1 /* 2 * Copyright (c) 2000, 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/shared/cardTableModRefBS.inline.hpp" 27 #include "gc/shared/collectedHeap.hpp" 28 #include "gc/shared/genCollectedHeap.hpp" 29 #include "gc/shared/space.inline.hpp" 30 #include "logging/log.hpp" 31 #include "memory/virtualspace.hpp" 32 #include "oops/oop.inline.hpp" 33 #include "runtime/thread.hpp" 34 #include "services/memTracker.hpp" 35 #include "utilities/align.hpp" 36 #include "utilities/macros.hpp" 37 38 // This kind of "BarrierSet" allows a "CollectedHeap" to detect and 39 // enumerate ref fields that have been modified (since the last 40 // enumeration.) 41 42 size_t CardTableModRefBS::compute_byte_map_size() 43 { 44 assert(_guard_index == cards_required(_whole_heap.word_size()) - 1, 45 "uninitialized, check declaration order"); 46 assert(_page_size != 0, "uninitialized, check declaration order"); 47 const size_t granularity = os::vm_allocation_granularity(); 48 return align_up(_guard_index + 1, MAX2(_page_size, granularity)); 49 } 50 51 CardTableModRefBS::CardTableModRefBS( 52 MemRegion whole_heap, 53 const BarrierSet::FakeRtti& fake_rtti) : 54 ModRefBarrierSet(fake_rtti.add_tag(BarrierSet::CardTableModRef)), 55 _whole_heap(whole_heap), 56 _guard_index(0), 57 _guard_region(), 58 _last_valid_index(0), 59 _page_size(os::vm_page_size()), 60 _byte_map_size(0), 61 _covered(NULL), 62 _committed(NULL), 63 _cur_covered_regions(0), 64 _byte_map(NULL), 65 byte_map_base(NULL), 66 _defer_initial_card_mark(false) 67 { 68 assert((uintptr_t(_whole_heap.start()) & (card_size - 1)) == 0, "heap must start at card boundary"); 69 assert((uintptr_t(_whole_heap.end()) & (card_size - 1)) == 0, "heap must end at card boundary"); 70 71 assert(card_size <= 512, "card_size must be less than 512"); // why? 72 73 _covered = new MemRegion[_max_covered_regions]; 74 if (_covered == NULL) { 75 vm_exit_during_initialization("Could not allocate card table covered region set."); 76 } 77 } 78 79 void CardTableModRefBS::initialize() { 80 initialize_deferred_card_mark_barriers(); 81 _guard_index = cards_required(_whole_heap.word_size()) - 1; 82 _last_valid_index = _guard_index - 1; 83 84 _byte_map_size = compute_byte_map_size(); 85 86 HeapWord* low_bound = _whole_heap.start(); 87 HeapWord* high_bound = _whole_heap.end(); 88 89 _cur_covered_regions = 0; 90 _committed = new MemRegion[_max_covered_regions]; 91 if (_committed == NULL) { 92 vm_exit_during_initialization("Could not allocate card table committed region set."); 93 } 94 95 const size_t rs_align = _page_size == (size_t) os::vm_page_size() ? 0 : 96 MAX2(_page_size, (size_t) os::vm_allocation_granularity()); 97 ReservedSpace heap_rs(_byte_map_size, rs_align, false); 98 99 MemTracker::record_virtual_memory_type((address)heap_rs.base(), mtGC); 100 101 os::trace_page_sizes("Card Table", _guard_index + 1, _guard_index + 1, 102 _page_size, heap_rs.base(), heap_rs.size()); 103 if (!heap_rs.is_reserved()) { 104 vm_exit_during_initialization("Could not reserve enough space for the " 105 "card marking array"); 106 } 107 108 // The assembler store_check code will do an unsigned shift of the oop, 109 // then add it to byte_map_base, i.e. 110 // 111 // _byte_map = byte_map_base + (uintptr_t(low_bound) >> card_shift) 112 _byte_map = (jbyte*) heap_rs.base(); 113 byte_map_base = _byte_map - (uintptr_t(low_bound) >> card_shift); 114 assert(byte_for(low_bound) == &_byte_map[0], "Checking start of map"); 115 