1 /*
2 * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26
27 #include "gc/shenandoah/shenandoahAgeCensus.hpp"
28 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
29 #include "gc/shenandoah/shenandoahFreeSet.hpp"
30 #include "gc/shenandoah/shenandoahGenerationalControlThread.hpp"
31 #include "gc/shenandoah/shenandoahGenerationalEvacuationTask.hpp"
32 #include "gc/shenandoah/shenandoahGenerationalHeap.hpp"
33 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
34 #include "gc/shenandoah/shenandoahHeapRegion.hpp"
35 #include "gc/shenandoah/shenandoahHeapRegionClosures.hpp"
36 #include "gc/shenandoah/shenandoahInitLogger.hpp"
37 #include "gc/shenandoah/shenandoahMemoryPool.hpp"
38 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
39 #include "gc/shenandoah/shenandoahOldGeneration.hpp"
40 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
41 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
42 #include "gc/shenandoah/shenandoahRegulatorThread.hpp"
43 #include "gc/shenandoah/shenandoahScanRemembered.inline.hpp"
44 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
45 #include "gc/shenandoah/shenandoahYoungGeneration.hpp"
46 #include "gc/shenandoah/shenandoahUtils.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
58 void print_heap() override {
59 ShenandoahInitLogger::print_heap();
60
61 ShenandoahGenerationalHeap* heap = ShenandoahGenerationalHeap::heap();
62
63 ShenandoahYoungGeneration* young = heap->young_generation();
64 log_info(gc, init)("Young Generation Soft Size: " EXACTFMT, EXACTFMTARGS(young->soft_max_capacity()));
65 log_info(gc, init)("Young Generation Max: " EXACTFMT, EXACTFMTARGS(young->max_capacity()));
66
67 ShenandoahOldGeneration* old = heap->old_generation();
68 log_info(gc, init)("Old Generation Soft Size: " EXACTFMT, EXACTFMTARGS(old->soft_max_capacity()));
69 log_info(gc, init)("Old Generation Max: " EXACTFMT, EXACTFMTARGS(old->max_capacity()));
70 }
71
72 protected:
73 void print_gc_specific() override {
74 ShenandoahInitLogger::print_gc_specific();
75
76 ShenandoahGenerationalHeap* heap = ShenandoahGenerationalHeap::heap();
77 log_info(gc, init)("Young Heuristics: %s", heap->young_generation()->heuristics()->name());
78 log_info(gc, init)("Old Heuristics: %s", heap->old_generation()->heuristics()->name());
79 }
80 };
81
82 size_t ShenandoahGenerationalHeap::calculate_min_plab() {
83 return align_up(PLAB::min_size(), CardTable::card_size_in_words());
84 }
85
86 size_t ShenandoahGenerationalHeap::calculate_max_plab() {
87 size_t MaxTLABSizeWords = ShenandoahHeapRegion::max_tlab_size_words();
88 return align_down(MaxTLABSizeWords, CardTable::card_size_in_words());
89 }
90
91 // Returns size in bytes
92 size_t ShenandoahGenerationalHeap::unsafe_max_tlab_alloc(Thread *thread) const {
93 return MIN2(ShenandoahHeapRegion::max_tlab_size_bytes(), young_generation()->available());
94 }
95
96 ShenandoahGenerationalHeap::ShenandoahGenerationalHeap(ShenandoahCollectorPolicy* policy) :
97 ShenandoahHeap(policy),
98 _age_census(nullptr),
99 _evac_tracker(new ShenandoahEvacuationTracker()),
100 _min_plab_size(calculate_min_plab()),
101 _max_plab_size(calculate_max_plab()),
102 _regulator_thread(nullptr),
103 _young_gen_memory_pool(nullptr),
104 _old_gen_memory_pool(nullptr) {
105 assert(is_aligned(_min_plab_size, CardTable::card_size_in_words()), "min_plab_size must be aligned");
106 assert(is_aligned(_max_plab_size, CardTable::card_size_in_words()), "max_plab_size must be aligned");
107 }
108
109 void ShenandoahGenerationalHeap::post_initialize() {
110 ShenandoahHeap::post_initialize();
111 _age_census = new ShenandoahAgeCensus();
112 }
113
114 void ShenandoahGenerationalHeap::print_init_logger() const {
115 ShenandoahGenerationalInitLogger logger;
116 logger.print_all();
117 }
118
119 void ShenandoahGenerationalHeap::print_tracing_info() const {
120 ShenandoahHeap::print_tracing_info();
121
122 LogTarget(Info, gc, stats) lt;
123 if (lt.is_enabled()) {
124 LogStream ls(lt);
125 ls.cr();
126 ls.cr();
127 evac_tracker()->print_global_on(&ls);
128 }
129 }
130
131 void ShenandoahGenerationalHeap::initialize_heuristics() {
132 // Initialize global generation and heuristics even in generational mode.
133 ShenandoahHeap::initialize_heuristics();
134
135 // Max capacity is the maximum _allowed_ capacity. That is, the maximum allowed capacity
136 // for old would be total heap - minimum capacity of young. This means the sum of the maximum
137 // allowed for old and young could exceed the total heap size. It remains the case that the
138 // _actual_ capacity of young + old = total.
