1 /*
2 * Copyright (c) 2014, 2021, Red Hat, Inc. 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
27 #include "compiler/oopMap.hpp"
28 #include "gc/shared/continuationGCSupport.hpp"
29 #include "gc/shared/gcTraceTime.inline.hpp"
30 #include "gc/shared/preservedMarks.inline.hpp"
31 #include "gc/shared/slidingForwarding.inline.hpp"
32 #include "gc/shared/tlab_globals.hpp"
33 #include "gc/shared/workerThread.hpp"
34 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
35 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
36 #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
37 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
38 #include "gc/shenandoah/shenandoahFreeSet.hpp"
39 #include "gc/shenandoah/shenandoahFullGC.hpp"
40 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
41 #include "gc/shenandoah/shenandoahMark.inline.hpp"
42 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
43 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp"
44 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
45 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
46 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
47 #include "gc/shenandoah/shenandoahMetrics.hpp"
48 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
49 #include "gc/shenandoah/shenandoahReferenceProcessor.hpp"
50 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
51 #include "gc/shenandoah/shenandoahSTWMark.hpp"
52 #include "gc/shenandoah/shenandoahUtils.hpp"
53 #include "gc/shenandoah/shenandoahVerifier.hpp"
54 #include "gc/shenandoah/shenandoahVMOperations.hpp"
55 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
56 #include "memory/metaspaceUtils.hpp"
57 #include "memory/universe.hpp"
58 #include "oops/compressedOops.inline.hpp"
59 #include "oops/oop.inline.hpp"
60 #include "runtime/javaThread.hpp"
61 #include "runtime/orderAccess.hpp"
62 #include "runtime/vmThread.hpp"
63 #include "utilities/copy.hpp"
64 #include "utilities/events.hpp"
65 #include "utilities/growableArray.hpp"
66
67 ShenandoahFullGC::ShenandoahFullGC() :
68 _gc_timer(ShenandoahHeap::heap()->gc_timer()),
69 _preserved_marks(new PreservedMarksSet(true)) {}
70
71 ShenandoahFullGC::~ShenandoahFullGC() {
72 delete _preserved_marks;
73 }
74
75 bool ShenandoahFullGC::collect(GCCause::Cause cause) {
76 vmop_entry_full(cause);
77 // Always success
78 return true;
79 }
80
81 void ShenandoahFullGC::vmop_entry_full(GCCause::Cause cause) {
82 ShenandoahHeap* const heap = ShenandoahHeap::heap();
83 TraceCollectorStats tcs(heap->monitoring_support()->full_stw_collection_counters());
84 ShenandoahTimingsTracker timing(ShenandoahPhaseTimings::full_gc_gross);
85
86 heap->try_inject_alloc_failure();
87 VM_ShenandoahFullGC op(cause, this);
88 VMThread::execute(&op);
89 }
90
91 void ShenandoahFullGC::entry_full(GCCause::Cause cause) {
92 static const char* msg = "Pause Full";
93 ShenandoahPausePhase gc_phase(msg, ShenandoahPhaseTimings::full_gc, true /* log_heap_usage */);
94 EventMark em("%s", msg);
95
96 ShenandoahWorkerScope scope(ShenandoahHeap::heap()->workers(),
97 ShenandoahWorkerPolicy::calc_workers_for_fullgc(),
98 "full gc");
99
100 op_full(cause);
101 }
102
103 void ShenandoahFullGC::op_full(GCCause::Cause cause) {
104 ShenandoahMetricsSnapshot metrics;
105 metrics.snap_before();
106
107 // Perform full GC
108 do_it(cause);
109
110 ShenandoahHeap* const heap = ShenandoahHeap::heap();
111
112 metrics.snap_after();
113
114 if (metrics.is_good_progress()) {
115 heap->notify_gc_progress();
116 } else {
117 // Nothing to do. Tell the allocation path that we have failed to make
118 // progress, and it can finally fail.
119 heap->notify_gc_no_progress();
120 }
121
122 // Regardless if progress was made, we record that we completed a "successful" full GC.
123 heap->heuristics()->record_success_full();
124 heap->shenandoah_policy()->record_success_full();
125 }
126
127 void ShenandoahFullGC::do_it(GCCause::Cause gc_cause) {
128 ShenandoahHeap* heap = ShenandoahHeap::heap();
129
130 if (ShenandoahVerify) {
131 heap->verifier()->verify_before_fullgc();
132 }
133
134 if (VerifyBeforeGC) {
135 Universe::verify();
136 }
137
138 // Degenerated GC may carry concurrent root flags when upgrading to
139 // full GC. We need to reset it before mutators resume.
