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.
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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.
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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/oop.inline.hpp"
32 #include "runtime/atomic.hpp"
33 #include "runtime/java.hpp"
34 #include "runtime/os.hpp"
35 #include "utilities/macros.hpp"
36
37 class HasAccumulatedModifiedOopsClosure : public CLDClosure {
38 bool _found;
39 public:
40 HasAccumulatedModifiedOopsClosure() : _found(false) {}
41 void do_cld(ClassLoaderData* cld) {
42 if (_found) {
43 return;
44 }
45
46 if (cld->has_accumulated_modified_oops()) {
47 _found = true;
48 }
49 }
50 bool found() {
51 return _found;
52 }
53 };
54
55 bool CLDRemSet::mod_union_is_clear() {
56 HasAccumulatedModifiedOopsClosure closure;
57 ClassLoaderDataGraph::cld_do(&closure);
58
59 return !closure.found();
60 }
61
62
63 class ClearCLDModUnionClosure : public CLDClosure {
64 public:
65 void do_cld(ClassLoaderData* cld) {
66 if (cld->has_accumulated_modified_oops()) {
67 cld->clear_accumulated_modified_oops();
68 }
69 }
70 };
71
72 void CLDRemSet::clear_mod_union() {
73 ClearCLDModUnionClosure closure;
74 ClassLoaderDataGraph::cld_do(&closure);
75 }
76
77
78 jbyte CardTableRS::find_unused_youngergenP_card_value() {
79 for (jbyte v = youngergenP1_card;
80 v < cur_youngergen_and_prev_nonclean_card;
81 v++) {
82 bool seen = false;
83 for (int g = 0; g < _regions_to_iterate; g++) {
84 if (_last_cur_val_in_gen[g] == v) {
85 seen = true;
86 break;
87 }
88 }
89 if (!seen) {
90 return v;
91 }
92 }
93 ShouldNotReachHere();
94 return 0;
95 }
96
97 void CardTableRS::prepare_for_younger_refs_iterate(bool parallel) {
98 // Parallel or sequential, we must always set the prev to equal the
99 // last one written.
100 if (parallel) {
101 // Find a parallel value to be used next.
102 jbyte next_val = find_unused_youngergenP_card_value();
103 set_cur_youngergen_card_val(next_val);
104
105 } else {
106 // In an sequential traversal we will always write youngergen, so that
107 // the inline barrier is correct.
108 set_cur_youngergen_card_val(youngergen_card);
109 }
110 }
111
112 void CardTableRS::younger_refs_iterate(Generation* g,
113 OopsInGenClosure* blk,
114 uint n_threads) {
115 // The indexing in this array is slightly odd. We want to access
116 // the old generation record here, which is at index 2.
117 _last_cur_val_in_gen[2] = cur_youngergen_card_val();
118 g->younger_refs_iterate(blk, n_threads);
119 }
120
121 inline bool ClearNoncleanCardWrapper::clear_card(jbyte* entry) {
122 if (_is_par) {
123 return clear_card_parallel(entry);
124 } else {
125 return clear_card_serial(entry);
126 }
127 }
128
129 inline bool ClearNoncleanCardWrapper::clear_card_parallel(jbyte* entry) {
130 while (true) {
131 // In the parallel case, we may have to do this several times.
132 jbyte entry_val = *entry;
133 assert(entry_val != CardTableRS::clean_card_val(),
134 "We shouldn't be looking at clean cards, and this should "
135 "be the only place they get cleaned.");
136 if (CardTableRS::card_is_dirty_wrt_gen_iter(entry_val)
137 || _ct->is_prev_youngergen_card_val(entry_val)) {
138 jbyte res =
139 Atomic::cmpxchg(CardTableRS::clean_card_val(), entry, entry_val);
140 if (res == entry_val) {
141 break;
142 } else {
143 assert(res == CardTableRS::cur_youngergen_and_prev_nonclean_card,
144 "The CAS above should only fail if another thread did "
145 "a GC write barrier.");
146 }
147 } else if (entry_val ==
148 CardTableRS::cur_youngergen_and_prev_nonclean_card) {
149 // Parallelism shouldn't matter in this case. Only the thread
150 // assigned to scan the card should change this value.