139 _generation_sizer.heap_size_changed(max_capacity());
140 size_t initial_capacity_young = _generation_sizer.max_young_size();
141 size_t max_capacity_young = _generation_sizer.max_young_size();
142 size_t initial_capacity_old = max_capacity() - max_capacity_young;
143 size_t max_capacity_old = max_capacity() - initial_capacity_young;
144
145 _young_generation = new ShenandoahYoungGeneration(max_workers(), max_capacity_young, initial_capacity_young);
146 _old_generation = new ShenandoahOldGeneration(max_workers(), max_capacity_old, initial_capacity_old);
147 _young_generation->initialize_heuristics(mode());
148 _old_generation->initialize_heuristics(mode());
149 }
150
151 void ShenandoahGenerationalHeap::initialize_serviceability() {
152 assert(mode()->is_generational(), "Only for the generational mode");
153 _young_gen_memory_pool = new ShenandoahYoungGenMemoryPool(this);
154 _old_gen_memory_pool = new ShenandoahOldGenMemoryPool(this);
155 cycle_memory_manager()->add_pool(_young_gen_memory_pool);
156 cycle_memory_manager()->add_pool(_old_gen_memory_pool);
157 stw_memory_manager()->add_pool(_young_gen_memory_pool);
158 stw_memory_manager()->add_pool(_old_gen_memory_pool);
159 }
160
161 GrowableArray<MemoryPool*> ShenandoahGenerationalHeap::memory_pools() {
162 assert(mode()->is_generational(), "Only for the generational mode");
163 GrowableArray<MemoryPool*> memory_pools(2);
164 memory_pools.append(_young_gen_memory_pool);
165 memory_pools.append(_old_gen_memory_pool);
166 return memory_pools;
167 }
168
169 void ShenandoahGenerationalHeap::initialize_controller() {
170 auto control_thread = new ShenandoahGenerationalControlThread();
171 _control_thread = control_thread;
172 _regulator_thread = new ShenandoahRegulatorThread(control_thread);
173 }
174
175 void ShenandoahGenerationalHeap::gc_threads_do(ThreadClosure* tcl) const {
176 if (!shenandoah_policy()->is_at_shutdown()) {
177 ShenandoahHeap::gc_threads_do(tcl);
178 tcl->do_thread(regulator_thread());
179 }
180 }
181
182 void ShenandoahGenerationalHeap::stop() {
183 ShenandoahHeap::stop();
184 regulator_thread()->stop();
185 }
186
187 bool ShenandoahGenerationalHeap::requires_barriers(stackChunkOop obj) const {
188 if (is_idle()) {
189 return false;
190 }
191
192 if (is_concurrent_young_mark_in_progress() && is_in_young(obj) && !marking_context()->allocated_after_mark_start(obj)) {
193 // We are marking young, this object is in young, and it is below the TAMS
194 return true;
195 }
196
197 if (is_in_old(obj)) {
198 // Card marking barriers are required for objects in the old generation
199 return true;
200 }
201
202 if (has_forwarded_objects()) {
203 // Object may have pointers that need to be updated
204 return true;
205 }
206
207 return false;
208 }
209
210 void ShenandoahGenerationalHeap::evacuate_collection_set(bool concurrent) {
211 ShenandoahRegionIterator regions;
212 ShenandoahGenerationalEvacuationTask task(this, ®ions, concurrent, false /* only promote regions */);
213 workers()->run_task(&task);
214 }
215
216 void ShenandoahGenerationalHeap::promote_regions_in_place(bool concurrent) {
217 ShenandoahRegionIterator regions;
218 ShenandoahGenerationalEvacuationTask task(this, ®ions, concurrent, true /* only promote regions */);
219 workers()->run_task(&task);
220 }
221
222 oop ShenandoahGenerationalHeap::evacuate_object(oop p, Thread* thread) {
223 assert(thread == Thread::current(), "Expected thread parameter to be current thread.");
224 if (ShenandoahThreadLocalData::is_oom_during_evac(thread)) {
225 // This thread went through the OOM during evac protocol and it is safe to return
226 // the forward pointer. It must not attempt to evacuate anymore.
227 return ShenandoahBarrierSet::resolve_forwarded(p);
228 }
229
230 assert(ShenandoahThreadLocalData::is_evac_allowed(thread), "must be enclosed in oom-evac scope");
231
232 ShenandoahHeapRegion* r = heap_region_containing(p);
233 assert(!r->is_humongous(), "never evacuate humongous objects");
234
235 ShenandoahAffiliation target_gen = r->affiliation();
236 // gc_generation() can change asynchronously and should not be used here.
237 assert(active_generation() != nullptr, "Error");
238 if (active_generation()->is_young() && target_gen == YOUNG_GENERATION) {
239 markWord mark = p->mark();
240 if (mark.is_marked()) {
241 // Already forwarded.
242 return ShenandoahBarrierSet::resolve_forwarded(p);
243 }
244
245 if (mark.has_displaced_mark_helper()) {
246 // We don't want to deal with MT here just to ensure we read the right mark word.
247 // Skip the potential promotion attempt for this one.
248 } else if (r->age() + mark.age() >= age_census()->tenuring_threshold()) {
249 oop result = try_evacuate_object(p, thread, r, OLD_GENERATION);
250 if (result != nullptr) {
251 return result;
252 }
253 // If we failed to promote this aged object, we'll fall through to code below and evacuate to young-gen.
254 }
255 }
256 return try_evacuate_object(p, thread, r, target_gen);
257 }
258
259 // try_evacuate_object registers the object and dirties the associated remembered set information when evacuating
260 // to OLD_GENERATION.
261 oop ShenandoahGenerationalHeap::try_evacuate_object(oop p, Thread* thread, ShenandoahHeapRegion* from_region,
262 ShenandoahAffiliation target_gen) {
263 bool alloc_from_lab = true;
264 bool has_plab = false;
265 HeapWord* copy = nullptr;
266 size_t size = p->size();
267 bool is_promotion = (target_gen == OLD_GENERATION) && from_region->is_young();
268
269 #ifdef ASSERT
270 if (ShenandoahOOMDuringEvacALot &&
271 (os::random() & 1) == 0) { // Simulate OOM every ~2nd slow-path call
272 copy = nullptr;
273 } else {
274 #endif
275 if (UseTLAB) {
276 switch (target_gen) {
277 case YOUNG_GENERATION: {
278 copy = allocate_from_gclab(thread, size);
279 if ((copy == nullptr) && (size < ShenandoahThreadLocalData::gclab_size(thread))) {
280 // GCLAB allocation failed because we are bumping up against the limit on young evacuation reserve. Try resetting
281 // the desired GCLAB size and retry GCLAB allocation to avoid cascading of shared memory allocations.
282 ShenandoahThreadLocalData::set_gclab_size(thread, PLAB::min_size());
283 copy = allocate_from_gclab(thread, size);
284 // If we still get nullptr, we'll try a shared allocation below.
285 }
286 break;
287 }
288 case OLD_GENERATION: {
289 PLAB* plab = ShenandoahThreadLocalData::plab(thread);
290 if (plab != nullptr) {
291 has_plab = true;
292 copy = allocate_from_plab(thread, size, is_promotion);
293 if ((copy == nullptr) && (size < ShenandoahThreadLocalData::plab_size(thread)) &&
294 ShenandoahThreadLocalData::plab_retries_enabled(thread)) {
295 // PLAB allocation failed because we are bumping up against the limit on old evacuation reserve or because
296 // the requested object does not fit within the current plab but the plab still has an "abundance" of memory,
297 // where abundance is defined as >= ShenGenHeap::plab_min_size(). In the former case, we try shrinking the
298 // desired PLAB size to the minimum and retry PLAB allocation to avoid cascading of shared memory allocations.
299 if (plab->words_remaining() < plab_min_size()) {
300 ShenandoahThreadLocalData::set_plab_size(thread, plab_min_size());
301 copy = allocate_from_plab(thread, size, is_promotion);
302 // If we still get nullptr, we'll try a shared allocation below.
303 if (copy == nullptr) {
304 // If retry fails, don't continue to retry until we have success (probably in next GC pass)
305 ShenandoahThreadLocalData::disable_plab_retries(thread);
306 }
307 }
308 // else, copy still equals nullptr. this causes shared allocation below, preserving this plab for future needs.
309 }
310 }
311 break;
312 }
313 default: {
314 ShouldNotReachHere();
315 break;
316 }
317 }
318 }
319
320 if (copy == nullptr) {
321 // If we failed to allocate in LAB, we'll try a shared allocation.
