1 /*
2 * Copyright (c) 2001, 2018, 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/dirtyCardQueue.hpp"
27 #include "gc/g1/g1BarrierSet.hpp"
28 #include "gc/g1/g1BlockOffsetTable.inline.hpp"
29 #include "gc/g1/g1CardTable.inline.hpp"
30 #include "gc/g1/g1CollectedHeap.inline.hpp"
31 #include "gc/g1/g1ConcurrentRefine.hpp"
32 #include "gc/g1/g1FromCardCache.hpp"
33 #include "gc/g1/g1GCPhaseTimes.hpp"
34 #include "gc/g1/g1HotCardCache.hpp"
35 #include "gc/g1/g1OopClosures.inline.hpp"
36 #include "gc/g1/g1RootClosures.hpp"
37 #include "gc/g1/g1RemSet.hpp"
38 #include "gc/g1/heapRegion.inline.hpp"
39 #include "gc/g1/heapRegionManager.inline.hpp"
40 #include "gc/g1/heapRegionRemSet.hpp"
41 #include "gc/shared/gcTraceTime.inline.hpp"
42 #include "gc/shared/suspendibleThreadSet.hpp"
43 #include "memory/iterator.hpp"
44 #include "memory/resourceArea.hpp"
45 #include "oops/access.inline.hpp"
46 #include "oops/oop.inline.hpp"
47 #include "utilities/align.hpp"
48 #include "utilities/globalDefinitions.hpp"
49 #include "utilities/intHisto.hpp"
50 #include "utilities/stack.inline.hpp"
51 #include "utilities/ticks.inline.hpp"
52
53 // Collects information about the overall remembered set scan progress during an evacuation.
54 class G1RemSetScanState : public CHeapObj<mtGC> {
55 private:
56 class G1ClearCardTableTask : public AbstractGangTask {
57 G1CollectedHeap* _g1h;
58 uint* _dirty_region_list;
59 size_t _num_dirty_regions;
60 size_t _chunk_length;
61
62 size_t volatile _cur_dirty_regions;
63 public:
64 G1ClearCardTableTask(G1CollectedHeap* g1h,
65 uint* dirty_region_list,
66 size_t num_dirty_regions,
67 size_t chunk_length) :
68 AbstractGangTask("G1 Clear Card Table Task"),
69 _g1h(g1h),
70 _dirty_region_list(dirty_region_list),
71 _num_dirty_regions(num_dirty_regions),
72 _chunk_length(chunk_length),
73 _cur_dirty_regions(0) {
74
75 assert(chunk_length > 0, "must be");
76 }
77
78 static size_t chunk_size() { return M; }
79
80 void work(uint worker_id) {
81 while (_cur_dirty_regions < _num_dirty_regions) {
82 size_t next = Atomic::add(_chunk_length, &_cur_dirty_regions) - _chunk_length;
83 size_t max = MIN2(next + _chunk_length, _num_dirty_regions);
84
85 for (size_t i = next; i < max; i++) {
86 HeapRegion* r = _g1h->region_at(_dirty_region_list[i]);
87 if (!r->is_survivor()) {
88 r->clear_cardtable();
89 }
90 }
91 }
92 }
93 };
94
95 size_t _max_regions;
96
97 // Scan progress for the remembered set of a single region. Transitions from
98 // Unclaimed -> Claimed -> Complete.
99 // At each of the transitions the thread that does the transition needs to perform
100 // some special action once. This is the reason for the extra "Claimed" state.
101 typedef jint G1RemsetIterState;
102
103 static const G1RemsetIterState Unclaimed = 0; // The remembered set has not been scanned yet.
104 static const G1RemsetIterState Claimed = 1; // The remembered set is currently being scanned.
105 static const G1RemsetIterState Complete = 2; // The remembered set has been completely scanned.
106
107 G1RemsetIterState volatile* _iter_states;
108 // The current location where the next thread should continue scanning in a region's
109 // remembered set.
110 size_t volatile* _iter_claims;
111
112 // Temporary buffer holding the regions we used to store remembered set scan duplicate
113 // information. These are also called "dirty". Valid entries are from [0.._cur_dirty_region)
114 uint* _dirty_region_buffer;
115
116 typedef jbyte IsDirtyRegionState;
117 static const IsDirtyRegionState Clean = 0;
118 static const IsDirtyRegionState Dirty = 1;
119 // Holds a flag for every region whether it is in the _dirty_region_buffer already
120 // to avoid duplicates. Uses jbyte since there are no atomic instructions for bools.
121 IsDirtyRegionState* _in_dirty_region_buffer;
122 size_t _cur_dirty_region;
123
124 // Creates a snapshot of the current _top values at the start of collection to
125 // filter out card marks that we do not want to scan.
126 class G1ResetScanTopClosure : public HeapRegionClosure {
127 private:
128 HeapWord** _scan_top;
129 public:
130 G1ResetScanTopClosure(HeapWord** scan_top) : _scan_top(scan_top) { }
131
132 virtual bool do_heap_region(HeapRegion* r) {
133 uint hrm_index = r->hrm_index();
134 if (!r->in_collection_set() && r->is_old_or_humongous()) {
135 _scan_top[hrm_index] = r->top();
136 } else {
137 _scan_top[hrm_index] = r->bottom();
138 }
139 return false;
140 }
141 };
142
143 // For each region, contains the maximum top() value to be used during this garbage
144 // collection. Subsumes common checks like filtering out everything but old and
145 // humongous regions outside the collection set.
