Fri, 10 Feb 2012 17:40:20 -0800
7144296: PS: Optimize nmethods processing
Summary: Prunes scavenge roots in code list every young GC, promote objects directly pointed by the code immediately
Reviewed-by: johnc, jcoomes
1 /*
2 * Copyright (c) 2002, 2012, 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.
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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).
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23 */
25 #include "precompiled.hpp"
26 #include "classfile/symbolTable.hpp"
27 #include "code/codeCache.hpp"
28 #include "gc_implementation/parallelScavenge/cardTableExtension.hpp"
29 #include "gc_implementation/parallelScavenge/gcTaskManager.hpp"
30 #include "gc_implementation/parallelScavenge/generationSizer.hpp"
31 #include "gc_implementation/parallelScavenge/parallelScavengeHeap.hpp"
32 #include "gc_implementation/parallelScavenge/psAdaptiveSizePolicy.hpp"
33 #include "gc_implementation/parallelScavenge/psMarkSweep.hpp"
34 #include "gc_implementation/parallelScavenge/psParallelCompact.hpp"
35 #include "gc_implementation/parallelScavenge/psScavenge.inline.hpp"
36 #include "gc_implementation/parallelScavenge/psTasks.hpp"
37 #include "gc_implementation/shared/isGCActiveMark.hpp"
38 #include "gc_implementation/shared/spaceDecorator.hpp"
39 #include "gc_interface/gcCause.hpp"
40 #include "memory/collectorPolicy.hpp"
41 #include "memory/gcLocker.inline.hpp"
42 #include "memory/referencePolicy.hpp"
43 #include "memory/referenceProcessor.hpp"
44 #include "memory/resourceArea.hpp"
45 #include "oops/oop.inline.hpp"
46 #include "oops/oop.psgc.inline.hpp"
47 #include "runtime/biasedLocking.hpp"
48 #include "runtime/fprofiler.hpp"
49 #include "runtime/handles.inline.hpp"
50 #include "runtime/threadCritical.hpp"
51 #include "runtime/vmThread.hpp"
52 #include "runtime/vm_operations.hpp"
53 #include "services/memoryService.hpp"
54 #include "utilities/stack.inline.hpp"
57 HeapWord* PSScavenge::_to_space_top_before_gc = NULL;
58 int PSScavenge::_consecutive_skipped_scavenges = 0;
59 ReferenceProcessor* PSScavenge::_ref_processor = NULL;
60 CardTableExtension* PSScavenge::_card_table = NULL;
61 bool PSScavenge::_survivor_overflow = false;
62 int PSScavenge::_tenuring_threshold = 0;
63 HeapWord* PSScavenge::_young_generation_boundary = NULL;
64 elapsedTimer PSScavenge::_accumulated_time;
65 Stack<markOop> PSScavenge::_preserved_mark_stack;
66 Stack<oop> PSScavenge::_preserved_oop_stack;
67 CollectorCounters* PSScavenge::_counters = NULL;
68 bool PSScavenge::_promotion_failed = false;
70 // Define before use
71 class PSIsAliveClosure: public BoolObjectClosure {
72 public:
73 void do_object(oop p) {
74 assert(false, "Do not call.");
75 }
76 bool do_object_b(oop p) {
77 return (!PSScavenge::is_obj_in_young((HeapWord*) p)) || p->is_forwarded();
78 }
79 };
81 PSIsAliveClosure PSScavenge::_is_alive_closure;
83 class PSKeepAliveClosure: public OopClosure {
84 protected:
85 MutableSpace* _to_space;
86 PSPromotionManager* _promotion_manager;
88 public:
89 PSKeepAliveClosure(PSPromotionManager* pm) : _promotion_manager(pm) {
90 ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
91 assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
92 _to_space = heap->young_gen()->to_space();
94 assert(_promotion_manager != NULL, "Sanity");
95 }
97 template <class T> void do_oop_work(T* p) {
98 assert (!oopDesc::is_null(*p), "expected non-null ref");
99 assert ((oopDesc::load_decode_heap_oop_not_null(p))->is_oop(),
100 "expected an oop while scanning weak refs");
102 // Weak refs may be visited more than once.
