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/shenandoahConcurrentMark.inline.hpp"
29 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
30 #include "gc/shenandoah/shenandoahFreeSet.hpp"
31 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
32 #include "gc/shenandoah/shenandoahMarkCompact.hpp"
33 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp"
34 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
35 #include "gc/shenandoah/shenandoahHeuristics.hpp"
36 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
37 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
38 #include "gc/shenandoah/shenandoahTraversalGC.hpp"
39 #include "gc/shenandoah/shenandoahTaskqueue.inline.hpp"
40 #include "gc/shenandoah/shenandoahUtils.hpp"
41 #include "gc/shenandoah/shenandoahVerifier.hpp"
42 #include "gc/shenandoah/shenandoahVMOperations.hpp"
43 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
44 #include "memory/metaspace.hpp"
45 #include "oops/oop.inline.hpp"
46 #include "runtime/thread.hpp"
47 #include "utilities/copy.hpp"
48 #include "utilities/growableArray.hpp"
49 #include "gc/shared/workgroup.hpp"
50
51 void ShenandoahMarkCompact::initialize(GCTimer* gc_timer) {
52 _gc_timer = gc_timer;
53 }
54
55 void ShenandoahMarkCompact::do_it(GCCause::Cause gc_cause) {
56 ShenandoahHeap* heap = ShenandoahHeap::heap();
57
58 if (ShenandoahVerify) {
59 heap->verifier()->verify_before_fullgc();
60 }
61
62 if (VerifyBeforeGC) {
63 Universe::verify();
64 }
65
66 heap->set_full_gc_in_progress(true);
67
68 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
69 assert(Thread::current()->is_VM_thread(), "Do full GC only while world is stopped");
70
71 {
72 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdumps);
73 heap->pre_full_gc_dump(_gc_timer);
74 }
75
76 {
77 ShenandoahGCPhase prepare_phase(ShenandoahPhaseTimings::full_gc_prepare);
78 // Full GC is supposed to recover from any GC state:
79
80 // a0. Remember if we have forwarded objects
81 bool has_forwarded_objects = heap->has_forwarded_objects();
82
83 // a1. Cancel evacuation, if in progress
84 if (heap->is_evacuation_in_progress()) {
85 heap->set_evacuation_in_progress(false);
86 }
87 assert(!heap->is_evacuation_in_progress(), "sanity");
88
89 // a2. Cancel update-refs, if in progress
90 if (heap->is_update_refs_in_progress()) {
91 heap->set_update_refs_in_progress(false);
92 }
93 assert(!heap->is_update_refs_in_progress(), "sanity");
94
95 // a3. Cancel concurrent traversal GC, if in progress
96 if (heap->is_concurrent_traversal_in_progress()) {
97 heap->traversal_gc()->reset();
98 heap->set_concurrent_traversal_in_progress(false);
99 }
100
101 // b. Cancel concurrent mark, if in progress
102 if (heap->is_concurrent_mark_in_progress()) {
103 heap->concurrent_mark()->cancel();
104 heap->stop_concurrent_marking();
105 }
106 assert(!heap->is_concurrent_mark_in_progress(), "sanity");
107
108 // c. Reset the bitmaps for new marking
109 heap->reset_mark_bitmap();
110 assert(heap->marking_context()->is_bitmap_clear(), "sanity");
111 assert(!heap->marking_context()->is_complete(), "sanity");
112
113 // d. Abandon reference discovery and clear all discovered references.
114 ReferenceProcessor* rp = heap->ref_processor();
115 rp->disable_discovery();
116 rp->abandon_partial_discovery();
117 rp->verify_no_references_recorded();
118
119 // e. Set back forwarded objects bit back, in case some steps above dropped it.
120 heap->set_has_forwarded_objects(has_forwarded_objects);
121 }
122
123 heap->make_parsable(true);
124
125 OrderAccess::fence();
126
127 phase1_mark_heap();
128
129 // Once marking is done, which may have fixed up forwarded objects, we can drop it.
130 // Coming out of Full GC, we would not have any forwarded objects.
