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/shenandoahFreeSet.hpp"
28 #include "gc/shenandoah/shenandoahGeneration.hpp"
29 #include "gc/shenandoah/shenandoahHeap.hpp"
30 #include "gc/shenandoah/shenandoahMarkClosures.hpp"
31 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
32 #include "gc/shenandoah/shenandoahOldGeneration.hpp"
33 #include "gc/shenandoah/shenandoahReferenceProcessor.hpp"
34 #include "gc/shenandoah/shenandoahTaskqueue.inline.hpp"
35 #include "gc/shenandoah/shenandoahUtils.hpp"
36 #include "gc/shenandoah/shenandoahVerifier.hpp"
37 #include "gc/shenandoah/shenandoahYoungGeneration.hpp"
38 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
39
40 #include "utilities/quickSort.hpp"
41
42 class ShenandoahResetUpdateRegionStateClosure : public ShenandoahHeapRegionClosure {
43 private:
44 ShenandoahHeap* _heap;
45 ShenandoahMarkingContext* const _ctx;
46 public:
47 ShenandoahResetUpdateRegionStateClosure() :
48 _heap(ShenandoahHeap::heap()),
49 _ctx(_heap->marking_context()) {}
50
51 void heap_region_do(ShenandoahHeapRegion* r) override {
52 if (_heap->is_bitmap_slice_committed(r)) {
53 _ctx->clear_bitmap(r);
54 }
55
56 if (r->is_active()) {
57 // Reset live data and set TAMS optimistically. We would recheck these under the pause
58 // anyway to capture any updates that happened since now.
59 _ctx->capture_top_at_mark_start(r);
60 r->clear_live_data();
61 }
62 }
63
64 bool is_thread_safe() override { return true; }
65 };
66
67 class ShenandoahResetBitmapTask : public ShenandoahHeapRegionClosure {
68 private:
69 ShenandoahHeap* _heap;
70 ShenandoahMarkingContext* const _ctx;
71 public:
72 ShenandoahResetBitmapTask() :
73 _heap(ShenandoahHeap::heap()),
74 _ctx(_heap->marking_context()) {}
75
76 void heap_region_do(ShenandoahHeapRegion* region) {
77 if (_heap->is_bitmap_slice_committed(region)) {
78 _ctx->clear_bitmap(region);
79 }
80 }
81
82 bool is_thread_safe() { return true; }
83 };
84
85 class ShenandoahMergeWriteTable: public ShenandoahHeapRegionClosure {
86 private:
87 ShenandoahHeap* _heap;
88 RememberedScanner* _scanner;
89 public:
90 ShenandoahMergeWriteTable() : _heap(ShenandoahHeap::heap()), _scanner(_heap->card_scan()) {}
91
92 virtual void heap_region_do(ShenandoahHeapRegion* r) override {
93 if (r->is_old()) {
94 _scanner->merge_write_table(r->bottom(), ShenandoahHeapRegion::region_size_words());
95 }
96 }
97
98 virtual bool is_thread_safe() override {
99 return true;
100 }
101 };
102
103 class ShenandoahSquirrelAwayCardTable: public ShenandoahHeapRegionClosure {
104 private:
105 ShenandoahHeap* _heap;
106 RememberedScanner* _scanner;
107 public:
108 ShenandoahSquirrelAwayCardTable() :
109 _heap(ShenandoahHeap::heap()),
110 _scanner(_heap->card_scan()) {}
111
112 void heap_region_do(ShenandoahHeapRegion* region) {
113 if (region->is_old()) {
114 _scanner->reset_remset(region->bottom(), ShenandoahHeapRegion::region_size_words());
115 }
116 }
117
118 bool is_thread_safe() { return true; }
119 };
120
121 void ShenandoahGeneration::confirm_heuristics_mode() {
122 if (_heuristics->is_diagnostic() && !UnlockDiagnosticVMOptions) {
123 vm_exit_during_initialization(
124 err_msg("Heuristics \"%s\" is diagnostic, and must be enabled via -XX:+UnlockDiagnosticVMOptions.",
125 _heuristics->name()));
126 }
127 if (_heuristics->is_experimental() && !UnlockExperimentalVMOptions) {
128 vm_exit_during_initialization(
129 err_msg("Heuristics \"%s\" is experimental, and must be enabled via -XX:+UnlockExperimentalVMOptions.",
130 _heuristics->name()));
131 }
132 }
133
134 ShenandoahHeuristics* ShenandoahGeneration::initialize_heuristics(ShenandoahMode* gc_mode) {
135 _heuristics = gc_mode->initialize_heuristics(this);
136 _heuristics->set_guaranteed_gc_interval(ShenandoahGuaranteedGCInterval);
137 confirm_heuristics_mode();
138 return _heuristics;
139 }
140
141 size_t ShenandoahGeneration::bytes_allocated_since_gc_start() const {
142 return Atomic::load(&_bytes_allocated_since_gc_start);
143 }
144
145 void ShenandoahGeneration::reset_bytes_allocated_since_gc_start() {
146 Atomic::store(&_bytes_allocated_since_gc_start, (size_t)0);
147 }
148
149 void ShenandoahGeneration::increase_allocated(size_t bytes) {
150 Atomic::add(&_bytes_allocated_since_gc_start, bytes, memory_order_relaxed);
151 }
152
153 void ShenandoahGeneration::log_status(const char *msg) const {
154 typedef LogTarget(Info, gc, ergo) LogGcInfo;
155
156 if (!LogGcInfo::is_enabled()) {
157 return;
158 }
159
160 // Not under a lock here, so read each of these once to make sure
161 // byte size in proper unit and proper unit for byte size are consistent.
