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 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
27 #include "gc/shenandoah/shenandoahCollectionSetPreselector.hpp"
28 #include "gc/shenandoah/shenandoahFreeSet.hpp"
29 #include "gc/shenandoah/shenandoahGeneration.hpp"
30 #include "gc/shenandoah/shenandoahGenerationalHeap.hpp"
31 #include "gc/shenandoah/shenandoahMarkClosures.hpp"
32 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
33 #include "gc/shenandoah/shenandoahOldGeneration.hpp"
34 #include "gc/shenandoah/shenandoahReferenceProcessor.hpp"
35 #include "gc/shenandoah/shenandoahScanRemembered.inline.hpp"
36 #include "gc/shenandoah/shenandoahTaskqueue.inline.hpp"
37 #include "gc/shenandoah/shenandoahUtils.hpp"
38 #include "gc/shenandoah/shenandoahVerifier.hpp"
39 #include "gc/shenandoah/shenandoahYoungGeneration.hpp"
40 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
41
42 #include "utilities/quickSort.hpp"
43
44
45 class ShenandoahResetUpdateRegionStateClosure : public ShenandoahHeapRegionClosure {
46 private:
47 ShenandoahHeap* _heap;
48 ShenandoahMarkingContext* const _ctx;
49 public:
50 ShenandoahResetUpdateRegionStateClosure() :
51 _heap(ShenandoahHeap::heap()),
52 _ctx(_heap->marking_context()) {}
53
54 void heap_region_do(ShenandoahHeapRegion* r) override {
55 if (r->is_active()) {
56 // Reset live data and set TAMS optimistically. We would recheck these under the pause
57 // anyway to capture any updates that happened since now.
58 _ctx->capture_top_at_mark_start(r);
59 r->clear_live_data();
60 }
61 }
62
63 bool is_thread_safe() override { return true; }
64 };
65
66 class ShenandoahResetBitmapTask : public WorkerTask {
67 private:
68 ShenandoahRegionIterator _regions;
69 ShenandoahGeneration* _generation;
70
71 public:
72 ShenandoahResetBitmapTask(ShenandoahGeneration* generation) :
73 WorkerTask("Shenandoah Reset Bitmap"), _generation(generation) {}
74
75 void work(uint worker_id) {
76 ShenandoahHeapRegion* region = _regions.next();
77 ShenandoahHeap* heap = ShenandoahHeap::heap();
78 ShenandoahMarkingContext* const ctx = heap->marking_context();
79 while (region != nullptr) {
80 bool needs_reset = _generation->contains(region) || !region->is_affiliated();
81 if (needs_reset && heap->is_bitmap_slice_committed(region)) {
82 ctx->clear_bitmap(region);
83 }
84 region = _regions.next();
85 }
86 }
87 };
88
89 // Copy the write-version of the card-table into the read-version, clearing the
90 // write-copy.
91 class ShenandoahMergeWriteTable: public ShenandoahHeapRegionClosure {
92 private:
93 ShenandoahScanRemembered* _scanner;
94 public:
95 ShenandoahMergeWriteTable(ShenandoahScanRemembered* scanner) : _scanner(scanner) {}
96
97 void heap_region_do(ShenandoahHeapRegion* r) override {
98 assert(r->is_old(), "Don't waste time doing this for non-old regions");
99 _scanner->merge_write_table(r->bottom(), ShenandoahHeapRegion::region_size_words());
100 }
101
102 bool is_thread_safe() override {
103 return true;
104 }
105 };
106
107 class ShenandoahCopyWriteCardTableToRead: public ShenandoahHeapRegionClosure {
108 private:
109 ShenandoahScanRemembered* _scanner;
110 public:
111 ShenandoahCopyWriteCardTableToRead(ShenandoahScanRemembered* scanner) : _scanner(scanner) {}
112
113 void heap_region_do(ShenandoahHeapRegion* region) override {
114 assert(region->is_old(), "Don't waste time doing this for non-old regions");
115 _scanner->reset_remset(region->bottom(), ShenandoahHeapRegion::region_size_words());
116 }
117
118 bool is_thread_safe() override { return true; }
119 };
120
121 void ShenandoahGeneration::confirm_heuristics_mode() {
122 if (_heuristics->is_diagnostic() && !UnlockDiagnosticVMOptions) {
123 vm_exit_during_initialization(
124 err_msg("Heuristics \"%s\" is diagnostic, and must be enabled via -XX:+UnlockDiagnosticVMOptions.",
125 _heuristics->name()));
126 }
127 if (_heuristics->is_experimental() && !UnlockExperimentalVMOptions) {
128 vm_exit_during_initialization(
129 err_msg("Heuristics \"%s\" is experimental, and must be enabled via -XX:+UnlockExperimentalVMOptions.",
130 _heuristics->name()));
131 }
132 }
133
134 ShenandoahHeuristics* ShenandoahGeneration::initialize_heuristics(ShenandoahMode* gc_mode) {
135 _heuristics = gc_mode->initialize_heuristics(this);
136 _heuristics->set_guaranteed_gc_interval(ShenandoahGuaranteedGCInterval);
137 confirm_heuristics_mode();
138 return _heuristics;
139 }
140
141 size_t ShenandoahGeneration::bytes_allocated_since_gc_start() const {
142 return Atomic::load(&_bytes_allocated_since_gc_start);
143 }
144
145 void ShenandoahGeneration::reset_bytes_allocated_since_gc_start() {
146 Atomic::store(&_bytes_allocated_since_gc_start, (size_t)0);
147 }
148
149 void ShenandoahGeneration::increase_allocated(size_t bytes) {
150 Atomic::add(&_bytes_allocated_since_gc_start, bytes, memory_order_relaxed);
151 }
152
153 void ShenandoahGeneration::set_evacuation_reserve(size_t new_val) {
154 _evacuation_reserve = new_val;
155 }
156
157 size_t ShenandoahGeneration::get_evacuation_reserve() const {
158 return _evacuation_reserve;
159 }
160
161 void ShenandoahGeneration::augment_evacuation_reserve(size_t increment) {
162 _evacuation_reserve += increment;
163 }
164
165 void ShenandoahGeneration::log_status(const char *msg) const {
166 typedef LogTarget(Info, gc, ergo) LogGcInfo;
167
168 if (!LogGcInfo::is_enabled()) {
169 return;
170 }
171
172 // Not under a lock here, so read each of these once to make sure
173 // byte size in proper unit and proper unit for byte size are consistent.
