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/gcTraceTime.inline.hpp"
29 #include "gc/shared/preservedMarks.inline.hpp"
30 #include "gc/shared/slidingForwarding.inline.hpp"
31 #include "gc/shared/tlab_globals.hpp"
32 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
33 #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
34 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
35 #include "gc/shenandoah/shenandoahFreeSet.hpp"
36 #include "gc/shenandoah/shenandoahFullGC.hpp"
37 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
38 #include "gc/shenandoah/shenandoahMark.inline.hpp"
39 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
40 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp"
41 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
42 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
43 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
44 #include "gc/shenandoah/shenandoahMetrics.hpp"
45 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
46 #include "gc/shenandoah/shenandoahReferenceProcessor.hpp"
47 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
48 #include "gc/shenandoah/shenandoahSTWMark.hpp"
49 #include "gc/shenandoah/shenandoahUtils.hpp"
50 #include "gc/shenandoah/shenandoahVerifier.hpp"
51 #include "gc/shenandoah/shenandoahVMOperations.hpp"
52 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
53 #include "memory/metaspaceUtils.hpp"
54 #include "memory/universe.hpp"
55 #include "oops/compressedOops.inline.hpp"
56 #include "oops/oop.inline.hpp"
57 #include "runtime/biasedLocking.hpp"
58 #include "runtime/orderAccess.hpp"
59 #include "runtime/thread.hpp"
60 #include "runtime/vmThread.hpp"
61 #include "utilities/copy.hpp"
62 #include "utilities/events.hpp"
63 #include "utilities/growableArray.hpp"
64 #include "gc/shared/workgroup.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 BiasedLocking::preserve_marks();
191 _preserved_marks->init(heap->workers()->active_workers());
192 heap->forwarding()->clear();
193
194 assert(heap->has_forwarded_objects() == has_forwarded_objects, "This should not change");
195 }
196
197 if (UseTLAB) {
198 heap->gclabs_retire(ResizeTLAB);
199 heap->tlabs_retire(ResizeTLAB);
200 }
201
202 OrderAccess::fence();
203
204 phase1_mark_heap();
205
206 // Once marking is done, which may have fixed up forwarded objects, we can drop it.
207 // Coming out of Full GC, we would not have any forwarded objects.
208 // This also prevents resolves with fwdptr from kicking in while adjusting pointers in phase3.
209 heap->set_has_forwarded_objects(false);
210
211 heap->set_full_gc_move_in_progress(true);
212
213 // Setup workers for the rest
214 OrderAccess::fence();
215
216 // Initialize worker slices
217 ShenandoahHeapRegionSet** worker_slices = NEW_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, heap->max_workers(), mtGC);
218 for (uint i = 0; i < heap->max_workers(); i++) {
219 worker_slices[i] = new ShenandoahHeapRegionSet();
220 }
221
222 {
223 // The rest of code performs region moves, where region status is undefined
224 // until all phases run together.
225 ShenandoahHeapLocker lock(heap->lock());
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 BiasedLocking::restore_marks();
240 _preserved_marks->reclaim();
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 class ShenandoahPrepareForCompactionObjectClosure : public ObjectClosure {
303 private:
304 PreservedMarks* const _preserved_marks;
305 SlidingForwarding* const _forwarding;
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 _forwarding(ShenandoahHeap::heap()->forwarding()),
319 _heap(ShenandoahHeap::heap()),
320 _empty_regions(empty_regions),
321 _empty_regions_pos(0),
322 _to_region(to_region),
323 _from_region(NULL),
324 _compact_point(to_region->bottom()) {}
325
326 void set_from_region(ShenandoahHeapRegion* from_region) {
327 _from_region = from_region;
328 }
329
330 void finish_region() {
331 assert(_to_region != NULL, "should not happen");
332 _to_region->set_new_top(_compact_point);
333 }
334
335 bool is_compact_same_region() {
336 return _from_region == _to_region;
337 }
338
339 int empty_regions_pos() {
340 return _empty_regions_pos;
341 }
342
343 void do_object(oop p) {
344 assert(_from_region != NULL, "must set before work");
345 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
346 assert(!_heap->complete_marking_context()->allocated_after_mark_start(p), "must be truly marked");
347
348 size_t obj_size = p->size();
349 if (_compact_point + obj_size > _to_region->end()) {
350 finish_region();
351
352 // Object doesn't fit. Pick next empty region and start compacting there.