103 if (PSScavenge::should_scavenge(p, _to_space)) {
104 PSScavenge::copy_and_push_safe_barrier<T, /*promote_immediately=*/false>(_promotion_manager, p);
105 }
106 }
107 virtual void do_oop(oop* p) { PSKeepAliveClosure::do_oop_work(p); }
108 virtual void do_oop(narrowOop* p) { PSKeepAliveClosure::do_oop_work(p); }
109 };
111 class PSEvacuateFollowersClosure: public VoidClosure {
112 private:
113 PSPromotionManager* _promotion_manager;
114 public:
115 PSEvacuateFollowersClosure(PSPromotionManager* pm) : _promotion_manager(pm) {}
117 virtual void do_void() {
118 assert(_promotion_manager != NULL, "Sanity");
119 _promotion_manager->drain_stacks(true);
120 guarantee(_promotion_manager->stacks_empty(),
121 "stacks should be empty at this point");
122 }
123 };
125 class PSPromotionFailedClosure : public ObjectClosure {
126 virtual void do_object(oop obj) {
127 if (obj->is_forwarded()) {
128 obj->init_mark();
129 }
130 }
131 };
133 class PSRefProcTaskProxy: public GCTask {
134 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
135 ProcessTask & _rp_task;
136 uint _work_id;
137 public:
138 PSRefProcTaskProxy(ProcessTask & rp_task, uint work_id)
139 : _rp_task(rp_task),
140 _work_id(work_id)
141 { }
143 private:
144 virtual char* name() { return (char *)"Process referents by policy in parallel"; }
145 virtual void do_it(GCTaskManager* manager, uint which);
146 };
148 void PSRefProcTaskProxy::do_it(GCTaskManager* manager, uint which)
149 {
150 PSPromotionManager* promotion_manager =
151 PSPromotionManager::gc_thread_promotion_manager(which);
152 assert(promotion_manager != NULL, "sanity check");
153 PSKeepAliveClosure keep_alive(promotion_manager);
154 PSEvacuateFollowersClosure evac_followers(promotion_manager);
155 PSIsAliveClosure is_alive;
156 _rp_task.work(_work_id, is_alive, keep_alive, evac_followers);
157 }
159 class PSRefEnqueueTaskProxy: public GCTask {
160 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
161 EnqueueTask& _enq_task;
162 uint _work_id;
164 public:
165 PSRefEnqueueTaskProxy(EnqueueTask& enq_task, uint work_id)
166 : _enq_task(enq_task),
167 _work_id(work_id)
168 { }
170 virtual char* name() { return (char *)"Enqueue reference objects in parallel"; }
171 virtual void do_it(GCTaskManager* manager, uint which)
172 {
173 _enq_task.work(_work_id);
174 }
175 };
177 class PSRefProcTaskExecutor: public AbstractRefProcTaskExecutor {
178 virtual void execute(ProcessTask& task);
179 virtual void execute(EnqueueTask& task);
180 };
182 void PSRefProcTaskExecutor::execute(ProcessTask& task)
183 {
184 GCTaskQueue* q = GCTaskQueue::create();
185 GCTaskManager* manager = ParallelScavengeHeap::gc_task_manager();
186 for(uint i=0; i < manager->active_workers(); i++) {
187 q->enqueue(new PSRefProcTaskProxy(task, i));
188 }
189 ParallelTaskTerminator terminator(manager->active_workers(),
190 (TaskQueueSetSuper*) PSPromotionManager::stack_array_depth());
191 if (task.marks_oops_alive() && manager->active_workers() > 1) {
192 for (uint j = 0; j < manager->active_workers(); j++) {
193 q->enqueue(new StealTask(&terminator));
194 }
195 }
196 manager->execute_and_wait(q);
197 }
200 void PSRefProcTaskExecutor::execute(EnqueueTask& task)
201 {
202 GCTaskQueue* q = GCTaskQueue::create();
203 GCTaskManager* manager = ParallelScavengeHeap::gc_task_manager();
204 for(uint i=0; i < manager->active_workers(); i++) {
205 q->enqueue(new PSRefEnqueueTaskProxy(task, i));
206 }
207 manager->execute_and_wait(q);
208 }
210 // This method contains all heap specific policy for invoking scavenge.
