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/shenandoahHeapRegionClosures.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 template <bool PREPARE_FOR_CURRENT_CYCLE, bool FULL_GC = false>
45 class ShenandoahResetBitmapClosure final : public ShenandoahHeapRegionClosure {
46 private:
47 ShenandoahHeap* _heap;
48 ShenandoahMarkingContext* _ctx;
49
50 public:
51 explicit ShenandoahResetBitmapClosure() :
52 ShenandoahHeapRegionClosure(), _heap(ShenandoahHeap::heap()), _ctx(_heap->marking_context()) {}
53
54 void heap_region_do(ShenandoahHeapRegion* region) override {
55 assert(!_heap->is_uncommit_in_progress(), "Cannot uncommit bitmaps while resetting them.");
56 if (PREPARE_FOR_CURRENT_CYCLE) {
57 if (region->need_bitmap_reset() && _heap->is_bitmap_slice_committed(region)) {
58 _ctx->clear_bitmap(region);
59 } else {
60 region->set_needs_bitmap_reset();
61 }
62 // Capture Top At Mark Start for this generation.
63 if (FULL_GC || region->is_active()) {
64 // Reset live data and set TAMS optimistically. We would recheck these under the pause
65 // anyway to capture any updates that happened since now.
66 _ctx->capture_top_at_mark_start(region);
67 region->clear_live_data();
68 }
69 } else {
70 if (_heap->is_bitmap_slice_committed(region)) {
71 _ctx->clear_bitmap(region);
72 region->unset_needs_bitmap_reset();
73 } else {
74 region->set_needs_bitmap_reset();
75 }
76 }
77 }
78
79 bool is_thread_safe() override { return true; }
80 };
81
82 // Copy the write-version of the card-table into the read-version, clearing the
83 // write-copy.
84 class ShenandoahMergeWriteTable: public ShenandoahHeapRegionClosure {
85 private:
86 ShenandoahScanRemembered* _scanner;
87 public:
88 ShenandoahMergeWriteTable(ShenandoahScanRemembered* scanner) : _scanner(scanner) {}
89
90 void heap_region_do(ShenandoahHeapRegion* r) override {
91 assert(r->is_old(), "Don't waste time doing this for non-old regions");
92 _scanner->merge_write_table(r->bottom(), ShenandoahHeapRegion::region_size_words());
93 }
94
95 bool is_thread_safe() override {
96 return true;
97 }
98 };
99
100 // Add [TAMS, top) volume over young regions. Used to correct age 0 cohort census
101 // for adaptive tenuring when census is taken during marking.
102 // In non-product builds, for the purposes of verification, we also collect the total
103 // live objects in young regions as well.
104 class ShenandoahUpdateCensusZeroCohortClosure : public ShenandoahHeapRegionClosure {
105 private:
106 ShenandoahMarkingContext* const _ctx;
107 // Population size units are words (not bytes)
108 size_t _age0_pop; // running tally of age0 population size
109 size_t _total_pop; // total live population size
110 public:
111 explicit ShenandoahUpdateCensusZeroCohortClosure(ShenandoahMarkingContext* ctx)
112 : _ctx(ctx), _age0_pop(0), _total_pop(0) {}
113
114 void heap_region_do(ShenandoahHeapRegion* r) override {
115 if (_ctx != nullptr && r->is_active()) {
116 assert(r->is_young(), "Young regions only");
117 HeapWord* tams = _ctx->top_at_mark_start(r);
118 HeapWord* top = r->top();
119 if (top > tams) {
120 _age0_pop += pointer_delta(top, tams);
121 }
122 // TODO: check significance of _ctx != nullptr above, can that
123 // spoof _total_pop in some corner cases?
124 NOT_PRODUCT(_total_pop += r->get_live_data_words();)
125 }
126 }
127
128 size_t get_age0_population() const { return _age0_pop; }
129 size_t get_total_population() const { return _total_pop; }
130 };
131
132 void ShenandoahGeneration::confirm_heuristics_mode() {
133 if (_heuristics->is_diagnostic() && !UnlockDiagnosticVMOptions) {
134 vm_exit_during_initialization(
135 err_msg("Heuristics \"%s\" is diagnostic, and must be enabled via -XX:+UnlockDiagnosticVMOptions.",
136 _heuristics->name()));
137 }
138 if (_heuristics->is_experimental() && !UnlockExperimentalVMOptions) {
139 vm_exit_during_initialization(
140 err_msg("Heuristics \"%s\" is experimental, and must be enabled via -XX:+UnlockExperimentalVMOptions.",
141 _heuristics->name()));
142 }
143 }
144
145 ShenandoahHeuristics* ShenandoahGeneration::initialize_heuristics(ShenandoahMode* gc_mode) {
146 _heuristics = gc_mode->initialize_heuristics(this);
147 _heuristics->set_guaranteed_gc_interval(ShenandoahGuaranteedGCInterval);
148 confirm_heuristics_mode();
149 return _heuristics;
150 }
151
152 size_t ShenandoahGeneration::bytes_allocated_since_gc_start() const {
153 return Atomic::load(&_bytes_allocated_since_gc_start);
154 }
155
156 void ShenandoahGeneration::reset_bytes_allocated_since_gc_start() {
157 Atomic::store(&_bytes_allocated_since_gc_start, (size_t)0);
158 }
159
160 void ShenandoahGeneration::increase_allocated(size_t bytes) {
161 Atomic::add(&_bytes_allocated_since_gc_start, bytes, memory_order_relaxed);
162 }
163
164 void ShenandoahGeneration::set_evacuation_reserve(size_t new_val) {
165 _evacuation_reserve = new_val;
166 }
167
168 size_t ShenandoahGeneration::get_evacuation_reserve() const {
169 return _evacuation_reserve;
170 }
171
172 void ShenandoahGeneration::augment_evacuation_reserve(size_t increment) {
173 _evacuation_reserve += increment;
174 }
175
176 void ShenandoahGeneration::log_status(const char *msg) const {
177 typedef LogTarget(Info, gc, ergo) LogGcInfo;
178
179 if (!LogGcInfo::is_enabled()) {
180 return;
181 }
182
183 // Not under a lock here, so read each of these once to make sure
184 // byte size in proper unit and proper unit for byte size are consistent.
