1 /*
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4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
5 *
6 * This code is free software; you can redistribute it and/or modify it
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12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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24 */
25
26 #include "gc/shenandoah/shenandoahAgeCensus.hpp"
27 #include "gc/shenandoah/shenandoahClosures.inline.hpp"
28 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
29 #include "gc/shenandoah/shenandoahFreeSet.hpp"
30 #include "gc/shenandoah/shenandoahGenerationalControlThread.hpp"
31 #include "gc/shenandoah/shenandoahGenerationalEvacuationTask.hpp"
32 #include "gc/shenandoah/shenandoahGenerationalHeap.hpp"
33 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
34 #include "gc/shenandoah/shenandoahHeapRegion.hpp"
35 #include "gc/shenandoah/shenandoahHeapRegionClosures.hpp"
36 #include "gc/shenandoah/shenandoahInitLogger.hpp"
37 #include "gc/shenandoah/shenandoahMemoryPool.hpp"
38 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
39 #include "gc/shenandoah/shenandoahOldGeneration.hpp"
40 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
41 #include "gc/shenandoah/shenandoahRegulatorThread.hpp"
42 #include "gc/shenandoah/shenandoahScanRemembered.inline.hpp"
43 #include "gc/shenandoah/shenandoahUtils.hpp"
44 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
45 #include "gc/shenandoah/shenandoahYoungGeneration.hpp"
46 #include "logging/log.hpp"
47 #include "utilities/events.hpp"
48
49
50 class ShenandoahGenerationalInitLogger : public ShenandoahInitLogger {
51 public:
52 static void print() {
53 ShenandoahGenerationalInitLogger logger;
54 logger.print_all();
55 }
56
57 void print_heap() override {
58 ShenandoahInitLogger::print_heap();
59
60 ShenandoahGenerationalHeap* heap = ShenandoahGenerationalHeap::heap();
61
62 ShenandoahYoungGeneration* young = heap->young_generation();
63 log_info(gc, init)("Young Generation Soft Size: " EXACTFMT, EXACTFMTARGS(young->soft_max_capacity()));
64 log_info(gc, init)("Young Generation Max: " EXACTFMT, EXACTFMTARGS(young->max_capacity()));
65
66 ShenandoahOldGeneration* old = heap->old_generation();
67 log_info(gc, init)("Old Generation Soft Size: " EXACTFMT, EXACTFMTARGS(old->soft_max_capacity()));
68 log_info(gc, init)("Old Generation Max: " EXACTFMT, EXACTFMTARGS(old->max_capacity()));
69 }
70
71 protected:
72 void print_gc_specific() override {
73 ShenandoahInitLogger::print_gc_specific();
74
75 ShenandoahGenerationalHeap* heap = ShenandoahGenerationalHeap::heap();
76 log_info(gc, init)("Young Heuristics: %s", heap->young_generation()->heuristics()->name());
77 log_info(gc, init)("Old Heuristics: %s", heap->old_generation()->heuristics()->name());
78 }
79 };
80
81 size_t ShenandoahGenerationalHeap::calculate_min_plab() {
82 return align_up(PLAB::min_size(), CardTable::card_size_in_words());
83 }
84
85 size_t ShenandoahGenerationalHeap::calculate_max_plab() {
86 size_t MaxTLABSizeWords = ShenandoahHeapRegion::max_tlab_size_words();
87 return align_down(MaxTLABSizeWords, CardTable::card_size_in_words());
88 }
89
90 // Returns size in bytes
91 size_t ShenandoahGenerationalHeap::unsafe_max_tlab_alloc(Thread *thread) const {
92 return MIN2(ShenandoahHeapRegion::max_tlab_size_bytes(), young_generation()->available());
93 }
94
95 ShenandoahGenerationalHeap::ShenandoahGenerationalHeap(ShenandoahCollectorPolicy* policy) :
96 ShenandoahHeap(policy),
97 _age_census(nullptr),
98 _evac_tracker(new ShenandoahEvacuationTracker()),
99 _min_plab_size(calculate_min_plab()),
100 _max_plab_size(calculate_max_plab()),
101 _regulator_thread(nullptr),
102 _young_gen_memory_pool(nullptr),
103 _old_gen_memory_pool(nullptr) {
104 assert(is_aligned(_min_plab_size, CardTable::card_size_in_words()), "min_plab_size must be aligned");
105 assert(is_aligned(_max_plab_size, CardTable::card_size_in_words()), "max_plab_size must be aligned");
106 }
107
108 void ShenandoahGenerationalHeap::post_initialize() {
109 ShenandoahHeap::post_initialize();
110 _age_census = new ShenandoahAgeCensus();
111 }
112
113 void ShenandoahGenerationalHeap::print_init_logger() const {
114 ShenandoahGenerationalInitLogger logger;
115 logger.print_all();
116 }
117
118 void ShenandoahGenerationalHeap::print_tracing_info() const {
119 ShenandoahHeap::print_tracing_info();
120
121 LogTarget(Info, gc, stats) lt;
122 if (lt.is_enabled()) {
123 LogStream ls(lt);
124 ls.cr();
125 ls.cr();
126 evac_tracker()->print_global_on(&ls);
127 }
128 }
129
130 void ShenandoahGenerationalHeap::initialize_heuristics() {
131 // Initialize global generation and heuristics even in generational mode.
132 ShenandoahHeap::initialize_heuristics();
133
134 // Max capacity is the maximum _allowed_ capacity. That is, the maximum allowed capacity
135 // for old would be total heap - minimum capacity of young. This means the sum of the maximum
136 // allowed for old and young could exceed the total heap size. It remains the case that the
137 // _actual_ capacity of young + old = total.
