1 /*
2 * Copyright (c) 2014, 2019, Red Hat, Inc. All rights reserved.
3 *
4 * This code is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 only, as
6 * published by the Free Software Foundation.
7 *
8 * This code is distributed in the hope that it will be useful, but WITHOUT
9 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
10 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
11 * version 2 for more details (a copy is included in the LICENSE file that
12 * accompanied this code).
13 *
14 * You should have received a copy of the GNU General Public License version
15 * 2 along with this work; if not, write to the Free Software Foundation,
16 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
17 *
18 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
19 * or visit www.oracle.com if you need additional information or have any
20 * questions.
21 *
22 */
23
24 #include "precompiled.hpp"
25
26 #include "code/codeCache.hpp"
27 #include "gc/shared/gcTraceTime.inline.hpp"
28 #include "gc/shenandoah/shenandoahBrooksPointer.hpp"
29 #include "gc/shenandoah/shenandoahConcurrentMark.inline.hpp"
30 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
31 #include "gc/shenandoah/shenandoahFreeSet.hpp"
32 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
33 #include "gc/shenandoah/shenandoahMarkCompact.hpp"
34 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp"
35 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
36 #include "gc/shenandoah/shenandoahHeuristics.hpp"
37 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
38 #include "gc/shenandoah/shenandoahRootProcessor.hpp"
39 #include "gc/shenandoah/shenandoahTraversalGC.hpp"
40 #include "gc/shenandoah/shenandoahTaskqueue.inline.hpp"
41 #include "gc/shenandoah/shenandoahUtils.hpp"
42 #include "gc/shenandoah/shenandoahVerifier.hpp"
43 #include "gc/shenandoah/shenandoahVMOperations.hpp"
44 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
45 #include "memory/metaspace.hpp"
46 #include "oops/oop.inline.hpp"
47 #include "runtime/thread.hpp"
48 #include "utilities/copy.hpp"
49 #include "utilities/growableArray.hpp"
50 #include "gc/shared/workgroup.hpp"
51
52 void ShenandoahMarkCompact::initialize(GCTimer* gc_timer) {
53 _gc_timer = gc_timer;
54 }
55
56 void ShenandoahMarkCompact::do_it(GCCause::Cause gc_cause) {
57 ShenandoahHeap* heap = ShenandoahHeap::heap();
58
59 if (ShenandoahVerify) {
60 heap->verifier()->verify_before_fullgc();
61 }
62
63 if (VerifyBeforeGC) {
64 Universe::verify();
65 }
66
67 heap->set_full_gc_in_progress(true);
68
69 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
70 assert(Thread::current()->is_VM_thread(), "Do full GC only while world is stopped");
71
72 {
73 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdumps);
74 heap->pre_full_gc_dump(_gc_timer);
75 }
76
77 {
78 ShenandoahGCPhase prepare_phase(ShenandoahPhaseTimings::full_gc_prepare);
79 // Full GC is supposed to recover from any GC state:
80
81 // a0. Remember if we have forwarded objects
82 bool has_forwarded_objects = heap->has_forwarded_objects();
83
84 // a1. Cancel evacuation, if in progress
85 if (heap->is_evacuation_in_progress()) {
86 heap->set_evacuation_in_progress(false);
87 }
88 assert(!heap->is_evacuation_in_progress(), "sanity");
89
90 // a2. Cancel update-refs, if in progress
91 if (heap->is_update_refs_in_progress()) {
92 heap->set_update_refs_in_progress(false);
93 }
94 assert(!heap->is_update_refs_in_progress(), "sanity");
95
96 // a3. Cancel concurrent traversal GC, if in progress
97 if (heap->is_concurrent_traversal_in_progress()) {
98 heap->traversal_gc()->reset();
99 heap->set_concurrent_traversal_in_progress(false);
100 }
101
102 // b. Cancel concurrent mark, if in progress
103 if (heap->is_concurrent_mark_in_progress()) {
104 heap->concurrent_mark()->cancel();
105 heap->stop_concurrent_marking();
106 }
107 assert(!heap->is_concurrent_mark_in_progress(), "sanity");
108
109 // c. Reset the bitmaps for new marking
110 heap->reset_mark_bitmap();
111 assert(heap->marking_context()->is_bitmap_clear(), "sanity");
112 assert(!heap->marking_context()->is_complete(), "sanity");
113
114 // d. Abandon reference discovery and clear all discovered references.