131 // This also prevents resolves with fwdptr from kicking in while adjusting pointers in phase3.
132 heap->set_has_forwarded_objects(false);
133
134 heap->set_full_gc_move_in_progress(true);
135
136 // Setup workers for the rest
137 OrderAccess::fence();
138
139 // Initialize worker slices
140 ShenandoahHeapRegionSet** worker_slices = NEW_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, heap->max_workers(), mtGC);
141 for (uint i = 0; i < heap->max_workers(); i++) {
142 worker_slices[i] = new ShenandoahHeapRegionSet();
143 }
144
145 {
146 // The rest of code performs region moves, where region status is undefined
147 // until all phases run together.
148 ShenandoahHeapLocker lock(heap->lock());
149
150 phase2_calculate_target_addresses(worker_slices);
151
152 OrderAccess::fence();
153
154 phase3_update_references();
155
156 phase4_compact_objects(worker_slices);
157 }
158
159 // Resize metaspace
160 MetaspaceGC::compute_new_size();
161
162 // Free worker slices
163 for (uint i = 0; i < heap->max_workers(); i++) {
164 delete worker_slices[i];
165 }
166 FREE_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, worker_slices);
167
168 JvmtiExport::gc_epilogue();
169
170 heap->set_full_gc_move_in_progress(false);
171 heap->set_full_gc_in_progress(false);
172
173 if (ShenandoahVerify) {
174 heap->verifier()->verify_after_fullgc();
175 }
176
177 if (VerifyAfterGC) {
178 Universe::verify();
179 }
180
181 {
182 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdumps);
183 heap->post_full_gc_dump(_gc_timer);
184 }
185 }
186
187 class ShenandoahPrepareForMarkClosure: public ShenandoahHeapRegionClosure {
188 private:
189 ShenandoahMarkingContext* const _ctx;
190
191 public:
192 ShenandoahPrepareForMarkClosure() : _ctx(ShenandoahHeap::heap()->marking_context()) {}
193
194 void heap_region_do(ShenandoahHeapRegion *r) {
195 _ctx->capture_top_at_mark_start(r);
196 r->clear_live_data();
197 r->set_concurrent_iteration_safe_limit(r->top());
198 }
199 };
200
201 void ShenandoahMarkCompact::phase1_mark_heap() {
202 GCTraceTime(Info, gc, phases) time("Phase 1: Mark live objects", _gc_timer);
203 ShenandoahGCPhase mark_phase(ShenandoahPhaseTimings::full_gc_mark);
204
205 ShenandoahHeap* heap = ShenandoahHeap::heap();
206
207 ShenandoahPrepareForMarkClosure cl;
208 heap->heap_region_iterate(&cl);
209
210 ShenandoahConcurrentMark* cm = heap->concurrent_mark();
211
212 heap->set_process_references(heap->heuristics()->can_process_references());
213 heap->set_unload_classes(heap->heuristics()->can_unload_classes());
214
215 ReferenceProcessor* rp = heap->ref_processor();
216 // enable ("weak") refs discovery
217 rp->enable_discovery(true /*verify_no_refs*/);
218 rp->setup_policy(true); // forcefully purge all soft references
219 rp->set_active_mt_degree(heap->workers()->active_workers());
220
221 cm->update_roots(ShenandoahPhaseTimings::full_gc_roots);
222 cm->mark_roots(ShenandoahPhaseTimings::full_gc_roots);
223 cm->finish_mark_from_roots(/* full_gc = */ true);
224
225 heap->mark_complete_marking_context();
226 }
227
228 class ShenandoahPrepareForCompactionObjectClosure : public ObjectClosure {
229 private:
230 ShenandoahMarkCompact* const _mark_compact;
231 ShenandoahHeap* const _heap;
232 GrowableArray<ShenandoahHeapRegion*>& _empty_regions;
233 int _empty_regions_pos;
234 ShenandoahHeapRegion* _to_region;
235 ShenandoahHeapRegion* _from_region;
236 HeapWord* _compact_point;
237
238 public:
239 ShenandoahPrepareForCompactionObjectClosure(ShenandoahMarkCompact* mc, GrowableArray<ShenandoahHeapRegion*>& empty_regions, ShenandoahHeapRegion* to_region) :
240 _mark_compact(mc),
241 _heap(ShenandoahHeap::heap()),
242 _empty_regions(empty_regions),
243 _empty_regions_pos(0),
