1 /*
2 * Copyright (c) 2014, 2017, Red Hat, Inc. and/or its affiliates.
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 "classfile/javaClasses.inline.hpp"
27 #include "code/codeCache.hpp"
28 #include "gc/shared/gcTraceTime.inline.hpp"
29 #include "gc/shenandoah/brooksPointer.hpp"
30 #include "gc/shenandoah/shenandoahConcurrentMark.inline.hpp"
31 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
32 #include "gc/shenandoah/shenandoahFreeSet.hpp"
33 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
34 #include "gc/shenandoah/shenandoahMarkCompact.hpp"
35 #include "gc/shenandoah/shenandoahBarrierSet.hpp"
36 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp"
37 #include "gc/shenandoah/shenandoahHeap.hpp"
38 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
39 #include "gc/shenandoah/shenandoahPartialGC.hpp"
40 #include "gc/shenandoah/shenandoahRootProcessor.hpp"
41 #include "gc/shenandoah/shenandoahTraversalGC.hpp"
42 #include "gc/shenandoah/shenandoahUtils.hpp"
43 #include "gc/shenandoah/shenandoahVerifier.hpp"
44 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
45 #include "gc/shenandoah/vm_operations_shenandoah.hpp"
46 #include "oops/oop.inline.hpp"
47 #include "runtime/biasedLocking.hpp"
48 #include "runtime/thread.hpp"
49 #include "utilities/copy.hpp"
50 #include "utilities/growableArray.hpp"
51 #include "gc/shared/taskqueue.inline.hpp"
52 #include "gc/shared/workgroup.hpp"
53
54 class ShenandoahClearRegionStatusClosure: public ShenandoahHeapRegionClosure {
55 private:
56 ShenandoahHeap* const _heap;
57
58 public:
59 ShenandoahClearRegionStatusClosure() : _heap(ShenandoahHeap::heap()) {}
60
61 bool heap_region_do(ShenandoahHeapRegion *r) {
62 _heap->set_next_top_at_mark_start(r->bottom(), r->top());
63 r->clear_live_data();
64 r->set_concurrent_iteration_safe_limit(r->top());
65 return false;
66 }
67 };
68
69 class ShenandoahEnsureHeapActiveClosure: public ShenandoahHeapRegionClosure {
70 private:
71 ShenandoahHeap* const _heap;
72
73 public:
74 ShenandoahEnsureHeapActiveClosure() : _heap(ShenandoahHeap::heap()) {}
75 bool heap_region_do(ShenandoahHeapRegion* r) {
76 if (r->is_trash()) {
77 r->recycle();
78 }
79 if (r->is_cset()) {
80 r->make_regular_bypass();
81 }
82 if (r->is_empty_uncommitted()) {
83 r->make_committed_bypass();
84 }
85 assert (r->is_committed(), "only committed regions in heap now, see region " SIZE_FORMAT, r->region_number());
86
87 // Record current region occupancy: this communicates empty regions are free
88 // to the rest of Full GC code.
89 r->set_new_top(r->top());
90 return false;
91 }
92 };
93
94 void ShenandoahMarkCompact::initialize(GCTimer* gc_timer) {
95 _gc_timer = gc_timer;
96 }
97
98 void ShenandoahMarkCompact::do_it(GCCause::Cause gc_cause) {
99 ShenandoahHeap* heap = ShenandoahHeap::heap();
100
101 {
102 if (ShenandoahVerify) {
103 heap->verifier()->verify_before_fullgc();
104 }
105
106 heap->set_full_gc_in_progress(true);
107
108 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
109 assert(Thread::current()->is_VM_thread(), "Do full GC only while world is stopped");
110
111 {
112 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdumps);
113 heap->pre_full_gc_dump(_gc_timer);
114 }
115
116 {
117 ShenandoahGCPhase prepare_phase(ShenandoahPhaseTimings::full_gc_prepare);
118 // Full GC is supposed to recover from any GC state:
119
120 // a1. Cancel evacuation, if in progress
121 if (heap->is_evacuation_in_progress()) {
122 heap->set_evacuation_in_progress(false);
123 }
124 assert(!heap->is_evacuation_in_progress(), "sanity");
125
126 // a2. Cancel update-refs, if in progress
127 if (heap->is_update_refs_in_progress()) {
128 heap->set_update_refs_in_progress(false);
129 }
130 assert(!heap->is_update_refs_in_progress(), "sanity");
131
132 // a3. Cancel concurrent partial GC, if in progress
133 if (heap->is_concurrent_partial_in_progress()) {
134 heap->partial_gc()->reset();
135 heap->set_concurrent_partial_in_progress(false);
136 }
137
138 // a3. Cancel concurrent traversal GC, if in progress
139 if (heap->is_concurrent_traversal_in_progress()) {
140 heap->traversal_gc()->reset();
141 heap->set_concurrent_traversal_in_progress(false);
142 }
143
144 // b. Cancel concurrent mark, if in progress
145 if (heap->is_concurrent_mark_in_progress()) {
146 heap->concurrentMark()->cancel();
147 heap->stop_concurrent_marking();
148 }
149 assert(!heap->is_concurrent_mark_in_progress(), "sanity");
150
151 // c. Reset the bitmaps for new marking
152 heap->reset_next_mark_bitmap();
153 assert(heap->is_next_bitmap_clear(), "sanity");
154
155 // d. Abandon reference discovery and clear all discovered references.