211 // PSScavenge::invoke_no_policy() will do nothing but attempt to
212 // scavenge. It will not clean up after failed promotions, bail out if
213 // we've exceeded policy time limits, or any other special behavior.
214 // All such policy should be placed here.
215 //
216 // Note that this method should only be called from the vm_thread while
217 // at a safepoint!
218 void PSScavenge::invoke() {
219 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
220 assert(Thread::current() == (Thread*)VMThread::vm_thread(), "should be in vm thread");
221 assert(!Universe::heap()->is_gc_active(), "not reentrant");
223 ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
224 assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
226 PSAdaptiveSizePolicy* policy = heap->size_policy();
227 IsGCActiveMark mark;
229 bool scavenge_was_done = PSScavenge::invoke_no_policy();
231 PSGCAdaptivePolicyCounters* counters = heap->gc_policy_counters();
232 if (UsePerfData)
233 counters->update_full_follows_scavenge(0);
234 if (!scavenge_was_done ||
235 policy->should_full_GC(heap->old_gen()->free_in_bytes())) {
236 if (UsePerfData)
237 counters->update_full_follows_scavenge(full_follows_scavenge);
238 GCCauseSetter gccs(heap, GCCause::_adaptive_size_policy);
239 CollectorPolicy* cp = heap->collector_policy();
240 const bool clear_all_softrefs = cp->should_clear_all_soft_refs();
242 if (UseParallelOldGC) {
243 PSParallelCompact::invoke_no_policy(clear_all_softrefs);
244 } else {
245 PSMarkSweep::invoke_no_policy(clear_all_softrefs);
246 }
247 }
248 }
250 // This method contains no policy. You should probably
251 // be calling invoke() instead.
252 bool PSScavenge::invoke_no_policy() {
253 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
254 assert(Thread::current() == (Thread*)VMThread::vm_thread(), "should be in vm thread");
256 assert(_preserved_mark_stack.is_empty(), "should be empty");
257 assert(_preserved_oop_stack.is_empty(), "should be empty");
259 TimeStamp scavenge_entry;
260 TimeStamp scavenge_midpoint;
261 TimeStamp scavenge_exit;
263 scavenge_entry.update();
265 if (GC_locker::check_active_before_gc()) {
266 return false;
267 }
269 ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
270 GCCause::Cause gc_cause = heap->gc_cause();
271 assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
273 // Check for potential problems.
274 if (!should_attempt_scavenge()) {
275 return false;
276 }
278 bool promotion_failure_occurred = false;
280 PSYoungGen* young_gen = heap->young_gen();
281 PSOldGen* old_gen = heap->old_gen();
282 PSPermGen* perm_gen = heap->perm_gen();
283 PSAdaptiveSizePolicy* size_policy = heap->size_policy();
284 heap->increment_total_collections();
286 AdaptiveSizePolicyOutput(size_policy, heap->total_collections());
288 if ((gc_cause != GCCause::_java_lang_system_gc) ||
289 UseAdaptiveSizePolicyWithSystemGC) {
290 // Gather the feedback data for eden occupancy.
