1 /*
2 * Copyright (c) 2001, 2017, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "gc/g1/concurrentG1Refine.hpp"
27 #include "gc/g1/dirtyCardQueue.hpp"
28 #include "gc/g1/g1BlockOffsetTable.inline.hpp"
29 #include "gc/g1/g1CollectedHeap.inline.hpp"
30 #include "gc/g1/g1FromCardCache.hpp"
31 #include "gc/g1/g1GCPhaseTimes.hpp"
32 #include "gc/g1/g1HotCardCache.hpp"
33 #include "gc/g1/g1OopClosures.inline.hpp"
34 #include "gc/g1/g1RemSet.inline.hpp"
35 #include "gc/g1/g1SATBCardTableModRefBS.inline.hpp"
36 #include "gc/g1/heapRegion.inline.hpp"
37 #include "gc/g1/heapRegionManager.inline.hpp"
38 #include "gc/g1/heapRegionRemSet.hpp"
39 #include "gc/shared/gcTraceTime.inline.hpp"
40 #include "memory/iterator.hpp"
41 #include "memory/resourceArea.hpp"
42 #include "oops/oop.inline.hpp"
43 #include "utilities/globalDefinitions.hpp"
44 #include "utilities/intHisto.hpp"
45 #include "utilities/stack.inline.hpp"
46
47 // Collects information about the overall remembered set scan progress during an evacuation.
48 class G1RemSetScanState : public CHeapObj<mtGC> {
49 private:
50 class G1ClearCardTableTask : public AbstractGangTask {
51 G1CollectedHeap* _g1h;
52 uint* _dirty_region_list;
53 size_t _num_dirty_regions;
54 size_t _chunk_length;
55
56 size_t volatile _cur_dirty_regions;
57 public:
58 G1ClearCardTableTask(G1CollectedHeap* g1h,
59 uint* dirty_region_list,
60 size_t num_dirty_regions,
61 size_t chunk_length) :
62 AbstractGangTask("G1 Clear Card Table Task"),
63 _g1h(g1h),
64 _dirty_region_list(dirty_region_list),
65 _num_dirty_regions(num_dirty_regions),
66 _chunk_length(chunk_length),
67 _cur_dirty_regions(0) {
68
69 assert(chunk_length > 0, "must be");
70 }
71
72 static size_t chunk_size() { return M; }
73
74 void work(uint worker_id) {
75 G1SATBCardTableModRefBS* ct_bs = _g1h->g1_barrier_set();
76
77 while (_cur_dirty_regions < _num_dirty_regions) {
78 size_t next = Atomic::add(_chunk_length, &_cur_dirty_regions) - _chunk_length;
79 size_t max = MIN2(next + _chunk_length, _num_dirty_regions);
80
81 for (size_t i = next; i < max; i++) {
82 HeapRegion* r = _g1h->region_at(_dirty_region_list[i]);
83 if (!r->is_survivor()) {
84 ct_bs->clear(MemRegion(r->bottom(), r->end()));
85 }
86 }
87 }
88 }
89 };
90
91 size_t _max_regions;
92
93 // Scan progress for the remembered set of a single region. Transitions from
94 // Unclaimed -> Claimed -> Complete.
95 // At each of the transitions the thread that does the transition needs to perform
96 // some special action once. This is the reason for the extra "Claimed" state.
97 typedef jint G1RemsetIterState;
98
99 static const G1RemsetIterState Unclaimed = 0; // The remembered set has not been scanned yet.
100 static const G1RemsetIterState Claimed = 1; // The remembered set is currently being scanned.
101 static const G1RemsetIterState Complete = 2; // The remembered set has been completely scanned.
102
103 G1RemsetIterState volatile* _iter_states;
104 // The current location where the next thread should continue scanning in a region's
105 // remembered set.
