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/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 metrics.snap_after();
110
111 if (metrics.is_good_progress()) {
112 ShenandoahHeap::heap()->notify_gc_progress();
113 } else {
114 // Nothing to do. Tell the allocation path that we have failed to make
115 // progress, and it can finally fail.
116 ShenandoahHeap::heap()->notify_gc_no_progress();
117 }
118 }
119
120 void ShenandoahFullGC::do_it(GCCause::Cause gc_cause) {
121 ShenandoahHeap* heap = ShenandoahHeap::heap();
122
123 if (ShenandoahVerify) {
124 heap->verifier()->verify_before_fullgc();
125 }
126
127 if (VerifyBeforeGC) {
128 Universe::verify();
129 }
130
131 // Degenerated GC may carry concurrent root flags when upgrading to
132 // full GC. We need to reset it before mutators resume.
133 heap->set_concurrent_strong_root_in_progress(false);
134 heap->set_concurrent_weak_root_in_progress(false);
135
136 heap->set_full_gc_in_progress(true);
137
138 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
139 assert(Thread::current()->is_VM_thread(), "Do full GC only while world is stopped");
140
141 {
142 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdump_pre);
143 heap->pre_full_gc_dump(_gc_timer);
144 }
145
146 {
147 ShenandoahGCPhase prepare_phase(ShenandoahPhaseTimings::full_gc_prepare);
148 // Full GC is supposed to recover from any GC state:
149
150 // a0. Remember if we have forwarded objects
151 bool has_forwarded_objects = heap->has_forwarded_objects();
152
153 // a1. Cancel evacuation, if in progress
154 if (heap->is_evacuation_in_progress()) {
155 heap->set_evacuation_in_progress(false);
156 }
157 assert(!heap->is_evacuation_in_progress(), "sanity");
158
159 // a2. Cancel update-refs, if in progress
160 if (heap->is_update_refs_in_progress()) {
161 heap->set_update_refs_in_progress(false);
162 }
163 assert(!heap->is_update_refs_in_progress(), "sanity");
164
165 // b. Cancel concurrent mark, if in progress
166 if (heap->is_concurrent_mark_in_progress()) {
167 ShenandoahConcurrentGC::cancel();
168 heap->set_concurrent_mark_in_progress(false);
169 }
170 assert(!heap->is_concurrent_mark_in_progress(), "sanity");
171
172 // c. Update roots if this full GC is due to evac-oom, which may carry from-space pointers in roots.
173 if (has_forwarded_objects) {
174 update_roots(true /*full_gc*/);
175 }
176
177 // d. Reset the bitmaps for new marking
178 heap->reset_mark_bitmap();
179 assert(heap->marking_context()->is_bitmap_clear(), "sanity");
180 assert(!heap->marking_context()->is_complete(), "sanity");
181
182 // e. Abandon reference discovery and clear all discovered references.
183 ShenandoahReferenceProcessor* rp = heap->ref_processor();
184 rp->abandon_partial_discovery();
185
186 // f. Sync pinned region status from the CP marks
187 heap->sync_pinned_region_status();
188
189 // The rest of prologue:
190 _preserved_marks->init(heap->workers()->active_workers());
191
192 assert(heap->has_forwarded_objects() == has_forwarded_objects, "This should not change");
193 }
194
195 if (UseTLAB) {
196 heap->gclabs_retire(ResizeTLAB);
197 heap->tlabs_retire(ResizeTLAB);
198 }
199
200 OrderAccess::fence();
201
202 phase1_mark_heap();
203
204 // Once marking is done, which may have fixed up forwarded objects, we can drop it.
205 // Coming out of Full GC, we would not have any forwarded objects.
206 // This also prevents resolves with fwdptr from kicking in while adjusting pointers in phase3.
207 heap->set_has_forwarded_objects(false);
208
209 heap->set_full_gc_move_in_progress(true);
210
211 // Setup workers for the rest
212 OrderAccess::fence();
213
214 // Initialize worker slices
215 ShenandoahHeapRegionSet** worker_slices = NEW_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, heap->max_workers(), mtGC);
216 for (uint i = 0; i < heap->max_workers(); i++) {
217 worker_slices[i] = new ShenandoahHeapRegionSet();
218 }
219
220 {
221 // The rest of code performs region moves, where region status is undefined
222 // until all phases run together.
