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/shenandoahClosures.inline.hpp"
29 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
30 #include "gc/shenandoah/shenandoahFreeSet.hpp"
31 #include "gc/shenandoah/shenandoahGenerationalControlThread.hpp"
32 #include "gc/shenandoah/shenandoahGenerationalEvacuationTask.hpp"
33 #include "gc/shenandoah/shenandoahGenerationalHeap.hpp"
34 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
35 #include "gc/shenandoah/shenandoahHeapRegion.hpp"
36 #include "gc/shenandoah/shenandoahHeapRegionClosures.hpp"
37 #include "gc/shenandoah/shenandoahInitLogger.hpp"
38 #include "gc/shenandoah/shenandoahMemoryPool.hpp"
39 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
40 #include "gc/shenandoah/shenandoahOldGeneration.hpp"
41 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
42 #include "gc/shenandoah/shenandoahRegulatorThread.hpp"
43 #include "gc/shenandoah/shenandoahScanRemembered.inline.hpp"
44 #include "gc/shenandoah/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 regulator_thread()->stop();
184 ShenandoahHeap::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
244 markWord mark = p->mark();
245 if (ShenandoahForwarding::is_forwarded(mark)) {
246 return ShenandoahForwarding::get_forwardee(p);
247 }
248 size_t old_size = ShenandoahForwarding::size(p);
249 size_t size = p->copy_size(old_size, mark);
250
251 bool is_promotion = (target_gen == OLD_GENERATION) && from_region->is_young();
252
253 #ifdef ASSERT
254 if (ShenandoahOOMDuringEvacALot &&
255 (os::random() & 1) == 0) { // Simulate OOM every ~2nd slow-path call
256 copy = nullptr;
257 } else {
258 #endif
259 if (UseTLAB) {
260 switch (target_gen) {
261 case YOUNG_GENERATION: {
262 copy = allocate_from_gclab(thread, size);
263 if ((copy == nullptr) && (size < ShenandoahThreadLocalData::gclab_size(thread))) {
264 // GCLAB allocation failed because we are bumping up against the limit on young evacuation reserve. Try resetting
265 // the desired GCLAB size and retry GCLAB allocation to avoid cascading of shared memory allocations.
266 ShenandoahThreadLocalData::set_gclab_size(thread, PLAB::min_size());
267 copy = allocate_from_gclab(thread, size);
268 // If we still get nullptr, we'll try a shared allocation below.
269 }
270 break;
271 }
272 case OLD_GENERATION: {
273 PLAB* plab = ShenandoahThreadLocalData::plab(thread);
274 if (plab != nullptr) {
275 has_plab = true;
276 copy = allocate_from_plab(thread, size, is_promotion);
277 if ((copy == nullptr) && (size < ShenandoahThreadLocalData::plab_size(thread)) &&
278 ShenandoahThreadLocalData::plab_retries_enabled(thread)) {
279 // PLAB allocation failed because we are bumping up against the limit on old evacuation reserve or because
280 // the requested object does not fit within the current plab but the plab still has an "abundance" of memory,
281 // where abundance is defined as >= ShenGenHeap::plab_min_size(). In the former case, we try shrinking the
282 // desired PLAB size to the minimum and retry PLAB allocation to avoid cascading of shared memory allocations.
283 if (plab->words_remaining() < plab_min_size()) {
284 ShenandoahThreadLocalData::set_plab_size(thread, plab_min_size());
285 copy = allocate_from_plab(thread, size, is_promotion);
286 // If we still get nullptr, we'll try a shared allocation below.
287 if (copy == nullptr) {
288 // If retry fails, don't continue to retry until we have success (probably in next GC pass)
289 ShenandoahThreadLocalData::disable_plab_retries(thread);
290 }
291 }
292 // else, copy still equals nullptr. this causes shared allocation below, preserving this plab for future needs.
293 }
294 }
295 break;
296 }
297 default: {
298 ShouldNotReachHere();
299 break;
300 }
301 }
302 }
303
304 if (copy == nullptr) {
305 // If we failed to allocate in LAB, we'll try a shared allocation.
306 if (!is_promotion || !has_plab || (size > PLAB::min_size())) {
307 ShenandoahAllocRequest req = ShenandoahAllocRequest::for_shared_gc(size, target_gen, is_promotion);
308 copy = allocate_memory(req);
309 alloc_from_lab = false;
310 }
311 // else, we leave copy equal to nullptr, signaling a promotion failure below if appropriate.
312 // We choose not to promote objects smaller than PLAB::min_size() by way of shared allocations, as this is too
313 // costly. Instead, we'll simply "evacuate" to young-gen memory (using a GCLAB) and will promote in a future
314 // evacuation pass. This condition is denoted by: is_promotion && has_plab && (size <= PLAB::min_size())
315 }
316 #ifdef ASSERT
317 }
318 #endif
319
320 if (copy == nullptr) {
321 if (target_gen == OLD_GENERATION) {
322 if (from_region->is_young()) {
323 // Signal that promotion failed. Will evacuate this old object somewhere in young gen.
324 old_generation()->handle_failed_promotion(thread, size);
325 return nullptr;
326 } else {
327 // Remember that evacuation to old gen failed. We'll want to trigger a full gc to recover from this
328 // after the evacuation threads have finished.
329 old_generation()->handle_failed_evacuation();
330 }
331 }
332
333 control_thread()->handle_alloc_failure_evac(size);
334
335 oom_evac_handler()->handle_out_of_memory_during_evacuation();
336
337 return ShenandoahBarrierSet::resolve_forwarded(p);
338 }
339
340 // Copy the object:
341 NOT_PRODUCT(evac_tracker()->begin_evacuation(thread, size * HeapWordSize));
342 Copy::aligned_disjoint_words(cast_from_oop<HeapWord*>(p), copy, old_size);
343 oop copy_val = cast_to_oop(copy);
344
345 // Update the age of the evacuated object
346 if (target_gen == YOUNG_GENERATION && is_aging_cycle()) {
347 ShenandoahHeap::increase_object_age(copy_val, from_region->age() + 1);
348 }
349
350 // Try to install the new forwarding pointer.
