1 /*
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4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
5 *
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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/shenandoahGeneration.hpp"
31 #include "gc/shenandoah/shenandoahGenerationalControlThread.hpp"
32 #include "gc/shenandoah/shenandoahGenerationalEvacuationTask.hpp"
33 #include "gc/shenandoah/shenandoahGenerationalHeap.hpp"
34 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
35 #include "gc/shenandoah/shenandoahHeapRegion.hpp"
36 #include "gc/shenandoah/shenandoahHeapRegionClosures.hpp"
37 #include "gc/shenandoah/shenandoahInitLogger.hpp"
38 #include "gc/shenandoah/shenandoahMemoryPool.hpp"
39 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
40 #include "gc/shenandoah/shenandoahOldGeneration.hpp"
41 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
42 #include "gc/shenandoah/shenandoahRegulatorThread.hpp"
43 #include "gc/shenandoah/shenandoahScanRemembered.inline.hpp"
44 #include "gc/shenandoah/shenandoahUtils.hpp"
45 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
46 #include "gc/shenandoah/shenandoahYoungGeneration.hpp"
47 #include "logging/log.hpp"
48 #include "utilities/events.hpp"
49
50
51 class ShenandoahGenerationalInitLogger : public ShenandoahInitLogger {
52 public:
53 static void print() {
54 ShenandoahGenerationalInitLogger logger;
55 logger.print_all();
56 }
57 protected:
58 void print_gc_specific() override {
59 ShenandoahInitLogger::print_gc_specific();
60
61 ShenandoahGenerationalHeap* heap = ShenandoahGenerationalHeap::heap();
62 log_info(gc, init)("Young Heuristics: %s", heap->young_generation()->heuristics()->name());
63 log_info(gc, init)("Old Heuristics: %s", heap->old_generation()->heuristics()->name());
64 }
65 };
66
67 size_t ShenandoahGenerationalHeap::calculate_min_plab() {
68 return align_up(PLAB::min_size(), CardTable::card_size_in_words());
69 }
70
71 size_t ShenandoahGenerationalHeap::calculate_max_plab() {
72 size_t MaxTLABSizeWords = ShenandoahHeapRegion::max_tlab_size_words();
73 return align_down(MaxTLABSizeWords, CardTable::card_size_in_words());
74 }
75
76 // Returns size in bytes
77 size_t ShenandoahGenerationalHeap::unsafe_max_tlab_alloc() const {
78 return MIN2(ShenandoahHeapRegion::max_tlab_size_bytes(), young_generation()->available());
79 }
80
81 ShenandoahGenerationalHeap::ShenandoahGenerationalHeap(ShenandoahCollectorPolicy* policy) :
82 ShenandoahHeap(policy),
83 _age_census(nullptr),
84 _min_plab_size(calculate_min_plab()),
85 _max_plab_size(calculate_max_plab()),
86 _regulator_thread(nullptr),
87 _young_gen_memory_pool(nullptr),
88 _old_gen_memory_pool(nullptr) {
89 assert(is_aligned(_min_plab_size, CardTable::card_size_in_words()), "min_plab_size must be aligned");
90 assert(is_aligned(_max_plab_size, CardTable::card_size_in_words()), "max_plab_size must be aligned");
91 }
92
93 void ShenandoahGenerationalHeap::initialize_generations() {
94 ShenandoahHeap::initialize_generations();
95 _young_generation->post_initialize(this);
96 _old_generation->post_initialize(this);
97 }
98
99 void ShenandoahGenerationalHeap::post_initialize() {
100 ShenandoahHeap::post_initialize();
101 _age_census = new ShenandoahAgeCensus();
102 }
103
104 void ShenandoahGenerationalHeap::post_initialize_heuristics() {
105 ShenandoahHeap::post_initialize_heuristics();
106 _young_generation->post_initialize_heuristics();
107 _old_generation->post_initialize_heuristics();
108 }
109
110 void ShenandoahGenerationalHeap::print_init_logger() const {
111 ShenandoahGenerationalInitLogger logger;
112 logger.print_all();
113 }
114
115 void ShenandoahGenerationalHeap::initialize_heuristics() {
116 // Initialize global generation and heuristics even in generational mode.
117 ShenandoahHeap::initialize_heuristics();
118
119 _young_generation = new ShenandoahYoungGeneration(max_workers());
120 _old_generation = new ShenandoahOldGeneration(max_workers());
121 _young_generation->initialize_heuristics(mode());
122 _old_generation->initialize_heuristics(mode());
123 }
124
125 void ShenandoahGenerationalHeap::initialize_serviceability() {
126 assert(mode()->is_generational(), "Only for the generational mode");
127 _young_gen_memory_pool = new ShenandoahYoungGenMemoryPool(this);
128 _old_gen_memory_pool = new ShenandoahOldGenMemoryPool(this);
129 cycle_memory_manager()->add_pool(_young_gen_memory_pool);
130 cycle_memory_manager()->add_pool(_old_gen_memory_pool);
131 stw_memory_manager()->add_pool(_young_gen_memory_pool);
132 stw_memory_manager()->add_pool(_old_gen_memory_pool);
133 }
134
135 GrowableArray<MemoryPool*> ShenandoahGenerationalHeap::memory_pools() {
136 assert(mode()->is_generational(), "Only for the generational mode");
137 GrowableArray<MemoryPool*> memory_pools(2);
138 memory_pools.append(_young_gen_memory_pool);
139 memory_pools.append(_old_gen_memory_pool);
140 return memory_pools;
141 }
142
143 void ShenandoahGenerationalHeap::initialize_controller() {
144 auto control_thread = new ShenandoahGenerationalControlThread();
145 _control_thread = control_thread;
146 _regulator_thread = new ShenandoahRegulatorThread(control_thread);
147 }
148
149 void ShenandoahGenerationalHeap::gc_threads_do(ThreadClosure* tcl) const {
150 if (!shenandoah_policy()->is_at_shutdown()) {
151 ShenandoahHeap::gc_threads_do(tcl);
152 tcl->do_thread(regulator_thread());
153 }
154 }
155
156 void ShenandoahGenerationalHeap::stop() {
157 ShenandoahHeap::stop();
158 regulator_thread()->stop();
159 }
160
161 void ShenandoahGenerationalHeap::start_idle_span() {
162 young_generation()->heuristics()->start_idle_span();
163 }
164
165 bool ShenandoahGenerationalHeap::requires_barriers(stackChunkOop obj) const {
166 if (is_idle()) {
167 return false;
168 }
169
170 if (is_concurrent_young_mark_in_progress() && is_in_young(obj) && !marking_context()->allocated_after_mark_start(obj)) {
171 // We are marking young, this object is in young, and it is below the TAMS
172 return true;
173 }
174
175 if (is_in_old(obj)) {
176 // Card marking barriers are required for objects in the old generation
177 return true;
178 }
179
180 if (has_forwarded_objects()) {
181 // Object may have pointers that need to be updated
182 return true;
183 }
184
185 return false;
186 }
187
188 void ShenandoahGenerationalHeap::evacuate_collection_set(ShenandoahGeneration* generation, bool concurrent) {
189 ShenandoahRegionIterator regions;
190 ShenandoahGenerationalEvacuationTask task(this, generation, ®ions, concurrent,
191 (ShenandoahGCStateCheckHotpatch ? collection_set()->is_empty() : false) /* only promote regions */);
192 workers()->run_task(&task);
193 }
194
195 void ShenandoahGenerationalHeap::promote_regions_in_place(ShenandoahGeneration* generation, bool concurrent) {
196 ShenandoahRegionIterator regions;
197 ShenandoahGenerationalEvacuationTask task(this, generation, ®ions, concurrent, true /* only promote regions */);
198 workers()->run_task(&task);
199 }
200
201 oop ShenandoahGenerationalHeap::evacuate_object(oop p, Thread* thread) {
202 assert(thread == Thread::current(), "Expected thread parameter to be current thread.");
203 if (ShenandoahThreadLocalData::is_oom_during_evac(thread)) {
204 // This thread went through the OOM during evac protocol and it is safe to return
205 // the forward pointer. It must not attempt to evacuate anymore.
