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/shenandoahInitLogger.hpp"
36 #include "gc/shenandoah/shenandoahMemoryPool.hpp"
37 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
38 #include "gc/shenandoah/shenandoahOldGeneration.hpp"
39 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
40 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
41 #include "gc/shenandoah/shenandoahRegulatorThread.hpp"
42 #include "gc/shenandoah/shenandoahScanRemembered.inline.hpp"
43 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
44 #include "gc/shenandoah/shenandoahYoungGeneration.hpp"
45 #include "gc/shenandoah/shenandoahUtils.hpp"
46 #include "logging/log.hpp"
47 #include "utilities/events.hpp"
48
49
50 class ShenandoahGenerationalInitLogger : public ShenandoahInitLogger {
51 public:
52 static void print() {
53 ShenandoahGenerationalInitLogger logger;
54 logger.print_all();
55 }
56
57 void print_heap() override {
58 ShenandoahInitLogger::print_heap();
59
60 ShenandoahGenerationalHeap* heap = ShenandoahGenerationalHeap::heap();
61
62 ShenandoahYoungGeneration* young = heap->young_generation();
63 log_info(gc, init)("Young Generation Soft Size: " EXACTFMT, EXACTFMTARGS(young->soft_max_capacity()));
64 log_info(gc, init)("Young Generation Max: " EXACTFMT, EXACTFMTARGS(young->max_capacity()));
65
66 ShenandoahOldGeneration* old = heap->old_generation();
67 log_info(gc, init)("Old Generation Soft Size: " EXACTFMT, EXACTFMTARGS(old->soft_max_capacity()));
68 log_info(gc, init)("Old Generation Max: " EXACTFMT, EXACTFMTARGS(old->max_capacity()));
69 }
70
71 protected:
72 void print_gc_specific() override {
73 ShenandoahInitLogger::print_gc_specific();
74
75 ShenandoahGenerationalHeap* heap = ShenandoahGenerationalHeap::heap();
76 log_info(gc, init)("Young Heuristics: %s", heap->young_generation()->heuristics()->name());
77 log_info(gc, init)("Old Heuristics: %s", heap->old_generation()->heuristics()->name());
78 }
79 };
80
81 ShenandoahGenerationalHeap* ShenandoahGenerationalHeap::heap() {
82 shenandoah_assert_generational();
83 CollectedHeap* heap = Universe::heap();
84 return cast(heap);
85 }
86
87 ShenandoahGenerationalHeap* ShenandoahGenerationalHeap::cast(CollectedHeap* heap) {
88 shenandoah_assert_generational();
89 return checked_cast<ShenandoahGenerationalHeap*>(heap);
90 }
91
92 size_t ShenandoahGenerationalHeap::calculate_min_plab() {
93 return align_up(PLAB::min_size(), CardTable::card_size_in_words());
94 }
95
96 size_t ShenandoahGenerationalHeap::calculate_max_plab() {
97 size_t MaxTLABSizeWords = ShenandoahHeapRegion::max_tlab_size_words();
98 return align_down(MaxTLABSizeWords, CardTable::card_size_in_words());
99 }
100
101 // Returns size in bytes
102 size_t ShenandoahGenerationalHeap::unsafe_max_tlab_alloc(Thread *thread) const {
103 return MIN2(ShenandoahHeapRegion::max_tlab_size_bytes(), young_generation()->available());
104 }
105
106 ShenandoahGenerationalHeap::ShenandoahGenerationalHeap(ShenandoahCollectorPolicy* policy) :
107 ShenandoahHeap(policy),
108 _age_census(nullptr),
109 _min_plab_size(calculate_min_plab()),
110 _max_plab_size(calculate_max_plab()),
111 _regulator_thread(nullptr),
112 _young_gen_memory_pool(nullptr),
113 _old_gen_memory_pool(nullptr) {
114 assert(is_aligned(_min_plab_size, CardTable::card_size_in_words()), "min_plab_size must be aligned");
115 assert(is_aligned(_max_plab_size, CardTable::card_size_in_words()), "max_plab_size must be aligned");
116 }
117
118 void ShenandoahGenerationalHeap::post_initialize() {
119 ShenandoahHeap::post_initialize();
120 _age_census = new ShenandoahAgeCensus();
121 }
122
123 void ShenandoahGenerationalHeap::print_init_logger() const {
124 ShenandoahGenerationalInitLogger logger;
125 logger.print_all();
126 }
127
128 void ShenandoahGenerationalHeap::initialize_heuristics() {
129 // Initialize global generation and heuristics even in generational mode.
130 ShenandoahHeap::initialize_heuristics();
131
132 // Max capacity is the maximum _allowed_ capacity. That is, the maximum allowed capacity
133 // for old would be total heap - minimum capacity of young. This means the sum of the maximum
134 // allowed for old and young could exceed the total heap size. It remains the case that the
135 // _actual_ capacity of young + old = total.
136 _generation_sizer.heap_size_changed(max_capacity());
137 size_t initial_capacity_young = _generation_sizer.max_young_size();
138 size_t max_capacity_young = _generation_sizer.max_young_size();
139 size_t initial_capacity_old = max_capacity() - max_capacity_young;
140 size_t max_capacity_old = max_capacity() - initial_capacity_young;
141
142 _young_generation = new ShenandoahYoungGeneration(max_workers(), max_capacity_young, initial_capacity_young);
143 _old_generation = new ShenandoahOldGeneration(max_workers(), max_capacity_old, initial_capacity_old);
144 _young_generation->initialize_heuristics(mode());
145 _old_generation->initialize_heuristics(mode());
146 }
147
148 void ShenandoahGenerationalHeap::initialize_serviceability() {
149 assert(mode()->is_generational(), "Only for the generational mode");
150 _young_gen_memory_pool = new ShenandoahYoungGenMemoryPool(this);
151 _old_gen_memory_pool = new ShenandoahOldGenMemoryPool(this);
152 cycle_memory_manager()->add_pool(_young_gen_memory_pool);
153 cycle_memory_manager()->add_pool(_old_gen_memory_pool);
154 stw_memory_manager()->add_pool(_young_gen_memory_pool);
155 stw_memory_manager()->add_pool(_old_gen_memory_pool);
156 }
157
158 GrowableArray<MemoryPool*> ShenandoahGenerationalHeap::memory_pools() {
159 assert(mode()->is_generational(), "Only for the generational mode");
160 GrowableArray<MemoryPool*> memory_pools(2);
161 memory_pools.append(_young_gen_memory_pool);
162 memory_pools.append(_old_gen_memory_pool);
163 return memory_pools;
164 }
165
166 void ShenandoahGenerationalHeap::initialize_controller() {
167 auto control_thread = new ShenandoahGenerationalControlThread();
168 _control_thread = control_thread;
169 _regulator_thread = new ShenandoahRegulatorThread(control_thread);
170 }
171
172 void ShenandoahGenerationalHeap::gc_threads_do(ThreadClosure* tcl) const {
173 if (!shenandoah_policy()->is_at_shutdown()) {
174 ShenandoahHeap::gc_threads_do(tcl);
175 tcl->do_thread(regulator_thread());
176 }
177 }
178
179 void ShenandoahGenerationalHeap::stop() {
180 regulator_thread()->stop();
181 ShenandoahHeap::stop();
182 }
183
184 oop ShenandoahGenerationalHeap::evacuate_object(oop p, Thread* thread) {
185 assert(thread == Thread::current(), "Expected thread parameter to be current thread.");
186 if (ShenandoahThreadLocalData::is_oom_during_evac(thread)) {
187 // This thread went through the OOM during evac protocol and it is safe to return
188 // the forward pointer. It must not attempt to evacuate anymore.