assert(byte_for(high_bound-1) <= &_byte_map[_last_valid_index], "Checking end of map"); 116 117 jbyte* guard_card = &_byte_map[_guard_index]; 118 uintptr_t guard_page = align_down((uintptr_t)guard_card, _page_size); 119 _guard_region = MemRegion((HeapWord*)guard_page, _page_size); 120 os::commit_memory_or_exit((char*)guard_page, _page_size, _page_size, 121 !ExecMem, "card table last card"); 122 *guard_card = last_card; 123 124 log_trace(gc, barrier)("CardTableModRefBS::CardTableModRefBS: "); 125 log_trace(gc, barrier)(" &_byte_map[0]: " INTPTR_FORMAT " &_byte_map[_last_valid_index]: " INTPTR_FORMAT, 126 p2i(&_byte_map[0]), p2i(&_byte_map[_last_valid_index])); 127 log_trace(gc, barrier)(" byte_map_base: " INTPTR_FORMAT, p2i(byte_map_base)); 128 } 129 130 CardTableModRefBS::~CardTableModRefBS() { 131 if (_covered) { 132 delete[] _covered; 133 _covered = NULL; 134 } 135 if (_committed) { 136 delete[] _committed; 137 _committed = NULL; 138 } 139 } 140 141 int CardTableModRefBS::find_covering_region_by_base(HeapWord* base) { 142 int i; 143 for (i = 0; i < _cur_covered_regions; i++) { 144 if (_covered[i].start() == base) return i; 145 if (_covered[i].start() > base) break; 146 } 147 // If we didn't find it, create a new one. 148 assert(_cur_covered_regions < _max_covered_regions, 149 "too many covered regions"); 150 // Move the ones above up, to maintain sorted order. 151 for (int j = _cur_covered_regions; j > i; j--) { 152 _covered[j] = _covered[j-1]; 153 _committed[j] = _committed[j-1]; 154 } 155 int res = i; 156 _cur_covered_regions++; 157 _covered[res].set_start(base); 158 _covered[res].set_word_size(0); 159 jbyte* ct_start = byte_for(base); 160 uintptr_t ct_start_aligned = align_down((uintptr_t)ct_start, _page_size); 161 _committed[res].set_start((HeapWord*)ct_start_aligned); 162 _committed[res].set_word_size(0); 163 return res; 164 } 165 166 int CardTableModRefBS::find_covering_region_containing(HeapWord* addr) { 167 for (int i = 0; i < _cur_covered_regions; i++) { 168 if (_covered[i].contains(addr)) { 169 return i; 170 } 171 } 172 assert(0, "address outside of heap?"); 173 return -1; 174 } 175 176 HeapWord* CardTableModRefBS::largest_prev_committed_end(int ind) const { 177 HeapWord* max_end = NULL; 178 for (int j = 0; j < ind; j++) { 179 HeapWord* this_end = _committed[j].end(); 180 if (this_end > max_end) max_end = this_end; 181 } 182 return max_end; 183 } 184 185 MemRegion CardTableModRefBS::committed_unique_to_self(int self, 186 MemRegion mr) const { 187 MemRegion result = mr; 188 for (int r = 0; r < _cur_covered_regions; r += 1) { 189 if (r != self) { 190 result = result.minus(_committed[r]); 191 } 192 } 193 // Never include the guard page. 194 result = result.minus(_guard_region); 195 return result; 196 } 197 198 void CardTableModRefBS::resize_covered_region(MemRegion new_region) { 199 // We don't change the start of a region, only the end. 200 assert(_whole_heap.contains(new_region), 201 "attempt to cover area not in reserved area"); 202 debug_only(verify_guard();) 203 // collided is true if the expansion would push into another committed region 204 debug_only(bool collided = false;) 205 int const ind = find_covering_region_by_base(new_region.start()); 206 MemRegion const old_region = _covered[ind]; 207 assert(old_region.start() == new_region.start(), "just checking"); 208 if (new_region.word_size() != old_region.word_size()) { 209 // Commit new or uncommit old pages, if necessary. 210 MemRegion cur_committed = _committed[ind]; 211 // Extend the end of this _committed region 212 // to cover the end of any lower _committed regions. 