1 /*
2 * Copyright (c) 2015, 2025, 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 #include "gc/shared/gc_globals.hpp"
25 #include "gc/shared/suspendibleThreadSet.hpp"
26 #include "gc/z/zAbort.inline.hpp"
27 #include "gc/z/zAddress.inline.hpp"
28 #include "gc/z/zAllocator.inline.hpp"
29 #include "gc/z/zBarrier.inline.hpp"
30 #include "gc/z/zCollectedHeap.hpp"
31 #include "gc/z/zForwarding.inline.hpp"
32 #include "gc/z/zGeneration.inline.hpp"
33 #include "gc/z/zHeap.inline.hpp"
34 #include "gc/z/zIndexDistributor.inline.hpp"
35 #include "gc/z/zIterator.inline.hpp"
36 #include "gc/z/zPage.inline.hpp"
37 #include "gc/z/zPageAge.hpp"
38 #include "gc/z/zRelocate.hpp"
39 #include "gc/z/zRelocationSet.inline.hpp"
40 #include "gc/z/zRootsIterator.hpp"
41 #include "gc/z/zStackWatermark.hpp"
42 #include "gc/z/zStat.hpp"
43 #include "gc/z/zTask.hpp"
44 #include "gc/z/zUncoloredRoot.inline.hpp"
45 #include "gc/z/zVerify.hpp"
46 #include "gc/z/zWorkers.hpp"
47 #include "prims/jvmtiTagMap.hpp"
48 #include "runtime/atomic.hpp"
49 #include "utilities/debug.hpp"
50
51 static const ZStatCriticalPhase ZCriticalPhaseRelocationStall("Relocation Stall");
52 static const ZStatSubPhase ZSubPhaseConcurrentRelocateRememberedSetFlipPromotedYoung("Concurrent Relocate Remset FP", ZGenerationId::young);
53
54 ZRelocateQueue::ZRelocateQueue()
55 : _lock(),
56 _queue(),
57 _nworkers(0),
58 _nsynchronized(0),
59 _synchronize(false),
60 _is_active(false),
61 _needs_attention(0) {}
62
63 bool ZRelocateQueue::needs_attention() const {
64 return Atomic::load(&_needs_attention) != 0;
65 }
66
67 void ZRelocateQueue::inc_needs_attention() {
68 const int needs_attention = Atomic::add(&_needs_attention, 1);
69 assert(needs_attention == 1 || needs_attention == 2, "Invalid state");
70 }
71
72 void ZRelocateQueue::dec_needs_attention() {
73 const int needs_attention = Atomic::sub(&_needs_attention, 1);
74 assert(needs_attention == 0 || needs_attention == 1, "Invalid state");
75 }
76
77 void ZRelocateQueue::activate(uint nworkers) {
78 _is_active = true;
79 join(nworkers);
80 }
81
82 void ZRelocateQueue::deactivate() {
83 Atomic::store(&_is_active, false);
84 clear();
85 }
86
87 bool ZRelocateQueue::is_active() const {
88 return Atomic::load(&_is_active);
89 }
90
91 void ZRelocateQueue::join(uint nworkers) {
92 assert(nworkers != 0, "Must request at least one worker");
93 assert(_nworkers == 0, "Invalid state");
94 assert(_nsynchronized == 0, "Invalid state");
95
96 log_debug(gc, reloc)("Joining workers: %u", nworkers);
97
98 _nworkers = nworkers;
99 }
100
101 void ZRelocateQueue::resize_workers(uint nworkers) {
102 assert(nworkers != 0, "Must request at least one worker");
103 assert(_nworkers == 0, "Invalid state");
104 assert(_nsynchronized == 0, "Invalid state");
105
106 log_debug(gc, reloc)("Resize workers: %u", nworkers);
107
108 ZLocker<ZConditionLock> locker(&_lock);
109 _nworkers = nworkers;
110 }
111
112 void ZRelocateQueue::leave() {
113 ZLocker<ZConditionLock> locker(&_lock);
114 _nworkers--;
115
116 assert(_nsynchronized <= _nworkers, "_nsynchronized: %u _nworkers: %u", _nsynchronized, _nworkers);
117
118 log_debug(gc, reloc)("Leaving workers: left: %u _synchronize: %d _nsynchronized: %u", _nworkers, _synchronize, _nsynchronized);
119
120 // Prune done forwardings
121 const bool forwardings_done = prune();
122
123 // Check if all workers synchronized
124 const bool last_synchronized = _synchronize && _nworkers == _nsynchronized;
125
126 if (forwardings_done || last_synchronized) {
127 _lock.notify_all();
128 }
129 }
130
131 void ZRelocateQueue::add_and_wait(ZForwarding* forwarding) {
132 ZStatTimer timer(ZCriticalPhaseRelocationStall);
133 ZLocker<ZConditionLock> locker(&_lock);
134
135 if (forwarding->is_done()) {
136 return;
137 }
138
139 _queue.append(forwarding);
140 if (_queue.length() == 1) {
141 // Queue became non-empty
142 inc_needs_attention();
143 _lock.notify_all();
144 }
145
146 while (!forwarding->is_done()) {
147 _lock.wait();
148 }
149 }
150
151 bool ZRelocateQueue::prune() {
152 if (_queue.is_empty()) {
153 return false;
154 }
155
156 bool done = false;
157
158 for (int i = 0; i < _queue.length();) {
159 const ZForwarding* const forwarding = _queue.at(i);
160 if (forwarding->is_done()) {
161 done = true;
162
163 _queue.delete_at(i);
164 } else {
165 i++;
166 }
167 }
168
169 if (_queue.is_empty()) {
170 dec_needs_attention();
171 }
172
173 return done;
174 }
175
176 ZForwarding* ZRelocateQueue::prune_and_claim() {
177 if (prune()) {
178 _lock.notify_all();
179 }
180
181 for (int i = 0; i < _queue.length(); i++) {
182 ZForwarding* const forwarding = _queue.at(i);
183 if (forwarding->claim()) {
184 return forwarding;
185 }
186 }
187
188 return nullptr;
189 }
190
191 class ZRelocateQueueSynchronizeThread {
192 private:
193 ZRelocateQueue* const _queue;
194
195 public:
196 ZRelocateQueueSynchronizeThread(ZRelocateQueue* queue)
197 : _queue(queue) {
198 _queue->synchronize_thread();
199 }
200
201 ~ZRelocateQueueSynchronizeThread() {
