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/shenandoahCollectorPolicy.hpp"
28 #include "gc/shenandoah/shenandoahFreeSet.hpp"
29 #include "gc/shenandoah/shenandoahGenerationalControlThread.hpp"
30 #include "gc/shenandoah/shenandoahGenerationalEvacuationTask.hpp"
31 #include "gc/shenandoah/shenandoahGenerationalHeap.hpp"
32 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
33 #include "gc/shenandoah/shenandoahHeapRegion.hpp"
34 #include "gc/shenandoah/shenandoahInitLogger.hpp"
35 #include "gc/shenandoah/shenandoahMemoryPool.hpp"
36 #include "gc/shenandoah/shenandoahOldGeneration.hpp"
37 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
38 #include "gc/shenandoah/shenandoahRegulatorThread.hpp"
39 #include "gc/shenandoah/shenandoahScanRemembered.inline.hpp"
40 #include "gc/shenandoah/shenandoahYoungGeneration.hpp"
41 #include "gc/shenandoah/shenandoahUtils.hpp"
42 #include "logging/log.hpp"
43
44
45 class ShenandoahGenerationalInitLogger : public ShenandoahInitLogger {
46 public:
47 static void print() {
48 ShenandoahGenerationalInitLogger logger;
49 logger.print_all();
50 }
51
52 void print_heap() override {
53 ShenandoahInitLogger::print_heap();
54
55 ShenandoahGenerationalHeap* heap = ShenandoahGenerationalHeap::heap();
56
57 ShenandoahYoungGeneration* young = heap->young_generation();
58 log_info(gc, init)("Young Generation Soft Size: " EXACTFMT, EXACTFMTARGS(young->soft_max_capacity()));
59 log_info(gc, init)("Young Generation Max: " EXACTFMT, EXACTFMTARGS(young->max_capacity()));
60
61 ShenandoahOldGeneration* old = heap->old_generation();
62 log_info(gc, init)("Old Generation Soft Size: " EXACTFMT, EXACTFMTARGS(old->soft_max_capacity()));
63 log_info(gc, init)("Old Generation Max: " EXACTFMT, EXACTFMTARGS(old->max_capacity()));
64 }
65
66 protected:
67 void print_gc_specific() override {
68 ShenandoahInitLogger::print_gc_specific();
69
70 ShenandoahGenerationalHeap* heap = ShenandoahGenerationalHeap::heap();
71 log_info(gc, init)("Young Heuristics: %s", heap->young_generation()->heuristics()->name());
72 log_info(gc, init)("Old Heuristics: %s", heap->old_generation()->heuristics()->name());
73 }
74 };
75
76 ShenandoahGenerationalHeap* ShenandoahGenerationalHeap::heap() {
77 shenandoah_assert_generational();
78 CollectedHeap* heap = Universe::heap();
79 return checked_cast<ShenandoahGenerationalHeap*>(heap);
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 ((ShenandoahMaxEvacLABRatio > 0)?
89 align_down(MIN2(MaxTLABSizeWords, PLAB::min_size() * ShenandoahMaxEvacLABRatio), CardTable::card_size_in_words()):
90 align_down(MaxTLABSizeWords, CardTable::card_size_in_words()));
91 }
92
93 // Returns size in bytes
94 size_t ShenandoahGenerationalHeap::unsafe_max_tlab_alloc(Thread *thread) const {
95 return MIN2(ShenandoahHeapRegion::max_tlab_size_bytes(), young_generation()->available());
96 }
97
98 ShenandoahGenerationalHeap::ShenandoahGenerationalHeap(ShenandoahCollectorPolicy* policy) :
99 ShenandoahHeap(policy),
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::print_init_logger() const {
110 ShenandoahGenerationalInitLogger logger;
111 logger.print_all();
112 }
113
114 void ShenandoahGenerationalHeap::initialize_serviceability() {
115 assert(mode()->is_generational(), "Only for the generational mode");
116 _young_gen_memory_pool = new ShenandoahYoungGenMemoryPool(this);
117 _old_gen_memory_pool = new ShenandoahOldGenMemoryPool(this);
118 cycle_memory_manager()->add_pool(_young_gen_memory_pool);
119 cycle_memory_manager()->add_pool(_old_gen_memory_pool);
120 stw_memory_manager()->add_pool(_young_gen_memory_pool);
121 stw_memory_manager()->add_pool(_old_gen_memory_pool);
122 }
123
124 GrowableArray<MemoryPool*> ShenandoahGenerationalHeap::memory_pools() {
