!r->is_humongous_continuation() && r->has_live()) { 791 _heap->marked_object_iterate(r, &obj_cl); 792 } 793 r = _regions.next(); 794 } 795 } 796 }; 797 798 class ShenandoahAdjustRootPointersTask : public AbstractGangTask { 799 private: 800 ShenandoahRootAdjuster* _rp; 801 PreservedMarksSet* _preserved_marks; 802 public: 803 ShenandoahAdjustRootPointersTask(ShenandoahRootAdjuster* rp, PreservedMarksSet* preserved_marks) : 804 AbstractGangTask("Shenandoah Adjust Root Pointers"), 805 _rp(rp), 806 _preserved_marks(preserved_marks) {} 807 808 void work(uint worker_id) { 809 ShenandoahParallelWorkerSession worker_session(worker_id); 810 ShenandoahAdjustPointersClosure cl; 811 _rp->roots_do(worker_id, &cl); 812 const SlidingForwarding* const forwarding = ShenandoahHeap::heap()->forwarding(); 813 _preserved_marks->get(worker_id)->adjust_during_full_gc(forwarding); 814 } 815 }; 816 817 void ShenandoahFullGC::phase3_update_references() { 818 GCTraceTime(Info, gc, phases) time("Phase 3: Adjust pointers", _gc_timer); 819 ShenandoahGCPhase adjust_pointer_phase(ShenandoahPhaseTimings::full_gc_adjust_pointers); 820 821 ShenandoahHeap* heap = ShenandoahHeap::heap(); 822 823 WorkGang* workers = heap->workers(); 824 uint nworkers = workers->active_workers(); 825 { 826 #if COMPILER2_OR_JVMCI 827 DerivedPointerTable::clear(); 828 #endif 829 ShenandoahRootAdjuster rp(nworkers, ShenandoahPhaseTimings::full_gc_adjust_roots); 830 ShenandoahAdjustRootPointersTask task(&rp, _preserved_marks); 831 workers->run_task(&task); 832 #if COMPILER2_OR_JVMCI 833 DerivedPointerTable::update_pointers(); 834 #endif 835 } 836 837 ShenandoahAdjustPointersTask adjust_pointers_task; 838 workers->run_task(&adjust_pointers_task); 839 } 840 841 class ShenandoahCompactObjectsClosure : public ObjectClosure { 842 private: 843 ShenandoahHeap* const _heap; 844 const SlidingForwarding* const _forwarding; 845 uint const _worker_id; 846 847 public: 848 ShenandoahCompactObjectsClosure(uint worker_id) : 849 _heap(ShenandoahHeap::heap()), _forwarding(_heap->forwarding()), _worker_id(worker_id) {} 850 851 void do_object(oop p) { 852 assert(_heap->complete_marking_context()->is_marked(p), "must be marked"); 853 size_t size = (size_t)p->size(); 854 if (p->is_forwarded()) { 855 HeapWord* compact_from = cast_from_oop<HeapWord*>(p); 856 HeapWord* compact_to = cast_from_oop<HeapWord*>(_forwarding->forwardee(p)); 857 Copy::aligned_conjoint_words(compact_from, compact_to, size); 858 oop new_obj = cast_to_oop(compact_to); 859 new_obj->init_mark(); 860 } 861 } 862 }; 863 864 class ShenandoahCompactObjectsTask : public AbstractGangTask { 865 private: 866 ShenandoahHeap* const _heap; 867 ShenandoahHeapRegionSet** const _worker_slices; 868 869 public: 870 ShenandoahCompactObjectsTask(ShenandoahHeapRegionSet** worker_slices) : 871 AbstractGangTask("Shenandoah Compact Objects"), 872 _heap(ShenandoahHeap::heap()), 873 _worker_slices(worker_slices) { 874 } 875 876 void work(uint worker_id) { 877 ShenandoahParallelWorkerSession worker_session(worker_id); 878 ShenandoahHeapRegionSetIterator slice(_worker_slices[worker_id]); 879 880 ShenandoahCompactObjectsClosure cl(worker_id); 881 ShenandoahHeapRegion* r = slice.next(); 882 while (r != NULL) { 883 assert(!r->is_humongous(), "must not get humongous regions here"); 884 if (r->has_live()) { 