115 ReferenceProcessor* rp = heap->ref_processor();
116 rp->disable_discovery();
117 rp->abandon_partial_discovery();
118 rp->verify_no_references_recorded();
119
120 // e. Set back forwarded objects bit back, in case some steps above dropped it.
121 heap->set_has_forwarded_objects(has_forwarded_objects);
122 }
123
124 heap->make_parsable(true);
125
126 CodeCache::gc_prologue();
127
128 OrderAccess::fence();
129
130 phase1_mark_heap();
131
132 // Once marking is done, which may have fixed up forwarded objects, we can drop it.
133 // Coming out of Full GC, we would not have any forwarded objects.
134 // This also prevents read barrier from kicking in while adjusting pointers in phase3.
135 heap->set_has_forwarded_objects(false);
136
137 heap->set_full_gc_move_in_progress(true);
138
139 // Setup workers for the rest
140 OrderAccess::fence();
141
142 // Initialize worker slices
143 ShenandoahHeapRegionSet** worker_slices = NEW_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, heap->max_workers(), mtGC);
144 for (uint i = 0; i < heap->max_workers(); i++) {
145 worker_slices[i] = new ShenandoahHeapRegionSet();
146 }
147
148 {
149 // The rest of code performs region moves, where region status is undefined
150 // until all phases run together.
151 ShenandoahHeapLocker lock(heap->lock());
152
153 phase2_calculate_target_addresses(worker_slices);
154
155 OrderAccess::fence();
156
157 phase3_update_references();
158
159 phase4_compact_objects(worker_slices);
160 }
161
162 // Resize metaspace
163 MetaspaceGC::compute_new_size();
164
165 // Free worker slices
166 for (uint i = 0; i < heap->max_workers(); i++) {
167 delete worker_slices[i];
168 }
169 FREE_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, worker_slices);
170
171 CodeCache::gc_epilogue();
172 JvmtiExport::gc_epilogue();
173
174 heap->set_full_gc_move_in_progress(false);
175 heap->set_full_gc_in_progress(false);
176
177 if (ShenandoahVerify) {
178 heap->verifier()->verify_after_fullgc();
179 }
180
181 if (VerifyAfterGC) {
182 Universe::verify();
183 }
184
185 {
186 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdumps);
187 heap->post_full_gc_dump(_gc_timer);
188 }
189 }
190
191 class ShenandoahPrepareForMarkClosure: public ShenandoahHeapRegionClosure {
192 private:
193 ShenandoahMarkingContext* const _ctx;
194
195 public:
196 ShenandoahPrepareForMarkClosure() : _ctx(ShenandoahHeap::heap()->marking_context()) {}
197
198 void heap_region_do(ShenandoahHeapRegion *r) {
199 _ctx->capture_top_at_mark_start(r);
200 r->clear_live_data();
201 r->set_concurrent_iteration_safe_limit(r->top());
202 }
203 };
204
205 void ShenandoahMarkCompact::phase1_mark_heap() {
206 GCTraceTime(Info, gc, phases) time("Phase 1: Mark live objects", _gc_timer);
207 ShenandoahGCPhase mark_phase(ShenandoahPhaseTimings::full_gc_mark);
208
209 ShenandoahHeap* heap = ShenandoahHeap::heap();
210
211 ShenandoahPrepareForMarkClosure cl;
212 heap->heap_region_iterate(&cl);
213
214 ShenandoahConcurrentMark* cm = heap->concurrent_mark();
215
216 heap->set_process_references(heap->heuristics()->can_process_references());
217 heap->set_unload_classes(heap->heuristics()->can_unload_classes());
218
219 ReferenceProcessor* rp = heap->ref_processor();
220 // enable ("weak") refs discovery
221 rp->enable_discovery(true /*verify_no_refs*/);
222 rp->setup_policy(true); // forcefully purge all soft references
223 rp->set_active_mt_degree(heap->workers()->active_workers());
224
225 cm->update_roots(ShenandoahPhaseTimings::full_gc_roots);
226 cm->mark_roots(ShenandoahPhaseTimings::full_gc_roots);
227 cm->finish_mark_from_roots(/* full_gc = */ true);
228
229 heap->mark_complete_marking_context();