151 *entry = _ct->cur_youngergen_card_val();
152 break;
153 } else {
154 assert(entry_val == _ct->cur_youngergen_card_val(),
155 "Should be the only possibility.");
156 // In this case, the card was clean before, and become
157 // cur_youngergen only because of processing of a promoted object.
158 // We don't have to look at the card.
159 return false;
160 }
161 }
162 return true;
163 }
164
165
166 inline bool ClearNoncleanCardWrapper::clear_card_serial(jbyte* entry) {
167 jbyte entry_val = *entry;
168 assert(entry_val != CardTableRS::clean_card_val(),
169 "We shouldn't be looking at clean cards, and this should "
170 "be the only place they get cleaned.");
171 assert(entry_val != CardTableRS::cur_youngergen_and_prev_nonclean_card,
172 "This should be possible in the sequential case.");
173 *entry = CardTableRS::clean_card_val();
174 return true;
175 }
176
177 ClearNoncleanCardWrapper::ClearNoncleanCardWrapper(
178 DirtyCardToOopClosure* dirty_card_closure, CardTableRS* ct, bool is_par) :
179 _dirty_card_closure(dirty_card_closure), _ct(ct), _is_par(is_par) {
180 }
181
182 bool ClearNoncleanCardWrapper::is_word_aligned(jbyte* entry) {
183 return (((intptr_t)entry) & (BytesPerWord-1)) == 0;
184 }
185
186 // The regions are visited in *decreasing* address order.
187 // This order aids with imprecise card marking, where a dirty
188 // card may cause scanning, and summarization marking, of objects
189 // that extend onto subsequent cards.
190 void ClearNoncleanCardWrapper::do_MemRegion(MemRegion mr) {
191 assert(mr.word_size() > 0, "Error");
192 assert(_ct->is_aligned(mr.start()), "mr.start() should be card aligned");
193 // mr.end() may not necessarily be card aligned.
194 jbyte* cur_entry = _ct->byte_for(mr.last());
195 const jbyte* limit = _ct->byte_for(mr.start());
196 HeapWord* end_of_non_clean = mr.end();
197 HeapWord* start_of_non_clean = end_of_non_clean;
198 while (cur_entry >= limit) {
199 HeapWord* cur_hw = _ct->addr_for(cur_entry);
200 if ((*cur_entry != CardTableRS::clean_card_val()) && clear_card(cur_entry)) {
201 // Continue the dirty range by opening the
202 // dirty window one card to the left.
203 start_of_non_clean = cur_hw;
204 } else {
205 // We hit a "clean" card; process any non-empty
206 // "dirty" range accumulated so far.
207 if (start_of_non_clean < end_of_non_clean) {
208 const MemRegion mrd(start_of_non_clean, end_of_non_clean);
209 _dirty_card_closure->do_MemRegion(mrd);
210 }
211
212 // fast forward through potential continuous whole-word range of clean cards beginning at a word-boundary
213 if (is_word_aligned(cur_entry)) {
214 jbyte* cur_row = cur_entry - BytesPerWord;
215 while (cur_row >= limit && *((intptr_t*)cur_row) == CardTableRS::clean_card_row_val()) {
216 cur_row -= BytesPerWord;
217 }
218 cur_entry = cur_row + BytesPerWord;
219 cur_hw = _ct->addr_for(cur_entry);
220 }
221
222 // Reset the dirty window, while continuing to look
223 // for the next dirty card that will start a
224 // new dirty window.