140 heap->set_concurrent_strong_root_in_progress(false);
141 heap->set_concurrent_weak_root_in_progress(false);
142
143 heap->set_full_gc_in_progress(true);
144
145 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
146 assert(Thread::current()->is_VM_thread(), "Do full GC only while world is stopped");
147
148 {
149 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdump_pre);
150 heap->pre_full_gc_dump(_gc_timer);
151 }
152
153 {
154 ShenandoahGCPhase prepare_phase(ShenandoahPhaseTimings::full_gc_prepare);
155 // Full GC is supposed to recover from any GC state:
156
157 // a0. Remember if we have forwarded objects
158 bool has_forwarded_objects = heap->has_forwarded_objects();
159
160 // a1. Cancel evacuation, if in progress
161 if (heap->is_evacuation_in_progress()) {
162 heap->set_evacuation_in_progress(false);
163 }
164 assert(!heap->is_evacuation_in_progress(), "sanity");
165
166 // a2. Cancel update-refs, if in progress
167 if (heap->is_update_refs_in_progress()) {
168 heap->set_update_refs_in_progress(false);
169 }
170 assert(!heap->is_update_refs_in_progress(), "sanity");
171
172 // b. Cancel concurrent mark, if in progress
173 if (heap->is_concurrent_mark_in_progress()) {
174 ShenandoahConcurrentGC::cancel();
175 heap->set_concurrent_mark_in_progress(false);
176 }
177 assert(!heap->is_concurrent_mark_in_progress(), "sanity");
178
179 // c. Update roots if this full GC is due to evac-oom, which may carry from-space pointers in roots.
180 if (has_forwarded_objects) {
181 update_roots(true /*full_gc*/);
182 }
183
184 // d. Reset the bitmaps for new marking
185 heap->reset_mark_bitmap();
186 assert(heap->marking_context()->is_bitmap_clear(), "sanity");
187 assert(!heap->marking_context()->is_complete(), "sanity");
188
189 // e. Abandon reference discovery and clear all discovered references.
190 ShenandoahReferenceProcessor* rp = heap->ref_processor();
191 rp->abandon_partial_discovery();
192
193 // f. Sync pinned region status from the CP marks
194 heap->sync_pinned_region_status();
195
196 // The rest of prologue:
197 _preserved_marks->init(heap->workers()->active_workers());
198
199 assert(heap->has_forwarded_objects() == has_forwarded_objects, "This should not change");
200 }
201
202 if (UseTLAB) {
203 heap->gclabs_retire(ResizeTLAB);
204 heap->tlabs_retire(ResizeTLAB);
205 }
206
207 OrderAccess::fence();
208
209 phase1_mark_heap();
210
211 // Once marking is done, which may have fixed up forwarded objects, we can drop it.
212 // Coming out of Full GC, we would not have any forwarded objects.
213 // This also prevents resolves with fwdptr from kicking in while adjusting pointers in phase3.
214 heap->set_has_forwarded_objects(false);
215
216 heap->set_full_gc_move_in_progress(true);
217
218 // Setup workers for the rest
219 OrderAccess::fence();
220
221 // Initialize worker slices
222 ShenandoahHeapRegionSet** worker_slices = NEW_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, heap->max_workers(), mtGC);
223 for (uint i = 0; i < heap->max_workers(); i++) {
224 worker_slices[i] = new ShenandoahHeapRegionSet();
225 }
226
227 {
228 // The rest of code performs region moves, where region status is undefined
229 // until all phases run together.
230 ShenandoahHeapLocker lock(heap->lock());
231
232 SlidingForwarding::begin();
233
234 phase2_calculate_target_addresses(worker_slices);
235
236 OrderAccess::fence();
237
238 phase3_update_references();
239
240 phase4_compact_objects(worker_slices);
241
242 phase5_epilog();
243
244 SlidingForwarding::end();
245 }
246
247 // Resize metaspace
248 MetaspaceGC::compute_new_size();
249
250 // Free worker slices
251 for (uint i = 0; i < heap->max_workers(); i++) {
252 delete worker_slices[i];
253 }
254 FREE_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, worker_slices);
255
256 heap->set_full_gc_move_in_progress(false);
257 heap->set_full_gc_in_progress(false);
258
259 if (ShenandoahVerify) {
260 heap->verifier()->verify_after_fullgc();
261 }
262
263 if (VerifyAfterGC) {
264 Universe::verify();
265 }
266
267 {
268 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdump_post);
269 heap->post_full_gc_dump(_gc_timer);
270 }
271 }
272
273 class ShenandoahPrepareForMarkClosure: public ShenandoahHeapRegionClosure {
274 private:
275 ShenandoahMarkingContext* const _ctx;
276
277 public:
278 ShenandoahPrepareForMarkClosure() : _ctx(ShenandoahHeap::heap()->marking_context()) {}
279
280 void heap_region_do(ShenandoahHeapRegion *r) {
281 _ctx->capture_top_at_mark_start(r);
282 r->clear_live_data();
283 }
284
285 bool is_thread_safe() { return true; }
286 };
287
288 void ShenandoahFullGC::phase1_mark_heap() {
289 GCTraceTime(Info, gc, phases) time("Phase 1: Mark live objects", _gc_timer);
290 ShenandoahGCPhase mark_phase(ShenandoahPhaseTimings::full_gc_mark);
291
292 ShenandoahHeap* heap = ShenandoahHeap::heap();
293
294 ShenandoahPrepareForMarkClosure cl;
