1 /*
2 * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
3 * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
5 *
6 * This code is free software; you can redistribute it and/or modify it
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8 * published by the Free Software Foundation.
9 *
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11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
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17 * 2 along with this work; if not, write to the Free Software Foundation,
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20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 * or visit www.oracle.com if you need additional information or have any
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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, false /* only promote regions */);
191 workers()->run_task(&task);
192 }
193
194 void ShenandoahGenerationalHeap::promote_regions_in_place(ShenandoahGeneration* generation, bool concurrent) {
195 ShenandoahRegionIterator regions;
196 ShenandoahGenerationalEvacuationTask task(this, generation, ®ions, concurrent, true /* only promote regions */);
197 workers()->run_task(&task);
198 }
199
200 oop ShenandoahGenerationalHeap::evacuate_object(oop p, Thread* thread) {
201 assert(thread == Thread::current(), "Expected thread parameter to be current thread.");
202
203 ShenandoahHeapRegion* from_region = heap_region_containing(p);
204 assert(!from_region->is_humongous(), "never evacuate humongous objects");
205
206 // Try to keep the object in the same generation
207 const ShenandoahAffiliation target_gen = from_region->affiliation();
208
209 if (target_gen == YOUNG_GENERATION) {
210 markWord mark = p->mark();
211 if (mark.is_marked()) {
212 // Already forwarded.
213 return ShenandoahBarrierSet::resolve_forwarded(p);
214 }
215
216 if (mark.has_displaced_mark_helper()) {
217 // We don't want to deal with MT here just to ensure we read the right mark word.
218 // Skip the potential promotion attempt for this one.
219 } else if (age_census()->is_tenurable(from_region->age() + mark.age())) {
220 // If the object is tenurable, try to promote it
221 oop result = try_evacuate_object<YOUNG_GENERATION, OLD_GENERATION>(p, thread, from_region->age());
222
223 // If we failed to promote this aged object, we'll fall through to code below and evacuate to young-gen.
224 if (result != nullptr) {
225 return result;
226 }
227 }
228 return try_evacuate_object<YOUNG_GENERATION, YOUNG_GENERATION>(p, thread, from_region->age());
229 }
230
231 assert(target_gen == OLD_GENERATION, "Expected evacuation to old");
232 return try_evacuate_object<OLD_GENERATION, OLD_GENERATION>(p, thread, from_region->age());
233 }
234
235 // try_evacuate_object registers the object and dirties the associated remembered set information when evacuating
236 // to OLD_GENERATION.
237 template<ShenandoahAffiliation FROM_GENERATION, ShenandoahAffiliation TO_GENERATION>
238 oop ShenandoahGenerationalHeap::try_evacuate_object(oop p, Thread* thread, uint from_region_age) {
239 bool alloc_from_lab = true;
240 bool has_plab = false;
241 HeapWord* copy = nullptr;
242 size_t size = ShenandoahForwarding::size(p);
243 constexpr bool is_promotion = (TO_GENERATION == OLD_GENERATION) && (FROM_GENERATION == YOUNG_GENERATION);
244
245 #ifdef ASSERT
246 if (ShenandoahOOMDuringEvacALot &&
247 (os::random() & 1) == 0) { // Simulate OOM every ~2nd slow-path call
248 copy = nullptr;
249 } else {
250 #endif
251 if (UseTLAB) {
252 switch (TO_GENERATION) {
253 case YOUNG_GENERATION: {
254 copy = allocate_from_gclab(thread, size);
255 if ((copy == nullptr) && (size < ShenandoahThreadLocalData::gclab_size(thread))) {
256 // GCLAB allocation failed because we are bumping up against the limit on young evacuation reserve. Try resetting
257 // the desired GCLAB size and retry GCLAB allocation to avoid cascading of shared memory allocations.
258 ShenandoahThreadLocalData::set_gclab_size(thread, PLAB::min_size());
259 copy = allocate_from_gclab(thread, size);
260 // If we still get nullptr, we'll try a shared allocation below.
261 }
262 break;
263 }
264 case OLD_GENERATION: {
265 ShenandoahPLAB* shenandoah_plab = ShenandoahThreadLocalData::shenandoah_plab(thread);
266 if (shenandoah_plab != nullptr) {
267 has_plab = true;
268 copy = shenandoah_plab->allocate(size, is_promotion);
269 if (copy == nullptr && size < shenandoah_plab->desired_size() && shenandoah_plab->retries_enabled()) {
270 // PLAB allocation failed because we are bumping up against the limit on old evacuation reserve or because
271 // the requested object does not fit within the current plab but the plab still has an "abundance" of memory,
272 // where abundance is defined as >= ShenGenHeap::plab_min_size(). In the former case, we try shrinking the
273 // desired PLAB size to the minimum and retry PLAB allocation to avoid cascading of shared memory allocations.
274 // Shrinking the desired PLAB size may allow us to eke out a small PLAB while staying beneath evacuation reserve.
275 if (shenandoah_plab->plab()->words_remaining() < plab_min_size()) {
276 shenandoah_plab->set_desired_size(plab_min_size());
277 copy = shenandoah_plab->allocate(size, is_promotion);
278 if (copy == nullptr) {
279 // If we still get nullptr, we'll try a shared allocation below.
280 // However, don't continue to retry until we have success (probably in next GC pass)
281 shenandoah_plab->disable_retries();
282 }
283 }
284 }
285 }
286 break;
287 }
288 default: {
289 ShouldNotReachHere();
290 break;
291 }
292 }
293 }
294
295 if (copy == nullptr) {
296 // If we failed to allocate in LAB, we'll try a shared allocation.
