1 /* 2 * Copyright (c) 2001, 2017, 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/dirtyCardQueue.hpp" 28 #include "gc/g1/g1BlockOffsetTable.inline.hpp" 29 #include "gc/g1/g1CollectedHeap.inline.hpp" 30 #include "gc/g1/g1FromCardCache.hpp" 31 #include "gc/g1/g1GCPhaseTimes.hpp" 32 #include "gc/g1/g1HotCardCache.hpp" 33 #include "gc/g1/g1OopClosures.inline.hpp" 34 #include "gc/g1/g1RemSet.inline.hpp" 35 #include "gc/g1/g1SATBCardTableModRefBS.inline.hpp" 36 #include "gc/g1/heapRegion.inline.hpp" 37 #include "gc/g1/heapRegionManager.inline.hpp" 38 #include "gc/g1/heapRegionRemSet.hpp" 39 #include "gc/g1/suspendibleThreadSet.hpp" 40 #include "gc/shared/gcTraceTime.inline.hpp" 41 #include "memory/iterator.hpp" 42 #include "memory/resourceArea.hpp" 43 #include "oops/oop.inline.hpp" 44 #include "utilities/align.hpp" 45 #include "utilities/globalDefinitions.hpp" 46 #include "utilities/intHisto.hpp" 47 #include "utilities/stack.inline.hpp" 48 49 // Collects information about the overall remembered set scan progress during an evacuation. 50 class G1RemSetScanState : public CHeapObj<mtGC> { 51 private: 52 class G1ClearCardTableTask : public AbstractGangTask { 53 G1CollectedHeap* _g1h; 54 uint* _dirty_region_list; 55 size_t _num_dirty_regions; 56 size_t _chunk_length; 57 58 size_t volatile _cur_dirty_regions; 59 public: 60 G1ClearCardTableTask(G1CollectedHeap* g1h, 61 uint* dirty_region_list, 62 size_t num_dirty_regions, 63 size_t chunk_length) : 64 AbstractGangTask("G1 Clear Card Table Task"), 65 _g1h(g1h), 66 _dirty_region_list(dirty_region_list), 67 _num_dirty_regions(num_dirty_regions), 68 _chunk_length(chunk_length), 69 _cur_dirty_regions(0) { 70 71 assert(chunk_length > 0, "must be"); 72 } 73 74 static size_t chunk_size() { return M; } 75 76 void work(uint worker_id) { 77 G1SATBCardTableModRefBS* ct_bs = _g1h->g1_barrier_set(); 78 79 while (_cur_dirty_regions < _num_dirty_regions) { 80 size_t next = Atomic::add(_chunk_length, &_cur_dirty_regions) - _chunk_length; 81 size_t max = MIN2(next + _chunk_length, _num_dirty_regions); 82 83 for (size_t i = next; i < max; i++) { 84 HeapRegion* r = _g1h->region_at(_dirty_region_list[i]); 85 if (!r->is_survivor()) { 86 ct_bs->clear(MemRegion(r->bottom(), r->end())); 87 } 88 } 89 } 90 } 91 }; 92 93 size_t _max_regions; 94 95 // Scan progress for the remembered set of a single region. Transitions from 96 // Unclaimed -> Claimed -> Complete. 97 // At each of the transitions the thread that does the transition needs to perform 98 // some special action once. This is the reason for the extra "Claimed" state. 99 typedef jint G1RemsetIterState; 100 101 static const G1RemsetIterState Unclaimed = 0; // The remembered set has not been scanned yet. 102 static const G1RemsetIterState Claimed = 1; // The remembered set is currently being scanned. 103 static const G1RemsetIterState Complete = 2; // The remembered set has been completely scanned. 104 105 G1RemsetIterState volatile* _iter_states; 106 // The current location where the next thread should continue scanning in a region's 107 // remembered set. 108 size_t volatile* _iter_claims; 109 110 // Temporary buffer holding the regions we used to store remembered set scan duplicate 111 // information. These are also called "dirty". Valid entries are from [0.._cur_dirty_region) 112 uint* _dirty_region_buffer; 113 114 typedef jbyte IsDirtyRegionState; 115 static const IsDirtyRegionState Clean = 0; 116 static const IsDirtyRegionState Dirty = 1; 117 // Holds a flag for every region whether it is in the _dirty_region_buffer already 118 // to avoid duplicates. Uses jbyte since there are no atomic instructions for bools. 