156 ReferenceProcessor* rp = heap->ref_processor();
157 rp->disable_discovery();
158 rp->abandon_partial_discovery();
159 rp->verify_no_references_recorded();
160
161 {
162 ShenandoahHeapLocker lock(heap->lock());
163
164 // f. Make sure all regions are active. This is needed because we are potentially
165 // sliding the data through them
166 ShenandoahEnsureHeapActiveClosure ecl;
167 heap->heap_region_iterate(&ecl, false, false);
168
169 // g. Clear region statuses, including collection set status
170 ShenandoahClearRegionStatusClosure cl;
171 heap->heap_region_iterate(&cl, false, false);
172 }
173 }
174
175 {
176 if (UseTLAB) {
177 heap->make_tlabs_parsable(true);
178 }
179
180 CodeCache::gc_prologue();
181
182 // TODO: We don't necessarily need to update refs. We might want to clean
183 // up managing has_forwarded_objects when diving into degen/full-gc.
184 heap->set_has_forwarded_objects(true);
185
186 OrderAccess::fence();
187
188 phase1_mark_heap();
189
190 // Prevent read-barrier from kicking in while adjusting pointers in phase3.
191 heap->set_has_forwarded_objects(false);
192
193 heap->set_full_gc_move_in_progress(true);
194
195 // Setup workers for the rest
196 {
197 OrderAccess::fence();
198
199 // Initialize worker slices
200 ShenandoahHeapRegionSet** worker_slices = NEW_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, heap->max_workers(), mtGC);
201 for (uint i = 0; i < heap->max_workers(); i++) {
202 worker_slices[i] = new ShenandoahHeapRegionSet();
203 }
204
205 phase2_calculate_target_addresses(worker_slices);
206
207 OrderAccess::fence();
208
209 phase3_update_references();
210
211 phase4_compact_objects(worker_slices);
212
213 // Free worker slices
214 for (uint i = 0; i < heap->max_workers(); i++) {
215 delete worker_slices[i];
216 }
217 FREE_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, worker_slices);
218
219 CodeCache::gc_epilogue();
220 JvmtiExport::gc_epilogue();
221 }
222
223 heap->set_full_gc_move_in_progress(false);
224 heap->set_full_gc_in_progress(false);
225
226 if (ShenandoahVerify) {
227 heap->verifier()->verify_after_fullgc();
228 }
229 }
230
231 {
232 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdumps);
233 heap->post_full_gc_dump(_gc_timer);
234 }
235
236 if (UseTLAB) {
237 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_resize_tlabs);
238 heap->resize_all_tlabs();
239 }
240 }
241
242
243 if (UseShenandoahMatrix && PrintShenandoahMatrix) {
244 LogTarget(Info, gc) lt;
245 LogStream ls(lt);
246 heap->connection_matrix()->print_on(&ls);
247 }
248 }
249
250 void ShenandoahMarkCompact::phase1_mark_heap() {
251 GCTraceTime(Info, gc, phases) time("Phase 1: Mark live objects", _gc_timer);
252 ShenandoahGCPhase mark_phase(ShenandoahPhaseTimings::full_gc_mark);
253
254 ShenandoahHeap* heap = ShenandoahHeap::heap();
255
256 ShenandoahConcurrentMark* cm = heap->concurrentMark();
257
258 // Do not trust heuristics, because this can be our last resort collection.