162 size_t v_used = used();
163 size_t v_used_regions = used_regions_size();
164 size_t v_soft_max_capacity = soft_max_capacity();
165 size_t v_max_capacity = max_capacity();
166 size_t v_available = available();
167 size_t v_humongous_waste = get_humongous_waste();
168 LogGcInfo::print("%s: %s generation used: " SIZE_FORMAT "%s, used regions: " SIZE_FORMAT "%s, "
169 "humongous waste: " SIZE_FORMAT "%s, soft capacity: " SIZE_FORMAT "%s, max capacity: " SIZE_FORMAT "%s, "
170 "available: " SIZE_FORMAT "%s", msg, name(),
171 byte_size_in_proper_unit(v_used), proper_unit_for_byte_size(v_used),
172 byte_size_in_proper_unit(v_used_regions), proper_unit_for_byte_size(v_used_regions),
173 byte_size_in_proper_unit(v_humongous_waste), proper_unit_for_byte_size(v_humongous_waste),
174 byte_size_in_proper_unit(v_soft_max_capacity), proper_unit_for_byte_size(v_soft_max_capacity),
175 byte_size_in_proper_unit(v_max_capacity), proper_unit_for_byte_size(v_max_capacity),
176 byte_size_in_proper_unit(v_available), proper_unit_for_byte_size(v_available));
177 }
178
179 void ShenandoahGeneration::reset_mark_bitmap() {
180 ShenandoahHeap* heap = ShenandoahHeap::heap();
181 heap->assert_gc_workers(heap->workers()->active_workers());
182
183 set_mark_incomplete();
184
185 ShenandoahResetBitmapTask task;
186 parallel_heap_region_iterate(&task);
187 }
188
189 // The ideal is to swap the remembered set so the safepoint effort is no more than a few pointer manipulations.
190 // However, limitations in the implementation of the mutator write-barrier make it difficult to simply change the
191 // location of the card table. So the interim implementation of swap_remembered_set will copy the write-table
192 // onto the read-table and will then clear the write-table.
193 void ShenandoahGeneration::swap_remembered_set() {
194 // Must be sure that marking is complete before we swap remembered set.
195 ShenandoahHeap* heap = ShenandoahHeap::heap();
196 heap->assert_gc_workers(heap->workers()->active_workers());
197 shenandoah_assert_safepoint();
198
199 // TODO: Eventually, we want replace this with a constant-time exchange of pointers.
200 ShenandoahSquirrelAwayCardTable task;
201 heap->old_generation()->parallel_heap_region_iterate(&task);
202 }
203
204 // If a concurrent cycle fails _after_ the card table has been swapped we need to update the read card
205 // table with any writes that have occurred during the transition to the degenerated cycle. Without this,
206 // newly created objects which are only referenced by old objects could be lost when the remembered set
207 // is scanned during the degenerated mark.
208 void ShenandoahGeneration::merge_write_table() {
209 // This should only happen for degenerated cycles
210 ShenandoahHeap* heap = ShenandoahHeap::heap();
211 heap->assert_gc_workers(heap->workers()->active_workers());
212 shenandoah_assert_safepoint();
213
214 ShenandoahMergeWriteTable task;
215 heap->old_generation()->parallel_heap_region_iterate(&task);
216 }
217
218 void ShenandoahGeneration::prepare_gc() {
219 // Invalidate the marking context
220 set_mark_incomplete();
221
222 // Capture Top At Mark Start for this generation (typically young) and reset mark bitmap.