297 if (!is_promotion || !has_plab || (size > PLAB::min_size())) {
298 ShenandoahAllocRequest req = ShenandoahAllocRequest::for_shared_gc(size, TO_GENERATION, is_promotion);
299 copy = allocate_memory(req);
300 alloc_from_lab = false;
301 }
302 // else, we leave copy equal to nullptr, signaling a promotion failure below if appropriate.
303 // We choose not to promote objects smaller than size_threshold by way of shared allocations as this is too
304 // costly. Instead, we'll simply "evacuate" to young-gen memory (using a GCLAB) and will promote in a future
305 // evacuation pass. This condition is denoted by: is_promotion && has_plab && (size <= size_threshhold).
306 }
307 #ifdef ASSERT
308 }
309 #endif
310
311 if (copy == nullptr) {
312 if (TO_GENERATION == OLD_GENERATION) {
313 if (FROM_GENERATION == YOUNG_GENERATION) {
314 // Signal that promotion failed. Will evacuate this old object somewhere in young gen.
315 old_generation()->handle_failed_promotion(thread, size);
316 return nullptr;
317 } else {
318 // Remember that evacuation to old gen failed. We'll want to trigger a full gc to recover from this
319 // after the evacuation threads have finished.
320 old_generation()->handle_failed_evacuation();
321 }
322 }
323
324 control_thread()->handle_alloc_failure_evac(size);
325
326 // Install the self-forwarded bit so other evacuators/LRBs see the
327 // object as "already handled, do not try to evacuate". The CAS may
328 // fail if another thread concurrently installed a real forwardee or
329 // self-forwarded first.
330 markWord old_mark = p->mark();
331 if (old_mark.is_forwarded()) {
332 return ShenandoahForwarding::get_forwardee(p);
333 }
334 oop winner = ShenandoahForwarding::try_forward_to_self(p, old_mark);
335 if (winner == nullptr) {
336 // We own the self-forwarding. Flag the from-region so the degen/full
337 // GC entry drain knows to scan it for self_fwd bits to clear.
338 heap_region_containing(p)->set_has_self_forwards();
339 return p;
340 }
341 return winner;
342 }
343
344 if (ShenandoahEvacTracking) {
345 evac_tracker()->begin_evacuation(thread, size * HeapWordSize, FROM_GENERATION, TO_GENERATION);
346 }
347
348 // Copy the object:
349 Copy::aligned_disjoint_words(cast_from_oop<HeapWord*>(p), copy, size);
350 oop copy_val = cast_to_oop(copy);
351
352 // Update the age of the evacuated object
353 if (TO_GENERATION == YOUNG_GENERATION && is_aging_cycle()) {
354 increase_object_age(copy_val, from_region_age + 1);
355 }
356
357 // Relativize stack chunks before publishing the copy. After the forwarding CAS,
358 // mutators can see the copy and thaw it via the fast path if flags == 0. We must
359 // relativize derived pointers and set gc_mode before that happens. Skip if the
360 // copy's mark word is already a forwarding pointer (another thread won the race
361 // and overwrote the original's header before we copied it).
362 if (!ShenandoahForwarding::is_forwarded(copy_val)) {
363 ContinuationGCSupport::relativize_stack_chunk(copy_val);
364 }
365
366 // Try to install the new forwarding pointer.
367 oop result = ShenandoahForwarding::try_update_forwardee(p, copy_val);
368 if (result == copy_val) {
369 // Successfully evacuated. Our copy is now the public one!
370 if (ShenandoahEvacTracking) {
371 // Record that the evacuation succeeded
372 evac_tracker()->end_evacuation(thread, size * HeapWordSize, FROM_GENERATION, TO_GENERATION);
373 }
374 } else {
375 // Failed to evacuate. We need to deal with the object that is left behind. Since this
376 // new allocation is certainly after TAMS, it will be considered live in the next cycle.
377 // But if it happens to contain references to evacuated regions, those references would
378 // not get updated for this stale copy during this cycle, and we will crash while scanning
379 // it the next cycle.
380 if (alloc_from_lab) {
381 // For LAB allocations, it is enough to rollback the allocation ptr. Either the next
382 // object will overwrite this stale copy, or the filler object on LAB retirement will
383 // do this.
384 switch (TO_GENERATION) {
385 case YOUNG_GENERATION: {
386 ShenandoahThreadLocalData::gclab(thread)->undo_allocation(copy, size);
387 break;
388 }
389 case OLD_GENERATION: {
390 ShenandoahThreadLocalData::shenandoah_plab(thread)->plab()->undo_allocation(copy, size);
391 if (is_promotion) {
392 ShenandoahThreadLocalData::shenandoah_plab(thread)->subtract_from_promoted(size * HeapWordSize);
393 }
394 break;
395 }
396 default: {
397 ShouldNotReachHere();
398 break;
399 }
400 }
401 } else {
402 // For non-LAB allocations, we have no way to retract the allocation, and
403 // have to explicitly overwrite the copy with the filler object. With that overwrite,
404 // we have to keep the fwdptr initialized and pointing to our (stale) copy.