223 ShenandoahHeapLocker lock(heap->lock());
224
225 SlidingForwarding::begin();
226
227 phase2_calculate_target_addresses(worker_slices);
228
229 OrderAccess::fence();
230
231 phase3_update_references();
232
233 phase4_compact_objects(worker_slices);
234 }
235
236 {
237 // Epilogue
238 _preserved_marks->restore(heap->workers());
239 _preserved_marks->reclaim();
240 SlidingForwarding::end();
241 }
242
243 // Resize metaspace
244 MetaspaceGC::compute_new_size();
245
246 // Free worker slices
247 for (uint i = 0; i < heap->max_workers(); i++) {
248 delete worker_slices[i];
249 }
250 FREE_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, worker_slices);
251
252 heap->set_full_gc_move_in_progress(false);
253 heap->set_full_gc_in_progress(false);
254
255 if (ShenandoahVerify) {
256 heap->verifier()->verify_after_fullgc();
257 }
258
259 if (VerifyAfterGC) {
260 Universe::verify();
261 }
262
263 {
264 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdump_post);
265 heap->post_full_gc_dump(_gc_timer);
266 }
267 }
268
269 class ShenandoahPrepareForMarkClosure: public ShenandoahHeapRegionClosure {
270 private:
271 ShenandoahMarkingContext* const _ctx;
272
273 public:
274 ShenandoahPrepareForMarkClosure() : _ctx(ShenandoahHeap::heap()->marking_context()) {}
275
276 void heap_region_do(ShenandoahHeapRegion *r) {
277 _ctx->capture_top_at_mark_start(r);
278 r->clear_live_data();
279 }
280 };
281
282 void ShenandoahFullGC::phase1_mark_heap() {
283 GCTraceTime(Info, gc, phases) time("Phase 1: Mark live objects", _gc_timer);
284 ShenandoahGCPhase mark_phase(ShenandoahPhaseTimings::full_gc_mark);
285
286 ShenandoahHeap* heap = ShenandoahHeap::heap();
287
288 ShenandoahPrepareForMarkClosure cl;
289 heap->heap_region_iterate(&cl);
290
291 heap->set_unload_classes(heap->heuristics()->can_unload_classes());
292
293 ShenandoahReferenceProcessor* rp = heap->ref_processor();
294 // enable ("weak") refs discovery
295 rp->set_soft_reference_policy(true); // forcefully purge all soft references
296
297 ShenandoahSTWMark mark(true /*full_gc*/);
298 mark.mark();
299 heap->parallel_cleaning(true /* full_gc */);
300 }
301
302 template <bool ALT_FWD>
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_region() {
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_region();
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 SlidingForwarding::forward_to<ALT_FWD>(p, 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) {
404 if (UseAltGCForwarding) {
405 work_impl<true>(worker_id);
406 } else {
407 work_impl<false>(worker_id);
408 }
409 }
410
411 private:
412 template <bool ALT_FWD>
413 void work_impl(uint worker_id) {
414 ShenandoahParallelWorkerSession worker_session(worker_id);
415 ShenandoahHeapRegionSet* slice = _worker_slices[worker_id];
416 ShenandoahHeapRegionSetIterator it(slice);
417 ShenandoahHeapRegion* from_region = it.next();
418 // No work?
419 if (from_region == nullptr) {
420 return;
421 }
422
423 // Sliding compaction. Walk all regions in the slice, and compact them.
424 // Remember empty regions and reuse them as needed.
425 ResourceMark rm;
426
427 GrowableArray<ShenandoahHeapRegion*> empty_regions((int)_heap->num_regions());
428
429 ShenandoahPrepareForCompactionObjectClosure<ALT_FWD> cl(_preserved_marks->get(worker_id), empty_regions, from_region);
430
431 while (from_region != nullptr) {
432 assert(is_candidate_region(from_region), "Sanity");
433
434 cl.set_from_region(from_region);
435 if (from_region->has_live()) {
436 _heap->marked_object_iterate(from_region, &cl);
437 }
438
439 // Compacted the region to somewhere else? From-region is empty then.
440 if (!cl.is_compact_same_region()) {
441 empty_regions.append(from_region);
442 }
443 from_region = it.next();
444 }
445 cl.finish_region();
446
447 // Mark all remaining regions as empty
448 for (int pos = cl.empty_regions_pos(); pos < empty_regions.length(); ++pos) {
449 ShenandoahHeapRegion* r = empty_regions.at(pos);
450 r->set_new_top(r->bottom());
451 }
452 }
453 };
454
455 template <bool ALT_FWD>
456 void ShenandoahFullGC::calculate_target_humongous_objects_impl() {
457 ShenandoahHeap* heap = ShenandoahHeap::heap();
458
459 // Compute the new addresses for humongous objects. We need to do this after addresses
460 // for regular objects are calculated, and we know what regions in heap suffix are
461 // available for humongous moves.
