1 /* 2 * Copyright (c) 2001, 2019, 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 "classfile/classLoaderDataGraph.hpp" 27 #include "gc/shared/cardTableRS.hpp" 28 #include "gc/shared/genCollectedHeap.hpp" 29 #include "gc/shared/genOopClosures.hpp" 30 #include "gc/shared/generation.hpp" 31 #include "gc/shared/space.inline.hpp" 32 #include "memory/allocation.inline.hpp" 33 #include "memory/iterator.inline.hpp" 34 #include "oops/access.inline.hpp" 35 #include "oops/oop.inline.hpp" 36 #include "runtime/atomic.hpp" 37 #include "runtime/java.hpp" 38 #include "runtime/os.hpp" 39 #include "utilities/macros.hpp" 40 41 class HasAccumulatedModifiedOopsClosure : public CLDClosure { 42 bool _found; 43 public: 44 HasAccumulatedModifiedOopsClosure() : _found(false) {} 45 void do_cld(ClassLoaderData* cld) { 46 if (_found) { 47 return; 48 } 49 50 if (cld->has_accumulated_modified_oops()) { 51 _found = true; 52 } 53 } 54 bool found() { 55 return _found; 56 } 57 }; 58 59 bool CLDRemSet::mod_union_is_clear() { 60 HasAccumulatedModifiedOopsClosure closure; 61 ClassLoaderDataGraph::cld_do(&closure); 62 63 return !closure.found(); 64 } 65 66 67 class ClearCLDModUnionClosure : public CLDClosure { 68 public: 69 void do_cld(ClassLoaderData* cld) { 70 if (cld->has_accumulated_modified_oops()) { 71 cld->clear_accumulated_modified_oops(); 72 } 73 } 74 }; 75 76 void CLDRemSet::clear_mod_union() { 77 ClearCLDModUnionClosure closure; 78 ClassLoaderDataGraph::cld_do(&closure); 79 } 80 81 CardTable::CardValue CardTableRS::find_unused_youngergenP_card_value() { 82 for (CardValue v = youngergenP1_card; 83 v < cur_youngergen_and_prev_nonclean_card; 84 v++) { 85 bool seen = false; 86 for (int g = 0; g < _regions_to_iterate; g++) { 87 if (_last_cur_val_in_gen[g] == v) { 88 seen = true; 89 break; 90 } 91 } 92 if (!seen) { 93 return v; 94 } 95 } 96 ShouldNotReachHere(); 97 return 0; 98 } 99 100 void CardTableRS::prepare_for_younger_refs_iterate(bool parallel) { 101 // Parallel or sequential, we must always set the prev to equal the 102 // last one written. 103 if (parallel) { 104 // Find a parallel value to be used next. 105 jbyte next_val = find_unused_youngergenP_card_value(); 106 set_cur_youngergen_card_val(next_val); 107 108 } else { 109 // In an sequential traversal we will always write youngergen, so that 110 // the inline barrier is correct. 111 set_cur_youngergen_card_val(youngergen_card); 112 } 113 } 114 115 void CardTableRS::younger_refs_iterate(Generation* g, 116 OopsInGenClosure* blk, 117 uint n_threads) { 118 // The indexing in this array is slightly odd. We want to access 119 // the old generation record here, which is at index 2. 120 _last_cur_val_in_gen[2] = cur_youngergen_card_val(); 121 g->younger_refs_iterate(blk, n_threads); 122 } 123 124 inline bool ClearNoncleanCardWrapper::clear_card(CardValue* entry) { 125 if (_is_par) { 126 return clear_card_parallel(entry); 127 } else { 128 return clear_card_serial(entry); 129 } 130 } 131 132 inline bool ClearNoncleanCardWrapper::clear_card_parallel(CardValue* entry) { 133 while (true) { 134 // In the parallel case, we may have to do this several times. 135 CardValue entry_val = *entry; 136 assert(entry_val != CardTableRS::clean_card_val(), 137 "We shouldn't be looking at clean cards, and this should " 138 "be the only place they get cleaned."); 139 if (CardTableRS::card_is_dirty_wrt_gen_iter(entry_val) 140 || _ct->is_prev_youngergen_card_val(entry_val)) { 141 CardValue res = 142 Atomic::cmpxchg(CardTableRS::clean_card_val(), entry, entry_val); 143 if (res == entry_val) { 144 break; 145 } else { 146 assert(res == CardTableRS::cur_youngergen_and_prev_nonclean_card, 147 "The CAS above should only fail if another thread did " 148 "a GC write barrier."); 149 } 150 } else if (entry_val == 151 CardTableRS::cur_youngergen_and_prev_nonclean_card) { 152 // Parallelism shouldn't matter in this case. Only the thread 153 // assigned to scan the card should change this value. 