206 return ShenandoahBarrierSet::resolve_forwarded(p);
207 }
208
209 assert(ShenandoahThreadLocalData::is_evac_allowed(thread), "must be enclosed in oom-evac scope");
210
211 ShenandoahHeapRegion* from_region = heap_region_containing(p);
212 assert(!from_region->is_humongous(), "never evacuate humongous objects");
213
214 // Try to keep the object in the same generation
215 const ShenandoahAffiliation target_gen = from_region->affiliation();
216
217 if (target_gen == YOUNG_GENERATION) {
218 markWord mark = p->mark();
219 if (mark.is_marked()) {
220 // Already forwarded.
221 return ShenandoahBarrierSet::resolve_forwarded(p);
222 }
223
224 if (mark.has_displaced_mark_helper()) {
225 // We don't want to deal with MT here just to ensure we read the right mark word.
226 // Skip the potential promotion attempt for this one.
227 } else if (age_census()->is_tenurable(from_region->age() + mark.age())) {
228 // If the object is tenurable, try to promote it
229 oop result = try_evacuate_object<YOUNG_GENERATION, OLD_GENERATION>(p, thread, from_region->age());
230
231 // If we failed to promote this aged object, we'll fall through to code below and evacuate to young-gen.
232 if (result != nullptr) {
233 return result;
234 }
235 }
236 return try_evacuate_object<YOUNG_GENERATION, YOUNG_GENERATION>(p, thread, from_region->age());
237 }
238
239 assert(target_gen == OLD_GENERATION, "Expected evacuation to old");
240 return try_evacuate_object<OLD_GENERATION, OLD_GENERATION>(p, thread, from_region->age());
241 }
242
243 // try_evacuate_object registers the object and dirties the associated remembered set information when evacuating
244 // to OLD_GENERATION.
245 template<ShenandoahAffiliation FROM_GENERATION, ShenandoahAffiliation TO_GENERATION>
246 oop ShenandoahGenerationalHeap::try_evacuate_object(oop p, Thread* thread, uint from_region_age) {
247 bool alloc_from_lab = true;
248 bool has_plab = false;
249 HeapWord* copy = nullptr;
250 size_t size = ShenandoahForwarding::size(p);
251 constexpr bool is_promotion = (TO_GENERATION == OLD_GENERATION) && (FROM_GENERATION == YOUNG_GENERATION);
252
253 #ifdef ASSERT
254 if (ShenandoahOOMDuringEvacALot &&
255 (os::random() & 1) == 0) { // Simulate OOM every ~2nd slow-path call
256 copy = nullptr;
257 } else {
258 #endif
259 if (UseTLAB) {
260 switch (TO_GENERATION) {
261 case YOUNG_GENERATION: {
262 copy = allocate_from_gclab(thread, size);
263 if ((copy == nullptr) && (size < ShenandoahThreadLocalData::gclab_size(thread))) {
264 // GCLAB allocation failed because we are bumping up against the limit on young evacuation reserve. Try resetting
265 // the desired GCLAB size and retry GCLAB allocation to avoid cascading of shared memory allocations.
266 ShenandoahThreadLocalData::set_gclab_size(thread, PLAB::min_size());
267 copy = allocate_from_gclab(thread, size);
268 // If we still get nullptr, we'll try a shared allocation below.
269 }
270 break;
271 }
272 case OLD_GENERATION: {
273 PLAB* plab = ShenandoahThreadLocalData::plab(thread);
274 if (plab != nullptr) {
275 has_plab = true;
276 copy = allocate_from_plab(thread, size, is_promotion);
277 if ((copy == nullptr) && (size < ShenandoahThreadLocalData::plab_size(thread)) &&
278 ShenandoahThreadLocalData::plab_retries_enabled(thread)) {
279 // PLAB allocation failed because we are bumping up against the limit on old evacuation reserve or because
280 // the requested object does not fit within the current plab but the plab still has an "abundance" of memory,
281 // where abundance is defined as >= ShenGenHeap::plab_min_size(). In the former case, we try shrinking the
282 // desired PLAB size to the minimum and retry PLAB allocation to avoid cascading of shared memory allocations.
283 // Shrinking the desired PLAB size may allow us to eke out a small PLAB while staying beneath evacuation reserve.
284 if (plab->words_remaining() < plab_min_size()) {
285 ShenandoahThreadLocalData::set_plab_size(thread, plab_min_size());
286 copy = allocate_from_plab(thread, size, is_promotion);
287 // If we still get nullptr, we'll try a shared allocation below.
288 if (copy == nullptr) {
289 // If retry fails, don't continue to retry until we have success (probably in next GC pass)
290 ShenandoahThreadLocalData::disable_plab_retries(thread);
291 }
292 }
293 // else, copy still equals nullptr. this causes shared allocation below, preserving this plab for future needs.
294 }
295 }
296 break;
297 }
298 default: {
299 ShouldNotReachHere();
300 break;
301 }
302 }
303 }
304
305 if (copy == nullptr) {
306 // If we failed to allocate in LAB, we'll try a shared allocation.
307 if (!is_promotion || !has_plab || (size > PLAB::min_size())) {
308 ShenandoahAllocRequest req = ShenandoahAllocRequest::for_shared_gc(size, TO_GENERATION, is_promotion);
309 copy = allocate_memory(req);
310 alloc_from_lab = false;
311 }
312 // else, we leave copy equal to nullptr, signaling a promotion failure below if appropriate.
313 // We choose not to promote objects smaller than size_threshold by way of shared allocations as this is too
314 // costly. Instead, we'll simply "evacuate" to young-gen memory (using a GCLAB) and will promote in a future
315 // evacuation pass. This condition is denoted by: is_promotion && has_plab && (size <= size_threshhold).
316 }
317 #ifdef ASSERT
318 }
319 #endif
320
321 if (copy == nullptr) {
322 if (TO_GENERATION == OLD_GENERATION) {
323 if (FROM_GENERATION == YOUNG_GENERATION) {
324 // Signal that promotion failed. Will evacuate this old object somewhere in young gen.
325 old_generation()->handle_failed_promotion(thread, size);
326 return nullptr;
327 } else {
328 // Remember that evacuation to old gen failed. We'll want to trigger a full gc to recover from this
329 // after the evacuation threads have finished.
330 old_generation()->handle_failed_evacuation();
331 }
332 }
333
334 control_thread()->handle_alloc_failure_evac(size);
335 oom_evac_handler()->handle_out_of_memory_during_evacuation();
336 return ShenandoahBarrierSet::resolve_forwarded(p);
337 }
338
339 if (ShenandoahEvacTracking) {
340 evac_tracker()->begin_evacuation(thread, size * HeapWordSize, FROM_GENERATION, TO_GENERATION);
341 }
342
343 // Copy the object:
344 Copy::aligned_disjoint_words(cast_from_oop<HeapWord*>(p), copy, size);
345 oop copy_val = cast_to_oop(copy);
346
347 // Update the age of the evacuated object
348 if (TO_GENERATION == YOUNG_GENERATION && is_aging_cycle()) {
349 increase_object_age(copy_val, from_region_age + 1);
350 }
351
352 // Try to install the new forwarding pointer.
