Tue, 09 Aug 2011 10:16:01 -0700
6593758: RFE: Enhance GC ergonomics to dynamically choose ParallelGCThreads
Summary: Select number of GC threads dynamically based on heap usage and number of Java threads
Reviewed-by: johnc, ysr, jcoomes
1 /*
2 * Copyright (c) 2002, 2011, 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 *
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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 *
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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.
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23 */
25 #include "precompiled.hpp"
26 #include "classfile/symbolTable.hpp"
27 #include "gc_implementation/parallelScavenge/cardTableExtension.hpp"
28 #include "gc_implementation/parallelScavenge/gcTaskManager.hpp"
29 #include "gc_implementation/parallelScavenge/generationSizer.hpp"
30 #include "gc_implementation/parallelScavenge/parallelScavengeHeap.hpp"
31 #include "gc_implementation/parallelScavenge/psAdaptiveSizePolicy.hpp"
32 #include "gc_implementation/parallelScavenge/psMarkSweep.hpp"
33 #include "gc_implementation/parallelScavenge/psParallelCompact.hpp"
34 #include "gc_implementation/parallelScavenge/psScavenge.inline.hpp"
35 #include "gc_implementation/parallelScavenge/psTasks.hpp"
36 #include "gc_implementation/shared/isGCActiveMark.hpp"
37 #include "gc_implementation/shared/spaceDecorator.hpp"
38 #include "gc_interface/gcCause.hpp"
39 #include "memory/collectorPolicy.hpp"
40 #include "memory/gcLocker.inline.hpp"
41 #include "memory/referencePolicy.hpp"
42 #include "memory/referenceProcessor.hpp"
43 #include "memory/resourceArea.hpp"
44 #include "oops/oop.inline.hpp"
45 #include "oops/oop.psgc.inline.hpp"
46 #include "runtime/biasedLocking.hpp"
47 #include "runtime/fprofiler.hpp"
48 #include "runtime/handles.inline.hpp"
49 #include "runtime/threadCritical.hpp"
50 #include "runtime/vmThread.hpp"
51 #include "runtime/vm_operations.hpp"
52 #include "services/memoryService.hpp"
53 #include "utilities/stack.inline.hpp"
56 HeapWord* PSScavenge::_to_space_top_before_gc = NULL;
57 int PSScavenge::_consecutive_skipped_scavenges = 0;
58 ReferenceProcessor* PSScavenge::_ref_processor = NULL;
59 CardTableExtension* PSScavenge::_card_table = NULL;
60 bool PSScavenge::_survivor_overflow = false;
61 int PSScavenge::_tenuring_threshold = 0;
62 HeapWord* PSScavenge::_young_generation_boundary = NULL;
63 elapsedTimer PSScavenge::_accumulated_time;
64 Stack<markOop> PSScavenge::_preserved_mark_stack;
65 Stack<oop> PSScavenge::_preserved_oop_stack;
66 CollectorCounters* PSScavenge::_counters = NULL;
67 bool PSScavenge::_promotion_failed = false;
69 // Define before use
70 class PSIsAliveClosure: public BoolObjectClosure {
71 public:
72 void do_object(oop p) {
73 assert(false, "Do not call.");
74 }
75 bool do_object_b(oop p) {
76 return (!PSScavenge::is_obj_in_young((HeapWord*) p)) || p->is_forwarded();
77 }
78 };
80 PSIsAliveClosure PSScavenge::_is_alive_closure;
82 class PSKeepAliveClosure: public OopClosure {
83 protected:
84 MutableSpace* _to_space;
85 PSPromotionManager* _promotion_manager;
87 public:
88 PSKeepAliveClosure(PSPromotionManager* pm) : _promotion_manager(pm) {
89 ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
90 assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
91 _to_space = heap->young_gen()->to_space();
93 assert(_promotion_manager != NULL, "Sanity");
94 }
96 template <class T> void do_oop_work(T* p) {
97 assert (!oopDesc::is_null(*p), "expected non-null ref");
98 assert ((oopDesc::load_decode_heap_oop_not_null(p))->is_oop(),
99 "expected an oop while scanning weak refs");
101 // Weak refs may be visited more than once.