244 _to_region(to_region),
245 _from_region(NULL),
246 _compact_point(to_region->bottom()) {}
247
248 void set_from_region(ShenandoahHeapRegion* from_region) {
249 _from_region = from_region;
250 }
251
252 void finish_region() {
253 assert(_to_region != NULL, "should not happen");
254 _to_region->set_new_top(_compact_point);
255 }
256
257 bool is_compact_same_region() {
258 return _from_region == _to_region;
259 }
260
261 int empty_regions_pos() {
262 return _empty_regions_pos;
263 }
264
265 void do_object(oop p) {
266 assert(_from_region != NULL, "must set before work");
267 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
268 assert(!_heap->complete_marking_context()->allocated_after_mark_start((HeapWord*) p), "must be truly marked");
269
270 size_t obj_size = p->size();
271 if (_compact_point + obj_size > _to_region->end()) {
272 finish_region();
273
274 // Object doesn't fit. Pick next empty region and start compacting there.
275 ShenandoahHeapRegion* new_to_region;
276 if (_empty_regions_pos < _empty_regions.length()) {
277 new_to_region = _empty_regions.at(_empty_regions_pos);
278 _empty_regions_pos++;
279 } else {
280 // Out of empty region? Compact within the same region.
281 new_to_region = _from_region;
282 }
283
284 assert(new_to_region != _to_region, "must not reuse same to-region");
285 assert(new_to_region != NULL, "must not be NULL");
286 _to_region = new_to_region;
287 _compact_point = _to_region->bottom();
288 }
289
290 // Object fits into current region, record new location:
291 assert(_compact_point + obj_size <= _to_region->end(), "must fit");
292 shenandoah_assert_not_forwarded(NULL, p);
293 _mark_compact->preserve_mark(p);
294 p->forward_to(oop(_compact_point));
295 _compact_point += obj_size;
296 }
297 };
298
299 class ShenandoahPrepareForCompactionTask : public AbstractGangTask {
300 private:
301 ShenandoahMarkCompact* const _mark_compact;
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(ShenandoahMarkCompact* mc, ShenandoahHeapRegionSet** worker_slices) :
325 AbstractGangTask("Shenandoah Prepare For Compaction Task"),
326 _mark_compact(mc),
327 _heap(ShenandoahHeap::heap()), _worker_slices(worker_slices) {
328 }
329
330 void work(uint worker_id) {
331 ShenandoahHeapRegionSet* slice = _worker_slices[worker_id];
332 ShenandoahHeapRegion* from_region = next_from_region(slice);
333 // No work?
334 if (from_region == NULL) {
335 return;
336 }
337
338 // Sliding compaction. Walk all regions in the slice, and compact them.
339 // Remember empty regions and reuse them as needed.
340 ResourceMark rm;
341 GrowableArray<ShenandoahHeapRegion*> empty_regions((int)_heap->num_regions());
342 ShenandoahPrepareForCompactionObjectClosure cl(_mark_compact, empty_regions, from_region);
343 while (from_region != NULL) {
344 cl.set_from_region(from_region);
345 if (from_region->has_live()) {
346 _heap->marked_object_iterate(from_region, &cl);
347 }
348
349 // Compacted the region to somewhere else? From-region is empty then.
350 if (!cl.is_compact_same_region()) {
351 empty_regions.append(from_region);
352 }
353 from_region = next_from_region(slice);
354 }
355 cl.finish_region();
356
357 // Mark all remaining regions as empty
358 for (int pos = cl.empty_regions_pos(); pos < empty_regions.length(); ++pos) {
359 ShenandoahHeapRegion* r = empty_regions.at(pos);
360 r->set_new_top(r->bottom());
361 }
362 }
363 };
364
365 void ShenandoahMarkCompact::calculate_target_humongous_objects() {
366 ShenandoahHeap* heap = ShenandoahHeap::heap();
367
368 // Compute the new addresses for humongous objects. We need to do this after addresses
369 // for regular objects are calculated, and we know what regions in heap suffix are
370 // available for humongous moves.