295 heap->parallel_heap_region_iterate(&cl);
296
297 heap->set_unload_classes(heap->heuristics()->can_unload_classes());
298
299 ShenandoahReferenceProcessor* rp = heap->ref_processor();
300 // enable ("weak") refs discovery
301 rp->set_soft_reference_policy(true); // forcefully purge all soft references
302
303 ShenandoahSTWMark mark(true /*full_gc*/);
304 mark.mark();
305 heap->parallel_cleaning(true /* full_gc */);
306 }
307
308 class ShenandoahPrepareForCompactionObjectClosure : public ObjectClosure {
309 private:
310 PreservedMarks* const _preserved_marks;
311 ShenandoahHeap* const _heap;
312 GrowableArray<ShenandoahHeapRegion*>& _empty_regions;
313 int _empty_regions_pos;
314 ShenandoahHeapRegion* _to_region;
315 ShenandoahHeapRegion* _from_region;
316 HeapWord* _compact_point;
317
318 public:
319 ShenandoahPrepareForCompactionObjectClosure(PreservedMarks* preserved_marks,
320 GrowableArray<ShenandoahHeapRegion*>& empty_regions,
321 ShenandoahHeapRegion* to_region) :
322 _preserved_marks(preserved_marks),
323 _heap(ShenandoahHeap::heap()),
324 _empty_regions(empty_regions),
325 _empty_regions_pos(0),
326 _to_region(to_region),
327 _from_region(nullptr),
328 _compact_point(to_region->bottom()) {}
329
330 void set_from_region(ShenandoahHeapRegion* from_region) {
331 _from_region = from_region;
332 }
333
334 void finish() {
335 assert(_to_region != nullptr, "should not happen");
336 _to_region->set_new_top(_compact_point);
337 }
338
339 bool is_compact_same_region() {
340 return _from_region == _to_region;
341 }
342
343 int empty_regions_pos() {
344 return _empty_regions_pos;
345 }
346
347 void do_object(oop p) {
348 assert(_from_region != nullptr, "must set before work");
349 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
350 assert(!_heap->complete_marking_context()->allocated_after_mark_start(p), "must be truly marked");
351
352 size_t obj_size = p->size();
353 if (_compact_point + obj_size > _to_region->end()) {
354 finish();
355
356 // Object doesn't fit. Pick next empty region and start compacting there.
357 ShenandoahHeapRegion* new_to_region;
358 if (_empty_regions_pos < _empty_regions.length()) {
359 new_to_region = _empty_regions.at(_empty_regions_pos);
360 _empty_regions_pos++;
361 } else {
362 // Out of empty region? Compact within the same region.
363 new_to_region = _from_region;
364 }
365
366 assert(new_to_region != _to_region, "must not reuse same to-region");
367 assert(new_to_region != nullptr, "must not be null");
368 _to_region = new_to_region;
369 _compact_point = _to_region->bottom();
370 }
371
372 // Object fits into current region, record new location, if object does not move:
373 assert(_compact_point + obj_size <= _to_region->end(), "must fit");
374 shenandoah_assert_not_forwarded(nullptr, p);
375 if (_compact_point != cast_from_oop<HeapWord*>(p)) {
376 _preserved_marks->push_if_necessary(p, p->mark());
377 SlidingForwarding::forward_to(p, cast_to_oop(_compact_point));
378 }
379 _compact_point += obj_size;
380 }
381 };
382
383 class ShenandoahPrepareForCompactionTask : public WorkerTask {
384 private:
385 PreservedMarksSet* const _preserved_marks;
386 ShenandoahHeap* const _heap;
387 ShenandoahHeapRegionSet** const _worker_slices;
388
389 public:
390 ShenandoahPrepareForCompactionTask(PreservedMarksSet *preserved_marks, ShenandoahHeapRegionSet **worker_slices) :
391 WorkerTask("Shenandoah Prepare For Compaction"),
392 _preserved_marks(preserved_marks),
393 _heap(ShenandoahHeap::heap()), _worker_slices(worker_slices) {
394 }
395
396 static bool is_candidate_region(ShenandoahHeapRegion* r) {
397 // Empty region: get it into the slice to defragment the slice itself.
398 // We could have skipped this without violating correctness, but we really
399 // want to compact all live regions to the start of the heap, which sometimes
400 // means moving them into the fully empty regions.
401 if (r->is_empty()) return true;
402
403 // Can move the region, and this is not the humongous region. Humongous
404 // moves are special cased here, because their moves are handled separately.
405 return r->is_stw_move_allowed() && !r->is_humongous();
406 }
407
408 void work(uint worker_id) override;
409 private:
410 template<typename ClosureType>
411 void prepare_for_compaction(ClosureType& cl,
412 GrowableArray<ShenandoahHeapRegion*>& empty_regions,
413 ShenandoahHeapRegionSetIterator& it,
414 ShenandoahHeapRegion* from_region);
415 };
416
417 void ShenandoahPrepareForCompactionTask::work(uint worker_id) {
418 ShenandoahParallelWorkerSession worker_session(worker_id);
419 ShenandoahHeapRegionSet* slice = _worker_slices[worker_id];
420 ShenandoahHeapRegionSetIterator it(slice);
421 ShenandoahHeapRegion* from_region = it.next();
422 // No work?
423 if (from_region == nullptr) {
424 return;
425 }
426
427 // Sliding compaction. Walk all regions in the slice, and compact them.
428 // Remember empty regions and reuse them as needed.