462 //
463 // Scan the heap backwards, because we are compacting humongous regions towards the end.
464 // Maintain the contiguous compaction window in [to_begin; to_end), so that we can slide
465 // humongous start there.
466 //
467 // The complication is potential non-movable regions during the scan. If such region is
468 // detected, then sliding restarts towards that non-movable region.
469
470 size_t to_begin = heap->num_regions();
471 size_t to_end = heap->num_regions();
472
473 for (size_t c = heap->num_regions(); c > 0; c--) {
474 ShenandoahHeapRegion *r = heap->get_region(c - 1);
475 if (r->is_humongous_continuation() || (r->new_top() == r->bottom())) {
476 // To-region candidate: record this, and continue scan
477 to_begin = r->index();
478 continue;
479 }
480
481 if (r->is_humongous_start() && r->is_stw_move_allowed()) {
482 // From-region candidate: movable humongous region
483 oop old_obj = cast_to_oop(r->bottom());
484 size_t words_size = old_obj->size();
485 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
486
487 size_t start = to_end - num_regions;
488
489 if (start >= to_begin && start != r->index()) {
490 // Fits into current window, and the move is non-trivial. Record the move then, and continue scan.
491 _preserved_marks->get(0)->push_if_necessary(old_obj, old_obj->mark());
492 SlidingForwarding::forward_to<ALT_FWD>(old_obj, cast_to_oop(heap->get_region(start)->bottom()));
493 to_end = start;
494 continue;
495 }
496 }
497
498 // Failed to fit. Scan starting from current region.
499 to_begin = r->index();
500 to_end = r->index();
501 }
502 }
503
504 void ShenandoahFullGC::calculate_target_humongous_objects() {
505 if (UseAltGCForwarding) {
506 calculate_target_humongous_objects_impl<true>();
507 } else {
508 calculate_target_humongous_objects_impl<false>();
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 template <bool ALT_FWD>
750 class ShenandoahAdjustPointersClosure : public MetadataVisitingOopIterateClosure {
751 private:
752 ShenandoahHeap* const _heap;
753 ShenandoahMarkingContext* const _ctx;
754
755 template <class T>
756 inline void do_oop_work(T* p) {
757 T o = RawAccess<>::oop_load(p);
758 if (!CompressedOops::is_null(o)) {
759 oop obj = CompressedOops::decode_not_null(o);
760 assert(_ctx->is_marked(obj), "must be marked");
761 if (SlidingForwarding::is_forwarded(obj)) {
762 oop forw = SlidingForwarding::forwardee<ALT_FWD>(obj);
763 RawAccess<IS_NOT_NULL>::oop_store(p, forw);
764 }
765 }
766 }
767
768 public:
769 ShenandoahAdjustPointersClosure() :
770 _heap(ShenandoahHeap::heap()),
771 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
772
773 void do_oop(oop* p) { do_oop_work(p); }
774 void do_oop(narrowOop* p) { do_oop_work(p); }
775 void do_method(Method* m) {}
776 void do_nmethod(nmethod* nm) {}
777 };
778
779 template <bool ALT_FWD>
780 class ShenandoahAdjustPointersObjectClosure : public ObjectClosure {
781 private:
782 ShenandoahHeap* const _heap;
783 ShenandoahAdjustPointersClosure<ALT_FWD> _cl;
784
785 public:
786 ShenandoahAdjustPointersObjectClosure() :
787 _heap(ShenandoahHeap::heap()) {
788 }
789 void do_object(oop p) {
790 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
791 p->oop_iterate(&_cl);
792 }
793 };
794
