1 /*
2 * Copyright (c) 2014, 2015, 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 #include "code/codeCache.hpp"
26 #include "gc_implementation/shenandoah/shenandoahGCTraceTime.hpp"
27 #include "gc_implementation/shared/gcTimer.hpp"
28 #include "gc_implementation/shenandoah/brooksPointer.hpp"
29 #include "gc_implementation/shenandoah/shenandoahCollectorPolicy.hpp"
30 #include "gc_implementation/shenandoah/shenandoahConcurrentMark.inline.hpp"
31 #include "gc_implementation/shenandoah/shenandoahCollectionSet.hpp"
32 #include "gc_implementation/shenandoah/shenandoahFreeSet.hpp"
33 #include "gc_implementation/shenandoah/shenandoahPhaseTimings.hpp"
34 #include "gc_implementation/shenandoah/shenandoahMarkCompact.hpp"
35 #include "gc_implementation/shenandoah/shenandoahBarrierSet.hpp"
36 #include "gc_implementation/shenandoah/shenandoahHeapRegionSet.hpp"
37 #include "gc_implementation/shenandoah/shenandoahHeap.hpp"
38 #include "gc_implementation/shenandoah/shenandoahHeap.inline.hpp"
39 #include "gc_implementation/shenandoah/shenandoahMarkingContext.inline.hpp"
40 #include "gc_implementation/shenandoah/shenandoahRootProcessor.hpp"
41 #include "gc_implementation/shenandoah/shenandoahUtils.hpp"
42 #include "gc_implementation/shenandoah/shenandoahVerifier.hpp"
43 #include "gc_implementation/shenandoah/shenandoahWorkerPolicy.hpp"
44 #include "gc_implementation/shenandoah/vm_operations_shenandoah.hpp"
45 #include "oops/oop.inline.hpp"
46 #include "runtime/biasedLocking.hpp"
47 #include "runtime/thread.hpp"
48 #include "utilities/copy.hpp"
49 #include "utilities/growableArray.hpp"
50 #include "utilities/taskqueue.hpp"
51 #include "utilities/workgroup.hpp"
52
53 void ShenandoahMarkCompact::initialize(GCTimer* gc_timer) {
54 _gc_timer = gc_timer;
55 }
56
57 void ShenandoahMarkCompact::do_it(GCCause::Cause gc_cause) {
58 ShenandoahHeap* heap = ShenandoahHeap::heap();
59
60 {
61 if (ShenandoahVerify) {
62 heap->verifier()->verify_before_fullgc();
63 }
64
65 heap->set_full_gc_in_progress(true);
66
67 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
68 assert(Thread::current()->is_VM_thread(), "Do full GC only while world is stopped");
69
70 {
71 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdumps);
72 heap->pre_full_gc_dump(_gc_timer);
73 }
74
75 {
76 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_prepare);
77 // Full GC is supposed to recover from any GC state:
78
79 // 0. Remember if we have forwarded objects
80 bool has_forwarded_objects = heap->has_forwarded_objects();
81
82 // a. Cancel concurrent mark, if in progress
83 if (heap->is_concurrent_mark_in_progress()) {
84 heap->concurrentMark()->cancel();
85 heap->stop_concurrent_marking();
86 }
87 assert(!heap->is_concurrent_mark_in_progress(), "sanity");
88
89 // b1. Cancel evacuation, if in progress
90 if (heap->is_evacuation_in_progress()) {
91 heap->set_evacuation_in_progress(false);
92 }
93 assert(!heap->is_evacuation_in_progress(), "sanity");
94
95 // b2. Cancel update-refs, if in progress
96 if (heap->is_update_refs_in_progress()) {
97 heap->set_update_refs_in_progress(false);
98 }
99 assert(!heap->is_update_refs_in_progress(), "sanity");
100
101 // c. Reset the bitmaps for new marking
102 heap->reset_next_mark_bitmap();
103 assert(heap->next_marking_context()->is_bitmap_clear(), "sanity");
104
105 // d. Abandon reference discovery and clear all discovered references.
