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
295 G1RemSet::~G1RemSet() {
296 if (_scan_state != NULL) {
297 delete _scan_state;
298 }
299 }
300
301 uint G1RemSet::num_par_rem_sets() {
302 return MAX2(DirtyCardQueueSet::num_par_ids() + ConcurrentG1Refine::thread_num(), ParallelGCThreads);
303 }
304
305 void G1RemSet::initialize(size_t capacity, uint max_regions) {
306 G1FromCardCache::initialize(num_par_rem_sets(), max_regions);
307 _scan_state->initialize(max_regions);
308 {
309 GCTraceTime(Debug, gc, marking)("Initialize Card Live Data");
310 _card_live_data.initialize(capacity, max_regions);
311 }
312 if (G1PretouchAuxiliaryMemory) {
313 GCTraceTime(Debug, gc, marking)("Pre-Touch Card Live Data");
314 _card_live_data.pretouch();
315 }
316 }
317
318 G1ScanRSForRegionClosure::G1ScanRSForRegionClosure(G1RemSetScanState* scan_state,
319 G1ScanObjsDuringScanRSClosure* scan_obj_on_card,
320 CodeBlobClosure* code_root_cl,
321 uint worker_i) :
322 _scan_state(scan_state),
323 _scan_objs_on_card_cl(scan_obj_on_card),
324 _code_root_cl(code_root_cl),
325 _strong_code_root_scan_time_sec(0.0),
326 _cards_claimed(0),
327 _cards_scanned(0),
328 _cards_skipped(0),
329 _worker_i(worker_i) {
330 _g1h = G1CollectedHeap::heap();
331 _bot = _g1h->bot();
332 _ct_bs = _g1h->g1_barrier_set();
333 }
334
335 void G1ScanRSForRegionClosure::scan_card(MemRegion mr, uint region_idx_for_card) {
336 HeapRegion* const card_region = _g1h->region_at(region_idx_for_card);
337 _scan_objs_on_card_cl->set_region(card_region);
338 card_region->oops_on_card_seq_iterate_careful<true>(mr, _scan_objs_on_card_cl);
339 _cards_scanned++;
340 }
341
342 void G1ScanRSForRegionClosure::scan_strong_code_roots(HeapRegion* r) {
343 double scan_start = os::elapsedTime();
344 r->strong_code_roots_do(_code_root_cl);
345 _strong_code_root_scan_time_sec += (os::elapsedTime() - scan_start);
346 }
347
348 void G1ScanRSForRegionClosure::claim_card(size_t card_index, const uint region_idx_for_card){
349 _ct_bs->set_card_claimed(card_index);
350 _scan_state->add_dirty_region(region_idx_for_card);
351 }
352
353 bool G1ScanRSForRegionClosure::doHeapRegion(HeapRegion* r) {
354 assert(r->in_collection_set(), "should only be called on elements of CS.");
355 uint region_idx = r->hrm_index();
356
357 if (_scan_state->iter_is_complete(region_idx)) {
358 return false;
359 }
360 if (_scan_state->claim_iter(region_idx)) {
361 // If we ever free the collection set concurrently, we should also
362 // clear the card table concurrently therefore we won't need to
363 // add regions of the collection set to the dirty cards region.
364 _scan_state->add_dirty_region(region_idx);
365 }
366
367 // We claim cards in blocks so as to reduce the contention.
368 size_t const block_size = G1RSetScanBlockSize;
369
370 HeapRegionRemSetIterator iter(r->rem_set());
371 size_t card_index;
372
373 size_t claimed_card_block = _scan_state->iter_claimed_next(region_idx, block_size);
374 for (size_t current_card = 0; iter.has_next(card_index); current_card++) {
375 if (current_card >= claimed_card_block + block_size) {
376 claimed_card_block = _scan_state->iter_claimed_next(region_idx, block_size);
377 }
378 if (current_card < claimed_card_block) {
379 _cards_skipped++;
380 continue;
381 }
382 _cards_claimed++;
383
384 // If the card is dirty, then G1 will scan it during Update RS.
