1 /*
2 * Copyright (c) 2001, 2013, 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_implementation/g1/bufferingOopClosure.hpp"
27 #include "gc_implementation/g1/concurrentG1Refine.hpp"
28 #include "gc_implementation/g1/concurrentG1RefineThread.hpp"
29 #include "gc_implementation/g1/g1BlockOffsetTable.inline.hpp"
30 #include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
31 #include "gc_implementation/g1/g1CollectorPolicy.hpp"
32 #include "gc_implementation/g1/g1HotCardCache.hpp"
33 #include "gc_implementation/g1/g1GCPhaseTimes.hpp"
34 #include "gc_implementation/g1/g1OopClosures.inline.hpp"
35 #include "gc_implementation/g1/g1RemSet.inline.hpp"
36 #include "gc_implementation/g1/heapRegionSeq.inline.hpp"
37 #include "gc_implementation/g1/heapRegionRemSet.hpp"
38 #include "memory/iterator.hpp"
39 #include "oops/oop.inline.hpp"
40 #include "utilities/intHisto.hpp"
41
42 #define CARD_REPEAT_HISTO 0
43
44 #if CARD_REPEAT_HISTO
45 static size_t ct_freq_sz;
46 static jbyte* ct_freq = NULL;
47
48 void init_ct_freq_table(size_t heap_sz_bytes) {
49 if (ct_freq == NULL) {
50 ct_freq_sz = heap_sz_bytes/CardTableModRefBS::card_size;
51 ct_freq = new jbyte[ct_freq_sz];
52 for (size_t j = 0; j < ct_freq_sz; j++) ct_freq[j] = 0;
53 }
54 }
55
56 void ct_freq_note_card(size_t index) {
57 assert(0 <= index && index < ct_freq_sz, "Bounds error.");
58 if (ct_freq[index] < 100) { ct_freq[index]++; }
59 }
60
61 static IntHistogram card_repeat_count(10, 10);
62
63 void ct_freq_update_histo_and_reset() {
64 for (size_t j = 0; j < ct_freq_sz; j++) {
65 card_repeat_count.add_entry(ct_freq[j]);
66 ct_freq[j] = 0;
67 }
68
69 }
70 #endif
71
72 G1RemSet::G1RemSet(G1CollectedHeap* g1, CardTableModRefBS* ct_bs)
73 : _g1(g1), _conc_refine_cards(0),
74 _ct_bs(ct_bs), _g1p(_g1->g1_policy()),
75 _cg1r(g1->concurrent_g1_refine()),
76 _cset_rs_update_cl(NULL),
77 _cards_scanned(NULL), _total_cards_scanned(0),
78 _prev_period_summary()
79 {
80 _seq_task = new SubTasksDone(NumSeqTasks);
81 guarantee(n_workers() > 0, "There should be some workers");
82 _cset_rs_update_cl = NEW_C_HEAP_ARRAY(OopsInHeapRegionClosure*, n_workers(), mtGC);
83 for (uint i = 0; i < n_workers(); i++) {
84 _cset_rs_update_cl[i] = NULL;
85 }
86 if (G1SummarizeRSetStats) {
87 _prev_period_summary.initialize(this);
88 }
89 }
90
91 G1RemSet::~G1RemSet() {
92 delete _seq_task;
93 for (uint i = 0; i < n_workers(); i++) {
94 assert(_cset_rs_update_cl[i] == NULL, "it should be");
95 }
96 FREE_C_HEAP_ARRAY(OopsInHeapRegionClosure*, _cset_rs_update_cl, mtGC);
97 }
98
99 void CountNonCleanMemRegionClosure::do_MemRegion(MemRegion mr) {
100 if (_g1->is_in_g1_reserved(mr.start())) {
101 _n += (int) ((mr.byte_size() / CardTableModRefBS::card_size));
102 if (_start_first == NULL) _start_first = mr.start();
103 }
104 }
105
106 class ScanRSClosure : public HeapRegionClosure {
107 size_t _cards_done, _cards;
108 G1CollectedHeap* _g1h;
109
110 OopsInHeapRegionClosure* _oc;
111 CodeBlobToOopClosure* _code_root_cl;
112
113 G1BlockOffsetSharedArray* _bot_shared;
114 G1SATBCardTableModRefBS *_ct_bs;
115
116 double _strong_code_root_scan_time_sec;
117 int _worker_i;
118 int _block_size;
119 bool _try_claimed;
120
121 public:
122 ScanRSClosure(OopsInHeapRegionClosure* oc,
123 CodeBlobToOopClosure* code_root_cl,
124 int worker_i) :
125 _oc(oc),
126 _code_root_cl(code_root_cl),
127 _strong_code_root_scan_time_sec(0.0),
128 _cards(0),
129 _cards_done(0),
130 _worker_i(worker_i),
131 _try_claimed(false)
132 {
133 _g1h = G1CollectedHeap::heap();
134 _bot_shared = _g1h->bot_shared();
135 _ct_bs = _g1h->g1_barrier_set();
136 _block_size = MAX2<int>(G1RSetScanBlockSize, 1);
137 }
138
139 void set_try_claimed() { _try_claimed = true; }
140
141 void scanCard(size_t index, HeapRegion *r) {
142 // Stack allocate the DirtyCardToOopClosure instance
143 HeapRegionDCTOC cl(_g1h, r, _oc,
144 CardTableModRefBS::Precise,
145 HeapRegionDCTOC::IntoCSFilterKind);
146
147 // Set the "from" region in the closure.