202 _queue->desynchronize_thread();
203 }
204 };
205
206 void ZRelocateQueue::synchronize_thread() {
207 _nsynchronized++;
208
209 log_debug(gc, reloc)("Synchronize worker _nsynchronized %u", _nsynchronized);
210
211 assert(_nsynchronized <= _nworkers, "_nsynchronized: %u _nworkers: %u", _nsynchronized, _nworkers);
212 if (_nsynchronized == _nworkers) {
213 // All workers synchronized
214 _lock.notify_all();
215 }
216 }
217
218 void ZRelocateQueue::desynchronize_thread() {
219 _nsynchronized--;
220
221 log_debug(gc, reloc)("Desynchronize worker _nsynchronized %u", _nsynchronized);
222
223 assert(_nsynchronized < _nworkers, "_nsynchronized: %u _nworkers: %u", _nsynchronized, _nworkers);
224 }
225
226 ZForwarding* ZRelocateQueue::synchronize_poll() {
227 // Fast path avoids locking
228 if (!needs_attention()) {
229 return nullptr;
230 }
231
232 // Slow path to get the next forwarding and/or synchronize
233 ZLocker<ZConditionLock> locker(&_lock);
234
235 {
236 ZForwarding* const forwarding = prune_and_claim();
237 if (forwarding != nullptr) {
238 // Don't become synchronized while there are elements in the queue
239 return forwarding;
240 }
241 }
242
243 if (!_synchronize) {
244 return nullptr;
245 }
246
247 ZRelocateQueueSynchronizeThread rqst(this);
248
249 do {
250 _lock.wait();
251
252 ZForwarding* const forwarding = prune_and_claim();
253 if (forwarding != nullptr) {
254 return forwarding;
255 }
256 } while (_synchronize);
257
258 return nullptr;
259 }
260
261 void ZRelocateQueue::clear() {
262 assert(_nworkers == 0, "Invalid state");
263
264 if (_queue.is_empty()) {
265 return;
266 }
267
268 ZArrayIterator<ZForwarding*> iter(&_queue);
269 for (ZForwarding* forwarding; iter.next(&forwarding);) {
270 assert(forwarding->is_done(), "All should be done");
271 }
272
273 assert(false, "Clear was not empty");
274
275 _queue.clear();
276 dec_needs_attention();
277 }
278
279 void ZRelocateQueue::synchronize() {
280 ZLocker<ZConditionLock> locker(&_lock);
281 _synchronize = true;
282
283 inc_needs_attention();
284
285 log_debug(gc, reloc)("Synchronize all workers 1 _nworkers: %u _nsynchronized: %u", _nworkers, _nsynchronized);
286
287 while (_nworkers != _nsynchronized) {
288 _lock.wait();
289 log_debug(gc, reloc)("Synchronize all workers 2 _nworkers: %u _nsynchronized: %u", _nworkers, _nsynchronized);
290 }
291 }
292
293 void ZRelocateQueue::desynchronize() {
294 ZLocker<ZConditionLock> locker(&_lock);
295 _synchronize = false;
296
297 log_debug(gc, reloc)("Desynchronize all workers _nworkers: %u _nsynchronized: %u", _nworkers, _nsynchronized);
298
299 assert(_nsynchronized <= _nworkers, "_nsynchronized: %u _nworkers: %u", _nsynchronized, _nworkers);
300
301 dec_needs_attention();
302
303 _lock.notify_all();
304 }
305
306 ZRelocate::ZRelocate(ZGeneration* generation)
307 : _generation(generation),
308 _queue() {}
309
310 ZWorkers* ZRelocate::workers() const {
311 return _generation->workers();
312 }
313
314 void ZRelocate::start() {
315 _queue.activate(workers()->active_workers());
316 }
317
318 void ZRelocate::add_remset(volatile zpointer* p) {
319 ZGeneration::young()->remember(p);
320 }
321
322 static zaddress relocate_object_inner(ZForwarding* forwarding, zaddress from_addr, ZForwardingCursor* cursor) {
323 assert(ZHeap::heap()->is_object_live(from_addr), "Should be live");
324
325 // Allocate object
326 const size_t old_size = ZUtils::object_size(from_addr);
327 const size_t size = ZUtils::copy_size(from_addr, old_size);
328
329 ZAllocatorForRelocation* allocator = ZAllocator::relocation(forwarding->to_age());
330
331 const zaddress to_addr = allocator->alloc_object(size);
332
333 if (is_null(to_addr)) {
334 // Allocation failed
335 return zaddress::null;
336 }
337 assert(to_addr != from_addr, "addresses must be different");
338
339 // Copy object
340 ZUtils::object_copy_disjoint(from_addr, to_addr, old_size);
341 ZUtils::initialize_hash_if_necessary(to_addr, from_addr);
342
343 // Insert forwarding
344 const zaddress to_addr_final = forwarding->insert(from_addr, to_addr, cursor);
345
346 if (to_addr_final != to_addr) {
347 // Already relocated, try undo allocation
348 allocator->undo_alloc_object(to_addr, size);
349 }
350
351 return to_addr_final;
352 }
353
354 zaddress ZRelocate::relocate_object(ZForwarding* forwarding, zaddress_unsafe from_addr) {
355 ZForwardingCursor cursor;
356
357 // Lookup forwarding
358 zaddress to_addr = forwarding->find(from_addr, &cursor);
359 if (!is_null(to_addr)) {
360 // Already relocated
361 return to_addr;
362 }
363
364 // Relocate object
365 if (forwarding->retain_page(&_queue)) {
366 assert(_generation->is_phase_relocate(), "Must be");
367 to_addr = relocate_object_inner(forwarding, safe(from_addr), &cursor);
368 forwarding->release_page();
369
370 if (!is_null(to_addr)) {
371 // Success
372 return to_addr;
373 }
374
375 // Failed to relocate object. Signal and wait for a worker thread to
376 // complete relocation of this page, and then forward the object.