125 assert(mode()->is_generational(), "Only for the generational mode");
126 GrowableArray<MemoryPool*> memory_pools(2);
127 memory_pools.append(_young_gen_memory_pool);
128 memory_pools.append(_old_gen_memory_pool);
129 return memory_pools;
130 }
131
132 void ShenandoahGenerationalHeap::initialize_controller() {
133 auto control_thread = new ShenandoahGenerationalControlThread();
134 _control_thread = control_thread;
135 _regulator_thread = new ShenandoahRegulatorThread(control_thread);
136 }
137
138 void ShenandoahGenerationalHeap::gc_threads_do(ThreadClosure* tcl) const {
139 if (!shenandoah_policy()->is_at_shutdown()) {
140 ShenandoahHeap::gc_threads_do(tcl);
141 tcl->do_thread(regulator_thread());
142 }
143 }
144
145 void ShenandoahGenerationalHeap::stop() {
146 regulator_thread()->stop();
147 ShenandoahHeap::stop();
148 }
149
150 oop ShenandoahGenerationalHeap::evacuate_object(oop p, Thread* thread) {
151 assert(thread == Thread::current(), "Expected thread parameter to be current thread.");
152 if (ShenandoahThreadLocalData::is_oom_during_evac(thread)) {
153 // This thread went through the OOM during evac protocol and it is safe to return
154 // the forward pointer. It must not attempt to evacuate anymore.
155 return ShenandoahBarrierSet::resolve_forwarded(p);
156 }
157
158 assert(ShenandoahThreadLocalData::is_evac_allowed(thread), "must be enclosed in oom-evac scope");
159
160 ShenandoahHeapRegion* r = heap_region_containing(p);
161 assert(!r->is_humongous(), "never evacuate humongous objects");
162
163 ShenandoahAffiliation target_gen = r->affiliation();
164 if (active_generation()->is_young() && target_gen == YOUNG_GENERATION) {
165 markWord mark = p->mark();
166 if (mark.is_marked()) {
167 // Already forwarded.
168 return ShenandoahBarrierSet::resolve_forwarded(p);
169 }
170
171 if (mark.has_displaced_mark_helper()) {
172 // We don't want to deal with MT here just to ensure we read the right mark word.
173 // Skip the potential promotion attempt for this one.
174 } else if (r->age() + mark.age() >= age_census()->tenuring_threshold()) {
175 oop result = try_evacuate_object(p, thread, r, OLD_GENERATION);
176 if (result != nullptr) {
177 return result;
178 }
179 // If we failed to promote this aged object, we'll fall through to code below and evacuate to young-gen.
180 }
181 }
182 return try_evacuate_object(p, thread, r, target_gen);
183 }
184
185 // try_evacuate_object registers the object and dirties the associated remembered set information when evacuating
186 // to OLD_GENERATION.
187 oop ShenandoahGenerationalHeap::try_evacuate_object(oop p, Thread* thread, ShenandoahHeapRegion* from_region,
188 ShenandoahAffiliation target_gen) {
189 bool alloc_from_lab = true;
190 bool has_plab = false;
191 HeapWord* copy = nullptr;
192 size_t size = p->size();
193 bool is_promotion = (target_gen == OLD_GENERATION) && from_region->is_young();
194
195 #ifdef ASSERT
196 if (ShenandoahOOMDuringEvacALot &&
197 (os::random() & 1) == 0) { // Simulate OOM every ~2nd slow-path call
198 copy = nullptr;
199 } else {
200 #endif
201 if (UseTLAB) {
202 switch (target_gen) {
203 case YOUNG_GENERATION: {
204 copy = allocate_from_gclab(thread, size);
205 if ((copy == nullptr) && (size < ShenandoahThreadLocalData::gclab_size(thread))) {
206 // GCLAB allocation failed because we are bumping up against the limit on young evacuation reserve. Try resetting
207 // the desired GCLAB size and retry GCLAB allocation to avoid cascading of shared memory allocations.
208 ShenandoahThreadLocalData::set_gclab_size(thread, PLAB::min_size());
209 copy = allocate_from_gclab(thread, size);
210 // If we still get nullptr, we'll try a shared allocation below.
