1 /*
2 * Copyright (c) 2017, 2023, Oracle and/or its affiliates. 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 #include "classfile/classLoaderDataGraph.hpp"
27 #include "classfile/systemDictionary.hpp"
28 #include "code/codeCache.hpp"
29 #include "compiler/oopMap.hpp"
30 #include "gc/g1/g1CollectedHeap.hpp"
31 #include "gc/g1/g1FullCollector.inline.hpp"
32 #include "gc/g1/g1FullGCAdjustTask.hpp"
33 #include "gc/g1/g1FullGCCompactTask.hpp"
34 #include "gc/g1/g1FullGCMarker.inline.hpp"
35 #include "gc/g1/g1FullGCMarkTask.hpp"
36 #include "gc/g1/g1FullGCPrepareTask.inline.hpp"
37 #include "gc/g1/g1FullGCResetMetadataTask.hpp"
38 #include "gc/g1/g1FullGCScope.hpp"
39 #include "gc/g1/g1OopClosures.hpp"
40 #include "gc/g1/g1Policy.hpp"
41 #include "gc/g1/g1RegionMarkStatsCache.inline.hpp"
42 #include "gc/shared/gcTraceTime.inline.hpp"
43 #include "gc/shared/preservedMarks.hpp"
44 #include "gc/shared/referenceProcessor.hpp"
45 #include "gc/shared/verifyOption.hpp"
46 #include "gc/shared/weakProcessor.inline.hpp"
47 #include "gc/shared/workerPolicy.hpp"
48 #include "logging/log.hpp"
49 #include "runtime/handles.inline.hpp"
50 #include "utilities/debug.hpp"
51
52 static void clear_and_activate_derived_pointers() {
53 #if COMPILER2_OR_JVMCI
54 DerivedPointerTable::clear();
55 #endif
56 }
57
58 static void deactivate_derived_pointers() {
59 #if COMPILER2_OR_JVMCI
60 DerivedPointerTable::set_active(false);
61 #endif
62 }
63
64 static void update_derived_pointers() {
65 #if COMPILER2_OR_JVMCI
66 DerivedPointerTable::update_pointers();
67 #endif
68 }
69
70 G1CMBitMap* G1FullCollector::mark_bitmap() {
71 return _heap->concurrent_mark()->mark_bitmap();
72 }
73
74 ReferenceProcessor* G1FullCollector::reference_processor() {
75 return _heap->ref_processor_stw();
76 }
77
78 uint G1FullCollector::calc_active_workers() {
79 G1CollectedHeap* heap = G1CollectedHeap::heap();
80 uint max_worker_count = heap->workers()->max_workers();
81 // Only calculate number of workers if UseDynamicNumberOfGCThreads
82 // is enabled, otherwise use max.
83 if (!UseDynamicNumberOfGCThreads) {
84 return max_worker_count;
85 }
86
87 // Consider G1HeapWastePercent to decide max number of workers. Each worker
88 // will in average cause half a region waste.
89 uint max_wasted_regions_allowed = ((heap->num_regions() * G1HeapWastePercent) / 100);
90 uint waste_worker_count = MAX2((max_wasted_regions_allowed * 2) , 1u);
91 uint heap_waste_worker_limit = MIN2(waste_worker_count, max_worker_count);
92
93 // Also consider HeapSizePerGCThread by calling WorkerPolicy to calculate
94 // the number of workers.
95 uint current_active_workers = heap->workers()->active_workers();
96 uint active_worker_limit = WorkerPolicy::calc_active_workers(max_worker_count, current_active_workers, 0);
97
98 // Finally consider the amount of used regions.
99 uint used_worker_limit = heap->num_used_regions();
100 assert(used_worker_limit > 0, "Should never have zero used regions.");
101
102 // Update active workers to the lower of the limits.
