1 /* 2 * Copyright (c) 2001, 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/cardTableRS.hpp" 27 #include "gc/shared/genCollectedHeap.hpp" 28 #include "gc/shared/generation.hpp" 29 #include "gc/shared/space.inline.hpp" 30 #include "memory/allocation.inline.hpp" 31 #include "oops/access.inline.hpp" 32 #include "oops/oop.inline.hpp" 33 #include "runtime/atomic.hpp" 34 #include "runtime/java.hpp" 35 #include "runtime/os.hpp" 36 #include "utilities/macros.hpp" 37 38 class HasAccumulatedModifiedOopsClosure : public CLDClosure { 39 bool _found; 40 public: 41 HasAccumulatedModifiedOopsClosure() : _found(false) {} 42 void do_cld(ClassLoaderData* cld) { 43 if (_found) { 44 return; 45 } 46 47 if (cld->has_accumulated_modified_oops()) { 48 _found = true; 49 } 50 } 51 bool found() { 52 return _found; 53 } 54 }; 55 56 bool CLDRemSet::mod_union_is_clear() { 57 HasAccumulatedModifiedOopsClosure closure; 58 ClassLoaderDataGraph::cld_do(&closure); 59 60 return !closure.found(); 61 } 62 63 64 class ClearCLDModUnionClosure : public CLDClosure { 65 public: 66 void do_cld(ClassLoaderData* cld) { 67 if (cld->has_accumulated_modified_oops()) { 68 cld->clear_accumulated_modified_oops(); 69 } 70 } 71 }; 72 73 void CLDRemSet::clear_mod_union() { 74 ClearCLDModUnionClosure closure; 75 ClassLoaderDataGraph::cld_do(&closure); 76 } 77 78 79 jbyte CardTableRS::find_unused_youngergenP_card_value() { 80 for (jbyte v = youngergenP1_card; 81 v < cur_youngergen_and_prev_nonclean_card; 82 v++) { 83 bool seen = false; 84 for (int g = 0; g < _regions_to_iterate; g++) { 85 if (_last_cur_val_in_gen[g] == v) { 86 seen = true; 87 break; 88 } 89 } 90 if (!seen) { 91 return v; 92 } 93 } 94 ShouldNotReachHere(); 95 return 0; 96 } 97 98 void CardTableRS::prepare_for_younger_refs_iterate(bool parallel) { 99 // Parallel or sequential, we must always set the prev to equal the 100 // last one written. 101 if (parallel) { 102 // Find a parallel value to be used next. 103 jbyte next_val = find_unused_youngergenP_card_value(); 104 set_cur_youngergen_card_val(next_val); 105 106 } else { 107 // In an sequential traversal we will always write youngergen, so that 108 // the inline barrier is correct. 109 set_cur_youngergen_card_val(youngergen_card); 110 } 111 } 112 113 void CardTableRS::younger_refs_iterate(Generation* g, 114 OopsInGenClosure* blk, 115 uint n_threads) { 116 // The indexing in this array is slightly odd. We want to access 117 // the old generation record here, which is at index 2. 118 _last_cur_val_in_gen[2] = cur_youngergen_card_val(); 119 g->younger_refs_iterate(blk, n_threads); 120 } 121 122 inline bool ClearNoncleanCardWrapper::clear_card(jbyte* entry) { 123 if (_is_par) { 124 return clear_card_parallel(entry); 125 } else { 126 return clear_card_serial(entry); 127 } 128 } 129 130 inline bool ClearNoncleanCardWrapper::clear_card_parallel(jbyte* entry) { 131 while (true) { 132 // In the parallel case, we may have to do this several times. 133 jbyte entry_val = *entry; 134 assert(entry_val != CardTableRS::clean_card_val(), 135 "We shouldn't be looking at clean cards, and this should " 136 "be the only place they get cleaned."); 137 if (CardTableRS::card_is_dirty_wrt_gen_iter(entry_val) 138 || _ct->is_prev_youngergen_card_val(entry_val)) { 139 jbyte res = 140 Atomic::cmpxchg(CardTableRS::clean_card_val(), entry, entry_val); 141 if (res == entry_val) { 142 break; 143 } else { 144 assert(res == CardTableRS::cur_youngergen_and_prev_nonclean_card, 145 "The CAS above should only fail if another thread did " 146 "a GC write barrier."); 147 } 148 } else if (entry_val == 149 CardTableRS::cur_youngergen_and_prev_nonclean_card) { 150 // Parallelism shouldn't matter in this case. Only the thread 151 // assigned to scan the card should change this value. 