371 //
372 // Scan the heap backwards, because we are compacting humongous regions towards the end.
373 // Maintain the contiguous compaction window in [to_begin; to_end), so that we can slide
374 // humongous start there.
375 //
376 // The complication is potential non-movable regions during the scan. If such region is
377 // detected, then sliding restarts towards that non-movable region.
378
379 size_t to_begin = heap->num_regions();
380 size_t to_end = heap->num_regions();
381
382 for (size_t c = heap->num_regions(); c > 0; c--) {
383 ShenandoahHeapRegion *r = heap->get_region(c - 1);
384 if (r->is_humongous_continuation() || (r->new_top() == r->bottom())) {
385 // To-region candidate: record this, and continue scan
386 to_begin = r->region_number();
387 continue;
388 }
389
390 if (r->is_humongous_start() && r->is_move_allowed()) {
391 // From-region candidate: movable humongous region
392 oop old_obj = oop(r->bottom());
393 size_t words_size = old_obj->size();
394 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
395
396 size_t start = to_end - num_regions;
397
398 if (start >= to_begin && start != r->region_number()) {
399 // Fits into current window, and the move is non-trivial. Record the move then, and continue scan.
400 old_obj->forward_to(oop(heap->get_region(start)->bottom()));
401 to_end = start;
402 continue;
403 }
404 }
405
406 // Failed to fit. Scan starting from current region.
407 to_begin = r->region_number();
408 to_end = r->region_number();
409 }
410 }
411
412 class ShenandoahEnsureHeapActiveClosure: public ShenandoahHeapRegionClosure {
413 private:
414 ShenandoahHeap* const _heap;
415
416 public:
417 ShenandoahEnsureHeapActiveClosure() : _heap(ShenandoahHeap::heap()) {}
418 void heap_region_do(ShenandoahHeapRegion* r) {
419 if (r->is_trash()) {
420 r->recycle();
421 }
422 if (r->is_cset()) {
423 r->make_regular_bypass();
424 }
425 if (r->is_empty_uncommitted()) {
426 r->make_committed_bypass();
427 }
428 assert (r->is_committed(), "only committed regions in heap now, see region " SIZE_FORMAT, r->region_number());
429
430 // Record current region occupancy: this communicates empty regions are free
431 // to the rest of Full GC code.
432 r->set_new_top(r->top());
433 }
434 };
435
436 class ShenandoahTrashImmediateGarbageClosure: public ShenandoahHeapRegionClosure {
437 private:
438 ShenandoahHeap* const _heap;
439 ShenandoahMarkingContext* const _ctx;
440
441 public:
442 ShenandoahTrashImmediateGarbageClosure() :
443 _heap(ShenandoahHeap::heap()),
444 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
445
446 void heap_region_do(ShenandoahHeapRegion* r) {
447 if (r->is_humongous_start()) {
448 oop humongous_obj = oop(r->bottom());
449 if (!_ctx->is_marked(humongous_obj)) {
450 assert(!r->has_live(),
451 "Region " SIZE_FORMAT " is not marked, should not have live", r->region_number());
452 _heap->trash_humongous_region_at(r);
453 } else {
454 assert(r->has_live(),
455 "Region " SIZE_FORMAT " should have live", r->region_number());
456 }
457 } else if (r->is_humongous_continuation()) {
458 // If we hit continuation, the non-live humongous starts should have been trashed already
459 assert(r->humongous_start_region()->has_live(),
460 "Region " SIZE_FORMAT " should have live", r->region_number());
461 } else if (r->is_regular()) {
462 if (!r->has_live()) {
463 r->make_trash_immediate();
464 }
465 }
466 }
467 };
468
469 void ShenandoahMarkCompact::phase2_calculate_target_addresses(ShenandoahHeapRegionSet** worker_slices) {
470 GCTraceTime(Info, gc, phases) time("Phase 2: Compute new object addresses", _gc_timer);
471 ShenandoahGCPhase calculate_address_phase(ShenandoahPhaseTimings::full_gc_calculate_addresses);
472
473 ShenandoahHeap* heap = ShenandoahHeap::heap();
474
475 {
476 // Trash the immediately collectible regions before computing addresses
477 ShenandoahTrashImmediateGarbageClosure tigcl;
478 heap->heap_region_iterate(&tigcl);
479
480 // Make sure regions are in good state: committed, active, clean.