174 size_t v_used = used();
175 size_t v_used_regions = used_regions_size();
176 size_t v_soft_max_capacity = soft_max_capacity();
177 size_t v_max_capacity = max_capacity();
178 size_t v_available = available();
179 size_t v_humongous_waste = get_humongous_waste();
180 LogGcInfo::print("%s: %s generation used: " SIZE_FORMAT "%s, used regions: " SIZE_FORMAT "%s, "
181 "humongous waste: " SIZE_FORMAT "%s, soft capacity: " SIZE_FORMAT "%s, max capacity: " SIZE_FORMAT "%s, "
182 "available: " SIZE_FORMAT "%s", msg, name(),
183 byte_size_in_proper_unit(v_used), proper_unit_for_byte_size(v_used),
184 byte_size_in_proper_unit(v_used_regions), proper_unit_for_byte_size(v_used_regions),
185 byte_size_in_proper_unit(v_humongous_waste), proper_unit_for_byte_size(v_humongous_waste),
186 byte_size_in_proper_unit(v_soft_max_capacity), proper_unit_for_byte_size(v_soft_max_capacity),
187 byte_size_in_proper_unit(v_max_capacity), proper_unit_for_byte_size(v_max_capacity),
188 byte_size_in_proper_unit(v_available), proper_unit_for_byte_size(v_available));
189 }
190
191 void ShenandoahGeneration::reset_mark_bitmap() {
192 ShenandoahHeap* heap = ShenandoahHeap::heap();
193 heap->assert_gc_workers(heap->workers()->active_workers());
194
195 set_mark_incomplete();
196
197 ShenandoahResetBitmapTask task(this);
198 heap->workers()->run_task(&task);
199 }
200
201 // The ideal is to swap the remembered set so the safepoint effort is no more than a few pointer manipulations.
202 // However, limitations in the implementation of the mutator write-barrier make it difficult to simply change the
203 // location of the card table. So the interim implementation of swap_remembered_set will copy the write-table
204 // onto the read-table and will then clear the write-table.
205 void ShenandoahGeneration::swap_remembered_set() {
206 // Must be sure that marking is complete before we swap remembered set.
207 ShenandoahGenerationalHeap* heap = ShenandoahGenerationalHeap::heap();
208 heap->assert_gc_workers(heap->workers()->active_workers());
209 shenandoah_assert_safepoint();
210
211 ShenandoahOldGeneration* old_generation = heap->old_generation();
212 ShenandoahCopyWriteCardTableToRead task(old_generation->card_scan());
213 old_generation->parallel_heap_region_iterate(&task);
214 }
215
216 // Copy the write-version of the card-table into the read-version, clearing the
217 // write-version. The work is done at a safepoint and in parallel by the GC
218 // worker threads.
219 void ShenandoahGeneration::merge_write_table() {
220 // This should only happen for degenerated cycles
221 ShenandoahGenerationalHeap* heap = ShenandoahGenerationalHeap::heap();
222 heap->assert_gc_workers(heap->workers()->active_workers());
223 shenandoah_assert_safepoint();
224
225 ShenandoahOldGeneration* old_generation = heap->old_generation();
226 ShenandoahMergeWriteTable task(old_generation->card_scan());
227 old_generation->parallel_heap_region_iterate(&task);
228 }
229
230 void ShenandoahGeneration::prepare_gc() {
231
232 reset_mark_bitmap();
233
234 // Capture Top At Mark Start for this generation (typically young) and reset mark bitmap.
235 ShenandoahResetUpdateRegionStateClosure cl;
236 parallel_region_iterate_free(&cl);
237 }
238
239 void ShenandoahGeneration::parallel_region_iterate_free(ShenandoahHeapRegionClosure* cl) {
240 ShenandoahHeap::heap()->parallel_heap_region_iterate(cl);
241 }
242
243 void ShenandoahGeneration::compute_evacuation_budgets(ShenandoahHeap* const heap) {
244 shenandoah_assert_generational();
245
246 ShenandoahOldGeneration* const old_generation = heap->old_generation();
247 ShenandoahYoungGeneration* const young_generation = heap->young_generation();
248
249 // During initialization and phase changes, it is more likely that fewer objects die young and old-gen
250 // memory is not yet full (or is in the process of being replaced). During these times especially, it
251 // is beneficial to loan memory from old-gen to young-gen during the evacuation and update-refs phases
252 // of execution.
253
254 // Calculate EvacuationReserve before PromotionReserve. Evacuation is more critical than promotion.
255 // If we cannot evacuate old-gen, we will not be able to reclaim old-gen memory. Promotions are less
256 // critical. If we cannot promote, there may be degradation of young-gen memory because old objects
257 // accumulate there until they can be promoted. This increases the young-gen marking and evacuation work.
258
259 // First priority is to reclaim the easy garbage out of young-gen.
260
261 // maximum_young_evacuation_reserve is upper bound on memory to be evacuated out of young
262 const size_t maximum_young_evacuation_reserve = (young_generation->max_capacity() * ShenandoahEvacReserve) / 100;
263 const size_t young_evacuation_reserve = MIN2(maximum_young_evacuation_reserve, young_generation->available_with_reserve());
264
265 // maximum_old_evacuation_reserve is an upper bound on memory evacuated from old and evacuated to old (promoted),
266 // clamped by the old generation space available.
267 //
268 // Here's the algebra.
269 // Let SOEP = ShenandoahOldEvacRatioPercent,
270 // OE = old evac,
271 // YE = young evac, and
272 // TE = total evac = OE + YE
273 // By definition:
274 // SOEP/100 = OE/TE
275 // = OE/(OE+YE)
276 // => SOEP/(100-SOEP) = OE/((OE+YE)-OE) // componendo-dividendo: If a/b = c/d, then a/(b-a) = c/(d-c)
277 // = OE/YE
278 // => OE = YE*SOEP/(100-SOEP)
279
280 // We have to be careful in the event that SOEP is set to 100 by the user.