138 _generation_sizer.heap_size_changed(max_capacity());
139 size_t initial_capacity_young = _generation_sizer.max_young_size();
140 size_t max_capacity_young = _generation_sizer.max_young_size();
141 size_t initial_capacity_old = max_capacity() - max_capacity_young;
142 size_t max_capacity_old = max_capacity() - initial_capacity_young;
143
144 _young_generation = new ShenandoahYoungGeneration(max_workers(), max_capacity_young, initial_capacity_young);
145 _old_generation = new ShenandoahOldGeneration(max_workers(), max_capacity_old, initial_capacity_old);
146 _young_generation->initialize_heuristics(mode());
147 _old_generation->initialize_heuristics(mode());
148 }
149
150 void ShenandoahGenerationalHeap::initialize_serviceability() {
151 assert(mode()->is_generational(), "Only for the generational mode");
152 _young_gen_memory_pool = new ShenandoahYoungGenMemoryPool(this);
153 _old_gen_memory_pool = new ShenandoahOldGenMemoryPool(this);
154 cycle_memory_manager()->add_pool(_young_gen_memory_pool);
155 cycle_memory_manager()->add_pool(_old_gen_memory_pool);
156 stw_memory_manager()->add_pool(_young_gen_memory_pool);
157 stw_memory_manager()->add_pool(_old_gen_memory_pool);
158 }
159
160 GrowableArray<MemoryPool*> ShenandoahGenerationalHeap::memory_pools() {
161 assert(mode()->is_generational(), "Only for the generational mode");
162 GrowableArray<MemoryPool*> memory_pools(2);
163 memory_pools.append(_young_gen_memory_pool);
164 memory_pools.append(_old_gen_memory_pool);
165 return memory_pools;
166 }
167
168 void ShenandoahGenerationalHeap::initialize_controller() {
169 auto control_thread = new ShenandoahGenerationalControlThread();
170 _control_thread = control_thread;
171 _regulator_thread = new ShenandoahRegulatorThread(control_thread);
172 }
173
174 void ShenandoahGenerationalHeap::gc_threads_do(ThreadClosure* tcl) const {
175 if (!shenandoah_policy()->is_at_shutdown()) {
176 ShenandoahHeap::gc_threads_do(tcl);
177 tcl->do_thread(regulator_thread());
178 }
179 }
180
181 void ShenandoahGenerationalHeap::stop() {
182 ShenandoahHeap::stop();
183 regulator_thread()->stop();
184 }
185
186 bool ShenandoahGenerationalHeap::requires_barriers(stackChunkOop obj) const {
187 if (is_idle()) {
188 return false;
189 }
190
191 if (is_concurrent_young_mark_in_progress() && is_in_young(obj) && !marking_context()->allocated_after_mark_start(obj)) {
192 // We are marking young, this object is in young, and it is below the TAMS
193 return true;
194 }
195
196 if (is_in_old(obj)) {
197 // Card marking barriers are required for objects in the old generation
198 return true;
199 }
200
201 if (has_forwarded_objects()) {
202 // Object may have pointers that need to be updated
203 return true;
204 }
205
206 return false;
207 }
208
209 void ShenandoahGenerationalHeap::evacuate_collection_set(bool concurrent) {
210 ShenandoahRegionIterator regions;
211 ShenandoahGenerationalEvacuationTask task(this, ®ions, concurrent, false /* only promote regions */);
212 workers()->run_task(&task);
213 }
214
215 void ShenandoahGenerationalHeap::promote_regions_in_place(bool concurrent) {
216 ShenandoahRegionIterator regions;
217 ShenandoahGenerationalEvacuationTask task(this, ®ions, concurrent, true /* only promote regions */);
218 workers()->run_task(&task);
219 }
220
221 oop ShenandoahGenerationalHeap::evacuate_object(oop p, Thread* thread) {
222 assert(thread == Thread::current(), "Expected thread parameter to be current thread.");
223 if (ShenandoahThreadLocalData::is_oom_during_evac(thread)) {
224 // This thread went through the OOM during evac protocol and it is safe to return
225 // the forward pointer. It must not attempt to evacuate anymore.
226 return ShenandoahBarrierSet::resolve_forwarded(p);
227 }
228
229 assert(ShenandoahThreadLocalData::is_evac_allowed(thread), "must be enclosed in oom-evac scope");
230
231 ShenandoahHeapRegion* r = heap_region_containing(p);
232 assert(!r->is_humongous(), "never evacuate humongous objects");
233
234 ShenandoahAffiliation target_gen = r->affiliation();
235 // gc_generation() can change asynchronously and should not be used here.
236 assert(active_generation() != nullptr, "Error");
237 if (active_generation()->is_young() && target_gen == YOUNG_GENERATION) {
238 markWord mark = p->mark();
239 if (mark.is_marked()) {
240 // Already forwarded.
241 return ShenandoahBarrierSet::resolve_forwarded(p);
242 }
243
244 if (mark.has_displaced_mark_helper()) {
245 // We don't want to deal with MT here just to ensure we read the right mark word.
246 // Skip the potential promotion attempt for this one.
247 } else if (r->age() + mark.age() >= age_census()->tenuring_threshold()) {
248 oop result = try_evacuate_object(p, thread, r, OLD_GENERATION);
249 if (result != nullptr) {
250 return result;
251 }
252 // If we failed to promote this aged object, we'll fall through to code below and evacuate to young-gen.
253 }
254 }
255 return try_evacuate_object(p, thread, r, target_gen);
256 }
257
258 // try_evacuate_object registers the object and dirties the associated remembered set information when evacuating
259 // to OLD_GENERATION.
260 oop ShenandoahGenerationalHeap::try_evacuate_object(oop p, Thread* thread, ShenandoahHeapRegion* from_region,
261 ShenandoahAffiliation target_gen) {
262 bool alloc_from_lab = true;
263 bool has_plab = false;
264 HeapWord* copy = nullptr;
265 size_t size = ShenandoahForwarding::size(p);
266 bool is_promotion = (target_gen == OLD_GENERATION) && from_region->is_young();
267
268 #ifdef ASSERT
269 if (ShenandoahOOMDuringEvacALot &&
270 (os::random() & 1) == 0) { // Simulate OOM every ~2nd slow-path call
271 copy = nullptr;
272 } else {
273 #endif
274 if (UseTLAB) {
275 switch (target_gen) {
276 case YOUNG_GENERATION: {
277 copy = allocate_from_gclab(thread, size);
278 if ((copy == nullptr) && (size < ShenandoahThreadLocalData::gclab_size(thread))) {
279 // GCLAB allocation failed because we are bumping up against the limit on young evacuation reserve. Try resetting
280 // the desired GCLAB size and retry GCLAB allocation to avoid cascading of shared memory allocations.
281 ShenandoahThreadLocalData::set_gclab_size(thread, PLAB::min_size());
282 copy = allocate_from_gclab(thread, size);
283 // If we still get nullptr, we'll try a shared allocation below.
284 }
285 break;
286 }
287 case OLD_GENERATION: {
288 PLAB* plab = ShenandoahThreadLocalData::plab(thread);
289 if (plab != nullptr) {
290 has_plab = true;
291 copy = allocate_from_plab(thread, size, is_promotion);
292 if ((copy == nullptr) && (size < ShenandoahThreadLocalData::plab_size(thread)) &&
293 ShenandoahThreadLocalData::plab_retries_enabled(thread)) {
294 // PLAB allocation failed because we are bumping up against the limit on old evacuation reserve or because
295 // the requested object does not fit within the current plab but the plab still has an "abundance" of memory,
296 // where abundance is defined as >= ShenGenHeap::plab_min_size(). In the former case, we try shrinking the
297 // desired PLAB size to the minimum and retry PLAB allocation to avoid cascading of shared memory allocations.
298 if (plab->words_remaining() < plab_min_size()) {
299 ShenandoahThreadLocalData::set_plab_size(thread, plab_min_size());
300 copy = allocate_from_plab(thread, size, is_promotion);
301 // If we still get nullptr, we'll try a shared allocation below.
