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24 
25 #include "precompiled.hpp"
26 #include "code/codeCache.hpp"
27 #include "gc/g1/g1CollectedHeap.hpp"
28 #include "gc/g1/g1FullCollector.hpp"
29 #include "gc/g1/g1FullGCAdjustTask.hpp"
30 #include "gc/g1/g1FullGCCompactTask.hpp"
31 #include "gc/g1/g1FullGCMarker.inline.hpp"
32 #include "gc/g1/g1FullGCMarkTask.hpp"
33 #include "gc/g1/g1FullGCPrepareTask.hpp"
34 #include "gc/g1/g1FullGCReferenceProcessorExecutor.hpp"
35 #include "gc/g1/g1FullGCScope.hpp"
36 #include "gc/g1/g1OopClosures.hpp"
37 #include "gc/g1/g1Policy.hpp"
38 #include "gc/g1/g1StringDedup.hpp"
39 #include "gc/shared/gcTraceTime.inline.hpp"
40 #include "gc/shared/preservedMarks.hpp"
41 #include "gc/shared/referenceProcessor.hpp"
42 #include "gc/shared/verifyOption.hpp"
43 #include "gc/shared/weakProcessor.inline.hpp"
44 #include "gc/shared/workerPolicy.hpp"
45 #include "logging/log.hpp"
46 #include "runtime/biasedLocking.hpp"
47 #include "runtime/handles.inline.hpp"
48 #include "utilities/debug.hpp"
49 
clear_and_activate_derived_pointers()50 static void clear_and_activate_derived_pointers() {
51 #if COMPILER2_OR_JVMCI
52   DerivedPointerTable::clear();
53 #endif
54 }
55 
deactivate_derived_pointers()56 static void deactivate_derived_pointers() {
57 #if COMPILER2_OR_JVMCI
58   DerivedPointerTable::set_active(false);
59 #endif
60 }
61 
update_derived_pointers()62 static void update_derived_pointers() {
63 #if COMPILER2_OR_JVMCI
64   DerivedPointerTable::update_pointers();
65 #endif
66 }
67 
mark_bitmap()68 G1CMBitMap* G1FullCollector::mark_bitmap() {
69   return _heap->concurrent_mark()->next_mark_bitmap();
70 }
71 
reference_processor()72 ReferenceProcessor* G1FullCollector::reference_processor() {
73   return _heap->ref_processor_stw();
74 }
75 
calc_active_workers()76 uint G1FullCollector::calc_active_workers() {
77   G1CollectedHeap* heap = G1CollectedHeap::heap();
78   uint max_worker_count = heap->workers()->total_workers();
79   // Only calculate number of workers if UseDynamicNumberOfGCThreads
80   // is enabled, otherwise use max.
81   if (!UseDynamicNumberOfGCThreads) {
82     return max_worker_count;
83   }
84 
85   // Consider G1HeapWastePercent to decide max number of workers. Each worker
86   // will in average cause half a region waste.
87   uint max_wasted_regions_allowed = ((heap->num_regions() * G1HeapWastePercent) / 100);
88   uint waste_worker_count = MAX2((max_wasted_regions_allowed * 2) , 1u);
89   uint heap_waste_worker_limit = MIN2(waste_worker_count, max_worker_count);
90 
91   // Also consider HeapSizePerGCThread by calling WorkerPolicy to calculate
92   // the number of workers.
93   uint current_active_workers = heap->workers()->active_workers();
94   uint active_worker_limit = WorkerPolicy::calc_active_workers(max_worker_count, current_active_workers, 0);
95 
96   // Update active workers to the lower of the limits.