146 // This is valid because we are not interested in scanning stray remembered set
147 // entries from free or archive regions.
148 HeapWord** _scan_top;
149 public:
150 G1RemSetScanState() :
151 _max_regions(0),
152 _iter_states(NULL),
153 _iter_claims(NULL),
154 _dirty_region_buffer(NULL),
155 _in_dirty_region_buffer(NULL),
156 _cur_dirty_region(0),
157 _scan_top(NULL) {
158 }
159
160 ~G1RemSetScanState() {
161 if (_iter_states != NULL) {
162 FREE_C_HEAP_ARRAY(G1RemsetIterState, _iter_states);
163 }
164 if (_iter_claims != NULL) {
165 FREE_C_HEAP_ARRAY(size_t, _iter_claims);
166 }
167 if (_dirty_region_buffer != NULL) {
168 FREE_C_HEAP_ARRAY(uint, _dirty_region_buffer);
169 }
170 if (_in_dirty_region_buffer != NULL) {
171 FREE_C_HEAP_ARRAY(IsDirtyRegionState, _in_dirty_region_buffer);
172 }
173 if (_scan_top != NULL) {
174 FREE_C_HEAP_ARRAY(HeapWord*, _scan_top);
175 }
176 }
177
178 void initialize(uint max_regions) {
179 assert(_iter_states == NULL, "Must not be initialized twice");
180 assert(_iter_claims == NULL, "Must not be initialized twice");
181 _max_regions = max_regions;
182 _iter_states = NEW_C_HEAP_ARRAY(G1RemsetIterState, max_regions, mtGC);
183 _iter_claims = NEW_C_HEAP_ARRAY(size_t, max_regions, mtGC);
184 _dirty_region_buffer = NEW_C_HEAP_ARRAY(uint, max_regions, mtGC);
185 _in_dirty_region_buffer = NEW_C_HEAP_ARRAY(IsDirtyRegionState, max_regions, mtGC);
186 _scan_top = NEW_C_HEAP_ARRAY(HeapWord*, max_regions, mtGC);
187 }
188
189 void reset() {
190 for (uint i = 0; i < _max_regions; i++) {
191 _iter_states[i] = Unclaimed;
192 }
193
194 G1ResetScanTopClosure cl(_scan_top);
195 G1CollectedHeap::heap()->heap_region_iterate(&cl);
196
197 memset((void*)_iter_claims, 0, _max_regions * sizeof(size_t));
198 memset(_in_dirty_region_buffer, Clean, _max_regions * sizeof(IsDirtyRegionState));
199 _cur_dirty_region = 0;
200 }
201
202 // Attempt to claim the remembered set of the region for iteration. Returns true
203 // if this call caused the transition from Unclaimed to Claimed.
204 inline bool claim_iter(uint region) {
205 assert(region < _max_regions, "Tried to access invalid region %u", region);
206 if (_iter_states[region] != Unclaimed) {
207 return false;
208 }
209 G1RemsetIterState res = Atomic::cmpxchg(Claimed, &_iter_states[region], Unclaimed);
210 return (res == Unclaimed);
211 }
212
213 // Try to atomically sets the iteration state to "complete". Returns true for the
214 // thread that caused the transition.
215 inline bool set_iter_complete(uint region) {
216 if (iter_is_complete(region)) {
217 return false;
218 }
219 G1RemsetIterState res = Atomic::cmpxchg(Complete, &_iter_states[region], Claimed);
220 return (res == Claimed);
221 }
222
223 // Returns true if the region's iteration is complete.
224 inline bool iter_is_complete(uint region) const {
225 assert(region < _max_regions, "Tried to access invalid region %u", region);
226 return _iter_states[region] == Complete;
227 }
228
229 // The current position within the remembered set of the given region.
230 inline size_t iter_claimed(uint region) const {
231 assert(region < _max_regions, "Tried to access invalid region %u", region);
232 return _iter_claims[region];
233 }
234
235 // Claim the next block of cards within the remembered set of the region with
236 // step size.
237 inline size_t iter_claimed_next(uint region, size_t step) {
238 return Atomic::add(step, &_iter_claims[region]) - step;
239 }
240
241 void add_dirty_region(uint region) {
242 if (_in_dirty_region_buffer[region] == Dirty) {
243 return;
244 }
245
246 bool marked_as_dirty = Atomic::cmpxchg(Dirty, &_in_dirty_region_buffer[region], Clean) == Clean;
247 if (marked_as_dirty) {
248 size_t allocated = Atomic::add(1u, &_cur_dirty_region) - 1;
249 _dirty_region_buffer[allocated] = region;
250 }
251 }
252
253 HeapWord* scan_top(uint region_idx) const {
254 return _scan_top[region_idx];
255 }
256
257 // Clear the card table of "dirty" regions.
258 void clear_card_table(WorkGang* workers) {
259 if (_cur_dirty_region == 0) {
260 return;
261 }
262
263 size_t const num_chunks = align_up(_cur_dirty_region * HeapRegion::CardsPerRegion, G1ClearCardTableTask::chunk_size()) / G1ClearCardTableTask::chunk_size();
264 uint const num_workers = (uint)MIN2(num_chunks, (size_t)workers->active_workers());
265 size_t const chunk_length = G1ClearCardTableTask::chunk_size() / HeapRegion::CardsPerRegion;
266
267 // Iterate over the dirty cards region list.
