1 /*
2 * Copyright (c) 2014, 2020, Red Hat, Inc. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26
27 #include "code/codeCache.hpp"
28 #include "gc/shared/gcTraceTime.inline.hpp"
29 #include "gc/shared/preservedMarks.inline.hpp"
30 #include "gc/shenandoah/shenandoahForwarding.inline.hpp"
31 #include "gc/shenandoah/shenandoahConcurrentMark.inline.hpp"
32 #include "gc/shenandoah/shenandoahConcurrentRoots.hpp"
33 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
34 #include "gc/shenandoah/shenandoahFreeSet.hpp"
35 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
36 #include "gc/shenandoah/shenandoahMarkCompact.hpp"
37 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp"
38 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
39 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
40 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
41 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
42 #include "gc/shenandoah/shenandoahTaskqueue.inline.hpp"
43 #include "gc/shenandoah/shenandoahUtils.hpp"
44 #include "gc/shenandoah/shenandoahVerifier.hpp"
45 #include "gc/shenandoah/shenandoahVMOperations.hpp"
46 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
47 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
48 #include "memory/metaspace.hpp"
49 #include "memory/universe.hpp"
50 #include "oops/compressedOops.inline.hpp"
51 #include "oops/oop.inline.hpp"
52 #include "runtime/biasedLocking.hpp"
53 #include "runtime/orderAccess.hpp"
54 #include "runtime/thread.hpp"
55 #include "utilities/copy.hpp"
56 #include "utilities/growableArray.hpp"
57 #include "gc/shared/workgroup.hpp"
58
59 ShenandoahMarkCompact::ShenandoahMarkCompact() :
60 _gc_timer(NULL),
61 _preserved_marks(new PreservedMarksSet(true)) {}
62
63 void ShenandoahMarkCompact::initialize(GCTimer* gc_timer) {
64 _gc_timer = gc_timer;
65 }
66
67 void ShenandoahMarkCompact::do_it(GCCause::Cause gc_cause) {
68 ShenandoahHeap* heap = ShenandoahHeap::heap();
69
70 if (ShenandoahVerify) {
71 heap->verifier()->verify_before_fullgc();
72 }
73
74 if (VerifyBeforeGC) {
75 Universe::verify();
76 }
77
78 // Degenerated GC may carry concurrent root flags when upgrading to
79 // full GC. We need to reset it before mutators resume.
80 if (ShenandoahConcurrentRoots::can_do_concurrent_class_unloading()) {
81 heap->set_concurrent_strong_root_in_progress(false);
82 heap->set_concurrent_weak_root_in_progress(false);
83 }
84
85 heap->set_full_gc_in_progress(true);
86
87 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
88 assert(Thread::current()->is_VM_thread(), "Do full GC only while world is stopped");
89
90 {
91 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdump_pre);
92 heap->pre_full_gc_dump(_gc_timer);
93 }
94
95 {
96 ShenandoahGCPhase prepare_phase(ShenandoahPhaseTimings::full_gc_prepare);
97 // Full GC is supposed to recover from any GC state:
98
99 // a0. Remember if we have forwarded objects
100 bool has_forwarded_objects = heap->has_forwarded_objects();
101
102 // a1. Cancel evacuation, if in progress
103 if (heap->is_evacuation_in_progress()) {
104 heap->set_evacuation_in_progress(false);
105 }
106 assert(!heap->is_evacuation_in_progress(), "sanity");
107
108 // a2. Cancel update-refs, if in progress
109 if (heap->is_update_refs_in_progress()) {
110 heap->set_update_refs_in_progress(false);
111 }
112 assert(!heap->is_update_refs_in_progress(), "sanity");
113
114 // b. Cancel concurrent mark, if in progress
115 if (heap->is_concurrent_mark_in_progress()) {
116 heap->concurrent_mark()->cancel();
117 heap->set_concurrent_mark_in_progress(false);
118 }
119 assert(!heap->is_concurrent_mark_in_progress(), "sanity");
120
121 // c. Reset the bitmaps for new marking
122 heap->reset_mark_bitmap();
123 assert(heap->marking_context()->is_bitmap_clear(), "sanity");
124 assert(!heap->marking_context()->is_complete(), "sanity");
125
126 // d. Abandon reference discovery and clear all discovered references.
127 ReferenceProcessor* rp = heap->ref_processor();
128 rp->disable_discovery();
129 rp->abandon_partial_discovery();
130 rp->verify_no_references_recorded();
131
132 // e. Set back forwarded objects bit back, in case some steps above dropped it.
133 heap->set_has_forwarded_objects(has_forwarded_objects);
134
135 // f. Sync pinned region status from the CP marks
136 heap->sync_pinned_region_status();
137
138 // The rest of prologue:
139 BiasedLocking::preserve_marks();
140 _preserved_marks->init(heap->workers()->active_workers());
141 }
142
143 heap->make_parsable(true);
144
145 OrderAccess::fence();
146
147 phase1_mark_heap();
148
149 // Once marking is done, which may have fixed up forwarded objects, we can drop it.