211 }
212 break;
213 }
214 case OLD_GENERATION: {
215 assert(mode()->is_generational(), "OLD Generation only exists in generational mode");
216 PLAB* plab = ShenandoahThreadLocalData::plab(thread);
217 if (plab != nullptr) {
218 has_plab = true;
219 }
220 copy = allocate_from_plab(thread, size, is_promotion);
221 if ((copy == nullptr) && (size < ShenandoahThreadLocalData::plab_size(thread)) &&
222 ShenandoahThreadLocalData::plab_retries_enabled(thread)) {
223 // PLAB allocation failed because we are bumping up against the limit on old evacuation reserve or because
224 // the requested object does not fit within the current plab but the plab still has an "abundance" of memory,
225 // where abundance is defined as >= ShenGenHeap::plab_min_size(). In the former case, we try resetting the desired
226 // PLAB size and retry PLAB allocation to avoid cascading of shared memory allocations.
227
228 // In this situation, PLAB memory is precious. We'll try to preserve our existing PLAB by forcing
229 // this particular allocation to be shared.
230 if (plab->words_remaining() < plab_min_size()) {
231 ShenandoahThreadLocalData::set_plab_size(thread, plab_min_size());
232 copy = allocate_from_plab(thread, size, is_promotion);
233 // If we still get nullptr, we'll try a shared allocation below.
234 if (copy == nullptr) {
235 // If retry fails, don't continue to retry until we have success (probably in next GC pass)
236 ShenandoahThreadLocalData::disable_plab_retries(thread);
237 }
238 }
239 // else, copy still equals nullptr. this causes shared allocation below, preserving this plab for future needs.
240 }
241 break;
242 }
243 default: {
244 ShouldNotReachHere();
245 break;
246 }
247 }
248 }
249
250 if (copy == nullptr) {
251 // If we failed to allocate in LAB, we'll try a shared allocation.
252 if (!is_promotion || !has_plab || (size > PLAB::min_size())) {
253 ShenandoahAllocRequest req = ShenandoahAllocRequest::for_shared_gc(size, target_gen, is_promotion);
254 copy = allocate_memory(req);
255 alloc_from_lab = false;
256 }
257 // else, we leave copy equal to nullptr, signaling a promotion failure below if appropriate.
258 // We choose not to promote objects smaller than PLAB::min_size() by way of shared allocations, as this is too
259 // costly. Instead, we'll simply "evacuate" to young-gen memory (using a GCLAB) and will promote in a future
260 // evacuation pass. This condition is denoted by: is_promotion && has_plab && (size <= PLAB::min_size())
261 }
262 #ifdef ASSERT
263 }
264 #endif
265
266 if (copy == nullptr) {
267 if (target_gen == OLD_GENERATION) {
268 if (from_region->is_young()) {
269 // Signal that promotion failed. Will evacuate this old object somewhere in young gen.
270 old_generation()->handle_failed_promotion(thread, size);
271 return nullptr;
272 } else {
273 // Remember that evacuation to old gen failed. We'll want to trigger a full gc to recover from this
274 // after the evacuation threads have finished.
275 old_generation()->handle_failed_evacuation();
276 }
277 }
278
279 control_thread()->handle_alloc_failure_evac(size);
280
281 oom_evac_handler()->handle_out_of_memory_during_evacuation();
282
283 return ShenandoahBarrierSet::resolve_forwarded(p);
284 }
285
286 // Copy the object:
287 evac_tracker()->begin_evacuation(thread, size * HeapWordSize);
288 Copy::aligned_disjoint_words(cast_from_oop<HeapWord*>(p), copy, size);
289
290 oop copy_val = cast_to_oop(copy);
291
292 if (target_gen == YOUNG_GENERATION && is_aging_cycle()) {
293 ShenandoahHeap::increase_object_age(copy_val, from_region->age() + 1);
294 }
295
296 // Try to install the new forwarding pointer.
297 ContinuationGCSupport::relativize_stack_chunk(copy_val);
298
299 oop result = ShenandoahForwarding::try_update_forwardee(p, copy_val);
300 if (result == copy_val) {
301 // Successfully evacuated. Our copy is now the public one!
302 evac_tracker()->end_evacuation(thread, size * HeapWordSize);
303 if (target_gen == OLD_GENERATION) {
304 old_generation()->handle_evacuation(copy, size, from_region->is_young());
305 } else {
306 // When copying to the old generation above, we don't care
307 // about recording object age in the census stats.