106 ReferenceProcessor *rp = heap->ref_processor();
107 rp->disable_discovery();
108 rp->abandon_partial_discovery();
109 rp->verify_no_references_recorded();
110
111 // e. Set back forwarded objects bit back, in case some steps above dropped it.
112 heap->set_has_forwarded_objects(has_forwarded_objects);
113 }
114
115 {
116 heap->make_parsable(true);
117
118 CodeCache::gc_prologue();
119
120 OrderAccess::fence();
121
122 phase1_mark_heap();
123
124 // Once marking is done, which may have fixed up forwarded objects, we can drop it.
125 // Coming out of Full GC, we would not have any forwarded objects.
126 // This also prevents read barrier from kicking in while adjusting pointers in phase3.
127 heap->set_has_forwarded_objects(false);
128
129 heap->set_full_gc_move_in_progress(true);
130
131 // Setup workers for the rest
132 {
133 OrderAccess::fence();
134
135 // Initialize worker slices
136 ShenandoahHeapRegionSet** worker_slices = NEW_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, heap->max_workers(), mtGC);
137 for (uint i = 0; i < heap->max_workers(); i++) {
138 worker_slices[i] = new ShenandoahHeapRegionSet();
139 }
140
141 phase2_calculate_target_addresses(worker_slices);
142
143 OrderAccess::fence();
144
145 phase3_update_references();
146
147 phase4_compact_objects(worker_slices);
148
149 // Free worker slices
150 for (uint i = 0; i < heap->max_workers(); i++) {
151 delete worker_slices[i];
152 }
153 FREE_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, worker_slices, mtGC);
154
155 CodeCache::gc_epilogue();
156 JvmtiExport::gc_epilogue();
157 }
158
159 heap->set_full_gc_move_in_progress(false);
160 heap->set_full_gc_in_progress(false);
161
162 if (ShenandoahVerify) {
163 heap->verifier()->verify_after_fullgc();
164 }
165 }
166
167 {
168 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdumps);
169 heap->post_full_gc_dump(_gc_timer);
170 }
171
172 if (UseTLAB) {
173 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_resize_tlabs);
174 heap->resize_all_tlabs();
175 }
176 }
177 }
178
179 class ShenandoahPrepareForMarkClosure: public ShenandoahHeapRegionClosure {
180 private:
181 ShenandoahMarkingContext* const _ctx;
182
183 public:
184 ShenandoahPrepareForMarkClosure() : _ctx(ShenandoahHeap::heap()->next_marking_context()) {}
185
186 bool heap_region_do(ShenandoahHeapRegion *r) {
187 _ctx->set_top_at_mark_start(r->region_number(), r->top());
188 r->clear_live_data();
189 r->set_concurrent_iteration_safe_limit(r->top());
190 return false;
191 }
192 };
193
194 void ShenandoahMarkCompact::phase1_mark_heap() {
195 ShenandoahHeap* heap = ShenandoahHeap::heap();
196 GCTraceTime time("Phase 1: Mark live objects", ShenandoahLogDebug, _gc_timer, heap->tracer()->gc_id());
197 ShenandoahGCPhase mark_phase(ShenandoahPhaseTimings::full_gc_mark);
198
199 {
200 ShenandoahHeapLocker lock(heap->lock());
201 ShenandoahPrepareForMarkClosure cl;
202 heap->heap_region_iterate(&cl, false, false);
203 }
204
205 ShenandoahConcurrentMark* cm = heap->concurrentMark();
206
207 // Do not trust heuristics, because this can be our last resort collection.
208 // Only ignore processing references and class unloading if explicitly disabled.