353 oop result = ShenandoahForwarding::try_update_forwardee(p, copy_val);
354 if (result == copy_val) {
355 // Successfully evacuated. Our copy is now the public one!
356
357 // This is necessary for virtual thread support. This uses the mark word without
358 // considering that it may now be a forwarding pointer (and could therefore crash).
359 // Secondarily, we do not want to spend cycles relativizing stack chunks for oops
360 // that lost the evacuation race (and will therefore not become visible). It is
361 // safe to do this on the public copy (this is also done during concurrent mark).
362 ContinuationGCSupport::relativize_stack_chunk(copy_val);
363
364 if (ShenandoahEvacTracking) {
365 // Record that the evacuation succeeded
366 evac_tracker()->end_evacuation(thread, size * HeapWordSize, FROM_GENERATION, TO_GENERATION);
367 }
368
369 if (TO_GENERATION == OLD_GENERATION) {
370 old_generation()->handle_evacuation(copy, size);
371 }
372 } else {
373 // Failed to evacuate. We need to deal with the object that is left behind. Since this
374 // new allocation is certainly after TAMS, it will be considered live in the next cycle.
375 // But if it happens to contain references to evacuated regions, those references would
376 // not get updated for this stale copy during this cycle, and we will crash while scanning
377 // it the next cycle.
378 if (alloc_from_lab) {
379 // For LAB allocations, it is enough to rollback the allocation ptr. Either the next
380 // object will overwrite this stale copy, or the filler object on LAB retirement will
381 // do this.
382 switch (TO_GENERATION) {
383 case YOUNG_GENERATION: {
384 ShenandoahThreadLocalData::gclab(thread)->undo_allocation(copy, size);
385 break;
386 }
387 case OLD_GENERATION: {
388 ShenandoahThreadLocalData::plab(thread)->undo_allocation(copy, size);
389 if (is_promotion) {
390 ShenandoahThreadLocalData::subtract_from_plab_promoted(thread, size * HeapWordSize);
391 }
392 break;
393 }
394 default: {
395 ShouldNotReachHere();
396 break;
397 }
398 }
399 } else {
400 // For non-LAB allocations, we have no way to retract the allocation, and
401 // have to explicitly overwrite the copy with the filler object. With that overwrite,
402 // we have to keep the fwdptr initialized and pointing to our (stale) copy.
403 assert(size >= ShenandoahHeap::min_fill_size(), "previously allocated object known to be larger than min_size");
404 fill_with_object(copy, size);
405 }
406 }
407 shenandoah_assert_correct(nullptr, result);
408 return result;
409 }
410
411 template oop ShenandoahGenerationalHeap::try_evacuate_object<YOUNG_GENERATION, YOUNG_GENERATION>(oop p, Thread* thread, uint from_region_age);
412 template oop ShenandoahGenerationalHeap::try_evacuate_object<YOUNG_GENERATION, OLD_GENERATION>(oop p, Thread* thread, uint from_region_age);
413 template oop ShenandoahGenerationalHeap::try_evacuate_object<OLD_GENERATION, OLD_GENERATION>(oop p, Thread* thread, uint from_region_age);
414
415 inline HeapWord* ShenandoahGenerationalHeap::allocate_from_plab(Thread* thread, size_t size, bool is_promotion) {
416 assert(UseTLAB, "TLABs should be enabled");
417
418 PLAB* plab = ShenandoahThreadLocalData::plab(thread);
419 HeapWord* obj;
420
421 if (plab == nullptr) {
422 assert(!thread->is_Java_thread() && !thread->is_Worker_thread(), "Performance: thread should have PLAB: %s", thread->name());
423 // No PLABs in this thread, fallback to shared allocation
424 return nullptr;
425 } else if (is_promotion && !ShenandoahThreadLocalData::allow_plab_promotions(thread)) {
426 return nullptr;
427 }
428 // if plab->word_size() <= 0, thread's plab not yet initialized for this pass, so allow_plab_promotions() is not trustworthy
429 obj = plab->allocate(size);
430 if ((obj == nullptr) && (plab->words_remaining() < plab_min_size())) {
431 // allocate_from_plab_slow will establish allow_plab_promotions(thread) for future invocations
432 obj = allocate_from_plab_slow(thread, size, is_promotion);
433 }
434 // if plab->words_remaining() >= ShenGenHeap::heap()->plab_min_size(), just return nullptr so we can use a shared allocation
435 if (obj == nullptr) {
436 return nullptr;
437 }
438
439 if (is_promotion) {
440 ShenandoahThreadLocalData::add_to_plab_promoted(thread, size * HeapWordSize);
441 }
442 return obj;
443 }
444
445 // Establish a new PLAB and allocate size HeapWords within it.
446 HeapWord* ShenandoahGenerationalHeap::allocate_from_plab_slow(Thread* thread, size_t size, bool is_promotion) {
447 assert(mode()->is_generational(), "PLABs only relevant to generational GC");
448
449 const size_t plab_min_size = this->plab_min_size();
450 // PLABs are aligned to card boundaries to avoid synchronization with concurrent
451 // allocations in other PLABs.
452 const size_t min_size = (size > plab_min_size)? align_up(size, CardTable::card_size_in_words()): plab_min_size;
453
454 // Figure out size of new PLAB, using value determined at last refill.
455 size_t cur_size = ShenandoahThreadLocalData::plab_size(thread);
456 if (cur_size == 0) {
457 cur_size = plab_min_size;
458 }
459
460 // Expand aggressively, doubling at each refill in this epoch, ceiling at plab_max_size()
461 const size_t future_size = MIN2(cur_size * 2, plab_max_size());
462 // Doubling, starting at a card-multiple, should give us a card-multiple. (Ceiling and floor
463 // are card multiples.)
464 assert(is_aligned(future_size, CardTable::card_size_in_words()), "Card multiple by construction, future_size: %zu"
465 ", card_size: %u, cur_size: %zu, max: %zu",
466 future_size, CardTable::card_size_in_words(), cur_size, plab_max_size());
467
468 // Record new heuristic value even if we take any shortcut. This captures
469 // the case when moderately-sized objects always take a shortcut. At some point,
470 // heuristics should catch up with them. Note that the requested cur_size may
471 // not be honored, but we remember that this is the preferred size.
472 log_debug(gc, plab)("Set next PLAB refill size: %zu bytes", future_size * HeapWordSize);
473 ShenandoahThreadLocalData::set_plab_size(thread, future_size);
474
475 if (cur_size < size) {
476 // The PLAB to be allocated is still not large enough to hold the object. Fall back to shared allocation.
477 // This avoids retiring perfectly good PLABs in order to represent a single large object allocation.
478 log_debug(gc, plab)("Current PLAB size (%zu) is too small for %zu", cur_size * HeapWordSize, size * HeapWordSize);
479 return nullptr;
480 }
481
482 // Retire current PLAB, and allocate a new one.
483 PLAB* plab = ShenandoahThreadLocalData::plab(thread);
484 if (plab->words_remaining() < plab_min_size) {
485 // Retire current PLAB. This takes care of any PLAB book-keeping.
486 // retire_plab() registers the remnant filler object with the remembered set scanner without a lock.
487 // Since PLABs are card-aligned, concurrent registrations in other PLABs don't interfere.