385 if (_ct_bs->is_card_claimed(card_index) || _ct_bs->is_card_dirty(card_index)) {
386 continue;
387 }
388
389 HeapWord* const card_start = _g1h->bot()->address_for_index(card_index);
390 uint const region_idx_for_card = _g1h->addr_to_region(card_start);
391
392 assert(_g1h->region_at(region_idx_for_card)->is_in_reserved(card_start),
393 "Card start " PTR_FORMAT " to scan outside of region %u", p2i(card_start), _g1h->region_at(region_idx_for_card)->hrm_index());
394 HeapWord* const top = _scan_state->scan_top(region_idx_for_card);
395 if (card_start >= top) {
396 continue;
397 }
398
399 // We claim lazily (so races are possible but they're benign), which reduces the
400 // number of duplicate scans (the rsets of the regions in the cset can intersect).
401 // Claim the card after checking bounds above: the remembered set may contain
402 // random cards into current survivor, and we would then have an incorrectly
403 // claimed card in survivor space. Card table clear does not reset the card table
404 // of survivor space regions.
405 claim_card(card_index, region_idx_for_card);
406
407 MemRegion const mr(card_start, MIN2(card_start + BOTConstants::N_words, top));
408
409 scan_card(mr, region_idx_for_card);
410 }
411 if (_scan_state->set_iter_complete(region_idx)) {
412 // Scan the strong code root list attached to the current region
413 scan_strong_code_roots(r);
414 }
415 return false;
416 }
417
418 void G1RemSet::scan_rem_set(G1ParScanThreadState* pss,
419 CodeBlobClosure* heap_region_codeblobs,
420 uint worker_i) {
421 double rs_time_start = os::elapsedTime();
422
423 G1ScanObjsDuringScanRSClosure scan_cl(_g1, pss);
424 G1ScanRSForRegionClosure cl(_scan_state, &scan_cl, heap_region_codeblobs, worker_i);
425 _g1->collection_set_iterate_from(&cl, worker_i);
426
427 double scan_rs_time_sec = (os::elapsedTime() - rs_time_start) -
428 cl.strong_code_root_scan_time_sec();
429
430 G1GCPhaseTimes* p = _g1p->phase_times();
431
432 p->record_time_secs(G1GCPhaseTimes::ScanRS, worker_i, scan_rs_time_sec);
433 p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_scanned(), G1GCPhaseTimes::ScanRSScannedCards);
434 p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_claimed(), G1GCPhaseTimes::ScanRSClaimedCards);
435 p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_skipped(), G1GCPhaseTimes::ScanRSSkippedCards);
436
437 p->record_time_secs(G1GCPhaseTimes::CodeRoots, worker_i, cl.strong_code_root_scan_time_sec());
438 }
439
440 // Closure used for updating rem sets. Only called during an evacuation pause.
441 class G1RefineCardClosure: public CardTableEntryClosure {
442 G1RemSet* _g1rs;
443 G1ScanObjsDuringUpdateRSClosure* _update_rs_cl;
444
445 size_t _cards_scanned;
446 size_t _cards_skipped;
447 public:
448 G1RefineCardClosure(G1CollectedHeap* g1h, G1ScanObjsDuringUpdateRSClosure* update_rs_cl) :
449 _g1rs(g1h->g1_rem_set()), _update_rs_cl(update_rs_cl), _cards_scanned(0), _cards_skipped(0)
450 {}
451
452 bool do_card_ptr(jbyte* card_ptr, uint worker_i) {
453 assert(SafepointSynchronize::is_at_safepoint(), "not during an evacuation pause");
454
455 bool card_scanned = _g1rs->refine_card_during_gc(card_ptr, _update_rs_cl);
456
457 if (card_scanned) {
458 _cards_scanned++;
459 } else {
460 _cards_skipped++;
461 }
462 return true;
463 }
464
465 size_t cards_scanned() const { return _cards_scanned; }
466 size_t cards_skipped() const { return _cards_skipped; }
467 };
468
469 void G1RemSet::update_rem_set(G1ParScanThreadState* pss, uint worker_i) {
470 G1ScanObjsDuringUpdateRSClosure update_rs_cl(_g1, pss, worker_i);
471 G1RefineCardClosure refine_card_cl(_g1, &update_rs_cl);
472
473 G1GCParPhaseTimesTracker x(_g1p->phase_times(), G1GCPhaseTimes::UpdateRS, worker_i);
474 if (G1HotCardCache::default_use_cache()) {
475 // Apply the closure to the entries of the hot card cache.
