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
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 // Add [TAMS, top) volume over young regions. Used to correct age 0 cohort census
123 // for adaptive tenuring when census is taken during marking.
124 // In non-product builds, for the purposes of verification, we also collect the total
125 // live objects in young regions as well.
126 class ShenandoahUpdateCensusZeroCohortClosure : public ShenandoahHeapRegionClosure {
127 private:
128 ShenandoahMarkingContext* const _ctx;
129 // Population size units are words (not bytes)
130 size_t _age0_pop; // running tally of age0 population size
131 size_t _total_pop; // total live population size
132 public:
133 explicit ShenandoahUpdateCensusZeroCohortClosure(ShenandoahMarkingContext* ctx)
134 : _ctx(ctx), _age0_pop(0), _total_pop(0) {}
135
136 void heap_region_do(ShenandoahHeapRegion* r) override {
137 if (_ctx != nullptr && r->is_active()) {
138 assert(r->is_young(), "Young regions only");
139 HeapWord* tams = _ctx->top_at_mark_start(r);
140 HeapWord* top = r->top();
141 if (top > tams) {
142 _age0_pop += pointer_delta(top, tams);
143 }
144 // TODO: check significance of _ctx != nullptr above, can that
145 // spoof _total_pop in some corner cases?
146 NOT_PRODUCT(_total_pop += r->get_live_data_words();)
147 }
148 }
149
150 size_t get_age0_population() const { return _age0_pop; }
151 size_t get_total_population() const { return _total_pop; }
152 };
153
154 void ShenandoahGeneration::confirm_heuristics_mode() {
155 if (_heuristics->is_diagnostic() && !UnlockDiagnosticVMOptions) {
156 vm_exit_during_initialization(
157 err_msg("Heuristics \"%s\" is diagnostic, and must be enabled via -XX:+UnlockDiagnosticVMOptions.",
158 _heuristics->name()));
159 }
160 if (_heuristics->is_experimental() && !UnlockExperimentalVMOptions) {
161 vm_exit_during_initialization(
162 err_msg("Heuristics \"%s\" is experimental, and must be enabled via -XX:+UnlockExperimentalVMOptions.",
163 _heuristics->name()));
164 }
165 }
166
167 ShenandoahHeuristics* ShenandoahGeneration::initialize_heuristics(ShenandoahMode* gc_mode) {
168 _heuristics = gc_mode->initialize_heuristics(this);
169 _heuristics->set_guaranteed_gc_interval(ShenandoahGuaranteedGCInterval);
170 confirm_heuristics_mode();
171 return _heuristics;
172 }
173
174 size_t ShenandoahGeneration::bytes_allocated_since_gc_start() const {
175 return Atomic::load(&_bytes_allocated_since_gc_start);
176 }
177
178 void ShenandoahGeneration::reset_bytes_allocated_since_gc_start() {
179 Atomic::store(&_bytes_allocated_since_gc_start, (size_t)0);
180 }
181
182 void ShenandoahGeneration::increase_allocated(size_t bytes) {
183 Atomic::add(&_bytes_allocated_since_gc_start, bytes, memory_order_relaxed);
184 }
185
186 void ShenandoahGeneration::set_evacuation_reserve(size_t new_val) {
187 _evacuation_reserve = new_val;
188 }
189
190 size_t ShenandoahGeneration::get_evacuation_reserve() const {
191 return _evacuation_reserve;
192 }
193
194 void ShenandoahGeneration::augment_evacuation_reserve(size_t increment) {
195 _evacuation_reserve += increment;
196 }
197
198 void ShenandoahGeneration::log_status(const char *msg) const {
199 typedef LogTarget(Info, gc, ergo) LogGcInfo;
200
201 if (!LogGcInfo::is_enabled()) {
202 return;
203 }
204
205 // Not under a lock here, so read each of these once to make sure
206 // byte size in proper unit and proper unit for byte size are consistent.
207 const size_t v_used = used();
208 const size_t v_used_regions = used_regions_size();
209 const size_t v_soft_max_capacity = soft_max_capacity();
210 const size_t v_max_capacity = max_capacity();
211 const size_t v_available = available();
212 const size_t v_humongous_waste = get_humongous_waste();
213
214 const LogGcInfo target;
215 LogStream ls(target);
216 ls.print("%s: ", msg);
217 if (_type != NON_GEN) {
218 ls.print("%s generation ", name());
219 }
220
221 ls.print_cr("used: " PROPERFMT ", used regions: " PROPERFMT ", humongous waste: " PROPERFMT
222 ", soft capacity: " PROPERFMT ", max capacity: " PROPERFMT ", available: " PROPERFMT,
223 PROPERFMTARGS(v_used), PROPERFMTARGS(v_used_regions), PROPERFMTARGS(v_humongous_waste),
224 PROPERFMTARGS(v_soft_max_capacity), PROPERFMTARGS(v_max_capacity), PROPERFMTARGS(v_available));
225 }
226
227 void ShenandoahGeneration::reset_mark_bitmap() {
228 ShenandoahHeap* heap = ShenandoahHeap::heap();
229 heap->assert_gc_workers(heap->workers()->active_workers());
230
231 set_mark_incomplete();
232
233 ShenandoahResetBitmapTask task(this);
234 heap->workers()->run_task(&task);
235 }
236
237 // The ideal is to swap the remembered set so the safepoint effort is no more than a few pointer manipulations.
238 // However, limitations in the implementation of the mutator write-barrier make it difficult to simply change the
239 // location of the card table. So the interim implementation of swap_remembered_set will copy the write-table
240 // onto the read-table and will then clear the write-table.
241 void ShenandoahGeneration::swap_remembered_set() {
242 // Must be sure that marking is complete before we swap remembered set.