377 _queue.add_and_wait(forwarding);
378 }
379
380 // Forward object
381 return forward_object(forwarding, from_addr);
382 }
383
384 zaddress ZRelocate::forward_object(ZForwarding* forwarding, zaddress_unsafe from_addr) {
385 const zaddress to_addr = forwarding->find(from_addr);
386 assert(!is_null(to_addr), "Should be forwarded: " PTR_FORMAT, untype(from_addr));
387 return to_addr;
388 }
389
390 static ZPage* alloc_page(ZAllocatorForRelocation* allocator, ZPageType type, size_t size) {
391 if (ZStressRelocateInPlace) {
392 // Simulate failure to allocate a new page. This will
393 // cause the page being relocated to be relocated in-place.
394 return nullptr;
395 }
396
397 ZAllocationFlags flags;
398 flags.set_non_blocking();
399 flags.set_gc_relocation();
400
401 return allocator->alloc_page_for_relocation(type, size, flags);
402 }
403
404 static void retire_target_page(ZGeneration* generation, ZPage* page) {
405 if (generation->is_young() && page->is_old()) {
406 generation->increase_promoted(page->used());
407 } else {
408 generation->increase_compacted(page->used());
409 }
410
411 // Free target page if it is empty. We can end up with an empty target
412 // page if we allocated a new target page, and then lost the race to
413 // relocate the remaining objects, leaving the target page empty when
414 // relocation completed.
415 if (page->used() == 0) {
416 ZHeap::heap()->free_page(page, true /* allow_defragment */);
417 }
418 }
419
420 class ZRelocateSmallAllocator {
421 private:
422 ZGeneration* const _generation;
423 volatile size_t _in_place_count;
424
425 public:
426 ZRelocateSmallAllocator(ZGeneration* generation)
427 : _generation(generation),
428 _in_place_count(0) {}
429
430 ZPage* alloc_and_retire_target_page(ZForwarding* forwarding, ZPage* target) {
431 ZAllocatorForRelocation* const allocator = ZAllocator::relocation(forwarding->to_age());
432 ZPage* const page = alloc_page(allocator, forwarding->type(), forwarding->size());
433 if (page == nullptr) {
434 Atomic::inc(&_in_place_count);
435 }
436
437 if (target != nullptr) {
438 // Retire the old target page
439 retire_target_page(_generation, target);
440 }
441
442 return page;
443 }
444
445 void share_target_page(ZPage* page) {
446 // Does nothing
447 }
448
449 void free_target_page(ZPage* page) {
450 if (page != nullptr) {
451 retire_target_page(_generation, page);
452 }
453 }
454
455 zaddress alloc_object(ZPage* page, size_t size) const {
456 return (page != nullptr) ? page->alloc_object(size) : zaddress::null;
457 }
458
459 void undo_alloc_object(ZPage* page, zaddress addr, size_t size) const {
460 page->undo_alloc_object(addr, size);
461 }
462
463 size_t in_place_count() const {
464 return _in_place_count;
465 }
466 };
467
468 class ZRelocateMediumAllocator {
469 private:
470 ZGeneration* const _generation;
471 ZConditionLock _lock;
472 ZPage* _shared[ZAllocator::_relocation_allocators];
473 bool _in_place;
474 volatile size_t _in_place_count;
475
476 public:
477 ZRelocateMediumAllocator(ZGeneration* generation)
478 : _generation(generation),
479 _lock(),
480 _shared(),
481 _in_place(false),
482 _in_place_count(0) {}
483
484 ~ZRelocateMediumAllocator() {
485 for (uint i = 0; i < ZAllocator::_relocation_allocators; ++i) {
486 if (_shared[i] != nullptr) {
487 retire_target_page(_generation, _shared[i]);
488 }
489 }
490 }
491
492 ZPage* shared(ZPageAge age) {
493 return _shared[static_cast<uint>(age) - 1];
494 }
495
496 void set_shared(ZPageAge age, ZPage* page) {
497 _shared[static_cast<uint>(age) - 1] = page;
498 }
499
500 ZPage* alloc_and_retire_target_page(ZForwarding* forwarding, ZPage* target) {
501 ZLocker<ZConditionLock> locker(&_lock);
502
503 // Wait for any ongoing in-place relocation to complete
504 while (_in_place) {
505 _lock.wait();
506 }
507
508 // Allocate a new page only if the shared page is the same as the
509 // current target page. The shared page will be different from the
510 // current target page if another thread shared a page, or allocated
511 // a new page.