154 *entry = _ct->cur_youngergen_card_val(); 155 break; 156 } else { 157 assert(entry_val == _ct->cur_youngergen_card_val(), 158 "Should be the only possibility."); 159 // In this case, the card was clean before, and become 160 // cur_youngergen only because of processing of a promoted object. 161 // We don't have to look at the card. 162 return false; 163 } 164 } 165 return true; 166 } 167 168 169 inline bool ClearNoncleanCardWrapper::clear_card_serial(CardValue* entry) { 170 CardValue entry_val = *entry; 171 assert(entry_val != CardTableRS::clean_card_val(), 172 "We shouldn't be looking at clean cards, and this should " 173 "be the only place they get cleaned."); 174 assert(entry_val != CardTableRS::cur_youngergen_and_prev_nonclean_card, 175 "This should be possible in the sequential case."); 176 *entry = CardTableRS::clean_card_val(); 177 return true; 178 } 179 180 ClearNoncleanCardWrapper::ClearNoncleanCardWrapper( 181 DirtyCardToOopClosure* dirty_card_closure, CardTableRS* ct, bool is_par) : 182 _dirty_card_closure(dirty_card_closure), _ct(ct), _is_par(is_par) { 183 } 184 185 bool ClearNoncleanCardWrapper::is_word_aligned(CardTable::CardValue* entry) { 186 return (((intptr_t)entry) & (BytesPerWord-1)) == 0; 187 } 188 189 // The regions are visited in *decreasing* address order. 190 // This order aids with imprecise card marking, where a dirty 191 // card may cause scanning, and summarization marking, of objects 192 // that extend onto subsequent cards. 193 void ClearNoncleanCardWrapper::do_MemRegion(MemRegion mr) { 194 assert(mr.word_size() > 0, "Error"); 195 assert(_ct->is_aligned(mr.start()), "mr.start() should be card aligned"); 196 // mr.end() may not necessarily be card aligned. 197 CardValue* cur_entry = _ct->byte_for(mr.last()); 198 const CardValue* limit = _ct->byte_for(mr.start()); 199 HeapWord* end_of_non_clean = mr.end(); 200 HeapWord* start_of_non_clean = end_of_non_clean; 201 while (cur_entry >= limit) { 202 HeapWord* cur_hw = _ct->addr_for(cur_entry); 203 if ((*cur_entry != CardTableRS::clean_card_val()) && clear_card(cur_entry)) { 204 // Continue the dirty range by opening the 205 // dirty window one card to the left. 206 start_of_non_clean = cur_hw; 207 } else { 208 // We hit a "clean" card; process any non-empty 209 // "dirty" range accumulated so far. 210 if (start_of_non_clean < end_of_non_clean) { 211 const MemRegion mrd(start_of_non_clean, end_of_non_clean); 212 _dirty_card_closure->do_MemRegion(mrd); 213 } 214 215 // fast forward through potential continuous whole-word range of clean cards beginning at a word-boundary 216 if (is_word_aligned(cur_entry)) { 217 CardValue* cur_row = cur_entry - BytesPerWord; 218 while (cur_row >= limit && *((intptr_t*)cur_row) == CardTableRS::clean_card_row_val()) { 219 cur_row -= BytesPerWord; 220 } 221 cur_entry = cur_row + BytesPerWord; 222 cur_hw = _ct->addr_for(cur_entry); 223 } 224 225 // Reset the dirty window, while continuing to look 226 // for the next dirty card that will start a 227 // new dirty window. 228 end_of_non_clean = cur_hw; 229 start_of_non_clean = cur_hw; 230 } 231 // Note that "cur_entry" leads "start_of_non_clean" in 232 // its leftward excursion after this point 233 // in the loop and, when we hit the left end of "mr", 234 // will point off of the left end of the card-table 235 // for "mr". 236 cur_entry--; 237 } 238 // If the first card of "mr" was dirty, we will have 239 // been left with a dirty window, co-initial with "mr", 240 // which we now process. 241 if (start_of_non_clean < end_of_non_clean) { 242 const MemRegion mrd(start_of_non_clean, end_of_non_clean); 243 _dirty_card_closure->do_MemRegion(mrd); 244 } 245 } 246 247 // clean (by dirty->clean before) ==> cur_younger_gen 248 // dirty ==> cur_youngergen_and_prev_nonclean_card 249 // precleaned ==> cur_youngergen_and_prev_nonclean_card 250 // prev-younger-gen ==> cur_youngergen_and_prev_nonclean_card 251 // cur-younger-gen ==> cur_younger_gen 252 // cur_youngergen_and_prev_nonclean_card ==> no change. 