103 uint worker_count = MIN3(heap_waste_worker_limit, active_worker_limit, used_worker_limit);
104 log_debug(gc, task)("Requesting %u active workers for full compaction (waste limited workers: %u, "
105 "adaptive workers: %u, used limited workers: %u)",
106 worker_count, heap_waste_worker_limit, active_worker_limit, used_worker_limit);
107 worker_count = heap->workers()->set_active_workers(worker_count);
108 log_info(gc, task)("Using %u workers of %u for full compaction", worker_count, max_worker_count);
109
110 return worker_count;
111 }
112
113 G1FullCollector::G1FullCollector(G1CollectedHeap* heap,
114 bool explicit_gc,
115 bool clear_soft_refs,
116 bool do_maximal_compaction,
117 G1FullGCTracer* tracer) :
118 _heap(heap),
119 _scope(heap->monitoring_support(), explicit_gc, clear_soft_refs, do_maximal_compaction, tracer),
120 _num_workers(calc_active_workers()),
121 _has_compaction_targets(false),
122 _oop_queue_set(_num_workers),
123 _array_queue_set(_num_workers),
124 _preserved_marks_set(true),
125 _serial_compaction_point(this),
126 _is_alive(this, heap->concurrent_mark()->mark_bitmap()),
127 _is_alive_mutator(heap->ref_processor_stw(), &_is_alive),
128 _always_subject_to_discovery(),
129 _is_subject_mutator(heap->ref_processor_stw(), &_always_subject_to_discovery),
130 _region_attr_table() {
131 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
132
133 _preserved_marks_set.init(_num_workers);
134 _markers = NEW_C_HEAP_ARRAY(G1FullGCMarker*, _num_workers, mtGC);
135 _compaction_points = NEW_C_HEAP_ARRAY(G1FullGCCompactionPoint*, _num_workers, mtGC);
136
137 _live_stats = NEW_C_HEAP_ARRAY(G1RegionMarkStats, _heap->max_regions(), mtGC);
138 _compaction_tops = NEW_C_HEAP_ARRAY(HeapWord*, _heap->max_regions(), mtGC);
139 for (uint j = 0; j < heap->max_regions(); j++) {
140 _live_stats[j].clear();
141 _compaction_tops[j] = nullptr;
142 }
143
144 for (uint i = 0; i < _num_workers; i++) {
145 _markers[i] = new G1FullGCMarker(this, i, _preserved_marks_set.get(i), _live_stats);
146 _compaction_points[i] = new G1FullGCCompactionPoint(this);
147 _oop_queue_set.register_queue(i, marker(i)->oop_stack());
148 _array_queue_set.register_queue(i, marker(i)->objarray_stack());
149 }
150 _region_attr_table.initialize(heap->reserved(), HeapRegion::GrainBytes);
151 }
152
153 G1FullCollector::~G1FullCollector() {
154 for (uint i = 0; i < _num_workers; i++) {
155 delete _markers[i];
156 delete _compaction_points[i];
157 }
158 FREE_C_HEAP_ARRAY(G1FullGCMarker*, _markers);
159 FREE_C_HEAP_ARRAY(G1FullGCCompactionPoint*, _compaction_points);
160 FREE_C_HEAP_ARRAY(HeapWord*, _compaction_tops);
161 FREE_C_HEAP_ARRAY(G1RegionMarkStats, _live_stats);
162 }
163
164 class PrepareRegionsClosure : public HeapRegionClosure {
165 G1FullCollector* _collector;
166
167 public:
168 PrepareRegionsClosure(G1FullCollector* collector) : _collector(collector) { }
169
170 bool do_heap_region(HeapRegion* hr) {
171 G1CollectedHeap::heap()->prepare_region_for_full_compaction(hr);
172 _collector->before_marking_update_attribute_table(hr);
173 return false;
174 }
175 };
176
177 void G1FullCollector::prepare_collection() {
178 _heap->policy()->record_full_collection_start();
179
180 // Verification needs the bitmap, so we should clear the bitmap only later.
181 bool in_concurrent_cycle = _heap->abort_concurrent_cycle();
182 _heap->verify_before_full_collection(scope()->is_explicit_gc());
183 if (in_concurrent_cycle) {
184 GCTraceTime(Debug, gc) debug("Clear Bitmap");
185 _heap->concurrent_mark()->clear_bitmap(_heap->workers());
186 }
187
188 _heap->gc_prologue(true);
189 _heap->retire_tlabs();
190 _heap->prepare_heap_for_full_collection();
191
192 PrepareRegionsClosure cl(this);
193 _heap->heap_region_iterate(&cl);
194
195 reference_processor()->start_discovery(scope()->should_clear_soft_refs());
196
197 // Clear and activate derived pointer collection.