885 _heap->marked_object_iterate(r, &cl); 886 } 887 r->set_top(r->new_top()); 888 r = slice.next(); 889 } 890 } 891 }; 892 893 class ShenandoahPostCompactClosure : public ShenandoahHeapRegionClosure { 894 private: 895 ShenandoahHeap* const _heap; 896 size_t _live; 897 898 public: 899 ShenandoahPostCompactClosure() : _heap(ShenandoahHeap::heap()), _live(0) { 900 _heap->free_set()->clear(); 901 } 902 903 void heap_region_do(ShenandoahHeapRegion* r) { 904 assert (!r->is_cset(), "cset regions should have been demoted already"); 905 906 // Need to reset the complete-top-at-mark-start pointer here because 907 // the complete marking bitmap is no longer valid. This ensures 908 // size-based iteration in marked_object_iterate(). 909 // NOTE: See blurb at ShenandoahMCResetCompleteBitmapTask on why we need to skip 910 // pinned regions. 911 if (!r->is_pinned()) { 912 _heap->complete_marking_context()->reset_top_at_mark_start(r); 913 } 914 915 size_t live = r->used(); 916 917 // Make empty regions that have been allocated into regular 918 if (r->is_empty() && live > 0) { 919 r->make_regular_bypass(); 920 } 921 922 // Reclaim regular regions that became empty 923 if (r->is_regular() && live == 0) { 924 r->make_trash(); 925 } 926 927 // Recycle all trash regions 928 if (r->is_trash()) { 929 live = 0; 930 r->recycle(); 931 } 932 933 r->set_live_data(live); 934 r->reset_alloc_metadata(); 935 _live += live; 936 } 937 938 size_t get_live() { 939 return _live; 940 } 941 }; 942 943 void ShenandoahFullGC::compact_humongous_objects() { 944 // Compact humongous regions, based on their fwdptr objects. 945 // 946 // This code is serial, because doing the in-slice parallel sliding is tricky. In most cases, 947 // humongous regions are already compacted, and do not require further moves, which alleviates 948 // sliding costs. We may consider doing this in parallel in future. 949 950 ShenandoahHeap* heap = ShenandoahHeap::heap(); 951 const SlidingForwarding* const forwarding = heap->forwarding(); 952 953 for (size_t c = heap->num_regions(); c > 0; c--) { 954 ShenandoahHeapRegion* r = heap->get_region(c - 1); 955 if (r->is_humongous_start()) { 956 oop old_obj = cast_to_oop(r->bottom()); 957 if (!old_obj->is_forwarded()) { 958 // No need to move the object, it stays at the same slot 959 continue; 960 } 961 size_t words_size = old_obj->size(); 962 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize); 963 964 size_t old_start = r->index(); 965 size_t old_end = old_start + num_regions - 1; 966 size_t new_start = heap->heap_region_index_containing(forwarding->forwardee(old_obj)); 967 size_t new_end = new_start + num_regions - 1; 968 assert(old_start != new_start, "must be real move"); 969 assert(r->is_stw_move_allowed(), "Region " SIZE_FORMAT " should be movable", r->index()); 970 971 Copy::aligned_conjoint_words(heap->get_region(old_start)->bottom(), 972 heap->get_region(new_start)->bottom(), 973 words_size); 974 975 oop new_obj = cast_to_oop(heap->get_region(new_start)->bottom()); 976 new_obj->init_mark(); 977 978 { 979 for (size_t c = old_start; c <= old_end; c++) { 980 ShenandoahHeapRegion* r = heap->get_region(c); 981 r->make_regular_bypass(); 982 r->set_top(r->bottom()); 983 } 984 985 for (size_t c = new_start; c <= new_end; c++) { 986 ShenandoahHeapRegion* r = heap->get_region(c); 