253 void CardTableRS::write_ref_field_gc_par(void* field, oop new_val) { 254 volatile CardValue* entry = byte_for(field); 255 do { 256 CardValue entry_val = *entry; 257 // We put this first because it's probably the most common case. 258 if (entry_val == clean_card_val()) { 259 // No threat of contention with cleaning threads. 260 *entry = cur_youngergen_card_val(); 261 return; 262 } else if (card_is_dirty_wrt_gen_iter(entry_val) 263 || is_prev_youngergen_card_val(entry_val)) { 264 // Mark it as both cur and prev youngergen; card cleaning thread will 265 // eventually remove the previous stuff. 266 CardValue new_val = cur_youngergen_and_prev_nonclean_card; 267 CardValue res = Atomic::cmpxchg(new_val, entry, entry_val); 268 // Did the CAS succeed? 269 if (res == entry_val) return; 270 // Otherwise, retry, to see the new value. 271 continue; 272 } else { 273 assert(entry_val == cur_youngergen_and_prev_nonclean_card 274 || entry_val == cur_youngergen_card_val(), 275 "should be only possibilities."); 276 return; 277 } 278 } while (true); 279 } 280 281 void CardTableRS::younger_refs_in_space_iterate(Space* sp, 282 OopsInGenClosure* cl, 283 uint n_threads) { 284 verify_used_region_at_save_marks(sp); 285 286 const MemRegion urasm = sp->used_region_at_save_marks(); 287 non_clean_card_iterate_possibly_parallel(sp, urasm, cl, this, n_threads); 288 } 289 290 #ifdef ASSERT 291 void CardTableRS::verify_used_region_at_save_marks(Space* sp) const { 292 MemRegion ur = sp->used_region(); 293 MemRegion urasm = sp->used_region_at_save_marks(); 294 295 assert(ur.contains(urasm), 296 "Did you forget to call save_marks()? " 297 "[" PTR_FORMAT ", " PTR_FORMAT ") is not contained in " 298 "[" PTR_FORMAT ", " PTR_FORMAT ")", 299 p2i(urasm.start()), p2i(urasm.end()), p2i(ur.start()), p2i(ur.end())); 300 } 301 #endif 302 303 void CardTableRS::clear_into_younger(Generation* old_gen) { 304 assert(GenCollectedHeap::heap()->is_old_gen(old_gen), 305 "Should only be called for the old generation"); 306 // The card tables for the youngest gen need never be cleared. 307 // There's a bit of subtlety in the clear() and invalidate() 308 // methods that we exploit here and in invalidate_or_clear() 309 // below to avoid missing cards at the fringes. If clear() or 310 // invalidate() are changed in the future, this code should 311 // be revisited. 20040107.ysr 312 clear(old_gen->prev_used_region()); 313 } 314 315 void CardTableRS::invalidate_or_clear(Generation* old_gen) { 316 assert(GenCollectedHeap::heap()->is_old_gen(old_gen), 317 "Should only be called for the old generation"); 318 // Invalidate the cards for the currently occupied part of 319 // the old generation and clear the cards for the 320 // unoccupied part of the generation (if any, making use 321 // of that generation's prev_used_region to determine that 322 // region). No need to do anything for the youngest 323 // generation. Also see note#20040107.ysr above. 324 MemRegion used_mr = old_gen->used_region(); 325 MemRegion to_be_cleared_mr = old_gen->prev_used_region().minus(used_mr); 326 if (!to_be_cleared_mr.is_empty()) { 327 clear(to_be_cleared_mr); 328 } 329 invalidate(used_mr); 330 } 331 332 333 class VerifyCleanCardClosure: public BasicOopIterateClosure { 334 private: 335 HeapWord* _boundary; 336 HeapWord* _begin; 337 HeapWord* _end; 338 protected: 339 template <class T> void do_oop_work(T* p) { 340 HeapWord* jp = (HeapWord*)p; 341 assert(jp >= _begin && jp < _end, 342 "Error: jp " PTR_FORMAT " should be within " 343 "[_begin, _end) = [" PTR_FORMAT "," PTR_FORMAT ")", 344 p2i(jp), p2i(_begin), p2i(_end)); 345 oop obj = RawAccess<>::oop_load(p); 346 guarantee(obj == NULL || (HeapWord*)obj >= _boundary, 347 "pointer " PTR_FORMAT " at " PTR_FORMAT " on " 348 "clean card crosses boundary" PTR_FORMAT, 349 p2i(obj), p2i(jp), p2i(_boundary)); 350 } 351 352 public: 353 VerifyCleanCardClosure(HeapWord* b, HeapWord* begin, HeapWord* end) : 