488 retire_plab(plab, thread);
489
490 size_t actual_size = 0;
491 HeapWord* plab_buf = allocate_new_plab(min_size, cur_size, &actual_size);
492 if (plab_buf == nullptr) {
493 if (min_size == plab_min_size) {
494 // Disable PLAB promotions for this thread because we cannot even allocate a minimal PLAB. This allows us
495 // to fail faster on subsequent promotion attempts.
496 ShenandoahThreadLocalData::disable_plab_promotions(thread);
497 }
498 return nullptr;
499 } else {
500 ShenandoahThreadLocalData::enable_plab_retries(thread);
501 }
502 // Since the allocated PLAB may have been down-sized for alignment, plab->allocate(size) below may still fail.
503 if (ZeroTLAB) {
504 // ... and clear it.
505 Copy::zero_to_words(plab_buf, actual_size);
506 } else {
507 // ...and zap just allocated object.
508 #ifdef ASSERT
509 // Skip mangling the space corresponding to the object header to
510 // ensure that the returned space is not considered parsable by
511 // any concurrent GC thread.
512 size_t hdr_size = oopDesc::header_size();
513 Copy::fill_to_words(plab_buf + hdr_size, actual_size - hdr_size, badHeapWordVal);
514 #endif // ASSERT
515 }
516 assert(is_aligned(actual_size, CardTable::card_size_in_words()), "Align by design");
517 plab->set_buf(plab_buf, actual_size);
518 if (is_promotion && !ShenandoahThreadLocalData::allow_plab_promotions(thread)) {
519 return nullptr;
520 }
521 return plab->allocate(size);
522 } else {
523 // If there's still at least min_size() words available within the current plab, don't retire it. Let's nibble
524 // away on this plab as long as we can. Meanwhile, return nullptr to force this particular allocation request
525 // to be satisfied with a shared allocation. By packing more promotions into the previously allocated PLAB, we
526 // reduce the likelihood of evacuation failures, and we reduce the need for downsizing our PLABs.
527 return nullptr;
528 }
529 }
530
531 HeapWord* ShenandoahGenerationalHeap::allocate_new_plab(size_t min_size, size_t word_size, size_t* actual_size) {
532 // Align requested sizes to card-sized multiples. Align down so that we don't violate max size of TLAB.
533 assert(is_aligned(min_size, CardTable::card_size_in_words()), "Align by design");
534 assert(word_size >= min_size, "Requested PLAB is too small");
535
536 ShenandoahAllocRequest req = ShenandoahAllocRequest::for_plab(min_size, word_size);
537 // Note that allocate_memory() sets a thread-local flag to prohibit further promotions by this thread
538 // if we are at risk of infringing on the old-gen evacuation budget.
539 HeapWord* res = allocate_memory(req);
540 if (res != nullptr) {
541 *actual_size = req.actual_size();
542 } else {
543 *actual_size = 0;
544 }
545 assert(is_aligned(res, CardTable::card_size_in_words()), "Align by design");
546 return res;
547 }
548
549 void ShenandoahGenerationalHeap::retire_plab(PLAB* plab, Thread* thread) {
550 // We don't enforce limits on plab evacuations. We let it consume all available old-gen memory in order to reduce
551 // probability of an evacuation failure. We do enforce limits on promotion, to make sure that excessive promotion
552 // does not result in an old-gen evacuation failure. Note that a failed promotion is relatively harmless. Any
553 // object that fails to promote in the current cycle will be eligible for promotion in a subsequent cycle.
554
555 // When the plab was instantiated, its entirety was treated as if the entire buffer was going to be dedicated to
556 // promotions. Now that we are retiring the buffer, we adjust for the reality that the plab is not entirely promotions.
557 // 1. Some of the plab may have been dedicated to evacuations.
558 // 2. Some of the plab may have been abandoned due to waste (at the end of the plab).
559 size_t not_promoted =
560 ShenandoahThreadLocalData::get_plab_actual_size(thread) - ShenandoahThreadLocalData::get_plab_promoted(thread);
561 ShenandoahThreadLocalData::reset_plab_promoted(thread);
562 ShenandoahThreadLocalData::set_plab_actual_size(thread, 0);
563 if (not_promoted > 0) {
564 log_debug(gc, plab)("Retire PLAB, unexpend unpromoted: %zu", not_promoted * HeapWordSize);
565 old_generation()->unexpend_promoted(not_promoted);
566 }
567 const size_t original_waste = plab->waste();
568 HeapWord* const top = plab->top();
569
570 // plab->retire() overwrites unused memory between plab->top() and plab->hard_end() with a dummy object to make memory parsable.
571 // It adds the size of this unused memory, in words, to plab->waste().
572 plab->retire();
573 if (top != nullptr && plab->waste() > original_waste && is_in_old(top)) {
574 // If retiring the plab created a filler object, then we need to register it with our card scanner so it can
575 // safely walk the region backing the plab.
576 log_debug(gc, plab)("retire_plab() is registering remnant of size %zu at " PTR_FORMAT,
577 (plab->waste() - original_waste) * HeapWordSize, p2i(top));
578 // No lock is necessary because the PLAB memory is aligned on card boundaries.
579 old_generation()->card_scan()->register_object_without_lock(top);
580 }
581 }
582
583 void ShenandoahGenerationalHeap::retire_plab(PLAB* plab) {
584 Thread* thread = Thread::current();
585 retire_plab(plab, thread);
586 }
587
588 // Make sure old-generation is large enough, but no larger than is necessary, to hold mixed evacuations
589 // and promotions, if we anticipate either. Any deficit is provided by the young generation, subject to
590 // mutator_xfer_limit, and any surplus is transferred to the young generation. mutator_xfer_limit is
591 // the maximum we're able to transfer from young to old. This is called at the end of GC, as we prepare
592 // for the idle span that precedes the next GC.
593 void ShenandoahGenerationalHeap::compute_old_generation_balance(size_t mutator_xfer_limit,
594 size_t old_trashed_regions, size_t young_trashed_regions) {
595 shenandoah_assert_heaplocked();
596 // We can limit the old reserve to the size of anticipated promotions:
597 // max_old_reserve is an upper bound on memory evacuated from old and promoted to old,
598 // clamped by the old generation space available.
599 //
600 // Here's the algebra.
601 // Let SOEP = ShenandoahOldEvacPercent,
602 // OE = old evac,
603 // YE = young evac, and
604 // TE = total evac = OE + YE
605 // By definition:
606 // SOEP/100 = OE/TE
607 // = OE/(OE+YE)
608 // => SOEP/(100-SOEP) = OE/((OE+YE)-OE) // componendo-dividendo: If a/b = c/d, then a/(b-a) = c/(d-c)
609 // = OE/YE
610 // => OE = YE*SOEP/(100-SOEP)
611
612 // We have to be careful in the event that SOEP is set to 100 by the user.
613 assert(ShenandoahOldEvacPercent <= 100, "Error");
614 const size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
615
616 ShenandoahOldGeneration* old_gen = old_generation();
617 size_t old_capacity = old_gen->max_capacity();
618 size_t old_usage = old_gen->used(); // includes humongous waste
619 size_t old_currently_available =
620 ((old_capacity >= old_usage)? old_capacity - old_usage: 0) + old_trashed_regions * region_size_bytes;
621
622 ShenandoahYoungGeneration* young_gen = young_generation();
623 size_t young_capacity = young_gen->max_capacity();
624 size_t young_usage = young_gen->used(); // includes humongous waste
625 size_t young_available = ((young_capacity >= young_usage)? young_capacity - young_usage: 0);
626 size_t freeset_available = free_set()->available_locked();
627 if (young_available > freeset_available) {
628 young_available = freeset_available;
629 }
630 young_available += young_trashed_regions * region_size_bytes;
631
632 // The free set will reserve this amount of memory to hold young evacuations (initialized to the ideal reserve)
633 size_t young_reserve = (young_generation()->max_capacity() * ShenandoahEvacReserve) / 100;
634
635 // If ShenandoahOldEvacPercent equals 100, max_old_reserve is limited only by mutator_xfer_limit and young_reserve
636 const size_t bound_on_old_reserve =
637 ((old_currently_available + mutator_xfer_limit + young_reserve) * ShenandoahOldEvacPercent) / 100;
638 size_t proposed_max_old = ((ShenandoahOldEvacPercent == 100)?
