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