476 G1GCParPhaseTimesTracker y(_g1p->phase_times(), G1GCPhaseTimes::ScanHCC, worker_i);
477 _g1->iterate_hcc_closure(&refine_card_cl, worker_i);
478 }
479 // Apply the closure to all remaining log entries.
480 _g1->iterate_dirty_card_closure(&refine_card_cl, worker_i);
481
482 G1GCPhaseTimes* p = _g1p->phase_times();
483 p->record_thread_work_item(G1GCPhaseTimes::UpdateRS, worker_i, refine_card_cl.cards_scanned(), G1GCPhaseTimes::UpdateRSScannedCards);
484 p->record_thread_work_item(G1GCPhaseTimes::UpdateRS, worker_i, refine_card_cl.cards_skipped(), G1GCPhaseTimes::UpdateRSSkippedCards);
485 }
486
487 void G1RemSet::cleanupHRRS() {
488 HeapRegionRemSet::cleanup();
489 }
490
491 void G1RemSet::oops_into_collection_set_do(G1ParScanThreadState* pss,
492 CodeBlobClosure* heap_region_codeblobs,
493 uint worker_i) {
494 update_rem_set(pss, worker_i);
495 scan_rem_set(pss, heap_region_codeblobs, worker_i);;
496 }
497
498 void G1RemSet::prepare_for_oops_into_collection_set_do() {
499 DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();
500 dcqs.concatenate_logs();
501
502 _scan_state->reset();
503 }
504
505 void G1RemSet::cleanup_after_oops_into_collection_set_do() {
506 G1GCPhaseTimes* phase_times = _g1->g1_policy()->phase_times();
507
508 // Set all cards back to clean.
509 double start = os::elapsedTime();
510 _scan_state->clear_card_table(_g1->workers());
511 phase_times->record_clear_ct_time((os::elapsedTime() - start) * 1000.0);
512 }
513
514 class G1ScrubRSClosure: public HeapRegionClosure {
515 G1CollectedHeap* _g1h;
516 G1CardLiveData* _live_data;
517 public:
518 G1ScrubRSClosure(G1CardLiveData* live_data) :
519 _g1h(G1CollectedHeap::heap()),
520 _live_data(live_data) { }
521
522 bool doHeapRegion(HeapRegion* r) {
523 if (!r->is_continues_humongous()) {
524 r->rem_set()->scrub(_live_data);
525 }
526 return false;
527 }
528 };
529
530 void G1RemSet::scrub(uint worker_num, HeapRegionClaimer *hrclaimer) {
531 G1ScrubRSClosure scrub_cl(&_card_live_data);
532 _g1->heap_region_par_iterate(&scrub_cl, worker_num, hrclaimer);
533 }
534
535 inline void check_card_ptr(jbyte* card_ptr, CardTableModRefBS* ct_bs) {
536 #ifdef ASSERT
537 G1CollectedHeap* g1 = G1CollectedHeap::heap();
538 assert(g1->is_in_exact(ct_bs->addr_for(card_ptr)),
539 "Card at " PTR_FORMAT " index " SIZE_FORMAT " representing heap at " PTR_FORMAT " (%u) must be in committed heap",
540 p2i(card_ptr),
541 ct_bs->index_for(ct_bs->addr_for(card_ptr)),
542 p2i(ct_bs->addr_for(card_ptr)),
543 g1->addr_to_region(ct_bs->addr_for(card_ptr)));
544 #endif
545 }
546
547 void G1RemSet::refine_card_concurrently(jbyte* card_ptr,
548 uint worker_i) {
549 assert(!_g1->is_gc_active(), "Only call concurrently");
550
551 check_card_ptr(card_ptr, _ct_bs);
552
553 // If the card is no longer dirty, nothing to do.
554 if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
555 return;
556 }
557
558 // Construct the region representing the card.
559 HeapWord* start = _ct_bs->addr_for(card_ptr);
560 // And find the region containing it.
561 HeapRegion* r = _g1->heap_region_containing(start);
562
563 // This check is needed for some uncommon cases where we should
564 // ignore the card.
565 //
566 // The region could be young. Cards for young regions are
567 // distinctly marked (set to g1_young_gen), so the post-barrier will
568 // filter them out. However, that marking is performed
569 // concurrently. A write to a young object could occur before the
570 // card has been marked young, slipping past the filter.