639 bound_on_old_reserve:
640 MIN2((young_reserve * ShenandoahOldEvacPercent) / (100 - ShenandoahOldEvacPercent),
641 bound_on_old_reserve));
642 if (young_reserve > young_available) {
643 young_reserve = young_available;
644 }
645
646 // Decide how much old space we should reserve for a mixed collection
647 size_t proposed_reserve_for_mixed = 0;
648 const size_t old_fragmented_available =
649 old_currently_available - (old_generation()->free_unaffiliated_regions() + old_trashed_regions) * region_size_bytes;
650
651 if (old_fragmented_available > proposed_max_old) {
652 // In this case, the old_fragmented_available is greater than the desired amount of evacuation to old.
653 // We'll use all of this memory to hold results of old evacuation, and we'll give back to the young generation
654 // any old regions that are not fragmented.
655 //
656 // This scenario may happen after we have promoted many regions in place, and each of these regions had non-zero
657 // unused memory, so there is now an abundance of old-fragmented available memory, even more than the desired
658 // percentage for old reserve. We cannot transfer these fragmented regions back to young. Instead we make the
659 // best of the situation by using this fragmented memory for both promotions and evacuations.
660
661 proposed_max_old = old_fragmented_available;
662 }
663 // Otherwise: old_fragmented_available <= proposed_max_old. Do not shrink proposed_max_old from the original computation.
664
665 // Though we initially set proposed_reserve_for_promo to equal the entirety of old fragmented available, we have the
666 // opportunity below to shift some of this memory into the proposed_reserve_for_mixed.
667 size_t proposed_reserve_for_promo = old_fragmented_available;
668 const size_t max_old_reserve = proposed_max_old;
669
670 const size_t mixed_candidate_live_memory = old_generation()->unprocessed_collection_candidates_live_memory();
671 const bool doing_mixed = (mixed_candidate_live_memory > 0);
672 if (doing_mixed) {
673 // In the ideal, all of the memory reserved for mixed evacuation would be unfragmented, but we don't enforce
674 // this. Note that the initial value of max_evac_need is conservative because we may not evacuate all of the
675 // remaining mixed evacuation candidates in a single cycle.
676 const size_t max_evac_need = (size_t) (mixed_candidate_live_memory * ShenandoahOldEvacWaste);
677 assert(old_currently_available >= old_generation()->free_unaffiliated_regions() * region_size_bytes,
678 "Unaffiliated available must be less than total available");
679
680 // We prefer to evacuate all of mixed into unfragmented memory, and will expand old in order to do so, unless
681 // we already have too much fragmented available memory in old.
682 proposed_reserve_for_mixed = max_evac_need;
683 if (proposed_reserve_for_mixed + proposed_reserve_for_promo > max_old_reserve) {
684 // We're trying to reserve more memory than is available. So we need to shrink our reserves.
685 size_t excess_reserves = (proposed_reserve_for_mixed + proposed_reserve_for_promo) - max_old_reserve;
686 // We need to shrink reserves by excess_reserves. We prefer to shrink by reducing promotion, giving priority to mixed
687 // evacuation. If the promotion reserve is larger than the amount we need to shrink by, do all the shrinkage there.
688 if (proposed_reserve_for_promo > excess_reserves) {
689 proposed_reserve_for_promo -= excess_reserves;
690 } else {
691 // Otherwise, we'll shrink promotion reserve to zero and we'll shrink the mixed-evac reserve by the remaining excess.
692 excess_reserves -= proposed_reserve_for_promo;
693 proposed_reserve_for_promo = 0;
694 proposed_reserve_for_mixed -= excess_reserves;
695 }
696 }
697 }
698 assert(proposed_reserve_for_mixed + proposed_reserve_for_promo <= max_old_reserve,
699 "Reserve for mixed (%zu) plus reserve for promotions (%zu) must be less than maximum old reserve (%zu)",
700 proposed_reserve_for_mixed, proposed_reserve_for_promo, max_old_reserve);
701
702 // Decide how much additional space we should reserve for promotions from young. We give priority to mixed evacations
703 // over promotions.
704 const size_t promo_load = old_generation()->get_promotion_potential();
705 const bool doing_promotions = promo_load > 0;
706
707 // promo_load represents the combined total of live memory within regions that have reached tenure age. The true
708 // promotion potential is larger than this, because individual objects within regions that have not yet reached tenure
709 // age may be promotable. On the other hand, some of the objects that we intend to promote in the next GC cycle may
710 // die before they are next marked. In the future, the promo_load will include the total size of tenurable objects
711 // residing in regions that have not yet reached tenure age.
712
713 if (doing_promotions) {
714 // We are always doing promotions, even when old_generation->get_promotion_potential() returns 0. As currently implemented,
715 // get_promotion_potential() only knows the total live memory contained within young-generation regions whose age is
716 // tenurable. It does not know whether that memory will still be live at the end of the next mark cycle, and it doesn't
717 // know how much memory is contained within objects whose individual ages are tenurable, which reside in regions with
718 // non-tenurable age. We use this, as adjusted by ShenandoahPromoEvacWaste, as an approximation of the total amount of
719 // memory to be promoted. In the near future, we expect to implement a change that will allow get_promotion_potential()
720 // to account also for the total memory contained within individual objects that are tenure-ready even when they do
721 // not reside in aged regions. This will represent a conservative over approximation of promotable memory because
722 // some of these objects may die before the next GC cycle executes.
723
724 // Be careful not to ask for too much promotion reserves. We have observed jtreg test failures under which a greedy
725 // promotion reserve causes a humongous allocation which is awaiting a full GC to fail (specifically
726 // gc/TestAllocHumongousFragment.java). This happens if too much of the memory reclaimed by the full GC
727 // is immediately reserved so that it cannot be allocated by the waiting mutator. It's not clear that this
728 // particular test is representative of the needs of typical GenShen users. It is really a test of high frequency
729 // Full GCs under heap fragmentation stress.
730
731 size_t promo_need = (size_t) (promo_load * ShenandoahPromoEvacWaste);
732 if (promo_need > proposed_reserve_for_promo) {
733 const size_t available_for_additional_promotions =
734 max_old_reserve - (proposed_reserve_for_mixed + proposed_reserve_for_promo);
735 if (proposed_reserve_for_promo + available_for_additional_promotions >= promo_need) {
736 proposed_reserve_for_promo = promo_need;
737 } else {
738 proposed_reserve_for_promo += available_for_additional_promotions;
739 }
740 }
741 }
742 // else, leave proposed_reserve_for_promo as is. By default, it is initialized to represent old_fragmented_available.
743
744 // This is the total old we want to reserve (initialized to the ideal reserve)
745 size_t proposed_old_reserve = proposed_reserve_for_mixed + proposed_reserve_for_promo;
746
747 // We now check if the old generation is running a surplus or a deficit.