405 assert(size >= ShenandoahHeap::min_fill_size(), "previously allocated object known to be larger than min_size");
406 fill_with_object(copy, size);
407 }
408 }
409 shenandoah_assert_correct(nullptr, result);
410 return result;
411 }
412
413 template oop ShenandoahGenerationalHeap::try_evacuate_object<YOUNG_GENERATION, YOUNG_GENERATION>(oop p, Thread* thread, uint from_region_age);
414 template oop ShenandoahGenerationalHeap::try_evacuate_object<YOUNG_GENERATION, OLD_GENERATION>(oop p, Thread* thread, uint from_region_age);
415 template oop ShenandoahGenerationalHeap::try_evacuate_object<OLD_GENERATION, OLD_GENERATION>(oop p, Thread* thread, uint from_region_age);
416
417 // Call this function at the end of a GC cycle in order to establish proper sizes of young and old reserves,
418 // setting the old-generation balance so that GC can perform the anticipated evacuations.
419 //
420 // Make sure old-generation is large enough, but no larger than is necessary, to hold mixed evacuations
421 // and promotions, if we anticipate either. Any deficit is provided by the young generation, subject to
422 // mutator_xfer_limit, and any surplus is transferred to the young generation. mutator_xfer_limit is
423 // the maximum we're able to transfer from young to old. The mutator_xfer_limit constrains the transfer
424 // of memory from young to old. It does not limit young reserves.
425 void ShenandoahGenerationalHeap::compute_old_generation_balance(size_t mutator_xfer_limit,
426 size_t old_trashed_regions, size_t young_trashed_regions) {
427 shenandoah_assert_heaplocked();
428 // We can limit the old reserve to the size of anticipated promotions:
429 // max_old_reserve is an upper bound on memory evacuated from old and promoted to old,
430 // clamped by the old generation space available.
431 //
432 // Here's the algebra.
433 // Let SOEP = ShenandoahOldEvacPercent,
434 // OE = old evac,
435 // YE = young evac, and
436 // TE = total evac = OE + YE
437 // By definition:
438 // SOEP/100 = OE/TE
439 // = OE/(OE+YE)
440 // => SOEP/(100-SOEP) = OE/((OE+YE)-OE) // componendo-dividendo: If a/b = c/d, then a/(b-a) = c/(d-c)
441 // = OE/YE
442 // => OE = YE*SOEP/(100-SOEP)
443
444 // We have to be careful in the event that SOEP is set to 100 by the user.
445 assert(ShenandoahOldEvacPercent <= 100, "Error");
446 const size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
447
448 ShenandoahOldGeneration* old_gen = old_generation();
449 size_t old_capacity = old_gen->max_capacity();
450 size_t old_usage = old_gen->used(); // includes humongous waste
451 size_t old_currently_available =
452 ((old_capacity >= old_usage)? old_capacity - old_usage: 0) + old_trashed_regions * region_size_bytes;
453
454 ShenandoahYoungGeneration* young_gen = young_generation();
455 size_t young_capacity = young_gen->max_capacity();
456 size_t young_usage = young_gen->used(); // includes humongous waste
457 size_t young_available = ((young_capacity >= young_usage)? young_capacity - young_usage: 0);
458 size_t freeset_available = free_set()->available_locked();
459 if (young_available > freeset_available) {
460 young_available = freeset_available;
461 }
462 young_available += young_trashed_regions * region_size_bytes;
463
464 // The free set will reserve this amount of memory to hold young evacuations (initialized to the ideal reserve)
465 size_t young_reserve = (young_generation()->max_capacity() * ShenandoahEvacReserve) / 100;
466
467 // If ShenandoahOldEvacPercent equals 100, max_old_reserve is limited only by mutator_xfer_limit and young_reserve
468 const size_t bound_on_old_reserve =
469 ((old_currently_available + mutator_xfer_limit + young_reserve) * ShenandoahOldEvacPercent) / 100;
470 size_t proposed_max_old = ((ShenandoahOldEvacPercent == 100)?
471 bound_on_old_reserve:
472 MIN2((young_reserve * ShenandoahOldEvacPercent) / (100 - ShenandoahOldEvacPercent),
473 bound_on_old_reserve));
474 assert(mutator_xfer_limit <= young_available,
475 "Cannot transfer (%zu) memory that is not available (%zu)", mutator_xfer_limit, young_available);
476
477 if (young_reserve > young_available) {
478 young_reserve = young_available;
479 }
480 // We allow young_reserve to exceed mutator_xfer_limit. Essentially, this means the GC is already behind the pace
481 // of mutator allocations, and we'll need to trigger the next GC as soon as possible.
482 if (mutator_xfer_limit > young_reserve) {
483 mutator_xfer_limit -= young_reserve;
484 } else {
485 mutator_xfer_limit = 0;
486 }
487
488 // Decide how much old space we should reserve for a mixed collection
489 size_t proposed_reserve_for_mixed = 0;
490 const size_t old_fragmented_available =
491 old_currently_available - (old_generation()->free_unaffiliated_regions() + old_trashed_regions) * region_size_bytes;
492
493 if (old_fragmented_available > proposed_max_old) {
494 // In this case, the old_fragmented_available is greater than the desired amount of evacuation to old.
495 // We'll use all of this memory to hold results of old evacuation, and we'll give back to the young generation
496 // any old regions that are not fragmented.
497 //
498 // This scenario may happen after we have promoted many regions in place, and each of these regions had non-zero
499 // unused memory, so there is now an abundance of old-fragmented available memory, even more than the desired
500 // percentage for old reserve. We cannot transfer these fragmented regions back to young. Instead we make the
501 // best of the situation by using this fragmented memory for both promotions and evacuations.
502
503 proposed_max_old = old_fragmented_available;
504 }
505 // Otherwise: old_fragmented_available <= proposed_max_old. Do not shrink proposed_max_old from the original computation.