106 size_t volatile* _iter_claims;
107
108 // Temporary buffer holding the regions we used to store remembered set scan duplicate
109 // information. These are also called "dirty". Valid entries are from [0.._cur_dirty_region)
110 uint* _dirty_region_buffer;
111
112 typedef jbyte IsDirtyRegionState;
113 static const IsDirtyRegionState Clean = 0;
114 static const IsDirtyRegionState Dirty = 1;
115 // Holds a flag for every region whether it is in the _dirty_region_buffer already
116 // to avoid duplicates. Uses jbyte since there are no atomic instructions for bools.
117 IsDirtyRegionState* _in_dirty_region_buffer;
118 size_t _cur_dirty_region;
119
120 // Creates a snapshot of the current _top values at the start of collection to
121 // filter out card marks that we do not want to scan.
122 class G1ResetScanTopClosure : public HeapRegionClosure {
123 private:
124 HeapWord** _scan_top;
125 public:
126 G1ResetScanTopClosure(HeapWord** scan_top) : _scan_top(scan_top) { }
127
128 virtual bool doHeapRegion(HeapRegion* r) {
129 uint hrm_index = r->hrm_index();
130 if (!r->in_collection_set() && r->is_old_or_humongous()) {
131 _scan_top[hrm_index] = r->top();
132 } else {
133 _scan_top[hrm_index] = r->bottom();
134 }
135 return false;
136 }
137 };
138
139 // For each region, contains the maximum top() value to be used during this garbage
140 // collection. Subsumes common checks like filtering out everything but old and
141 // humongous regions outside the collection set.
142 // This is valid because we are not interested in scanning stray remembered set
143 // entries from free or archive regions.
144 HeapWord** _scan_top;
145 public:
146 G1RemSetScanState() :
147 _max_regions(0),
148 _iter_states(NULL),
149 _iter_claims(NULL),
150 _dirty_region_buffer(NULL),
151 _in_dirty_region_buffer(NULL),
152 _cur_dirty_region(0),
153 _scan_top(NULL) {
154 }
155
156 ~G1RemSetScanState() {
157 if (_iter_states != NULL) {
158 FREE_C_HEAP_ARRAY(G1RemsetIterState, _iter_states);
159 }
160 if (_iter_claims != NULL) {
161 FREE_C_HEAP_ARRAY(size_t, _iter_claims);
162 }
163 if (_dirty_region_buffer != NULL) {
164 FREE_C_HEAP_ARRAY(uint, _dirty_region_buffer);
165 }
166 if (_in_dirty_region_buffer != NULL) {
167 FREE_C_HEAP_ARRAY(IsDirtyRegionState, _in_dirty_region_buffer);
168 }
169 if (_scan_top != NULL) {
170 FREE_C_HEAP_ARRAY(HeapWord*, _scan_top);
171 }
172 }
173
174 void initialize(uint max_regions) {
175 assert(_iter_states == NULL, "Must not be initialized twice");
176 assert(_iter_claims == NULL, "Must not be initialized twice");
177 _max_regions = max_regions;
178 _iter_states = NEW_C_HEAP_ARRAY(G1RemsetIterState, max_regions, mtGC);
179 _iter_claims = NEW_C_HEAP_ARRAY(size_t, max_regions, mtGC);
180 _dirty_region_buffer = NEW_C_HEAP_ARRAY(uint, max_regions, mtGC);
181 _in_dirty_region_buffer = NEW_C_HEAP_ARRAY(IsDirtyRegionState, max_regions, mtGC);
182 _scan_top = NEW_C_HEAP_ARRAY(HeapWord*, max_regions, mtGC);
183 }
184
185 void reset() {
186 for (uint i = 0; i < _max_regions; i++) {
187 _iter_states[i] = Unclaimed;
188 }
189
190 G1ResetScanTopClosure cl(_scan_top);
191 G1CollectedHeap::heap()->heap_region_iterate(&cl);
192
193 memset((void*)_iter_claims, 0, _max_regions * sizeof(size_t));
194 memset(_in_dirty_region_buffer, Clean, _max_regions * sizeof(IsDirtyRegionState));
195 _cur_dirty_region = 0;
196 }
197
198 // Attempt to claim the remembered set of the region for iteration. Returns true
199 // if this call caused the transition from Unclaimed to Claimed.