302 if (copy == nullptr) {
303 // If retry fails, don't continue to retry until we have success (probably in next GC pass)
304 ShenandoahThreadLocalData::disable_plab_retries(thread);
305 }
306 }
307 // else, copy still equals nullptr. this causes shared allocation below, preserving this plab for future needs.
308 }
309 }
310 break;
311 }
312 default: {
313 ShouldNotReachHere();
314 break;
315 }
316 }
317 }
318
319 if (copy == nullptr) {
320 // If we failed to allocate in LAB, we'll try a shared allocation.
321 if (!is_promotion || !has_plab || (size > PLAB::min_size())) {
322 ShenandoahAllocRequest req = ShenandoahAllocRequest::for_shared_gc(size, target_gen, is_promotion);
323 copy = allocate_memory(req);
324 alloc_from_lab = false;
325 }
326 // else, we leave copy equal to nullptr, signaling a promotion failure below if appropriate.
327 // We choose not to promote objects smaller than PLAB::min_size() by way of shared allocations, as this is too
328 // costly. Instead, we'll simply "evacuate" to young-gen memory (using a GCLAB) and will promote in a future
329 // evacuation pass. This condition is denoted by: is_promotion && has_plab && (size <= PLAB::min_size())
330 }
331 #ifdef ASSERT
332 }
333 #endif
334
335 if (copy == nullptr) {
336 if (target_gen == OLD_GENERATION) {
337 if (from_region->is_young()) {
338 // Signal that promotion failed. Will evacuate this old object somewhere in young gen.
339 old_generation()->handle_failed_promotion(thread, size);
340 return nullptr;
341 } else {
342 // Remember that evacuation to old gen failed. We'll want to trigger a full gc to recover from this
343 // after the evacuation threads have finished.
344 old_generation()->handle_failed_evacuation();
345 }
346 }
347
348 control_thread()->handle_alloc_failure_evac(size);
349
350 oom_evac_handler()->handle_out_of_memory_during_evacuation();
351
352 return ShenandoahBarrierSet::resolve_forwarded(p);
353 }
354
355 // Copy the object:
356 NOT_PRODUCT(evac_tracker()->begin_evacuation(thread, size * HeapWordSize));
357 Copy::aligned_disjoint_words(cast_from_oop<HeapWord*>(p), copy, size);
358 oop copy_val = cast_to_oop(copy);
359
360 // Update the age of the evacuated object
361 if (target_gen == YOUNG_GENERATION && is_aging_cycle()) {
362 ShenandoahHeap::increase_object_age(copy_val, from_region->age() + 1);
363 }
364
365 // Try to install the new forwarding pointer.
366 oop result = ShenandoahForwarding::try_update_forwardee(p, copy_val);
367 if (result == copy_val) {
368 // Successfully evacuated. Our copy is now the public one!
369
370 // This is necessary for virtual thread support. This uses the mark word without
371 // considering that it may now be a forwarding pointer (and could therefore crash).
372 // Secondarily, we do not want to spend cycles relativizing stack chunks for oops
373 // that lost the evacuation race (and will therefore not become visible). It is
374 // safe to do this on the public copy (this is also done during concurrent mark).
375 ContinuationGCSupport::relativize_stack_chunk(copy_val);
376
377 // Record that the evacuation succeeded
378 NOT_PRODUCT(evac_tracker()->end_evacuation(thread, size * HeapWordSize));
379
380 if (target_gen == OLD_GENERATION) {
381 old_generation()->handle_evacuation(copy, size, from_region->is_young());
382 } else {
383 // When copying to the old generation above, we don't care
384 // about recording object age in the census stats.
385 assert(target_gen == YOUNG_GENERATION, "Error");
386 // We record this census only when simulating pre-adaptive tenuring behavior, or
387 // when we have been asked to record the census at evacuation rather than at mark
388 if (ShenandoahGenerationalCensusAtEvac || !ShenandoahGenerationalAdaptiveTenuring) {
389 evac_tracker()->record_age(thread, size * HeapWordSize, ShenandoahHeap::get_object_age(copy_val));
390 }
391 }
392 shenandoah_assert_correct(nullptr, copy_val);
393 return copy_val;
394 } else {
395 // Failed to evacuate. We need to deal with the object that is left behind. Since this
396 // new allocation is certainly after TAMS, it will be considered live in the next cycle.
397 // But if it happens to contain references to evacuated regions, those references would
398 // not get updated for this stale copy during this cycle, and we will crash while scanning
399 // it the next cycle.
400 if (alloc_from_lab) {
401 // For LAB allocations, it is enough to rollback the allocation ptr. Either the next
402 // object will overwrite this stale copy, or the filler object on LAB retirement will
403 // do this.
404 switch (target_gen) {
405 case YOUNG_GENERATION: {
406 ShenandoahThreadLocalData::gclab(thread)->undo_allocation(copy, size);
407 break;
408 }
409 case OLD_GENERATION: {
410 ShenandoahThreadLocalData::plab(thread)->undo_allocation(copy, size);
411 if (is_promotion) {
412 ShenandoahThreadLocalData::subtract_from_plab_promoted(thread, size * HeapWordSize);
413 }
414 break;
415 }
416 default: {
417 ShouldNotReachHere();
418 break;
419 }
420 }
421 } else {
422 // For non-LAB allocations, we have no way to retract the allocation, and
423 // have to explicitly overwrite the copy with the filler object. With that overwrite,
424 // we have to keep the fwdptr initialized and pointing to our (stale) copy.
425 assert(size >= ShenandoahHeap::min_fill_size(), "previously allocated object known to be larger than min_size");
426 fill_with_object(copy, size);
427 shenandoah_assert_correct(nullptr, copy_val);
428 // For non-LAB allocations, the object has already been registered
429 }
430 shenandoah_assert_correct(nullptr, result);
431 return result;
432 }
433 }
434
435 inline HeapWord* ShenandoahGenerationalHeap::allocate_from_plab(Thread* thread, size_t size, bool is_promotion) {
436 assert(UseTLAB, "TLABs should be enabled");
437
438 PLAB* plab = ShenandoahThreadLocalData::plab(thread);
439 HeapWord* obj;
440
441 if (plab == nullptr) {
442 assert(!thread->is_Java_thread() && !thread->is_Worker_thread(), "Performance: thread should have PLAB: %s", thread->name());
443 // No PLABs in this thread, fallback to shared allocation
444 return nullptr;
445 } else if (is_promotion && !ShenandoahThreadLocalData::allow_plab_promotions(thread)) {
446 return nullptr;
447 }
448 // if plab->word_size() <= 0, thread's plab not yet initialized for this pass, so allow_plab_promotions() is not trustworthy
449 obj = plab->allocate(size);
450 if ((obj == nullptr) && (plab->words_remaining() < plab_min_size())) {
451 // allocate_from_plab_slow will establish allow_plab_promotions(thread) for future invocations
452 obj = allocate_from_plab_slow(thread, size, is_promotion);
453 }
454 // if plab->words_remaining() >= ShenGenHeap::heap()->plab_min_size(), just return nullptr so we can use a shared allocation
455 if (obj == nullptr) {
456 return nullptr;
457 }
458
459 if (is_promotion) {
460 ShenandoahThreadLocalData::add_to_plab_promoted(thread, size * HeapWordSize);
461 }
462 return obj;
463 }
464
465 // Establish a new PLAB and allocate size HeapWords within it.