322 if (!is_promotion || !has_plab || (size > PLAB::min_size())) {
323 ShenandoahAllocRequest req = ShenandoahAllocRequest::for_shared_gc(size, target_gen, is_promotion);
324 copy = allocate_memory(req);
325 alloc_from_lab = false;
326 }
327 // else, we leave copy equal to nullptr, signaling a promotion failure below if appropriate.
328 // We choose not to promote objects smaller than PLAB::min_size() by way of shared allocations, as this is too
329 // costly. Instead, we'll simply "evacuate" to young-gen memory (using a GCLAB) and will promote in a future
330 // evacuation pass. This condition is denoted by: is_promotion && has_plab && (size <= PLAB::min_size())
331 }
332 #ifdef ASSERT
333 }
334 #endif
335
336 if (copy == nullptr) {
337 if (target_gen == OLD_GENERATION) {
338 if (from_region->is_young()) {
339 // Signal that promotion failed. Will evacuate this old object somewhere in young gen.
340 old_generation()->handle_failed_promotion(thread, size);
341 return nullptr;
342 } else {
343 // Remember that evacuation to old gen failed. We'll want to trigger a full gc to recover from this
344 // after the evacuation threads have finished.
345 old_generation()->handle_failed_evacuation();
346 }
347 }
348
349 control_thread()->handle_alloc_failure_evac(size);
350
351 oom_evac_handler()->handle_out_of_memory_during_evacuation();
352
353 return ShenandoahBarrierSet::resolve_forwarded(p);
354 }
355
356 // Copy the object:
357 NOT_PRODUCT(evac_tracker()->begin_evacuation(thread, size * HeapWordSize));
358 Copy::aligned_disjoint_words(cast_from_oop<HeapWord*>(p), copy, size);
359 oop copy_val = cast_to_oop(copy);
360
361 // Update the age of the evacuated object
362 if (target_gen == YOUNG_GENERATION && is_aging_cycle()) {
363 ShenandoahHeap::increase_object_age(copy_val, from_region->age() + 1);
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
371 // This is necessary for virtual thread support. This uses the mark word without
372 // considering that it may now be a forwarding pointer (and could therefore crash).
373 // Secondarily, we do not want to spend cycles relativizing stack chunks for oops
374 // that lost the evacuation race (and will therefore not become visible). It is
375 // safe to do this on the public copy (this is also done during concurrent mark).
376 ContinuationGCSupport::relativize_stack_chunk(copy_val);
377
378 // Record that the evacuation succeeded
379 NOT_PRODUCT(evac_tracker()->end_evacuation(thread, size * HeapWordSize));
380
381 if (target_gen == OLD_GENERATION) {
382 old_generation()->handle_evacuation(copy, size, from_region->is_young());
383 } else {
384 // When copying to the old generation above, we don't care
385 // about recording object age in the census stats.
386 assert(target_gen == YOUNG_GENERATION, "Error");
387 // We record this census only when simulating pre-adaptive tenuring behavior, or
388 // when we have been asked to record the census at evacuation rather than at mark
389 if (ShenandoahGenerationalCensusAtEvac || !ShenandoahGenerationalAdaptiveTenuring) {
390 evac_tracker()->record_age(thread, size * HeapWordSize, ShenandoahHeap::get_object_age(copy_val));
391 }
392 }
393 shenandoah_assert_correct(nullptr, copy_val);
394 return copy_val;
395 } else {
396 // Failed to evacuate. We need to deal with the object that is left behind. Since this
397 // new allocation is certainly after TAMS, it will be considered live in the next cycle.
398 // But if it happens to contain references to evacuated regions, those references would
399 // not get updated for this stale copy during this cycle, and we will crash while scanning
400 // it the next cycle.
401 if (alloc_from_lab) {
402 // For LAB allocations, it is enough to rollback the allocation ptr. Either the next
403 // object will overwrite this stale copy, or the filler object on LAB retirement will
404 // do this.
405 switch (target_gen) {
406 case YOUNG_GENERATION: {
407 ShenandoahThreadLocalData::gclab(thread)->undo_allocation(copy, size);
408 break;
409 }
410 case OLD_GENERATION: {
411 ShenandoahThreadLocalData::plab(thread)->undo_allocation(copy, size);
412 if (is_promotion) {
413 ShenandoahThreadLocalData::subtract_from_plab_promoted(thread, size * HeapWordSize);
414 }
415 break;
416 }
417 default: {
418 ShouldNotReachHere();
419 break;
420 }
421 }
422 } else {
423 // For non-LAB allocations, we have no way to retract the allocation, and
424 // have to explicitly overwrite the copy with the filler object. With that overwrite,
425 // we have to keep the fwdptr initialized and pointing to our (stale) copy.
426 assert(size >= ShenandoahHeap::min_fill_size(), "previously allocated object known to be larger than min_size");
427 fill_with_object(copy, size);
428 shenandoah_assert_correct(nullptr, copy_val);
429 // For non-LAB allocations, the object has already been registered
430 }
431 shenandoah_assert_correct(nullptr, result);
432 return result;
433 }
434 }
435
436 inline HeapWord* ShenandoahGenerationalHeap::allocate_from_plab(Thread* thread, size_t size, bool is_promotion) {
437 assert(UseTLAB, "TLABs should be enabled");
438
439 PLAB* plab = ShenandoahThreadLocalData::plab(thread);
440 HeapWord* obj;
441
442 if (plab == nullptr) {
443 assert(!thread->is_Java_thread() && !thread->is_Worker_thread(), "Performance: thread should have PLAB: %s", thread->name());
444 // No PLABs in this thread, fallback to shared allocation
445 return nullptr;
446 } else if (is_promotion && !ShenandoahThreadLocalData::allow_plab_promotions(thread)) {
447 return nullptr;
448 }
449 // if plab->word_size() <= 0, thread's plab not yet initialized for this pass, so allow_plab_promotions() is not trustworthy
450 obj = plab->allocate(size);
451 if ((obj == nullptr) && (plab->words_remaining() < plab_min_size())) {
452 // allocate_from_plab_slow will establish allow_plab_promotions(thread) for future invocations
453 obj = allocate_from_plab_slow(thread, size, is_promotion);
454 }
455 // if plab->words_remaining() >= ShenGenHeap::heap()->plab_min_size(), just return nullptr so we can use a shared allocation
456 if (obj == nullptr) {
457 return nullptr;
458 }
459
460 if (is_promotion) {
461 ShenandoahThreadLocalData::add_to_plab_promoted(thread, size * HeapWordSize);
462 }
463 return obj;
464 }
465
466 // Establish a new PLAB and allocate size HeapWords within it.