291 young_gen->eden_space()->accumulate_statistics();
292 }
294 if (ZapUnusedHeapArea) {
295 // Save information needed to minimize mangling
296 heap->record_gen_tops_before_GC();
297 }
299 heap->print_heap_before_gc();
301 assert(!NeverTenure || _tenuring_threshold == markOopDesc::max_age + 1, "Sanity");
302 assert(!AlwaysTenure || _tenuring_threshold == 0, "Sanity");
304 size_t prev_used = heap->used();
305 assert(promotion_failed() == false, "Sanity");
307 // Fill in TLABs
308 heap->accumulate_statistics_all_tlabs();
309 heap->ensure_parsability(true); // retire TLABs
311 if (VerifyBeforeGC && heap->total_collections() >= VerifyGCStartAt) {
312 HandleMark hm; // Discard invalid handles created during verification
313 gclog_or_tty->print(" VerifyBeforeGC:");
314 Universe::verify(true);
315 }
317 {
318 ResourceMark rm;
319 HandleMark hm;
321 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
322 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
323 TraceTime t1("GC", PrintGC, !PrintGCDetails, gclog_or_tty);
324 TraceCollectorStats tcs(counters());
325 TraceMemoryManagerStats tms(false /* not full GC */,gc_cause);
327 if (TraceGen0Time) accumulated_time()->start();
329 // Let the size policy know we're starting
330 size_policy->minor_collection_begin();
332 // Verify the object start arrays.
333 if (VerifyObjectStartArray &&
334 VerifyBeforeGC) {
335 old_gen->verify_object_start_array();
336 perm_gen->verify_object_start_array();
337 }
339 // Verify no unmarked old->young roots
340 if (VerifyRememberedSets) {
341 CardTableExtension::verify_all_young_refs_imprecise();
342 }
344 if (!ScavengeWithObjectsInToSpace) {
345 assert(young_gen->to_space()->is_empty(),
346 "Attempt to scavenge with live objects in to_space");
347 young_gen->to_space()->clear(SpaceDecorator::Mangle);
348 } else if (ZapUnusedHeapArea) {
349 young_gen->to_space()->mangle_unused_area();
350 }
351 save_to_space_top_before_gc();
353 COMPILER2_PRESENT(DerivedPointerTable::clear());
355 reference_processor()->enable_discovery(true /*verify_disabled*/, true /*verify_no_refs*/);
356 reference_processor()->setup_policy(false);
358 // We track how much was promoted to the next generation for
359 // the AdaptiveSizePolicy.
360 size_t old_gen_used_before = old_gen->used_in_bytes();
362 // For PrintGCDetails
363 size_t young_gen_used_before = young_gen->used_in_bytes();
365 // Reset our survivor overflow.
366 set_survivor_overflow(false);
368 // We need to save the old/perm top values before
369 // creating the promotion_manager. We pass the top
370 // values to the card_table, to prevent it from
371 // straying into the promotion labs.
372 HeapWord* old_top = old_gen->object_space()->top();
373 HeapWord* perm_top = perm_gen->object_space()->top();
375 // Release all previously held resources
376 gc_task_manager()->release_all_resources();
378 // Set the number of GC threads to be used in this collection
379 gc_task_manager()->set_active_gang();
380 gc_task_manager()->task_idle_workers();
381 // Get the active number of workers here and use that value
382 // throughout the methods.
383 uint active_workers = gc_task_manager()->active_workers();
384 heap->set_par_threads(active_workers);
386 PSPromotionManager::pre_scavenge();
388 // We'll use the promotion manager again later.
389 PSPromotionManager* promotion_manager = PSPromotionManager::vm_thread_promotion_manager();
390 {
391 // TraceTime("Roots");
392 ParallelScavengeHeap::ParStrongRootsScope psrs;
394 GCTaskQueue* q = GCTaskQueue::create();
396 uint stripe_total = active_workers;
397 for(uint i=0; i < stripe_total; i++) {
398 q->enqueue(new OldToYoungRootsTask(old_gen, old_top, i, stripe_total));
399 }
401 q->enqueue(new SerialOldToYoungRootsTask(perm_gen, perm_top));
403 q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::universe));
404 q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::jni_handles));
405 // We scan the thread roots in parallel
406 Threads::create_thread_roots_tasks(q);
407 q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::object_synchronizer));
408 q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::flat_profiler));
409 q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::management));
410 q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::system_dictionary));
411 q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::jvmti));
412 q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::code_cache));
414 ParallelTaskTerminator terminator(
415 active_workers,
416 (TaskQueueSetSuper*) promotion_manager->stack_array_depth());
417 if (active_workers > 1) {
418 for (uint j = 0; j < active_workers; j++) {
419 q->enqueue(new StealTask(&terminator));
420 }
421 }
423 gc_task_manager()->execute_and_wait(q);
424 }
426 scavenge_midpoint.update();
428 // Process reference objects discovered during scavenge
429 {
430 reference_processor()->setup_policy(false); // not always_clear
431 reference_processor()->set_active_mt_degree(active_workers);
432 PSKeepAliveClosure keep_alive(promotion_manager);
433 PSEvacuateFollowersClosure evac_followers(promotion_manager);
434 if (reference_processor()->processing_is_mt()) {
435 PSRefProcTaskExecutor task_executor;
436 reference_processor()->process_discovered_references(
437 &_is_alive_closure, &keep_alive, &evac_followers, &task_executor);
438 } else {
439 reference_processor()->process_discovered_references(
440 &_is_alive_closure, &keep_alive, &evac_followers, NULL);
441 }
442 }
444 // Enqueue reference objects discovered during scavenge.