150 // Coming out of Full GC, we would not have any forwarded objects.
151 // This also prevents resolves with fwdptr from kicking in while adjusting pointers in phase3.
152 heap->set_has_forwarded_objects(false);
153
154 heap->set_full_gc_move_in_progress(true);
155
156 // Setup workers for the rest
157 OrderAccess::fence();
158
159 // Initialize worker slices
160 ShenandoahHeapRegionSet** worker_slices = NEW_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, heap->max_workers(), mtGC);
161 for (uint i = 0; i < heap->max_workers(); i++) {
162 worker_slices[i] = new ShenandoahHeapRegionSet();
163 }
164
165 {
166 // The rest of code performs region moves, where region status is undefined
167 // until all phases run together.
168 ShenandoahHeapLocker lock(heap->lock());
169
170 phase2_calculate_target_addresses(worker_slices);
171
172 OrderAccess::fence();
173
174 phase3_update_references();
175
176 phase4_compact_objects(worker_slices);
177 }
178
179 {
180 // Epilogue
181 _preserved_marks->restore(heap->workers());
182 BiasedLocking::restore_marks();
183 _preserved_marks->reclaim();
184 }
185
186 // Resize metaspace
187 MetaspaceGC::compute_new_size();
188
189 // Free worker slices
190 for (uint i = 0; i < heap->max_workers(); i++) {
191 delete worker_slices[i];
192 }
193 FREE_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, worker_slices);
194
195 heap->set_full_gc_move_in_progress(false);
196 heap->set_full_gc_in_progress(false);
197
198 if (ShenandoahVerify) {
199 heap->verifier()->verify_after_fullgc();
200 }
201
202 if (VerifyAfterGC) {
203 Universe::verify();
204 }
205
206 {
207 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdump_post);
208 heap->post_full_gc_dump(_gc_timer);
209 }
210 }
211
212 class ShenandoahPrepareForMarkClosure: public ShenandoahHeapRegionClosure {
213 private:
214 ShenandoahMarkingContext* const _ctx;
215
216 public:
217 ShenandoahPrepareForMarkClosure() : _ctx(ShenandoahHeap::heap()->marking_context()) {}
218
219 void heap_region_do(ShenandoahHeapRegion *r) {
220 _ctx->capture_top_at_mark_start(r);
221 r->clear_live_data();
222 }
223 };
224
225 void ShenandoahMarkCompact::phase1_mark_heap() {
226 GCTraceTime(Info, gc, phases) time("Phase 1: Mark live objects", _gc_timer);
227 ShenandoahGCPhase mark_phase(ShenandoahPhaseTimings::full_gc_mark);
228
229 ShenandoahHeap* heap = ShenandoahHeap::heap();
230
231 ShenandoahPrepareForMarkClosure cl;
232 heap->heap_region_iterate(&cl);
233
234 ShenandoahConcurrentMark* cm = heap->concurrent_mark();
235
236 heap->set_process_references(heap->heuristics()->can_process_references());
237 heap->set_unload_classes(heap->heuristics()->can_unload_classes());
238
239 ReferenceProcessor* rp = heap->ref_processor();
240 // enable ("weak") refs discovery
241 rp->enable_discovery(true /*verify_no_refs*/);
242 rp->setup_policy(true); // forcefully purge all soft references
243 rp->set_active_mt_degree(heap->workers()->active_workers());
244
245 cm->update_roots(ShenandoahPhaseTimings::full_gc_update_roots);
246 cm->mark_roots(ShenandoahPhaseTimings::full_gc_scan_roots);
247 cm->finish_mark_from_roots(/* full_gc = */ true);
248 heap->mark_complete_marking_context();
249 heap->parallel_cleaning(true /* full_gc */);
250 }
251
252 class ShenandoahPrepareForCompactionObjectClosure : public ObjectClosure {
253 private:
254 PreservedMarks* const _preserved_marks;
255 ShenandoahHeap* const _heap;
256 GrowableArray<ShenandoahHeapRegion*>& _empty_regions;
257 int _empty_regions_pos;
258 ShenandoahHeapRegion* _to_region;
259 ShenandoahHeapRegion* _from_region;
260 HeapWord* _compact_point;
261
262 public:
263 ShenandoahPrepareForCompactionObjectClosure(PreservedMarks* preserved_marks,
264 GrowableArray<ShenandoahHeapRegion*>& empty_regions,
265 ShenandoahHeapRegion* to_region) :
266 _preserved_marks(preserved_marks),
267 _heap(ShenandoahHeap::heap()),
268 _empty_regions(empty_regions),
269 _empty_regions_pos(0),
270 _to_region(to_region),
271 _from_region(NULL),
272 _compact_point(to_region->bottom()) {}
273
274 void set_from_region(ShenandoahHeapRegion* from_region) {
275 _from_region = from_region;
276 }
277
278 void finish_region() {
279 assert(_to_region != NULL, "should not happen");
280 _to_region->set_new_top(_compact_point);
281 }
282
283 bool is_compact_same_region() {
284 return _from_region == _to_region;
285 }
286
287 int empty_regions_pos() {
288 return _empty_regions_pos;
289 }
290
291 void do_object(oop p) {
292 assert(_from_region != NULL, "must set before work");
293 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
294 assert(!_heap->complete_marking_context()->allocated_after_mark_start(p), "must be truly marked");
295
296 size_t obj_size = p->size();
297 if (_compact_point + obj_size > _to_region->end()) {
298 finish_region();
299
300 // Object doesn't fit. Pick next empty region and start compacting there.