467 HeapWord* ShenandoahGenerationalHeap::allocate_from_plab_slow(Thread* thread, size_t size, bool is_promotion) {
468 // New object should fit the PLAB size
469
470 assert(mode()->is_generational(), "PLABs only relevant to generational GC");
471 const size_t plab_min_size = this->plab_min_size();
472 // PLABs are aligned to card boundaries to avoid synchronization with concurrent
473 // allocations in other PLABs.
474 const size_t min_size = (size > plab_min_size)? align_up(size, CardTable::card_size_in_words()): plab_min_size;
475
476 // Figure out size of new PLAB, using value determined at last refill.
477 size_t cur_size = ShenandoahThreadLocalData::plab_size(thread);
478 if (cur_size == 0) {
479 cur_size = plab_min_size;
480 }
481
482 // Expand aggressively, doubling at each refill in this epoch, ceiling at plab_max_size()
483 size_t future_size = MIN2(cur_size * 2, plab_max_size());
484 // Doubling, starting at a card-multiple, should give us a card-multiple. (Ceiling and floor
485 // are card multiples.)
486 assert(is_aligned(future_size, CardTable::card_size_in_words()), "Card multiple by construction, future_size: " SIZE_FORMAT
487 ", card_size: " SIZE_FORMAT ", cur_size: " SIZE_FORMAT ", max: " SIZE_FORMAT,
488 future_size, (size_t) CardTable::card_size_in_words(), cur_size, plab_max_size());
489
490 // Record new heuristic value even if we take any shortcut. This captures
491 // the case when moderately-sized objects always take a shortcut. At some point,
492 // heuristics should catch up with them. Note that the requested cur_size may
493 // not be honored, but we remember that this is the preferred size.
494 log_debug(gc, free)("Set new PLAB size: " SIZE_FORMAT, future_size);
495 ShenandoahThreadLocalData::set_plab_size(thread, future_size);
496 if (cur_size < size) {
497 // The PLAB to be allocated is still not large enough to hold the object. Fall back to shared allocation.
498 // This avoids retiring perfectly good PLABs in order to represent a single large object allocation.
499 log_debug(gc, free)("Current PLAB size (" SIZE_FORMAT ") is too small for " SIZE_FORMAT, cur_size, size);
500 return nullptr;
501 }
502
503 // Retire current PLAB, and allocate a new one.
504 PLAB* plab = ShenandoahThreadLocalData::plab(thread);
505 if (plab->words_remaining() < plab_min_size) {
506 // Retire current PLAB. This takes care of any PLAB book-keeping.
507 // retire_plab() registers the remnant filler object with the remembered set scanner without a lock.
508 // Since PLABs are card-aligned, concurrent registrations in other PLABs don't interfere.
509 retire_plab(plab, thread);
510
511 size_t actual_size = 0;
512 HeapWord* plab_buf = allocate_new_plab(min_size, cur_size, &actual_size);
513 if (plab_buf == nullptr) {
514 if (min_size == plab_min_size) {
515 // Disable PLAB promotions for this thread because we cannot even allocate a minimal PLAB. This allows us
516 // to fail faster on subsequent promotion attempts.
517 ShenandoahThreadLocalData::disable_plab_promotions(thread);
518 }
519 return nullptr;
520 } else {
521 ShenandoahThreadLocalData::enable_plab_retries(thread);
522 }
523 // Since the allocated PLAB may have been down-sized for alignment, plab->allocate(size) below may still fail.
524 if (ZeroTLAB) {
525 // ... and clear it.
526 Copy::zero_to_words(plab_buf, actual_size);
527 } else {
528 // ...and zap just allocated object.
529 #ifdef ASSERT
530 // Skip mangling the space corresponding to the object header to
531 // ensure that the returned space is not considered parsable by
532 // any concurrent GC thread.
533 size_t hdr_size = oopDesc::header_size();
534 Copy::fill_to_words(plab_buf + hdr_size, actual_size - hdr_size, badHeapWordVal);
535 #endif // ASSERT
536 }
537 assert(is_aligned(actual_size, CardTable::card_size_in_words()), "Align by design");
538 plab->set_buf(plab_buf, actual_size);
539 if (is_promotion && !ShenandoahThreadLocalData::allow_plab_promotions(thread)) {
540 return nullptr;
541 }
542 return plab->allocate(size);
543 } else {
544 // If there's still at least min_size() words available within the current plab, don't retire it. Let's nibble
545 // away on this plab as long as we can. Meanwhile, return nullptr to force this particular allocation request
546 // to be satisfied with a shared allocation. By packing more promotions into the previously allocated PLAB, we
547 // reduce the likelihood of evacuation failures, and we reduce the need for downsizing our PLABs.
548 return nullptr;
549 }
550 }
551
552 HeapWord* ShenandoahGenerationalHeap::allocate_new_plab(size_t min_size, size_t word_size, size_t* actual_size) {
553 // Align requested sizes to card-sized multiples. Align down so that we don't violate max size of TLAB.
554 assert(is_aligned(min_size, CardTable::card_size_in_words()), "Align by design");
555 assert(word_size >= min_size, "Requested PLAB is too small");
556
557 ShenandoahAllocRequest req = ShenandoahAllocRequest::for_plab(min_size, word_size);
558 // Note that allocate_memory() sets a thread-local flag to prohibit further promotions by this thread
559 // if we are at risk of infringing on the old-gen evacuation budget.
560 HeapWord* res = allocate_memory(req);
561 if (res != nullptr) {
562 *actual_size = req.actual_size();
563 } else {
564 *actual_size = 0;
565 }
566 assert(is_aligned(res, CardTable::card_size_in_words()), "Align by design");
567 return res;
568 }
569
570 void ShenandoahGenerationalHeap::retire_plab(PLAB* plab, Thread* thread) {
571 // We don't enforce limits on plab evacuations. We let it consume all available old-gen memory in order to reduce
572 // probability of an evacuation failure. We do enforce limits on promotion, to make sure that excessive promotion
573 // does not result in an old-gen evacuation failure. Note that a failed promotion is relatively harmless. Any
574 // object that fails to promote in the current cycle will be eligible for promotion in a subsequent cycle.
575
576 // When the plab was instantiated, its entirety was treated as if the entire buffer was going to be dedicated to
577 // promotions. Now that we are retiring the buffer, we adjust for the reality that the plab is not entirely promotions.
578 // 1. Some of the plab may have been dedicated to evacuations.
579 // 2. Some of the plab may have been abandoned due to waste (at the end of the plab).
580 size_t not_promoted =
581 ShenandoahThreadLocalData::get_plab_actual_size(thread) - ShenandoahThreadLocalData::get_plab_promoted(thread);
582 ShenandoahThreadLocalData::reset_plab_promoted(thread);
583 ShenandoahThreadLocalData::set_plab_actual_size(thread, 0);
584 if (not_promoted > 0) {
585 old_generation()->unexpend_promoted(not_promoted);
586 }
587 const size_t original_waste = plab->waste();
588 HeapWord* const top = plab->top();
589
590 // plab->retire() overwrites unused memory between plab->top() and plab->hard_end() with a dummy object to make memory parsable.