512 const ZPageAge to_age = forwarding->to_age();
513 if (shared(to_age) == target) {
514 ZAllocatorForRelocation* const allocator = ZAllocator::relocation(forwarding->to_age());
515 ZPage* const to_page = alloc_page(allocator, forwarding->type(), forwarding->size());
516 set_shared(to_age, to_page);
517 if (to_page == nullptr) {
518 Atomic::inc(&_in_place_count);
519 _in_place = true;
520 }
521
522 // This thread is responsible for retiring the shared target page
523 if (target != nullptr) {
524 retire_target_page(_generation, target);
525 }
526 }
527
528 return shared(to_age);
529 }
530
531 void share_target_page(ZPage* page) {
532 const ZPageAge age = page->age();
533
534 ZLocker<ZConditionLock> locker(&_lock);
535 assert(_in_place, "Invalid state");
536 assert(shared(age) == nullptr, "Invalid state");
537 assert(page != nullptr, "Invalid page");
538
539 set_shared(age, page);
540 _in_place = false;
541
542 _lock.notify_all();
543 }
544
545 void free_target_page(ZPage* page) {
546 // Does nothing
547 }
548
549 zaddress alloc_object(ZPage* page, size_t size) const {
550 return (page != nullptr) ? page->alloc_object_atomic(size) : zaddress::null;
551 }
552
553 void undo_alloc_object(ZPage* page, zaddress addr, size_t size) const {
554 page->undo_alloc_object_atomic(addr, size);
555 }
556
557 size_t in_place_count() const {
558 return _in_place_count;
559 }
560 };
561
562 template <typename Allocator>
563 class ZRelocateWork : public StackObj {
564 private:
565 Allocator* const _allocator;
566 ZForwarding* _forwarding;
567 ZPage* _target[ZAllocator::_relocation_allocators];
568 ZGeneration* const _generation;
569 size_t _other_promoted;
570 size_t _other_compacted;
571
572 ZPage* target(ZPageAge age) {
573 return _target[static_cast<uint>(age) - 1];
574 }
575
576 void set_target(ZPageAge age, ZPage* page) {
577 _target[static_cast<uint>(age) - 1] = page;
578 }
579
580 size_t object_alignment() const {
581 return (size_t)1 << _forwarding->object_alignment_shift();
582 }
583
584 void increase_other_forwarded(size_t unaligned_object_size) {
585 const size_t aligned_size = align_up(unaligned_object_size, object_alignment());
586 if (_forwarding->is_promotion()) {
587 _other_promoted += aligned_size;
588 } else {
589 _other_compacted += aligned_size;
590 }
591 }
592
593 zaddress try_relocate_object_inner(zaddress from_addr, size_t old_size) {
594 ZForwardingCursor cursor;
595 ZPage* const to_page = target(_forwarding->to_age());
596 zoffset_end from_offset = to_zoffset_end(ZAddress::offset(from_addr));
597 zoffset_end top = to_page != nullptr ? to_page->top() : to_zoffset_end(0);
598 const size_t new_size = ZUtils::copy_size(from_addr, old_size);
599 const size_t size = top == from_offset ? old_size : new_size;
600
601 // Lookup forwarding
602 {
603 const zaddress to_addr = _forwarding->find(from_addr, &cursor);
604 if (!is_null(to_addr)) {
605 // Already relocated
606 increase_other_forwarded(size);
607 return to_addr;
608 }
609 }
610
611 // Allocate object
612 const zaddress allocated_addr = _allocator->alloc_object(to_page, size);
613 if (is_null(allocated_addr)) {
614 // Allocation failed
615 return zaddress::null;
616 }
617 if (old_size != new_size && ((top == from_offset) != (allocated_addr == from_addr))) {
618 _allocator->undo_alloc_object(to_page, allocated_addr, size);
619 return zaddress::null;
620 }
621
622 // Copy object. Use conjoint copying if we are relocating
623 // in-place and the new object overlaps with the old object.
624 if (_forwarding->in_place_relocation() && allocated_addr + old_size > from_addr) {
625 ZUtils::object_copy_conjoint(from_addr, allocated_addr, old_size);
626 } else {
627 ZUtils::object_copy_disjoint(from_addr, allocated_addr, old_size);
628 }
629 if (from_addr != allocated_addr) {
630 ZUtils::initialize_hash_if_necessary(allocated_addr, from_addr);
631 }
632
633 // Insert forwarding
634 const zaddress to_addr = _forwarding->insert(from_addr, allocated_addr, &cursor);
635 if (to_addr != allocated_addr) {
636 // Already relocated, undo allocation
637 _allocator->undo_alloc_object(to_page, to_addr, size);
638 increase_other_forwarded(size);
639 }
640
641 return to_addr;
642 }
643
644 void update_remset_old_to_old(zaddress from_addr, zaddress to_addr, size_t size) const {
645 // Old-to-old relocation - move existing remset bits
646
647 // If this is called for an in-place relocated page, then this code has the
648 // responsibility to clear the old remset bits. Extra care is needed because:
649 //
650 // 1) The to-object copy can overlap with the from-object copy
651 // 2) Remset bits of old objects need to be cleared
652 //
653 // A watermark is used to keep track of how far the old remset bits have been removed.
654
655 const bool in_place = _forwarding->in_place_relocation();
656 ZPage* const from_page = _forwarding->page();
657 const uintptr_t from_local_offset = from_page->local_offset(from_addr);
658
659 // Note: even with in-place relocation, the to_page could be another page
660 ZPage* const to_page = ZHeap::heap()->page(to_addr);
661
662 // Uses _relaxed version to handle that in-place relocation resets _top
663 assert(ZHeap::heap()->is_in_page_relaxed(from_page, from_addr), "Must be");
664 assert(to_page->is_in(to_addr), "Must be");
665
666 assert(size <= ZUtils::object_size(to_addr), "old size must be <= new size");
667 assert(size > 0, "size must be set");
668
669 // If a young generation collection started while the old generation
670 // relocated objects, the remember set bits were flipped from "current"
671 // to "previous".
672 //
673 // We need to select the correct remembered sets bitmap to ensure that the
674 // old remset bits are found.
675 //
676 // Note that if the young generation marking (remset scanning) finishes
677 // before the old generation relocation has relocated this page, then the
678 // young generation will visit this page's previous remembered set bits and
679 // moved them over to the current bitmap.
680 //
681 // If the young generation runs multiple cycles while the old generation is
682 // relocating, then the first cycle will have consume the the old remset,
683 // bits and moved associated objects to a new old page. The old relocation
684 // could find either the the two bitmaps. So, either it will find the original
685 // remset bits for the page, or it will find an empty bitmap for the page. It
686 // doesn't matter for correctness, because the young generation marking has
687 // already taken care of the bits.
