1 /*
2 * Copyright (c) 2001, 2020, 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/g1BarrierSet.hpp"
27 #include "gc/g1/g1BlockOffsetTable.inline.hpp"
28 #include "gc/g1/g1CardTable.inline.hpp"
29 #include "gc/g1/g1CardTableEntryClosure.hpp"
30 #include "gc/g1/g1CollectedHeap.inline.hpp"
31 #include "gc/g1/g1ConcurrentRefine.hpp"
32 #include "gc/g1/g1DirtyCardQueue.hpp"
33 #include "gc/g1/g1FromCardCache.hpp"
34 #include "gc/g1/g1GCParPhaseTimesTracker.hpp"
35 #include "gc/g1/g1GCPhaseTimes.hpp"
36 #include "gc/g1/g1HotCardCache.hpp"
37 #include "gc/g1/g1OopClosures.inline.hpp"
38 #include "gc/g1/g1RootClosures.hpp"
39 #include "gc/g1/g1RemSet.hpp"
40 #include "gc/g1/g1SharedDirtyCardQueue.hpp"
41 #include "gc/g1/heapRegion.inline.hpp"
42 #include "gc/g1/heapRegionManager.inline.hpp"
43 #include "gc/g1/heapRegionRemSet.inline.hpp"
44 #include "gc/g1/sparsePRT.hpp"
45 #include "gc/shared/gcTraceTime.inline.hpp"
46 #include "gc/shared/ptrQueue.hpp"
47 #include "gc/shared/suspendibleThreadSet.hpp"
48 #include "jfr/jfrEvents.hpp"
49 #include "memory/iterator.hpp"
50 #include "memory/resourceArea.hpp"
51 #include "oops/access.inline.hpp"
52 #include "oops/oop.inline.hpp"
53 #include "runtime/atomic.hpp"
54 #include "runtime/os.hpp"
55 #include "utilities/align.hpp"
56 #include "utilities/globalDefinitions.hpp"
57 #include "utilities/stack.inline.hpp"
58 #include "utilities/ticks.hpp"
59
60 // Collects information about the overall heap root scan progress during an evacuation.
61 //
62 // Scanning the remembered sets works by first merging all sources of cards to be
63 // scanned (log buffers, hcc, remembered sets) into a single data structure to remove
64 // duplicates and simplify work distribution.
65 //
66 // During the following card scanning we not only scan this combined set of cards, but
67 // also remember that these were completely scanned. The following evacuation passes
68 // do not scan these cards again, and so need to be preserved across increments.
69 //
70 // The representation for all the cards to scan is the card table: cards can have
71 // one of three states during GC:
72 // - clean: these cards will not be scanned in this pass
73 // - dirty: these cards will be scanned in this pass
74 // - scanned: these cards have already been scanned in a previous pass
75 //
76 // After all evacuation is done, we reset the card table to clean.
77 //
78 // Work distribution occurs on "chunk" basis, i.e. contiguous ranges of cards. As an
79 // additional optimization, during card merging we remember which regions and which
80 // chunks actually contain cards to be scanned. Threads iterate only across these
81 // regions, and only compete for chunks containing any cards.
82 //
83 // Within these chunks, a worker scans the card table on "blocks" of cards, i.e.
84 // contiguous ranges of dirty cards to be scanned. These blocks are converted to actual
85 // memory ranges and then passed on to actual scanning.
86 class G1RemSetScanState : public CHeapObj<mtGC> {
87 class G1DirtyRegions;
88
89 size_t _max_regions;
90
91 // Has this region that is part of the regions in the collection set been processed yet.
92 typedef bool G1RemsetIterState;
93
94 G1RemsetIterState volatile* _collection_set_iter_state;
95
96 // Card table iteration claim for each heap region, from 0 (completely unscanned)
97 // to (>=) HeapRegion::CardsPerRegion (completely scanned).
98 uint volatile* _card_table_scan_state;
99
100 // Return "optimal" number of chunks per region we want to use for claiming areas
101 // within a region to claim. Dependent on the region size as proxy for the heap
102 // size, we limit the total number of chunks to limit memory usage and maintenance
103 // effort of that table vs. granularity of distributing scanning work.
104 // Testing showed that 8 for 1M/2M region, 16 for 4M/8M regions, 32 for 16/32M regions
105 // seems to be such a good trade-off.
106 static uint get_chunks_per_region(uint log_region_size) {
107 // Limit the expected input values to current known possible values of the
108 // (log) region size. Adjust as necessary after testing if changing the permissible
109 // values for region size.
110 assert(log_region_size >= 20 && log_region_size <= 25,
111 "expected value in [20,25], but got %u", log_region_size);
112 return 1u << (log_region_size / 2 - 7);
113 }
114
115 uint _scan_chunks_per_region; // Number of chunks per region.
116 uint8_t _log_scan_chunks_per_region; // Log of number of chunks per region.
117 bool* _region_scan_chunks;
118 size_t _num_total_scan_chunks; // Total number of elements in _region_scan_chunks.
119 uint8_t _scan_chunks_shift; // For conversion between card index and chunk index.
120 public:
121 uint scan_chunk_size() const { return (uint)1 << _scan_chunks_shift; }
122
123 // Returns whether the chunk corresponding to the given region/card in region contain a
124 // dirty card, i.e. actually needs scanning.
125 bool chunk_needs_scan(uint const region_idx, uint const card_in_region) const {
126 size_t const idx = ((size_t)region_idx << _log_scan_chunks_per_region) + (card_in_region >> _scan_chunks_shift);
127 assert(idx < _num_total_scan_chunks, "Index " SIZE_FORMAT " out of bounds " SIZE_FORMAT,
128 idx, _num_total_scan_chunks);
129 return _region_scan_chunks[idx];
130 }
131
132 private:
133 // The complete set of regions which card table needs to be cleared at the end of GC because
134 // we scribbled all over them.
135 G1DirtyRegions* _all_dirty_regions;
136 // The set of regions which card table needs to be scanned for new dirty cards
137 // in the current evacuation pass.
138 G1DirtyRegions* _next_dirty_regions;
139
140 // Set of (unique) regions that can be added to concurrently.
141 class G1DirtyRegions : public CHeapObj<mtGC> {
142 uint* _buffer;
143 uint _cur_idx;
144 size_t _max_regions;
145
146 bool* _contains;
147
148 public:
149 G1DirtyRegions(size_t max_regions) :
150 _buffer(NEW_C_HEAP_ARRAY(uint, max_regions, mtGC)),
151 _cur_idx(0),
152 _max_regions(max_regions),
153 _contains(NEW_C_HEAP_ARRAY(bool, max_regions, mtGC)) {
154
155 reset();
156 }
157
158 static size_t chunk_size() { return M; }
159
160 ~G1DirtyRegions() {
161 FREE_C_HEAP_ARRAY(uint, _buffer);
162 FREE_C_HEAP_ARRAY(bool, _contains);
163 }
164
165 void reset() {
166 _cur_idx = 0;
167 ::memset(_contains, false, _max_regions * sizeof(bool));
168 }
169
170 uint size() const { return _cur_idx; }
171
172 uint at(uint idx) const {
173 assert(idx < _cur_idx, "Index %u beyond valid regions", idx);
174 return _buffer[idx];
175 }
176
177 void add_dirty_region(uint region) {
178 if (_contains[region]) {
179 return;
180 }
181
182 bool marked_as_dirty = Atomic::cmpxchg(&_contains[region], false, true) == false;
183 if (marked_as_dirty) {
184 uint allocated = Atomic::fetch_and_add(&_cur_idx, 1u);
185 _buffer[allocated] = region;
186 }
187 }
188
189 // Creates the union of this and the other G1DirtyRegions.
190 void merge(const G1DirtyRegions* other) {
191 for (uint i = 0; i < other->size(); i++) {
192 uint region = other->at(i);
193 if (!_contains[region]) {
194 _buffer[_cur_idx++] = region;
195 _contains[region] = true;
196 }
197 }
198 }
199 };
200
201 // For each region, contains the maximum top() value to be used during this garbage
202 // collection. Subsumes common checks like filtering out everything but old and
203 // humongous regions outside the collection set.
204 // This is valid because we are not interested in scanning stray remembered set
205 // entries from free or archive regions.
206 HeapWord** _scan_top;
207
208 class G1ClearCardTableTask : public AbstractGangTask {
209 G1CollectedHeap* _g1h;
210 G1DirtyRegions* _regions;
211 uint _chunk_length;
212
213 uint volatile _cur_dirty_regions;
214
215 G1RemSetScanState* _scan_state;
216
217 public:
218 G1ClearCardTableTask(G1CollectedHeap* g1h,
219 G1DirtyRegions* regions,
220 uint chunk_length,
221 G1RemSetScanState* scan_state) :
222 AbstractGangTask("G1 Clear Card Table Task"),
223 _g1h(g1h),
224 _regions(regions),
225 _chunk_length(chunk_length),
226 _cur_dirty_regions(0),
227 _scan_state(scan_state) {
228
229 assert(chunk_length > 0, "must be");
230 }
231
232 static uint chunk_size() { return M; }
233
234 void work(uint worker_id) {
235 while (_cur_dirty_regions < _regions->size()) {
236 uint next = Atomic::fetch_and_add(&_cur_dirty_regions, _chunk_length);
237 uint max = MIN2(next + _chunk_length, _regions->size());
238
239 for (uint i = next; i < max; i++) {
240 HeapRegion* r = _g1h->region_at(_regions->at(i));
241 if (!r->is_survivor()) {
242 r->clear_cardtable();
243 }
244 }
245 }
246 }
247 };
248
249 // Clear the card table of "dirty" regions.