259 // Only ignore processing references and class unloading if explicitly disabled.
260 heap->set_process_references(ShenandoahRefProcFrequency != 0);
261 heap->set_unload_classes(ShenandoahUnloadClassesFrequency != 0);
262
263 ReferenceProcessor* rp = heap->ref_processor();
264 // enable ("weak") refs discovery
265 rp->enable_discovery(true /*verify_no_refs*/);
266 rp->setup_policy(true); // snapshot the soft ref policy to be used in this cycle
267 rp->set_active_mt_degree(heap->workers()->active_workers());
268
269 cm->update_roots(ShenandoahPhaseTimings::full_gc_roots);
270 cm->mark_roots(ShenandoahPhaseTimings::full_gc_roots);
271 cm->shared_finish_mark_from_roots(/* full_gc = */ true);
272
273 heap->swap_mark_bitmaps();
274
275 if (UseShenandoahMatrix && PrintShenandoahMatrix) {
276 LogTarget(Info, gc) lt;
277 LogStream ls(lt);
278 heap->connection_matrix()->print_on(&ls);
279 }
280 }
281
282 class ShenandoahMCReclaimHumongousRegionClosure : public ShenandoahHeapRegionClosure {
283 private:
284 ShenandoahHeap* const _heap;
285 public:
286 ShenandoahMCReclaimHumongousRegionClosure() : _heap(ShenandoahHeap::heap()) {}
287
288 bool heap_region_do(ShenandoahHeapRegion* r) {
289 if (r->is_humongous_start()) {
290 oop humongous_obj = oop(r->bottom() + BrooksPointer::word_size());
291 if (!_heap->is_marked_complete(humongous_obj)) {
292 _heap->trash_humongous_region_at(r);
293 }
294 }
295 return false;
296 }
297 };
298
299 class ShenandoahPrepareForCompactionObjectClosure : public ObjectClosure {
300 private:
301 ShenandoahHeap* const _heap;
302 GrowableArray<ShenandoahHeapRegion*>& _empty_regions;
303 int _empty_regions_pos;
304 ShenandoahHeapRegion* _to_region;
305 ShenandoahHeapRegion* _from_region;
306 HeapWord* _compact_point;
307
308 public:
309 ShenandoahPrepareForCompactionObjectClosure(GrowableArray<ShenandoahHeapRegion*>& empty_regions, ShenandoahHeapRegion* to_region) :
310 _heap(ShenandoahHeap::heap()),
311 _empty_regions(empty_regions),
312 _empty_regions_pos(0),
313 _to_region(to_region),
314 _from_region(NULL),
315 _compact_point(to_region->bottom()) {}
316
317 void set_from_region(ShenandoahHeapRegion* from_region) {
318 _from_region = from_region;
319 }
320
321 void finish_region() {
322 assert(_to_region != NULL, "should not happen");
323 _to_region->set_new_top(_compact_point);
324 }
325
326 bool is_compact_same_region() {
327 return _from_region == _to_region;
328 }
329
330 int empty_regions_pos() {
331 return _empty_regions_pos;
332 }
333
334 void do_object(oop p) {
335 assert(_from_region != NULL, "must set before work");
336 assert(_heap->is_marked_complete(p), "must be marked");
337 assert(!_heap->allocated_after_complete_mark_start((HeapWord*) p), "must be truly marked");
338
339 size_t obj_size = p->size() + BrooksPointer::word_size();
340 if (_compact_point + obj_size > _to_region->end()) {
341 finish_region();
342
343 // Object doesn't fit. Pick next empty region and start compacting there.
344 ShenandoahHeapRegion* new_to_region;
345 if (_empty_regions_pos < _empty_regions.length()) {
346 new_to_region = _empty_regions.at(_empty_regions_pos);
347 _empty_regions_pos++;
348 } else {
349 // Out of empty region? Compact within the same region.