591 // It adds the size of this unused memory, in words, to plab->waste().
592 plab->retire();
593 if (top != nullptr && plab->waste() > original_waste && is_in_old(top)) {
594 // If retiring the plab created a filler object, then we need to register it with our card scanner so it can
595 // safely walk the region backing the plab.
596 log_debug(gc)("retire_plab() is registering remnant of size " SIZE_FORMAT " at " PTR_FORMAT,
597 plab->waste() - original_waste, p2i(top));
598 // No lock is necessary because the PLAB memory is aligned on card boundaries.
599 old_generation()->card_scan()->register_object_without_lock(top);
600 }
601 }
602
603 void ShenandoahGenerationalHeap::retire_plab(PLAB* plab) {
604 Thread* thread = Thread::current();
605 retire_plab(plab, thread);
606 }
607
608 ShenandoahGenerationalHeap::TransferResult ShenandoahGenerationalHeap::balance_generations() {
609 shenandoah_assert_heaplocked_or_safepoint();
610
611 ShenandoahOldGeneration* old_gen = old_generation();
612 const ssize_t old_region_balance = old_gen->get_region_balance();
613 old_gen->set_region_balance(0);
614
615 if (old_region_balance > 0) {
616 const auto old_region_surplus = checked_cast<size_t>(old_region_balance);
617 const bool success = generation_sizer()->transfer_to_young(old_region_surplus);
618 return TransferResult {
619 success, old_region_surplus, "young"
620 };
621 }
622
623 if (old_region_balance < 0) {
624 const auto old_region_deficit = checked_cast<size_t>(-old_region_balance);
625 const bool success = generation_sizer()->transfer_to_old(old_region_deficit);
626 if (!success) {
627 old_gen->handle_failed_transfer();
628 }
629 return TransferResult {
630 success, old_region_deficit, "old"
631 };
632 }
633
634 return TransferResult {true, 0, "none"};
635 }
636
637 // Make sure old-generation is large enough, but no larger than is necessary, to hold mixed evacuations
638 // and promotions, if we anticipate either. Any deficit is provided by the young generation, subject to
639 // xfer_limit, and any surplus is transferred to the young generation.
640 // xfer_limit is the maximum we're able to transfer from young to old.
641 void ShenandoahGenerationalHeap::compute_old_generation_balance(size_t old_xfer_limit, size_t old_cset_regions) {
642
643 // We can limit the old reserve to the size of anticipated promotions:
644 // max_old_reserve is an upper bound on memory evacuated from old and promoted to old,
645 // clamped by the old generation space available.
646 //
647 // Here's the algebra.
648 // Let SOEP = ShenandoahOldEvacRatioPercent,
649 // OE = old evac,
650 // YE = young evac, and
651 // TE = total evac = OE + YE
652 // By definition:
653 // SOEP/100 = OE/TE
654 // = OE/(OE+YE)
655 // => SOEP/(100-SOEP) = OE/((OE+YE)-OE) // componendo-dividendo: If a/b = c/d, then a/(b-a) = c/(d-c)
656 // = OE/YE
657 // => OE = YE*SOEP/(100-SOEP)
658
659 // We have to be careful in the event that SOEP is set to 100 by the user.
660 assert(ShenandoahOldEvacRatioPercent <= 100, "Error");
661 const size_t old_available = old_generation()->available();
662 // The free set will reserve this amount of memory to hold young evacuations
663 const size_t young_reserve = (young_generation()->max_capacity() * ShenandoahEvacReserve) / 100;
664
665 // In the case that ShenandoahOldEvacRatioPercent equals 100, max_old_reserve is limited only by xfer_limit.
666
667 const double bound_on_old_reserve = old_available + old_xfer_limit + young_reserve;
668 const double max_old_reserve = (ShenandoahOldEvacRatioPercent == 100)?
669 bound_on_old_reserve: MIN2(double(young_reserve * ShenandoahOldEvacRatioPercent) / double(100 - ShenandoahOldEvacRatioPercent),
670 bound_on_old_reserve);
671
672 const size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
673
674 // Decide how much old space we should reserve for a mixed collection
675 double reserve_for_mixed = 0;
676 if (old_generation()->has_unprocessed_collection_candidates()) {
677 // We want this much memory to be unfragmented in order to reliably evacuate old. This is conservative because we
678 // may not evacuate the entirety of unprocessed candidates in a single mixed evacuation.
679 const double max_evac_need = (double(old_generation()->unprocessed_collection_candidates_live_memory()) * ShenandoahOldEvacWaste);
680 assert(old_available >= old_generation()->free_unaffiliated_regions() * region_size_bytes,
681 "Unaffiliated available must be less than total available");
682 const double old_fragmented_available = double(old_available - old_generation()->free_unaffiliated_regions() * region_size_bytes);
683 reserve_for_mixed = max_evac_need + old_fragmented_available;
684 if (reserve_for_mixed > max_old_reserve) {
685 reserve_for_mixed = max_old_reserve;
686 }
687 }
688
689 // Decide how much space we should reserve for promotions from young
690 size_t reserve_for_promo = 0;
691 const size_t promo_load = old_generation()->get_promotion_potential();
692 const bool doing_promotions = promo_load > 0;
693 if (doing_promotions) {
694 // We're promoting and have a bound on the maximum amount that can be promoted
695 assert(max_old_reserve >= reserve_for_mixed, "Sanity");
696 const size_t available_for_promotions = max_old_reserve - reserve_for_mixed;
697 reserve_for_promo = MIN2((size_t)(promo_load * ShenandoahPromoEvacWaste), available_for_promotions);
698 }
699
700 // This is the total old we want to ideally reserve
701 const size_t old_reserve = reserve_for_mixed + reserve_for_promo;
702 assert(old_reserve <= max_old_reserve, "cannot reserve more than max for old evacuations");
703
704 // We now check if the old generation is running a surplus or a deficit.
705 const size_t max_old_available = old_generation()->available() + old_cset_regions * region_size_bytes;
706 if (max_old_available >= old_reserve) {
707 // We are running a surplus, so the old region surplus can go to young
708 const size_t old_surplus = (max_old_available - old_reserve) / region_size_bytes;
709 const size_t unaffiliated_old_regions = old_generation()->free_unaffiliated_regions() + old_cset_regions;
710 const size_t old_region_surplus = MIN2(old_surplus, unaffiliated_old_regions);
711 old_generation()->set_region_balance(checked_cast<ssize_t>(old_region_surplus));
712 } else {
713 // We are running a deficit which we'd like to fill from young.
714 // Ignore that this will directly impact young_generation()->max_capacity(),
715 // indirectly impacting young_reserve and old_reserve. These computations are conservative.
716 // Note that deficit is rounded up by one region.