351 oop result = ShenandoahForwarding::try_update_forwardee(p, copy_val);
352 if (result == copy_val) {
353 // Successfully evacuated. Our copy is now the public one!
354
355 // This is necessary for virtual thread support. This uses the mark word without
356 // considering that it may now be a forwarding pointer (and could therefore crash).
357 // Secondarily, we do not want to spend cycles relativizing stack chunks for oops
358 // that lost the evacuation race (and will therefore not become visible). It is
359 // safe to do this on the public copy (this is also done during concurrent mark).
360 copy_val->initialize_hash_if_necessary(p);
361 ContinuationGCSupport::relativize_stack_chunk(copy_val);
362
363 // Record that the evacuation succeeded
364 NOT_PRODUCT(evac_tracker()->end_evacuation(thread, size * HeapWordSize));
365
366 if (target_gen == OLD_GENERATION) {
367 old_generation()->handle_evacuation(copy, size, from_region->is_young());
368 } else {
369 // When copying to the old generation above, we don't care
370 // about recording object age in the census stats.
371 assert(target_gen == YOUNG_GENERATION, "Error");
372 // We record this census only when simulating pre-adaptive tenuring behavior, or
373 // when we have been asked to record the census at evacuation rather than at mark
374 if (ShenandoahGenerationalCensusAtEvac || !ShenandoahGenerationalAdaptiveTenuring) {
375 evac_tracker()->record_age(thread, size * HeapWordSize, ShenandoahHeap::get_object_age(copy_val));
376 }
377 }
378 shenandoah_assert_correct(nullptr, copy_val);
379 return copy_val;
380 } else {
381 // Failed to evacuate. We need to deal with the object that is left behind. Since this
382 // new allocation is certainly after TAMS, it will be considered live in the next cycle.
383 // But if it happens to contain references to evacuated regions, those references would
384 // not get updated for this stale copy during this cycle, and we will crash while scanning
385 // it the next cycle.
386 if (alloc_from_lab) {
387 // For LAB allocations, it is enough to rollback the allocation ptr. Either the next
388 // object will overwrite this stale copy, or the filler object on LAB retirement will
389 // do this.
390 switch (target_gen) {
391 case YOUNG_GENERATION: {
392 ShenandoahThreadLocalData::gclab(thread)->undo_allocation(copy, size);
393 break;
394 }
395 case OLD_GENERATION: {
396 ShenandoahThreadLocalData::plab(thread)->undo_allocation(copy, size);
397 if (is_promotion) {
398 ShenandoahThreadLocalData::subtract_from_plab_promoted(thread, size * HeapWordSize);
399 }
400 break;
401 }
402 default: {
403 ShouldNotReachHere();
404 break;
405 }
406 }
407 } else {
408 // For non-LAB allocations, we have no way to retract the allocation, and
409 // have to explicitly overwrite the copy with the filler object. With that overwrite,
410 // we have to keep the fwdptr initialized and pointing to our (stale) copy.
411 assert(size >= ShenandoahHeap::min_fill_size(), "previously allocated object known to be larger than min_size");
412 fill_with_object(copy, size);
413 shenandoah_assert_correct(nullptr, copy_val);
414 // For non-LAB allocations, the object has already been registered
415 }
416 shenandoah_assert_correct(nullptr, result);
417 return result;
418 }
419 }
420
421 inline HeapWord* ShenandoahGenerationalHeap::allocate_from_plab(Thread* thread, size_t size, bool is_promotion) {
422 assert(UseTLAB, "TLABs should be enabled");
423
424 PLAB* plab = ShenandoahThreadLocalData::plab(thread);
425 HeapWord* obj;
426
427 if (plab == nullptr) {
428 assert(!thread->is_Java_thread() && !thread->is_Worker_thread(), "Performance: thread should have PLAB: %s", thread->name());
429 // No PLABs in this thread, fallback to shared allocation
430 return nullptr;
431 } else if (is_promotion && !ShenandoahThreadLocalData::allow_plab_promotions(thread)) {
432 return nullptr;
433 }
434 // if plab->word_size() <= 0, thread's plab not yet initialized for this pass, so allow_plab_promotions() is not trustworthy
435 obj = plab->allocate(size);
436 if ((obj == nullptr) && (plab->words_remaining() < plab_min_size())) {
437 // allocate_from_plab_slow will establish allow_plab_promotions(thread) for future invocations
438 obj = allocate_from_plab_slow(thread, size, is_promotion);
439 }
440 // if plab->words_remaining() >= ShenGenHeap::heap()->plab_min_size(), just return nullptr so we can use a shared allocation
441 if (obj == nullptr) {
442 return nullptr;
443 }
444
445 if (is_promotion) {
446 ShenandoahThreadLocalData::add_to_plab_promoted(thread, size * HeapWordSize);
447 }
448 return obj;
449 }
450
451 // Establish a new PLAB and allocate size HeapWords within it.
452 HeapWord* ShenandoahGenerationalHeap::allocate_from_plab_slow(Thread* thread, size_t size, bool is_promotion) {
453 // New object should fit the PLAB size
454
455 assert(mode()->is_generational(), "PLABs only relevant to generational GC");
456 const size_t plab_min_size = this->plab_min_size();
457 // PLABs are aligned to card boundaries to avoid synchronization with concurrent
458 // allocations in other PLABs.