301 ShenandoahHeapRegion* new_to_region;
302 if (_empty_regions_pos < _empty_regions.length()) {
303 new_to_region = _empty_regions.at(_empty_regions_pos);
304 _empty_regions_pos++;
305 } else {
306 // Out of empty region? Compact within the same region.
307 new_to_region = _from_region;
308 }
309
310 assert(new_to_region != _to_region, "must not reuse same to-region");
311 assert(new_to_region != NULL, "must not be NULL");
312 _to_region = new_to_region;
313 _compact_point = _to_region->bottom();
314 }
315
316 // Object fits into current region, record new location:
317 assert(_compact_point + obj_size <= _to_region->end(), "must fit");
318 shenandoah_assert_not_forwarded(NULL, p);
319 _preserved_marks->push_if_necessary(p, p->mark_raw());
320 p->forward_to(oop(_compact_point));
321 _compact_point += obj_size;
322 }
323 };
324
325 class ShenandoahPrepareForCompactionTask : public AbstractGangTask {
326 private:
327 PreservedMarksSet* const _preserved_marks;
328 ShenandoahHeap* const _heap;
329 ShenandoahHeapRegionSet** const _worker_slices;
330
331 public:
332 ShenandoahPrepareForCompactionTask(PreservedMarksSet *preserved_marks, ShenandoahHeapRegionSet **worker_slices) :
333 AbstractGangTask("Shenandoah Prepare For Compaction Task"),
334 _preserved_marks(preserved_marks),
335 _heap(ShenandoahHeap::heap()), _worker_slices(worker_slices) {
336 }
337
338 static bool is_candidate_region(ShenandoahHeapRegion* r) {
339 // Empty region: get it into the slice to defragment the slice itself.
340 // We could have skipped this without violating correctness, but we really
341 // want to compact all live regions to the start of the heap, which sometimes
342 // means moving them into the fully empty regions.
343 if (r->is_empty()) return true;
344
345 // Can move the region, and this is not the humongous region. Humongous
346 // moves are special cased here, because their moves are handled separately.
347 return r->is_stw_move_allowed() && !r->is_humongous();
348 }
349
350 void work(uint worker_id) {
351 ShenandoahParallelWorkerSession worker_session(worker_id);
352 ShenandoahHeapRegionSet* slice = _worker_slices[worker_id];
353 ShenandoahHeapRegionSetIterator it(slice);
354 ShenandoahHeapRegion* from_region = it.next();
355 // No work?
356 if (from_region == NULL) {
357 return;
358 }
359
360 // Sliding compaction. Walk all regions in the slice, and compact them.
361 // Remember empty regions and reuse them as needed.
362 ResourceMark rm;
363
364 GrowableArray<ShenandoahHeapRegion*> empty_regions((int)_heap->num_regions());
365
366 ShenandoahPrepareForCompactionObjectClosure cl(_preserved_marks->get(worker_id), empty_regions, from_region);
367
368 while (from_region != NULL) {
369 assert(is_candidate_region(from_region), "Sanity");
370
371 cl.set_from_region(from_region);
372 if (from_region->has_live()) {
373 _heap->marked_object_iterate(from_region, &cl);
374 }
375
376 // Compacted the region to somewhere else? From-region is empty then.
377 if (!cl.is_compact_same_region()) {
378 empty_regions.append(from_region);
379 }
380 from_region = it.next();
381 }
382 cl.finish_region();
383
384 // Mark all remaining regions as empty
385 for (int pos = cl.empty_regions_pos(); pos < empty_regions.length(); ++pos) {
386 ShenandoahHeapRegion* r = empty_regions.at(pos);
387 r->set_new_top(r->bottom());
388 }
389 }
390 };
391
392 void ShenandoahMarkCompact::calculate_target_humongous_objects() {
393 ShenandoahHeap* heap = ShenandoahHeap::heap();
394
395 // Compute the new addresses for humongous objects. We need to do this after addresses
396 // for regular objects are calculated, and we know what regions in heap suffix are
397 // available for humongous moves.