429 ResourceMark rm;
430
431 GrowableArray<ShenandoahHeapRegion*> empty_regions((int)_heap->num_regions());
432
433 ShenandoahPrepareForCompactionObjectClosure cl(_preserved_marks->get(worker_id), empty_regions, from_region);
434 prepare_for_compaction(cl, empty_regions, it, from_region);
435 }
436
437 template<typename ClosureType>
438 void ShenandoahPrepareForCompactionTask::prepare_for_compaction(ClosureType& cl,
439 GrowableArray<ShenandoahHeapRegion*>& empty_regions,
440 ShenandoahHeapRegionSetIterator& it,
441 ShenandoahHeapRegion* from_region) {
442 while (from_region != nullptr) {
443 assert(is_candidate_region(from_region), "Sanity");
444 cl.set_from_region(from_region);
445 if (from_region->has_live()) {
446 _heap->marked_object_iterate(from_region, &cl);
447 }
448
449 // Compacted the region to somewhere else? From-region is empty then.
450 if (!cl.is_compact_same_region()) {
451 empty_regions.append(from_region);
452 }
453 from_region = it.next();
454 }
455 cl.finish();
456
457 // Mark all remaining regions as empty
458 for (int pos = cl.empty_regions_pos(); pos < empty_regions.length(); ++pos) {
459 ShenandoahHeapRegion* r = empty_regions.at(pos);
460 r->set_new_top(r->bottom());
461 }
462 }
463
464 void ShenandoahFullGC::calculate_target_humongous_objects() {
465 ShenandoahHeap* heap = ShenandoahHeap::heap();
466
467 // Compute the new addresses for humongous objects. We need to do this after addresses
468 // for regular objects are calculated, and we know what regions in heap suffix are
469 // available for humongous moves.
470 //
471 // Scan the heap backwards, because we are compacting humongous regions towards the end.
472 // Maintain the contiguous compaction window in [to_begin; to_end), so that we can slide
473 // humongous start there.
474 //
475 // The complication is potential non-movable regions during the scan. If such region is
476 // detected, then sliding restarts towards that non-movable region.
477
478 size_t to_begin = heap->num_regions();
479 size_t to_end = heap->num_regions();
480
481 for (size_t c = heap->num_regions(); c > 0; c--) {
482 ShenandoahHeapRegion *r = heap->get_region(c - 1);
483 if (r->is_humongous_continuation() || (r->new_top() == r->bottom())) {
484 // To-region candidate: record this, and continue scan
485 to_begin = r->index();
486 continue;
487 }
488
489 if (r->is_humongous_start() && r->is_stw_move_allowed()) {
490 // From-region candidate: movable humongous region
491 oop old_obj = cast_to_oop(r->bottom());
492 size_t words_size = old_obj->size();
493 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
494
495 size_t start = to_end - num_regions;
496
497 if (start >= to_begin && start != r->index()) {
498 // Fits into current window, and the move is non-trivial. Record the move then, and continue scan.
499 _preserved_marks->get(0)->push_if_necessary(old_obj, old_obj->mark());
500 SlidingForwarding::forward_to(old_obj, cast_to_oop(heap->get_region(start)->bottom()));
501 to_end = start;
502 continue;
503 }
504 }
505
506 // Failed to fit. Scan starting from current region.
507 to_begin = r->index();
508 to_end = r->index();
509 }
510 }
511
512 class ShenandoahEnsureHeapActiveClosure: public ShenandoahHeapRegionClosure {
513 private:
514 ShenandoahHeap* const _heap;
515
516 public:
517 ShenandoahEnsureHeapActiveClosure() : _heap(ShenandoahHeap::heap()) {}
518 void heap_region_do(ShenandoahHeapRegion* r) {
519 if (r->is_trash()) {
520 r->recycle();
521 }
522 if (r->is_cset()) {
523 r->make_regular_bypass();
524 }
525 if (r->is_empty_uncommitted()) {
526 r->make_committed_bypass();
527 }
528 assert (r->is_committed(), "only committed regions in heap now, see region " SIZE_FORMAT, r->index());
529
530 // Record current region occupancy: this communicates empty regions are free
531 // to the rest of Full GC code.
532 r->set_new_top(r->top());
533 }
534 };
535
536 class ShenandoahTrashImmediateGarbageClosure: public ShenandoahHeapRegionClosure {
537 private:
538 ShenandoahHeap* const _heap;
539 ShenandoahMarkingContext* const _ctx;
540
541 public:
542 ShenandoahTrashImmediateGarbageClosure() :
543 _heap(ShenandoahHeap::heap()),
544 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
545
546 void heap_region_do(ShenandoahHeapRegion* r) {
547 if (r->is_humongous_start()) {
548 oop humongous_obj = cast_to_oop(r->bottom());
549 if (!_ctx->is_marked(humongous_obj)) {
550 assert(!r->has_live(),
551 "Region " SIZE_FORMAT " is not marked, should not have live", r->index());
552 _heap->trash_humongous_region_at(r);
553 } else {
554 assert(r->has_live(),
555 "Region " SIZE_FORMAT " should have live", r->index());
556 }
557 } else if (r->is_humongous_continuation()) {
558 // If we hit continuation, the non-live humongous starts should have been trashed already
559 assert(r->humongous_start_region()->has_live(),
560 "Region " SIZE_FORMAT " should have live", r->index());
561 } else if (r->is_regular()) {
562 if (!r->has_live()) {
563 r->make_trash_immediate();
564 }
565 }
566 }
567 };
568
569 void ShenandoahFullGC::distribute_slices(ShenandoahHeapRegionSet** worker_slices) {
570 ShenandoahHeap* heap = ShenandoahHeap::heap();
571
572 uint n_workers = heap->workers()->active_workers();
573 size_t n_regions = heap->num_regions();
574
575 // What we want to accomplish: have the dense prefix of data, while still balancing
576 // out the parallel work.