308 assert(target_gen == YOUNG_GENERATION, "Error");
309 // We record this census only when simulating pre-adaptive tenuring behavior, or
310 // when we have been asked to record the census at evacuation rather than at mark
311 if (ShenandoahGenerationalCensusAtEvac || !ShenandoahGenerationalAdaptiveTenuring) {
312 evac_tracker()->record_age(thread, size * HeapWordSize, ShenandoahHeap::get_object_age(copy_val));
313 }
314 }
315 shenandoah_assert_correct(nullptr, copy_val);
316 return copy_val;
317 } else {
318 // Failed to evacuate. We need to deal with the object that is left behind. Since this
319 // new allocation is certainly after TAMS, it will be considered live in the next cycle.
320 // But if it happens to contain references to evacuated regions, those references would
321 // not get updated for this stale copy during this cycle, and we will crash while scanning
322 // it the next cycle.
323 if (alloc_from_lab) {
324 // For LAB allocations, it is enough to rollback the allocation ptr. Either the next
325 // object will overwrite this stale copy, or the filler object on LAB retirement will
326 // do this.
327 switch (target_gen) {
328 case YOUNG_GENERATION: {
329 ShenandoahThreadLocalData::gclab(thread)->undo_allocation(copy, size);
330 break;
331 }
332 case OLD_GENERATION: {
333 ShenandoahThreadLocalData::plab(thread)->undo_allocation(copy, size);
334 if (is_promotion) {
335 ShenandoahThreadLocalData::subtract_from_plab_promoted(thread, size * HeapWordSize);
336 } else {
337 ShenandoahThreadLocalData::subtract_from_plab_evacuated(thread, size * HeapWordSize);
338 }
339 break;
340 }
341 default: {
342 ShouldNotReachHere();
343 break;
344 }
345 }
346 } else {
347 // For non-LAB allocations, we have no way to retract the allocation, and
348 // have to explicitly overwrite the copy with the filler object. With that overwrite,
349 // we have to keep the fwdptr initialized and pointing to our (stale) copy.
350 assert(size >= ShenandoahHeap::min_fill_size(), "previously allocated object known to be larger than min_size");
351 fill_with_object(copy, size);
352 shenandoah_assert_correct(nullptr, copy_val);
353 // For non-LAB allocations, the object has already been registered
354 }
355 shenandoah_assert_correct(nullptr, result);
356 return result;
357 }
358 }
359
360 inline HeapWord* ShenandoahGenerationalHeap::allocate_from_plab(Thread* thread, size_t size, bool is_promotion) {
361 assert(UseTLAB, "TLABs should be enabled");
362
363 PLAB* plab = ShenandoahThreadLocalData::plab(thread);
364 HeapWord* obj;
365
366 if (plab == nullptr) {
367 assert(!thread->is_Java_thread() && !thread->is_Worker_thread(), "Performance: thread should have PLAB: %s", thread->name());
368 // No PLABs in this thread, fallback to shared allocation
369 return nullptr;
370 } else if (is_promotion && !ShenandoahThreadLocalData::allow_plab_promotions(thread)) {
371 return nullptr;
372 }
373 // if plab->word_size() <= 0, thread's plab not yet initialized for this pass, so allow_plab_promotions() is not trustworthy
374 obj = plab->allocate(size);
375 if ((obj == nullptr) && (plab->words_remaining() < plab_min_size())) {
376 // allocate_from_plab_slow will establish allow_plab_promotions(thread) for future invocations
377 obj = allocate_from_plab_slow(thread, size, is_promotion);
378 }
379 // if plab->words_remaining() >= ShenGenHeap::heap()->plab_min_size(), just return nullptr so we can use a shared allocation
380 if (obj == nullptr) {
381 return nullptr;
382 }
383
384 if (is_promotion) {
385 ShenandoahThreadLocalData::add_to_plab_promoted(thread, size * HeapWordSize);
386 } else {
387 ShenandoahThreadLocalData::add_to_plab_evacuated(thread, size * HeapWordSize);
388 }
389 return obj;
390 }
391
392 // Establish a new PLAB and allocate size HeapWords within it.
393 HeapWord* ShenandoahGenerationalHeap::allocate_from_plab_slow(Thread* thread, size_t size, bool is_promotion) {
394 // New object should fit the PLAB size
395
396 assert(mode()->is_generational(), "PLABs only relevant to generational GC");
397 const size_t plab_min_size = this->plab_min_size();
398 const size_t min_size = (size > plab_min_size)? align_up(size, CardTable::card_size_in_words()): plab_min_size;
399
400 // Figure out size of new PLAB, looking back at heuristics. Expand aggressively. PLABs must align on size
401 // of card table in order to avoid the need for synchronization when registering newly allocated objects within
402 // the card table.