230 }
231
232 class ShenandoahPrepareForCompactionObjectClosure : public ObjectClosure {
233 private:
234 ShenandoahHeap* const _heap;
235 GrowableArray<ShenandoahHeapRegion*>& _empty_regions;
236 int _empty_regions_pos;
237 ShenandoahHeapRegion* _to_region;
238 ShenandoahHeapRegion* _from_region;
239 HeapWord* _compact_point;
240
241 public:
242 ShenandoahPrepareForCompactionObjectClosure(GrowableArray<ShenandoahHeapRegion*>& empty_regions, ShenandoahHeapRegion* to_region) :
243 _heap(ShenandoahHeap::heap()),
244 _empty_regions(empty_regions),
245 _empty_regions_pos(0),
246 _to_region(to_region),
247 _from_region(NULL),
248 _compact_point(to_region->bottom()) {}
249
250 void set_from_region(ShenandoahHeapRegion* from_region) {
251 _from_region = from_region;
252 }
253
254 void finish_region() {
255 assert(_to_region != NULL, "should not happen");
256 _to_region->set_new_top(_compact_point);
257 }
258
259 bool is_compact_same_region() {
260 return _from_region == _to_region;
261 }
262
263 int empty_regions_pos() {
264 return _empty_regions_pos;
265 }
266
267 void do_object(oop p) {
268 assert(_from_region != NULL, "must set before work");
269 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
270 assert(!_heap->complete_marking_context()->allocated_after_mark_start((HeapWord*) p), "must be truly marked");
271
272 size_t obj_size = p->size() + ShenandoahBrooksPointer::word_size();
273 if (_compact_point + obj_size > _to_region->end()) {
274 finish_region();
275
276 // Object doesn't fit. Pick next empty region and start compacting there.
277 ShenandoahHeapRegion* new_to_region;
278 if (_empty_regions_pos < _empty_regions.length()) {
279 new_to_region = _empty_regions.at(_empty_regions_pos);
280 _empty_regions_pos++;
281 } else {
282 // Out of empty region? Compact within the same region.
283 new_to_region = _from_region;
284 }
285
286 assert(new_to_region != _to_region, "must not reuse same to-region");
287 assert(new_to_region != NULL, "must not be NULL");
288 _to_region = new_to_region;
289 _compact_point = _to_region->bottom();
290 }
291
292 // Object fits into current region, record new location:
293 assert(_compact_point + obj_size <= _to_region->end(), "must fit");
294 shenandoah_assert_not_forwarded(NULL, p);
295 ShenandoahBrooksPointer::set_raw(p, _compact_point + ShenandoahBrooksPointer::word_size());
296 _compact_point += obj_size;
297 }
298 };
299
300 class ShenandoahPrepareForCompactionTask : public AbstractGangTask {
301 private:
302 ShenandoahHeap* const _heap;
303 ShenandoahHeapRegionSet** const _worker_slices;
304 ShenandoahRegionIterator _heap_regions;
305
306 ShenandoahHeapRegion* next_from_region(ShenandoahHeapRegionSet* slice) {
307 ShenandoahHeapRegion* from_region = _heap_regions.next();
308
309 while (from_region != NULL && (!from_region->is_move_allowed() || from_region->is_humongous())) {
310 from_region = _heap_regions.next();
311 }
312
313 if (from_region != NULL) {
314 assert(slice != NULL, "sanity");
315 assert(!from_region->is_humongous(), "this path cannot handle humongous regions");
316 assert(from_region->is_move_allowed(), "only regions that can be moved in mark-compact");
317 slice->add_region(from_region);
318 }
319
320 return from_region;
321 }
322
323 public:
324 ShenandoahPrepareForCompactionTask(ShenandoahHeapRegionSet** worker_slices) :
325 AbstractGangTask("Shenandoah Prepare For Compaction Task"),
326 _heap(ShenandoahHeap::heap()), _worker_slices(worker_slices) {
327 }
328
329 void work(uint worker_id) {
330 ShenandoahHeapRegionSet* slice = _worker_slices[worker_id];
331 ShenandoahHeapRegion* from_region = next_from_region(slice);
332 // No work?