268 G1ClearCardTableTask cl(G1CollectedHeap::heap(), _dirty_region_buffer, _cur_dirty_region, chunk_length);
269
270 log_debug(gc, ergo)("Running %s using %u workers for " SIZE_FORMAT " "
271 "units of work for " SIZE_FORMAT " regions.",
272 cl.name(), num_workers, num_chunks, _cur_dirty_region);
273 workers->run_task(&cl, num_workers);
274
275 #ifndef PRODUCT
276 G1CollectedHeap::heap()->verifier()->verify_card_table_cleanup();
277 #endif
278 }
279 };
280
281 G1RemSet::G1RemSet(G1CollectedHeap* g1h,
282 G1CardTable* ct,
283 G1HotCardCache* hot_card_cache) :
284 _g1h(g1h),
285 _scan_state(new G1RemSetScanState()),
286 _num_conc_refined_cards(0),
287 _ct(ct),
288 _g1p(_g1h->g1_policy()),
289 _hot_card_cache(hot_card_cache),
290 _prev_period_summary() {
291 }
292
293 G1RemSet::~G1RemSet() {
294 if (_scan_state != NULL) {
295 delete _scan_state;
296 }
297 }
298
299 uint G1RemSet::num_par_rem_sets() {
300 return DirtyCardQueueSet::num_par_ids() + G1ConcurrentRefine::max_num_threads() + MAX2(ConcGCThreads, ParallelGCThreads);
301 }
302
303 void G1RemSet::initialize(size_t capacity, uint max_regions) {
304 G1FromCardCache::initialize(num_par_rem_sets(), max_regions);
305 _scan_state->initialize(max_regions);
306 }
307
308 G1ScanRSForRegionClosure::G1ScanRSForRegionClosure(G1RemSetScanState* scan_state,
309 G1ScanObjsDuringScanRSClosure* scan_obj_on_card,
310 G1ParScanThreadState* pss,
311 uint worker_i) :
312 _g1h(G1CollectedHeap::heap()),
313 _ct(_g1h->card_table()),
314 _pss(pss),
315 _scan_objs_on_card_cl(scan_obj_on_card),
316 _scan_state(scan_state),
317 _worker_i(worker_i),
318 _cards_claimed(0),
319 _cards_scanned(0),
320 _cards_skipped(0),
321 _rem_set_root_scan_time(),
322 _rem_set_trim_partially_time(),
323 _strong_code_root_scan_time(),
324 _strong_code_trim_partially_time() {
325 }
326
327 void G1ScanRSForRegionClosure::claim_card(size_t card_index, const uint region_idx_for_card){
328 _ct->set_card_claimed(card_index);
329 _scan_state->add_dirty_region(region_idx_for_card);
330 }
331
332 void G1ScanRSForRegionClosure::scan_card(MemRegion mr, uint region_idx_for_card) {
333 HeapRegion* const card_region = _g1h->region_at(region_idx_for_card);
334 _scan_objs_on_card_cl->set_region(card_region);
335 card_region->oops_on_card_seq_iterate_careful<true>(mr, _scan_objs_on_card_cl);
336 _scan_objs_on_card_cl->trim_queue_partially();
337 _cards_scanned++;
338 }
339
340 void G1ScanRSForRegionClosure::scan_rem_set_roots(HeapRegion* r) {
341 uint const region_idx = r->hrm_index();
342
343 if (_scan_state->claim_iter(region_idx)) {
344 // If we ever free the collection set concurrently, we should also
345 // clear the card table concurrently therefore we won't need to
346 // add regions of the collection set to the dirty cards region.
347 _scan_state->add_dirty_region(region_idx);
348 }
349
350 // We claim cards in blocks so as to reduce the contention.
351 size_t const block_size = G1RSetScanBlockSize;
352
353 HeapRegionRemSetIterator iter(r->rem_set());
354 size_t card_index;
355
356 size_t claimed_card_block = _scan_state->iter_claimed_next(region_idx, block_size);
357 for (size_t current_card = 0; iter.has_next(card_index); current_card++) {
358 if (current_card >= claimed_card_block + block_size) {
359 claimed_card_block = _scan_state->iter_claimed_next(region_idx, block_size);
360 }
361 if (current_card < claimed_card_block) {
362 _cards_skipped++;
363 continue;
364 }
365 _cards_claimed++;
366
367 // If the card is dirty, then G1 will scan it during Update RS.
368 if (_ct->is_card_claimed(card_index) || _ct->is_card_dirty(card_index)) {
369 continue;
370 }
371
372 HeapWord* const card_start = _g1h->bot()->address_for_index(card_index);
373 uint const region_idx_for_card = _g1h->addr_to_region(card_start);
374
375 assert(_g1h->region_at(region_idx_for_card)->is_in_reserved(card_start),
376 "Card start " PTR_FORMAT " to scan outside of region %u", p2i(card_start), _g1h->region_at(region_idx_for_card)->hrm_index());
377 HeapWord* const top = _scan_state->scan_top(region_idx_for_card);
378 if (card_start >= top) {
379 continue;
380 }
381
382 // We claim lazily (so races are possible but they're benign), which reduces the
383 // number of duplicate scans (the rsets of the regions in the cset can intersect).
384 // Claim the card after checking bounds above: the remembered set may contain
385 // random cards into current survivor, and we would then have an incorrectly
386 // claimed card in survivor space. Card table clear does not reset the card table
387 // of survivor space regions.