119 IsDirtyRegionState* _in_dirty_region_buffer; 120 size_t _cur_dirty_region; 121 122 // Creates a snapshot of the current _top values at the start of collection to 123 // filter out card marks that we do not want to scan. 124 class G1ResetScanTopClosure : public HeapRegionClosure { 125 private: 126 HeapWord** _scan_top; 127 public: 128 G1ResetScanTopClosure(HeapWord** scan_top) : _scan_top(scan_top) { } 129 130 virtual bool doHeapRegion(HeapRegion* r) { 131 uint hrm_index = r->hrm_index(); 132 if (!r->in_collection_set() && r->is_old_or_humongous()) { 133 _scan_top[hrm_index] = r->top(); 134 } else { 135 _scan_top[hrm_index] = r->bottom(); 136 } 137 return false; 138 } 139 }; 140 141 // For each region, contains the maximum top() value to be used during this garbage 142 // collection. Subsumes common checks like filtering out everything but old and 143 // humongous regions outside the collection set. 144 // This is valid because we are not interested in scanning stray remembered set 145 // entries from free or archive regions. 146 HeapWord** _scan_top; 147 public: 148 G1RemSetScanState() : 149 _max_regions(0), 150 _iter_states(NULL), 151 _iter_claims(NULL), 152 _dirty_region_buffer(NULL), 153 _in_dirty_region_buffer(NULL), 154 _cur_dirty_region(0), 155 _scan_top(NULL) { 156 } 157 158 ~G1RemSetScanState() { 159 if (_iter_states != NULL) { 160 FREE_C_HEAP_ARRAY(G1RemsetIterState, _iter_states); 161 } 162 if (_iter_claims != NULL) { 163 FREE_C_HEAP_ARRAY(size_t, _iter_claims); 164 } 165 if (_dirty_region_buffer != NULL) { 166 FREE_C_HEAP_ARRAY(uint, _dirty_region_buffer); 167 } 168 if (_in_dirty_region_buffer != NULL) { 169 FREE_C_HEAP_ARRAY(IsDirtyRegionState, _in_dirty_region_buffer); 170 } 171 if (_scan_top != NULL) { 172 FREE_C_HEAP_ARRAY(HeapWord*, _scan_top); 173 } 174 } 175 176 void initialize(uint max_regions) { 177 assert(_iter_states == NULL, "Must not be initialized twice"); 178 assert(_iter_claims == NULL, "Must not be initialized twice"); 179 _max_regions = max_regions; 180 _iter_states = NEW_C_HEAP_ARRAY(G1RemsetIterState, max_regions, mtGC); 181 _iter_claims = NEW_C_HEAP_ARRAY(size_t, max_regions, mtGC); 182 _dirty_region_buffer = NEW_C_HEAP_ARRAY(uint, max_regions, mtGC); 183 _in_dirty_region_buffer = NEW_C_HEAP_ARRAY(IsDirtyRegionState, max_regions, mtGC); 184 _scan_top = NEW_C_HEAP_ARRAY(HeapWord*, max_regions, mtGC); 185 } 186 187 void reset() { 188 for (uint i = 0; i < _max_regions; i++) { 189 _iter_states[i] = Unclaimed; 190 } 191 192 G1ResetScanTopClosure cl(_scan_top); 193 G1CollectedHeap::heap()->heap_region_iterate(&cl); 194 195 memset((void*)_iter_claims, 0, _max_regions * sizeof(size_t)); 196 memset(_in_dirty_region_buffer, Clean, _max_regions * sizeof(IsDirtyRegionState)); 197 _cur_dirty_region = 0; 198 } 199 200 // Attempt to claim the remembered set of the region for iteration. Returns true 201 // if this call caused the transition from Unclaimed to Claimed. 202 inline bool claim_iter(uint region) { 203 assert(region < _max_regions, "Tried to access invalid region %u", region); 204 if (_iter_states[region] != Unclaimed) { 205 return false; 206 } 207 jint res = Atomic::cmpxchg(Claimed, (jint*)(&_iter_states[region]), Unclaimed); 208 return (res == Unclaimed); 209 } 210 211 // Try to atomically sets the iteration state to "complete". Returns true for the 212 // thread that caused the transition. 213 inline bool set_iter_complete(uint region) { 214 if (iter_is_complete(region)) { 215 return false; 216 } 217 jint res = Atomic::cmpxchg(Complete, (jint*)(&_iter_states[region]), Claimed); 218 return (res == Claimed); 219 } 220 221 // Returns true if the region's iteration is complete. 