198 clear_and_activate_derived_pointers();
199 }
200
201 void G1FullCollector::collect() {
202 G1CollectedHeap::start_codecache_marking_cycle_if_inactive(false /* concurrent_mark_start */);
203
204 phase1_mark_live_objects();
205 verify_after_marking();
206
207 // Don't add any more derived pointers during later phases
208 deactivate_derived_pointers();
209
210 phase2_prepare_compaction();
211
212 if (has_compaction_targets()) {
213 phase3_adjust_pointers();
214
215 phase4_do_compaction();
216 } else {
217 // All regions have a high live ratio thus will not be compacted.
218 // The live ratio is only considered if do_maximal_compaction is false.
219 log_info(gc, phases) ("No Regions selected for compaction. Skipping Phase 3: Adjust pointers and Phase 4: Compact heap");
220 }
221
222 phase5_reset_metadata();
223
224 G1CollectedHeap::finish_codecache_marking_cycle();
225 }
226
227 void G1FullCollector::complete_collection() {
228 // Restore all marks.
229 restore_marks();
230
231 // When the pointers have been adjusted and moved, we can
232 // update the derived pointer table.
233 update_derived_pointers();
234
235 // Need completely cleared claim bits for the next concurrent marking or full gc.
236 ClassLoaderDataGraph::clear_claimed_marks();
237
238 // Prepare the bitmap for the next (potentially concurrent) marking.
239 _heap->concurrent_mark()->clear_bitmap(_heap->workers());
240
241 _heap->prepare_for_mutator_after_full_collection();
242
243 _heap->resize_all_tlabs();
244
245 _heap->policy()->record_full_collection_end();
246 _heap->gc_epilogue(true);
247
248 _heap->verify_after_full_collection();
249 }
250
251 void G1FullCollector::before_marking_update_attribute_table(HeapRegion* hr) {
252 if (hr->is_free()) {
253 _region_attr_table.set_free(hr->hrm_index());
254 } else if (hr->is_closed_archive()) {
255 _region_attr_table.set_skip_marking(hr->hrm_index());
256 } else if (hr->is_pinned()) {
257 _region_attr_table.set_skip_compacting(hr->hrm_index());
258 } else {
259 // Everything else should be compacted.
260 _region_attr_table.set_compacting(hr->hrm_index());
261 }
262 }
263
264 class G1FullGCRefProcProxyTask : public RefProcProxyTask {
265 G1FullCollector& _collector;
266
267 public:
268 G1FullGCRefProcProxyTask(G1FullCollector &collector, uint max_workers)
269 : RefProcProxyTask("G1FullGCRefProcProxyTask", max_workers),
270 _collector(collector) {}
271
272 void work(uint worker_id) override {
273 assert(worker_id < _max_workers, "sanity");
274 G1IsAliveClosure is_alive(&_collector);
275 uint index = (_tm == RefProcThreadModel::Single) ? 0 : worker_id;
276 G1FullKeepAliveClosure keep_alive(_collector.marker(index));
277 BarrierEnqueueDiscoveredFieldClosure enqueue;
278 G1FollowStackClosure* complete_gc = _collector.marker(index)->stack_closure();
279 _rp_task->rp_work(worker_id, &is_alive, &keep_alive, &enqueue, complete_gc);
280 }
281 };
282
283 void G1FullCollector::phase1_mark_live_objects() {
284 // Recursively traverse all live objects and mark them.
285 GCTraceTime(Info, gc, phases) info("Phase 1: Mark live objects", scope()->timer());
286
287 {
288 // Do the actual marking.
289 G1FullGCMarkTask marking_task(this);
290 run_task(&marking_task);
291 }
292
293 {
294 uint old_active_mt_degree = reference_processor()->num_queues();
295 reference_processor()->set_active_mt_degree(workers());
296 GCTraceTime(Debug, gc, phases) debug("Phase 1: Reference Processing", scope()->timer());
297 // Process reference objects found during marking.