481 // This is needed because we are potentially sliding the data through them.
482 ShenandoahEnsureHeapActiveClosure ecl;
483 heap->heap_region_iterate(&ecl);
484 }
485
486 // Compute the new addresses for regular objects
487 {
488 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_regular);
489 ShenandoahPrepareForCompactionTask prepare_task(this, worker_slices);
490 heap->workers()->run_task(&prepare_task);
491 }
492
493 // Compute the new addresses for humongous objects
494 {
495 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_humong);
496 calculate_target_humongous_objects();
497 }
498 }
499
500 class ShenandoahAdjustPointersClosure : public MetadataVisitingOopIterateClosure {
501 private:
502 ShenandoahHeap* const _heap;
503 ShenandoahMarkingContext* const _ctx;
504
505 template <class T>
506 inline void do_oop_work(T* p) {
507 T o = RawAccess<>::oop_load(p);
508 if (!CompressedOops::is_null(o)) {
509 oop obj = CompressedOops::decode_not_null(o);
510 assert(_ctx->is_marked(obj), "must be marked");
511 if (obj->is_forwarded()) {
512 oop forw = obj->forwardee();
513 RawAccess<IS_NOT_NULL>::oop_store(p, forw);
514 }
515 }
516 }
517
518 public:
519 ShenandoahAdjustPointersClosure() :
520 _heap(ShenandoahHeap::heap()),
521 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
522
523 void do_oop(oop* p) { do_oop_work(p); }
524 void do_oop(narrowOop* p) { do_oop_work(p); }
525 };
526
527 class ShenandoahAdjustPointersObjectClosure : public ObjectClosure {
528 private:
529 ShenandoahHeap* const _heap;
530 ShenandoahAdjustPointersClosure _cl;
531
532 public:
533 ShenandoahAdjustPointersObjectClosure() :
534 _heap(ShenandoahHeap::heap()) {
535 }
536 void do_object(oop p) {
537 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
538 p->oop_iterate(&_cl);
539 }
540 };
541
542 class ShenandoahAdjustPointersTask : public AbstractGangTask {
543 private:
544 ShenandoahHeap* const _heap;
545 ShenandoahRegionIterator _regions;
546
547 public:
548 ShenandoahAdjustPointersTask() :
549 AbstractGangTask("Shenandoah Adjust Pointers Task"),
550 _heap(ShenandoahHeap::heap()) {
551 }
552
553 void work(uint worker_id) {
554 ShenandoahAdjustPointersObjectClosure obj_cl;
555 ShenandoahHeapRegion* r = _regions.next();
556 while (r != NULL) {
557 if (!r->is_humongous_continuation() && r->has_live()) {
558 _heap->marked_object_iterate(r, &obj_cl);
559 }
560 r = _regions.next();
561 }
562 }
563 };
564
565 class ShenandoahAdjustRootPointersTask : public AbstractGangTask {
566 private:
567 ShenandoahRootProcessor* _rp;
568
569 public:
570 ShenandoahAdjustRootPointersTask(ShenandoahRootProcessor* rp) :
571 AbstractGangTask("Shenandoah Adjust Root Pointers Task"),
572 _rp(rp) {}
573
574 void work(uint worker_id) {
575 ShenandoahAdjustPointersClosure cl;
576 CLDToOopClosure adjust_cld_closure(&cl, ClassLoaderData::_claim_strong);
577 MarkingCodeBlobClosure adjust_code_closure(&cl,
578 CodeBlobToOopClosure::FixRelocations);
579
580 _rp->update_all_roots<AlwaysTrueClosure>(&cl,
581 &adjust_cld_closure,
