1 /*
   2  * Copyright (c) 2001, 2014, 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/concurrentG1Refine.hpp"
  27 #include "gc_implementation/g1/concurrentG1RefineThread.hpp"
  28 #include "gc_implementation/g1/g1BlockOffsetTable.inline.hpp"
  29 #include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
  30 #include "gc_implementation/g1/g1CollectorPolicy.hpp"
  31 #include "gc_implementation/g1/g1HotCardCache.hpp"
  32 #include "gc_implementation/g1/g1GCPhaseTimes.hpp"
  33 #include "gc_implementation/g1/g1OopClosures.inline.hpp"
  34 #include "gc_implementation/g1/g1RemSet.inline.hpp"
  35 #include "gc_implementation/g1/heapRegionManager.inline.hpp"
  36 #include "gc_implementation/g1/heapRegionRemSet.hpp"
  37 #include "memory/iterator.hpp"
  38 #include "oops/oop.inline.hpp"
  39 #include "utilities/globalDefinitions.hpp"
  40 #include "utilities/intHisto.hpp"
  41 
  42 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
  43 
  44 #define CARD_REPEAT_HISTO 0
  45 
  46 #if CARD_REPEAT_HISTO
  47 static size_t ct_freq_sz;
  48 static jbyte* ct_freq = NULL;
  49 
  50 void init_ct_freq_table(size_t heap_sz_bytes) {
  51   if (ct_freq == NULL) {
  52     ct_freq_sz = heap_sz_bytes/CardTableModRefBS::card_size;
  53     ct_freq = new jbyte[ct_freq_sz];
  54     for (size_t j = 0; j < ct_freq_sz; j++) ct_freq[j] = 0;
  55   }
  56 }
  57 
  58 void ct_freq_note_card(size_t index) {
  59   assert(0 <= index && index < ct_freq_sz, "Bounds error.");
  60   if (ct_freq[index] < 100) { ct_freq[index]++; }
  61 }
  62 
  63 static IntHistogram card_repeat_count(10, 10);
  64 
  65 void ct_freq_update_histo_and_reset() {
  66   for (size_t j = 0; j < ct_freq_sz; j++) {
  67     card_repeat_count.add_entry(ct_freq[j]);
  68     ct_freq[j] = 0;
  69   }
  70 
  71 }
  72 #endif
  73 
  74 G1RemSet::G1RemSet(G1CollectedHeap* g1, CardTableModRefBS* ct_bs)
  75   : _g1(g1), _conc_refine_cards(0),
  76     _ct_bs(ct_bs), _g1p(_g1->g1_policy()),
  77     _cg1r(g1->concurrent_g1_refine()),
  78     _cset_rs_update_cl(NULL),
  79     _cards_scanned(NULL), _total_cards_scanned(0),
  80     _prev_period_summary()
  81 {
  82   _seq_task = new SubTasksDone(NumSeqTasks);
  83   _cset_rs_update_cl = NEW_C_HEAP_ARRAY(OopsInHeapRegionClosure*, n_workers(), mtGC);
  84   for (uint i = 0; i < n_workers(); i++) {
  85     _cset_rs_update_cl[i] = NULL;
  86   }
  87   if (G1SummarizeRSetStats) {
  88     _prev_period_summary.initialize(this);
  89   }
  90 }
  91 
  92 G1RemSet::~G1RemSet() {
  93   delete _seq_task;
  94   for (uint i = 0; i < n_workers(); i++) {
  95     assert(_cset_rs_update_cl[i] == NULL, "it should be");
  96   }
  97   FREE_C_HEAP_ARRAY(OopsInHeapRegionClosure*, _cset_rs_update_cl, mtGC);
  98 }
  99 
 100 void CountNonCleanMemRegionClosure::do_MemRegion(MemRegion mr) {
 101   if (_g1->is_in_g1_reserved(mr.start())) {
 102     _n += (int) ((mr.byte_size() / CardTableModRefBS::card_size));
 103     if (_start_first == NULL) _start_first = mr.start();
 104   }
 105 }
 106 
 107 class ScanRSClosure : public HeapRegionClosure {
 108   size_t _cards_done, _cards;
 109   G1CollectedHeap* _g1h;
 110 
 111   OopsInHeapRegionClosure* _oc;
 112   CodeBlobClosure* _code_root_cl;
 113 
 114   G1BlockOffsetSharedArray* _bot_shared;
 115   G1SATBCardTableModRefBS *_ct_bs;
 116 
 117   double _strong_code_root_scan_time_sec;
 118   uint   _worker_i;
 119   int    _block_size;
 120   bool   _try_claimed;
 121 
 122 public:
 123   ScanRSClosure(OopsInHeapRegionClosure* oc,