398 //
399 // Scan the heap backwards, because we are compacting humongous regions towards the end.
400 // Maintain the contiguous compaction window in [to_begin; to_end), so that we can slide
401 // humongous start there.
402 //
403 // The complication is potential non-movable regions during the scan. If such region is
404 // detected, then sliding restarts towards that non-movable region.
405
406 size_t to_begin = heap->num_regions();
407 size_t to_end = heap->num_regions();
408
409 for (size_t c = heap->num_regions(); c > 0; c--) {
410 ShenandoahHeapRegion *r = heap->get_region(c - 1);
411 if (r->is_humongous_continuation() || (r->new_top() == r->bottom())) {
412 // To-region candidate: record this, and continue scan
413 to_begin = r->index();
414 continue;
415 }
416
417 if (r->is_humongous_start() && r->is_stw_move_allowed()) {
418 // From-region candidate: movable humongous region
419 oop old_obj = oop(r->bottom());
420 size_t words_size = old_obj->size();
421 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
422
423 size_t start = to_end - num_regions;
424
425 if (start >= to_begin && start != r->index()) {
426 // Fits into current window, and the move is non-trivial. Record the move then, and continue scan.
427 _preserved_marks->get(0)->push_if_necessary(old_obj, old_obj->mark_raw());
428 old_obj->forward_to(oop(heap->get_region(start)->bottom()));
429 to_end = start;
430 continue;
431 }
432 }
433
434 // Failed to fit. Scan starting from current region.
435 to_begin = r->index();
436 to_end = r->index();
437 }
438 }
439
440 class ShenandoahEnsureHeapActiveClosure: public ShenandoahHeapRegionClosure {
441 private:
442 ShenandoahHeap* const _heap;
443
444 public:
445 ShenandoahEnsureHeapActiveClosure() : _heap(ShenandoahHeap::heap()) {}
446 void heap_region_do(ShenandoahHeapRegion* r) {
447 if (r->is_trash()) {
448 r->recycle();
449 }
450 if (r->is_cset()) {
451 r->make_regular_bypass();
452 }
453 if (r->is_empty_uncommitted()) {
454 r->make_committed_bypass();
455 }
456 assert (r->is_committed(), "only committed regions in heap now, see region " SIZE_FORMAT, r->index());
457
458 // Record current region occupancy: this communicates empty regions are free
459 // to the rest of Full GC code.
460 r->set_new_top(r->top());
461 }
462 };
463
464 class ShenandoahTrashImmediateGarbageClosure: public ShenandoahHeapRegionClosure {
465 private:
466 ShenandoahHeap* const _heap;
467 ShenandoahMarkingContext* const _ctx;
468
469 public:
470 ShenandoahTrashImmediateGarbageClosure() :
471 _heap(ShenandoahHeap::heap()),
472 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
473
474 void heap_region_do(ShenandoahHeapRegion* r) {
475 if (r->is_humongous_start()) {
476 oop humongous_obj = oop(r->bottom());
477 if (!_ctx->is_marked(humongous_obj)) {
478 assert(!r->has_live(),
479 "Region " SIZE_FORMAT " is not marked, should not have live", r->index());
480 _heap->trash_humongous_region_at(r);
481 } else {
482 assert(r->has_live(),
483 "Region " SIZE_FORMAT " should have live", r->index());
484 }
485 } else if (r->is_humongous_continuation()) {
486 // If we hit continuation, the non-live humongous starts should have been trashed already
487 assert(r->humongous_start_region()->has_live(),
488 "Region " SIZE_FORMAT " should have live", r->index());
489 } else if (r->is_regular()) {
490 if (!r->has_live()) {
491 r->make_trash_immediate();
492 }
493 }
494 }
495 };
496
497 void ShenandoahMarkCompact::distribute_slices(ShenandoahHeapRegionSet** worker_slices) {
498 ShenandoahHeap* heap = ShenandoahHeap::heap();
499
500 uint n_workers = heap->workers()->active_workers();
501 size_t n_regions = heap->num_regions();
502
503 // What we want to accomplish: have the dense prefix of data, while still balancing
504 // out the parallel work.
505 //
506 // Assuming the amount of work is driven by the live data that needs moving, we can slice
507 // the entire heap into equal-live-sized prefix slices, and compact into them. So, each
508 // thread takes all regions in its prefix subset, and then it takes some regions from
509 // the tail.
510 //
511 // Tail region selection becomes interesting.
512 //
513 // First, we want to distribute the regions fairly between the workers, and those regions
514 // might have different amount of live data. So, until we sure no workers need live data,
515 // we need to only take what the worker needs.
516 //
517 // Second, since we slide everything to the left in each slice, the most busy regions
518 // would be the ones on the left. Which means we want to have all workers have their after-tail
519 // regions as close to the left as possible.