148 _oc->set_region(r);
149 HeapWord* card_start = _bot_shared->address_for_index(index);
150 HeapWord* card_end = card_start + G1BlockOffsetSharedArray::N_words;
151 Space *sp = SharedHeap::heap()->space_containing(card_start);
152 MemRegion sm_region = sp->used_region_at_save_marks();
153 MemRegion mr = sm_region.intersection(MemRegion(card_start,card_end));
154 if (!mr.is_empty() && !_ct_bs->is_card_claimed(index)) {
155 // We make the card as "claimed" lazily (so races are possible
156 // but they're benign), which reduces the number of duplicate
157 // scans (the rsets of the regions in the cset can intersect).
158 _ct_bs->set_card_claimed(index);
159 _cards_done++;
160 cl.do_MemRegion(mr);
161 }
162 }
163
164 void printCard(HeapRegion* card_region, size_t card_index,
165 HeapWord* card_start) {
166 gclog_or_tty->print_cr("T %d Region [" PTR_FORMAT ", " PTR_FORMAT ") "
167 "RS names card %p: "
168 "[" PTR_FORMAT ", " PTR_FORMAT ")",
169 _worker_i,
170 card_region->bottom(), card_region->end(),
171 card_index,
172 card_start, card_start + G1BlockOffsetSharedArray::N_words);
173 }
174
175 void scan_strong_code_roots(HeapRegion* r) {
176 double scan_start = os::elapsedTime();
177 r->strong_code_roots_do(_code_root_cl);
178 _strong_code_root_scan_time_sec += (os::elapsedTime() - scan_start);
179 }
180
181 bool doHeapRegion(HeapRegion* r) {
182 assert(r->in_collection_set(), "should only be called on elements of CS.");
183 HeapRegionRemSet* hrrs = r->rem_set();
184 if (hrrs->iter_is_complete()) return false; // All done.
185 if (!_try_claimed && !hrrs->claim_iter()) return false;
186 // If we ever free the collection set concurrently, we should also
187 // clear the card table concurrently therefore we won't need to
188 // add regions of the collection set to the dirty cards region.
189 _g1h->push_dirty_cards_region(r);
190 // If we didn't return above, then
191 // _try_claimed || r->claim_iter()
192 // is true: either we're supposed to work on claimed-but-not-complete
193 // regions, or we successfully claimed the region.
194
195 HeapRegionRemSetIterator iter(hrrs);
196 size_t card_index;
197
198 // We claim cards in block so as to recude the contention. The block size is determined by
199 // the G1RSetScanBlockSize parameter.