189 return ShenandoahBarrierSet::resolve_forwarded(p);
190 }
191
192 assert(ShenandoahThreadLocalData::is_evac_allowed(thread), "must be enclosed in oom-evac scope");
193
194 ShenandoahHeapRegion* r = heap_region_containing(p);
195 assert(!r->is_humongous(), "never evacuate humongous objects");
196
197 ShenandoahAffiliation target_gen = r->affiliation();
198 // gc_generation() can change asynchronously and should not be used here.
199 assert(active_generation() != nullptr, "Error");
200 if (active_generation()->is_young() && target_gen == YOUNG_GENERATION) {
201 markWord mark = p->mark();
202 if (mark.is_marked()) {
203 // Already forwarded.
204 return ShenandoahBarrierSet::resolve_forwarded(p);
205 }
206
207 if (mark.has_displaced_mark_helper()) {
208 // We don't want to deal with MT here just to ensure we read the right mark word.
209 // Skip the potential promotion attempt for this one.
210 } else if (r->age() + mark.age() >= age_census()->tenuring_threshold()) {
211 oop result = try_evacuate_object(p, thread, r, OLD_GENERATION);
212 if (result != nullptr) {
213 return result;
214 }
215 // If we failed to promote this aged object, we'll fall through to code below and evacuate to young-gen.
216 }
217 }
218 return try_evacuate_object(p, thread, r, target_gen);
219 }
220
221 // try_evacuate_object registers the object and dirties the associated remembered set information when evacuating
222 // to OLD_GENERATION.
223 oop ShenandoahGenerationalHeap::try_evacuate_object(oop p, Thread* thread, ShenandoahHeapRegion* from_region,
224 ShenandoahAffiliation target_gen) {
225 bool alloc_from_lab = true;
226 bool has_plab = false;
227 HeapWord* copy = nullptr;
228 size_t size = p->size();
229 bool is_promotion = (target_gen == OLD_GENERATION) && from_region->is_young();
230
231 #ifdef ASSERT
232 if (ShenandoahOOMDuringEvacALot &&
233 (os::random() & 1) == 0) { // Simulate OOM every ~2nd slow-path call
234 copy = nullptr;
235 } else {
236 #endif
237 if (UseTLAB) {
238 switch (target_gen) {
239 case YOUNG_GENERATION: {
240 copy = allocate_from_gclab(thread, size);
241 if ((copy == nullptr) && (size < ShenandoahThreadLocalData::gclab_size(thread))) {
242 // GCLAB allocation failed because we are bumping up against the limit on young evacuation reserve. Try resetting
243 // the desired GCLAB size and retry GCLAB allocation to avoid cascading of shared memory allocations.
244 ShenandoahThreadLocalData::set_gclab_size(thread, PLAB::min_size());
245 copy = allocate_from_gclab(thread, size);
246 // If we still get nullptr, we'll try a shared allocation below.
247 }
248 break;
249 }
250 case OLD_GENERATION: {
251 assert(mode()->is_generational(), "OLD Generation only exists in generational mode");
252 PLAB* plab = ShenandoahThreadLocalData::plab(thread);
253 if (plab != nullptr) {
254 has_plab = true;
255 }
256 copy = allocate_from_plab(thread, size, is_promotion);
257 if ((copy == nullptr) && (size < ShenandoahThreadLocalData::plab_size(thread)) &&
258 ShenandoahThreadLocalData::plab_retries_enabled(thread)) {
259 // PLAB allocation failed because we are bumping up against the limit on old evacuation reserve or because
260 // the requested object does not fit within the current plab but the plab still has an "abundance" of memory,
261 // where abundance is defined as >= ShenGenHeap::plab_min_size(). In the former case, we try resetting the desired
262 // PLAB size and retry PLAB allocation to avoid cascading of shared memory allocations.
263
264 // In this situation, PLAB memory is precious. We'll try to preserve our existing PLAB by forcing
265 // this particular allocation to be shared.
266 if (plab->words_remaining() < plab_min_size()) {
267 ShenandoahThreadLocalData::set_plab_size(thread, plab_min_size());
268 copy = allocate_from_plab(thread, size, is_promotion);
269 // If we still get nullptr, we'll try a shared allocation below.
270 if (copy == nullptr) {
271 // If retry fails, don't continue to retry until we have success (probably in next GC pass)
272 ShenandoahThreadLocalData::disable_plab_retries(thread);
273 }
274 }
275 // else, copy still equals nullptr. this causes shared allocation below, preserving this plab for future needs.
276 }
277 break;
278 }
279 default: {
280 ShouldNotReachHere();
281 break;
282 }
283 }
284 }
285
286 if (copy == nullptr) {
287 // If we failed to allocate in LAB, we'll try a shared allocation.
288 if (!is_promotion || !has_plab || (size > PLAB::min_size())) {
289 ShenandoahAllocRequest req = ShenandoahAllocRequest::for_shared_gc(size, target_gen, is_promotion);
290 copy = allocate_memory(req);
291 alloc_from_lab = false;
292 }
293 // else, we leave copy equal to nullptr, signaling a promotion failure below if appropriate.
294 // We choose not to promote objects smaller than PLAB::min_size() by way of shared allocations, as this is too
295 // costly. Instead, we'll simply "evacuate" to young-gen memory (using a GCLAB) and will promote in a future
296 // evacuation pass. This condition is denoted by: is_promotion && has_plab && (size <= PLAB::min_size())
297 }
298 #ifdef ASSERT
299 }
300 #endif
301
302 if (copy == nullptr) {
303 if (target_gen == OLD_GENERATION) {
304 if (from_region->is_young()) {
305 // Signal that promotion failed. Will evacuate this old object somewhere in young gen.