795 class ShenandoahAdjustPointersTask : public WorkerTask {
796 private:
797 ShenandoahHeap* const _heap;
798 ShenandoahRegionIterator _regions;
799
800 public:
801 ShenandoahAdjustPointersTask() :
802 WorkerTask("Shenandoah Adjust Pointers"),
803 _heap(ShenandoahHeap::heap()) {
804 }
805
806 private:
807 template <bool ALT_FWD>
808 void work_impl(uint worker_id) {
809 ShenandoahParallelWorkerSession worker_session(worker_id);
810 ShenandoahAdjustPointersObjectClosure<ALT_FWD> obj_cl;
811 ShenandoahHeapRegion* r = _regions.next();
812 while (r != nullptr) {
813 if (!r->is_humongous_continuation() && r->has_live()) {
814 _heap->marked_object_iterate(r, &obj_cl);
815 }
816 r = _regions.next();
817 }
818 }
819
820 public:
821 void work(uint worker_id) {
822 if (UseAltGCForwarding) {
823 work_impl<true>(worker_id);
824 } else {
825 work_impl<false>(worker_id);
826 }
827 }
828 };
829
830 class ShenandoahAdjustRootPointersTask : public WorkerTask {
831 private:
832 ShenandoahRootAdjuster* _rp;
833 PreservedMarksSet* _preserved_marks;
834
835 public:
836 ShenandoahAdjustRootPointersTask(ShenandoahRootAdjuster* rp, PreservedMarksSet* preserved_marks) :
837 WorkerTask("Shenandoah Adjust Root Pointers"),
838 _rp(rp),
839 _preserved_marks(preserved_marks) {}
840
841 private:
842 template <bool ALT_FWD>
843 void work_impl(uint worker_id) {
844 ShenandoahParallelWorkerSession worker_session(worker_id);
845 ShenandoahAdjustPointersClosure<ALT_FWD> cl;
846 _rp->roots_do(worker_id, &cl);
847 _preserved_marks->get(worker_id)->adjust_during_full_gc();
848 }
849
850 public:
851 void work(uint worker_id) {
852 if (UseAltGCForwarding) {
853 work_impl<true>(worker_id);
854 } else {
855 work_impl<false>(worker_id);
856 }
857 }
858 };
859
860 void ShenandoahFullGC::phase3_update_references() {
861 GCTraceTime(Info, gc, phases) time("Phase 3: Adjust pointers", _gc_timer);
862 ShenandoahGCPhase adjust_pointer_phase(ShenandoahPhaseTimings::full_gc_adjust_pointers);
863
864 ShenandoahHeap* heap = ShenandoahHeap::heap();
865
866 WorkerThreads* workers = heap->workers();
867 uint nworkers = workers->active_workers();
868 {
869 #if COMPILER2_OR_JVMCI
870 DerivedPointerTable::clear();
871 #endif
872 ShenandoahRootAdjuster rp(nworkers, ShenandoahPhaseTimings::full_gc_adjust_roots);
873 ShenandoahAdjustRootPointersTask task(&rp, _preserved_marks);
874 workers->run_task(&task);
875 #if COMPILER2_OR_JVMCI
876 DerivedPointerTable::update_pointers();
877 #endif
878 }
879
880 ShenandoahAdjustPointersTask adjust_pointers_task;
881 workers->run_task(&adjust_pointers_task);
882 }
883
884 template <bool ALT_FWD>
885 class ShenandoahCompactObjectsClosure : public ObjectClosure {
886 private:
887 ShenandoahHeap* const _heap;
888 uint const _worker_id;
889
890 public:
891 ShenandoahCompactObjectsClosure(uint worker_id) :
892 _heap(ShenandoahHeap::heap()), _worker_id(worker_id) {}
893
894 void do_object(oop p) {
895 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
896 size_t size = p->size();
897 if (SlidingForwarding::is_forwarded(p)) {
898 HeapWord* compact_from = cast_from_oop<HeapWord*>(p);
899 HeapWord* compact_to = cast_from_oop<HeapWord*>(SlidingForwarding::forwardee<ALT_FWD>(p));
900 assert(compact_from != compact_to, "Forwarded object should move");