185 const size_t v_used = used();
186 const size_t v_used_regions = used_regions_size();
187 const size_t v_soft_max_capacity = ShenandoahHeap::heap()->soft_max_capacity();
188 const size_t v_max_capacity = max_capacity();
189 const size_t v_available = available();
190 const size_t v_humongous_waste = get_humongous_waste();
191
192 const LogGcInfo target;
193 LogStream ls(target);
194 ls.print("%s: ", msg);
195 if (_type != NON_GEN) {
196 ls.print("%s generation ", name());
197 }
198
199 ls.print_cr("used: " PROPERFMT ", used regions: " PROPERFMT ", humongous waste: " PROPERFMT
200 ", soft capacity: " PROPERFMT ", max capacity: " PROPERFMT ", available: " PROPERFMT,
201 PROPERFMTARGS(v_used), PROPERFMTARGS(v_used_regions), PROPERFMTARGS(v_humongous_waste),
202 PROPERFMTARGS(v_soft_max_capacity), PROPERFMTARGS(v_max_capacity), PROPERFMTARGS(v_available));
203 }
204
205 template <bool PREPARE_FOR_CURRENT_CYCLE, bool FULL_GC>
206 void ShenandoahGeneration::reset_mark_bitmap() {
207 ShenandoahHeap* heap = ShenandoahHeap::heap();
208 heap->assert_gc_workers(heap->workers()->active_workers());
209
210 set_mark_incomplete();
211
212 ShenandoahResetBitmapClosure<PREPARE_FOR_CURRENT_CYCLE, FULL_GC> closure;
213 parallel_heap_region_iterate_free(&closure);
214 }
215 // Explicit specializations
216 template void ShenandoahGeneration::reset_mark_bitmap<true, false>();
217 template void ShenandoahGeneration::reset_mark_bitmap<true, true>();
218 template void ShenandoahGeneration::reset_mark_bitmap<false, false>();
219
220 // Swap the read and write card table pointers prior to the next remset scan.
221 // This avoids the need to synchronize reads of the table by the GC workers
222 // doing remset scanning, on the one hand, with the dirtying of the table by
223 // mutators on the other.
224 void ShenandoahGeneration::swap_card_tables() {
225 // Must be sure that marking is complete before we swap remembered set.
226 ShenandoahGenerationalHeap* heap = ShenandoahGenerationalHeap::heap();
227 heap->assert_gc_workers(heap->workers()->active_workers());
228 shenandoah_assert_safepoint();
229
230 ShenandoahOldGeneration* old_generation = heap->old_generation();
231 old_generation->card_scan()->swap_card_tables();
232 }
233
234 // Copy the write-version of the card-table into the read-version, clearing the
235 // write-version. The work is done at a safepoint and in parallel by the GC
236 // worker threads.
237 void ShenandoahGeneration::merge_write_table() {
238 // This should only happen for degenerated cycles
239 ShenandoahGenerationalHeap* heap = ShenandoahGenerationalHeap::heap();
240 heap->assert_gc_workers(heap->workers()->active_workers());
241 shenandoah_assert_safepoint();
242
243 ShenandoahOldGeneration* old_generation = heap->old_generation();
244 ShenandoahMergeWriteTable task(old_generation->card_scan());
245 old_generation->parallel_heap_region_iterate(&task);
246 }
247
248 void ShenandoahGeneration::prepare_gc() {
249 reset_mark_bitmap<true>();
250 }
251
252 void ShenandoahGeneration::parallel_heap_region_iterate_free(ShenandoahHeapRegionClosure* cl) {
253 ShenandoahHeap::heap()->parallel_heap_region_iterate(cl);
254 }
255
256 void ShenandoahGeneration::compute_evacuation_budgets(ShenandoahHeap* const heap) {
257 shenandoah_assert_generational();
258
259 ShenandoahOldGeneration* const old_generation = heap->old_generation();
260 ShenandoahYoungGeneration* const young_generation = heap->young_generation();
261
262 // During initialization and phase changes, it is more likely that fewer objects die young and old-gen
263 // memory is not yet full (or is in the process of being replaced). During these times especially, it
264 // is beneficial to loan memory from old-gen to young-gen during the evacuation and update-refs phases
265 // of execution.
266
267 // Calculate EvacuationReserve before PromotionReserve. Evacuation is more critical than promotion.
268 // If we cannot evacuate old-gen, we will not be able to reclaim old-gen memory. Promotions are less
269 // critical. If we cannot promote, there may be degradation of young-gen memory because old objects
270 // accumulate there until they can be promoted. This increases the young-gen marking and evacuation work.
271
272 // First priority is to reclaim the easy garbage out of young-gen.
273
274 // maximum_young_evacuation_reserve is upper bound on memory to be evacuated out of young
275 const size_t maximum_young_evacuation_reserve = (young_generation->max_capacity() * ShenandoahEvacReserve) / 100;
276 const size_t young_evacuation_reserve = MIN2(maximum_young_evacuation_reserve, young_generation->available_with_reserve());
277
278 // maximum_old_evacuation_reserve is an upper bound on memory evacuated from old and evacuated to old (promoted),
279 // clamped by the old generation space available.
280 //
281 // Here's the algebra.
282 // Let SOEP = ShenandoahOldEvacRatioPercent,
283 // OE = old evac,
284 // YE = young evac, and
285 // TE = total evac = OE + YE
286 // By definition:
287 // SOEP/100 = OE/TE
288 // = OE/(OE+YE)
289 // => SOEP/(100-SOEP) = OE/((OE+YE)-OE) // componendo-dividendo: If a/b = c/d, then a/(b-a) = c/(d-c)
290 // = OE/YE
291 // => OE = YE*SOEP/(100-SOEP)
292
293 // We have to be careful in the event that SOEP is set to 100 by the user.
294 assert(ShenandoahOldEvacRatioPercent <= 100, "Error");
295 const size_t old_available = old_generation->available();
296 const size_t maximum_old_evacuation_reserve = (ShenandoahOldEvacRatioPercent == 100) ?