571 //
572 // The card could be stale, because the region has been freed since
573 // the card was recorded. In this case the region type could be
574 // anything. If (still) free or (reallocated) young, just ignore
575 // it. If (reallocated) old or humongous, the later card trimming
576 // and additional checks in iteration may detect staleness. At
577 // worst, we end up processing a stale card unnecessarily.
578 //
579 // In the normal (non-stale) case, the synchronization between the
580 // enqueueing of the card and processing it here will have ensured
581 // we see the up-to-date region type here.
582 if (!r->is_old_or_humongous()) {
583 return;
584 }
585
586 // While we are processing RSet buffers during the collection, we
587 // actually don't want to scan any cards on the collection set,
588 // since we don't want to update remembered sets with entries that
589 // point into the collection set, given that live objects from the
590 // collection set are about to move and such entries will be stale
591 // very soon. This change also deals with a reliability issue which
592 // involves scanning a card in the collection set and coming across
593 // an array that was being chunked and looking malformed. Note,
594 // however, that if evacuation fails, we have to scan any objects
595 // that were not moved and create any missing entries.
596 if (r->in_collection_set()) {
597 return;
598 }
599
600 // The result from the hot card cache insert call is either:
601 // * pointer to the current card
602 // (implying that the current card is not 'hot'),
603 // * null
604 // (meaning we had inserted the card ptr into the "hot" card cache,
605 // which had some headroom),
606 // * a pointer to a "hot" card that was evicted from the "hot" cache.
607 //
608
609 if (_hot_card_cache->use_cache()) {
610 assert(!SafepointSynchronize::is_at_safepoint(), "sanity");
611
612 const jbyte* orig_card_ptr = card_ptr;
613 card_ptr = _hot_card_cache->insert(card_ptr);
614 if (card_ptr == NULL) {
615 // There was no eviction. Nothing to do.
616 return;
617 } else if (card_ptr != orig_card_ptr) {
618 // Original card was inserted and an old card was evicted.
619 start = _ct_bs->addr_for(card_ptr);
620 r = _g1->heap_region_containing(start);
621
622 // Check whether the region formerly in the cache should be
623 // ignored, as discussed earlier for the original card. The
624 // region could have been freed while in the cache. The cset is
625 // not relevant here, since we're in concurrent phase.
626 if (!r->is_old_or_humongous()) {
627 return;
628 }
629 } // Else we still have the original card.
630 }
631
632 // Trim the region designated by the card to what's been allocated
633 // in the region. The card could be stale, or the card could cover
634 // (part of) an object at the end of the allocated space and extend
635 // beyond the end of allocation.
636
637 // Non-humongous objects are only allocated in the old-gen during
638 // GC, so if region is old then top is stable. Humongous object
639 // allocation sets top last; if top has not yet been set, this is
640 // a stale card and we'll end up with an empty intersection. If
641 // this is not a stale card, the synchronization between the
642 // enqueuing of the card and processing it here will have ensured
643 // we see the up-to-date top here.
644 HeapWord* scan_limit = r->top();
645
646 if (scan_limit <= start) {
647 // If the trimmed region is empty, the card must be stale.
648 return;
649 }
650
651 // Okay to clean and process the card now. There are still some
652 // stale card cases that may be detected by iteration and dealt with
653 // as iteration failure.
654 *const_cast<volatile jbyte*>(card_ptr) = CardTableModRefBS::clean_card_val();
655
656 // This fence serves two purposes. First, the card must be cleaned
657 // before processing the contents. Second, we can't proceed with
658 // processing until after the read of top, for synchronization with
659 // possibly concurrent humongous object allocation. It's okay that
660 // reading top and reading type were racy wrto each other. We need
661 // both set, in any order, to proceed.
662 OrderAccess::fence();
663
664 // Don't use addr_for(card_ptr + 1) which can ask for
665 // a card beyond the heap.
666 HeapWord* end = start + CardTableModRefBS::card_size_in_words;
667 MemRegion dirty_region(start, MIN2(scan_limit, end));
668 assert(!dirty_region.is_empty(), "sanity");
669
670 G1ConcurrentRefineOopClosure conc_refine_cl(_g1, worker_i);
671
672 bool card_processed =
673 r->oops_on_card_seq_iterate_careful<false>(dirty_region, &conc_refine_cl);
674
675 // If unable to process the card then we encountered an unparsable
676 // part of the heap (e.g. a partially allocated object) while
677 // processing a stale card. Despite the card being stale, redirty
678 // and re-enqueue, because we've already cleaned the card. Without
679 // this we could incorrectly discard a non-stale card.