901 Copy::aligned_conjoint_words(compact_from, compact_to, size);
902 oop new_obj = cast_to_oop(compact_to);
903
904 ContinuationGCSupport::relativize_stack_chunk(new_obj);
905 new_obj->init_mark();
906 }
907 }
908 };
909
910 class ShenandoahCompactObjectsTask : public WorkerTask {
911 private:
912 ShenandoahHeap* const _heap;
913 ShenandoahHeapRegionSet** const _worker_slices;
914
915 public:
916 ShenandoahCompactObjectsTask(ShenandoahHeapRegionSet** worker_slices) :
917 WorkerTask("Shenandoah Compact Objects"),
918 _heap(ShenandoahHeap::heap()),
919 _worker_slices(worker_slices) {
920 }
921
922 private:
923 template <bool ALT_FWD>
924 void work_impl(uint worker_id) {
925 ShenandoahParallelWorkerSession worker_session(worker_id);
926 ShenandoahHeapRegionSetIterator slice(_worker_slices[worker_id]);
927
928 ShenandoahCompactObjectsClosure<ALT_FWD> cl(worker_id);
929 ShenandoahHeapRegion* r = slice.next();
930 while (r != nullptr) {
931 assert(!r->is_humongous(), "must not get humongous regions here");
932 if (r->has_live()) {
933 _heap->marked_object_iterate(r, &cl);
934 }
935 r->set_top(r->new_top());
936 r = slice.next();
937 }
938 }
939
940 public:
941 void work(uint worker_id) {
942 if (UseAltGCForwarding) {
943 work_impl<true>(worker_id);
944 } else {
945 work_impl<false>(worker_id);
946 }
947 }
948 };
949
950 class ShenandoahPostCompactClosure : public ShenandoahHeapRegionClosure {
951 private:
952 ShenandoahHeap* const _heap;
953 size_t _live;
954
955 public:
956 ShenandoahPostCompactClosure() : _heap(ShenandoahHeap::heap()), _live(0) {
957 _heap->free_set()->clear();
958 }
959
960 void heap_region_do(ShenandoahHeapRegion* r) {
961 assert (!r->is_cset(), "cset regions should have been demoted already");
962
963 // Need to reset the complete-top-at-mark-start pointer here because
964 // the complete marking bitmap is no longer valid. This ensures
965 // size-based iteration in marked_object_iterate().
966 // NOTE: See blurb at ShenandoahMCResetCompleteBitmapTask on why we need to skip
967 // pinned regions.
968 if (!r->is_pinned()) {
969 _heap->complete_marking_context()->reset_top_at_mark_start(r);
970 }
971
972 size_t live = r->used();
973
974 // Make empty regions that have been allocated into regular
975 if (r->is_empty() && live > 0) {
976 r->make_regular_bypass();
977 if (ZapUnusedHeapArea) {
978 SpaceMangler::mangle_region(MemRegion(r->top(), r->end()));
979 }
980 }
981
982 // Reclaim regular regions that became empty
983 if (r->is_regular() && live == 0) {
984 r->make_trash();
985 }
986
987 // Recycle all trash regions
988 if (r->is_trash()) {
989 live = 0;
990 r->recycle();
991 }
992
993 r->set_live_data(live);
994 r->reset_alloc_metadata();
995 _live += live;
996 }
997
998 size_t get_live() {
999 return _live;
1000 }
1001 };
1002
1003 template <bool ALT_FWD>
1004 void ShenandoahFullGC::compact_humongous_objects_impl() {
1005 // Compact humongous regions, based on their fwdptr objects.
1006 //
1007 // This code is serial, because doing the in-slice parallel sliding is tricky. In most cases,
1008 // humongous regions are already compacted, and do not require further moves, which alleviates
1009 // sliding costs. We may consider doing this in parallel in future.