466 HeapWord* ShenandoahGenerationalHeap::allocate_from_plab_slow(Thread* thread, size_t size, bool is_promotion) {
467 // New object should fit the PLAB size
468
469 assert(mode()->is_generational(), "PLABs only relevant to generational GC");
470 const size_t plab_min_size = this->plab_min_size();
471 // PLABs are aligned to card boundaries to avoid synchronization with concurrent
472 // allocations in other PLABs.
473 const size_t min_size = (size > plab_min_size)? align_up(size, CardTable::card_size_in_words()): plab_min_size;
474
475 // Figure out size of new PLAB, using value determined at last refill.
476 size_t cur_size = ShenandoahThreadLocalData::plab_size(thread);
477 if (cur_size == 0) {
478 cur_size = plab_min_size;
479 }
480
481 // Expand aggressively, doubling at each refill in this epoch, ceiling at plab_max_size()
482 size_t future_size = MIN2(cur_size * 2, plab_max_size());
483 // Doubling, starting at a card-multiple, should give us a card-multiple. (Ceiling and floor
484 // are card multiples.)
485 assert(is_aligned(future_size, CardTable::card_size_in_words()), "Card multiple by construction, future_size: %zu"
486 ", card_size: %zu, cur_size: %zu, max: %zu",
487 future_size, (size_t) CardTable::card_size_in_words(), cur_size, plab_max_size());
488
489 // Record new heuristic value even if we take any shortcut. This captures
490 // the case when moderately-sized objects always take a shortcut. At some point,
491 // heuristics should catch up with them. Note that the requested cur_size may
492 // not be honored, but we remember that this is the preferred size.
493 log_debug(gc, free)("Set new PLAB size: %zu", future_size);
494 ShenandoahThreadLocalData::set_plab_size(thread, future_size);
495 if (cur_size < size) {
496 // The PLAB to be allocated is still not large enough to hold the object. Fall back to shared allocation.
497 // This avoids retiring perfectly good PLABs in order to represent a single large object allocation.
498 log_debug(gc, free)("Current PLAB size (%zu) is too small for %zu", cur_size, size);
499 return nullptr;
500 }
501
502 // Retire current PLAB, and allocate a new one.
503 PLAB* plab = ShenandoahThreadLocalData::plab(thread);
504 if (plab->words_remaining() < plab_min_size) {
505 // Retire current PLAB. This takes care of any PLAB book-keeping.
506 // retire_plab() registers the remnant filler object with the remembered set scanner without a lock.
507 // Since PLABs are card-aligned, concurrent registrations in other PLABs don't interfere.
508 retire_plab(plab, thread);
509
510 size_t actual_size = 0;
511 HeapWord* plab_buf = allocate_new_plab(min_size, cur_size, &actual_size);
512 if (plab_buf == nullptr) {
513 if (min_size == plab_min_size) {
514 // Disable PLAB promotions for this thread because we cannot even allocate a minimal PLAB. This allows us
515 // to fail faster on subsequent promotion attempts.
516 ShenandoahThreadLocalData::disable_plab_promotions(thread);
517 }
518 return nullptr;
519 } else {
520 ShenandoahThreadLocalData::enable_plab_retries(thread);
521 }
522 // Since the allocated PLAB may have been down-sized for alignment, plab->allocate(size) below may still fail.
523 if (ZeroTLAB) {
524 // ... and clear it.
525 Copy::zero_to_words(plab_buf, actual_size);
526 } else {
527 // ...and zap just allocated object.
528 #ifdef ASSERT
529 // Skip mangling the space corresponding to the object header to
530 // ensure that the returned space is not considered parsable by
531 // any concurrent GC thread.
532 size_t hdr_size = oopDesc::header_size();
533 Copy::fill_to_words(plab_buf + hdr_size, actual_size - hdr_size, badHeapWordVal);
534 #endif // ASSERT
535 }
536 assert(is_aligned(actual_size, CardTable::card_size_in_words()), "Align by design");
537 plab->set_buf(plab_buf, actual_size);
538 if (is_promotion && !ShenandoahThreadLocalData::allow_plab_promotions(thread)) {
539 return nullptr;
540 }
541 return plab->allocate(size);
542 } else {
543 // If there's still at least min_size() words available within the current plab, don't retire it. Let's nibble
544 // away on this plab as long as we can. Meanwhile, return nullptr to force this particular allocation request
545 // to be satisfied with a shared allocation. By packing more promotions into the previously allocated PLAB, we
546 // reduce the likelihood of evacuation failures, and we reduce the need for downsizing our PLABs.
547 return nullptr;
548 }
549 }
550
551 HeapWord* ShenandoahGenerationalHeap::allocate_new_plab(size_t min_size, size_t word_size, size_t* actual_size) {
552 // Align requested sizes to card-sized multiples. Align down so that we don't violate max size of TLAB.
553 assert(is_aligned(min_size, CardTable::card_size_in_words()), "Align by design");
554 assert(word_size >= min_size, "Requested PLAB is too small");
555
556 ShenandoahAllocRequest req = ShenandoahAllocRequest::for_plab(min_size, word_size);
557 // Note that allocate_memory() sets a thread-local flag to prohibit further promotions by this thread
558 // if we are at risk of infringing on the old-gen evacuation budget.
559 HeapWord* res = allocate_memory(req);
560 if (res != nullptr) {
561 *actual_size = req.actual_size();
562 } else {
563 *actual_size = 0;
564 }
565 assert(is_aligned(res, CardTable::card_size_in_words()), "Align by design");
566 return res;
567 }
568
569 void ShenandoahGenerationalHeap::retire_plab(PLAB* plab, Thread* thread) {
570 // We don't enforce limits on plab evacuations. We let it consume all available old-gen memory in order to reduce
571 // probability of an evacuation failure. We do enforce limits on promotion, to make sure that excessive promotion
572 // does not result in an old-gen evacuation failure. Note that a failed promotion is relatively harmless. Any
573 // object that fails to promote in the current cycle will be eligible for promotion in a subsequent cycle.
574
575 // When the plab was instantiated, its entirety was treated as if the entire buffer was going to be dedicated to
576 // promotions. Now that we are retiring the buffer, we adjust for the reality that the plab is not entirely promotions.
577 // 1. Some of the plab may have been dedicated to evacuations.
578 // 2. Some of the plab may have been abandoned due to waste (at the end of the plab).
