1 /*
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3 * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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6 * This code is free software; you can redistribute it and/or modify it
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8 * published by the Free Software Foundation.
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14 * accompanied this code).
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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 PLAB::min_size();
69 }
70
71 size_t ShenandoahGenerationalHeap::calculate_max_plab() {
72 return ShenandoahHeapRegion::max_tlab_size_words();
73 }
74
75 // Returns size in bytes
76 size_t ShenandoahGenerationalHeap::unsafe_max_tlab_alloc() const {
77 return MIN2(ShenandoahHeapRegion::max_tlab_size_bytes(), young_generation()->available());
78 }
79
80 ShenandoahGenerationalHeap::ShenandoahGenerationalHeap(ShenandoahCollectorPolicy* policy) :
81 ShenandoahHeap(policy),
82 _age_census(nullptr),
83 _min_plab_size(calculate_min_plab()),
84 _max_plab_size(calculate_max_plab()),
85 _regulator_thread(nullptr),
86 _young_gen_memory_pool(nullptr),
87 _old_gen_memory_pool(nullptr) {
88 }
89
90 void ShenandoahGenerationalHeap::initialize_generations() {
91 ShenandoahHeap::initialize_generations();
92 _young_generation->post_initialize(this);
93 _old_generation->post_initialize(this);
94 }
95
96 void ShenandoahGenerationalHeap::post_initialize() {
97 ShenandoahHeap::post_initialize();
98 _age_census = new ShenandoahAgeCensus();
99 }
100
101 void ShenandoahGenerationalHeap::post_initialize_heuristics() {
102 ShenandoahHeap::post_initialize_heuristics();
103 _young_generation->post_initialize_heuristics();
104 _old_generation->post_initialize_heuristics();
105 }
106
107 void ShenandoahGenerationalHeap::print_init_logger() const {
108 ShenandoahGenerationalInitLogger logger;
109 logger.print_all();
110 }
111
112 void ShenandoahGenerationalHeap::initialize_heuristics() {
113 // Initialize global generation and heuristics even in generational mode.
114 ShenandoahHeap::initialize_heuristics();
115
116 _young_generation = new ShenandoahYoungGeneration(max_workers());
117 _old_generation = new ShenandoahOldGeneration(max_workers());
118 _young_generation->initialize_heuristics(mode());
119 _old_generation->initialize_heuristics(mode());
120 }
121
122 void ShenandoahGenerationalHeap::initialize_serviceability() {
123 assert(mode()->is_generational(), "Only for the generational mode");
124 _young_gen_memory_pool = new ShenandoahYoungGenMemoryPool(this);
125 _old_gen_memory_pool = new ShenandoahOldGenMemoryPool(this);
126 cycle_memory_manager()->add_pool(_young_gen_memory_pool);
127 cycle_memory_manager()->add_pool(_old_gen_memory_pool);
128 stw_memory_manager()->add_pool(_young_gen_memory_pool);
129 stw_memory_manager()->add_pool(_old_gen_memory_pool);
130 }
131
132 GrowableArray<MemoryPool*> ShenandoahGenerationalHeap::memory_pools() {
133 assert(mode()->is_generational(), "Only for the generational mode");
134 GrowableArray<MemoryPool*> memory_pools(2);
135 memory_pools.append(_young_gen_memory_pool);
136 memory_pools.append(_old_gen_memory_pool);
137 return memory_pools;
138 }
139
140 void ShenandoahGenerationalHeap::initialize_controller() {
141 auto control_thread = new ShenandoahGenerationalControlThread();
142 _control_thread = control_thread;
143 _regulator_thread = new ShenandoahRegulatorThread(control_thread);
144 }
145
146 void ShenandoahGenerationalHeap::gc_threads_do(ThreadClosure* tcl) const {
147 if (!shenandoah_policy()->is_at_shutdown()) {
148 ShenandoahHeap::gc_threads_do(tcl);
149 tcl->do_thread(regulator_thread());
150 }
151 }
152
153 void ShenandoahGenerationalHeap::stop() {
154 ShenandoahHeap::stop();
155 regulator_thread()->stop();
156 }
157
158 void ShenandoahGenerationalHeap::start_idle_span() {
159 young_generation()->heuristics()->start_idle_span();
160 }
161
162 bool ShenandoahGenerationalHeap::requires_barriers(stackChunkOop obj) const {
163 if (is_idle()) {
164 return false;
165 }
166
167 if (is_concurrent_young_mark_in_progress() && is_in_young(obj) && !marking_context()->allocated_after_mark_start(obj)) {
168 // We are marking young, this object is in young, and it is below the TAMS
169 return true;
170 }
171
172 if (is_in_old(obj)) {
173 // Card marking barriers are required for objects in the old generation
174 return true;
175 }
176
177 if (has_forwarded_objects()) {
178 // Object may have pointers that need to be updated
179 return true;
180 }
181
182 return false;
183 }
184
185 void ShenandoahGenerationalHeap::evacuate_collection_set(ShenandoahGeneration* generation, bool concurrent) {
186 ShenandoahRegionIterator regions;
187 ShenandoahGenerationalEvacuationTask task(this, generation, ®ions, concurrent, false /* only promote regions */);
188 workers()->run_task(&task);
189 }
190
191 void ShenandoahGenerationalHeap::promote_regions_in_place(ShenandoahGeneration* generation, bool concurrent) {
192 ShenandoahRegionIterator regions;
193 ShenandoahGenerationalEvacuationTask task(this, generation, ®ions, concurrent, true /* only promote regions */);
194 workers()->run_task(&task);
195 }
196
197 oop ShenandoahGenerationalHeap::evacuate_object(oop p, Thread* thread) {
198 assert(thread == Thread::current(), "Expected thread parameter to be current thread.");
199
200 ShenandoahHeapRegion* from_region = heap_region_containing(p);
201 assert(!from_region->is_humongous(), "never evacuate humongous objects");
202
203 // Try to keep the object in the same generation
204 const ShenandoahAffiliation target_gen = from_region->affiliation();
205
206 if (target_gen == YOUNG_GENERATION) {
207 markWord mark = p->mark();
208 if (mark.is_marked()) {
209 // Already forwarded.