306 old_generation()->handle_failed_promotion(thread, size);
307 return nullptr;
308 } else {
309 // Remember that evacuation to old gen failed. We'll want to trigger a full gc to recover from this
310 // after the evacuation threads have finished.
311 old_generation()->handle_failed_evacuation();
312 }
313 }
314
315 control_thread()->handle_alloc_failure_evac(size);
316
317 oom_evac_handler()->handle_out_of_memory_during_evacuation();
318
319 return ShenandoahBarrierSet::resolve_forwarded(p);
320 }
321
322 // Copy the object:
323 evac_tracker()->begin_evacuation(thread, size * HeapWordSize);
324 Copy::aligned_disjoint_words(cast_from_oop<HeapWord*>(p), copy, size);
325
326 oop copy_val = cast_to_oop(copy);
327
328 if (target_gen == YOUNG_GENERATION && is_aging_cycle()) {
329 ShenandoahHeap::increase_object_age(copy_val, from_region->age() + 1);
330 }
331
332 // Try to install the new forwarding pointer.
333 ContinuationGCSupport::relativize_stack_chunk(copy_val);
334
335 oop result = ShenandoahForwarding::try_update_forwardee(p, copy_val);
336 if (result == copy_val) {
337 // Successfully evacuated. Our copy is now the public one!
338 evac_tracker()->end_evacuation(thread, size * HeapWordSize);
339 if (target_gen == OLD_GENERATION) {
340 old_generation()->handle_evacuation(copy, size, from_region->is_young());
341 } else {
342 // When copying to the old generation above, we don't care
343 // about recording object age in the census stats.
344 assert(target_gen == YOUNG_GENERATION, "Error");
345 // We record this census only when simulating pre-adaptive tenuring behavior, or
346 // when we have been asked to record the census at evacuation rather than at mark
347 if (ShenandoahGenerationalCensusAtEvac || !ShenandoahGenerationalAdaptiveTenuring) {
348 evac_tracker()->record_age(thread, size * HeapWordSize, ShenandoahHeap::get_object_age(copy_val));
349 }
350 }
351 shenandoah_assert_correct(nullptr, copy_val);
352 return copy_val;
353 } else {
354 // Failed to evacuate. We need to deal with the object that is left behind. Since this
355 // new allocation is certainly after TAMS, it will be considered live in the next cycle.
356 // But if it happens to contain references to evacuated regions, those references would
357 // not get updated for this stale copy during this cycle, and we will crash while scanning
358 // it the next cycle.
359 if (alloc_from_lab) {
360 // For LAB allocations, it is enough to rollback the allocation ptr. Either the next
361 // object will overwrite this stale copy, or the filler object on LAB retirement will
362 // do this.
363 switch (target_gen) {
364 case YOUNG_GENERATION: {
365 ShenandoahThreadLocalData::gclab(thread)->undo_allocation(copy, size);
366 break;
367 }
368 case OLD_GENERATION: {
369 ShenandoahThreadLocalData::plab(thread)->undo_allocation(copy, size);
370 if (is_promotion) {
371 ShenandoahThreadLocalData::subtract_from_plab_promoted(thread, size * HeapWordSize);
372 }
373 break;
374 }
375 default: {
376 ShouldNotReachHere();
377 break;
378 }
379 }
380 } else {
381 // For non-LAB allocations, we have no way to retract the allocation, and
382 // have to explicitly overwrite the copy with the filler object. With that overwrite,
383 // we have to keep the fwdptr initialized and pointing to our (stale) copy.
384 assert(size >= ShenandoahHeap::min_fill_size(), "previously allocated object known to be larger than min_size");
385 fill_with_object(copy, size);
386 shenandoah_assert_correct(nullptr, copy_val);
387 // For non-LAB allocations, the object has already been registered
388 }
389 shenandoah_assert_correct(nullptr, result);
390 return result;
391 }
392 }
393
394 inline HeapWord* ShenandoahGenerationalHeap::allocate_from_plab(Thread* thread, size_t size, bool is_promotion) {
395 assert(UseTLAB, "TLABs should be enabled");
396
397 PLAB* plab = ShenandoahThreadLocalData::plab(thread);
398 HeapWord* obj;
399
400 if (plab == nullptr) {
401 assert(!thread->is_Java_thread() && !thread->is_Worker_thread(), "Performance: thread should have PLAB: %s", thread->name());
402 // No PLABs in this thread, fallback to shared allocation
403 return nullptr;
404 } else if (is_promotion && !ShenandoahThreadLocalData::allow_plab_promotions(thread)) {
405 return nullptr;
406 }
407 // if plab->word_size() <= 0, thread's plab not yet initialized for this pass, so allow_plab_promotions() is not trustworthy
408 obj = plab->allocate(size);
409 if ((obj == nullptr) && (plab->words_remaining() < plab_min_size())) {
410 // allocate_from_plab_slow will establish allow_plab_promotions(thread) for future invocations
411 obj = allocate_from_plab_slow(thread, size, is_promotion);
412 }
413 // if plab->words_remaining() >= ShenGenHeap::heap()->plab_min_size(), just return nullptr so we can use a shared allocation
414 if (obj == nullptr) {
415 return nullptr;
416 }
417
418 if (is_promotion) {
419 ShenandoahThreadLocalData::add_to_plab_promoted(thread, size * HeapWordSize);
420 }
421 return obj;
422 }
423
424 // Establish a new PLAB and allocate size HeapWords within it.
425 HeapWord* ShenandoahGenerationalHeap::allocate_from_plab_slow(Thread* thread, size_t size, bool is_promotion) {
426 // New object should fit the PLAB size
427
428 assert(mode()->is_generational(), "PLABs only relevant to generational GC");
429 const size_t plab_min_size = this->plab_min_size();
430 // PLABs are aligned to card boundaries to avoid synchronization with concurrent
431 // allocations in other PLABs.
432 const size_t min_size = (size > plab_min_size)? align_up(size, CardTable::card_size_in_words()): plab_min_size;
433
434 // Figure out size of new PLAB, using value determined at last refill.
435 size_t cur_size = ShenandoahThreadLocalData::plab_size(thread);
436 if (cur_size == 0) {
437 cur_size = plab_min_size;
438 }
439
440 // Expand aggressively, doubling at each refill in this epoch, ceiling at plab_max_size()
441 size_t future_size = MIN2(cur_size * 2, plab_max_size());
442 // Doubling, starting at a card-multiple, should give us a card-multiple. (Ceiling and floor
443 // are card multiples.)
444 assert(is_aligned(future_size, CardTable::card_size_in_words()), "Card multiple by construction, future_size: " SIZE_FORMAT
445 ", card_size: " SIZE_FORMAT ", cur_size: " SIZE_FORMAT ", max: " SIZE_FORMAT,
446 future_size, (size_t) CardTable::card_size_in_words(), cur_size, plab_max_size());
447
448 // Record new heuristic value even if we take any shortcut. This captures
449 // the case when moderately-sized objects always take a shortcut. At some point,
450 // heuristics should catch up with them. Note that the requested cur_size may
451 // not be honored, but we remember that this is the preferred size.