506
507 // Though we initially set proposed_reserve_for_promo to equal the entirety of old fragmented available, we have the
508 // opportunity below to shift some of this memory into the proposed_reserve_for_mixed.
509 size_t proposed_reserve_for_promo = old_fragmented_available;
510 const size_t max_old_reserve = proposed_max_old;
511
512 const size_t mixed_candidate_live_memory = old_generation()->unprocessed_collection_candidates_live_memory();
513 const bool doing_mixed = (mixed_candidate_live_memory > 0);
514 if (doing_mixed) {
515 // In the ideal, all of the memory reserved for mixed evacuation would be unfragmented, but we don't enforce
516 // this. Note that the initial value of max_evac_need is conservative because we may not evacuate all of the
517 // remaining mixed evacuation candidates in a single cycle.
518 const size_t max_evac_need = (size_t) (mixed_candidate_live_memory * ShenandoahOldEvacWaste);
519 assert(old_currently_available >= old_generation()->free_unaffiliated_regions() * region_size_bytes,
520 "Unaffiliated available must be less than total available");
521
522 // We prefer to evacuate all of mixed into unfragmented memory, and will expand old in order to do so, unless
523 // we already have too much fragmented available memory in old.
524 proposed_reserve_for_mixed = max_evac_need;
525 if (proposed_reserve_for_mixed + proposed_reserve_for_promo > max_old_reserve) {
526 // We're trying to reserve more memory than is available. So we need to shrink our reserves.
527 size_t excess_reserves = (proposed_reserve_for_mixed + proposed_reserve_for_promo) - max_old_reserve;
528 // We need to shrink reserves by excess_reserves. We prefer to shrink by reducing promotion, giving priority to mixed
529 // evacuation. If the promotion reserve is larger than the amount we need to shrink by, do all the shrinkage there.
530 if (proposed_reserve_for_promo > excess_reserves) {
531 proposed_reserve_for_promo -= excess_reserves;
532 } else {
533 // Otherwise, we'll shrink promotion reserve to zero and we'll shrink the mixed-evac reserve by the remaining excess.
534 excess_reserves -= proposed_reserve_for_promo;
535 proposed_reserve_for_promo = 0;
536 proposed_reserve_for_mixed -= excess_reserves;
537 }
538 }
539 }
540 assert(proposed_reserve_for_mixed + proposed_reserve_for_promo <= max_old_reserve,
541 "Reserve for mixed (%zu) plus reserve for promotions (%zu) must be less than maximum old reserve (%zu)",
542 proposed_reserve_for_mixed, proposed_reserve_for_promo, max_old_reserve);
543
544 // Decide how much additional space we should reserve for promotions from young. We give priority to mixed evacations
545 // over promotions.
546 const size_t promo_load = old_generation()->get_promotion_potential();
547 const bool doing_promotions = promo_load > 0;
548
549 // promo_load represents the combined total of live memory within regions that have reached tenure age. The true
550 // promotion potential is larger than this, because individual objects within regions that have not yet reached tenure
551 // age may be promotable. On the other hand, some of the objects that we intend to promote in the next GC cycle may
552 // die before they are next marked. In the future, the promo_load will include the total size of tenurable objects
553 // residing in regions that have not yet reached tenure age.
554
555 if (doing_promotions) {
556 // We are always doing promotions, even when old_generation->get_promotion_potential() returns 0. As currently implemented,
557 // get_promotion_potential() only knows the total live memory contained within young-generation regions whose age is
558 // tenurable. It does not know whether that memory will still be live at the end of the next mark cycle, and it doesn't
559 // know how much memory is contained within objects whose individual ages are tenurable, which reside in regions with
560 // non-tenurable age. We use this, as adjusted by ShenandoahPromoEvacWaste, as an approximation of the total amount of
561 // memory to be promoted. In the near future, we expect to implement a change that will allow get_promotion_potential()
562 // to account also for the total memory contained within individual objects that are tenure-ready even when they do
563 // not reside in aged regions. This will represent a conservative over approximation of promotable memory because
564 // some of these objects may die before the next GC cycle executes.
565
566 // Be careful not to ask for too much promotion reserves. We have observed jtreg test failures under which a greedy
567 // promotion reserve causes a humongous allocation which is awaiting a full GC to fail (specifically
568 // gc/TestAllocHumongousFragment.java). This happens if too much of the memory reclaimed by the full GC
569 // is immediately reserved so that it cannot be allocated by the waiting mutator. It's not clear that this
570 // particular test is representative of the needs of typical GenShen users. It is really a test of high frequency
571 // Full GCs under heap fragmentation stress.
572
573 size_t promo_need = (size_t) (promo_load * ShenandoahPromoEvacWaste);
574 if (promo_need > proposed_reserve_for_promo) {
575 const size_t available_for_additional_promotions =
576 max_old_reserve - (proposed_reserve_for_mixed + proposed_reserve_for_promo);
577 if (proposed_reserve_for_promo + available_for_additional_promotions >= promo_need) {
578 proposed_reserve_for_promo = promo_need;
579 } else {
580 proposed_reserve_for_promo += available_for_additional_promotions;
581 }
582 }
583 }
584 // else, leave proposed_reserve_for_promo as is. By default, it is initialized to represent old_fragmented_available.
585
586 // This is the total old we want to reserve (initialized to the ideal reserve)
587 size_t proposed_old_reserve = proposed_reserve_for_mixed + proposed_reserve_for_promo;
588
589 // We now check if the old generation is running a surplus or a deficit.