250 void clear_card_table(WorkGang* workers) {
251 uint num_regions = _all_dirty_regions->size();
252
253 if (num_regions == 0) {
254 return;
255 }
256
257 uint const num_chunks = (uint)(align_up((size_t)num_regions << HeapRegion::LogCardsPerRegion, G1ClearCardTableTask::chunk_size()) / G1ClearCardTableTask::chunk_size());
258 uint const num_workers = MIN2(num_chunks, workers->active_workers());
259 uint const chunk_length = G1ClearCardTableTask::chunk_size() / (uint)HeapRegion::CardsPerRegion;
260
261 // Iterate over the dirty cards region list.
262 G1ClearCardTableTask cl(G1CollectedHeap::heap(), _all_dirty_regions, chunk_length, this);
263
264 log_debug(gc, ergo)("Running %s using %u workers for %u "
265 "units of work for %u regions.",
266 cl.name(), num_workers, num_chunks, num_regions);
267 workers->run_task(&cl, num_workers);
268
269 #ifndef PRODUCT
270 G1CollectedHeap::heap()->verifier()->verify_card_table_cleanup();
271 #endif
272 }
273
274 public:
275 G1RemSetScanState() :
276 _max_regions(0),
277 _collection_set_iter_state(NULL),
278 _card_table_scan_state(NULL),
279 _scan_chunks_per_region(get_chunks_per_region(HeapRegion::LogOfHRGrainBytes)),
280 _log_scan_chunks_per_region(log2_uint(_scan_chunks_per_region)),
281 _region_scan_chunks(NULL),
282 _num_total_scan_chunks(0),
283 _scan_chunks_shift(0),
284 _all_dirty_regions(NULL),
285 _next_dirty_regions(NULL),
286 _scan_top(NULL) {
287 }
288
289 ~G1RemSetScanState() {
290 FREE_C_HEAP_ARRAY(G1RemsetIterState, _collection_set_iter_state);
291 FREE_C_HEAP_ARRAY(uint, _card_table_scan_state);
292 FREE_C_HEAP_ARRAY(bool, _region_scan_chunks);
293 FREE_C_HEAP_ARRAY(HeapWord*, _scan_top);
294 }
295
296 void initialize(size_t max_regions) {
297 assert(_collection_set_iter_state == NULL, "Must not be initialized twice");
298 _max_regions = max_regions;
299 _collection_set_iter_state = NEW_C_HEAP_ARRAY(G1RemsetIterState, max_regions, mtGC);
300 _card_table_scan_state = NEW_C_HEAP_ARRAY(uint, max_regions, mtGC);
301 _num_total_scan_chunks = max_regions * _scan_chunks_per_region;
302 _region_scan_chunks = NEW_C_HEAP_ARRAY(bool, _num_total_scan_chunks, mtGC);
303
304 _scan_chunks_shift = (uint8_t)log2_intptr(HeapRegion::CardsPerRegion / _scan_chunks_per_region);
305 _scan_top = NEW_C_HEAP_ARRAY(HeapWord*, max_regions, mtGC);
306 }
307
308 void prepare() {
309 // Reset the claim and clear scan top for all regions, including
310 // regions currently not available or free. Since regions might
311 // become used during the collection these values must be valid
312 // for those regions as well.
313 for (size_t i = 0; i < _max_regions; i++) {
314 reset_region_claim((uint)i);
315 clear_scan_top((uint)i);
316 }
317
318 _all_dirty_regions = new G1DirtyRegions(_max_regions);
319 _next_dirty_regions = new G1DirtyRegions(_max_regions);
320 }
321
322 void prepare_for_merge_heap_roots() {
323 _all_dirty_regions->merge(_next_dirty_regions);
324
325 _next_dirty_regions->reset();
326 for (size_t i = 0; i < _max_regions; i++) {
327 _card_table_scan_state[i] = 0;
328 }
329
330 ::memset(_region_scan_chunks, false, _num_total_scan_chunks * sizeof(*_region_scan_chunks));
331 }
332
333 // Returns whether the given region contains cards we need to scan. The remembered
334 // set and other sources may contain cards that
335 // - are in uncommitted regions
336 // - are located in the collection set
337 // - are located in free regions
338 // as we do not clean up remembered sets before merging heap roots.
339 bool contains_cards_to_process(uint const region_idx) const {
340 HeapRegion* hr = G1CollectedHeap::heap()->region_at_or_null(region_idx);
341 return (hr != NULL && !hr->in_collection_set() && hr->is_old_or_humongous_or_archive());
342 }
343
344 size_t num_visited_cards() const {
345 size_t result = 0;
346 for (uint i = 0; i < _num_total_scan_chunks; i++) {
347 if (_region_scan_chunks[i]) {
348 result++;
349 }
350 }
351 return result * (HeapRegion::CardsPerRegion / _scan_chunks_per_region);
352 }
353
354 size_t num_cards_in_dirty_regions() const {
355 return _next_dirty_regions->size() * HeapRegion::CardsPerRegion;
356 }
357
358 void set_chunk_region_dirty(size_t const region_card_idx) {
359 size_t chunk_idx = region_card_idx >> _scan_chunks_shift;
360 for (uint i = 0; i < _scan_chunks_per_region; i++) {
361 _region_scan_chunks[chunk_idx++] = true;
362 }
363 }
364
365 void set_chunk_dirty(size_t const card_idx) {
366 assert((card_idx >> _scan_chunks_shift) < _num_total_scan_chunks,
367 "Trying to access index " SIZE_FORMAT " out of bounds " SIZE_FORMAT,
368 card_idx >> _scan_chunks_shift, _num_total_scan_chunks);
369 size_t const chunk_idx = card_idx >> _scan_chunks_shift;
370 if (!_region_scan_chunks[chunk_idx]) {
371 _region_scan_chunks[chunk_idx] = true;
372 }
373 }
374
375 void cleanup(WorkGang* workers) {
376 _all_dirty_regions->merge(_next_dirty_regions);
377
378 clear_card_table(workers);
379
380 delete _all_dirty_regions;
381 _all_dirty_regions = NULL;
382
383 delete _next_dirty_regions;
384 _next_dirty_regions = NULL;
385 }
386
387 void iterate_dirty_regions_from(HeapRegionClosure* cl, uint worker_id) {
388 uint num_regions = _next_dirty_regions->size();
389
390 if (num_regions == 0) {
391 return;
392 }
393
394 G1CollectedHeap* g1h = G1CollectedHeap::heap();
395
396 WorkGang* workers = g1h->workers();
397 uint const max_workers = workers->active_workers();
398
399 uint const start_pos = num_regions * worker_id / max_workers;
400 uint cur = start_pos;
401
402 do {
403 bool result = cl->do_heap_region(g1h->region_at(_next_dirty_regions->at(cur)));
404 guarantee(!result, "Not allowed to ask for early termination.");
405 cur++;
406 if (cur == _next_dirty_regions->size()) {
407 cur = 0;
408 }
409 } while (cur != start_pos);
410 }
411
412 void reset_region_claim(uint region_idx) {
413 _collection_set_iter_state[region_idx] = false;
414 }
415
416 // Attempt to claim the given region in the collection set for iteration. Returns true
417 // if this call caused the transition from Unclaimed to Claimed.
418 inline bool claim_collection_set_region(uint region) {
419 assert(region < _max_regions, "Tried to access invalid region %u", region);
420 if (_collection_set_iter_state[region]) {
421 return false;
422 }
423 return !Atomic::cmpxchg(&_collection_set_iter_state[region], false, true);
424 }
425
426 bool has_cards_to_scan(uint region) {
427 assert(region < _max_regions, "Tried to access invalid region %u", region);
428 return _card_table_scan_state[region] < HeapRegion::CardsPerRegion;
429 }
430
431 uint claim_cards_to_scan(uint region, uint increment) {
432 assert(region < _max_regions, "Tried to access invalid region %u", region);
433 return Atomic::fetch_and_add(&_card_table_scan_state[region], increment);
434 }
435
436 void add_dirty_region(uint const region) {
437 #ifdef ASSERT
438 HeapRegion* hr = G1CollectedHeap::heap()->region_at(region);
439 assert(!hr->in_collection_set() && hr->is_old_or_humongous_or_archive(),
440 "Region %u is not suitable for scanning, is %sin collection set or %s",
441 hr->hrm_index(), hr->in_collection_set() ? "" : "not ", hr->get_short_type_str());
442 #endif
443 _next_dirty_regions->add_dirty_region(region);
444 }
445
446 void add_all_dirty_region(uint region) {
447 #ifdef ASSERT
448 HeapRegion* hr = G1CollectedHeap::heap()->region_at(region);
449 assert(hr->in_collection_set(),
450 "Only add young regions to all dirty regions directly but %u is %s",
451 hr->hrm_index(), hr->get_short_type_str());
452 #endif
453 _all_dirty_regions->add_dirty_region(region);
454 }
455
456 void set_scan_top(uint region_idx, HeapWord* value) {
457 _scan_top[region_idx] = value;
458 }
459
460 HeapWord* scan_top(uint region_idx) const {
461 return _scan_top[region_idx];
462 }
463
464 void clear_scan_top(uint region_idx) {
465 set_scan_top(region_idx, NULL);
466 }
467 };
468
469 G1RemSet::G1RemSet(G1CollectedHeap* g1h,
470 G1CardTable* ct,
471 G1HotCardCache* hot_card_cache) :
472 _scan_state(new G1RemSetScanState()),
473 _prev_period_summary(false),
474 _g1h(g1h),
475 _ct(ct),
476 _g1p(_g1h->policy()),
477 _hot_card_cache(hot_card_cache) {
478 }
479
480 G1RemSet::~G1RemSet() {
481 delete _scan_state;
482 }
483
484 uint G1RemSet::num_par_rem_sets() {
485 return G1DirtyCardQueueSet::num_par_ids() + G1ConcurrentRefine::max_num_threads() + MAX2(ConcGCThreads, ParallelGCThreads);
486 }
487
488 void G1RemSet::initialize(size_t capacity, uint max_regions) {
489 G1FromCardCache::initialize(num_par_rem_sets(), max_regions);
490 _scan_state->initialize(max_regions);
491 }
492
493 // Helper class to scan and detect ranges of cards that need to be scanned on the
494 // card table.