152 *entry = _ct->cur_youngergen_card_val(); 153 break; 154 } else { 155 assert(entry_val == _ct->cur_youngergen_card_val(), 156 "Should be the only possibility."); 157 // In this case, the card was clean before, and become 158 // cur_youngergen only because of processing of a promoted object. 159 // We don't have to look at the card. 160 return false; 161 } 162 } 163 return true; 164 } 165 166 167 inline bool ClearNoncleanCardWrapper::clear_card_serial(jbyte* entry) { 168 jbyte entry_val = *entry; 169 assert(entry_val != CardTableRS::clean_card_val(), 170 "We shouldn't be looking at clean cards, and this should " 171 "be the only place they get cleaned."); 172 assert(entry_val != CardTableRS::cur_youngergen_and_prev_nonclean_card, 173 "This should be possible in the sequential case."); 174 *entry = CardTableRS::clean_card_val(); 175 return true; 176 } 177 178 ClearNoncleanCardWrapper::ClearNoncleanCardWrapper( 179 DirtyCardToOopClosure* dirty_card_closure, CardTableRS* ct, bool is_par) : 180 _dirty_card_closure(dirty_card_closure), _ct(ct), _is_par(is_par) { 181 } 182 183 bool ClearNoncleanCardWrapper::is_word_aligned(jbyte* entry) { 184 return (((intptr_t)entry) & (BytesPerWord-1)) == 0; 185 } 186 187 // The regions are visited in *decreasing* address order. 188 // This order aids with imprecise card marking, where a dirty 189 // card may cause scanning, and summarization marking, of objects 190 // that extend onto subsequent cards. 191 void ClearNoncleanCardWrapper::do_MemRegion(MemRegion mr) { 192 assert(mr.word_size() > 0, "Error"); 193 assert(_ct->is_aligned(mr.start()), "mr.start() should be card aligned"); 194 // mr.end() may not necessarily be card aligned. 195 jbyte* cur_entry = _ct->byte_for(mr.last()); 196 const jbyte* limit = _ct->byte_for(mr.start()); 197 HeapWord* end_of_non_clean = mr.end(); 198 HeapWord* start_of_non_clean = end_of_non_clean; 199 while (cur_entry >= limit) { 200 HeapWord* cur_hw = _ct->addr_for(cur_entry); 201 if ((*cur_entry != CardTableRS::clean_card_val()) && clear_card(cur_entry)) { 202 // Continue the dirty range by opening the 203 // dirty window one card to the left. 204 start_of_non_clean = cur_hw; 205 } else { 206 // We hit a "clean" card; process any non-empty 207 // "dirty" range accumulated so far. 208 if (start_of_non_clean < end_of_non_clean) { 209 const MemRegion mrd(start_of_non_clean, end_of_non_clean); 210 _dirty_card_closure->do_MemRegion(mrd); 211 } 212 213 // fast forward through potential continuous whole-word range of clean cards beginning at a word-boundary 214 if (is_word_aligned(cur_entry)) { 215 jbyte* cur_row = cur_entry - BytesPerWord; 216 while (cur_row >= limit && *((intptr_t*)cur_row) == CardTableRS::clean_card_row_val()) { 217 cur_row -= BytesPerWord; 218 } 219 cur_entry = cur_row + BytesPerWord; 220 cur_hw = _ct->addr_for(cur_entry); 221 } 222 223 // Reset the dirty window, while continuing to look 224 // for the next dirty card that will start a 225 // new dirty window. 226 end_of_non_clean = cur_hw; 227 start_of_non_clean = cur_hw; 228 } 229 // Note that "cur_entry" leads "start_of_non_clean" in 230 // its leftward excursion after this point 231 // in the loop and, when we hit the left end of "mr", 232 // will point off of the left end of the card-table 233 // for "mr". 