281 assert(ShenandoahOldEvacRatioPercent <= 100, "Error");
282 const size_t old_available = old_generation->available();
283 const size_t maximum_old_evacuation_reserve = (ShenandoahOldEvacRatioPercent == 100) ?
284 old_available : MIN2((maximum_young_evacuation_reserve * ShenandoahOldEvacRatioPercent) / (100 - ShenandoahOldEvacRatioPercent),
285 old_available);
286
287
288 // Second priority is to reclaim garbage out of old-gen if there are old-gen collection candidates. Third priority
289 // is to promote as much as we have room to promote. However, if old-gen memory is in short supply, this means young
290 // GC is operating under "duress" and was unable to transfer the memory that we would normally expect. In this case,
291 // old-gen will refrain from compacting itself in order to allow a quicker young-gen cycle (by avoiding the update-refs
292 // through ALL of old-gen). If there is some memory available in old-gen, we will use this for promotions as promotions
293 // do not add to the update-refs burden of GC.
294
295 size_t old_evacuation_reserve, old_promo_reserve;
296 if (is_global()) {
297 // Global GC is typically triggered by user invocation of System.gc(), and typically indicates that there is lots
298 // of garbage to be reclaimed because we are starting a new phase of execution. Marking for global GC may take
299 // significantly longer than typical young marking because we must mark through all old objects. To expedite
300 // evacuation and update-refs, we give emphasis to reclaiming garbage first, wherever that garbage is found.
301 // Global GC will adjust generation sizes to accommodate the collection set it chooses.
302
303 // Set old_promo_reserve to enforce that no regions are preselected for promotion. Such regions typically
304 // have relatively high memory utilization. We still call select_aged_regions() because this will prepare for
305 // promotions in place, if relevant.
306 old_promo_reserve = 0;
307
308 // Dedicate all available old memory to old_evacuation reserve. This may be small, because old-gen is only
309 // expanded based on an existing mixed evacuation workload at the end of the previous GC cycle. We'll expand
310 // the budget for evacuation of old during GLOBAL cset selection.
311 old_evacuation_reserve = maximum_old_evacuation_reserve;
312 } else if (old_generation->has_unprocessed_collection_candidates()) {
313 // We reserved all old-gen memory at end of previous GC to hold anticipated evacuations to old-gen. If this is
314 // mixed evacuation, reserve all of this memory for compaction of old-gen and do not promote. Prioritize compaction
315 // over promotion in order to defragment OLD so that it will be better prepared to efficiently receive promoted memory.
316 old_evacuation_reserve = maximum_old_evacuation_reserve;
317 old_promo_reserve = 0;
318 } else {
319 // Make all old-evacuation memory for promotion, but if we can't use it all for promotion, we'll allow some evacuation.
320 old_evacuation_reserve = 0;
321 old_promo_reserve = maximum_old_evacuation_reserve;
322 }
323 assert(old_evacuation_reserve <= old_available, "Error");
324
325 // We see too many old-evacuation failures if we force ourselves to evacuate into regions that are not initially empty.
326 // So we limit the old-evacuation reserve to unfragmented memory. Even so, old-evacuation is free to fill in nooks and
327 // crannies within existing partially used regions and it generally tries to do so.
328 const size_t old_free_unfragmented = old_generation->free_unaffiliated_regions() * ShenandoahHeapRegion::region_size_bytes();
329 if (old_evacuation_reserve > old_free_unfragmented) {
330 const size_t delta = old_evacuation_reserve - old_free_unfragmented;
331 old_evacuation_reserve -= delta;
332 // Let promo consume fragments of old-gen memory if not global
333 if (!is_global()) {
334 old_promo_reserve += delta;
335 }
336 }
337
338 // Preselect regions for promotion by evacuation (obtaining the live data to seed promoted_reserve),
339 // and identify regions that will promote in place. These use the tenuring threshold.
340 const size_t consumed_by_advance_promotion = select_aged_regions(old_promo_reserve);
341 assert(consumed_by_advance_promotion <= maximum_old_evacuation_reserve, "Cannot promote more than available old-gen memory");
342
343 // Note that unused old_promo_reserve might not be entirely consumed_by_advance_promotion. Do not transfer this
344 // to old_evacuation_reserve because this memory is likely very fragmented, and we do not want to increase the likelihood
345 // of old evacuation failure.
346 young_generation->set_evacuation_reserve(young_evacuation_reserve);
347 old_generation->set_evacuation_reserve(old_evacuation_reserve);
348 old_generation->set_promoted_reserve(consumed_by_advance_promotion);
349
350 // There is no need to expand OLD because all memory used here was set aside at end of previous GC, except in the
351 // case of a GLOBAL gc. During choose_collection_set() of GLOBAL, old will be expanded on demand.
352 }
353
354 // Having chosen the collection set, adjust the budgets for generational mode based on its composition. Note
355 // that young_generation->available() now knows about recently discovered immediate garbage.
356 //
357 void ShenandoahGeneration::adjust_evacuation_budgets(ShenandoahHeap* const heap, ShenandoahCollectionSet* const collection_set) {
358 shenandoah_assert_generational();
359 // We may find that old_evacuation_reserve and/or loaned_for_young_evacuation are not fully consumed, in which case we may
360 // be able to increase regions_available_to_loan
361
362 // The role of adjust_evacuation_budgets() is to compute the correct value of regions_available_to_loan and to make
363 // effective use of this memory, including the remnant memory within these regions that may result from rounding loan to
364 // integral number of regions. Excess memory that is available to be loaned is applied to an allocation supplement,
365 // which allows mutators to allocate memory beyond the current capacity of young-gen on the promise that the loan
366 // will be repaid as soon as we finish updating references for the recently evacuated collection set.
367
368 // We cannot recalculate regions_available_to_loan by simply dividing old_generation->available() by region_size_bytes
369 // because the available memory may be distributed between many partially occupied regions that are already holding old-gen
370 // objects. Memory in partially occupied regions is not "available" to be loaned. Note that an increase in old-gen
371 // available that results from a decrease in memory consumed by old evacuation is not necessarily available to be loaned
372 // to young-gen.