350 new_to_region = _from_region;
351 }
352
353 assert(new_to_region != _to_region, "must not reuse same to-region");
354 assert(new_to_region != NULL, "must not be NULL");
355 _to_region = new_to_region;
356 _compact_point = _to_region->bottom();
357 }
358
359 // Object fits into current region, record new location:
360 assert(_compact_point + obj_size <= _to_region->end(), "must fit");
361 shenandoah_assert_not_forwarded(NULL, p);
362 BrooksPointer::set_raw(p, _compact_point + BrooksPointer::word_size());
363 _compact_point += obj_size;
364 }
365 };
366
367 class ShenandoahPrepareForCompactionTask : public AbstractGangTask {
368 private:
369 ShenandoahHeap* const _heap;
370 ShenandoahHeapRegionSet** const _worker_slices;
371 ShenandoahRegionIterator _heap_regions;
372
373 ShenandoahHeapRegion* next_from_region(ShenandoahHeapRegionSet* slice) {
374 ShenandoahHeapRegion* from_region = _heap_regions.next();
375
376 while (from_region != NULL && (!from_region->is_move_allowed() || from_region->is_humongous())) {
377 from_region = _heap_regions.next();
378 }
379
380 if (from_region != NULL) {
381 assert(slice != NULL, "sanity");
382 assert(!from_region->is_humongous(), "this path cannot handle humongous regions");
383 assert(from_region->is_move_allowed(), "only regions that can be moved in mark-compact");
384 slice->add_region(from_region);
385 }
386
387 return from_region;
388 }
389
390 public:
391 ShenandoahPrepareForCompactionTask(ShenandoahHeapRegionSet** worker_slices) :
392 AbstractGangTask("Shenandoah Prepare For Compaction Task"),
393 _heap(ShenandoahHeap::heap()), _heap_regions(_heap->region_iterator()), _worker_slices(worker_slices) {
394 }
395
396 void work(uint worker_id) {
397 ShenandoahHeapRegionSet* slice = _worker_slices[worker_id];
398 ShenandoahHeapRegion* from_region = next_from_region(slice);
399 // No work?
400 if (from_region == NULL) {
401 return;
402 }
403
404 // Sliding compaction. Walk all regions in the slice, and compact them.
405 // Remember empty regions and reuse them as needed.
406 ResourceMark rm;
407 GrowableArray<ShenandoahHeapRegion*> empty_regions(_heap->num_regions());
408 ShenandoahPrepareForCompactionObjectClosure cl(empty_regions, from_region);
409 while (from_region != NULL) {
410 cl.set_from_region(from_region);
411 _heap->marked_object_iterate(from_region, &cl);
412
413 // Compacted the region to somewhere else? From-region is empty then.
414 if (!cl.is_compact_same_region()) {
415 empty_regions.append(from_region);
416 }
417 from_region = next_from_region(slice);
418 }
419 cl.finish_region();
420
421 // Mark all remaining regions as empty
422 for (int pos = cl.empty_regions_pos(); pos < empty_regions.length(); ++pos) {
423 ShenandoahHeapRegion* r = empty_regions.at(pos);
424 r->set_new_top(r->bottom());
425 }
426 }
427 };
428
429 void ShenandoahMarkCompact::calculate_target_humongous_objects() {
430 ShenandoahHeap* heap = ShenandoahHeap::heap();
431
432 // Compute the new addresses for humongous objects. We need to do this after addresses
433 // for regular objects are calculated, and we know what regions in heap suffix are
434 // available for humongous moves.
435 //
436 // Scan the heap backwards, because we are compacting humongous regions towards the end.
437 // Maintain the contiguous compaction window in [to_begin; to_end), so that we can slide
438 // humongous start there.
439 //
440 // The complication is potential non-movable regions during the scan. If such region is
441 // detected, then sliding restarts towards that non-movable region.
