1 /*
2 * Copyright (c) 2001, 2017, 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/parallel/cardTableExtension.hpp"
27 #include "gc/parallel/gcTaskManager.hpp"
28 #include "gc/parallel/objectStartArray.inline.hpp"
29 #include "gc/parallel/parallelScavengeHeap.hpp"
30 #include "gc/parallel/psPromotionManager.inline.hpp"
31 #include "gc/parallel/psScavenge.hpp"
32 #include "gc/parallel/psTasks.hpp"
33 #include "gc/parallel/psYoungGen.hpp"
34 #include "oops/oop.inline.hpp"
35 #include "runtime/prefetch.inline.hpp"
36 #include "utilities/align.hpp"
37
38 // Checks an individual oop for missing precise marks. Mark
39 // may be either dirty or newgen.
40 class CheckForUnmarkedOops : public OopClosure {
41 private:
42 PSYoungGen* _young_gen;
43 CardTableExtension* _card_table;
44 HeapWord* _unmarked_addr;
45
46 protected:
47 template <class T> void do_oop_work(T* p) {
48 oop obj = oopDesc::load_decode_heap_oop(p);
49 if (_young_gen->is_in_reserved(obj) &&
50 !_card_table->addr_is_marked_imprecise(p)) {
51 // Don't overwrite the first missing card mark
52 if (_unmarked_addr == NULL) {
53 _unmarked_addr = (HeapWord*)p;
54 }
55 }
56 }
57
58 public:
59 CheckForUnmarkedOops(PSYoungGen* young_gen, CardTableExtension* card_table) :
60 _young_gen(young_gen), _card_table(card_table), _unmarked_addr(NULL) { }
61
62 virtual void do_oop(oop* p) { CheckForUnmarkedOops::do_oop_work(p); }
63 virtual void do_oop(narrowOop* p) { CheckForUnmarkedOops::do_oop_work(p); }
64
65 bool has_unmarked_oop() {
66 return _unmarked_addr != NULL;
67 }
68 };
69
70 // Checks all objects for the existence of some type of mark,
71 // precise or imprecise, dirty or newgen.
72 class CheckForUnmarkedObjects : public ObjectClosure {
73 private:
74 PSYoungGen* _young_gen;
75 CardTableExtension* _card_table;
76
77 public:
78 CheckForUnmarkedObjects() {
79 ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
80 _young_gen = heap->young_gen();
81 _card_table = barrier_set_cast<CardTableExtension>(heap->barrier_set());
82 // No point in asserting barrier set type here. Need to make CardTableExtension
83 // a unique barrier set type.
84 }
85
86 // Card marks are not precise. The current system can leave us with
87 // a mismatch of precise marks and beginning of object marks. This means
88 // we test for missing precise marks first. If any are found, we don't
89 // fail unless the object head is also unmarked.
90 virtual void do_object(oop obj) {
91 CheckForUnmarkedOops object_check(_young_gen, _card_table);
92 obj->oop_iterate_no_header(&object_check);
93 if (object_check.has_unmarked_oop()) {
94 guarantee(_card_table->addr_is_marked_imprecise(obj), "Found unmarked young_gen object");
95 }
96 }
97 };
98
99 // Checks for precise marking of oops as newgen.
100 class CheckForPreciseMarks : public OopClosure {
101 private:
102 PSYoungGen* _young_gen;
103 CardTableExtension* _card_table;
104
105 protected:
106 template <class T> void do_oop_work(T* p) {
107 oop obj = oopDesc::load_decode_heap_oop_not_null(p);
108 if (_young_gen->is_in_reserved(obj)) {
109 assert(_card_table->addr_is_marked_precise(p), "Found unmarked precise oop");
110 _card_table->set_card_newgen(p);
111 }
112 }
113
114 public:
115 CheckForPreciseMarks( PSYoungGen* young_gen, CardTableExtension* card_table ) :
116 _young_gen(young_gen), _card_table(card_table) { }
117
118 virtual void do_oop(oop* p) { CheckForPreciseMarks::do_oop_work(p); }
119 virtual void do_oop(narrowOop* p) { CheckForPreciseMarks::do_oop_work(p); }
120 };
121
122 // We get passed the space_top value to prevent us from traversing into
123 // the old_gen promotion labs, which cannot be safely parsed.
124
125 // Do not call this method if the space is empty.