373
374 size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
375 ShenandoahOldGeneration* const old_generation = heap->old_generation();
376 ShenandoahYoungGeneration* const young_generation = heap->young_generation();
377
378 size_t old_evacuated = collection_set->get_old_bytes_reserved_for_evacuation();
379 size_t old_evacuated_committed = (size_t) (ShenandoahOldEvacWaste * old_evacuated);
380 size_t old_evacuation_reserve = old_generation->get_evacuation_reserve();
381
382 if (old_evacuated_committed > old_evacuation_reserve) {
383 // This should only happen due to round-off errors when enforcing ShenandoahOldEvacWaste
384 assert(old_evacuated_committed <= (33 * old_evacuation_reserve) / 32,
385 "Round-off errors should be less than 3.125%%, committed: " SIZE_FORMAT ", reserved: " SIZE_FORMAT,
386 old_evacuated_committed, old_evacuation_reserve);
387 old_evacuated_committed = old_evacuation_reserve;
388 // Leave old_evac_reserve as previously configured
389 } else if (old_evacuated_committed < old_evacuation_reserve) {
390 // This happens if the old-gen collection consumes less than full budget.
391 old_evacuation_reserve = old_evacuated_committed;
392 old_generation->set_evacuation_reserve(old_evacuation_reserve);
393 }
394
395 size_t young_advance_promoted = collection_set->get_young_bytes_to_be_promoted();
396 size_t young_advance_promoted_reserve_used = (size_t) (ShenandoahPromoEvacWaste * young_advance_promoted);
397
398 size_t young_evacuated = collection_set->get_young_bytes_reserved_for_evacuation();
399 size_t young_evacuated_reserve_used = (size_t) (ShenandoahEvacWaste * young_evacuated);
400
401 size_t total_young_available = young_generation->available_with_reserve();
402 assert(young_evacuated_reserve_used <= total_young_available, "Cannot evacuate more than is available in young");
403 young_generation->set_evacuation_reserve(young_evacuated_reserve_used);
404
405 size_t old_available = old_generation->available();
406 // Now that we've established the collection set, we know how much memory is really required by old-gen for evacuation
407 // and promotion reserves. Try shrinking OLD now in case that gives us a bit more runway for mutator allocations during
408 // evac and update phases.
409 size_t old_consumed = old_evacuated_committed + young_advance_promoted_reserve_used;
410
411 if (old_available < old_consumed) {
412 // This can happen due to round-off errors when adding the results of truncated integer arithmetic.
413 // We've already truncated old_evacuated_committed. Truncate young_advance_promoted_reserve_used here.
414 assert(young_advance_promoted_reserve_used <= (33 * (old_available - old_evacuated_committed)) / 32,
415 "Round-off errors should be less than 3.125%%, committed: " SIZE_FORMAT ", reserved: " SIZE_FORMAT,
416 young_advance_promoted_reserve_used, old_available - old_evacuated_committed);
417 young_advance_promoted_reserve_used = old_available - old_evacuated_committed;
418 old_consumed = old_evacuated_committed + young_advance_promoted_reserve_used;
419 }
420
421 assert(old_available >= old_consumed, "Cannot consume (" SIZE_FORMAT ") more than is available (" SIZE_FORMAT ")",
422 old_consumed, old_available);
423 size_t excess_old = old_available - old_consumed;
424 size_t unaffiliated_old_regions = old_generation->free_unaffiliated_regions();
425 size_t unaffiliated_old = unaffiliated_old_regions * region_size_bytes;
426 assert(old_available >= unaffiliated_old, "Unaffiliated old is a subset of old available");
427
428 // Make sure old_evac_committed is unaffiliated
429 if (old_evacuated_committed > 0) {
430 if (unaffiliated_old > old_evacuated_committed) {
431 size_t giveaway = unaffiliated_old - old_evacuated_committed;
432 size_t giveaway_regions = giveaway / region_size_bytes; // round down
433 if (giveaway_regions > 0) {
434 excess_old = MIN2(excess_old, giveaway_regions * region_size_bytes);
435 } else {
436 excess_old = 0;
437 }
438 } else {
439 excess_old = 0;
440 }
441 }
442
443 // If we find that OLD has excess regions, give them back to YOUNG now to reduce likelihood we run out of allocation
444 // runway during evacuation and update-refs.
445 size_t regions_to_xfer = 0;
446 if (excess_old > unaffiliated_old) {
447 // we can give back unaffiliated_old (all of unaffiliated is excess)
448 if (unaffiliated_old_regions > 0) {
449 regions_to_xfer = unaffiliated_old_regions;
450 }
451 } else if (unaffiliated_old_regions > 0) {
452 // excess_old < unaffiliated old: we can give back MIN(excess_old/region_size_bytes, unaffiliated_old_regions)
453 size_t excess_regions = excess_old / region_size_bytes;
454 size_t regions_to_xfer = MIN2(excess_regions, unaffiliated_old_regions);
455 }
456
457 if (regions_to_xfer > 0) {
458 bool result = ShenandoahGenerationalHeap::cast(heap)->generation_sizer()->transfer_to_young(regions_to_xfer);
459 assert(excess_old > regions_to_xfer * region_size_bytes, "Cannot xfer more than excess old");
460 excess_old -= regions_to_xfer * region_size_bytes;
461 log_info(gc, ergo)("%s transferred " SIZE_FORMAT " excess regions to young before start of evacuation",
462 result? "Successfully": "Unsuccessfully", regions_to_xfer);
463 }
464
465 // Add in the excess_old memory to hold unanticipated promotions, if any. If there are more unanticipated
466 // promotions than fit in reserved memory, they will be deferred until a future GC pass.
467 size_t total_promotion_reserve = young_advance_promoted_reserve_used + excess_old;
468 old_generation->set_promoted_reserve(total_promotion_reserve);
469 old_generation->reset_promoted_expended();
470 }
471
472 typedef struct {
473 ShenandoahHeapRegion* _region;
474 size_t _live_data;
475 } AgedRegionData;
476
477 static int compare_by_aged_live(AgedRegionData a, AgedRegionData b) {
478 if (a._live_data < b._live_data)
479 return -1;
480 else if (a._live_data > b._live_data)
481 return 1;
482 else return 0;
483 }
484
485 inline void assert_no_in_place_promotions() {
486 #ifdef ASSERT
487 class ShenandoahNoInPlacePromotions : public ShenandoahHeapRegionClosure {
488 public:
489 void heap_region_do(ShenandoahHeapRegion *r) override {
490 assert(r->get_top_before_promote() == nullptr,
491 "Region " SIZE_FORMAT " should not be ready for in-place promotion", r->index());
492 }
493 } cl;
494 ShenandoahHeap::heap()->heap_region_iterate(&cl);
495 #endif
496 }
497
498 // Preselect for inclusion into the collection set regions whose age is at or above tenure age which contain more than
499 // ShenandoahOldGarbageThreshold amounts of garbage. We identify these regions by setting the appropriate entry of
500 // the collection set's preselected regions array to true. All entries are initialized to false before calling this
501 // function.