577 //
578 // Assuming the amount of work is driven by the live data that needs moving, we can slice
579 // the entire heap into equal-live-sized prefix slices, and compact into them. So, each
580 // thread takes all regions in its prefix subset, and then it takes some regions from
581 // the tail.
582 //
583 // Tail region selection becomes interesting.
584 //
585 // First, we want to distribute the regions fairly between the workers, and those regions
586 // might have different amount of live data. So, until we sure no workers need live data,
587 // we need to only take what the worker needs.
588 //
589 // Second, since we slide everything to the left in each slice, the most busy regions
590 // would be the ones on the left. Which means we want to have all workers have their after-tail
591 // regions as close to the left as possible.
592 //
593 // The easiest way to do this is to distribute after-tail regions in round-robin between
594 // workers that still need live data.
595 //
596 // Consider parallel workers A, B, C, then the target slice layout would be:
597 //
598 // AAAAAAAABBBBBBBBCCCCCCCC|ABCABCABCABCABCABCABCABABABABABABABABABABAAAAA
599 //
600 // (.....dense-prefix.....) (.....................tail...................)
601 // [all regions fully live] [left-most regions are fuller that right-most]
602 //
603
604 // Compute how much live data is there. This would approximate the size of dense prefix
605 // we target to create.
606 size_t total_live = 0;
607 for (size_t idx = 0; idx < n_regions; idx++) {
608 ShenandoahHeapRegion *r = heap->get_region(idx);
609 if (ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
610 total_live += r->get_live_data_words();
611 }
612 }
613
614 // Estimate the size for the dense prefix. Note that we specifically count only the
615 // "full" regions, so there would be some non-full regions in the slice tail.
616 size_t live_per_worker = total_live / n_workers;
617 size_t prefix_regions_per_worker = live_per_worker / ShenandoahHeapRegion::region_size_words();
618 size_t prefix_regions_total = prefix_regions_per_worker * n_workers;
619 prefix_regions_total = MIN2(prefix_regions_total, n_regions);
620 assert(prefix_regions_total <= n_regions, "Sanity");
621
622 // There might be non-candidate regions in the prefix. To compute where the tail actually
623 // ends up being, we need to account those as well.
624 size_t prefix_end = prefix_regions_total;
625 for (size_t idx = 0; idx < prefix_regions_total; idx++) {
626 ShenandoahHeapRegion *r = heap->get_region(idx);
627 if (!ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
628 prefix_end++;
629 }
630 }
631 prefix_end = MIN2(prefix_end, n_regions);
632 assert(prefix_end <= n_regions, "Sanity");
633
634 // Distribute prefix regions per worker: each thread definitely gets its own same-sized
635 // subset of dense prefix.
636 size_t prefix_idx = 0;
637
638 size_t* live = NEW_C_HEAP_ARRAY(size_t, n_workers, mtGC);
639
640 for (size_t wid = 0; wid < n_workers; wid++) {
641 ShenandoahHeapRegionSet* slice = worker_slices[wid];
642
643 live[wid] = 0;
644 size_t regs = 0;
645
646 // Add all prefix regions for this worker
647 while (prefix_idx < prefix_end && regs < prefix_regions_per_worker) {
648 ShenandoahHeapRegion *r = heap->get_region(prefix_idx);
649 if (ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
650 slice->add_region(r);
651 live[wid] += r->get_live_data_words();
652 regs++;
653 }
654 prefix_idx++;
655 }
656 }
657
658 // Distribute the tail among workers in round-robin fashion.
659 size_t wid = n_workers - 1;
660
661 for (size_t tail_idx = prefix_end; tail_idx < n_regions; tail_idx++) {
662 ShenandoahHeapRegion *r = heap->get_region(tail_idx);
663 if (ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
664 assert(wid < n_workers, "Sanity");
665
666 size_t live_region = r->get_live_data_words();
667
668 // Select next worker that still needs live data.
669 size_t old_wid = wid;
670 do {
671 wid++;
672 if (wid == n_workers) wid = 0;
673 } while (live[wid] + live_region >= live_per_worker && old_wid != wid);
674
675 if (old_wid == wid) {
676 // Circled back to the same worker? This means liveness data was
677 // miscalculated. Bump the live_per_worker limit so that
678 // everyone gets a piece of the leftover work.