210 return ShenandoahBarrierSet::resolve_forwarded(p);
211 }
212
213 if (mark.has_displaced_mark_helper()) {
214 // We don't want to deal with MT here just to ensure we read the right mark word.
215 // Skip the potential promotion attempt for this one.
216 } else if (age_census()->is_tenurable(from_region->age() + mark.age())) {
217 // If the object is tenurable, try to promote it
218 oop result = try_evacuate_object<YOUNG_GENERATION, OLD_GENERATION>(p, thread, from_region->age());
219
220 // If we failed to promote this aged object, we'll fall through to code below and evacuate to young-gen.
221 if (result != nullptr) {
222 return result;
223 }
224 }
225 return try_evacuate_object<YOUNG_GENERATION, YOUNG_GENERATION>(p, thread, from_region->age());
226 }
227
228 assert(target_gen == OLD_GENERATION, "Expected evacuation to old");
229 return try_evacuate_object<OLD_GENERATION, OLD_GENERATION>(p, thread, from_region->age());
230 }
231
232 // try_evacuate_object registers the object and dirties the associated remembered set information when evacuating
233 // to OLD_GENERATION.
234 template<ShenandoahAffiliation FROM_GENERATION, ShenandoahAffiliation TO_GENERATION>
235 oop ShenandoahGenerationalHeap::try_evacuate_object(oop p, Thread* thread, uint from_region_age) {
236 bool alloc_from_lab = true;
237 bool has_plab = false;
238 HeapWord* copy = nullptr;
239 size_t size = ShenandoahForwarding::size(p);
240 constexpr bool is_promotion = (TO_GENERATION == OLD_GENERATION) && (FROM_GENERATION == YOUNG_GENERATION);
241
242 #ifdef ASSERT
243 if (ShenandoahOOMDuringEvacALot &&
244 (os::random() & 1) == 0) { // Simulate OOM every ~2nd slow-path call
245 copy = nullptr;
246 } else {
247 #endif
248 if (UseTLAB) {
249 switch (TO_GENERATION) {
250 case YOUNG_GENERATION: {
251 copy = allocate_from_gclab(thread, size);
252 if ((copy == nullptr) && (size < ShenandoahThreadLocalData::gclab_size(thread))) {
253 // GCLAB allocation failed because we are bumping up against the limit on young evacuation reserve. Try resetting
254 // the desired GCLAB size and retry GCLAB allocation to avoid cascading of shared memory allocations.
255 ShenandoahThreadLocalData::set_gclab_size(thread, PLAB::min_size());
256 copy = allocate_from_gclab(thread, size);
257 // If we still get nullptr, we'll try a shared allocation below.
258 }
259 break;
260 }
261 case OLD_GENERATION: {
262 ShenandoahPLAB* shenandoah_plab = ShenandoahThreadLocalData::shenandoah_plab(thread);
263 if (shenandoah_plab != nullptr) {
264 has_plab = true;
265 copy = shenandoah_plab->allocate(size, is_promotion);
266 if (copy == nullptr && size < shenandoah_plab->desired_size() && shenandoah_plab->retries_enabled()) {
267 // PLAB allocation failed because we are bumping up against the limit on old evacuation reserve or because
268 // the requested object does not fit within the current plab but the plab still has an "abundance" of memory,
269 // where abundance is defined as >= ShenGenHeap::plab_min_size(). In the former case, we try shrinking the
270 // desired PLAB size to the minimum and retry PLAB allocation to avoid cascading of shared memory allocations.
271 // Shrinking the desired PLAB size may allow us to eke out a small PLAB while staying beneath evacuation reserve.
272 if (shenandoah_plab->plab()->words_remaining() < plab_min_size()) {
273 shenandoah_plab->set_desired_size(plab_min_size());
274 copy = shenandoah_plab->allocate(size, is_promotion);
275 if (copy == nullptr) {
276 // If we still get nullptr, we'll try a shared allocation below.
277 // However, don't continue to retry until we have success (probably in next GC pass)
278 shenandoah_plab->disable_retries();
279 }
280 }
281 }
282 }
283 break;
284 }
285 default: {
286 ShouldNotReachHere();
287 break;
288 }
289 }
290 }
291
292 if (copy == nullptr) {
293 // If we failed to allocate in LAB, we'll try a shared allocation.
294 if (!is_promotion || !has_plab || (size > PLAB::min_size())) {
295 ShenandoahAllocRequest req = ShenandoahAllocRequest::for_shared_gc(size, TO_GENERATION, is_promotion);
296 copy = allocate_memory(req);
297 alloc_from_lab = false;
298 }
299 // else, we leave copy equal to nullptr, signaling a promotion failure below if appropriate.
300 // We choose not to promote objects smaller than size_threshold by way of shared allocations as this is too
301 // costly. Instead, we'll simply "evacuate" to young-gen memory (using a GCLAB) and will promote in a future
302 // evacuation pass. This condition is denoted by: is_promotion && has_plab && (size <= size_threshhold).
303 }
304 #ifdef ASSERT
305 }
306 #endif
307
308 if (copy == nullptr) {
309 if (TO_GENERATION == OLD_GENERATION) {
310 if (FROM_GENERATION == YOUNG_GENERATION) {
311 // Signal that promotion failed. Will evacuate this old object somewhere in young gen.
312 old_generation()->handle_failed_promotion(thread, size);
313 return nullptr;
314 } else {
315 // Remember that evacuation to old gen failed. We'll want to trigger a full gc to recover from this
316 // after the evacuation threads have finished.
317 old_generation()->handle_failed_evacuation();
318 }
319 }
320
321 control_thread()->handle_alloc_failure_evac(size);
322
323 // Install the self-forwarded bit so other evacuators/LRBs see the
324 // object as "already handled, do not try to evacuate". The CAS may
325 // fail if another thread concurrently installed a real forwardee or
326 // self-forwarded first.