502 //
503 // During the subsequent selection of the collection set, we give priority to these promotion set candidates.
504 // Without this prioritization, we found that the aged regions tend to be ignored because they typically have
505 // much less garbage and much more live data than the recently allocated "eden" regions. When aged regions are
506 // repeatedly excluded from the collection set, the amount of live memory within the young generation tends to
507 // accumulate and this has the undesirable side effect of causing young-generation collections to require much more
508 // CPU and wall-clock time.
509 //
510 // A second benefit of treating aged regions differently than other regions during collection set selection is
511 // that this allows us to more accurately budget memory to hold the results of evacuation. Memory for evacuation
512 // of aged regions must be reserved in the old generation. Memory for evacuation of all other regions must be
513 // reserved in the young generation.
514 size_t ShenandoahGeneration::select_aged_regions(size_t old_available) {
515
516 // There should be no regions configured for subsequent in-place-promotions carried over from the previous cycle.
517 assert_no_in_place_promotions();
518
519 auto const heap = ShenandoahGenerationalHeap::heap();
520 bool* const candidate_regions_for_promotion_by_copy = heap->collection_set()->preselected_regions();
521 ShenandoahMarkingContext* const ctx = heap->marking_context();
522
523 const uint tenuring_threshold = heap->age_census()->tenuring_threshold();
524 const size_t old_garbage_threshold = (ShenandoahHeapRegion::region_size_bytes() * ShenandoahOldGarbageThreshold) / 100;
525
526 size_t old_consumed = 0;
527 size_t promo_potential = 0;
528 size_t candidates = 0;
529
530 // Tracks the padding of space above top in regions eligible for promotion in place
531 size_t promote_in_place_pad = 0;
532
533 // Sort the promotion-eligible regions in order of increasing live-data-bytes so that we can first reclaim regions that require
534 // less evacuation effort. This prioritizes garbage first, expanding the allocation pool early before we reclaim regions that
535 // have more live data.
536 const size_t num_regions = heap->num_regions();
537
538 ResourceMark rm;
539 AgedRegionData* sorted_regions = NEW_RESOURCE_ARRAY(AgedRegionData, num_regions);
540
541 for (size_t i = 0; i < num_regions; i++) {
542 ShenandoahHeapRegion* const r = heap->get_region(i);
543 if (r->is_empty() || !r->has_live() || !r->is_young() || !r->is_regular()) {
544 // skip over regions that aren't regular young with some live data
545 continue;
546 }
547 if (r->age() >= tenuring_threshold) {
548 if ((r->garbage() < old_garbage_threshold)) {
549 // This tenure-worthy region has too little garbage, so we do not want to expend the copying effort to
550 // reclaim the garbage; instead this region may be eligible for promotion-in-place to the
551 // old generation.
552 HeapWord* tams = ctx->top_at_mark_start(r);
553 HeapWord* original_top = r->top();
554 if (!heap->is_concurrent_old_mark_in_progress() && tams == original_top) {
555 // No allocations from this region have been made during concurrent mark. It meets all the criteria
556 // for in-place-promotion. Though we only need the value of top when we fill the end of the region,
557 // we use this field to indicate that this region should be promoted in place during the evacuation
558 // phase.
559 r->save_top_before_promote();
560
561 size_t remnant_size = r->free() / HeapWordSize;
562 if (remnant_size > ShenandoahHeap::min_fill_size()) {
563 ShenandoahHeap::fill_with_object(original_top, remnant_size);
564 // Fill the remnant memory within this region to assure no allocations prior to promote in place. Otherwise,
565 // newly allocated objects will not be parsable when promote in place tries to register them. Furthermore, any
566 // new allocations would not necessarily be eligible for promotion. This addresses both issues.
567 r->set_top(r->end());
568 promote_in_place_pad += remnant_size * HeapWordSize;
569 } else {
570 // Since the remnant is so small that it cannot be filled, we don't have to worry about any accidental
571 // allocations occurring within this region before the region is promoted in place.
572 }
573 }
574 // Else, we do not promote this region (either in place or by copy) because it has received new allocations.
575
576 // During evacuation, we exclude from promotion regions for which age > tenure threshold, garbage < garbage-threshold,
577 // and get_top_before_promote() != tams
578 } else {
579 // Record this promotion-eligible candidate region. After sorting and selecting the best candidates below,
580 // we may still decide to exclude this promotion-eligible region from the current collection set. If this
581 // happens, we will consider this region as part of the anticipated promotion potential for the next GC
582 // pass; see further below.
583 sorted_regions[candidates]._region = r;
584 sorted_regions[candidates++]._live_data = r->get_live_data_bytes();
585 }
586 } else {
587 // We only evacuate & promote objects from regular regions whose garbage() is above old-garbage-threshold.
588 // Objects in tenure-worthy regions with less garbage are promoted in place. These take a different path to
589 // old-gen. Regions excluded from promotion because their garbage content is too low (causing us to anticipate that
590 // the region would be promoted in place) may be eligible for evacuation promotion by the time promotion takes
591 // place during a subsequent GC pass because more garbage is found within the region between now and then. This
592 // should not happen if we are properly adapting the tenure age. The theory behind adaptive tenuring threshold
593 // is to choose the youngest age that demonstrates no "significant" further loss of population since the previous
594 // age. If not this, we expect the tenure age to demonstrate linear population decay for at least two population
595 // samples, whereas we expect to observe exponential population decay for ages younger than the tenure age.