582 &adjust_code_closure, NULL, worker_id);
583 }
584 };
585
586 void ShenandoahMarkCompact::phase3_update_references() {
587 GCTraceTime(Info, gc, phases) time("Phase 3: Adjust pointers", _gc_timer);
588 ShenandoahGCPhase adjust_pointer_phase(ShenandoahPhaseTimings::full_gc_adjust_pointers);
589
590 ShenandoahHeap* heap = ShenandoahHeap::heap();
591
592 WorkGang* workers = heap->workers();
593 uint nworkers = workers->active_workers();
594 {
595 #if COMPILER2_OR_JVMCI
596 DerivedPointerTable::clear();
597 #endif
598 ShenandoahRootProcessor rp(heap, nworkers, ShenandoahPhaseTimings::full_gc_roots);
599 ShenandoahAdjustRootPointersTask task(&rp);
600 workers->run_task(&task);
601 #if COMPILER2_OR_JVMCI
602 DerivedPointerTable::update_pointers();
603 #endif
604 }
605
606 ShenandoahAdjustPointersTask adjust_pointers_task;
607 workers->run_task(&adjust_pointers_task);
608
609 adjust_marks();
610 }
611
612 class ShenandoahCompactObjectsClosure : public ObjectClosure {
613 private:
614 ShenandoahHeap* const _heap;
615 uint const _worker_id;
616
617 public:
618 ShenandoahCompactObjectsClosure(uint worker_id) :
619 _heap(ShenandoahHeap::heap()), _worker_id(worker_id) {}
620
621 void do_object(oop p) {
622 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
623 size_t size = (size_t)p->size();
624 if (p->is_forwarded()) {
625 HeapWord* compact_from = (HeapWord*) p;
626 HeapWord* compact_to = (HeapWord*) p->forwardee();
627 Copy::aligned_conjoint_words(compact_from, compact_to, size);
628 oop new_obj = oop(compact_to);
629 new_obj->init_mark();
630 }
631 }
632 };
633
634 class ShenandoahCompactObjectsTask : public AbstractGangTask {
635 private:
636 ShenandoahHeap* const _heap;
637 ShenandoahHeapRegionSet** const _worker_slices;
638
639 public:
640 ShenandoahCompactObjectsTask(ShenandoahHeapRegionSet** worker_slices) :
641 AbstractGangTask("Shenandoah Compact Objects Task"),
642 _heap(ShenandoahHeap::heap()),
643 _worker_slices(worker_slices) {
644 }
645
646 void work(uint worker_id) {
647 ShenandoahHeapRegionSetIterator slice(_worker_slices[worker_id]);
648
649 ShenandoahCompactObjectsClosure cl(worker_id);
650 ShenandoahHeapRegion* r = slice.next();
651 while (r != NULL) {
652 assert(!r->is_humongous(), "must not get humongous regions here");
653 if (r->has_live()) {
654 _heap->marked_object_iterate(r, &cl);
655 }
656 r->set_top(r->new_top());
657 r = slice.next();
658 }
659 }
660 };
661
662 class ShenandoahPostCompactClosure : public ShenandoahHeapRegionClosure {
663 private:
664 ShenandoahHeap* const _heap;
665 size_t _live;
666
667 public:
668 ShenandoahPostCompactClosure() : _heap(ShenandoahHeap::heap()), _live(0) {
669 _heap->free_set()->clear();
670 }
671
672 void heap_region_do(ShenandoahHeapRegion* r) {
673 assert (!r->is_cset(), "cset regions should have been demoted already");
674
675 // Need to reset the complete-top-at-mark-start pointer here because
676 // the complete marking bitmap is no longer valid. This ensures
677 // size-based iteration in marked_object_iterate().