222 inline bool iter_is_complete(uint region) const { 223 assert(region < _max_regions, "Tried to access invalid region %u", region); 224 return _iter_states[region] == Complete; 225 } 226 227 // The current position within the remembered set of the given region. 228 inline size_t iter_claimed(uint region) const { 229 assert(region < _max_regions, "Tried to access invalid region %u", region); 230 return _iter_claims[region]; 231 } 232 233 // Claim the next block of cards within the remembered set of the region with 234 // step size. 235 inline size_t iter_claimed_next(uint region, size_t step) { 236 return Atomic::add(step, &_iter_claims[region]) - step; 237 } 238 239 void add_dirty_region(uint region) { 240 if (_in_dirty_region_buffer[region] == Dirty) { 241 return; 242 } 243 244 bool marked_as_dirty = Atomic::cmpxchg(Dirty, &_in_dirty_region_buffer[region], Clean) == Clean; 245 if (marked_as_dirty) { 246 size_t allocated = Atomic::add(1, &_cur_dirty_region) - 1; 247 _dirty_region_buffer[allocated] = region; 248 } 249 } 250 251 HeapWord* scan_top(uint region_idx) const { 252 return _scan_top[region_idx]; 253 } 254 255 // Clear the card table of "dirty" regions. 256 void clear_card_table(WorkGang* workers) { 257 if (_cur_dirty_region == 0) { 258 return; 259 } 260 261 size_t const num_chunks = align_up(_cur_dirty_region * HeapRegion::CardsPerRegion, G1ClearCardTableTask::chunk_size()) / G1ClearCardTableTask::chunk_size(); 262 uint const num_workers = (uint)MIN2(num_chunks, (size_t)workers->active_workers()); 263 size_t const chunk_length = G1ClearCardTableTask::chunk_size() / HeapRegion::CardsPerRegion; 264 265 // Iterate over the dirty cards region list. 266 G1ClearCardTableTask cl(G1CollectedHeap::heap(), _dirty_region_buffer, _cur_dirty_region, chunk_length); 267 268 log_debug(gc, ergo)("Running %s using %u workers for " SIZE_FORMAT " " 269 "units of work for " SIZE_FORMAT " regions.", 270 cl.name(), num_workers, num_chunks, _cur_dirty_region); 271 workers->run_task(&cl, num_workers); 272 273 #ifndef PRODUCT 274 // Need to synchronize with concurrent cleanup since it needs to 275 // finish its card table clearing before we can verify. 276 G1CollectedHeap::heap()->wait_while_free_regions_coming(); 277 G1CollectedHeap::heap()->verifier()->verify_card_table_cleanup(); 278 #endif 279 } 280 }; 281 282 G1RemSet::G1RemSet(G1CollectedHeap* g1, 283 CardTableModRefBS* ct_bs, 284 G1HotCardCache* hot_card_cache) : 285 _g1(g1), 286 _scan_state(new G1RemSetScanState()), 287 _num_conc_refined_cards(0), 288 _ct_bs(ct_bs), 289 _g1p(_g1->g1_policy()), 290 _hot_card_cache(hot_card_cache), 291 _prev_period_summary() { 292 } 293 294 G1RemSet::~G1RemSet() { 295 if (_scan_state != NULL) { 296 delete _scan_state; 297 } 298 } 299 300 uint G1RemSet::num_par_rem_sets() { 301 return MAX2(DirtyCardQueueSet::num_par_ids() + ConcurrentG1Refine::thread_num(), ParallelGCThreads); 302 } 303 304 void G1RemSet::initialize(size_t capacity, uint max_regions) { 305 G1FromCardCache::initialize(num_par_rem_sets(), max_regions); 306 _scan_state->initialize(max_regions); 307 { 308 GCTraceTime(Debug, gc, marking)("Initialize Card Live Data"); 309 _card_live_data.initialize(capacity, max_regions); 310 } 311 if (G1PretouchAuxiliaryMemory) { 312 GCTraceTime(Debug, gc, marking)("Pre-Touch Card Live Data"); 313 _card_live_data.pretouch(); 314 } 315 } 316 317 G1ScanRSForRegionClosure::G1ScanRSForRegionClosure(G1RemSetScanState* scan_state, 318 G1ScanObjsDuringScanRSClosure* scan_obj_on_card, 319 CodeBlobClosure* code_root_cl, 320 uint worker_i) : 321 _scan_state(scan_state), 322 _scan_objs_on_card_cl(scan_obj_on_card), 323 _code_root_cl(code_root_cl), 324 _strong_code_root_scan_time_sec(0.0), 325 _cards_claimed(0), 326 _cards_scanned(0), 327 _cards_skipped(0), 328 _worker_i(worker_i) { 329 _g1h = G1CollectedHeap::heap(); 330 _bot = _g1h->bot(); 331 _ct_bs = _g1h->g1_barrier_set(); 332 } 333 334 void G1ScanRSForRegionClosure::scan_card(MemRegion mr, uint region_idx_for_card) { 335 HeapRegion* const card_region = _g1h->region_at(region_idx_for_card); 336 _scan_objs_on_card_cl->set_region(card_region); 337 card_region->oops_on_card_seq_iterate_careful<true>(mr, _scan_objs_on_card_cl); 338 _cards_scanned++; 339 } 340 341 void G1ScanRSForRegionClosure::scan_strong_code_roots(HeapRegion* r) { 342 double scan_start = os::elapsedTime(); 343 r->strong_code_roots_do(_code_root_cl); 344 _strong_code_root_scan_time_sec += (os::elapsedTime() - scan_start); 345 } 346 347 void G1ScanRSForRegionClosure::claim_card(size_t card_index, const uint region_idx_for_card){ 348 _ct_bs->set_card_claimed(card_index); 349 _scan_state->add_dirty_region(region_idx_for_card); 350 } 351 352 bool G1ScanRSForRegionClosure::doHeapRegion(HeapRegion* r) { 353 assert(r->in_collection_set(), "should only be called on elements of CS."); 354 uint region_idx = r->hrm_index(); 355 356 if (_scan_state->iter_is_complete(region_idx)) { 357 return false; 358 } 359 if (_scan_state->claim_iter(region_idx)) { 360 // If we ever free the collection set concurrently, we should also 361 // clear the card table concurrently therefore we won't need to 362 // add regions of the collection set to the dirty cards region. 363 _scan_state->add_dirty_region(region_idx); 364 } 365 366 // We claim cards in blocks so as to reduce the contention. 367 size_t const block_size = G1RSetScanBlockSize; 368 369 HeapRegionRemSetIterator iter(r->rem_set()); 370 size_t card_index; 371 372 size_t claimed_card_block = _scan_state->iter_claimed_next(region_idx, block_size); 373 for (size_t current_card = 0; iter.has_next(card_index); current_card++) { 374 if (current_card >= claimed_card_block + block_size) { 375 claimed_card_block = _scan_state->iter_claimed_next(region_idx, block_size); 376 } 377 if (current_card < claimed_card_block) { 378 _cards_skipped++; 379 continue; 380 } 381 _cards_claimed++; 382 383 // If the card is dirty, then G1 will scan it during Update RS. 384 if (_ct_bs->is_card_claimed(card_index) || _ct_bs->is_card_dirty(card_index)) { 385 continue; 386 } 387 388 HeapWord* const card_start = _g1h->bot()->address_for_index(card_index); 389 uint const region_idx_for_card = _g1h->addr_to_region(card_start); 390 391 assert(_g1h->region_at(region_idx_for_card)->is_in_reserved(card_start), 392 "Card start " PTR_FORMAT " to scan outside of region %u", p2i(card_start), _g1h->region_at(region_idx_for_card)->hrm_index()); 393 HeapWord* const top = _scan_state->scan_top(region_idx_for_card); 394 if (card_start >= top) { 395 continue; 396 } 397 398 // We claim lazily (so races are possible but they're benign), which reduces the 399 // number of duplicate scans (the rsets of the regions in the cset can intersect). 400 // Claim the card after checking bounds above: the remembered set may contain 401 // random cards into current survivor, and we would then have an incorrectly 402 // claimed card in survivor space. Card table clear does not reset the card table 403 // of survivor space regions. 