596 //
597 // In the case that certain regions which were anticipated to be promoted in place need to be promoted by
598 // evacuation, it may be the case that there is not sufficient reserve within old-gen to hold evacuation of
599 // these regions. The likely outcome is that these regions will not be selected for evacuation or promotion
600 // in the current cycle and we will anticipate that they will be promoted in the next cycle. This will cause
601 // us to reserve more old-gen memory so that these objects can be promoted in the subsequent cycle.
602 if (heap->is_aging_cycle() && (r->age() + 1 == tenuring_threshold)) {
603 if (r->garbage() >= old_garbage_threshold) {
604 promo_potential += r->get_live_data_bytes();
605 }
606 }
607 }
608 // Note that we keep going even if one region is excluded from selection.
609 // Subsequent regions may be selected if they have smaller live data.
610 }
611 // Sort in increasing order according to live data bytes. Note that candidates represents the number of regions
612 // that qualify to be promoted by evacuation.
613 if (candidates > 0) {
614 size_t selected_regions = 0;
615 size_t selected_live = 0;
616 QuickSort::sort<AgedRegionData>(sorted_regions, candidates, compare_by_aged_live, false);
617 for (size_t i = 0; i < candidates; i++) {
618 ShenandoahHeapRegion* const region = sorted_regions[i]._region;
619 size_t region_live_data = sorted_regions[i]._live_data;
620 size_t promotion_need = (size_t) (region_live_data * ShenandoahPromoEvacWaste);
621 if (old_consumed + promotion_need <= old_available) {
622 old_consumed += promotion_need;
623 candidate_regions_for_promotion_by_copy[region->index()] = true;
624 selected_regions++;
625 selected_live += region_live_data;
626 } else {
627 // We rejected this promotable region from the collection set because we had no room to hold its copy.
628 // Add this region to promo potential for next GC.
629 promo_potential += region_live_data;
630 assert(!candidate_regions_for_promotion_by_copy[region->index()], "Shouldn't be selected");
631 }
632 // We keep going even if one region is excluded from selection because we need to accumulate all eligible
633 // regions that are not preselected into promo_potential
634 }
635 log_info(gc)("Preselected " SIZE_FORMAT " regions containing " SIZE_FORMAT " live bytes,"
636 " consuming: " SIZE_FORMAT " of budgeted: " SIZE_FORMAT,
637 selected_regions, selected_live, old_consumed, old_available);
638 }
639
640 heap->old_generation()->set_pad_for_promote_in_place(promote_in_place_pad);
641 heap->old_generation()->set_promotion_potential(promo_potential);
642 return old_consumed;
643 }
644
645 void ShenandoahGeneration::prepare_regions_and_collection_set(bool concurrent) {
646 ShenandoahHeap* heap = ShenandoahHeap::heap();
647 ShenandoahCollectionSet* collection_set = heap->collection_set();
648 bool is_generational = heap->mode()->is_generational();
649
650 assert(!heap->is_full_gc_in_progress(), "Only for concurrent and degenerated GC");
651 assert(!is_old(), "Only YOUNG and GLOBAL GC perform evacuations");
652 {
653 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::final_update_region_states :
654 ShenandoahPhaseTimings::degen_gc_final_update_region_states);
655 ShenandoahFinalMarkUpdateRegionStateClosure cl(complete_marking_context());
656 parallel_heap_region_iterate(&cl);
657
658 if (is_young()) {
659 // We always need to update the watermark for old regions. If there
660 // are mixed collections pending, we also need to synchronize the
661 // pinned status for old regions. Since we are already visiting every
662 // old region here, go ahead and sync the pin status too.
663 ShenandoahFinalMarkUpdateRegionStateClosure old_cl(nullptr);
664 heap->old_generation()->parallel_heap_region_iterate(&old_cl);
665 }
666 }
667
668 // Tally the census counts and compute the adaptive tenuring threshold
669 if (is_generational && ShenandoahGenerationalAdaptiveTenuring && !ShenandoahGenerationalCensusAtEvac) {
670 // Objects above TAMS weren't included in the age census. Since they were all
671 // allocated in this cycle they belong in the age 0 cohort. We walk over all
672 // young regions and sum the volume of objects between TAMS and top.
673 ShenandoahUpdateCensusZeroCohortClosure age0_cl(complete_marking_context());
674 heap->young_generation()->heap_region_iterate(&age0_cl);
675 size_t age0_pop = age0_cl.get_age0_population();
676
677 // Update the global census, including the missed age 0 cohort above,
678 // along with the census done during marking, and compute the tenuring threshold.
679 ShenandoahAgeCensus* census = ShenandoahGenerationalHeap::heap()->age_census();
680 census->update_census(age0_pop);
681 #ifndef PRODUCT
682 size_t total_pop = age0_cl.get_total_population();
683 size_t total_census = census->get_total();
684 // Usually total_pop > total_census, but not by too much.
685 // We use integer division so anything up to just less than 2 is considered
686 // reasonable, and the "+1" is to avoid divide-by-zero.
687 assert((total_pop+1)/(total_census+1) == 1, "Extreme divergence: "
688 SIZE_FORMAT "/" SIZE_FORMAT, total_pop, total_census);
689 #endif
690 }
691
692 {
693 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::choose_cset :
694 ShenandoahPhaseTimings::degen_gc_choose_cset);
695
696 collection_set->clear();
697 ShenandoahHeapLocker locker(heap->lock());
698 if (is_generational) {
699 // Seed the collection set with resource area-allocated
700 // preselected regions, which are removed when we exit this scope.
701 ResourceMark rm;
702 ShenandoahCollectionSetPreselector preselector(collection_set, heap->num_regions());
703
704 // Find the amount that will be promoted, regions that will be promoted in
705 // place, and preselect older regions that will be promoted by evacuation.
706 compute_evacuation_budgets(heap);
707
708 // Choose the collection set, including the regions preselected above for
709 // promotion into the old generation.