442
443 size_t to_begin = heap->num_regions();
444 size_t to_end = heap->num_regions();
445
446 for (size_t c = heap->num_regions() - 1; c > 0; c--) {
447 ShenandoahHeapRegion *r = heap->get_region(c);
448 if (r->is_humongous_continuation() || (r->new_top() == r->bottom())) {
449 // To-region candidate: record this, and continue scan
450 to_begin = r->region_number();
451 continue;
452 }
453
454 if (r->is_humongous_start() && r->is_move_allowed()) {
455 // From-region candidate: movable humongous region
456 oop old_obj = oop(r->bottom() + BrooksPointer::word_size());
457 size_t words_size = old_obj->size() + BrooksPointer::word_size();
458 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
459
460 size_t start = to_end - num_regions;
461
462 if (start >= to_begin && start != r->region_number()) {
463 // Fits into current window, and the move is non-trivial. Record the move then, and continue scan.
464 BrooksPointer::set_raw(old_obj, heap->get_region(start)->bottom() + BrooksPointer::word_size());
465 to_end = start;
466 continue;
467 }
468 }
469
470 // Failed to fit. Scan starting from current region.
471 to_begin = r->region_number();
472 to_end = r->region_number();
473 }
474 }
475
476 void ShenandoahMarkCompact::phase2_calculate_target_addresses(ShenandoahHeapRegionSet** worker_slices) {
477 GCTraceTime(Info, gc, phases) time("Phase 2: Compute new object addresses", _gc_timer);
478 ShenandoahGCPhase calculate_address_phase(ShenandoahPhaseTimings::full_gc_calculate_addresses);
479
480 ShenandoahHeap* heap = ShenandoahHeap::heap();
481
482 {
483 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_regular);
484
485 {
486 ShenandoahHeapLocker lock(heap->lock());
487
488 ShenandoahMCReclaimHumongousRegionClosure cl;
489 heap->heap_region_iterate(&cl);
490
491 // After some humongous regions were reclaimed, we need to ensure their
492 // backing storage is active. This is needed because we are potentially
493 // sliding the data through them.
494 ShenandoahEnsureHeapActiveClosure ecl;
495 heap->heap_region_iterate(&ecl, false, false);
496 }
497
498 // Compute the new addresses for regular objects
499 ShenandoahPrepareForCompactionTask prepare_task(worker_slices);
500 heap->workers()->run_task(&prepare_task);
501 }
502
503 // Compute the new addresses for humongous objects
504 {
505 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_humong);
506 calculate_target_humongous_objects();
507 }
508 }
509
510 class ShenandoahAdjustPointersClosure : public MetadataAwareOopClosure {
511 private:
512 ShenandoahHeap* const _heap;
513 size_t _new_obj_offset;
514
515 template <class T>
516 inline void do_oop_work(T* p) {
517 T o = oopDesc::load_heap_oop(p);
518 if (! oopDesc::is_null(o)) {
519 oop obj = oopDesc::decode_heap_oop_not_null(o);
520 assert(_heap->is_marked_complete(obj), "must be marked");
521 oop forw = oop(BrooksPointer::get_raw(obj));
522 oopDesc::encode_store_heap_oop(p, forw);
523 if (UseShenandoahMatrix) {
524 if (_heap->is_in_reserved(p)) {
525 assert(_heap->is_in_reserved(forw), "must be in heap");
526 assert(_new_obj_offset != SIZE_MAX, "should be set");
527 // We're moving a to a', which points to b, about to be moved to b'.
528 // We already know b' from the fwd pointer of b.
529 // In the object closure, we see a, and we know a' (by looking at its
530 // fwd ptr). We store the offset in the OopClosure, which is going
531 // to visit all of a's fields, and then, when we see each field, we
532 // subtract the offset from each field address to get the final ptr.