590 size_t old_region_deficit = 0;
591 size_t old_region_surplus = 0;
592
593 size_t mutator_region_xfer_limit = mutator_xfer_limit / region_size_bytes;
594 // align the mutator_xfer_limit on region size
595 mutator_xfer_limit = mutator_region_xfer_limit * region_size_bytes;
596
597 if (old_currently_available >= proposed_old_reserve) {
598 // We are running a surplus, so the old region surplus can go to young
599 const size_t old_surplus = old_currently_available - proposed_old_reserve;
600 old_region_surplus = old_surplus / region_size_bytes;
601 const size_t unaffiliated_old_regions = old_generation()->free_unaffiliated_regions() + old_trashed_regions;
602 old_region_surplus = MIN2(old_region_surplus, unaffiliated_old_regions);
603 old_generation()->set_region_balance(checked_cast<ssize_t>(old_region_surplus));
604 old_currently_available -= old_region_surplus * region_size_bytes;
605 young_available += old_region_surplus * region_size_bytes;
606 } else if (old_currently_available + mutator_xfer_limit >= proposed_old_reserve) {
607 // We know that old_currently_available < proposed_old_reserve because above test failed. Expand old_currently_available.
608 // Mutator's xfer limit is sufficient to satisfy our need: transfer all memory from there.
609 size_t old_deficit = proposed_old_reserve - old_currently_available;
610 old_region_deficit = (old_deficit + region_size_bytes - 1) / region_size_bytes;
611 old_generation()->set_region_balance(0 - checked_cast<ssize_t>(old_region_deficit));
612 old_currently_available += old_region_deficit * region_size_bytes;
613 young_available -= old_region_deficit * region_size_bytes;
614 } else {
615 // We know that (old_currently_available < proposed_old_reserve) and
616 // (old_currently_available + mutator_xfer_limit < proposed_old_reserve) because above tests failed.
617 // We need to shrink proposed_old_reserves.
618
619 // We could potentially shrink young_reserves in order to further expand proposed_old_reserves. Let's not bother. The
620 // important thing is that we keep a total amount of memory in reserve in preparation for the next GC cycle. At
621 // the time we choose the next collection set, we'll have an opportunity to shift some of these young reserves
622 // into old reserves if that makes sense.
623
624 // Start by taking all of mutator_xfer_limit into old_currently_available.
625 size_t old_region_deficit = mutator_region_xfer_limit;
626 old_generation()->set_region_balance(0 - checked_cast<ssize_t>(old_region_deficit));
627 old_currently_available += old_region_deficit * region_size_bytes;
628 young_available -= old_region_deficit * region_size_bytes;
629
630 assert(old_currently_available < proposed_old_reserve,
631 "Old currently available (%zu) must be less than old reserve (%zu)", old_currently_available, proposed_old_reserve);
632
633 // There's not enough memory to satisfy our desire. Scale back our old-gen intentions. We prefer to satisfy
634 // the budget_overrun entirely from the promotion reserve, if that is large enough. Otherwise, we'll satisfy
635 // the overrun from a combination of promotion and mixed-evacuation reserves.
636 size_t budget_overrun = proposed_old_reserve - old_currently_available;
637 if (proposed_reserve_for_promo > budget_overrun) {
638 proposed_reserve_for_promo -= budget_overrun;
639 // Dead code:
640 // proposed_old_reserve -= budget_overrun;
641 } else {
642 budget_overrun -= proposed_reserve_for_promo;
643 proposed_reserve_for_promo = 0;
644 proposed_reserve_for_mixed = (proposed_reserve_for_mixed > budget_overrun)? proposed_reserve_for_mixed - budget_overrun: 0;
645 // Dead code:
646 // Note: proposed_reserve_for_promo is 0 and proposed_reserve_for_mixed may equal 0.
647 // proposed_old_reserve = proposed_reserve_for_mixed;
648 }
649 }
650
651 assert(old_region_deficit == 0 || old_region_surplus == 0,
652 "Only surplus (%zu) or deficit (%zu), never both", old_region_surplus, old_region_deficit);
653 assert(young_reserve + proposed_reserve_for_mixed + proposed_reserve_for_promo <= old_currently_available + young_available,
654 "Cannot reserve more memory than is available: %zu + %zu + %zu <= %zu + %zu",
655 young_reserve, proposed_reserve_for_mixed, proposed_reserve_for_promo, old_currently_available, young_available);
656
657 // deficit/surplus adjustments to generation sizes will precede rebuild
658 young_generation()->set_evacuation_reserve(young_reserve);
659 old_generation()->set_evacuation_reserve(proposed_reserve_for_mixed);
660 old_generation()->set_promoted_reserve(proposed_reserve_for_promo);
661 }
662
663 void ShenandoahGenerationalHeap::coalesce_and_fill_old_regions(bool concurrent) {
664 class ShenandoahGlobalCoalesceAndFill : public WorkerTask {
665 private:
666 ShenandoahPhaseTimings::Phase _phase;
667 ShenandoahRegionIterator _regions;
668 public:
669 explicit ShenandoahGlobalCoalesceAndFill(ShenandoahPhaseTimings::Phase phase) :
670 WorkerTask("Shenandoah Global Coalesce"),
671 _phase(phase) {}
672
673 void work(uint worker_id) override {
674 ShenandoahWorkerTimingsTracker timer(_phase,
675 ShenandoahPhaseTimings::ScanClusters,
676 worker_id, true);
677 ShenandoahHeapRegion* region;
678 while ((region = _regions.next()) != nullptr) {
679 // old region is not in the collection set and was not immediately trashed
680 if (region->is_old() && region->is_active() && !region->is_humongous()) {
681 // Reset the coalesce and fill boundary because this is a global collect
682 // and cannot be preempted by young collects. We want to be sure the entire
683 // region is coalesced here and does not resume from a previously interrupted
684 // or completed coalescing.