213 // This forms overlapping regions, but never interior regions. 214 HeapWord* const max_prev_end = largest_prev_committed_end(ind); 215 if (max_prev_end > cur_committed.end()) { 216 cur_committed.set_end(max_prev_end); 217 } 218 // Align the end up to a page size (starts are already aligned). 219 jbyte* const new_end = byte_after(new_region.last()); 220 HeapWord* new_end_aligned = (HeapWord*) align_up(new_end, _page_size); 221 assert((void*)new_end_aligned >= (void*) new_end, "align up, but less"); 222 // Check the other regions (excludes "ind") to ensure that 223 // the new_end_aligned does not intrude onto the committed 224 // space of another region. 225 int ri = 0; 226 for (ri = ind + 1; ri < _cur_covered_regions; ri++) { 227 if (new_end_aligned > _committed[ri].start()) { 228 assert(new_end_aligned <= _committed[ri].end(), 229 "An earlier committed region can't cover a later committed region"); 230 // Any region containing the new end 231 // should start at or beyond the region found (ind) 232 // for the new end (committed regions are not expected to 233 // be proper subsets of other committed regions). 234 assert(_committed[ri].start() >= _committed[ind].start(), 235 "New end of committed region is inconsistent"); 236 new_end_aligned = _committed[ri].start(); 237 // new_end_aligned can be equal to the start of its 238 // committed region (i.e., of "ind") if a second 239 // region following "ind" also start at the same location 240 // as "ind". 241 assert(new_end_aligned >= _committed[ind].start(), 242 "New end of committed region is before start"); 243 debug_only(collided = true;) 244 // Should only collide with 1 region 245 break; 246 } 247 } 248 #ifdef ASSERT 249 for (++ri; ri < _cur_covered_regions; ri++) { 250 assert(!_committed[ri].contains(new_end_aligned), 251 "New end of committed region is in a second committed region"); 252 } 253 #endif 254 // The guard page is always committed and should not be committed over. 255 // "guarded" is used for assertion checking below and recalls the fact 256 // that the would-be end of the new committed region would have 257 // penetrated the guard page. 258 HeapWord* new_end_for_commit = new_end_aligned; 259 260 DEBUG_ONLY(bool guarded = false;) 261 if (new_end_for_commit > _guard_region.start()) { 262 new_end_for_commit = _guard_region.start(); 263 DEBUG_ONLY(guarded = true;) 264 } 265 266 if (new_end_for_commit > cur_committed.end()) { 267 // Must commit new pages. 268 MemRegion const new_committed = 269 MemRegion(cur_committed.end(), new_end_for_commit); 270 271 assert(!new_committed.is_empty(), "Region should not be empty here"); 272 os::commit_memory_or_exit((char*)new_committed.start(), 273 new_committed.byte_size(), _page_size, 274 !ExecMem, "card table expansion"); 275 // Use new_end_aligned (as opposed to new_end_for_commit) because 276 // the cur_committed region may include the guard region. 277 } else if (new_end_aligned < cur_committed.end()) { 278 // Must uncommit pages. 279 MemRegion const uncommit_region = 280 committed_unique_to_self(ind, MemRegion(new_end_aligned, 281 cur_committed.end())); 282 if (!uncommit_region.is_empty()) { 283 // It is not safe to uncommit cards if the boundary between 284 // the generations is moving. A shrink can uncommit cards 285 // owned by generation A but being used by generation B. 286 if (!UseAdaptiveGCBoundary) { 287 if (!os::uncommit_memory((char*)uncommit_region.start(), 288 uncommit_region.byte_size())) { 289 assert(false, "Card table contraction failed"); 290 // The call failed so don't change the end of the 291 // committed region. This is better than taking the 292 // VM down. 293 new_end_aligned = _committed[ind].end(); 294 } 295 } else { 296 new_end_aligned = _committed[ind].end(); 297 } 298 } 299 } 300 // In any case, we can reset the end of the current committed entry. 