200 size_t jump_to_card = hrrs->iter_claimed_next(_block_size);
201 for (size_t current_card = 0; iter.has_next(card_index); current_card++) {
202 if (current_card >= jump_to_card + _block_size) {
203 jump_to_card = hrrs->iter_claimed_next(_block_size);
204 }
205 if (current_card < jump_to_card) continue;
206 HeapWord* card_start = _g1h->bot_shared()->address_for_index(card_index);
207 #if 0
208 gclog_or_tty->print("Rem set iteration yielded card [" PTR_FORMAT ", " PTR_FORMAT ").\n",
209 card_start, card_start + CardTableModRefBS::card_size_in_words);
210 #endif
211
212 HeapRegion* card_region = _g1h->heap_region_containing(card_start);
213 assert(card_region != NULL, "Yielding cards not in the heap?");
214 _cards++;
215
216 if (!card_region->is_on_dirty_cards_region_list()) {
217 _g1h->push_dirty_cards_region(card_region);
218 }
219
220 // If the card is dirty, then we will scan it during updateRS.
221 if (!card_region->in_collection_set() &&
222 !_ct_bs->is_card_dirty(card_index)) {
223 scanCard(card_index, card_region);
224 }
225 }
226 if (!_try_claimed) {
227 // Scan the strong code root list attached to the current region
228 scan_strong_code_roots(r);
229
230 hrrs->set_iter_complete();
231 }
232 return false;
233 }
234
235 double strong_code_root_scan_time_sec() {
236 return _strong_code_root_scan_time_sec;
237 }
238
239 size_t cards_done() { return _cards_done;}
240 size_t cards_looked_up() { return _cards;}
241 };
242
243 void G1RemSet::scanRS(OopsInHeapRegionClosure* oc,
244 CodeBlobToOopClosure* code_root_cl,
245 int worker_i) {
246 double rs_time_start = os::elapsedTime();
247 HeapRegion *startRegion = _g1->start_cset_region_for_worker(worker_i);
248
249 ScanRSClosure scanRScl(oc, code_root_cl, worker_i);
250
251 _g1->collection_set_iterate_from(startRegion, &scanRScl);
252 scanRScl.set_try_claimed();
253 _g1->collection_set_iterate_from(startRegion, &scanRScl);
254
255 double scan_rs_time_sec = (os::elapsedTime() - rs_time_start)
256 - scanRScl.strong_code_root_scan_time_sec();
257
258 assert(_cards_scanned != NULL, "invariant");
259 _cards_scanned[worker_i] = scanRScl.cards_done();
260
261 _g1p->phase_times()->record_scan_rs_time(worker_i, scan_rs_time_sec * 1000.0);
262 _g1p->phase_times()->record_strong_code_root_scan_time(worker_i,
263 scanRScl.strong_code_root_scan_time_sec() * 1000.0);
264 }
265
266 // Closure used for updating RSets and recording references that
267 // point into the collection set. Only called during an
268 // evacuation pause.
269
270 class RefineRecordRefsIntoCSCardTableEntryClosure: public CardTableEntryClosure {
271 G1RemSet* _g1rs;
272 DirtyCardQueue* _into_cset_dcq;
273 public:
274 RefineRecordRefsIntoCSCardTableEntryClosure(G1CollectedHeap* g1h,
275 DirtyCardQueue* into_cset_dcq) :
276 _g1rs(g1h->g1_rem_set()), _into_cset_dcq(into_cset_dcq)
277 {}
278 bool do_card_ptr(jbyte* card_ptr, int worker_i) {
279 // The only time we care about recording cards that
280 // contain references that point into the collection set
281 // is during RSet updating within an evacuation pause.
282 // In this case worker_i should be the id of a GC worker thread.
283 assert(SafepointSynchronize::is_at_safepoint(), "not during an evacuation pause");
284 assert(worker_i < (int) (ParallelGCThreads == 0 ? 1 : ParallelGCThreads), "should be a GC worker");
285
286 if (_g1rs->refine_card(card_ptr, worker_i, true)) {
287 // 'card_ptr' contains references that point into the collection
288 // set. We need to record the card in the DCQS
289 // (G1CollectedHeap::into_cset_dirty_card_queue_set())
290 // that's used for that purpose.
291 //
292 // Enqueue the card
293 _into_cset_dcq->enqueue(card_ptr);
294 }
295 return true;
296 }
297 };
298
299 void G1RemSet::updateRS(DirtyCardQueue* into_cset_dcq, int worker_i) {
300 double start = os::elapsedTime();
301 // Apply the given closure to all remaining log entries.