533 _heap->connection_matrix()->set_connected(((HeapWord*) p) - _new_obj_offset, forw);
534 }
535 }
536 }
537 }
538
539 public:
540 ShenandoahAdjustPointersClosure() : _heap(ShenandoahHeap::heap()), _new_obj_offset(SIZE_MAX) {}
541
542 void do_oop(oop* p) { do_oop_work(p); }
543 void do_oop(narrowOop* p) { do_oop_work(p); }
544
545 void set_new_obj_offset(size_t new_obj_offset) {
546 _new_obj_offset = new_obj_offset;
547 }
548 };
549
550 class ShenandoahAdjustPointersObjectClosure : public ObjectClosure {
551 private:
552 ShenandoahHeap* const _heap;
553 ShenandoahAdjustPointersClosure _cl;
554
555 public:
556 ShenandoahAdjustPointersObjectClosure() :
557 _heap(ShenandoahHeap::heap()) {
558 }
559 void do_object(oop p) {
560 assert(_heap->is_marked_complete(p), "must be marked");
561 HeapWord* forw = BrooksPointer::get_raw(p);
562 _cl.set_new_obj_offset(pointer_delta((HeapWord*) p, forw));
563 p->oop_iterate(&_cl);
564 }
565 };
566
567 class ShenandoahAdjustPointersTask : public AbstractGangTask {
568 private:
569 ShenandoahHeap* const _heap;
570 ShenandoahRegionIterator _regions;
571
572 public:
573 ShenandoahAdjustPointersTask() :
574 AbstractGangTask("Shenandoah Adjust Pointers Task"),
575 _heap(ShenandoahHeap::heap()), _regions(_heap->region_iterator()) {
576 }
577
578 void work(uint worker_id) {
579 ShenandoahAdjustPointersObjectClosure obj_cl;
580 ShenandoahHeapRegion* r = _regions.next();
581 while (r != NULL) {
582 if (!r->is_humongous_continuation()) {
583 _heap->marked_object_iterate(r, &obj_cl);
584 }
585 r = _regions.next();
586 }
587 }
588 };
589
590 class ShenandoahAdjustRootPointersTask : public AbstractGangTask {
591 private:
592 ShenandoahRootProcessor* _rp;
593
594 public:
595 ShenandoahAdjustRootPointersTask(ShenandoahRootProcessor* rp) :
596 AbstractGangTask("Shenandoah Adjust Root Pointers Task"),
597 _rp(rp) {}
598
599 void work(uint worker_id) {
600 ShenandoahAdjustPointersClosure cl;
601 CLDToOopClosure adjust_cld_closure(&cl, true);
602 MarkingCodeBlobClosure adjust_code_closure(&cl,
603 CodeBlobToOopClosure::FixRelocations);
604
605 _rp->process_all_roots(&cl, &cl,
606 &adjust_cld_closure,
607 &adjust_code_closure, NULL, worker_id);
608 }
609 };
610
611 void ShenandoahMarkCompact::phase3_update_references() {
612 GCTraceTime(Info, gc, phases) time("Phase 3: Adjust pointers", _gc_timer);
613 ShenandoahGCPhase adjust_pointer_phase(ShenandoahPhaseTimings::full_gc_adjust_pointers);
614
615 ShenandoahHeap* heap = ShenandoahHeap::heap();
616
617 if (UseShenandoahMatrix) {
618 heap->connection_matrix()->clear_all();
619 }
620
621 WorkGang* workers = heap->workers();
622 uint nworkers = workers->active_workers();
623 {
624 #if COMPILER2_OR_JVMCI
625 DerivedPointerTable::clear();
626 #endif
627 ShenandoahRootProcessor rp(heap, nworkers, ShenandoahPhaseTimings::full_gc_roots);
628 ShenandoahAdjustRootPointersTask task(&rp);
629 workers->run_task(&task);
630 #if COMPILER2_OR_JVMCI
631 DerivedPointerTable::update_pointers();
632 #endif
633 }
634
635 ShenandoahAdjustPointersTask adjust_pointers_task;
636 workers->run_task(&adjust_pointers_task);
637 }
638
639 class ShenandoahCompactObjectsClosure : public ObjectClosure {
640 private:
641 ShenandoahHeap* const _heap;
642 uint const _worker_id;
643
644 public:
645 ShenandoahCompactObjectsClosure(uint worker_id) :
646 _heap(ShenandoahHeap::heap()), _worker_id(worker_id) {}
647
648 void do_object(oop p) {
649 assert(_heap->is_marked_complete(p), "must be marked");
650 size_t size = (size_t)p->size();
651 HeapWord* compact_to = BrooksPointer::get_raw(p);
652 HeapWord* compact_from = (HeapWord*) p;
653 if (compact_from != compact_to) {
654 Copy::aligned_conjoint_words(compact_from, compact_to, size);
655 }
656 oop new_obj = oop(compact_to);
657 BrooksPointer::initialize(new_obj);
658 }
659 };
660
661 class ShenandoahCompactObjectsTask : public AbstractGangTask {
662 private:
663 ShenandoahHeap* const _heap;
664 ShenandoahHeapRegionSet** const _worker_slices;
665
666 public:
667 ShenandoahCompactObjectsTask(ShenandoahHeapRegionSet** worker_slices) :
668 AbstractGangTask("Shenandoah Compact Objects Task"),
669 _heap(ShenandoahHeap::heap()),
670 _worker_slices(worker_slices) {
671 }
672
673 void work(uint worker_id) {