678 // NOTE: See blurb at ShenandoahMCResetCompleteBitmapTask on why we need to skip
679 // pinned regions.
680 if (!r->is_pinned()) {
681 _heap->complete_marking_context()->reset_top_at_mark_start(r);
682 }
683
684 size_t live = r->used();
685
686 // Make empty regions that have been allocated into regular
687 if (r->is_empty() && live > 0) {
688 r->make_regular_bypass();
689 }
690
691 // Reclaim regular regions that became empty
692 if (r->is_regular() && live == 0) {
693 r->make_trash();
694 }
695
696 // Recycle all trash regions
697 if (r->is_trash()) {
698 live = 0;
699 r->recycle();
700 }
701
702 r->set_live_data(live);
703 r->reset_alloc_metadata_to_shared();
704 _live += live;
705 }
706
707 size_t get_live() {
708 return _live;
709 }
710 };
711
712 void ShenandoahMarkCompact::compact_humongous_objects() {
713 // Compact humongous regions, based on their fwdptr objects.
714 //
715 // This code is serial, because doing the in-slice parallel sliding is tricky. In most cases,
716 // humongous regions are already compacted, and do not require further moves, which alleviates
717 // sliding costs. We may consider doing this in parallel in future.
718
719 ShenandoahHeap* heap = ShenandoahHeap::heap();
720
721 for (size_t c = heap->num_regions(); c > 0; c--) {
722 ShenandoahHeapRegion* r = heap->get_region(c - 1);
723 if (r->is_humongous_start()) {
724 oop old_obj = oop(r->bottom());
725 if (!old_obj->is_forwarded()) {
726 // No need to move the object, it stays at the same slot
727 continue;
728 }
729 size_t words_size = old_obj->size();
730 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
731
732 size_t old_start = r->region_number();
733 size_t old_end = old_start + num_regions - 1;
734 size_t new_start = heap->heap_region_index_containing(old_obj->forwardee());
735 size_t new_end = new_start + num_regions - 1;
736 assert(old_start != new_start, "must be real move");
737 assert (r->is_move_allowed(), "should be movable");
738
739 Copy::aligned_conjoint_words(heap->get_region(old_start)->bottom(),
740 heap->get_region(new_start)->bottom(),
741 ShenandoahHeapRegion::region_size_words()*num_regions);
742
743 oop new_obj = oop(heap->get_region(new_start)->bottom());
744 new_obj->init_mark();
745
746 {
747 for (size_t c = old_start; c <= old_end; c++) {
748 ShenandoahHeapRegion* r = heap->get_region(c);
749 r->make_regular_bypass();
750 r->set_top(r->bottom());
751 }
752
753 for (size_t c = new_start; c <= new_end; c++) {
754 ShenandoahHeapRegion* r = heap->get_region(c);
755 if (c == new_start) {
756 r->make_humongous_start_bypass();
757 } else {
758 r->make_humongous_cont_bypass();
759 }
760
761 // Trailing region may be non-full, record the remainder there
762 size_t remainder = words_size & ShenandoahHeapRegion::region_size_words_mask();
763 if ((c == new_end) && (remainder != 0)) {
764 r->set_top(r->bottom() + remainder);
765 } else {
766 r->set_top(r->end());
767 }
768
769 r->reset_alloc_metadata_to_shared();
770 }
771 }
772 }
773 }
774 }
775
776 // This is slightly different to ShHeap::reset_next_mark_bitmap:
777 // we need to remain able to walk pinned regions.
778 // Since pinned region do not move and don't get compacted, we will get holes with
779 // unreachable objects in them (which may have pointers to unloaded Klasses and thus
780 // cannot be iterated over using oop->size(). The only way to safely iterate over those is using
781 // a valid marking bitmap and valid TAMS pointer. This class only resets marking
782 // bitmaps for un-pinned regions, and later we only reset TAMS for unpinned regions.