200 inline bool claim_iter(uint region) {
201 assert(region < _max_regions, "Tried to access invalid region %u", region);
202 if (_iter_states[region] != Unclaimed) {
203 return false;
204 }
205 jint res = Atomic::cmpxchg(Claimed, (jint*)(&_iter_states[region]), Unclaimed);
206 return (res == Unclaimed);
207 }
208
209 // Try to atomically sets the iteration state to "complete". Returns true for the
210 // thread that caused the transition.
211 inline bool set_iter_complete(uint region) {
212 if (iter_is_complete(region)) {
213 return false;
214 }
215 jint res = Atomic::cmpxchg(Complete, (jint*)(&_iter_states[region]), Claimed);
216 return (res == Claimed);
217 }
218
219 // Returns true if the region's iteration is complete.
220 inline bool iter_is_complete(uint region) const {
221 assert(region < _max_regions, "Tried to access invalid region %u", region);
222 return _iter_states[region] == Complete;
223 }
224
225 // The current position within the remembered set of the given region.
226 inline size_t iter_claimed(uint region) const {
227 assert(region < _max_regions, "Tried to access invalid region %u", region);
228 return _iter_claims[region];
229 }
230
231 // Claim the next block of cards within the remembered set of the region with
232 // step size.
233 inline size_t iter_claimed_next(uint region, size_t step) {
234 return Atomic::add(step, &_iter_claims[region]) - step;
235 }
236
237 void add_dirty_region(uint region) {
238 if (_in_dirty_region_buffer[region] == Dirty) {
239 return;
240 }
241
242 bool marked_as_dirty = Atomic::cmpxchg(Dirty, &_in_dirty_region_buffer[region], Clean) == Clean;
243 if (marked_as_dirty) {
244 size_t allocated = Atomic::add(1, &_cur_dirty_region) - 1;
245 _dirty_region_buffer[allocated] = region;
246 }
247 }
248
249 HeapWord* scan_top(uint region_idx) const {
250 return _scan_top[region_idx];
251 }
252
253 // Clear the card table of "dirty" regions.
254 void clear_card_table(WorkGang* workers) {
255 if (_cur_dirty_region == 0) {
256 return;
257 }
258
259 size_t const num_chunks = align_size_up(_cur_dirty_region * HeapRegion::CardsPerRegion, G1ClearCardTableTask::chunk_size()) / G1ClearCardTableTask::chunk_size();
260 uint const num_workers = (uint)MIN2(num_chunks, (size_t)workers->active_workers());
261 size_t const chunk_length = G1ClearCardTableTask::chunk_size() / HeapRegion::CardsPerRegion;
262
263 // Iterate over the dirty cards region list.
264 G1ClearCardTableTask cl(G1CollectedHeap::heap(), _dirty_region_buffer, _cur_dirty_region, chunk_length);
265
266 log_debug(gc, ergo)("Running %s using %u workers for " SIZE_FORMAT " "
267 "units of work for " SIZE_FORMAT " regions.",
268 cl.name(), num_workers, num_chunks, _cur_dirty_region);
269 workers->run_task(&cl, num_workers);
270
271 #ifndef PRODUCT
272 // Need to synchronize with concurrent cleanup since it needs to
273 // finish its card table clearing before we can verify.