495 class G1CardTableScanner : public StackObj {
496 public:
497 typedef CardTable::CardValue CardValue;
498
499 private:
500 CardValue* const _base_addr;
501
502 CardValue* _cur_addr;
503 CardValue* const _end_addr;
504
505 static const size_t ToScanMask = G1CardTable::g1_card_already_scanned;
506 static const size_t ExpandedToScanMask = G1CardTable::WordAlreadyScanned;
507
508 bool cur_addr_aligned() const {
509 return ((uintptr_t)_cur_addr) % sizeof(size_t) == 0;
510 }
511
512 bool cur_card_is_dirty() const {
513 CardValue value = *_cur_addr;
514 return (value & ToScanMask) == 0;
515 }
516
517 bool cur_word_of_cards_contains_any_dirty_card() const {
518 assert(cur_addr_aligned(), "Current address should be aligned");
519 size_t const value = *(size_t*)_cur_addr;
520 return (~value & ExpandedToScanMask) != 0;
521 }
522
523 bool cur_word_of_cards_all_dirty_cards() const {
524 size_t const value = *(size_t*)_cur_addr;
525 return value == G1CardTable::WordAllDirty;
526 }
527
528 size_t get_and_advance_pos() {
529 _cur_addr++;
530 return pointer_delta(_cur_addr, _base_addr, sizeof(CardValue)) - 1;
531 }
532
533 public:
534 G1CardTableScanner(CardValue* start_card, size_t size) :
535 _base_addr(start_card),
536 _cur_addr(start_card),
537 _end_addr(start_card + size) {
538
539 assert(is_aligned(start_card, sizeof(size_t)), "Unaligned start addr " PTR_FORMAT, p2i(start_card));
540 assert(is_aligned(size, sizeof(size_t)), "Unaligned size " SIZE_FORMAT, size);
541 }
542
543 size_t find_next_dirty() {
544 while (!cur_addr_aligned()) {
545 if (cur_card_is_dirty()) {
546 return get_and_advance_pos();
547 }
548 _cur_addr++;
549 }
550
551 assert(cur_addr_aligned(), "Current address should be aligned now.");
552 while (_cur_addr != _end_addr) {
553 if (cur_word_of_cards_contains_any_dirty_card()) {
554 for (size_t i = 0; i < sizeof(size_t); i++) {
555 if (cur_card_is_dirty()) {
556 return get_and_advance_pos();
557 }
558 _cur_addr++;
559 }
560 assert(false, "Should not reach here given we detected a dirty card in the word.");
561 }
562 _cur_addr += sizeof(size_t);
563 }
564 return get_and_advance_pos();
565 }
566
567 size_t find_next_non_dirty() {
568 assert(_cur_addr <= _end_addr, "Not allowed to search for marks after area.");
569
570 while (!cur_addr_aligned()) {
571 if (!cur_card_is_dirty()) {
572 return get_and_advance_pos();
573 }
574 _cur_addr++;
575 }
576
577 assert(cur_addr_aligned(), "Current address should be aligned now.");
578 while (_cur_addr != _end_addr) {
579 if (!cur_word_of_cards_all_dirty_cards()) {
580 for (size_t i = 0; i < sizeof(size_t); i++) {
581 if (!cur_card_is_dirty()) {
582 return get_and_advance_pos();
583 }
584 _cur_addr++;
585 }
586 assert(false, "Should not reach here given we detected a non-dirty card in the word.");
587 }
588 _cur_addr += sizeof(size_t);
589 }
590 return get_and_advance_pos();
591 }
592 };
593
594 // Helper class to claim dirty chunks within the card table.
595 class G1CardTableChunkClaimer {
596 G1RemSetScanState* _scan_state;
597 uint _region_idx;
598 uint _cur_claim;
599
600 public:
601 G1CardTableChunkClaimer(G1RemSetScanState* scan_state, uint region_idx) :
602 _scan_state(scan_state),
603 _region_idx(region_idx),
604 _cur_claim(0) {
605 guarantee(size() <= HeapRegion::CardsPerRegion, "Should not claim more space than possible.");
606 }
607
608 bool has_next() {
609 while (true) {
610 _cur_claim = _scan_state->claim_cards_to_scan(_region_idx, size());
611 if (_cur_claim >= HeapRegion::CardsPerRegion) {
612 return false;
613 }
614 if (_scan_state->chunk_needs_scan(_region_idx, _cur_claim)) {
615 return true;
616 }
617 }
618 }
619
620 uint value() const { return _cur_claim; }
621 uint size() const { return _scan_state->scan_chunk_size(); }
622 };
623
624 // Scans a heap region for dirty cards.
625 class G1ScanHRForRegionClosure : public HeapRegionClosure {
626 G1CollectedHeap* _g1h;
627 G1CardTable* _ct;
628 G1BlockOffsetTable* _bot;
629
630 G1ParScanThreadState* _pss;
631
632 G1RemSetScanState* _scan_state;
633
634 G1GCPhaseTimes::GCParPhases _phase;
635
636 uint _worker_id;
637
638 size_t _cards_scanned;
639 size_t _blocks_scanned;
640 size_t _chunks_claimed;
641
642 Tickspan _rem_set_root_scan_time;
643 Tickspan _rem_set_trim_partially_time;
644
645 // The address to which this thread already scanned (walked the heap) up to during
646 // card scanning (exclusive).
647 HeapWord* _scanned_to;
648
649 HeapWord* scan_memregion(uint region_idx_for_card, MemRegion mr) {
650 HeapRegion* const card_region = _g1h->region_at(region_idx_for_card);
651 G1ScanCardClosure card_cl(_g1h, _pss);
652
653 HeapWord* const scanned_to = card_region->oops_on_memregion_seq_iterate_careful<true>(mr, &card_cl);
654 assert(scanned_to != NULL, "Should be able to scan range");
655 assert(scanned_to >= mr.end(), "Scanned to " PTR_FORMAT " less than range " PTR_FORMAT, p2i(scanned_to), p2i(mr.end()));
656
657 _pss->trim_queue_partially();
658 return scanned_to;
659 }
660
661 void do_claimed_block(uint const region_idx_for_card, size_t const first_card, size_t const num_cards) {
662 HeapWord* const card_start = _bot->address_for_index_raw(first_card);
663 #ifdef ASSERT
664 HeapRegion* hr = _g1h->region_at_or_null(region_idx_for_card);
665 assert(hr == NULL || hr->is_in_reserved(card_start),
666 "Card start " PTR_FORMAT " to scan outside of region %u", p2i(card_start), _g1h->region_at(region_idx_for_card)->hrm_index());
667 #endif
668 HeapWord* const top = _scan_state->scan_top(region_idx_for_card);
669 if (card_start >= top) {
670 return;
671 }
672
673 HeapWord* scan_end = MIN2(card_start + (num_cards << BOTConstants::LogN_words), top);
674 if (_scanned_to >= scan_end) {
675 return;
676 }
677 MemRegion mr(MAX2(card_start, _scanned_to), scan_end);
678 _scanned_to = scan_memregion(region_idx_for_card, mr);
679
680 _cards_scanned += num_cards;
681 }
682
683 ALWAYSINLINE void do_card_block(uint const region_idx, size_t const first_card, size_t const num_cards) {
684 _ct->mark_as_scanned(first_card, num_cards);
685 do_claimed_block(region_idx, first_card, num_cards);
686 _blocks_scanned++;
687 }
688
689 void scan_heap_roots(HeapRegion* r) {
690 EventGCPhaseParallel event;
691 uint const region_idx = r->hrm_index();
692
693 ResourceMark rm;
694
695 G1CardTableChunkClaimer claim(_scan_state, region_idx);
696
697 // Set the current scan "finger" to NULL for every heap region to scan. Since
698 // the claim value is monotonically increasing, the check to not scan below this
699 // will filter out objects spanning chunks within the region too then, as opposed
700 // to resetting this value for every claim.