404 claim_card(card_index, region_idx_for_card); 405 406 MemRegion const mr(card_start, MIN2(card_start + BOTConstants::N_words, top)); 407 408 scan_card(mr, region_idx_for_card); 409 } 410 if (_scan_state->set_iter_complete(region_idx)) { 411 // Scan the strong code root list attached to the current region 412 scan_strong_code_roots(r); 413 } 414 return false; 415 } 416 417 void G1RemSet::scan_rem_set(G1ParScanThreadState* pss, 418 CodeBlobClosure* heap_region_codeblobs, 419 uint worker_i) { 420 double rs_time_start = os::elapsedTime(); 421 422 G1ScanObjsDuringScanRSClosure scan_cl(_g1, pss); 423 G1ScanRSForRegionClosure cl(_scan_state, &scan_cl, heap_region_codeblobs, worker_i); 424 _g1->collection_set_iterate_from(&cl, worker_i); 425 426 double scan_rs_time_sec = (os::elapsedTime() - rs_time_start) - 427 cl.strong_code_root_scan_time_sec(); 428 429 G1GCPhaseTimes* p = _g1p->phase_times(); 430 431 p->record_time_secs(G1GCPhaseTimes::ScanRS, worker_i, scan_rs_time_sec); 432 p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_scanned(), G1GCPhaseTimes::ScanRSScannedCards); 433 p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_claimed(), G1GCPhaseTimes::ScanRSClaimedCards); 434 p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_skipped(), G1GCPhaseTimes::ScanRSSkippedCards); 435 436 p->record_time_secs(G1GCPhaseTimes::CodeRoots, worker_i, cl.strong_code_root_scan_time_sec()); 437 } 438 439 // Closure used for updating rem sets. Only called during an evacuation pause. 440 class G1RefineCardClosure: public CardTableEntryClosure { 441 G1RemSet* _g1rs; 442 G1ScanObjsDuringUpdateRSClosure* _update_rs_cl; 443 444 size_t _cards_scanned; 445 size_t _cards_skipped; 446 public: 447 G1RefineCardClosure(G1CollectedHeap* g1h, G1ScanObjsDuringUpdateRSClosure* update_rs_cl) : 448 _g1rs(g1h->g1_rem_set()), _update_rs_cl(update_rs_cl), _cards_scanned(0), _cards_skipped(0) 449 {} 450 451 bool do_card_ptr(jbyte* card_ptr, uint worker_i) { 452 // The only time we care about recording cards that 453 // contain references that point into the collection set 454 // is during RSet updating within an evacuation pause. 455 // In this case worker_i should be the id of a GC worker thread. 456 assert(SafepointSynchronize::is_at_safepoint(), "not during an evacuation pause"); 457 458 bool card_scanned = _g1rs->refine_card_during_gc(card_ptr, _update_rs_cl); 459 460 if (card_scanned) { 461 _cards_scanned++; 462 } else { 463 _cards_skipped++; 464 } 465 return true; 466 } 467 468 size_t cards_scanned() const { return _cards_scanned; } 469 size_t cards_skipped() const { return _cards_skipped; } 470 }; 471 472 void G1RemSet::update_rem_set(G1ParScanThreadState* pss, uint worker_i) { 473 G1ScanObjsDuringUpdateRSClosure update_rs_cl(_g1, pss, worker_i); 474 G1RefineCardClosure refine_card_cl(_g1, &update_rs_cl); 475 476 G1GCParPhaseTimesTracker x(_g1p->phase_times(), G1GCPhaseTimes::UpdateRS, worker_i); 477 if (G1HotCardCache::default_use_cache()) { 478 // Apply the closure to the entries of the hot card cache. 479 G1GCParPhaseTimesTracker y(_g1p->phase_times(), G1GCPhaseTimes::ScanHCC, worker_i); 480 _g1->iterate_hcc_closure(&refine_card_cl, worker_i); 481 } 482 // Apply the closure to all remaining log entries. 483 _g1->iterate_dirty_card_closure(&refine_card_cl, worker_i); 484 485 G1GCPhaseTimes* p = _g1p->phase_times(); 486 p->record_thread_work_item(G1GCPhaseTimes::UpdateRS, worker_i, refine_card_cl.cards_scanned(), G1GCPhaseTimes::UpdateRSScannedCards); 487 p->record_thread_work_item(G1GCPhaseTimes::UpdateRS, worker_i, refine_card_cl.cards_skipped(), G1GCPhaseTimes::UpdateRSSkippedCards); 488 } 489 490 void G1RemSet::cleanupHRRS() { 491 HeapRegionRemSet::cleanup(); 492 } 493 494 void G1RemSet::oops_into_collection_set_do(G1ParScanThreadState* pss, 495 CodeBlobClosure* heap_region_codeblobs, 496 uint worker_i) { 497 update_rem_set(pss, worker_i); 498 scan_rem_set(pss, heap_region_codeblobs, worker_i);; 499 } 500 501 void G1RemSet::prepare_for_oops_into_collection_set_do() { 502 DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set(); 503 dcqs.concatenate_logs(); 504 505 _scan_state->reset(); 506 } 507 508 void G1RemSet::cleanup_after_oops_into_collection_set_do() { 509 G1GCPhaseTimes* phase_times = _g1->g1_policy()->phase_times(); 510 511 // Set all cards back to clean. 