225 end_of_non_clean = cur_hw;
226 start_of_non_clean = cur_hw;
227 }
228 // Note that "cur_entry" leads "start_of_non_clean" in
229 // its leftward excursion after this point
230 // in the loop and, when we hit the left end of "mr",
231 // will point off of the left end of the card-table
232 // for "mr".
233 cur_entry--;
234 }
235 // If the first card of "mr" was dirty, we will have
236 // been left with a dirty window, co-initial with "mr",
237 // which we now process.
238 if (start_of_non_clean < end_of_non_clean) {
239 const MemRegion mrd(start_of_non_clean, end_of_non_clean);
240 _dirty_card_closure->do_MemRegion(mrd);
241 }
242 }
243
244 // clean (by dirty->clean before) ==> cur_younger_gen
245 // dirty ==> cur_youngergen_and_prev_nonclean_card
246 // precleaned ==> cur_youngergen_and_prev_nonclean_card
247 // prev-younger-gen ==> cur_youngergen_and_prev_nonclean_card
248 // cur-younger-gen ==> cur_younger_gen
249 // cur_youngergen_and_prev_nonclean_card ==> no change.
250 void CardTableRS::write_ref_field_gc_par(void* field, oop new_val) {
251 volatile jbyte* entry = byte_for(field);
252 do {
253 jbyte entry_val = *entry;
254 // We put this first because it's probably the most common case.
255 if (entry_val == clean_card_val()) {
256 // No threat of contention with cleaning threads.
257 *entry = cur_youngergen_card_val();
258 return;
259 } else if (card_is_dirty_wrt_gen_iter(entry_val)
260 || is_prev_youngergen_card_val(entry_val)) {
261 // Mark it as both cur and prev youngergen; card cleaning thread will
262 // eventually remove the previous stuff.
263 jbyte new_val = cur_youngergen_and_prev_nonclean_card;
264 jbyte res = Atomic::cmpxchg(new_val, entry, entry_val);
265 // Did the CAS succeed?
266 if (res == entry_val) return;
267 // Otherwise, retry, to see the new value.
268 continue;
269 } else {
270 assert(entry_val == cur_youngergen_and_prev_nonclean_card
271 || entry_val == cur_youngergen_card_val(),
272 "should be only possibilities.");
273 return;
274 }
275 } while (true);
276 }
277
278 void CardTableRS::younger_refs_in_space_iterate(Space* sp,
279 OopsInGenClosure* cl,
280 uint n_threads) {
281 const MemRegion urasm = sp->used_region_at_save_marks();
282 #ifdef ASSERT
283 // Convert the assertion check to a warning if we are running
284 // CMS+ParNew until related bug is fixed.
285 MemRegion ur = sp->used_region();
286 assert(ur.contains(urasm) || (UseConcMarkSweepGC),
287 "Did you forget to call save_marks()? "
288 "[" PTR_FORMAT ", " PTR_FORMAT ") is not contained in "
289 "[" PTR_FORMAT ", " PTR_FORMAT ")",
290 p2i(urasm.start()), p2i(urasm.end()), p2i(ur.start()), p2i(ur.end()));
291 // In the case of CMS+ParNew, issue a warning
292 if (!ur.contains(urasm)) {
293 assert(UseConcMarkSweepGC, "Tautology: see assert above");
294 log_warning(gc)("CMS+ParNew: 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 MemRegion ur2 = sp->used_region();
299 MemRegion urasm2 = sp->used_region_at_save_marks();
300 if (!ur.equals(ur2)) {
301 log_warning(gc)("CMS+ParNew: Flickering used_region()!!");
302 }
303 if (!urasm.equals(urasm2)) {
304 log_warning(gc)("CMS+ParNew: Flickering used_region_at_save_marks()!!");
305 }
306 ShouldNotReachHere();
307 }
308 #endif
309 non_clean_card_iterate_possibly_parallel(sp, urasm, cl, this, n_threads);
310 }
311
312 void CardTableRS::clear_into_younger(Generation* old_gen) {
313 assert(GenCollectedHeap::heap()->is_old_gen(old_gen),
314 "Should only be called for the old generation");
315 // The card tables for the youngest gen need never be cleared.