102 if (PSScavenge::should_scavenge(p, _to_space)) {
103 PSScavenge::copy_and_push_safe_barrier(_promotion_manager, p);
104 }
105 }
106 virtual void do_oop(oop* p) { PSKeepAliveClosure::do_oop_work(p); }
107 virtual void do_oop(narrowOop* p) { PSKeepAliveClosure::do_oop_work(p); }
108 };
110 class PSEvacuateFollowersClosure: public VoidClosure {
111 private:
112 PSPromotionManager* _promotion_manager;
113 public:
114 PSEvacuateFollowersClosure(PSPromotionManager* pm) : _promotion_manager(pm) {}
116 virtual void do_void() {
117 assert(_promotion_manager != NULL, "Sanity");
118 _promotion_manager->drain_stacks(true);
119 guarantee(_promotion_manager->stacks_empty(),
120 "stacks should be empty at this point");
121 }
122 };
124 class PSPromotionFailedClosure : public ObjectClosure {
125 virtual void do_object(oop obj) {
126 if (obj->is_forwarded()) {
127 obj->init_mark();
128 }
129 }
130 };
132 class PSRefProcTaskProxy: public GCTask {
133 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
134 ProcessTask & _rp_task;
135 uint _work_id;
136 public:
137 PSRefProcTaskProxy(ProcessTask & rp_task, uint work_id)
138 : _rp_task(rp_task),
139 _work_id(work_id)
140 { }
142 private:
143 virtual char* name() { return (char *)"Process referents by policy in parallel"; }
144 virtual void do_it(GCTaskManager* manager, uint which);
145 };
147 void PSRefProcTaskProxy::do_it(GCTaskManager* manager, uint which)
148 {
149 PSPromotionManager* promotion_manager =
150 PSPromotionManager::gc_thread_promotion_manager(which);
151 assert(promotion_manager != NULL, "sanity check");
152 PSKeepAliveClosure keep_alive(promotion_manager);
153 PSEvacuateFollowersClosure evac_followers(promotion_manager);
154 PSIsAliveClosure is_alive;
155 _rp_task.work(_work_id, is_alive, keep_alive, evac_followers);
156 }
158 class PSRefEnqueueTaskProxy: public GCTask {
159 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
160 EnqueueTask& _enq_task;
161 uint _work_id;
163 public:
164 PSRefEnqueueTaskProxy(EnqueueTask& enq_task, uint work_id)
165 : _enq_task(enq_task),
166 _work_id(work_id)
167 { }
169 virtual char* name() { return (char *)"Enqueue reference objects in parallel"; }
170 virtual void do_it(GCTaskManager* manager, uint which)
171 {
172 _enq_task.work(_work_id);
173 }
174 };
176 class PSRefProcTaskExecutor: public AbstractRefProcTaskExecutor {
177 virtual void execute(ProcessTask& task);
178 virtual void execute(EnqueueTask& task);
179 };
181 void PSRefProcTaskExecutor::execute(ProcessTask& task)
182 {
183 GCTaskQueue* q = GCTaskQueue::create();
184 GCTaskManager* manager = ParallelScavengeHeap::gc_task_manager();
185 for(uint i=0; i < manager->active_workers(); i++) {
186 q->enqueue(new PSRefProcTaskProxy(task, i));
187 }
188 ParallelTaskTerminator terminator(manager->active_workers(),
189 (TaskQueueSetSuper*) PSPromotionManager::stack_array_depth());
190 if (task.marks_oops_alive() && manager->active_workers() > 1) {
191 for (uint j = 0; j < manager->active_workers(); j++) {
192 q->enqueue(new StealTask(&terminator));
193 }
194 }
195 manager->execute_and_wait(q);
196 }
199 void PSRefProcTaskExecutor::execute(EnqueueTask& task)
200 {
201 GCTaskQueue* q = GCTaskQueue::create();
202 GCTaskManager* manager = ParallelScavengeHeap::gc_task_manager();
203 for(uint i=0; i < manager->active_workers(); i++) {
204 q->enqueue(new PSRefEnqueueTaskProxy(task, i));
205 }
206 manager->execute_and_wait(q);
207 }
209 // This method contains all heap specific policy for invoking scavenge.
