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