459 const size_t min_size = (size > plab_min_size)? align_up(size, CardTable::card_size_in_words()): plab_min_size;
460
461 // Figure out size of new PLAB, using value determined at last refill.
462 size_t cur_size = ShenandoahThreadLocalData::plab_size(thread);
463 if (cur_size == 0) {
464 cur_size = plab_min_size;
465 }
466
467 // Expand aggressively, doubling at each refill in this epoch, ceiling at plab_max_size()
468 size_t future_size = MIN2(cur_size * 2, plab_max_size());
469 // Doubling, starting at a card-multiple, should give us a card-multiple. (Ceiling and floor
470 // are card multiples.)
471 assert(is_aligned(future_size, CardTable::card_size_in_words()), "Card multiple by construction, future_size: " SIZE_FORMAT
472 ", card_size: " SIZE_FORMAT ", cur_size: " SIZE_FORMAT ", max: " SIZE_FORMAT,
473 future_size, (size_t) CardTable::card_size_in_words(), cur_size, plab_max_size());
474
475 // Record new heuristic value even if we take any shortcut. This captures
476 // the case when moderately-sized objects always take a shortcut. At some point,
477 // heuristics should catch up with them. Note that the requested cur_size may
478 // not be honored, but we remember that this is the preferred size.
479 log_debug(gc, free)("Set new PLAB size: " SIZE_FORMAT, future_size);
480 ShenandoahThreadLocalData::set_plab_size(thread, future_size);
481 if (cur_size < size) {
482 // The PLAB to be allocated is still not large enough to hold the object. Fall back to shared allocation.
483 // This avoids retiring perfectly good PLABs in order to represent a single large object allocation.
484 log_debug(gc, free)("Current PLAB size (" SIZE_FORMAT ") is too small for " SIZE_FORMAT, cur_size, size);
485 return nullptr;
486 }
487
488 // Retire current PLAB, and allocate a new one.
489 PLAB* plab = ShenandoahThreadLocalData::plab(thread);
490 if (plab->words_remaining() < plab_min_size) {
491 // Retire current PLAB. This takes care of any PLAB book-keeping.
492 // retire_plab() registers the remnant filler object with the remembered set scanner without a lock.
493 // Since PLABs are card-aligned, concurrent registrations in other PLABs don't interfere.
494 retire_plab(plab, thread);
495
496 size_t actual_size = 0;
497 HeapWord* plab_buf = allocate_new_plab(min_size, cur_size, &actual_size);
498 if (plab_buf == nullptr) {
499 if (min_size == plab_min_size) {
500 // Disable PLAB promotions for this thread because we cannot even allocate a minimal PLAB. This allows us
501 // to fail faster on subsequent promotion attempts.
502 ShenandoahThreadLocalData::disable_plab_promotions(thread);
503 }
504 return nullptr;
505 } else {
506 ShenandoahThreadLocalData::enable_plab_retries(thread);
507 }
508 // Since the allocated PLAB may have been down-sized for alignment, plab->allocate(size) below may still fail.
509 if (ZeroTLAB) {
510 // ... and clear it.
511 Copy::zero_to_words(plab_buf, actual_size);
512 } else {
513 // ...and zap just allocated object.
514 #ifdef ASSERT
515 // Skip mangling the space corresponding to the object header to
516 // ensure that the returned space is not considered parsable by
517 // any concurrent GC thread.
518 size_t hdr_size = oopDesc::header_size();
519 Copy::fill_to_words(plab_buf + hdr_size, actual_size - hdr_size, badHeapWordVal);
520 #endif // ASSERT
521 }
522 assert(is_aligned(actual_size, CardTable::card_size_in_words()), "Align by design");
523 plab->set_buf(plab_buf, actual_size);
524 if (is_promotion && !ShenandoahThreadLocalData::allow_plab_promotions(thread)) {
525 return nullptr;
526 }
527 return plab->allocate(size);
528 } else {
529 // If there's still at least min_size() words available within the current plab, don't retire it. Let's nibble
530 // away on this plab as long as we can. Meanwhile, return nullptr to force this particular allocation request
531 // to be satisfied with a shared allocation. By packing more promotions into the previously allocated PLAB, we
532 // reduce the likelihood of evacuation failures, and we reduce the need for downsizing our PLABs.
533 return nullptr;
534 }
535 }
536
537 HeapWord* ShenandoahGenerationalHeap::allocate_new_plab(size_t min_size, size_t word_size, size_t* actual_size) {
538 // Align requested sizes to card-sized multiples. Align down so that we don't violate max size of TLAB.
539 assert(is_aligned(min_size, CardTable::card_size_in_words()), "Align by design");
540 assert(word_size >= min_size, "Requested PLAB is too small");
541
542 ShenandoahAllocRequest req = ShenandoahAllocRequest::for_plab(min_size, word_size);
543 // Note that allocate_memory() sets a thread-local flag to prohibit further promotions by this thread
544 // if we are at risk of infringing on the old-gen evacuation budget.
545 HeapWord* res = allocate_memory(req);
546 if (res != nullptr) {
547 *actual_size = req.actual_size();
548 } else {
549 *actual_size = 0;
550 }
551 assert(is_aligned(res, CardTable::card_size_in_words()), "Align by design");
552 return res;
553 }
554
555 void ShenandoahGenerationalHeap::retire_plab(PLAB* plab, Thread* thread) {
556 // We don't enforce limits on plab evacuations. We let it consume all available old-gen memory in order to reduce
557 // probability of an evacuation failure. We do enforce limits on promotion, to make sure that excessive promotion
558 // does not result in an old-gen evacuation failure. Note that a failed promotion is relatively harmless. Any
559 // object that fails to promote in the current cycle will be eligible for promotion in a subsequent cycle.