316 // There's a bit of subtlety in the clear() and invalidate()
317 // methods that we exploit here and in invalidate_or_clear()
318 // below to avoid missing cards at the fringes. If clear() or
319 // invalidate() are changed in the future, this code should
320 // be revisited. 20040107.ysr
321 clear(old_gen->prev_used_region());
322 }
323
324 void CardTableRS::invalidate_or_clear(Generation* old_gen) {
325 assert(GenCollectedHeap::heap()->is_old_gen(old_gen),
326 "Should only be called for the old generation");
327 // Invalidate the cards for the currently occupied part of
328 // the old generation and clear the cards for the
329 // unoccupied part of the generation (if any, making use
330 // of that generation's prev_used_region to determine that
331 // region). No need to do anything for the youngest
332 // generation. Also see note#20040107.ysr above.
333 MemRegion used_mr = old_gen->used_region();
334 MemRegion to_be_cleared_mr = old_gen->prev_used_region().minus(used_mr);
335 if (!to_be_cleared_mr.is_empty()) {
336 clear(to_be_cleared_mr);
337 }
338 invalidate(used_mr);
339 }
340
341
342 class VerifyCleanCardClosure: public OopClosure {
343 private:
344 HeapWord* _boundary;
345 HeapWord* _begin;
346 HeapWord* _end;
347 protected:
348 template <class T> void do_oop_work(T* p) {
349 HeapWord* jp = (HeapWord*)p;
350 assert(jp >= _begin && jp < _end,
351 "Error: jp " PTR_FORMAT " should be within "
352 "[_begin, _end) = [" PTR_FORMAT "," PTR_FORMAT ")",
353 p2i(jp), p2i(_begin), p2i(_end));
354 oop obj = oopDesc::load_decode_heap_oop(p);
355 guarantee(obj == NULL || (HeapWord*)obj >= _boundary,
356 "pointer " PTR_FORMAT " at " PTR_FORMAT " on "
357 "clean card crosses boundary" PTR_FORMAT,
358 p2i(obj), p2i(jp), p2i(_boundary));
359 }
360
361 public:
362 VerifyCleanCardClosure(HeapWord* b, HeapWord* begin, HeapWord* end) :
363 _boundary(b), _begin(begin), _end(end) {
364 assert(b <= begin,
365 "Error: boundary " PTR_FORMAT " should be at or below begin " PTR_FORMAT,
366 p2i(b), p2i(begin));
367 assert(begin <= end,
368 "Error: begin " PTR_FORMAT " should be strictly below end " PTR_FORMAT,
369 p2i(begin), p2i(end));
370 }
371
372 virtual void do_oop(oop* p) { VerifyCleanCardClosure::do_oop_work(p); }
373 virtual void do_oop(narrowOop* p) { VerifyCleanCardClosure::do_oop_work(p); }
374 };
375
376 class VerifyCTSpaceClosure: public SpaceClosure {
377 private:
378 CardTableRS* _ct;
379 HeapWord* _boundary;
380 public:
381 VerifyCTSpaceClosure(CardTableRS* ct, HeapWord* boundary) :
382 _ct(ct), _boundary(boundary) {}
383 virtual void do_space(Space* s) { _ct->verify_space(s, _boundary); }
384 };
385
386 class VerifyCTGenClosure: public GenCollectedHeap::GenClosure {
387 CardTableRS* _ct;
388 public:
389 VerifyCTGenClosure(CardTableRS* ct) : _ct(ct) {}
390 void do_generation(Generation* gen) {
391 // Skip the youngest generation.
392 if (GenCollectedHeap::heap()->is_young_gen(gen)) {
393 return;
394 }
395 // Normally, we're interested in pointers to younger generations.
