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/gcForwarding.hpp"
 43 #include "gc/shared/gcTraceTime.inline.hpp"
 44 #include "gc/shared/preservedMarks.inline.hpp"
 45 #include "gc/shared/referenceProcessor.hpp"
 46 #include "gc/shared/verifyOption.hpp"
 47 #include "gc/shared/weakProcessor.inline.hpp"
 48 #include "gc/shared/workerPolicy.hpp"
 49 #include "logging/log.hpp"
 50 #include "runtime/handles.inline.hpp"
 51 #include "utilities/debug.hpp"
 52 
 53 static void clear_and_activate_derived_pointers() {
 54 #if COMPILER2_OR_JVMCI
 55   DerivedPointerTable::clear();
 56 #endif
 57 }
 58 
 59 static void deactivate_derived_pointers() {
 60 #if COMPILER2_OR_JVMCI
 61   DerivedPointerTable::set_active(false);
 62 #endif
 63 }
 64 
 65 static void update_derived_pointers() {
 66 #if COMPILER2_OR_JVMCI
 67   DerivedPointerTable::update_pointers();
 68 #endif
 69 }
 70 
 71 G1CMBitMap* G1FullCollector::mark_bitmap() {
 72   return _heap->concurrent_mark()->mark_bitmap();
 73 }
 74 
 75 ReferenceProcessor* G1FullCollector::reference_processor() {
 76   return _heap->ref_processor_stw();
 77 }
 78 
 79 uint G1FullCollector::calc_active_workers() {
 80   G1CollectedHeap* heap = G1CollectedHeap::heap();
 81   uint max_worker_count = heap->workers()->max_workers();
 82   // Only calculate number of workers if UseDynamicNumberOfGCThreads
 83   // is enabled, otherwise use max.
 84   if (!UseDynamicNumberOfGCThreads) {
 85     return max_worker_count;
 86   }
 87 
 88   // Consider G1HeapWastePercent to decide max number of workers. Each worker
 89   // will in average cause half a region waste.
 90   uint max_wasted_regions_allowed = ((heap->num_regions() * G1HeapWastePercent) / 100);
 91   uint waste_worker_count = MAX2((max_wasted_regions_allowed * 2) , 1u);
 92   uint heap_waste_worker_limit = MIN2(waste_worker_count, max_worker_count);
 93 
 94   // Also consider HeapSizePerGCThread by calling WorkerPolicy to calculate
 95   // the number of workers.
 96   uint current_active_workers = heap->workers()->active_workers();
 97   uint active_worker_limit = WorkerPolicy::calc_active_workers(max_worker_count, current_active_workers, 0);
 98 
 99   // Finally consider the amount of used regions.
100   uint used_worker_limit = heap->num_used_regions();
101   assert(used_worker_limit > 0, "Should never have zero used regions.");
102 
103   // Update active workers to the lower of the limits.
104   uint worker_count = MIN3(heap_waste_worker_limit, active_worker_limit, used_worker_limit);
105   log_debug(gc, task)("Requesting %u active workers for full compaction (waste limited workers: %u, "
106                       "adaptive workers: %u, used limited workers: %u)",
107                       worker_count, heap_waste_worker_limit, active_worker_limit, used_worker_limit);
108   worker_count = heap->workers()->set_active_workers(worker_count);
109   log_info(gc, task)("Using %u workers of %u for full compaction", worker_count, max_worker_count);
110 
111   return worker_count;
112 }
113 
114 G1FullCollector::G1FullCollector(G1CollectedHeap* heap,
115                                  bool clear_soft_refs,
116                                  bool do_maximal_compaction,
117                                  G1FullGCTracer* tracer) :
118     _heap(heap),
119     _scope(heap->monitoring_support(), clear_soft_refs, do_maximal_compaction, tracer),
120     _num_workers(calc_active_workers()),
121     _has_compaction_targets(false),
122     _has_humongous(false),
123     _oop_queue_set(_num_workers),
124     _array_queue_set(_num_workers),
125     _preserved_marks_set(true),
126     _serial_compaction_point(this),
127     _humongous_compaction_point(this),
128     _is_alive(this, heap->concurrent_mark()->mark_bitmap()),
129     _is_alive_mutator(heap->ref_processor_stw(), &_is_alive),
130     _humongous_compaction_regions(8),