 124                 CodeBlobClosure* code_root_cl,
 125                 uint worker_i) :
 126     _oc(oc),
 127     _code_root_cl(code_root_cl),
 128     _strong_code_root_scan_time_sec(0.0),
 129     _cards(0),
 130     _cards_done(0),
 131     _worker_i(worker_i),
 132     _try_claimed(false)
 133   {
 134     _g1h = G1CollectedHeap::heap();
 135     _bot_shared = _g1h->bot_shared();
 136     _ct_bs = _g1h->g1_barrier_set();
 137     _block_size = MAX2<int>(G1RSetScanBlockSize, 1);
 138   }
 139 
 140   void set_try_claimed() { _try_claimed = true; }
 141 
 142   void scanCard(size_t index, HeapRegion *r) {
 143     // Stack allocate the DirtyCardToOopClosure instance
 144     HeapRegionDCTOC cl(_g1h, r, _oc,
 145                        CardTableModRefBS::Precise,
 146                        HeapRegionDCTOC::IntoCSFilterKind);
 147 
 148     // Set the "from" region in the closure.
 149     _oc->set_region(r);
 150     HeapWord* card_start = _bot_shared->address_for_index(index);
 151     HeapWord* card_end = card_start + G1BlockOffsetSharedArray::N_words;
 152     Space *sp = SharedHeap::heap()->space_containing(card_start);
 153     MemRegion sm_region = sp->used_region_at_save_marks();
 154     MemRegion mr = sm_region.intersection(MemRegion(card_start,card_end));
 155     if (!mr.is_empty() && !_ct_bs->is_card_claimed(index)) {
 156       // We make the card as "claimed" lazily (so races are possible
 157       // but they're benign), which reduces the number of duplicate
 158       // scans (the rsets of the regions in the cset can intersect).
 159       _ct_bs->set_card_claimed(index);
 160       _cards_done++;
 161       cl.do_MemRegion(mr);
 162     }
 163   }
 164 
 165   void printCard(HeapRegion* card_region, size_t card_index,
 166                  HeapWord* card_start) {
 167     gclog_or_tty->print_cr("T %u Region [" PTR_FORMAT ", " PTR_FORMAT ") "
 168                            "RS names card " SIZE_FORMAT_HEX ": "
 169                            "[" PTR_FORMAT ", " PTR_FORMAT ")",
 170                            _worker_i,
 171                            card_region->bottom(), card_region->end(),
 172                            card_index,
 173                            card_start, card_start + G1BlockOffsetSharedArray::N_words);
 174   }
 175 
 176   void scan_strong_code_roots(HeapRegion* r) {
 177     double scan_start = os::elapsedTime();
 178     r->strong_code_roots_do(_code_root_cl);
 179     _strong_code_root_scan_time_sec += (os::elapsedTime() - scan_start);
 180   }
 181 
 182   bool doHeapRegion(HeapRegion* r) {
 183     assert(r->in_collection_set(), "should only be called on elements of CS.");
 184     HeapRegionRemSet* hrrs = r->rem_set();
 185     if (hrrs->iter_is_complete()) return false; // All done.
 186     if (!_try_claimed && !hrrs->claim_iter()) return false;
 187     // If we ever free the collection set concurrently, we should also
 188     // clear the card table concurrently therefore we won't need to
 189     // add regions of the collection set to the dirty cards region.
 190     _g1h->push_dirty_cards_region(r);
 191     // If we didn't return above, then
 192     //   _try_claimed || r->claim_iter()
 193     // is true: either we're supposed to work on claimed-but-not-complete
 194     // regions, or we successfully claimed the region.
 195 
 196     HeapRegionRemSetIterator iter(hrrs);
 197     size_t card_index;
 198 
 199     // We claim cards in block so as to reduce the contention. The block size is determined by
 200     // the G1RSetScanBlockSize parameter.