783 class ShenandoahMCResetCompleteBitmapTask : public AbstractGangTask {
784 private:
785 ShenandoahRegionIterator _regions;
786
787 public:
788 ShenandoahMCResetCompleteBitmapTask() :
789 AbstractGangTask("Parallel Reset Bitmap Task") {
790 }
791
792 void work(uint worker_id) {
793 ShenandoahHeapRegion* region = _regions.next();
794 ShenandoahHeap* heap = ShenandoahHeap::heap();
795 ShenandoahMarkingContext* const ctx = heap->complete_marking_context();
796 while (region != NULL) {
797 if (heap->is_bitmap_slice_committed(region) && !region->is_pinned() && region->has_live()) {
798 ctx->clear_bitmap(region);
799 }
800 region = _regions.next();
801 }
802 }
803 };
804
805 void ShenandoahMarkCompact::phase4_compact_objects(ShenandoahHeapRegionSet** worker_slices) {
806 GCTraceTime(Info, gc, phases) time("Phase 4: Move objects", _gc_timer);
807 ShenandoahGCPhase compaction_phase(ShenandoahPhaseTimings::full_gc_copy_objects);
808
809 ShenandoahHeap* heap = ShenandoahHeap::heap();
810
811 // Compact regular objects first
812 {
813 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_regular);
814 ShenandoahCompactObjectsTask compact_task(worker_slices);
815 heap->workers()->run_task(&compact_task);
816 }
817
818 // Compact humongous objects after regular object moves
819 {
820 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_humong);
821 compact_humongous_objects();
822 }
823
824 restore_marks();
825
826 // Reset complete bitmap. We're about to reset the complete-top-at-mark-start pointer
827 // and must ensure the bitmap is in sync.
828 {
829 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_reset_complete);
830 ShenandoahMCResetCompleteBitmapTask task;
831 heap->workers()->run_task(&task);
832 }
833
834 // Bring regions in proper states after the collection, and set heap properties.
835 {
836 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_rebuild);
837
838 ShenandoahPostCompactClosure post_compact;
839 heap->heap_region_iterate(&post_compact);
840 heap->set_used(post_compact.get_live());
841
842 heap->collection_set()->clear();
843 heap->free_set()->rebuild();
844 }
845
846 heap->clear_cancelled_gc();
847 }
848
849 void ShenandoahMarkCompact::preserve_mark(oop obj) {
850 markOop mark = obj->mark_raw();
851 if (mark->must_be_preserved(obj)) {
852 MutexLocker ml(&_preserved_mark_lock, Mutex::_no_safepoint_check_flag);
853 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
854 "inconsistent preserved oop stacks: oop_stack size: " SIZE_FORMAT ", mark_stack size: " SIZE_FORMAT, _preserved_oop_stack.size(), _preserved_mark_stack.size());
855 _preserved_mark_stack.push(mark);
856 _preserved_oop_stack.push(obj);
857 }
858 }
859
860 void ShenandoahMarkCompact::restore_marks() {
861 MutexLocker ml(&_preserved_mark_lock, Mutex::_no_safepoint_check_flag);
862 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
863 "inconsistent preserved oop stacks: oop_stack size: " SIZE_FORMAT ", mark_stack size: " SIZE_FORMAT, _preserved_oop_stack.size(), _preserved_mark_stack.size());
864 while (!_preserved_oop_stack.is_empty()) {
865 oop obj = _preserved_oop_stack.pop();
866 markOop mark = _preserved_mark_stack.pop();
867 obj->set_mark_raw(mark);
868 }
869 }
870
871 void ShenandoahMarkCompact::adjust_marks() {
872 MutexLocker ml(&_preserved_mark_lock, Mutex::_no_safepoint_check_flag);
873 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
874 "inconsistent preserved oop stacks: oop_stack size: " SIZE_FORMAT ", mark_stack size: " SIZE_FORMAT, _preserved_oop_stack.size(), _preserved_mark_stack.size());
875 StackIterator<oop, mtGC> iter(_preserved_oop_stack);
876 while (!iter.is_empty()) {
877 oop* p = iter.next_addr();
878 oop obj = *p;
879 oop fwd = obj->forwardee();
880 *p = fwd;
881 }
882 }