210 // PSScavenge::invoke_no_policy() will do nothing but attempt to
211 // scavenge. It will not clean up after failed promotions, bail out if
212 // we've exceeded policy time limits, or any other special behavior.
213 // All such policy should be placed here.
214 //
215 // Note that this method should only be called from the vm_thread while
216 // at a safepoint!
217 void PSScavenge::invoke() {
218 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
219 assert(Thread::current() == (Thread*)VMThread::vm_thread(), "should be in vm thread");
220 assert(!Universe::heap()->is_gc_active(), "not reentrant");
222 ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
223 assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
225 PSAdaptiveSizePolicy* policy = heap->size_policy();
226 IsGCActiveMark mark;
228 bool scavenge_was_done = PSScavenge::invoke_no_policy();
230 PSGCAdaptivePolicyCounters* counters = heap->gc_policy_counters();
231 if (UsePerfData)
232 counters->update_full_follows_scavenge(0);
233 if (!scavenge_was_done ||
234 policy->should_full_GC(heap->old_gen()->free_in_bytes())) {
235 if (UsePerfData)
236 counters->update_full_follows_scavenge(full_follows_scavenge);
237 GCCauseSetter gccs(heap, GCCause::_adaptive_size_policy);
238 CollectorPolicy* cp = heap->collector_policy();
239 const bool clear_all_softrefs = cp->should_clear_all_soft_refs();
241 if (UseParallelOldGC) {
242 PSParallelCompact::invoke_no_policy(clear_all_softrefs);
243 } else {
244 PSMarkSweep::invoke_no_policy(clear_all_softrefs);
245 }
246 }
247 }
249 // This method contains no policy. You should probably
250 // be calling invoke() instead.
251 bool PSScavenge::invoke_no_policy() {
252 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
253 assert(Thread::current() == (Thread*)VMThread::vm_thread(), "should be in vm thread");
255 assert(_preserved_mark_stack.is_empty(), "should be empty");
256 assert(_preserved_oop_stack.is_empty(), "should be empty");
258 TimeStamp scavenge_entry;
259 TimeStamp scavenge_midpoint;
260 TimeStamp scavenge_exit;
262 scavenge_entry.update();
264 if (GC_locker::check_active_before_gc()) {
265 return false;
266 }
268 ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
269 GCCause::Cause gc_cause = heap->gc_cause();
270 assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
272 // Check for potential problems.
273 if (!should_attempt_scavenge()) {
274 return false;
275 }
277 bool promotion_failure_occurred = false;
279 PSYoungGen* young_gen = heap->young_gen();
280 PSOldGen* old_gen = heap->old_gen();
281 PSPermGen* perm_gen = heap->perm_gen();
282 PSAdaptiveSizePolicy* size_policy = heap->size_policy();
283 heap->increment_total_collections();
285 AdaptiveSizePolicyOutput(size_policy, heap->total_collections());
287 if ((gc_cause != GCCause::_java_lang_system_gc) ||
288 UseAdaptiveSizePolicyWithSystemGC) {
289 // Gather the feedback data for eden occupancy.