701 _scanned_to = NULL;
702
703 while (claim.has_next()) {
704 size_t const region_card_base_idx = ((size_t)region_idx << HeapRegion::LogCardsPerRegion) + claim.value();
705 CardTable::CardValue* const base_addr = _ct->byte_for_index(region_card_base_idx);
706
707 G1CardTableScanner scan(base_addr, claim.size());
708
709 size_t first_scan_idx = scan.find_next_dirty();
710 while (first_scan_idx != claim.size()) {
711 assert(*_ct->byte_for_index(region_card_base_idx + first_scan_idx) <= 0x1, "is %d at region %u idx " SIZE_FORMAT, *_ct->byte_for_index(region_card_base_idx + first_scan_idx), region_idx, first_scan_idx);
712
713 size_t const last_scan_idx = scan.find_next_non_dirty();
714 size_t const len = last_scan_idx - first_scan_idx;
715
716 do_card_block(region_idx, region_card_base_idx + first_scan_idx, len);
717
718 if (last_scan_idx == claim.size()) {
719 break;
720 }
721
722 first_scan_idx = scan.find_next_dirty();
723 }
724 _chunks_claimed++;
725 }
726
727 event.commit(GCId::current(), _worker_id, G1GCPhaseTimes::phase_name(G1GCPhaseTimes::ScanHR));
728 }
729
730 public:
731 G1ScanHRForRegionClosure(G1RemSetScanState* scan_state,
732 G1ParScanThreadState* pss,
733 uint worker_id,
734 G1GCPhaseTimes::GCParPhases phase) :
735 _g1h(G1CollectedHeap::heap()),
736 _ct(_g1h->card_table()),
737 _bot(_g1h->bot()),
738 _pss(pss),
739 _scan_state(scan_state),
740 _phase(phase),
741 _worker_id(worker_id),
742 _cards_scanned(0),
743 _blocks_scanned(0),
744 _chunks_claimed(0),
745 _rem_set_root_scan_time(),
746 _rem_set_trim_partially_time(),
747 _scanned_to(NULL) {
748 }
749
750 bool do_heap_region(HeapRegion* r) {
751 assert(!r->in_collection_set() && r->is_old_or_humongous_or_archive(),
752 "Should only be called on old gen non-collection set regions but region %u is not.",
753 r->hrm_index());
754 uint const region_idx = r->hrm_index();
755
756 if (_scan_state->has_cards_to_scan(region_idx)) {
757 G1EvacPhaseWithTrimTimeTracker timer(_pss, _rem_set_root_scan_time, _rem_set_trim_partially_time);
758 scan_heap_roots(r);
759 }
760 return false;
761 }
762
763 Tickspan rem_set_root_scan_time() const { return _rem_set_root_scan_time; }
764 Tickspan rem_set_trim_partially_time() const { return _rem_set_trim_partially_time; }
765
766 size_t cards_scanned() const { return _cards_scanned; }
767 size_t blocks_scanned() const { return _blocks_scanned; }
768 size_t chunks_claimed() const { return _chunks_claimed; }
769 };
770
771 void G1RemSet::scan_heap_roots(G1ParScanThreadState* pss,
772 uint worker_id,
773 G1GCPhaseTimes::GCParPhases scan_phase,
774 G1GCPhaseTimes::GCParPhases objcopy_phase) {
775 G1ScanHRForRegionClosure cl(_scan_state, pss, worker_id, scan_phase);
776 _scan_state->iterate_dirty_regions_from(&cl, worker_id);
777
778 G1GCPhaseTimes* p = _g1p->phase_times();
779
780 p->record_or_add_time_secs(objcopy_phase, worker_id, cl.rem_set_trim_partially_time().seconds());
781
782 p->record_or_add_time_secs(scan_phase, worker_id, cl.rem_set_root_scan_time().seconds());
783 p->record_or_add_thread_work_item(scan_phase, worker_id, cl.cards_scanned(), G1GCPhaseTimes::ScanHRScannedCards);
784 p->record_or_add_thread_work_item(scan_phase, worker_id, cl.blocks_scanned(), G1GCPhaseTimes::ScanHRScannedBlocks);
785 p->record_or_add_thread_work_item(scan_phase, worker_id, cl.chunks_claimed(), G1GCPhaseTimes::ScanHRClaimedChunks);
786 }
787
788 // Heap region closure to be applied to all regions in the current collection set
789 // increment to fix up non-card related roots.
790 class G1ScanCollectionSetRegionClosure : public HeapRegionClosure {
791 G1ParScanThreadState* _pss;
792 G1RemSetScanState* _scan_state;
793
794 G1GCPhaseTimes::GCParPhases _scan_phase;
795 G1GCPhaseTimes::GCParPhases _code_roots_phase;
796
797 uint _worker_id;
798
799 size_t _opt_refs_scanned;
800 size_t _opt_refs_memory_used;
801
802 Tickspan _strong_code_root_scan_time;
803 Tickspan _strong_code_trim_partially_time;
804
805 Tickspan _rem_set_opt_root_scan_time;
806 Tickspan _rem_set_opt_trim_partially_time;
807
808 void scan_opt_rem_set_roots(HeapRegion* r) {
809 EventGCPhaseParallel event;
810
811 G1OopStarChunkedList* opt_rem_set_list = _pss->oops_into_optional_region(r);
812
813 G1ScanCardClosure scan_cl(G1CollectedHeap::heap(), _pss);
814 G1ScanRSForOptionalClosure cl(G1CollectedHeap::heap(), &scan_cl);
815 _opt_refs_scanned += opt_rem_set_list->oops_do(&cl, _pss->closures()->strong_oops());
816 _opt_refs_memory_used += opt_rem_set_list->used_memory();
817
818 event.commit(GCId::current(), _worker_id, G1GCPhaseTimes::phase_name(_scan_phase));
819 }
820
821 public:
822 G1ScanCollectionSetRegionClosure(G1RemSetScanState* scan_state,
823 G1ParScanThreadState* pss,
824 uint worker_id,
825 G1GCPhaseTimes::GCParPhases scan_phase,
826 G1GCPhaseTimes::GCParPhases code_roots_phase) :
827 _pss(pss),
828 _scan_state(scan_state),
829 _scan_phase(scan_phase),
830 _code_roots_phase(code_roots_phase),
831 _worker_id(worker_id),
832 _opt_refs_scanned(0),
833 _opt_refs_memory_used(0),
834 _strong_code_root_scan_time(),
835 _strong_code_trim_partially_time(),
836 _rem_set_opt_root_scan_time(),
837 _rem_set_opt_trim_partially_time() { }
838
839 bool do_heap_region(HeapRegion* r) {
840 uint const region_idx = r->hrm_index();
841
842 // The individual references for the optional remembered set are per-worker, so we
843 // always need to scan them.
844 if (r->has_index_in_opt_cset()) {
845 G1EvacPhaseWithTrimTimeTracker timer(_pss, _rem_set_opt_root_scan_time, _rem_set_opt_trim_partially_time);
846 scan_opt_rem_set_roots(r);
847 }
848
849 if (_scan_state->claim_collection_set_region(region_idx)) {
850 EventGCPhaseParallel event;
851
852 G1EvacPhaseWithTrimTimeTracker timer(_pss, _strong_code_root_scan_time, _strong_code_trim_partially_time);
853 // Scan the strong code root list attached to the current region
854 r->strong_code_roots_do(_pss->closures()->weak_codeblobs());
855
856 event.commit(GCId::current(), _worker_id, G1GCPhaseTimes::phase_name(_code_roots_phase));
857 }
858
859 return false;
860 }
861
862 Tickspan strong_code_root_scan_time() const { return _strong_code_root_scan_time; }
863 Tickspan strong_code_root_trim_partially_time() const { return _strong_code_trim_partially_time; }
864
865 Tickspan rem_set_opt_root_scan_time() const { return _rem_set_opt_root_scan_time; }
866 Tickspan rem_set_opt_trim_partially_time() const { return _rem_set_opt_trim_partially_time; }
867
868 size_t opt_refs_scanned() const { return _opt_refs_scanned; }
869 size_t opt_refs_memory_used() const { return _opt_refs_memory_used; }
870 };
871
872 void G1RemSet::scan_collection_set_regions(G1ParScanThreadState* pss,
873 uint worker_id,
874 G1GCPhaseTimes::GCParPhases scan_phase,
875 G1GCPhaseTimes::GCParPhases coderoots_phase,
876 G1GCPhaseTimes::GCParPhases objcopy_phase) {
877 G1ScanCollectionSetRegionClosure cl(_scan_state, pss, worker_id, scan_phase, coderoots_phase);
878 _g1h->collection_set_iterate_increment_from(&cl, worker_id);
879
880 G1GCPhaseTimes* p = _g1h->phase_times();
881
882 p->record_or_add_time_secs(scan_phase, worker_id, cl.rem_set_opt_root_scan_time().seconds());
883 p->record_or_add_time_secs(scan_phase, worker_id, cl.rem_set_opt_trim_partially_time().seconds());
884
885 p->record_or_add_time_secs(coderoots_phase, worker_id, cl.strong_code_root_scan_time().seconds());
886 p->add_time_secs(objcopy_phase, worker_id, cl.strong_code_root_trim_partially_time().seconds());
887
888 // At this time we record some metrics only for the evacuations after the initial one.
889 if (scan_phase == G1GCPhaseTimes::OptScanHR) {
890 p->record_or_add_thread_work_item(scan_phase, worker_id, cl.opt_refs_scanned(), G1GCPhaseTimes::ScanHRScannedOptRefs);
891 p->record_or_add_thread_work_item(scan_phase, worker_id, cl.opt_refs_memory_used(), G1GCPhaseTimes::ScanHRUsedMemory);
892 }
893 }
894
895 void G1RemSet::prepare_region_for_scan(HeapRegion* region) {
896 uint hrm_index = region->hrm_index();
897
898 if (region->in_collection_set()) {
899 // Young regions had their card table marked as young at their allocation;
900 // we need to make sure that these marks are cleared at the end of GC, *but*
901 // they should not be scanned for cards.
902 // So directly add them to the "all_dirty_regions".
903 // Same for regions in the (initial) collection set: they may contain cards from
904 // the log buffers, make sure they are cleaned.