512 double start = os::elapsedTime(); 513 _scan_state->clear_card_table(_g1->workers()); 514 phase_times->record_clear_ct_time((os::elapsedTime() - start) * 1000.0); 515 } 516 517 class G1ScrubRSClosure: public HeapRegionClosure { 518 G1CollectedHeap* _g1h; 519 G1CardLiveData* _live_data; 520 public: 521 G1ScrubRSClosure(G1CardLiveData* live_data) : 522 _g1h(G1CollectedHeap::heap()), 523 _live_data(live_data) { } 524 525 bool doHeapRegion(HeapRegion* r) { 526 if (!r->is_continues_humongous()) { 527 r->rem_set()->scrub(_live_data); 528 } 529 return false; 530 } 531 }; 532 533 void G1RemSet::scrub(uint worker_num, HeapRegionClaimer *hrclaimer) { 534 G1ScrubRSClosure scrub_cl(&_card_live_data); 535 _g1->heap_region_par_iterate(&scrub_cl, worker_num, hrclaimer); 536 } 537 538 inline void check_card_ptr(jbyte* card_ptr, CardTableModRefBS* ct_bs) { 539 #ifdef ASSERT 540 G1CollectedHeap* g1 = G1CollectedHeap::heap(); 541 assert(g1->is_in_exact(ct_bs->addr_for(card_ptr)), 542 "Card at " PTR_FORMAT " index " SIZE_FORMAT " representing heap at " PTR_FORMAT " (%u) must be in committed heap", 543 p2i(card_ptr), 544 ct_bs->index_for(ct_bs->addr_for(card_ptr)), 545 p2i(ct_bs->addr_for(card_ptr)), 546 g1->addr_to_region(ct_bs->addr_for(card_ptr))); 547 #endif 548 } 549 550 void G1RemSet::refine_card_concurrently(jbyte* card_ptr, 551 uint worker_i) { 552 assert(!_g1->is_gc_active(), "Only call concurrently"); 553 554 check_card_ptr(card_ptr, _ct_bs); 555 556 // If the card is no longer dirty, nothing to do. 557 if (*card_ptr != CardTableModRefBS::dirty_card_val()) { 558 return; 559 } 560 561 // Construct the region representing the card. 562 HeapWord* start = _ct_bs->addr_for(card_ptr); 563 // And find the region containing it. 564 HeapRegion* r = _g1->heap_region_containing(start); 565 566 // This check is needed for some uncommon cases where we should 567 // ignore the card. 568 // 569 // The region could be young. Cards for young regions are 570 // distinctly marked (set to g1_young_gen), so the post-barrier will 571 // filter them out. However, that marking is performed 572 // concurrently. A write to a young object could occur before the 573 // card has been marked young, slipping past the filter. 574 // 575 // The card could be stale, because the region has been freed since 576 // the card was recorded. In this case the region type could be 577 // anything. If (still) free or (reallocated) young, just ignore 578 // it. If (reallocated) old or humongous, the later card trimming 579 // and additional checks in iteration may detect staleness. At 580 // worst, we end up processing a stale card unnecessarily. 581 // 582 // In the normal (non-stale) case, the synchronization between the 583 // enqueueing of the card and processing it here will have ensured 584 // we see the up-to-date region type here. 585 if (!r->is_old_or_humongous()) { 586 return; 587 } 588 589 // While we are processing RSet buffers during the collection, we 590 // actually don't want to scan any cards on the collection set, 591 // since we don't want to update remembered sets with entries that 592 // point into the collection set, given that live objects from the 593 // collection set are about to move and such entries will be stale 594 // very soon. This change also deals with a reliability issue which 595 // involves scanning a card in the collection set and coming across 596 // an array that was being chunked and looking malformed. Note, 597 // however, that if evacuation fails, we have to scan any objects 598 // that were not moved and create any missing entries. 