290 young_gen->eden_space()->accumulate_statistics();
291 }
293 if (ZapUnusedHeapArea) {
294 // Save information needed to minimize mangling
295 heap->record_gen_tops_before_GC();
296 }
298 if (PrintHeapAtGC) {
299 Universe::print_heap_before_gc();
300 }
302 assert(!NeverTenure || _tenuring_threshold == markOopDesc::max_age + 1, "Sanity");
303 assert(!AlwaysTenure || _tenuring_threshold == 0, "Sanity");
305 size_t prev_used = heap->used();
306 assert(promotion_failed() == false, "Sanity");
308 // Fill in TLABs
309 heap->accumulate_statistics_all_tlabs();
310 heap->ensure_parsability(true); // retire TLABs
312 if (VerifyBeforeGC && heap->total_collections() >= VerifyGCStartAt) {
313 HandleMark hm; // Discard invalid handles created during verification
314 gclog_or_tty->print(" VerifyBeforeGC:");
315 Universe::verify(true);
316 }
318 {
319 ResourceMark rm;
320 HandleMark hm;
322 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
323 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
324 TraceTime t1("GC", PrintGC, !PrintGCDetails, gclog_or_tty);
325 TraceCollectorStats tcs(counters());
326 TraceMemoryManagerStats tms(false /* not full GC */,gc_cause);
328 if (TraceGen0Time) accumulated_time()->start();
330 // Let the size policy know we're starting
331 size_policy->minor_collection_begin();
333 // Verify the object start arrays.
334 if (VerifyObjectStartArray &&
335 VerifyBeforeGC) {
336 old_gen->verify_object_start_array();
337 perm_gen->verify_object_start_array();
338 }
340 // Verify no unmarked old->young roots
341 if (VerifyRememberedSets) {
342 CardTableExtension::verify_all_young_refs_imprecise();
343 }
345 if (!ScavengeWithObjectsInToSpace) {
346 assert(young_gen->to_space()->is_empty(),
347 "Attempt to scavenge with live objects in to_space");
348 young_gen->to_space()->clear(SpaceDecorator::Mangle);
349 } else if (ZapUnusedHeapArea) {
350 young_gen->to_space()->mangle_unused_area();
351 }
352 save_to_space_top_before_gc();
354 COMPILER2_PRESENT(DerivedPointerTable::clear());
356 reference_processor()->enable_discovery(true /*verify_disabled*/, true /*verify_no_refs*/);
357 reference_processor()->setup_policy(false);
359 // We track how much was promoted to the next generation for
360 // the AdaptiveSizePolicy.
361 size_t old_gen_used_before = old_gen->used_in_bytes();
363 // For PrintGCDetails
364 size_t young_gen_used_before = young_gen->used_in_bytes();
366 // Reset our survivor overflow.
367 set_survivor_overflow(false);
369 // We need to save the old/perm top values before
370 // creating the promotion_manager. We pass the top
371 // values to the card_table, to prevent it from
372 // straying into the promotion labs.
373 HeapWord* old_top = old_gen->object_space()->top();
374 HeapWord* perm_top = perm_gen->object_space()->top();
376 // Release all previously held resources
377 gc_task_manager()->release_all_resources();
379 // Set the number of GC threads to be used in this collection
380 gc_task_manager()->set_active_gang();
381 gc_task_manager()->task_idle_workers();
382 // Get the active number of workers here and use that value
383 // throughout the methods.
384 uint active_workers = gc_task_manager()->active_workers();
385 heap->set_par_threads(active_workers);
387 PSPromotionManager::pre_scavenge();
389 // We'll use the promotion manager again later.
390 PSPromotionManager* promotion_manager = PSPromotionManager::vm_thread_promotion_manager();
391 {
392 // TraceTime("Roots");
393 ParallelScavengeHeap::ParStrongRootsScope psrs;
395 GCTaskQueue* q = GCTaskQueue::create();
397 uint stripe_total = active_workers;
398 for(uint i=0; i < stripe_total; i++) {
399 q->enqueue(new OldToYoungRootsTask(old_gen, old_top, i, stripe_total));
400 }
402 q->enqueue(new SerialOldToYoungRootsTask(perm_gen, perm_top));
404 q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::universe));
405 q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::jni_handles));
406 // We scan the thread roots in parallel
407 Threads::create_thread_roots_tasks(q);
408 q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::object_synchronizer));
409 q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::flat_profiler));
410 q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::management));
411 q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::system_dictionary));
412 q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::jvmti));
413 q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::code_cache));
415 ParallelTaskTerminator terminator(
416 active_workers,
417 (TaskQueueSetSuper*) promotion_manager->stack_array_depth());
418 if (active_workers > 1) {
419 for (uint j = 0; j < active_workers; j++) {
420 q->enqueue(new StealTask(&terminator));
421 }
422 }
424 gc_task_manager()->execute_and_wait(q);
425 }
427 scavenge_midpoint.update();
429 // Process reference objects discovered during scavenge
430 {
431 reference_processor()->setup_policy(false); // not always_clear
432 reference_processor()->set_active_mt_degree(active_workers);
433 PSKeepAliveClosure keep_alive(promotion_manager);
434 PSEvacuateFollowersClosure evac_followers(promotion_manager);
435 if (reference_processor()->processing_is_mt()) {
436 PSRefProcTaskExecutor task_executor;
437 reference_processor()->process_discovered_references(
438 &_is_alive_closure, &keep_alive, &evac_followers, &task_executor);
439 } else {
440 reference_processor()->process_discovered_references(
441 &_is_alive_closure, &keep_alive, &evac_followers, NULL);
442 }
443 }
445 // Enqueue reference objects discovered during scavenge.