301 _committed[ind].set_end(new_end_aligned); 302 303 #ifdef ASSERT 304 // Check that the last card in the new region is committed according 305 // to the tables. 306 bool covered = false; 307 for (int cr = 0; cr < _cur_covered_regions; cr++) { 308 if (_committed[cr].contains(new_end - 1)) { 309 covered = true; 310 break; 311 } 312 } 313 assert(covered, "Card for end of new region not committed"); 314 #endif 315 316 // The default of 0 is not necessarily clean cards. 317 jbyte* entry; 318 if (old_region.last() < _whole_heap.start()) { 319 entry = byte_for(_whole_heap.start()); 320 } else { 321 entry = byte_after(old_region.last()); 322 } 323 assert(index_for(new_region.last()) < _guard_index, 324 "The guard card will be overwritten"); 325 // This line commented out cleans the newly expanded region and 326 // not the aligned up expanded region. 327 // jbyte* const end = byte_after(new_region.last()); 328 jbyte* const end = (jbyte*) new_end_for_commit; 329 assert((end >= byte_after(new_region.last())) || collided || guarded, 330 "Expect to be beyond new region unless impacting another region"); 331 // do nothing if we resized downward. 332 #ifdef ASSERT 333 for (int ri = 0; ri < _cur_covered_regions; ri++) { 334 if (ri != ind) { 335 // The end of the new committed region should not 336 // be in any existing region unless it matches 337 // the start of the next region. 338 assert(!_committed[ri].contains(end) || 339 (_committed[ri].start() == (HeapWord*) end), 340 "Overlapping committed regions"); 341 } 342 } 343 #endif 344 if (entry < end) { 345 memset(entry, clean_card, pointer_delta(end, entry, sizeof(jbyte))); 346 } 347 } 348 // In any case, the covered size changes. 349 _covered[ind].set_word_size(new_region.word_size()); 350 351 log_trace(gc, barrier)("CardTableModRefBS::resize_covered_region: "); 352 log_trace(gc, barrier)(" _covered[%d].start(): " INTPTR_FORMAT " _covered[%d].last(): " INTPTR_FORMAT, 353 ind, p2i(_covered[ind].start()), ind, p2i(_covered[ind].last())); 354 log_trace(gc, barrier)(" _committed[%d].start(): " INTPTR_FORMAT " _committed[%d].last(): " INTPTR_FORMAT, 355 ind, p2i(_committed[ind].start()), ind, p2i(_committed[ind].last())); 356 log_trace(gc, barrier)(" byte_for(start): " INTPTR_FORMAT " byte_for(last): " INTPTR_FORMAT, 357 p2i(byte_for(_covered[ind].start())), p2i(byte_for(_covered[ind].last()))); 358 log_trace(gc, barrier)(" addr_for(start): " INTPTR_FORMAT " addr_for(last): " INTPTR_FORMAT, 359 p2i(addr_for((jbyte*) _committed[ind].start())), p2i(addr_for((jbyte*) _committed[ind].last()))); 360 361 // Touch the last card of the covered region to show that it 362 // is committed (or SEGV). 363 debug_only((void) (*byte_for(_covered[ind].last()));) 364 debug_only(verify_guard();) 365 } 366 367 // Note that these versions are precise! The scanning code has to handle the 368 // fact that the write barrier may be either precise or imprecise. 