679 live_per_worker += ShenandoahHeapRegion::region_size_words();
680 }
681
682 worker_slices[wid]->add_region(r);
683 live[wid] += live_region;
684 }
685 }
686
687 FREE_C_HEAP_ARRAY(size_t, live);
688
689 #ifdef ASSERT
690 ResourceBitMap map(n_regions);
691 for (size_t wid = 0; wid < n_workers; wid++) {
692 ShenandoahHeapRegionSetIterator it(worker_slices[wid]);
693 ShenandoahHeapRegion* r = it.next();
694 while (r != nullptr) {
695 size_t idx = r->index();
696 assert(ShenandoahPrepareForCompactionTask::is_candidate_region(r), "Sanity: " SIZE_FORMAT, idx);
697 assert(!map.at(idx), "No region distributed twice: " SIZE_FORMAT, idx);
698 map.at_put(idx, true);
699 r = it.next();
700 }
701 }
702
703 for (size_t rid = 0; rid < n_regions; rid++) {
704 bool is_candidate = ShenandoahPrepareForCompactionTask::is_candidate_region(heap->get_region(rid));
705 bool is_distributed = map.at(rid);
706 assert(is_distributed || !is_candidate, "All candidates are distributed: " SIZE_FORMAT, rid);
707 }
708 #endif
709 }
710
711 void ShenandoahFullGC::phase2_calculate_target_addresses(ShenandoahHeapRegionSet** worker_slices) {
712 GCTraceTime(Info, gc, phases) time("Phase 2: Compute new object addresses", _gc_timer);
713 ShenandoahGCPhase calculate_address_phase(ShenandoahPhaseTimings::full_gc_calculate_addresses);
714
715 ShenandoahHeap* heap = ShenandoahHeap::heap();
716
717 // About to figure out which regions can be compacted, make sure pinning status
718 // had been updated in GC prologue.
719 heap->assert_pinned_region_status();
720
721 {
722 // Trash the immediately collectible regions before computing addresses
723 ShenandoahTrashImmediateGarbageClosure tigcl;
724 heap->heap_region_iterate(&tigcl);
725
726 // Make sure regions are in good state: committed, active, clean.
727 // This is needed because we are potentially sliding the data through them.
728 ShenandoahEnsureHeapActiveClosure ecl;
729 heap->heap_region_iterate(&ecl);
730 }
731
732 // Compute the new addresses for regular objects
733 {
734 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_regular);
735
736 distribute_slices(worker_slices);
737
738 ShenandoahPrepareForCompactionTask task(_preserved_marks, worker_slices);
739 heap->workers()->run_task(&task);
740 }
741
742 // Compute the new addresses for humongous objects
743 {
744 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_humong);
745 calculate_target_humongous_objects();
746 }
747 }
748
749 class ShenandoahAdjustPointersClosure : public MetadataVisitingOopIterateClosure {
750 private:
751 ShenandoahHeap* const _heap;
752 ShenandoahMarkingContext* const _ctx;
753
754 template <class T>
755 inline void do_oop_work(T* p) {
756 T o = RawAccess<>::oop_load(p);
757 if (!CompressedOops::is_null(o)) {
758 oop obj = CompressedOops::decode_not_null(o);
759 assert(_ctx->is_marked(obj), "must be marked");
760 if (SlidingForwarding::is_forwarded(obj)) {
761 oop forw = SlidingForwarding::forwardee(obj);
762 RawAccess<IS_NOT_NULL>::oop_store(p, forw);
763 }
764 }
765 }
766
767 public:
768 ShenandoahAdjustPointersClosure() :
769 _heap(ShenandoahHeap::heap()),
770 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
771
772 void do_oop(oop* p) { do_oop_work(p); }
773 void do_oop(narrowOop* p) { do_oop_work(p); }
774 void do_method(Method* m) {}
775 void do_nmethod(nmethod* nm) {}
776 };
777
778 class ShenandoahAdjustPointersObjectClosure : public ObjectClosure {
779 private:
780 ShenandoahHeap* const _heap;
781 ShenandoahAdjustPointersClosure _cl;
782
783 public:
784 ShenandoahAdjustPointersObjectClosure() :
785 _heap(ShenandoahHeap::heap()) {
786 }
787 void do_object(oop p) {
788 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
789 p->oop_iterate(&_cl);
790 }
791 };
792
793 class ShenandoahAdjustPointersTask : public WorkerTask {
794 private:
795 ShenandoahHeap* const _heap;
796 ShenandoahRegionIterator _regions;
797
798 public:
799 ShenandoahAdjustPointersTask() :
800 WorkerTask("Shenandoah Adjust Pointers"),
801 _heap(ShenandoahHeap::heap()) {
802 }
803
804 void work(uint worker_id) {
805 ShenandoahParallelWorkerSession worker_session(worker_id);
806 ShenandoahAdjustPointersObjectClosure obj_cl;
807 ShenandoahHeapRegion* r = _regions.next();
808 while (r != nullptr) {
809 if (!r->is_humongous_continuation() && r->has_live()) {
810 _heap->marked_object_iterate(r, &obj_cl);
811 }
812 r = _regions.next();
813 }
814 }
815 };
816
817 class ShenandoahAdjustRootPointersTask : public WorkerTask {
818 private:
819 ShenandoahRootAdjuster* _rp;
820 PreservedMarksSet* _preserved_marks;
821 public:
822 ShenandoahAdjustRootPointersTask(ShenandoahRootAdjuster* rp, PreservedMarksSet* preserved_marks) :
823 WorkerTask("Shenandoah Adjust Root Pointers"),