403 size_t cur_size = ShenandoahThreadLocalData::plab_size(thread);
404 if (cur_size == 0) {
405 cur_size = plab_min_size;
406 }
407
408 // Limit growth of PLABs to the smaller of ShenandoahMaxEvacLABRatio * the minimum size and ShenandoahHumongousThreshold.
409 // This minimum value is represented by generational_heap->plab_max_size(). Enforcing this limit enables more equitable
410 // distribution of available evacuation budget between the many threads that are coordinating in the evacuation effort.
411 size_t future_size = MIN2(cur_size * 2, plab_max_size());
412 assert(is_aligned(future_size, CardTable::card_size_in_words()), "Align by design, future_size: " SIZE_FORMAT
413 ", alignment: " SIZE_FORMAT ", cur_size: " SIZE_FORMAT ", max: " SIZE_FORMAT,
414 future_size, (size_t) CardTable::card_size_in_words(), cur_size, plab_max_size());
415
416 // Record new heuristic value even if we take any shortcut. This captures
417 // the case when moderately-sized objects always take a shortcut. At some point,
418 // heuristics should catch up with them. Note that the requested cur_size may
419 // not be honored, but we remember that this is the preferred size.
420 ShenandoahThreadLocalData::set_plab_size(thread, future_size);
421 if (cur_size < size) {
422 // The PLAB to be allocated is still not large enough to hold the object. Fall back to shared allocation.
423 // This avoids retiring perfectly good PLABs in order to represent a single large object allocation.
424 return nullptr;
425 }
426
427 // Retire current PLAB, and allocate a new one.
428 PLAB* plab = ShenandoahThreadLocalData::plab(thread);
429 if (plab->words_remaining() < plab_min_size) {
430 // Retire current PLAB, and allocate a new one.
431 // CAUTION: retire_plab may register the remnant filler object with the remembered set scanner without a lock. This
432 // is safe iff it is assured that each PLAB is a whole-number multiple of card-mark memory size and each PLAB is
433 // aligned with the start of a card's memory range.
434 retire_plab(plab, thread);
435
436 size_t actual_size = 0;
437 // allocate_new_plab resets plab_evacuated and plab_promoted and disables promotions if old-gen available is
438 // less than the remaining evacuation need. It also adjusts plab_preallocated and expend_promoted if appropriate.
439 HeapWord* plab_buf = allocate_new_plab(min_size, cur_size, &actual_size);
440 if (plab_buf == nullptr) {
441 if (min_size == plab_min_size) {
442 // Disable plab promotions for this thread because we cannot even allocate a plab of minimal size. This allows us
443 // to fail faster on subsequent promotion attempts.
444 ShenandoahThreadLocalData::disable_plab_promotions(thread);
445 }
446 return nullptr;
447 } else {
448 ShenandoahThreadLocalData::enable_plab_retries(thread);
449 }
450 // Since the allocated PLAB may have been down-sized for alignment, plab->allocate(size) below may still fail.
451 if (ZeroTLAB) {
452 // ... and clear it.
453 Copy::zero_to_words(plab_buf, actual_size);
454 } else {
455 // ...and zap just allocated object.
456 #ifdef ASSERT
457 // Skip mangling the space corresponding to the object header to
458 // ensure that the returned space is not considered parsable by
459 // any concurrent GC thread.
460 size_t hdr_size = oopDesc::header_size();
461 Copy::fill_to_words(plab_buf + hdr_size, actual_size - hdr_size, badHeapWordVal);
462 #endif // ASSERT
463 }
464 assert(is_aligned(actual_size, CardTable::card_size_in_words()), "Align by design");
465 plab->set_buf(plab_buf, actual_size);
466 if (is_promotion && !ShenandoahThreadLocalData::allow_plab_promotions(thread)) {
467 return nullptr;
468 }
469 return plab->allocate(size);
470 } else {
471 // If there's still at least min_size() words available within the current plab, don't retire it. Let's gnaw
472 // away on this plab as long as we can. Meanwhile, return nullptr to force this particular allocation request
473 // to be satisfied with a shared allocation. By packing more promotions into the previously allocated PLAB, we
474 // reduce the likelihood of evacuation failures, and we reduce the need for downsizing our PLABs.