599 if (r->in_collection_set()) { 600 return; 601 } 602 603 // The result from the hot card cache insert call is either: 604 // * pointer to the current card 605 // (implying that the current card is not 'hot'), 606 // * null 607 // (meaning we had inserted the card ptr into the "hot" card cache, 608 // which had some headroom), 609 // * a pointer to a "hot" card that was evicted from the "hot" cache. 610 // 611 612 if (_hot_card_cache->use_cache()) { 613 assert(!SafepointSynchronize::is_at_safepoint(), "sanity"); 614 615 const jbyte* orig_card_ptr = card_ptr; 616 card_ptr = _hot_card_cache->insert(card_ptr); 617 if (card_ptr == NULL) { 618 // There was no eviction. Nothing to do. 619 return; 620 } else if (card_ptr != orig_card_ptr) { 621 // Original card was inserted and an old card was evicted. 622 start = _ct_bs->addr_for(card_ptr); 623 r = _g1->heap_region_containing(start); 624 625 // Check whether the region formerly in the cache should be 626 // ignored, as discussed earlier for the original card. The 627 // region could have been freed while in the cache. The cset is 628 // not relevant here, since we're in concurrent phase. 629 if (!r->is_old_or_humongous()) { 630 return; 631 } 632 } // Else we still have the original card. 633 } 634 635 // Trim the region designated by the card to what's been allocated 636 // in the region. The card could be stale, or the card could cover 637 // (part of) an object at the end of the allocated space and extend 638 // beyond the end of allocation. 639 640 // Non-humongous objects are only allocated in the old-gen during 641 // GC, so if region is old then top is stable. Humongous object 642 // allocation sets top last; if top has not yet been set, this is 643 // a stale card and we'll end up with an empty intersection. If 644 // this is not a stale card, the synchronization between the 645 // enqueuing of the card and processing it here will have ensured 646 // we see the up-to-date top here. 647 HeapWord* scan_limit = r->top(); 648 649 if (scan_limit <= start) { 650 // If the trimmed region is empty, the card must be stale. 651 return; 652 } 653 654 // Okay to clean and process the card now. There are still some 655 // stale card cases that may be detected by iteration and dealt with 656 // as iteration failure. 657 *const_cast<volatile jbyte*>(card_ptr) = CardTableModRefBS::clean_card_val(); 658 659 // This fence serves two purposes. First, the card must be cleaned 660 // before processing the contents. Second, we can't proceed with 661 // processing until after the read of top, for synchronization with 662 // possibly concurrent humongous object allocation. It's okay that 663 // reading top and reading type were racy wrto each other. We need 664 // both set, in any order, to proceed. 665 OrderAccess::fence(); 666 667 // Don't use addr_for(card_ptr + 1) which can ask for 668 // a card beyond the heap. 669 HeapWord* end = start + CardTableModRefBS::card_size_in_words; 670 MemRegion dirty_region(start, MIN2(scan_limit, end)); 671 assert(!dirty_region.is_empty(), "sanity"); 672 673 G1ConcurrentRefineOopClosure conc_refine_cl(_g1, worker_i); 674 675 bool card_processed = 676 r->oops_on_card_seq_iterate_careful<false>(dirty_region, &conc_refine_cl); 677 678 // If unable to process the card then we encountered an unparsable 679 // part of the heap (e.g. a partially allocated object) while 680 // processing a stale card. Despite the card being stale, redirty 681 // and re-enqueue, because we've already cleaned the card. Without 682 // this we could incorrectly discard a non-stale card. 683 if (!card_processed) { 684 // The card might have gotten re-dirtied and re-enqueued while we 685 // worked. (In fact, it's pretty likely.) 