824 _rp(rp),
825 _preserved_marks(preserved_marks) {}
826
827 void work(uint worker_id) {
828 ShenandoahParallelWorkerSession worker_session(worker_id);
829 ShenandoahAdjustPointersClosure cl;
830 _rp->roots_do(worker_id, &cl);
831 _preserved_marks->get(worker_id)->adjust_during_full_gc();
832 }
833 };
834
835 void ShenandoahFullGC::phase3_update_references() {
836 GCTraceTime(Info, gc, phases) time("Phase 3: Adjust pointers", _gc_timer);
837 ShenandoahGCPhase adjust_pointer_phase(ShenandoahPhaseTimings::full_gc_adjust_pointers);
838
839 ShenandoahHeap* heap = ShenandoahHeap::heap();
840
841 WorkerThreads* workers = heap->workers();
842 uint nworkers = workers->active_workers();
843 {
844 #if COMPILER2_OR_JVMCI
845 DerivedPointerTable::clear();
846 #endif
847 ShenandoahRootAdjuster rp(nworkers, ShenandoahPhaseTimings::full_gc_adjust_roots);
848 ShenandoahAdjustRootPointersTask task(&rp, _preserved_marks);
849 workers->run_task(&task);
850 #if COMPILER2_OR_JVMCI
851 DerivedPointerTable::update_pointers();
852 #endif
853 }
854
855 ShenandoahAdjustPointersTask adjust_pointers_task;
856 workers->run_task(&adjust_pointers_task);
857 }
858
859 class ShenandoahCompactObjectsClosure : public ObjectClosure {
860 private:
861 ShenandoahHeap* const _heap;
862 uint const _worker_id;
863
864 public:
865 ShenandoahCompactObjectsClosure(uint worker_id) :
866 _heap(ShenandoahHeap::heap()), _worker_id(worker_id) {}
867
868 void do_object(oop p) {
869 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
870 size_t size = p->size();
871 if (SlidingForwarding::is_forwarded(p)) {
872 HeapWord* compact_from = cast_from_oop<HeapWord*>(p);
873 HeapWord* compact_to = cast_from_oop<HeapWord*>(SlidingForwarding::forwardee(p));
874 assert(compact_from != compact_to, "Forwarded object should move");
875 Copy::aligned_conjoint_words(compact_from, compact_to, size);
876 oop new_obj = cast_to_oop(compact_to);
877
878 ContinuationGCSupport::relativize_stack_chunk(new_obj);
879 new_obj->init_mark();
880 }
881 }
882 };
883
884 class ShenandoahCompactObjectsTask : public WorkerTask {
885 private:
886 ShenandoahHeap* const _heap;
887 ShenandoahHeapRegionSet** const _worker_slices;
888
889 public:
890 ShenandoahCompactObjectsTask(ShenandoahHeapRegionSet** worker_slices) :
891 WorkerTask("Shenandoah Compact Objects"),
892 _heap(ShenandoahHeap::heap()),
893 _worker_slices(worker_slices) {
894 }
895
896 void work(uint worker_id) {
897 ShenandoahParallelWorkerSession worker_session(worker_id);
898 ShenandoahHeapRegionSetIterator slice(_worker_slices[worker_id]);
899
900 ShenandoahCompactObjectsClosure cl(worker_id);
901 ShenandoahHeapRegion* r = slice.next();
902 while (r != nullptr) {
903 assert(!r->is_humongous(), "must not get humongous regions here");
904 if (r->has_live()) {
905 _heap->marked_object_iterate(r, &cl);
906 }
907 r->set_top(r->new_top());
908 r = slice.next();
909 }
910 }
911 };
912
913 class ShenandoahPostCompactClosure : public ShenandoahHeapRegionClosure {
914 private:
915 ShenandoahHeap* const _heap;
916 size_t _live;
917
918 public:
919 ShenandoahPostCompactClosure() : _heap(ShenandoahHeap::heap()), _live(0) {
920 }
921
922 void heap_region_do(ShenandoahHeapRegion* r) {
923 assert (!r->is_cset(), "cset regions should have been demoted already");
924
925 // Need to reset the complete-top-at-mark-start pointer here because
926 // the complete marking bitmap is no longer valid. This ensures
927 // size-based iteration in marked_object_iterate().
928 // NOTE: See blurb at ShenandoahMCResetCompleteBitmapTask on why we need to skip
929 // pinned regions.
930 if (!r->is_pinned()) {
931 _heap->complete_marking_context()->reset_top_at_mark_start(r);
932 }
933
934 size_t live = r->used();
935
936 // Make empty regions that have been allocated into regular
937 if (r->is_empty() && live > 0) {
938 r->make_regular_bypass();
939 if (ZapUnusedHeapArea) {
940 SpaceMangler::mangle_region(MemRegion(r->top(), r->end()));
941 }
942 }
943
944 // Reclaim regular regions that became empty
945 if (r->is_regular() && live == 0) {
946 r->make_trash();
947 }
948
949 // Recycle all trash regions
950 if (r->is_trash()) {
951 live = 0;
952 r->recycle();
953 }
954
955 r->set_live_data(live);
956 r->reset_alloc_metadata();
957 _live += live;
958 }
959
960 size_t get_live() {
961 return _live;
962 }
963 };
964
965 void ShenandoahFullGC::compact_humongous_objects() {
966 // Compact humongous regions, based on their fwdptr objects.
967 //
968 // This code is serial, because doing the in-slice parallel sliding is tricky. In most cases,
969 // humongous regions are already compacted, and do not require further moves, which alleviates
970 // sliding costs. We may consider doing this in parallel in the future.