297 old_available : MIN2((maximum_young_evacuation_reserve * ShenandoahOldEvacRatioPercent) / (100 - ShenandoahOldEvacRatioPercent),
298 old_available);
299
300
301 // Second priority is to reclaim garbage out of old-gen if there are old-gen collection candidates. Third priority
302 // is to promote as much as we have room to promote. However, if old-gen memory is in short supply, this means young
303 // GC is operating under "duress" and was unable to transfer the memory that we would normally expect. In this case,
304 // old-gen will refrain from compacting itself in order to allow a quicker young-gen cycle (by avoiding the update-refs
305 // through ALL of old-gen). If there is some memory available in old-gen, we will use this for promotions as promotions
306 // do not add to the update-refs burden of GC.
307
308 size_t old_evacuation_reserve, old_promo_reserve;
309 if (is_global()) {
310 // Global GC is typically triggered by user invocation of System.gc(), and typically indicates that there is lots
311 // of garbage to be reclaimed because we are starting a new phase of execution. Marking for global GC may take
312 // significantly longer than typical young marking because we must mark through all old objects. To expedite
313 // evacuation and update-refs, we give emphasis to reclaiming garbage first, wherever that garbage is found.
314 // Global GC will adjust generation sizes to accommodate the collection set it chooses.
315
316 // Set old_promo_reserve to enforce that no regions are preselected for promotion. Such regions typically
317 // have relatively high memory utilization. We still call select_aged_regions() because this will prepare for
318 // promotions in place, if relevant.
319 old_promo_reserve = 0;
320
321 // Dedicate all available old memory to old_evacuation reserve. This may be small, because old-gen is only
322 // expanded based on an existing mixed evacuation workload at the end of the previous GC cycle. We'll expand
323 // the budget for evacuation of old during GLOBAL cset selection.
324 old_evacuation_reserve = maximum_old_evacuation_reserve;
325 } else if (old_generation->has_unprocessed_collection_candidates()) {
326 // We reserved all old-gen memory at end of previous GC to hold anticipated evacuations to old-gen. If this is
327 // mixed evacuation, reserve all of this memory for compaction of old-gen and do not promote. Prioritize compaction
328 // over promotion in order to defragment OLD so that it will be better prepared to efficiently receive promoted memory.
329 old_evacuation_reserve = maximum_old_evacuation_reserve;
330 old_promo_reserve = 0;
331 } else {
332 // Make all old-evacuation memory for promotion, but if we can't use it all for promotion, we'll allow some evacuation.
333 old_evacuation_reserve = 0;
334 old_promo_reserve = maximum_old_evacuation_reserve;
335 }
336 assert(old_evacuation_reserve <= old_available, "Error");
337
338 // We see too many old-evacuation failures if we force ourselves to evacuate into regions that are not initially empty.
339 // So we limit the old-evacuation reserve to unfragmented memory. Even so, old-evacuation is free to fill in nooks and
340 // crannies within existing partially used regions and it generally tries to do so.
341 const size_t old_free_unfragmented = old_generation->free_unaffiliated_regions() * ShenandoahHeapRegion::region_size_bytes();
342 if (old_evacuation_reserve > old_free_unfragmented) {
343 const size_t delta = old_evacuation_reserve - old_free_unfragmented;
344 old_evacuation_reserve -= delta;
345 // Let promo consume fragments of old-gen memory if not global
346 if (!is_global()) {
347 old_promo_reserve += delta;
348 }
349 }
350
351 // Preselect regions for promotion by evacuation (obtaining the live data to seed promoted_reserve),
352 // and identify regions that will promote in place. These use the tenuring threshold.
353 const size_t consumed_by_advance_promotion = select_aged_regions(old_promo_reserve);
354 assert(consumed_by_advance_promotion <= maximum_old_evacuation_reserve, "Cannot promote more than available old-gen memory");
355
356 // Note that unused old_promo_reserve might not be entirely consumed_by_advance_promotion. Do not transfer this
357 // to old_evacuation_reserve because this memory is likely very fragmented, and we do not want to increase the likelihood
358 // of old evacuation failure.
359 young_generation->set_evacuation_reserve(young_evacuation_reserve);
360 old_generation->set_evacuation_reserve(old_evacuation_reserve);
361 old_generation->set_promoted_reserve(consumed_by_advance_promotion);
362
363 // There is no need to expand OLD because all memory used here was set aside at end of previous GC, except in the
364 // case of a GLOBAL gc. During choose_collection_set() of GLOBAL, old will be expanded on demand.
365 }
366
367 // Having chosen the collection set, adjust the budgets for generational mode based on its composition. Note
368 // that young_generation->available() now knows about recently discovered immediate garbage.
369 //
370 void ShenandoahGeneration::adjust_evacuation_budgets(ShenandoahHeap* const heap, ShenandoahCollectionSet* const collection_set) {
371 shenandoah_assert_generational();
372 // We may find that old_evacuation_reserve and/or loaned_for_young_evacuation are not fully consumed, in which case we may
373 // be able to increase regions_available_to_loan
374
375 // The role of adjust_evacuation_budgets() is to compute the correct value of regions_available_to_loan and to make
376 // effective use of this memory, including the remnant memory within these regions that may result from rounding loan to
377 // integral number of regions. Excess memory that is available to be loaned is applied to an allocation supplement,
378 // which allows mutators to allocate memory beyond the current capacity of young-gen on the promise that the loan
379 // will be repaid as soon as we finish updating references for the recently evacuated collection set.
380
381 // We cannot recalculate regions_available_to_loan by simply dividing old_generation->available() by region_size_bytes
382 // because the available memory may be distributed between many partially occupied regions that are already holding old-gen
383 // objects. Memory in partially occupied regions is not "available" to be loaned. Note that an increase in old-gen
384 // available that results from a decrease in memory consumed by old evacuation is not necessarily available to be loaned
385 // to young-gen.