126 // It is a waste to start tasks and get here only to
127 // do no work. If this method needs to be called
128 // when the space is empty, fix the calculation of
129 // end_card to allow sp_top == sp->bottom().
130
131 void CardTableExtension::scavenge_contents_parallel(ObjectStartArray* start_array,
132 MutableSpace* sp,
133 HeapWord* space_top,
134 PSPromotionManager* pm,
135 uint stripe_number,
136 uint stripe_total) {
137 int ssize = 128; // Naked constant! Work unit = 64k.
138 int dirty_card_count = 0;
139
140 // It is a waste to get here if empty.
141 assert(sp->bottom() < sp->top(), "Should not be called if empty");
142 oop* sp_top = (oop*)space_top;
143 jbyte* start_card = byte_for(sp->bottom());
144 jbyte* end_card = byte_for(sp_top - 1) + 1;
145 oop* last_scanned = NULL; // Prevent scanning objects more than once
146 // The width of the stripe ssize*stripe_total must be
147 // consistent with the number of stripes so that the complete slice
148 // is covered.
149 size_t slice_width = ssize * stripe_total;
150 for (jbyte* slice = start_card; slice < end_card; slice += slice_width) {
151 jbyte* worker_start_card = slice + stripe_number * ssize;
152 if (worker_start_card >= end_card)
153 return; // We're done.
154
155 jbyte* worker_end_card = worker_start_card + ssize;
156 if (worker_end_card > end_card)
157 worker_end_card = end_card;
158
159 // We do not want to scan objects more than once. In order to accomplish
160 // this, we assert that any object with an object head inside our 'slice'
161 // belongs to us. We may need to extend the range of scanned cards if the
162 // last object continues into the next 'slice'.
163 //
164 // Note! ending cards are exclusive!
165 HeapWord* slice_start = addr_for(worker_start_card);
166 HeapWord* slice_end = MIN2((HeapWord*) sp_top, addr_for(worker_end_card));
167
168 #ifdef ASSERT
169 if (GCWorkerDelayMillis > 0) {
170 // Delay 1 worker so that it proceeds after all the work
171 // has been completed.
172 if (stripe_number < 2) {
173 os::sleep(Thread::current(), GCWorkerDelayMillis, false);
174 }
175 }
176 #endif
177
178 // If there are not objects starting within the chunk, skip it.
179 if (!start_array->object_starts_in_range(slice_start, slice_end)) {
180 continue;
181 }
182 // Update our beginning addr
183 HeapWord* first_object = start_array->object_start(slice_start);
184 debug_only(oop* first_object_within_slice = (oop*) first_object;)
185 if (first_object < slice_start) {
186 last_scanned = (oop*)(first_object + oop(first_object)->size());
187 debug_only(first_object_within_slice = last_scanned;)
188 worker_start_card = byte_for(last_scanned);
189 }
190
191 // Update the ending addr
192 if (slice_end < (HeapWord*)sp_top) {
193 // The subtraction is important! An object may start precisely at slice_end.
194 HeapWord* last_object = start_array->object_start(slice_end - 1);
195 slice_end = last_object + oop(last_object)->size();
196 // worker_end_card is exclusive, so bump it one past the end of last_object's
197 // covered span.
198 worker_end_card = byte_for(slice_end) + 1;
199
200 if (worker_end_card > end_card)
201 worker_end_card = end_card;
202 }
203
204 assert(slice_end <= (HeapWord*)sp_top, "Last object in slice crosses space boundary");
205 assert(is_valid_card_address(worker_start_card), "Invalid worker start card");
206 assert(is_valid_card_address(worker_end_card), "Invalid worker end card");
207 // Note that worker_start_card >= worker_end_card is legal, and happens when
208 // an object spans an entire slice.
209 assert(worker_start_card <= end_card, "worker start card beyond end card");
210 assert(worker_end_card <= end_card, "worker end card beyond end card");
211
212 jbyte* current_card = worker_start_card;
213 while (current_card < worker_end_card) {
214 // Find an unclean card.
215 while (current_card < worker_end_card && card_is_clean(*current_card)) {
216 current_card++;
217 }
218 jbyte* first_unclean_card = current_card;
219
220 // Find the end of a run of contiguous unclean cards
221 while (current_card < worker_end_card && !card_is_clean(*current_card)) {
222 while (current_card < worker_end_card && !card_is_clean(*current_card)) {
223 current_card++;
224 }
225
226 if (current_card < worker_end_card) {
227 // Some objects may be large enough to span several cards. If such
228 // an object has more than one dirty card, separated by a clean card,
229 // we will attempt to scan it twice. The test against "last_scanned"
230 // prevents the redundant object scan, but it does not prevent newly
231 // marked cards from being cleaned.