748 size_t old_region_deficit = 0;
749 size_t old_region_surplus = 0;
750
751 size_t mutator_region_xfer_limit = mutator_xfer_limit / region_size_bytes;
752 // align the mutator_xfer_limit on region size
753 mutator_xfer_limit = mutator_region_xfer_limit * region_size_bytes;
754
755 if (old_currently_available >= proposed_old_reserve) {
756 // We are running a surplus, so the old region surplus can go to young
757 const size_t old_surplus = old_currently_available - proposed_old_reserve;
758 old_region_surplus = old_surplus / region_size_bytes;
759 const size_t unaffiliated_old_regions = old_generation()->free_unaffiliated_regions() + old_trashed_regions;
760 old_region_surplus = MIN2(old_region_surplus, unaffiliated_old_regions);
761 old_generation()->set_region_balance(checked_cast<ssize_t>(old_region_surplus));
762 old_currently_available -= old_region_surplus * region_size_bytes;
763 young_available += old_region_surplus * region_size_bytes;
764 } else if (old_currently_available + mutator_xfer_limit >= proposed_old_reserve) {
765 // We know that old_currently_available < proposed_old_reserve because above test failed. Expand old_currently_available.
766 // Mutator's xfer limit is sufficient to satisfy our need: transfer all memory from there.
767 size_t old_deficit = proposed_old_reserve - old_currently_available;
768 old_region_deficit = (old_deficit + region_size_bytes - 1) / region_size_bytes;
769 old_generation()->set_region_balance(0 - checked_cast<ssize_t>(old_region_deficit));
770 old_currently_available += old_region_deficit * region_size_bytes;
771 young_available -= old_region_deficit * region_size_bytes;
772 } else {
773 // We know that (old_currently_available < proposed_old_reserve) and
774 // (old_currently_available + mutator_xfer_limit < proposed_old_reserve) because above tests failed.
775 // We need to shrink proposed_old_reserves.
776
777 // We could potentially shrink young_reserves in order to further expand proposed_old_reserves. Let's not bother. The
778 // important thing is that we keep a total amount of memory in reserve in preparation for the next GC cycle. At
779 // the time we choose the next collection set, we'll have an opportunity to shift some of these young reserves
780 // into old reserves if that makes sense.
781
782 // Start by taking all of mutator_xfer_limit into old_currently_available.
783 size_t old_region_deficit = mutator_region_xfer_limit;
784 old_generation()->set_region_balance(0 - checked_cast<ssize_t>(old_region_deficit));
785 old_currently_available += old_region_deficit * region_size_bytes;
786 young_available -= old_region_deficit * region_size_bytes;
787
788 assert(old_currently_available < proposed_old_reserve,
789 "Old currently available (%zu) must be less than old reserve (%zu)", old_currently_available, proposed_old_reserve);
790
791 // There's not enough memory to satisfy our desire. Scale back our old-gen intentions. We prefer to satisfy
792 // the budget_overrun entirely from the promotion reserve, if that is large enough. Otherwise, we'll satisfy
793 // the overrun from a combination of promotion and mixed-evacuation reserves.
794 size_t budget_overrun = proposed_old_reserve - old_currently_available;
795 if (proposed_reserve_for_promo > budget_overrun) {
796 proposed_reserve_for_promo -= budget_overrun;
797 // Dead code:
798 // proposed_old_reserve -= budget_overrun;
799 } else {
800 budget_overrun -= proposed_reserve_for_promo;
801 proposed_reserve_for_promo = 0;
802 proposed_reserve_for_mixed = (proposed_reserve_for_mixed > budget_overrun)? proposed_reserve_for_mixed - budget_overrun: 0;
803 // Dead code:
804 // Note: proposed_reserve_for_promo is 0 and proposed_reserve_for_mixed may equal 0.
805 // proposed_old_reserve = proposed_reserve_for_mixed;
806 }
807 }
808
809 assert(old_region_deficit == 0 || old_region_surplus == 0,
810 "Only surplus (%zu) or deficit (%zu), never both", old_region_surplus, old_region_deficit);
811 assert(young_reserve + proposed_reserve_for_mixed + proposed_reserve_for_promo <= old_currently_available + young_available,
812 "Cannot reserve more memory than is available: %zu + %zu + %zu <= %zu + %zu",
813 young_reserve, proposed_reserve_for_mixed, proposed_reserve_for_promo, old_currently_available, young_available);
814
815 // deficit/surplus adjustments to generation sizes will precede rebuild
816 young_generation()->set_evacuation_reserve(young_reserve);
817 old_generation()->set_evacuation_reserve(proposed_reserve_for_mixed);
818 old_generation()->set_promoted_reserve(proposed_reserve_for_promo);
819 }
820
821 void ShenandoahGenerationalHeap::coalesce_and_fill_old_regions(bool concurrent) {
822 class ShenandoahGlobalCoalesceAndFill : public WorkerTask {
823 private:
824 ShenandoahPhaseTimings::Phase _phase;
825 ShenandoahRegionIterator _regions;
826 public:
827 explicit ShenandoahGlobalCoalesceAndFill(ShenandoahPhaseTimings::Phase phase) :
828 WorkerTask("Shenandoah Global Coalesce"),
829 _phase(phase) {}
830
831 void work(uint worker_id) override {
832 ShenandoahWorkerTimingsTracker timer(_phase,
833 ShenandoahPhaseTimings::ScanClusters,
834 worker_id, true);
835 ShenandoahHeapRegion* region;
836 while ((region = _regions.next()) != nullptr) {
837 // old region is not in the collection set and was not immediately trashed
838 if (region->is_old() && region->is_active() && !region->is_humongous()) {
839 // Reset the coalesce and fill boundary because this is a global collect
840 // and cannot be preempted by young collects. We want to be sure the entire
841 // region is coalesced here and does not resume from a previously interrupted
842 // or completed coalescing.
843 region->begin_preemptible_coalesce_and_fill();
844 region->oop_coalesce_and_fill(false);
845 }
846 }
847 }
848 };
849
850 ShenandoahPhaseTimings::Phase phase = concurrent ?
851 ShenandoahPhaseTimings::conc_coalesce_and_fill :
852 ShenandoahPhaseTimings::degen_gc_coalesce_and_fill;
853
854 // This is not cancellable
855 ShenandoahGlobalCoalesceAndFill coalesce(phase);
856 workers()->run_task(&coalesce);
857 old_generation()->set_parsable(true);
858 }
859
860 template<bool CONCURRENT>
861 class ShenandoahGenerationalUpdateHeapRefsTask : public WorkerTask {
862 private:
863 // For update refs, _generation will be young or global. Mixed collections use the young generation.
864 ShenandoahGeneration* _generation;
865 ShenandoahGenerationalHeap* _heap;
866 ShenandoahRegionIterator* _regions;
867 ShenandoahRegionChunkIterator* _work_chunks;
868
869 public:
870 ShenandoahGenerationalUpdateHeapRefsTask(ShenandoahGeneration* generation,
871 ShenandoahRegionIterator* regions,
872 ShenandoahRegionChunkIterator* work_chunks) :
873 WorkerTask("Shenandoah Update References"),
874 _generation(generation),
875 _heap(ShenandoahGenerationalHeap::heap()),
876 _regions(regions),
877 _work_chunks(work_chunks)
878 {
879 const bool old_bitmap_stable = _heap->old_generation()->is_mark_complete();
880 log_debug(gc, remset)("Update refs, scan remembered set using bitmap: %s", BOOL_TO_STR(old_bitmap_stable));
881 }
882
883 void work(uint worker_id) override {
884 if (CONCURRENT) {
885 ShenandoahConcurrentWorkerSession worker_session(worker_id);
886 ShenandoahSuspendibleThreadSetJoiner stsj;
887 do_work<ShenandoahConcUpdateRefsClosure>(worker_id);
888 } else {
889 ShenandoahParallelWorkerSession worker_session(worker_id);
890 do_work<ShenandoahNonConcUpdateRefsClosure>(worker_id);
891 }
892 }
893
894 private:
895 template<class T>
896 void do_work(uint worker_id) {
897 T cl;
898
899 if (CONCURRENT && (worker_id == 0)) {
900 // We ask the first worker to replenish the Mutator free set by moving regions previously reserved to hold the
901 // results of evacuation. These reserves are no longer necessary because evacuation has completed.
