1 /*
  2  * Copyright (c) 2017, 2021, 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/systemDictionary.hpp"
 27 #include "code/codeCache.hpp"
 28 #include "compiler/oopMap.hpp"
 29 #include "gc/g1/g1CollectedHeap.hpp"
 30 #include "gc/g1/g1FullCollector.inline.hpp"
 31 #include "gc/g1/g1FullGCAdjustTask.hpp"
 32 #include "gc/g1/g1FullGCCompactTask.hpp"
 33 #include "gc/g1/g1FullGCMarker.inline.hpp"
 34 #include "gc/g1/g1FullGCMarkTask.hpp"
 35 #include "gc/g1/g1FullGCPrepareTask.hpp"
 36 #include "gc/g1/g1FullGCScope.hpp"
 37 #include "gc/g1/g1OopClosures.hpp"
 38 #include "gc/g1/g1Policy.hpp"
 39 #include "gc/g1/g1RegionMarkStatsCache.inline.hpp"
 40 #include "gc/shared/gcTraceTime.inline.hpp"
 41 #include "gc/shared/preservedMarks.hpp"
 42 #include "gc/shared/referenceProcessor.hpp"
 43 #include "gc/shared/slidingForwarding.hpp"
 44 #include "gc/shared/verifyOption.hpp"
 45 #include "gc/shared/weakProcessor.inline.hpp"
 46 #include "gc/shared/workerPolicy.hpp"
 47 #include "logging/log.hpp"
 48 #include "runtime/handles.inline.hpp"
 49 #include "utilities/debug.hpp"
 50 
 51 static void clear_and_activate_derived_pointers() {
 52 #if COMPILER2_OR_JVMCI
 53   DerivedPointerTable::clear();
 54 #endif
 55 }
 56 
 57 static void deactivate_derived_pointers() {
 58 #if COMPILER2_OR_JVMCI
 59   DerivedPointerTable::set_active(false);
 60 #endif
 61 }
 62 
 63 static void update_derived_pointers() {
 64 #if COMPILER2_OR_JVMCI
 65   DerivedPointerTable::update_pointers();
 66 #endif
 67 }
 68 
 69 G1CMBitMap* G1FullCollector::mark_bitmap() {
 70   return _heap->concurrent_mark()->next_mark_bitmap();
 71 }
 72 
 73 ReferenceProcessor* G1FullCollector::reference_processor() {
 74   return _heap->ref_processor_stw();
 75 }
 76 
 77 uint G1FullCollector::calc_active_workers() {
 78   G1CollectedHeap* heap = G1CollectedHeap::heap();
 79   uint max_worker_count = heap->workers()->max_workers();
 80   // Only calculate number of workers if UseDynamicNumberOfGCThreads
 81   // is enabled, otherwise use max.
 82   if (!UseDynamicNumberOfGCThreads) {
 83     return max_worker_count;
 84   }
 85 
 86   // Consider G1HeapWastePercent to decide max number of workers. Each worker
 87   // will in average cause half a region waste.
 88   uint max_wasted_regions_allowed = ((heap->num_regions() * G1HeapWastePercent) / 100);
 89   uint waste_worker_count = MAX2((max_wasted_regions_allowed * 2) , 1u);
 90   uint heap_waste_worker_limit = MIN2(waste_worker_count, max_worker_count);
 91 
 92   // Also consider HeapSizePerGCThread by calling WorkerPolicy to calculate
 93   // the number of workers.
 94   uint current_active_workers = heap->workers()->active_workers();
 95   uint active_worker_limit = WorkerPolicy::calc_active_workers(max_worker_count, current_active_workers, 0);
 96 
 97   // Finally consider the amount of used regions.
 98   uint used_worker_limit = heap->num_used_regions();
 99   assert(used_worker_limit > 0, "Should never have zero used regions.");
100 
101   // Update active workers to the lower of the limits.