388 claim_card(card_index, region_idx_for_card);
389
390 MemRegion const mr(card_start, MIN2(card_start + BOTConstants::N_words, top));
391
392 scan_card(mr, region_idx_for_card);
393 }
394 }
395
396 void G1ScanRSForRegionClosure::scan_strong_code_roots(HeapRegion* r) {
397 r->strong_code_roots_do(_pss->closures()->weak_codeblobs());
398 }
399
400 bool G1ScanRSForRegionClosure::do_heap_region(HeapRegion* r) {
401 assert(r->in_collection_set(),
402 "Should only be called on elements of the collection set but region %u is not.",
403 r->hrm_index());
404 uint const region_idx = r->hrm_index();
405
406 // Do an early out if we know we are complete.
407 if (_scan_state->iter_is_complete(region_idx)) {
408 return false;
409 }
410
411 {
412 G1EvacPhaseWithTrimTimeTracker timer(_pss, _rem_set_root_scan_time, _rem_set_trim_partially_time);
413 scan_rem_set_roots(r);
414 }
415
416 if (_scan_state->set_iter_complete(region_idx)) {
417 G1EvacPhaseWithTrimTimeTracker timer(_pss, _strong_code_root_scan_time, _strong_code_trim_partially_time);
418 // Scan the strong code root list attached to the current region
419 scan_strong_code_roots(r);
420 }
421 return false;
422 }
423
424 void G1RemSet::scan_rem_set(G1ParScanThreadState* pss, uint worker_i) {
425 G1ScanObjsDuringScanRSClosure scan_cl(_g1h, pss);
426 G1ScanRSForRegionClosure cl(_scan_state, &scan_cl, pss, worker_i);
427 _g1h->collection_set_iterate_from(&cl, worker_i);
428
429 G1GCPhaseTimes* p = _g1p->phase_times();
430
431 p->record_time_secs(G1GCPhaseTimes::ScanRS, worker_i, TicksToTimeHelper::seconds(cl.rem_set_root_scan_time()));
432 p->add_time_secs(G1GCPhaseTimes::ObjCopy, worker_i, TicksToTimeHelper::seconds(cl.rem_set_trim_partially_time()));
433
434 p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_scanned(), G1GCPhaseTimes::ScanRSScannedCards);
435 p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_claimed(), G1GCPhaseTimes::ScanRSClaimedCards);
436 p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_skipped(), G1GCPhaseTimes::ScanRSSkippedCards);
437
438 p->record_time_secs(G1GCPhaseTimes::CodeRoots, worker_i, TicksToTimeHelper::seconds(cl.strong_code_root_scan_time()));
439 p->add_time_secs(G1GCPhaseTimes::ObjCopy, worker_i, TicksToTimeHelper::seconds(cl.strong_code_root_trim_partially_time()));
440 }
441
442 // Closure used for updating rem sets. Only called during an evacuation pause.
443 class G1RefineCardClosure: public CardTableEntryClosure {
444 G1RemSet* _g1rs;
445 G1ScanObjsDuringUpdateRSClosure* _update_rs_cl;
446
447 size_t _cards_scanned;
448 size_t _cards_skipped;
449 public:
450 G1RefineCardClosure(G1CollectedHeap* g1h, G1ScanObjsDuringUpdateRSClosure* update_rs_cl) :
451 _g1rs(g1h->g1_rem_set()), _update_rs_cl(update_rs_cl), _cards_scanned(0), _cards_skipped(0)
452 {}
453
454 bool do_card_ptr(jbyte* card_ptr, uint worker_i) {
455 // The only time we care about recording cards that
456 // contain references that point into the collection set
457 // is during RSet updating within an evacuation pause.
458 // In this case worker_i should be the id of a GC worker thread.
459 assert(SafepointSynchronize::is_at_safepoint(), "not during an evacuation pause");
460
461 bool card_scanned = _g1rs->refine_card_during_gc(card_ptr, _update_rs_cl);
462
463 if (card_scanned) {
464 _update_rs_cl->trim_queue_partially();
465 _cards_scanned++;
466 } else {
467 _cards_skipped++;
468 }
469 return true;
470 }
471
472 size_t cards_scanned() const { return _cards_scanned; }
473 size_t cards_skipped() const { return _cards_skipped; }
474 };
475
476 void G1RemSet::update_rem_set(G1ParScanThreadState* pss, uint worker_i) {
477 G1GCPhaseTimes* p = _g1p->phase_times();
478
479 // Apply closure to log entries in the HCC.
480 if (G1HotCardCache::default_use_cache()) {
481 G1EvacPhaseTimesTracker x(p, pss, G1GCPhaseTimes::ScanHCC, worker_i);
482
483 G1ScanObjsDuringUpdateRSClosure scan_hcc_cl(_g1h, pss, worker_i);
484 G1RefineCardClosure refine_card_cl(_g1h, &scan_hcc_cl);
485 _g1h->iterate_hcc_closure(&refine_card_cl, worker_i);
486 }
487
488 // Now apply the closure to all remaining log entries.
