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 auto const affiliation = region->affiliation();
81 bool needs_reset = affiliation == FREE || _generation->contains(affiliation);
82 if (needs_reset && heap->is_bitmap_slice_committed(region)) {
83 ctx->clear_bitmap(region);
84 }
85 region = _regions.next();
86 }
87 }
88 };
89
90 // Copy the write-version of the card-table into the read-version, clearing the
91 // write-copy.
92 class ShenandoahMergeWriteTable: public ShenandoahHeapRegionClosure {
93 private:
94 ShenandoahScanRemembered* _scanner;
95 public:
96 ShenandoahMergeWriteTable(ShenandoahScanRemembered* scanner) : _scanner(scanner) {}
97
98 void heap_region_do(ShenandoahHeapRegion* r) override {
99 assert(r->is_old(), "Don't waste time doing this for non-old regions");
100 _scanner->merge_write_table(r->bottom(), ShenandoahHeapRegion::region_size_words());
101 }
102
103 bool is_thread_safe() override {
104 return true;
105 }
106 };
107
108 class ShenandoahCopyWriteCardTableToRead: public ShenandoahHeapRegionClosure {
109 private:
110 ShenandoahScanRemembered* _scanner;
111 public:
112 ShenandoahCopyWriteCardTableToRead(ShenandoahScanRemembered* scanner) : _scanner(scanner) {}
113
114 void heap_region_do(ShenandoahHeapRegion* region) override {
115 assert(region->is_old(), "Don't waste time doing this for non-old regions");
116 _scanner->reset_remset(region->bottom(), ShenandoahHeapRegion::region_size_words());
117 }
118
119 bool is_thread_safe() override { return true; }
120 };
121
122 void ShenandoahGeneration::confirm_heuristics_mode() {
123 if (_heuristics->is_diagnostic() && !UnlockDiagnosticVMOptions) {
124 vm_exit_during_initialization(
125 err_msg("Heuristics \"%s\" is diagnostic, and must be enabled via -XX:+UnlockDiagnosticVMOptions.",
126 _heuristics->name()));
127 }
128 if (_heuristics->is_experimental() && !UnlockExperimentalVMOptions) {
129 vm_exit_during_initialization(
130 err_msg("Heuristics \"%s\" is experimental, and must be enabled via -XX:+UnlockExperimentalVMOptions.",
131 _heuristics->name()));
132 }
133 }
134
135 ShenandoahHeuristics* ShenandoahGeneration::initialize_heuristics(ShenandoahMode* gc_mode) {
136 _heuristics = gc_mode->initialize_heuristics(this);
137 _heuristics->set_guaranteed_gc_interval(ShenandoahGuaranteedGCInterval);
138 confirm_heuristics_mode();
139 return _heuristics;
140 }
141
142 size_t ShenandoahGeneration::bytes_allocated_since_gc_start() const {
143 return Atomic::load(&_bytes_allocated_since_gc_start);
144 }
145
146 void ShenandoahGeneration::reset_bytes_allocated_since_gc_start() {
147 Atomic::store(&_bytes_allocated_since_gc_start, (size_t)0);
148 }
149
150 void ShenandoahGeneration::increase_allocated(size_t bytes) {
151 Atomic::add(&_bytes_allocated_since_gc_start, bytes, memory_order_relaxed);
152 }
153
154 void ShenandoahGeneration::set_evacuation_reserve(size_t new_val) {
155 _evacuation_reserve = new_val;
156 }
157
158 size_t ShenandoahGeneration::get_evacuation_reserve() const {
159 return _evacuation_reserve;
160 }
161
162 void ShenandoahGeneration::augment_evacuation_reserve(size_t increment) {
163 _evacuation_reserve += increment;
164 }
165
166 void ShenandoahGeneration::log_status(const char *msg) const {
167 typedef LogTarget(Info, gc, ergo) LogGcInfo;
168
169 if (!LogGcInfo::is_enabled()) {
170 return;
171 }
172
173 // Not under a lock here, so read each of these once to make sure
174 // byte size in proper unit and proper unit for byte size are consistent.
175 size_t v_used = used();
176 size_t v_used_regions = used_regions_size();
177 size_t v_soft_max_capacity = soft_max_capacity();
178 size_t v_max_capacity = max_capacity();
179 size_t v_available = available();
180 size_t v_humongous_waste = get_humongous_waste();
181 LogGcInfo::print("%s: %s generation used: " SIZE_FORMAT "%s, used regions: " SIZE_FORMAT "%s, "
182 "humongous waste: " SIZE_FORMAT "%s, soft capacity: " SIZE_FORMAT "%s, max capacity: " SIZE_FORMAT "%s, "
183 "available: " SIZE_FORMAT "%s", msg, name(),
184 byte_size_in_proper_unit(v_used), proper_unit_for_byte_size(v_used),
185 byte_size_in_proper_unit(v_used_regions), proper_unit_for_byte_size(v_used_regions),
186 byte_size_in_proper_unit(v_humongous_waste), proper_unit_for_byte_size(v_humongous_waste),
187 byte_size_in_proper_unit(v_soft_max_capacity), proper_unit_for_byte_size(v_soft_max_capacity),
188 byte_size_in_proper_unit(v_max_capacity), proper_unit_for_byte_size(v_max_capacity),
189 byte_size_in_proper_unit(v_available), proper_unit_for_byte_size(v_available));
190 }
191
192 void ShenandoahGeneration::reset_mark_bitmap() {
193 ShenandoahHeap* heap = ShenandoahHeap::heap();
194 heap->assert_gc_workers(heap->workers()->active_workers());
195
196 set_mark_incomplete();
197
198 ShenandoahResetBitmapTask task(this);
199 heap->workers()->run_task(&task);
200 }
201
202 // The ideal is to swap the remembered set so the safepoint effort is no more than a few pointer manipulations.
203 // However, limitations in the implementation of the mutator write-barrier make it difficult to simply change the
204 // location of the card table. So the interim implementation of swap_remembered_set will copy the write-table
205 // onto the read-table and will then clear the write-table.