274 G1CollectedHeap::heap()->wait_while_free_regions_coming();
275 G1CollectedHeap::heap()->verifier()->verify_card_table_cleanup();
276 #endif
277 }
278 };
279
280 G1RemSet::G1RemSet(G1CollectedHeap* g1,
281 CardTableModRefBS* ct_bs,
282 G1HotCardCache* hot_card_cache) :
283 _g1(g1),
284 _scan_state(new G1RemSetScanState()),
285 _conc_refine_cards(0),
286 _ct_bs(ct_bs),
287 _g1p(_g1->g1_policy()),
288 _hot_card_cache(hot_card_cache),
289 _prev_period_summary()
290 {
291 if (log_is_enabled(Trace, gc, remset)) {
292 _prev_period_summary.initialize(this);
293 }
294 }
295
296 G1RemSet::~G1RemSet() {
297 if (_scan_state != NULL) {
298 delete _scan_state;
299 }
300 }
301
302 uint G1RemSet::num_par_rem_sets() {
303 return MAX2(DirtyCardQueueSet::num_par_ids() + ConcurrentG1Refine::thread_num(), ParallelGCThreads);
304 }
305
306 void G1RemSet::initialize(size_t capacity, uint max_regions) {
307 G1FromCardCache::initialize(num_par_rem_sets(), max_regions);
308 _scan_state->initialize(max_regions);
309 {
310 GCTraceTime(Debug, gc, marking)("Initialize Card Live Data");
311 _card_live_data.initialize(capacity, max_regions);
312 }
313 if (G1PretouchAuxiliaryMemory) {
314 GCTraceTime(Debug, gc, marking)("Pre-Touch Card Live Data");
315 _card_live_data.pretouch();
316 }
317 }
318
319 G1ScanRSForRegionClosure::G1ScanRSForRegionClosure(G1RemSetScanState* scan_state,
320 G1ScanObjsDuringScanRSClosure* scan_obj_on_card,
321 CodeBlobClosure* code_root_cl,
322 uint worker_i) :
323 _scan_state(scan_state),
324 _scan_objs_on_card_cl(scan_obj_on_card),
325 _code_root_cl(code_root_cl),
326 _strong_code_root_scan_time_sec(0.0),
327 _cards_claimed(0),
328 _cards_scanned(0),
329 _cards_skipped(0),
330 _worker_i(worker_i) {
331 _g1h = G1CollectedHeap::heap();
332 _bot = _g1h->bot();
333 _ct_bs = _g1h->g1_barrier_set();
334 }
335
336 void G1ScanRSForRegionClosure::scan_card(size_t index, HeapWord* card_start, HeapRegion *r) {
337 MemRegion card_region(card_start, BOTConstants::N_words);
338 MemRegion pre_gc_allocated(r->bottom(), _scan_state->scan_top(r->hrm_index()));
339 MemRegion mr = pre_gc_allocated.intersection(card_region);
340 if (!mr.is_empty() && !_ct_bs->is_card_claimed(index)) {
341 // We make the card as "claimed" lazily (so races are possible
342 // but they're benign), which reduces the number of duplicate
343 // scans (the rsets of the regions in the cset can intersect).
344 _ct_bs->set_card_claimed(index);
345 _scan_objs_on_card_cl->set_region(r);
346 r->oops_on_card_seq_iterate_careful<true>(mr, _scan_objs_on_card_cl);
347 _cards_scanned++;
348 }
349 }
350
351 void G1ScanRSForRegionClosure::scan_strong_code_roots(HeapRegion* r) {
352 double scan_start = os::elapsedTime();
353 r->strong_code_roots_do(_code_root_cl);
354 _strong_code_root_scan_time_sec += (os::elapsedTime() - scan_start);
355 }
356
357 bool G1ScanRSForRegionClosure::doHeapRegion(HeapRegion* r) {
358 assert(r->in_collection_set(), "should only be called on elements of CS.");
359 uint region_idx = r->hrm_index();
360
361 if (_scan_state->iter_is_complete(region_idx)) {
362 return false;
363 }
364 if (_scan_state->claim_iter(region_idx)) {
365 // If we ever free the collection set concurrently, we should also
366 // clear the card table concurrently therefore we won't need to
367 // add regions of the collection set to the dirty cards region.
368 _scan_state->add_dirty_region(region_idx);
369 }
370
371 // We claim cards in blocks so as to reduce the contention.