560
561 // When the plab was instantiated, its entirety was treated as if the entire buffer was going to be dedicated to
562 // promotions. Now that we are retiring the buffer, we adjust for the reality that the plab is not entirely promotions.
563 // 1. Some of the plab may have been dedicated to evacuations.
564 // 2. Some of the plab may have been abandoned due to waste (at the end of the plab).
565 size_t not_promoted =
566 ShenandoahThreadLocalData::get_plab_actual_size(thread) - ShenandoahThreadLocalData::get_plab_promoted(thread);
567 ShenandoahThreadLocalData::reset_plab_promoted(thread);
568 ShenandoahThreadLocalData::set_plab_actual_size(thread, 0);
569 if (not_promoted > 0) {
570 old_generation()->unexpend_promoted(not_promoted);
571 }
572 const size_t original_waste = plab->waste();
573 HeapWord* const top = plab->top();
574
575 // plab->retire() overwrites unused memory between plab->top() and plab->hard_end() with a dummy object to make memory parsable.
576 // It adds the size of this unused memory, in words, to plab->waste().
577 plab->retire();
578 if (top != nullptr && plab->waste() > original_waste && is_in_old(top)) {
579 // If retiring the plab created a filler object, then we need to register it with our card scanner so it can
580 // safely walk the region backing the plab.
581 log_debug(gc)("retire_plab() is registering remnant of size " SIZE_FORMAT " at " PTR_FORMAT,
582 plab->waste() - original_waste, p2i(top));
583 // No lock is necessary because the PLAB memory is aligned on card boundaries.
584 old_generation()->card_scan()->register_object_without_lock(top);
585 }
586 }
587
588 void ShenandoahGenerationalHeap::retire_plab(PLAB* plab) {
589 Thread* thread = Thread::current();
590 retire_plab(plab, thread);
591 }
592
593 ShenandoahGenerationalHeap::TransferResult ShenandoahGenerationalHeap::balance_generations() {
594 shenandoah_assert_heaplocked_or_safepoint();
595
596 ShenandoahOldGeneration* old_gen = old_generation();
597 const ssize_t old_region_balance = old_gen->get_region_balance();
598 old_gen->set_region_balance(0);
599
600 if (old_region_balance > 0) {
601 const auto old_region_surplus = checked_cast<size_t>(old_region_balance);
602 const bool success = generation_sizer()->transfer_to_young(old_region_surplus);
603 return TransferResult {
604 success, old_region_surplus, "young"
605 };
606 }
607
608 if (old_region_balance < 0) {
609 const auto old_region_deficit = checked_cast<size_t>(-old_region_balance);
610 const bool success = generation_sizer()->transfer_to_old(old_region_deficit);
611 if (!success) {
612 old_gen->handle_failed_transfer();
613 }
614 return TransferResult {
615 success, old_region_deficit, "old"
616 };
617 }
618
619 return TransferResult {true, 0, "none"};
620 }
621
622 // Make sure old-generation is large enough, but no larger than is necessary, to hold mixed evacuations
623 // and promotions, if we anticipate either. Any deficit is provided by the young generation, subject to
624 // xfer_limit, and any surplus is transferred to the young generation.
625 // xfer_limit is the maximum we're able to transfer from young to old.
626 void ShenandoahGenerationalHeap::compute_old_generation_balance(size_t old_xfer_limit, size_t old_cset_regions) {
627
628 // We can limit the old reserve to the size of anticipated promotions:
629 // max_old_reserve is an upper bound on memory evacuated from old and promoted to old,
630 // clamped by the old generation space available.
631 //
632 // Here's the algebra.
633 // Let SOEP = ShenandoahOldEvacRatioPercent,
634 // OE = old evac,
635 // YE = young evac, and
636 // TE = total evac = OE + YE
637 // By definition:
638 // SOEP/100 = OE/TE
639 // = OE/(OE+YE)
640 // => SOEP/(100-SOEP) = OE/((OE+YE)-OE) // componendo-dividendo: If a/b = c/d, then a/(b-a) = c/(d-c)
641 // = OE/YE
642 // => OE = YE*SOEP/(100-SOEP)
643
644 // We have to be careful in the event that SOEP is set to 100 by the user.
645 assert(ShenandoahOldEvacRatioPercent <= 100, "Error");
646 const size_t old_available = old_generation()->available();
647 // The free set will reserve this amount of memory to hold young evacuations
648 const size_t young_reserve = (young_generation()->max_capacity() * ShenandoahEvacReserve) / 100;
649
650 // In the case that ShenandoahOldEvacRatioPercent equals 100, max_old_reserve is limited only by xfer_limit.
651
652 const double bound_on_old_reserve = old_available + old_xfer_limit + young_reserve;
653 const double max_old_reserve = (ShenandoahOldEvacRatioPercent == 100)?
654 bound_on_old_reserve: MIN2(double(young_reserve * ShenandoahOldEvacRatioPercent) / double(100 - ShenandoahOldEvacRatioPercent),
655 bound_on_old_reserve);
656
657 const size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
658
659 // Decide how much old space we should reserve for a mixed collection
660 double reserve_for_mixed = 0;
661 if (old_generation()->has_unprocessed_collection_candidates()) {
662 // We want this much memory to be unfragmented in order to reliably evacuate old. This is conservative because we
663 // may not evacuate the entirety of unprocessed candidates in a single mixed evacuation.