396 VerifyCTSpaceClosure blk(_ct, gen->reserved().start());
397 gen->space_iterate(&blk, true);
398 }
399 };
400
401 void CardTableRS::verify_space(Space* s, HeapWord* gen_boundary) {
402 // We don't need to do young-gen spaces.
403 if (s->end() <= gen_boundary) return;
404 MemRegion used = s->used_region();
405
406 jbyte* cur_entry = byte_for(used.start());
407 jbyte* limit = byte_after(used.last());
408 while (cur_entry < limit) {
409 if (*cur_entry == clean_card_val()) {
410 jbyte* first_dirty = cur_entry+1;
411 while (first_dirty < limit &&
412 *first_dirty == clean_card_val()) {
413 first_dirty++;
414 }
415 // If the first object is a regular object, and it has a
416 // young-to-old field, that would mark the previous card.
417 HeapWord* boundary = addr_for(cur_entry);
418 HeapWord* end = (first_dirty >= limit) ? used.end() : addr_for(first_dirty);
419 HeapWord* boundary_block = s->block_start(boundary);
420 HeapWord* begin = boundary; // Until proven otherwise.
421 HeapWord* start_block = boundary_block; // Until proven otherwise.
422 if (boundary_block < boundary) {
423 if (s->block_is_obj(boundary_block) && s->obj_is_alive(boundary_block)) {
424 oop boundary_obj = oop(boundary_block);
425 if (!boundary_obj->is_objArray() &&
426 !boundary_obj->is_typeArray()) {
427 guarantee(cur_entry > byte_for(used.start()),
428 "else boundary would be boundary_block");
429 if (*byte_for(boundary_block) != clean_card_val()) {
430 begin = boundary_block + s->block_size(boundary_block);
431 start_block = begin;
432 }
433 }
434 }
435 }
436 // Now traverse objects until end.
437 if (begin < end) {
438 MemRegion mr(begin, end);
439 VerifyCleanCardClosure verify_blk(gen_boundary, begin, end);
440 for (HeapWord* cur = start_block; cur < end; cur += s->block_size(cur)) {
441 if (s->block_is_obj(cur) && s->obj_is_alive(cur)) {
442 oop(cur)->oop_iterate_no_header(&verify_blk, mr);
443 }
444 }
445 }
446 cur_entry = first_dirty;
447 } else {
448 // We'd normally expect that cur_youngergen_and_prev_nonclean_card
449 // is a transient value, that cannot be in the card table
450 // except during GC, and thus assert that:
451 // guarantee(*cur_entry != cur_youngergen_and_prev_nonclean_card,
452 // "Illegal CT value");
453 // That however, need not hold, as will become clear in the
454 // following...
455
456 // We'd normally expect that if we are in the parallel case,
457 // we can't have left a prev value (which would be different
458 // from the current value) in the card table, and so we'd like to
459 // assert that:
460 // guarantee(cur_youngergen_card_val() == youngergen_card
461 // || !is_prev_youngergen_card_val(*cur_entry),
462 // "Illegal CT value");
463 // That, however, may not hold occasionally, because of
464 // CMS or MSC in the old gen. To wit, consider the
465 // following two simple illustrative scenarios:
466 // (a) CMS: Consider the case where a large object L
467 // spanning several cards is allocated in the old
468 // gen, and has a young gen reference stored in it, dirtying
469 // some interior cards. A young collection scans the card,
470 // finds a young ref and installs a youngergenP_n value.
471 // L then goes dead. Now a CMS collection starts,
472 // finds L dead and sweeps it up. Assume that L is
473 // abutting _unallocated_blk, so _unallocated_blk is
474 // adjusted down to (below) L. Assume further that
475 // no young collection intervenes during this CMS cycle.
476 // The next young gen cycle will not get to look at this
477 // youngergenP_n card since it lies in the unoccupied
478 // part of the space.
479 // Some young collections later the blocks on this
480 // card can be re-allocated either due to direct allocation
481 // or due to absorbing promotions. At this time, the
482 // before-gc verification will fail the above assert.