243 ShenandoahGenerationalHeap* heap = ShenandoahGenerationalHeap::heap();
244 heap->assert_gc_workers(heap->workers()->active_workers());
245 shenandoah_assert_safepoint();
246
247 ShenandoahOldGeneration* old_generation = heap->old_generation();
248 ShenandoahCopyWriteCardTableToRead task(old_generation->card_scan());
249 old_generation->parallel_heap_region_iterate(&task);
250 }
251
252 // Copy the write-version of the card-table into the read-version, clearing the
253 // write-version. The work is done at a safepoint and in parallel by the GC
254 // worker threads.
255 void ShenandoahGeneration::merge_write_table() {
256 // This should only happen for degenerated cycles
257 ShenandoahGenerationalHeap* heap = ShenandoahGenerationalHeap::heap();
258 heap->assert_gc_workers(heap->workers()->active_workers());
259 shenandoah_assert_safepoint();
260
261 ShenandoahOldGeneration* old_generation = heap->old_generation();
262 ShenandoahMergeWriteTable task(old_generation->card_scan());
263 old_generation->parallel_heap_region_iterate(&task);
264 }
265
266 void ShenandoahGeneration::prepare_gc() {
267
268 reset_mark_bitmap();
269
270 // Capture Top At Mark Start for this generation (typically young) and reset mark bitmap.
271 ShenandoahResetUpdateRegionStateClosure cl;
272 parallel_heap_region_iterate_free(&cl);
273 }
274
275 void ShenandoahGeneration::parallel_heap_region_iterate_free(ShenandoahHeapRegionClosure* cl) {
276 ShenandoahHeap::heap()->parallel_heap_region_iterate(cl);
277 }
278
279 void ShenandoahGeneration::compute_evacuation_budgets(ShenandoahHeap* const heap) {
280 shenandoah_assert_generational();
281
282 ShenandoahOldGeneration* const old_generation = heap->old_generation();
283 ShenandoahYoungGeneration* const young_generation = heap->young_generation();
284
285 // During initialization and phase changes, it is more likely that fewer objects die young and old-gen
286 // memory is not yet full (or is in the process of being replaced). During these times especially, it
287 // is beneficial to loan memory from old-gen to young-gen during the evacuation and update-refs phases
288 // of execution.
289
290 // Calculate EvacuationReserve before PromotionReserve. Evacuation is more critical than promotion.
291 // If we cannot evacuate old-gen, we will not be able to reclaim old-gen memory. Promotions are less
292 // critical. If we cannot promote, there may be degradation of young-gen memory because old objects
293 // accumulate there until they can be promoted. This increases the young-gen marking and evacuation work.
294
295 // First priority is to reclaim the easy garbage out of young-gen.
296
297 // maximum_young_evacuation_reserve is upper bound on memory to be evacuated out of young
298 const size_t maximum_young_evacuation_reserve = (young_generation->max_capacity() * ShenandoahEvacReserve) / 100;
299 const size_t young_evacuation_reserve = MIN2(maximum_young_evacuation_reserve, young_generation->available_with_reserve());
300
301 // maximum_old_evacuation_reserve is an upper bound on memory evacuated from old and evacuated to old (promoted),
302 // clamped by the old generation space available.
303 //
304 // Here's the algebra.
305 // Let SOEP = ShenandoahOldEvacRatioPercent,
306 // OE = old evac,
307 // YE = young evac, and
308 // TE = total evac = OE + YE
309 // By definition:
310 // SOEP/100 = OE/TE
311 // = OE/(OE+YE)
312 // => SOEP/(100-SOEP) = OE/((OE+YE)-OE) // componendo-dividendo: If a/b = c/d, then a/(b-a) = c/(d-c)
313 // = OE/YE
314 // => OE = YE*SOEP/(100-SOEP)
315
316 // We have to be careful in the event that SOEP is set to 100 by the user.
317 assert(ShenandoahOldEvacRatioPercent <= 100, "Error");
318 const size_t old_available = old_generation->available();
319 const size_t maximum_old_evacuation_reserve = (ShenandoahOldEvacRatioPercent == 100) ?
320 old_available : MIN2((maximum_young_evacuation_reserve * ShenandoahOldEvacRatioPercent) / (100 - ShenandoahOldEvacRatioPercent),
321 old_available);
322
323
324 // Second priority is to reclaim garbage out of old-gen if there are old-gen collection candidates. Third priority
325 // is to promote as much as we have room to promote. However, if old-gen memory is in short supply, this means young
326 // GC is operating under "duress" and was unable to transfer the memory that we would normally expect. In this case,
327 // old-gen will refrain from compacting itself in order to allow a quicker young-gen cycle (by avoiding the update-refs
328 // through ALL of old-gen). If there is some memory available in old-gen, we will use this for promotions as promotions
329 // do not add to the update-refs burden of GC.
330
331 size_t old_evacuation_reserve, old_promo_reserve;
332 if (is_global()) {
333 // Global GC is typically triggered by user invocation of System.gc(), and typically indicates that there is lots
334 // of garbage to be reclaimed because we are starting a new phase of execution. Marking for global GC may take
335 // significantly longer than typical young marking because we must mark through all old objects. To expedite
336 // evacuation and update-refs, we give emphasis to reclaiming garbage first, wherever that garbage is found.
337 // Global GC will adjust generation sizes to accommodate the collection set it chooses.
338
339 // Set old_promo_reserve to enforce that no regions are preselected for promotion. Such regions typically
340 // have relatively high memory utilization. We still call select_aged_regions() because this will prepare for
341 // promotions in place, if relevant.
342 old_promo_reserve = 0;
343
344 // Dedicate all available old memory to old_evacuation reserve. This may be small, because old-gen is only
345 // expanded based on an existing mixed evacuation workload at the end of the previous GC cycle. We'll expand
346 // the budget for evacuation of old during GLOBAL cset selection.
347 old_evacuation_reserve = maximum_old_evacuation_reserve;
348 } else if (old_generation->has_unprocessed_collection_candidates()) {
349 // We reserved all old-gen memory at end of previous GC to hold anticipated evacuations to old-gen. If this is
350 // mixed evacuation, reserve all of this memory for compaction of old-gen and do not promote. Prioritize compaction
351 // over promotion in order to defragment OLD so that it will be better prepared to efficiently receive promoted memory.