664 const double max_evac_need = (double(old_generation()->unprocessed_collection_candidates_live_memory()) * ShenandoahOldEvacWaste);
665 assert(old_available >= old_generation()->free_unaffiliated_regions() * region_size_bytes,
666 "Unaffiliated available must be less than total available");
667 const double old_fragmented_available = double(old_available - old_generation()->free_unaffiliated_regions() * region_size_bytes);
668 reserve_for_mixed = max_evac_need + old_fragmented_available;
669 if (reserve_for_mixed > max_old_reserve) {
670 reserve_for_mixed = max_old_reserve;
671 }
672 }
673
674 // Decide how much space we should reserve for promotions from young
675 size_t reserve_for_promo = 0;
676 const size_t promo_load = old_generation()->get_promotion_potential();
677 const bool doing_promotions = promo_load > 0;
678 if (doing_promotions) {
679 // We're promoting and have a bound on the maximum amount that can be promoted
680 assert(max_old_reserve >= reserve_for_mixed, "Sanity");
681 const size_t available_for_promotions = max_old_reserve - reserve_for_mixed;
682 reserve_for_promo = MIN2((size_t)(promo_load * ShenandoahPromoEvacWaste), available_for_promotions);
683 }
684
685 // This is the total old we want to ideally reserve
686 const size_t old_reserve = reserve_for_mixed + reserve_for_promo;
687 assert(old_reserve <= max_old_reserve, "cannot reserve more than max for old evacuations");
688
689 // We now check if the old generation is running a surplus or a deficit.
690 const size_t max_old_available = old_generation()->available() + old_cset_regions * region_size_bytes;
691 if (max_old_available >= old_reserve) {
692 // We are running a surplus, so the old region surplus can go to young
693 const size_t old_surplus = (max_old_available - old_reserve) / region_size_bytes;
694 const size_t unaffiliated_old_regions = old_generation()->free_unaffiliated_regions() + old_cset_regions;
695 const size_t old_region_surplus = MIN2(old_surplus, unaffiliated_old_regions);
696 old_generation()->set_region_balance(checked_cast<ssize_t>(old_region_surplus));
697 } else {
698 // We are running a deficit which we'd like to fill from young.
699 // Ignore that this will directly impact young_generation()->max_capacity(),
700 // indirectly impacting young_reserve and old_reserve. These computations are conservative.
701 // Note that deficit is rounded up by one region.
702 const size_t old_need = (old_reserve - max_old_available + region_size_bytes - 1) / region_size_bytes;
703 const size_t max_old_region_xfer = old_xfer_limit / region_size_bytes;
704
705 // Round down the regions we can transfer from young to old. If we're running short
706 // on young-gen memory, we restrict the xfer. Old-gen collection activities will be
707 // curtailed if the budget is restricted.
708 const size_t old_region_deficit = MIN2(old_need, max_old_region_xfer);
709 old_generation()->set_region_balance(0 - checked_cast<ssize_t>(old_region_deficit));
710 }
711 }
712
713 void ShenandoahGenerationalHeap::reset_generation_reserves() {
714 young_generation()->set_evacuation_reserve(0);
715 old_generation()->set_evacuation_reserve(0);
716 old_generation()->set_promoted_reserve(0);
717 }
718
719 void ShenandoahGenerationalHeap::TransferResult::print_on(const char* when, outputStream* ss) const {
720 auto heap = ShenandoahGenerationalHeap::heap();
721 ShenandoahYoungGeneration* const young_gen = heap->young_generation();
722 ShenandoahOldGeneration* const old_gen = heap->old_generation();
723 const size_t young_available = young_gen->available();
724 const size_t old_available = old_gen->available();
725 ss->print_cr("After %s, %s " SIZE_FORMAT " regions to %s to prepare for next gc, old available: "
726 PROPERFMT ", young_available: " PROPERFMT,
727 when,
728 success? "successfully transferred": "failed to transfer", region_count, region_destination,
729 PROPERFMTARGS(old_available), PROPERFMTARGS(young_available));
730 }
731
732 void ShenandoahGenerationalHeap::coalesce_and_fill_old_regions(bool concurrent) {
733 class ShenandoahGlobalCoalesceAndFill : public WorkerTask {
734 private:
735 ShenandoahPhaseTimings::Phase _phase;
736 ShenandoahRegionIterator _regions;
737 public:
738 explicit ShenandoahGlobalCoalesceAndFill(ShenandoahPhaseTimings::Phase phase) :
739 WorkerTask("Shenandoah Global Coalesce"),
740 _phase(phase) {}
741
742 void work(uint worker_id) override {
743 ShenandoahWorkerTimingsTracker timer(_phase,
744 ShenandoahPhaseTimings::ScanClusters,
745 worker_id, true);
746 ShenandoahHeapRegion* region;
747 while ((region = _regions.next()) != nullptr) {
748 // old region is not in the collection set and was not immediately trashed
749 if (region->is_old() && region->is_active() && !region->is_humongous()) {
750 // Reset the coalesce and fill boundary because this is a global collect
751 // and cannot be preempted by young collects. We want to be sure the entire
752 // region is coalesced here and does not resume from a previously interrupted
753 // or completed coalescing.