905 _scan_state->add_all_dirty_region(hrm_index);
906 } else if (region->is_old_or_humongous_or_archive()) {
907 _scan_state->set_scan_top(hrm_index, region->top());
908 } else {
909 assert(region->is_free(), "Should only be free region at this point %s", region->get_type_str());
910 }
911 }
912
913 void G1RemSet::prepare_for_scan_heap_roots() {
914 _scan_state->prepare();
915 }
916
917 class G1MergeHeapRootsTask : public AbstractGangTask {
918
919 // Visitor for remembered sets, dropping entries onto the card table.
920 class G1MergeCardSetClosure : public HeapRegionClosure {
921 G1RemSetScanState* _scan_state;
922 G1CardTable* _ct;
923
924 uint _merged_sparse;
925 uint _merged_fine;
926 uint _merged_coarse;
927
928 size_t _cards_dirty;
929
930 // Returns if the region contains cards we need to scan. If so, remember that
931 // region in the current set of dirty regions.
932 bool remember_if_interesting(uint const region_idx) {
933 if (!_scan_state->contains_cards_to_process(region_idx)) {
934 return false;
935 }
936 _scan_state->add_dirty_region(region_idx);
937 return true;
938 }
939 public:
940 G1MergeCardSetClosure(G1RemSetScanState* scan_state) :
941 _scan_state(scan_state),
942 _ct(G1CollectedHeap::heap()->card_table()),
943 _merged_sparse(0),
944 _merged_fine(0),
945 _merged_coarse(0),
946 _cards_dirty(0) { }
947
948 void next_coarse_prt(uint const region_idx) {
949 if (!remember_if_interesting(region_idx)) {
950 return;
951 }
952
953 _merged_coarse++;
954
955 size_t region_base_idx = (size_t)region_idx << HeapRegion::LogCardsPerRegion;
956 _cards_dirty += _ct->mark_region_dirty(region_base_idx, HeapRegion::CardsPerRegion);
957 _scan_state->set_chunk_region_dirty(region_base_idx);
958 }
959
960 void next_fine_prt(uint const region_idx, BitMap* bm) {
961 if (!remember_if_interesting(region_idx)) {
962 return;
963 }
964
965 _merged_fine++;
966
967 size_t const region_base_idx = (size_t)region_idx << HeapRegion::LogCardsPerRegion;
968 BitMap::idx_t cur = bm->get_next_one_offset(0);
969 while (cur != bm->size()) {
970 _cards_dirty += _ct->mark_clean_as_dirty(region_base_idx + cur);
971 _scan_state->set_chunk_dirty(region_base_idx + cur);
972 cur = bm->get_next_one_offset(cur + 1);
973 }
974 }
975
976 void next_sparse_prt(uint const region_idx, SparsePRTEntry::card_elem_t* cards, uint const num_cards) {
977 if (!remember_if_interesting(region_idx)) {
978 return;
979 }
980
981 _merged_sparse++;
982
983 size_t const region_base_idx = (size_t)region_idx << HeapRegion::LogCardsPerRegion;
984 for (uint i = 0; i < num_cards; i++) {
985 size_t card_idx = region_base_idx + cards[i];
986 _cards_dirty += _ct->mark_clean_as_dirty(card_idx);
987 _scan_state->set_chunk_dirty(card_idx);
988 }
989 }
990
991 virtual bool do_heap_region(HeapRegion* r) {
992 assert(r->in_collection_set() || r->is_starts_humongous(), "must be");
993
994 HeapRegionRemSet* rem_set = r->rem_set();
995 if (!rem_set->is_empty()) {
996 rem_set->iterate_prts(*this);
997 }
998
999 return false;
1000 }
1001
1002 size_t merged_sparse() const { return _merged_sparse; }
1003 size_t merged_fine() const { return _merged_fine; }
1004 size_t merged_coarse() const { return _merged_coarse; }
1005
1006 size_t cards_dirty() const { return _cards_dirty; }
1007 };
1008
1009 // Visitor for the remembered sets of humongous candidate regions to merge their
1010 // remembered set into the card table.
1011 class G1FlushHumongousCandidateRemSets : public HeapRegionClosure {
1012 G1MergeCardSetClosure _cl;
1013
1014 public:
1015 G1FlushHumongousCandidateRemSets(G1RemSetScanState* scan_state) : _cl(scan_state) { }
1016
1017 virtual bool do_heap_region(HeapRegion* r) {
1018 G1CollectedHeap* g1h = G1CollectedHeap::heap();
1019
1020 if (!r->is_starts_humongous() ||
1021 !g1h->region_attr(r->hrm_index()).is_humongous() ||
1022 r->rem_set()->is_empty()) {
1023 return false;
1024 }
1025
1026 guarantee(r->rem_set()->occupancy_less_or_equal_than(G1RSetSparseRegionEntries),
1027 "Found a not-small remembered set here. This is inconsistent with previous assumptions.");
1028
1029 _cl.do_heap_region(r);
1030
1031 // We should only clear the card based remembered set here as we will not
1032 // implicitly rebuild anything else during eager reclaim. Note that at the moment
1033 // (and probably never) we do not enter this path if there are other kind of
1034 // remembered sets for this region.
1035 r->rem_set()->clear_locked(true /* only_cardset */);
1036 // Clear_locked() above sets the state to Empty. However we want to continue
1037 // collecting remembered set entries for humongous regions that were not
1038 // reclaimed.
1039 r->rem_set()->set_state_complete();
1040 #ifdef ASSERT
1041 G1HeapRegionAttr region_attr = g1h->region_attr(r->hrm_index());
1042 assert(region_attr.needs_remset_update(), "must be");
1043 #endif
1044 assert(r->rem_set()->is_empty(), "At this point any humongous candidate remembered set must be empty.");
1045
1046 return false;
1047 }
1048
1049 size_t merged_sparse() const { return _cl.merged_sparse(); }
1050 size_t merged_fine() const { return _cl.merged_fine(); }
1051 size_t merged_coarse() const { return _cl.merged_coarse(); }
1052
1053 size_t cards_dirty() const { return _cl.cards_dirty(); }
1054 };
1055
1056 // Visitor for the log buffer entries to merge them into the card table.
1057 class G1MergeLogBufferCardsClosure : public G1CardTableEntryClosure {
1058 G1RemSetScanState* _scan_state;
1059 G1CardTable* _ct;
1060
1061 size_t _cards_dirty;
1062 size_t _cards_skipped;
1063 public:
1064 G1MergeLogBufferCardsClosure(G1CollectedHeap* g1h, G1RemSetScanState* scan_state) :
1065 _scan_state(scan_state), _ct(g1h->card_table()), _cards_dirty(0), _cards_skipped(0)
1066 {}
1067
1068 void do_card_ptr(CardValue* card_ptr, uint worker_id) {
1069 // The only time we care about recording cards that
1070 // contain references that point into the collection set
1071 // is during RSet updating within an evacuation pause.
1072 // In this case worker_id should be the id of a GC worker thread.
1073 assert(SafepointSynchronize::is_at_safepoint(), "not during an evacuation pause");
1074
1075 uint const region_idx = _ct->region_idx_for(card_ptr);
1076
1077 // The second clause must come after - the log buffers might contain cards to uncommited
1078 // regions.
1079 // This code may count duplicate entries in the log buffers (even if rare) multiple
1080 // times.
1081 if (_scan_state->contains_cards_to_process(region_idx) && (*card_ptr == G1CardTable::dirty_card_val())) {
1082 _scan_state->add_dirty_region(region_idx);
1083 _scan_state->set_chunk_dirty(_ct->index_for_cardvalue(card_ptr));
1084 _cards_dirty++;
1085 } else {
1086 // We may have had dirty cards in the (initial) collection set (or the
1087 // young regions which are always in the initial collection set). We do
1088 // not fix their cards here: we already added these regions to the set of
1089 // regions to clear the card table at the end during the prepare() phase.
1090 _cards_skipped++;
1091 }
1092 }
1093
1094 size_t cards_dirty() const { return _cards_dirty; }
1095 size_t cards_skipped() const { return _cards_skipped; }
1096 };
1097
1098 HeapRegionClaimer _hr_claimer;
1099 G1RemSetScanState* _scan_state;
1100 BufferNode::Stack _dirty_card_buffers;
1101 bool _initial_evacuation;
1102
1103 volatile bool _fast_reclaim_handled;
1104
1105 void apply_closure_to_dirty_card_buffers(G1MergeLogBufferCardsClosure* cl, uint worker_id) {
1106 G1DirtyCardQueueSet& dcqs = G1BarrierSet::dirty_card_queue_set();
1107 size_t buffer_size = dcqs.buffer_size();
1108 while (BufferNode* node = _dirty_card_buffers.pop()) {
1109 cl->apply_to_buffer(node, buffer_size, worker_id);
1110 dcqs.deallocate_buffer(node);
1111 }
1112 }
1113
1114 public:
1115 G1MergeHeapRootsTask(G1RemSetScanState* scan_state, uint num_workers, bool initial_evacuation) :
1116 AbstractGangTask("G1 Merge Heap Roots"),
1117 _hr_claimer(num_workers),
1118 _scan_state(scan_state),
1119 _dirty_card_buffers(),
1120 _initial_evacuation(initial_evacuation),
1121 _fast_reclaim_handled(false)
1122 {
1123 if (initial_evacuation) {
1124 G1DirtyCardQueueSet& dcqs = G1BarrierSet::dirty_card_queue_set();
1125 G1BufferNodeList buffers = dcqs.take_all_completed_buffers();
1126 if (buffers._entry_count != 0) {
1127 _dirty_card_buffers.prepend(*buffers._head, *buffers._tail);
1128 }
1129 }
1130 }
1131
1132 virtual void work(uint worker_id) {
1133 G1CollectedHeap* g1h = G1CollectedHeap::heap();
1134 G1GCPhaseTimes* p = g1h->phase_times();
1135
1136 G1GCPhaseTimes::GCParPhases merge_remset_phase = _initial_evacuation ?
1137 G1GCPhaseTimes::MergeRS :
1138 G1GCPhaseTimes::OptMergeRS;
1139
1140 // We schedule flushing the remembered sets of humongous fast reclaim candidates
1141 // onto the card table first to allow the remaining parallelized tasks hide it.