302 RefineRecordRefsIntoCSCardTableEntryClosure into_cset_update_rs_cl(_g1, into_cset_dcq);
303
304 _g1->iterate_dirty_card_closure(&into_cset_update_rs_cl, into_cset_dcq, false, worker_i);
305
306 // Now there should be no dirty cards.
307 if (G1RSLogCheckCardTable) {
308 CountNonCleanMemRegionClosure cl(_g1);
309 _ct_bs->mod_card_iterate(&cl);
310 // XXX This isn't true any more: keeping cards of young regions
311 // marked dirty broke it. Need some reasonable fix.
312 guarantee(cl.n() == 0, "Card table should be clean.");
313 }
314
315 _g1p->phase_times()->record_update_rs_time(worker_i, (os::elapsedTime() - start) * 1000.0);
316 }
317
318 void G1RemSet::cleanupHRRS() {
319 HeapRegionRemSet::cleanup();
320 }
321
322 void G1RemSet::oops_into_collection_set_do(OopsInHeapRegionClosure* oc,
323 CodeBlobToOopClosure* code_root_cl,
324 int worker_i) {
325 #if CARD_REPEAT_HISTO
326 ct_freq_update_histo_and_reset();
327 #endif
328
329 // We cache the value of 'oc' closure into the appropriate slot in the
330 // _cset_rs_update_cl for this worker
331 assert(worker_i < (int)n_workers(), "sanity");
332 _cset_rs_update_cl[worker_i] = oc;
333
334 // A DirtyCardQueue that is used to hold cards containing references
335 // that point into the collection set. This DCQ is associated with a
336 // special DirtyCardQueueSet (see g1CollectedHeap.hpp). Under normal
337 // circumstances (i.e. the pause successfully completes), these cards
338 // are just discarded (there's no need to update the RSets of regions
339 // that were in the collection set - after the pause these regions
340 // are wholly 'free' of live objects. In the event of an evacuation
341 // failure the cards/buffers in this queue set are:
342 // * passed to the DirtyCardQueueSet that is used to manage deferred
343 // RSet updates, or
344 // * scanned for references that point into the collection set
345 // and the RSet of the corresponding region in the collection set
346 // is updated immediately.
347 DirtyCardQueue into_cset_dcq(&_g1->into_cset_dirty_card_queue_set());
348
349 assert((ParallelGCThreads > 0) || worker_i == 0, "invariant");
350
351 // The two flags below were introduced temporarily to serialize
352 // the updating and scanning of remembered sets. There are some
353 // race conditions when these two operations are done in parallel
354 // and they are causing failures. When we resolve said race
355 // conditions, we'll revert back to parallel remembered set
356 // updating and scanning. See CRs 6677707 and 6677708.
357 if (G1UseParallelRSetUpdating || (worker_i == 0)) {
358 updateRS(&into_cset_dcq, worker_i);
359 } else {
360 _g1p->phase_times()->record_update_rs_processed_buffers(worker_i, 0);
361 _g1p->phase_times()->record_update_rs_time(worker_i, 0.0);
362 }
363 if (G1UseParallelRSetScanning || (worker_i == 0)) {
364 scanRS(oc, code_root_cl, worker_i);
365 } else {
366 _g1p->phase_times()->record_scan_rs_time(worker_i, 0.0);
367 }
368
369 // We now clear the cached values of _cset_rs_update_cl for this worker
370 _cset_rs_update_cl[worker_i] = NULL;
371 }
372
373 void G1RemSet::prepare_for_oops_into_collection_set_do() {
374 cleanupHRRS();
375 ConcurrentG1Refine* cg1r = _g1->concurrent_g1_refine();
376 _g1->set_refine_cte_cl_concurrency(false);
377 DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();
378 dcqs.concatenate_logs();
379
380 guarantee( _cards_scanned == NULL, "invariant" );
381 _cards_scanned = NEW_C_HEAP_ARRAY(size_t, n_workers(), mtGC);
382 for (uint i = 0; i < n_workers(); ++i) {
383 _cards_scanned[i] = 0;
384 }
385 _total_cards_scanned = 0;
386 }
387
388
389 // This closure, applied to a DirtyCardQueueSet, is used to immediately
390 // update the RSets for the regions in the CSet. For each card it iterates
391 // through the oops which coincide with that card. It scans the reference
392 // fields in each oop; when it finds an oop that points into the collection
393 // set, the RSet for the region containing the referenced object is updated.