685 region->begin_preemptible_coalesce_and_fill();
686 region->oop_coalesce_and_fill(false);
687 }
688 }
689 }
690 };
691
692 ShenandoahPhaseTimings::Phase phase = concurrent ?
693 ShenandoahPhaseTimings::conc_coalesce_and_fill :
694 ShenandoahPhaseTimings::degen_gc_coalesce_and_fill;
695
696 // This is not cancellable
697 ShenandoahGlobalCoalesceAndFill coalesce(phase);
698 workers()->run_task(&coalesce);
699 old_generation()->set_parsable(true);
700 }
701
702 template<bool CONCURRENT>
703 class ShenandoahGenerationalUpdateHeapRefsTask : public WorkerTask {
704 private:
705 // For update refs, _generation will be young or global. Mixed collections use the young generation.
706 ShenandoahGeneration* _generation;
707 ShenandoahGenerationalHeap* _heap;
708 ShenandoahRegionIterator* _regions;
709 ShenandoahRegionChunkIterator* _work_chunks;
710
711 public:
712 ShenandoahGenerationalUpdateHeapRefsTask(ShenandoahGeneration* generation,
713 ShenandoahRegionIterator* regions,
714 ShenandoahRegionChunkIterator* work_chunks) :
715 WorkerTask("Shenandoah Update References"),
716 _generation(generation),
717 _heap(ShenandoahGenerationalHeap::heap()),
718 _regions(regions),
719 _work_chunks(work_chunks)
720 {
721 const bool old_bitmap_stable = _heap->old_generation()->is_mark_complete();
722 log_debug(gc, remset)("Update refs, scan remembered set using bitmap: %s", BOOL_TO_STR(old_bitmap_stable));
723 }
724
725 void work(uint worker_id) override {
726 if (CONCURRENT) {
727 ShenandoahConcurrentWorkerSession worker_session(worker_id);
728 SuspendibleThreadSetJoiner stsj;
729 do_work<ShenandoahConcUpdateRefsClosure>(worker_id);
730 } else {
731 ShenandoahParallelWorkerSession worker_session(worker_id);
732 do_work<ShenandoahNonConcUpdateRefsClosure>(worker_id);
733 }
734 }
735
736 private:
737 template<class T>
738 void do_work(uint worker_id) {
739 T cl;
740
741 if (CONCURRENT && (worker_id == 0)) {
742 // We ask the first worker to replenish the Mutator free set by moving regions previously reserved to hold the
743 // results of evacuation. These reserves are no longer necessary because evacuation has completed.
744 size_t cset_regions = _heap->collection_set()->count();
745
746 // Now that evacuation is done, we can reassign any regions that had been reserved to hold the results of evacuation
747 // to the mutator free set. At the end of GC, we will have cset_regions newly evacuated fully empty regions from
748 // which we will be able to replenish the Collector free set and the OldCollector free set in preparation for the
749 // next GC cycle.
750 _heap->free_set()->move_regions_from_collector_to_mutator(cset_regions);
751 }
752 // If !CONCURRENT, there's no value in expanding Mutator free set
753
754 ShenandoahHeapRegion* r = _regions->next();
755 // We update references for global, mixed, and young collections.
756 assert(_generation->is_mark_complete(), "Expected complete marking");
757 ShenandoahMarkingContext* const ctx = _heap->marking_context();
758 bool is_mixed = _heap->collection_set()->has_old_regions();
759 while (r != nullptr) {
760 HeapWord* update_watermark = r->get_update_watermark();
761 assert(update_watermark >= r->bottom(), "sanity");
762
763 log_debug(gc)("Update refs worker " UINT32_FORMAT ", looking at region %zu", worker_id, r->index());
764 if (r->is_active() && !r->is_cset()) {
765 if (r->is_young()) {
766 _heap->marked_object_oop_iterate(r, &cl, update_watermark);
767 } else if (r->is_old()) {
768 if (_generation->is_global()) {
769
770 _heap->marked_object_oop_iterate(r, &cl, update_watermark);
771 }
772 // Otherwise, this is an old region in a young or mixed cycle. Process it during a second phase, below.
773 } else {
774 // Because updating of references runs concurrently, it is possible that a FREE inactive region transitions
775 // to a non-free active region while this loop is executing. Whenever this happens, the changing of a region's
776 // active status may propagate at a different speed than the changing of the region's affiliation.
777
778 // When we reach this control point, it is because a race has allowed a region's is_active() status to be seen
779 // by this thread before the region's affiliation() is seen by this thread.
780
781 // It's ok for this race to occur because the newly transformed region does not have any references to be
782 // updated.
783
784 assert(r->get_update_watermark() == r->bottom(),
785 "%s Region %zu is_active but not recognized as YOUNG or OLD so must be newly transitioned from FREE",
786 r->affiliation_name(), r->index());
787 }
788 }
789
790 if (_heap->check_cancelled_gc_and_yield(CONCURRENT)) {
791 return;
792 }
793
794 r = _regions->next();
795 }
796
797 if (_generation->is_young()) {
798 // Since this is generational and not GLOBAL, we have to process the remembered set. There's no remembered
799 // set processing if not in generational mode or if GLOBAL mode.