1142 if (_initial_evacuation &&
1143 p->fast_reclaim_humongous_candidates() > 0 &&
1144 !_fast_reclaim_handled &&
1145 !Atomic::cmpxchg(&_fast_reclaim_handled, false, true)) {
1146
1147 G1GCParPhaseTimesTracker x(p, G1GCPhaseTimes::MergeER, worker_id);
1148
1149 G1FlushHumongousCandidateRemSets cl(_scan_state);
1150 g1h->heap_region_iterate(&cl);
1151
1152 p->record_or_add_thread_work_item(merge_remset_phase, worker_id, cl.merged_sparse(), G1GCPhaseTimes::MergeRSMergedSparse);
1153 p->record_or_add_thread_work_item(merge_remset_phase, worker_id, cl.merged_fine(), G1GCPhaseTimes::MergeRSMergedFine);
1154 p->record_or_add_thread_work_item(merge_remset_phase, worker_id, cl.merged_coarse(), G1GCPhaseTimes::MergeRSMergedCoarse);
1155 p->record_or_add_thread_work_item(merge_remset_phase, worker_id, cl.cards_dirty(), G1GCPhaseTimes::MergeRSDirtyCards);
1156 }
1157
1158 // Merge remembered sets of current candidates.
1159 {
1160 G1GCParPhaseTimesTracker x(p, merge_remset_phase, worker_id, _initial_evacuation /* must_record */);
1161 G1MergeCardSetClosure cl(_scan_state);
1162 g1h->collection_set_iterate_increment_from(&cl, &_hr_claimer, worker_id);
1163
1164 p->record_or_add_thread_work_item(merge_remset_phase, worker_id, cl.merged_sparse(), G1GCPhaseTimes::MergeRSMergedSparse);
1165 p->record_or_add_thread_work_item(merge_remset_phase, worker_id, cl.merged_fine(), G1GCPhaseTimes::MergeRSMergedFine);
1166 p->record_or_add_thread_work_item(merge_remset_phase, worker_id, cl.merged_coarse(), G1GCPhaseTimes::MergeRSMergedCoarse);
1167 p->record_or_add_thread_work_item(merge_remset_phase, worker_id, cl.cards_dirty(), G1GCPhaseTimes::MergeRSDirtyCards);
1168 }
1169
1170 // Apply closure to log entries in the HCC.
1171 if (_initial_evacuation && G1HotCardCache::default_use_cache()) {
1172 assert(merge_remset_phase == G1GCPhaseTimes::MergeRS, "Wrong merge phase");
1173 G1GCParPhaseTimesTracker x(p, G1GCPhaseTimes::MergeHCC, worker_id);
1174 G1MergeLogBufferCardsClosure cl(g1h, _scan_state);
1175 g1h->iterate_hcc_closure(&cl, worker_id);
1176
1177 p->record_thread_work_item(G1GCPhaseTimes::MergeHCC, worker_id, cl.cards_dirty(), G1GCPhaseTimes::MergeHCCDirtyCards);
1178 p->record_thread_work_item(G1GCPhaseTimes::MergeHCC, worker_id, cl.cards_skipped(), G1GCPhaseTimes::MergeHCCSkippedCards);
1179 }
1180
1181 // Now apply the closure to all remaining log entries.
1182 if (_initial_evacuation) {
1183 assert(merge_remset_phase == G1GCPhaseTimes::MergeRS, "Wrong merge phase");
1184 G1GCParPhaseTimesTracker x(p, G1GCPhaseTimes::MergeLB, worker_id);
1185
1186 G1MergeLogBufferCardsClosure cl(g1h, _scan_state);
1187 apply_closure_to_dirty_card_buffers(&cl, worker_id);
1188
1189 p->record_thread_work_item(G1GCPhaseTimes::MergeLB, worker_id, cl.cards_dirty(), G1GCPhaseTimes::MergeLBDirtyCards);
1190 p->record_thread_work_item(G1GCPhaseTimes::MergeLB, worker_id, cl.cards_skipped(), G1GCPhaseTimes::MergeLBSkippedCards);
1191 }
1192 }
1193 };
1194
1195 void G1RemSet::print_merge_heap_roots_stats() {
1196 size_t num_visited_cards = _scan_state->num_visited_cards();
1197
1198 size_t total_dirty_region_cards = _scan_state->num_cards_in_dirty_regions();
1199
1200 G1CollectedHeap* g1h = G1CollectedHeap::heap();
1201 size_t total_old_region_cards =
1202 (g1h->num_regions() - (g1h->num_free_regions() - g1h->collection_set()->cur_length())) * HeapRegion::CardsPerRegion;
1203
1204 log_debug(gc,remset)("Visited cards " SIZE_FORMAT " Total dirty " SIZE_FORMAT " (%.2lf%%) Total old " SIZE_FORMAT " (%.2lf%%)",
1205 num_visited_cards,
1206 total_dirty_region_cards,
1207 percent_of(num_visited_cards, total_dirty_region_cards),
1208 total_old_region_cards,
1209 percent_of(num_visited_cards, total_old_region_cards));
1210 }
1211
1212 void G1RemSet::merge_heap_roots(bool initial_evacuation) {
1213 G1CollectedHeap* g1h = G1CollectedHeap::heap();
1214
1215 {
1216 Ticks start = Ticks::now();
1217
1218 _scan_state->prepare_for_merge_heap_roots();
1219
1220 Tickspan total = Ticks::now() - start;
1221 if (initial_evacuation) {
1222 g1h->phase_times()->record_prepare_merge_heap_roots_time(total.seconds() * 1000.0);
1223 } else {
1224 g1h->phase_times()->record_or_add_optional_prepare_merge_heap_roots_time(total.seconds() * 1000.0);
1225 }
1226 }
1227
1228 WorkGang* workers = g1h->workers();
1229 size_t const increment_length = g1h->collection_set()->increment_length();
1230
1231 uint const num_workers = initial_evacuation ? workers->active_workers() :
1232 MIN2(workers->active_workers(), (uint)increment_length);
1233
1234 {
1235 G1MergeHeapRootsTask cl(_scan_state, num_workers, initial_evacuation);
1236 log_debug(gc, ergo)("Running %s using %u workers for " SIZE_FORMAT " regions",
1237 cl.name(), num_workers, increment_length);
1238 workers->run_task(&cl, num_workers);
1239 }
1240
1241 if (log_is_enabled(Debug, gc, remset)) {
1242 print_merge_heap_roots_stats();
1243 }
1244 }
1245
1246 void G1RemSet::exclude_region_from_scan(uint region_idx) {
1247 _scan_state->clear_scan_top(region_idx);
1248 }
1249
1250 void G1RemSet::cleanup_after_scan_heap_roots() {
1251 G1GCPhaseTimes* phase_times = _g1h->phase_times();
1252
1253 // Set all cards back to clean.
1254 double start = os::elapsedTime();
1255 _scan_state->cleanup(_g1h->workers());
1256 phase_times->record_clear_ct_time((os::elapsedTime() - start) * 1000.0);
1257 }
1258
1259 inline void check_card_ptr(CardTable::CardValue* card_ptr, G1CardTable* ct) {
1260 #ifdef ASSERT
1261 G1CollectedHeap* g1h = G1CollectedHeap::heap();
1262 assert(g1h->is_in_exact(ct->addr_for(card_ptr)),
1263 "Card at " PTR_FORMAT " index " SIZE_FORMAT " representing heap at " PTR_FORMAT " (%u) must be in committed heap",
1264 p2i(card_ptr),
1265 ct->index_for(ct->addr_for(card_ptr)),
1266 p2i(ct->addr_for(card_ptr)),
1267 g1h->addr_to_region(ct->addr_for(card_ptr)));
1268 #endif
1269 }
1270
1271 bool G1RemSet::clean_card_before_refine(CardValue** const card_ptr_addr) {
1272 assert(!_g1h->is_gc_active(), "Only call concurrently");
1273
1274 CardValue* card_ptr = *card_ptr_addr;
1275 // Find the start address represented by the card.
1276 HeapWord* start = _ct->addr_for(card_ptr);
1277 // And find the region containing it.
1278 HeapRegion* r = _g1h->heap_region_containing_or_null(start);
1279
1280 // If this is a (stale) card into an uncommitted region, exit.
1281 if (r == NULL) {
1282 return false;
1283 }
1284
1285 check_card_ptr(card_ptr, _ct);
1286
1287 // If the card is no longer dirty, nothing to do.
1288 // We cannot load the card value before the "r == NULL" check, because G1
1289 // could uncommit parts of the card table covering uncommitted regions.
1290 if (*card_ptr != G1CardTable::dirty_card_val()) {
1291 return false;
1292 }
1293
1294 // This check is needed for some uncommon cases where we should
1295 // ignore the card.
1296 //
1297 // The region could be young. Cards for young regions are
1298 // distinctly marked (set to g1_young_gen), so the post-barrier will
1299 // filter them out. However, that marking is performed
1300 // concurrently. A write to a young object could occur before the
1301 // card has been marked young, slipping past the filter.