688
689 const bool active_remset_is_current = ZGeneration::old()->active_remset_is_current();
690
691 // When in-place relocation is done and the old remset bits are located in
692 // the bitmap that is going to be used for the new remset bits, then we
693 // need to clear the old bits before the new bits are inserted.
694 const bool iterate_current_remset = active_remset_is_current && !in_place;
695
696 BitMap::Iterator iter = iterate_current_remset
697 ? from_page->remset_iterator_limited_current(from_local_offset, size)
698 : from_page->remset_iterator_limited_previous(from_local_offset, size);
699
700 for (BitMap::idx_t field_bit : iter) {
701 const uintptr_t field_local_offset = ZRememberedSet::to_offset(field_bit);
702
703 // Add remset entry in the to-page
704 const uintptr_t offset = field_local_offset - from_local_offset;
705 const zaddress to_field = to_addr + offset;
706 log_trace(gc, reloc)("Remember: from: " PTR_FORMAT " to: " PTR_FORMAT " current: %d marking: %d page: " PTR_FORMAT " remset: " PTR_FORMAT,
707 untype(from_page->start() + field_local_offset), untype(to_field), active_remset_is_current, ZGeneration::young()->is_phase_mark(), p2i(to_page), p2i(to_page->remset_current()));
708
709 volatile zpointer* const p = (volatile zpointer*)to_field;
710
711 if (ZGeneration::young()->is_phase_mark()) {
712 // Young generation remembered set scanning needs to know about this
713 // field. It will take responsibility to add a new remember set entry if needed.
714 _forwarding->relocated_remembered_fields_register(p);
715 } else {
716 to_page->remember(p);
717 if (in_place) {
718 assert(to_page->is_remembered(p), "p: " PTR_FORMAT, p2i(p));
719 }
720 }
721 }
722 }
723
724 static bool add_remset_if_young(volatile zpointer* p, zaddress addr) {
725 if (ZHeap::heap()->is_young(addr)) {
726 ZRelocate::add_remset(p);
727 return true;
728 }
729
730 return false;
731 }
732
733 static void update_remset_promoted_filter_and_remap_per_field(volatile zpointer* p) {
734 const zpointer ptr = Atomic::load(p);
735
736 assert(ZPointer::is_old_load_good(ptr), "Should be at least old load good: " PTR_FORMAT, untype(ptr));
737
738 if (ZPointer::is_store_good(ptr)) {
739 // Already has a remset entry
740 return;
741 }
742
743 if (ZPointer::is_load_good(ptr)) {
744 if (!is_null_any(ptr)) {
745 const zaddress addr = ZPointer::uncolor(ptr);
746 add_remset_if_young(p, addr);
747 }
748 // No need to remap it is already load good
749 return;
750 }
751
752 if (is_null_any(ptr)) {
753 // Eagerly remap to skip adding a remset entry just to get deferred remapping
754 ZBarrier::remap_young_relocated(p, ptr);
755 return;
756 }
757
758 const zaddress_unsafe addr_unsafe = ZPointer::uncolor_unsafe(ptr);
759 ZForwarding* const forwarding = ZGeneration::young()->forwarding(addr_unsafe);
760
761 if (forwarding == nullptr) {
762 // Object isn't being relocated
763 const zaddress addr = safe(addr_unsafe);
764 if (!add_remset_if_young(p, addr)) {
765 // Not young - eagerly remap to skip adding a remset entry just to get deferred remapping
766 ZBarrier::remap_young_relocated(p, ptr);
767 }
768 return;
769 }
770
771 const zaddress addr = forwarding->find(addr_unsafe);
772
773 if (!is_null(addr)) {
774 // Object has already been relocated
775 if (!add_remset_if_young(p, addr)) {
776 // Not young - eagerly remap to skip adding a remset entry just to get deferred remapping
777 ZBarrier::remap_young_relocated(p, ptr);
778 }
779 return;
780 }
781
782 // Object has not been relocated yet
783 // Don't want to eagerly relocate objects, so just add a remset
784 ZRelocate::add_remset(p);
785 return;
786 }
787
788 void update_remset_promoted(zaddress to_addr) const {
789 ZIterator::basic_oop_iterate(to_oop(to_addr), update_remset_promoted_filter_and_remap_per_field);
790 }
791
792 void update_remset_for_fields(zaddress from_addr, zaddress to_addr, size_t size) const {
793 if (_forwarding->to_age() != ZPageAge::old) {
794 // No remembered set in young pages
795 return;
796 }
797
798 // Need to deal with remset when moving objects to the old generation
799 if (_forwarding->from_age() == ZPageAge::old) {
800 update_remset_old_to_old(from_addr, to_addr, size);
801 return;
802 }
803
804 // Normal promotion
805 update_remset_promoted(to_addr);
806 }
807
808 bool try_relocate_object(zaddress from_addr) {
809 size_t size = ZUtils::object_size(from_addr);
810 const zaddress to_addr = try_relocate_object_inner(from_addr, size);
811
812 if (is_null(to_addr)) {
813 return false;
814 }
815
816 update_remset_for_fields(from_addr, to_addr, size);
817
818 return true;
819 }
820
821 void start_in_place_relocation_prepare_remset(ZPage* from_page) {
822 if (_forwarding->from_age() != ZPageAge::old) {
823 // Only old pages have use remset bits
824 return;
825 }
826
827 if (ZGeneration::old()->active_remset_is_current()) {
828 // We want to iterate over and clear the remset bits of the from-space page,
829 // and insert current bits in the to-space page. However, with in-place
830 // relocation, the from-space and to-space pages are the same. Clearing
831 // is destructive, and is difficult to perform before or during the iteration.
832 // However, clearing of the current bits has to be done before exposing the
833 // to-space objects in the forwarding table.