452 log_debug(gc, free)("Set new PLAB size: " SIZE_FORMAT, future_size);
453 ShenandoahThreadLocalData::set_plab_size(thread, future_size);
454 if (cur_size < size) {
455 // The PLAB to be allocated is still not large enough to hold the object. Fall back to shared allocation.
456 // This avoids retiring perfectly good PLABs in order to represent a single large object allocation.
457 log_debug(gc, free)("Current PLAB size (" SIZE_FORMAT ") is too small for " SIZE_FORMAT, cur_size, size);
458 return nullptr;
459 }
460
461 // Retire current PLAB, and allocate a new one.
462 PLAB* plab = ShenandoahThreadLocalData::plab(thread);
463 if (plab->words_remaining() < plab_min_size) {
464 // Retire current PLAB. This takes care of any PLAB book-keeping.
465 // retire_plab() registers the remnant filler object with the remembered set scanner without a lock.
466 // Since PLABs are card-aligned, concurrent registrations in other PLABs don't interfere.
467 retire_plab(plab, thread);
468
469 size_t actual_size = 0;
470 HeapWord* plab_buf = allocate_new_plab(min_size, cur_size, &actual_size);
471 if (plab_buf == nullptr) {
472 if (min_size == plab_min_size) {
473 // Disable PLAB promotions for this thread because we cannot even allocate a minimal PLAB. This allows us
474 // to fail faster on subsequent promotion attempts.
475 ShenandoahThreadLocalData::disable_plab_promotions(thread);
476 }
477 return nullptr;
478 } else {
479 ShenandoahThreadLocalData::enable_plab_retries(thread);
480 }
481 // Since the allocated PLAB may have been down-sized for alignment, plab->allocate(size) below may still fail.
482 if (ZeroTLAB) {
483 // ... and clear it.
484 Copy::zero_to_words(plab_buf, actual_size);
485 } else {
486 // ...and zap just allocated object.
487 #ifdef ASSERT
488 // Skip mangling the space corresponding to the object header to
489 // ensure that the returned space is not considered parsable by
490 // any concurrent GC thread.
491 size_t hdr_size = oopDesc::header_size();
492 Copy::fill_to_words(plab_buf + hdr_size, actual_size - hdr_size, badHeapWordVal);
493 #endif // ASSERT
494 }
495 assert(is_aligned(actual_size, CardTable::card_size_in_words()), "Align by design");
496 plab->set_buf(plab_buf, actual_size);
497 if (is_promotion && !ShenandoahThreadLocalData::allow_plab_promotions(thread)) {
498 return nullptr;
499 }
500 return plab->allocate(size);
501 } else {
502 // If there's still at least min_size() words available within the current plab, don't retire it. Let's nibble
503 // away on this plab as long as we can. Meanwhile, return nullptr to force this particular allocation request
504 // to be satisfied with a shared allocation. By packing more promotions into the previously allocated PLAB, we
505 // reduce the likelihood of evacuation failures, and we reduce the need for downsizing our PLABs.
506 return nullptr;
507 }
508 }
509
510 HeapWord* ShenandoahGenerationalHeap::allocate_new_plab(size_t min_size, size_t word_size, size_t* actual_size) {
511 // Align requested sizes to card-sized multiples. Align down so that we don't violate max size of TLAB.
512 assert(is_aligned(min_size, CardTable::card_size_in_words()), "Align by design");
513 assert(word_size >= min_size, "Requested PLAB is too small");
514
515 ShenandoahAllocRequest req = ShenandoahAllocRequest::for_plab(min_size, word_size);
516 // Note that allocate_memory() sets a thread-local flag to prohibit further promotions by this thread
517 // if we are at risk of infringing on the old-gen evacuation budget.
518 HeapWord* res = allocate_memory(req);
519 if (res != nullptr) {
520 *actual_size = req.actual_size();
521 } else {
522 *actual_size = 0;
523 }
524 assert(is_aligned(res, CardTable::card_size_in_words()), "Align by design");
525 return res;
526 }
527
528 // TODO: It is probably most efficient to register all objects (both promotions and evacuations) that were allocated within
529 // this plab at the time we retire the plab. A tight registration loop will run within both code and data caches. This change
530 // would allow smaller and faster in-line implementation of alloc_from_plab(). Since plabs are aligned on card-table boundaries,
531 // this object registration loop can be performed without acquiring a lock.
532 void ShenandoahGenerationalHeap::retire_plab(PLAB* plab, Thread* thread) {
533 // We don't enforce limits on plab evacuations. We let it consume all available old-gen memory in order to reduce
534 // probability of an evacuation failure. We do enforce limits on promotion, to make sure that excessive promotion
535 // does not result in an old-gen evacuation failure. Note that a failed promotion is relatively harmless. Any
536 // object that fails to promote in the current cycle will be eligible for promotion in a subsequent cycle.
537
538 // When the plab was instantiated, its entirety was treated as if the entire buffer was going to be dedicated to
539 // promotions. Now that we are retiring the buffer, we adjust for the reality that the plab is not entirely promotions.
540 // 1. Some of the plab may have been dedicated to evacuations.
541 // 2. Some of the plab may have been abandoned due to waste (at the end of the plab).
542 size_t not_promoted =
543 ShenandoahThreadLocalData::get_plab_actual_size(thread) - ShenandoahThreadLocalData::get_plab_promoted(thread);
544 ShenandoahThreadLocalData::reset_plab_promoted(thread);
545 ShenandoahThreadLocalData::set_plab_actual_size(thread, 0);
546 if (not_promoted > 0) {
547 old_generation()->unexpend_promoted(not_promoted);
548 }
549 const size_t original_waste = plab->waste();
550 HeapWord* const top = plab->top();
551
552 // plab->retire() overwrites unused memory between plab->top() and plab->hard_end() with a dummy object to make memory parsable.
553 // It adds the size of this unused memory, in words, to plab->waste().
554 plab->retire();
555 if (top != nullptr && plab->waste() > original_waste && is_in_old(top)) {
556 // If retiring the plab created a filler object, then we need to register it with our card scanner so it can
557 // safely walk the region backing the plab.