1302 //
1303 // The card could be stale, because the region has been freed since
1304 // the card was recorded. In this case the region type could be
1305 // anything. If (still) free or (reallocated) young, just ignore
1306 // it. If (reallocated) old or humongous, the later card trimming
1307 // and additional checks in iteration may detect staleness. At
1308 // worst, we end up processing a stale card unnecessarily.
1309 //
1310 // In the normal (non-stale) case, the synchronization between the
1311 // enqueueing of the card and processing it here will have ensured
1312 // we see the up-to-date region type here.
1313 if (!r->is_old_or_humongous_or_archive()) {
1314 return false;
1315 }
1316
1317 // The result from the hot card cache insert call is either:
1318 // * pointer to the current card
1319 // (implying that the current card is not 'hot'),
1320 // * null
1321 // (meaning we had inserted the card ptr into the "hot" card cache,
1322 // which had some headroom),
1323 // * a pointer to a "hot" card that was evicted from the "hot" cache.
1324 //
1325
1326 if (_hot_card_cache->use_cache()) {
1327 assert(!SafepointSynchronize::is_at_safepoint(), "sanity");
1328
1329 const CardValue* orig_card_ptr = card_ptr;
1330 card_ptr = _hot_card_cache->insert(card_ptr);
1331 if (card_ptr == NULL) {
1332 // There was no eviction. Nothing to do.
1333 return false;
1334 } else if (card_ptr != orig_card_ptr) {
1335 // Original card was inserted and an old card was evicted.
1336 start = _ct->addr_for(card_ptr);
1337 r = _g1h->heap_region_containing(start);
1338
1339 // Check whether the region formerly in the cache should be
1340 // ignored, as discussed earlier for the original card. The
1341 // region could have been freed while in the cache.
1342 if (!r->is_old_or_humongous_or_archive()) {
1343 return false;
1344 }
1345 *card_ptr_addr = card_ptr;
1346 } // Else we still have the original card.
1347 }
1348
1349 // Trim the region designated by the card to what's been allocated
1350 // in the region. The card could be stale, or the card could cover
1351 // (part of) an object at the end of the allocated space and extend
1352 // beyond the end of allocation.
1353
1354 // Non-humongous objects are either allocated in the old regions during GC,
1355 // or mapped in archive regions during startup. So if region is old or
1356 // archive then top is stable.
1357 // Humongous object allocation sets top last; if top has not yet been set,
1358 // this is a stale card and we'll end up with an empty intersection.
1359 // If this is not a stale card, the synchronization between the
1360 // enqueuing of the card and processing it here will have ensured
1361 // we see the up-to-date top here.
1362 HeapWord* scan_limit = r->top();
1363
1364 if (scan_limit <= start) {
1365 // If the trimmed region is empty, the card must be stale.
1366 return false;
1367 }
1368
1369 // Okay to clean and process the card now. There are still some
1370 // stale card cases that may be detected by iteration and dealt with
1371 // as iteration failure.
1372 *const_cast<volatile CardValue*>(card_ptr) = G1CardTable::clean_card_val();
1373
1374 return true;
1375 }
1376
1377 void G1RemSet::refine_card_concurrently(CardValue* const card_ptr,
1378 const uint worker_id) {
1379 assert(!_g1h->is_gc_active(), "Only call concurrently");
1380 check_card_ptr(card_ptr, _ct);
1381
1382 // Construct the MemRegion representing the card.
1383 HeapWord* start = _ct->addr_for(card_ptr);
1384 // And find the region containing it.
1385 HeapRegion* r = _g1h->heap_region_containing(start);
1386 // This reload of the top is safe even though it happens after the full
1387 // fence, because top is stable for old, archive and unfiltered humongous
1388 // regions, so it must return the same value as the previous load when
1389 // cleaning the card. Also cleaning the card and refinement of the card
1390 // cannot span across safepoint, so we don't need to worry about top being
1391 // changed during safepoint.
1392 HeapWord* scan_limit = r->top();
1393 assert(scan_limit > start, "sanity");
1394
1395 // Don't use addr_for(card_ptr + 1) which can ask for
1396 // a card beyond the heap.
1397 HeapWord* end = start + G1CardTable::card_size_in_words;
1398 MemRegion dirty_region(start, MIN2(scan_limit, end));
1399 assert(!dirty_region.is_empty(), "sanity");
1400
1401 G1ConcurrentRefineOopClosure conc_refine_cl(_g1h, worker_id);
1402 if (r->oops_on_memregion_seq_iterate_careful<false>(dirty_region, &conc_refine_cl) != NULL) {
1403 return;
1404 }
1405
1406 // If unable to process the card then we encountered an unparsable
1407 // part of the heap (e.g. a partially allocated object, so only
1408 // temporarily a problem) while processing a stale card. Despite
1409 // the card being stale, we can't simply ignore it, because we've
1410 // already marked the card cleaned, so taken responsibility for
1411 // ensuring the card gets scanned.
1412 //
1413 // However, the card might have gotten re-dirtied and re-enqueued
1414 // while we worked. (In fact, it's pretty likely.)
1415 if (*card_ptr == G1CardTable::dirty_card_val()) {
1416 return;
1417 }
1418
1419 // Re-dirty the card and enqueue in the *shared* queue. Can't use
1420 // the thread-local queue, because that might be the queue that is
1421 // being processed by us; we could be a Java thread conscripted to
1422 // perform refinement on our queue's current buffer.
1423 *card_ptr = G1CardTable::dirty_card_val();
1424 G1BarrierSet::shared_dirty_card_queue().enqueue(card_ptr);
1425 }
1426
1427 void G1RemSet::print_periodic_summary_info(const char* header, uint period_count) {
1428 if ((G1SummarizeRSetStatsPeriod > 0) && log_is_enabled(Trace, gc, remset) &&
1429 (period_count % G1SummarizeRSetStatsPeriod == 0)) {
1430
1431 G1RemSetSummary current;
1432 _prev_period_summary.subtract_from(¤t);
1433
1434 Log(gc, remset) log;
1435 log.trace("%s", header);
1436 ResourceMark rm;
1437 LogStream ls(log.trace());
1438 _prev_period_summary.print_on(&ls);
1439
1440 _prev_period_summary.set(¤t);
1441 }
1442 }
1443
1444 void G1RemSet::print_summary_info() {
1445 Log(gc, remset, exit) log;
1446 if (log.is_trace()) {
1447 log.trace(" Cumulative RS summary");
1448 G1RemSetSummary current;
1449 ResourceMark rm;
1450 LogStream ls(log.trace());
1451 current.print_on(&ls);
1452 }
1453 }
1454
1455 class G1RebuildRemSetTask: public AbstractGangTask {
1456 // Aggregate the counting data that was constructed concurrently
1457 // with marking.
1458 class G1RebuildRemSetHeapRegionClosure : public HeapRegionClosure {
1459 G1ConcurrentMark* _cm;
1460 G1RebuildRemSetClosure _update_cl;
1461
1462 // Applies _update_cl to the references of the given object, limiting objArrays
1463 // to the given MemRegion. Returns the amount of words actually scanned.
1464 size_t scan_for_references(oop const obj, MemRegion mr) {
1465 size_t const obj_size = obj->size();
1466 // All non-objArrays and objArrays completely within the mr
1467 // can be scanned without passing the mr.
1468 if (!obj->is_objArray() || mr.contains(MemRegion(cast_from_oop<HeapWord*>(obj), obj_size))) {
1469 obj->oop_iterate(&_update_cl);
1470 return obj_size;
1471 }
1472 // This path is for objArrays crossing the given MemRegion. Only scan the
1473 // area within the MemRegion.
1474 obj->oop_iterate(&_update_cl, mr);
1475 return mr.intersection(MemRegion(cast_from_oop<HeapWord*>(obj), obj_size)).word_size();
1476 }
1477
1478 // A humongous object is live (with respect to the scanning) either
1479 // a) it is marked on the bitmap as such
1480 // b) its TARS is larger than TAMS, i.e. has been allocated during marking.
1481 bool is_humongous_live(oop const humongous_obj, const G1CMBitMap* const bitmap, HeapWord* tams, HeapWord* tars) const {
1482 return bitmap->is_marked(humongous_obj) || (tars > tams);
1483 }
1484
1485 // Iterator over the live objects within the given MemRegion.
1486 class LiveObjIterator : public StackObj {
1487 const G1CMBitMap* const _bitmap;
1488 const HeapWord* _tams;
1489 const MemRegion _mr;
1490 HeapWord* _current;
1491
1492 bool is_below_tams() const {
1493 return _current < _tams;
1494 }
1495
1496 bool is_live(HeapWord* obj) const {
1497 return !is_below_tams() || _bitmap->is_marked(obj);
1498 }
1499
1500 HeapWord* bitmap_limit() const {
1501 return MIN2(const_cast<HeapWord*>(_tams), _mr.end());
1502 }
1503
1504 void move_if_below_tams() {
1505 if (is_below_tams() && has_next()) {
1506 _current = _bitmap->get_next_marked_addr(_current, bitmap_limit());
1507 }
1508 }
1509 public:
1510 LiveObjIterator(const G1CMBitMap* const bitmap, const HeapWord* tams, const MemRegion mr, HeapWord* first_oop_into_mr) :
1511 _bitmap(bitmap),
1512 _tams(tams),
1513 _mr(mr),
1514 _current(first_oop_into_mr) {
1515
1516 assert(_current <= _mr.start(),
1517 "First oop " PTR_FORMAT " should extend into mr [" PTR_FORMAT ", " PTR_FORMAT ")",
1518 p2i(first_oop_into_mr), p2i(mr.start()), p2i(mr.end()));
1519
1520 // Step to the next live object within the MemRegion if needed.