394 class UpdateRSetCardTableEntryIntoCSetClosure: public CardTableEntryClosure {
395 G1CollectedHeap* _g1;
396 CardTableModRefBS* _ct_bs;
397 public:
398 UpdateRSetCardTableEntryIntoCSetClosure(G1CollectedHeap* g1,
399 CardTableModRefBS* bs):
400 _g1(g1), _ct_bs(bs)
401 { }
402
403 bool do_card_ptr(jbyte* card_ptr, int worker_i) {
404 // Construct the region representing the card.
405 HeapWord* start = _ct_bs->addr_for(card_ptr);
406 // And find the region containing it.
407 HeapRegion* r = _g1->heap_region_containing(start);
408 assert(r != NULL, "unexpected null");
409
410 // Scan oops in the card looking for references into the collection set
411 // Don't use addr_for(card_ptr + 1) which can ask for
412 // a card beyond the heap. This is not safe without a perm
413 // gen.
414 HeapWord* end = start + CardTableModRefBS::card_size_in_words;
415 MemRegion scanRegion(start, end);
416
417 UpdateRSetImmediate update_rs_cl(_g1->g1_rem_set());
418 FilterIntoCSClosure update_rs_cset_oop_cl(NULL, _g1, &update_rs_cl);
419 FilterOutOfRegionClosure filter_then_update_rs_cset_oop_cl(r, &update_rs_cset_oop_cl);
420
421 // We can pass false as the "filter_young" parameter here as:
422 // * we should be in a STW pause,
423 // * the DCQS to which this closure is applied is used to hold
424 // references that point into the collection set from the prior
425 // RSet updating,
426 // * the post-write barrier shouldn't be logging updates to young
427 // regions (but there is a situation where this can happen - see
428 // the comment in G1RemSet::refine_card() below -
429 // that should not be applicable here), and
430 // * during actual RSet updating, the filtering of cards in young
431 // regions in HeapRegion::oops_on_card_seq_iterate_careful is
432 // employed.
433 // As a result, when this closure is applied to "refs into cset"
434 // DCQS, we shouldn't see any cards in young regions.
435 update_rs_cl.set_region(r);
436 HeapWord* stop_point =
437 r->oops_on_card_seq_iterate_careful(scanRegion,
438 &filter_then_update_rs_cset_oop_cl,
439 false /* filter_young */,
440 NULL /* card_ptr */);
441
442 // Since this is performed in the event of an evacuation failure, we
443 // we shouldn't see a non-null stop point
444 assert(stop_point == NULL, "saw an unallocated region");
445 return true;
446 }
447 };
448
449 void G1RemSet::cleanup_after_oops_into_collection_set_do() {
450 guarantee( _cards_scanned != NULL, "invariant" );
451 _total_cards_scanned = 0;
452 for (uint i = 0; i < n_workers(); ++i) {
453 _total_cards_scanned += _cards_scanned[i];
454 }
455 FREE_C_HEAP_ARRAY(size_t, _cards_scanned, mtGC);
456 _cards_scanned = NULL;
457 // Cleanup after copy
458 _g1->set_refine_cte_cl_concurrency(true);
459 // Set all cards back to clean.
460 _g1->cleanUpCardTable();
461
462 DirtyCardQueueSet& into_cset_dcqs = _g1->into_cset_dirty_card_queue_set();
463 int into_cset_n_buffers = into_cset_dcqs.completed_buffers_num();
464
465 if (_g1->evacuation_failed()) {
466 // Restore remembered sets for the regions pointing into the collection set.
467
468 if (G1DeferredRSUpdate) {
469 // If deferred RS updates are enabled then we just need to transfer
470 // the completed buffers from (a) the DirtyCardQueueSet used to hold
471 // cards that contain references that point into the collection set
472 // to (b) the DCQS used to hold the deferred RS updates
473 _g1->dirty_card_queue_set().merge_bufferlists(&into_cset_dcqs);
474 } else {
475
476 CardTableModRefBS* bs = (CardTableModRefBS*)_g1->barrier_set();
477 UpdateRSetCardTableEntryIntoCSetClosure update_rs_cset_immediate(_g1, bs);
478
479 int n_completed_buffers = 0;
480 while (into_cset_dcqs.apply_closure_to_completed_buffer(&update_rs_cset_immediate,
481 0, 0, true)) {
482 n_completed_buffers++;
483 }
484 assert(n_completed_buffers == into_cset_n_buffers, "missed some buffers");
485 }
486 }
487
488 // Free any completed buffers in the DirtyCardQueueSet used to hold cards
489 // which contain references that point into the collection.