717 const size_t old_need = (old_reserve - max_old_available + region_size_bytes - 1) / region_size_bytes;
718 const size_t max_old_region_xfer = old_xfer_limit / region_size_bytes;
719
720 // Round down the regions we can transfer from young to old. If we're running short
721 // on young-gen memory, we restrict the xfer. Old-gen collection activities will be
722 // curtailed if the budget is restricted.
723 const size_t old_region_deficit = MIN2(old_need, max_old_region_xfer);
724 old_generation()->set_region_balance(0 - checked_cast<ssize_t>(old_region_deficit));
725 }
726 }
727
728 void ShenandoahGenerationalHeap::reset_generation_reserves() {
729 young_generation()->set_evacuation_reserve(0);
730 old_generation()->set_evacuation_reserve(0);
731 old_generation()->set_promoted_reserve(0);
732 }
733
734 void ShenandoahGenerationalHeap::TransferResult::print_on(const char* when, outputStream* ss) const {
735 auto heap = ShenandoahGenerationalHeap::heap();
736 ShenandoahYoungGeneration* const young_gen = heap->young_generation();
737 ShenandoahOldGeneration* const old_gen = heap->old_generation();
738 const size_t young_available = young_gen->available();
739 const size_t old_available = old_gen->available();
740 ss->print_cr("After %s, %s " SIZE_FORMAT " regions to %s to prepare for next gc, old available: "
741 PROPERFMT ", young_available: " PROPERFMT,
742 when,
743 success? "successfully transferred": "failed to transfer", region_count, region_destination,
744 PROPERFMTARGS(old_available), PROPERFMTARGS(young_available));
745 }
746
747 void ShenandoahGenerationalHeap::coalesce_and_fill_old_regions(bool concurrent) {
748 class ShenandoahGlobalCoalesceAndFill : public WorkerTask {
749 private:
750 ShenandoahPhaseTimings::Phase _phase;
751 ShenandoahRegionIterator _regions;
752 public:
753 explicit ShenandoahGlobalCoalesceAndFill(ShenandoahPhaseTimings::Phase phase) :
754 WorkerTask("Shenandoah Global Coalesce"),
755 _phase(phase) {}
756
757 void work(uint worker_id) override {
758 ShenandoahWorkerTimingsTracker timer(_phase,
759 ShenandoahPhaseTimings::ScanClusters,
760 worker_id, true);
761 ShenandoahHeapRegion* region;
762 while ((region = _regions.next()) != nullptr) {
763 // old region is not in the collection set and was not immediately trashed
764 if (region->is_old() && region->is_active() && !region->is_humongous()) {
765 // Reset the coalesce and fill boundary because this is a global collect
766 // and cannot be preempted by young collects. We want to be sure the entire
767 // region is coalesced here and does not resume from a previously interrupted
768 // or completed coalescing.
769 region->begin_preemptible_coalesce_and_fill();
770 region->oop_coalesce_and_fill(false);
771 }
772 }
773 }
774 };
775
776 ShenandoahPhaseTimings::Phase phase = concurrent ?
777 ShenandoahPhaseTimings::conc_coalesce_and_fill :
778 ShenandoahPhaseTimings::degen_gc_coalesce_and_fill;
779
780 // This is not cancellable
781 ShenandoahGlobalCoalesceAndFill coalesce(phase);
782 workers()->run_task(&coalesce);
783 old_generation()->set_parsable(true);
784 }
785
786 template<bool CONCURRENT>
787 class ShenandoahGenerationalUpdateHeapRefsTask : public WorkerTask {
788 private:
789 ShenandoahGenerationalHeap* _heap;
790 ShenandoahRegionIterator* _regions;
791 ShenandoahRegionChunkIterator* _work_chunks;
792
793 public:
794 explicit ShenandoahGenerationalUpdateHeapRefsTask(ShenandoahRegionIterator* regions,
795 ShenandoahRegionChunkIterator* work_chunks) :
796 WorkerTask("Shenandoah Update References"),
797 _heap(ShenandoahGenerationalHeap::heap()),
798 _regions(regions),
799 _work_chunks(work_chunks)
800 {
801 bool old_bitmap_stable = _heap->old_generation()->is_mark_complete();
802 log_debug(gc, remset)("Update refs, scan remembered set using bitmap: %s", BOOL_TO_STR(old_bitmap_stable));
803 }
804
805 void work(uint worker_id) {
806 if (CONCURRENT) {
807 ShenandoahConcurrentWorkerSession worker_session(worker_id);
808 ShenandoahSuspendibleThreadSetJoiner stsj;
809 do_work<ShenandoahConcUpdateRefsClosure>(worker_id);
810 } else {
811 ShenandoahParallelWorkerSession worker_session(worker_id);
812 do_work<ShenandoahSTWUpdateRefsClosure>(worker_id);
813 }
814 }
815
816 private:
817 template<class T>
818 void do_work(uint worker_id) {
819 T cl;
820
821 if (CONCURRENT && (worker_id == 0)) {
822 // We ask the first worker to replenish the Mutator free set by moving regions previously reserved to hold the
823 // results of evacuation. These reserves are no longer necessary because evacuation has completed.
824 size_t cset_regions = _heap->collection_set()->count();
825
826 // Now that evacuation is done, we can reassign any regions that had been reserved to hold the results of evacuation
827 // to the mutator free set. At the end of GC, we will have cset_regions newly evacuated fully empty regions from
828 // which we will be able to replenish the Collector free set and the OldCollector free set in preparation for the
829 // next GC cycle.
830 _heap->free_set()->move_regions_from_collector_to_mutator(cset_regions);
831 }
832 // If !CONCURRENT, there's no value in expanding Mutator free set
833
834 ShenandoahHeapRegion* r = _regions->next();
835 // We update references for global, old, and young collections.
836 ShenandoahGeneration* const gc_generation = _heap->gc_generation();
837 shenandoah_assert_generations_reconciled();
838 assert(gc_generation->is_mark_complete(), "Expected complete marking");
839 ShenandoahMarkingContext* const ctx = _heap->marking_context();
840 bool is_mixed = _heap->collection_set()->has_old_regions();
841 while (r != nullptr) {
842 HeapWord* update_watermark = r->get_update_watermark();
843 assert(update_watermark >= r->bottom(), "sanity");
844
845 log_debug(gc)("Update refs worker " UINT32_FORMAT ", looking at region " SIZE_FORMAT, worker_id, r->index());
846 bool region_progress = false;
847 if (r->is_active() && !r->is_cset()) {
848 if (r->is_young()) {
849 _heap->marked_object_oop_iterate(r, &cl, update_watermark);
850 region_progress = true;
851 } else if (r->is_old()) {
852 if (gc_generation->is_global()) {
853
854 _heap->marked_object_oop_iterate(r, &cl, update_watermark);
855 region_progress = true;
856 }
857 // Otherwise, this is an old region in a young or mixed cycle. Process it during a second phase, below.