369 370 void CardTableModRefBS::dirty_MemRegion(MemRegion mr) { 371 assert(align_down(mr.start(), HeapWordSize) == mr.start(), "Unaligned start"); 372 assert(align_up (mr.end(), HeapWordSize) == mr.end(), "Unaligned end" ); 373 jbyte* cur = byte_for(mr.start()); 374 jbyte* last = byte_after(mr.last()); 375 while (cur < last) { 376 *cur = dirty_card; 377 cur++; 378 } 379 } 380 381 void CardTableModRefBS::invalidate(MemRegion mr) { 382 assert(align_down(mr.start(), HeapWordSize) == mr.start(), "Unaligned start"); 383 assert(align_up (mr.end(), HeapWordSize) == mr.end(), "Unaligned end" ); 384 for (int i = 0; i < _cur_covered_regions; i++) { 385 MemRegion mri = mr.intersection(_covered[i]); 386 if (!mri.is_empty()) dirty_MemRegion(mri); 387 } 388 } 389 390 void CardTableModRefBS::clear_MemRegion(MemRegion mr) { 391 // Be conservative: only clean cards entirely contained within the 392 // region. 393 jbyte* cur; 394 if (mr.start() == _whole_heap.start()) { 395 cur = byte_for(mr.start()); 396 } else { 397 assert(mr.start() > _whole_heap.start(), "mr is not covered."); 398 cur = byte_after(mr.start() - 1); 399 } 400 jbyte* last = byte_after(mr.last()); 401 memset(cur, clean_card, pointer_delta(last, cur, sizeof(jbyte))); 402 } 403 404 void CardTableModRefBS::clear(MemRegion mr) { 405 for (int i = 0; i < _cur_covered_regions; i++) { 406 MemRegion mri = mr.intersection(_covered[i]); 407 if (!mri.is_empty()) clear_MemRegion(mri); 408 } 409 } 410 411 void CardTableModRefBS::dirty(MemRegion mr) { 412 jbyte* first = byte_for(mr.start()); 413 jbyte* last = byte_after(mr.last()); 414 memset(first, dirty_card, last-first); 415 } 416 417 // Unlike several other card table methods, dirty_card_iterate() 418 // iterates over dirty cards ranges in increasing address order. 419 void CardTableModRefBS::dirty_card_iterate(MemRegion mr, 420 MemRegionClosure* cl) { 421 for (int i = 0; i < _cur_covered_regions; i++) { 422 MemRegion mri = mr.intersection(_covered[i]); 423 if (!mri.is_empty()) { 424 jbyte *cur_entry, *next_entry, *limit; 425 for (cur_entry = byte_for(mri.start()), limit = byte_for(mri.last()); 426 cur_entry <= limit; 427 cur_entry = next_entry) { 428 next_entry = cur_entry + 1; 429 if (*cur_entry == dirty_card) { 430 size_t dirty_cards; 431 // Accumulate maximal dirty card range, starting at cur_entry 432 for (dirty_cards = 1; 433 next_entry <= limit && *next_entry == dirty_card; 434 dirty_cards++, next_entry++); 435 MemRegion cur_cards(addr_for(cur_entry), 436 dirty_cards*card_size_in_words); 437 cl->do_MemRegion(cur_cards); 438 } 439 } 440 } 441 } 442 } 443 444 MemRegion CardTableModRefBS::dirty_card_range_after_reset(MemRegion mr, 445 bool reset, 446 int reset_val) { 447 for (int i = 0; i < _cur_covered_regions; i++) { 448 MemRegion mri = mr.intersection(_covered[i]); 449 if (!mri.is_empty()) { 450 jbyte* cur_entry, *next_entry, *limit; 451 for (cur_entry = byte_for(mri.start()), limit = byte_for(mri.last()); 452 cur_entry <= limit; 453 cur_entry = next_entry) { 454 next_entry = cur_entry + 1; 455 if (*cur_entry == dirty_card) { 456 size_t dirty_cards; 457 // Accumulate maximal dirty card range, starting at cur_entry 458 for (dirty_cards = 1; 459 next_entry <= limit && *next_entry == dirty_card; 460 dirty_cards++, next_entry++); 461 MemRegion cur_cards(addr_for(cur_entry), 462 dirty_cards*card_size_in_words); 463 if (reset) { 464 for (size_t i = 0; i < dirty_cards; i++) { 465 cur_entry[i] = reset_val; 466 } 467 } 468 return cur_cards; 469 } 470 } 471 } 472 } 473 return MemRegion(mr.end(), mr.end()); 474 } 475 476 uintx CardTableModRefBS::ct_max_alignment_constraint() { 477 return