489 {
490 G1EvacPhaseTimesTracker x(p, pss, G1GCPhaseTimes::UpdateRS, worker_i);
491
492 G1ScanObjsDuringUpdateRSClosure update_rs_cl(_g1h, pss, worker_i);
493 G1RefineCardClosure refine_card_cl(_g1h, &update_rs_cl);
494 _g1h->iterate_dirty_card_closure(&refine_card_cl, worker_i);
495
496 p->record_thread_work_item(G1GCPhaseTimes::UpdateRS, worker_i, refine_card_cl.cards_scanned(), G1GCPhaseTimes::UpdateRSScannedCards);
497 p->record_thread_work_item(G1GCPhaseTimes::UpdateRS, worker_i, refine_card_cl.cards_skipped(), G1GCPhaseTimes::UpdateRSSkippedCards);
498 }
499 }
500
501 void G1RemSet::cleanupHRRS() {
502 HeapRegionRemSet::cleanup();
503 }
504
505 void G1RemSet::oops_into_collection_set_do(G1ParScanThreadState* pss, uint worker_i) {
506 update_rem_set(pss, worker_i);
507 scan_rem_set(pss, worker_i);;
508 }
509
510 void G1RemSet::prepare_for_oops_into_collection_set_do() {
511 DirtyCardQueueSet& dcqs = G1BarrierSet::dirty_card_queue_set();
512 dcqs.concatenate_logs();
513
514 _scan_state->reset();
515 }
516
517 void G1RemSet::cleanup_after_oops_into_collection_set_do() {
518 G1GCPhaseTimes* phase_times = _g1h->g1_policy()->phase_times();
519
520 // Set all cards back to clean.
521 double start = os::elapsedTime();
522 _scan_state->clear_card_table(_g1h->workers());
523 phase_times->record_clear_ct_time((os::elapsedTime() - start) * 1000.0);
524 }
525
526 inline void check_card_ptr(jbyte* card_ptr, G1CardTable* ct) {
527 #ifdef ASSERT
528 G1CollectedHeap* g1h = G1CollectedHeap::heap();
529 assert(g1h->is_in_exact(ct->addr_for(card_ptr)),
530 "Card at " PTR_FORMAT " index " SIZE_FORMAT " representing heap at " PTR_FORMAT " (%u) must be in committed heap",
531 p2i(card_ptr),
532 ct->index_for(ct->addr_for(card_ptr)),
533 p2i(ct->addr_for(card_ptr)),
534 g1h->addr_to_region(ct->addr_for(card_ptr)));
535 #endif
536 }
537
538 void G1RemSet::refine_card_concurrently(jbyte* card_ptr,
539 uint worker_i) {
540 assert(!_g1h->is_gc_active(), "Only call concurrently");
541
542 check_card_ptr(card_ptr, _ct);
543
544 // If the card is no longer dirty, nothing to do.
545 if (*card_ptr != G1CardTable::dirty_card_val()) {
546 return;
547 }
548
549 // Construct the region representing the card.
550 HeapWord* start = _ct->addr_for(card_ptr);
551 // And find the region containing it.
552 HeapRegion* r = _g1h->heap_region_containing(start);
553
554 // This check is needed for some uncommon cases where we should
555 // ignore the card.
556 //
557 // The region could be young. Cards for young regions are
558 // distinctly marked (set to g1_young_gen), so the post-barrier will
559 // filter them out. However, that marking is performed
560 // concurrently. A write to a young object could occur before the
561 // card has been marked young, slipping past the filter.
562 //
563 // The card could be stale, because the region has been freed since
564 // the card was recorded. In this case the region type could be
565 // anything. If (still) free or (reallocated) young, just ignore
566 // it. If (reallocated) old or humongous, the later card trimming
567 // and additional checks in iteration may detect staleness. At
568 // worst, we end up processing a stale card unnecessarily.
569 //
570 // In the normal (non-stale) case, the synchronization between the
571 // enqueueing of the card and processing it here will have ensured
572 // we see the up-to-date region type here.
573 if (!r->is_old_or_humongous()) {
574 return;
575 }
576
577 // The result from the hot card cache insert call is either:
578 // * pointer to the current card
579 // (implying that the current card is not 'hot'),
580 // * null
581 // (meaning we had inserted the card ptr into the "hot" card cache,
582 // which had some headroom),
583 // * a pointer to a "hot" card that was evicted from the "hot" cache.
584 //
585
586 if (_hot_card_cache->use_cache()) {
587 assert(!SafepointSynchronize::is_at_safepoint(), "sanity");
588
589 const jbyte* orig_card_ptr = card_ptr;
590 card_ptr = _hot_card_cache->insert(card_ptr);
591 if (card_ptr == NULL) {
592 // There was no eviction. Nothing to do.
593 return;
594 } else if (card_ptr != orig_card_ptr) {
595 // Original card was inserted and an old card was evicted.
596 start = _ct->addr_for(card_ptr);
597 r = _g1h->heap_region_containing(start);
598
599 // Check whether the region formerly in the cache should be
600 // ignored, as discussed earlier for the original card. The
601 // region could have been freed while in the cache.
602 if (!r->is_old_or_humongous()) {
603 return;
604 }
605 } // Else we still have the original card.
606 }
607
608 // Trim the region designated by the card to what's been allocated
609 // in the region. The card could be stale, or the card could cover
610 // (part of) an object at the end of the allocated space and extend
611 // beyond the end of allocation.
612
613 // Non-humongous objects are only allocated in the old-gen during
614 // GC, so if region is old then top is stable. Humongous object
615 // allocation sets top last; if top has not yet been set, this is
616 // a stale card and we'll end up with an empty intersection. If
617 // this is not a stale card, the synchronization between the
618 // enqueuing of the card and processing it here will have ensured
619 // we see the up-to-date top here.
620 HeapWord* scan_limit = r->top();
621
622 if (scan_limit <= start) {
623 // If the trimmed region is empty, the card must be stale.
624 return;
625 }
626
627 // Okay to clean and process the card now. There are still some
628 // stale card cases that may be detected by iteration and dealt with
629 // as iteration failure.
630 *const_cast<volatile jbyte*>(card_ptr) = G1CardTable::clean_card_val();
631
632 // This fence serves two purposes. First, the card must be cleaned
633 // before processing the contents. Second, we can't proceed with
634 // processing until after the read of top, for synchronization with
635 // possibly concurrent humongous object allocation. It's okay that
636 // reading top and reading type were racy wrto each other. We need
637 // both set, in any order, to proceed.