354 _boundary(b), _begin(begin), _end(end) { 355 assert(b <= begin, 356 "Error: boundary " PTR_FORMAT " should be at or below begin " PTR_FORMAT, 357 p2i(b), p2i(begin)); 358 assert(begin <= end, 359 "Error: begin " PTR_FORMAT " should be strictly below end " PTR_FORMAT, 360 p2i(begin), p2i(end)); 361 } 362 363 virtual void do_oop(oop* p) { VerifyCleanCardClosure::do_oop_work(p); } 364 virtual void do_oop(narrowOop* p) { VerifyCleanCardClosure::do_oop_work(p); } 365 }; 366 367 class VerifyCTSpaceClosure: public SpaceClosure { 368 private: 369 CardTableRS* _ct; 370 HeapWord* _boundary; 371 public: 372 VerifyCTSpaceClosure(CardTableRS* ct, HeapWord* boundary) : 373 _ct(ct), _boundary(boundary) {} 374 virtual void do_space(Space* s) { _ct->verify_space(s, _boundary); } 375 }; 376 377 class VerifyCTGenClosure: public GenCollectedHeap::GenClosure { 378 CardTableRS* _ct; 379 public: 380 VerifyCTGenClosure(CardTableRS* ct) : _ct(ct) {} 381 void do_generation(Generation* gen) { 382 // Skip the youngest generation. 383 if (GenCollectedHeap::heap()->is_young_gen(gen)) { 384 return; 385 } 386 // Normally, we're interested in pointers to younger generations. 387 VerifyCTSpaceClosure blk(_ct, gen->reserved().start()); 388 gen->space_iterate(&blk, true); 389 } 390 }; 391 392 void CardTableRS::verify_space(Space* s, HeapWord* gen_boundary) { 393 // We don't need to do young-gen spaces. 394 if (s->end() <= gen_boundary) return; 395 MemRegion used = s->used_region(); 396 397 CardValue* cur_entry = byte_for(used.start()); 398 CardValue* limit = byte_after(used.last()); 399 while (cur_entry < limit) { 400 if (*cur_entry == clean_card_val()) { 401 CardValue* first_dirty = cur_entry+1; 402 while (first_dirty < limit && 403 *first_dirty == clean_card_val()) { 404 first_dirty++; 405 } 406 // If the first object is a regular object, and it has a 407 // young-to-old field, that would mark the previous card. 408 HeapWord* boundary = addr_for(cur_entry); 409 HeapWord* end = (first_dirty >= limit) ? used.end() : addr_for(first_dirty); 410 HeapWord* boundary_block = s->block_start(boundary); 411 HeapWord* begin = boundary; // Until proven otherwise. 412 HeapWord* start_block = boundary_block; // Until proven otherwise. 413 if (boundary_block < boundary) { 414 if (s->block_is_obj(boundary_block) && s->obj_is_alive(boundary_block)) { 415 oop boundary_obj = oop(boundary_block); 416 if (!boundary_obj->is_objArray() && 417 !boundary_obj->is_typeArray()) { 418 guarantee(cur_entry > byte_for(used.start()), 419 "else boundary would be boundary_block"); 420 if (*byte_for(boundary_block) != clean_card_val()) { 421 begin = boundary_block + s->block_size(boundary_block); 422 start_block = begin; 423 } 424 } 425 } 426 } 427 // Now traverse objects until end. 428 if (begin < end) { 429 MemRegion mr(begin, end); 430 VerifyCleanCardClosure verify_blk(gen_boundary, begin, end); 431 for (HeapWord* cur = start_block; cur < end; cur += s->block_size(cur)) { 432 if (s->block_is_obj(cur) && s->obj_is_alive(cur)) { 433 oop(cur)->oop_iterate(&verify_blk, mr); 434 } 435 } 436 } 437 cur_entry = first_dirty; 438 } else { 439 // We'd normally expect that cur_youngergen_and_prev_nonclean_card 440 // is a transient value, that cannot be in the card table 441 // except during GC, and thus assert that: 442 // guarantee(*cur_entry != cur_youngergen_and_prev_nonclean_card, 443 // "Illegal CT value"); 444 // That however, need not hold, as will become clear in the 445 // following... 446 447 // We'd normally expect that if we are in the parallel case, 448 // we can't have left a prev value (which would be different 449 // from the current value) in the card table, and so we'd like to 450 // assert that: 451 // guarantee(cur_youngergen_card_val() == youngergen_card 452 // || !is_prev_youngergen_card_val(*cur_entry), 453 // "Illegal CT value"); 454 // That, however, may not hold occasionally, because of 455 // CMS or MSC in the old gen. To wit, consider the 456 // following two simple illustrative scenarios: 457 // (a) CMS: Consider the case where a large object L 458 // spanning several cards is allocated in the old 459 // gen, and has a young gen reference stored in it, dirtying 460 // some interior cards. A young collection scans the card, 461 // finds a young ref and installs a youngergenP_n value. 