234 cur_entry--; 235 } 236 // If the first card of "mr" was dirty, we will have 237 // been left with a dirty window, co-initial with "mr", 238 // which we now process. 239 if (start_of_non_clean < end_of_non_clean) { 240 const MemRegion mrd(start_of_non_clean, end_of_non_clean); 241 _dirty_card_closure->do_MemRegion(mrd); 242 } 243 } 244 245 // clean (by dirty->clean before) ==> cur_younger_gen 246 // dirty ==> cur_youngergen_and_prev_nonclean_card 247 // precleaned ==> cur_youngergen_and_prev_nonclean_card 248 // prev-younger-gen ==> cur_youngergen_and_prev_nonclean_card 249 // cur-younger-gen ==> cur_younger_gen 250 // cur_youngergen_and_prev_nonclean_card ==> no change. 251 void CardTableRS::write_ref_field_gc_par(void* field, oop new_val) { 252 volatile jbyte* entry = byte_for(field); 253 do { 254 jbyte entry_val = *entry; 255 // We put this first because it's probably the most common case. 256 if (entry_val == clean_card_val()) { 257 // No threat of contention with cleaning threads. 258 *entry = cur_youngergen_card_val(); 259 return; 260 } else if (card_is_dirty_wrt_gen_iter(entry_val) 261 || is_prev_youngergen_card_val(entry_val)) { 262 // Mark it as both cur and prev youngergen; card cleaning thread will 263 // eventually remove the previous stuff. 264 jbyte new_val = cur_youngergen_and_prev_nonclean_card; 265 jbyte res = Atomic::cmpxchg(new_val, entry, entry_val); 266 // Did the CAS succeed? 267 if (res == entry_val) return; 268 // Otherwise, retry, to see the new value. 269 continue; 270 } else { 271 assert(entry_val == cur_youngergen_and_prev_nonclean_card 272 || entry_val == cur_youngergen_card_val(), 273 "should be only possibilities."); 274 return; 275 } 276 } while (true); 277 } 278 279 void CardTableRS::younger_refs_in_space_iterate(Space* sp, 280 OopsInGenClosure* cl, 281 uint n_threads) { 282 verify_used_region_at_save_marks(sp); 283 284 const MemRegion urasm = sp->used_region_at_save_marks(); 285 non_clean_card_iterate_possibly_parallel(sp, urasm, cl, this, n_threads); 286 } 287 288 #ifdef ASSERT 289 void CardTableRS::verify_used_region_at_save_marks(Space* sp) const { 290 MemRegion ur = sp->used_region(); 291 MemRegion urasm = sp->used_region_at_save_marks(); 292 293 assert(ur.contains(urasm), 294 "Did you forget to call save_marks()? " 295 "[" PTR_FORMAT ", " PTR_FORMAT ") is not contained in " 296 "[" PTR_FORMAT ", " PTR_FORMAT ")", 297 p2i(urasm.start()), p2i(urasm.end()), p2i(ur.start()), p2i(ur.end())); 298 } 299 #endif 300 301 void CardTableRS::clear_into_younger(Generation* old_gen) { 302 assert(GenCollectedHeap::heap()->is_old_gen(old_gen), 303 "Should only be called for the old generation"); 304 // The card tables for the youngest gen need never be cleared. 305 // There's a bit of subtlety in the clear() and invalidate() 306 // methods that we exploit here and in invalidate_or_clear() 307 // below to avoid missing cards at the fringes. If clear() or 308 // invalidate() are changed in the future, this code should 309 // be revisited. 20040107.ysr 310 clear(old_gen->prev_used_region()); 311 } 312 313 void CardTableRS::invalidate_or_clear(Generation* old_gen) { 314 assert(GenCollectedHeap::heap()->is_old_gen(old_gen), 315 "Should only be called for the old generation"); 316 // Invalidate the cards for the currently occupied part of 317 // the old generation and clear the cards for the 318 // unoccupied part of the generation (if any, making use 319 // of that generation's prev_used_region to determine that 320 // region). No need to do anything for the youngest 321 // generation. Also see note#20040107.ysr above. 