327 markWord old_mark = p->mark();
328 if (old_mark.is_forwarded()) {
329 return ShenandoahForwarding::get_forwardee(p);
330 }
331 oop winner = ShenandoahForwarding::try_forward_to_self(p, old_mark);
332 if (winner == nullptr) {
333 // We own the self-forwarding. Flag the from-region so the degen/full
334 // GC entry drain knows to scan it for self_fwd bits to clear.
335 heap_region_containing(p)->set_has_self_forwards();
336 return p;
337 }
338 return winner;
339 }
340
341 if (ShenandoahEvacTracking) {
342 evac_tracker()->begin_evacuation(thread, size * HeapWordSize, FROM_GENERATION, TO_GENERATION);
343 }
344
345 // Copy the object:
346 Copy::aligned_disjoint_words(cast_from_oop<HeapWord*>(p), copy, size);
347 oop copy_val = cast_to_oop(copy);
348
349 // Update the age of the evacuated object
350 if (TO_GENERATION == YOUNG_GENERATION) {
351 increase_object_age(copy_val, from_region_age + 1);
352 }
353
354 // Relativize stack chunks before publishing the copy. After the forwarding CAS,
355 // mutators can see the copy and thaw it via the fast path if flags == 0. We must
356 // relativize derived pointers and set gc_mode before that happens. Skip if the
357 // copy's mark word is already a forwarding pointer (another thread won the race
358 // and overwrote the original's header before we copied it).
359 if (!ShenandoahForwarding::is_forwarded(copy_val)) {
360 ContinuationGCSupport::relativize_stack_chunk(copy_val);
361 }
362
363 // Try to install the new forwarding pointer.
364 oop result = ShenandoahForwarding::try_update_forwardee(p, copy_val);
365 if (result == copy_val) {
366 // Successfully evacuated. Our copy is now the public one!
367 if (ShenandoahEvacTracking) {
368 // Record that the evacuation succeeded
369 evac_tracker()->end_evacuation(thread, size * HeapWordSize, FROM_GENERATION, TO_GENERATION);
370 }
371 } else {
372 // Failed to evacuate. We need to deal with the object that is left behind. Since this
373 // new allocation is certainly after TAMS, it will be considered live in the next cycle.
374 // But if it happens to contain references to evacuated regions, those references would
375 // not get updated for this stale copy during this cycle, and we will crash while scanning
376 // it the next cycle.
377 if (alloc_from_lab) {
378 // For LAB allocations, it is enough to rollback the allocation ptr. Either the next
379 // object will overwrite this stale copy, or the filler object on LAB retirement will
380 // do this.
381 switch (TO_GENERATION) {
382 case YOUNG_GENERATION: {
383 ShenandoahThreadLocalData::gclab(thread)->undo_allocation(copy, size);
384 break;
385 }
386 case OLD_GENERATION: {
387 ShenandoahThreadLocalData::shenandoah_plab(thread)->plab()->undo_allocation(copy, size);
388 if (is_promotion) {
389 ShenandoahThreadLocalData::shenandoah_plab(thread)->subtract_from_promoted(size * HeapWordSize);
390 }
391 break;
392 }
393 default: {
394 ShouldNotReachHere();
395 break;
396 }
397 }
398 } else {
399 // For non-LAB allocations, we have no way to retract the allocation, and
400 // have to explicitly overwrite the copy with the filler object. With that overwrite,
401 // we have to keep the fwdptr initialized and pointing to our (stale) copy.
402 assert(size >= ShenandoahHeap::min_fill_size(), "previously allocated object known to be larger than min_size");
403 fill_with_object(copy, size);
404 }
405 }
406 shenandoah_assert_correct(nullptr, result);
407 return result;
408 }
409
410 template oop ShenandoahGenerationalHeap::try_evacuate_object<YOUNG_GENERATION, YOUNG_GENERATION>(oop p, Thread* thread, uint from_region_age);
411 template oop ShenandoahGenerationalHeap::try_evacuate_object<YOUNG_GENERATION, OLD_GENERATION>(oop p, Thread* thread, uint from_region_age);
412 template oop ShenandoahGenerationalHeap::try_evacuate_object<OLD_GENERATION, OLD_GENERATION>(oop p, Thread* thread, uint from_region_age);
413
414 // Call this function at the end of a GC cycle in order to establish proper sizes of young and old reserves,
415 // setting the old-generation balance so that GC can perform the anticipated evacuations.
416 //
417 // Make sure old-generation is large enough, but no larger than is necessary, to hold mixed evacuations
418 // and promotions, if we anticipate either. Any deficit is provided by the young generation, subject to
419 // mutator_xfer_limit, and any surplus is transferred to the young generation. mutator_xfer_limit is
420 // the maximum we're able to transfer from young to old. The mutator_xfer_limit constrains the transfer
421 // of memory from young to old. It does not limit young reserves.
422 void ShenandoahGenerationalHeap::compute_old_generation_balance(size_t mutator_xfer_limit,
423 size_t old_trashed_regions, size_t young_trashed_regions) {
424 shenandoah_assert_heaplocked();
425 // We can limit the old reserve to the size of anticipated promotions:
426 // max_old_reserve is an upper bound on memory evacuated from old and promoted to old,
427 // clamped by the old generation space available.
428 //
429 // Here's the algebra.
430 // Let SOEP = ShenandoahOldEvacPercent,
431 // OE = old evac,
432 // YE = young evac, and
433 // TE = total evac = OE + YE
434 // By definition:
435 // SOEP/100 = OE/TE
436 // = OE/(OE+YE)
437 // => SOEP/(100-SOEP) = OE/((OE+YE)-OE) // componendo-dividendo: If a/b = c/d, then a/(b-a) = c/(d-c)
438 // = OE/YE
439 // => OE = YE*SOEP/(100-SOEP)
440
441 // We have to be careful in the event that SOEP is set to 100 by the user.