209 heap->set_process_references(ShenandoahRefProcFrequency != 0);
210 heap->set_unload_classes(ClassUnloading);
211
212 ReferenceProcessor* rp = heap->ref_processor();
213 // enable ("weak") refs discovery
214 rp->enable_discovery(true /*verify_no_refs*/, true);
215 rp->setup_policy(true); // forcefully purge all soft references
216 rp->set_active_mt_degree(heap->workers()->active_workers());
217
218 cm->update_roots(ShenandoahPhaseTimings::full_gc_roots);
219 cm->mark_roots(ShenandoahPhaseTimings::full_gc_roots);
220 cm->shared_finish_mark_from_roots(/* full_gc = */ true);
221
222 heap->swap_mark_contexts();
223 }
224
225 class ShenandoahPrepareForCompactionObjectClosure : public ObjectClosure {
226 private:
227 ShenandoahHeap* const _heap;
228 GrowableArray<ShenandoahHeapRegion*>& _empty_regions;
229 int _empty_regions_pos;
230 ShenandoahHeapRegion* _to_region;
231 ShenandoahHeapRegion* _from_region;
232 HeapWord* _compact_point;
233
234 public:
235 ShenandoahPrepareForCompactionObjectClosure(GrowableArray<ShenandoahHeapRegion*>& empty_regions, ShenandoahHeapRegion* to_region) :
236 _heap(ShenandoahHeap::heap()),
237 _empty_regions(empty_regions),
238 _empty_regions_pos(0),
239 _to_region(to_region),
240 _from_region(NULL),
241 _compact_point(to_region->bottom()) {}
242
243 void set_from_region(ShenandoahHeapRegion* from_region) {
244 _from_region = from_region;
245 }
246
247 void finish_region() {
248 assert(_to_region != NULL, "should not happen");
249 _to_region->set_new_top(_compact_point);
250 }
251
252 bool is_compact_same_region() {
253 return _from_region == _to_region;
254 }
255
256 int empty_regions_pos() {
257 return _empty_regions_pos;
258 }
259
260 void do_object(oop p) {
261 assert(_from_region != NULL, "must set before work");
262 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
263 assert(!_heap->complete_marking_context()->allocated_after_mark_start((HeapWord*) p), "must be truly marked");
264
265 size_t obj_size = p->size() + BrooksPointer::word_size();
266 if (_compact_point + obj_size > _to_region->end()) {
267 finish_region();
268
269 // Object doesn't fit. Pick next empty region and start compacting there.
270 ShenandoahHeapRegion* new_to_region;
271 if (_empty_regions_pos < _empty_regions.length()) {
272 new_to_region = _empty_regions.at(_empty_regions_pos);
273 _empty_regions_pos++;
274 } else {
275 // Out of empty region? Compact within the same region.
276 new_to_region = _from_region;
277 }
278
279 assert(new_to_region != _to_region, "must not reuse same to-region");
280 assert(new_to_region != NULL, "must not be NULL");
281 _to_region = new_to_region;
282 _compact_point = _to_region->bottom();
283 }
284
285 // Object fits into current region, record new location:
286 assert(_compact_point + obj_size <= _to_region->end(), "must fit");
287 shenandoah_assert_not_forwarded(NULL, p);
288 BrooksPointer::set_raw(p, _compact_point + BrooksPointer::word_size());
289 _compact_point += obj_size;
290 }
291 };
292
293 class ShenandoahPrepareForCompactionTask : public AbstractGangTask {
294 private:
295 ShenandoahHeap* const _heap;
296 ShenandoahHeapRegionSet** const _worker_slices;
297 ShenandoahRegionIterator _heap_regions;
298
299 ShenandoahHeapRegion* next_from_region(ShenandoahHeapRegionSet* slice) {
300 ShenandoahHeapRegion* from_region = _heap_regions.next();
301
302 while (from_region != NULL && (!from_region->is_move_allowed() || from_region->is_humongous())) {
303 from_region = _heap_regions.next();
304 }
305
306 if (from_region != NULL) {
307 assert(slice != NULL, "sanity");
308 assert(!from_region->is_humongous(), "this path cannot handle humongous regions");
309 assert(from_region->is_move_allowed(), "only regions that can be moved in mark-compact");
310 slice->add_region(from_region);
311 }
312
313 return from_region;
314 }
315
316 public:
317 ShenandoahPrepareForCompactionTask(ShenandoahHeapRegionSet** worker_slices) :
318 AbstractGangTask("Shenandoah Prepare For Compaction Task"),
319 _heap(ShenandoahHeap::heap()), _worker_slices(worker_slices) {
320 }
321
322 void work(uint worker_id) {
323 ShenandoahHeapRegionSet* slice = _worker_slices[worker_id];
324 ShenandoahHeapRegion* from_region = next_from_region(slice);
325
326 // No work?