102   uint worker_count = MIN3(heap_waste_worker_limit, active_worker_limit, used_worker_limit);
103   log_debug(gc, task)("Requesting %u active workers for full compaction (waste limited workers: %u, "
104                       "adaptive workers: %u, used limited workers: %u)",
105                       worker_count, heap_waste_worker_limit, active_worker_limit, used_worker_limit);
106   worker_count = heap->workers()->set_active_workers(worker_count);
107   log_info(gc, task)("Using %u workers of %u for full compaction", worker_count, max_worker_count);
108 
109   return worker_count;
110 }
111 
112 G1FullCollector::G1FullCollector(G1CollectedHeap* heap,
113                                  bool explicit_gc,
114                                  bool clear_soft_refs,
115                                  bool do_maximum_compaction) :
116     _heap(heap),
117     _scope(heap->monitoring_support(), explicit_gc, clear_soft_refs, do_maximum_compaction),
118     _num_workers(calc_active_workers()),
119     _oop_queue_set(_num_workers),
120     _array_queue_set(_num_workers),
121     _preserved_marks_set(true),
122     _serial_compaction_point(),
123     _is_alive(this, heap->concurrent_mark()->next_mark_bitmap()),
124     _is_alive_mutator(heap->ref_processor_stw(), &_is_alive),
125     _always_subject_to_discovery(),
126     _is_subject_mutator(heap->ref_processor_stw(), &_always_subject_to_discovery),
127     _region_attr_table() {
128   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
129 
130   _preserved_marks_set.init(_num_workers);
131   _markers = NEW_C_HEAP_ARRAY(G1FullGCMarker*, _num_workers, mtGC);
132   _compaction_points = NEW_C_HEAP_ARRAY(G1FullGCCompactionPoint*, _num_workers, mtGC);
133 
134   _live_stats = NEW_C_HEAP_ARRAY(G1RegionMarkStats, _heap->max_regions(), mtGC);
135   for (uint j = 0; j < heap->max_regions(); j++) {
136     _live_stats[j].clear();
137   }
138 
139   for (uint i = 0; i < _num_workers; i++) {
140     _markers[i] = new G1FullGCMarker(this, i, _preserved_marks_set.get(i), _live_stats);
141     _compaction_points[i] = new G1FullGCCompactionPoint();
142     _oop_queue_set.register_queue(i, marker(i)->oop_stack());
143     _array_queue_set.register_queue(i, marker(i)->objarray_stack());
144   }
145   _region_attr_table.initialize(heap->reserved(), HeapRegion::GrainBytes);
146 }
147 
148 G1FullCollector::~G1FullCollector() {
149   for (uint i = 0; i < _num_workers; i++) {
150     delete _markers[i];
151     delete _compaction_points[i];
152   }
153   FREE_C_HEAP_ARRAY(G1FullGCMarker*, _markers);
154   FREE_C_HEAP_ARRAY(G1FullGCCompactionPoint*, _compaction_points);
155   FREE_C_HEAP_ARRAY(G1RegionMarkStats, _live_stats);
156 }
157 
158 class PrepareRegionsClosure : public HeapRegionClosure {
159   G1FullCollector* _collector;
160 
161 public:
162   PrepareRegionsClosure(G1FullCollector* collector) : _collector(collector) { }
163 
164   bool do_heap_region(HeapRegion* hr) {
165     G1CollectedHeap::heap()->prepare_region_for_full_compaction(hr);
166     _collector->before_marking_update_attribute_table(hr);
167     return false;
168   }
169 };
170 
171 void G1FullCollector::prepare_collection() {
172   _heap->policy()->record_full_collection_start();
173 
174   _heap->abort_concurrent_cycle();
175   _heap->verify_before_full_collection(scope()->is_explicit_gc());
176 
177   _heap->gc_prologue(true);
178   _heap->retire_tlabs();
179   _heap->prepare_heap_for_full_collection();
180 
181   PrepareRegionsClosure cl(this);
182   _heap->heap_region_iterate(&cl);
183 
184   reference_processor()->start_discovery(scope()->should_clear_soft_refs());
185 
186   // Clear and activate derived pointer collection.