232 HeapWord* last_object_in_dirty_region = start_array->object_start(addr_for(current_card)-1);
233 size_t size_of_last_object = oop(last_object_in_dirty_region)->size();
234 HeapWord* end_of_last_object = last_object_in_dirty_region + size_of_last_object;
235 jbyte* ending_card_of_last_object = byte_for(end_of_last_object);
236 assert(ending_card_of_last_object <= worker_end_card, "ending_card_of_last_object is greater than worker_end_card");
237 if (ending_card_of_last_object > current_card) {
238 // This means the object spans the next complete card.
239 // We need to bump the current_card to ending_card_of_last_object
240 current_card = ending_card_of_last_object;
241 }
242 }
243 }
244 jbyte* following_clean_card = current_card;
245
246 if (first_unclean_card < worker_end_card) {
247 oop* p = (oop*) start_array->object_start(addr_for(first_unclean_card));
248 assert((HeapWord*)p <= addr_for(first_unclean_card), "checking");
249 // "p" should always be >= "last_scanned" because newly GC dirtied
250 // cards are no longer scanned again (see comment at end
251 // of loop on the increment of "current_card"). Test that
252 // hypothesis before removing this code.
253 // If this code is removed, deal with the first time through
254 // the loop when the last_scanned is the object starting in
255 // the previous slice.
256 assert((p >= last_scanned) ||
257 (last_scanned == first_object_within_slice),
258 "Should no longer be possible");
259 if (p < last_scanned) {
260 // Avoid scanning more than once; this can happen because
261 // newgen cards set by GC may a different set than the
262 // originally dirty set
263 p = last_scanned;
264 }
265 oop* to = (oop*)addr_for(following_clean_card);
266
267 // Test slice_end first!
268 if ((HeapWord*)to > slice_end) {
269 to = (oop*)slice_end;
270 } else if (to > sp_top) {
271 to = sp_top;
272 }
273
274 // we know which cards to scan, now clear them
275 if (first_unclean_card <= worker_start_card+1)
276 first_unclean_card = worker_start_card+1;
277 if (following_clean_card >= worker_end_card-1)
278 following_clean_card = worker_end_card-1;
279
280 while (first_unclean_card < following_clean_card) {
281 *first_unclean_card++ = clean_card;
282 }
283
284 const int interval = PrefetchScanIntervalInBytes;
285 // scan all objects in the range
286 if (interval != 0) {
287 while (p < to) {
288 Prefetch::write(p, interval);
289 oop m = oop(p);
290 assert(oopDesc::is_oop_or_null(m), "Expected an oop or NULL for header field at " PTR_FORMAT, p2i(m));
291 pm->push_contents(m);
292 p += m->size();
293 }
294 pm->drain_stacks_cond_depth();
295 } else {
296 while (p < to) {
297 oop m = oop(p);
298 assert(oopDesc::is_oop_or_null(m), "Expected an oop or NULL for header field at " PTR_FORMAT, p2i(m));
299 pm->push_contents(m);
300 p += m->size();
301 }
302 pm->drain_stacks_cond_depth();
303 }
304 last_scanned = p;
305 }
306 // "current_card" is still the "following_clean_card" or
307 // the current_card is >= the worker_end_card so the
308 // loop will not execute again.
309 assert((current_card == following_clean_card) ||
310 (current_card >= worker_end_card),
311 "current_card should only be incremented if it still equals "
312 "following_clean_card");
313 // Increment current_card so that it is not processed again.
314 // It may now be dirty because a old-to-young pointer was
315 // found on it an updated. If it is now dirty, it cannot be
316 // be safely cleaned in the next iteration.
317 current_card++;
318 }
319 }
320 }
321
322 // This should be called before a scavenge.
323 void CardTableExtension::verify_all_young_refs_imprecise() {
324 CheckForUnmarkedObjects check;
325
326 ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
327 PSOldGen* old_gen = heap->old_gen();
328
329 old_gen->object_iterate(&check);
330 }
331
332 // This should be called immediately after a scavenge, before mutators resume.