1521 if (is_live(_current)) {
1522 // Non-objArrays were scanned by the previous part of that region.
1523 if (_current < mr.start() && !oop(_current)->is_objArray()) {
1524 _current += oop(_current)->size();
1525 // We might have positioned _current on a non-live object. Reposition to the next
1526 // live one if needed.
1527 move_if_below_tams();
1528 }
1529 } else {
1530 // The object at _current can only be dead if below TAMS, so we can use the bitmap.
1531 // immediately.
1532 _current = _bitmap->get_next_marked_addr(_current, bitmap_limit());
1533 assert(_current == _mr.end() || is_live(_current),
1534 "Current " PTR_FORMAT " should be live (%s) or beyond the end of the MemRegion (" PTR_FORMAT ")",
1535 p2i(_current), BOOL_TO_STR(is_live(_current)), p2i(_mr.end()));
1536 }
1537 }
1538
1539 void move_to_next() {
1540 _current += next()->size();
1541 move_if_below_tams();
1542 }
1543
1544 oop next() const {
1545 oop result = oop(_current);
1546 assert(is_live(_current),
1547 "Object " PTR_FORMAT " must be live TAMS " PTR_FORMAT " below %d mr " PTR_FORMAT " " PTR_FORMAT " outside %d",
1548 p2i(_current), p2i(_tams), _tams > _current, p2i(_mr.start()), p2i(_mr.end()), _mr.contains(result));
1549 return result;
1550 }
1551
1552 bool has_next() const {
1553 return _current < _mr.end();
1554 }
1555 };
1556
1557 // Rebuild remembered sets in the part of the region specified by mr and hr.
1558 // Objects between the bottom of the region and the TAMS are checked for liveness
1559 // using the given bitmap. Objects between TAMS and TARS are assumed to be live.
1560 // Returns the number of live words between bottom and TAMS.
1561 size_t rebuild_rem_set_in_region(const G1CMBitMap* const bitmap,
1562 HeapWord* const top_at_mark_start,
1563 HeapWord* const top_at_rebuild_start,
1564 HeapRegion* hr,
1565 MemRegion mr) {
1566 size_t marked_words = 0;
1567
1568 if (hr->is_humongous()) {
1569 oop const humongous_obj = oop(hr->humongous_start_region()->bottom());
1570 if (is_humongous_live(humongous_obj, bitmap, top_at_mark_start, top_at_rebuild_start)) {
1571 // We need to scan both [bottom, TAMS) and [TAMS, top_at_rebuild_start);
1572 // however in case of humongous objects it is sufficient to scan the encompassing
1573 // area (top_at_rebuild_start is always larger or equal to TAMS) as one of the
1574 // two areas will be zero sized. I.e. TAMS is either
1575 // the same as bottom or top(_at_rebuild_start). There is no way TAMS has a different
1576 // value: this would mean that TAMS points somewhere into the object.
1577 assert(hr->top() == top_at_mark_start || hr->top() == top_at_rebuild_start,
1578 "More than one object in the humongous region?");
1579 humongous_obj->oop_iterate(&_update_cl, mr);
1580 return top_at_mark_start != hr->bottom() ? mr.intersection(MemRegion(cast_from_oop<HeapWord*>(humongous_obj), humongous_obj->size())).byte_size() : 0;
1581 } else {
1582 return 0;
1583 }
1584 }
1585
1586 for (LiveObjIterator it(bitmap, top_at_mark_start, mr, hr->block_start(mr.start())); it.has_next(); it.move_to_next()) {
1587 oop obj = it.next();
1588 size_t scanned_size = scan_for_references(obj, mr);
1589 if (cast_from_oop<HeapWord*>(obj) < top_at_mark_start) {
1590 marked_words += scanned_size;
1591 }
1592 }
1593
1594 return marked_words * HeapWordSize;
1595 }
1596 public:
1597 G1RebuildRemSetHeapRegionClosure(G1CollectedHeap* g1h,
1598 G1ConcurrentMark* cm,
1599 uint worker_id) :
1600 HeapRegionClosure(),
1601 _cm(cm),
1602 _update_cl(g1h, worker_id) { }
1603
1604 bool do_heap_region(HeapRegion* hr) {
1605 if (_cm->has_aborted()) {
1606 return true;
1607 }
1608
1609 uint const region_idx = hr->hrm_index();
1610 DEBUG_ONLY(HeapWord* const top_at_rebuild_start_check = _cm->top_at_rebuild_start(region_idx);)
1611 assert(top_at_rebuild_start_check == NULL ||
1612 top_at_rebuild_start_check > hr->bottom(),
1613 "A TARS (" PTR_FORMAT ") == bottom() (" PTR_FORMAT ") indicates the old region %u is empty (%s)",
1614 p2i(top_at_rebuild_start_check), p2i(hr->bottom()), region_idx, hr->get_type_str());
1615
1616 size_t total_marked_bytes = 0;
1617 size_t const chunk_size_in_words = G1RebuildRemSetChunkSize / HeapWordSize;
1618
1619 HeapWord* const top_at_mark_start = hr->prev_top_at_mark_start();
1620
1621 HeapWord* cur = hr->bottom();
1622 while (cur < hr->end()) {
1623 // After every iteration (yield point) we need to check whether the region's
1624 // TARS changed due to e.g. eager reclaim.
1625 HeapWord* const top_at_rebuild_start = _cm->top_at_rebuild_start(region_idx);
1626 if (top_at_rebuild_start == NULL) {
1627 return false;
1628 }
1629
1630 MemRegion next_chunk = MemRegion(hr->bottom(), top_at_rebuild_start).intersection(MemRegion(cur, chunk_size_in_words));
1631 if (next_chunk.is_empty()) {
1632 break;
1633 }
1634
1635 const Ticks start = Ticks::now();
1636 size_t marked_bytes = rebuild_rem_set_in_region(_cm->prev_mark_bitmap(),
1637 top_at_mark_start,
1638 top_at_rebuild_start,
1639 hr,
1640 next_chunk);
1641 Tickspan time = Ticks::now() - start;
1642
1643 log_trace(gc, remset, tracking)("Rebuilt region %u "
1644 "live " SIZE_FORMAT " "
1645 "time %.3fms "
1646 "marked bytes " SIZE_FORMAT " "
1647 "bot " PTR_FORMAT " "
1648 "TAMS " PTR_FORMAT " "
1649 "TARS " PTR_FORMAT,
1650 region_idx,
1651 _cm->liveness(region_idx) * HeapWordSize,
1652 time.seconds() * 1000.0,
1653 marked_bytes,
1654 p2i(hr->bottom()),
1655 p2i(top_at_mark_start),
1656 p2i(top_at_rebuild_start));
1657
1658 if (marked_bytes > 0) {
1659 total_marked_bytes += marked_bytes;
1660 }
1661 cur += chunk_size_in_words;
1662
1663 _cm->do_yield_check();
1664 if (_cm->has_aborted()) {
1665 return true;
1666 }
1667 }
1668 // In the final iteration of the loop the region might have been eagerly reclaimed.
1669 // Simply filter out those regions. We can not just use region type because there
1670 // might have already been new allocations into these regions.
1671 DEBUG_ONLY(HeapWord* const top_at_rebuild_start = _cm->top_at_rebuild_start(region_idx);)
1672 assert(top_at_rebuild_start == NULL ||
1673 total_marked_bytes == hr->marked_bytes(),
1674 "Marked bytes " SIZE_FORMAT " for region %u (%s) in [bottom, TAMS) do not match calculated marked bytes " SIZE_FORMAT " "
1675 "(" PTR_FORMAT " " PTR_FORMAT " " PTR_FORMAT ")",
1676 total_marked_bytes, hr->hrm_index(), hr->get_type_str(), hr->marked_bytes(),
1677 p2i(hr->bottom()), p2i(top_at_mark_start), p2i(top_at_rebuild_start));
1678 // Abort state may have changed after the yield check.
1679 return _cm->has_aborted();
1680 }
1681 };
1682
1683 HeapRegionClaimer _hr_claimer;
1684 G1ConcurrentMark* _cm;
1685
1686 uint _worker_id_offset;
1687 public:
1688 G1RebuildRemSetTask(G1ConcurrentMark* cm,
1689 uint n_workers,
1690 uint worker_id_offset) :
1691 AbstractGangTask("G1 Rebuild Remembered Set"),
1692 _hr_claimer(n_workers),
1693 _cm(cm),
1694 _worker_id_offset(worker_id_offset) {
1695 }
1696
1697 void work(uint worker_id) {
1698 SuspendibleThreadSetJoiner sts_join;
1699
1700 G1CollectedHeap* g1h = G1CollectedHeap::heap();
1701
1702 G1RebuildRemSetHeapRegionClosure cl(g1h, _cm, _worker_id_offset + worker_id);
1703 g1h->heap_region_par_iterate_from_worker_offset(&cl, &_hr_claimer, worker_id);
1704 }
1705 };
1706
1707 void G1RemSet::rebuild_rem_set(G1ConcurrentMark* cm,
1708 WorkGang* workers,
1709 uint worker_id_offset) {
1710 uint num_workers = workers->active_workers();
1711
1712 G1RebuildRemSetTask cl(cm,
1713 num_workers,
1714 worker_id_offset);
1715 workers->run_task(&cl, num_workers);
1716 }