858 // Don't bother to report pacing progress in this case.
859 } else {
860 // Because updating of references runs concurrently, it is possible that a FREE inactive region transitions
861 // to a non-free active region while this loop is executing. Whenever this happens, the changing of a region's
862 // active status may propagate at a different speed than the changing of the region's affiliation.
863
864 // When we reach this control point, it is because a race has allowed a region's is_active() status to be seen
865 // by this thread before the region's affiliation() is seen by this thread.
866
867 // It's ok for this race to occur because the newly transformed region does not have any references to be
868 // updated.
869
870 assert(r->get_update_watermark() == r->bottom(),
871 "%s Region " SIZE_FORMAT " is_active but not recognized as YOUNG or OLD so must be newly transitioned from FREE",
872 r->affiliation_name(), r->index());
873 }
874 }
875
876 if (region_progress && ShenandoahPacing) {
877 _heap->pacer()->report_update_refs(pointer_delta(update_watermark, r->bottom()));
878 }
879
880 if (_heap->check_cancelled_gc_and_yield(CONCURRENT)) {
881 return;
882 }
883
884 r = _regions->next();
885 }
886
887 if (!gc_generation->is_global()) {
888 // Since this is generational and not GLOBAL, we have to process the remembered set. There's no remembered
889 // set processing if not in generational mode or if GLOBAL mode.
890
891 // After this thread has exhausted its traditional update-refs work, it continues with updating refs within
892 // remembered set. The remembered set workload is better balanced between threads, so threads that are "behind"
893 // can catch up with other threads during this phase, allowing all threads to work more effectively in parallel.
894 update_references_in_remembered_set(worker_id, cl, ctx, is_mixed);
895 }
896 }
897
898 template<class T>
899 void update_references_in_remembered_set(uint worker_id, T &cl, const ShenandoahMarkingContext* ctx, bool is_mixed) {
900
901 struct ShenandoahRegionChunk assignment;
902 ShenandoahScanRemembered* scanner = _heap->old_generation()->card_scan();
903
904 while (!_heap->check_cancelled_gc_and_yield(CONCURRENT) && _work_chunks->next(&assignment)) {
905 // Keep grabbing next work chunk to process until finished, or asked to yield
906 ShenandoahHeapRegion* r = assignment._r;
907 if (r->is_active() && !r->is_cset() && r->is_old()) {
908 HeapWord* start_of_range = r->bottom() + assignment._chunk_offset;
909 HeapWord* end_of_range = r->get_update_watermark();
910 if (end_of_range > start_of_range + assignment._chunk_size) {
911 end_of_range = start_of_range + assignment._chunk_size;
912 }
913
914 if (start_of_range >= end_of_range) {
915 continue;
916 }
917
918 // Old region in a young cycle or mixed cycle.
919 if (is_mixed) {
920 if (r->is_humongous()) {
921 // Need to examine both dirty and clean cards during mixed evac.
922 r->oop_iterate_humongous_slice_all(&cl,start_of_range, assignment._chunk_size);
923 } else {
924 // Since this is mixed evacuation, old regions that are candidates for collection have not been coalesced
925 // and filled. This will use mark bits to find objects that need to be updated.
926 update_references_in_old_region(cl, ctx, scanner, r, start_of_range, end_of_range);
927 }
928 } else {
929 // This is a young evacuation
930 size_t cluster_size = CardTable::card_size_in_words() * ShenandoahCardCluster::CardsPerCluster;
931 size_t clusters = assignment._chunk_size / cluster_size;
932 assert(clusters * cluster_size == assignment._chunk_size, "Chunk assignment must align on cluster boundaries");
933 scanner->process_region_slice(r, assignment._chunk_offset, clusters, end_of_range, &cl, true, worker_id);
934 }
935
936 if (ShenandoahPacing) {
937 _heap->pacer()->report_update_refs(pointer_delta(end_of_range, start_of_range));
938 }
939 }
940 }
941 }
942
943 template<class T>
944 void update_references_in_old_region(T &cl, const ShenandoahMarkingContext* ctx, ShenandoahScanRemembered* scanner,
945 const ShenandoahHeapRegion* r, HeapWord* start_of_range,
946 HeapWord* end_of_range) const {
947 // In case last object in my range spans boundary of my chunk, I may need to scan all the way to top()
948 ShenandoahObjectToOopBoundedClosure<T> objs(&cl, start_of_range, r->top());
949
950 // Any object that begins in a previous range is part of a different scanning assignment. Any object that
951 // starts after end_of_range is also not my responsibility. (Either allocated during evacuation, so does
952 // not hold pointers to from-space, or is beyond the range of my assigned work chunk.)
953
954 // Find the first object that begins in my range, if there is one. Note that `p` will be set to `end_of_range`
955 // when no live object is found in the range.
956 HeapWord* tams = ctx->top_at_mark_start(r);
957 HeapWord* p = get_first_object_start_word(ctx, scanner, tams, start_of_range, end_of_range);
958
959 while (p < end_of_range) {
960 // p is known to point to the beginning of marked object obj
961 oop obj = cast_to_oop(p);
962 objs.do_object(obj);
963 HeapWord* prev_p = p;
964 p += obj->size();
965 if (p < tams) {
966 p = ctx->get_next_marked_addr(p, tams);
967 // If there are no more marked objects before tams, this returns tams. Note that tams is
968 // either >= end_of_range, or tams is the start of an object that is marked.
969 }
970 assert(p != prev_p, "Lack of forward progress");
971 }
972 }
973
974 HeapWord* get_first_object_start_word(const ShenandoahMarkingContext* ctx, ShenandoahScanRemembered* scanner, HeapWord* tams,
975 HeapWord* start_of_range, HeapWord* end_of_range) const {
976 HeapWord* p = start_of_range;
977
978 if (p >= tams) {
979 // We cannot use ctx->is_marked(obj) to test whether an object begins at this address. Instead,
980 // we need to use the remembered set crossing map to advance p to the first object that starts
981 // within the enclosing card.
982 size_t card_index = scanner->card_index_for_addr(start_of_range);
983 while (true) {
984 HeapWord* first_object = scanner->first_object_in_card(card_index);
985 if (first_object != nullptr) {
986 p = first_object;
987 break;
988 } else if (scanner->addr_for_card_index(card_index + 1) < end_of_range) {
989 card_index++;
990 } else {
991 // Signal that no object was found in range
992 p = end_of_range;
993 break;
994 }
995 }
996 } else if (!ctx->is_marked(cast_to_oop(p))) {
997 p = ctx->get_next_marked_addr(p, tams);
998 // If there are no more marked objects before tams, this returns tams.
999 // Note that tams is either >= end_of_range, or tams is the start of an object that is marked.