131     _always_subject_to_discovery(),
132     _is_subject_mutator(heap->ref_processor_stw(), &_always_subject_to_discovery),
133     _region_attr_table() {
134   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
135 
136   _preserved_marks_set.init(_num_workers);
137   _markers = NEW_C_HEAP_ARRAY(G1FullGCMarker*, _num_workers, mtGC);
138   _compaction_points = NEW_C_HEAP_ARRAY(G1FullGCCompactionPoint*, _num_workers, mtGC);
139 
140   _live_stats = NEW_C_HEAP_ARRAY(G1RegionMarkStats, _heap->max_regions(), mtGC);
141   _compaction_tops = NEW_C_HEAP_ARRAY(HeapWord*, _heap->max_regions(), mtGC);
142   for (uint j = 0; j < heap->max_regions(); j++) {
143     _live_stats[j].clear();
144     _compaction_tops[j] = nullptr;
145   }
146 
147   for (uint i = 0; i < _num_workers; i++) {
148     _markers[i] = new G1FullGCMarker(this, i, _preserved_marks_set.get(i), _live_stats);
149     _compaction_points[i] = new G1FullGCCompactionPoint(this);
150     _oop_queue_set.register_queue(i, marker(i)->oop_stack());
151     _array_queue_set.register_queue(i, marker(i)->objarray_stack());
152   }
153   _region_attr_table.initialize(heap->reserved(), HeapRegion::GrainBytes);
154 }
155 
156 G1FullCollector::~G1FullCollector() {
157   for (uint i = 0; i < _num_workers; i++) {
158     delete _markers[i];
159     delete _compaction_points[i];
160   }
161 
162   FREE_C_HEAP_ARRAY(G1FullGCMarker*, _markers);
163   FREE_C_HEAP_ARRAY(G1FullGCCompactionPoint*, _compaction_points);
164   FREE_C_HEAP_ARRAY(HeapWord*, _compaction_tops);
165   FREE_C_HEAP_ARRAY(G1RegionMarkStats, _live_stats);
166 }
167 
168 class PrepareRegionsClosure : public HeapRegionClosure {
169   G1FullCollector* _collector;
170 
171 public:
172   PrepareRegionsClosure(G1FullCollector* collector) : _collector(collector) { }
173 
174   bool do_heap_region(HeapRegion* hr) {
175     G1CollectedHeap::heap()->prepare_region_for_full_compaction(hr);
176     _collector->before_marking_update_attribute_table(hr);
177     return false;
178   }
179 };
180 
181 void G1FullCollector::prepare_collection() {
182   _heap->policy()->record_full_collection_start();
183 
184   // Verification needs the bitmap, so we should clear the bitmap only later.
185   bool in_concurrent_cycle = _heap->abort_concurrent_cycle();
186   _heap->verify_before_full_collection();
187   if (in_concurrent_cycle) {
188     GCTraceTime(Debug, gc) debug("Clear Bitmap");
189     _heap->concurrent_mark()->clear_bitmap(_heap->workers());
190   }
191 
192   _heap->gc_prologue(true);
193   _heap->retire_tlabs();
194   _heap->prepare_heap_for_full_collection();
195 
196   PrepareRegionsClosure cl(this);
197   _heap->heap_region_iterate(&cl);
198 
199   reference_processor()->start_discovery(scope()->should_clear_soft_refs());
200 
201   // Clear and activate derived pointer collection.
202   clear_and_activate_derived_pointers();
203 }
204 
205 void G1FullCollector::collect() {
206   G1CollectedHeap::start_codecache_marking_cycle_if_inactive(false /* concurrent_mark_start */);
207 
208   phase1_mark_live_objects();
209   verify_after_marking();
210 
211   // Don't add any more derived pointers during later phases
212   deactivate_derived_pointers();
213 
214   GCForwarding::begin();
215   phase2_prepare_compaction();
216 
217   if (has_compaction_targets()) {
218     phase3_adjust_pointers();
219 
220     phase4_do_compaction();
221   } else {
222     // All regions have a high live ratio thus will not be compacted.
223     // The live ratio is only considered if do_maximal_compaction is false.
224     log_info(gc, phases) ("No Regions selected for compaction. Skipping Phase 3: Adjust pointers and Phase 4: Compact heap");
225   }
226 
227   GCForwarding::end();
228 
229   phase5_reset_metadata();
230 
231   G1CollectedHeap::finish_codecache_marking_cycle();
232 }
233 
234 void G1FullCollector::complete_collection() {
235   // Restore all marks.