206 void ShenandoahGeneration::swap_remembered_set() {
207 // Must be sure that marking is complete before we swap remembered set.
208 ShenandoahGenerationalHeap* heap = ShenandoahGenerationalHeap::heap();
209 heap->assert_gc_workers(heap->workers()->active_workers());
210 shenandoah_assert_safepoint();
211
212 ShenandoahOldGeneration* old_generation = heap->old_generation();
213 ShenandoahCopyWriteCardTableToRead task(old_generation->card_scan());
214 old_generation->parallel_heap_region_iterate(&task);
215 }
216
217 // Copy the write-version of the card-table into the read-version, clearing the
218 // write-version. The work is done at a safepoint and in parallel by the GC
219 // worker threads.
220 void ShenandoahGeneration::merge_write_table() {
221 // This should only happen for degenerated cycles
222 ShenandoahGenerationalHeap* heap = ShenandoahGenerationalHeap::heap();
223 heap->assert_gc_workers(heap->workers()->active_workers());
224 shenandoah_assert_safepoint();
225
226 ShenandoahOldGeneration* old_generation = heap->old_generation();
227 ShenandoahMergeWriteTable task(old_generation->card_scan());
228 old_generation->parallel_heap_region_iterate(&task);
229 }
230
231 void ShenandoahGeneration::prepare_gc() {
232
233 reset_mark_bitmap();
234
235 // Capture Top At Mark Start for this generation (typically young) and reset mark bitmap.
236 ShenandoahResetUpdateRegionStateClosure cl;
237 parallel_heap_region_iterate_free(&cl);
238 }
239
240 void ShenandoahGeneration::parallel_heap_region_iterate_free(ShenandoahHeapRegionClosure* cl) {
241 ShenandoahHeap::heap()->parallel_heap_region_iterate(cl);
242 }
243
244 void ShenandoahGeneration::compute_evacuation_budgets(ShenandoahHeap* const heap) {
245 shenandoah_assert_generational();
246
247 ShenandoahOldGeneration* const old_generation = heap->old_generation();
248 ShenandoahYoungGeneration* const young_generation = heap->young_generation();
249
250 // During initialization and phase changes, it is more likely that fewer objects die young and old-gen
251 // memory is not yet full (or is in the process of being replaced). During these times especially, it
252 // is beneficial to loan memory from old-gen to young-gen during the evacuation and update-refs phases
253 // of execution.
254
255 // Calculate EvacuationReserve before PromotionReserve. Evacuation is more critical than promotion.
256 // If we cannot evacuate old-gen, we will not be able to reclaim old-gen memory. Promotions are less
257 // critical. If we cannot promote, there may be degradation of young-gen memory because old objects
258 // accumulate there until they can be promoted. This increases the young-gen marking and evacuation work.
259
260 // First priority is to reclaim the easy garbage out of young-gen.
261
262 // maximum_young_evacuation_reserve is upper bound on memory to be evacuated out of young
263 const size_t maximum_young_evacuation_reserve = (young_generation->max_capacity() * ShenandoahEvacReserve) / 100;
264 const size_t young_evacuation_reserve = MIN2(maximum_young_evacuation_reserve, young_generation->available_with_reserve());
265
266 // maximum_old_evacuation_reserve is an upper bound on memory evacuated from old and evacuated to old (promoted),
267 // clamped by the old generation space available.
268 //
269 // Here's the algebra.
270 // Let SOEP = ShenandoahOldEvacRatioPercent,
271 // OE = old evac,
272 // YE = young evac, and
273 // TE = total evac = OE + YE
274 // By definition:
275 // SOEP/100 = OE/TE
276 // = OE/(OE+YE)
277 // => SOEP/(100-SOEP) = OE/((OE+YE)-OE) // componendo-dividendo: If a/b = c/d, then a/(b-a) = c/(d-c)
278 // = OE/YE
279 // => OE = YE*SOEP/(100-SOEP)
280
281 // We have to be careful in the event that SOEP is set to 100 by the user.
282 assert(ShenandoahOldEvacRatioPercent <= 100, "Error");
283 const size_t old_available = old_generation->available();
284 const size_t maximum_old_evacuation_reserve = (ShenandoahOldEvacRatioPercent == 100) ?
285 old_available : MIN2((maximum_young_evacuation_reserve * ShenandoahOldEvacRatioPercent) / (100 - ShenandoahOldEvacRatioPercent),
286 old_available);
287
288
289 // Second priority is to reclaim garbage out of old-gen if there are old-gen collection candidates. Third priority
290 // is to promote as much as we have room to promote. However, if old-gen memory is in short supply, this means young
291 // GC is operating under "duress" and was unable to transfer the memory that we would normally expect. In this case,
292 // old-gen will refrain from compacting itself in order to allow a quicker young-gen cycle (by avoiding the update-refs
293 // through ALL of old-gen). If there is some memory available in old-gen, we will use this for promotions as promotions
294 // do not add to the update-refs burden of GC.
295
296 size_t old_evacuation_reserve, old_promo_reserve;
297 if (is_global()) {
298 // Global GC is typically triggered by user invocation of System.gc(), and typically indicates that there is lots
299 // of garbage to be reclaimed because we are starting a new phase of execution. Marking for global GC may take
300 // significantly longer than typical young marking because we must mark through all old objects. To expedite
301 // evacuation and update-refs, we give emphasis to reclaiming garbage first, wherever that garbage is found.
302 // Global GC will adjust generation sizes to accommodate the collection set it chooses.
303
304 // Set old_promo_reserve to enforce that no regions are preselected for promotion. Such regions typically
305 // have relatively high memory utilization. We still call select_aged_regions() because this will prepare for
306 // promotions in place, if relevant.
307 old_promo_reserve = 0;
308
309 // Dedicate all available old memory to old_evacuation reserve. This may be small, because old-gen is only
310 // expanded based on an existing mixed evacuation workload at the end of the previous GC cycle. We'll expand
311 // the budget for evacuation of old during GLOBAL cset selection.