 201     size_t jump_to_card = hrrs->iter_claimed_next(_block_size);
 202     for (size_t current_card = 0; iter.has_next(card_index); current_card++) {
 203       if (current_card >= jump_to_card + _block_size) {
 204         jump_to_card = hrrs->iter_claimed_next(_block_size);
 205       }
 206       if (current_card < jump_to_card) continue;
 207       HeapWord* card_start = _g1h->bot_shared()->address_for_index(card_index);
 208 #if 0
 209       gclog_or_tty->print("Rem set iteration yielded card [" PTR_FORMAT ", " PTR_FORMAT ").\n",
 210                           card_start, card_start + CardTableModRefBS::card_size_in_words);
 211 #endif
 212 
 213       HeapRegion* card_region = _g1h->heap_region_containing(card_start);
 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                       CodeBlobClosure* code_root_cl,
 245                       uint 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, uint 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 < 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, uint 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                                            CodeBlobClosure* code_root_cl,
 324                                            uint 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 < 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 passed to the
 342   // DirtyCardQueueSet that is used to manage RSet updates
 343   DirtyCardQueue into_cset_dcq(&_g1->into_cset_dirty_card_queue_set());
 344 
 345   updateRS(&into_cset_dcq, worker_i);
 346   scanRS(oc, code_root_cl, worker_i);
 347 
 348   // We now clear the cached values of _cset_rs_update_cl for this worker
 349   _cset_rs_update_cl[worker_i] = NULL;
 350 }
 351 
 352 void G1RemSet::prepare_for_oops_into_collection_set_do() {
 353   cleanupHRRS();
 354   _g1->set_refine_cte_cl_concurrency(false);
 355   DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();
 356   dcqs.concatenate_logs();
 357 
 358   guarantee( _cards_scanned == NULL, "invariant" );
 359   _cards_scanned = NEW_C_HEAP_ARRAY(size_t, n_workers(), mtGC);
 360   for (uint i = 0; i < n_workers(); ++i) {
 361     _cards_scanned[i] = 0;
 362   }
 363   _total_cards_scanned = 0;
 364 }
 365 
 366 void G1RemSet::cleanup_after_oops_into_collection_set_do() {
 367   guarantee( _cards_scanned != NULL, "invariant" );
 368   _total_cards_scanned = 0;
 369   for (uint i = 0; i < n_workers(); ++i) {
 370     _total_cards_scanned += _cards_scanned[i];
 371   }
 372   FREE_C_HEAP_ARRAY(size_t, _cards_scanned, mtGC);
 373   _cards_scanned = NULL;
 374   // Cleanup after copy
 375   _g1->set_refine_cte_cl_concurrency(true);
 376   // Set all cards back to clean.
 377   _g1->cleanUpCardTable();
 378 
 379   DirtyCardQueueSet& into_cset_dcqs = _g1->into_cset_dirty_card_queue_set();
 380   int into_cset_n_buffers = into_cset_dcqs.completed_buffers_num();
 381 
 382   if (_g1->evacuation_failed()) {
 383     double restore_remembered_set_start = os::elapsedTime();
 384 
 385     // Restore remembered sets for the regions pointing into the collection set.
 386     // We just need to transfer the completed buffers from the DirtyCardQueueSet
 387     // used to hold cards that contain references that point into the collection set
 388     // to the DCQS used to hold the deferred RS updates.
 389     _g1->dirty_card_queue_set().merge_bufferlists(&into_cset_dcqs);
 390     _g1->g1_policy()->phase_times()->record_evac_fail_restore_remsets((os::elapsedTime() - restore_remembered_set_start) * 1000.0);
 391   }
 392 
 393   // Free any completed buffers in the DirtyCardQueueSet used to hold cards
 394   // which contain references that point into the collection.