333 if (from_region == NULL) {
334 return;
335 }
336
337 // Sliding compaction. Walk all regions in the slice, and compact them.
338 // Remember empty regions and reuse them as needed.
339 ResourceMark rm;
340 GrowableArray<ShenandoahHeapRegion*> empty_regions((int)_heap->num_regions());
341 ShenandoahPrepareForCompactionObjectClosure cl(empty_regions, from_region);
342 while (from_region != NULL) {
343 cl.set_from_region(from_region);
344 if (from_region->has_live()) {
345 _heap->marked_object_iterate(from_region, &cl);
346 }
347
348 // Compacted the region to somewhere else? From-region is empty then.
349 if (!cl.is_compact_same_region()) {
350 empty_regions.append(from_region);
351 }
352 from_region = next_from_region(slice);
353 }
354 cl.finish_region();
355
356 // Mark all remaining regions as empty
357 for (int pos = cl.empty_regions_pos(); pos < empty_regions.length(); ++pos) {
358 ShenandoahHeapRegion* r = empty_regions.at(pos);
359 r->set_new_top(r->bottom());
360 }
361 }
362 };
363
364 void ShenandoahMarkCompact::calculate_target_humongous_objects() {
365 ShenandoahHeap* heap = ShenandoahHeap::heap();
366
367 // Compute the new addresses for humongous objects. We need to do this after addresses
368 // for regular objects are calculated, and we know what regions in heap suffix are
369 // available for humongous moves.
370 //
371 // Scan the heap backwards, because we are compacting humongous regions towards the end.
372 // Maintain the contiguous compaction window in [to_begin; to_end), so that we can slide
373 // humongous start there.
374 //
375 // The complication is potential non-movable regions during the scan. If such region is
376 // detected, then sliding restarts towards that non-movable region.
377
378 size_t to_begin = heap->num_regions();
379 size_t to_end = heap->num_regions();
380
381 for (size_t c = heap->num_regions() - 1; c > 0; c--) {
382 ShenandoahHeapRegion *r = heap->get_region(c);
383 if (r->is_humongous_continuation() || (r->new_top() == r->bottom())) {
384 // To-region candidate: record this, and continue scan
385 to_begin = r->region_number();
386 continue;
387 }
388
389 if (r->is_humongous_start() && r->is_move_allowed()) {
390 // From-region candidate: movable humongous region
391 oop old_obj = oop(r->bottom() + ShenandoahBrooksPointer::word_size());
392 size_t words_size = old_obj->size() + ShenandoahBrooksPointer::word_size();
393 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
394
395 size_t start = to_end - num_regions;
396
397 if (start >= to_begin && start != r->region_number()) {
398 // Fits into current window, and the move is non-trivial. Record the move then, and continue scan.
399 ShenandoahBrooksPointer::set_raw(old_obj, heap->get_region(start)->bottom() + ShenandoahBrooksPointer::word_size());
400 to_end = start;
401 continue;
402 }
403 }
404
405 // Failed to fit. Scan starting from current region.
406 to_begin = r->region_number();
407 to_end = r->region_number();
408 }
409 }
410
411 class ShenandoahEnsureHeapActiveClosure: public ShenandoahHeapRegionClosure {
412 private:
413 ShenandoahHeap* const _heap;
414
415 public:
416 ShenandoahEnsureHeapActiveClosure() : _heap(ShenandoahHeap::heap()) {}
417 void heap_region_do(ShenandoahHeapRegion* r) {
418 if (r->is_trash()) {
419 r->recycle();
420 }
421 if (r->is_cset()) {
422 r->make_regular_bypass();
423 }
424 if (r->is_empty_uncommitted()) {
425 r->make_committed_bypass();
426 }
427 assert (r->is_committed(), "only committed regions in heap now, see region " SIZE_FORMAT, r->region_number());
428
429 // Record current region occupancy: this communicates empty regions are free
430 // to the rest of Full GC code.