312 old_evacuation_reserve = maximum_old_evacuation_reserve;
313 } else if (old_generation->has_unprocessed_collection_candidates()) {
314 // We reserved all old-gen memory at end of previous GC to hold anticipated evacuations to old-gen. If this is
315 // mixed evacuation, reserve all of this memory for compaction of old-gen and do not promote. Prioritize compaction
316 // over promotion in order to defragment OLD so that it will be better prepared to efficiently receive promoted memory.
317 old_evacuation_reserve = maximum_old_evacuation_reserve;
318 old_promo_reserve = 0;
319 } else {
320 // Make all old-evacuation memory for promotion, but if we can't use it all for promotion, we'll allow some evacuation.
321 old_evacuation_reserve = 0;
322 old_promo_reserve = maximum_old_evacuation_reserve;
323 }
324 assert(old_evacuation_reserve <= old_available, "Error");
325
326 // We see too many old-evacuation failures if we force ourselves to evacuate into regions that are not initially empty.
327 // So we limit the old-evacuation reserve to unfragmented memory. Even so, old-evacuation is free to fill in nooks and
328 // crannies within existing partially used regions and it generally tries to do so.
329 const size_t old_free_unfragmented = old_generation->free_unaffiliated_regions() * ShenandoahHeapRegion::region_size_bytes();
330 if (old_evacuation_reserve > old_free_unfragmented) {
331 const size_t delta = old_evacuation_reserve - old_free_unfragmented;
332 old_evacuation_reserve -= delta;
333 // Let promo consume fragments of old-gen memory if not global
334 if (!is_global()) {
335 old_promo_reserve += delta;
336 }
337 }
338
339 // Preselect regions for promotion by evacuation (obtaining the live data to seed promoted_reserve),
340 // and identify regions that will promote in place. These use the tenuring threshold.
341 const size_t consumed_by_advance_promotion = select_aged_regions(old_promo_reserve);
342 assert(consumed_by_advance_promotion <= maximum_old_evacuation_reserve, "Cannot promote more than available old-gen memory");
343
344 // Note that unused old_promo_reserve might not be entirely consumed_by_advance_promotion. Do not transfer this
345 // to old_evacuation_reserve because this memory is likely very fragmented, and we do not want to increase the likelihood
346 // of old evacuation failure.
347 young_generation->set_evacuation_reserve(young_evacuation_reserve);
348 old_generation->set_evacuation_reserve(old_evacuation_reserve);
349 old_generation->set_promoted_reserve(consumed_by_advance_promotion);
350
351 // There is no need to expand OLD because all memory used here was set aside at end of previous GC, except in the
352 // case of a GLOBAL gc. During choose_collection_set() of GLOBAL, old will be expanded on demand.
353 }
354
355 // Having chosen the collection set, adjust the budgets for generational mode based on its composition. Note
356 // that young_generation->available() now knows about recently discovered immediate garbage.
357 //
358 void ShenandoahGeneration::adjust_evacuation_budgets(ShenandoahHeap* const heap, ShenandoahCollectionSet* const collection_set) {
359 shenandoah_assert_generational();
360 // We may find that old_evacuation_reserve and/or loaned_for_young_evacuation are not fully consumed, in which case we may
361 // be able to increase regions_available_to_loan
362
363 // The role of adjust_evacuation_budgets() is to compute the correct value of regions_available_to_loan and to make
364 // effective use of this memory, including the remnant memory within these regions that may result from rounding loan to
365 // integral number of regions. Excess memory that is available to be loaned is applied to an allocation supplement,
366 // which allows mutators to allocate memory beyond the current capacity of young-gen on the promise that the loan
367 // will be repaid as soon as we finish updating references for the recently evacuated collection set.
368
369 // We cannot recalculate regions_available_to_loan by simply dividing old_generation->available() by region_size_bytes
370 // because the available memory may be distributed between many partially occupied regions that are already holding old-gen
371 // objects. Memory in partially occupied regions is not "available" to be loaned. Note that an increase in old-gen
372 // available that results from a decrease in memory consumed by old evacuation is not necessarily available to be loaned
373 // to young-gen.
374
375 size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
376 ShenandoahOldGeneration* const old_generation = heap->old_generation();
377 ShenandoahYoungGeneration* const young_generation = heap->young_generation();
378
379 size_t old_evacuated = collection_set->get_old_bytes_reserved_for_evacuation();
380 size_t old_evacuated_committed = (size_t) (ShenandoahOldEvacWaste * double(old_evacuated));
381 size_t old_evacuation_reserve = old_generation->get_evacuation_reserve();
382
383 if (old_evacuated_committed > old_evacuation_reserve) {
384 // This should only happen due to round-off errors when enforcing ShenandoahOldEvacWaste
385 assert(old_evacuated_committed <= (33 * old_evacuation_reserve) / 32,
386 "Round-off errors should be less than 3.125%%, committed: " SIZE_FORMAT ", reserved: " SIZE_FORMAT,
387 old_evacuated_committed, old_evacuation_reserve);
388 old_evacuated_committed = old_evacuation_reserve;
389 // Leave old_evac_reserve as previously configured
390 } else if (old_evacuated_committed < old_evacuation_reserve) {
391 // This happens if the old-gen collection consumes less than full budget.
392 old_evacuation_reserve = old_evacuated_committed;
393 old_generation->set_evacuation_reserve(old_evacuation_reserve);
394 }
395
396 size_t young_advance_promoted = collection_set->get_young_bytes_to_be_promoted();
397 size_t young_advance_promoted_reserve_used = (size_t) (ShenandoahPromoEvacWaste * double(young_advance_promoted));
398
399 size_t young_evacuated = collection_set->get_young_bytes_reserved_for_evacuation();
400 size_t young_evacuated_reserve_used = (size_t) (ShenandoahEvacWaste * double(young_evacuated));
401
402 size_t total_young_available = young_generation->available_with_reserve();
403 assert(young_evacuated_reserve_used <= total_young_available, "Cannot evacuate more than is available in young");
404 young_generation->set_evacuation_reserve(young_evacuated_reserve_used);
405
406 size_t old_available = old_generation->available();
407 // Now that we've established the collection set, we know how much memory is really required by old-gen for evacuation
408 // and promotion reserves. Try shrinking OLD now in case that gives us a bit more runway for mutator allocations during
409 // evac and update phases.