353 ShenandoahHeapRegion* new_to_region;
354 if (_empty_regions_pos < _empty_regions.length()) {
355 new_to_region = _empty_regions.at(_empty_regions_pos);
356 _empty_regions_pos++;
357 } else {
358 // Out of empty region? Compact within the same region.
359 new_to_region = _from_region;
360 }
361
362 assert(new_to_region != _to_region, "must not reuse same to-region");
363 assert(new_to_region != NULL, "must not be NULL");
364 _to_region = new_to_region;
365 _compact_point = _to_region->bottom();
366 }
367
368 // Object fits into current region, record new location:
369 assert(_compact_point + obj_size <= _to_region->end(), "must fit");
370 shenandoah_assert_not_forwarded(NULL, p);
371 _preserved_marks->push_if_necessary(p, p->mark());
372 _forwarding->forward_to(p, cast_to_oop(_compact_point));
373 _compact_point += obj_size;
374 }
375 };
376
377 class ShenandoahPrepareForCompactionTask : public AbstractGangTask {
378 private:
379 PreservedMarksSet* const _preserved_marks;
380 ShenandoahHeap* const _heap;
381 ShenandoahHeapRegionSet** const _worker_slices;
382
383 public:
384 ShenandoahPrepareForCompactionTask(PreservedMarksSet *preserved_marks, ShenandoahHeapRegionSet **worker_slices) :
385 AbstractGangTask("Shenandoah Prepare For Compaction"),
386 _preserved_marks(preserved_marks),
387 _heap(ShenandoahHeap::heap()), _worker_slices(worker_slices) {
388 }
389
390 static bool is_candidate_region(ShenandoahHeapRegion* r) {
391 // Empty region: get it into the slice to defragment the slice itself.
392 // We could have skipped this without violating correctness, but we really
393 // want to compact all live regions to the start of the heap, which sometimes
394 // means moving them into the fully empty regions.
395 if (r->is_empty()) return true;
396
397 // Can move the region, and this is not the humongous region. Humongous
398 // moves are special cased here, because their moves are handled separately.
399 return r->is_stw_move_allowed() && !r->is_humongous();
400 }
401
402 void work(uint worker_id) {
403 ShenandoahParallelWorkerSession worker_session(worker_id);
404 ShenandoahHeapRegionSet* slice = _worker_slices[worker_id];
405 ShenandoahHeapRegionSetIterator it(slice);
406 ShenandoahHeapRegion* from_region = it.next();
407 // No work?
408 if (from_region == NULL) {
409 return;
410 }
411
412 // Sliding compaction. Walk all regions in the slice, and compact them.
413 // Remember empty regions and reuse them as needed.
414 ResourceMark rm;
415
416 GrowableArray<ShenandoahHeapRegion*> empty_regions((int)_heap->num_regions());
417
418 ShenandoahPrepareForCompactionObjectClosure cl(_preserved_marks->get(worker_id), empty_regions, from_region);
419
420 while (from_region != NULL) {
421 assert(is_candidate_region(from_region), "Sanity");
422
423 cl.set_from_region(from_region);
424 if (from_region->has_live()) {
425 _heap->marked_object_iterate(from_region, &cl);
426 }
427
428 // Compacted the region to somewhere else? From-region is empty then.
429 if (!cl.is_compact_same_region()) {
430 empty_regions.append(from_region);
431 }
432 from_region = it.next();
433 }
434 cl.finish_region();
435
436 // Mark all remaining regions as empty
437 for (int pos = cl.empty_regions_pos(); pos < empty_regions.length(); ++pos) {
438 ShenandoahHeapRegion* r = empty_regions.at(pos);
439 r->set_new_top(r->bottom());
440 }
441 }
442 };
443
444 void ShenandoahFullGC::calculate_target_humongous_objects() {
445 ShenandoahHeap* heap = ShenandoahHeap::heap();
446 SlidingForwarding* forwarding = heap->forwarding();
447
448 // Compute the new addresses for humongous objects. We need to do this after addresses
449 // for regular objects are calculated, and we know what regions in heap suffix are
450 // available for humongous moves.