462 // L then goes dead. Now a CMS collection starts, 463 // finds L dead and sweeps it up. Assume that L is 464 // abutting _unallocated_blk, so _unallocated_blk is 465 // adjusted down to (below) L. Assume further that 466 // no young collection intervenes during this CMS cycle. 467 // The next young gen cycle will not get to look at this 468 // youngergenP_n card since it lies in the unoccupied 469 // part of the space. 470 // Some young collections later the blocks on this 471 // card can be re-allocated either due to direct allocation 472 // or due to absorbing promotions. At this time, the 473 // before-gc verification will fail the above assert. 474 // (b) MSC: In this case, an object L with a young reference 475 // is on a card that (therefore) holds a youngergen_n value. 476 // Suppose also that L lies towards the end of the used 477 // the used space before GC. An MSC collection 478 // occurs that compacts to such an extent that this 479 // card is no longer in the occupied part of the space. 480 // Since current code in MSC does not always clear cards 481 // in the unused part of old gen, this stale youngergen_n 482 // value is left behind and can later be covered by 483 // an object when promotion or direct allocation 484 // re-allocates that part of the heap. 485 // 486 // Fortunately, the presence of such stale card values is 487 // "only" a minor annoyance in that subsequent young collections 488 // might needlessly scan such cards, but would still never corrupt 489 // the heap as a result. However, it's likely not to be a significant 490 // performance inhibitor in practice. For instance, 491 // some recent measurements with unoccupied cards eagerly cleared 492 // out to maintain this invariant, showed next to no 493 // change in young collection times; of course one can construct 494 // degenerate examples where the cost can be significant.) 495 // Note, in particular, that if the "stale" card is modified 496 // after re-allocation, it would be dirty, not "stale". Thus, 497 // we can never have a younger ref in such a card and it is 498 // safe not to scan that card in any collection. [As we see 499 // below, we do some unnecessary scanning 500 // in some cases in the current parallel scanning algorithm.] 501 // 502 // The main point below is that the parallel card scanning code 503 // deals correctly with these stale card values. There are two main 504 // cases to consider where we have a stale "young gen" value and a 505 // "derivative" case to consider, where we have a stale 506 // "cur_younger_gen_and_prev_non_clean" value, as will become 507 // apparent in the case analysis below. 508 // o Case 1. If the stale value corresponds to a younger_gen_n 509 // value other than the cur_younger_gen value then the code 510 // treats this as being tantamount to a prev_younger_gen 511 // card. This means that the card may be unnecessarily scanned. 512 // There are two sub-cases to consider: 513 // o Case 1a. Let us say that the card is in the occupied part 514 // of the generation at the time the collection begins. In 515 // that case the card will be either cleared when it is scanned 516 // for young pointers, or will be set to cur_younger_gen as a 517 // result of promotion. (We have elided the normal case where 518 // the scanning thread and the promoting thread interleave 519 // possibly resulting in a transient 520 // cur_younger_gen_and_prev_non_clean value before settling 521 // to cur_younger_gen. [End Case 1a.] 522 // o Case 1b. Consider now the case when the card is in the unoccupied 523 // part of the space