386
387 size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
388 ShenandoahOldGeneration* const old_generation = heap->old_generation();
389 ShenandoahYoungGeneration* const young_generation = heap->young_generation();
390
391 size_t old_evacuated = collection_set->get_old_bytes_reserved_for_evacuation();
392 size_t old_evacuated_committed = (size_t) (ShenandoahOldEvacWaste * double(old_evacuated));
393 size_t old_evacuation_reserve = old_generation->get_evacuation_reserve();
394
395 if (old_evacuated_committed > old_evacuation_reserve) {
396 // This should only happen due to round-off errors when enforcing ShenandoahOldEvacWaste
397 assert(old_evacuated_committed <= (33 * old_evacuation_reserve) / 32,
398 "Round-off errors should be less than 3.125%%, committed: " SIZE_FORMAT ", reserved: " SIZE_FORMAT,
399 old_evacuated_committed, old_evacuation_reserve);
400 old_evacuated_committed = old_evacuation_reserve;
401 // Leave old_evac_reserve as previously configured
402 } else if (old_evacuated_committed < old_evacuation_reserve) {
403 // This happens if the old-gen collection consumes less than full budget.
404 old_evacuation_reserve = old_evacuated_committed;
405 old_generation->set_evacuation_reserve(old_evacuation_reserve);
406 }
407
408 size_t young_advance_promoted = collection_set->get_young_bytes_to_be_promoted();
409 size_t young_advance_promoted_reserve_used = (size_t) (ShenandoahPromoEvacWaste * double(young_advance_promoted));
410
411 size_t young_evacuated = collection_set->get_young_bytes_reserved_for_evacuation();
412 size_t young_evacuated_reserve_used = (size_t) (ShenandoahEvacWaste * double(young_evacuated));
413
414 size_t total_young_available = young_generation->available_with_reserve();
415 assert(young_evacuated_reserve_used <= total_young_available, "Cannot evacuate more than is available in young");
416 young_generation->set_evacuation_reserve(young_evacuated_reserve_used);
417
418 size_t old_available = old_generation->available();
419 // Now that we've established the collection set, we know how much memory is really required by old-gen for evacuation
420 // and promotion reserves. Try shrinking OLD now in case that gives us a bit more runway for mutator allocations during
421 // evac and update phases.
422 size_t old_consumed = old_evacuated_committed + young_advance_promoted_reserve_used;
423
424 if (old_available < old_consumed) {
425 // This can happen due to round-off errors when adding the results of truncated integer arithmetic.
426 // We've already truncated old_evacuated_committed. Truncate young_advance_promoted_reserve_used here.
427 assert(young_advance_promoted_reserve_used <= (33 * (old_available - old_evacuated_committed)) / 32,
428 "Round-off errors should be less than 3.125%%, committed: " SIZE_FORMAT ", reserved: " SIZE_FORMAT,
429 young_advance_promoted_reserve_used, old_available - old_evacuated_committed);
430 young_advance_promoted_reserve_used = old_available - old_evacuated_committed;
431 old_consumed = old_evacuated_committed + young_advance_promoted_reserve_used;
432 }
433
434 assert(old_available >= old_consumed, "Cannot consume (" SIZE_FORMAT ") more than is available (" SIZE_FORMAT ")",
435 old_consumed, old_available);
436 size_t excess_old = old_available - old_consumed;
437 size_t unaffiliated_old_regions = old_generation->free_unaffiliated_regions();
438 size_t unaffiliated_old = unaffiliated_old_regions * region_size_bytes;
439 assert(old_available >= unaffiliated_old, "Unaffiliated old is a subset of old available");
440
441 // Make sure old_evac_committed is unaffiliated
442 if (old_evacuated_committed > 0) {
443 if (unaffiliated_old > old_evacuated_committed) {
444 size_t giveaway = unaffiliated_old - old_evacuated_committed;
445 size_t giveaway_regions = giveaway / region_size_bytes; // round down
446 if (giveaway_regions > 0) {
447 excess_old = MIN2(excess_old, giveaway_regions * region_size_bytes);
448 } else {
449 excess_old = 0;
450 }
451 } else {
452 excess_old = 0;
453 }
454 }
455
456 // If we find that OLD has excess regions, give them back to YOUNG now to reduce likelihood we run out of allocation
457 // runway during evacuation and update-refs.
458 size_t regions_to_xfer = 0;
459 if (excess_old > unaffiliated_old) {
460 // we can give back unaffiliated_old (all of unaffiliated is excess)
461 if (unaffiliated_old_regions > 0) {
462 regions_to_xfer = unaffiliated_old_regions;
463 }
464 } else if (unaffiliated_old_regions > 0) {
465 // excess_old < unaffiliated old: we can give back MIN(excess_old/region_size_bytes, unaffiliated_old_regions)
466 size_t excess_regions = excess_old / region_size_bytes;
467 regions_to_xfer = MIN2(excess_regions, unaffiliated_old_regions);
468 }
469
470 if (regions_to_xfer > 0) {
471 bool result = ShenandoahGenerationalHeap::cast(heap)->generation_sizer()->transfer_to_young(regions_to_xfer);
472 assert(excess_old >= regions_to_xfer * region_size_bytes,
473 "Cannot transfer (" SIZE_FORMAT ", " SIZE_FORMAT ") more than excess old (" SIZE_FORMAT ")",
474 regions_to_xfer, region_size_bytes, excess_old);
475 excess_old -= regions_to_xfer * region_size_bytes;
476 log_debug(gc, ergo)("%s transferred " SIZE_FORMAT " excess regions to young before start of evacuation",
477 result? "Successfully": "Unsuccessfully", regions_to_xfer);
478 }
479
480 // Add in the excess_old memory to hold unanticipated promotions, if any. If there are more unanticipated
481 // promotions than fit in reserved memory, they will be deferred until a future GC pass.
482 size_t total_promotion_reserve = young_advance_promoted_reserve_used + excess_old;
483 old_generation->set_promoted_reserve(total_promotion_reserve);
484 old_generation->reset_promoted_expended();
485 }
486
487 typedef struct {
488 ShenandoahHeapRegion* _region;
489 size_t _live_data;
490 } AgedRegionData;
491
492 static int compare_by_aged_live(AgedRegionData a, AgedRegionData b) {
493 if (a._live_data < b._live_data)
494 return -1;
495 else if (a._live_data > b._live_data)
496 return 1;
497 else return 0;
498 }
499
500 inline void assert_no_in_place_promotions() {
501 #ifdef ASSERT
502 class ShenandoahNoInPlacePromotions : public ShenandoahHeapRegionClosure {
503 public:
504 void heap_region_do(ShenandoahHeapRegion *r) override {
505 assert(r->get_top_before_promote() == nullptr,
506 "Region " SIZE_FORMAT " should not be ready for in-place promotion", r->index());
507 }
508 } cl;
509 ShenandoahHeap::heap()->heap_region_iterate(&cl);
510 #endif
511 }
512
513 // Preselect for inclusion into the collection set regions whose age is at or above tenure age which contain more than
514 // ShenandoahOldGarbageThreshold amounts of garbage. We identify these regions by setting the appropriate entry of
515 // the collection set's preselected regions array to true. All entries are initialized to false before calling this
516 // function.