322 MemRegion used_mr = old_gen->used_region(); 323 MemRegion to_be_cleared_mr = old_gen->prev_used_region().minus(used_mr); 324 if (!to_be_cleared_mr.is_empty()) { 325 clear(to_be_cleared_mr); 326 } 327 invalidate(used_mr); 328 } 329 330 331 class VerifyCleanCardClosure: public OopClosure { 332 private: 333 HeapWord* _boundary; 334 HeapWord* _begin; 335 HeapWord* _end; 336 protected: 337 template <class T> void do_oop_work(T* p) { 338 HeapWord* jp = (HeapWord*)p; 339 assert(jp >= _begin && jp < _end, 340 "Error: jp " PTR_FORMAT " should be within " 341 "[_begin, _end) = [" PTR_FORMAT "," PTR_FORMAT ")", 342 p2i(jp), p2i(_begin), p2i(_end)); 343 oop obj = RawAccess<>::oop_load(p); 344 guarantee(obj == NULL || (HeapWord*)obj >= _boundary, 345 "pointer " PTR_FORMAT " at " PTR_FORMAT " on " 346 "clean card crosses boundary" PTR_FORMAT, 347 p2i(obj), p2i(jp), p2i(_boundary)); 348 } 349 350 public: 351 VerifyCleanCardClosure(HeapWord* b, HeapWord* begin, HeapWord* end) : 352 _boundary(b), _begin(begin), _end(end) { 353 assert(b <= begin, 354 "Error: boundary " PTR_FORMAT " should be at or below begin " PTR_FORMAT, 355 p2i(b), p2i(begin)); 356 assert(begin <= end, 357 "Error: begin " PTR_FORMAT " should be strictly below end " PTR_FORMAT, 358 p2i(begin), p2i(end)); 359 } 360 361 virtual void do_oop(oop* p) { VerifyCleanCardClosure::do_oop_work(p); } 362 virtual void do_oop(narrowOop* p) { VerifyCleanCardClosure::do_oop_work(p); } 363 }; 364 365 class VerifyCTSpaceClosure: public SpaceClosure { 366 private: 367 CardTableRS* _ct; 368 HeapWord* _boundary; 369 public: 370 VerifyCTSpaceClosure(CardTableRS* ct, HeapWord* boundary) : 371 _ct(ct), _boundary(boundary) {} 372 virtual void do_space(Space* s) { _ct->verify_space(s, _boundary); } 373 }; 374 375 class VerifyCTGenClosure: public GenCollectedHeap::GenClosure { 376 CardTableRS* _ct; 377 public: 378 VerifyCTGenClosure(CardTableRS* ct) : _ct(ct) {} 379 void do_generation(Generation* gen) { 380 // Skip the youngest generation. 381 if (GenCollectedHeap::heap()->is_young_gen(gen)) { 382 return; 383 } 384 // Normally, we're interested in pointers to younger generations. 385 VerifyCTSpaceClosure blk(_ct, gen->reserved().start()); 386 gen->space_iterate(&blk, true); 387 } 388 }; 389 390 void CardTableRS::verify_space(Space* s, HeapWord* gen_boundary) { 391 // We don't need to do young-gen spaces. 392 if (s->end() <= gen_boundary) return; 393 MemRegion used = s->used_region(); 394 395 jbyte* cur_entry = byte_for(used.start()); 396 jbyte* limit = byte_after(used.last()); 397 while (cur_entry < limit) { 398 if (*cur_entry == clean_card_val()) { 399 jbyte* first_dirty = cur_entry+1; 400 while (first_dirty < limit && 401 *first_dirty == clean_card_val()) { 402 first_dirty++; 403 } 404 // If the first object is a regular object, and it has a 405 // young-to-old field, that would mark the previous card. 406 HeapWord* boundary = addr_for(cur_entry); 407 HeapWord* end = (first_dirty >= limit) ? used.end() : addr_for(first_dirty); 408 HeapWord* boundary_block = s->block_start(boundary); 409 HeapWord* begin = boundary; // Until proven otherwise. 410 HeapWord* start_block = boundary_block; // Until proven otherwise. 