298 ReferenceProcessorPhaseTimes pt(scope()->timer(), reference_processor()->max_num_queues());
299 G1FullGCRefProcProxyTask task(*this, reference_processor()->max_num_queues());
300 const ReferenceProcessorStats& stats = reference_processor()->process_discovered_references(task, pt);
301 scope()->tracer()->report_gc_reference_stats(stats);
302 pt.print_all_references();
303 assert(marker(0)->oop_stack()->is_empty(), "Should be no oops on the stack");
304
305 reference_processor()->set_active_mt_degree(old_active_mt_degree);
306 }
307
308 // Weak oops cleanup.
309 {
310 GCTraceTime(Debug, gc, phases) debug("Phase 1: Weak Processing", scope()->timer());
311 WeakProcessor::weak_oops_do(_heap->workers(), &_is_alive, &do_nothing_cl, 1);
312 }
313
314 // Class unloading and cleanup.
315 if (ClassUnloading) {
316 GCTraceTime(Debug, gc, phases) debug("Phase 1: Class Unloading and Cleanup", scope()->timer());
317 CodeCache::UnloadingScope unloading_scope(&_is_alive);
318 // Unload classes and purge the SystemDictionary.
319 bool purged_class = SystemDictionary::do_unloading(scope()->timer());
320 _heap->complete_cleaning(purged_class);
321 }
322
323 scope()->tracer()->report_object_count_after_gc(&_is_alive);
324 #if TASKQUEUE_STATS
325 oop_queue_set()->print_and_reset_taskqueue_stats("Oop Queue");
326 array_queue_set()->print_and_reset_taskqueue_stats("ObjArrayOop Queue");
327 #endif
328 }
329
330 void G1FullCollector::phase2_prepare_compaction() {
331 GCTraceTime(Info, gc, phases) info("Phase 2: Prepare compaction", scope()->timer());
332
333 phase2a_determine_worklists();
334
335 if (!has_compaction_targets()) {
336 return;
337 }
338
339 bool has_free_compaction_targets = phase2b_forward_oops();
340
341 // Try to avoid OOM immediately after Full GC in case there are no free regions
342 // left after determining the result locations (i.e. this phase). Prepare to
343 // maximally compact the tail regions of the compaction queues serially.
344 if (scope()->do_maximal_compaction() || !has_free_compaction_targets) {
345 phase2c_prepare_serial_compaction();
346 }
347 }
348
349 void G1FullCollector::phase2a_determine_worklists() {
350 GCTraceTime(Debug, gc, phases) debug("Phase 2: Determine work lists", scope()->timer());
351
352 G1DetermineCompactionQueueClosure cl(this);
353 _heap->heap_region_iterate(&cl);
354 }
355
356 bool G1FullCollector::phase2b_forward_oops() {
357 GCTraceTime(Debug, gc, phases) debug("Phase 2: Prepare parallel compaction", scope()->timer());
358
359 G1FullGCPrepareTask task(this);
360 run_task(&task);
361
362 return task.has_free_compaction_targets();
363 }
364
365 uint G1FullCollector::truncate_parallel_cps() {
366 uint lowest_current = (uint)-1;
367 for (uint i = 0; i < workers(); i++) {
368 G1FullGCCompactionPoint* cp = compaction_point(i);
369 if (cp->has_regions()) {
370 lowest_current = MIN2(lowest_current, cp->current_region()->hrm_index());
371 }
372 }
373
374 for (uint i = 0; i < workers(); i++) {
375 G1FullGCCompactionPoint* cp = compaction_point(i);
376 if (cp->has_regions()) {
377 cp->remove_at_or_above(lowest_current);
378 }
379 }
380 return lowest_current;
381 }
382
383 void G1FullCollector::phase2c_prepare_serial_compaction() {
384 GCTraceTime(Debug, gc, phases) debug("Phase 2: Prepare serial compaction", scope()->timer());
385 // At this point, we know that after parallel compaction there will be regions that
386 // are partially compacted into. Thus, the last compaction region of all
387 // compaction queues still have space in them. We try to re-compact these regions
388 // in serial to avoid a premature OOM when the mutator wants to allocate the first
389 // eden region after gc.