971
972 ShenandoahHeap* heap = ShenandoahHeap::heap();
973
974 for (size_t c = heap->num_regions(); c > 0; c--) {
975 ShenandoahHeapRegion* r = heap->get_region(c - 1);
976 if (r->is_humongous_start()) {
977 oop old_obj = cast_to_oop(r->bottom());
978 if (SlidingForwarding::is_not_forwarded(old_obj)) {
979 // No need to move the object, it stays at the same slot
980 continue;
981 }
982 size_t words_size = old_obj->size();
983 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
984
985 size_t old_start = r->index();
986 size_t old_end = old_start + num_regions - 1;
987 size_t new_start = heap->heap_region_index_containing(SlidingForwarding::forwardee(old_obj));
988 size_t new_end = new_start + num_regions - 1;
989 assert(old_start != new_start, "must be real move");
990 assert(r->is_stw_move_allowed(), "Region " SIZE_FORMAT " should be movable", r->index());
991
992 Copy::aligned_conjoint_words(r->bottom(), heap->get_region(new_start)->bottom(), words_size);
993 ContinuationGCSupport::relativize_stack_chunk(cast_to_oop<HeapWord*>(r->bottom()));
994
995 oop new_obj = cast_to_oop(heap->get_region(new_start)->bottom());
996 new_obj->init_mark();
997
998 {
999 for (size_t c = old_start; c <= old_end; c++) {
1000 ShenandoahHeapRegion* r = heap->get_region(c);
1001 r->make_regular_bypass();
1002 r->set_top(r->bottom());
1003 }
1004
1005 for (size_t c = new_start; c <= new_end; c++) {
1006 ShenandoahHeapRegion* r = heap->get_region(c);
1007 if (c == new_start) {
1008 r->make_humongous_start_bypass();
1009 } else {
1010 r->make_humongous_cont_bypass();
1011 }
1012
1013 // Trailing region may be non-full, record the remainder there
1014 size_t remainder = words_size & ShenandoahHeapRegion::region_size_words_mask();
1015 if ((c == new_end) && (remainder != 0)) {
1016 r->set_top(r->bottom() + remainder);
1017 } else {
1018 r->set_top(r->end());
1019 }
1020
1021 r->reset_alloc_metadata();
1022 }
1023 }
1024 }
1025 }
1026 }
1027
1028 // This is slightly different to ShHeap::reset_next_mark_bitmap:
1029 // we need to remain able to walk pinned regions.
1030 // Since pinned region do not move and don't get compacted, we will get holes with
1031 // unreachable objects in them (which may have pointers to unloaded Klasses and thus
1032 // cannot be iterated over using oop->size(). The only way to safely iterate over those is using
1033 // a valid marking bitmap and valid TAMS pointer. This class only resets marking
1034 // bitmaps for un-pinned regions, and later we only reset TAMS for unpinned regions.
1035 class ShenandoahMCResetCompleteBitmapTask : public WorkerTask {
1036 private:
1037 ShenandoahRegionIterator _regions;
1038
1039 public:
1040 ShenandoahMCResetCompleteBitmapTask() :
1041 WorkerTask("Shenandoah Reset Bitmap") {
1042 }
1043
1044 void work(uint worker_id) {
1045 ShenandoahParallelWorkerSession worker_session(worker_id);
1046 ShenandoahHeapRegion* region = _regions.next();
1047 ShenandoahHeap* heap = ShenandoahHeap::heap();
1048 ShenandoahMarkingContext* const ctx = heap->complete_marking_context();
1049 while (region != nullptr) {
1050 if (heap->is_bitmap_slice_committed(region) && !region->is_pinned() && region->has_live()) {
1051 ctx->clear_bitmap(region);
1052 }
1053 region = _regions.next();
1054 }
1055 }
1056 };
1057
1058 void ShenandoahFullGC::phase4_compact_objects(ShenandoahHeapRegionSet** worker_slices) {
1059 GCTraceTime(Info, gc, phases) time("Phase 4: Move objects", _gc_timer);
1060 ShenandoahGCPhase compaction_phase(ShenandoahPhaseTimings::full_gc_copy_objects);
1061
1062 ShenandoahHeap* heap = ShenandoahHeap::heap();
1063
1064 // Compact regular objects first
1065 {
1066 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_regular);
1067 ShenandoahCompactObjectsTask compact_task(worker_slices);
1068 heap->workers()->run_task(&compact_task);
1069 }
1070
1071 // Compact humongous objects after regular object moves
1072 {
1073 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_humong);
1074 compact_humongous_objects();
1075 }
1076 }
1077
1078 void ShenandoahFullGC::phase5_epilog() {
1079 GCTraceTime(Info, gc, phases) time("Phase 5: Full GC epilog", _gc_timer);
1080 ShenandoahHeap* heap = ShenandoahHeap::heap();
1081
1082 // Reset complete bitmap. We're about to reset the complete-top-at-mark-start pointer
1083 // and must ensure the bitmap is in sync.
1084 {
1085 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_reset_complete);
1086 ShenandoahMCResetCompleteBitmapTask task;
1087 heap->workers()->run_task(&task);
1088 }
1089
1090 // Bring regions in proper states after the collection, and set heap properties.
1091 {
1092 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_rebuild);
1093 ShenandoahPostCompactClosure post_compact;
1094 heap->heap_region_iterate(&post_compact);
1095 heap->set_used(post_compact.get_live());
1096
1097 heap->collection_set()->clear();
1098 heap->free_set()->rebuild();
1099 heap->clear_cancelled_gc();
1100 }
1101
1102 _preserved_marks->restore(heap->workers());
1103 _preserved_marks->reclaim();
1104 }