which becomes occupied because of promotions 524 // into it during the current young GC. In this case the card 525 // will never be scanned for young references. The current 526 // code will set the card value to either 527 // cur_younger_gen_and_prev_non_clean or leave 528 // it with its stale value -- because the promotions didn't 529 // result in any younger refs on that card. Of these two 530 // cases, the latter will be covered in Case 1a during 531 // a subsequent scan. To deal with the former case, we need 532 // to further consider how we deal with a stale value of 533 // cur_younger_gen_and_prev_non_clean in our case analysis 534 // below. This we do in Case 3 below. [End Case 1b] 535 // [End Case 1] 536 // o Case 2. If the stale value corresponds to cur_younger_gen being 537 // a value not necessarily written by a current promotion, the 538 // card will not be scanned by the younger refs scanning code. 539 // (This is OK since as we argued above such cards cannot contain 540 // any younger refs.) The result is that this value will be 541 // treated as a prev_younger_gen value in a subsequent collection, 542 // which is addressed in Case 1 above. [End Case 2] 543 // o Case 3. We here consider the "derivative" case from Case 1b. above 544 // because of which we may find a stale 545 // cur_younger_gen_and_prev_non_clean card value in the table. 546 // Once again, as in Case 1, we consider two subcases, depending 547 // on whether the card lies in the occupied or unoccupied part 548 // of the space at the start of the young collection. 549 // o Case 3a. Let us say the card is in the occupied part of 550 // the old gen at the start of the young collection. In that 551 // case, the card will be scanned by the younger refs scanning 552 // code which will set it to cur_younger_gen. In a subsequent 553 // scan, the card will be considered again and get its final 554 // correct value. [End Case 3a] 555 // o Case 3b. Now consider the case where the card is in the 556 // unoccupied part of the old gen, and is occupied as a result 557 // of promotions during thus young gc. In that case, 558 // the card will not be scanned for younger refs. The presence 559 // of newly promoted objects on the card will then result in 560 // its keeping the value cur_younger_gen_and_prev_non_clean 561 // value, which we have dealt with in Case 3 here. [End Case 3b] 562 // [End Case 3] 563 // 564 // (Please refer to the code in the helper class 565 // ClearNonCleanCardWrapper and in CardTable for details.) 566 // 567 // The informal arguments above can be tightened into a formal 568 // correctness proof and it behooves us to write up such a proof, 569 // or to use model checking to prove that there are no lingering 570 // concerns. 571 // 572 // Clearly because of Case 3b one cannot bound the time for 573 // which a card will retain what we have called a "stale" value. 574 // However, one can obtain a Loose upper bound on the redundant 575 // work as a result of such stale values. Note first that any 576 // time a stale card lies in the occupied part of the space at 577 // the start of the collection, it is scanned by younger refs 578 // code and we can define a rank function on card values that 579 // declines when this is so. Note also that when a card does not 580 // lie in the occupied part of the space at the beginning of a 581 // young collection, its rank can either decline or stay unchanged. 582 // In this case, no extra work is done in terms of redundant 583 // younger refs scanning of that card. 584 // Then, the case analysis above reveals that, in the worst case, 585 // any such stale card will be scanned unnecessarily at most twice. 586 // 587 // It is nonetheless advisable to try and get rid of some of this 588 // redundant work in a subsequent (low priority) re-design of 589 // the card-scanning code, if only to simplify the underlying 590 // state machine analysis/proof. ysr 1/28/2002. XXX 591 cur_entry++; 592 } 593 } 594 } 595 596 void CardTableRS::verify() { 597 // At present, we only know how to verify the card table RS for 598 // generational heaps. 