754 region->begin_preemptible_coalesce_and_fill();
755 region->oop_coalesce_and_fill(false);
756 }
757 }
758 }
759 };
760
761 ShenandoahPhaseTimings::Phase phase = concurrent ?
762 ShenandoahPhaseTimings::conc_coalesce_and_fill :
763 ShenandoahPhaseTimings::degen_gc_coalesce_and_fill;
764
765 // This is not cancellable
766 ShenandoahGlobalCoalesceAndFill coalesce(phase);
767 workers()->run_task(&coalesce);
768 old_generation()->set_parsable(true);
769 }
770
771 template<bool CONCURRENT>
772 class ShenandoahGenerationalUpdateHeapRefsTask : public WorkerTask {
773 private:
774 ShenandoahGenerationalHeap* _heap;
775 ShenandoahRegionIterator* _regions;
776 ShenandoahRegionChunkIterator* _work_chunks;
777
778 public:
779 explicit ShenandoahGenerationalUpdateHeapRefsTask(ShenandoahRegionIterator* regions,
780 ShenandoahRegionChunkIterator* work_chunks) :
781 WorkerTask("Shenandoah Update References"),
782 _heap(ShenandoahGenerationalHeap::heap()),
783 _regions(regions),
784 _work_chunks(work_chunks)
785 {
786 bool old_bitmap_stable = _heap->old_generation()->is_mark_complete();
787 log_debug(gc, remset)("Update refs, scan remembered set using bitmap: %s", BOOL_TO_STR(old_bitmap_stable));
788 }
789
790 void work(uint worker_id) {
791 if (CONCURRENT) {
792 ShenandoahConcurrentWorkerSession worker_session(worker_id);
793 ShenandoahSuspendibleThreadSetJoiner stsj;
794 do_work<ShenandoahConcUpdateRefsClosure>(worker_id);
795 } else {
796 ShenandoahParallelWorkerSession worker_session(worker_id);
797 do_work<ShenandoahNonConcUpdateRefsClosure>(worker_id);
798 }
799 }
800
801 private:
802 template<class T>
803 void do_work(uint worker_id) {
804 T cl;
805
806 if (CONCURRENT && (worker_id == 0)) {
807 // We ask the first worker to replenish the Mutator free set by moving regions previously reserved to hold the
808 // results of evacuation. These reserves are no longer necessary because evacuation has completed.
809 size_t cset_regions = _heap->collection_set()->count();
810
811 // Now that evacuation is done, we can reassign any regions that had been reserved to hold the results of evacuation
812 // to the mutator free set. At the end of GC, we will have cset_regions newly evacuated fully empty regions from
813 // which we will be able to replenish the Collector free set and the OldCollector free set in preparation for the
814 // next GC cycle.
815 _heap->free_set()->move_regions_from_collector_to_mutator(cset_regions);
816 }
817 // If !CONCURRENT, there's no value in expanding Mutator free set
818
819 ShenandoahHeapRegion* r = _regions->next();
820 // We update references for global, old, and young collections.
821 ShenandoahGeneration* const gc_generation = _heap->gc_generation();
822 shenandoah_assert_generations_reconciled();
823 assert(gc_generation->is_mark_complete(), "Expected complete marking");
824 ShenandoahMarkingContext* const ctx = _heap->marking_context();
825 bool is_mixed = _heap->collection_set()->has_old_regions();
826 while (r != nullptr) {
827 HeapWord* update_watermark = r->get_update_watermark();
828 assert(update_watermark >= r->bottom(), "sanity");
829
830 log_debug(gc)("Update refs worker " UINT32_FORMAT ", looking at region " SIZE_FORMAT, worker_id, r->index());
831 bool region_progress = false;
832 if (r->is_active() && !r->is_cset()) {
833 if (r->is_young()) {
834 _heap->marked_object_oop_iterate(r, &cl, update_watermark);
835 region_progress = true;
836 } else if (r->is_old()) {
837 if (gc_generation->is_global()) {
838
839 _heap->marked_object_oop_iterate(r, &cl, update_watermark);
840 region_progress = true;
841 }
842 // Otherwise, this is an old region in a young or mixed cycle. Process it during a second phase, below.
843 // Don't bother to report pacing progress in this case.
844 } else {
845 // Because updating of references runs concurrently, it is possible that a FREE inactive region transitions
846 // to a non-free active region while this loop is executing. Whenever this happens, the changing of a region's
847 // active status may propagate at a different speed than the changing of the region's affiliation.
848
849 // When we reach this control point, it is because a race has allowed a region's is_active() status to be seen
850 // by this thread before the region's affiliation() is seen by this thread.
851
852 // It's ok for this race to occur because the newly transformed region does not have any references to be
853 // updated.
854
855 assert(r->get_update_watermark() == r->bottom(),
856 "%s Region " SIZE_FORMAT " is_active but not recognized as YOUNG or OLD so must be newly transitioned from FREE",
857 r->affiliation_name(), r->index());
858 }
859 }
860
861 if (region_progress && ShenandoahPacing) {
862 _heap->pacer()->report_updaterefs(pointer_delta(update_watermark, r->bottom()));
863 }
864
865 if (_heap->check_cancelled_gc_and_yield(CONCURRENT)) {
866 return;
867 }
868
869 r = _regions->next();
870 }
871
872 if (!gc_generation->is_global()) {
873 // Since this is generational and not GLOBAL, we have to process the remembered set. There's no remembered
874 // set processing if not in generational mode or if GLOBAL mode.
875
876 // After this thread has exhausted its traditional update-refs work, it continues with updating refs within
877 // remembered set. The remembered set workload is better balanced between threads, so threads that are "behind"
878 // can catch up with other threads during this phase, allowing all threads to work more effectively in parallel.
879 update_references_in_remembered_set(worker_id, cl, ctx, is_mixed);
880 }
881 }
882
883 template<class T>
884 void update_references_in_remembered_set(uint worker_id, T &cl, const ShenandoahMarkingContext* ctx, bool is_mixed) {
885
886 struct ShenandoahRegionChunk assignment;
887 ShenandoahScanRemembered* scanner = _heap->old_generation()->card_scan();
888
889 while (!_heap->check_cancelled_gc_and_yield(CONCURRENT) && _work_chunks->next(&assignment)) {
890 // Keep grabbing next work chunk to process until finished, or asked to yield
891 ShenandoahHeapRegion* r = assignment._r;
892 if (r->is_active() && !r->is_cset() && r->is_old()) {
893 HeapWord* start_of_range = r->bottom() + assignment._chunk_offset;
894 HeapWord* end_of_range = r->get_update_watermark();
895 if (end_of_range > start_of_range + assignment._chunk_size) {
896 end_of_range = start_of_range + assignment._chunk_size;
897 }
898
899 if (start_of_range >= end_of_range) {
900 continue;
901 }
902
903 // Old region in a young cycle or mixed cycle.