card_size * os::vm_page_size(); 478 } 479 480 void CardTableModRefBS::verify_guard() { 481 // For product build verification 482 guarantee(_byte_map[_guard_index] == last_card, 483 "card table guard has been modified"); 484 } 485 486 void CardTableModRefBS::verify() { 487 verify_guard(); 488 } 489 490 #ifndef PRODUCT 491 void CardTableModRefBS::verify_region(MemRegion mr, 492 jbyte val, bool val_equals) { 493 jbyte* start = byte_for(mr.start()); 494 jbyte* end = byte_for(mr.last()); 495 bool failures = false; 496 for (jbyte* curr = start; curr <= end; ++curr) { 497 jbyte curr_val = *curr; 498 bool failed = (val_equals) ? (curr_val != val) : (curr_val == val); 499 if (failed) { 500 if (!failures) { 501 log_error(gc, verify)("== CT verification failed: [" INTPTR_FORMAT "," INTPTR_FORMAT "]", p2i(start), p2i(end)); 502 log_error(gc, verify)("== %sexpecting value: %d", (val_equals) ? "" : "not ", val); 503 failures = true; 504 } 505 log_error(gc, verify)("== card " PTR_FORMAT " [" PTR_FORMAT "," PTR_FORMAT "], val: %d", 506 p2i(curr), p2i(addr_for(curr)), 507 p2i((HeapWord*) (((size_t) addr_for(curr)) + card_size)), 508 (int) curr_val); 509 } 510 } 511 guarantee(!failures, "there should not have been any failures"); 512 } 513 514 void CardTableModRefBS::verify_not_dirty_region(MemRegion mr) { 515 verify_region(mr, dirty_card, false /* val_equals */); 516 } 517 518 void CardTableModRefBS::verify_dirty_region(MemRegion mr) { 519 verify_region(mr, dirty_card, true /* val_equals */); 520 } 521 #endif 522 523 void CardTableModRefBS::print_on(outputStream* st) const { 524 st->print_cr("Card table byte_map: [" INTPTR_FORMAT "," INTPTR_FORMAT "] byte_map_base: " INTPTR_FORMAT, 525 p2i(_byte_map), p2i(_byte_map + _byte_map_size), p2i(byte_map_base)); 526 } 527 528 // Helper for ReduceInitialCardMarks. For performance, 529 // compiled code may elide card-marks for initializing stores 530 // to a newly allocated object along the fast-path. We 531 // compensate for such elided card-marks as follows: 532 // (a) Generational, non-concurrent collectors, such as 533 // GenCollectedHeap(ParNew,DefNew,Tenured) and 534 // ParallelScavengeHeap(ParallelGC, ParallelOldGC) 535 // need the card-mark if and only if the region is 536 // in the old gen, and do not care if the card-mark 537 // succeeds or precedes the initializing stores themselves, 538 // so long as the card-mark is completed before the next 539 // scavenge. For all these cases, we can do a card mark 540 // at the point at which we do a slow path allocation 541 // in the old gen, i.e. in this call. 542 // (b) GenCollectedHeap(ConcurrentMarkSweepGeneration) requires 543 // in addition that the card-mark for an old gen allocated 544 // object strictly follow any associated initializing stores. 545 // In these cases, the memRegion remembered below is 546 // used to card-mark the entire region either just before the next 547 // slow-path allocation by this thread or just before the next scavenge or 548 // CMS-associated safepoint, whichever of these events happens first. 