410 size_t old_consumed = old_evacuated_committed + young_advance_promoted_reserve_used;
411
412 if (old_available < old_consumed) {
413 // This can happen due to round-off errors when adding the results of truncated integer arithmetic.
414 // We've already truncated old_evacuated_committed. Truncate young_advance_promoted_reserve_used here.
415 assert(young_advance_promoted_reserve_used <= (33 * (old_available - old_evacuated_committed)) / 32,
416 "Round-off errors should be less than 3.125%%, committed: " SIZE_FORMAT ", reserved: " SIZE_FORMAT,
417 young_advance_promoted_reserve_used, old_available - old_evacuated_committed);
418 young_advance_promoted_reserve_used = old_available - old_evacuated_committed;
419 old_consumed = old_evacuated_committed + young_advance_promoted_reserve_used;
420 }
421
422 assert(old_available >= old_consumed, "Cannot consume (" SIZE_FORMAT ") more than is available (" SIZE_FORMAT ")",
423 old_consumed, old_available);
424 size_t excess_old = old_available - old_consumed;
425 size_t unaffiliated_old_regions = old_generation->free_unaffiliated_regions();
426 size_t unaffiliated_old = unaffiliated_old_regions * region_size_bytes;
427 assert(old_available >= unaffiliated_old, "Unaffiliated old is a subset of old available");
428
429 // Make sure old_evac_committed is unaffiliated
430 if (old_evacuated_committed > 0) {
431 if (unaffiliated_old > old_evacuated_committed) {
432 size_t giveaway = unaffiliated_old - old_evacuated_committed;
433 size_t giveaway_regions = giveaway / region_size_bytes; // round down
434 if (giveaway_regions > 0) {
435 excess_old = MIN2(excess_old, giveaway_regions * region_size_bytes);
436 } else {
437 excess_old = 0;
438 }
439 } else {
440 excess_old = 0;
441 }
442 }
443
444 // If we find that OLD has excess regions, give them back to YOUNG now to reduce likelihood we run out of allocation
445 // runway during evacuation and update-refs.
446 size_t regions_to_xfer = 0;
447 if (excess_old > unaffiliated_old) {
448 // we can give back unaffiliated_old (all of unaffiliated is excess)
449 if (unaffiliated_old_regions > 0) {
450 regions_to_xfer = unaffiliated_old_regions;
451 }
452 } else if (unaffiliated_old_regions > 0) {
453 // excess_old < unaffiliated old: we can give back MIN(excess_old/region_size_bytes, unaffiliated_old_regions)
454 size_t excess_regions = excess_old / region_size_bytes;
455 regions_to_xfer = MIN2(excess_regions, unaffiliated_old_regions);
456 }
457
458 if (regions_to_xfer > 0) {
459 bool result = ShenandoahGenerationalHeap::cast(heap)->generation_sizer()->transfer_to_young(regions_to_xfer);
460 assert(excess_old >= regions_to_xfer * region_size_bytes,
461 "Cannot transfer (" SIZE_FORMAT ", " SIZE_FORMAT ") more than excess old (" SIZE_FORMAT ")",
462 regions_to_xfer, region_size_bytes, excess_old);
463 excess_old -= regions_to_xfer * region_size_bytes;
464 log_debug(gc, ergo)("%s transferred " SIZE_FORMAT " excess regions to young before start of evacuation",
465 result? "Successfully": "Unsuccessfully", regions_to_xfer);
466 }
467
468 // Add in the excess_old memory to hold unanticipated promotions, if any. If there are more unanticipated
469 // promotions than fit in reserved memory, they will be deferred until a future GC pass.
470 size_t total_promotion_reserve = young_advance_promoted_reserve_used + excess_old;
471 old_generation->set_promoted_reserve(total_promotion_reserve);
472 old_generation->reset_promoted_expended();
473 }
474
475 typedef struct {
476 ShenandoahHeapRegion* _region;
477 size_t _live_data;
478 } AgedRegionData;
479
480 static int compare_by_aged_live(AgedRegionData a, AgedRegionData b) {
481 if (a._live_data < b._live_data)
482 return -1;
483 else if (a._live_data > b._live_data)
484 return 1;
485 else return 0;
486 }
487
488 inline void assert_no_in_place_promotions() {
489 #ifdef ASSERT
490 class ShenandoahNoInPlacePromotions : public ShenandoahHeapRegionClosure {
491 public:
492 void heap_region_do(ShenandoahHeapRegion *r) override {
493 assert(r->get_top_before_promote() == nullptr,
494 "Region " SIZE_FORMAT " should not be ready for in-place promotion", r->index());
495 }
496 } cl;
497 ShenandoahHeap::heap()->heap_region_iterate(&cl);
498 #endif
499 }
500
501 // Preselect for inclusion into the collection set regions whose age is at or above tenure age which contain more than
502 // ShenandoahOldGarbageThreshold amounts of garbage. We identify these regions by setting the appropriate entry of
503 // the collection set's preselected regions array to true. All entries are initialized to false before calling this
504 // function.
505 //
506 // During the subsequent selection of the collection set, we give priority to these promotion set candidates.
507 // Without this prioritization, we found that the aged regions tend to be ignored because they typically have
508 // much less garbage and much more live data than the recently allocated "eden" regions. When aged regions are
509 // repeatedly excluded from the collection set, the amount of live memory within the young generation tends to
510 // accumulate and this has the undesirable side effect of causing young-generation collections to require much more
511 // CPU and wall-clock time.