451 //
452 // Scan the heap backwards, because we are compacting humongous regions towards the end.
453 // Maintain the contiguous compaction window in [to_begin; to_end), so that we can slide
454 // humongous start there.
455 //
456 // The complication is potential non-movable regions during the scan. If such region is
457 // detected, then sliding restarts towards that non-movable region.
458
459 size_t to_begin = heap->num_regions();
460 size_t to_end = heap->num_regions();
461
462 for (size_t c = heap->num_regions(); c > 0; c--) {
463 ShenandoahHeapRegion *r = heap->get_region(c - 1);
464 if (r->is_humongous_continuation() || (r->new_top() == r->bottom())) {
465 // To-region candidate: record this, and continue scan
466 to_begin = r->index();
467 continue;
468 }
469
470 if (r->is_humongous_start() && r->is_stw_move_allowed()) {
471 // From-region candidate: movable humongous region
472 oop old_obj = cast_to_oop(r->bottom());
473 size_t words_size = old_obj->size();
474 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
475
476 size_t start = to_end - num_regions;
477
478 if (start >= to_begin && start != r->index()) {
479 // Fits into current window, and the move is non-trivial. Record the move then, and continue scan.
480 _preserved_marks->get(0)->push_if_necessary(old_obj, old_obj->mark());
481 forwarding->forward_to(old_obj, cast_to_oop(heap->get_region(start)->bottom()));
482 to_end = start;
483 continue;
484 }
485 }
486
487 // Failed to fit. Scan starting from current region.
488 to_begin = r->index();
489 to_end = r->index();
490 }
491 }
492
493 class ShenandoahEnsureHeapActiveClosure: public ShenandoahHeapRegionClosure {
494 private:
495 ShenandoahHeap* const _heap;
496
497 public:
498 ShenandoahEnsureHeapActiveClosure() : _heap(ShenandoahHeap::heap()) {}
499 void heap_region_do(ShenandoahHeapRegion* r) {
500 if (r->is_trash()) {
501 r->recycle();
502 }
503 if (r->is_cset()) {
504 r->make_regular_bypass();
505 }
506 if (r->is_empty_uncommitted()) {
507 r->make_committed_bypass();
508 }
509 assert (r->is_committed(), "only committed regions in heap now, see region " SIZE_FORMAT, r->index());
510
511 // Record current region occupancy: this communicates empty regions are free
512 // to the rest of Full GC code.
513 r->set_new_top(r->top());
514 }
515 };
516
517 class ShenandoahTrashImmediateGarbageClosure: public ShenandoahHeapRegionClosure {
518 private:
519 ShenandoahHeap* const _heap;
520 ShenandoahMarkingContext* const _ctx;
521
522 public:
523 ShenandoahTrashImmediateGarbageClosure() :
524 _heap(ShenandoahHeap::heap()),
525 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
526
527 void heap_region_do(ShenandoahHeapRegion* r) {
528 if (r->is_humongous_start()) {
529 oop humongous_obj = cast_to_oop(r->bottom());
530 if (!_ctx->is_marked(humongous_obj)) {
531 assert(!r->has_live(),
532 "Region " SIZE_FORMAT " is not marked, should not have live", r->index());
533 _heap->trash_humongous_region_at(r);
534 } else {
535 assert(r->has_live(),
536 "Region " SIZE_FORMAT " should have live", r->index());
537 }
538 } else if (r->is_humongous_continuation()) {
539 // If we hit continuation, the non-live humongous starts should have been trashed already
540 assert(r->humongous_start_region()->has_live(),
541 "Region " SIZE_FORMAT " should have live", r->index());
542 } else if (r->is_regular()) {
543 if (!r->has_live()) {
544 r->make_trash_immediate();
545 }
546 }
547 }
548 };
549
550 void ShenandoahFullGC::distribute_slices(ShenandoahHeapRegionSet** worker_slices) {
551 ShenandoahHeap* heap = ShenandoahHeap::heap();
552
553 uint n_workers = heap->workers()->active_workers();
554 size_t n_regions = heap->num_regions();
555
556 // What we want to accomplish: have the dense prefix of data, while still balancing
557 // out the parallel work.