446 if (reference_processor()->processing_is_mt()) {
447 PSRefProcTaskExecutor task_executor;
448 reference_processor()->enqueue_discovered_references(&task_executor);
449 } else {
450 reference_processor()->enqueue_discovered_references(NULL);
451 }
453 if (!JavaObjectsInPerm) {
454 // Unlink any dead interned Strings
455 StringTable::unlink(&_is_alive_closure);
456 // Process the remaining live ones
457 PSScavengeRootsClosure root_closure(promotion_manager);
458 StringTable::oops_do(&root_closure);
459 }
461 // Finally, flush the promotion_manager's labs, and deallocate its stacks.
462 PSPromotionManager::post_scavenge();
464 promotion_failure_occurred = promotion_failed();
465 if (promotion_failure_occurred) {
466 clean_up_failed_promotion();
467 if (PrintGC) {
468 gclog_or_tty->print("--");
469 }
470 }
472 // Let the size policy know we're done. Note that we count promotion
473 // failure cleanup time as part of the collection (otherwise, we're
474 // implicitly saying it's mutator time).
475 size_policy->minor_collection_end(gc_cause);
477 if (!promotion_failure_occurred) {
478 // Swap the survivor spaces.
481 young_gen->eden_space()->clear(SpaceDecorator::Mangle);
482 young_gen->from_space()->clear(SpaceDecorator::Mangle);
483 young_gen->swap_spaces();
485 size_t survived = young_gen->from_space()->used_in_bytes();
486 size_t promoted = old_gen->used_in_bytes() - old_gen_used_before;
487 size_policy->update_averages(_survivor_overflow, survived, promoted);
489 // A successful scavenge should restart the GC time limit count which is
490 // for full GC's.
491 size_policy->reset_gc_overhead_limit_count();
492 if (UseAdaptiveSizePolicy) {
493 // Calculate the new survivor size and tenuring threshold
495 if (PrintAdaptiveSizePolicy) {
496 gclog_or_tty->print("AdaptiveSizeStart: ");
497 gclog_or_tty->stamp();
498 gclog_or_tty->print_cr(" collection: %d ",
499 heap->total_collections());
501 if (Verbose) {
502 gclog_or_tty->print("old_gen_capacity: %d young_gen_capacity: %d"
503 " perm_gen_capacity: %d ",
504 old_gen->capacity_in_bytes(), young_gen->capacity_in_bytes(),
505 perm_gen->capacity_in_bytes());
506 }
507 }
510 if (UsePerfData) {
511 PSGCAdaptivePolicyCounters* counters = heap->gc_policy_counters();
512 counters->update_old_eden_size(
513 size_policy->calculated_eden_size_in_bytes());
514 counters->update_old_promo_size(
515 size_policy->calculated_promo_size_in_bytes());
516 counters->update_old_capacity(old_gen->capacity_in_bytes());
517 counters->update_young_capacity(young_gen->capacity_in_bytes());
518 counters->update_survived(survived);
519 counters->update_promoted(promoted);
520 counters->update_survivor_overflowed(_survivor_overflow);
521 }
523 size_t survivor_limit =
524 size_policy->max_survivor_size(young_gen->max_size());
525 _tenuring_threshold =
526 size_policy->compute_survivor_space_size_and_threshold(
527 _survivor_overflow,
528 _tenuring_threshold,
529 survivor_limit);
531 if (PrintTenuringDistribution) {
532 gclog_or_tty->cr();
533 gclog_or_tty->print_cr("Desired survivor size %ld bytes, new threshold %d (max %d)",
534 size_policy->calculated_survivor_size_in_bytes(),
535 _tenuring_threshold, MaxTenuringThreshold);
536 }
538 if (UsePerfData) {
539 PSGCAdaptivePolicyCounters* counters = heap->gc_policy_counters();
540 counters->update_tenuring_threshold(_tenuring_threshold);
541 counters->update_survivor_size_counters();
542 }
544 // Do call at minor collections?