710 _heuristics->choose_collection_set(collection_set);
711 if (!collection_set->is_empty()) {
712 // only make use of evacuation budgets when we are evacuating
713 adjust_evacuation_budgets(heap, collection_set);
714 }
715
716 if (is_global()) {
717 // We have just chosen a collection set for a global cycle. The mark bitmap covering old regions is complete, so
718 // the remembered set scan can use that to avoid walking into garbage. When the next old mark begins, we will
719 // use the mark bitmap to make the old regions parsable by coalescing and filling any unmarked objects. Thus,
720 // we prepare for old collections by remembering which regions are old at this time. Note that any objects
721 // promoted into old regions will be above TAMS, and so will be considered marked. However, free regions that
722 // become old after this point will not be covered correctly by the mark bitmap, so we must be careful not to
723 // coalesce those regions. Only the old regions which are not part of the collection set at this point are
724 // eligible for coalescing. As implemented now, this has the side effect of possibly initiating mixed-evacuations
725 // after a global cycle for old regions that were not included in this collection set.
726 heap->old_generation()->prepare_for_mixed_collections_after_global_gc();
727 }
728 } else {
729 _heuristics->choose_collection_set(collection_set);
730 }
731 }
732
733
734 {
735 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::final_rebuild_freeset :
736 ShenandoahPhaseTimings::degen_gc_final_rebuild_freeset);
737 ShenandoahHeapLocker locker(heap->lock());
738 size_t young_cset_regions, old_cset_regions;
739
740 // We are preparing for evacuation. At this time, we ignore cset region tallies.
741 size_t first_old, last_old, num_old;
742 heap->free_set()->prepare_to_rebuild(young_cset_regions, old_cset_regions, first_old, last_old, num_old);
743 // Free set construction uses reserve quantities, because they are known to be valid here
744 heap->free_set()->finish_rebuild(young_cset_regions, old_cset_regions, num_old, true);
745 }
746 }
747
748 bool ShenandoahGeneration::is_bitmap_clear() {
749 ShenandoahHeap* heap = ShenandoahHeap::heap();
750 ShenandoahMarkingContext* context = heap->marking_context();
751 const size_t num_regions = heap->num_regions();
752 for (size_t idx = 0; idx < num_regions; idx++) {
753 ShenandoahHeapRegion* r = heap->get_region(idx);
754 if (contains(r) && r->is_affiliated()) {
755 if (heap->is_bitmap_slice_committed(r) && (context->top_at_mark_start(r) > r->bottom()) &&
756 !context->is_bitmap_clear_range(r->bottom(), r->end())) {
757 return false;
758 }
759 }
760 }
761 return true;
762 }
763
764 bool ShenandoahGeneration::is_mark_complete() {
765 return _is_marking_complete.is_set();
766 }
767
768 void ShenandoahGeneration::set_mark_complete() {
769 _is_marking_complete.set();
770 }
771
772 void ShenandoahGeneration::set_mark_incomplete() {
773 _is_marking_complete.unset();
774 }
775
776 ShenandoahMarkingContext* ShenandoahGeneration::complete_marking_context() {
777 assert(is_mark_complete(), "Marking must be completed.");
778 return ShenandoahHeap::heap()->marking_context();
779 }
780
781 void ShenandoahGeneration::cancel_marking() {
782 log_info(gc)("Cancel marking: %s", name());
783 if (is_concurrent_mark_in_progress()) {
784 set_mark_incomplete();
785 }
786 _task_queues->clear();
787 ref_processor()->abandon_partial_discovery();
788 set_concurrent_mark_in_progress(false);
789 }
790
791 ShenandoahGeneration::ShenandoahGeneration(ShenandoahGenerationType type,
792 uint max_workers,
793 size_t max_capacity,
794 size_t soft_max_capacity) :
795 _type(type),
796 _task_queues(new ShenandoahObjToScanQueueSet(max_workers)),
797 _ref_processor(new ShenandoahReferenceProcessor(MAX2(max_workers, 1U))),
798 _affiliated_region_count(0), _humongous_waste(0), _evacuation_reserve(0),
799 _used(0), _bytes_allocated_since_gc_start(0),
800 _max_capacity(max_capacity), _soft_max_capacity(soft_max_capacity),
801 _heuristics(nullptr)
802 {
803 _is_marking_complete.set();
804 assert(max_workers > 0, "At least one queue");
805 for (uint i = 0; i < max_workers; ++i) {
806 ShenandoahObjToScanQueue* task_queue = new ShenandoahObjToScanQueue();
807 _task_queues->register_queue(i, task_queue);
808 }
809 }
810
811 ShenandoahGeneration::~ShenandoahGeneration() {
812 for (uint i = 0; i < _task_queues->size(); ++i) {
813 ShenandoahObjToScanQueue* q = _task_queues->queue(i);
814 delete q;
815 }
816 delete _task_queues;
817 }
818
819 void ShenandoahGeneration::reserve_task_queues(uint workers) {
820 _task_queues->reserve(workers);
821 }
822
823 ShenandoahObjToScanQueueSet* ShenandoahGeneration::old_gen_task_queues() const {
824 return nullptr;
825 }
826
827 void ShenandoahGeneration::scan_remembered_set(bool is_concurrent) {
828 assert(is_young(), "Should only scan remembered set for young generation.");
829
830 ShenandoahGenerationalHeap* const heap = ShenandoahGenerationalHeap::heap();
831 uint nworkers = heap->workers()->active_workers();
832 reserve_task_queues(nworkers);
833
834 ShenandoahReferenceProcessor* rp = ref_processor();
835 ShenandoahRegionChunkIterator work_list(nworkers);
836 ShenandoahScanRememberedTask task(task_queues(), old_gen_task_queues(), rp, &work_list, is_concurrent);
837 heap->assert_gc_workers(nworkers);
838 heap->workers()->run_task(&task);
839 if (ShenandoahEnableCardStats) {
840 ShenandoahScanRemembered* scanner = heap->old_generation()->card_scan();
841 assert(scanner != nullptr, "Not generational");
842 scanner->log_card_stats(nworkers, CARD_STAT_SCAN_RS);
843 }
844 }
845
846 size_t ShenandoahGeneration::increment_affiliated_region_count() {
847 shenandoah_assert_heaplocked_or_safepoint();
848 // During full gc, multiple GC worker threads may change region affiliations without a lock. No lock is enforced
849 // on read and write of _affiliated_region_count. At the end of full gc, a single thread overwrites the count with
850 // a coherent value.