333 void CardTableExtension::verify_all_young_refs_precise() {
334 ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
335 PSOldGen* old_gen = heap->old_gen();
336
337 CheckForPreciseMarks check(
338 heap->young_gen(),
339 barrier_set_cast<CardTableExtension>(heap->barrier_set()));
340
341 old_gen->oop_iterate_no_header(&check);
342
343 verify_all_young_refs_precise_helper(old_gen->object_space()->used_region());
344 }
345
346 void CardTableExtension::verify_all_young_refs_precise_helper(MemRegion mr) {
347 CardTableExtension* card_table =
348 barrier_set_cast<CardTableExtension>(ParallelScavengeHeap::heap()->barrier_set());
349
350 jbyte* bot = card_table->byte_for(mr.start());
351 jbyte* top = card_table->byte_for(mr.end());
352 while(bot <= top) {
353 assert(*bot == clean_card || *bot == verify_card, "Found unwanted or unknown card mark");
354 if (*bot == verify_card)
355 *bot = youngergen_card;
356 bot++;
357 }
358 }
359
360 bool CardTableExtension::addr_is_marked_imprecise(void *addr) {
361 jbyte* p = byte_for(addr);
362 jbyte val = *p;
363
364 if (card_is_dirty(val))
365 return true;
366
367 if (card_is_newgen(val))
368 return true;
369
370 if (card_is_clean(val))
371 return false;
372
373 assert(false, "Found unhandled card mark type");
374
375 return false;
376 }
377
378 // Also includes verify_card
379 bool CardTableExtension::addr_is_marked_precise(void *addr) {
380 jbyte* p = byte_for(addr);
381 jbyte val = *p;
382
383 if (card_is_newgen(val))
384 return true;
385
386 if (card_is_verify(val))
387 return true;
388
389 if (card_is_clean(val))
390 return false;
391
392 if (card_is_dirty(val))
393 return false;
394
395 assert(false, "Found unhandled card mark type");
396
397 return false;
398 }
399
400 // Assumes that only the base or the end changes. This allows indentification
401 // of the region that is being resized. The
402 // CardTableModRefBS::resize_covered_region() is used for the normal case
403 // where the covered regions are growing or shrinking at the high end.
404 // The method resize_covered_region_by_end() is analogous to
405 // CardTableModRefBS::resize_covered_region() but
406 // for regions that grow or shrink at the low end.
407 void CardTableExtension::resize_covered_region(MemRegion new_region) {
408
409 for (int i = 0; i < _cur_covered_regions; i++) {
410 if (_covered[i].start() == new_region.start()) {
411 // Found a covered region with the same start as the
412 // new region. The region is growing or shrinking
413 // from the start of the region.
414 resize_covered_region_by_start(new_region);
415 return;
416 }
417 if (_covered[i].start() > new_region.start()) {
418 break;
419 }
420 }
421
422 int changed_region = -1;
423 for (int j = 0; j < _cur_covered_regions; j++) {
424 if (_covered[j].end() == new_region.end()) {
425 changed_region = j;
426 // This is a case where the covered region is growing or shrinking
427 // at the start of the region.
428 assert(changed_region != -1, "Don't expect to add a covered region");
429 assert(_covered[changed_region].byte_size() != new_region.byte_size(),
430 "The sizes should be different here");
431 resize_covered_region_by_end(changed_region, new_region);
432 return;
433 }
434 }
435 // This should only be a new covered region (where no existing
436 // covered region matches at the start or the end).
437 assert(_cur_covered_regions < _max_covered_regions,
438 "An existing region should have been found");
439 resize_covered_region_by_start(new_region);
440 }
441
442 void CardTableExtension::resize_covered_region_by_start(MemRegion new_region) {
443 CardTableModRefBS::resize_covered_region(new_region);
444 debug_only(verify_guard();)
445 }
446
447 void CardTableExtension::resize_covered_region_by_end(int changed_region,
448 MemRegion new_region) {
449 assert(SafepointSynchronize::is_at_safepoint(),
450 "Only expect an expansion at the low end at a GC");
451 debug_only(verify_guard();)
452 #ifdef ASSERT
453 for (int k = 0; k < _cur_covered_regions; k++) {
454 if (_covered[k].end() == new_region.end()) {
455 assert(changed_region == k, "Changed region is incorrect");
456 break;
457 }
458 }
459 #endif
460
461 // Commit new or uncommit old pages, if necessary.