445 if (reference_processor()->processing_is_mt()) {
446 PSRefProcTaskExecutor task_executor;
447 reference_processor()->enqueue_discovered_references(&task_executor);
448 } else {
449 reference_processor()->enqueue_discovered_references(NULL);
450 }
452 if (!JavaObjectsInPerm) {
453 // Unlink any dead interned Strings
454 StringTable::unlink(&_is_alive_closure);
455 // Process the remaining live ones
456 PSScavengeRootsClosure root_closure(promotion_manager);
457 StringTable::oops_do(&root_closure);
458 }
460 // Finally, flush the promotion_manager's labs, and deallocate its stacks.
461 PSPromotionManager::post_scavenge();
463 promotion_failure_occurred = promotion_failed();
464 if (promotion_failure_occurred) {
465 clean_up_failed_promotion();
466 if (PrintGC) {
467 gclog_or_tty->print("--");
468 }
469 }
471 // Let the size policy know we're done. Note that we count promotion
472 // failure cleanup time as part of the collection (otherwise, we're
473 // implicitly saying it's mutator time).
474 size_policy->minor_collection_end(gc_cause);
476 if (!promotion_failure_occurred) {
477 // Swap the survivor spaces.
480 young_gen->eden_space()->clear(SpaceDecorator::Mangle);
481 young_gen->from_space()->clear(SpaceDecorator::Mangle);
482 young_gen->swap_spaces();
484 size_t survived = young_gen->from_space()->used_in_bytes();
485 size_t promoted = old_gen->used_in_bytes() - old_gen_used_before;
486 size_policy->update_averages(_survivor_overflow, survived, promoted);
488 // A successful scavenge should restart the GC time limit count which is
489 // for full GC's.
490 size_policy->reset_gc_overhead_limit_count();
491 if (UseAdaptiveSizePolicy) {
492 // Calculate the new survivor size and tenuring threshold
494 if (PrintAdaptiveSizePolicy) {
495 gclog_or_tty->print("AdaptiveSizeStart: ");
496 gclog_or_tty->stamp();
497 gclog_or_tty->print_cr(" collection: %d ",
498 heap->total_collections());
500 if (Verbose) {
501 gclog_or_tty->print("old_gen_capacity: %d young_gen_capacity: %d"
502 " perm_gen_capacity: %d ",
503 old_gen->capacity_in_bytes(), young_gen->capacity_in_bytes(),
504 perm_gen->capacity_in_bytes());
505 }
506 }
509 if (UsePerfData) {
510 PSGCAdaptivePolicyCounters* counters = heap->gc_policy_counters();
511 counters->update_old_eden_size(
512 size_policy->calculated_eden_size_in_bytes());
513 counters->update_old_promo_size(
514 size_policy->calculated_promo_size_in_bytes());
515 counters->update_old_capacity(old_gen->capacity_in_bytes());
516 counters->update_young_capacity(young_gen->capacity_in_bytes());
517 counters->update_survived(survived);
518 counters->update_promoted(promoted);
519 counters->update_survivor_overflowed(_survivor_overflow);
520 }
522 size_t survivor_limit =
523 size_policy->max_survivor_size(young_gen->max_size());
524 _tenuring_threshold =
525 size_policy->compute_survivor_space_size_and_threshold(
526 _survivor_overflow,
527 _tenuring_threshold,
528 survivor_limit);
530 if (PrintTenuringDistribution) {
531 gclog_or_tty->cr();
532 gclog_or_tty->print_cr("Desired survivor size %ld bytes, new threshold %d (max %d)",
533 size_policy->calculated_survivor_size_in_bytes(),
534 _tenuring_threshold, MaxTenuringThreshold);
535 }
537 if (UsePerfData) {
538 PSGCAdaptivePolicyCounters* counters = heap->gc_policy_counters();
539 counters->update_tenuring_threshold(_tenuring_threshold);
540 counters->update_survivor_size_counters();
541 }
543 // Do call at minor collections?