558 //
559 // Assuming the amount of work is driven by the live data that needs moving, we can slice
560 // the entire heap into equal-live-sized prefix slices, and compact into them. So, each
561 // thread takes all regions in its prefix subset, and then it takes some regions from
562 // the tail.
563 //
564 // Tail region selection becomes interesting.
565 //
566 // First, we want to distribute the regions fairly between the workers, and those regions
567 // might have different amount of live data. So, until we sure no workers need live data,
568 // we need to only take what the worker needs.
569 //
570 // Second, since we slide everything to the left in each slice, the most busy regions
571 // would be the ones on the left. Which means we want to have all workers have their after-tail
572 // regions as close to the left as possible.
573 //
574 // The easiest way to do this is to distribute after-tail regions in round-robin between
575 // workers that still need live data.
576 //
577 // Consider parallel workers A, B, C, then the target slice layout would be:
578 //
579 // AAAAAAAABBBBBBBBCCCCCCCC|ABCABCABCABCABCABCABCABABABABABABABABABABAAAAA
580 //
581 // (.....dense-prefix.....) (.....................tail...................)
582 // [all regions fully live] [left-most regions are fuller that right-most]
583 //
584
585 // Compute how much live data is there. This would approximate the size of dense prefix
586 // we target to create.
587 size_t total_live = 0;
588 for (size_t idx = 0; idx < n_regions; idx++) {
589 ShenandoahHeapRegion *r = heap->get_region(idx);
590 if (ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
591 total_live += r->get_live_data_words();
592 }
593 }
594
595 // Estimate the size for the dense prefix. Note that we specifically count only the
596 // "full" regions, so there would be some non-full regions in the slice tail.
597 size_t live_per_worker = total_live / n_workers;
598 size_t prefix_regions_per_worker = live_per_worker / ShenandoahHeapRegion::region_size_words();
599 size_t prefix_regions_total = prefix_regions_per_worker * n_workers;
600 prefix_regions_total = MIN2(prefix_regions_total, n_regions);
601 assert(prefix_regions_total <= n_regions, "Sanity");
602
603 // There might be non-candidate regions in the prefix. To compute where the tail actually
604 // ends up being, we need to account those as well.
605 size_t prefix_end = prefix_regions_total;
606 for (size_t idx = 0; idx < prefix_regions_total; idx++) {
607 ShenandoahHeapRegion *r = heap->get_region(idx);
608 if (!ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
609 prefix_end++;
610 }
611 }
612 prefix_end = MIN2(prefix_end, n_regions);
613 assert(prefix_end <= n_regions, "Sanity");
614
615 // Distribute prefix regions per worker: each thread definitely gets its own same-sized
616 // subset of dense prefix.
617 size_t prefix_idx = 0;
618
619 size_t* live = NEW_C_HEAP_ARRAY(size_t, n_workers, mtGC);
620
621 for (size_t wid = 0; wid < n_workers; wid++) {
622 ShenandoahHeapRegionSet* slice = worker_slices[wid];
623
624 live[wid] = 0;
625 size_t regs = 0;
626
627 // Add all prefix regions for this worker
628 while (prefix_idx < prefix_end && regs < prefix_regions_per_worker) {
629 ShenandoahHeapRegion *r = heap->get_region(prefix_idx);
630 if (ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
631 slice->add_region(r);
632 live[wid] += r->get_live_data_words();
633 regs++;
634 }
635 prefix_idx++;
636 }
637 }
638
639 // Distribute the tail among workers in round-robin fashion.
640 size_t wid = n_workers - 1;
641
642 for (size_t tail_idx = prefix_end; tail_idx < n_regions; tail_idx++) {
643 ShenandoahHeapRegion *r = heap->get_region(tail_idx);
644 if (ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
645 assert(wid < n_workers, "Sanity");
646
647 size_t live_region = r->get_live_data_words();
648
649 // Select next worker that still needs live data.