 395   _g1->into_cset_dirty_card_queue_set().clear();
 396   assert(_g1->into_cset_dirty_card_queue_set().completed_buffers_num() == 0,
 397          "all buffers should be freed");
 398   _g1->into_cset_dirty_card_queue_set().clear_n_completed_buffers();
 399 }
 400 
 401 class ScrubRSClosure: public HeapRegionClosure {
 402   G1CollectedHeap* _g1h;
 403   BitMap* _region_bm;
 404   BitMap* _card_bm;
 405   CardTableModRefBS* _ctbs;
 406 public:
 407   ScrubRSClosure(BitMap* region_bm, BitMap* card_bm) :
 408     _g1h(G1CollectedHeap::heap()),
 409     _region_bm(region_bm), _card_bm(card_bm),
 410     _ctbs(_g1h->g1_barrier_set()) {}
 411 
 412   bool doHeapRegion(HeapRegion* r) {
 413     if (!r->is_continues_humongous()) {
 414       r->rem_set()->scrub(_ctbs, _region_bm, _card_bm);
 415     }
 416     return false;
 417   }
 418 };
 419 
 420 void G1RemSet::scrub(BitMap* region_bm, BitMap* card_bm, uint worker_num, HeapRegionClaimer *hrclaimer) {
 421   ScrubRSClosure scrub_cl(region_bm, card_bm);
 422   _g1->heap_region_par_iterate(&scrub_cl, worker_num, hrclaimer);
 423 }
 424 
 425 G1TriggerClosure::G1TriggerClosure() :
 426   _triggered(false) { }
 427 
 428 G1InvokeIfNotTriggeredClosure::G1InvokeIfNotTriggeredClosure(G1TriggerClosure* t_cl,
 429                                                              OopClosure* oop_cl)  :
 430   _trigger_cl(t_cl), _oop_cl(oop_cl) { }
 431 
 432 G1Mux2Closure::G1Mux2Closure(OopClosure *c1, OopClosure *c2) :
 433   _c1(c1), _c2(c2) { }
 434 
 435 G1UpdateRSOrPushRefOopClosure::
 436 G1UpdateRSOrPushRefOopClosure(G1CollectedHeap* g1h,
 437                               G1RemSet* rs,
 438                               OopsInHeapRegionClosure* push_ref_cl,
 439                               bool record_refs_into_cset,
 440                               uint worker_i) :
 441   _g1(g1h), _g1_rem_set(rs), _from(NULL),
 442   _record_refs_into_cset(record_refs_into_cset),
 443   _push_ref_cl(push_ref_cl), _worker_i(worker_i) { }
 444 
 445 // Returns true if the given card contains references that point
 446 // into the collection set, if we're checking for such references;
 447 // false otherwise.
 448 
 449 bool G1RemSet::refine_card(jbyte* card_ptr, uint worker_i,
 450                            bool check_for_refs_into_cset) {
 451   assert(_g1->is_in_exact(_ct_bs->addr_for(card_ptr)),
 452          err_msg("Card at "PTR_FORMAT" index "SIZE_FORMAT" representing heap at "PTR_FORMAT" (%u) must be in committed heap",
 453                  p2i(card_ptr),
 454                  _ct_bs->index_for(_ct_bs->addr_for(card_ptr)),
 455                  _ct_bs->addr_for(card_ptr),
 456                  _g1->addr_to_region(_ct_bs->addr_for(card_ptr))));
 457 
 458   // If the card is no longer dirty, nothing to do.
 459   if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
 460     // No need to return that this card contains refs that point
 461     // into the collection set.
 462     return false;
 463   }
 464 
 465   // Construct the region representing the card.
 466   HeapWord* start = _ct_bs->addr_for(card_ptr);
 467   // And find the region containing it.
 468   HeapRegion* r = _g1->heap_region_containing(start);
 469 
 470   // Why do we have to check here whether a card is on a young region,
 471   // given that we dirty young regions and, as a result, the
 472   // post-barrier is supposed to filter them out and never to enqueue
 473   // them? When we allocate a new region as the "allocation region" we
 474   // actually dirty its cards after we release the lock, since card
 475   // dirtying while holding the lock was a performance bottleneck. So,
 476   // as a result, it is possible for other threads to actually
 477   // allocate objects in the region (after the acquire the lock)
 478   // before all the cards on the region are dirtied. This is unlikely,
 479   // and it doesn't happen often, but it can happen. So, the extra
 480   // check below filters out those cards.
 481   if (r->is_young()) {
 482     return false;
 483   }
 484 
 485   // While we are processing RSet buffers during the collection, we
 486   // actually don't want to scan any cards on the collection set,
 487   // since we don't want to update remembered sets with entries that
 488   // point into the collection set, given that live objects from the
 489   // collection set are about to move and such entries will be stale
 490   // very soon. This change also deals with a reliability issue which
 491   // involves scanning a card in the collection set and coming across
 492   // an array that was being chunked and looking malformed. Note,
 493   // however, that if evacuation fails, we have to scan any objects
 494   // that were not moved and create any missing entries.