517 //
518 // During the subsequent selection of the collection set, we give priority to these promotion set candidates.
519 // Without this prioritization, we found that the aged regions tend to be ignored because they typically have
520 // much less garbage and much more live data than the recently allocated "eden" regions. When aged regions are
521 // repeatedly excluded from the collection set, the amount of live memory within the young generation tends to
522 // accumulate and this has the undesirable side effect of causing young-generation collections to require much more
523 // CPU and wall-clock time.
524 //
525 // A second benefit of treating aged regions differently than other regions during collection set selection is
526 // that this allows us to more accurately budget memory to hold the results of evacuation. Memory for evacuation
527 // of aged regions must be reserved in the old generation. Memory for evacuation of all other regions must be
528 // reserved in the young generation.
529 size_t ShenandoahGeneration::select_aged_regions(size_t old_available) {
530
531 // There should be no regions configured for subsequent in-place-promotions carried over from the previous cycle.
532 assert_no_in_place_promotions();
533
534 auto const heap = ShenandoahGenerationalHeap::heap();
535 bool* const candidate_regions_for_promotion_by_copy = heap->collection_set()->preselected_regions();
536 ShenandoahMarkingContext* const ctx = heap->marking_context();
537
538 const uint tenuring_threshold = heap->age_census()->tenuring_threshold();
539 const size_t old_garbage_threshold = (ShenandoahHeapRegion::region_size_bytes() * ShenandoahOldGarbageThreshold) / 100;
540
541 size_t old_consumed = 0;
542 size_t promo_potential = 0;
543 size_t candidates = 0;
544
545 // Tracks the padding of space above top in regions eligible for promotion in place
546 size_t promote_in_place_pad = 0;
547
548 // Sort the promotion-eligible regions in order of increasing live-data-bytes so that we can first reclaim regions that require
549 // less evacuation effort. This prioritizes garbage first, expanding the allocation pool early before we reclaim regions that
550 // have more live data.
551 const size_t num_regions = heap->num_regions();
552
553 ResourceMark rm;
554 AgedRegionData* sorted_regions = NEW_RESOURCE_ARRAY(AgedRegionData, num_regions);
555
556 for (size_t i = 0; i < num_regions; i++) {
557 ShenandoahHeapRegion* const r = heap->get_region(i);
558 if (r->is_empty() || !r->has_live() || !r->is_young() || !r->is_regular()) {
559 // skip over regions that aren't regular young with some live data
560 continue;
561 }
562 if (r->age() >= tenuring_threshold) {
563 if ((r->garbage() < old_garbage_threshold)) {
564 // This tenure-worthy region has too little garbage, so we do not want to expend the copying effort to
565 // reclaim the garbage; instead this region may be eligible for promotion-in-place to the
566 // old generation.
567 HeapWord* tams = ctx->top_at_mark_start(r);
568 HeapWord* original_top = r->top();
569 if (!heap->is_concurrent_old_mark_in_progress() && tams == original_top) {
570 // No allocations from this region have been made during concurrent mark. It meets all the criteria
571 // for in-place-promotion. Though we only need the value of top when we fill the end of the region,
572 // we use this field to indicate that this region should be promoted in place during the evacuation
573 // phase.
574 r->save_top_before_promote();
575
576 size_t remnant_size = r->free() / HeapWordSize;
577 if (remnant_size > ShenandoahHeap::min_fill_size()) {
578 ShenandoahHeap::fill_with_object(original_top, remnant_size);
579 // Fill the remnant memory within this region to assure no allocations prior to promote in place. Otherwise,
580 // newly allocated objects will not be parsable when promote in place tries to register them. Furthermore, any
581 // new allocations would not necessarily be eligible for promotion. This addresses both issues.
582 r->set_top(r->end());
583 promote_in_place_pad += remnant_size * HeapWordSize;
584 } else {
585 // Since the remnant is so small that it cannot be filled, we don't have to worry about any accidental
586 // allocations occurring within this region before the region is promoted in place.
587 }
588 }
589 // Else, we do not promote this region (either in place or by copy) because it has received new allocations.
590
591 // During evacuation, we exclude from promotion regions for which age > tenure threshold, garbage < garbage-threshold,
592 // and get_top_before_promote() != tams
593 } else {
594 // Record this promotion-eligible candidate region. After sorting and selecting the best candidates below,
595 // we may still decide to exclude this promotion-eligible region from the current collection set. If this
596 // happens, we will consider this region as part of the anticipated promotion potential for the next GC
597 // pass; see further below.
598 sorted_regions[candidates]._region = r;
599 sorted_regions[candidates++]._live_data = r->get_live_data_bytes();
600 }
601 } else {
602 // We only evacuate & promote objects from regular regions whose garbage() is above old-garbage-threshold.
603 // Objects in tenure-worthy regions with less garbage are promoted in place. These take a different path to
604 // old-gen. Regions excluded from promotion because their garbage content is too low (causing us to anticipate that
605 // the region would be promoted in place) may be eligible for evacuation promotion by the time promotion takes
606 // place during a subsequent GC pass because more garbage is found within the region between now and then. This
607 // should not happen if we are properly adapting the tenure age. The theory behind adaptive tenuring threshold
608 // is to choose the youngest age that demonstrates no "significant" further loss of population since the previous
609 // age. If not this, we expect the tenure age to demonstrate linear population decay for at least two population
610 // samples, whereas we expect to observe exponential population decay for ages younger than the tenure age.