442 assert(ShenandoahOldEvacPercent <= 100, "Error");
443 const size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
444
445 ShenandoahOldGeneration* old_gen = old_generation();
446 size_t old_capacity = old_gen->max_capacity();
447 size_t old_usage = old_gen->used(); // includes humongous waste
448 size_t old_currently_available =
449 ((old_capacity >= old_usage)? old_capacity - old_usage: 0) + old_trashed_regions * region_size_bytes;
450
451 ShenandoahYoungGeneration* young_gen = young_generation();
452 size_t young_capacity = young_gen->max_capacity();
453 size_t young_usage = young_gen->used(); // includes humongous waste
454 size_t young_available = ((young_capacity >= young_usage)? young_capacity - young_usage: 0);
455 size_t freeset_available = free_set()->available_locked();
456 if (young_available > freeset_available) {
457 young_available = freeset_available;
458 }
459 young_available += young_trashed_regions * region_size_bytes;
460
461 // The free set will reserve this amount of memory to hold young evacuations (initialized to the ideal reserve)
462 size_t young_reserve = (young_generation()->max_capacity() * ShenandoahEvacReserve) / 100;
463
464 // If ShenandoahOldEvacPercent equals 100, max_old_reserve is limited only by mutator_xfer_limit and young_reserve
465 const size_t bound_on_old_reserve =
466 ((old_currently_available + mutator_xfer_limit + young_reserve) * ShenandoahOldEvacPercent) / 100;
467 size_t proposed_max_old = ((ShenandoahOldEvacPercent == 100)?
468 bound_on_old_reserve:
469 MIN2((young_reserve * ShenandoahOldEvacPercent) / (100 - ShenandoahOldEvacPercent),
470 bound_on_old_reserve));
471 assert(mutator_xfer_limit <= young_available,
472 "Cannot transfer (%zu) memory that is not available (%zu)", mutator_xfer_limit, young_available);
473
474 if (young_reserve > young_available) {
475 young_reserve = young_available;
476 }
477 // We allow young_reserve to exceed mutator_xfer_limit. Essentially, this means the GC is already behind the pace
478 // of mutator allocations, and we'll need to trigger the next GC as soon as possible.
479 if (mutator_xfer_limit > young_reserve) {
480 mutator_xfer_limit -= young_reserve;
481 } else {
482 mutator_xfer_limit = 0;
483 }
484
485 // Decide how much old space we should reserve for a mixed collection
486 size_t proposed_reserve_for_mixed = 0;
487 const size_t old_fragmented_available =
488 old_currently_available - (old_generation()->free_unaffiliated_regions() + old_trashed_regions) * region_size_bytes;
489
490 if (old_fragmented_available > proposed_max_old) {
491 // In this case, the old_fragmented_available is greater than the desired amount of evacuation to old.
492 // We'll use all of this memory to hold results of old evacuation, and we'll give back to the young generation
493 // any old regions that are not fragmented.
494 //
495 // This scenario may happen after we have promoted many regions in place, and each of these regions had non-zero
496 // unused memory, so there is now an abundance of old-fragmented available memory, even more than the desired
497 // percentage for old reserve. We cannot transfer these fragmented regions back to young. Instead we make the
498 // best of the situation by using this fragmented memory for both promotions and evacuations.
499
500 proposed_max_old = old_fragmented_available;
501 }
502 // Otherwise: old_fragmented_available <= proposed_max_old. Do not shrink proposed_max_old from the original computation.
503
504 // Though we initially set proposed_reserve_for_promo to equal the entirety of old fragmented available, we have the
505 // opportunity below to shift some of this memory into the proposed_reserve_for_mixed.
506 size_t proposed_reserve_for_promo = old_fragmented_available;
507 const size_t max_old_reserve = proposed_max_old;
508
509 const size_t mixed_candidate_live_memory = old_generation()->unprocessed_collection_candidates_live_memory();
510 const bool doing_mixed = (mixed_candidate_live_memory > 0);
511 if (doing_mixed) {
512 // In the ideal, all of the memory reserved for mixed evacuation would be unfragmented, but we don't enforce
513 // this. Note that the initial value of max_evac_need is conservative because we may not evacuate all of the
514 // remaining mixed evacuation candidates in a single cycle.
515 const size_t max_evac_need = (size_t) (mixed_candidate_live_memory * ShenandoahOldEvacWaste);
516 assert(old_currently_available >= old_generation()->free_unaffiliated_regions() * region_size_bytes,
517 "Unaffiliated available must be less than total available");
518
519 // We prefer to evacuate all of mixed into unfragmented memory, and will expand old in order to do so, unless
520 // we already have too much fragmented available memory in old.
521 proposed_reserve_for_mixed = max_evac_need;
522 if (proposed_reserve_for_mixed + proposed_reserve_for_promo > max_old_reserve) {
523 // We're trying to reserve more memory than is available. So we need to shrink our reserves.
524 size_t excess_reserves = (proposed_reserve_for_mixed + proposed_reserve_for_promo) - max_old_reserve;
525 // We need to shrink reserves by excess_reserves. We prefer to shrink by reducing promotion, giving priority to mixed
526 // evacuation. If the promotion reserve is larger than the amount we need to shrink by, do all the shrinkage there.
527 if (proposed_reserve_for_promo > excess_reserves) {
528 proposed_reserve_for_promo -= excess_reserves;
529 } else {
530 // Otherwise, we'll shrink promotion reserve to zero and we'll shrink the mixed-evac reserve by the remaining excess.
531 excess_reserves -= proposed_reserve_for_promo;
532 proposed_reserve_for_promo = 0;
533 proposed_reserve_for_mixed -= excess_reserves;
534 }
535 }
536 }
537 assert(proposed_reserve_for_mixed + proposed_reserve_for_promo <= max_old_reserve,
538 "Reserve for mixed (%zu) plus reserve for promotions (%zu) must be less than maximum old reserve (%zu)",
539 proposed_reserve_for_mixed, proposed_reserve_for_promo, max_old_reserve);
540
541 // Decide how much additional space we should reserve for promotions from young. We give priority to mixed evacations
542 // over promotions.
543 const size_t promo_load = old_generation()->get_promotion_potential();
544 const bool doing_promotions = promo_load > 0;
545
546 // promo_load represents the combined total of live memory within regions that have reached tenure age. The true
547 // promotion potential is larger than this, because individual objects within regions that have not yet reached tenure
548 // age may be promotable. On the other hand, some of the objects that we intend to promote in the next GC cycle may
549 // die before they are next marked. In the future, the promo_load will include the total size of tenurable objects
550 // residing in regions that have not yet reached tenure age.