411 if (boundary_block < boundary) { 412 if (s->block_is_obj(boundary_block) && s->obj_is_alive(boundary_block)) { 413 oop boundary_obj = oop(boundary_block); 414 if (!boundary_obj->is_objArray() && 415 !boundary_obj->is_typeArray()) { 416 guarantee(cur_entry > byte_for(used.start()), 417 "else boundary would be boundary_block"); 418 if (*byte_for(boundary_block) != clean_card_val()) { 419 begin = boundary_block + s->block_size(boundary_block); 420 start_block = begin; 421 } 422 } 423 } 424 } 425 // Now traverse objects until end. 426 if (begin < end) { 427 MemRegion mr(begin, end); 428 VerifyCleanCardClosure verify_blk(gen_boundary, begin, end); 429 for (HeapWord* cur = start_block; cur < end; cur += s->block_size(cur)) { 430 if (s->block_is_obj(cur) && s->obj_is_alive(cur)) { 431 oop(cur)->oop_iterate_no_header(&verify_blk, mr); 432 } 433 } 434 } 435 cur_entry = first_dirty; 436 } else { 437 // We'd normally expect that cur_youngergen_and_prev_nonclean_card 438 // is a transient value, that cannot be in the card table 439 // except during GC, and thus assert that: 440 // guarantee(*cur_entry != cur_youngergen_and_prev_nonclean_card, 441 // "Illegal CT value"); 442 // That however, need not hold, as will become clear in the 443 // following... 444 445 // We'd normally expect that if we are in the parallel case, 446 // we can't have left a prev value (which would be different 447 // from the current value) in the card table, and so we'd like to 448 // assert that: 449 // guarantee(cur_youngergen_card_val() == youngergen_card 450 // || !is_prev_youngergen_card_val(*cur_entry), 451 // "Illegal CT value"); 452 // That, however, may not hold occasionally, because of 453 // CMS or MSC in the old gen. To wit, consider the 454 // following two simple illustrative scenarios: 455 // (a) CMS: Consider the case where a large object L 456 // spanning several cards is allocated in the old 457 // gen, and has a young gen reference stored in it, dirtying 458 // some interior cards. A young collection scans the card, 459 // finds a young ref and installs a youngergenP_n value. 460 // L then goes dead. Now a CMS collection starts, 461 // finds L dead and sweeps it up. Assume that L is 462 // abutting _unallocated_blk, so _unallocated_blk is 463 // adjusted down to (below) L. Assume further that 464 // no young collection intervenes during this CMS cycle. 465 // The next young gen cycle will not get to look at this 466 // youngergenP_n card since it lies in the unoccupied 467 // part of the space. 468 // Some young collections later the blocks on this 469 // card can be re-allocated either due to direct allocation 470 // or due to absorbing promotions. At this time, the 471 // before-gc verification will fail the above assert. 472 // (b) MSC: In this case, an object L with a young reference 473 // is on a card that (therefore) holds a youngergen_n value. 474 // Suppose also that L lies towards the end of the used 475 // the used space before GC. An MSC collection 476 // occurs that compacts to such an extent that this 477 // card is no longer in the occupied part of the space. 