1000 }
1001 return p;
1002 }
1003 };
1004
1005 void ShenandoahGenerationalHeap::update_heap_references(bool concurrent) {
1006 assert(!is_full_gc_in_progress(), "Only for concurrent and degenerated GC");
1007 const uint nworkers = workers()->active_workers();
1008 ShenandoahRegionChunkIterator work_list(nworkers);
1009 if (concurrent) {
1010 ShenandoahGenerationalUpdateHeapRefsTask<true> task(&_update_refs_iterator, &work_list);
1011 workers()->run_task(&task);
1012 } else {
1013 ShenandoahGenerationalUpdateHeapRefsTask<false> task(&_update_refs_iterator, &work_list);
1014 workers()->run_task(&task);
1015 }
1016
1017 if (ShenandoahEnableCardStats) {
1018 // Only do this if we are collecting card stats
1019 ShenandoahScanRemembered* card_scan = old_generation()->card_scan();
1020 assert(card_scan != nullptr, "Card table must exist when card stats are enabled");
1021 card_scan->log_card_stats(nworkers, CARD_STAT_UPDATE_REFS);
1022 }
1023 }
1024
1025 struct ShenandoahCompositeRegionClosure {
1026 template<typename C1, typename C2>
1027 class Closure : public ShenandoahHeapRegionClosure {
1028 private:
1029 C1 &_c1;
1030 C2 &_c2;
1031
1032 public:
1033 Closure(C1 &c1, C2 &c2) : ShenandoahHeapRegionClosure(), _c1(c1), _c2(c2) {}
1034
1035 void heap_region_do(ShenandoahHeapRegion* r) override {
1036 _c1.heap_region_do(r);
1037 _c2.heap_region_do(r);
1038 }
1039
1040 bool is_thread_safe() override {
1041 return _c1.is_thread_safe() && _c2.is_thread_safe();
1042 }
1043 };
1044
1045 template<typename C1, typename C2>
1046 static Closure<C1, C2> of(C1 &c1, C2 &c2) {
1047 return Closure<C1, C2>(c1, c2);
1048 }
1049 };
1050
1051 class ShenandoahUpdateRegionAges : public ShenandoahHeapRegionClosure {
1052 private:
1053 ShenandoahMarkingContext* _ctx;
1054
1055 public:
1056 explicit ShenandoahUpdateRegionAges(ShenandoahMarkingContext* ctx) : _ctx(ctx) { }
1057
1058 void heap_region_do(ShenandoahHeapRegion* r) override {
1059 // Maintenance of region age must follow evacuation in order to account for
1060 // evacuation allocations within survivor regions. We consult region age during
1061 // the subsequent evacuation to determine whether certain objects need to
1062 // be promoted.
1063 if (r->is_young() && r->is_active()) {
1064 HeapWord *tams = _ctx->top_at_mark_start(r);
1065 HeapWord *top = r->top();
1066
1067 // Allocations move the watermark when top moves. However, compacting
1068 // objects will sometimes lower top beneath the watermark, after which,
1069 // attempts to read the watermark will assert out (watermark should not be
1070 // higher than top).
1071 if (top > tams) {
1072 // There have been allocations in this region since the start of the cycle.
1073 // Any objects new to this region must not assimilate elevated age.
1074 r->reset_age();
1075 } else if (ShenandoahGenerationalHeap::heap()->is_aging_cycle()) {
1076 r->increment_age();
1077 }
1078 }
1079 }
1080
1081 bool is_thread_safe() override {
1082 return true;
1083 }
1084 };
1085
1086 void ShenandoahGenerationalHeap::final_update_refs_update_region_states() {
1087 ShenandoahSynchronizePinnedRegionStates pins;
1088 ShenandoahUpdateRegionAges ages(active_generation()->complete_marking_context());
1089 auto cl = ShenandoahCompositeRegionClosure::of(pins, ages);
1090 parallel_heap_region_iterate(&cl);
1091 }
1092
1093 void ShenandoahGenerationalHeap::complete_degenerated_cycle() {
1094 shenandoah_assert_heaplocked_or_safepoint();
1095 if (is_concurrent_old_mark_in_progress()) {
1096 // This is still necessary for degenerated cycles because the degeneration point may occur
1097 // after final mark of the young generation. See ShenandoahConcurrentGC::op_final_update_refs for
1098 // a more detailed explanation.
1099 old_generation()->transfer_pointers_from_satb();
1100 }
1101
1102 // We defer generation resizing actions until after cset regions have been recycled.
1103 TransferResult result = balance_generations();
1104 LogTarget(Info, gc, ergo) lt;
1105 if (lt.is_enabled()) {
1106 LogStream ls(lt);
1107 result.print_on("Degenerated GC", &ls);
1108 }
1109
1110 // In case degeneration interrupted concurrent evacuation or update references, we need to clean up
1111 // transient state. Otherwise, these actions have no effect.
1112 reset_generation_reserves();
1113
1114 if (!old_generation()->is_parsable()) {
1115 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_coalesce_and_fill);
1116 coalesce_and_fill_old_regions(false);
1117 }
1118 }
1119
1120 void ShenandoahGenerationalHeap::complete_concurrent_cycle() {
1121 if (!old_generation()->is_parsable()) {
1122 // Class unloading may render the card offsets unusable, so we must rebuild them before
1123 // the next remembered set scan. We _could_ let the control thread do this sometime after
1124 // the global cycle has completed and before the next young collection, but under memory
1125 // pressure the control thread may not have the time (that is, because it's running back
1126 // to back GCs). In that scenario, we would have to make the old regions parsable before
1127 // we could start a young collection. This could delay the start of the young cycle and
1128 // throw off the heuristics.
1129 entry_global_coalesce_and_fill();
1130 }
1131
1132 TransferResult result;
1133 {
1134 ShenandoahHeapLocker locker(lock());
1135
1136 result = balance_generations();
1137 reset_generation_reserves();
1138 }
1139
1140 LogTarget(Info, gc, ergo) lt;
1141 if (lt.is_enabled()) {
1142 LogStream ls(lt);
1143 result.print_on("Concurrent GC", &ls);
1144 }
1145 }
1146
1147 void ShenandoahGenerationalHeap::entry_global_coalesce_and_fill() {
1148 const char* msg = "Coalescing and filling old regions";
1149 ShenandoahConcurrentPhase gc_phase(msg, ShenandoahPhaseTimings::conc_coalesce_and_fill);
1150
1151 TraceCollectorStats tcs(monitoring_support()->concurrent_collection_counters());
1152 EventMark em("%s", msg);
1153 ShenandoahWorkerScope scope(workers(),
1154 ShenandoahWorkerPolicy::calc_workers_for_conc_marking(),
1155 "concurrent coalesce and fill");
1156
1157 coalesce_and_fill_old_regions(true);
1158 }
1159
1160 void ShenandoahGenerationalHeap::update_region_ages(ShenandoahMarkingContext* ctx) {
1161 ShenandoahUpdateRegionAges cl(ctx);
1162 parallel_heap_region_iterate(&cl);
1163 }