236   restore_marks();
237 
238   // When the pointers have been adjusted and moved, we can
239   // update the derived pointer table.
240   update_derived_pointers();
241 
242   // Need completely cleared claim bits for the next concurrent marking or full gc.
243   ClassLoaderDataGraph::clear_claimed_marks();
244 
245   // Prepare the bitmap for the next (potentially concurrent) marking.
246   _heap->concurrent_mark()->clear_bitmap(_heap->workers());
247 
248   _heap->prepare_for_mutator_after_full_collection();
249 
250   _heap->resize_all_tlabs();
251 
252   _heap->policy()->record_full_collection_end();
253   _heap->gc_epilogue(true);
254 
255   _heap->verify_after_full_collection();
256 
257   _heap->print_heap_after_full_collection();
258 }
259 
260 void G1FullCollector::before_marking_update_attribute_table(HeapRegion* hr) {
261   if (hr->is_free()) {
262     _region_attr_table.set_free(hr->hrm_index());
263   } else if (hr->is_humongous()) {
264     // Humongous objects will never be moved in the "main" compaction phase, but
265     // afterwards in a special phase if needed.
266     _region_attr_table.set_skip_compacting(hr->hrm_index());
267   } else {
268     // Everything else should be compacted.
269     _region_attr_table.set_compacting(hr->hrm_index());
270   }
271 }
272 
273 class G1FullGCRefProcProxyTask : public RefProcProxyTask {
274   G1FullCollector& _collector;
275 
276 public:
277   G1FullGCRefProcProxyTask(G1FullCollector &collector, uint max_workers)
278     : RefProcProxyTask("G1FullGCRefProcProxyTask", max_workers),
279       _collector(collector) {}
280 
281   void work(uint worker_id) override {
282     assert(worker_id < _max_workers, "sanity");
283     G1IsAliveClosure is_alive(&_collector);
284     uint index = (_tm == RefProcThreadModel::Single) ? 0 : worker_id;
285     G1FullKeepAliveClosure keep_alive(_collector.marker(index));
286     BarrierEnqueueDiscoveredFieldClosure enqueue;
287     G1FollowStackClosure* complete_gc = _collector.marker(index)->stack_closure();
288     _rp_task->rp_work(worker_id, &is_alive, &keep_alive, &enqueue, complete_gc);
289   }
290 };
291 
292 void G1FullCollector::phase1_mark_live_objects() {
293   // Recursively traverse all live objects and mark them.
294   GCTraceTime(Info, gc, phases) info("Phase 1: Mark live objects", scope()->timer());
295 
296   {
297     // Do the actual marking.
298     G1FullGCMarkTask marking_task(this);
299     run_task(&marking_task);
300   }
301 
302   {
303     uint old_active_mt_degree = reference_processor()->num_queues();
304     reference_processor()->set_active_mt_degree(workers());
305     GCTraceTime(Debug, gc, phases) debug("Phase 1: Reference Processing", scope()->timer());
306     // Process reference objects found during marking.
307     ReferenceProcessorPhaseTimes pt(scope()->timer(), reference_processor()->max_num_queues());
308     G1FullGCRefProcProxyTask task(*this, reference_processor()->max_num_queues());
309     const ReferenceProcessorStats& stats = reference_processor()->process_discovered_references(task, pt);
310     scope()->tracer()->report_gc_reference_stats(stats);
311     pt.print_all_references();
312     assert(marker(0)->oop_stack()->is_empty(), "Should be no oops on the stack");
313 
314     reference_processor()->set_active_mt_degree(old_active_mt_degree);
315   }
316 
317   // Weak oops cleanup.
318   {
319     GCTraceTime(Debug, gc, phases) debug("Phase 1: Weak Processing", scope()->timer());
320     WeakProcessor::weak_oops_do(_heap->workers(), &_is_alive, &do_nothing_cl, 1);
321   }
322 
323   // Class unloading and cleanup.
324   if (ClassUnloading) {
325     GCTraceTime(Debug, gc, phases) debug("Phase 1: Class Unloading and Cleanup", scope()->timer());
326     CodeCache::UnloadingScope unloading_scope(&_is_alive);
327     // Unload classes and purge the SystemDictionary.