902 size_t cset_regions = _heap->collection_set()->count();
903
904 // Now that evacuation is done, we can reassign any regions that had been reserved to hold the results of evacuation
905 // to the mutator free set. At the end of GC, we will have cset_regions newly evacuated fully empty regions from
906 // which we will be able to replenish the Collector free set and the OldCollector free set in preparation for the
907 // next GC cycle.
908 _heap->free_set()->move_regions_from_collector_to_mutator(cset_regions);
909 }
910 // If !CONCURRENT, there's no value in expanding Mutator free set
911
912 ShenandoahHeapRegion* r = _regions->next();
913 // We update references for global, mixed, and young collections.
914 assert(_generation->is_mark_complete(), "Expected complete marking");
915 ShenandoahMarkingContext* const ctx = _heap->marking_context();
916 bool is_mixed = _heap->collection_set()->has_old_regions();
917 while (r != nullptr) {
918 HeapWord* update_watermark = r->get_update_watermark();
919 assert(update_watermark >= r->bottom(), "sanity");
920
921 log_debug(gc)("Update refs worker " UINT32_FORMAT ", looking at region %zu", worker_id, r->index());
922 if (r->is_active() && !r->is_cset()) {
923 if (r->is_young()) {
924 _heap->marked_object_oop_iterate(r, &cl, update_watermark);
925 } else if (r->is_old()) {
926 if (_generation->is_global()) {
927
928 _heap->marked_object_oop_iterate(r, &cl, update_watermark);
929 }
930 // Otherwise, this is an old region in a young or mixed cycle. Process it during a second phase, below.
931 } else {
932 // Because updating of references runs concurrently, it is possible that a FREE inactive region transitions
933 // to a non-free active region while this loop is executing. Whenever this happens, the changing of a region's
934 // active status may propagate at a different speed than the changing of the region's affiliation.
935
936 // When we reach this control point, it is because a race has allowed a region's is_active() status to be seen
937 // by this thread before the region's affiliation() is seen by this thread.
938
939 // It's ok for this race to occur because the newly transformed region does not have any references to be
940 // updated.
941
942 assert(r->get_update_watermark() == r->bottom(),
943 "%s Region %zu is_active but not recognized as YOUNG or OLD so must be newly transitioned from FREE",
944 r->affiliation_name(), r->index());
945 }
946 }
947
948 if (_heap->check_cancelled_gc_and_yield(CONCURRENT)) {
949 return;
950 }
951
952 r = _regions->next();
953 }
954
955 if (_generation->is_young()) {
956 // Since this is generational and not GLOBAL, we have to process the remembered set. There's no remembered
957 // set processing if not in generational mode or if GLOBAL mode.
958
959 // After this thread has exhausted its traditional update-refs work, it continues with updating refs within
960 // remembered set. The remembered set workload is better balanced between threads, so threads that are "behind"
961 // can catch up with other threads during this phase, allowing all threads to work more effectively in parallel.
962 update_references_in_remembered_set(worker_id, cl, ctx, is_mixed);
963 }
964 }
965
966 template<class T>
967 void update_references_in_remembered_set(uint worker_id, T &cl, const ShenandoahMarkingContext* ctx, bool is_mixed) {
968
969 struct ShenandoahRegionChunk assignment;
970 ShenandoahScanRemembered* scanner = _heap->old_generation()->card_scan();
971
972 while (!_heap->check_cancelled_gc_and_yield(CONCURRENT) && _work_chunks->next(&assignment)) {
973 // Keep grabbing next work chunk to process until finished, or asked to yield
974 ShenandoahHeapRegion* r = assignment._r;
975 if (r->is_active() && !r->is_cset() && r->is_old()) {
976 HeapWord* start_of_range = r->bottom() + assignment._chunk_offset;
977 HeapWord* end_of_range = r->get_update_watermark();
978 if (end_of_range > start_of_range + assignment._chunk_size) {
979 end_of_range = start_of_range + assignment._chunk_size;
980 }
981
982 if (start_of_range >= end_of_range) {
983 continue;
984 }
985
986 // Old region in a young cycle or mixed cycle.
987 if (is_mixed) {
988 if (r->is_humongous()) {
989 // Need to examine both dirty and clean cards during mixed evac.
990 r->oop_iterate_humongous_slice_all(&cl,start_of_range, assignment._chunk_size);
991 } else {
992 // Since this is mixed evacuation, old regions that are candidates for collection have not been coalesced
993 // and filled. This will use mark bits to find objects that need to be updated.
994 update_references_in_old_region(cl, ctx, scanner, r, start_of_range, end_of_range);
995 }
996 } else {
997 // This is a young evacuation
998 size_t cluster_size = CardTable::card_size_in_words() * ShenandoahCardCluster::CardsPerCluster;
999 size_t clusters = assignment._chunk_size / cluster_size;
1000 assert(clusters * cluster_size == assignment._chunk_size, "Chunk assignment must align on cluster boundaries");
1001 scanner->process_region_slice(r, assignment._chunk_offset, clusters, end_of_range, &cl, true, worker_id);
1002 }
1003 }
1004 }
1005 }
1006
1007 template<class T>
1008 void update_references_in_old_region(T &cl, const ShenandoahMarkingContext* ctx, ShenandoahScanRemembered* scanner,
1009 const ShenandoahHeapRegion* r, HeapWord* start_of_range,
1010 HeapWord* end_of_range) const {
1011 // In case last object in my range spans boundary of my chunk, I may need to scan all the way to top()
1012 ShenandoahObjectToOopBoundedClosure<T> objs(&cl, start_of_range, r->top());
1013
1014 // Any object that begins in a previous range is part of a different scanning assignment. Any object that
1015 // starts after end_of_range is also not my responsibility. (Either allocated during evacuation, so does
1016 // not hold pointers to from-space, or is beyond the range of my assigned work chunk.)
1017
1018 // Find the first object that begins in my range, if there is one. Note that `p` will be set to `end_of_range`
1019 // when no live object is found in the range.
1020 HeapWord* tams = ctx->top_at_mark_start(r);
1021 HeapWord* p = get_first_object_start_word(ctx, scanner, tams, start_of_range, end_of_range);
1022
1023 while (p < end_of_range) {
1024 // p is known to point to the beginning of marked object obj
1025 oop obj = cast_to_oop(p);
1026 objs.do_object(obj);
1027 HeapWord* prev_p = p;
1028 p += obj->size();
1029 if (p < tams) {
1030 p = ctx->get_next_marked_addr(p, tams);
1031 // If there are no more marked objects before tams, this returns tams. Note that tams is
1032 // either >= end_of_range, or tams is the start of an object that is marked.
1033 }
1034 assert(p != prev_p, "Lack of forward progress");
1035 }
1036 }
1037
1038 HeapWord* get_first_object_start_word(const ShenandoahMarkingContext* ctx, ShenandoahScanRemembered* scanner, HeapWord* tams,
1039 HeapWord* start_of_range, HeapWord* end_of_range) const {
1040 HeapWord* p = start_of_range;
1041
1042 if (p >= tams) {
1043 // We cannot use ctx->is_marked(obj) to test whether an object begins at this address. Instead,
1044 // we need to use the remembered set crossing map to advance p to the first object that starts
1045 // within the enclosing card.