544 // Don't check if the size_policy is ready at this
545 // level. Let the size_policy check that internally.
546 if (UseAdaptiveSizePolicy &&
547 UseAdaptiveGenerationSizePolicyAtMinorCollection &&
548 ((gc_cause != GCCause::_java_lang_system_gc) ||
549 UseAdaptiveSizePolicyWithSystemGC)) {
551 // Calculate optimial free space amounts
552 assert(young_gen->max_size() >
553 young_gen->from_space()->capacity_in_bytes() +
554 young_gen->to_space()->capacity_in_bytes(),
555 "Sizes of space in young gen are out-of-bounds");
556 size_t max_eden_size = young_gen->max_size() -
557 young_gen->from_space()->capacity_in_bytes() -
558 young_gen->to_space()->capacity_in_bytes();
559 size_policy->compute_generation_free_space(young_gen->used_in_bytes(),
560 young_gen->eden_space()->used_in_bytes(),
561 old_gen->used_in_bytes(),
562 perm_gen->used_in_bytes(),
563 young_gen->eden_space()->capacity_in_bytes(),
564 old_gen->max_gen_size(),
565 max_eden_size,
566 false /* full gc*/,
567 gc_cause,
568 heap->collector_policy());
570 }
571 // Resize the young generation at every collection
572 // even if new sizes have not been calculated. This is
573 // to allow resizes that may have been inhibited by the
574 // relative location of the "to" and "from" spaces.
576 // Resizing the old gen at minor collects can cause increases
577 // that don't feed back to the generation sizing policy until
578 // a major collection. Don't resize the old gen here.
580 heap->resize_young_gen(size_policy->calculated_eden_size_in_bytes(),
581 size_policy->calculated_survivor_size_in_bytes());
583 if (PrintAdaptiveSizePolicy) {
584 gclog_or_tty->print_cr("AdaptiveSizeStop: collection: %d ",
585 heap->total_collections());
586 }
587 }
589 // Update the structure of the eden. With NUMA-eden CPU hotplugging or offlining can
590 // cause the change of the heap layout. Make sure eden is reshaped if that's the case.
591 // Also update() will case adaptive NUMA chunk resizing.
592 assert(young_gen->eden_space()->is_empty(), "eden space should be empty now");
593 young_gen->eden_space()->update();
595 heap->gc_policy_counters()->update_counters();
597 heap->resize_all_tlabs();
599 assert(young_gen->to_space()->is_empty(), "to space should be empty now");
600 }
602 COMPILER2_PRESENT(DerivedPointerTable::update_pointers());
604 NOT_PRODUCT(reference_processor()->verify_no_references_recorded());
606 CodeCache::prune_scavenge_root_nmethods();
608 // Re-verify object start arrays
609 if (VerifyObjectStartArray &&
610 VerifyAfterGC) {
611 old_gen->verify_object_start_array();
612 perm_gen->verify_object_start_array();
613 }
615 // Verify all old -> young cards are now precise
616 if (VerifyRememberedSets) {
617 // Precise verification will give false positives. Until this is fixed,
618 // use imprecise verification.