800
801 // After this thread has exhausted its traditional update-refs work, it continues with updating refs within
802 // remembered set. The remembered set workload is better balanced between threads, so threads that are "behind"
803 // can catch up with other threads during this phase, allowing all threads to work more effectively in parallel.
804 update_references_in_remembered_set(worker_id, cl, ctx, is_mixed);
805 }
806 }
807
808 template<class T>
809 void update_references_in_remembered_set(uint worker_id, T &cl, const ShenandoahMarkingContext* ctx, bool is_mixed) {
810
811 struct ShenandoahRegionChunk assignment;
812 ShenandoahScanRemembered* scanner = _heap->old_generation()->card_scan();
813
814 while (!_heap->check_cancelled_gc_and_yield(CONCURRENT) && _work_chunks->next(&assignment)) {
815 // Keep grabbing next work chunk to process until finished, or asked to yield
816 ShenandoahHeapRegion* r = assignment._r;
817 if (r->is_active() && !r->is_cset() && r->is_old()) {
818 HeapWord* start_of_range = r->bottom() + assignment._chunk_offset;
819 HeapWord* end_of_range = r->get_update_watermark();
820 if (end_of_range > start_of_range + assignment._chunk_size) {
821 end_of_range = start_of_range + assignment._chunk_size;
822 }
823
824 if (start_of_range >= end_of_range) {
825 continue;
826 }
827
828 // Old region in a young cycle or mixed cycle.
829 if (is_mixed) {
830 if (r->is_humongous()) {
831 // Need to examine both dirty and clean cards during mixed evac.
832 r->oop_iterate_humongous_slice_all(&cl,start_of_range, assignment._chunk_size);
833 } else {
834 // Since this is mixed evacuation, old regions that are candidates for collection have not been coalesced
835 // and filled. This will use mark bits to find objects that need to be updated.
836 update_references_in_old_region(cl, ctx, scanner, r, start_of_range, end_of_range);
837 }
838 } else {
839 // This is a young evacuation
840 size_t cluster_size = CardTable::card_size_in_words() * ShenandoahCardCluster::CardsPerCluster;
841 size_t clusters = assignment._chunk_size / cluster_size;
842 assert(clusters * cluster_size == assignment._chunk_size, "Chunk assignment must align on cluster boundaries");
843 scanner->process_region_slice(r, assignment._chunk_offset, clusters, end_of_range, &cl, true, worker_id);
844 }
845 }
846 }
847 }
848
849 template<class T>
850 void update_references_in_old_region(T &cl, const ShenandoahMarkingContext* ctx, ShenandoahScanRemembered* scanner,
851 const ShenandoahHeapRegion* r, HeapWord* start_of_range,
852 HeapWord* end_of_range) const {
853 // In case last object in my range spans boundary of my chunk, I may need to scan all the way to top()
854 ShenandoahObjectToOopBoundedClosure<T> objs(&cl, start_of_range, r->top());
855
856 // Any object that begins in a previous range is part of a different scanning assignment. Any object that
857 // starts after end_of_range is also not my responsibility. (Either allocated during evacuation, so does
858 // not hold pointers to from-space, or is beyond the range of my assigned work chunk.)
859
860 // Find the first object that begins in my range, if there is one. Note that `p` will be set to `end_of_range`
861 // when no live object is found in the range.
862 HeapWord* tams = ctx->top_at_mark_start(r);
863 HeapWord* p = get_first_object_start_word(ctx, scanner, tams, start_of_range, end_of_range);
864
865 while (p < end_of_range) {
866 // p is known to point to the beginning of marked object obj
867 oop obj = cast_to_oop(p);
868 objs.do_object(obj);
869 HeapWord* prev_p = p;
870 p += obj->size();
871 if (p < tams) {
872 p = ctx->get_next_marked_addr(p, tams);
873 // If there are no more marked objects before tams, this returns tams. Note that tams is
874 // either >= end_of_range, or tams is the start of an object that is marked.
875 }
876 assert(p != prev_p, "Lack of forward progress");
877 }
878 }
879
880 HeapWord* get_first_object_start_word(const ShenandoahMarkingContext* ctx, ShenandoahScanRemembered* scanner, HeapWord* tams,
881 HeapWord* start_of_range, HeapWord* end_of_range) const {
882 HeapWord* p = start_of_range;
883
884 if (p >= tams) {
885 // We cannot use ctx->is_marked(obj) to test whether an object begins at this address. Instead,
886 // we need to use the remembered set crossing map to advance p to the first object that starts
887 // within the enclosing card.
888 size_t card_index = scanner->card_index_for_addr(start_of_range);
889 while (true) {
890 HeapWord* first_object = scanner->first_object_in_card(card_index);
891 if (first_object != nullptr) {
892 p = first_object;
893 break;
894 } else if (scanner->addr_for_card_index(card_index + 1) < end_of_range) {
895 card_index++;
896 } else {
897 // Signal that no object was found in range
898 p = end_of_range;
899 break;
900 }
901 }
902 } else if (!ctx->is_marked(cast_to_oop(p))) {
903 p = ctx->get_next_marked_addr(p, tams);
904 // If there are no more marked objects before tams, this returns tams.
905 // Note that tams is either >= end_of_range, or tams is the start of an object that is marked.