352 old_evacuation_reserve = maximum_old_evacuation_reserve;
353 old_promo_reserve = 0;
354 } else {
355 // Make all old-evacuation memory for promotion, but if we can't use it all for promotion, we'll allow some evacuation.
356 old_evacuation_reserve = 0;
357 old_promo_reserve = maximum_old_evacuation_reserve;
358 }
359 assert(old_evacuation_reserve <= old_available, "Error");
360
361 // We see too many old-evacuation failures if we force ourselves to evacuate into regions that are not initially empty.
362 // So we limit the old-evacuation reserve to unfragmented memory. Even so, old-evacuation is free to fill in nooks and
363 // crannies within existing partially used regions and it generally tries to do so.
364 const size_t old_free_unfragmented = old_generation->free_unaffiliated_regions() * ShenandoahHeapRegion::region_size_bytes();
365 if (old_evacuation_reserve > old_free_unfragmented) {
366 const size_t delta = old_evacuation_reserve - old_free_unfragmented;
367 old_evacuation_reserve -= delta;
368 // Let promo consume fragments of old-gen memory if not global
369 if (!is_global()) {
370 old_promo_reserve += delta;
371 }
372 }
373
374 // Preselect regions for promotion by evacuation (obtaining the live data to seed promoted_reserve),
375 // and identify regions that will promote in place. These use the tenuring threshold.
376 const size_t consumed_by_advance_promotion = select_aged_regions(old_promo_reserve);
377 assert(consumed_by_advance_promotion <= maximum_old_evacuation_reserve, "Cannot promote more than available old-gen memory");
378
379 // Note that unused old_promo_reserve might not be entirely consumed_by_advance_promotion. Do not transfer this
380 // to old_evacuation_reserve because this memory is likely very fragmented, and we do not want to increase the likelihood
381 // of old evacuation failure.
382 young_generation->set_evacuation_reserve(young_evacuation_reserve);
383 old_generation->set_evacuation_reserve(old_evacuation_reserve);
384 old_generation->set_promoted_reserve(consumed_by_advance_promotion);
385
386 // There is no need to expand OLD because all memory used here was set aside at end of previous GC, except in the
387 // case of a GLOBAL gc. During choose_collection_set() of GLOBAL, old will be expanded on demand.
388 }
389
390 // Having chosen the collection set, adjust the budgets for generational mode based on its composition. Note
391 // that young_generation->available() now knows about recently discovered immediate garbage.
392 //
393 void ShenandoahGeneration::adjust_evacuation_budgets(ShenandoahHeap* const heap, ShenandoahCollectionSet* const collection_set) {
394 shenandoah_assert_generational();
395 // We may find that old_evacuation_reserve and/or loaned_for_young_evacuation are not fully consumed, in which case we may
396 // be able to increase regions_available_to_loan
397
398 // The role of adjust_evacuation_budgets() is to compute the correct value of regions_available_to_loan and to make
399 // effective use of this memory, including the remnant memory within these regions that may result from rounding loan to
400 // integral number of regions. Excess memory that is available to be loaned is applied to an allocation supplement,
401 // which allows mutators to allocate memory beyond the current capacity of young-gen on the promise that the loan
402 // will be repaid as soon as we finish updating references for the recently evacuated collection set.
403
404 // We cannot recalculate regions_available_to_loan by simply dividing old_generation->available() by region_size_bytes
405 // because the available memory may be distributed between many partially occupied regions that are already holding old-gen
406 // objects. Memory in partially occupied regions is not "available" to be loaned. Note that an increase in old-gen
407 // available that results from a decrease in memory consumed by old evacuation is not necessarily available to be loaned
408 // to young-gen.
409
410 size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
411 ShenandoahOldGeneration* const old_generation = heap->old_generation();
412 ShenandoahYoungGeneration* const young_generation = heap->young_generation();
413
414 size_t old_evacuated = collection_set->get_old_bytes_reserved_for_evacuation();
415 size_t old_evacuated_committed = (size_t) (ShenandoahOldEvacWaste * double(old_evacuated));
416 size_t old_evacuation_reserve = old_generation->get_evacuation_reserve();
417
418 if (old_evacuated_committed > old_evacuation_reserve) {
419 // This should only happen due to round-off errors when enforcing ShenandoahOldEvacWaste
420 assert(old_evacuated_committed <= (33 * old_evacuation_reserve) / 32,
421 "Round-off errors should be less than 3.125%%, committed: " SIZE_FORMAT ", reserved: " SIZE_FORMAT,
422 old_evacuated_committed, old_evacuation_reserve);
423 old_evacuated_committed = old_evacuation_reserve;
424 // Leave old_evac_reserve as previously configured
425 } else if (old_evacuated_committed < old_evacuation_reserve) {
426 // This happens if the old-gen collection consumes less than full budget.
427 old_evacuation_reserve = old_evacuated_committed;
428 old_generation->set_evacuation_reserve(old_evacuation_reserve);
429 }
430
431 size_t young_advance_promoted = collection_set->get_young_bytes_to_be_promoted();
432 size_t young_advance_promoted_reserve_used = (size_t) (ShenandoahPromoEvacWaste * double(young_advance_promoted));
433
434 size_t young_evacuated = collection_set->get_young_bytes_reserved_for_evacuation();
435 size_t young_evacuated_reserve_used = (size_t) (ShenandoahEvacWaste * double(young_evacuated));
436
437 size_t total_young_available = young_generation->available_with_reserve();
438 assert(young_evacuated_reserve_used <= total_young_available, "Cannot evacuate more than is available in young");
439 young_generation->set_evacuation_reserve(young_evacuated_reserve_used);
440
441 size_t old_available = old_generation->available();
442 // Now that we've established the collection set, we know how much memory is really required by old-gen for evacuation
443 // and promotion reserves. Try shrinking OLD now in case that gives us a bit more runway for mutator allocations during
444 // evac and update phases.