328     bool purged_class = SystemDictionary::do_unloading(scope()->timer());
329     _heap->complete_cleaning(purged_class);
330   }
331 
332   {
333     GCTraceTime(Debug, gc, phases) debug("Report Object Count", scope()->timer());
334     scope()->tracer()->report_object_count_after_gc(&_is_alive, _heap->workers());
335   }
336 #if TASKQUEUE_STATS
337   oop_queue_set()->print_and_reset_taskqueue_stats("Oop Queue");
338   array_queue_set()->print_and_reset_taskqueue_stats("ObjArrayOop Queue");
339 #endif
340 }
341 
342 void G1FullCollector::phase2_prepare_compaction() {
343   GCTraceTime(Info, gc, phases) info("Phase 2: Prepare compaction", scope()->timer());
344 
345   phase2a_determine_worklists();
346 
347   if (!has_compaction_targets()) {
348     return;
349   }
350 
351   bool has_free_compaction_targets = phase2b_forward_oops();
352 
353   // Try to avoid OOM immediately after Full GC in case there are no free regions
354   // left after determining the result locations (i.e. this phase). Prepare to
355   // maximally compact the tail regions of the compaction queues serially.
356   if (scope()->do_maximal_compaction() || !has_free_compaction_targets) {
357     phase2c_prepare_serial_compaction();
358 
359     if (scope()->do_maximal_compaction() &&
360         has_humongous() &&
361         serial_compaction_point()->has_regions()) {
362       phase2d_prepare_humongous_compaction();
363     }
364   }
365 }
366 
367 void G1FullCollector::phase2a_determine_worklists() {
368   GCTraceTime(Debug, gc, phases) debug("Phase 2: Determine work lists", scope()->timer());
369 
370   G1DetermineCompactionQueueClosure cl(this);
371   _heap->heap_region_iterate(&cl);
372 }
373 
374 bool G1FullCollector::phase2b_forward_oops() {
375   GCTraceTime(Debug, gc, phases) debug("Phase 2: Prepare parallel compaction", scope()->timer());
376 
377   G1FullGCPrepareTask task(this);
378   run_task(&task);
379 
380   return task.has_free_compaction_targets();
381 }
382 
383 uint G1FullCollector::truncate_parallel_cps() {
384   uint lowest_current = UINT_MAX;
385   for (uint i = 0; i < workers(); i++) {
386     G1FullGCCompactionPoint* cp = compaction_point(i);
387     if (cp->has_regions()) {
388       lowest_current = MIN2(lowest_current, cp->current_region()->hrm_index());
389     }
390   }
391 
392   for (uint i = 0; i < workers(); i++) {
393     G1FullGCCompactionPoint* cp = compaction_point(i);
394     if (cp->has_regions()) {
395       cp->remove_at_or_above(lowest_current);
396     }
397   }
398   return lowest_current;
399 }
400 
401 void G1FullCollector::phase2c_prepare_serial_compaction() {
402   GCTraceTime(Debug, gc, phases) debug("Phase 2: Prepare serial compaction", scope()->timer());
403   // At this point, we know that after parallel compaction there will be regions that
404   // are partially compacted into. Thus, the last compaction region of all
405   // compaction queues still have space in them. We try to re-compact these regions
406   // in serial to avoid a premature OOM when the mutator wants to allocate the first
407   // eden region after gc.
408 
409   // For maximum compaction, we need to re-prepare all objects above the lowest
410   // region among the current regions for all thread compaction points. It may
411   // happen that due to the uneven distribution of objects to parallel threads, holes
412   // have been created as threads compact to different target regions between the
413   // lowest and the highest region in the tails of the compaction points.