904 if (is_mixed) {
905 if (r->is_humongous()) {
906 // Need to examine both dirty and clean cards during mixed evac.
907 r->oop_iterate_humongous_slice_all(&cl,start_of_range, assignment._chunk_size);
908 } else {
909 // Since this is mixed evacuation, old regions that are candidates for collection have not been coalesced
910 // and filled. This will use mark bits to find objects that need to be updated.
911 update_references_in_old_region(cl, ctx, scanner, r, start_of_range, end_of_range);
912 }
913 } else {
914 // This is a young evacuation
915 size_t cluster_size = CardTable::card_size_in_words() * ShenandoahCardCluster::CardsPerCluster;
916 size_t clusters = assignment._chunk_size / cluster_size;
917 assert(clusters * cluster_size == assignment._chunk_size, "Chunk assignment must align on cluster boundaries");
918 scanner->process_region_slice(r, assignment._chunk_offset, clusters, end_of_range, &cl, true, worker_id);
919 }
920
921 if (ShenandoahPacing) {
922 _heap->pacer()->report_updaterefs(pointer_delta(end_of_range, start_of_range));
923 }
924 }
925 }
926 }
927
928 template<class T>
929 void update_references_in_old_region(T &cl, const ShenandoahMarkingContext* ctx, ShenandoahScanRemembered* scanner,
930 const ShenandoahHeapRegion* r, HeapWord* start_of_range,
931 HeapWord* end_of_range) const {
932 // In case last object in my range spans boundary of my chunk, I may need to scan all the way to top()
933 ShenandoahObjectToOopBoundedClosure<T> objs(&cl, start_of_range, r->top());
934
935 // Any object that begins in a previous range is part of a different scanning assignment. Any object that
936 // starts after end_of_range is also not my responsibility. (Either allocated during evacuation, so does
937 // not hold pointers to from-space, or is beyond the range of my assigned work chunk.)
938
939 // Find the first object that begins in my range, if there is one. Note that `p` will be set to `end_of_range`
940 // when no live object is found in the range.
941 HeapWord* tams = ctx->top_at_mark_start(r);
942 HeapWord* p = get_first_object_start_word(ctx, scanner, tams, start_of_range, end_of_range);
943
944 while (p < end_of_range) {
945 // p is known to point to the beginning of marked object obj
946 oop obj = cast_to_oop(p);
947 objs.do_object(obj);
948 HeapWord* prev_p = p;
949 p += obj->size();
950 if (p < tams) {
951 p = ctx->get_next_marked_addr(p, tams);
952 // If there are no more marked objects before tams, this returns tams. Note that tams is
953 // either >= end_of_range, or tams is the start of an object that is marked.
954 }
955 assert(p != prev_p, "Lack of forward progress");
956 }
957 }
958
959 HeapWord* get_first_object_start_word(const ShenandoahMarkingContext* ctx, ShenandoahScanRemembered* scanner, HeapWord* tams,
960 HeapWord* start_of_range, HeapWord* end_of_range) const {
961 HeapWord* p = start_of_range;
962
963 if (p >= tams) {
964 // We cannot use ctx->is_marked(obj) to test whether an object begins at this address. Instead,
965 // we need to use the remembered set crossing map to advance p to the first object that starts
966 // within the enclosing card.
967 size_t card_index = scanner->card_index_for_addr(start_of_range);
968 while (true) {
969 HeapWord* first_object = scanner->first_object_in_card(card_index);
970 if (first_object != nullptr) {
971 p = first_object;
972 break;
973 } else if (scanner->addr_for_card_index(card_index + 1) < end_of_range) {
974 card_index++;
975 } else {
976 // Signal that no object was found in range
977 p = end_of_range;
978 break;
979 }
980 }
981 } else if (!ctx->is_marked(cast_to_oop(p))) {
982 p = ctx->get_next_marked_addr(p, tams);
983 // If there are no more marked objects before tams, this returns tams.
984 // Note that tams is either >= end_of_range, or tams is the start of an object that is marked.
985 }
986 return p;
987 }
988 };
989
990 void ShenandoahGenerationalHeap::update_heap_references(bool concurrent) {
991 assert(!is_full_gc_in_progress(), "Only for concurrent and degenerated GC");
992 const uint nworkers = workers()->active_workers();
993 ShenandoahRegionChunkIterator work_list(nworkers);
994 if (concurrent) {
995 ShenandoahGenerationalUpdateHeapRefsTask<true> task(&_update_refs_iterator, &work_list);
996 workers()->run_task(&task);
997 } else {
998 ShenandoahGenerationalUpdateHeapRefsTask<false> task(&_update_refs_iterator, &work_list);
999 workers()->run_task(&task);
1000 }
1001
1002 if (ShenandoahEnableCardStats) {
1003 // Only do this if we are collecting card stats
1004 ShenandoahScanRemembered* card_scan = old_generation()->card_scan();
1005 assert(card_scan != nullptr, "Card table must exist when card stats are enabled");
1006 card_scan->log_card_stats(nworkers, CARD_STAT_UPDATE_REFS);
1007 }
1008 }
1009
1010 struct ShenandoahCompositeRegionClosure {
1011 template<typename C1, typename C2>
1012 class Closure : public ShenandoahHeapRegionClosure {
1013 private:
1014 C1 &_c1;
1015 C2 &_c2;
1016
1017 public:
1018 Closure(C1 &c1, C2 &c2) : ShenandoahHeapRegionClosure(), _c1(c1), _c2(c2) {}
1019
1020 void heap_region_do(ShenandoahHeapRegion* r) override {
1021 _c1.heap_region_do(r);
1022 _c2.heap_region_do(r);
1023 }
1024
1025 bool is_thread_safe() override {
1026 return _c1.is_thread_safe() && _c2.is_thread_safe();
1027 }
1028 };
1029
1030 template<typename C1, typename C2>
1031 static Closure<C1, C2> of(C1 &c1, C2 &c2) {
1032 return Closure<C1, C2>(c1, c2);
1033 }
1034 };
1035
1036 class ShenandoahUpdateRegionAges : public ShenandoahHeapRegionClosure {
1037 private:
1038 ShenandoahMarkingContext* _ctx;
1039
1040 public:
1041 explicit ShenandoahUpdateRegionAges(ShenandoahMarkingContext* ctx) : _ctx(ctx) { }
1042
1043 void heap_region_do(ShenandoahHeapRegion* r) override {
1044 // Maintenance of region age must follow evacuation in order to account for
1045 // evacuation allocations within survivor regions. We consult region age during
1046 // the subsequent evacuation to determine whether certain objects need to
1047 // be promoted.