558 log_debug(gc)("retire_plab() is registering remnant of size " SIZE_FORMAT " at " PTR_FORMAT,
559 plab->waste() - original_waste, p2i(top));
560 old_generation()->card_scan()->register_object_without_lock(top);
561 }
562 }
563
564 void ShenandoahGenerationalHeap::retire_plab(PLAB* plab) {
565 Thread* thread = Thread::current();
566 retire_plab(plab, thread);
567 }
568
569 ShenandoahGenerationalHeap::TransferResult ShenandoahGenerationalHeap::balance_generations() {
570 shenandoah_assert_heaplocked_or_safepoint();
571
572 ShenandoahOldGeneration* old_gen = old_generation();
573 const ssize_t old_region_balance = old_gen->get_region_balance();
574 old_gen->set_region_balance(0);
575
576 if (old_region_balance > 0) {
577 const auto old_region_surplus = checked_cast<size_t>(old_region_balance);
578 const bool success = generation_sizer()->transfer_to_young(old_region_surplus);
579 return TransferResult {
580 success, old_region_surplus, "young"
581 };
582 }
583
584 if (old_region_balance < 0) {
585 const auto old_region_deficit = checked_cast<size_t>(-old_region_balance);
586 const bool success = generation_sizer()->transfer_to_old(old_region_deficit);
587 if (!success) {
588 old_gen->handle_failed_transfer();
589 }
590 return TransferResult {
591 success, old_region_deficit, "old"
592 };
593 }
594
595 return TransferResult {true, 0, "none"};
596 }
597
598 // Make sure old-generation is large enough, but no larger than is necessary, to hold mixed evacuations
599 // and promotions, if we anticipate either. Any deficit is provided by the young generation, subject to
600 // xfer_limit, and any surplus is transferred to the young generation.
601 // xfer_limit is the maximum we're able to transfer from young to old.
602 void ShenandoahGenerationalHeap::compute_old_generation_balance(size_t old_xfer_limit, size_t old_cset_regions) {
603
604 // We can limit the old reserve to the size of anticipated promotions:
605 // max_old_reserve is an upper bound on memory evacuated from old and promoted to old,
606 // clamped by the old generation space available.
607 //
608 // Here's the algebra.
609 // Let SOEP = ShenandoahOldEvacRatioPercent,
610 // OE = old evac,
611 // YE = young evac, and
612 // TE = total evac = OE + YE
613 // By definition:
614 // SOEP/100 = OE/TE
615 // = OE/(OE+YE)
616 // => SOEP/(100-SOEP) = OE/((OE+YE)-OE) // componendo-dividendo: If a/b = c/d, then a/(b-a) = c/(d-c)
617 // = OE/YE
618 // => OE = YE*SOEP/(100-SOEP)
619
620 // We have to be careful in the event that SOEP is set to 100 by the user.
621 assert(ShenandoahOldEvacRatioPercent <= 100, "Error");
622 const size_t old_available = old_generation()->available();
623 // The free set will reserve this amount of memory to hold young evacuations
624 const size_t young_reserve = (young_generation()->max_capacity() * ShenandoahEvacReserve) / 100;
625
626 // In the case that ShenandoahOldEvacRatioPercent equals 100, max_old_reserve is limited only by xfer_limit.
627
628 const size_t bound_on_old_reserve = old_available + old_xfer_limit + young_reserve;
629 const size_t max_old_reserve = (ShenandoahOldEvacRatioPercent == 100)?
630 bound_on_old_reserve: MIN2((young_reserve * ShenandoahOldEvacRatioPercent) / (100 - ShenandoahOldEvacRatioPercent),
631 bound_on_old_reserve);
632
633 const size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
634
635 // Decide how much old space we should reserve for a mixed collection
636 size_t reserve_for_mixed = 0;
637 if (old_generation()->has_unprocessed_collection_candidates()) {
638 // We want this much memory to be unfragmented in order to reliably evacuate old. This is conservative because we
639 // may not evacuate the entirety of unprocessed candidates in a single mixed evacuation.
640 const size_t max_evac_need = (size_t)
641 (old_generation()->unprocessed_collection_candidates_live_memory() * ShenandoahOldEvacWaste);
642 assert(old_available >= old_generation()->free_unaffiliated_regions() * region_size_bytes,
643 "Unaffiliated available must be less than total available");
644 const size_t old_fragmented_available =
645 old_available - old_generation()->free_unaffiliated_regions() * region_size_bytes;
646 reserve_for_mixed = max_evac_need + old_fragmented_available;
647 if (reserve_for_mixed > max_old_reserve) {
648 reserve_for_mixed = max_old_reserve;
649 }
650 }
651
652 // Decide how much space we should reserve for promotions from young
653 size_t reserve_for_promo = 0;
654 const size_t promo_load = old_generation()->get_promotion_potential();
655 const bool doing_promotions = promo_load > 0;
656 if (doing_promotions) {
657 // We're promoting and have a bound on the maximum amount that can be promoted
658 assert(max_old_reserve >= reserve_for_mixed, "Sanity");
659 const size_t available_for_promotions = max_old_reserve - reserve_for_mixed;
660 reserve_for_promo = MIN2((size_t)(promo_load * ShenandoahPromoEvacWaste), available_for_promotions);
661 }
662
663 // This is the total old we want to ideally reserve
664 const size_t old_reserve = reserve_for_mixed + reserve_for_promo;
665 assert(old_reserve <= max_old_reserve, "cannot reserve more than max for old evacuations");
666
667 // We now check if the old generation is running a surplus or a deficit.
668 const size_t max_old_available = old_generation()->available() + old_cset_regions * region_size_bytes;
669 if (max_old_available >= old_reserve) {
670 // We are running a surplus, so the old region surplus can go to young
671 const size_t old_surplus = (max_old_available - old_reserve) / region_size_bytes;
672 const size_t unaffiliated_old_regions = old_generation()->free_unaffiliated_regions() + old_cset_regions;
673 const size_t old_region_surplus = MIN2(old_surplus, unaffiliated_old_regions);
674 old_generation()->set_region_balance(checked_cast<ssize_t>(old_region_surplus));
675 } else {
676 // We are running a deficit which we'd like to fill from young.
677 // Ignore that this will directly impact young_generation()->max_capacity(),
678 // indirectly impacting young_reserve and old_reserve. These computations are conservative.
679 // Note that deficit is rounded up by one region.
680 const size_t old_need = (old_reserve - max_old_available + region_size_bytes - 1) / region_size_bytes;
681 const size_t max_old_region_xfer = old_xfer_limit / region_size_bytes;
682
683 // Round down the regions we can transfer from young to old. If we're running short
684 // on young-gen memory, we restrict the xfer. Old-gen collection activities will be
685 // curtailed if the budget is restricted.