520 //
521 // The easiest way to do this is to distribute after-tail regions in round-robin between
522 // workers that still need live data.
523 //
524 // Consider parallel workers A, B, C, then the target slice layout would be:
525 //
526 // AAAAAAAABBBBBBBBCCCCCCCC|ABCABCABCABCABCABCABCABABABABABABABABABABAAAAA
527 //
528 // (.....dense-prefix.....) (.....................tail...................)
529 // [all regions fully live] [left-most regions are fuller that right-most]
530 //
531
532 // Compute how much live data is there. This would approximate the size of dense prefix
533 // we target to create.
534 size_t total_live = 0;
535 for (size_t idx = 0; idx < n_regions; idx++) {
536 ShenandoahHeapRegion *r = heap->get_region(idx);
537 if (ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
538 total_live += r->get_live_data_words();
539 }
540 }
541
542 // Estimate the size for the dense prefix. Note that we specifically count only the
543 // "full" regions, so there would be some non-full regions in the slice tail.
544 size_t live_per_worker = total_live / n_workers;
545 size_t prefix_regions_per_worker = live_per_worker / ShenandoahHeapRegion::region_size_words();
546 size_t prefix_regions_total = prefix_regions_per_worker * n_workers;
547 prefix_regions_total = MIN2(prefix_regions_total, n_regions);
548 assert(prefix_regions_total <= n_regions, "Sanity");
549
550 // There might be non-candidate regions in the prefix. To compute where the tail actually
551 // ends up being, we need to account those as well.
552 size_t prefix_end = prefix_regions_total;
553 for (size_t idx = 0; idx < prefix_regions_total; idx++) {
554 ShenandoahHeapRegion *r = heap->get_region(idx);
555 if (!ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
556 prefix_end++;
557 }
558 }
559 prefix_end = MIN2(prefix_end, n_regions);
560 assert(prefix_end <= n_regions, "Sanity");
561
562 // Distribute prefix regions per worker: each thread definitely gets its own same-sized
563 // subset of dense prefix.
564 size_t prefix_idx = 0;
565
566 size_t* live = NEW_C_HEAP_ARRAY(size_t, n_workers, mtGC);
567
568 for (size_t wid = 0; wid < n_workers; wid++) {
569 ShenandoahHeapRegionSet* slice = worker_slices[wid];
570
571 live[wid] = 0;
572 size_t regs = 0;
573
574 // Add all prefix regions for this worker
575 while (prefix_idx < prefix_end && regs < prefix_regions_per_worker) {
576 ShenandoahHeapRegion *r = heap->get_region(prefix_idx);
577 if (ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
578 slice->add_region(r);
579 live[wid] += r->get_live_data_words();
580 regs++;
581 }
582 prefix_idx++;
583 }
584 }
585
586 // Distribute the tail among workers in round-robin fashion.
587 size_t wid = n_workers - 1;
588
589 for (size_t tail_idx = prefix_end; tail_idx < n_regions; tail_idx++) {
590 ShenandoahHeapRegion *r = heap->get_region(tail_idx);
591 if (ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
592 assert(wid < n_workers, "Sanity");
593
594 size_t live_region = r->get_live_data_words();
595
596 // Select next worker that still needs live data.
597 size_t old_wid = wid;
598 do {
599 wid++;
600 if (wid == n_workers) wid = 0;
601 } while (live[wid] + live_region >= live_per_worker && old_wid != wid);
602
603 if (old_wid == wid) {
604 // Circled back to the same worker? This means liveness data was
605 // miscalculated. Bump the live_per_worker limit so that
606 // everyone gets a piece of the leftover work.
607 live_per_worker += ShenandoahHeapRegion::region_size_words();
608 }
609
610 worker_slices[wid]->add_region(r);
611 live[wid] += live_region;
612 }
613 }
614
615 FREE_C_HEAP_ARRAY(size_t, live);
616
617 #ifdef ASSERT
618 ResourceBitMap map(n_regions);
619 for (size_t wid = 0; wid < n_workers; wid++) {
620 ShenandoahHeapRegionSetIterator it(worker_slices[wid]);
621 ShenandoahHeapRegion* r = it.next();
622 while (r != NULL) {
623 size_t idx = r->index();
624 assert(ShenandoahPrepareForCompactionTask::is_candidate_region(r), "Sanity: " SIZE_FORMAT, idx);
625 assert(!map.at(idx), "No region distributed twice: " SIZE_FORMAT, idx);
626 map.at_put(idx, true);
627 r = it.next();
628 }
629 }
630
631 for (size_t rid = 0; rid < n_regions; rid++) {
632 bool is_candidate = ShenandoahPrepareForCompactionTask::is_candidate_region(heap->get_region(rid));
633 bool is_distributed = map.at(rid);
634 assert(is_distributed || !is_candidate, "All candidates are distributed: " SIZE_FORMAT, rid);
635 }
636 #endif
637 }
638
639 void ShenandoahMarkCompact::phase2_calculate_target_addresses(ShenandoahHeapRegionSet** worker_slices) {
640 GCTraceTime(Info, gc, phases) time("Phase 2: Compute new object addresses", _gc_timer);
641 ShenandoahGCPhase calculate_address_phase(ShenandoahPhaseTimings::full_gc_calculate_addresses);
642
643 ShenandoahHeap* heap = ShenandoahHeap::heap();
644
645 // About to figure out which regions can be compacted, make sure pinning status
646 // had been updated in GC prologue.