445 size_t old_consumed = old_evacuated_committed + young_advance_promoted_reserve_used;
446
447 if (old_available < old_consumed) {
448 // This can happen due to round-off errors when adding the results of truncated integer arithmetic.
449 // We've already truncated old_evacuated_committed. Truncate young_advance_promoted_reserve_used here.
450 assert(young_advance_promoted_reserve_used <= (33 * (old_available - old_evacuated_committed)) / 32,
451 "Round-off errors should be less than 3.125%%, committed: " SIZE_FORMAT ", reserved: " SIZE_FORMAT,
452 young_advance_promoted_reserve_used, old_available - old_evacuated_committed);
453 young_advance_promoted_reserve_used = old_available - old_evacuated_committed;
454 old_consumed = old_evacuated_committed + young_advance_promoted_reserve_used;
455 }
456
457 assert(old_available >= old_consumed, "Cannot consume (" SIZE_FORMAT ") more than is available (" SIZE_FORMAT ")",
458 old_consumed, old_available);
459 size_t excess_old = old_available - old_consumed;
460 size_t unaffiliated_old_regions = old_generation->free_unaffiliated_regions();
461 size_t unaffiliated_old = unaffiliated_old_regions * region_size_bytes;
462 assert(old_available >= unaffiliated_old, "Unaffiliated old is a subset of old available");
463
464 // Make sure old_evac_committed is unaffiliated
465 if (old_evacuated_committed > 0) {
466 if (unaffiliated_old > old_evacuated_committed) {
467 size_t giveaway = unaffiliated_old - old_evacuated_committed;
468 size_t giveaway_regions = giveaway / region_size_bytes; // round down
469 if (giveaway_regions > 0) {
470 excess_old = MIN2(excess_old, giveaway_regions * region_size_bytes);
471 } else {
472 excess_old = 0;
473 }
474 } else {
475 excess_old = 0;
476 }
477 }
478
479 // If we find that OLD has excess regions, give them back to YOUNG now to reduce likelihood we run out of allocation
480 // runway during evacuation and update-refs.
481 size_t regions_to_xfer = 0;
482 if (excess_old > unaffiliated_old) {
483 // we can give back unaffiliated_old (all of unaffiliated is excess)
484 if (unaffiliated_old_regions > 0) {
485 regions_to_xfer = unaffiliated_old_regions;
486 }
487 } else if (unaffiliated_old_regions > 0) {
488 // excess_old < unaffiliated old: we can give back MIN(excess_old/region_size_bytes, unaffiliated_old_regions)
489 size_t excess_regions = excess_old / region_size_bytes;
490 regions_to_xfer = MIN2(excess_regions, unaffiliated_old_regions);
491 }
492
493 if (regions_to_xfer > 0) {
494 bool result = ShenandoahGenerationalHeap::cast(heap)->generation_sizer()->transfer_to_young(regions_to_xfer);
495 assert(excess_old >= regions_to_xfer * region_size_bytes,
496 "Cannot transfer (" SIZE_FORMAT ", " SIZE_FORMAT ") more than excess old (" SIZE_FORMAT ")",
497 regions_to_xfer, region_size_bytes, excess_old);
498 excess_old -= regions_to_xfer * region_size_bytes;
499 log_debug(gc, ergo)("%s transferred " SIZE_FORMAT " excess regions to young before start of evacuation",
500 result? "Successfully": "Unsuccessfully", regions_to_xfer);
501 }
502
503 // Add in the excess_old memory to hold unanticipated promotions, if any. If there are more unanticipated
504 // promotions than fit in reserved memory, they will be deferred until a future GC pass.
505 size_t total_promotion_reserve = young_advance_promoted_reserve_used + excess_old;
506 old_generation->set_promoted_reserve(total_promotion_reserve);
507 old_generation->reset_promoted_expended();
508 }
509
510 typedef struct {
511 ShenandoahHeapRegion* _region;
512 size_t _live_data;
513 } AgedRegionData;
514
515 static int compare_by_aged_live(AgedRegionData a, AgedRegionData b) {
516 if (a._live_data < b._live_data)
517 return -1;
518 else if (a._live_data > b._live_data)
519 return 1;
520 else return 0;
521 }
522
523 inline void assert_no_in_place_promotions() {
524 #ifdef ASSERT
525 class ShenandoahNoInPlacePromotions : public ShenandoahHeapRegionClosure {
526 public:
527 void heap_region_do(ShenandoahHeapRegion *r) override {
528 assert(r->get_top_before_promote() == nullptr,
529 "Region " SIZE_FORMAT " should not be ready for in-place promotion", r->index());
530 }
531 } cl;
532 ShenandoahHeap::heap()->heap_region_iterate(&cl);
533 #endif
534 }
535
536 // Preselect for inclusion into the collection set regions whose age is at or above tenure age which contain more than
537 // ShenandoahOldGarbageThreshold amounts of garbage. We identify these regions by setting the appropriate entry of
538 // the collection set's preselected regions array to true. All entries are initialized to false before calling this
539 // function.
540 //
541 // During the subsequent selection of the collection set, we give priority to these promotion set candidates.
542 // Without this prioritization, we found that the aged regions tend to be ignored because they typically have
543 // much less garbage and much more live data than the recently allocated "eden" regions. When aged regions are
544 // repeatedly excluded from the collection set, the amount of live memory within the young generation tends to
545 // accumulate and this has the undesirable side effect of causing young-generation collections to require much more
546 // CPU and wall-clock time.
547 //
548 // A second benefit of treating aged regions differently than other regions during collection set selection is
549 // that this allows us to more accurately budget memory to hold the results of evacuation. Memory for evacuation
550 // of aged regions must be reserved in the old generation. Memory for evacuation of all other regions must be
551 // reserved in the young generation.