490 _g1->into_cset_dirty_card_queue_set().clear();
491 assert(_g1->into_cset_dirty_card_queue_set().completed_buffers_num() == 0,
492 "all buffers should be freed");
493 _g1->into_cset_dirty_card_queue_set().clear_n_completed_buffers();
494 }
495
496 class ScrubRSClosure: public HeapRegionClosure {
497 G1CollectedHeap* _g1h;
498 BitMap* _region_bm;
499 BitMap* _card_bm;
500 CardTableModRefBS* _ctbs;
501 public:
502 ScrubRSClosure(BitMap* region_bm, BitMap* card_bm) :
503 _g1h(G1CollectedHeap::heap()),
504 _region_bm(region_bm), _card_bm(card_bm),
505 _ctbs(_g1h->g1_barrier_set()) {}
506
507 bool doHeapRegion(HeapRegion* r) {
508 if (!r->continuesHumongous()) {
509 r->rem_set()->scrub(_ctbs, _region_bm, _card_bm);
510 }
511 return false;
512 }
513 };
514
515 void G1RemSet::scrub(BitMap* region_bm, BitMap* card_bm) {
516 ScrubRSClosure scrub_cl(region_bm, card_bm);
517 _g1->heap_region_iterate(&scrub_cl);
518 }
519
520 void G1RemSet::scrub_par(BitMap* region_bm, BitMap* card_bm,
521 uint worker_num, int claim_val) {
522 ScrubRSClosure scrub_cl(region_bm, card_bm);
523 _g1->heap_region_par_iterate_chunked(&scrub_cl,
524 worker_num,
525 n_workers(),
526 claim_val);
527 }
528
529 G1TriggerClosure::G1TriggerClosure() :
530 _triggered(false) { }
531
532 G1InvokeIfNotTriggeredClosure::G1InvokeIfNotTriggeredClosure(G1TriggerClosure* t_cl,
533 OopClosure* oop_cl) :
534 _trigger_cl(t_cl), _oop_cl(oop_cl) { }
535
536 G1Mux2Closure::G1Mux2Closure(OopClosure *c1, OopClosure *c2) :
537 _c1(c1), _c2(c2) { }
538
539 G1UpdateRSOrPushRefOopClosure::
540 G1UpdateRSOrPushRefOopClosure(G1CollectedHeap* g1h,
541 G1RemSet* rs,
542 OopsInHeapRegionClosure* push_ref_cl,
543 bool record_refs_into_cset,
544 int worker_i) :
545 _g1(g1h), _g1_rem_set(rs), _from(NULL),
546 _record_refs_into_cset(record_refs_into_cset),
547 _push_ref_cl(push_ref_cl), _worker_i(worker_i) { }
548
549 // Returns true if the given card contains references that point
550 // into the collection set, if we're checking for such references;
551 // false otherwise.
552
553 bool G1RemSet::refine_card(jbyte* card_ptr, int worker_i,
554 bool check_for_refs_into_cset) {
555
556 // If the card is no longer dirty, nothing to do.
557 if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
558 // No need to return that this card contains refs that point
559 // into the collection set.
560 return false;
561 }
562
563 // Construct the region representing the card.
564 HeapWord* start = _ct_bs->addr_for(card_ptr);
565 // And find the region containing it.
566 HeapRegion* r = _g1->heap_region_containing(start);
567 if (r == NULL) {
568 // Again no need to return that this card contains refs that
569 // point into the collection set.
570 return false; // Not in the G1 heap (might be in perm, for example.)
571 }
572
573 // Why do we have to check here whether a card is on a young region,
574 // given that we dirty young regions and, as a result, the
575 // post-barrier is supposed to filter them out and never to enqueue
576 // them? When we allocate a new region as the "allocation region" we
577 // actually dirty its cards after we release the lock, since card
578 // dirtying while holding the lock was a performance bottleneck. So,
579 // as a result, it is possible for other threads to actually
580 // allocate objects in the region (after the acquire the lock)
581 // before all the cards on the region are dirtied. This is unlikely,
582 // and it doesn't happen often, but it can happen. So, the extra
583 // check below filters out those cards.