834 //
835 // To solve this tricky dependency problem, we start by stashing away the
836 // current bits in the previous bits, and clearing the current bits
837 // (implemented by swapping the bits). This way, the current bits are
838 // cleared before copying the objects (like a normal to-space page),
839 // and the previous bits are representing a copy of the current bits
840 // of the from-space page, and are used for iteration.
841 from_page->swap_remset_bitmaps();
842 }
843 }
844
845 ZPage* start_in_place_relocation(zoffset relocated_watermark) {
846 _forwarding->in_place_relocation_claim_page();
847 _forwarding->in_place_relocation_start(relocated_watermark);
848
849 ZPage* const from_page = _forwarding->page();
850
851 const ZPageAge to_age = _forwarding->to_age();
852 const bool promotion = _forwarding->is_promotion();
853
854 // Promotions happen through a new cloned page
855 ZPage* const to_page = promotion ? from_page->clone_limited() : from_page;
856
857 // Reset page for in-place relocation
858 to_page->reset(to_age);
859 to_page->reset_top_for_allocation();
860 if (promotion) {
861 to_page->remset_alloc();
862 }
863
864 // Verify that the inactive remset is clear when resetting the page for
865 // in-place relocation.
866 if (from_page->age() == ZPageAge::old) {
867 if (ZGeneration::old()->active_remset_is_current()) {
868 to_page->verify_remset_cleared_previous();
869 } else {
870 to_page->verify_remset_cleared_current();
871 }
872 }
873
874 // Clear remset bits for all objects that were relocated
875 // before this page became an in-place relocated page.
876 start_in_place_relocation_prepare_remset(from_page);
877
878 if (promotion) {
879 // Register the the promotion
880 ZGeneration::young()->in_place_relocate_promote(from_page, to_page);
881 ZGeneration::young()->register_in_place_relocate_promoted(from_page);
882 }
883
884 return to_page;
885 }
886
887 void relocate_object(oop obj) {
888 const zaddress addr = to_zaddress(obj);
889 assert(ZHeap::heap()->is_object_live(addr), "Should be live");
890
891 while (!try_relocate_object(addr)) {
892 // Allocate a new target page, or if that fails, use the page being
893 // relocated as the new target, which will cause it to be relocated
894 // in-place.
895 const ZPageAge to_age = _forwarding->to_age();
896 ZPage* to_page = _allocator->alloc_and_retire_target_page(_forwarding, target(to_age));
897 set_target(to_age, to_page);
898 if (to_page != nullptr) {
899 continue;
900 }
901
902 // Start in-place relocation to block other threads from accessing
903 // the page, or its forwarding table, until it has been released
904 // (relocation completed).
905 to_page = start_in_place_relocation(ZAddress::offset(addr));
906 set_target(to_age, to_page);
907 }
908 }
909
910 public:
911 ZRelocateWork(Allocator* allocator, ZGeneration* generation)
912 : _allocator(allocator),
913 _forwarding(nullptr),
914 _target(),
915 _generation(generation),
916 _other_promoted(0),
917 _other_compacted(0) {}
918
919 ~ZRelocateWork() {
920 for (uint i = 0; i < ZAllocator::_relocation_allocators; ++i) {
921 _allocator->free_target_page(_target[i]);
922 }
923 // Report statistics on-behalf of non-worker threads
924 _generation->increase_promoted(_other_promoted);
925 _generation->increase_compacted(_other_compacted);
926 }
927
928 bool active_remset_is_current() const {
929 // Normal old-to-old relocation can treat the from-page remset as a
930 // read-only copy, and then copy over the appropriate remset bits to the
931 // cleared to-page's 'current' remset bitmap.
932 //
933 // In-place relocation is more complicated. Since, the same page is both
934 // a from-page and a to-page, we need to remove the old remset bits, and
935 // add remset bits that corresponds to the new locations of the relocated
936 // objects.
937 //
938 // Depending on how long ago (in terms of number of young GC's and the
939 // current young GC's phase), the page was allocated, the active
940 // remembered set will be in either the 'current' or 'previous' bitmap.
941 //
942 // If the active bits are in the 'previous' bitmap, we know that the
943 // 'current' bitmap was cleared at some earlier point in time, and we can
944 // simply set new bits in 'current' bitmap, and later when relocation has
945 // read all the old remset bits, we could just clear the 'previous' remset
946 // bitmap.
947 //
948 // If, on the other hand, the active bits are in the 'current' bitmap, then
949 // that bitmap will be used to both read the old remset bits, and the
950 // destination for the remset bits that we copy when an object is copied
951 // to it's new location within the page. We need to *carefully* remove all
952 // all old remset bits, without clearing out the newly set bits.
953 return ZGeneration::old()->active_remset_is_current();
954 }
955
956 void clear_remset_before_in_place_reuse(ZPage* page) {
957 if (_forwarding->from_age() != ZPageAge::old) {
958 // No remset bits
959 return;
960 }
961
962 // Clear 'previous' remset bits. For in-place relocated pages, the previous
963 // remset bits are always used, even when active_remset_is_current().