552 size_t ShenandoahGeneration::select_aged_regions(size_t old_available) {
553
554 // There should be no regions configured for subsequent in-place-promotions carried over from the previous cycle.
555 assert_no_in_place_promotions();
556
557 auto const heap = ShenandoahGenerationalHeap::heap();
558 bool* const candidate_regions_for_promotion_by_copy = heap->collection_set()->preselected_regions();
559 ShenandoahMarkingContext* const ctx = heap->marking_context();
560
561 const uint tenuring_threshold = heap->age_census()->tenuring_threshold();
562 const size_t old_garbage_threshold = (ShenandoahHeapRegion::region_size_bytes() * ShenandoahOldGarbageThreshold) / 100;
563
564 size_t old_consumed = 0;
565 size_t promo_potential = 0;
566 size_t candidates = 0;
567
568 // Tracks the padding of space above top in regions eligible for promotion in place
569 size_t promote_in_place_pad = 0;
570
571 // Sort the promotion-eligible regions in order of increasing live-data-bytes so that we can first reclaim regions that require
572 // less evacuation effort. This prioritizes garbage first, expanding the allocation pool early before we reclaim regions that
573 // have more live data.
574 const size_t num_regions = heap->num_regions();
575
576 ResourceMark rm;
577 AgedRegionData* sorted_regions = NEW_RESOURCE_ARRAY(AgedRegionData, num_regions);
578
579 for (size_t i = 0; i < num_regions; i++) {
580 ShenandoahHeapRegion* const r = heap->get_region(i);
581 if (r->is_empty() || !r->has_live() || !r->is_young() || !r->is_regular()) {
582 // skip over regions that aren't regular young with some live data
583 continue;
584 }
585 if (r->age() >= tenuring_threshold) {
586 if ((r->garbage() < old_garbage_threshold)) {
587 // This tenure-worthy region has too little garbage, so we do not want to expend the copying effort to
588 // reclaim the garbage; instead this region may be eligible for promotion-in-place to the
589 // old generation.
590 HeapWord* tams = ctx->top_at_mark_start(r);
591 HeapWord* original_top = r->top();
592 if (!heap->is_concurrent_old_mark_in_progress() && tams == original_top) {
593 // No allocations from this region have been made during concurrent mark. It meets all the criteria
594 // for in-place-promotion. Though we only need the value of top when we fill the end of the region,
595 // we use this field to indicate that this region should be promoted in place during the evacuation
596 // phase.
597 r->save_top_before_promote();
598
599 size_t remnant_size = r->free() / HeapWordSize;
600 if (remnant_size > ShenandoahHeap::min_fill_size()) {
601 ShenandoahHeap::fill_with_object(original_top, remnant_size);
602 // Fill the remnant memory within this region to assure no allocations prior to promote in place. Otherwise,
603 // newly allocated objects will not be parsable when promote in place tries to register them. Furthermore, any
604 // new allocations would not necessarily be eligible for promotion. This addresses both issues.
605 r->set_top(r->end());
606 promote_in_place_pad += remnant_size * HeapWordSize;
607 } else {
608 // Since the remnant is so small that it cannot be filled, we don't have to worry about any accidental
609 // allocations occurring within this region before the region is promoted in place.
610 }
611 }
612 // Else, we do not promote this region (either in place or by copy) because it has received new allocations.
613
614 // During evacuation, we exclude from promotion regions for which age > tenure threshold, garbage < garbage-threshold,
615 // and get_top_before_promote() != tams
616 } else {
617 // Record this promotion-eligible candidate region. After sorting and selecting the best candidates below,
618 // we may still decide to exclude this promotion-eligible region from the current collection set. If this
619 // happens, we will consider this region as part of the anticipated promotion potential for the next GC
620 // pass; see further below.
621 sorted_regions[candidates]._region = r;
622 sorted_regions[candidates++]._live_data = r->get_live_data_bytes();
623 }
624 } else {
625 // We only evacuate & promote objects from regular regions whose garbage() is above old-garbage-threshold.
626 // Objects in tenure-worthy regions with less garbage are promoted in place. These take a different path to
627 // old-gen. Regions excluded from promotion because their garbage content is too low (causing us to anticipate that
628 // the region would be promoted in place) may be eligible for evacuation promotion by the time promotion takes
629 // place during a subsequent GC pass because more garbage is found within the region between now and then. This
630 // should not happen if we are properly adapting the tenure age. The theory behind adaptive tenuring threshold
631 // is to choose the youngest age that demonstrates no "significant" further loss of population since the previous
632 // age. If not this, we expect the tenure age to demonstrate linear population decay for at least two population
633 // samples, whereas we expect to observe exponential population decay for ages younger than the tenure age.
634 //
635 // In the case that certain regions which were anticipated to be promoted in place need to be promoted by
636 // evacuation, it may be the case that there is not sufficient reserve within old-gen to hold evacuation of
637 // these regions. The likely outcome is that these regions will not be selected for evacuation or promotion
638 // in the current cycle and we will anticipate that they will be promoted in the next cycle. This will cause
639 // us to reserve more old-gen memory so that these objects can be promoted in the subsequent cycle.
640 if (heap->is_aging_cycle() && (r->age() + 1 == tenuring_threshold)) {
641 if (r->garbage() >= old_garbage_threshold) {
642 promo_potential += r->get_live_data_bytes();
643 }
644 }
645 }
646 // Note that we keep going even if one region is excluded from selection.
647 // Subsequent regions may be selected if they have smaller live data.
648 }
649 // Sort in increasing order according to live data bytes. Note that candidates represents the number of regions
650 // that qualify to be promoted by evacuation.