599 VerifyCTGenClosure blk(this); 600 GenCollectedHeap::heap()->generation_iterate(&blk, false); 601 CardTable::verify(); 602 } 603 604 CardTableRS::CardTableRS(MemRegion whole_heap, bool scanned_concurrently) : 605 CardTable(whole_heap, scanned_concurrently), 606 _cur_youngergen_card_val(youngergenP1_card), 607 // LNC functionality 608 _lowest_non_clean(NULL), 609 _lowest_non_clean_chunk_size(NULL), 610 _lowest_non_clean_base_chunk_index(NULL), 611 _last_LNC_resizing_collection(NULL) 612 { 613 // max_gens is really GenCollectedHeap::heap()->gen_policy()->number_of_generations() 614 // (which is always 2, young & old), but GenCollectedHeap has not been initialized yet. 615 uint max_gens = 2; 616 _last_cur_val_in_gen = NEW_C_HEAP_ARRAY3(CardValue, max_gens + 1, 617 mtGC, CURRENT_PC, AllocFailStrategy::RETURN_NULL); 618 if (_last_cur_val_in_gen == NULL) { 619 vm_exit_during_initialization("Could not create last_cur_val_in_gen array."); 620 } 621 for (uint i = 0; i < max_gens + 1; i++) { 622 _last_cur_val_in_gen[i] = clean_card_val(); 623 } 624 } 625 626 CardTableRS::~CardTableRS() { 627 if (_last_cur_val_in_gen) { 628 FREE_C_HEAP_ARRAY(CardValue, _last_cur_val_in_gen); 629 _last_cur_val_in_gen = NULL; 630 } 631 if (_lowest_non_clean) { 632 FREE_C_HEAP_ARRAY(CardArr, _lowest_non_clean); 633 _lowest_non_clean = NULL; 634 } 635 if (_lowest_non_clean_chunk_size) { 636 FREE_C_HEAP_ARRAY(size_t, _lowest_non_clean_chunk_size); 637 _lowest_non_clean_chunk_size = NULL; 638 } 639 if (_lowest_non_clean_base_chunk_index) { 640 FREE_C_HEAP_ARRAY(uintptr_t, _lowest_non_clean_base_chunk_index); 641 _lowest_non_clean_base_chunk_index = NULL; 642 } 643 if (_last_LNC_resizing_collection) { 644 FREE_C_HEAP_ARRAY(int, _last_LNC_resizing_collection); 645 _last_LNC_resizing_collection = NULL; 646 } 647 } 648 649 void CardTableRS::initialize() { 650 CardTable::initialize(); 651 _lowest_non_clean = 652 NEW_C_HEAP_ARRAY(CardArr, _max_covered_regions, mtGC); 653 _lowest_non_clean_chunk_size = 654 NEW_C_HEAP_ARRAY(size_t, _max_covered_regions, mtGC); 655 _lowest_non_clean_base_chunk_index = 656 NEW_C_HEAP_ARRAY(uintptr_t, _max_covered_regions, mtGC); 657 _last_LNC_resizing_collection = 658 NEW_C_HEAP_ARRAY(int, _max_covered_regions, mtGC); 659 660 for (int i = 0; i < _max_covered_regions; i++) { 661 _lowest_non_clean[i] = NULL; 662 _lowest_non_clean_chunk_size[i] = 0; 663 _last_LNC_resizing_collection[i] = -1; 664 } 665 } 666 667 bool CardTableRS::card_will_be_scanned(CardValue cv) { 668 return card_is_dirty_wrt_gen_iter(cv) || is_prev_nonclean_card_val(cv); 669 } 670 671 bool CardTableRS::card_may_have_been_dirty(CardValue cv) { 672 return 673 cv != clean_card && 674 (card_is_dirty_wrt_gen_iter(cv) || 675 CardTableRS::youngergen_may_have_been_dirty(cv)); 676 } 677 678 void CardTableRS::non_clean_card_iterate_possibly_parallel( 679 Space* sp, 680 MemRegion mr, 681 OopsInGenClosure* cl, 682 CardTableRS* ct, 683 uint n_threads) 684 { 685 if (!mr.is_empty()) { 686 if (n_threads > 0) { 687 non_clean_card_iterate_parallel_work(sp, mr, cl, ct, n_threads); 688 } else { 689 // clear_cl finds contiguous dirty ranges of cards to process and clear. 690 691 // This is the single-threaded version used by DefNew. 692 const bool parallel = false; 693 694 DirtyCardToOopClosure* dcto_cl = sp->new_dcto_cl(cl, precision(), cl->gen_boundary(), parallel); 695 ClearNoncleanCardWrapper clear_cl(dcto_cl, ct, parallel); 696 697 clear_cl.do_MemRegion(mr); 698 } 699 } 700 } 701 702 void CardTableRS::non_clean_card_iterate_parallel_work(Space* sp, MemRegion mr, 703 OopsInGenClosure* cl, CardTableRS* ct, 704 uint n_threads) { 705 fatal("Parallel gc not supported here."); 706 } 707 708 bool CardTableRS::is_in_young(oop obj) const { 709 return GenCollectedHeap::heap()->is_in_young(obj); 710 }