478 // Since current code in MSC does not always clear cards 479 // in the unused part of old gen, this stale youngergen_n 480 // value is left behind and can later be covered by 481 // an object when promotion or direct allocation 482 // re-allocates that part of the heap. 483 // 484 // Fortunately, the presence of such stale card values is 485 // "only" a minor annoyance in that subsequent young collections 486 // might needlessly scan such cards, but would still never corrupt 487 // the heap as a result. However, it's likely not to be a significant 488 // performance inhibitor in practice. For instance, 489 // some recent measurements with unoccupied cards eagerly cleared 490 // out to maintain this invariant, showed next to no 491 // change in young collection times; of course one can construct 492 // degenerate examples where the cost can be significant.) 493 // Note, in particular, that if the "stale" card is modified 494 // after re-allocation, it would be dirty, not "stale". Thus, 495 // we can never have a younger ref in such a card and it is 496 // safe not to scan that card in any collection. [As we see 497 // below, we do some unnecessary scanning 498 // in some cases in the current parallel scanning algorithm.] 499 // 500 // The main point below is that the parallel card scanning code 501 // deals correctly with these stale card values. There are two main 502 // cases to consider where we have a stale "young gen" value and a 503 // "derivative" case to consider, where we have a stale 504 // "cur_younger_gen_and_prev_non_clean" value, as will become 505 // apparent in the case analysis below. 506 // o Case 1. If the stale value corresponds to a younger_gen_n 507 // value other than the cur_younger_gen value then the code 508 // treats this as being tantamount to a prev_younger_gen 509 // card. This means that the card may be unnecessarily scanned. 510 // There are two sub-cases to consider: 511 // o Case 1a. Let us say that the card is in the occupied part 512 // of the generation at the time the collection begins. In 513 // that case the card will be either cleared when it is scanned 514 // for young pointers, or will be set to cur_younger_gen as a 515 // result of promotion. (We have elided the normal case where 516 // the scanning thread and the promoting thread interleave 517 // possibly resulting in a transient 518 // cur_younger_gen_and_prev_non_clean value before settling 519 // to cur_younger_gen. [End Case 1a.] 520 // o Case 1b. Consider now the case when the card is in the unoccupied 521 // part of the space which becomes occupied because of promotions 522 // into it during the current young GC. In this case the card 523 // will never be scanned for young references. The current 524 // code will set the card value to either 525 // cur_younger_gen_and_prev_non_clean or leave 526 // it with its stale value -- because the promotions didn't 527 // result in any younger refs on that card. Of these two 528 // cases, the latter will be covered in Case 1a during 529 // a subsequent scan. To deal with the former case, we need 530 // to further consider how we deal with a stale value of 531 // cur_younger_gen_and_prev_non_clean in our case analysis 532 // below. This we do in Case 3 below. [End Case 1b] 533 // [End Case 1] 534 // o Case 2. If the stale value corresponds to cur_younger_gen being 535 // a value not necessarily written by a current promotion, the 536 // card will not be scanned by the younger refs scanning code. 537 // (This is OK since as we argued above such cards cannot contain 538 // any younger refs.) The result is that this value will be 539 // treated as a prev_younger_gen value in a subsequent collection, 540 // which is addressed in Case 1 above. [End Case 2] 541 // o Case 3. We here consider the "derivative" case from Case 1b. above 542 // because of which we may find a stale 543 // cur_younger_gen_and_prev_non_clean card value in the table. 