619 // CardTableExtension::verify_all_young_refs_precise();
620 CardTableExtension::verify_all_young_refs_imprecise();
621 }
623 if (TraceGen0Time) accumulated_time()->stop();
625 if (PrintGC) {
626 if (PrintGCDetails) {
627 // Don't print a GC timestamp here. This is after the GC so
628 // would be confusing.
629 young_gen->print_used_change(young_gen_used_before);
630 }
631 heap->print_heap_change(prev_used);
632 }
634 // Track memory usage and detect low memory
635 MemoryService::track_memory_usage();
636 heap->update_counters();
638 gc_task_manager()->release_idle_workers();
639 }
641 if (VerifyAfterGC && heap->total_collections() >= VerifyGCStartAt) {
642 HandleMark hm; // Discard invalid handles created during verification
643 gclog_or_tty->print(" VerifyAfterGC:");
644 Universe::verify(false);
645 }
647 heap->print_heap_after_gc();
649 if (ZapUnusedHeapArea) {
650 young_gen->eden_space()->check_mangled_unused_area_complete();
651 young_gen->from_space()->check_mangled_unused_area_complete();
652 young_gen->to_space()->check_mangled_unused_area_complete();
653 }
655 scavenge_exit.update();
657 if (PrintGCTaskTimeStamps) {
658 tty->print_cr("VM-Thread " INT64_FORMAT " " INT64_FORMAT " " INT64_FORMAT,
659 scavenge_entry.ticks(), scavenge_midpoint.ticks(),
660 scavenge_exit.ticks());
661 gc_task_manager()->print_task_time_stamps();
662 }
664 #ifdef TRACESPINNING
665 ParallelTaskTerminator::print_termination_counts();
666 #endif
668 return !promotion_failure_occurred;
669 }
671 // This method iterates over all objects in the young generation,
672 // unforwarding markOops. It then restores any preserved mark oops,
673 // and clears the _preserved_mark_stack.
674 void PSScavenge::clean_up_failed_promotion() {
675 ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
676 assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
677 assert(promotion_failed(), "Sanity");
679 PSYoungGen* young_gen = heap->young_gen();
681 {
682 ResourceMark rm;
684 // Unforward all pointers in the young gen.
685 PSPromotionFailedClosure unforward_closure;
686 young_gen->object_iterate(&unforward_closure);
688 if (PrintGC && Verbose) {
689 gclog_or_tty->print_cr("Restoring %d marks", _preserved_oop_stack.size());
690 }
692 // Restore any saved marks.
693 while (!_preserved_oop_stack.is_empty()) {
694 oop obj = _preserved_oop_stack.pop();
695 markOop mark = _preserved_mark_stack.pop();
696 obj->set_mark(mark);
697 }
699 // Clear the preserved mark and oop stack caches.
700 _preserved_mark_stack.clear(true);
701 _preserved_oop_stack.clear(true);
702 _promotion_failed = false;
703 }
705 // Reset the PromotionFailureALot counters.
706 NOT_PRODUCT(Universe::heap()->reset_promotion_should_fail();)
707 }
709 // This method is called whenever an attempt to promote an object
710 // fails. Some markOops will need preservation, some will not. Note
711 // that the entire eden is traversed after a failed promotion, with
712 // all forwarded headers replaced by the default markOop. This means
713 // it is not neccessary to preserve most markOops.
714 void PSScavenge::oop_promotion_failed(oop obj, markOop obj_mark) {
715 _promotion_failed = true;
716 if (obj_mark->must_be_preserved_for_promotion_failure(obj)) {
717 // Should use per-worker private stakcs hetre rather than
718 // locking a common pair of stacks.
719 ThreadCritical tc;
720 _preserved_oop_stack.push(obj);
721 _preserved_mark_stack.push(obj_mark);
722 }
723 }
725 bool PSScavenge::should_attempt_scavenge() {
726 ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
727 assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
728 PSGCAdaptivePolicyCounters* counters = heap->gc_policy_counters();
730 if (UsePerfData) {
731 counters->update_scavenge_skipped(not_skipped);
732 }
734 PSYoungGen* young_gen = heap->young_gen();
735 PSOldGen* old_gen = heap->old_gen();
737 if (!ScavengeWithObjectsInToSpace) {
738 // Do not attempt to promote unless to_space is empty
739 if (!young_gen->to_space()->is_empty()) {
740 _consecutive_skipped_scavenges++;
741 if (UsePerfData) {
742 counters->update_scavenge_skipped(to_space_not_empty);
743 }
744 return false;
745 }
746 }
748 // Test to see if the scavenge will likely fail.