651 if (candidates > 0) {
652 size_t selected_regions = 0;
653 size_t selected_live = 0;
654 QuickSort::sort<AgedRegionData>(sorted_regions, candidates, compare_by_aged_live, false);
655 for (size_t i = 0; i < candidates; i++) {
656 ShenandoahHeapRegion* const region = sorted_regions[i]._region;
657 size_t region_live_data = sorted_regions[i]._live_data;
658 size_t promotion_need = (size_t) (region_live_data * ShenandoahPromoEvacWaste);
659 if (old_consumed + promotion_need <= old_available) {
660 old_consumed += promotion_need;
661 candidate_regions_for_promotion_by_copy[region->index()] = true;
662 selected_regions++;
663 selected_live += region_live_data;
664 } else {
665 // We rejected this promotable region from the collection set because we had no room to hold its copy.
666 // Add this region to promo potential for next GC.
667 promo_potential += region_live_data;
668 assert(!candidate_regions_for_promotion_by_copy[region->index()], "Shouldn't be selected");
669 }
670 // We keep going even if one region is excluded from selection because we need to accumulate all eligible
671 // regions that are not preselected into promo_potential
672 }
673 log_debug(gc)("Preselected " SIZE_FORMAT " regions containing " SIZE_FORMAT " live bytes,"
674 " consuming: " SIZE_FORMAT " of budgeted: " SIZE_FORMAT,
675 selected_regions, selected_live, old_consumed, old_available);
676 }
677
678 heap->old_generation()->set_pad_for_promote_in_place(promote_in_place_pad);
679 heap->old_generation()->set_promotion_potential(promo_potential);
680 return old_consumed;
681 }
682
683 void ShenandoahGeneration::prepare_regions_and_collection_set(bool concurrent) {
684 ShenandoahHeap* heap = ShenandoahHeap::heap();
685 ShenandoahCollectionSet* collection_set = heap->collection_set();
686 bool is_generational = heap->mode()->is_generational();
687
688 assert(!heap->is_full_gc_in_progress(), "Only for concurrent and degenerated GC");
689 assert(!is_old(), "Only YOUNG and GLOBAL GC perform evacuations");
690 {
691 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::final_update_region_states :
692 ShenandoahPhaseTimings::degen_gc_final_update_region_states);
693 ShenandoahFinalMarkUpdateRegionStateClosure cl(complete_marking_context());
694 parallel_heap_region_iterate(&cl);
695
696 if (is_young()) {
697 // We always need to update the watermark for old regions. If there
698 // are mixed collections pending, we also need to synchronize the
699 // pinned status for old regions. Since we are already visiting every
700 // old region here, go ahead and sync the pin status too.
701 ShenandoahFinalMarkUpdateRegionStateClosure old_cl(nullptr);
702 heap->old_generation()->parallel_heap_region_iterate(&old_cl);
703 }
704 }
705
706 // Tally the census counts and compute the adaptive tenuring threshold
707 if (is_generational && ShenandoahGenerationalAdaptiveTenuring && !ShenandoahGenerationalCensusAtEvac) {
708 // Objects above TAMS weren't included in the age census. Since they were all
709 // allocated in this cycle they belong in the age 0 cohort. We walk over all
710 // young regions and sum the volume of objects between TAMS and top.
711 ShenandoahUpdateCensusZeroCohortClosure age0_cl(complete_marking_context());
712 heap->young_generation()->heap_region_iterate(&age0_cl);
713 size_t age0_pop = age0_cl.get_age0_population();
714
715 // Update the global census, including the missed age 0 cohort above,
716 // along with the census done during marking, and compute the tenuring threshold.
717 ShenandoahAgeCensus* census = ShenandoahGenerationalHeap::heap()->age_census();
718 census->update_census(age0_pop);
719 #ifndef PRODUCT
720 size_t total_pop = age0_cl.get_total_population();
721 size_t total_census = census->get_total();
722 // Usually total_pop > total_census, but not by too much.
723 // We use integer division so anything up to just less than 2 is considered
724 // reasonable, and the "+1" is to avoid divide-by-zero.
725 assert((total_pop+1)/(total_census+1) == 1, "Extreme divergence: "
726 SIZE_FORMAT "/" SIZE_FORMAT, total_pop, total_census);
727 #endif
728 }
729
730 {
731 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::choose_cset :
732 ShenandoahPhaseTimings::degen_gc_choose_cset);
733
734 collection_set->clear();
735 ShenandoahHeapLocker locker(heap->lock());
736 if (is_generational) {
737 // Seed the collection set with resource area-allocated
738 // preselected regions, which are removed when we exit this scope.
739 ShenandoahCollectionSetPreselector preselector(collection_set, heap->num_regions());
740
741 // Find the amount that will be promoted, regions that will be promoted in
742 // place, and preselect older regions that will be promoted by evacuation.
743 compute_evacuation_budgets(heap);
744
745 // Choose the collection set, including the regions preselected above for
746 // promotion into the old generation.
747 _heuristics->choose_collection_set(collection_set);
748 if (!collection_set->is_empty()) {
749 // only make use of evacuation budgets when we are evacuating
750 adjust_evacuation_budgets(heap, collection_set);
751 }
752
753 if (is_global()) {
754 // We have just chosen a collection set for a global cycle. The mark bitmap covering old regions is complete, so
755 // the remembered set scan can use that to avoid walking into garbage. When the next old mark begins, we will
756 // use the mark bitmap to make the old regions parsable by coalescing and filling any unmarked objects. Thus,
757 // we prepare for old collections by remembering which regions are old at this time. Note that any objects
758 // promoted into old regions will be above TAMS, and so will be considered marked. However, free regions that
759 // become old after this point will not be covered correctly by the mark bitmap, so we must be careful not to
760 // coalesce those regions. Only the old regions which are not part of the collection set at this point are
761 // eligible for coalescing. As implemented now, this has the side effect of possibly initiating mixed-evacuations
762 // after a global cycle for old regions that were not included in this collection set.