647 heap->assert_pinned_region_status();
648
649 {
650 // Trash the immediately collectible regions before computing addresses
651 ShenandoahTrashImmediateGarbageClosure tigcl;
652 heap->heap_region_iterate(&tigcl);
653
654 // Make sure regions are in good state: committed, active, clean.
655 // This is needed because we are potentially sliding the data through them.
656 ShenandoahEnsureHeapActiveClosure ecl;
657 heap->heap_region_iterate(&ecl);
658 }
659
660 // Compute the new addresses for regular objects
661 {
662 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_regular);
663
664 distribute_slices(worker_slices);
665
666 ShenandoahPrepareForCompactionTask task(_preserved_marks, worker_slices);
667 heap->workers()->run_task(&task);
668 }
669
670 // Compute the new addresses for humongous objects
671 {
672 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_humong);
673 calculate_target_humongous_objects();
674 }
675 }
676
677 class ShenandoahAdjustPointersClosure : public MetadataVisitingOopIterateClosure {
678 private:
679 ShenandoahHeap* const _heap;
680 ShenandoahMarkingContext* const _ctx;
681
682 template <class T>
683 inline void do_oop_work(T* p) {
684 T o = RawAccess<>::oop_load(p);
685 if (!CompressedOops::is_null(o)) {
686 oop obj = CompressedOops::decode_not_null(o);
687 assert(_ctx->is_marked(obj), "must be marked");
688 if (obj->is_forwarded()) {
689 oop forw = obj->forwardee();
690 RawAccess<IS_NOT_NULL>::oop_store(p, forw);
691 }
692 }
693 }
694
695 public:
696 ShenandoahAdjustPointersClosure() :
697 _heap(ShenandoahHeap::heap()),
698 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
699
700 void do_oop(oop* p) { do_oop_work(p); }
701 void do_oop(narrowOop* p) { do_oop_work(p); }
702 };
703
704 class ShenandoahAdjustPointersObjectClosure : public ObjectClosure {
705 private:
706 ShenandoahHeap* const _heap;
707 ShenandoahAdjustPointersClosure _cl;
708
709 public:
710 ShenandoahAdjustPointersObjectClosure() :
711 _heap(ShenandoahHeap::heap()) {
712 }
713 void do_object(oop p) {
714 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
715 p->oop_iterate(&_cl);
716 }
717 };
718
719 class ShenandoahAdjustPointersTask : public AbstractGangTask {
720 private:
721 ShenandoahHeap* const _heap;
722 ShenandoahRegionIterator _regions;
723
724 public:
725 ShenandoahAdjustPointersTask() :
726 AbstractGangTask("Shenandoah Adjust Pointers Task"),
727 _heap(ShenandoahHeap::heap()) {
728 }
729
730 void work(uint worker_id) {
731 ShenandoahParallelWorkerSession worker_session(worker_id);
732 ShenandoahAdjustPointersObjectClosure obj_cl;
733 ShenandoahHeapRegion* r = _regions.next();
734 while (r != NULL) {
735 if (!r->is_humongous_continuation() && r->has_live()) {
736 _heap->marked_object_iterate(r, &obj_cl);
737 }
738 r = _regions.next();
739 }
740 }
741 };
742
743 class ShenandoahAdjustRootPointersTask : public AbstractGangTask {
744 private:
745 ShenandoahRootAdjuster* _rp;
746 PreservedMarksSet* _preserved_marks;
747 public:
748 ShenandoahAdjustRootPointersTask(ShenandoahRootAdjuster* rp, PreservedMarksSet* preserved_marks) :
749 AbstractGangTask("Shenandoah Adjust Root Pointers Task"),
750 _rp(rp),
751 _preserved_marks(preserved_marks) {}
752
753 void work(uint worker_id) {
754 ShenandoahParallelWorkerSession worker_session(worker_id);
755 ShenandoahAdjustPointersClosure cl;
756 _rp->roots_do(worker_id, &cl);
757 _preserved_marks->get(worker_id)->adjust_during_full_gc();
758 }
759 };
760
761 void ShenandoahMarkCompact::phase3_update_references() {
762 GCTraceTime(Info, gc, phases) time("Phase 3: Adjust pointers", _gc_timer);
763 ShenandoahGCPhase adjust_pointer_phase(ShenandoahPhaseTimings::full_gc_adjust_pointers);
764
765 ShenandoahHeap* heap = ShenandoahHeap::heap();
766
767 WorkGang* workers = heap->workers();
768 uint nworkers = workers->active_workers();