680 if (!card_processed) {
681 // The card might have gotten re-dirtied and re-enqueued while we
682 // worked. (In fact, it's pretty likely.)
683 if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
684 *card_ptr = CardTableModRefBS::dirty_card_val();
685 MutexLockerEx x(Shared_DirtyCardQ_lock,
686 Mutex::_no_safepoint_check_flag);
687 DirtyCardQueue* sdcq =
688 JavaThread::dirty_card_queue_set().shared_dirty_card_queue();
689 sdcq->enqueue(card_ptr);
690 }
691 } else {
692 _num_conc_refined_cards++; // Unsynchronized update, only used for logging.
693 }
694 }
695
696 bool G1RemSet::refine_card_during_gc(jbyte* card_ptr,
697 G1ScanObjsDuringUpdateRSClosure* update_rs_cl) {
698 assert(_g1->is_gc_active(), "Only call during GC");
699
700 check_card_ptr(card_ptr, _ct_bs);
701
702 // If the card is no longer dirty, nothing to do. This covers cards that were already
703 // scanned as parts of the remembered sets.
704 if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
705 return false;
706 }
707
708 // During GC we can immediately clean the card since we will not re-enqueue stale
709 // cards as we know they can be disregarded.
710 *card_ptr = CardTableModRefBS::clean_card_val();
711
712 // Construct the region representing the card.
713 HeapWord* card_start = _ct_bs->addr_for(card_ptr);
714 // And find the region containing it.
715 HeapRegion* r = _g1->heap_region_containing(card_start);
716
717 HeapWord* scan_limit = _scan_state->scan_top(r->hrm_index());
718 if (scan_limit <= card_start) {
719 // If the card starts above the area in the region containing objects to scan, skip it.
720 return false;
721 }
722
723 // Don't use addr_for(card_ptr + 1) which can ask for
724 // a card beyond the heap.
725 HeapWord* card_end = card_start + CardTableModRefBS::card_size_in_words;
726 MemRegion dirty_region(card_start, MIN2(scan_limit, card_end));
727 assert(!dirty_region.is_empty(), "sanity");
728
729 update_rs_cl->set_region(r);
730 bool card_processed = r->oops_on_card_seq_iterate_careful<true>(dirty_region, update_rs_cl);
731 assert(card_processed, "must be");
732 return true;
733 }
734
735 void G1RemSet::print_periodic_summary_info(const char* header, uint period_count) {
736 if ((G1SummarizeRSetStatsPeriod > 0) && log_is_enabled(Trace, gc, remset) &&
737 (period_count % G1SummarizeRSetStatsPeriod == 0)) {
738
739 G1RemSetSummary current(this);
740 _prev_period_summary.subtract_from(¤t);
741
742 Log(gc, remset) log;
743 log.trace("%s", header);
744 ResourceMark rm;
745 _prev_period_summary.print_on(log.trace_stream());
746
747 _prev_period_summary.set(¤t);
748 }
749 }
750
751 void G1RemSet::print_summary_info() {
752 Log(gc, remset, exit) log;
753 if (log.is_trace()) {
754 log.trace(" Cumulative RS summary");
755 G1RemSetSummary current(this);
756 ResourceMark rm;
757 current.print_on(log.trace_stream());
758 }
759 }
760
761 void G1RemSet::create_card_live_data(WorkGang* workers, G1CMBitMap* mark_bitmap) {
762 _card_live_data.create(workers, mark_bitmap);
763 }
764
765 void G1RemSet::finalize_card_live_data(WorkGang* workers, G1CMBitMap* mark_bitmap) {
766 _card_live_data.finalize(workers, mark_bitmap);
767 }
768
769 void G1RemSet::verify_card_live_data(WorkGang* workers, G1CMBitMap* bitmap) {
770 _card_live_data.verify(workers, bitmap);
771 }
772
773 void G1RemSet::clear_card_live_data(WorkGang* workers) {
774 _card_live_data.clear(workers);
775 }
776
777 #ifdef ASSERT
778 void G1RemSet::verify_card_live_data_is_clear() {
779 _card_live_data.verify_is_clear();
780 }
781 #endif