512 //
513 // A second benefit of treating aged regions differently than other regions during collection set selection is
514 // that this allows us to more accurately budget memory to hold the results of evacuation. Memory for evacuation
515 // of aged regions must be reserved in the old generation. Memory for evacuation of all other regions must be
516 // reserved in the young generation.
517 size_t ShenandoahGeneration::select_aged_regions(size_t old_available) {
518
519 // There should be no regions configured for subsequent in-place-promotions carried over from the previous cycle.
520 assert_no_in_place_promotions();
521
522 auto const heap = ShenandoahGenerationalHeap::heap();
523 bool* const candidate_regions_for_promotion_by_copy = heap->collection_set()->preselected_regions();
524 ShenandoahMarkingContext* const ctx = heap->marking_context();
525
526 const uint tenuring_threshold = heap->age_census()->tenuring_threshold();
527 const size_t old_garbage_threshold = (ShenandoahHeapRegion::region_size_bytes() * ShenandoahOldGarbageThreshold) / 100;
528
529 size_t old_consumed = 0;
530 size_t promo_potential = 0;
531 size_t candidates = 0;
532
533 // Tracks the padding of space above top in regions eligible for promotion in place
534 size_t promote_in_place_pad = 0;
535
536 // Sort the promotion-eligible regions in order of increasing live-data-bytes so that we can first reclaim regions that require
537 // less evacuation effort. This prioritizes garbage first, expanding the allocation pool early before we reclaim regions that
538 // have more live data.
539 const size_t num_regions = heap->num_regions();
540
541 ResourceMark rm;
542 AgedRegionData* sorted_regions = NEW_RESOURCE_ARRAY(AgedRegionData, num_regions);
543
544 for (size_t i = 0; i < num_regions; i++) {
545 ShenandoahHeapRegion* const r = heap->get_region(i);
546 if (r->is_empty() || !r->has_live() || !r->is_young() || !r->is_regular()) {
547 // skip over regions that aren't regular young with some live data
548 continue;
549 }
550 if (r->age() >= tenuring_threshold) {
551 if ((r->garbage() < old_garbage_threshold)) {
552 // This tenure-worthy region has too little garbage, so we do not want to expend the copying effort to
553 // reclaim the garbage; instead this region may be eligible for promotion-in-place to the
554 // old generation.
555 HeapWord* tams = ctx->top_at_mark_start(r);
556 HeapWord* original_top = r->top();
557 if (!heap->is_concurrent_old_mark_in_progress() && tams == original_top) {
558 // No allocations from this region have been made during concurrent mark. It meets all the criteria
559 // for in-place-promotion. Though we only need the value of top when we fill the end of the region,
560 // we use this field to indicate that this region should be promoted in place during the evacuation
561 // phase.
562 r->save_top_before_promote();
563
564 size_t remnant_size = r->free() / HeapWordSize;
565 if (remnant_size > ShenandoahHeap::min_fill_size()) {
566 ShenandoahHeap::fill_with_object(original_top, remnant_size);
567 // Fill the remnant memory within this region to assure no allocations prior to promote in place. Otherwise,
568 // newly allocated objects will not be parsable when promote in place tries to register them. Furthermore, any
569 // new allocations would not necessarily be eligible for promotion. This addresses both issues.
570 r->set_top(r->end());
571 promote_in_place_pad += remnant_size * HeapWordSize;
572 } else {
573 // Since the remnant is so small that it cannot be filled, we don't have to worry about any accidental
574 // allocations occurring within this region before the region is promoted in place.
575 }
576 }
577 // Else, we do not promote this region (either in place or by copy) because it has received new allocations.
578
579 // During evacuation, we exclude from promotion regions for which age > tenure threshold, garbage < garbage-threshold,
580 // and get_top_before_promote() != tams
581 } else {
582 // Record this promotion-eligible candidate region. After sorting and selecting the best candidates below,
583 // we may still decide to exclude this promotion-eligible region from the current collection set. If this
584 // happens, we will consider this region as part of the anticipated promotion potential for the next GC
585 // pass; see further below.
586 sorted_regions[candidates]._region = r;
587 sorted_regions[candidates++]._live_data = r->get_live_data_bytes();
588 }
589 } else {
590 // We only evacuate & promote objects from regular regions whose garbage() is above old-garbage-threshold.
591 // Objects in tenure-worthy regions with less garbage are promoted in place. These take a different path to
592 // old-gen. Regions excluded from promotion because their garbage content is too low (causing us to anticipate that
593 // the region would be promoted in place) may be eligible for evacuation promotion by the time promotion takes
594 // place during a subsequent GC pass because more garbage is found within the region between now and then. This
595 // should not happen if we are properly adapting the tenure age. The theory behind adaptive tenuring threshold
596 // is to choose the youngest age that demonstrates no "significant" further loss of population since the previous
597 // age. If not this, we expect the tenure age to demonstrate linear population decay for at least two population
598 // samples, whereas we expect to observe exponential population decay for ages younger than the tenure age.
599 //
600 // In the case that certain regions which were anticipated to be promoted in place need to be promoted by
601 // evacuation, it may be the case that there is not sufficient reserve within old-gen to hold evacuation of
602 // these regions. The likely outcome is that these regions will not be selected for evacuation or promotion
603 // in the current cycle and we will anticipate that they will be promoted in the next cycle. This will cause
604 // us to reserve more old-gen memory so that these objects can be promoted in the subsequent cycle.
605 if (heap->is_aging_cycle() && (r->age() + 1 == tenuring_threshold)) {
606 if (r->garbage() >= old_garbage_threshold) {
607 promo_potential += r->get_live_data_bytes();
608 }
609 }
610 }
611 // Note that we keep going even if one region is excluded from selection.
612 // Subsequent regions may be selected if they have smaller live data.
613 }
614 // Sort in increasing order according to live data bytes. Note that candidates represents the number of regions
615 // that qualify to be promoted by evacuation.
