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