686 if (*card_ptr != CardTableModRefBS::dirty_card_val()) { 687 *card_ptr = CardTableModRefBS::dirty_card_val(); 688 MutexLockerEx x(Shared_DirtyCardQ_lock, 689 Mutex::_no_safepoint_check_flag); 690 DirtyCardQueue* sdcq = 691 JavaThread::dirty_card_queue_set().shared_dirty_card_queue(); 692 sdcq->enqueue(card_ptr); 693 } 694 } else { 695 _num_conc_refined_cards++; // Unsynchronized update, only used for logging. 696 } 697 } 698 699 bool G1RemSet::refine_card_during_gc(jbyte* card_ptr, 700 G1ScanObjsDuringUpdateRSClosure* update_rs_cl) { 701 assert(_g1->is_gc_active(), "Only call during GC"); 702 703 check_card_ptr(card_ptr, _ct_bs); 704 705 // If the card is no longer dirty, nothing to do. This covers cards that were already 706 // scanned as parts of the remembered sets. 707 if (*card_ptr != CardTableModRefBS::dirty_card_val()) { 708 return false; 709 } 710 711 // We claim lazily (so races are possible but they're benign), which reduces the 712 // number of potential duplicate scans (multiple threads may enqueue the same card twice). 713 *card_ptr = CardTableModRefBS::clean_card_val() | CardTableModRefBS::claimed_card_val(); 714 715 // Construct the region representing the card. 716 HeapWord* card_start = _ct_bs->addr_for(card_ptr); 717 // And find the region containing it. 718 uint const card_region_idx = _g1->addr_to_region(card_start); 719 720 _scan_state->add_dirty_region(card_region_idx); 721 HeapWord* scan_limit = _scan_state->scan_top(card_region_idx); 722 if (scan_limit <= card_start) { 723 // If the card starts above the area in the region containing objects to scan, skip it. 724 return false; 725 } 726 727 // Don't use addr_for(card_ptr + 1) which can ask for 728 // a card beyond the heap. 729 HeapWord* card_end = card_start + CardTableModRefBS::card_size_in_words; 730 MemRegion dirty_region(card_start, MIN2(scan_limit, card_end)); 731 assert(!dirty_region.is_empty(), "sanity"); 732 733 HeapRegion* const card_region = _g1->region_at(card_region_idx); 734 update_rs_cl->set_region(card_region); 735 bool card_processed = card_region->oops_on_card_seq_iterate_careful<true>(dirty_region, update_rs_cl); 736 assert(card_processed, "must be"); 737 return true; 738 } 739 740 void G1RemSet::print_periodic_summary_info(const char* header, uint period_count) { 741 if ((G1SummarizeRSetStatsPeriod > 0) && log_is_enabled(Trace, gc, remset) && 742 (period_count % G1SummarizeRSetStatsPeriod == 0)) { 743 744 G1RemSetSummary current(this); 745 _prev_period_summary.subtract_from(¤t); 746 747 Log(gc, remset) log; 748 log.trace("%s", header); 749 ResourceMark rm; 750 LogStream ls(log.trace()); 751 _prev_period_summary.print_on(&ls); 752 753 _prev_period_summary.set(¤t); 754 } 755 } 756 757 void G1RemSet::print_summary_info() { 758 Log(gc, remset, exit) log; 759 if (log.is_trace()) { 760 log.trace(" Cumulative RS summary"); 761 G1RemSetSummary current(this); 762 ResourceMark rm; 763 LogStream ls(log.trace()); 764 current.print_on(&ls); 765 } 766 } 767 768 void G1RemSet::create_card_live_data(WorkGang* workers, G1CMBitMap* mark_bitmap) { 769 _card_live_data.create(workers, mark_bitmap); 770 } 771 772 void G1RemSet::finalize_card_live_data(WorkGang* workers, G1CMBitMap* mark_bitmap) { 773 _card_live_data.finalize(workers, mark_bitmap); 774 } 775 776 void G1RemSet::verify_card_live_data(WorkGang* workers, G1CMBitMap* bitmap) { 777 _card_live_data.verify(workers, bitmap); 778 } 779 780 void G1RemSet::clear_card_live_data(WorkGang* workers) { 781 _card_live_data.clear(workers); 782 } 783 784 #ifdef ASSERT 785 void G1RemSet::verify_card_live_data_is_clear() { 786 _card_live_data.verify_is_clear(); 787 } 788 #endif