650 size_t old_wid = wid;
651 do {
652 wid++;
653 if (wid == n_workers) wid = 0;
654 } while (live[wid] + live_region >= live_per_worker && old_wid != wid);
655
656 if (old_wid == wid) {
657 // Circled back to the same worker? This means liveness data was
658 // miscalculated. Bump the live_per_worker limit so that
659 // everyone gets a piece of the leftover work.
660 live_per_worker += ShenandoahHeapRegion::region_size_words();
661 }
662
663 worker_slices[wid]->add_region(r);
664 live[wid] += live_region;
665 }
666 }
667
668 FREE_C_HEAP_ARRAY(size_t, live);
669
670 #ifdef ASSERT
671 ResourceBitMap map(n_regions);
672 for (size_t wid = 0; wid < n_workers; wid++) {
673 ShenandoahHeapRegionSetIterator it(worker_slices[wid]);
674 ShenandoahHeapRegion* r = it.next();
675 while (r != NULL) {
676 size_t idx = r->index();
677 assert(ShenandoahPrepareForCompactionTask::is_candidate_region(r), "Sanity: " SIZE_FORMAT, idx);
678 assert(!map.at(idx), "No region distributed twice: " SIZE_FORMAT, idx);
679 map.at_put(idx, true);
680 r = it.next();
681 }
682 }
683
684 for (size_t rid = 0; rid < n_regions; rid++) {
685 bool is_candidate = ShenandoahPrepareForCompactionTask::is_candidate_region(heap->get_region(rid));
686 bool is_distributed = map.at(rid);
687 assert(is_distributed || !is_candidate, "All candidates are distributed: " SIZE_FORMAT, rid);
688 }
689 #endif
690 }
691
692 void ShenandoahFullGC::phase2_calculate_target_addresses(ShenandoahHeapRegionSet** worker_slices) {
693 GCTraceTime(Info, gc, phases) time("Phase 2: Compute new object addresses", _gc_timer);
694 ShenandoahGCPhase calculate_address_phase(ShenandoahPhaseTimings::full_gc_calculate_addresses);
695
696 ShenandoahHeap* heap = ShenandoahHeap::heap();
697
698 // About to figure out which regions can be compacted, make sure pinning status
699 // had been updated in GC prologue.
700 heap->assert_pinned_region_status();
701
702 {
703 // Trash the immediately collectible regions before computing addresses
704 ShenandoahTrashImmediateGarbageClosure tigcl;
705 heap->heap_region_iterate(&tigcl);
706
707 // Make sure regions are in good state: committed, active, clean.
708 // This is needed because we are potentially sliding the data through them.
709 ShenandoahEnsureHeapActiveClosure ecl;
710 heap->heap_region_iterate(&ecl);
711 }
712
713 // Compute the new addresses for regular objects
714 {
715 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_regular);
716
717 distribute_slices(worker_slices);
718
719 ShenandoahPrepareForCompactionTask task(_preserved_marks, worker_slices);
720 heap->workers()->run_task(&task);
721 }
722
723 // Compute the new addresses for humongous objects
724 {
725 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_humong);
726 calculate_target_humongous_objects();
727 }
728 }
729
730 class ShenandoahAdjustPointersClosure : public MetadataVisitingOopIterateClosure {
731 private:
732 ShenandoahHeap* const _heap;
733 const SlidingForwarding* const _forwarding;
734 ShenandoahMarkingContext* const _ctx;
735
736 template <class T>
737 inline void do_oop_work(T* p) {
738 T o = RawAccess<>::oop_load(p);
739 if (!CompressedOops::is_null(o)) {
740 oop obj = CompressedOops::decode_not_null(o);
741 assert(_ctx->is_marked(obj), "must be marked");