1046 size_t card_index = scanner->card_index_for_addr(start_of_range);
1047 while (true) {
1048 HeapWord* first_object = scanner->first_object_in_card(card_index);
1049 if (first_object != nullptr) {
1050 p = first_object;
1051 break;
1052 } else if (scanner->addr_for_card_index(card_index + 1) < end_of_range) {
1053 card_index++;
1054 } else {
1055 // Signal that no object was found in range
1056 p = end_of_range;
1057 break;
1058 }
1059 }
1060 } else if (!ctx->is_marked(cast_to_oop(p))) {
1061 p = ctx->get_next_marked_addr(p, tams);
1062 // If there are no more marked objects before tams, this returns tams.
1063 // Note that tams is either >= end_of_range, or tams is the start of an object that is marked.
1064 }
1065 return p;
1066 }
1067 };
1068
1069 void ShenandoahGenerationalHeap::update_heap_references(ShenandoahGeneration* generation, bool concurrent) {
1070 assert(!is_full_gc_in_progress(), "Only for concurrent and degenerated GC");
1071 const uint nworkers = workers()->active_workers();
1072 ShenandoahRegionChunkIterator work_list(nworkers);
1073 if (concurrent) {
1074 ShenandoahGenerationalUpdateHeapRefsTask<true> task(generation, &_update_refs_iterator, &work_list);
1075 workers()->run_task(&task);
1076 } else {
1077 ShenandoahGenerationalUpdateHeapRefsTask<false> task(generation, &_update_refs_iterator, &work_list);
1078 workers()->run_task(&task);
1079 }
1080
1081 if (ShenandoahEnableCardStats) {
1082 // Only do this if we are collecting card stats
1083 ShenandoahScanRemembered* card_scan = old_generation()->card_scan();
1084 assert(card_scan != nullptr, "Card table must exist when card stats are enabled");
1085 card_scan->log_card_stats(nworkers, CARD_STAT_UPDATE_REFS);
1086 }
1087 }
1088
1089 struct ShenandoahCompositeRegionClosure {
1090 template<typename C1, typename C2>
1091 class Closure : public ShenandoahHeapRegionClosure {
1092 private:
1093 C1 &_c1;
1094 C2 &_c2;
1095
1096 public:
1097 Closure(C1 &c1, C2 &c2) : ShenandoahHeapRegionClosure(), _c1(c1), _c2(c2) {}
1098
1099 void heap_region_do(ShenandoahHeapRegion* r) override {
1100 _c1.heap_region_do(r);
1101 _c2.heap_region_do(r);
1102 }
1103
1104 bool is_thread_safe() override {
1105 return _c1.is_thread_safe() && _c2.is_thread_safe();
1106 }
1107 };
1108
1109 template<typename C1, typename C2>
1110 static Closure<C1, C2> of(C1 &c1, C2 &c2) {
1111 return Closure<C1, C2>(c1, c2);
1112 }
1113 };
1114
1115 class ShenandoahUpdateRegionAges : public ShenandoahHeapRegionClosure {
1116 private:
1117 ShenandoahMarkingContext* _ctx;
1118
1119 public:
1120 explicit ShenandoahUpdateRegionAges(ShenandoahMarkingContext* ctx) : _ctx(ctx) { }
1121
1122 void heap_region_do(ShenandoahHeapRegion* r) override {
1123 // Maintenance of region age must follow evacuation in order to account for
1124 // evacuation allocations within survivor regions. We consult region age during
1125 // the subsequent evacuation to determine whether certain objects need to
1126 // be promoted.
1127 if (r->is_young() && r->is_active()) {
1128 HeapWord *tams = _ctx->top_at_mark_start(r);
1129 HeapWord *top = r->top();
1130
1131 // Allocations move the watermark when top moves. However, compacting
1132 // objects will sometimes lower top beneath the watermark, after which,
1133 // attempts to read the watermark will assert out (watermark should not be
1134 // higher than top).
1135 if (top > tams) {
1136 // There have been allocations in this region since the start of the cycle.
1137 // Any objects new to this region must not assimilate elevated age.
1138 r->reset_age();
1139 } else if (ShenandoahGenerationalHeap::heap()->is_aging_cycle()) {
1140 r->increment_age();
1141 }
1142 }
1143 }
1144
1145 bool is_thread_safe() override {
1146 return true;
1147 }
1148 };
1149
1150 void ShenandoahGenerationalHeap::final_update_refs_update_region_states() {
1151 ShenandoahSynchronizePinnedRegionStates pins;
1152 ShenandoahUpdateRegionAges ages(marking_context());
1153 auto cl = ShenandoahCompositeRegionClosure::of(pins, ages);
1154 parallel_heap_region_iterate(&cl);
1155 }
1156
1157 void ShenandoahGenerationalHeap::complete_degenerated_cycle() {
1158 shenandoah_assert_heaplocked_or_safepoint();
1159 if (!old_generation()->is_parsable()) {
1160 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_coalesce_and_fill);
1161 coalesce_and_fill_old_regions(false);
1162 }
1163
1164 log_info(gc, cset)("Degenerated cycle complete, promotions reserved: %zu, promotions expended: %zu, failed count: %zu, failed bytes: %zu",
1165 old_generation()->get_promoted_reserve(), old_generation()->get_promoted_expended(),
1166 old_generation()->get_promotion_failed_count(), old_generation()->get_promotion_failed_words() * HeapWordSize);
1167 }
1168
1169 void ShenandoahGenerationalHeap::complete_concurrent_cycle() {
1170 if (!old_generation()->is_parsable()) {
1171 // Class unloading may render the card offsets unusable, so we must rebuild them before
1172 // the next remembered set scan. We _could_ let the control thread do this sometime after
1173 // the global cycle has completed and before the next young collection, but under memory
1174 // pressure the control thread may not have the time (that is, because it's running back
1175 // to back GCs). In that scenario, we would have to make the old regions parsable before
1176 // we could start a young collection. This could delay the start of the young cycle and
1177 // throw off the heuristics.
1178 entry_global_coalesce_and_fill();
1179 }
1180
1181 log_info(gc, cset)("Concurrent cycle complete, promotions reserved: %zu, promotions expended: %zu, failed count: %zu, failed bytes: %zu",
1182 old_generation()->get_promoted_reserve(), old_generation()->get_promoted_expended(),
1183 old_generation()->get_promotion_failed_count(), old_generation()->get_promotion_failed_words() * HeapWordSize);
1184 }
1185
1186 void ShenandoahGenerationalHeap::entry_global_coalesce_and_fill() {
1187 const char* msg = "Coalescing and filling old regions";
1188 ShenandoahConcurrentPhase gc_phase(msg, ShenandoahPhaseTimings::conc_coalesce_and_fill);
1189
1190 TraceCollectorStats tcs(monitoring_support()->concurrent_collection_counters());
1191 EventMark em("%s", msg);
1192 ShenandoahWorkerScope scope(workers(),
1193 ShenandoahWorkerPolicy::calc_workers_for_conc_marking(),
1194 "concurrent coalesce and fill");
1195
1196 coalesce_and_fill_old_regions(true);
1197 }
1198
1199 void ShenandoahGenerationalHeap::update_region_ages(ShenandoahMarkingContext* ctx) {
1200 ShenandoahUpdateRegionAges cl(ctx);
1201 parallel_heap_region_iterate(&cl);
1202 }