475 return nullptr;
476 }
477 }
478
479 HeapWord* ShenandoahGenerationalHeap::allocate_new_plab(size_t min_size, size_t word_size, size_t* actual_size) {
480 // Align requested sizes to card-sized multiples. Align down so that we don't violate max size of TLAB.
481 assert(is_aligned(min_size, CardTable::card_size_in_words()), "Align by design");
482 assert(word_size >= min_size, "Requested PLAB is too small");
483
484 ShenandoahAllocRequest req = ShenandoahAllocRequest::for_plab(min_size, word_size);
485 // Note that allocate_memory() sets a thread-local flag to prohibit further promotions by this thread
486 // if we are at risk of infringing on the old-gen evacuation budget.
487 HeapWord* res = allocate_memory(req);
488 if (res != nullptr) {
489 *actual_size = req.actual_size();
490 } else {
491 *actual_size = 0;
492 }
493 assert(is_aligned(res, CardTable::card_size_in_words()), "Align by design");
494 return res;
495 }
496
497 // TODO: It is probably most efficient to register all objects (both promotions and evacuations) that were allocated within
498 // this plab at the time we retire the plab. A tight registration loop will run within both code and data caches. This change
499 // would allow smaller and faster in-line implementation of alloc_from_plab(). Since plabs are aligned on card-table boundaries,
500 // this object registration loop can be performed without acquiring a lock.
501 void ShenandoahGenerationalHeap::retire_plab(PLAB* plab, Thread* thread) {
502 // We don't enforce limits on plab_evacuated. We let it consume all available old-gen memory in order to reduce
503 // probability of an evacuation failure. We do enforce limits on promotion, to make sure that excessive promotion
504 // does not result in an old-gen evacuation failure. Note that a failed promotion is relatively harmless. Any
505 // object that fails to promote in the current cycle will be eligible for promotion in a subsequent cycle.
506
507 // When the plab was instantiated, its entirety was treated as if the entire buffer was going to be dedicated to
508 // promotions. Now that we are retiring the buffer, we adjust for the reality that the plab is not entirely promotions.
509 // 1. Some of the plab may have been dedicated to evacuations.
510 // 2. Some of the plab may have been abandoned due to waste (at the end of the plab).
511 size_t not_promoted =
512 ShenandoahThreadLocalData::get_plab_preallocated_promoted(thread) - ShenandoahThreadLocalData::get_plab_promoted(thread);
513 ShenandoahThreadLocalData::reset_plab_promoted(thread);
514 ShenandoahThreadLocalData::reset_plab_evacuated(thread);
515 ShenandoahThreadLocalData::set_plab_preallocated_promoted(thread, 0);
516 if (not_promoted > 0) {
517 old_generation()->unexpend_promoted(not_promoted);
518 }
519 const size_t original_waste = plab->waste();
520 HeapWord* const top = plab->top();
521
522 // plab->retire() overwrites unused memory between plab->top() and plab->hard_end() with a dummy object to make memory parsable.
523 // It adds the size of this unused memory, in words, to plab->waste().
524 plab->retire();
525 if (top != nullptr && plab->waste() > original_waste && is_in_old(top)) {
526 // If retiring the plab created a filler object, then we need to register it with our card scanner so it can
527 // safely walk the region backing the plab.
528 log_debug(gc)("retire_plab() is registering remnant of size " SIZE_FORMAT " at " PTR_FORMAT,
529 plab->waste() - original_waste, p2i(top));
530 card_scan()->register_object_without_lock(top);
531 }
532 }
533
534 void ShenandoahGenerationalHeap::retire_plab(PLAB* plab) {
535 Thread* thread = Thread::current();
536 retire_plab(plab, thread);
537 }
538
539 ShenandoahGenerationalHeap::TransferResult ShenandoahGenerationalHeap::balance_generations() {
540 shenandoah_assert_heaplocked_or_safepoint();
541
542 ShenandoahOldGeneration* old_gen = old_generation();
543 const ssize_t old_region_balance = old_gen->get_region_balance();
544 old_gen->set_region_balance(0);
545
546 if (old_region_balance > 0) {
547 const auto old_region_surplus = checked_cast<size_t>(old_region_balance);
548 const bool success = generation_sizer()->transfer_to_young(old_region_surplus);
549 return TransferResult {
550 success, old_region_surplus, "young"
551 };
552 }
553
554 if (old_region_balance < 0) {
555 const auto old_region_deficit = checked_cast<size_t>(-old_region_balance);
556 const bool success = generation_sizer()->transfer_to_old(old_region_deficit);
557 if (!success) {
558 old_gen->handle_failed_transfer();
559 }
560 return TransferResult {
561 success, old_region_deficit, "old"
562 };
563 }
564
565 return TransferResult {true, 0, "none"};
566 }
567
568 // Make sure old-generation is large enough, but no larger than is necessary, to hold mixed evacuations
569 // and promotions, if we anticipate either. Any deficit is provided by the young generation, subject to
570 // xfer_limit, and any surplus is transferred to the young generation.