545 // Don't check if the size_policy is ready at this
546 // level. Let the size_policy check that internally.
547 if (UseAdaptiveSizePolicy &&
548 UseAdaptiveGenerationSizePolicyAtMinorCollection &&
549 ((gc_cause != GCCause::_java_lang_system_gc) ||
550 UseAdaptiveSizePolicyWithSystemGC)) {
552 // Calculate optimial free space amounts
553 assert(young_gen->max_size() >
554 young_gen->from_space()->capacity_in_bytes() +
555 young_gen->to_space()->capacity_in_bytes(),
556 "Sizes of space in young gen are out-of-bounds");
557 size_t max_eden_size = young_gen->max_size() -
558 young_gen->from_space()->capacity_in_bytes() -
559 young_gen->to_space()->capacity_in_bytes();
560 size_policy->compute_generation_free_space(young_gen->used_in_bytes(),
561 young_gen->eden_space()->used_in_bytes(),
562 old_gen->used_in_bytes(),
563 perm_gen->used_in_bytes(),
564 young_gen->eden_space()->capacity_in_bytes(),
565 old_gen->max_gen_size(),
566 max_eden_size,
567 false /* full gc*/,
568 gc_cause,
569 heap->collector_policy());
571 }
572 // Resize the young generation at every collection
573 // even if new sizes have not been calculated. This is
574 // to allow resizes that may have been inhibited by the
575 // relative location of the "to" and "from" spaces.
577 // Resizing the old gen at minor collects can cause increases
578 // that don't feed back to the generation sizing policy until
579 // a major collection. Don't resize the old gen here.
581 heap->resize_young_gen(size_policy->calculated_eden_size_in_bytes(),
582 size_policy->calculated_survivor_size_in_bytes());
584 if (PrintAdaptiveSizePolicy) {
585 gclog_or_tty->print_cr("AdaptiveSizeStop: collection: %d ",
586 heap->total_collections());
587 }
588 }
590 // Update the structure of the eden. With NUMA-eden CPU hotplugging or offlining can
591 // cause the change of the heap layout. Make sure eden is reshaped if that's the case.
592 // Also update() will case adaptive NUMA chunk resizing.
593 assert(young_gen->eden_space()->is_empty(), "eden space should be empty now");
594 young_gen->eden_space()->update();
596 heap->gc_policy_counters()->update_counters();
598 heap->resize_all_tlabs();
600 assert(young_gen->to_space()->is_empty(), "to space should be empty now");
601 }
603 COMPILER2_PRESENT(DerivedPointerTable::update_pointers());
605 NOT_PRODUCT(reference_processor()->verify_no_references_recorded());
607 // Re-verify object start arrays
608 if (VerifyObjectStartArray &&
609 VerifyAfterGC) {
610 old_gen->verify_object_start_array();
611 perm_gen->verify_object_start_array();
612 }
614 // Verify all old -> young cards are now precise
615 if (VerifyRememberedSets) {
616 // Precise verification will give false positives. Until this is fixed,
617 // use imprecise verification.
618 // CardTableExtension::verify_all_young_refs_precise();
619 CardTableExtension::verify_all_young_refs_imprecise();
620 }
622 if (TraceGen0Time) accumulated_time()->stop();
624 if (PrintGC) {
625 if (PrintGCDetails) {
626 // Don't print a GC timestamp here. This is after the GC so
627 // would be confusing.