327 if (from_region == NULL) {
328 return;
329 }
330
331 // Sliding compaction. Walk all regions in the slice, and compact them.
332 // Remember empty regions and reuse them as needed.
333 ResourceMark rm;
334 GrowableArray<ShenandoahHeapRegion*> empty_regions((int)_heap->num_regions());
335 ShenandoahPrepareForCompactionObjectClosure cl(empty_regions, from_region);
336 while (from_region != NULL) {
337 cl.set_from_region(from_region);
338 if (from_region->has_live()) {
339 _heap->marked_object_iterate(from_region, &cl);
340 }
341
342 // Compacted the region to somewhere else? From-region is empty then.
343 if (!cl.is_compact_same_region()) {
344 empty_regions.append(from_region);
345 }
346 from_region = next_from_region(slice);
347 }
348 cl.finish_region();
349
350 // Mark all remaining regions as empty
351 for (int pos = cl.empty_regions_pos(); pos < empty_regions.length(); ++pos) {
352 ShenandoahHeapRegion* r = empty_regions.at(pos);
353 r->set_new_top(r->bottom());
354 }
355 }
356 };
357
358 void ShenandoahMarkCompact::calculate_target_humongous_objects() {
359 ShenandoahHeap* heap = ShenandoahHeap::heap();
360
361 // Compute the new addresses for humongous objects. We need to do this after addresses
362 // for regular objects are calculated, and we know what regions in heap suffix are
363 // available for humongous moves.
364 //
365 // Scan the heap backwards, because we are compacting humongous regions towards the end.
366 // Maintain the contiguous compaction window in [to_begin; to_end), so that we can slide
367 // humongous start there.
368 //
369 // The complication is potential non-movable regions during the scan. If such region is
370 // detected, then sliding restarts towards that non-movable region.
371
372 size_t to_begin = heap->num_regions();
373 size_t to_end = heap->num_regions();
374
375 for (size_t c = heap->num_regions() - 1; c > 0; c--) {
376 ShenandoahHeapRegion *r = heap->get_region(c);
377 if (r->is_humongous_continuation() || (r->new_top() == r->bottom())) {
378 // To-region candidate: record this, and continue scan
379 to_begin = r->region_number();
380 continue;
381 }
382
383 if (r->is_humongous_start() && r->is_move_allowed()) {
384 // From-region candidate: movable humongous region
385 oop old_obj = oop(r->bottom() + BrooksPointer::word_size());
386 size_t words_size = old_obj->size() + BrooksPointer::word_size();
387 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
388
389 size_t start = to_end - num_regions;
390
391 if (start >= to_begin && start != r->region_number()) {
392 // Fits into current window, and the move is non-trivial. Record the move then, and continue scan.
393 BrooksPointer::set_raw(old_obj, heap->get_region(start)->bottom() + BrooksPointer::word_size());
394 to_end = start;
395 continue;
396 }
397 }
398
399 // Failed to fit. Scan starting from current region.
400 to_begin = r->region_number();
401 to_end = r->region_number();
402 }
403 }
404
405 class ShenandoahEnsureHeapActiveClosure: public ShenandoahHeapRegionClosure {
406 private:
407 ShenandoahHeap* const _heap;
408
409 public:
410 ShenandoahEnsureHeapActiveClosure() : _heap(ShenandoahHeap::heap()) {}
411 bool heap_region_do(ShenandoahHeapRegion* r) {
412 if (r->is_trash()) {
413 r->recycle();
414 }
415 if (r->is_cset()) {
416 r->make_regular_bypass();
417 }
418 if (r->is_empty_uncommitted()) {
419 r->make_committed_bypass();
420 }
421 assert (r->is_committed(), err_msg("only committed regions in heap now, see region " SIZE_FORMAT, r->region_number()));
422
423 // Record current region occupancy: this communicates empty regions are free
424 // to the rest of Full GC code.