674 ShenandoahHeapRegionSetIterator slice = _worker_slices[worker_id]->iterator();
675
676 ShenandoahCompactObjectsClosure cl(worker_id);
677 ShenandoahHeapRegion* r = slice.next();
678 while (r != NULL) {
679 assert(!r->is_humongous(), "must not get humongous regions here");
680 _heap->marked_object_iterate(r, &cl);
681 r->set_top(r->new_top());
682 r = slice.next();
683 }
684 }
685 };
686
687 class ShenandoahPostCompactClosure : public ShenandoahHeapRegionClosure {
688 private:
689 ShenandoahHeap* const _heap;
690 size_t _live;
691
692 public:
693 ShenandoahPostCompactClosure() : _live(0), _heap(ShenandoahHeap::heap()) {
694 _heap->free_set()->clear();
695 }
696
697 bool heap_region_do(ShenandoahHeapRegion* r) {
698 assert (!r->is_cset(), "cset regions should have been demoted already");
699
700 // Need to reset the complete-top-at-mark-start pointer here because
701 // the complete marking bitmap is no longer valid. This ensures
702 // size-based iteration in marked_object_iterate().
703 // NOTE: See blurb at ShenandoahMCResetCompleteBitmapTask on why we need to skip
704 // pinned regions.
705 if (!r->is_pinned()) {
706 _heap->set_complete_top_at_mark_start(r->bottom(), r->bottom());
707 }
708
709 size_t live = r->used();
710
711 // Make empty regions that have been allocated into regular
712 if (r->is_empty() && live > 0) {
713 r->make_regular_bypass();
714 }
715
716 // Reclaim regular regions that became empty
717 if (r->is_regular() && live == 0) {
718 r->make_trash();
719 }
720
721 // Recycle all trash regions
722 if (r->is_trash()) {
723 live = 0;
724 r->recycle();
725 }
726
727 r->set_live_data(live);
728 r->reset_alloc_metadata_to_shared();
729 _live += live;
730 return false;
731 }
732
733 size_t get_live() {
734 return _live;
735 }
736 };
737
738 void ShenandoahMarkCompact::compact_humongous_objects() {
739 // Compact humongous regions, based on their fwdptr objects.
740 //
741 // This code is serial, because doing the in-slice parallel sliding is tricky. In most cases,
742 // humongous regions are already compacted, and do not require further moves, which alleviates
743 // sliding costs. We may consider doing this in parallel in future.
744
745 ShenandoahHeap* heap = ShenandoahHeap::heap();
746
747 for (size_t c = heap->num_regions() - 1; c > 0; c--) {
748 ShenandoahHeapRegion* r = heap->get_region(c);
749 if (r->is_humongous_start()) {
750 oop old_obj = oop(r->bottom() + BrooksPointer::word_size());
751 size_t words_size = old_obj->size() + BrooksPointer::word_size();
752 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
753
754 size_t old_start = r->region_number();
755 size_t old_end = old_start + num_regions - 1;
756 size_t new_start = heap->heap_region_index_containing(BrooksPointer::get_raw(old_obj));
757 size_t new_end = new_start + num_regions - 1;
758
759 if (old_start == new_start) {
760 // No need to move the object, it stays at the same slot
761 continue;
762 }
763
764 assert (r->is_move_allowed(), "should be movable");
765
766 Copy::aligned_conjoint_words(heap->get_region(old_start)->bottom(),
767 heap->get_region(new_start)->bottom(),
768 ShenandoahHeapRegion::region_size_words()*num_regions);
769
770 oop new_obj = oop(heap->get_region(new_start)->bottom() + BrooksPointer::word_size());
771 BrooksPointer::initialize(new_obj);
772
773 {
774 ShenandoahHeapLocker lock(heap->lock());
775
776 for (size_t c = old_start; c <= old_end; c++) {
777 ShenandoahHeapRegion* r = heap->get_region(c);
778 r->make_regular_bypass();
779 r->set_top(r->bottom());
780 }
781
782 for (size_t c = new_start; c <= new_end; c++) {
783 ShenandoahHeapRegion* r = heap->get_region(c);
784 if (c == new_start) {
785 r->make_humongous_start_bypass();
786 } else {
787 r->make_humongous_cont_bypass();
788 }
789
790 // Trailing region may be non-full, record the remainder there
791 size_t remainder = words_size & ShenandoahHeapRegion::region_size_words_mask();
792 if ((c == new_end) && (remainder != 0)) {
793 r->set_top(r->bottom() + remainder);
794 } else {
795 r->set_top(r->end());
796 }
797
798 r->reset_alloc_metadata_to_shared();
799 }
800 }
801 }
802 }
803 }
804
805 // This is slightly different to ShHeap::reset_next_mark_bitmap:
806 // we need to remain able to walk pinned regions.