611 //
612 // In the case that certain regions which were anticipated to be promoted in place need to be promoted by
613 // evacuation, it may be the case that there is not sufficient reserve within old-gen to hold evacuation of
614 // these regions. The likely outcome is that these regions will not be selected for evacuation or promotion
615 // in the current cycle and we will anticipate that they will be promoted in the next cycle. This will cause
616 // us to reserve more old-gen memory so that these objects can be promoted in the subsequent cycle.
617 if (heap->is_aging_cycle() && (r->age() + 1 == tenuring_threshold)) {
618 if (r->garbage() >= old_garbage_threshold) {
619 promo_potential += r->get_live_data_bytes();
620 }
621 }
622 }
623 // Note that we keep going even if one region is excluded from selection.
624 // Subsequent regions may be selected if they have smaller live data.
625 }
626 // Sort in increasing order according to live data bytes. Note that candidates represents the number of regions
627 // that qualify to be promoted by evacuation.
628 if (candidates > 0) {
629 size_t selected_regions = 0;
630 size_t selected_live = 0;
631 QuickSort::sort<AgedRegionData>(sorted_regions, candidates, compare_by_aged_live, false);
632 for (size_t i = 0; i < candidates; i++) {
633 ShenandoahHeapRegion* const region = sorted_regions[i]._region;
634 size_t region_live_data = sorted_regions[i]._live_data;
635 size_t promotion_need = (size_t) (region_live_data * ShenandoahPromoEvacWaste);
636 if (old_consumed + promotion_need <= old_available) {
637 old_consumed += promotion_need;
638 candidate_regions_for_promotion_by_copy[region->index()] = true;
639 selected_regions++;
640 selected_live += region_live_data;
641 } else {
642 // We rejected this promotable region from the collection set because we had no room to hold its copy.
643 // Add this region to promo potential for next GC.
644 promo_potential += region_live_data;
645 assert(!candidate_regions_for_promotion_by_copy[region->index()], "Shouldn't be selected");
646 }
647 // We keep going even if one region is excluded from selection because we need to accumulate all eligible
648 // regions that are not preselected into promo_potential
649 }
650 log_debug(gc)("Preselected " SIZE_FORMAT " regions containing " SIZE_FORMAT " live bytes,"
651 " consuming: " SIZE_FORMAT " of budgeted: " SIZE_FORMAT,
652 selected_regions, selected_live, old_consumed, old_available);
653 }
654
655 heap->old_generation()->set_pad_for_promote_in_place(promote_in_place_pad);
656 heap->old_generation()->set_promotion_potential(promo_potential);
657 return old_consumed;
658 }
659
660 void ShenandoahGeneration::prepare_regions_and_collection_set(bool concurrent) {
661 ShenandoahHeap* heap = ShenandoahHeap::heap();
662 ShenandoahCollectionSet* collection_set = heap->collection_set();
663 bool is_generational = heap->mode()->is_generational();
664
665 assert(!heap->is_full_gc_in_progress(), "Only for concurrent and degenerated GC");
666 assert(!is_old(), "Only YOUNG and GLOBAL GC perform evacuations");
667 {
668 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::final_update_region_states :
669 ShenandoahPhaseTimings::degen_gc_final_update_region_states);
670 ShenandoahFinalMarkUpdateRegionStateClosure cl(complete_marking_context());
671 parallel_heap_region_iterate(&cl);
672
673 if (is_young()) {
674 // We always need to update the watermark for old regions. If there
675 // are mixed collections pending, we also need to synchronize the
676 // pinned status for old regions. Since we are already visiting every
677 // old region here, go ahead and sync the pin status too.
678 ShenandoahFinalMarkUpdateRegionStateClosure old_cl(nullptr);
679 heap->old_generation()->parallel_heap_region_iterate(&old_cl);
680 }
681 }
682
683 // Tally the census counts and compute the adaptive tenuring threshold
684 if (is_generational && ShenandoahGenerationalAdaptiveTenuring && !ShenandoahGenerationalCensusAtEvac) {
685 // Objects above TAMS weren't included in the age census. Since they were all
686 // allocated in this cycle they belong in the age 0 cohort. We walk over all
687 // young regions and sum the volume of objects between TAMS and top.
688 ShenandoahUpdateCensusZeroCohortClosure age0_cl(complete_marking_context());
689 heap->young_generation()->heap_region_iterate(&age0_cl);
690 size_t age0_pop = age0_cl.get_age0_population();
691
692 // Update the global census, including the missed age 0 cohort above,
693 // along with the census done during marking, and compute the tenuring threshold.
694 ShenandoahAgeCensus* census = ShenandoahGenerationalHeap::heap()->age_census();
695 census->update_census(age0_pop);
696 #ifndef PRODUCT
697 size_t total_pop = age0_cl.get_total_population();
698 size_t total_census = census->get_total();
699 // Usually total_pop > total_census, but not by too much.
700 // We use integer division so anything up to just less than 2 is considered
701 // reasonable, and the "+1" is to avoid divide-by-zero.
702 assert((total_pop+1)/(total_census+1) == 1, "Extreme divergence: "
703 SIZE_FORMAT "/" SIZE_FORMAT, total_pop, total_census);
704 #endif
705 }
706
707 {
708 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::choose_cset :
709 ShenandoahPhaseTimings::degen_gc_choose_cset);
710
711 collection_set->clear();
712 ShenandoahHeapLocker locker(heap->lock());
713 if (is_generational) {
714 // Seed the collection set with resource area-allocated
715 // preselected regions, which are removed when we exit this scope.
716 ShenandoahCollectionSetPreselector preselector(collection_set, heap->num_regions());
717
718 // Find the amount that will be promoted, regions that will be promoted in
719 // place, and preselect older regions that will be promoted by evacuation.
720 compute_evacuation_budgets(heap);
721
722 // Choose the collection set, including the regions preselected above for
723 // promotion into the old generation.