579 size_t not_promoted =
580 ShenandoahThreadLocalData::get_plab_actual_size(thread) - ShenandoahThreadLocalData::get_plab_promoted(thread);
581 ShenandoahThreadLocalData::reset_plab_promoted(thread);
582 ShenandoahThreadLocalData::set_plab_actual_size(thread, 0);
583 if (not_promoted > 0) {
584 old_generation()->unexpend_promoted(not_promoted);
585 }
586 const size_t original_waste = plab->waste();
587 HeapWord* const top = plab->top();
588
589 // plab->retire() overwrites unused memory between plab->top() and plab->hard_end() with a dummy object to make memory parsable.
590 // It adds the size of this unused memory, in words, to plab->waste().
591 plab->retire();
592 if (top != nullptr && plab->waste() > original_waste && is_in_old(top)) {
593 // If retiring the plab created a filler object, then we need to register it with our card scanner so it can
594 // safely walk the region backing the plab.
595 log_debug(gc)("retire_plab() is registering remnant of size %zu at " PTR_FORMAT,
596 plab->waste() - original_waste, p2i(top));
597 // No lock is necessary because the PLAB memory is aligned on card boundaries.
598 old_generation()->card_scan()->register_object_without_lock(top);
599 }
600 }
601
602 void ShenandoahGenerationalHeap::retire_plab(PLAB* plab) {
603 Thread* thread = Thread::current();
604 retire_plab(plab, thread);
605 }
606
607 ShenandoahGenerationalHeap::TransferResult ShenandoahGenerationalHeap::balance_generations() {
608 shenandoah_assert_heaplocked_or_safepoint();
609
610 ShenandoahOldGeneration* old_gen = old_generation();
611 const ssize_t old_region_balance = old_gen->get_region_balance();
612 old_gen->set_region_balance(0);
613
614 if (old_region_balance > 0) {
615 const auto old_region_surplus = checked_cast<size_t>(old_region_balance);
616 const bool success = generation_sizer()->transfer_to_young(old_region_surplus);
617 return TransferResult {
618 success, old_region_surplus, "young"
619 };
620 }
621
622 if (old_region_balance < 0) {
623 const auto old_region_deficit = checked_cast<size_t>(-old_region_balance);
624 const bool success = generation_sizer()->transfer_to_old(old_region_deficit);
625 if (!success) {
626 old_gen->handle_failed_transfer();
627 }
628 return TransferResult {
629 success, old_region_deficit, "old"
630 };
631 }
632
633 return TransferResult {true, 0, "none"};
634 }
635
636 // Make sure old-generation is large enough, but no larger than is necessary, to hold mixed evacuations
637 // and promotions, if we anticipate either. Any deficit is provided by the young generation, subject to
638 // xfer_limit, and any surplus is transferred to the young generation.
639 // xfer_limit is the maximum we're able to transfer from young to old.
640 void ShenandoahGenerationalHeap::compute_old_generation_balance(size_t old_xfer_limit, size_t old_cset_regions) {
641
642 // We can limit the old reserve to the size of anticipated promotions:
643 // max_old_reserve is an upper bound on memory evacuated from old and promoted to old,
644 // clamped by the old generation space available.
645 //
646 // Here's the algebra.
647 // Let SOEP = ShenandoahOldEvacRatioPercent,
648 // OE = old evac,
649 // YE = young evac, and
650 // TE = total evac = OE + YE
651 // By definition:
652 // SOEP/100 = OE/TE
653 // = OE/(OE+YE)
654 // => SOEP/(100-SOEP) = OE/((OE+YE)-OE) // componendo-dividendo: If a/b = c/d, then a/(b-a) = c/(d-c)
655 // = OE/YE
656 // => OE = YE*SOEP/(100-SOEP)
657
658 // We have to be careful in the event that SOEP is set to 100 by the user.
659 assert(ShenandoahOldEvacRatioPercent <= 100, "Error");
660 const size_t old_available = old_generation()->available();
661 // The free set will reserve this amount of memory to hold young evacuations
662 const size_t young_reserve = (young_generation()->max_capacity() * ShenandoahEvacReserve) / 100;
663
664 // In the case that ShenandoahOldEvacRatioPercent equals 100, max_old_reserve is limited only by xfer_limit.
665
666 const double bound_on_old_reserve = old_available + old_xfer_limit + young_reserve;
667 const double max_old_reserve = (ShenandoahOldEvacRatioPercent == 100)?
668 bound_on_old_reserve: MIN2(double(young_reserve * ShenandoahOldEvacRatioPercent) / double(100 - ShenandoahOldEvacRatioPercent),
669 bound_on_old_reserve);
670
671 const size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
672
673 // Decide how much old space we should reserve for a mixed collection
674 double reserve_for_mixed = 0;
675 if (old_generation()->has_unprocessed_collection_candidates()) {
676 // We want this much memory to be unfragmented in order to reliably evacuate old. This is conservative because we
677 // may not evacuate the entirety of unprocessed candidates in a single mixed evacuation.
678 const double max_evac_need = (double(old_generation()->unprocessed_collection_candidates_live_memory()) * ShenandoahOldEvacWaste);
679 assert(old_available >= old_generation()->free_unaffiliated_regions() * region_size_bytes,
680 "Unaffiliated available must be less than total available");
681 const double old_fragmented_available = double(old_available - old_generation()->free_unaffiliated_regions() * region_size_bytes);
682 reserve_for_mixed = max_evac_need + old_fragmented_available;
683 if (reserve_for_mixed > max_old_reserve) {
684 reserve_for_mixed = max_old_reserve;
685 }
686 }
687
688 // Decide how much space we should reserve for promotions from young
689 size_t reserve_for_promo = 0;
690 const size_t promo_load = old_generation()->get_promotion_potential();
691 const bool doing_promotions = promo_load > 0;
692 if (doing_promotions) {
693 // We're promoting and have a bound on the maximum amount that can be promoted
694 assert(max_old_reserve >= reserve_for_mixed, "Sanity");
695 const size_t available_for_promotions = max_old_reserve - reserve_for_mixed;
696 reserve_for_promo = MIN2((size_t)(promo_load * ShenandoahPromoEvacWaste), available_for_promotions);
697 }
698
699 // This is the total old we want to ideally reserve
700 const size_t old_reserve = reserve_for_mixed + reserve_for_promo;
701 assert(old_reserve <= max_old_reserve, "cannot reserve more than max for old evacuations");
702
703 // We now check if the old generation is running a surplus or a deficit.
704 const size_t max_old_available = old_generation()->available() + old_cset_regions * region_size_bytes;
705 if (max_old_available >= old_reserve) {
706 // We are running a surplus, so the old region surplus can go to young
707 const size_t old_surplus = (max_old_available - old_reserve) / region_size_bytes;
708 const size_t unaffiliated_old_regions = old_generation()->free_unaffiliated_regions() + old_cset_regions;
709 const size_t old_region_surplus = MIN2(old_surplus, unaffiliated_old_regions);
710 old_generation()->set_region_balance(checked_cast<ssize_t>(old_region_surplus));
711 } else {
712 // We are running a deficit which we'd like to fill from young.