425 r->set_new_top(r->top());
426 return false;
427 }
428 };
429
430 class ShenandoahTrashImmediateGarbageClosure: public ShenandoahHeapRegionClosure {
431 private:
432 ShenandoahHeap* const _heap;
433 ShenandoahMarkingContext* const _ctx;
434
435 public:
436 ShenandoahTrashImmediateGarbageClosure() :
437 _heap(ShenandoahHeap::heap()),
438 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
439
440 bool heap_region_do(ShenandoahHeapRegion* r) {
441 if (r->is_humongous_start()) {
442 oop humongous_obj = oop(r->bottom() + BrooksPointer::word_size());
443 if (!_ctx->is_marked(humongous_obj)) {
444 assert(!r->has_live(),
445 err_msg("Region " SIZE_FORMAT " is not marked, should not have live", r->region_number()));
446 _heap->trash_humongous_region_at(r);
447 } else {
448 assert(r->has_live(),
449 err_msg("Region " SIZE_FORMAT " should have live", r->region_number()));
450 }
451 } else if (r->is_humongous_continuation()) {
452 // If we hit continuation, the non-live humongous starts should have been trashed already
453 assert(r->humongous_start_region()->has_live(),
454 err_msg("Region " SIZE_FORMAT " should have live", r->region_number()));
455 } else if (r->is_regular()) {
456 if (!r->has_live()) {
457 assert(_ctx->is_bitmap_clear_range(r->bottom(), r->end()),
458 err_msg("Region " SIZE_FORMAT " should not have marks in bitmap", r->region_number()));
459 r->make_trash();
460 }
461 }
462 return false;
463 }
464 };
465
466 void ShenandoahMarkCompact::phase2_calculate_target_addresses(ShenandoahHeapRegionSet** worker_slices) {
467 ShenandoahHeap* heap = ShenandoahHeap::heap();
468 GCTraceTime time("Phase 2: Compute new object addresses", ShenandoahLogDebug, _gc_timer, heap->tracer()->gc_id());
469 ShenandoahGCPhase calculate_address_phase(ShenandoahPhaseTimings::full_gc_calculate_addresses);
470
471 {
472 ShenandoahHeapLocker lock(heap->lock());
473
474 // Trash the immediately collectible regions before computing addresses
475 ShenandoahTrashImmediateGarbageClosure tigcl;
476 heap->heap_region_iterate(&tigcl, false, false);
477
478 // Make sure regions are in good state: committed, active, clean.
479 // This is needed because we are potentially sliding the data through them.
480 ShenandoahEnsureHeapActiveClosure ecl;
481 heap->heap_region_iterate(&ecl, false, false);
482 }
483
484 // Compute the new addresses for regular objects
485 {
486 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_regular);
487 ShenandoahPrepareForCompactionTask prepare_task(worker_slices);
488 heap->workers()->run_task(&prepare_task);
489 }
490
491 // Compute the new addresses for humongous objects
492 {
493 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_humong);
494 calculate_target_humongous_objects();
495 }
496 }
497
498 class ShenandoahAdjustPointersClosure : public MetadataAwareOopClosure {
499 private:
500 ShenandoahHeap* const _heap;
501 ShenandoahMarkingContext* const _ctx;
502
503 template <class T>
504 inline void do_oop_work(T* p) {
505 T o = oopDesc::load_heap_oop(p);
506 if (! oopDesc::is_null(o)) {
507 oop obj = oopDesc::decode_heap_oop_not_null(o);
508 assert(_ctx->is_marked(obj), "must be marked");
509 oop forw = oop(BrooksPointer::get_raw(obj));
510 oopDesc::encode_store_heap_oop(p, forw);
511 }
512 }
513
514 public:
515 ShenandoahAdjustPointersClosure() :
516 _heap(ShenandoahHeap::heap()),
517 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
518
519 void do_oop(oop* p) { do_oop_work(p); }
520 void do_oop(narrowOop* p) { do_oop_work(p); }
521 };
522
523 class ShenandoahAdjustPointersObjectClosure : public ObjectClosure {
524 private:
525 ShenandoahHeap* const _heap;
526 ShenandoahAdjustPointersClosure _cl;
527
528 public:
529 ShenandoahAdjustPointersObjectClosure() :
530 _heap(ShenandoahHeap::heap()) {