571 // xfer_limit is the maximum we're able to transfer from young to old.
572 void ShenandoahGenerationalHeap::compute_old_generation_balance(size_t old_xfer_limit, size_t old_cset_regions) {
573
574 // We can limit the old reserve to the size of anticipated promotions:
575 // max_old_reserve is an upper bound on memory evacuated from old and promoted to old,
576 // clamped by the old generation space available.
577 //
578 // Here's the algebra.
579 // Let SOEP = ShenandoahOldEvacRatioPercent,
580 // OE = old evac,
581 // YE = young evac, and
582 // TE = total evac = OE + YE
583 // By definition:
584 // SOEP/100 = OE/TE
585 // = OE/(OE+YE)
586 // => SOEP/(100-SOEP) = OE/((OE+YE)-OE) // componendo-dividendo: If a/b = c/d, then a/(b-a) = c/(d-c)
587 // = OE/YE
588 // => OE = YE*SOEP/(100-SOEP)
589
590 // We have to be careful in the event that SOEP is set to 100 by the user.
591 assert(ShenandoahOldEvacRatioPercent <= 100, "Error");
592 const size_t old_available = old_generation()->available();
593 // The free set will reserve this amount of memory to hold young evacuations
594 const size_t young_reserve = (young_generation()->max_capacity() * ShenandoahEvacReserve) / 100;
595
596 // In the case that ShenandoahOldEvacRatioPercent equals 100, max_old_reserve is limited only by xfer_limit.
597
598 const size_t bound_on_old_reserve = old_available + old_xfer_limit + young_reserve;
599 const size_t max_old_reserve = (ShenandoahOldEvacRatioPercent == 100)?
600 bound_on_old_reserve: MIN2((young_reserve * ShenandoahOldEvacRatioPercent) / (100 - ShenandoahOldEvacRatioPercent),
601 bound_on_old_reserve);
602
603 const size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
604
605 // Decide how much old space we should reserve for a mixed collection
606 size_t reserve_for_mixed = 0;
607 if (old_generation()->has_unprocessed_collection_candidates()) {
608 // We want this much memory to be unfragmented in order to reliably evacuate old. This is conservative because we
609 // may not evacuate the entirety of unprocessed candidates in a single mixed evacuation.
610 const size_t max_evac_need = (size_t)
611 (old_generation()->unprocessed_collection_candidates_live_memory() * ShenandoahOldEvacWaste);
612 assert(old_available >= old_generation()->free_unaffiliated_regions() * region_size_bytes,
613 "Unaffiliated available must be less than total available");
614 const size_t old_fragmented_available =
615 old_available - old_generation()->free_unaffiliated_regions() * region_size_bytes;
616 reserve_for_mixed = max_evac_need + old_fragmented_available;
617 if (reserve_for_mixed > max_old_reserve) {
618 reserve_for_mixed = max_old_reserve;
619 }
620 }
621
622 // Decide how much space we should reserve for promotions from young
623 size_t reserve_for_promo = 0;
624 const size_t promo_load = old_generation()->get_promotion_potential();
625 const bool doing_promotions = promo_load > 0;
626 if (doing_promotions) {
627 // We're promoting and have a bound on the maximum amount that can be promoted
628 assert(max_old_reserve >= reserve_for_mixed, "Sanity");
629 const size_t available_for_promotions = max_old_reserve - reserve_for_mixed;
630 reserve_for_promo = MIN2((size_t)(promo_load * ShenandoahPromoEvacWaste), available_for_promotions);
631 }
632
633 // This is the total old we want to ideally reserve
634 const size_t old_reserve = reserve_for_mixed + reserve_for_promo;
635 assert(old_reserve <= max_old_reserve, "cannot reserve more than max for old evacuations");
636
637 // We now check if the old generation is running a surplus or a deficit.