713 // Ignore that this will directly impact young_generation()->max_capacity(),
714 // indirectly impacting young_reserve and old_reserve. These computations are conservative.
715 // Note that deficit is rounded up by one region.
716 const size_t old_need = (old_reserve - max_old_available + region_size_bytes - 1) / region_size_bytes;
717 const size_t max_old_region_xfer = old_xfer_limit / region_size_bytes;
718
719 // Round down the regions we can transfer from young to old. If we're running short
720 // on young-gen memory, we restrict the xfer. Old-gen collection activities will be
721 // curtailed if the budget is restricted.
722 const size_t old_region_deficit = MIN2(old_need, max_old_region_xfer);
723 old_generation()->set_region_balance(0 - checked_cast<ssize_t>(old_region_deficit));
724 }
725 }
726
727 void ShenandoahGenerationalHeap::reset_generation_reserves() {
728 young_generation()->set_evacuation_reserve(0);
729 old_generation()->set_evacuation_reserve(0);
730 old_generation()->set_promoted_reserve(0);
731 }
732
733 void ShenandoahGenerationalHeap::TransferResult::print_on(const char* when, outputStream* ss) const {
734 auto heap = ShenandoahGenerationalHeap::heap();
735 ShenandoahYoungGeneration* const young_gen = heap->young_generation();
736 ShenandoahOldGeneration* const old_gen = heap->old_generation();
737 const size_t young_available = young_gen->available();
738 const size_t old_available = old_gen->available();
739 ss->print_cr("After %s, %s %zu regions to %s to prepare for next gc, old available: "
740 PROPERFMT ", young_available: " PROPERFMT,
741 when,
742 success? "successfully transferred": "failed to transfer", region_count, region_destination,
743 PROPERFMTARGS(old_available), PROPERFMTARGS(young_available));
744 }
745
746 void ShenandoahGenerationalHeap::coalesce_and_fill_old_regions(bool concurrent) {
747 class ShenandoahGlobalCoalesceAndFill : public WorkerTask {
748 private:
749 ShenandoahPhaseTimings::Phase _phase;
750 ShenandoahRegionIterator _regions;
751 public:
752 explicit ShenandoahGlobalCoalesceAndFill(ShenandoahPhaseTimings::Phase phase) :
753 WorkerTask("Shenandoah Global Coalesce"),
754 _phase(phase) {}
755
756 void work(uint worker_id) override {
757 ShenandoahWorkerTimingsTracker timer(_phase,
758 ShenandoahPhaseTimings::ScanClusters,
759 worker_id, true);
760 ShenandoahHeapRegion* region;
761 while ((region = _regions.next()) != nullptr) {
762 // old region is not in the collection set and was not immediately trashed
763 if (region->is_old() && region->is_active() && !region->is_humongous()) {
764 // Reset the coalesce and fill boundary because this is a global collect
765 // and cannot be preempted by young collects. We want to be sure the entire
766 // region is coalesced here and does not resume from a previously interrupted
767 // or completed coalescing.
768 region->begin_preemptible_coalesce_and_fill();
769 region->oop_coalesce_and_fill(false);
770 }
771 }
772 }
773 };
774
775 ShenandoahPhaseTimings::Phase phase = concurrent ?
776 ShenandoahPhaseTimings::conc_coalesce_and_fill :
777 ShenandoahPhaseTimings::degen_gc_coalesce_and_fill;
778
779 // This is not cancellable
780 ShenandoahGlobalCoalesceAndFill coalesce(phase);
781 workers()->run_task(&coalesce);
782 old_generation()->set_parsable(true);
783 }
784
785 template<bool CONCURRENT>
786 class ShenandoahGenerationalUpdateHeapRefsTask : public WorkerTask {
787 private:
788 ShenandoahGenerationalHeap* _heap;
789 ShenandoahRegionIterator* _regions;
790 ShenandoahRegionChunkIterator* _work_chunks;
791
792 public:
793 explicit ShenandoahGenerationalUpdateHeapRefsTask(ShenandoahRegionIterator* regions,
794 ShenandoahRegionChunkIterator* work_chunks) :
795 WorkerTask("Shenandoah Update References"),
796 _heap(ShenandoahGenerationalHeap::heap()),
797 _regions(regions),
798 _work_chunks(work_chunks)
799 {
800 bool old_bitmap_stable = _heap->old_generation()->is_mark_complete();
801 log_debug(gc, remset)("Update refs, scan remembered set using bitmap: %s", BOOL_TO_STR(old_bitmap_stable));
802 }
803
804 void work(uint worker_id) {
805 if (CONCURRENT) {
806 ShenandoahConcurrentWorkerSession worker_session(worker_id);
807 ShenandoahSuspendibleThreadSetJoiner stsj;
808 do_work<ShenandoahConcUpdateRefsClosure>(worker_id);
809 } else {
810 ShenandoahParallelWorkerSession worker_session(worker_id);
811 do_work<ShenandoahNonConcUpdateRefsClosure>(worker_id);
812 }
813 }
814
815 private:
816 template<class T>
817 void do_work(uint worker_id) {
818 T cl;
819
820 if (CONCURRENT && (worker_id == 0)) {
821 // We ask the first worker to replenish the Mutator free set by moving regions previously reserved to hold the
822 // results of evacuation. These reserves are no longer necessary because evacuation has completed.
823 size_t cset_regions = _heap->collection_set()->count();
824
825 // Now that evacuation is done, we can reassign any regions that had been reserved to hold the results of evacuation
826 // to the mutator free set. At the end of GC, we will have cset_regions newly evacuated fully empty regions from
827 // which we will be able to replenish the Collector free set and the OldCollector free set in preparation for the
828 // next GC cycle.
829 _heap->free_set()->move_regions_from_collector_to_mutator(cset_regions);
830 }
831 // If !CONCURRENT, there's no value in expanding Mutator free set
832
833 ShenandoahHeapRegion* r = _regions->next();
834 // We update references for global, old, and young collections.
835 ShenandoahGeneration* const gc_generation = _heap->gc_generation();
836 shenandoah_assert_generations_reconciled();
837 assert(gc_generation->is_mark_complete(), "Expected complete marking");
838 ShenandoahMarkingContext* const ctx = _heap->marking_context();
839 bool is_mixed = _heap->collection_set()->has_old_regions();
840 while (r != nullptr) {
841 HeapWord* update_watermark = r->get_update_watermark();
842 assert(update_watermark >= r->bottom(), "sanity");
843
844 log_debug(gc)("Update refs worker " UINT32_FORMAT ", looking at region %zu", worker_id, r->index());
845 bool region_progress = false;
846 if (r->is_active() && !r->is_cset()) {
847 if (r->is_young()) {
848 _heap->marked_object_oop_iterate(r, &cl, update_watermark);
849 region_progress = true;
850 } else if (r->is_old()) {
851 if (gc_generation->is_global()) {
852
853 _heap->marked_object_oop_iterate(r, &cl, update_watermark);
854 region_progress = true;
855 }
856 // Otherwise, this is an old region in a young or mixed cycle. Process it during a second phase, below.