187   clear_and_activate_derived_pointers();
188 }
189 
190 void G1FullCollector::collect() {
191   phase1_mark_live_objects();
192   verify_after_marking();
193 
194   // Don't add any more derived pointers during later phases
195   deactivate_derived_pointers();
196 
197   phase2_prepare_compaction();
198 
199   phase3_adjust_pointers();
200 
201   phase4_do_compaction();
202 }
203 
204 void G1FullCollector::complete_collection() {
205   // Restore all marks.
206   restore_marks();
207 
208   // When the pointers have been adjusted and moved, we can
209   // update the derived pointer table.
210   update_derived_pointers();
211 
212   _heap->concurrent_mark()->swap_mark_bitmaps();
213   // Prepare the bitmap for the next (potentially concurrent) marking.
214   _heap->concurrent_mark()->clear_next_bitmap(_heap->workers());
215 
216   _heap->prepare_heap_for_mutators();
217 
218   _heap->resize_all_tlabs();
219 
220   _heap->policy()->record_full_collection_end();
221   _heap->gc_epilogue(true);
222 
223   _heap->verify_after_full_collection();
224 }
225 
226 void G1FullCollector::before_marking_update_attribute_table(HeapRegion* hr) {
227   if (hr->is_free()) {
228     _region_attr_table.set_free(hr->hrm_index());
229   } else if (hr->is_closed_archive()) {
230     _region_attr_table.set_skip_marking(hr->hrm_index());
231   } else if (hr->is_pinned()) {
232     _region_attr_table.set_skip_compacting(hr->hrm_index());
233   } else {
234     // Everything else should be compacted.
235     _region_attr_table.set_compacting(hr->hrm_index());
236   }
237 }
238 
239 class G1FullGCRefProcProxyTask : public RefProcProxyTask {
240   G1FullCollector& _collector;
241 
242 public:
243   G1FullGCRefProcProxyTask(G1FullCollector &collector, uint max_workers)
244     : RefProcProxyTask("G1FullGCRefProcProxyTask", max_workers),
245       _collector(collector) {}
246 
247   void work(uint worker_id) override {
248     assert(worker_id < _max_workers, "sanity");
249     G1IsAliveClosure is_alive(&_collector);
250     uint index = (_tm == RefProcThreadModel::Single) ? 0 : worker_id;
251     G1FullKeepAliveClosure keep_alive(_collector.marker(index));
252     BarrierEnqueueDiscoveredFieldClosure enqueue;
253     G1FollowStackClosure* complete_gc = _collector.marker(index)->stack_closure();
254     _rp_task->rp_work(worker_id, &is_alive, &keep_alive, &enqueue, complete_gc);
255   }
256 };
257 
258 void G1FullCollector::phase1_mark_live_objects() {
259   // Recursively traverse all live objects and mark them.
260   GCTraceTime(Info, gc, phases) info("Phase 1: Mark live objects", scope()->timer());
261 
262   {
263     // Do the actual marking.
264     G1FullGCMarkTask marking_task(this);
265     run_task(&marking_task);
266   }
267 
268   {
269     uint old_active_mt_degree = reference_processor()->num_queues();
270     reference_processor()->set_active_mt_degree(workers());
271     GCTraceTime(Debug, gc, phases) debug("Phase 1: Reference Processing", scope()->timer());
272     // Process reference objects found during marking.