686 const size_t old_region_deficit = MIN2(old_need, max_old_region_xfer);
687 old_generation()->set_region_balance(0 - checked_cast<ssize_t>(old_region_deficit));
688 }
689 }
690
691 void ShenandoahGenerationalHeap::reset_generation_reserves() {
692 young_generation()->set_evacuation_reserve(0);
693 old_generation()->set_evacuation_reserve(0);
694 old_generation()->set_promoted_reserve(0);
695 }
696
697 void ShenandoahGenerationalHeap::TransferResult::print_on(const char* when, outputStream* ss) const {
698 auto heap = ShenandoahGenerationalHeap::heap();
699 ShenandoahYoungGeneration* const young_gen = heap->young_generation();
700 ShenandoahOldGeneration* const old_gen = heap->old_generation();
701 const size_t young_available = young_gen->available();
702 const size_t old_available = old_gen->available();
703 ss->print_cr("After %s, %s " SIZE_FORMAT " regions to %s to prepare for next gc, old available: "
704 PROPERFMT ", young_available: " PROPERFMT,
705 when,
706 success? "successfully transferred": "failed to transfer", region_count, region_destination,
707 PROPERFMTARGS(old_available), PROPERFMTARGS(young_available));
708 }
709
710 void ShenandoahGenerationalHeap::coalesce_and_fill_old_regions(bool concurrent) {
711 class ShenandoahGlobalCoalesceAndFill : public WorkerTask {
712 private:
713 ShenandoahPhaseTimings::Phase _phase;
714 ShenandoahRegionIterator _regions;
715 public:
716 explicit ShenandoahGlobalCoalesceAndFill(ShenandoahPhaseTimings::Phase phase) :
717 WorkerTask("Shenandoah Global Coalesce"),
718 _phase(phase) {}
719
720 void work(uint worker_id) override {
721 ShenandoahWorkerTimingsTracker timer(_phase,
722 ShenandoahPhaseTimings::ScanClusters,
723 worker_id, true);
724 ShenandoahHeapRegion* region;
725 while ((region = _regions.next()) != nullptr) {
726 // old region is not in the collection set and was not immediately trashed
727 if (region->is_old() && region->is_active() && !region->is_humongous()) {
728 // Reset the coalesce and fill boundary because this is a global collect
729 // and cannot be preempted by young collects. We want to be sure the entire
730 // region is coalesced here and does not resume from a previously interrupted
731 // or completed coalescing.
732 region->begin_preemptible_coalesce_and_fill();
733 region->oop_coalesce_and_fill(false);
734 }
735 }
736 }
737 };
738
739 ShenandoahPhaseTimings::Phase phase = concurrent ?
740 ShenandoahPhaseTimings::conc_coalesce_and_fill :
741 ShenandoahPhaseTimings::degen_gc_coalesce_and_fill;
742
743 // This is not cancellable
744 ShenandoahGlobalCoalesceAndFill coalesce(phase);
745 workers()->run_task(&coalesce);
746 old_generation()->set_parseable(true);
747 }
748
749 template<bool CONCURRENT>
750 class ShenandoahGenerationalUpdateHeapRefsTask : public WorkerTask {
751 private:
752 ShenandoahGenerationalHeap* _heap;
753 ShenandoahRegionIterator* _regions;
754 ShenandoahRegionChunkIterator* _work_chunks;
755
756 public:
757 explicit ShenandoahGenerationalUpdateHeapRefsTask(ShenandoahRegionIterator* regions,
758 ShenandoahRegionChunkIterator* work_chunks) :
759 WorkerTask("Shenandoah Update References"),
760 _heap(ShenandoahGenerationalHeap::heap()),
761 _regions(regions),
762 _work_chunks(work_chunks)
763 {
764 bool old_bitmap_stable = _heap->old_generation()->is_mark_complete();
765 log_debug(gc, remset)("Update refs, scan remembered set using bitmap: %s", BOOL_TO_STR(old_bitmap_stable));
766 }
767
768 void work(uint worker_id) {
769 if (CONCURRENT) {
770 ShenandoahConcurrentWorkerSession worker_session(worker_id);
771 ShenandoahSuspendibleThreadSetJoiner stsj;
772 do_work<ShenandoahConcUpdateRefsClosure>(worker_id);
773 } else {
774 ShenandoahParallelWorkerSession worker_session(worker_id);
775 do_work<ShenandoahSTWUpdateRefsClosure>(worker_id);
776 }
777 }
778
779 private:
780 template<class T>
781 void do_work(uint worker_id) {
782 T cl;
783
784 if (CONCURRENT && (worker_id == 0)) {
785 // We ask the first worker to replenish the Mutator free set by moving regions previously reserved to hold the
786 // results of evacuation. These reserves are no longer necessary because evacuation has completed.
787 size_t cset_regions = _heap->collection_set()->count();
788 // We cannot transfer any more regions than will be reclaimed when the existing collection set is recycled, because
789 // we need the reclaimed collection set regions to replenish the collector reserves
790 _heap->free_set()->move_collector_sets_to_mutator(cset_regions);
791 }
792 // If !CONCURRENT, there's no value in expanding Mutator free set
793
794 ShenandoahHeapRegion* r = _regions->next();
795 // We update references for global, old, and young collections.
796 ShenandoahGeneration* const gc_generation = _heap->gc_generation();
797 shenandoah_assert_generations_reconciled();
798 assert(gc_generation->is_mark_complete(), "Expected complete marking");
799 ShenandoahMarkingContext* const ctx = _heap->marking_context();
800 bool is_mixed = _heap->collection_set()->has_old_regions();
801 while (r != nullptr) {
802 HeapWord* update_watermark = r->get_update_watermark();
803 assert (update_watermark >= r->bottom(), "sanity");
804
805 log_debug(gc)("Update refs worker " UINT32_FORMAT ", looking at region " SIZE_FORMAT, worker_id, r->index());
806 bool region_progress = false;
807 if (r->is_active() && !r->is_cset()) {
808 if (r->is_young()) {
809 _heap->marked_object_oop_iterate(r, &cl, update_watermark);
810 region_progress = true;
811 } else if (r->is_old()) {
812 if (gc_generation->is_global()) {
813 // Note that GLOBAL collection is not as effectively balanced as young and mixed cycles. This is because
814 // concurrent GC threads are parceled out entire heap regions of work at a time and there
815 // is no "catchup phase" consisting of remembered set scanning, during which parcels of work are smaller
816 // and more easily distributed more fairly across threads.
817
818 // TODO: Consider an improvement to load balance GLOBAL GC.
819 _heap->marked_object_oop_iterate(r, &cl, update_watermark);
820 region_progress = true;
821 }
822 // Otherwise, this is an old region in a young or mixed cycle. Process it during a second phase, below.
823 // Don't bother to report pacing progress in this case.
824 } else {
825 // Because updating of references runs concurrently, it is possible that a FREE inactive region transitions
826 // to a non-free active region while this loop is executing. Whenever this happens, the changing of a region's
827 // active status may propagate at a different speed than the changing of the region's affiliation.