763 heap->old_generation()->prepare_for_mixed_collections_after_global_gc();
764 }
765 } else {
766 _heuristics->choose_collection_set(collection_set);
767 }
768 }
769
770
771 {
772 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::final_rebuild_freeset :
773 ShenandoahPhaseTimings::degen_gc_final_rebuild_freeset);
774 ShenandoahHeapLocker locker(heap->lock());
775 size_t young_cset_regions, old_cset_regions;
776
777 // We are preparing for evacuation. At this time, we ignore cset region tallies.
778 size_t first_old, last_old, num_old;
779 heap->free_set()->prepare_to_rebuild(young_cset_regions, old_cset_regions, first_old, last_old, num_old);
780 // Free set construction uses reserve quantities, because they are known to be valid here
781 heap->free_set()->finish_rebuild(young_cset_regions, old_cset_regions, num_old, true);
782 }
783 }
784
785 bool ShenandoahGeneration::is_bitmap_clear() {
786 ShenandoahHeap* heap = ShenandoahHeap::heap();
787 ShenandoahMarkingContext* context = heap->marking_context();
788 const size_t num_regions = heap->num_regions();
789 for (size_t idx = 0; idx < num_regions; idx++) {
790 ShenandoahHeapRegion* r = heap->get_region(idx);
791 if (contains(r) && r->is_affiliated()) {
792 if (heap->is_bitmap_slice_committed(r) && (context->top_at_mark_start(r) > r->bottom()) &&
793 !context->is_bitmap_range_within_region_clear(r->bottom(), r->end())) {
794 return false;
795 }
796 }
797 }
798 return true;
799 }
800
801 bool ShenandoahGeneration::is_mark_complete() {
802 return _is_marking_complete.is_set();
803 }
804
805 void ShenandoahGeneration::set_mark_complete() {
806 _is_marking_complete.set();
807 }
808
809 void ShenandoahGeneration::set_mark_incomplete() {
810 _is_marking_complete.unset();
811 }
812
813 ShenandoahMarkingContext* ShenandoahGeneration::complete_marking_context() {
814 assert(is_mark_complete(), "Marking must be completed.");
815 return ShenandoahHeap::heap()->marking_context();
816 }
817
818 void ShenandoahGeneration::cancel_marking() {
819 log_info(gc)("Cancel marking: %s", name());
820 if (is_concurrent_mark_in_progress()) {
821 set_mark_incomplete();
822 }
823 _task_queues->clear();
824 ref_processor()->abandon_partial_discovery();
825 set_concurrent_mark_in_progress(false);
826 }
827
828 ShenandoahGeneration::ShenandoahGeneration(ShenandoahGenerationType type,
829 uint max_workers,
830 size_t max_capacity,
831 size_t soft_max_capacity) :
832 _type(type),
833 _task_queues(new ShenandoahObjToScanQueueSet(max_workers)),
834 _ref_processor(new ShenandoahReferenceProcessor(MAX2(max_workers, 1U))),
835 _affiliated_region_count(0), _humongous_waste(0), _evacuation_reserve(0),
836 _used(0), _bytes_allocated_since_gc_start(0),
837 _max_capacity(max_capacity), _soft_max_capacity(soft_max_capacity),
838 _heuristics(nullptr)
839 {
840 _is_marking_complete.set();
841 assert(max_workers > 0, "At least one queue");
842 for (uint i = 0; i < max_workers; ++i) {
843 ShenandoahObjToScanQueue* task_queue = new ShenandoahObjToScanQueue();
844 _task_queues->register_queue(i, task_queue);
845 }
846 }
847
848 ShenandoahGeneration::~ShenandoahGeneration() {
849 for (uint i = 0; i < _task_queues->size(); ++i) {
850 ShenandoahObjToScanQueue* q = _task_queues->queue(i);
851 delete q;
852 }
853 delete _task_queues;
854 }
855
856 void ShenandoahGeneration::reserve_task_queues(uint workers) {
857 _task_queues->reserve(workers);
858 }
859
860 ShenandoahObjToScanQueueSet* ShenandoahGeneration::old_gen_task_queues() const {
861 return nullptr;
862 }
863
864 void ShenandoahGeneration::scan_remembered_set(bool is_concurrent) {
865 assert(is_young(), "Should only scan remembered set for young generation.");
866
867 ShenandoahGenerationalHeap* const heap = ShenandoahGenerationalHeap::heap();
868 uint nworkers = heap->workers()->active_workers();
869 reserve_task_queues(nworkers);
870
871 ShenandoahReferenceProcessor* rp = ref_processor();
872 ShenandoahRegionChunkIterator work_list(nworkers);
873 ShenandoahScanRememberedTask task(task_queues(), old_gen_task_queues(), rp, &work_list, is_concurrent);
874 heap->assert_gc_workers(nworkers);
875 heap->workers()->run_task(&task);
876 if (ShenandoahEnableCardStats) {
877 ShenandoahScanRemembered* scanner = heap->old_generation()->card_scan();
878 assert(scanner != nullptr, "Not generational");
879 scanner->log_card_stats(nworkers, CARD_STAT_SCAN_RS);
880 }
881 }
882
883 size_t ShenandoahGeneration::increment_affiliated_region_count() {
884 shenandoah_assert_heaplocked_or_safepoint();
885 // During full gc, multiple GC worker threads may change region affiliations without a lock. No lock is enforced
886 // on read and write of _affiliated_region_count. At the end of full gc, a single thread overwrites the count with
887 // a coherent value.
888 _affiliated_region_count++;
889 return _affiliated_region_count;
890 }
891
892 size_t ShenandoahGeneration::decrement_affiliated_region_count() {
893 shenandoah_assert_heaplocked_or_safepoint();
894 // During full gc, multiple GC worker threads may change region affiliations without a lock. No lock is enforced
895 // on read and write of _affiliated_region_count. At the end of full gc, a single thread overwrites the count with
896 // a coherent value.