531 }
532 void do_object(oop p) {
533 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
534 p->oop_iterate(&_cl);
535 }
536 };
537
538 class ShenandoahAdjustPointersTask : public AbstractGangTask {
539 private:
540 ShenandoahHeap* const _heap;
541 ShenandoahRegionIterator _regions;
542
543 public:
544 ShenandoahAdjustPointersTask() :
545 AbstractGangTask("Shenandoah Adjust Pointers Task"),
546 _heap(ShenandoahHeap::heap()) {
547 }
548
549 void work(uint worker_id) {
550 ShenandoahAdjustPointersObjectClosure obj_cl;
551 ShenandoahHeapRegion* r = _regions.next();
552 while (r != NULL) {
553 if (!r->is_humongous_continuation() && r->has_live()) {
554 _heap->marked_object_iterate(r, &obj_cl);
555 }
556 r = _regions.next();
557 }
558 }
559 };
560
561 class ShenandoahAdjustRootPointersTask : public AbstractGangTask {
562 private:
563 ShenandoahRootProcessor* _rp;
564
565 public:
566 ShenandoahAdjustRootPointersTask(ShenandoahRootProcessor* rp) :
567 AbstractGangTask("Shenandoah Adjust Root Pointers Task"),
568 _rp(rp) {}
569
570 void work(uint worker_id) {
571 ShenandoahAdjustPointersClosure cl;
572 CLDToOopClosure adjust_cld_closure(&cl, true);
573 MarkingCodeBlobClosure adjust_code_closure(&cl,
574 CodeBlobToOopClosure::FixRelocations);
575
576 _rp->process_all_roots(&cl, &cl,
577 &adjust_cld_closure,
578 &adjust_code_closure, NULL, worker_id);
579 }
580 };
581
582 void ShenandoahMarkCompact::phase3_update_references() {
583 ShenandoahHeap* heap = ShenandoahHeap::heap();
584 GCTraceTime time("Phase 3: Adjust pointers", ShenandoahLogDebug, _gc_timer, heap->tracer()->gc_id());
585 ShenandoahGCPhase adjust_pointer_phase(ShenandoahPhaseTimings::full_gc_adjust_pointers);
586
587 WorkGang* workers = heap->workers();
588 uint nworkers = workers->active_workers();
589 {
590 COMPILER2_PRESENT(DerivedPointerTable::clear());
591 ShenandoahRootProcessor rp(heap, nworkers, ShenandoahPhaseTimings::full_gc_roots);
592 ShenandoahAdjustRootPointersTask task(&rp);
593 workers->run_task(&task);
594 COMPILER2_PRESENT(DerivedPointerTable::update_pointers());
595 }
596
597 ShenandoahAdjustPointersTask adjust_pointers_task;
598 workers->run_task(&adjust_pointers_task);
599 }
600
601 class ShenandoahCompactObjectsClosure : public ObjectClosure {
602 private:
603 ShenandoahHeap* const _heap;
604
605 public:
606 ShenandoahCompactObjectsClosure() : _heap(ShenandoahHeap::heap()) {}
607
608 void do_object(oop p) {
609 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
610 size_t size = (size_t)p->size();
611 HeapWord* compact_to = BrooksPointer::get_raw(p);
612 HeapWord* compact_from = (HeapWord*) p;
613 if (compact_from != compact_to) {
614 Copy::aligned_conjoint_words(compact_from, compact_to, size);
615 }
616 oop new_obj = oop(compact_to);
617 BrooksPointer::initialize(new_obj);
618 }
619 };
620
621 class ShenandoahCompactObjectsTask : public AbstractGangTask {
622 private:
623 ShenandoahHeap* const _heap;
624 ShenandoahHeapRegionSet** const _worker_slices;
625
626 public:
627 ShenandoahCompactObjectsTask(ShenandoahHeapRegionSet** worker_slices) :
628 AbstractGangTask("Shenandoah Compact Objects Task"),
629 _heap(ShenandoahHeap::heap()),
630 _worker_slices(worker_slices) {
631 }
632
633 void work(uint worker_id) {
634 ShenandoahHeapRegionSetIterator slice(_worker_slices[worker_id]);
635
636 ShenandoahCompactObjectsClosure cl;
637 ShenandoahHeapRegion* r = slice.next();
638 while (r != NULL) {
639 assert(!r->is_humongous(), "must not get humongous regions here");
640 if (r->has_live()) {
641 _heap->marked_object_iterate(r, &cl);
642 }
643 r->set_top(r->new_top());
644 r = slice.next();
645 }
646 }
647 };
648
649 class ShenandoahPostCompactClosure : public ShenandoahHeapRegionClosure {
650 private:
651 ShenandoahHeap* const _heap;