964 page->clear_remset_previous();
965 }
966
967 void finish_in_place_relocation() {
968 // We are done with the from_space copy of the page
969 _forwarding->in_place_relocation_finish();
970 }
971
972 void do_forwarding(ZForwarding* forwarding) {
973 _forwarding = forwarding;
974
975 _forwarding->page()->log_msg(" (relocate page)");
976
977 ZVerify::before_relocation(_forwarding);
978
979 // Relocate objects
980 _forwarding->object_iterate([&](oop obj) { relocate_object(obj); });
981
982 ZVerify::after_relocation(_forwarding);
983
984 // Verify
985 if (ZVerifyForwarding) {
986 _forwarding->verify();
987 }
988
989 _generation->increase_freed(_forwarding->page()->size());
990
991 // Deal with in-place relocation
992 const bool in_place = _forwarding->in_place_relocation();
993 if (in_place) {
994 finish_in_place_relocation();
995 }
996
997 // Old from-space pages need to deal with remset bits
998 if (_forwarding->from_age() == ZPageAge::old) {
999 _forwarding->relocated_remembered_fields_after_relocate();
1000 }
1001
1002 // Release relocated page
1003 _forwarding->release_page();
1004
1005 if (in_place) {
1006 // Wait for all other threads to call release_page
1007 ZPage* const page = _forwarding->detach_page();
1008
1009 // Ensure that previous remset bits are cleared
1010 clear_remset_before_in_place_reuse(page);
1011
1012 page->log_msg(" (relocate page done in-place)");
1013
1014 // Different pages when promoting
1015 ZPage* const target_page = target(_forwarding->to_age());
1016 _allocator->share_target_page(target_page);
1017
1018 } else {
1019 // Wait for all other threads to call release_page
1020 ZPage* const page = _forwarding->detach_page();
1021
1022 page->log_msg(" (relocate page done normal)");
1023
1024 // Free page
1025 ZHeap::heap()->free_page(page, true /* allow_defragment */);
1026 }
1027 }
1028 };
1029
1030 class ZRelocateStoreBufferInstallBasePointersThreadClosure : public ThreadClosure {
1031 public:
1032 virtual void do_thread(Thread* thread) {
1033 JavaThread* const jt = JavaThread::cast(thread);
1034 ZStoreBarrierBuffer* buffer = ZThreadLocalData::store_barrier_buffer(jt);
1035 buffer->install_base_pointers();
1036 }
1037 };
1038
1039 // Installs the object base pointers (object starts), for the fields written
1040 // in the store buffer. The code that searches for the object start uses that
1041 // liveness information stored in the pages. That information is lost when the
1042 // pages have been relocated and then destroyed.
1043 class ZRelocateStoreBufferInstallBasePointersTask : public ZTask {
1044 private:
1045 ZJavaThreadsIterator _threads_iter;
1046
1047 public:
1048 ZRelocateStoreBufferInstallBasePointersTask(ZGeneration* generation)
1049 : ZTask("ZRelocateStoreBufferInstallBasePointersTask"),
1050 _threads_iter(generation->id_optional()) {}
1051
1052 virtual void work() {
1053 ZRelocateStoreBufferInstallBasePointersThreadClosure fix_store_buffer_cl;
1054 _threads_iter.apply(&fix_store_buffer_cl);
1055 }
1056 };
1057
1058 class ZRelocateTask : public ZRestartableTask {
1059 private:
1060 ZRelocationSetParallelIterator _iter;
1061 ZGeneration* const _generation;
1062 ZRelocateQueue* const _queue;
1063 ZRelocateSmallAllocator _small_allocator;
1064 ZRelocateMediumAllocator _medium_allocator;
1065
1066 public:
1067 ZRelocateTask(ZRelocationSet* relocation_set, ZRelocateQueue* queue)
1068 : ZRestartableTask("ZRelocateTask"),
1069 _iter(relocation_set),
1070 _generation(relocation_set->generation()),
1071 _queue(queue),
1072 _small_allocator(_generation),
1073 _medium_allocator(_generation) {}
1074
1075 ~ZRelocateTask() {
1076 _generation->stat_relocation()->at_relocate_end(_small_allocator.in_place_count(), _medium_allocator.in_place_count());
1077
1078 // Signal that we're not using the queue anymore. Used mostly for asserts.
1079 _queue->deactivate();
1080 }
1081
1082 virtual void work() {
1083 ZRelocateWork<ZRelocateSmallAllocator> small(&_small_allocator, _generation);
1084 ZRelocateWork<ZRelocateMediumAllocator> medium(&_medium_allocator, _generation);
1085
1086 const auto do_forwarding = [&](ZForwarding* forwarding) {
1087 ZPage* const page = forwarding->page();
1088 if (page->is_small()) {
1089 small.do_forwarding(forwarding);
1090 } else {
1091 medium.do_forwarding(forwarding);
1092 }
1093
1094 // Absolute last thing done while relocating a page.
1095 //
1096 // We don't use the SuspendibleThreadSet when relocating pages.
1097 // Instead the ZRelocateQueue is used as a pseudo STS joiner/leaver.
1098 //
1099 // After the mark_done call a safepointing could be completed and a
1100 // new GC phase could be entered.
1101 forwarding->mark_done();
1102 };
1103
1104 const auto claim_and_do_forwarding = [&](ZForwarding* forwarding) {
1105 if (forwarding->claim()) {
1106 do_forwarding(forwarding);
1107 }
1108 };
1109
1110 const auto do_forwarding_one_from_iter = [&]() {
1111 ZForwarding* forwarding;
1112
1113 if (_iter.next(&forwarding)) {
1114 claim_and_do_forwarding(forwarding);
1115 return true;
1116 }
1117
1118 return false;
1119 };
1120
1121 for (;;) {
1122 // As long as there are requests in the relocate queue, there are threads
1123 // waiting in a VM state that does not allow them to be blocked. The
1124 // worker thread needs to finish relocate these pages, and allow the
1125 // other threads to continue and proceed to a blocking state. After that,
1126 // the worker threads are allowed to safepoint synchronize.
1127 for (ZForwarding* forwarding; (forwarding = _queue->synchronize_poll()) != nullptr;) {
1128 do_forwarding(forwarding);
1129 }
1130
1131 if (!do_forwarding_one_from_iter()) {
1132 // No more work
1133 break;
1134 }
1135
1136 if (_generation->should_worker_resize()) {
1137 break;
1138 }
1139 }
1140
1141 _queue->leave();
1142 }
1143
1144 virtual void resize_workers(uint nworkers) {
1145 _queue->resize_workers(nworkers);
1146 }
1147 };
1148
1149 static void remap_and_maybe_add_remset(volatile zpointer* p) {
1150 const zpointer ptr = Atomic::load(p);
1151
1152 if (ZPointer::is_store_good(ptr)) {
1153 // Already has a remset entry
1154 return;
1155 }
1156
1157 // Remset entries are used for two reasons:
1158 // 1) Young marking old-to-young pointer roots
1159 // 2) Deferred remapping of stale old-to-young pointers
1160 //
1161 // This load barrier will up-front perform the remapping of (2),
1162 // and the code below only has to make sure we register up-to-date
1163 // old-to-young pointers for (1).