724 _heuristics->choose_collection_set(collection_set);
725 if (!collection_set->is_empty()) {
726 // only make use of evacuation budgets when we are evacuating
727 adjust_evacuation_budgets(heap, collection_set);
728 }
729
730 if (is_global()) {
731 // We have just chosen a collection set for a global cycle. The mark bitmap covering old regions is complete, so
732 // the remembered set scan can use that to avoid walking into garbage. When the next old mark begins, we will
733 // use the mark bitmap to make the old regions parsable by coalescing and filling any unmarked objects. Thus,
734 // we prepare for old collections by remembering which regions are old at this time. Note that any objects
735 // promoted into old regions will be above TAMS, and so will be considered marked. However, free regions that
736 // become old after this point will not be covered correctly by the mark bitmap, so we must be careful not to
737 // coalesce those regions. Only the old regions which are not part of the collection set at this point are
738 // eligible for coalescing. As implemented now, this has the side effect of possibly initiating mixed-evacuations
739 // after a global cycle for old regions that were not included in this collection set.
740 heap->old_generation()->prepare_for_mixed_collections_after_global_gc();
741 }
742 } else {
743 _heuristics->choose_collection_set(collection_set);
744 }
745 }
746
747
748 {
749 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::final_rebuild_freeset :
750 ShenandoahPhaseTimings::degen_gc_final_rebuild_freeset);
751 ShenandoahHeapLocker locker(heap->lock());
752 size_t young_cset_regions, old_cset_regions;
753
754 // We are preparing for evacuation. At this time, we ignore cset region tallies.
755 size_t first_old, last_old, num_old;
756 heap->free_set()->prepare_to_rebuild(young_cset_regions, old_cset_regions, first_old, last_old, num_old);
757 // Free set construction uses reserve quantities, because they are known to be valid here
758 heap->free_set()->finish_rebuild(young_cset_regions, old_cset_regions, num_old, true);
759 }
760 }
761
762 bool ShenandoahGeneration::is_bitmap_clear() {
763 ShenandoahHeap* heap = ShenandoahHeap::heap();
764 ShenandoahMarkingContext* context = heap->marking_context();
765 const size_t num_regions = heap->num_regions();
766 for (size_t idx = 0; idx < num_regions; idx++) {
767 ShenandoahHeapRegion* r = heap->get_region(idx);
768 if (contains(r) && r->is_affiliated()) {
769 if (heap->is_bitmap_slice_committed(r) && (context->top_at_mark_start(r) > r->bottom()) &&
770 !context->is_bitmap_range_within_region_clear(r->bottom(), r->end())) {
771 return false;
772 }
773 }
774 }
775 return true;
776 }
777
778 void ShenandoahGeneration::set_mark_complete() {
779 _is_marking_complete.set();
780 }
781
782 void ShenandoahGeneration::set_mark_incomplete() {
783 _is_marking_complete.unset();
784 }
785
786 ShenandoahMarkingContext* ShenandoahGeneration::complete_marking_context() {
787 assert(is_mark_complete(), "Marking must be completed.");
788 return ShenandoahHeap::heap()->marking_context();
789 }
790
791 void ShenandoahGeneration::cancel_marking() {
792 log_info(gc)("Cancel marking: %s", name());
793 if (is_concurrent_mark_in_progress()) {
794 set_mark_incomplete();
795 }
796 _task_queues->clear();
797 ref_processor()->abandon_partial_discovery();
798 set_concurrent_mark_in_progress(false);
799 }
800
801 ShenandoahGeneration::ShenandoahGeneration(ShenandoahGenerationType type,
802 uint max_workers,
803 size_t max_capacity) :
804 _type(type),
805 _task_queues(new ShenandoahObjToScanQueueSet(max_workers)),
806 _ref_processor(new ShenandoahReferenceProcessor(MAX2(max_workers, 1U))),
807 _affiliated_region_count(0), _humongous_waste(0), _evacuation_reserve(0),
808 _used(0), _bytes_allocated_since_gc_start(0),
809 _max_capacity(max_capacity),
810 _heuristics(nullptr)
811 {
812 _is_marking_complete.set();
813 assert(max_workers > 0, "At least one queue");
814 for (uint i = 0; i < max_workers; ++i) {
815 ShenandoahObjToScanQueue* task_queue = new ShenandoahObjToScanQueue();
816 _task_queues->register_queue(i, task_queue);
817 }
818 }
819
820 ShenandoahGeneration::~ShenandoahGeneration() {
821 for (uint i = 0; i < _task_queues->size(); ++i) {
822 ShenandoahObjToScanQueue* q = _task_queues->queue(i);
823 delete q;
824 }
825 delete _task_queues;
826 }
827
828 void ShenandoahGeneration::reserve_task_queues(uint workers) {
829 _task_queues->reserve(workers);
830 }
831
832 ShenandoahObjToScanQueueSet* ShenandoahGeneration::old_gen_task_queues() const {
833 return nullptr;
834 }
835
836 void ShenandoahGeneration::scan_remembered_set(bool is_concurrent) {
837 assert(is_young(), "Should only scan remembered set for young generation.");
838
839 ShenandoahGenerationalHeap* const heap = ShenandoahGenerationalHeap::heap();
840 uint nworkers = heap->workers()->active_workers();
841 reserve_task_queues(nworkers);
842
843 ShenandoahReferenceProcessor* rp = ref_processor();
844 ShenandoahRegionChunkIterator work_list(nworkers);
845 ShenandoahScanRememberedTask task(task_queues(), old_gen_task_queues(), rp, &work_list, is_concurrent);
846 heap->assert_gc_workers(nworkers);
847 heap->workers()->run_task(&task);
848 if (ShenandoahEnableCardStats) {
849 ShenandoahScanRemembered* scanner = heap->old_generation()->card_scan();
850 assert(scanner != nullptr, "Not generational");
851 scanner->log_card_stats(nworkers, CARD_STAT_SCAN_RS);
852 }
853 }
854
855 size_t ShenandoahGeneration::increment_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 return Atomic::add(&_affiliated_region_count, (size_t) 1);
861 }
862
863 size_t ShenandoahGeneration::decrement_affiliated_region_count() {
864 shenandoah_assert_heaplocked_or_safepoint();
865 // During full gc, multiple GC worker threads may change region affiliations without a lock. No lock is enforced
866 // on read and write of _affiliated_region_count. At the end of full gc, a single thread overwrites the count with
867 // a coherent value.