97   uint worker_count = MIN2(heap_waste_worker_limit, active_worker_limit);
98   log_debug(gc, task)("Requesting %u active workers for full compaction (waste limited workers: %u, adaptive workers: %u)",
99                       worker_count, heap_waste_worker_limit, active_worker_limit);
100   worker_count = heap->workers()->update_active_workers(worker_count);
101   log_info(gc, task)("Using %u workers of %u for full compaction", worker_count, max_worker_count);
102 
103   return worker_count;
104 }
105 
G1FullCollector(G1CollectedHeap * heap,bool explicit_gc,bool clear_soft_refs)106 G1FullCollector::G1FullCollector(G1CollectedHeap* heap, bool explicit_gc, bool clear_soft_refs) :
107     _heap(heap),
108     _scope(heap->g1mm(), explicit_gc, clear_soft_refs),
109     _num_workers(calc_active_workers()),
110     _oop_queue_set(_num_workers),
111     _array_queue_set(_num_workers),
112     _preserved_marks_set(true),
113     _serial_compaction_point(),
114     _is_alive(heap->concurrent_mark()->next_mark_bitmap()),
115     _is_alive_mutator(heap->ref_processor_stw(), &_is_alive),
116     _always_subject_to_discovery(),
117     _is_subject_mutator(heap->ref_processor_stw(), &_always_subject_to_discovery) {
118   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
119 
120   _preserved_marks_set.init(_num_workers);
121   _markers = NEW_C_HEAP_ARRAY(G1FullGCMarker*, _num_workers, mtGC);
122   _compaction_points = NEW_C_HEAP_ARRAY(G1FullGCCompactionPoint*, _num_workers, mtGC);
123   for (uint i = 0; i < _num_workers; i++) {
124     _markers[i] = new G1FullGCMarker(i, _preserved_marks_set.get(i), mark_bitmap());
125     _compaction_points[i] = new G1FullGCCompactionPoint();
126     _oop_queue_set.register_queue(i, marker(i)->oop_stack());
127     _array_queue_set.register_queue(i, marker(i)->objarray_stack());
128   }
129 }
130 
~G1FullCollector()131 G1FullCollector::~G1FullCollector() {
132   for (uint i = 0; i < _num_workers; i++) {
133     delete _markers[i];
134     delete _compaction_points[i];
135   }
136   FREE_C_HEAP_ARRAY(G1FullGCMarker*, _markers);
137   FREE_C_HEAP_ARRAY(G1FullGCCompactionPoint*, _compaction_points);
138 }
139 
prepare_collection()140 void G1FullCollector::prepare_collection() {
141   _heap->policy()->record_full_collection_start();
142 
143   _heap->print_heap_before_gc();
144   _heap->print_heap_regions();
145 
146   _heap->abort_concurrent_cycle();
147   _heap->verify_before_full_collection(scope()->is_explicit_gc());
148 
149   _heap->gc_prologue(true);
150   _heap->prepare_heap_for_full_collection();
151 
152   reference_processor()->enable_discovery();
153   reference_processor()->setup_policy(scope()->should_clear_soft_refs());
154 
155   // We should save the marks of the currently locked biased monitors.
156   // The marking doesn't preserve the marks of biased objects.
157   BiasedLocking::preserve_marks();
158 
159   // Clear and activate derived pointer collection.
160   clear_and_activate_derived_pointers();
161 }
162 
collect()163 void G1FullCollector::collect() {
164   phase1_mark_live_objects();
165   verify_after_marking();
166 
167   // Don't add any more derived pointers during later phases
168   deactivate_derived_pointers();
169 
170   phase2_prepare_compaction();
171 
172   phase3_adjust_pointers();
173 
174   phase4_do_compaction();
175 }
176 
complete_collection()177 void G1FullCollector::complete_collection() {
178   // Restore all marks.
179   restore_marks();
180 
181   // When the pointers have been adjusted and moved, we can
182   // update the derived pointer table.
183   update_derived_pointers();
184 
185   BiasedLocking::restore_marks();
186 
187   _heap->prepare_heap_for_mutators();
188 
189   _heap->policy()->record_full_collection_end();
190   _heap->gc_epilogue(true);
191 
192   _heap->verify_after_full_collection();
193 
194   _heap->print_heap_after_full_collection(scope()->heap_transition());
195 }
196 
phase1_mark_live_objects()197 void G1FullCollector::phase1_mark_live_objects() {
198   // Recursively traverse all live objects and mark them.
199   GCTraceTime(Info, gc, phases) info("Phase 1: Mark live objects", scope()->timer());
200 
201   {
202     // Do the actual marking.
203     G1FullGCMarkTask marking_task(this);
204     run_task(&marking_task);
205   }
206 
207   {
208     // Process references discovered during marking.