769 {
770 #if COMPILER2_OR_JVMCI
771 DerivedPointerTable::clear();
772 #endif
773 ShenandoahRootAdjuster rp(nworkers, ShenandoahPhaseTimings::full_gc_adjust_roots);
774 ShenandoahAdjustRootPointersTask task(&rp, _preserved_marks);
775 workers->run_task(&task);
776 #if COMPILER2_OR_JVMCI
777 DerivedPointerTable::update_pointers();
778 #endif
779 }
780
781 ShenandoahAdjustPointersTask adjust_pointers_task;
782 workers->run_task(&adjust_pointers_task);
783 }
784
785 class ShenandoahCompactObjectsClosure : public ObjectClosure {
786 private:
787 ShenandoahHeap* const _heap;
788 uint const _worker_id;
789
790 public:
791 ShenandoahCompactObjectsClosure(uint worker_id) :
792 _heap(ShenandoahHeap::heap()), _worker_id(worker_id) {}
793
794 void do_object(oop p) {
795 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
796 size_t size = (size_t)p->size();
797 if (p->is_forwarded()) {
798 HeapWord* compact_from = cast_from_oop<HeapWord*>(p);
799 HeapWord* compact_to = cast_from_oop<HeapWord*>(p->forwardee());
800 Copy::aligned_conjoint_words(compact_from, compact_to, size);
801 oop new_obj = oop(compact_to);
802 new_obj->init_mark_raw();
803 }
804 }
805 };
806
807 class ShenandoahCompactObjectsTask : public AbstractGangTask {
808 private:
809 ShenandoahHeap* const _heap;
810 ShenandoahHeapRegionSet** const _worker_slices;
811
812 public:
813 ShenandoahCompactObjectsTask(ShenandoahHeapRegionSet** worker_slices) :
814 AbstractGangTask("Shenandoah Compact Objects Task"),
815 _heap(ShenandoahHeap::heap()),
816 _worker_slices(worker_slices) {
817 }
818
819 void work(uint worker_id) {
820 ShenandoahParallelWorkerSession worker_session(worker_id);
821 ShenandoahHeapRegionSetIterator slice(_worker_slices[worker_id]);
822
823 ShenandoahCompactObjectsClosure cl(worker_id);
824 ShenandoahHeapRegion* r = slice.next();
825 while (r != NULL) {
826 assert(!r->is_humongous(), "must not get humongous regions here");
827 if (r->has_live()) {
828 _heap->marked_object_iterate(r, &cl);
829 }
830 r->set_top(r->new_top());
831 r = slice.next();
832 }
833 }
834 };
835
836 class ShenandoahPostCompactClosure : public ShenandoahHeapRegionClosure {
837 private:
838 ShenandoahHeap* const _heap;
839 size_t _live;
840
841 public:
842 ShenandoahPostCompactClosure() : _heap(ShenandoahHeap::heap()), _live(0) {
843 _heap->free_set()->clear();
844 }
845
846 void heap_region_do(ShenandoahHeapRegion* r) {
847 assert (!r->is_cset(), "cset regions should have been demoted already");
848
849 // Need to reset the complete-top-at-mark-start pointer here because
850 // the complete marking bitmap is no longer valid. This ensures
851 // size-based iteration in marked_object_iterate().
852 // NOTE: See blurb at ShenandoahMCResetCompleteBitmapTask on why we need to skip
853 // pinned regions.
854 if (!r->is_pinned()) {
855 _heap->complete_marking_context()->reset_top_at_mark_start(r);
856 }
857
858 size_t live = r->used();
859
860 // Make empty regions that have been allocated into regular
861 if (r->is_empty() && live > 0) {
862 r->make_regular_bypass();
863 }
864
865 // Reclaim regular regions that became empty
866 if (r->is_regular() && live == 0) {
867 r->make_trash();
868 }
869
870 // Recycle all trash regions
871 if (r->is_trash()) {
872 live = 0;
873 r->recycle();
874 }
875
876 r->set_live_data(live);
877 r->reset_alloc_metadata();
878 _live += live;
879 }
880
881 size_t get_live() {
882 return _live;
883 }
884 };
885
886 void ShenandoahMarkCompact::compact_humongous_objects() {
887 // Compact humongous regions, based on their fwdptr objects.
888 //
889 // This code is serial, because doing the in-slice parallel sliding is tricky. In most cases,
890 // humongous regions are already compacted, and do not require further moves, which alleviates
891 // sliding costs. We may consider doing this in parallel in future.