544 // Once again, as in Case 1, we consider two subcases, depending 545 // on whether the card lies in the occupied or unoccupied part 546 // of the space at the start of the young collection. 547 // o Case 3a. Let us say the card is in the occupied part of 548 // the old gen at the start of the young collection. In that 549 // case, the card will be scanned by the younger refs scanning 550 // code which will set it to cur_younger_gen. In a subsequent 551 // scan, the card will be considered again and get its final 552 // correct value. [End Case 3a] 553 // o Case 3b. Now consider the case where the card is in the 554 // unoccupied part of the old gen, and is occupied as a result 555 // of promotions during thus young gc. In that case, 556 // the card will not be scanned for younger refs. The presence 557 // of newly promoted objects on the card will then result in 558 // its keeping the value cur_younger_gen_and_prev_non_clean 559 // value, which we have dealt with in Case 3 here. [End Case 3b] 560 // [End Case 3] 561 // 562 // (Please refer to the code in the helper class 563 // ClearNonCleanCardWrapper and in CardTable for details.) 564 // 565 // The informal arguments above can be tightened into a formal 566 // correctness proof and it behooves us to write up such a proof, 567 // or to use model checking to prove that there are no lingering 568 // concerns. 569 // 570 // Clearly because of Case 3b one cannot bound the time for 571 // which a card will retain what we have called a "stale" value. 572 // However, one can obtain a Loose upper bound on the redundant 573 // work as a result of such stale values. Note first that any 574 // time a stale card lies in the occupied part of the space at 575 // the start of the collection, it is scanned by younger refs 576 // code and we can define a rank function on card values that 577 // declines when this is so. Note also that when a card does not 578 // lie in the occupied part of the space at the beginning of a 579 // young collection, its rank can either decline or stay unchanged. 580 // In this case, no extra work is done in terms of redundant 581 // younger refs scanning of that card. 582 // Then, the case analysis above reveals that, in the worst case, 583 // any such stale card will be scanned unnecessarily at most twice. 584 // 585 // It is nonetheless advisable to try and get rid of some of this 586 // redundant work in a subsequent (low priority) re-design of 587 // the card-scanning code, if only to simplify the underlying 588 // state machine analysis/proof. ysr 1/28/2002. XXX 589 cur_entry++; 590 } 591 } 592 } 593 594 void CardTableRS::verify() { 595 // At present, we only know how to verify the card table RS for 596 // generational heaps. 597 VerifyCTGenClosure blk(this); 598 GenCollectedHeap::heap()->generation_iterate(&blk, false); 599 CardTable::verify(); 600 } 601 602 CardTableRS::CardTableRS(MemRegion whole_heap, bool scanned_concurrently) : 603 CardTable(whole_heap, scanned_concurrently), 604 _cur_youngergen_card_val(youngergenP1_card), 605 // LNC functionality 606 _lowest_non_clean(NULL), 607 _lowest_non_clean_chunk_size(NULL), 608 _lowest_non_clean_base_chunk_index(NULL), 609 _last_LNC_resizing_collection(NULL) 610 { 611 // max_gens is really GenCollectedHeap::heap()->gen_policy()->number_of_generations() 