 495   if (r->in_collection_set()) {
 496     return false;
 497   }
 498 
 499   // The result from the hot card cache insert call is either:
 500   //   * pointer to the current card
 501   //     (implying that the current card is not 'hot'),
 502   //   * null
 503   //     (meaning we had inserted the card ptr into the "hot" card cache,
 504   //     which had some headroom),
 505   //   * a pointer to a "hot" card that was evicted from the "hot" cache.
 506   //
 507 
 508   G1HotCardCache* hot_card_cache = _cg1r->hot_card_cache();
 509   if (hot_card_cache->use_cache()) {
 510     assert(!check_for_refs_into_cset, "sanity");
 511     assert(!SafepointSynchronize::is_at_safepoint(), "sanity");
 512 
 513     card_ptr = hot_card_cache->insert(card_ptr);
 514     if (card_ptr == NULL) {
 515       // There was no eviction. Nothing to do.
 516       return false;
 517     }
 518 
 519     start = _ct_bs->addr_for(card_ptr);
 520     r = _g1->heap_region_containing(start);
 521 
 522     // Checking whether the region we got back from the cache
 523     // is young here is inappropriate. The region could have been
 524     // freed, reallocated and tagged as young while in the cache.
 525     // Hence we could see its young type change at any time.
 526   }
 527 
 528   // Don't use addr_for(card_ptr + 1) which can ask for
 529   // a card beyond the heap.  This is not safe without a perm
 530   // gen at the upper end of the heap.
 531   HeapWord* end   = start + CardTableModRefBS::card_size_in_words;
 532   MemRegion dirtyRegion(start, end);
 533 
 534 #if CARD_REPEAT_HISTO
 535   init_ct_freq_table(_g1->max_capacity());
 536   ct_freq_note_card(_ct_bs->index_for(start));
 537 #endif
 538 
 539   OopsInHeapRegionClosure* oops_in_heap_closure = NULL;
 540   if (check_for_refs_into_cset) {
 541     // ConcurrentG1RefineThreads have worker numbers larger than what
 542     // _cset_rs_update_cl[] is set up to handle. But those threads should
 543     // only be active outside of a collection which means that when they
 544     // reach here they should have check_for_refs_into_cset == false.
 545     assert((size_t)worker_i < n_workers(), "index of worker larger than _cset_rs_update_cl[].length");
 546     oops_in_heap_closure = _cset_rs_update_cl[worker_i];
 547   }
 548   G1UpdateRSOrPushRefOopClosure update_rs_oop_cl(_g1,
 549                                                  _g1->g1_rem_set(),
 550                                                  oops_in_heap_closure,
 551                                                  check_for_refs_into_cset,
 552                                                  worker_i);
 553   update_rs_oop_cl.set_from(r);
 554 
 555   G1TriggerClosure trigger_cl;
 556   FilterIntoCSClosure into_cs_cl(NULL, _g1, &trigger_cl);
 557   G1InvokeIfNotTriggeredClosure invoke_cl(&trigger_cl, &into_cs_cl);
 558   G1Mux2Closure mux(&invoke_cl, &update_rs_oop_cl);
 559 
 560   FilterOutOfRegionClosure filter_then_update_rs_oop_cl(r,
 561                         (check_for_refs_into_cset ?
 562                                 (OopClosure*)&mux :
 563                                 (OopClosure*)&update_rs_oop_cl));
 564 
 565   // The region for the current card may be a young region. The
 566   // current card may have been a card that was evicted from the
 567   // card cache. When the card was inserted into the cache, we had
 568   // determined that its region was non-young. While in the cache,
 569   // the region may have been freed during a cleanup pause, reallocated
 570   // and tagged as young.
 571   //
 572   // We wish to filter out cards for such a region but the current
 573   // thread, if we're running concurrently, may "see" the young type
 574   // change at any time (so an earlier "is_young" check may pass or
 575   // fail arbitrarily). We tell the iteration code to perform this
 576   // filtering when it has been determined that there has been an actual
 577   // allocation in this region and making it safe to check the young type.