628 young_gen->print_used_change(young_gen_used_before);
629 }
630 heap->print_heap_change(prev_used);
631 }
633 // Track memory usage and detect low memory
634 MemoryService::track_memory_usage();
635 heap->update_counters();
637 gc_task_manager()->release_idle_workers();
638 }
640 if (VerifyAfterGC && heap->total_collections() >= VerifyGCStartAt) {
641 HandleMark hm; // Discard invalid handles created during verification
642 gclog_or_tty->print(" VerifyAfterGC:");
643 Universe::verify(false);
644 }
646 if (PrintHeapAtGC) {
647 Universe::print_heap_after_gc();
648 }
650 if (ZapUnusedHeapArea) {
651 young_gen->eden_space()->check_mangled_unused_area_complete();
652 young_gen->from_space()->check_mangled_unused_area_complete();
653 young_gen->to_space()->check_mangled_unused_area_complete();
654 }
656 scavenge_exit.update();
658 if (PrintGCTaskTimeStamps) {
659 tty->print_cr("VM-Thread " INT64_FORMAT " " INT64_FORMAT " " INT64_FORMAT,
660 scavenge_entry.ticks(), scavenge_midpoint.ticks(),
661 scavenge_exit.ticks());
662 gc_task_manager()->print_task_time_stamps();
663 }
665 #ifdef TRACESPINNING
666 ParallelTaskTerminator::print_termination_counts();
667 #endif
669 return !promotion_failure_occurred;
670 }
672 // This method iterates over all objects in the young generation,
673 // unforwarding markOops. It then restores any preserved mark oops,
674 // and clears the _preserved_mark_stack.
675 void PSScavenge::clean_up_failed_promotion() {
676 ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
677 assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
678 assert(promotion_failed(), "Sanity");
680 PSYoungGen* young_gen = heap->young_gen();
682 {
683 ResourceMark rm;
685 // Unforward all pointers in the young gen.
686 PSPromotionFailedClosure unforward_closure;
687 young_gen->object_iterate(&unforward_closure);
689 if (PrintGC && Verbose) {
690 gclog_or_tty->print_cr("Restoring %d marks", _preserved_oop_stack.size());
691 }
693 // Restore any saved marks.
694 while (!_preserved_oop_stack.is_empty()) {
695 oop obj = _preserved_oop_stack.pop();
696 markOop mark = _preserved_mark_stack.pop();
697 obj->set_mark(mark);
698 }
700 // Clear the preserved mark and oop stack caches.
701 _preserved_mark_stack.clear(true);
702 _preserved_oop_stack.clear(true);
703 _promotion_failed = false;
704 }
706 // Reset the PromotionFailureALot counters.
707 NOT_PRODUCT(Universe::heap()->reset_promotion_should_fail();)
708 }
710 // This method is called whenever an attempt to promote an object
711 // fails. Some markOops will need preservation, some will not. Note
712 // that the entire eden is traversed after a failed promotion, with
713 // all forwarded headers replaced by the default markOop. This means
714 // it is not neccessary to preserve most markOops.
715 void PSScavenge::oop_promotion_failed(oop obj, markOop obj_mark) {
716 _promotion_failed = true;
717 if (obj_mark->must_be_preserved_for_promotion_failure(obj)) {
718 // Should use per-worker private stakcs hetre rather than
719 // locking a common pair of stacks.
720 ThreadCritical tc;
721 _preserved_oop_stack.push(obj);
722 _preserved_mark_stack.push(obj_mark);
723 }
724 }
726 bool PSScavenge::should_attempt_scavenge() {
727 ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
728 assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
729 PSGCAdaptivePolicyCounters* counters = heap->gc_policy_counters();
731 if (UsePerfData) {
732 counters->update_scavenge_skipped(not_skipped);
733 }
735 PSYoungGen* young_gen = heap->young_gen();
736 PSOldGen* old_gen = heap->old_gen();
738 if (!ScavengeWithObjectsInToSpace) {
739 // Do not attempt to promote unless to_space is empty
740 if (!young_gen->to_space()->is_empty()) {
741 _consecutive_skipped_scavenges++;
742 if (UsePerfData) {
743 counters->update_scavenge_skipped(to_space_not_empty);
744 }
745 return false;
746 }
747 }
749 // Test to see if the scavenge will likely fail.