828
829 // When we reach this control point, it is because a race has allowed a region's is_active() status to be seen
830 // by this thread before the region's affiliation() is seen by this thread.
831
832 // It's ok for this race to occur because the newly transformed region does not have any references to be
833 // updated.
834
835 assert(r->get_update_watermark() == r->bottom(),
836 "%s Region " SIZE_FORMAT " is_active but not recognized as YOUNG or OLD so must be newly transitioned from FREE",
837 r->affiliation_name(), r->index());
838 }
839 }
840 if (region_progress && ShenandoahPacing) {
841 _heap->pacer()->report_updaterefs(pointer_delta(update_watermark, r->bottom()));
842 }
843 if (_heap->check_cancelled_gc_and_yield(CONCURRENT)) {
844 return;
845 }
846 r = _regions->next();
847 }
848
849 if (!gc_generation->is_global()) {
850 // Since this is generational and not GLOBAL, we have to process the remembered set. There's no remembered
851 // set processing if not in generational mode or if GLOBAL mode.
852
853 // After this thread has exhausted its traditional update-refs work, it continues with updating refs within remembered set.
854 // The remembered set workload is better balanced between threads, so threads that are "behind" can catch up with other
855 // threads during this phase, allowing all threads to work more effectively in parallel.
856 struct ShenandoahRegionChunk assignment;
857 RememberedScanner* scanner = _heap->old_generation()->card_scan();
858
859 while (!_heap->check_cancelled_gc_and_yield(CONCURRENT) && _work_chunks->next(&assignment)) {
860 // Keep grabbing next work chunk to process until finished, or asked to yield
861 ShenandoahHeapRegion* r = assignment._r;
862 if (r->is_active() && !r->is_cset() && r->is_old()) {
863 HeapWord* start_of_range = r->bottom() + assignment._chunk_offset;
864 HeapWord* end_of_range = r->get_update_watermark();
865 if (end_of_range > start_of_range + assignment._chunk_size) {
866 end_of_range = start_of_range + assignment._chunk_size;
867 }
868
869 // Old region in a young cycle or mixed cycle.
870 if (is_mixed) {
871 // TODO: For mixed evac, consider building an old-gen remembered set that allows restricted updating
872 // within old-gen HeapRegions. This remembered set can be constructed by old-gen concurrent marking
873 // and augmented by card marking. For example, old-gen concurrent marking can remember for each old-gen
874 // card which other old-gen regions it refers to: none, one-other specifically, multiple-other non-specific.
875 // Update-references when _mixed_evac processess each old-gen memory range that has a traditional DIRTY
876 // card or if the "old-gen remembered set" indicates that this card holds pointers specifically to an
877 // old-gen region in the most recent collection set, or if this card holds pointers to other non-specific
878 // old-gen heap regions.
879
880 if (r->is_humongous()) {
881 if (start_of_range < end_of_range) {
882 // Need to examine both dirty and clean cards during mixed evac.
883 r->oop_iterate_humongous_slice(&cl, false, start_of_range, assignment._chunk_size, true);
884 }
885 } else {
886 // Since this is mixed evacuation, old regions that are candidates for collection have not been coalesced
887 // and filled. Use mark bits to find objects that need to be updated.
888 //
889 // Future TODO: establish a second remembered set to identify which old-gen regions point to other old-gen
890 // regions which are in the collection set for a particular mixed evacuation.
891 if (start_of_range < end_of_range) {
892 HeapWord* p = nullptr;
893 size_t card_index = scanner->card_index_for_addr(start_of_range);
894 // In case last object in my range spans boundary of my chunk, I may need to scan all the way to top()
895 ShenandoahObjectToOopBoundedClosure<T> objs(&cl, start_of_range, r->top());
896
897 // Any object that begins in a previous range is part of a different scanning assignment. Any object that
898 // starts after end_of_range is also not my responsibility. (Either allocated during evacuation, so does
899 // not hold pointers to from-space, or is beyond the range of my assigned work chunk.)
900
901 // Find the first object that begins in my range, if there is one.
902 p = start_of_range;
903 oop obj = cast_to_oop(p);
904 HeapWord* tams = ctx->top_at_mark_start(r);
905 if (p >= tams) {
906 // We cannot use ctx->is_marked(obj) to test whether an object begins at this address. Instead,
907 // we need to use the remembered set crossing map to advance p to the first object that starts
908 // within the enclosing card.
909
910 while (true) {
911 HeapWord* first_object = scanner->first_object_in_card(card_index);
912 if (first_object != nullptr) {
913 p = first_object;
914 break;
915 } else if (scanner->addr_for_card_index(card_index + 1) < end_of_range) {
916 card_index++;
917 } else {
918 // Force the loop that follows to immediately terminate.
919 p = end_of_range;
920 break;
921 }
922 }
923 obj = cast_to_oop(p);
924 // Note: p may be >= end_of_range
925 } else if (!ctx->is_marked(obj)) {
926 p = ctx->get_next_marked_addr(p, tams);
927 obj = cast_to_oop(p);
928 // If there are no more marked objects before tams, this returns tams.
929 // Note that tams is either >= end_of_range, or tams is the start of an object that is marked.
930 }
931 while (p < end_of_range) {
932 // p is known to point to the beginning of marked object obj
933 objs.do_object(obj);
934 HeapWord* prev_p = p;
935 p += obj->size();
936 if (p < tams) {
937 p = ctx->get_next_marked_addr(p, tams);
938 // If there are no more marked objects before tams, this returns tams. Note that tams is
939 // either >= end_of_range, or tams is the start of an object that is marked.
940 }
941 assert(p != prev_p, "Lack of forward progress");
942 obj = cast_to_oop(p);
943 }
944 }
945 }
946 } else {
947 // This is a young evac..