483 // (b) MSC: In this case, an object L with a young reference
484 // is on a card that (therefore) holds a youngergen_n value.
485 // Suppose also that L lies towards the end of the used
486 // the used space before GC. An MSC collection
487 // occurs that compacts to such an extent that this
488 // card is no longer in the occupied part of the space.
489 // Since current code in MSC does not always clear cards
490 // in the unused part of old gen, this stale youngergen_n
491 // value is left behind and can later be covered by
492 // an object when promotion or direct allocation
493 // re-allocates that part of the heap.
494 //
495 // Fortunately, the presence of such stale card values is
496 // "only" a minor annoyance in that subsequent young collections
497 // might needlessly scan such cards, but would still never corrupt
498 // the heap as a result. However, it's likely not to be a significant
499 // performance inhibitor in practice. For instance,
500 // some recent measurements with unoccupied cards eagerly cleared
501 // out to maintain this invariant, showed next to no
502 // change in young collection times; of course one can construct
503 // degenerate examples where the cost can be significant.)
504 // Note, in particular, that if the "stale" card is modified
505 // after re-allocation, it would be dirty, not "stale". Thus,
506 // we can never have a younger ref in such a card and it is
507 // safe not to scan that card in any collection. [As we see
508 // below, we do some unnecessary scanning
509 // in some cases in the current parallel scanning algorithm.]
510 //
511 // The main point below is that the parallel card scanning code
512 // deals correctly with these stale card values. There are two main
513 // cases to consider where we have a stale "young gen" value and a
514 // "derivative" case to consider, where we have a stale
515 // "cur_younger_gen_and_prev_non_clean" value, as will become
516 // apparent in the case analysis below.
517 // o Case 1. If the stale value corresponds to a younger_gen_n
518 // value other than the cur_younger_gen value then the code
519 // treats this as being tantamount to a prev_younger_gen
520 // card. This means that the card may be unnecessarily scanned.
521 // There are two sub-cases to consider:
522 // o Case 1a. Let us say that the card is in the occupied part
523 // of the generation at the time the collection begins. In
524 // that case the card will be either cleared when it is scanned
525 // for young pointers, or will be set to cur_younger_gen as a
526 // result of promotion. (We have elided the normal case where
527 // the scanning thread and the promoting thread interleave
528 // possibly resulting in a transient
529 // cur_younger_gen_and_prev_non_clean value before settling
530 // to cur_younger_gen. [End Case 1a.]
531 // o Case 1b. Consider now the case when the card is in the unoccupied
532 // part of the space which becomes occupied because of promotions
533 // into it during the current young GC. In this case the card
534 // will never be scanned for young references. The current
535 // code will set the card value to either
536 // cur_younger_gen_and_prev_non_clean or leave
537 // it with its stale value -- because the promotions didn't
538 // result in any younger refs on that card. Of these two
539 // cases, the latter will be covered in Case 1a during
540 // a subsequent scan. To deal with the former case, we need
541 // to further consider how we deal with a stale value of
542 // cur_younger_gen_and_prev_non_clean in our case analysis
543 // below. This we do in Case 3 below. [End Case 1b]
544 // [End Case 1]
545 // o Case 2. If the stale value corresponds to cur_younger_gen being
546 // a value not necessarily written by a current promotion, the
547 // card will not be scanned by the younger refs scanning code.
548 // (This is OK since as we argued above such cards cannot contain
549 // any younger refs.) The result is that this value will be
550 // treated as a prev_younger_gen value in a subsequent collection,
551 // which is addressed in Case 1 above. [End Case 2]
552 // o Case 3. We here consider the "derivative" case from Case 1b. above
553 // because of which we may find a stale
554 // cur_younger_gen_and_prev_non_clean card value in the table.
555 // Once again, as in Case 1, we consider two subcases, depending
556 // on whether the card lies in the occupied or unoccupied part
557 // of the space at the start of the young collection.