372 size_t const block_size = G1RSetScanBlockSize;
373
374 HeapRegionRemSetIterator iter(r->rem_set());
375 size_t card_index;
376
377 size_t claimed_card_block = _scan_state->iter_claimed_next(region_idx, block_size);
378 for (size_t current_card = 0; iter.has_next(card_index); current_card++) {
379 if (current_card >= claimed_card_block + block_size) {
380 claimed_card_block = _scan_state->iter_claimed_next(region_idx, block_size);
381 }
382 if (current_card < claimed_card_block) {
383 _cards_skipped++;
384 continue;
385 }
386 HeapWord* card_start = _g1h->bot()->address_for_index(card_index);
387
388 HeapRegion* card_region = _g1h->heap_region_containing(card_start);
389 _cards_claimed++;
390
391 _scan_state->add_dirty_region(card_region->hrm_index());
392
393 // If the card is dirty, then we will scan it during updateRS.
394 if (!card_region->in_collection_set() &&
395 !_ct_bs->is_card_dirty(card_index)) {
396 scan_card(card_index, card_start, card_region);
397 }
398 }
399 if (_scan_state->set_iter_complete(region_idx)) {
400 // Scan the strong code root list attached to the current region
401 scan_strong_code_roots(r);
402 }
403 return false;
404 }
405
406 void G1RemSet::scan_rem_set(G1ParScanThreadState* pss,
407 CodeBlobClosure* heap_region_codeblobs,
408 uint worker_i) {
409 double rs_time_start = os::elapsedTime();
410
411 G1ScanObjsDuringScanRSClosure scan_cl(_g1, pss);
412 G1ScanRSForRegionClosure cl(_scan_state, &scan_cl, heap_region_codeblobs, worker_i);
413 _g1->collection_set_iterate_from(&cl, worker_i);
414
415 double scan_rs_time_sec = (os::elapsedTime() - rs_time_start) -
416 cl.strong_code_root_scan_time_sec();
417
418 G1GCPhaseTimes* p = _g1p->phase_times();
419
420 p->record_time_secs(G1GCPhaseTimes::ScanRS, worker_i, scan_rs_time_sec);
421 p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_scanned(), G1GCPhaseTimes::ScannedCards);
422 p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_claimed(), G1GCPhaseTimes::ClaimedCards);
423 p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_skipped(), G1GCPhaseTimes::SkippedCards);
424
425 p->record_time_secs(G1GCPhaseTimes::CodeRoots, worker_i, cl.strong_code_root_scan_time_sec());
426 }
427
428 // Closure used for updating rem sets. Only called during an evacuation pause.
429 class G1RefineCardClosure: public CardTableEntryClosure {
430 G1RemSet* _g1rs;
431 G1ScanObjsDuringUpdateRSClosure* _update_rs_cl;
432 public:
433 G1RefineCardClosure(G1CollectedHeap* g1h, G1ScanObjsDuringUpdateRSClosure* update_rs_cl) :
434 _g1rs(g1h->g1_rem_set()), _update_rs_cl(update_rs_cl)
435 {}
436
437 bool do_card_ptr(jbyte* card_ptr, uint worker_i) {
438 assert(SafepointSynchronize::is_at_safepoint(), "not during an evacuation pause");
439
440 _g1rs->refine_card_during_gc(card_ptr, _update_rs_cl);
441 return true;
442 }
443 };
444
445 void G1RemSet::update_rem_set(G1ParScanThreadState* pss, uint worker_i) {
446 G1ScanObjsDuringUpdateRSClosure update_rs_cl(_g1, pss, worker_i);
447 G1RefineCardClosure refine_card_cl(_g1, &update_rs_cl);
448
449 G1GCParPhaseTimesTracker x(_g1p->phase_times(), G1GCPhaseTimes::UpdateRS, worker_i);
450 if (G1HotCardCache::default_use_cache()) {
451 // Apply the closure to the entries of the hot card cache.
452 G1GCParPhaseTimesTracker y(_g1p->phase_times(), G1GCPhaseTimes::ScanHCC, worker_i);
453 _g1->iterate_hcc_closure(&refine_card_cl, worker_i);
454 }
455 // Apply the closure to all remaining log entries.