584 if (r->is_young()) {
585 return false;
586 }
587
588 // While we are processing RSet buffers during the collection, we
589 // actually don't want to scan any cards on the collection set,
590 // since we don't want to update remebered sets with entries that
591 // point into the collection set, given that live objects from the
592 // collection set are about to move and such entries will be stale
593 // very soon. This change also deals with a reliability issue which
594 // involves scanning a card in the collection set and coming across
595 // an array that was being chunked and looking malformed. Note,
596 // however, that if evacuation fails, we have to scan any objects
597 // that were not moved and create any missing entries.
598 if (r->in_collection_set()) {
599 return false;
600 }
601
602 // The result from the hot card cache insert call is either:
603 // * pointer to the current card
604 // (implying that the current card is not 'hot'),
605 // * null
606 // (meaning we had inserted the card ptr into the "hot" card cache,
607 // which had some headroom),
608 // * a pointer to a "hot" card that was evicted from the "hot" cache.
609 //
610
611 G1HotCardCache* hot_card_cache = _cg1r->hot_card_cache();
612 if (hot_card_cache->use_cache()) {
613 assert(!check_for_refs_into_cset, "sanity");
614 assert(!SafepointSynchronize::is_at_safepoint(), "sanity");
615
616 card_ptr = hot_card_cache->insert(card_ptr);
617 if (card_ptr == NULL) {
618 // There was no eviction. Nothing to do.
619 return false;
620 }
621
622 start = _ct_bs->addr_for(card_ptr);
623 r = _g1->heap_region_containing(start);
624 if (r == NULL) {
625 // Not in the G1 heap
626 return false;
627 }
628
629 // Checking whether the region we got back from the cache
630 // is young here is inappropriate. The region could have been
631 // freed, reallocated and tagged as young while in the cache.
632 // Hence we could see its young type change at any time.
633 }
634
635 // Don't use addr_for(card_ptr + 1) which can ask for
636 // a card beyond the heap. This is not safe without a perm
637 // gen at the upper end of the heap.
638 HeapWord* end = start + CardTableModRefBS::card_size_in_words;
639 MemRegion dirtyRegion(start, end);
640
641 #if CARD_REPEAT_HISTO
642 init_ct_freq_table(_g1->max_capacity());
643 ct_freq_note_card(_ct_bs->index_for(start));
644 #endif
645
646 OopsInHeapRegionClosure* oops_in_heap_closure = NULL;
647 if (check_for_refs_into_cset) {
648 // ConcurrentG1RefineThreads have worker numbers larger than what
649 // _cset_rs_update_cl[] is set up to handle. But those threads should
650 // only be active outside of a collection which means that when they
651 // reach here they should have check_for_refs_into_cset == false.
652 assert((size_t)worker_i < n_workers(), "index of worker larger than _cset_rs_update_cl[].length");
653 oops_in_heap_closure = _cset_rs_update_cl[worker_i];
654 }
655 G1UpdateRSOrPushRefOopClosure update_rs_oop_cl(_g1,
656 _g1->g1_rem_set(),
657 oops_in_heap_closure,
658 check_for_refs_into_cset,
659 worker_i);
660 update_rs_oop_cl.set_from(r);
661
662 G1TriggerClosure trigger_cl;
663 FilterIntoCSClosure into_cs_cl(NULL, _g1, &trigger_cl);
664 G1InvokeIfNotTriggeredClosure invoke_cl(&trigger_cl, &into_cs_cl);
665 G1Mux2Closure mux(&invoke_cl, &update_rs_oop_cl);
666
667 FilterOutOfRegionClosure filter_then_update_rs_oop_cl(r,
668 (check_for_refs_into_cset ?
669 (OopClosure*)&mux :
670 (OopClosure*)&update_rs_oop_cl));
671
672 // The region for the current card may be a young region. The
673 // current card may have been a card that was evicted from the
674 // card cache. When the card was inserted into the cache, we had
675 // determined that its region was non-young. While in the cache,
676 // the region may have been freed during a cleanup pause, reallocated
677 // and tagged as young.