892
893 ShenandoahHeap* heap = ShenandoahHeap::heap();
894
895 for (size_t c = heap->num_regions(); c > 0; c--) {
896 ShenandoahHeapRegion* r = heap->get_region(c - 1);
897 if (r->is_humongous_start()) {
898 oop old_obj = oop(r->bottom());
899 if (!old_obj->is_forwarded()) {
900 // No need to move the object, it stays at the same slot
901 continue;
902 }
903 size_t words_size = old_obj->size();
904 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
905
906 size_t old_start = r->index();
907 size_t old_end = old_start + num_regions - 1;
908 size_t new_start = heap->heap_region_index_containing(old_obj->forwardee());
909 size_t new_end = new_start + num_regions - 1;
910 assert(old_start != new_start, "must be real move");
911 assert(r->is_stw_move_allowed(), "Region " SIZE_FORMAT " should be movable", r->index());
912
913 Copy::aligned_conjoint_words(heap->get_region(old_start)->bottom(),
914 heap->get_region(new_start)->bottom(),
915 ShenandoahHeapRegion::region_size_words()*num_regions);
916
917 oop new_obj = oop(heap->get_region(new_start)->bottom());
918 new_obj->init_mark_raw();
919
920 {
921 for (size_t c = old_start; c <= old_end; c++) {
922 ShenandoahHeapRegion* r = heap->get_region(c);
923 r->make_regular_bypass();
924 r->set_top(r->bottom());
925 }
926
927 for (size_t c = new_start; c <= new_end; c++) {
928 ShenandoahHeapRegion* r = heap->get_region(c);
929 if (c == new_start) {
930 r->make_humongous_start_bypass();
931 } else {
932 r->make_humongous_cont_bypass();
933 }
934
935 // Trailing region may be non-full, record the remainder there
936 size_t remainder = words_size & ShenandoahHeapRegion::region_size_words_mask();
937 if ((c == new_end) && (remainder != 0)) {
938 r->set_top(r->bottom() + remainder);
939 } else {
940 r->set_top(r->end());
941 }
942
943 r->reset_alloc_metadata();
944 }
945 }
946 }
947 }
948 }
949
950 // This is slightly different to ShHeap::reset_next_mark_bitmap:
951 // we need to remain able to walk pinned regions.
952 // Since pinned region do not move and don't get compacted, we will get holes with
953 // unreachable objects in them (which may have pointers to unloaded Klasses and thus
954 // cannot be iterated over using oop->size(). The only way to safely iterate over those is using
955 // a valid marking bitmap and valid TAMS pointer. This class only resets marking
956 // bitmaps for un-pinned regions, and later we only reset TAMS for unpinned regions.
957 class ShenandoahMCResetCompleteBitmapTask : public AbstractGangTask {
958 private:
959 ShenandoahRegionIterator _regions;
960
961 public:
962 ShenandoahMCResetCompleteBitmapTask() :
963 AbstractGangTask("Parallel Reset Bitmap Task") {
964 }
965
966 void work(uint worker_id) {
967 ShenandoahParallelWorkerSession worker_session(worker_id);
968 ShenandoahHeapRegion* region = _regions.next();
969 ShenandoahHeap* heap = ShenandoahHeap::heap();
970 ShenandoahMarkingContext* const ctx = heap->complete_marking_context();
971 while (region != NULL) {
972 if (heap->is_bitmap_slice_committed(region) && !region->is_pinned() && region->has_live()) {
973 ctx->clear_bitmap(region);
974 }
975 region = _regions.next();
976 }
977 }
978 };
979
980 void ShenandoahMarkCompact::phase4_compact_objects(ShenandoahHeapRegionSet** worker_slices) {
981 GCTraceTime(Info, gc, phases) time("Phase 4: Move objects", _gc_timer);
982 ShenandoahGCPhase compaction_phase(ShenandoahPhaseTimings::full_gc_copy_objects);
983
984 ShenandoahHeap* heap = ShenandoahHeap::heap();
985
986 // Compact regular objects first
987 {
988 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_regular);
989 ShenandoahCompactObjectsTask compact_task(worker_slices);
990 heap->workers()->run_task(&compact_task);
991 }
992
993 // Compact humongous objects after regular object moves
994 {
995 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_humong);
996 compact_humongous_objects();
997 }
998
999 // Reset complete bitmap. We're about to reset the complete-top-at-mark-start pointer
1000 // and must ensure the bitmap is in sync.
1001 {
1002 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_reset_complete);
1003 ShenandoahMCResetCompleteBitmapTask task;
1004 heap->workers()->run_task(&task);
1005 }
1006
1007 // Bring regions in proper states after the collection, and set heap properties.
1008 {
1009 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_rebuild);
1010
1011 ShenandoahPostCompactClosure post_compact;
1012 heap->heap_region_iterate(&post_compact);
1013 heap->set_used(post_compact.get_live());
1014
1015 heap->collection_set()->clear();
1016 heap->free_set()->rebuild();
1017 }
1018
1019 heap->clear_cancelled_gc();
1020 }