431 r->set_new_top(r->top());
432 }
433 };
434
435 class ShenandoahTrashImmediateGarbageClosure: public ShenandoahHeapRegionClosure {
436 private:
437 ShenandoahHeap* const _heap;
438 ShenandoahMarkingContext* const _ctx;
439
440 public:
441 ShenandoahTrashImmediateGarbageClosure() :
442 _heap(ShenandoahHeap::heap()),
443 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
444
445 void heap_region_do(ShenandoahHeapRegion* r) {
446 if (r->is_humongous_start()) {
447 oop humongous_obj = oop(r->bottom() + ShenandoahBrooksPointer::word_size());
448 if (!_ctx->is_marked(humongous_obj)) {
449 assert(!r->has_live(),
450 "Region " SIZE_FORMAT " is not marked, should not have live", r->region_number());
451 _heap->trash_humongous_region_at(r);
452 } else {
453 assert(r->has_live(),
454 "Region " SIZE_FORMAT " should have live", r->region_number());
455 }
456 } else if (r->is_humongous_continuation()) {
457 // If we hit continuation, the non-live humongous starts should have been trashed already
458 assert(r->humongous_start_region()->has_live(),
459 "Region " SIZE_FORMAT " should have live", r->region_number());
460 } else if (r->is_regular()) {
461 if (!r->has_live()) {
462 r->make_trash_immediate();
463 }
464 }
465 }
466 };
467
468 void ShenandoahMarkCompact::phase2_calculate_target_addresses(ShenandoahHeapRegionSet** worker_slices) {
469 GCTraceTime(Info, gc, phases) time("Phase 2: Compute new object addresses", _gc_timer);
470 ShenandoahGCPhase calculate_address_phase(ShenandoahPhaseTimings::full_gc_calculate_addresses);
471
472 ShenandoahHeap* heap = ShenandoahHeap::heap();
473
474 {
475 // Trash the immediately collectible regions before computing addresses
476 ShenandoahTrashImmediateGarbageClosure tigcl;
477 heap->heap_region_iterate(&tigcl);
478
479 // Make sure regions are in good state: committed, active, clean.
480 // This is needed because we are potentially sliding the data through them.
481 ShenandoahEnsureHeapActiveClosure ecl;
482 heap->heap_region_iterate(&ecl);
483 }
484
485 // Compute the new addresses for regular objects
486 {
487 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_regular);
488 ShenandoahPrepareForCompactionTask prepare_task(worker_slices);
489 heap->workers()->run_task(&prepare_task);
490 }
491
492 // Compute the new addresses for humongous objects
493 {
494 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_humong);
495 calculate_target_humongous_objects();
496 }
497 }
498
499 class ShenandoahAdjustPointersClosure : public MetadataVisitingOopIterateClosure {
500 private:
501 ShenandoahHeap* const _heap;
502 ShenandoahMarkingContext* const _ctx;
503
504 template <class T>
505 inline void do_oop_work(T* p) {
506 T o = RawAccess<>::oop_load(p);
507 if (!CompressedOops::is_null(o)) {
508 oop obj = CompressedOops::decode_not_null(o);
509 assert(_ctx->is_marked(obj), "must be marked");
510 oop forw = oop(ShenandoahBrooksPointer::get_raw(obj));
511 RawAccess<IS_NOT_NULL>::oop_store(p, forw);
512 }
513 }
514
515 public:
516 ShenandoahAdjustPointersClosure() :