638 OrderAccess::fence();
639
640 // Don't use addr_for(card_ptr + 1) which can ask for
641 // a card beyond the heap.
642 HeapWord* end = start + G1CardTable::card_size_in_words;
643 MemRegion dirty_region(start, MIN2(scan_limit, end));
644 assert(!dirty_region.is_empty(), "sanity");
645
646 G1ConcurrentRefineOopClosure conc_refine_cl(_g1h, worker_i);
647
648 bool card_processed =
649 r->oops_on_card_seq_iterate_careful<false>(dirty_region, &conc_refine_cl);
650
651 // If unable to process the card then we encountered an unparsable
652 // part of the heap (e.g. a partially allocated object) while
653 // processing a stale card. Despite the card being stale, redirty
654 // and re-enqueue, because we've already cleaned the card. Without
655 // this we could incorrectly discard a non-stale card.
656 if (!card_processed) {
657 // The card might have gotten re-dirtied and re-enqueued while we
658 // worked. (In fact, it's pretty likely.)
659 if (*card_ptr != G1CardTable::dirty_card_val()) {
660 *card_ptr = G1CardTable::dirty_card_val();
661 MutexLockerEx x(Shared_DirtyCardQ_lock,
662 Mutex::_no_safepoint_check_flag);
663 DirtyCardQueue* sdcq =
664 G1BarrierSet::dirty_card_queue_set().shared_dirty_card_queue();
665 sdcq->enqueue(card_ptr);
666 }
667 } else {
668 _num_conc_refined_cards++; // Unsynchronized update, only used for logging.
669 }
670 }
671
672 bool G1RemSet::refine_card_during_gc(jbyte* card_ptr,
673 G1ScanObjsDuringUpdateRSClosure* update_rs_cl) {
674 assert(_g1h->is_gc_active(), "Only call during GC");
675
676 check_card_ptr(card_ptr, _ct);
677
678 // If the card is no longer dirty, nothing to do. This covers cards that were already
679 // scanned as parts of the remembered sets.
680 if (*card_ptr != G1CardTable::dirty_card_val()) {
681 return false;
682 }
683
684 // We claim lazily (so races are possible but they're benign), which reduces the
685 // number of potential duplicate scans (multiple threads may enqueue the same card twice).
686 *card_ptr = G1CardTable::clean_card_val() | G1CardTable::claimed_card_val();
687
688 // Construct the region representing the card.
689 HeapWord* card_start = _ct->addr_for(card_ptr);
690 // And find the region containing it.
691 uint const card_region_idx = _g1h->addr_to_region(card_start);
692
693 _scan_state->add_dirty_region(card_region_idx);
694 HeapWord* scan_limit = _scan_state->scan_top(card_region_idx);
695 if (scan_limit <= card_start) {
696 // If the card starts above the area in the region containing objects to scan, skip it.
697 return false;
698 }
699
700 // Don't use addr_for(card_ptr + 1) which can ask for
701 // a card beyond the heap.
702 HeapWord* card_end = card_start + G1CardTable::card_size_in_words;
703 MemRegion dirty_region(card_start, MIN2(scan_limit, card_end));
704 assert(!dirty_region.is_empty(), "sanity");
705
706 HeapRegion* const card_region = _g1h->region_at(card_region_idx);
707 update_rs_cl->set_region(card_region);
708 bool card_processed = card_region->oops_on_card_seq_iterate_careful<true>(dirty_region, update_rs_cl);
709 assert(card_processed, "must be");
710 return true;
711 }
712
713 void G1RemSet::print_periodic_summary_info(const char* header, uint period_count) {
714 if ((G1SummarizeRSetStatsPeriod > 0) && log_is_enabled(Trace, gc, remset) &&
715 (period_count % G1SummarizeRSetStatsPeriod == 0)) {
716
717 G1RemSetSummary current(this);
718 _prev_period_summary.subtract_from(¤t);
719
720 Log(gc, remset) log;
721 log.trace("%s", header);
722 ResourceMark rm;
723 LogStream ls(log.trace());
724 _prev_period_summary.print_on(&ls);
725
726 _prev_period_summary.set(¤t);
727 }
728 }
729
730 void G1RemSet::print_summary_info() {
731 Log(gc, remset, exit) log;
732 if (log.is_trace()) {
733 log.trace(" Cumulative RS summary");
734 G1RemSetSummary current(this);
735 ResourceMark rm;
736 LogStream ls(log.trace());
737 current.print_on(&ls);
738 }
739 }
740
741 class G1RebuildRemSetTask: public AbstractGangTask {
742 // Aggregate the counting data that was constructed concurrently
743 // with marking.
744 class G1RebuildRemSetHeapRegionClosure : public HeapRegionClosure {
745 G1ConcurrentMark* _cm;
746 G1RebuildRemSetClosure _update_cl;
747
748 // Applies _update_cl to the references of the given object, limiting objArrays
749 // to the given MemRegion. Returns the amount of words actually scanned.
750 size_t scan_for_references(oop const obj, MemRegion mr) {
751 size_t const obj_size = obj->size();
752 // All non-objArrays and objArrays completely within the mr
753 // can be scanned without passing the mr.
754 if (!obj->is_objArray() || mr.contains(MemRegion((HeapWord*)obj, obj_size))) {
755 obj->oop_iterate(&_update_cl);
756 return obj_size;
757 }
758 // This path is for objArrays crossing the given MemRegion. Only scan the
759 // area within the MemRegion.