750 PSAdaptiveSizePolicy* policy = heap->size_policy();
752 // A similar test is done in the policy's should_full_GC(). If this is
753 // changed, decide if that test should also be changed.
754 size_t avg_promoted = (size_t) policy->padded_average_promoted_in_bytes();
755 size_t promotion_estimate = MIN2(avg_promoted, young_gen->used_in_bytes());
756 bool result = promotion_estimate < old_gen->free_in_bytes();
758 if (PrintGCDetails && Verbose) {
759 gclog_or_tty->print(result ? " do scavenge: " : " skip scavenge: ");
760 gclog_or_tty->print_cr(" average_promoted " SIZE_FORMAT
761 " padded_average_promoted " SIZE_FORMAT
762 " free in old gen " SIZE_FORMAT,
763 (size_t) policy->average_promoted_in_bytes(),
764 (size_t) policy->padded_average_promoted_in_bytes(),
765 old_gen->free_in_bytes());
766 if (young_gen->used_in_bytes() <
767 (size_t) policy->padded_average_promoted_in_bytes()) {
768 gclog_or_tty->print_cr(" padded_promoted_average is greater"
769 " than maximum promotion = " SIZE_FORMAT, young_gen->used_in_bytes());
770 }
771 }
773 if (result) {
774 _consecutive_skipped_scavenges = 0;
775 } else {
776 _consecutive_skipped_scavenges++;
777 if (UsePerfData) {
778 counters->update_scavenge_skipped(promoted_too_large);
779 }
780 }
781 return result;
782 }
784 // Used to add tasks
785 GCTaskManager* const PSScavenge::gc_task_manager() {
786 assert(ParallelScavengeHeap::gc_task_manager() != NULL,
787 "shouldn't return NULL");
788 return ParallelScavengeHeap::gc_task_manager();
789 }
791 void PSScavenge::initialize() {
792 // Arguments must have been parsed
794 if (AlwaysTenure) {
795 _tenuring_threshold = 0;
796 } else if (NeverTenure) {
797 _tenuring_threshold = markOopDesc::max_age + 1;
798 } else {
799 // We want to smooth out our startup times for the AdaptiveSizePolicy
800 _tenuring_threshold = (UseAdaptiveSizePolicy) ? InitialTenuringThreshold :
801 MaxTenuringThreshold;
802 }
804 ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
805 assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
807 PSYoungGen* young_gen = heap->young_gen();
808 PSOldGen* old_gen = heap->old_gen();
809 PSPermGen* perm_gen = heap->perm_gen();
811 // Set boundary between young_gen and old_gen
812 assert(perm_gen->reserved().end() <= old_gen->object_space()->bottom(),
813 "perm above old");
814 assert(old_gen->reserved().end() <= young_gen->eden_space()->bottom(),
815 "old above young");
816 _young_generation_boundary = young_gen->eden_space()->bottom();
818 // Initialize ref handling object for scavenging.
819 MemRegion mr = young_gen->reserved();
821 _ref_processor =
822 new ReferenceProcessor(mr, // span
823 ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing
824 (int) ParallelGCThreads, // mt processing degree
825 true, // mt discovery
826 (int) ParallelGCThreads, // mt discovery degree
827 true, // atomic_discovery
828 NULL, // header provides liveness info
829 false); // next field updates do not need write barrier
831 // Cache the cardtable
832 BarrierSet* bs = Universe::heap()->barrier_set();
833 assert(bs->kind() == BarrierSet::CardTableModRef, "Wrong barrier set kind");
834 _card_table = (CardTableExtension*)bs;
836 _counters = new CollectorCounters("PSScavenge", 0);
837 }