678 //
679 // We wish to filter out cards for such a region but the current
680 // thread, if we're running concurrently, may "see" the young type
681 // change at any time (so an earlier "is_young" check may pass or
682 // fail arbitrarily). We tell the iteration code to perform this
683 // filtering when it has been determined that there has been an actual
684 // allocation in this region and making it safe to check the young type.
685 bool filter_young = true;
686
687 HeapWord* stop_point =
688 r->oops_on_card_seq_iterate_careful(dirtyRegion,
689 &filter_then_update_rs_oop_cl,
690 filter_young,
691 card_ptr);
692
693 // If stop_point is non-null, then we encountered an unallocated region
694 // (perhaps the unfilled portion of a TLAB.) For now, we'll dirty the
695 // card and re-enqueue: if we put off the card until a GC pause, then the
696 // unallocated portion will be filled in. Alternatively, we might try
697 // the full complexity of the technique used in "regular" precleaning.
698 if (stop_point != NULL) {
699 // The card might have gotten re-dirtied and re-enqueued while we
700 // worked. (In fact, it's pretty likely.)
701 if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
702 *card_ptr = CardTableModRefBS::dirty_card_val();
703 MutexLockerEx x(Shared_DirtyCardQ_lock,
704 Mutex::_no_safepoint_check_flag);
705 DirtyCardQueue* sdcq =
706 JavaThread::dirty_card_queue_set().shared_dirty_card_queue();
707 sdcq->enqueue(card_ptr);
708 }
709 } else {
710 _conc_refine_cards++;
711 }
712
713 // This gets set to true if the card being refined has
714 // references that point into the collection set.
715 bool has_refs_into_cset = trigger_cl.triggered();
716
717 // We should only be detecting that the card contains references
718 // that point into the collection set if the current thread is
719 // a GC worker thread.
720 assert(!has_refs_into_cset || SafepointSynchronize::is_at_safepoint(),
721 "invalid result at non safepoint");
722
723 return has_refs_into_cset;
724 }
725
726 void G1RemSet::print_periodic_summary_info(const char* header) {
727 G1RemSetSummary current;
728 current.initialize(this);
729
730 _prev_period_summary.subtract_from(¤t);
731 print_summary_info(&_prev_period_summary, header);
732
733 _prev_period_summary.set(¤t);
734 }
735
736 void G1RemSet::print_summary_info() {
737 G1RemSetSummary current;
738 current.initialize(this);
739
740 print_summary_info(¤t, " Cumulative RS summary");
741 }
742
743 void G1RemSet::print_summary_info(G1RemSetSummary * summary, const char * header) {
744 assert(summary != NULL, "just checking");
745
746 if (header != NULL) {
747 gclog_or_tty->print_cr("%s", header);
748 }
749
750 #if CARD_REPEAT_HISTO
751 gclog_or_tty->print_cr("\nG1 card_repeat count histogram: ");
752 gclog_or_tty->print_cr(" # of repeats --> # of cards with that number.");
753 card_repeat_count.print_on(gclog_or_tty);
754 #endif
755
756 summary->print_on(gclog_or_tty);
757 }
758
759 void G1RemSet::prepare_for_verify() {
760 if (G1HRRSFlushLogBuffersOnVerify &&
761 (VerifyBeforeGC || VerifyAfterGC)
762 && (!_g1->full_collection() || G1VerifyRSetsDuringFullGC)) {
763 cleanupHRRS();
764 _g1->set_refine_cte_cl_concurrency(false);
765 if (SafepointSynchronize::is_at_safepoint()) {
766 DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();
767 dcqs.concatenate_logs();
768 }
769
770 G1HotCardCache* hot_card_cache = _cg1r->hot_card_cache();
771 bool use_hot_card_cache = hot_card_cache->use_cache();
772 hot_card_cache->set_use_cache(false);
773
774 DirtyCardQueue into_cset_dcq(&_g1->into_cset_dirty_card_queue_set());
775 updateRS(&into_cset_dcq, 0);
776 _g1->into_cset_dirty_card_queue_set().clear();
777
778 hot_card_cache->set_use_cache(use_hot_card_cache);
779 assert(JavaThread::dirty_card_queue_set().completed_buffers_num() == 0, "All should be consumed");
780 }
781 }