517 _heap(ShenandoahHeap::heap()),
518 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
519
520 void do_oop(oop* p) { do_oop_work(p); }
521 void do_oop(narrowOop* p) { do_oop_work(p); }
522 };
523
524 class ShenandoahAdjustPointersObjectClosure : public ObjectClosure {
525 private:
526 ShenandoahHeap* const _heap;
527 ShenandoahAdjustPointersClosure _cl;
528
529 public:
530 ShenandoahAdjustPointersObjectClosure() :
531 _heap(ShenandoahHeap::heap()) {
532 }
533 void do_object(oop p) {
534 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
535 HeapWord* forw = ShenandoahBrooksPointer::get_raw(p);
536 p->oop_iterate(&_cl);
537 }
538 };
539
540 class ShenandoahAdjustPointersTask : public AbstractGangTask {
541 private:
542 ShenandoahHeap* const _heap;
543 ShenandoahRegionIterator _regions;
544
545 public:
546 ShenandoahAdjustPointersTask() :
547 AbstractGangTask("Shenandoah Adjust Pointers Task"),
548 _heap(ShenandoahHeap::heap()) {
549 }
550
551 void work(uint worker_id) {
552 ShenandoahAdjustPointersObjectClosure obj_cl;
553 ShenandoahHeapRegion* r = _regions.next();
554 while (r != NULL) {
555 if (!r->is_humongous_continuation() && r->has_live()) {
556 _heap->marked_object_iterate(r, &obj_cl);
557 }
558 r = _regions.next();
559 }
560 }
561 };
562
563 class ShenandoahAdjustRootPointersTask : public AbstractGangTask {
564 private:
565 ShenandoahRootProcessor* _rp;
566
567 public:
568 ShenandoahAdjustRootPointersTask(ShenandoahRootProcessor* rp) :
569 AbstractGangTask("Shenandoah Adjust Root Pointers Task"),
570 _rp(rp) {}
571
572 void work(uint worker_id) {
573 ShenandoahAdjustPointersClosure cl;
574 CLDToOopClosure adjust_cld_closure(&cl, ClassLoaderData::_claim_strong);
575 MarkingCodeBlobClosure adjust_code_closure(&cl,
576 CodeBlobToOopClosure::FixRelocations);
577
578 _rp->process_all_roots(&cl, &cl,
579 &adjust_cld_closure,
580 &adjust_code_closure, NULL, worker_id);
581 }
582 };
583
584 void ShenandoahMarkCompact::phase3_update_references() {
585 GCTraceTime(Info, gc, phases) time("Phase 3: Adjust pointers", _gc_timer);
586 ShenandoahGCPhase adjust_pointer_phase(ShenandoahPhaseTimings::full_gc_adjust_pointers);
587
588 ShenandoahHeap* heap = ShenandoahHeap::heap();
589
590 WorkGang* workers = heap->workers();
591 uint nworkers = workers->active_workers();
592 {
593 #if COMPILER2_OR_JVMCI
594 DerivedPointerTable::clear();
595 #endif
596 ShenandoahRootProcessor rp(heap, nworkers, ShenandoahPhaseTimings::full_gc_roots);
597 ShenandoahAdjustRootPointersTask task(&rp);
598 workers->run_task(&task);
599 #if COMPILER2_OR_JVMCI
600 DerivedPointerTable::update_pointers();
601 #endif
602 }
603
604 ShenandoahAdjustPointersTask adjust_pointers_task;
605 workers->run_task(&adjust_pointers_task);
606 }
607
608 class ShenandoahCompactObjectsClosure : public ObjectClosure {
609 private:
610 ShenandoahHeap* const _heap;
611 uint const _worker_id;
612
613 public:
614 ShenandoahCompactObjectsClosure(uint worker_id) :
615 _heap(ShenandoahHeap::heap()), _worker_id(worker_id) {}
616