807 // Since pinned region do not move and don't get compacted, we will get holes with
808 // unreachable objects in them (which may have pointers to unloaded Klasses and thus
809 // cannot be iterated over using oop->size(). The only way to safely iterate over those is using
810 // a valid marking bitmap and valid TAMS pointer. This class only resets marking
811 // bitmaps for un-pinned regions, and later we only reset TAMS for unpinned regions.
812 class ShenandoahMCResetCompleteBitmapTask : public AbstractGangTask {
813 private:
814 ShenandoahRegionIterator _regions;
815
816 public:
817 ShenandoahMCResetCompleteBitmapTask(ShenandoahRegionIterator regions) :
818 AbstractGangTask("Parallel Reset Bitmap Task"),
819 _regions(regions) {
820 }
821
822 void work(uint worker_id) {
823 ShenandoahHeapRegion* region = _regions.next();
824 ShenandoahHeap* heap = ShenandoahHeap::heap();
825 while (region != NULL) {
826 if (heap->is_bitmap_slice_committed(region) && !region->is_pinned()) {
827 HeapWord* bottom = region->bottom();
828 HeapWord* top = heap->complete_top_at_mark_start(region->bottom());
829 if (top > bottom) {
830 heap->complete_mark_bit_map()->clear_range_large(MemRegion(bottom, top));
831 }
832 assert(heap->is_complete_bitmap_clear_range(bottom, region->end()), "must be clear");
833 }
834 region = _regions.next();
835 }
836 }
837 };
838
839 void ShenandoahMarkCompact::phase4_compact_objects(ShenandoahHeapRegionSet** worker_slices) {
840 GCTraceTime(Info, gc, phases) time("Phase 4: Move objects", _gc_timer);
841 ShenandoahGCPhase compaction_phase(ShenandoahPhaseTimings::full_gc_copy_objects);
842
843 ShenandoahHeap* heap = ShenandoahHeap::heap();
844
845 // Compact regular objects first
846 {
847 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_regular);
848 ShenandoahCompactObjectsTask compact_task(worker_slices);
849 heap->workers()->run_task(&compact_task);
850 }
851
852 // Compact humongous objects after regular object moves
853 {
854 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_humong);
855 compact_humongous_objects();
856 }
857
858 // Reset complete bitmap. We're about to reset the complete-top-at-mark-start pointer
859 // and must ensure the bitmap is in sync.
860 ShenandoahMCResetCompleteBitmapTask task(heap->region_iterator());
861 heap->workers()->run_task(&task);
862
863 // Bring regions in proper states after the collection, and set heap properties.
864 {
865 ShenandoahHeapLocker lock(heap->lock());
866 ShenandoahPostCompactClosure post_compact;
867 heap->heap_region_iterate(&post_compact);
868 heap->set_used(post_compact.get_live());
869
870 heap->collection_set()->clear();
871 heap->free_set()->rebuild();
872 }
873
874 heap->clear_cancelled_concgc();
875
876 // Also clear the next bitmap in preparation for next marking.
877 heap->reset_next_mark_bitmap();
878 }