868 auto affiliated_region_count = Atomic::sub(&_affiliated_region_count, (size_t) 1);
869 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
870 (used() + _humongous_waste <= affiliated_region_count * ShenandoahHeapRegion::region_size_bytes()),
871 "used + humongous cannot exceed regions");
872 return affiliated_region_count;
873 }
874
875 size_t ShenandoahGeneration::decrement_affiliated_region_count_without_lock() {
876 return Atomic::sub(&_affiliated_region_count, (size_t) 1);
877 }
878
879 size_t ShenandoahGeneration::increase_affiliated_region_count(size_t delta) {
880 shenandoah_assert_heaplocked_or_safepoint();
881 return Atomic::add(&_affiliated_region_count, delta);
882 }
883
884 size_t ShenandoahGeneration::decrease_affiliated_region_count(size_t delta) {
885 shenandoah_assert_heaplocked_or_safepoint();
886 assert(Atomic::load(&_affiliated_region_count) >= delta, "Affiliated region count cannot be negative");
887
888 auto const affiliated_region_count = Atomic::sub(&_affiliated_region_count, delta);
889 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
890 (_used + _humongous_waste <= affiliated_region_count * ShenandoahHeapRegion::region_size_bytes()),
891 "used + humongous cannot exceed regions");
892 return affiliated_region_count;
893 }
894
895 void ShenandoahGeneration::establish_usage(size_t num_regions, size_t num_bytes, size_t humongous_waste) {
896 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
897 Atomic::store(&_affiliated_region_count, num_regions);
898 Atomic::store(&_used, num_bytes);
899 _humongous_waste = humongous_waste;
900 }
901
902 void ShenandoahGeneration::increase_used(size_t bytes) {
903 Atomic::add(&_used, bytes);
904 }
905
906 void ShenandoahGeneration::increase_humongous_waste(size_t bytes) {
907 if (bytes > 0) {
908 Atomic::add(&_humongous_waste, bytes);
909 }
910 }
911
912 void ShenandoahGeneration::decrease_humongous_waste(size_t bytes) {
913 if (bytes > 0) {
914 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() || (_humongous_waste >= bytes),
915 "Waste (" SIZE_FORMAT ") cannot be negative (after subtracting " SIZE_FORMAT ")", _humongous_waste, bytes);
916 Atomic::sub(&_humongous_waste, bytes);
917 }
918 }
919
920 void ShenandoahGeneration::decrease_used(size_t bytes) {
921 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
922 (_used >= bytes), "cannot reduce bytes used by generation below zero");
923 Atomic::sub(&_used, bytes);
924 }
925
926 size_t ShenandoahGeneration::used_regions() const {
927 return Atomic::load(&_affiliated_region_count);
928 }
929
930 size_t ShenandoahGeneration::free_unaffiliated_regions() const {
931 size_t result = max_capacity() / ShenandoahHeapRegion::region_size_bytes();
932 auto const used_regions = this->used_regions();
933 if (used_regions > result) {
934 result = 0;
935 } else {
936 result -= used_regions;
937 }
938 return result;
939 }
940
941 size_t ShenandoahGeneration::used_regions_size() const {
942 return used_regions() * ShenandoahHeapRegion::region_size_bytes();
943 }
944
945 size_t ShenandoahGeneration::available() const {
946 return available(max_capacity());
947 }
948
949 // For ShenandoahYoungGeneration, Include the young available that may have been reserved for the Collector.
950 size_t ShenandoahGeneration::available_with_reserve() const {
951 return available(max_capacity());
952 }
953
954 size_t ShenandoahGeneration::soft_available() const {
955 return available(ShenandoahHeap::heap()->soft_max_capacity());
956 }
957
958 size_t ShenandoahGeneration::available(size_t capacity) const {
959 size_t in_use = used() + get_humongous_waste();
960 return in_use > capacity ? 0 : capacity - in_use;
961 }
962
963 size_t ShenandoahGeneration::increase_capacity(size_t increment) {
964 shenandoah_assert_heaplocked_or_safepoint();
965
966 // We do not enforce that new capacity >= heap->max_size_for(this). The maximum generation size is treated as a rule of thumb
967 // which may be violated during certain transitions, such as when we are forcing transfers for the purpose of promoting regions
968 // in place.
969 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
970 (_max_capacity + increment <= ShenandoahHeap::heap()->max_capacity()), "Generation cannot be larger than heap size");
971 assert(increment % ShenandoahHeapRegion::region_size_bytes() == 0, "Generation capacity must be multiple of region size");
972 _max_capacity += increment;
973
974 // This detects arithmetic wraparound on _used
975 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
976 (used_regions_size() >= used()),
977 "Affiliated regions must hold more than what is currently used");
978 return _max_capacity;
979 }
980
981 size_t ShenandoahGeneration::set_capacity(size_t byte_size) {
982 shenandoah_assert_heaplocked_or_safepoint();
983 _max_capacity = byte_size;
984 return _max_capacity;
985 }
986
987 size_t ShenandoahGeneration::decrease_capacity(size_t decrement) {
988 shenandoah_assert_heaplocked_or_safepoint();
989
990 // We do not enforce that new capacity >= heap->min_size_for(this). The minimum generation size is treated as a rule of thumb
991 // which may be violated during certain transitions, such as when we are forcing transfers for the purpose of promoting regions
992 // in place.
993 assert(decrement % ShenandoahHeapRegion::region_size_bytes() == 0, "Generation capacity must be multiple of region size");
994 assert(_max_capacity >= decrement, "Generation capacity cannot be negative");
995
996 _max_capacity -= decrement;
997
998 // This detects arithmetic wraparound on _used
999 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
1000 (used_regions_size() >= used()),
1001 "Affiliated regions must hold more than what is currently used");
1002 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
1003 (_used <= _max_capacity), "Cannot use more than capacity");
1004 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
1005 (used_regions_size() <= _max_capacity),
1006 "Cannot use more than capacity");
1007 return _max_capacity;
1008 }
1009
1010 void ShenandoahGeneration::record_success_concurrent(bool abbreviated) {
1011 heuristics()->record_success_concurrent();
1012 ShenandoahHeap::heap()->shenandoah_policy()->record_success_concurrent(is_young(), abbreviated);
1013 }