551
552 if (doing_promotions) {
553 // We are always doing promotions, even when old_generation->get_promotion_potential() returns 0. As currently implemented,
554 // get_promotion_potential() only knows the total live memory contained within young-generation regions whose age is
555 // tenurable. It does not know whether that memory will still be live at the end of the next mark cycle, and it doesn't
556 // know how much memory is contained within objects whose individual ages are tenurable, which reside in regions with
557 // non-tenurable age. We use this, as adjusted by ShenandoahPromoEvacWaste, as an approximation of the total amount of
558 // memory to be promoted. In the near future, we expect to implement a change that will allow get_promotion_potential()
559 // to account also for the total memory contained within individual objects that are tenure-ready even when they do
560 // not reside in aged regions. This will represent a conservative over approximation of promotable memory because
561 // some of these objects may die before the next GC cycle executes.
562
563 // Be careful not to ask for too much promotion reserves. We have observed jtreg test failures under which a greedy
564 // promotion reserve causes a humongous allocation which is awaiting a full GC to fail (specifically
565 // gc/TestAllocHumongousFragment.java). This happens if too much of the memory reclaimed by the full GC
566 // is immediately reserved so that it cannot be allocated by the waiting mutator. It's not clear that this
567 // particular test is representative of the needs of typical GenShen users. It is really a test of high frequency
568 // Full GCs under heap fragmentation stress.
569
570 size_t promo_need = (size_t) (promo_load * ShenandoahPromoEvacWaste);
571 if (promo_need > proposed_reserve_for_promo) {
572 const size_t available_for_additional_promotions =
573 max_old_reserve - (proposed_reserve_for_mixed + proposed_reserve_for_promo);
574 if (proposed_reserve_for_promo + available_for_additional_promotions >= promo_need) {
575 proposed_reserve_for_promo = promo_need;
576 } else {
577 proposed_reserve_for_promo += available_for_additional_promotions;
578 }
579 }
580 }
581 // else, leave proposed_reserve_for_promo as is. By default, it is initialized to represent old_fragmented_available.
582
583 // This is the total old we want to reserve (initialized to the ideal reserve)
584 size_t proposed_old_reserve = proposed_reserve_for_mixed + proposed_reserve_for_promo;
585
586 // We now check if the old generation is running a surplus or a deficit.
587 size_t old_region_deficit = 0;
588 size_t old_region_surplus = 0;
589
590 size_t mutator_region_xfer_limit = mutator_xfer_limit / region_size_bytes;
591 // align the mutator_xfer_limit on region size
592 mutator_xfer_limit = mutator_region_xfer_limit * region_size_bytes;
593
594 if (old_currently_available >= proposed_old_reserve) {
595 // We are running a surplus, so the old region surplus can go to young
596 const size_t old_surplus = old_currently_available - proposed_old_reserve;
597 old_region_surplus = old_surplus / region_size_bytes;
598 const size_t unaffiliated_old_regions = old_generation()->free_unaffiliated_regions() + old_trashed_regions;
599 old_region_surplus = MIN2(old_region_surplus, unaffiliated_old_regions);
600 old_generation()->set_region_balance(checked_cast<ssize_t>(old_region_surplus));
601 old_currently_available -= old_region_surplus * region_size_bytes;
602 young_available += old_region_surplus * region_size_bytes;
603 } else if (old_currently_available + mutator_xfer_limit >= proposed_old_reserve) {
604 // We know that old_currently_available < proposed_old_reserve because above test failed. Expand old_currently_available.
605 // Mutator's xfer limit is sufficient to satisfy our need: transfer all memory from there.
606 size_t old_deficit = proposed_old_reserve - old_currently_available;
607 old_region_deficit = (old_deficit + region_size_bytes - 1) / region_size_bytes;
608 old_generation()->set_region_balance(0 - checked_cast<ssize_t>(old_region_deficit));
609 old_currently_available += old_region_deficit * region_size_bytes;
610 young_available -= old_region_deficit * region_size_bytes;
611 } else {
612 // We know that (old_currently_available < proposed_old_reserve) and
613 // (old_currently_available + mutator_xfer_limit < proposed_old_reserve) because above tests failed.
614 // We need to shrink proposed_old_reserves.
615
616 // We could potentially shrink young_reserves in order to further expand proposed_old_reserves. Let's not bother. The
617 // important thing is that we keep a total amount of memory in reserve in preparation for the next GC cycle. At
618 // the time we choose the next collection set, we'll have an opportunity to shift some of these young reserves
619 // into old reserves if that makes sense.
620
621 // Start by taking all of mutator_xfer_limit into old_currently_available.
622 size_t old_region_deficit = mutator_region_xfer_limit;
623 old_generation()->set_region_balance(0 - checked_cast<ssize_t>(old_region_deficit));
624 old_currently_available += old_region_deficit * region_size_bytes;
625 young_available -= old_region_deficit * region_size_bytes;
626
627 assert(old_currently_available < proposed_old_reserve,
628 "Old currently available (%zu) must be less than old reserve (%zu)", old_currently_available, proposed_old_reserve);
629
630 // There's not enough memory to satisfy our desire. Scale back our old-gen intentions. We prefer to satisfy
631 // the budget_overrun entirely from the promotion reserve, if that is large enough. Otherwise, we'll satisfy
632 // the overrun from a combination of promotion and mixed-evacuation reserves.
633 size_t budget_overrun = proposed_old_reserve - old_currently_available;
634 if (proposed_reserve_for_promo > budget_overrun) {
635 proposed_reserve_for_promo -= budget_overrun;
636 // Dead code:
637 // proposed_old_reserve -= budget_overrun;
638 } else {
639 budget_overrun -= proposed_reserve_for_promo;
640 proposed_reserve_for_promo = 0;
641 proposed_reserve_for_mixed = (proposed_reserve_for_mixed > budget_overrun)? proposed_reserve_for_mixed - budget_overrun: 0;
642 // Dead code:
643 // Note: proposed_reserve_for_promo is 0 and proposed_reserve_for_mixed may equal 0.