857 // Don't bother to report pacing progress in this case.
858 } else {
859 // Because updating of references runs concurrently, it is possible that a FREE inactive region transitions
860 // to a non-free active region while this loop is executing. Whenever this happens, the changing of a region's
861 // active status may propagate at a different speed than the changing of the region's affiliation.
862
863 // When we reach this control point, it is because a race has allowed a region's is_active() status to be seen
864 // by this thread before the region's affiliation() is seen by this thread.
865
866 // It's ok for this race to occur because the newly transformed region does not have any references to be
867 // updated.
868
869 assert(r->get_update_watermark() == r->bottom(),
870 "%s Region %zu is_active but not recognized as YOUNG or OLD so must be newly transitioned from FREE",
871 r->affiliation_name(), r->index());
872 }
873 }
874
875 if (region_progress && ShenandoahPacing) {
876 _heap->pacer()->report_update_refs(pointer_delta(update_watermark, r->bottom()));
877 }
878
879 if (_heap->check_cancelled_gc_and_yield(CONCURRENT)) {
880 return;
881 }
882
883 r = _regions->next();
884 }
885
886 if (!gc_generation->is_global()) {
887 // Since this is generational and not GLOBAL, we have to process the remembered set. There's no remembered
888 // set processing if not in generational mode or if GLOBAL mode.
889
890 // After this thread has exhausted its traditional update-refs work, it continues with updating refs within
891 // remembered set. The remembered set workload is better balanced between threads, so threads that are "behind"
892 // can catch up with other threads during this phase, allowing all threads to work more effectively in parallel.
893 update_references_in_remembered_set(worker_id, cl, ctx, is_mixed);
894 }
895 }
896
897 template<class T>
898 void update_references_in_remembered_set(uint worker_id, T &cl, const ShenandoahMarkingContext* ctx, bool is_mixed) {
899
900 struct ShenandoahRegionChunk assignment;
901 ShenandoahScanRemembered* scanner = _heap->old_generation()->card_scan();
902
903 while (!_heap->check_cancelled_gc_and_yield(CONCURRENT) && _work_chunks->next(&assignment)) {
904 // Keep grabbing next work chunk to process until finished, or asked to yield
905 ShenandoahHeapRegion* r = assignment._r;
906 if (r->is_active() && !r->is_cset() && r->is_old()) {
907 HeapWord* start_of_range = r->bottom() + assignment._chunk_offset;
908 HeapWord* end_of_range = r->get_update_watermark();
909 if (end_of_range > start_of_range + assignment._chunk_size) {
910 end_of_range = start_of_range + assignment._chunk_size;
911 }
912
913 if (start_of_range >= end_of_range) {
914 continue;
915 }
916
917 // Old region in a young cycle or mixed cycle.
918 if (is_mixed) {
919 if (r->is_humongous()) {
920 // Need to examine both dirty and clean cards during mixed evac.
921 r->oop_iterate_humongous_slice_all(&cl,start_of_range, assignment._chunk_size);
922 } else {
923 // Since this is mixed evacuation, old regions that are candidates for collection have not been coalesced
924 // and filled. This will use mark bits to find objects that need to be updated.
925 update_references_in_old_region(cl, ctx, scanner, r, start_of_range, end_of_range);
926 }
927 } else {
928 // This is a young evacuation
929 size_t cluster_size = CardTable::card_size_in_words() * ShenandoahCardCluster::CardsPerCluster;
930 size_t clusters = assignment._chunk_size / cluster_size;
931 assert(clusters * cluster_size == assignment._chunk_size, "Chunk assignment must align on cluster boundaries");
932 scanner->process_region_slice(r, assignment._chunk_offset, clusters, end_of_range, &cl, true, worker_id);
933 }
934
935 if (ShenandoahPacing) {
936 _heap->pacer()->report_update_refs(pointer_delta(end_of_range, start_of_range));
937 }
938 }
939 }
940 }
941
942 template<class T>
943 void update_references_in_old_region(T &cl, const ShenandoahMarkingContext* ctx, ShenandoahScanRemembered* scanner,
944 const ShenandoahHeapRegion* r, HeapWord* start_of_range,
945 HeapWord* end_of_range) const {
946 // In case last object in my range spans boundary of my chunk, I may need to scan all the way to top()
947 ShenandoahObjectToOopBoundedClosure<T> objs(&cl, start_of_range, r->top());
948
949 // Any object that begins in a previous range is part of a different scanning assignment. Any object that
950 // starts after end_of_range is also not my responsibility. (Either allocated during evacuation, so does
951 // not hold pointers to from-space, or is beyond the range of my assigned work chunk.)
952
953 // Find the first object that begins in my range, if there is one. Note that `p` will be set to `end_of_range`
954 // when no live object is found in the range.
955 HeapWord* tams = ctx->top_at_mark_start(r);
956 HeapWord* p = get_first_object_start_word(ctx, scanner, tams, start_of_range, end_of_range);
957
958 while (p < end_of_range) {
959 // p is known to point to the beginning of marked object obj
960 oop obj = cast_to_oop(p);
961 objs.do_object(obj);
962 HeapWord* prev_p = p;
963 p += obj->size();
964 if (p < tams) {
965 p = ctx->get_next_marked_addr(p, tams);
966 // If there are no more marked objects before tams, this returns tams. Note that tams is
967 // either >= end_of_range, or tams is the start of an object that is marked.
968 }
969 assert(p != prev_p, "Lack of forward progress");
970 }
971 }
972
973 HeapWord* get_first_object_start_word(const ShenandoahMarkingContext* ctx, ShenandoahScanRemembered* scanner, HeapWord* tams,
974 HeapWord* start_of_range, HeapWord* end_of_range) const {
975 HeapWord* p = start_of_range;
976
977 if (p >= tams) {
978 // We cannot use ctx->is_marked(obj) to test whether an object begins at this address. Instead,
979 // we need to use the remembered set crossing map to advance p to the first object that starts
980 // within the enclosing card.
981 size_t card_index = scanner->card_index_for_addr(start_of_range);
982 while (true) {
983 HeapWord* first_object = scanner->first_object_in_card(card_index);
984 if (first_object != nullptr) {
985 p = first_object;
986 break;
987 } else if (scanner->addr_for_card_index(card_index + 1) < end_of_range) {
988 card_index++;
989 } else {
990 // Signal that no object was found in range
991 p = end_of_range;
992 break;
993 }
994 }
995 } else if (!ctx->is_marked(cast_to_oop(p))) {
996 p = ctx->get_next_marked_addr(p, tams);
997 // If there are no more marked objects before tams, this returns tams.
998 // Note that tams is either >= end_of_range, or tams is the start of an object that is marked.