616 if (candidates > 0) {
617 size_t selected_regions = 0;
618 size_t selected_live = 0;
619 QuickSort::sort<AgedRegionData>(sorted_regions, candidates, compare_by_aged_live);
620 for (size_t i = 0; i < candidates; i++) {
621 ShenandoahHeapRegion* const region = sorted_regions[i]._region;
622 size_t region_live_data = sorted_regions[i]._live_data;
623 size_t promotion_need = (size_t) (region_live_data * ShenandoahPromoEvacWaste);
624 if (old_consumed + promotion_need <= old_available) {
625 old_consumed += promotion_need;
626 candidate_regions_for_promotion_by_copy[region->index()] = true;
627 selected_regions++;
628 selected_live += region_live_data;
629 } else {
630 // We rejected this promotable region from the collection set because we had no room to hold its copy.
631 // Add this region to promo potential for next GC.
632 promo_potential += region_live_data;
633 assert(!candidate_regions_for_promotion_by_copy[region->index()], "Shouldn't be selected");
634 }
635 // We keep going even if one region is excluded from selection because we need to accumulate all eligible
636 // regions that are not preselected into promo_potential
637 }
638 log_debug(gc)("Preselected " SIZE_FORMAT " regions containing " SIZE_FORMAT " live bytes,"
639 " consuming: " SIZE_FORMAT " of budgeted: " SIZE_FORMAT,
640 selected_regions, selected_live, old_consumed, old_available);
641 }
642
643 heap->old_generation()->set_pad_for_promote_in_place(promote_in_place_pad);
644 heap->old_generation()->set_promotion_potential(promo_potential);
645 return old_consumed;
646 }
647
648 void ShenandoahGeneration::prepare_regions_and_collection_set(bool concurrent) {
649 ShenandoahHeap* heap = ShenandoahHeap::heap();
650 ShenandoahCollectionSet* collection_set = heap->collection_set();
651 bool is_generational = heap->mode()->is_generational();
652
653 assert(!heap->is_full_gc_in_progress(), "Only for concurrent and degenerated GC");
654 assert(!is_old(), "Only YOUNG and GLOBAL GC perform evacuations");
655 {
656 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::final_update_region_states :
657 ShenandoahPhaseTimings::degen_gc_final_update_region_states);
658 ShenandoahFinalMarkUpdateRegionStateClosure cl(complete_marking_context());
659 parallel_heap_region_iterate(&cl);
660
661 if (is_young()) {
662 // We always need to update the watermark for old regions. If there
663 // are mixed collections pending, we also need to synchronize the
664 // pinned status for old regions. Since we are already visiting every
665 // old region here, go ahead and sync the pin status too.
666 ShenandoahFinalMarkUpdateRegionStateClosure old_cl(nullptr);
667 heap->old_generation()->parallel_heap_region_iterate(&old_cl);
668 }
669 }
670
671 // Tally the census counts and compute the adaptive tenuring threshold
672 if (is_generational && ShenandoahGenerationalAdaptiveTenuring && !ShenandoahGenerationalCensusAtEvac) {
673 // Objects above TAMS weren't included in the age census. Since they were all
674 // allocated in this cycle they belong in the age 0 cohort. We walk over all
675 // young regions and sum the volume of objects between TAMS and top.
676 ShenandoahUpdateCensusZeroCohortClosure age0_cl(complete_marking_context());
677 heap->young_generation()->heap_region_iterate(&age0_cl);
678 size_t age0_pop = age0_cl.get_age0_population();
679
680 // Update the global census, including the missed age 0 cohort above,
681 // along with the census done during marking, and compute the tenuring threshold.
682 ShenandoahAgeCensus* census = ShenandoahGenerationalHeap::heap()->age_census();
683 census->update_census(age0_pop);
684 #ifndef PRODUCT
685 size_t total_pop = age0_cl.get_total_population();
686 size_t total_census = census->get_total();
687 // Usually total_pop > total_census, but not by too much.
688 // We use integer division so anything up to just less than 2 is considered
689 // reasonable, and the "+1" is to avoid divide-by-zero.
690 assert((total_pop+1)/(total_census+1) == 1, "Extreme divergence: "
691 SIZE_FORMAT "/" SIZE_FORMAT, total_pop, total_census);
692 #endif
693 }
694
695 {
696 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::choose_cset :
697 ShenandoahPhaseTimings::degen_gc_choose_cset);
698
699 collection_set->clear();
700 ShenandoahHeapLocker locker(heap->lock());
701 if (is_generational) {
702 // Seed the collection set with resource area-allocated
703 // preselected regions, which are removed when we exit this scope.
704 ShenandoahCollectionSetPreselector preselector(collection_set, heap->num_regions());
705
706 // Find the amount that will be promoted, regions that will be promoted in
707 // place, and preselect older regions that will be promoted by evacuation.
708 compute_evacuation_budgets(heap);
709
710 // Choose the collection set, including the regions preselected above for
711 // promotion into the old generation.
712 _heuristics->choose_collection_set(collection_set);
713 if (!collection_set->is_empty()) {
714 // only make use of evacuation budgets when we are evacuating
715 adjust_evacuation_budgets(heap, collection_set);
716 }
717
718 if (is_global()) {
719 // We have just chosen a collection set for a global cycle. The mark bitmap covering old regions is complete, so
720 // the remembered set scan can use that to avoid walking into garbage. When the next old mark begins, we will
721 // use the mark bitmap to make the old regions parsable by coalescing and filling any unmarked objects. Thus,
722 // we prepare for old collections by remembering which regions are old at this time. Note that any objects
723 // promoted into old regions will be above TAMS, and so will be considered marked. However, free regions that
724 // become old after this point will not be covered correctly by the mark bitmap, so we must be careful not to
725 // coalesce those regions. Only the old regions which are not part of the collection set at this point are
726 // eligible for coalescing. As implemented now, this has the side effect of possibly initiating mixed-evacuations
727 // after a global cycle for old regions that were not included in this collection set.