742 if (obj->is_forwarded()) {
743 oop forw = _forwarding->forwardee(obj);
744 RawAccess<IS_NOT_NULL>::oop_store(p, forw);
745 }
746 }
747 }
748
749 public:
750 ShenandoahAdjustPointersClosure() :
751 _heap(ShenandoahHeap::heap()),
752 _forwarding(_heap->forwarding()),
753 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
754
755 void do_oop(oop* p) { do_oop_work(p); }
756 void do_oop(narrowOop* p) { do_oop_work(p); }
757 };
758
759 class ShenandoahAdjustPointersObjectClosure : public ObjectClosure {
760 private:
761 ShenandoahHeap* const _heap;
762 ShenandoahAdjustPointersClosure _cl;
763
764 public:
765 ShenandoahAdjustPointersObjectClosure() :
766 _heap(ShenandoahHeap::heap()) {
767 }
768 void do_object(oop p) {
769 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
770 p->oop_iterate(&_cl);
771 }
772 };
773
774 class ShenandoahAdjustPointersTask : public AbstractGangTask {
775 private:
776 ShenandoahHeap* const _heap;
777 ShenandoahRegionIterator _regions;
778
779 public:
780 ShenandoahAdjustPointersTask() :
781 AbstractGangTask("Shenandoah Adjust Pointers"),
782 _heap(ShenandoahHeap::heap()) {
783 }
784
785 void work(uint worker_id) {
786 ShenandoahParallelWorkerSession worker_session(worker_id);
787 ShenandoahAdjustPointersObjectClosure obj_cl;
788 ShenandoahHeapRegion* r = _regions.next();
789 while (r != NULL) {
790 if (!r->is_humongous_continuation() && r->has_live()) {
791 _heap->marked_object_iterate(r, &obj_cl);
792 }
793 r = _regions.next();
794 }
795 }
796 };
797
798 class ShenandoahAdjustRootPointersTask : public AbstractGangTask {
799 private:
800 ShenandoahRootAdjuster* _rp;
801 PreservedMarksSet* _preserved_marks;
802 public:
803 ShenandoahAdjustRootPointersTask(ShenandoahRootAdjuster* rp, PreservedMarksSet* preserved_marks) :
804 AbstractGangTask("Shenandoah Adjust Root Pointers"),
805 _rp(rp),
806 _preserved_marks(preserved_marks) {}
807
808 void work(uint worker_id) {
809 ShenandoahParallelWorkerSession worker_session(worker_id);
810 ShenandoahAdjustPointersClosure cl;
811 _rp->roots_do(worker_id, &cl);
812 const SlidingForwarding* const forwarding = ShenandoahHeap::heap()->forwarding();
813 _preserved_marks->get(worker_id)->adjust_during_full_gc(forwarding);
814 }
815 };
816
817 void ShenandoahFullGC::phase3_update_references() {
818 GCTraceTime(Info, gc, phases) time("Phase 3: Adjust pointers", _gc_timer);
819 ShenandoahGCPhase adjust_pointer_phase(ShenandoahPhaseTimings::full_gc_adjust_pointers);
820
821 ShenandoahHeap* heap = ShenandoahHeap::heap();
822
823 WorkGang* workers = heap->workers();
824 uint nworkers = workers->active_workers();
825 {
826 #if COMPILER2_OR_JVMCI
827 DerivedPointerTable::clear();
828 #endif
829 ShenandoahRootAdjuster rp(nworkers, ShenandoahPhaseTimings::full_gc_adjust_roots);
830 ShenandoahAdjustRootPointersTask task(&rp, _preserved_marks);
831 workers->run_task(&task);
832 #if COMPILER2_OR_JVMCI
833 DerivedPointerTable::update_pointers();
834 #endif
835 }
836
837 ShenandoahAdjustPointersTask adjust_pointers_task;
838 workers->run_task(&adjust_pointers_task);
839 }
840
841 class ShenandoahCompactObjectsClosure : public ObjectClosure {
842 private:
843 ShenandoahHeap* const _heap;
844 const SlidingForwarding* const _forwarding;
845 uint const _worker_id;