390
391 // For maximum compaction, we need to re-prepare all objects above the lowest
392 // region among the current regions for all thread compaction points. It may
393 // happen that due to the uneven distribution of objects to parallel threads, holes
394 // have been created as threads compact to different target regions between the
395 // lowest and the highest region in the tails of the compaction points.
396
397 uint start_serial = truncate_parallel_cps();
398 assert(start_serial < _heap->max_reserved_regions(), "Called on empty parallel compaction queues");
399
400 G1FullGCCompactionPoint* serial_cp = serial_compaction_point();
401 assert(!serial_cp->is_initialized(), "sanity!");
402
403 HeapRegion* start_hr = _heap->region_at(start_serial);
404 serial_cp->add(start_hr);
405 serial_cp->initialize(start_hr);
406
407 HeapWord* dense_prefix_top = compaction_top(start_hr);
408 G1SerialRePrepareClosure re_prepare(serial_cp, dense_prefix_top);
409
410 for (uint i = start_serial + 1; i < _heap->max_reserved_regions(); i++) {
411 if (is_compaction_target(i)) {
412 HeapRegion* current = _heap->region_at(i);
413 set_compaction_top(current, current->bottom());
414 serial_cp->add(current);
415 current->apply_to_marked_objects(mark_bitmap(), &re_prepare);
416 }
417 }
418 serial_cp->update();
419 }
420
421 void G1FullCollector::phase3_adjust_pointers() {
422 // Adjust the pointers to reflect the new locations
423 GCTraceTime(Info, gc, phases) info("Phase 3: Adjust pointers", scope()->timer());
424
425 G1FullGCAdjustTask task(this);
426 run_task(&task);
427 }
428
429 void G1FullCollector::phase4_do_compaction() {
430 // Compact the heap using the compaction queues created in phase 2.
431 GCTraceTime(Info, gc, phases) info("Phase 4: Compact heap", scope()->timer());
432 G1FullGCCompactTask task(this);
433 run_task(&task);
434
435 // Serial compact to avoid OOM when very few free regions.
436 if (serial_compaction_point()->has_regions()) {
437 task.serial_compaction();
438 }
439 }
440
441 void G1FullCollector::phase5_reset_metadata() {
442 // Clear region metadata that is invalid after GC for all regions.
443 GCTraceTime(Info, gc, phases) info("Phase 5: Reset Metadata", scope()->timer());
444 G1FullGCResetMetadataTask task(this);
445 run_task(&task);
446 }
447
448 void G1FullCollector::restore_marks() {
449 _preserved_marks_set.restore(_heap->workers());
450 _preserved_marks_set.reclaim();
451 }
452
453 void G1FullCollector::run_task(WorkerTask* task) {
454 _heap->workers()->run_task(task, _num_workers);
455 }
456
457 void G1FullCollector::verify_after_marking() {
458 if (!VerifyDuringGC || !_heap->verifier()->should_verify(G1HeapVerifier::G1VerifyFull)) {
459 // Only do verification if VerifyDuringGC and G1VerifyFull is set.
460 return;
461 }
462
463 #if COMPILER2_OR_JVMCI
464 DerivedPointerTableDeactivate dpt_deact;
465 #endif
466 _heap->prepare_for_verify();
467 // Note: we can verify only the heap here. When an object is
468 // marked, the previous value of the mark word (including
469 // identity hash values, ages, etc) is preserved, and the mark
470 // word is set to markWord::marked_value - effectively removing
471 // any hash values from the mark word. These hash values are
472 // used when verifying the dictionaries and so removing them
473 // from the mark word can make verification of the dictionaries
474 // fail. At the end of the GC, the original mark word values
475 // (including hash values) are restored to the appropriate
476 // objects.
477 GCTraceTime(Info, gc, verify) tm("Verifying During GC (full)");
478 _heap->verify(VerifyOption::G1UseFullMarking);
479 }