209     G1FullGCReferenceProcessingExecutor reference_processing(this);
210     reference_processing.execute(scope()->timer(), scope()->tracer());
211   }
212 
213   // Weak oops cleanup.
214   {
215     GCTraceTime(Debug, gc, phases) debug("Phase 1: Weak Processing", scope()->timer());
216     WeakProcessor::weak_oops_do(_heap->workers(), &_is_alive, &do_nothing_cl, 1);
217   }
218 
219   // Class unloading and cleanup.
220   if (ClassUnloading) {
221     GCTraceTime(Debug, gc, phases) debug("Phase 1: Class Unloading and Cleanup", scope()->timer());
222     // Unload classes and purge the SystemDictionary.
223     bool purged_class = SystemDictionary::do_unloading(scope()->timer());
224     _heap->complete_cleaning(&_is_alive, purged_class);
225   } else if (G1StringDedup::is_enabled()) {
226     GCTraceTime(Debug, gc, phases) debug("Phase 1: String Dedup Cleanup", scope()->timer());
227     // If no class unloading just clean out string deduplication data.
228     _heap->string_dedup_cleaning(&_is_alive, NULL);
229   }
230 
231   scope()->tracer()->report_object_count_after_gc(&_is_alive);
232 }
233 
phase2_prepare_compaction()234 void G1FullCollector::phase2_prepare_compaction() {
235   GCTraceTime(Info, gc, phases) info("Phase 2: Prepare for compaction", scope()->timer());
236   G1FullGCPrepareTask task(this);
237   run_task(&task);
238 
239   // To avoid OOM when there is memory left.
240   if (!task.has_freed_regions()) {
241     task.prepare_serial_compaction();
242   }
243 }
244 
phase3_adjust_pointers()245 void G1FullCollector::phase3_adjust_pointers() {
246   // Adjust the pointers to reflect the new locations
247   GCTraceTime(Info, gc, phases) info("Phase 3: Adjust pointers", scope()->timer());
248 
249   G1FullGCAdjustTask task(this);
250   run_task(&task);
251 }
252 
phase4_do_compaction()253 void G1FullCollector::phase4_do_compaction() {
254   // Compact the heap using the compaction queues created in phase 2.
255   GCTraceTime(Info, gc, phases) info("Phase 4: Compact heap", scope()->timer());
256   G1FullGCCompactTask task(this);
257   run_task(&task);
258 
259   // Serial compact to avoid OOM when very few free regions.
260   if (serial_compaction_point()->has_regions()) {
261     task.serial_compaction();
262   }
263 }
264 
restore_marks()265 void G1FullCollector::restore_marks() {
266   _preserved_marks_set.restore(_heap->workers());
267   _preserved_marks_set.reclaim();
268 }
269 
run_task(AbstractGangTask * task)270 void G1FullCollector::run_task(AbstractGangTask* task) {
271   _heap->workers()->run_task(task, _num_workers);
272 }
273 
verify_after_marking()274 void G1FullCollector::verify_after_marking() {
275   if (!VerifyDuringGC || !_heap->verifier()->should_verify(G1HeapVerifier::G1VerifyFull)) {
276     // Only do verification if VerifyDuringGC and G1VerifyFull is set.
277     return;
278   }
279 
280   HandleMark hm;  // handle scope
281 #if COMPILER2_OR_JVMCI
282   DerivedPointerTableDeactivate dpt_deact;
283 #endif
284   _heap->prepare_for_verify();
285   // Note: we can verify only the heap here. When an object is
286   // marked, the previous value of the mark word (including
287   // identity hash values, ages, etc) is preserved, and the mark
288   // word is set to markWord::marked_value - effectively removing
289   // any hash values from the mark word. These hash values are
290   // used when verifying the dictionaries and so removing them
291   // from the mark word can make verification of the dictionaries
292   // fail. At the end of the GC, the original mark word values
293   // (including hash values) are restored to the appropriate
294   // objects.
295   GCTraceTime(Info, gc, verify) tm("Verifying During GC (full)");
296   _heap->verify(VerifyOption_G1UseFullMarking);
297 }
298