273     ReferenceProcessorPhaseTimes pt(scope()->timer(), reference_processor()->max_num_queues());
274     G1FullGCRefProcProxyTask task(*this, reference_processor()->max_num_queues());
275     const ReferenceProcessorStats& stats = reference_processor()->process_discovered_references(task, pt);
276     scope()->tracer()->report_gc_reference_stats(stats);
277     pt.print_all_references();
278     assert(marker(0)->oop_stack()->is_empty(), "Should be no oops on the stack");
279 
280     reference_processor()->set_active_mt_degree(old_active_mt_degree);
281   }
282 
283   // Weak oops cleanup.
284   {
285     GCTraceTime(Debug, gc, phases) debug("Phase 1: Weak Processing", scope()->timer());
286     WeakProcessor::weak_oops_do(_heap->workers(), &_is_alive, &do_nothing_cl, 1);
287   }
288 
289   // Class unloading and cleanup.
290   if (ClassUnloading) {
291     GCTraceTime(Debug, gc, phases) debug("Phase 1: Class Unloading and Cleanup", scope()->timer());
292     // Unload classes and purge the SystemDictionary.
293     bool purged_class = SystemDictionary::do_unloading(scope()->timer());
294     _heap->complete_cleaning(&_is_alive, purged_class);
295   }
296 
297   scope()->tracer()->report_object_count_after_gc(&_is_alive);
298 }
299 
300 void G1FullCollector::phase2_prepare_compaction() {
301   GCTraceTime(Info, gc, phases) info("Phase 2: Prepare for compaction", scope()->timer());
302   _heap->forwarding()->clear();
303   G1FullGCPrepareTask task(this);
304   run_task(&task);
305 
306   // To avoid OOM when there is memory left.
307   // TODO: Disabled for now because it violates sliding-forwarding assumption.
308   // if (!task.has_freed_regions()) {
309   //   task.prepare_serial_compaction();
310   // }
311 }
312 
313 void G1FullCollector::phase3_adjust_pointers() {
314   // Adjust the pointers to reflect the new locations
315   GCTraceTime(Info, gc, phases) info("Phase 3: Adjust pointers", scope()->timer());
316 
317   G1FullGCAdjustTask task(this);
318   run_task(&task);
319 }
320 
321 void G1FullCollector::phase4_do_compaction() {
322   // Compact the heap using the compaction queues created in phase 2.
323   GCTraceTime(Info, gc, phases) info("Phase 4: Compact heap", scope()->timer());
324   G1FullGCCompactTask task(this);
325   run_task(&task);
326 
327   // Serial compact to avoid OOM when very few free regions.
328   if (serial_compaction_point()->has_regions()) {
329     task.serial_compaction();
330   }
331 }
332 
333 void G1FullCollector::restore_marks() {
334   _preserved_marks_set.restore(_heap->workers());
335   _preserved_marks_set.reclaim();
336 }
337 
338 void G1FullCollector::run_task(WorkerTask* task) {
339   _heap->workers()->run_task(task, _num_workers);
340 }
341 
342 void G1FullCollector::verify_after_marking() {
343   if (!VerifyDuringGC || !_heap->verifier()->should_verify(G1HeapVerifier::G1VerifyFull)) {
344     // Only do verification if VerifyDuringGC and G1VerifyFull is set.
345     return;
346   }
347 
348 #if COMPILER2_OR_JVMCI
349   DerivedPointerTableDeactivate dpt_deact;
350 #endif
351   _heap->prepare_for_verify();
352   // Note: we can verify only the heap here. When an object is
353   // marked, the previous value of the mark word (including
354   // identity hash values, ages, etc) is preserved, and the mark
355   // word is set to markWord::marked_value - effectively removing
356   // any hash values from the mark word. These hash values are
357   // used when verifying the dictionaries and so removing them
358   // from the mark word can make verification of the dictionaries
359   // fail. At the end of the GC, the original mark word values
360   // (including hash values) are restored to the appropriate
361   // objects.
362   GCTraceTime(Info, gc, verify) tm("Verifying During GC (full)");
363   _heap->verify(VerifyOption_G1UseFullMarking);
364 }