987 if (c == new_start) { 988 r->make_humongous_start_bypass(); 989 } else { 990 r->make_humongous_cont_bypass(); 991 } 992 993 // Trailing region may be non-full, record the remainder there 994 size_t remainder = words_size & ShenandoahHeapRegion::region_size_words_mask(); 995 if ((c == new_end) && (remainder != 0)) { 996 r->set_top(r->bottom() + remainder); 997 } else { 998 r->set_top(r->end()); 999 } 1000 1001 r->reset_alloc_metadata(); 1002 } 1003 } 1004 } 1005 } 1006 } 1007 1008 // This is slightly different to ShHeap::reset_next_mark_bitmap: 1009 // we need to remain able to walk pinned regions. 1010 // Since pinned region do not move and don't get compacted, we will get holes with 1011 // unreachable objects in them (which may have pointers to unloaded Klasses and thus 1012 // cannot be iterated over using oop->size(). The only way to safely iterate over those is using 1013 // a valid marking bitmap and valid TAMS pointer. This class only resets marking 1014 // bitmaps for un-pinned regions, and later we only reset TAMS for unpinned regions. 1015 class ShenandoahMCResetCompleteBitmapTask : public AbstractGangTask { 1016 private: 1017 ShenandoahRegionIterator _regions; 1018 1019 public: 1020 ShenandoahMCResetCompleteBitmapTask() : 1021 AbstractGangTask("Shenandoah Reset Bitmap") { 1022 } 1023 1024 void work(uint worker_id) { 1025 ShenandoahParallelWorkerSession worker_session(worker_id); 1026 ShenandoahHeapRegion* region = _regions.next(); 1027 ShenandoahHeap* heap = ShenandoahHeap::heap(); 1028 ShenandoahMarkingContext* const ctx = heap->complete_marking_context(); 1029 while (region != NULL) { 1030 if (heap->is_bitmap_slice_committed(region) && !region->is_pinned() && region->has_live()) { 1031 ctx->clear_bitmap(region); 1032 } 1033 region = _regions.next(); 1034 } 1035 } 1036 }; 1037 1038 void ShenandoahFullGC::phase4_compact_objects(ShenandoahHeapRegionSet** worker_slices) { 1039 GCTraceTime(Info, gc, phases) time("Phase 4: Move objects", _gc_timer); 1040 ShenandoahGCPhase compaction_phase(ShenandoahPhaseTimings::full_gc_copy_objects); 1041 1042 ShenandoahHeap* heap = ShenandoahHeap::heap(); 1043 1044 // Compact regular objects first 1045 { 1046 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_regular); 1047 ShenandoahCompactObjectsTask compact_task(worker_slices); 1048 heap->workers()->run_task(&compact_task); 1049 } 1050 1051 // Compact humongous objects after regular object moves 1052 { 1053 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_humong); 1054 compact_humongous_objects(); 1055 } 1056 1057 // Reset complete bitmap. We're about to reset the complete-top-at-mark-start pointer 1058 // and must ensure the bitmap is in sync. 1059 { 1060 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_reset_complete); 1061 ShenandoahMCResetCompleteBitmapTask task; 1062 heap->workers()->run_task(&task); 1063 } 1064 1065 // Bring regions in proper states after the collection, and set heap properties. 1066 { 1067 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_rebuild); 1068 1069 ShenandoahPostCompactClosure post_compact; 1070 heap->heap_region_iterate(&post_compact); 1071 heap->set_used(post_compact.get_live()); 1072 1073 heap->collection_set()->clear(); 1074 heap->free_set()->rebuild(); 1075 } 1076 1077 heap->clear_cancelled_gc(); 1078 }