617 void do_object(oop p) {
618 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
619 size_t size = (size_t)p->size();
620 HeapWord* compact_to = ShenandoahBrooksPointer::get_raw(p);
621 HeapWord* compact_from = (HeapWord*) p;
622 if (compact_from != compact_to) {
623 Copy::aligned_conjoint_words(compact_from, compact_to, size);
624 }
625 oop new_obj = oop(compact_to);
626 ShenandoahBrooksPointer::initialize(new_obj);
627 }
628 };
629
630 class ShenandoahCompactObjectsTask : public AbstractGangTask {
631 private:
632 ShenandoahHeap* const _heap;
633 ShenandoahHeapRegionSet** const _worker_slices;
634
635 public:
636 ShenandoahCompactObjectsTask(ShenandoahHeapRegionSet** worker_slices) :
637 AbstractGangTask("Shenandoah Compact Objects Task"),
638 _heap(ShenandoahHeap::heap()),
639 _worker_slices(worker_slices) {
640 }
641
642 void work(uint worker_id) {
643 ShenandoahHeapRegionSetIterator slice(_worker_slices[worker_id]);
644
645 ShenandoahCompactObjectsClosure cl(worker_id);
646 ShenandoahHeapRegion* r = slice.next();
647 while (r != NULL) {
648 assert(!r->is_humongous(), "must not get humongous regions here");
649 if (r->has_live()) {
650 _heap->marked_object_iterate(r, &cl);
651 }
652 r->set_top(r->new_top());
653 r = slice.next();
654 }
655 }
656 };
657
658 class ShenandoahPostCompactClosure : public ShenandoahHeapRegionClosure {
659 private:
660 ShenandoahHeap* const _heap;
661 size_t _live;
662
663 public:
664 ShenandoahPostCompactClosure() : _heap(ShenandoahHeap::heap()), _live(0) {
665 _heap->free_set()->clear();
666 }
667
668 void heap_region_do(ShenandoahHeapRegion* r) {
669 assert (!r->is_cset(), "cset regions should have been demoted already");
670
671 // Need to reset the complete-top-at-mark-start pointer here because
672 // the complete marking bitmap is no longer valid. This ensures
673 // size-based iteration in marked_object_iterate().
674 // NOTE: See blurb at ShenandoahMCResetCompleteBitmapTask on why we need to skip
675 // pinned regions.
676 if (!r->is_pinned()) {
677 _heap->complete_marking_context()->reset_top_at_mark_start(r);
678 }
679
680 size_t live = r->used();
681
682 // Make empty regions that have been allocated into regular
683 if (r->is_empty() && live > 0) {
684 r->make_regular_bypass();
685 }
686
687 // Reclaim regular regions that became empty
688 if (r->is_regular() && live == 0) {
689 r->make_trash();
690 }
691
692 // Recycle all trash regions
693 if (r->is_trash()) {
694 live = 0;
695 r->recycle();
696 }
697
698 r->set_live_data(live);
699 r->reset_alloc_metadata_to_shared();
700 _live += live;
701 }
702
703 size_t get_live() {
704 return _live;
705 }
706 };
707
708 void ShenandoahMarkCompact::compact_humongous_objects() {
709 // Compact humongous regions, based on their fwdptr objects.
710 //
711 // This code is serial, because doing the in-slice parallel sliding is tricky. In most cases,
712 // humongous regions are already compacted, and do not require further moves, which alleviates
713 // sliding costs. We may consider doing this in parallel in future.