1164 const zaddress addr = ZBarrier::load_barrier_on_oop_field_preloaded(p, ptr);
1165
1166 if (is_null(addr)) {
1167 // No need for remset entries for null pointers
1168 return;
1169 }
1170
1171 if (ZHeap::heap()->is_old(addr)) {
1172 // No need for remset entries for pointers to old gen
1173 return;
1174 }
1175
1176 ZRelocate::add_remset(p);
1177 }
1178
1179 class ZRelocateAddRemsetForFlipPromoted : public ZRestartableTask {
1180 private:
1181 ZStatTimerYoung _timer;
1182 ZArrayParallelIterator<ZPage*> _iter;
1183
1184 public:
1185 ZRelocateAddRemsetForFlipPromoted(ZArray<ZPage*>* pages)
1186 : ZRestartableTask("ZRelocateAddRemsetForFlipPromoted"),
1187 _timer(ZSubPhaseConcurrentRelocateRememberedSetFlipPromotedYoung),
1188 _iter(pages) {}
1189
1190 virtual void work() {
1191 SuspendibleThreadSetJoiner sts_joiner;
1192
1193 for (ZPage* page; _iter.next(&page);) {
1194 page->object_iterate([&](oop obj) {
1195 ZIterator::basic_oop_iterate_safe(obj, remap_and_maybe_add_remset);
1196 });
1197
1198 SuspendibleThreadSet::yield();
1199 if (ZGeneration::young()->should_worker_resize()) {
1200 return;
1201 }
1202 }
1203 }
1204 };
1205
1206 void ZRelocate::relocate(ZRelocationSet* relocation_set) {
1207 {
1208 // Install the store buffer's base pointers before the
1209 // relocate task destroys the liveness information in
1210 // the relocated pages.
1211 ZRelocateStoreBufferInstallBasePointersTask buffer_task(_generation);
1212 workers()->run(&buffer_task);
1213 }
1214
1215 {
1216 ZRelocateTask relocate_task(relocation_set, &_queue);
1217 workers()->run(&relocate_task);
1218 }
1219
1220 if (relocation_set->generation()->is_young()) {
1221 ZRelocateAddRemsetForFlipPromoted task(relocation_set->flip_promoted_pages());
1222 workers()->run(&task);
1223 }
1224 }
1225
1226 ZPageAge ZRelocate::compute_to_age(ZPageAge from_age) {
1227 if (from_age == ZPageAge::old) {
1228 return ZPageAge::old;
1229 }
1230
1231 const uint age = static_cast<uint>(from_age);
1232 if (age >= ZGeneration::young()->tenuring_threshold()) {
1233 return ZPageAge::old;
1234 }
1235
1236 return static_cast<ZPageAge>(age + 1);
1237 }
1238
1239 class ZFlipAgePagesTask : public ZTask {
1240 private:
1241 ZArrayParallelIterator<ZPage*> _iter;
1242
1243 public:
1244 ZFlipAgePagesTask(const ZArray<ZPage*>* pages)
1245 : ZTask("ZPromotePagesTask"),
1246 _iter(pages) {}
1247
1248 virtual void work() {
1249 SuspendibleThreadSetJoiner sts_joiner;
1250 ZArray<ZPage*> promoted_pages;
1251
1252 for (ZPage* prev_page; _iter.next(&prev_page);) {
1253 const ZPageAge from_age = prev_page->age();
1254 const ZPageAge to_age = ZRelocate::compute_to_age(from_age);
1255 assert(from_age != ZPageAge::old, "invalid age for a young collection");
1256
1257 // Figure out if this is proper promotion
1258 const bool promotion = to_age == ZPageAge::old;
1259
1260 if (promotion) {
1261 // Before promoting an object (and before relocate start), we must ensure that all
1262 // contained zpointers are store good. The marking code ensures that for non-null
1263 // pointers, but null pointers are ignored. This code ensures that even null pointers
1264 // are made store good, for the promoted objects.
1265 prev_page->object_iterate([&](oop obj) {
1266 ZIterator::basic_oop_iterate_safe(obj, ZBarrier::promote_barrier_on_young_oop_field);
1267 });
1268 }
1269
1270 // Logging
1271 prev_page->log_msg(promotion ? " (flip promoted)" : " (flip survived)");
1272
1273 // Setup to-space page
1274 ZPage* const new_page = promotion ? prev_page->clone_limited() : prev_page;
1275
1276 // Reset page for flip aging
1277 new_page->reset(to_age);
1278 new_page->reset_livemap();
1279 if (promotion) {
1280 new_page->remset_alloc();
1281 }
1282
1283 if (promotion) {
1284 ZGeneration::young()->flip_promote(prev_page, new_page);
1285 // Defer promoted page registration times the lock is taken
1286 promoted_pages.push(prev_page);
1287 }
1288
1289 SuspendibleThreadSet::yield();
1290 }
1291
1292 ZGeneration::young()->register_flip_promoted(promoted_pages);
1293 }
1294 };
1295
1296 void ZRelocate::flip_age_pages(const ZArray<ZPage*>* pages) {
1297 ZFlipAgePagesTask flip_age_task(pages);
1298 workers()->run(&flip_age_task);
1299 }
1300
1301 void ZRelocate::synchronize() {
1302 _queue.synchronize();
1303 }
1304
1305 void ZRelocate::desynchronize() {
1306 _queue.desynchronize();
1307 }
1308
1309 ZRelocateQueue* ZRelocate::queue() {
1310 return &_queue;
1311 }
1312
1313 bool ZRelocate::is_queue_active() const {
1314 return _queue.is_active();
1315 }