851 _affiliated_region_count++;
852 return _affiliated_region_count;
853 }
854
855 size_t ShenandoahGeneration::decrement_affiliated_region_count() {
856 shenandoah_assert_heaplocked_or_safepoint();
857 // During full gc, multiple GC worker threads may change region affiliations without a lock. No lock is enforced
858 // on read and write of _affiliated_region_count. At the end of full gc, a single thread overwrites the count with
859 // a coherent value.
860 _affiliated_region_count--;
861 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
862 (_used + _humongous_waste <= _affiliated_region_count * ShenandoahHeapRegion::region_size_bytes()),
863 "used + humongous cannot exceed regions");
864 return _affiliated_region_count;
865 }
866
867 size_t ShenandoahGeneration::increase_affiliated_region_count(size_t delta) {
868 shenandoah_assert_heaplocked_or_safepoint();
869 _affiliated_region_count += delta;
870 return _affiliated_region_count;
871 }
872
873 size_t ShenandoahGeneration::decrease_affiliated_region_count(size_t delta) {
874 shenandoah_assert_heaplocked_or_safepoint();
875 assert(_affiliated_region_count >= delta, "Affiliated region count cannot be negative");
876
877 _affiliated_region_count -= delta;
878 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
879 (_used + _humongous_waste <= _affiliated_region_count * ShenandoahHeapRegion::region_size_bytes()),
880 "used + humongous cannot exceed regions");
881 return _affiliated_region_count;
882 }
883
884 void ShenandoahGeneration::establish_usage(size_t num_regions, size_t num_bytes, size_t humongous_waste) {
885 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
886 _affiliated_region_count = num_regions;
887 _used = num_bytes;
888 _humongous_waste = humongous_waste;
889 }
890
891 void ShenandoahGeneration::increase_used(size_t bytes) {
892 Atomic::add(&_used, bytes);
893 }
894
895 void ShenandoahGeneration::increase_humongous_waste(size_t bytes) {
896 if (bytes > 0) {
897 Atomic::add(&_humongous_waste, bytes);
898 }
899 }
900
901 void ShenandoahGeneration::decrease_humongous_waste(size_t bytes) {
902 if (bytes > 0) {
903 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() || (_humongous_waste >= bytes),
904 "Waste (" SIZE_FORMAT ") cannot be negative (after subtracting " SIZE_FORMAT ")", _humongous_waste, bytes);
905 Atomic::sub(&_humongous_waste, bytes);
906 }
907 }
908
909 void ShenandoahGeneration::decrease_used(size_t bytes) {
910 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
911 (_used >= bytes), "cannot reduce bytes used by generation below zero");
912 Atomic::sub(&_used, bytes);
913 }
914
915 size_t ShenandoahGeneration::used_regions() const {
916 return _affiliated_region_count;
917 }
918
919 size_t ShenandoahGeneration::free_unaffiliated_regions() const {
920 size_t result = max_capacity() / ShenandoahHeapRegion::region_size_bytes();
921 if (_affiliated_region_count > result) {
922 result = 0;
923 } else {
924 result -= _affiliated_region_count;
925 }
926 return result;
927 }
928
929 size_t ShenandoahGeneration::used_regions_size() const {
930 return _affiliated_region_count * ShenandoahHeapRegion::region_size_bytes();
931 }
932
933 size_t ShenandoahGeneration::available() const {
934 return available(max_capacity());
935 }
936
937 // For ShenandoahYoungGeneration, Include the young available that may have been reserved for the Collector.
938 size_t ShenandoahGeneration::available_with_reserve() const {
939 return available(max_capacity());
940 }
941
942 size_t ShenandoahGeneration::soft_available() const {
943 return available(soft_max_capacity());
944 }
945
946 size_t ShenandoahGeneration::available(size_t capacity) const {
947 size_t in_use = used() + get_humongous_waste();
948 return in_use > capacity ? 0 : capacity - in_use;
949 }
950
951 size_t ShenandoahGeneration::increase_capacity(size_t increment) {
952 shenandoah_assert_heaplocked_or_safepoint();
953
954 // We do not enforce that new capacity >= heap->max_size_for(this). The maximum generation size is treated as a rule of thumb
955 // which may be violated during certain transitions, such as when we are forcing transfers for the purpose of promoting regions
956 // in place.
957 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
958 (_max_capacity + increment <= ShenandoahHeap::heap()->max_capacity()), "Generation cannot be larger than heap size");
959 assert(increment % ShenandoahHeapRegion::region_size_bytes() == 0, "Generation capacity must be multiple of region size");
960 _max_capacity += increment;
961
962 // This detects arithmetic wraparound on _used
963 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
964 (_affiliated_region_count * ShenandoahHeapRegion::region_size_bytes() >= _used),
965 "Affiliated regions must hold more than what is currently used");
966 return _max_capacity;
967 }
968
969 size_t ShenandoahGeneration::set_capacity(size_t byte_size) {
970 shenandoah_assert_heaplocked_or_safepoint();
971 _max_capacity = byte_size;
972 return _max_capacity;
973 }
974
975 size_t ShenandoahGeneration::decrease_capacity(size_t decrement) {
976 shenandoah_assert_heaplocked_or_safepoint();
977
978 // We do not enforce that new capacity >= heap->min_size_for(this). The minimum generation size is treated as a rule of thumb
979 // which may be violated during certain transitions, such as when we are forcing transfers for the purpose of promoting regions
980 // in place.
981 assert(decrement % ShenandoahHeapRegion::region_size_bytes() == 0, "Generation capacity must be multiple of region size");
982 assert(_max_capacity >= decrement, "Generation capacity cannot be negative");
983
984 _max_capacity -= decrement;
985
986 // This detects arithmetic wraparound on _used
987 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
988 (_affiliated_region_count * ShenandoahHeapRegion::region_size_bytes() >= _used),
989 "Affiliated regions must hold more than what is currently used");
990 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
991 (_used <= _max_capacity), "Cannot use more than capacity");
992 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
993 (_affiliated_region_count * ShenandoahHeapRegion::region_size_bytes() <= _max_capacity),
994 "Cannot use more than capacity");
995 return _max_capacity;
996 }
997
998 void ShenandoahGeneration::record_success_concurrent(bool abbreviated) {
999 heuristics()->record_success_concurrent();
1000 ShenandoahHeap::heap()->shenandoah_policy()->record_success_concurrent(is_young(), abbreviated);
1001 }