1010
1011 ShenandoahHeap* heap = ShenandoahHeap::heap();
1012
1013 for (size_t c = heap->num_regions(); c > 0; c--) {
1014 ShenandoahHeapRegion* r = heap->get_region(c - 1);
1015 if (r->is_humongous_start()) {
1016 oop old_obj = cast_to_oop(r->bottom());
1017 if (SlidingForwarding::is_not_forwarded(old_obj)) {
1018 // No need to move the object, it stays at the same slot
1019 continue;
1020 }
1021 size_t words_size = old_obj->size();
1022 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
1023
1024 size_t old_start = r->index();
1025 size_t old_end = old_start + num_regions - 1;
1026 size_t new_start = heap->heap_region_index_containing(SlidingForwarding::forwardee<ALT_FWD>(old_obj));
1027 size_t new_end = new_start + num_regions - 1;
1028 assert(old_start != new_start, "must be real move");
1029 assert(r->is_stw_move_allowed(), "Region " SIZE_FORMAT " should be movable", r->index());
1030
1031 Copy::aligned_conjoint_words(r->bottom(), heap->get_region(new_start)->bottom(), words_size);
1032 ContinuationGCSupport::relativize_stack_chunk(cast_to_oop<HeapWord*>(r->bottom()));
1033
1034 oop new_obj = cast_to_oop(heap->get_region(new_start)->bottom());
1035 new_obj->init_mark();
1036
1037 {
1038 for (size_t c = old_start; c <= old_end; c++) {
1039 ShenandoahHeapRegion* r = heap->get_region(c);
1040 r->make_regular_bypass();
1041 r->set_top(r->bottom());
1042 }
1043
1044 for (size_t c = new_start; c <= new_end; c++) {
1045 ShenandoahHeapRegion* r = heap->get_region(c);
1046 if (c == new_start) {
1047 r->make_humongous_start_bypass();
1048 } else {
1049 r->make_humongous_cont_bypass();
1050 }
1051
1052 // Trailing region may be non-full, record the remainder there
1053 size_t remainder = words_size & ShenandoahHeapRegion::region_size_words_mask();
1054 if ((c == new_end) && (remainder != 0)) {
1055 r->set_top(r->bottom() + remainder);
1056 } else {
1057 r->set_top(r->end());
1058 }
1059
1060 r->reset_alloc_metadata();
1061 }
1062 }
1063 }
1064 }
1065 }
1066
1067 void ShenandoahFullGC::compact_humongous_objects() {
1068 if (UseAltGCForwarding) {
1069 compact_humongous_objects_impl<true>();
1070 } else {
1071 compact_humongous_objects_impl<false>();
1072 }
1073 }
1074
1075 // This is slightly different to ShHeap::reset_next_mark_bitmap:
1076 // we need to remain able to walk pinned regions.
1077 // Since pinned region do not move and don't get compacted, we will get holes with
1078 // unreachable objects in them (which may have pointers to unloaded Klasses and thus
1079 // cannot be iterated over using oop->size(). The only way to safely iterate over those is using
1080 // a valid marking bitmap and valid TAMS pointer. This class only resets marking
1081 // bitmaps for un-pinned regions, and later we only reset TAMS for unpinned regions.
1082 class ShenandoahMCResetCompleteBitmapTask : public WorkerTask {
1083 private:
1084 ShenandoahRegionIterator _regions;
1085
1086 public:
1087 ShenandoahMCResetCompleteBitmapTask() :
1088 WorkerTask("Shenandoah Reset Bitmap") {
1089 }
1090
1091 void work(uint worker_id) {
1092 ShenandoahParallelWorkerSession worker_session(worker_id);
1093 ShenandoahHeapRegion* region = _regions.next();
1094 ShenandoahHeap* heap = ShenandoahHeap::heap();
1095 ShenandoahMarkingContext* const ctx = heap->complete_marking_context();
1096 while (region != nullptr) {
1097 if (heap->is_bitmap_slice_committed(region) && !region->is_pinned() && region->has_live()) {
1098 ctx->clear_bitmap(region);
1099 }
1100 region = _regions.next();
1101 }
1102 }
1103 };
1104
1105 void ShenandoahFullGC::phase4_compact_objects(ShenandoahHeapRegionSet** worker_slices) {
1106 GCTraceTime(Info, gc, phases) time("Phase 4: Move objects", _gc_timer);
1107 ShenandoahGCPhase compaction_phase(ShenandoahPhaseTimings::full_gc_copy_objects);
1108
1109 ShenandoahHeap* heap = ShenandoahHeap::heap();
1110
1111 // Compact regular objects first
1112 {
1113 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_regular);
1114 ShenandoahCompactObjectsTask compact_task(worker_slices);
1115 heap->workers()->run_task(&compact_task);
1116 }
1117
1118 // Compact humongous objects after regular object moves
1119 {
1120 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_humong);
1121 compact_humongous_objects();
1122 }
1123
1124 // Reset complete bitmap. We're about to reset the complete-top-at-mark-start pointer
1125 // and must ensure the bitmap is in sync.
1126 {
1127 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_reset_complete);
1128 ShenandoahMCResetCompleteBitmapTask task;
1129 heap->workers()->run_task(&task);
1130 }
1131
1132 // Bring regions in proper states after the collection, and set heap properties.
1133 {
1134 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_rebuild);
1135
1136 ShenandoahPostCompactClosure post_compact;
1137 heap->heap_region_iterate(&post_compact);
1138 heap->set_used(post_compact.get_live());
1139
1140 heap->collection_set()->clear();
1141 heap->free_set()->rebuild();
1142 }
1143
1144 heap->clear_cancelled_gc();
1145 }