728 heap->old_generation()->prepare_for_mixed_collections_after_global_gc();
729 }
730 } else {
731 _heuristics->choose_collection_set(collection_set);
732 }
733 }
734
735
736 {
737 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::final_rebuild_freeset :
738 ShenandoahPhaseTimings::degen_gc_final_rebuild_freeset);
739 ShenandoahHeapLocker locker(heap->lock());
740 size_t young_cset_regions, old_cset_regions;
741
742 // We are preparing for evacuation. At this time, we ignore cset region tallies.
743 size_t first_old, last_old, num_old;
744 heap->free_set()->prepare_to_rebuild(young_cset_regions, old_cset_regions, first_old, last_old, num_old);
745 // Free set construction uses reserve quantities, because they are known to be valid here
746 heap->free_set()->finish_rebuild(young_cset_regions, old_cset_regions, num_old, true);
747 }
748 }
749
750 bool ShenandoahGeneration::is_bitmap_clear() {
751 ShenandoahHeap* heap = ShenandoahHeap::heap();
752 ShenandoahMarkingContext* context = heap->marking_context();
753 const size_t num_regions = heap->num_regions();
754 for (size_t idx = 0; idx < num_regions; idx++) {
755 ShenandoahHeapRegion* r = heap->get_region(idx);
756 if (contains(r) && r->is_affiliated()) {
757 if (heap->is_bitmap_slice_committed(r) && (context->top_at_mark_start(r) > r->bottom()) &&
758 !context->is_bitmap_clear_range(r->bottom(), r->end())) {
759 return false;
760 }
761 }
762 }
763 return true;
764 }
765
766 bool ShenandoahGeneration::is_mark_complete() {
767 return _is_marking_complete.is_set();
768 }
769
770 void ShenandoahGeneration::set_mark_complete() {
771 _is_marking_complete.set();
772 }
773
774 void ShenandoahGeneration::set_mark_incomplete() {
775 _is_marking_complete.unset();
776 }
777
778 ShenandoahMarkingContext* ShenandoahGeneration::complete_marking_context() {
779 assert(is_mark_complete(), "Marking must be completed.");
780 return ShenandoahHeap::heap()->marking_context();
781 }
782
783 void ShenandoahGeneration::cancel_marking() {
784 log_info(gc)("Cancel marking: %s", name());
785 if (is_concurrent_mark_in_progress()) {
786 set_mark_incomplete();
787 }
788 _task_queues->clear();
789 ref_processor()->abandon_partial_discovery();
790 set_concurrent_mark_in_progress(false);
791 }
792
793 ShenandoahGeneration::ShenandoahGeneration(ShenandoahGenerationType type,
794 uint max_workers,
795 size_t max_capacity,
796 size_t soft_max_capacity) :
797 _type(type),
798 _task_queues(new ShenandoahObjToScanQueueSet(max_workers)),
799 _ref_processor(new ShenandoahReferenceProcessor(MAX2(max_workers, 1U))),
800 _affiliated_region_count(0), _humongous_waste(0), _evacuation_reserve(0),
801 _used(0), _bytes_allocated_since_gc_start(0),
802 _max_capacity(max_capacity), _soft_max_capacity(soft_max_capacity),
803 _heuristics(nullptr)
804 {
805 _is_marking_complete.set();
806 assert(max_workers > 0, "At least one queue");
807 for (uint i = 0; i < max_workers; ++i) {
808 ShenandoahObjToScanQueue* task_queue = new ShenandoahObjToScanQueue();
809 _task_queues->register_queue(i, task_queue);
810 }
811 }
812
813 ShenandoahGeneration::~ShenandoahGeneration() {
814 for (uint i = 0; i < _task_queues->size(); ++i) {
815 ShenandoahObjToScanQueue* q = _task_queues->queue(i);
816 delete q;
817 }
818 delete _task_queues;
819 }
820
821 void ShenandoahGeneration::reserve_task_queues(uint workers) {
822 _task_queues->reserve(workers);
823 }
824
825 ShenandoahObjToScanQueueSet* ShenandoahGeneration::old_gen_task_queues() const {
826 return nullptr;
827 }
828
829 void ShenandoahGeneration::scan_remembered_set(bool is_concurrent) {
830 assert(is_young(), "Should only scan remembered set for young generation.");
831
832 ShenandoahGenerationalHeap* const heap = ShenandoahGenerationalHeap::heap();
833 uint nworkers = heap->workers()->active_workers();
834 reserve_task_queues(nworkers);
835
836 ShenandoahReferenceProcessor* rp = ref_processor();
837 ShenandoahRegionChunkIterator work_list(nworkers);
838 ShenandoahScanRememberedTask task(task_queues(), old_gen_task_queues(), rp, &work_list, is_concurrent);
839 heap->assert_gc_workers(nworkers);
840 heap->workers()->run_task(&task);
841 if (ShenandoahEnableCardStats) {
842 ShenandoahScanRemembered* scanner = heap->old_generation()->card_scan();
843 assert(scanner != nullptr, "Not generational");
844 scanner->log_card_stats(nworkers, CARD_STAT_SCAN_RS);
845 }
846 }
847
848 size_t ShenandoahGeneration::increment_affiliated_region_count() {
849 shenandoah_assert_heaplocked_or_safepoint();
850 // During full gc, multiple GC worker threads may change region affiliations without a lock. No lock is enforced
851 // on read and write of _affiliated_region_count. At the end of full gc, a single thread overwrites the count with
852 // a coherent value.
853 _affiliated_region_count++;
854 return _affiliated_region_count;
855 }
856
857 size_t ShenandoahGeneration::decrement_affiliated_region_count() {
858 shenandoah_assert_heaplocked_or_safepoint();
859 // During full gc, multiple GC worker threads may change region affiliations without a lock. No lock is enforced
860 // on read and write of _affiliated_region_count. At the end of full gc, a single thread overwrites the count with
861 // a coherent value.