644 // proposed_old_reserve = proposed_reserve_for_mixed;
645 }
646 }
647
648 assert(old_region_deficit == 0 || old_region_surplus == 0,
649 "Only surplus (%zu) or deficit (%zu), never both", old_region_surplus, old_region_deficit);
650 assert(young_reserve + proposed_reserve_for_mixed + proposed_reserve_for_promo <= old_currently_available + young_available,
651 "Cannot reserve more memory than is available: %zu + %zu + %zu <= %zu + %zu",
652 young_reserve, proposed_reserve_for_mixed, proposed_reserve_for_promo, old_currently_available, young_available);
653
654 // deficit/surplus adjustments to generation sizes will precede rebuild
655 young_generation()->set_evacuation_reserve(young_reserve);
656 old_generation()->set_evacuation_reserve(proposed_reserve_for_mixed);
657 old_generation()->set_promoted_reserve(proposed_reserve_for_promo);
658 }
659
660 void ShenandoahGenerationalHeap::coalesce_and_fill_old_regions(bool concurrent) {
661 class ShenandoahGlobalCoalesceAndFill : public WorkerTask {
662 private:
663 ShenandoahPhaseTimings::Phase _phase;
664 ShenandoahRegionIterator _regions;
665 public:
666 explicit ShenandoahGlobalCoalesceAndFill(ShenandoahPhaseTimings::Phase phase) :
667 WorkerTask("Shenandoah Global Coalesce"),
668 _phase(phase) {}
669
670 void work(uint worker_id) override {
671 ShenandoahWorkerTimingsTracker timer(_phase,
672 ShenandoahPhaseTimings::Work,
673 worker_id, true);
674 ShenandoahHeapRegion* region;
675 while ((region = _regions.next()) != nullptr) {
676 // old region is not in the collection set and was not immediately trashed
677 if (region->is_old() && region->is_active() && !region->is_humongous()) {
678 // Reset the coalesce and fill boundary because this is a global collect
679 // and cannot be preempted by young collects. We want to be sure the entire
680 // region is coalesced here and does not resume from a previously interrupted
681 // or completed coalescing.
682 region->begin_preemptible_coalesce_and_fill();
683 region->oop_coalesce_and_fill(false);
684 }
685 }
686 }
687 };
688
689 ShenandoahPhaseTimings::Phase phase = concurrent ?
690 ShenandoahPhaseTimings::conc_coalesce_and_fill :
691 ShenandoahPhaseTimings::degen_gc_coalesce_and_fill;
692
693 // This is not cancellable
694 ShenandoahGlobalCoalesceAndFill coalesce(phase);
695 workers()->run_task(&coalesce);
696 old_generation()->set_parsable(true);
697 }
698
699 template<bool CONCURRENT>
700 class ShenandoahGenerationalUpdateHeapRefsTask : public WorkerTask {
701 private:
702 // For update refs, _generation will be young or global. Mixed collections use the young generation.
703 ShenandoahGeneration* _generation;
704 ShenandoahGenerationalHeap* _heap;
705 ShenandoahRegionIterator* _regions;
706 ShenandoahRegionChunkIterator* _work_chunks;
707
708 public:
709 ShenandoahGenerationalUpdateHeapRefsTask(ShenandoahGeneration* generation,
710 ShenandoahRegionIterator* regions,
711 ShenandoahRegionChunkIterator* work_chunks) :
712 WorkerTask("Shenandoah Update References"),
713 _generation(generation),
714 _heap(ShenandoahGenerationalHeap::heap()),
715 _regions(regions),
716 _work_chunks(work_chunks)
717 {
718 const bool old_bitmap_stable = _heap->old_generation()->is_mark_complete();
719 log_debug(gc, remset)("Update refs, scan remembered set using bitmap: %s", BOOL_TO_STR(old_bitmap_stable));
720 }
721
722 void work(uint worker_id) override {
723 if (CONCURRENT) {
724 ShenandoahConcurrentWorkerSession worker_session(worker_id);
725 SuspendibleThreadSetJoiner stsj;
726 do_work<ShenandoahConcUpdateRefsClosure>(worker_id);
727 } else {
728 ShenandoahParallelWorkerSession worker_session(worker_id);
729 do_work<ShenandoahNonConcUpdateRefsClosure>(worker_id);
730 }
731 }
732
733 private:
734 template<class T>
735 void do_work(uint worker_id) {
736 T cl;
737
738 if (CONCURRENT && (worker_id == 0)) {
739 // We ask the first worker to replenish the Mutator free set by moving regions previously reserved to hold the
740 // results of evacuation. These reserves are no longer necessary because evacuation has completed.
741 size_t cset_regions = _heap->collection_set()->count();
742
743 // Now that evacuation is done, we can reassign any regions that had been reserved to hold the results of evacuation
744 // to the mutator free set. At the end of GC, we will have cset_regions newly evacuated fully empty regions from
745 // which we will be able to replenish the Collector free set and the OldCollector free set in preparation for the
746 // next GC cycle.
747 _heap->free_set()->move_regions_from_collector_to_mutator(cset_regions);
748 }
749 // If !CONCURRENT, there's no value in expanding Mutator free set
750
751 ShenandoahHeapRegion* r = _regions->next();
752 // We update references for global, mixed, and young collections.
753 assert(_generation->is_mark_complete(), "Expected complete marking");
754 ShenandoahMarkingContext* const ctx = _heap->marking_context();
755 bool is_mixed = _heap->collection_set()->has_old_regions();
756 while (r != nullptr) {
757 HeapWord* update_watermark = r->get_update_watermark();
758 assert(update_watermark >= r->bottom(), "sanity");
759
760 log_debug(gc)("Update refs worker " UINT32_FORMAT ", looking at region %zu", worker_id, r->index());
761 if (r->is_active() && !r->is_cset()) {
762 if (r->is_young()) {
763 _heap->marked_object_oop_iterate(r, &cl, update_watermark);
764 } else if (r->is_old()) {
765 if (_generation->is_global()) {
766
767 _heap->marked_object_oop_iterate(r, &cl, update_watermark);
768 }
769 // Otherwise, this is an old region in a young or mixed cycle. Process it during a second phase, below.