760 obj->oop_iterate(&_update_cl, mr);
761 return mr.intersection(MemRegion((HeapWord*)obj, obj_size)).word_size();
762 }
763
764 // A humongous object is live (with respect to the scanning) either
765 // a) it is marked on the bitmap as such
766 // b) its TARS is larger than TAMS, i.e. has been allocated during marking.
767 bool is_humongous_live(oop const humongous_obj, const G1CMBitMap* const bitmap, HeapWord* tams, HeapWord* tars) const {
768 return bitmap->is_marked(humongous_obj) || (tars > tams);
769 }
770
771 // Iterator over the live objects within the given MemRegion.
772 class LiveObjIterator : public StackObj {
773 const G1CMBitMap* const _bitmap;
774 const HeapWord* _tams;
775 const MemRegion _mr;
776 HeapWord* _current;
777
778 bool is_below_tams() const {
779 return _current < _tams;
780 }
781
782 bool is_live(HeapWord* obj) const {
783 return !is_below_tams() || _bitmap->is_marked(obj);
784 }
785
786 HeapWord* bitmap_limit() const {
787 return MIN2(const_cast<HeapWord*>(_tams), _mr.end());
788 }
789
790 void move_if_below_tams() {
791 if (is_below_tams() && has_next()) {
792 _current = _bitmap->get_next_marked_addr(_current, bitmap_limit());
793 }
794 }
795 public:
796 LiveObjIterator(const G1CMBitMap* const bitmap, const HeapWord* tams, const MemRegion mr, HeapWord* first_oop_into_mr) :
797 _bitmap(bitmap),
798 _tams(tams),
799 _mr(mr),
800 _current(first_oop_into_mr) {
801
802 assert(_current <= _mr.start(),
803 "First oop " PTR_FORMAT " should extend into mr [" PTR_FORMAT ", " PTR_FORMAT ")",
804 p2i(first_oop_into_mr), p2i(mr.start()), p2i(mr.end()));
805
806 // Step to the next live object within the MemRegion if needed.
807 if (is_live(_current)) {
808 // Non-objArrays were scanned by the previous part of that region.
809 if (_current < mr.start() && !oop(_current)->is_objArray()) {
810 _current += oop(_current)->size();
811 // We might have positioned _current on a non-live object. Reposition to the next
812 // live one if needed.
813 move_if_below_tams();
814 }
815 } else {
816 // The object at _current can only be dead if below TAMS, so we can use the bitmap.
817 // immediately.
818 _current = _bitmap->get_next_marked_addr(_current, bitmap_limit());
819 assert(_current == _mr.end() || is_live(_current),
820 "Current " PTR_FORMAT " should be live (%s) or beyond the end of the MemRegion (" PTR_FORMAT ")",
821 p2i(_current), BOOL_TO_STR(is_live(_current)), p2i(_mr.end()));
822 }
823 }
824
825 void move_to_next() {
826 _current += next()->size();
827 move_if_below_tams();
828 }
829
830 oop next() const {
831 oop result = oop(_current);
832 assert(is_live(_current),
833 "Object " PTR_FORMAT " must be live TAMS " PTR_FORMAT " below %d mr " PTR_FORMAT " " PTR_FORMAT " outside %d",
834 p2i(_current), p2i(_tams), _tams > _current, p2i(_mr.start()), p2i(_mr.end()), _mr.contains(result));
835 return result;
836 }
837
838 bool has_next() const {
839 return _current < _mr.end();
840 }
841 };
842
843 // Rebuild remembered sets in the part of the region specified by mr and hr.
844 // Objects between the bottom of the region and the TAMS are checked for liveness
845 // using the given bitmap. Objects between TAMS and TARS are assumed to be live.
846 // Returns the number of live words between bottom and TAMS.
847 size_t rebuild_rem_set_in_region(const G1CMBitMap* const bitmap,
848 HeapWord* const top_at_mark_start,
849 HeapWord* const top_at_rebuild_start,
850 HeapRegion* hr,
851 MemRegion mr) {
852 size_t marked_words = 0;
853
854 if (hr->is_humongous()) {
855 oop const humongous_obj = oop(hr->humongous_start_region()->bottom());
856 if (is_humongous_live(humongous_obj, bitmap, top_at_mark_start, top_at_rebuild_start)) {
857 // We need to scan both [bottom, TAMS) and [TAMS, top_at_rebuild_start);
858 // however in case of humongous objects it is sufficient to scan the encompassing
859 // area (top_at_rebuild_start is always larger or equal to TAMS) as one of the
860 // two areas will be zero sized. I.e. TAMS is either
861 // the same as bottom or top(_at_rebuild_start). There is no way TAMS has a different
862 // value: this would mean that TAMS points somewhere into the object.