414 
415   uint start_serial = truncate_parallel_cps();
416   assert(start_serial < _heap->max_reserved_regions(), "Called on empty parallel compaction queues");
417 
418   G1FullGCCompactionPoint* serial_cp = serial_compaction_point();
419   assert(!serial_cp->is_initialized(), "sanity!");
420 
421   HeapRegion* start_hr = _heap->region_at(start_serial);
422   serial_cp->add(start_hr);
423   serial_cp->initialize(start_hr);
424 
425   HeapWord* dense_prefix_top = compaction_top(start_hr);
426   G1SerialRePrepareClosure re_prepare(serial_cp, dense_prefix_top);
427 
428   for (uint i = start_serial + 1; i < _heap->max_reserved_regions(); i++) {
429     if (is_compaction_target(i)) {
430       HeapRegion* current = _heap->region_at(i);
431       set_compaction_top(current, current->bottom());
432       serial_cp->add(current);
433       current->apply_to_marked_objects(mark_bitmap(), &re_prepare);
434     }
435   }
436   serial_cp->update();
437 }
438 
439 void G1FullCollector::phase2d_prepare_humongous_compaction() {
440   GCTraceTime(Debug, gc, phases) debug("Phase 2: Prepare humongous compaction", scope()->timer());
441   G1FullGCCompactionPoint* serial_cp = serial_compaction_point();
442   assert(serial_cp->has_regions(), "Sanity!" );
443 
444   uint last_serial_target = serial_cp->current_region()->hrm_index();
445   uint region_index = last_serial_target + 1;
446   uint max_reserved_regions = _heap->max_reserved_regions();
447 
448   G1FullGCCompactionPoint* humongous_cp = humongous_compaction_point();
449 
450   while (region_index < max_reserved_regions) {
451     HeapRegion* hr = _heap->region_at_or_null(region_index);
452 
453     if (hr == nullptr) {
454       region_index++;
455       continue;
456     } else if (hr->is_starts_humongous()) {
457       uint num_regions = humongous_cp->forward_humongous(hr);
458       region_index += num_regions; // Skip over the continues humongous regions.
459       continue;
460     } else if (is_compaction_target(region_index)) {
461       // Add the region to the humongous compaction point.
462       humongous_cp->add(hr);
463     }
464     region_index++;
465   }
466 }
467 
468 void G1FullCollector::phase3_adjust_pointers() {
469   // Adjust the pointers to reflect the new locations
470   GCTraceTime(Info, gc, phases) info("Phase 3: Adjust pointers", scope()->timer());
471 
472   G1FullGCAdjustTask task(this);
473   run_task(&task);
474 }
475 
476 void G1FullCollector::phase4_do_compaction() {
477   // Compact the heap using the compaction queues created in phase 2.
478   GCTraceTime(Info, gc, phases) info("Phase 4: Compact heap", scope()->timer());
479   G1FullGCCompactTask task(this);
480   run_task(&task);
481 
482   // Serial compact to avoid OOM when very few free regions.
483   if (serial_compaction_point()->has_regions()) {
484     task.serial_compaction();
485   }
486 
487   if (!_humongous_compaction_regions.is_empty()) {
488     assert(scope()->do_maximal_compaction(), "Only compact humongous during maximal compaction");
489     task.humongous_compaction();
490   }
491 }
492 
493 void G1FullCollector::phase5_reset_metadata() {
494   // Clear region metadata that is invalid after GC for all regions.
495   GCTraceTime(Info, gc, phases) info("Phase 5: Reset Metadata", scope()->timer());
496   G1FullGCResetMetadataTask task(this);
497   run_task(&task);
498 }
499 
500 void G1FullCollector::restore_marks() {
501   _preserved_marks_set.restore(_heap->workers());
502   _preserved_marks_set.reclaim();
503 }
504 
505 void G1FullCollector::run_task(WorkerTask* task) {
506   _heap->workers()->run_task(task, _num_workers);
507 }
508 
509 void G1FullCollector::verify_after_marking() {
510   if (!VerifyDuringGC || !_heap->verifier()->should_verify(G1HeapVerifier::G1VerifyFull)) {
511     // Only do verification if VerifyDuringGC and G1VerifyFull is set.
512     return;
513   }
514 
515 #if COMPILER2_OR_JVMCI
516   DerivedPointerTableDeactivate dpt_deact;
517 #endif
518   _heap->prepare_for_verify();
519   // Note: we can verify only the heap here. When an object is
520   // marked, the previous value of the mark word (including
521   // identity hash values, ages, etc) is preserved, and the mark
522   // word is set to markWord::marked_value - effectively removing
523   // any hash values from the mark word. These hash values are
524   // used when verifying the dictionaries and so removing them
525   // from the mark word can make verification of the dictionaries
526   // fail. At the end of the GC, the original mark word values
527   // (including hash values) are restored to the appropriate
528   // objects.
529   GCTraceTime(Info, gc, verify) tm("Verifying During GC (full)");
530   _heap->verify(VerifyOption::G1UseFullMarking);
531 }