638 const size_t max_old_available = old_generation()->available() + old_cset_regions * region_size_bytes;
639 if (max_old_available >= old_reserve) {
640 // We are running a surplus, so the old region surplus can go to young
641 const size_t old_surplus = (max_old_available - old_reserve) / region_size_bytes;
642 const size_t unaffiliated_old_regions = old_generation()->free_unaffiliated_regions() + old_cset_regions;
643 const size_t old_region_surplus = MIN2(old_surplus, unaffiliated_old_regions);
644 old_generation()->set_region_balance(checked_cast<ssize_t>(old_region_surplus));
645 } else {
646 // We are running a deficit which we'd like to fill from young.
647 // Ignore that this will directly impact young_generation()->max_capacity(),
648 // indirectly impacting young_reserve and old_reserve. These computations are conservative.
649 // Note that deficit is rounded up by one region.
650 const size_t old_need = (old_reserve - max_old_available + region_size_bytes - 1) / region_size_bytes;
651 const size_t max_old_region_xfer = old_xfer_limit / region_size_bytes;
652
653 // Round down the regions we can transfer from young to old. If we're running short
654 // on young-gen memory, we restrict the xfer. Old-gen collection activities will be
655 // curtailed if the budget is restricted.
656 const size_t old_region_deficit = MIN2(old_need, max_old_region_xfer);
657 old_generation()->set_region_balance(0 - checked_cast<ssize_t>(old_region_deficit));
658 }
659 }
660
661 void ShenandoahGenerationalHeap::reset_generation_reserves() {
662 young_generation()->set_evacuation_reserve(0);
663 old_generation()->set_evacuation_reserve(0);
664 old_generation()->set_promoted_reserve(0);
665 }
666
667 void ShenandoahGenerationalHeap::TransferResult::print_on(const char* when, outputStream* ss) const {
668 auto heap = ShenandoahGenerationalHeap::heap();
669 ShenandoahYoungGeneration* const young_gen = heap->young_generation();
670 ShenandoahOldGeneration* const old_gen = heap->old_generation();
671 const size_t young_available = young_gen->available();
672 const size_t old_available = old_gen->available();
673 ss->print_cr("After %s, %s " SIZE_FORMAT " regions to %s to prepare for next gc, old available: "
674 PROPERFMT ", young_available: " PROPERFMT,
675 when,
676 success? "successfully transferred": "failed to transfer", region_count, region_destination,
677 PROPERFMTARGS(old_available), PROPERFMTARGS(young_available));
678 }
679
680 void ShenandoahGenerationalHeap::coalesce_and_fill_old_regions(bool concurrent) {
681 class ShenandoahGlobalCoalesceAndFill : public WorkerTask {
682 private:
683 ShenandoahPhaseTimings::Phase _phase;
684 ShenandoahRegionIterator _regions;
685 public:
686 explicit ShenandoahGlobalCoalesceAndFill(ShenandoahPhaseTimings::Phase phase) :
687 WorkerTask("Shenandoah Global Coalesce"),
688 _phase(phase) {}
689
690 void work(uint worker_id) override {
691 ShenandoahWorkerTimingsTracker timer(_phase,
692 ShenandoahPhaseTimings::ScanClusters,
693 worker_id, true);
694 ShenandoahHeapRegion* region;
695 while ((region = _regions.next()) != nullptr) {
696 // old region is not in the collection set and was not immediately trashed
697 if (region->is_old() && region->is_active() && !region->is_humongous()) {
698 // Reset the coalesce and fill boundary because this is a global collect
699 // and cannot be preempted by young collects. We want to be sure the entire
700 // region is coalesced here and does not resume from a previously interrupted
701 // or completed coalescing.
702 region->begin_preemptible_coalesce_and_fill();
703 region->oop_coalesce_and_fill(false);
704 }
705 }
706 }
707 };
708
709 ShenandoahPhaseTimings::Phase phase = concurrent ?
710 ShenandoahPhaseTimings::conc_coalesce_and_fill :
711 ShenandoahPhaseTimings::degen_gc_coalesce_and_fill;
712
713 // This is not cancellable
714 ShenandoahGlobalCoalesceAndFill coalesce(phase);
715 workers()->run_task(&coalesce);
716 old_generation()->set_parseable(true);
717 }
718