846
847 public:
848 ShenandoahCompactObjectsClosure(uint worker_id) :
849 _heap(ShenandoahHeap::heap()), _forwarding(_heap->forwarding()), _worker_id(worker_id) {}
850
851 void do_object(oop p) {
852 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
853 size_t size = (size_t)p->size();
854 if (p->is_forwarded()) {
855 HeapWord* compact_from = cast_from_oop<HeapWord*>(p);
856 HeapWord* compact_to = cast_from_oop<HeapWord*>(_forwarding->forwardee(p));
857 Copy::aligned_conjoint_words(compact_from, compact_to, size);
858 oop new_obj = cast_to_oop(compact_to);
859 new_obj->init_mark();
860 }
861 }
862 };
863
864 class ShenandoahCompactObjectsTask : public AbstractGangTask {
865 private:
866 ShenandoahHeap* const _heap;
867 ShenandoahHeapRegionSet** const _worker_slices;
868
869 public:
870 ShenandoahCompactObjectsTask(ShenandoahHeapRegionSet** worker_slices) :
871 AbstractGangTask("Shenandoah Compact Objects"),
872 _heap(ShenandoahHeap::heap()),
873 _worker_slices(worker_slices) {
874 }
875
876 void work(uint worker_id) {
877 ShenandoahParallelWorkerSession worker_session(worker_id);
878 ShenandoahHeapRegionSetIterator slice(_worker_slices[worker_id]);
879
880 ShenandoahCompactObjectsClosure cl(worker_id);
881 ShenandoahHeapRegion* r = slice.next();
882 while (r != NULL) {
883 assert(!r->is_humongous(), "must not get humongous regions here");
884 if (r->has_live()) {
885 _heap->marked_object_iterate(r, &cl);
886 }
887 r->set_top(r->new_top());
888 r = slice.next();
889 }
890 }
891 };
892
893 class ShenandoahPostCompactClosure : public ShenandoahHeapRegionClosure {
894 private:
895 ShenandoahHeap* const _heap;
896 size_t _live;
897
898 public:
899 ShenandoahPostCompactClosure() : _heap(ShenandoahHeap::heap()), _live(0) {
900 _heap->free_set()->clear();
901 }
902
903 void heap_region_do(ShenandoahHeapRegion* r) {
904 assert (!r->is_cset(), "cset regions should have been demoted already");
905
906 // Need to reset the complete-top-at-mark-start pointer here because
907 // the complete marking bitmap is no longer valid. This ensures
908 // size-based iteration in marked_object_iterate().
909 // NOTE: See blurb at ShenandoahMCResetCompleteBitmapTask on why we need to skip
910 // pinned regions.
911 if (!r->is_pinned()) {
912 _heap->complete_marking_context()->reset_top_at_mark_start(r);
913 }
914
915 size_t live = r->used();
916
917 // Make empty regions that have been allocated into regular
918 if (r->is_empty() && live > 0) {
919 r->make_regular_bypass();
920 }
921
922 // Reclaim regular regions that became empty
923 if (r->is_regular() && live == 0) {
924 r->make_trash();
925 }
926
927 // Recycle all trash regions
928 if (r->is_trash()) {
929 live = 0;
930 r->recycle();
931 }
932
933 r->set_live_data(live);
934 r->reset_alloc_metadata();
935 _live += live;
936 }
937
938 size_t get_live() {
939 return _live;
940 }
941 };
942
943 void ShenandoahFullGC::compact_humongous_objects() {
944 // Compact humongous regions, based on their fwdptr objects.
945 //
946 // This code is serial, because doing the in-slice parallel sliding is tricky. In most cases,
947 // humongous regions are already compacted, and do not require further moves, which alleviates
948 // sliding costs. We may consider doing this in parallel in future.