948 if (start_of_range < end_of_range) {
949 size_t cluster_size =
950 CardTable::card_size_in_words() * ShenandoahCardCluster<ShenandoahDirectCardMarkRememberedSet>::CardsPerCluster;
951 size_t clusters = assignment._chunk_size / cluster_size;
952 assert(clusters * cluster_size == assignment._chunk_size, "Chunk assignment must align on cluster boundaries");
953 scanner->process_region_slice(r, assignment._chunk_offset, clusters, end_of_range, &cl, true, worker_id);
954 }
955 }
956 if (ShenandoahPacing && (start_of_range < end_of_range)) {
957 _heap->pacer()->report_updaterefs(pointer_delta(end_of_range, start_of_range));
958 }
959 }
960 }
961 }
962 }
963 };
964
965 void ShenandoahGenerationalHeap::update_heap_references(bool concurrent) {
966 assert(!is_full_gc_in_progress(), "Only for concurrent and degenerated GC");
967 const uint nworkers = workers()->active_workers();
968 ShenandoahRegionChunkIterator work_list(nworkers);
969 if (concurrent) {
970 ShenandoahGenerationalUpdateHeapRefsTask<true> task(&_update_refs_iterator, &work_list);
971 workers()->run_task(&task);
972 } else {
973 ShenandoahGenerationalUpdateHeapRefsTask<false> task(&_update_refs_iterator, &work_list);
974 workers()->run_task(&task);
975 }
976
977 if (ShenandoahEnableCardStats) {
978 // Only do this if we are collecting card stats
979 RememberedScanner* card_scan = old_generation()->card_scan();
980 assert(card_scan != nullptr, "Card table must exist when card stats are enabled");
981 card_scan->log_card_stats(nworkers, CARD_STAT_UPDATE_REFS);
982 }
983 }
984
985 namespace ShenandoahCompositeRegionClosure {
986 template<typename C1, typename C2>
987 class Closure : public ShenandoahHeapRegionClosure {
988 private:
989 C1 &_c1;
990 C2 &_c2;
991
992 public:
993 Closure(C1 &c1, C2 &c2) : ShenandoahHeapRegionClosure(), _c1(c1), _c2(c2) {}
994
995 void heap_region_do(ShenandoahHeapRegion* r) override {
996 _c1.heap_region_do(r);
997 _c2.heap_region_do(r);
998 }
999
1000 bool is_thread_safe() override {
1001 return _c1.is_thread_safe() && _c2.is_thread_safe();
1002 }
1003 };
1004
1005
1006 template<typename C1, typename C2>
1007 Closure<C1, C2> of(C1 &c1, C2 &c2) {
1008 return Closure<C1, C2>(c1, c2);
1009 }
1010 }
1011
1012 class ShenandoahUpdateRegionAges : public ShenandoahHeapRegionClosure {
1013 private:
1014 ShenandoahMarkingContext* _ctx;
1015
1016 public:
1017 explicit ShenandoahUpdateRegionAges(ShenandoahMarkingContext* ctx) : _ctx(ctx) { }
1018
1019 void heap_region_do(ShenandoahHeapRegion* r) override {
1020 // Maintenance of region age must follow evacuation in order to account for
1021 // evacuation allocations within survivor regions. We consult region age during
1022 // the subsequent evacuation to determine whether certain objects need to
1023 // be promoted.
1024 if (r->is_young() && r->is_active()) {
1025 HeapWord *tams = _ctx->top_at_mark_start(r);
1026 HeapWord *top = r->top();
1027
1028 // Allocations move the watermark when top moves. However, compacting
1029 // objects will sometimes lower top beneath the watermark, after which,
1030 // attempts to read the watermark will assert out (watermark should not be
1031 // higher than top).
1032 if (top > tams) {
1033 // There have been allocations in this region since the start of the cycle.
1034 // Any objects new to this region must not assimilate elevated age.
1035 r->reset_age();
1036 } else if (ShenandoahGenerationalHeap::heap()->is_aging_cycle()) {
1037 r->increment_age();
1038 }
1039 }
1040 }
1041
1042 bool is_thread_safe() override {
1043 return true;
1044 }
1045 };
1046
1047 void ShenandoahGenerationalHeap::final_update_refs_update_region_states() {
1048 ShenandoahSynchronizePinnedRegionStates pins;
1049 ShenandoahUpdateRegionAges ages(active_generation()->complete_marking_context());
1050 auto cl = ShenandoahCompositeRegionClosure::of(pins, ages);
1051 parallel_heap_region_iterate(&cl);
1052 }
1053
1054 void ShenandoahGenerationalHeap::complete_degenerated_cycle() {
1055 shenandoah_assert_heaplocked_or_safepoint();
1056 if (is_concurrent_old_mark_in_progress()) {
1057 // This is still necessary for degenerated cycles because the degeneration point may occur
1058 // after final mark of the young generation. See ShenandoahConcurrentGC::op_final_updaterefs for
1059 // a more detailed explanation.
1060 old_generation()->transfer_pointers_from_satb();
1061 }
1062
1063 // We defer generation resizing actions until after cset regions have been recycled.
1064 TransferResult result = balance_generations();
1065 LogTarget(Info, gc, ergo) lt;
1066 if (lt.is_enabled()) {
1067 LogStream ls(lt);
1068 result.print_on("Degenerated GC", &ls);
1069 }
1070
1071 // In case degeneration interrupted concurrent evacuation or update references, we need to clean up
1072 // transient state. Otherwise, these actions have no effect.
1073 reset_generation_reserves();
1074
1075 if (!old_generation()->is_parseable()) {
1076 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_coalesce_and_fill);
1077 coalesce_and_fill_old_regions(false);
1078 }
1079 }
1080
1081 void ShenandoahGenerationalHeap::complete_concurrent_cycle() {
1082 if (!old_generation()->is_parseable()) {
1083 // Class unloading may render the card offsets unusable, so we must rebuild them before
1084 // the next remembered set scan. We _could_ let the control thread do this sometime after
1085 // the global cycle has completed and before the next young collection, but under memory
1086 // pressure the control thread may not have the time (that is, because it's running back
1087 // to back GCs). In that scenario, we would have to make the old regions parsable before
1088 // we could start a young collection. This could delay the start of the young cycle and
1089 // throw off the heuristics.
1090 entry_global_coalesce_and_fill();
1091 }
1092
1093 TransferResult result;
1094 {
1095 ShenandoahHeapLocker locker(lock());
1096
1097 result = balance_generations();
1098 reset_generation_reserves();
1099 }
1100
1101 LogTarget(Info, gc, ergo) lt;
1102 if (lt.is_enabled()) {
1103 LogStream ls(lt);
1104 result.print_on("Concurrent GC", &ls);
1105 }
1106 }
1107
1108 void ShenandoahGenerationalHeap::entry_global_coalesce_and_fill() {
1109 const char* msg = "Coalescing and filling old regions";
1110 ShenandoahConcurrentPhase gc_phase(msg, ShenandoahPhaseTimings::conc_coalesce_and_fill);
1111
1112 TraceCollectorStats tcs(monitoring_support()->concurrent_collection_counters());
1113 EventMark em("%s", msg);
1114 ShenandoahWorkerScope scope(workers(),
1115 ShenandoahWorkerPolicy::calc_workers_for_conc_marking(),
1116 "concurrent coalesce and fill");
1117
1118 coalesce_and_fill_old_regions(true);
1119 }
1120
1121 void ShenandoahGenerationalHeap::update_region_ages(ShenandoahMarkingContext* ctx) {
1122 ShenandoahUpdateRegionAges cl(ctx);
1123 parallel_heap_region_iterate(&cl);
1124 }