558 // o Case 3a. Let us say the card is in the occupied part of
559 // the old gen at the start of the young collection. In that
560 // case, the card will be scanned by the younger refs scanning
561 // code which will set it to cur_younger_gen. In a subsequent
562 // scan, the card will be considered again and get its final
563 // correct value. [End Case 3a]
564 // o Case 3b. Now consider the case where the card is in the
565 // unoccupied part of the old gen, and is occupied as a result
566 // of promotions during thus young gc. In that case,
567 // the card will not be scanned for younger refs. The presence
568 // of newly promoted objects on the card will then result in
569 // its keeping the value cur_younger_gen_and_prev_non_clean
570 // value, which we have dealt with in Case 3 here. [End Case 3b]
571 // [End Case 3]
572 //
573 // (Please refer to the code in the helper class
574 // ClearNonCleanCardWrapper and in CardTableModRefBS for details.)
575 //
576 // The informal arguments above can be tightened into a formal
577 // correctness proof and it behooves us to write up such a proof,
578 // or to use model checking to prove that there are no lingering
579 // concerns.
580 //
581 // Clearly because of Case 3b one cannot bound the time for
582 // which a card will retain what we have called a "stale" value.
583 // However, one can obtain a Loose upper bound on the redundant
584 // work as a result of such stale values. Note first that any
585 // time a stale card lies in the occupied part of the space at
586 // the start of the collection, it is scanned by younger refs
587 // code and we can define a rank function on card values that
588 // declines when this is so. Note also that when a card does not
589 // lie in the occupied part of the space at the beginning of a
590 // young collection, its rank can either decline or stay unchanged.
591 // In this case, no extra work is done in terms of redundant
592 // younger refs scanning of that card.
593 // Then, the case analysis above reveals that, in the worst case,
594 // any such stale card will be scanned unnecessarily at most twice.
595 //
596 // It is nonetheless advisable to try and get rid of some of this
597 // redundant work in a subsequent (low priority) re-design of
598 // the card-scanning code, if only to simplify the underlying
599 // state machine analysis/proof. ysr 1/28/2002. XXX
600 cur_entry++;
601 }
602 }
603 }
604
605 void CardTableRS::verify() {
606 // At present, we only know how to verify the card table RS for
607 // generational heaps.
608 VerifyCTGenClosure blk(this);
609 GenCollectedHeap::heap()->generation_iterate(&blk, false);
610 CardTable::verify();
611 }
612
613 CardTableRS::CardTableRS(MemRegion whole_heap) :
614 CardTable(whole_heap, /* scanned concurrently */ UseConcMarkSweepGC && CMSPrecleaningEnabled),
615 _cur_youngergen_card_val(youngergenP1_card),
616 // LNC functionality
617 _lowest_non_clean(NULL),
618 _lowest_non_clean_chunk_size(NULL),
619 _lowest_non_clean_base_chunk_index(NULL),
620 _last_LNC_resizing_collection(NULL)
621 {
622 // max_gens is really GenCollectedHeap::heap()->gen_policy()->number_of_generations()
623 // (which is always 2, young & old), but GenCollectedHeap has not been initialized yet.