1048 if (r->is_young() && r->is_active()) {
1049 HeapWord *tams = _ctx->top_at_mark_start(r);
1050 HeapWord *top = r->top();
1051
1052 // Allocations move the watermark when top moves. However, compacting
1053 // objects will sometimes lower top beneath the watermark, after which,
1054 // attempts to read the watermark will assert out (watermark should not be
1055 // higher than top).
1056 if (top > tams) {
1057 // There have been allocations in this region since the start of the cycle.
1058 // Any objects new to this region must not assimilate elevated age.
1059 r->reset_age();
1060 } else if (ShenandoahGenerationalHeap::heap()->is_aging_cycle()) {
1061 r->increment_age();
1062 }
1063 }
1064 }
1065
1066 bool is_thread_safe() override {
1067 return true;
1068 }
1069 };
1070
1071 void ShenandoahGenerationalHeap::final_update_refs_update_region_states() {
1072 ShenandoahSynchronizePinnedRegionStates pins;
1073 ShenandoahUpdateRegionAges ages(active_generation()->complete_marking_context());
1074 auto cl = ShenandoahCompositeRegionClosure::of(pins, ages);
1075 parallel_heap_region_iterate(&cl);
1076 }
1077
1078 void ShenandoahGenerationalHeap::complete_degenerated_cycle() {
1079 shenandoah_assert_heaplocked_or_safepoint();
1080 if (is_concurrent_old_mark_in_progress()) {
1081 // This is still necessary for degenerated cycles because the degeneration point may occur
1082 // after final mark of the young generation. See ShenandoahConcurrentGC::op_final_updaterefs for
1083 // a more detailed explanation.
1084 old_generation()->transfer_pointers_from_satb();
1085 }
1086
1087 // We defer generation resizing actions until after cset regions have been recycled.
1088 TransferResult result = balance_generations();
1089 LogTarget(Info, gc, ergo) lt;
1090 if (lt.is_enabled()) {
1091 LogStream ls(lt);
1092 result.print_on("Degenerated GC", &ls);
1093 }
1094
1095 // In case degeneration interrupted concurrent evacuation or update references, we need to clean up
1096 // transient state. Otherwise, these actions have no effect.
1097 reset_generation_reserves();
1098
1099 if (!old_generation()->is_parsable()) {
1100 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_coalesce_and_fill);
1101 coalesce_and_fill_old_regions(false);
1102 }
1103 }
1104
1105 void ShenandoahGenerationalHeap::complete_concurrent_cycle() {
1106 if (!old_generation()->is_parsable()) {
1107 // Class unloading may render the card offsets unusable, so we must rebuild them before
1108 // the next remembered set scan. We _could_ let the control thread do this sometime after
1109 // the global cycle has completed and before the next young collection, but under memory
1110 // pressure the control thread may not have the time (that is, because it's running back
1111 // to back GCs). In that scenario, we would have to make the old regions parsable before
1112 // we could start a young collection. This could delay the start of the young cycle and
1113 // throw off the heuristics.
1114 entry_global_coalesce_and_fill();
1115 }
1116
1117 TransferResult result;
1118 {
1119 ShenandoahHeapLocker locker(lock());
1120
1121 result = balance_generations();
1122 reset_generation_reserves();
1123 }
1124
1125 LogTarget(Info, gc, ergo) lt;
1126 if (lt.is_enabled()) {
1127 LogStream ls(lt);
1128 result.print_on("Concurrent GC", &ls);
1129 }
1130 }
1131
1132 void ShenandoahGenerationalHeap::entry_global_coalesce_and_fill() {
1133 const char* msg = "Coalescing and filling old regions";
1134 ShenandoahConcurrentPhase gc_phase(msg, ShenandoahPhaseTimings::conc_coalesce_and_fill);
1135
1136 TraceCollectorStats tcs(monitoring_support()->concurrent_collection_counters());
1137 EventMark em("%s", msg);
1138 ShenandoahWorkerScope scope(workers(),
1139 ShenandoahWorkerPolicy::calc_workers_for_conc_marking(),
1140 "concurrent coalesce and fill");
1141
1142 coalesce_and_fill_old_regions(true);
1143 }
1144
1145 void ShenandoahGenerationalHeap::update_region_ages(ShenandoahMarkingContext* ctx) {
1146 ShenandoahUpdateRegionAges cl(ctx);
1147 parallel_heap_region_iterate(&cl);
1148 }