906 }
907 return p;
908 }
909 };
910
911 void ShenandoahGenerationalHeap::update_heap_references(ShenandoahGeneration* generation, bool concurrent) {
912 assert(!is_full_gc_in_progress(), "Only for concurrent and degenerated GC");
913 const uint nworkers = workers()->active_workers();
914 ShenandoahRegionChunkIterator work_list(nworkers);
915 if (concurrent) {
916 ShenandoahGenerationalUpdateHeapRefsTask<true> task(generation, &_update_refs_iterator, &work_list);
917 workers()->run_task(&task);
918 } else {
919 ShenandoahGenerationalUpdateHeapRefsTask<false> task(generation, &_update_refs_iterator, &work_list);
920 workers()->run_task(&task);
921 }
922
923 if (ShenandoahEnableCardStats) {
924 // Only do this if we are collecting card stats
925 ShenandoahScanRemembered* card_scan = old_generation()->card_scan();
926 assert(card_scan != nullptr, "Card table must exist when card stats are enabled");
927 card_scan->log_card_stats(nworkers, CARD_STAT_UPDATE_REFS);
928 }
929 }
930
931 struct ShenandoahCompositeRegionClosure {
932 template<typename C1, typename C2>
933 class Closure : public ShenandoahHeapRegionClosure {
934 private:
935 C1 &_c1;
936 C2 &_c2;
937
938 public:
939 Closure(C1 &c1, C2 &c2) : ShenandoahHeapRegionClosure(), _c1(c1), _c2(c2) {}
940
941 void heap_region_do(ShenandoahHeapRegion* r) override {
942 _c1.heap_region_do(r);
943 _c2.heap_region_do(r);
944 }
945
946 bool is_thread_safe() override {
947 return _c1.is_thread_safe() && _c2.is_thread_safe();
948 }
949 };
950
951 template<typename C1, typename C2>
952 static Closure<C1, C2> of(C1 &c1, C2 &c2) {
953 return Closure<C1, C2>(c1, c2);
954 }
955 };
956
957 class ShenandoahUpdateRegionAges : public ShenandoahHeapRegionClosure {
958 private:
959 ShenandoahMarkingContext* _ctx;
960
961 public:
962 explicit ShenandoahUpdateRegionAges(ShenandoahMarkingContext* ctx) : _ctx(ctx) { }
963
964 void heap_region_do(ShenandoahHeapRegion* r) override {
965 // Maintenance of region age must follow evacuation in order to account for
966 // evacuation allocations within survivor regions. We consult region age during
967 // the subsequent evacuation to determine whether certain objects need to
968 // be promoted.
969 if (r->is_young() && r->is_active()) {
970 HeapWord *tams = _ctx->top_at_mark_start(r);
971 HeapWord *top = r->top();
972
973 // Allocations move the watermark when top moves. However, compacting
974 // objects will sometimes lower top beneath the watermark, after which,
975 // attempts to read the watermark will assert out (watermark should not be
976 // higher than top).
977 if (top > tams) {
978 // There have been allocations in this region since the start of the cycle.
979 // Any objects new to this region must not assimilate elevated age.
980 r->reset_age();
981 } else if (ShenandoahGenerationalHeap::heap()->is_aging_cycle()) {
982 r->increment_age();
983 }
984 }
985 }
986
987 bool is_thread_safe() override {
988 return true;
989 }
990 };
991
992 void ShenandoahGenerationalHeap::final_update_refs_update_region_states() {
993 ShenandoahSynchronizePinnedRegionStates pins;
994 ShenandoahUpdateRegionAges ages(marking_context());
995 auto cl = ShenandoahCompositeRegionClosure::of(pins, ages);
996 parallel_heap_region_iterate(&cl);
997 }
998
999 void ShenandoahGenerationalHeap::complete_degenerated_cycle() {
1000 shenandoah_assert_heaplocked_or_safepoint();
1001 if (!old_generation()->is_parsable()) {
1002 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_coalesce_and_fill);
1003 coalesce_and_fill_old_regions(false);
1004 }
1005
1006 old_generation()->maybe_log_promotion_failure_stats(false);
1007 }
1008
1009 void ShenandoahGenerationalHeap::complete_concurrent_cycle() {
1010 if (!old_generation()->is_parsable()) {
1011 // Class unloading may render the card offsets unusable, so we must rebuild them before
1012 // the next remembered set scan. We _could_ let the control thread do this sometime after
1013 // the global cycle has completed and before the next young collection, but under memory
1014 // pressure the control thread may not have the time (that is, because it's running back
1015 // to back GCs). In that scenario, we would have to make the old regions parsable before
1016 // we could start a young collection. This could delay the start of the young cycle and
1017 // throw off the heuristics.
1018 entry_global_coalesce_and_fill();
1019 }
1020
1021 old_generation()->maybe_log_promotion_failure_stats(true);
1022 }
1023
1024 void ShenandoahGenerationalHeap::entry_global_coalesce_and_fill() {
1025 const char* msg = "Coalescing and filling old regions";
1026 ShenandoahConcurrentPhase gc_phase(msg, ShenandoahPhaseTimings::conc_coalesce_and_fill);
1027
1028 TraceCollectorStats tcs(monitoring_support()->concurrent_collection_counters());
1029 EventMark em("%s", msg);
1030 ShenandoahWorkerScope scope(workers(),
1031 ShenandoahWorkerPolicy::calc_workers_for_conc_marking(),
1032 "concurrent coalesce and fill");
1033
1034 coalesce_and_fill_old_regions(true);
1035 }
1036
1037 void ShenandoahGenerationalHeap::update_region_ages(ShenandoahMarkingContext* ctx) {
1038 ShenandoahUpdateRegionAges cl(ctx);
1039 parallel_heap_region_iterate(&cl);
1040 }