456 _g1->iterate_dirty_card_closure(&refine_card_cl, worker_i);
457 }
458
459 void G1RemSet::cleanupHRRS() {
460 HeapRegionRemSet::cleanup();
461 }
462
463 void G1RemSet::oops_into_collection_set_do(G1ParScanThreadState* pss,
464 CodeBlobClosure* heap_region_codeblobs,
465 uint worker_i) {
466 update_rem_set(pss, worker_i);
467 scan_rem_set(pss, heap_region_codeblobs, worker_i);;
468 }
469
470 void G1RemSet::prepare_for_oops_into_collection_set_do() {
471 _g1->set_refine_cte_cl_concurrency(false);
472 DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();
473 dcqs.concatenate_logs();
474
475 _scan_state->reset();
476 }
477
478 void G1RemSet::cleanup_after_oops_into_collection_set_do() {
479 G1GCPhaseTimes* phase_times = _g1->g1_policy()->phase_times();
480 // Cleanup after copy
481 _g1->set_refine_cte_cl_concurrency(true);
482
483 // Set all cards back to clean.
484 double start = os::elapsedTime();
485 _scan_state->clear_card_table(_g1->workers());
486 phase_times->record_clear_ct_time((os::elapsedTime() - start) * 1000.0);
487 }
488
489 class G1ScrubRSClosure: public HeapRegionClosure {
490 G1CollectedHeap* _g1h;
491 G1CardLiveData* _live_data;
492 public:
493 G1ScrubRSClosure(G1CardLiveData* live_data) :
494 _g1h(G1CollectedHeap::heap()),
495 _live_data(live_data) { }
496
497 bool doHeapRegion(HeapRegion* r) {
498 if (!r->is_continues_humongous()) {
499 r->rem_set()->scrub(_live_data);
500 }
501 return false;
502 }
503 };
504
505 void G1RemSet::scrub(uint worker_num, HeapRegionClaimer *hrclaimer) {
506 G1ScrubRSClosure scrub_cl(&_card_live_data);
507 _g1->heap_region_par_iterate(&scrub_cl, worker_num, hrclaimer);
508 }
509
510 inline void check_card_ptr(jbyte* card_ptr, CardTableModRefBS* ct_bs) {
511 #ifdef ASSERT
512 G1CollectedHeap* g1 = G1CollectedHeap::heap();
513 assert(g1->is_in_exact(ct_bs->addr_for(card_ptr)),
514 "Card at " PTR_FORMAT " index " SIZE_FORMAT " representing heap at " PTR_FORMAT " (%u) must be in committed heap",
515 p2i(card_ptr),
516 ct_bs->index_for(ct_bs->addr_for(card_ptr)),
517 p2i(ct_bs->addr_for(card_ptr)),
518 g1->addr_to_region(ct_bs->addr_for(card_ptr)));
519 #endif
520 }
521
522 void G1RemSet::refine_card_concurrently(jbyte* card_ptr,
523 uint worker_i) {
524 assert(!_g1->is_gc_active(), "Only call concurrently");
525
526 check_card_ptr(card_ptr, _ct_bs);
527
528 // If the card is no longer dirty, nothing to do.
529 if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
530 return;
531 }
532
533 // Construct the region representing the card.
534 HeapWord* start = _ct_bs->addr_for(card_ptr);
535 // And find the region containing it.
536 HeapRegion* r = _g1->heap_region_containing(start);
537
538 // This check is needed for some uncommon cases where we should
539 // ignore the card.
540 //
541 // The region could be young. Cards for young regions are
542 // distinctly marked (set to g1_young_gen), so the post-barrier will
543 // filter them out. However, that marking is performed
544 // concurrently. A write to a young object could occur before the
545 // card has been marked young, slipping past the filter.
546 //
547 // The card could be stale, because the region has been freed since
548 // the card was recorded. In this case the region type could be
549 // anything. If (still) free or (reallocated) young, just ignore
550 // it. If (reallocated) old or humongous, the later card trimming
551 // and additional checks in iteration may detect staleness. At
552 // worst, we end up processing a stale card unnecessarily.
553 //
554 // In the normal (non-stale) case, the synchronization between the
555 // enqueueing of the card and processing it here will have ensured
556 // we see the up-to-date region type here.