999 }
1000 return p;
1001 }
1002 };
1003
1004 void ShenandoahGenerationalHeap::update_heap_references(bool concurrent) {
1005 assert(!is_full_gc_in_progress(), "Only for concurrent and degenerated GC");
1006 const uint nworkers = workers()->active_workers();
1007 ShenandoahRegionChunkIterator work_list(nworkers);
1008 if (concurrent) {
1009 ShenandoahGenerationalUpdateHeapRefsTask<true> task(&_update_refs_iterator, &work_list);
1010 workers()->run_task(&task);
1011 } else {
1012 ShenandoahGenerationalUpdateHeapRefsTask<false> task(&_update_refs_iterator, &work_list);
1013 workers()->run_task(&task);
1014 }
1015
1016 if (ShenandoahEnableCardStats) {
1017 // Only do this if we are collecting card stats
1018 ShenandoahScanRemembered* card_scan = old_generation()->card_scan();
1019 assert(card_scan != nullptr, "Card table must exist when card stats are enabled");
1020 card_scan->log_card_stats(nworkers, CARD_STAT_UPDATE_REFS);
1021 }
1022 }
1023
1024 struct ShenandoahCompositeRegionClosure {
1025 template<typename C1, typename C2>
1026 class Closure : public ShenandoahHeapRegionClosure {
1027 private:
1028 C1 &_c1;
1029 C2 &_c2;
1030
1031 public:
1032 Closure(C1 &c1, C2 &c2) : ShenandoahHeapRegionClosure(), _c1(c1), _c2(c2) {}
1033
1034 void heap_region_do(ShenandoahHeapRegion* r) override {
1035 _c1.heap_region_do(r);
1036 _c2.heap_region_do(r);
1037 }
1038
1039 bool is_thread_safe() override {
1040 return _c1.is_thread_safe() && _c2.is_thread_safe();
1041 }
1042 };
1043
1044 template<typename C1, typename C2>
1045 static Closure<C1, C2> of(C1 &c1, C2 &c2) {
1046 return Closure<C1, C2>(c1, c2);
1047 }
1048 };
1049
1050 class ShenandoahUpdateRegionAges : public ShenandoahHeapRegionClosure {
1051 private:
1052 ShenandoahMarkingContext* _ctx;
1053
1054 public:
1055 explicit ShenandoahUpdateRegionAges(ShenandoahMarkingContext* ctx) : _ctx(ctx) { }
1056
1057 void heap_region_do(ShenandoahHeapRegion* r) override {
1058 // Maintenance of region age must follow evacuation in order to account for
1059 // evacuation allocations within survivor regions. We consult region age during
1060 // the subsequent evacuation to determine whether certain objects need to
1061 // be promoted.
1062 if (r->is_young() && r->is_active()) {
1063 HeapWord *tams = _ctx->top_at_mark_start(r);
1064 HeapWord *top = r->top();
1065
1066 // Allocations move the watermark when top moves. However, compacting
1067 // objects will sometimes lower top beneath the watermark, after which,
1068 // attempts to read the watermark will assert out (watermark should not be
1069 // higher than top).
1070 if (top > tams) {
1071 // There have been allocations in this region since the start of the cycle.
1072 // Any objects new to this region must not assimilate elevated age.
1073 r->reset_age();
1074 } else if (ShenandoahGenerationalHeap::heap()->is_aging_cycle()) {
1075 r->increment_age();
1076 }
1077 }
1078 }
1079
1080 bool is_thread_safe() override {
1081 return true;
1082 }
1083 };
1084
1085 void ShenandoahGenerationalHeap::final_update_refs_update_region_states() {
1086 ShenandoahSynchronizePinnedRegionStates pins;
1087 ShenandoahUpdateRegionAges ages(active_generation()->complete_marking_context());
1088 auto cl = ShenandoahCompositeRegionClosure::of(pins, ages);
1089 parallel_heap_region_iterate(&cl);
1090 }
1091
1092 void ShenandoahGenerationalHeap::complete_degenerated_cycle() {
1093 shenandoah_assert_heaplocked_or_safepoint();
1094 if (is_concurrent_old_mark_in_progress()) {
1095 // This is still necessary for degenerated cycles because the degeneration point may occur
1096 // after final mark of the young generation. See ShenandoahConcurrentGC::op_final_update_refs for
1097 // a more detailed explanation.
1098 old_generation()->transfer_pointers_from_satb();
1099 }
1100
1101 // We defer generation resizing actions until after cset regions have been recycled.
1102 TransferResult result = balance_generations();
1103 LogTarget(Info, gc, ergo) lt;
1104 if (lt.is_enabled()) {
1105 LogStream ls(lt);
1106 result.print_on("Degenerated GC", &ls);
1107 }
1108
1109 // In case degeneration interrupted concurrent evacuation or update references, we need to clean up
1110 // transient state. Otherwise, these actions have no effect.
1111 reset_generation_reserves();
1112
1113 if (!old_generation()->is_parsable()) {
1114 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_coalesce_and_fill);
1115 coalesce_and_fill_old_regions(false);
1116 }
1117 }
1118
1119 void ShenandoahGenerationalHeap::complete_concurrent_cycle() {
1120 if (!old_generation()->is_parsable()) {
1121 // Class unloading may render the card offsets unusable, so we must rebuild them before
1122 // the next remembered set scan. We _could_ let the control thread do this sometime after
1123 // the global cycle has completed and before the next young collection, but under memory
1124 // pressure the control thread may not have the time (that is, because it's running back
1125 // to back GCs). In that scenario, we would have to make the old regions parsable before
1126 // we could start a young collection. This could delay the start of the young cycle and
1127 // throw off the heuristics.
1128 entry_global_coalesce_and_fill();
1129 }
1130
1131 TransferResult result;
1132 {
1133 ShenandoahHeapLocker locker(lock());
1134
1135 result = balance_generations();
1136 reset_generation_reserves();
1137 }
1138
1139 LogTarget(Info, gc, ergo) lt;
1140 if (lt.is_enabled()) {
1141 LogStream ls(lt);
1142 result.print_on("Concurrent GC", &ls);
1143 }
1144 }
1145
1146 void ShenandoahGenerationalHeap::entry_global_coalesce_and_fill() {
1147 const char* msg = "Coalescing and filling old regions";
1148 ShenandoahConcurrentPhase gc_phase(msg, ShenandoahPhaseTimings::conc_coalesce_and_fill);
1149
1150 TraceCollectorStats tcs(monitoring_support()->concurrent_collection_counters());
1151 EventMark em("%s", msg);
1152 ShenandoahWorkerScope scope(workers(),
1153 ShenandoahWorkerPolicy::calc_workers_for_conc_marking(),
1154 "concurrent coalesce and fill");
1155
1156 coalesce_and_fill_old_regions(true);
1157 }
1158
1159 void ShenandoahGenerationalHeap::update_region_ages(ShenandoahMarkingContext* ctx) {
1160 ShenandoahUpdateRegionAges cl(ctx);
1161 parallel_heap_region_iterate(&cl);
1162 }