462 if (resize_commit_uncommit(changed_region, new_region)) {
463 // Set the new start of the committed region
464 resize_update_committed_table(changed_region, new_region);
465 }
466
467 // Update card table entries
468 resize_update_card_table_entries(changed_region, new_region);
469
470 // Update the covered region
471 resize_update_covered_table(changed_region, new_region);
472
473 int ind = changed_region;
474 log_trace(gc, barrier)("CardTableModRefBS::resize_covered_region: ");
475 log_trace(gc, barrier)(" _covered[%d].start(): " INTPTR_FORMAT " _covered[%d].last(): " INTPTR_FORMAT,
476 ind, p2i(_covered[ind].start()), ind, p2i(_covered[ind].last()));
477 log_trace(gc, barrier)(" _committed[%d].start(): " INTPTR_FORMAT " _committed[%d].last(): " INTPTR_FORMAT,
478 ind, p2i(_committed[ind].start()), ind, p2i(_committed[ind].last()));
479 log_trace(gc, barrier)(" byte_for(start): " INTPTR_FORMAT " byte_for(last): " INTPTR_FORMAT,
480 p2i(byte_for(_covered[ind].start())), p2i(byte_for(_covered[ind].last())));
481 log_trace(gc, barrier)(" addr_for(start): " INTPTR_FORMAT " addr_for(last): " INTPTR_FORMAT,
482 p2i(addr_for((jbyte*) _committed[ind].start())), p2i(addr_for((jbyte*) _committed[ind].last())));
483
484 debug_only(verify_guard();)
485 }
486
487 bool CardTableExtension::resize_commit_uncommit(int changed_region,
488 MemRegion new_region) {
489 bool result = false;
490 // Commit new or uncommit old pages, if necessary.
491 MemRegion cur_committed = _committed[changed_region];
492 assert(_covered[changed_region].end() == new_region.end(),
493 "The ends of the regions are expected to match");
494 // Extend the start of this _committed region to
495 // to cover the start of any previous _committed region.
496 // This forms overlapping regions, but never interior regions.
497 HeapWord* min_prev_start = lowest_prev_committed_start(changed_region);
498 if (min_prev_start < cur_committed.start()) {
499 // Only really need to set start of "cur_committed" to
500 // the new start (min_prev_start) but assertion checking code
501 // below use cur_committed.end() so make it correct.
502 MemRegion new_committed =
503 MemRegion(min_prev_start, cur_committed.end());
504 cur_committed = new_committed;
505 }
506 #ifdef ASSERT
507 ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
508 assert(cur_committed.start() == align_up(cur_committed.start(), os::vm_page_size()),
509 "Starts should have proper alignment");
510 #endif
511
512 jbyte* new_start = byte_for(new_region.start());
513 // Round down because this is for the start address
514 HeapWord* new_start_aligned =
515 (HeapWord*)align_down((uintptr_t)new_start, os::vm_page_size());
516 // The guard page is always committed and should not be committed over.
517 // This method is used in cases where the generation is growing toward
518 // lower addresses but the guard region is still at the end of the
519 // card table. That still makes sense when looking for writes
520 // off the end of the card table.
521 if (new_start_aligned < cur_committed.start()) {
522 // Expand the committed region
523 //
524 // Case A
525 // |+ guard +|
526 // |+ cur committed +++++++++|
527 // |+ new committed +++++++++++++++++|
528 //
529 // Case B
530 // |+ guard +|
531 // |+ cur committed +|
532 // |+ new committed +++++++|
533 //
534 // These are not expected because the calculation of the
535 // cur committed region and the new committed region
536 // share the same end for the covered region.
537 // Case C
538 // |+ guard +|
539 // |+ cur committed +|
540 // |+ new committed +++++++++++++++++|
541 // Case D
542 // |+ guard +|
543 // |+ cur committed +++++++++++|
544 // |+ new committed +++++++|
545
546 HeapWord* new_end_for_commit =
547 MIN2(cur_committed.end(), _guard_region.start());
548 if(new_start_aligned < new_end_for_commit) {
549 MemRegion new_committed =
550 MemRegion(new_start_aligned, new_end_for_commit);
551 os::commit_memory_or_exit((char*)new_committed.start(),
552 new_committed.byte_size(), !ExecMem,
553 "card table expansion");
554 }
555 result = true;
556 } else if (new_start_aligned > cur_committed.start()) {
557 // Shrink the committed region
558 #if 0 // uncommitting space is currently unsafe because of the interactions
559 // of growing and shrinking regions. One region A can uncommit space
560 // that it owns but which is being used by another region B (maybe).