770 } else {
771 // Because updating of references runs concurrently, it is possible that a FREE inactive region transitions
772 // to a non-free active region while this loop is executing. Whenever this happens, the changing of a region's
773 // active status may propagate at a different speed than the changing of the region's affiliation.
774
775 // When we reach this control point, it is because a race has allowed a region's is_active() status to be seen
776 // by this thread before the region's affiliation() is seen by this thread.
777
778 // It's ok for this race to occur because the newly transformed region does not have any references to be
779 // updated.
780
781 assert(r->get_update_watermark() == r->bottom(),
782 "%s Region %zu is_active but not recognized as YOUNG or OLD so must be newly transitioned from FREE",
783 r->affiliation_name(), r->index());
784 }
785 }
786
787 if (_heap->check_cancelled_gc_and_yield(CONCURRENT)) {
788 return;
789 }
790
791 r = _regions->next();
792 }
793
794 if (_generation->is_young()) {
795 // Since this is generational and not GLOBAL, we have to process the remembered set. There's no remembered
796 // set processing if not in generational mode or if GLOBAL mode.
797
798 // After this thread has exhausted its traditional update-refs work, it continues with updating refs within
799 // remembered set. The remembered set workload is better balanced between threads, so threads that are "behind"
800 // can catch up with other threads during this phase, allowing all threads to work more effectively in parallel.
801 update_references_in_remembered_set(worker_id, cl, ctx, is_mixed);
802 }
803 }
804
805 template<class T>
806 void update_references_in_remembered_set(uint worker_id, T &cl, const ShenandoahMarkingContext* ctx, bool is_mixed) {
807
808 struct ShenandoahRegionChunk assignment;
809 ShenandoahScanRemembered* scanner = _heap->old_generation()->card_scan();
810
811 while (!_heap->check_cancelled_gc_and_yield(CONCURRENT) && _work_chunks->next(&assignment)) {
812 // Keep grabbing next work chunk to process until finished, or asked to yield
813 ShenandoahHeapRegion* r = assignment._r;
814 if (r->is_active() && !r->is_cset() && r->is_old()) {
815 HeapWord* start_of_range = r->bottom() + assignment._chunk_offset;
816 HeapWord* end_of_range = r->get_update_watermark();
817 if (end_of_range > start_of_range + assignment._chunk_size) {
818 end_of_range = start_of_range + assignment._chunk_size;
819 }
820
821 if (start_of_range >= end_of_range) {
822 continue;
823 }
824
825 // Old region in a young cycle or mixed cycle.
826 if (is_mixed) {
827 if (r->is_humongous()) {
828 // Need to examine both dirty and clean cards during mixed evac.
829 r->oop_iterate_humongous_slice_all(&cl,start_of_range, assignment._chunk_size);
830 } else {
831 // Since this is mixed evacuation, old regions that are candidates for collection have not been coalesced
832 // and filled. This will use mark bits to find objects that need to be updated.
833 update_references_in_old_region(cl, ctx, scanner, r, start_of_range, end_of_range);
834 }
835 } else {
836 // This is a young evacuation
837 size_t cluster_size = CardTable::card_size_in_words() * ShenandoahCardCluster::CardsPerCluster;
838 size_t clusters = assignment._chunk_size / cluster_size;
839 assert(clusters * cluster_size == assignment._chunk_size, "Chunk assignment must align on cluster boundaries");
840 scanner->process_region_slice(r, assignment._chunk_offset, clusters, end_of_range, &cl, true, worker_id);
841 }
842 }
843 }
844 }
845
846 template<class T>
847 void update_references_in_old_region(T &cl, const ShenandoahMarkingContext* ctx, ShenandoahScanRemembered* scanner,
848 const ShenandoahHeapRegion* r, HeapWord* start_of_range,
849 HeapWord* end_of_range) const {
850 // In case last object in my range spans boundary of my chunk, I may need to scan all the way to top()
851 ShenandoahObjectToOopBoundedClosure<T> objs(&cl, start_of_range, r->top());
852
853 // Any object that begins in a previous range is part of a different scanning assignment. Any object that
854 // starts after end_of_range is also not my responsibility. (Either allocated during evacuation, so does
855 // not hold pointers to from-space, or is beyond the range of my assigned work chunk.)
856
857 // Find the first object that begins in my range, if there is one. Note that `p` will be set to `end_of_range`
858 // when no live object is found in the range.
859 HeapWord* tams = ctx->top_at_mark_start(r);
860 HeapWord* p = get_first_object_start_word(ctx, scanner, tams, start_of_range, end_of_range);
861
862 while (p < end_of_range) {
863 // p is known to point to the beginning of marked object obj
864 oop obj = cast_to_oop(p);
865 objs.do_object(obj);
866 HeapWord* prev_p = p;
867 p += obj->size();
868 if (p < tams) {
869 p = ctx->get_next_marked_addr(p, tams);
870 // If there are no more marked objects before tams, this returns tams. Note that tams is
871 // either >= end_of_range, or tams is the start of an object that is marked.
872 }
873 assert(p != prev_p, "Lack of forward progress");
874 }
875 }
876
877 HeapWord* get_first_object_start_word(const ShenandoahMarkingContext* ctx, ShenandoahScanRemembered* scanner, HeapWord* tams,
878 HeapWord* start_of_range, HeapWord* end_of_range) const {
879 HeapWord* p = start_of_range;
880
881 if (p >= tams) {
882 // We cannot use ctx->is_marked(obj) to test whether an object begins at this address. Instead,
883 // we need to use the remembered set crossing map to advance p to the first object that starts
884 // within the enclosing card.