549 // (The implicit assumption is that the object has been fully 550 // initialized by this point, a fact that we assert when doing the 551 // card-mark.) 552 // (c) G1CollectedHeap(G1) uses two kinds of write barriers. When a 553 // G1 concurrent marking is in progress an SATB (pre-write-)barrier 554 // is used to remember the pre-value of any store. Initializing 555 // stores will not need this barrier, so we need not worry about 556 // compensating for the missing pre-barrier here. Turning now 557 // to the post-barrier, we note that G1 needs a RS update barrier 558 // which simply enqueues a (sequence of) dirty cards which may 559 // optionally be refined by the concurrent update threads. Note 560 // that this barrier need only be applied to a non-young write, 561 // but, like in CMS, because of the presence of concurrent refinement 562 // (much like CMS' precleaning), must strictly follow the oop-store. 563 // Thus, using the same protocol for maintaining the intended 564 // invariants turns out, serendepitously, to be the same for both 565 // G1 and CMS. 566 // 567 // For any future collector, this code should be reexamined with 568 // that specific collector in mind, and the documentation above suitably 569 // extended and updated. 570 void CardTableModRefBS::on_slowpath_allocation_exit(JavaThread* thread, oop new_obj) { 571 if (!ReduceInitialCardMarks) { 572 return; 573 } 574 // If a previous card-mark was deferred, flush it now. 575 flush_deferred_card_mark_barrier(thread); 576 if (new_obj->is_typeArray() || is_in_young(new_obj)) { 577 // Arrays of non-references don't need a post-barrier. 578 // The deferred_card_mark region should be empty 579 // following the flush above. 580 assert(thread->deferred_card_mark().is_empty(), "Error"); 581 } else { 582 MemRegion mr((HeapWord*)new_obj, new_obj->size()); 583 assert(!mr.is_empty(), "Error"); 584 if (_defer_initial_card_mark) { 585 // Defer the card mark 586 thread->set_deferred_card_mark(mr); 587 } else { 588 // Do the card mark 589 write_region(mr); 590 } 591 } 592 } 593 594 void CardTableModRefBS::initialize_deferred_card_mark_barriers() { 595 // Used for ReduceInitialCardMarks (when COMPILER2 or JVMCI is used); 596 // otherwise remains unused. 597 #if defined(COMPILER2) || INCLUDE_JVMCI 598 _defer_initial_card_mark = is_server_compilation_mode_vm() && ReduceInitialCardMarks && can_elide_tlab_store_barriers() 599 && (DeferInitialCardMark || card_mark_must_follow_store()); 600 #else 601 assert(_defer_initial_card_mark == false, "Who would set it?"); 602 #endif 603 } 604 605 void CardTableModRefBS::flush_deferred_card_mark_barrier(JavaThread* thread) { 606 #if defined(COMPILER2) || INCLUDE_JVMCI 607 MemRegion deferred = thread->deferred_card_mark(); 608 if (!deferred.is_empty()) { 609 assert(_defer_initial_card_mark, "Otherwise should be empty"); 610 { 611 // Verify that the storage points to a parsable object in heap 612 DEBUG_ONLY(oop old_obj = oop(deferred.start());) 613 assert(!is_in_young(old_obj), 614 "Else should have been filtered in on_slowpath_allocation_exit()"); 615 assert(oopDesc::is_oop(old_obj, true), "Not an oop"); 616 assert(deferred.word_size() == (size_t)(old_obj->size()), 617 "Mismatch: multiple objects?"); 618 } 619 write_region(deferred); 620 // "Clear" the deferred_card_mark field 621 thread->set_deferred_card_mark(MemRegion()); 622 } 623 assert(thread->deferred_card_mark().is_empty(), "invariant"); 624 #else 625 assert(!_defer_initial_card_mark, "Should be false"); 626 assert(thread->deferred_card_mark().is_empty(), "Should be empty"); 627 #endif 628 } 629 630 void CardTableModRefBS::flush_deferred_barriers(JavaThread* thread) { 631 // The deferred store barriers must all have been flushed to the 632 // card-table (or other remembered set structure) before GC starts 633 // processing the card-table (or other remembered set). 634 flush_deferred_card_mark_barrier(thread); 635 }