612 // (which is always 2, young & old), but GenCollectedHeap has not been initialized yet. 613 uint max_gens = 2; 614 _last_cur_val_in_gen = NEW_C_HEAP_ARRAY3(jbyte, max_gens + 1, 615 mtGC, CURRENT_PC, AllocFailStrategy::RETURN_NULL); 616 if (_last_cur_val_in_gen == NULL) { 617 vm_exit_during_initialization("Could not create last_cur_val_in_gen array."); 618 } 619 for (uint i = 0; i < max_gens + 1; i++) { 620 _last_cur_val_in_gen[i] = clean_card_val(); 621 } 622 } 623 624 CardTableRS::~CardTableRS() { 625 if (_last_cur_val_in_gen) { 626 FREE_C_HEAP_ARRAY(jbyte, _last_cur_val_in_gen); 627 _last_cur_val_in_gen = NULL; 628 } 629 if (_lowest_non_clean) { 630 FREE_C_HEAP_ARRAY(CardArr, _lowest_non_clean); 631 _lowest_non_clean = NULL; 632 } 633 if (_lowest_non_clean_chunk_size) { 634 FREE_C_HEAP_ARRAY(size_t, _lowest_non_clean_chunk_size); 635 _lowest_non_clean_chunk_size = NULL; 636 } 637 if (_lowest_non_clean_base_chunk_index) { 638 FREE_C_HEAP_ARRAY(uintptr_t, _lowest_non_clean_base_chunk_index); 639 _lowest_non_clean_base_chunk_index = NULL; 640 } 641 if (_last_LNC_resizing_collection) { 642 FREE_C_HEAP_ARRAY(int, _last_LNC_resizing_collection); 643 _last_LNC_resizing_collection = NULL; 644 } 645 } 646 647 void CardTableRS::initialize() { 648 CardTable::initialize(); 649 _lowest_non_clean = 650 NEW_C_HEAP_ARRAY(CardArr, _max_covered_regions, mtGC); 651 _lowest_non_clean_chunk_size = 652 NEW_C_HEAP_ARRAY(size_t, _max_covered_regions, mtGC); 653 _lowest_non_clean_base_chunk_index = 654 NEW_C_HEAP_ARRAY(uintptr_t, _max_covered_regions, mtGC); 655 _last_LNC_resizing_collection = 656 NEW_C_HEAP_ARRAY(int, _max_covered_regions, mtGC); 657 if (_lowest_non_clean == NULL 658 || _lowest_non_clean_chunk_size == NULL 659 || _lowest_non_clean_base_chunk_index == NULL 660 || _last_LNC_resizing_collection == NULL) 661 vm_exit_during_initialization("couldn't allocate an LNC array."); 662 for (int i = 0; i < _max_covered_regions; i++) { 663 _lowest_non_clean[i] = NULL; 664 _lowest_non_clean_chunk_size[i] = 0; 665 _last_LNC_resizing_collection[i] = -1; 666 } 667 } 668 669 bool CardTableRS::card_will_be_scanned(jbyte cv) { 670 return card_is_dirty_wrt_gen_iter(cv) || is_prev_nonclean_card_val(cv); 671 } 672 673 bool CardTableRS::card_may_have_been_dirty(jbyte cv) { 674 return 675 cv != clean_card && 676 (card_is_dirty_wrt_gen_iter(cv) || 677 CardTableRS::youngergen_may_have_been_dirty(cv)); 678 } 679 680 void CardTableRS::non_clean_card_iterate_possibly_parallel( 681 Space* sp, 682 MemRegion mr, 683 OopsInGenClosure* cl, 684 CardTableRS* ct, 685 uint n_threads) 686 { 687 if (!mr.is_empty()) { 688 if (n_threads > 0) { 689 non_clean_card_iterate_parallel_work(sp, mr, cl, ct, n_threads); 690 } else { 691 // clear_cl finds contiguous dirty ranges of cards to process and clear. 692 693 // This is the single-threaded version used by DefNew. 694 const bool parallel = false; 695 696 DirtyCardToOopClosure* dcto_cl = sp->new_dcto_cl(cl, precision(), cl->gen_boundary(), parallel); 697 ClearNoncleanCardWrapper clear_cl(dcto_cl, ct, parallel); 698 699 clear_cl.do_MemRegion(mr); 700 } 701 } 702 } 703 704 void CardTableRS::non_clean_card_iterate_parallel_work(Space* sp, MemRegion mr, 705 OopsInGenClosure* cl, CardTableRS* ct, 706 uint n_threads) { 707 fatal("Parallel gc not supported here."); 708 } 709 710 bool CardTableRS::is_in_young(oop obj) const { 711 return GenCollectedHeap::heap()->is_in_young(obj); 712 }