897 _affiliated_region_count--;
898 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
899 (_used + _humongous_waste <= _affiliated_region_count * ShenandoahHeapRegion::region_size_bytes()),
900 "used + humongous cannot exceed regions");
901 return _affiliated_region_count;
902 }
903
904 size_t ShenandoahGeneration::increase_affiliated_region_count(size_t delta) {
905 shenandoah_assert_heaplocked_or_safepoint();
906 _affiliated_region_count += delta;
907 return _affiliated_region_count;
908 }
909
910 size_t ShenandoahGeneration::decrease_affiliated_region_count(size_t delta) {
911 shenandoah_assert_heaplocked_or_safepoint();
912 assert(_affiliated_region_count >= delta, "Affiliated region count cannot be negative");
913
914 _affiliated_region_count -= delta;
915 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
916 (_used + _humongous_waste <= _affiliated_region_count * ShenandoahHeapRegion::region_size_bytes()),
917 "used + humongous cannot exceed regions");
918 return _affiliated_region_count;
919 }
920
921 void ShenandoahGeneration::establish_usage(size_t num_regions, size_t num_bytes, size_t humongous_waste) {
922 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
923 _affiliated_region_count = num_regions;
924 _used = num_bytes;
925 _humongous_waste = humongous_waste;
926 }
927
928 void ShenandoahGeneration::increase_used(size_t bytes) {
929 Atomic::add(&_used, bytes);
930 }
931
932 void ShenandoahGeneration::increase_humongous_waste(size_t bytes) {
933 if (bytes > 0) {
934 Atomic::add(&_humongous_waste, bytes);
935 }
936 }
937
938 void ShenandoahGeneration::decrease_humongous_waste(size_t bytes) {
939 if (bytes > 0) {
940 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() || (_humongous_waste >= bytes),
941 "Waste (" SIZE_FORMAT ") cannot be negative (after subtracting " SIZE_FORMAT ")", _humongous_waste, bytes);
942 Atomic::sub(&_humongous_waste, bytes);
943 }
944 }
945
946 void ShenandoahGeneration::decrease_used(size_t bytes) {
947 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
948 (_used >= bytes), "cannot reduce bytes used by generation below zero");
949 Atomic::sub(&_used, bytes);
950 }
951
952 size_t ShenandoahGeneration::used_regions() const {
953 return _affiliated_region_count;
954 }
955
956 size_t ShenandoahGeneration::free_unaffiliated_regions() const {
957 size_t result = max_capacity() / ShenandoahHeapRegion::region_size_bytes();
958 if (_affiliated_region_count > result) {
959 result = 0;
960 } else {
961 result -= _affiliated_region_count;
962 }
963 return result;
964 }
965
966 size_t ShenandoahGeneration::used_regions_size() const {
967 return _affiliated_region_count * ShenandoahHeapRegion::region_size_bytes();
968 }
969
970 size_t ShenandoahGeneration::available() const {
971 return available(max_capacity());
972 }
973
974 // For ShenandoahYoungGeneration, Include the young available that may have been reserved for the Collector.
975 size_t ShenandoahGeneration::available_with_reserve() const {
976 return available(max_capacity());
977 }
978
979 size_t ShenandoahGeneration::soft_available() const {
980 return available(soft_max_capacity());
981 }
982
983 size_t ShenandoahGeneration::available(size_t capacity) const {
984 size_t in_use = used() + get_humongous_waste();
985 return in_use > capacity ? 0 : capacity - in_use;
986 }
987
988 size_t ShenandoahGeneration::increase_capacity(size_t increment) {
989 shenandoah_assert_heaplocked_or_safepoint();
990
991 // We do not enforce that new capacity >= heap->max_size_for(this). The maximum generation size is treated as a rule of thumb
992 // which may be violated during certain transitions, such as when we are forcing transfers for the purpose of promoting regions
993 // in place.
994 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
995 (_max_capacity + increment <= ShenandoahHeap::heap()->max_capacity()), "Generation cannot be larger than heap size");
996 assert(increment % ShenandoahHeapRegion::region_size_bytes() == 0, "Generation capacity must be multiple of region size");
997 _max_capacity += increment;
998
999 // This detects arithmetic wraparound on _used
1000 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
1001 (_affiliated_region_count * ShenandoahHeapRegion::region_size_bytes() >= _used),
1002 "Affiliated regions must hold more than what is currently used");
1003 return _max_capacity;
1004 }
1005
1006 size_t ShenandoahGeneration::set_capacity(size_t byte_size) {
1007 shenandoah_assert_heaplocked_or_safepoint();
1008 _max_capacity = byte_size;
1009 return _max_capacity;
1010 }
1011
1012 size_t ShenandoahGeneration::decrease_capacity(size_t decrement) {
1013 shenandoah_assert_heaplocked_or_safepoint();
1014
1015 // We do not enforce that new capacity >= heap->min_size_for(this). The minimum generation size is treated as a rule of thumb
1016 // which may be violated during certain transitions, such as when we are forcing transfers for the purpose of promoting regions
1017 // in place.
1018 assert(decrement % ShenandoahHeapRegion::region_size_bytes() == 0, "Generation capacity must be multiple of region size");
1019 assert(_max_capacity >= decrement, "Generation capacity cannot be negative");
1020
1021 _max_capacity -= decrement;
1022
1023 // This detects arithmetic wraparound on _used
1024 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
1025 (_affiliated_region_count * ShenandoahHeapRegion::region_size_bytes() >= _used),
1026 "Affiliated regions must hold more than what is currently used");
1027 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
1028 (_used <= _max_capacity), "Cannot use more than capacity");
1029 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
1030 (_affiliated_region_count * ShenandoahHeapRegion::region_size_bytes() <= _max_capacity),
1031 "Cannot use more than capacity");
1032 return _max_capacity;
1033 }
1034
1035 void ShenandoahGeneration::record_success_concurrent(bool abbreviated) {
1036 heuristics()->record_success_concurrent();
1037 ShenandoahHeap::heap()->shenandoah_policy()->record_success_concurrent(is_young(), abbreviated);
1038 }