 578   bool filter_young = true;
 579 
 580   HeapWord* stop_point =
 581     r->oops_on_card_seq_iterate_careful(dirtyRegion,
 582                                         &filter_then_update_rs_oop_cl,
 583                                         filter_young,
 584                                         card_ptr);
 585 
 586   // If stop_point is non-null, then we encountered an unallocated region
 587   // (perhaps the unfilled portion of a TLAB.)  For now, we'll dirty the
 588   // card and re-enqueue: if we put off the card until a GC pause, then the
 589   // unallocated portion will be filled in.  Alternatively, we might try
 590   // the full complexity of the technique used in "regular" precleaning.
 591   if (stop_point != NULL) {
 592     // The card might have gotten re-dirtied and re-enqueued while we
 593     // worked.  (In fact, it's pretty likely.)
 594     if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
 595       *card_ptr = CardTableModRefBS::dirty_card_val();
 596       MutexLockerEx x(Shared_DirtyCardQ_lock,
 597                       Mutex::_no_safepoint_check_flag);
 598       DirtyCardQueue* sdcq =
 599         JavaThread::dirty_card_queue_set().shared_dirty_card_queue();
 600       sdcq->enqueue(card_ptr);
 601     }
 602   } else {
 603     _conc_refine_cards++;
 604   }
 605 
 606   // This gets set to true if the card being refined has
 607   // references that point into the collection set.
 608   bool has_refs_into_cset = trigger_cl.triggered();
 609 
 610   // We should only be detecting that the card contains references
 611   // that point into the collection set if the current thread is
 612   // a GC worker thread.
 613   assert(!has_refs_into_cset || SafepointSynchronize::is_at_safepoint(),
 614            "invalid result at non safepoint");
 615 
 616   return has_refs_into_cset;
 617 }
 618 
 619 void G1RemSet::print_periodic_summary_info(const char* header) {
 620   G1RemSetSummary current;
 621   current.initialize(this);
 622 
 623   _prev_period_summary.subtract_from(&current);
 624   print_summary_info(&_prev_period_summary, header);
 625 
 626   _prev_period_summary.set(&current);
 627 }
 628 
 629 void G1RemSet::print_summary_info() {
 630   G1RemSetSummary current;
 631   current.initialize(this);
 632 
 633   print_summary_info(&current, " Cumulative RS summary");
 634 }
 635 
 636 void G1RemSet::print_summary_info(G1RemSetSummary * summary, const char * header) {
 637   assert(summary != NULL, "just checking");
 638 
 639   if (header != NULL) {
 640     gclog_or_tty->print_cr("%s", header);
 641   }
 642 
 643 #if CARD_REPEAT_HISTO
 644   gclog_or_tty->print_cr("\nG1 card_repeat count histogram: ");
 645   gclog_or_tty->print_cr("  # of repeats --> # of cards with that number.");
 646   card_repeat_count.print_on(gclog_or_tty);
 647 #endif
 648 
 649   summary->print_on(gclog_or_tty);
 650 }
 651 
 652 void G1RemSet::prepare_for_verify() {
 653   if (G1HRRSFlushLogBuffersOnVerify &&
 654       (VerifyBeforeGC || VerifyAfterGC)
 655       &&  (!_g1->full_collection() || G1VerifyRSetsDuringFullGC)) {
 656     cleanupHRRS();
 657     _g1->set_refine_cte_cl_concurrency(false);
 658     if (SafepointSynchronize::is_at_safepoint()) {
 659       DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();
 660       dcqs.concatenate_logs();
 661     }
 662 
 663     G1HotCardCache* hot_card_cache = _cg1r->hot_card_cache();
 664     bool use_hot_card_cache = hot_card_cache->use_cache();
 665     hot_card_cache->set_use_cache(false);
 666 
 667     DirtyCardQueue into_cset_dcq(&_g1->into_cset_dirty_card_queue_set());
 668     updateRS(&into_cset_dcq, 0);
 669     _g1->into_cset_dirty_card_queue_set().clear();
 670 
 671     hot_card_cache->set_use_cache(use_hot_card_cache);
 672     assert(JavaThread::dirty_card_queue_set().completed_buffers_num() == 0, "All should be consumed");
 673   }
 674 }