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