652 size_t _live;
653
654 public:
655 ShenandoahPostCompactClosure() : _heap(ShenandoahHeap::heap()), _live(0) {
656 _heap->free_set()->clear();
657 }
658
659 bool heap_region_do(ShenandoahHeapRegion* r) {
660 assert (!r->is_cset(), "cset regions should have been demoted already");
661
662 // Need to reset the complete-top-at-mark-start pointer here because
663 // the complete marking bitmap is no longer valid. This ensures
664 // size-based iteration in marked_object_iterate().
665 // NOTE: See blurb at ShenandoahMCResetCompleteBitmapTask on why we need to skip
666 // pinned regions.
667 if (!r->is_pinned()) {
668 _heap->complete_marking_context()->set_top_at_mark_start(r->region_number(), r->bottom());
669 }
670
671 size_t live = r->used();
672
673 // Make empty regions that have been allocated into regular
674 if (r->is_empty() && live > 0) {
675 r->make_regular_bypass();
676 }
677
678 // Reclaim regular regions that became empty
679 if (r->is_regular() && live == 0) {
680 r->make_trash();
681 }
682
683 // Recycle all trash regions
684 if (r->is_trash()) {
685 live = 0;
686 r->recycle();
687 }
688
689 r->set_live_data(live);
690 r->reset_alloc_metadata_to_shared();
691 _live += live;
692 return false;
693 }
694
695 size_t get_live() {
696 return _live;
697 }
698 };
699
700 void ShenandoahMarkCompact::compact_humongous_objects() {
701 // Compact humongous regions, based on their fwdptr objects.
702 //
703 // This code is serial, because doing the in-slice parallel sliding is tricky. In most cases,
704 // humongous regions are already compacted, and do not require further moves, which alleviates
705 // sliding costs. We may consider doing this in parallel in future.
706
707 ShenandoahHeap* heap = ShenandoahHeap::heap();
708
709 for (size_t c = heap->num_regions() - 1; c > 0; c--) {
710 ShenandoahHeapRegion* r = heap->get_region(c);
711 if (r->is_humongous_start()) {
712 oop old_obj = oop(r->bottom() + BrooksPointer::word_size());
713 size_t words_size = old_obj->size() + BrooksPointer::word_size();
714 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
715
716 size_t old_start = r->region_number();
717 size_t old_end = old_start + num_regions - 1;
718 size_t new_start = heap->heap_region_index_containing(BrooksPointer::get_raw(old_obj));
719 size_t new_end = new_start + num_regions - 1;
720
721 if (old_start == new_start) {
722 // No need to move the object, it stays at the same slot
723 continue;
724 }
725
726 assert (r->is_move_allowed(), "should be movable");
727
728 Copy::aligned_conjoint_words(heap->get_region(old_start)->bottom(),
729 heap->get_region(new_start)->bottom(),
730 ShenandoahHeapRegion::region_size_words()*num_regions);
731
732 oop new_obj = oop(heap->get_region(new_start)->bottom() + BrooksPointer::word_size());
733 BrooksPointer::initialize(new_obj);
734
735 {
736 ShenandoahHeapLocker lock(heap->lock());
737
738 for (size_t c = old_start; c <= old_end; c++) {
739 ShenandoahHeapRegion* r = heap->get_region(c);
740 r->make_regular_bypass();
741 r->set_top(r->bottom());
742 }
743
744 for (size_t c = new_start; c <= new_end; c++) {
745 ShenandoahHeapRegion* r = heap->get_region(c);
746 if (c == new_start) {
747 r->make_humongous_start_bypass();
748 } else {
749 r->make_humongous_cont_bypass();
750 }
751
752 // Trailing region may be non-full, record the remainder there
753 size_t remainder = words_size & ShenandoahHeapRegion::region_size_words_mask();
754 if ((c == new_end) && (remainder != 0)) {
755 r->set_top(r->bottom() + remainder);
756 } else {
757 r->set_top(r->end());
758 }
759
760 r->reset_alloc_metadata_to_shared();
761 }
762 }
763 }
764 }
765 }
766
767
768 // This is slightly different to ShHeap::reset_next_mark_bitmap:
769 // we need to remain able to walk pinned regions.