885 size_t card_index = scanner->card_index_for_addr(start_of_range);
886 while (true) {
887 HeapWord* first_object = scanner->first_object_in_card(card_index);
888 if (first_object != nullptr) {
889 p = first_object;
890 break;
891 } else if (scanner->addr_for_card_index(card_index + 1) < end_of_range) {
892 card_index++;
893 } else {
894 // Signal that no object was found in range
895 p = end_of_range;
896 break;
897 }
898 }
899 } else if (!ctx->is_marked(cast_to_oop(p))) {
900 p = ctx->get_next_marked_addr(p, tams);
901 // If there are no more marked objects before tams, this returns tams.
902 // Note that tams is either >= end_of_range, or tams is the start of an object that is marked.
903 }
904 return p;
905 }
906 };
907
908 void ShenandoahGenerationalHeap::update_heap_references(ShenandoahGeneration* generation, bool concurrent) {
909 assert(!is_full_gc_in_progress(), "Only for concurrent and degenerated GC");
910 const uint nworkers = workers()->active_workers();
911 ShenandoahRegionChunkIterator work_list(nworkers);
912 if (concurrent) {
913 ShenandoahGenerationalUpdateHeapRefsTask<true> task(generation, &_update_refs_iterator, &work_list);
914 workers()->run_task(&task);
915 } else {
916 ShenandoahGenerationalUpdateHeapRefsTask<false> task(generation, &_update_refs_iterator, &work_list);
917 workers()->run_task(&task);
918 }
919
920 if (ShenandoahEnableCardStats) {
921 // Only do this if we are collecting card stats
922 ShenandoahScanRemembered* card_scan = old_generation()->card_scan();
923 assert(card_scan != nullptr, "Card table must exist when card stats are enabled");
924 card_scan->log_card_stats(nworkers, CARD_STAT_UPDATE_REFS);
925 }
926 }
927
928 struct ShenandoahCompositeRegionClosure {
929 template<typename C1, typename C2>
930 class Closure : public ShenandoahHeapRegionClosure {
931 private:
932 C1 &_c1;
933 C2 &_c2;
934
935 public:
936 Closure(C1 &c1, C2 &c2) : ShenandoahHeapRegionClosure(), _c1(c1), _c2(c2) {}
937
938 void heap_region_do(ShenandoahHeapRegion* r) override {
939 _c1.heap_region_do(r);
940 _c2.heap_region_do(r);
941 }
942
943 bool is_thread_safe() override {
944 return _c1.is_thread_safe() && _c2.is_thread_safe();
945 }
946 };
947
948 template<typename C1, typename C2>
949 static Closure<C1, C2> of(C1 &c1, C2 &c2) {
950 return Closure<C1, C2>(c1, c2);
951 }
952 };
953
954 class ShenandoahUpdateRegionAges : public ShenandoahHeapRegionClosure {
955 private:
956 ShenandoahMarkingContext* _ctx;
957
958 public:
959 explicit ShenandoahUpdateRegionAges(ShenandoahMarkingContext* ctx) : _ctx(ctx) { }
960
961 void heap_region_do(ShenandoahHeapRegion* r) override {
962 // Maintenance of region age must follow evacuation in order to account for
963 // evacuation allocations within survivor regions. We consult region age during
964 // the subsequent evacuation to determine whether certain objects need to
965 // be promoted.
966 if (r->is_young() && r->is_active()) {
967 HeapWord *tams = _ctx->top_at_mark_start(r);
968 HeapWord *top = r->top();
969
970 // Allocations move the watermark when top moves. However, compacting
971 // objects will sometimes lower top beneath the watermark, after which,
972 // attempts to read the watermark will assert out (watermark should not be
973 // higher than top).
974 if (top > tams) {
975 // There have been allocations in this region since the start of the cycle.
976 // Any objects new to this region must not assimilate elevated age.
977 r->reset_age();
978 } else {
979 r->increment_age();
980 }
981 }
982 }
983
984 bool is_thread_safe() override {
985 return true;
986 }
987 };
988
989 void ShenandoahGenerationalHeap::final_update_refs_update_region_states() {
990 ShenandoahSynchronizePinnedRegionStates pins;
991 ShenandoahUpdateRegionAges ages(marking_context());
992 auto cl = ShenandoahCompositeRegionClosure::of(pins, ages);
993 parallel_heap_region_iterate(&cl);
994 }
995
996 void ShenandoahGenerationalHeap::complete_degenerated_cycle() {
997 shenandoah_assert_heaplocked_or_safepoint();
998 if (!old_generation()->is_parsable()) {
999 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_coalesce_and_fill);
1000 coalesce_and_fill_old_regions(false);
1001 }
1002
1003 old_generation()->maybe_log_promotion_failure_stats(false);
1004 }
1005
1006 void ShenandoahGenerationalHeap::complete_concurrent_cycle() {
1007 if (!old_generation()->is_parsable()) {
1008 // Class unloading may render the card offsets unusable, so we must rebuild them before
1009 // the next remembered set scan. We _could_ let the control thread do this sometime after
1010 // the global cycle has completed and before the next young collection, but under memory
1011 // pressure the control thread may not have the time (that is, because it's running back
1012 // to back GCs). In that scenario, we would have to make the old regions parsable before
1013 // we could start a young collection. This could delay the start of the young cycle and
1014 // throw off the heuristics.
1015 entry_global_coalesce_and_fill();
1016 }
1017
1018 old_generation()->maybe_log_promotion_failure_stats(true);
1019 }
1020
1021 void ShenandoahGenerationalHeap::entry_global_coalesce_and_fill() {
1022 const char* msg = "Coalescing and filling old regions";
1023 ShenandoahConcurrentPhase gc_phase(msg, ShenandoahPhaseTimings::conc_coalesce_and_fill);
1024
1025 TraceCollectorStats tcs(monitoring_support()->concurrent_collection_counters());
1026 EventMark em("%s", msg);
1027 ShenandoahWorkerScope scope(workers(),
1028 ShenandoahWorkerPolicy::calc_workers_for_conc_marking(),
1029 "concurrent coalesce and fill");
1030
1031 coalesce_and_fill_old_regions(true);
1032 }
1033
1034 void ShenandoahGenerationalHeap::update_region_ages(ShenandoahMarkingContext* ctx) {
1035 ShenandoahUpdateRegionAges cl(ctx);
1036 parallel_heap_region_iterate(&cl);
1037 }