863 assert(hr->top() == top_at_mark_start || hr->top() == top_at_rebuild_start,
864 "More than one object in the humongous region?");
865 humongous_obj->oop_iterate(&_update_cl, mr);
866 return top_at_mark_start != hr->bottom() ? mr.intersection(MemRegion((HeapWord*)humongous_obj, humongous_obj->size())).byte_size() : 0;
867 } else {
868 return 0;
869 }
870 }
871
872 for (LiveObjIterator it(bitmap, top_at_mark_start, mr, hr->block_start(mr.start())); it.has_next(); it.move_to_next()) {
873 oop obj = it.next();
874 size_t scanned_size = scan_for_references(obj, mr);
875 if ((HeapWord*)obj < top_at_mark_start) {
876 marked_words += scanned_size;
877 }
878 }
879
880 return marked_words * HeapWordSize;
881 }
882 public:
883 G1RebuildRemSetHeapRegionClosure(G1CollectedHeap* g1h,
884 G1ConcurrentMark* cm,
885 uint worker_id) :
886 HeapRegionClosure(),
887 _cm(cm),
888 _update_cl(g1h, worker_id) { }
889
890 bool do_heap_region(HeapRegion* hr) {
891 if (_cm->has_aborted()) {
892 return true;
893 }
894
895 uint const region_idx = hr->hrm_index();
896 DEBUG_ONLY(HeapWord* const top_at_rebuild_start_check = _cm->top_at_rebuild_start(region_idx);)
897 assert(top_at_rebuild_start_check == NULL ||
898 top_at_rebuild_start_check > hr->bottom(),
899 "A TARS (" PTR_FORMAT ") == bottom() (" PTR_FORMAT ") indicates the old region %u is empty (%s)",
900 p2i(top_at_rebuild_start_check), p2i(hr->bottom()), region_idx, hr->get_type_str());
901
902 size_t total_marked_bytes = 0;
903 size_t const chunk_size_in_words = G1RebuildRemSetChunkSize / HeapWordSize;
904
905 HeapWord* const top_at_mark_start = hr->prev_top_at_mark_start();
906
907 HeapWord* cur = hr->bottom();
908 while (cur < hr->end()) {
909 // After every iteration (yield point) we need to check whether the region's
910 // TARS changed due to e.g. eager reclaim.
911 HeapWord* const top_at_rebuild_start = _cm->top_at_rebuild_start(region_idx);
912 if (top_at_rebuild_start == NULL) {
913 return false;
914 }
915
916 MemRegion next_chunk = MemRegion(hr->bottom(), top_at_rebuild_start).intersection(MemRegion(cur, chunk_size_in_words));
917 if (next_chunk.is_empty()) {
918 break;
919 }
920
921 const Ticks start = Ticks::now();
922 size_t marked_bytes = rebuild_rem_set_in_region(_cm->prev_mark_bitmap(),
923 top_at_mark_start,
924 top_at_rebuild_start,
925 hr,
926 next_chunk);
927 Tickspan time = Ticks::now() - start;
928
929 log_trace(gc, remset, tracking)("Rebuilt region %u "
930 "live " SIZE_FORMAT " "
931 "time %.3fms "
932 "marked bytes " SIZE_FORMAT " "
933 "bot " PTR_FORMAT " "
934 "TAMS " PTR_FORMAT " "
935 "TARS " PTR_FORMAT,
936 region_idx,
937 _cm->liveness(region_idx) * HeapWordSize,
938 TicksToTimeHelper::seconds(time) * 1000.0,
939 marked_bytes,
940 p2i(hr->bottom()),
941 p2i(top_at_mark_start),
942 p2i(top_at_rebuild_start));
943
944 if (marked_bytes > 0) {
945 total_marked_bytes += marked_bytes;
946 }
947 cur += chunk_size_in_words;
948
949 _cm->do_yield_check();
950 if (_cm->has_aborted()) {
951 return true;
952 }
953 }
954 // In the final iteration of the loop the region might have been eagerly reclaimed.
955 // Simply filter out those regions. We can not just use region type because there
956 // might have already been new allocations into these regions.
957 DEBUG_ONLY(HeapWord* const top_at_rebuild_start = _cm->top_at_rebuild_start(region_idx);)
958 assert(top_at_rebuild_start == NULL ||
959 total_marked_bytes == hr->marked_bytes(),
960 "Marked bytes " SIZE_FORMAT " for region %u (%s) in [bottom, TAMS) do not match calculated marked bytes " SIZE_FORMAT " "
961 "(" PTR_FORMAT " " PTR_FORMAT " " PTR_FORMAT ")",
962 total_marked_bytes, hr->hrm_index(), hr->get_type_str(), hr->marked_bytes(),
963 p2i(hr->bottom()), p2i(top_at_mark_start), p2i(top_at_rebuild_start));
964 // Abort state may have changed after the yield check.
965 return _cm->has_aborted();
966 }
967 };
968
969 HeapRegionClaimer _hr_claimer;
970 G1ConcurrentMark* _cm;
971
972 uint _worker_id_offset;
973 public:
974 G1RebuildRemSetTask(G1ConcurrentMark* cm,
975 uint n_workers,
976 uint worker_id_offset) :
977 AbstractGangTask("G1 Rebuild Remembered Set"),
978 _cm(cm),
979 _hr_claimer(n_workers),
980 _worker_id_offset(worker_id_offset) {
981 }
982
983 void work(uint worker_id) {
984 SuspendibleThreadSetJoiner sts_join;
985
986 G1CollectedHeap* g1h = G1CollectedHeap::heap();
987
988 G1RebuildRemSetHeapRegionClosure cl(g1h, _cm, _worker_id_offset + worker_id);
989 g1h->heap_region_par_iterate_from_worker_offset(&cl, &_hr_claimer, worker_id);
990 }
991 };
992
993 void G1RemSet::rebuild_rem_set(G1ConcurrentMark* cm,
994 WorkGang* workers,
995 uint worker_id_offset) {
996 uint num_workers = workers->active_workers();
997
998 G1RebuildRemSetTask cl(cm,
999 num_workers,
1000 worker_id_offset);
1001 workers->run_task(&cl, num_workers);
1002 }