557 if (!r->is_old_or_humongous()) {
558 return;
559 }
560
561 // While we are processing RSet buffers during the collection, we
562 // actually don't want to scan any cards on the collection set,
563 // since we don't want to update remembered sets with entries that
564 // point into the collection set, given that live objects from the
565 // collection set are about to move and such entries will be stale
566 // very soon. This change also deals with a reliability issue which
567 // involves scanning a card in the collection set and coming across
568 // an array that was being chunked and looking malformed. Note,
569 // however, that if evacuation fails, we have to scan any objects
570 // that were not moved and create any missing entries.
571 if (r->in_collection_set()) {
572 return;
573 }
574
575 // The result from the hot card cache insert call is either:
576 // * pointer to the current card
577 // (implying that the current card is not 'hot'),
578 // * null
579 // (meaning we had inserted the card ptr into the "hot" card cache,
580 // which had some headroom),
581 // * a pointer to a "hot" card that was evicted from the "hot" cache.
582 //
583
584 if (_hot_card_cache->use_cache()) {
585 assert(!SafepointSynchronize::is_at_safepoint(), "sanity");
586
587 const jbyte* orig_card_ptr = card_ptr;
588 card_ptr = _hot_card_cache->insert(card_ptr);
589 if (card_ptr == NULL) {
590 // There was no eviction. Nothing to do.
591 return;
592 } else if (card_ptr != orig_card_ptr) {
593 // Original card was inserted and an old card was evicted.
594 start = _ct_bs->addr_for(card_ptr);
595 r = _g1->heap_region_containing(start);
596
597 // Check whether the region formerly in the cache should be
598 // ignored, as discussed earlier for the original card. The
599 // region could have been freed while in the cache. The cset is
600 // not relevant here, since we're in concurrent phase.
601 if (!r->is_old_or_humongous()) {
602 return;
603 }
604 } // Else we still have the original card.
605 }
606
607 // Trim the region designated by the card to what's been allocated
608 // in the region. The card could be stale, or the card could cover
609 // (part of) an object at the end of the allocated space and extend
610 // beyond the end of allocation.
611
612 // Non-humongous objects are only allocated in the old-gen during
613 // GC, so if region is old then top is stable. Humongous object
614 // allocation sets top last; if top has not yet been set, this is
615 // a stale card and we'll end up with an empty intersection. If
616 // this is not a stale card, the synchronization between the
617 // enqueuing of the card and processing it here will have ensured
618 // we see the up-to-date top here.
619 HeapWord* scan_limit = r->top();
620
621 if (scan_limit <= start) {
622 // If the trimmed region is empty, the card must be stale.
623 return;
624 }
625
626 // Okay to clean and process the card now. There are still some
627 // stale card cases that may be detected by iteration and dealt with
628 // as iteration failure.
629 *const_cast<volatile jbyte*>(card_ptr) = CardTableModRefBS::clean_card_val();
630
631 // This fence serves two purposes. First, the card must be cleaned
632 // before processing the contents. Second, we can't proceed with
633 // processing until after the read of top, for synchronization with
634 // possibly concurrent humongous object allocation. It's okay that
635 // reading top and reading type were racy wrto each other. We need
636 // both set, in any order, to proceed.
637 OrderAccess::fence();
638
639 // Don't use addr_for(card_ptr + 1) which can ask for
640 // a card beyond the heap.
641 HeapWord* end = start + CardTableModRefBS::card_size_in_words;
642 MemRegion dirty_region(start, MIN2(scan_limit, end));
643 assert(!dirty_region.is_empty(), "sanity");
644
645 G1ConcurrentRefineOopClosure conc_refine_cl(_g1, worker_i);
646
647 bool card_processed =
648 r->oops_on_card_seq_iterate_careful<false>(dirty_region, &conc_refine_cl);
649
650 // If unable to process the card then we encountered an unparsable
651 // part of the heap (e.g. a partially allocated object) while
652 // processing a stale card. Despite the card being stale, redirty
653 // and re-enqueue, because we've already cleaned the card. Without
654 // this we could incorrectly discard a non-stale card.