770 // Since pinned region do not move and don't get compacted, we will get holes with
771 // unreachable objects in them (which may have pointers to unloaded Klasses and thus
772 // cannot be iterated over using oop->size(). The only way to safely iterate over those is using
773 // a valid marking bitmap and valid TAMS pointer. This class only resets marking
774 // bitmaps for un-pinned regions, and later we only reset TAMS for unpinned regions.
775 class ShenandoahMCResetCompleteBitmapTask : public AbstractGangTask {
776 private:
777 ShenandoahRegionIterator _regions;
778
779 public:
780 ShenandoahMCResetCompleteBitmapTask() :
781 AbstractGangTask("Parallel Reset Bitmap Task") {
782 }
783
784 void work(uint worker_id) {
785 ShenandoahHeapRegion* region = _regions.next();
786 ShenandoahHeap* heap = ShenandoahHeap::heap();
787 ShenandoahMarkingContext* const ctx = heap->complete_marking_context();
788 while (region != NULL) {
789 if (heap->is_bitmap_slice_committed(region) && !region->is_pinned()) {
790 HeapWord* bottom = region->bottom();
791 HeapWord* top = ctx->top_at_mark_start(region->region_number());
792 if (top > bottom && region->has_live()) {
793 ctx->clear_bitmap(bottom, top);
794 }
795 assert(ctx->is_bitmap_clear_range(bottom, region->end()), "must be clear");
796 }
797 region = _regions.next();
798 }
799 }
800 };
801
802 void ShenandoahMarkCompact::phase4_compact_objects(ShenandoahHeapRegionSet** worker_slices) {
803 ShenandoahHeap* heap = ShenandoahHeap::heap();
804 GCTraceTime time("Phase 4: Move objects", ShenandoahLogDebug, _gc_timer, heap->tracer()->gc_id());
805 ShenandoahGCPhase compaction_phase(ShenandoahPhaseTimings::full_gc_copy_objects);
806
807 // Compact regular objects first
808 {
809 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_regular);
810 ShenandoahCompactObjectsTask compact_task(worker_slices);
811 heap->workers()->run_task(&compact_task);
812 }
813
814 // Compact humongous objects after regular object moves
815 {
816 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_humong);
817 compact_humongous_objects();
818 }
819
820 // Reset complete bitmap. We're about to reset the complete-top-at-mark-start pointer
821 // and must ensure the bitmap is in sync.
822 {
823 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_reset_complete);
824 ShenandoahMCResetCompleteBitmapTask task;
825 heap->workers()->run_task(&task);
826 }
827
828 // Bring regions in proper states after the collection, and set heap properties.
829 {
830 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_rebuild);
831
832 ShenandoahHeapLocker lock(heap->lock());
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
843 // Also clear the next bitmap in preparation for next marking.
844 {
845 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_reset_next);
846 heap->reset_next_mark_bitmap();
847 }
848 }