862 _affiliated_region_count--;
863 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
864 (_used + _humongous_waste <= _affiliated_region_count * ShenandoahHeapRegion::region_size_bytes()),
865 "used + humongous cannot exceed regions");
866 return _affiliated_region_count;
867 }
868
869 size_t ShenandoahGeneration::increase_affiliated_region_count(size_t delta) {
870 shenandoah_assert_heaplocked_or_safepoint();
871 _affiliated_region_count += delta;
872 return _affiliated_region_count;
873 }
874
875 size_t ShenandoahGeneration::decrease_affiliated_region_count(size_t delta) {
876 shenandoah_assert_heaplocked_or_safepoint();
877 assert(_affiliated_region_count >= delta, "Affiliated region count cannot be negative");
878
879 _affiliated_region_count -= delta;
880 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
881 (_used + _humongous_waste <= _affiliated_region_count * ShenandoahHeapRegion::region_size_bytes()),
882 "used + humongous cannot exceed regions");
883 return _affiliated_region_count;
884 }
885
886 void ShenandoahGeneration::establish_usage(size_t num_regions, size_t num_bytes, size_t humongous_waste) {
887 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
888 _affiliated_region_count = num_regions;
889 _used = num_bytes;
890 _humongous_waste = humongous_waste;
891 }
892
893 void ShenandoahGeneration::increase_used(size_t bytes) {
894 Atomic::add(&_used, bytes);
895 }
896
897 void ShenandoahGeneration::increase_humongous_waste(size_t bytes) {
898 if (bytes > 0) {
899 Atomic::add(&_humongous_waste, bytes);
900 }
901 }
902
903 void ShenandoahGeneration::decrease_humongous_waste(size_t bytes) {
904 if (bytes > 0) {
905 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() || (_humongous_waste >= bytes),
906 "Waste (" SIZE_FORMAT ") cannot be negative (after subtracting " SIZE_FORMAT ")", _humongous_waste, bytes);
907 Atomic::sub(&_humongous_waste, bytes);
908 }
909 }
910
911 void ShenandoahGeneration::decrease_used(size_t bytes) {
912 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
913 (_used >= bytes), "cannot reduce bytes used by generation below zero");
914 Atomic::sub(&_used, bytes);
915 }
916
917 size_t ShenandoahGeneration::used_regions() const {
918 return _affiliated_region_count;
919 }
920
921 size_t ShenandoahGeneration::free_unaffiliated_regions() const {
922 size_t result = max_capacity() / ShenandoahHeapRegion::region_size_bytes();
923 if (_affiliated_region_count > result) {
924 result = 0;
925 } else {
926 result -= _affiliated_region_count;
927 }
928 return result;
929 }
930
931 size_t ShenandoahGeneration::used_regions_size() const {
932 return _affiliated_region_count * ShenandoahHeapRegion::region_size_bytes();
933 }
934
935 size_t ShenandoahGeneration::available() const {
936 return available(max_capacity());
937 }
938
939 // For ShenandoahYoungGeneration, Include the young available that may have been reserved for the Collector.
940 size_t ShenandoahGeneration::available_with_reserve() const {
941 return available(max_capacity());
942 }
943
944 size_t ShenandoahGeneration::soft_available() const {
945 return available(soft_max_capacity());
946 }
947
948 size_t ShenandoahGeneration::available(size_t capacity) const {
949 size_t in_use = used() + get_humongous_waste();
950 return in_use > capacity ? 0 : capacity - in_use;
951 }
952
953 size_t ShenandoahGeneration::increase_capacity(size_t increment) {
954 shenandoah_assert_heaplocked_or_safepoint();
955
956 // We do not enforce that new capacity >= heap->max_size_for(this). The maximum generation size is treated as a rule of thumb
957 // which may be violated during certain transitions, such as when we are forcing transfers for the purpose of promoting regions
958 // in place.
959 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
960 (_max_capacity + increment <= ShenandoahHeap::heap()->max_capacity()), "Generation cannot be larger than heap size");
961 assert(increment % ShenandoahHeapRegion::region_size_bytes() == 0, "Generation capacity must be multiple of region size");
962 _max_capacity += increment;
963
964 // This detects arithmetic wraparound on _used
965 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
966 (_affiliated_region_count * ShenandoahHeapRegion::region_size_bytes() >= _used),
967 "Affiliated regions must hold more than what is currently used");
968 return _max_capacity;
969 }
970
971 size_t ShenandoahGeneration::set_capacity(size_t byte_size) {
972 shenandoah_assert_heaplocked_or_safepoint();
973 _max_capacity = byte_size;
974 return _max_capacity;
975 }
976
977 size_t ShenandoahGeneration::decrease_capacity(size_t decrement) {
978 shenandoah_assert_heaplocked_or_safepoint();
979
980 // We do not enforce that new capacity >= heap->min_size_for(this). The minimum generation size is treated as a rule of thumb
981 // which may be violated during certain transitions, such as when we are forcing transfers for the purpose of promoting regions
982 // in place.
983 assert(decrement % ShenandoahHeapRegion::region_size_bytes() == 0, "Generation capacity must be multiple of region size");
984 assert(_max_capacity >= decrement, "Generation capacity cannot be negative");
985
986 _max_capacity -= decrement;
987
988 // This detects arithmetic wraparound on _used
989 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
990 (_affiliated_region_count * ShenandoahHeapRegion::region_size_bytes() >= _used),
991 "Affiliated regions must hold more than what is currently used");
992 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
993 (_used <= _max_capacity), "Cannot use more than capacity");
994 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
995 (_affiliated_region_count * ShenandoahHeapRegion::region_size_bytes() <= _max_capacity),
996 "Cannot use more than capacity");
997 return _max_capacity;
998 }
999
1000 void ShenandoahGeneration::record_success_concurrent(bool abbreviated) {
1001 heuristics()->record_success_concurrent();
1002 ShenandoahHeap::heap()->shenandoah_policy()->record_success_concurrent(is_young(), abbreviated);
1003 }