561 // Region B has not committed the space because it was already
562 // committed by region A.
563 MemRegion uncommit_region = committed_unique_to_self(changed_region,
564 MemRegion(cur_committed.start(), new_start_aligned));
565 if (!uncommit_region.is_empty()) {
566 if (!os::uncommit_memory((char*)uncommit_region.start(),
567 uncommit_region.byte_size())) {
568 // If the uncommit fails, ignore it. Let the
569 // committed table resizing go even though the committed
570 // table will over state the committed space.
571 }
572 }
573 #else
574 assert(!result, "Should be false with current workaround");
575 #endif
576 }
577 assert(_committed[changed_region].end() == cur_committed.end(),
578 "end should not change");
579 return result;
580 }
581
582 void CardTableExtension::resize_update_committed_table(int changed_region,
583 MemRegion new_region) {
584
585 jbyte* new_start = byte_for(new_region.start());
586 // Set the new start of the committed region
587 HeapWord* new_start_aligned =
588 (HeapWord*)align_down(new_start, os::vm_page_size());
589 MemRegion new_committed = MemRegion(new_start_aligned,
590 _committed[changed_region].end());
591 _committed[changed_region] = new_committed;
592 _committed[changed_region].set_start(new_start_aligned);
593 }
594
595 void CardTableExtension::resize_update_card_table_entries(int changed_region,
596 MemRegion new_region) {
597 debug_only(verify_guard();)
598 MemRegion original_covered = _covered[changed_region];
599 // Initialize the card entries. Only consider the
600 // region covered by the card table (_whole_heap)
601 jbyte* entry;
602 if (new_region.start() < _whole_heap.start()) {
603 entry = byte_for(_whole_heap.start());
604 } else {
605 entry = byte_for(new_region.start());
606 }
607 jbyte* end = byte_for(original_covered.start());
608 // If _whole_heap starts at the original covered regions start,
609 // this loop will not execute.
610 while (entry < end) { *entry++ = clean_card; }
611 }
612
613 void CardTableExtension::resize_update_covered_table(int changed_region,
614 MemRegion new_region) {
615 // Update the covered region
616 _covered[changed_region].set_start(new_region.start());
617 _covered[changed_region].set_word_size(new_region.word_size());
618
619 // reorder regions. There should only be at most 1 out
620 // of order.
621 for (int i = _cur_covered_regions-1 ; i > 0; i--) {
622 if (_covered[i].start() < _covered[i-1].start()) {
623 MemRegion covered_mr = _covered[i-1];
624 _covered[i-1] = _covered[i];
625 _covered[i] = covered_mr;
626 MemRegion committed_mr = _committed[i-1];
627 _committed[i-1] = _committed[i];
628 _committed[i] = committed_mr;
629 break;
630 }
631 }
632 #ifdef ASSERT
633 for (int m = 0; m < _cur_covered_regions-1; m++) {
634 assert(_covered[m].start() <= _covered[m+1].start(),
635 "Covered regions out of order");
636 assert(_committed[m].start() <= _committed[m+1].start(),
637 "Committed regions out of order");
638 }
639 #endif
640 }
641
642 // Returns the start of any committed region that is lower than
643 // the target committed region (index ind) and that intersects the
644 // target region. If none, return start of target region.
645 //
646 // -------------
647 // | |
648 // -------------
649 // ------------
650 // | target |
651 // ------------
652 // -------------
653 // | |
654 // -------------
655 // ^ returns this
656 //
657 // -------------
658 // | |
659 // -------------
660 // ------------
661 // | target |
662 // ------------
663 // -------------
664 // | |
665 // -------------
666 // ^ returns this
667
668 HeapWord* CardTableExtension::lowest_prev_committed_start(int ind) const {
669 assert(_cur_covered_regions >= 0, "Expecting at least on region");
670 HeapWord* min_start = _committed[ind].start();
671 for (int j = 0; j < ind; j++) {
672 HeapWord* this_start = _committed[j].start();
673 if ((this_start < min_start) &&
674 !(_committed[j].intersection(_committed[ind])).is_empty()) {
675 min_start = this_start;
676 }
677 }
678 return min_start;
679 }