624 uint max_gens = 2;
625 _last_cur_val_in_gen = NEW_C_HEAP_ARRAY3(jbyte, max_gens + 1,
626 mtGC, CURRENT_PC, AllocFailStrategy::RETURN_NULL);
627 if (_last_cur_val_in_gen == NULL) {
628 vm_exit_during_initialization("Could not create last_cur_val_in_gen array.");
629 }
630 for (uint i = 0; i < max_gens + 1; i++) {
631 _last_cur_val_in_gen[i] = clean_card_val();
632 }
633 }
634
635 CardTableRS::~CardTableRS() {
636 if (_last_cur_val_in_gen) {
637 FREE_C_HEAP_ARRAY(jbyte, _last_cur_val_in_gen);
638 _last_cur_val_in_gen = NULL;
639 }
640 if (_lowest_non_clean) {
641 FREE_C_HEAP_ARRAY(CardArr, _lowest_non_clean);
642 _lowest_non_clean = NULL;
643 }
644 if (_lowest_non_clean_chunk_size) {
645 FREE_C_HEAP_ARRAY(size_t, _lowest_non_clean_chunk_size);
646 _lowest_non_clean_chunk_size = NULL;
647 }
648 if (_lowest_non_clean_base_chunk_index) {
649 FREE_C_HEAP_ARRAY(uintptr_t, _lowest_non_clean_base_chunk_index);
650 _lowest_non_clean_base_chunk_index = NULL;
651 }
652 if (_last_LNC_resizing_collection) {
653 FREE_C_HEAP_ARRAY(int, _last_LNC_resizing_collection);
654 _last_LNC_resizing_collection = NULL;
655 }
656 }
657
658 void CardTableRS::initialize() {
659 CardTable::initialize();
660 _lowest_non_clean =
661 NEW_C_HEAP_ARRAY(CardArr, _max_covered_regions, mtGC);
662 _lowest_non_clean_chunk_size =
663 NEW_C_HEAP_ARRAY(size_t, _max_covered_regions, mtGC);
664 _lowest_non_clean_base_chunk_index =
665 NEW_C_HEAP_ARRAY(uintptr_t, _max_covered_regions, mtGC);
666 _last_LNC_resizing_collection =
667 NEW_C_HEAP_ARRAY(int, _max_covered_regions, mtGC);
668 if (_lowest_non_clean == NULL
669 || _lowest_non_clean_chunk_size == NULL
670 || _lowest_non_clean_base_chunk_index == NULL
671 || _last_LNC_resizing_collection == NULL)
672 vm_exit_during_initialization("couldn't allocate an LNC array.");
673 for (int i = 0; i < _max_covered_regions; i++) {
674 _lowest_non_clean[i] = NULL;
675 _lowest_non_clean_chunk_size[i] = 0;
676 _last_LNC_resizing_collection[i] = -1;
677 }
678 }
679
680 bool CardTableRS::card_will_be_scanned(jbyte cv) {
681 return card_is_dirty_wrt_gen_iter(cv) || is_prev_nonclean_card_val(cv);
682 }
683
684 bool CardTableRS::card_may_have_been_dirty(jbyte cv) {
685 return
686 cv != clean_card &&
687 (card_is_dirty_wrt_gen_iter(cv) ||
688 CardTableRS::youngergen_may_have_been_dirty(cv));
689 }
690
691 void CardTableRS::non_clean_card_iterate_possibly_parallel(
692 Space* sp,
693 MemRegion mr,
694 OopsInGenClosure* cl,
695 CardTableRS* ct,
696 uint n_threads)
697 {
698 if (!mr.is_empty()) {
699 if (n_threads > 0) {
700 #if INCLUDE_ALL_GCS
701 non_clean_card_iterate_parallel_work(sp, mr, cl, ct, n_threads);
702 #else // INCLUDE_ALL_GCS
703 fatal("Parallel gc not supported here.");
704 #endif // INCLUDE_ALL_GCS
705 } else {
706 // clear_cl finds contiguous dirty ranges of cards to process and clear.
707
708 // This is the single-threaded version used by DefNew.
709 const bool parallel = false;
710
711 DirtyCardToOopClosure* dcto_cl = sp->new_dcto_cl(cl, precision(), cl->gen_boundary(), parallel);
712 ClearNoncleanCardWrapper clear_cl(dcto_cl, ct, parallel);
713
714 clear_cl.do_MemRegion(mr);
715 }
716 }
717 }
718
719 bool CardTableRS::is_in_young(oop obj) const {
720 return GenCollectedHeap::heap()->is_in_young(obj);
721 }