749 PSAdaptiveSizePolicy* policy = heap->size_policy();
751 // A similar test is done in the policy's should_full_GC(). If this is
752 // changed, decide if that test should also be changed.
753 size_t avg_promoted = (size_t) policy->padded_average_promoted_in_bytes();
754 size_t promotion_estimate = MIN2(avg_promoted, young_gen->used_in_bytes());
755 bool result = promotion_estimate < old_gen->free_in_bytes();
757 if (PrintGCDetails && Verbose) {
758 gclog_or_tty->print(result ? " do scavenge: " : " skip scavenge: ");
759 gclog_or_tty->print_cr(" average_promoted " SIZE_FORMAT
760 " padded_average_promoted " SIZE_FORMAT
761 " free in old gen " SIZE_FORMAT,
762 (size_t) policy->average_promoted_in_bytes(),
763 (size_t) policy->padded_average_promoted_in_bytes(),
764 old_gen->free_in_bytes());
765 if (young_gen->used_in_bytes() <
766 (size_t) policy->padded_average_promoted_in_bytes()) {
767 gclog_or_tty->print_cr(" padded_promoted_average is greater"
768 " than maximum promotion = " SIZE_FORMAT, young_gen->used_in_bytes());
769 }
770 }
772 if (result) {
773 _consecutive_skipped_scavenges = 0;
774 } else {
775 _consecutive_skipped_scavenges++;
776 if (UsePerfData) {
777 counters->update_scavenge_skipped(promoted_too_large);
778 }
779 }
780 return result;
781 }
783 // Used to add tasks
784 GCTaskManager* const PSScavenge::gc_task_manager() {
785 assert(ParallelScavengeHeap::gc_task_manager() != NULL,
786 "shouldn't return NULL");
787 return ParallelScavengeHeap::gc_task_manager();
788 }
790 void PSScavenge::initialize() {
791 // Arguments must have been parsed
793 if (AlwaysTenure) {
794 _tenuring_threshold = 0;
795 } else if (NeverTenure) {
796 _tenuring_threshold = markOopDesc::max_age + 1;
797 } else {
798 // We want to smooth out our startup times for the AdaptiveSizePolicy
799 _tenuring_threshold = (UseAdaptiveSizePolicy) ? InitialTenuringThreshold :
800 MaxTenuringThreshold;
801 }
803 ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
804 assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
806 PSYoungGen* young_gen = heap->young_gen();
807 PSOldGen* old_gen = heap->old_gen();
808 PSPermGen* perm_gen = heap->perm_gen();
810 // Set boundary between young_gen and old_gen
811 assert(perm_gen->reserved().end() <= old_gen->object_space()->bottom(),
812 "perm above old");
813 assert(old_gen->reserved().end() <= young_gen->eden_space()->bottom(),
814 "old above young");
815 _young_generation_boundary = young_gen->eden_space()->bottom();
817 // Initialize ref handling object for scavenging.
818 MemRegion mr = young_gen->reserved();
820 _ref_processor =
821 new ReferenceProcessor(mr, // span
822 ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing
823 (int) ParallelGCThreads, // mt processing degree
824 true, // mt discovery
825 (int) ParallelGCThreads, // mt discovery degree
826 true, // atomic_discovery
827 NULL, // header provides liveness info
828 false); // next field updates do not need write barrier
830 // Cache the cardtable
831 BarrierSet* bs = Universe::heap()->barrier_set();
832 assert(bs->kind() == BarrierSet::CardTableModRef, "Wrong barrier set kind");
833 _card_table = (CardTableExtension*)bs;
835 _counters = new CollectorCounters("PSScavenge", 0);
836 }