714
715 ShenandoahHeap* heap = ShenandoahHeap::heap();
716
717 for (size_t c = heap->num_regions() - 1; c > 0; c--) {
718 ShenandoahHeapRegion* r = heap->get_region(c);
719 if (r->is_humongous_start()) {
720 oop old_obj = oop(r->bottom() + ShenandoahBrooksPointer::word_size());
721 size_t words_size = old_obj->size() + ShenandoahBrooksPointer::word_size();
722 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
723
724 size_t old_start = r->region_number();
725 size_t old_end = old_start + num_regions - 1;
726 size_t new_start = heap->heap_region_index_containing(ShenandoahBrooksPointer::get_raw(old_obj));
727 size_t new_end = new_start + num_regions - 1;
728
729 if (old_start == new_start) {
730 // No need to move the object, it stays at the same slot
731 continue;
732 }
733
734 assert (r->is_move_allowed(), "should be movable");
735
736 Copy::aligned_conjoint_words(heap->get_region(old_start)->bottom(),
737 heap->get_region(new_start)->bottom(),
738 ShenandoahHeapRegion::region_size_words()*num_regions);
739
740 oop new_obj = oop(heap->get_region(new_start)->bottom() + ShenandoahBrooksPointer::word_size());
741 ShenandoahBrooksPointer::initialize(new_obj);
742
743 {
744 for (size_t c = old_start; c <= old_end; c++) {
745 ShenandoahHeapRegion* r = heap->get_region(c);
746 r->make_regular_bypass();
747 r->set_top(r->bottom());
748 }
749
750 for (size_t c = new_start; c <= new_end; c++) {
751 ShenandoahHeapRegion* r = heap->get_region(c);
752 if (c == new_start) {
753 r->make_humongous_start_bypass();
754 } else {
755 r->make_humongous_cont_bypass();
756 }
757
758 // Trailing region may be non-full, record the remainder there
759 size_t remainder = words_size & ShenandoahHeapRegion::region_size_words_mask();
760 if ((c == new_end) && (remainder != 0)) {
761 r->set_top(r->bottom() + remainder);
762 } else {
763 r->set_top(r->end());
764 }
765
766 r->reset_alloc_metadata_to_shared();
767 }
768 }
769 }
770 }
771 }
772
773 // This is slightly different to ShHeap::reset_next_mark_bitmap:
774 // we need to remain able to walk pinned regions.
775 // Since pinned region do not move and don't get compacted, we will get holes with
776 // unreachable objects in them (which may have pointers to unloaded Klasses and thus
777 // cannot be iterated over using oop->size(). The only way to safely iterate over those is using
778 // a valid marking bitmap and valid TAMS pointer. This class only resets marking
779 // bitmaps for un-pinned regions, and later we only reset TAMS for unpinned regions.
780 class ShenandoahMCResetCompleteBitmapTask : public AbstractGangTask {
781 private:
782 ShenandoahRegionIterator _regions;
783
784 public:
785 ShenandoahMCResetCompleteBitmapTask() :
786 AbstractGangTask("Parallel Reset Bitmap Task") {
787 }
788
789 void work(uint worker_id) {
790 ShenandoahHeapRegion* region = _regions.next();
791 ShenandoahHeap* heap = ShenandoahHeap::heap();
792 ShenandoahMarkingContext* const ctx = heap->complete_marking_context();
793 while (region != NULL) {
794 if (heap->is_bitmap_slice_committed(region) && !region->is_pinned() && region->has_live()) {
795 ctx->clear_bitmap(region);
796 }
797 region = _regions.next();
798 }
799 }
800 };
801
802 void ShenandoahMarkCompact::phase4_compact_objects(ShenandoahHeapRegionSet** worker_slices) {
803 GCTraceTime(Info, gc, phases) time("Phase 4: Move objects", _gc_timer);
804 ShenandoahGCPhase compaction_phase(ShenandoahPhaseTimings::full_gc_copy_objects);
805
806 ShenandoahHeap* heap = ShenandoahHeap::heap();
807
808 // Compact regular objects first
809 {
810 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_regular);
811 ShenandoahCompactObjectsTask compact_task(worker_slices);
812 heap->workers()->run_task(&compact_task);
813 }
814
815 // Compact humongous objects after regular object moves
816 {
817 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_humong);
818 compact_humongous_objects();
819 }
820
821 // Reset complete bitmap. We're about to reset the complete-top-at-mark-start pointer
822 // and must ensure the bitmap is in sync.
823 {
824 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_reset_complete);
825 ShenandoahMCResetCompleteBitmapTask task;
826 heap->workers()->run_task(&task);
827 }
828
829 // Bring regions in proper states after the collection, and set heap properties.
830 {
831 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_rebuild);
832
833 ShenandoahPostCompactClosure post_compact;
834 heap->heap_region_iterate(&post_compact);
835 heap->set_used(post_compact.get_live());
836
837 heap->collection_set()->clear();
838 heap->free_set()->rebuild();
839 }
840
841 heap->clear_cancelled_gc();
842 }