655 if (!card_processed) {
656 // The card might have gotten re-dirtied and re-enqueued while we
657 // worked. (In fact, it's pretty likely.)
658 if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
659 *card_ptr = CardTableModRefBS::dirty_card_val();
660 MutexLockerEx x(Shared_DirtyCardQ_lock,
661 Mutex::_no_safepoint_check_flag);
662 DirtyCardQueue* sdcq =
663 JavaThread::dirty_card_queue_set().shared_dirty_card_queue();
664 sdcq->enqueue(card_ptr);
665 }
666 } else {
667 _conc_refine_cards++;
668 }
669 }
670
671 void G1RemSet::refine_card_during_gc(jbyte* card_ptr,
672 G1ScanObjsDuringUpdateRSClosure* update_rs_cl) {
673 assert(_g1->is_gc_active(), "Only call during GC");
674
675 check_card_ptr(card_ptr, _ct_bs);
676
677 // If the card is no longer dirty, nothing to do. This covers cards that were already
678 // scanned as parts of the remembered sets.
679 if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
680 return;
681 }
682
683 // During GC we can immediately clean the card since we will not re-enqueue stale
684 // cards as we know they can be disregarded.
685 *card_ptr = CardTableModRefBS::clean_card_val();
686
687 // Construct the region representing the card.
688 HeapWord* card_start = _ct_bs->addr_for(card_ptr);
689 // And find the region containing it.
690 HeapRegion* r = _g1->heap_region_containing(card_start);
691
692 HeapWord* scan_limit = _scan_state->scan_top(r->hrm_index());
693 if (scan_limit <= card_start) {
694 // If the card starts above the area in the region containing objects to scan, skip it.
695 return;
696 }
697
698 // Don't use addr_for(card_ptr + 1) which can ask for
699 // a card beyond the heap.
700 HeapWord* card_end = card_start + CardTableModRefBS::card_size_in_words;
701 MemRegion dirty_region(card_start, MIN2(scan_limit, card_end));
702 assert(!dirty_region.is_empty(), "sanity");
703
704 update_rs_cl->set_region(r);
705 bool card_processed = r->oops_on_card_seq_iterate_careful<true>(dirty_region, update_rs_cl);
706 assert(card_processed, "must be");
707
708 _conc_refine_cards++;
709
710 return;
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 if (!_prev_period_summary.initialized()) {
718 _prev_period_summary.initialize(this);
719 }
720
721 G1RemSetSummary current;
722 current.initialize(this);
723 _prev_period_summary.subtract_from(¤t);
724
725 Log(gc, remset) log;
726 log.trace("%s", header);
727 ResourceMark rm;
728 _prev_period_summary.print_on(log.trace_stream());
729
730 _prev_period_summary.set(¤t);
731 }
732 }
733
734 void G1RemSet::print_summary_info() {
735 Log(gc, remset, exit) log;
736 if (log.is_trace()) {
737 log.trace(" Cumulative RS summary");
738 G1RemSetSummary current;
739 current.initialize(this);
740 ResourceMark rm;
741 current.print_on(log.trace_stream());
742 }
743 }
744
745 void G1RemSet::create_card_live_data(WorkGang* workers, G1CMBitMap* mark_bitmap) {
746 _card_live_data.create(workers, mark_bitmap);
747 }
748
749 void G1RemSet::finalize_card_live_data(WorkGang* workers, G1CMBitMap* mark_bitmap) {
750 _card_live_data.finalize(workers, mark_bitmap);
751 }
752
753 void G1RemSet::verify_card_live_data(WorkGang* workers, G1CMBitMap* bitmap) {
754 _card_live_data.verify(workers, bitmap);
755 }
756
757 void G1RemSet::clear_card_live_data(WorkGang* workers) {
758 _card_live_data.clear(workers);
759 }
760
761 #ifdef ASSERT
762 void G1RemSet::verify_card_live_data_is_clear() {
763 _card_live_data.verify_is_clear();
764 }
765 #endif