949
950 ShenandoahHeap* heap = ShenandoahHeap::heap();
951 const SlidingForwarding* const forwarding = heap->forwarding();
952
953 for (size_t c = heap->num_regions(); c > 0; c--) {
954 ShenandoahHeapRegion* r = heap->get_region(c - 1);
955 if (r->is_humongous_start()) {
956 oop old_obj = cast_to_oop(r->bottom());
957 if (!old_obj->is_forwarded()) {
958 // No need to move the object, it stays at the same slot
959 continue;
960 }
961 size_t words_size = old_obj->size();
962 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
963
964 size_t old_start = r->index();
965 size_t old_end = old_start + num_regions - 1;
966 size_t new_start = heap->heap_region_index_containing(forwarding->forwardee(old_obj));
967 size_t new_end = new_start + num_regions - 1;
968 assert(old_start != new_start, "must be real move");
969 assert(r->is_stw_move_allowed(), "Region " SIZE_FORMAT " should be movable", r->index());
970
971 Copy::aligned_conjoint_words(heap->get_region(old_start)->bottom(),
972 heap->get_region(new_start)->bottom(),
973 words_size);
974
975 oop new_obj = cast_to_oop(heap->get_region(new_start)->bottom());
976 new_obj->init_mark();
977
978 {
979 for (size_t c = old_start; c <= old_end; c++) {
980 ShenandoahHeapRegion* r = heap->get_region(c);
981 r->make_regular_bypass();
982 r->set_top(r->bottom());
983 }
984
985 for (size_t c = new_start; c <= new_end; c++) {
986 ShenandoahHeapRegion* r = heap->get_region(c);
987 if (c == new_start) {
988 r->make_humongous_start_bypass();
989 } else {
990 r->make_humongous_cont_bypass();
991 }
992
993 // Trailing region may be non-full, record the remainder there
994 size_t remainder = words_size & ShenandoahHeapRegion::region_size_words_mask();
995 if ((c == new_end) && (remainder != 0)) {
996 r->set_top(r->bottom() + remainder);
997 } else {
998 r->set_top(r->end());
999 }
1000
1001 r->reset_alloc_metadata();
1002 }
1003 }
1004 }
1005 }
1006 }
1007
1008 // This is slightly different to ShHeap::reset_next_mark_bitmap:
1009 // we need to remain able to walk pinned regions.
1010 // Since pinned region do not move and don't get compacted, we will get holes with
1011 // unreachable objects in them (which may have pointers to unloaded Klasses and thus
1012 // cannot be iterated over using oop->size(). The only way to safely iterate over those is using
1013 // a valid marking bitmap and valid TAMS pointer. This class only resets marking
1014 // bitmaps for un-pinned regions, and later we only reset TAMS for unpinned regions.
1015 class ShenandoahMCResetCompleteBitmapTask : public AbstractGangTask {
1016 private:
1017 ShenandoahRegionIterator _regions;
1018
1019 public:
1020 ShenandoahMCResetCompleteBitmapTask() :
1021 AbstractGangTask("Shenandoah Reset Bitmap") {
1022 }
1023
1024 void work(uint worker_id) {
1025 ShenandoahParallelWorkerSession worker_session(worker_id);
1026 ShenandoahHeapRegion* region = _regions.next();
1027 ShenandoahHeap* heap = ShenandoahHeap::heap();
1028 ShenandoahMarkingContext* const ctx = heap->complete_marking_context();
1029 while (region != NULL) {
1030 if (heap->is_bitmap_slice_committed(region) && !region->is_pinned() && region->has_live()) {
1031 ctx->clear_bitmap(region);
1032 }
1033 region = _regions.next();
1034 }
1035 }
1036 };
1037
1038 void ShenandoahFullGC::phase4_compact_objects(ShenandoahHeapRegionSet** worker_slices) {
1039 GCTraceTime(Info, gc, phases) time("Phase 4: Move objects", _gc_timer);
1040 ShenandoahGCPhase compaction_phase(ShenandoahPhaseTimings::full_gc_copy_objects);
1041
1042 ShenandoahHeap* heap = ShenandoahHeap::heap();
1043
1044 // Compact regular objects first
1045 {
1046 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_regular);
1047 ShenandoahCompactObjectsTask compact_task(worker_slices);
1048 heap->workers()->run_task(&compact_task);
1049 }
1050
1051 // Compact humongous objects after regular object moves
1052 {
1053 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_humong);
1054 compact_humongous_objects();
1055 }
1056
1057 // Reset complete bitmap. We're about to reset the complete-top-at-mark-start pointer
1058 // and must ensure the bitmap is in sync.
1059 {
1060 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_reset_complete);
1061 ShenandoahMCResetCompleteBitmapTask task;
1062 heap->workers()->run_task(&task);
1063 }
1064
1065 // Bring regions in proper states after the collection, and set heap properties.
1066 {
1067 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_rebuild);
1068
1069 ShenandoahPostCompactClosure post_compact;
1070 heap->heap_region_iterate(&post_compact);
1071 heap->set_used(post_compact.get_live());
1072
1073 heap->collection_set()->clear();
1074 heap->free_set()->rebuild();
1075 }
1076
1077 heap->clear_cancelled_gc();
1078 }