223 ShenandoahResetUpdateRegionStateClosure cl;
224 parallel_heap_region_iterate(&cl);
225 }
226
227 void ShenandoahGeneration::compute_evacuation_budgets(ShenandoahHeap* heap, bool* preselected_regions,
228 ShenandoahCollectionSet* collection_set,
229 size_t &consumed_by_advance_promotion) {
230 size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
231 size_t regions_available_to_loan = 0;
232 size_t minimum_evacuation_reserve = ShenandoahOldCompactionReserve * region_size_bytes;
233 size_t old_regions_loaned_for_young_evac = 0;
234 consumed_by_advance_promotion = 0;
235
236 ShenandoahGeneration* old_generation = heap->old_generation();
237 ShenandoahYoungGeneration* young_generation = heap->young_generation();
238 size_t old_evacuation_reserve = 0;
239 size_t num_regions = heap->num_regions();
240
241 // During initialization and phase changes, it is more likely that fewer objects die young and old-gen
242 // memory is not yet full (or is in the process of being replaced). During these times especially, it
243 // is beneficial to loan memory from old-gen to young-gen during the evacuation and update-refs phases
244 // of execution.
245
246 // Calculate EvacuationReserve before PromotionReserve. Evacuation is more critical than promotion.
247 // If we cannot evacuate old-gen, we will not be able to reclaim old-gen memory. Promotions are less
248 // critical. If we cannot promote, there may be degradation of young-gen memory because old objects
249 // accumulate there until they can be promoted. This increases the young-gen marking and evacuation work.
250
251 // Do not fill up old-gen memory with promotions. Reserve some amount of memory for compaction purposes.
252 size_t young_evac_reserve_max = 0;
253
254 // First priority is to reclaim the easy garbage out of young-gen.
255
256 // maximum_young_evacuation_reserve is upper bound on memory to be evacuated out of young
257 size_t maximum_young_evacuation_reserve = (young_generation->max_capacity() * ShenandoahEvacReserve) / 100;
258 size_t young_evacuation_reserve = maximum_young_evacuation_reserve;
259 size_t excess_young;
260
261 size_t total_young_available = young_generation->available_with_reserve();
262 if (total_young_available > young_evacuation_reserve) {
263 excess_young = total_young_available - young_evacuation_reserve;
264 } else {
265 young_evacuation_reserve = total_young_available;
266 excess_young = 0;
267 }
268 size_t unaffiliated_young = young_generation->free_unaffiliated_regions() * region_size_bytes;
269 if (excess_young > unaffiliated_young) {
270 excess_young = unaffiliated_young;
271 } else {
272 // round down to multiple of region size
273 excess_young /= region_size_bytes;
274 excess_young *= region_size_bytes;
275 }
276 // excess_young is available to be transferred to OLD. Assume that OLD will not request any more than had
277 // already been set aside for its promotion and evacuation needs at the end of previous GC. No need to
278 // hold back memory for allocation runway.
279
280 // TODO: excess_young is unused. Did we want to add it old_promo_reserve and/or old_evacuation_reserve?
281
282 ShenandoahOldHeuristics* old_heuristics = heap->old_heuristics();
283
284 // maximum_old_evacuation_reserve is an upper bound on memory evacuated from old and evacuated to old (promoted).
285 size_t maximum_old_evacuation_reserve =
286 maximum_young_evacuation_reserve * ShenandoahOldEvacRatioPercent / (100 - ShenandoahOldEvacRatioPercent);
287 // Here's the algebra:
288 // TotalEvacuation = OldEvacuation + YoungEvacuation
289 // OldEvacuation = TotalEvacuation * (ShenandoahOldEvacRatioPercent/100)
290 // OldEvacuation = YoungEvacuation * (ShenandoahOldEvacRatioPercent/100)/(1 - ShenandoahOldEvacRatioPercent/100)
291 // OldEvacuation = YoungEvacuation * ShenandoahOldEvacRatioPercent/(100 - ShenandoahOldEvacRatioPercent)
292
293 if (maximum_old_evacuation_reserve > old_generation->available()) {
294 maximum_old_evacuation_reserve = old_generation->available();
295 }
296
297 // Second priority is to reclaim garbage out of old-gen if there are old-gen collection candidates. Third priority
298 // is to promote as much as we have room to promote. However, if old-gen memory is in short supply, this means young
299 // GC is operating under "duress" and was unable to transfer the memory that we would normally expect. In this case,
300 // old-gen will refrain from compacting itself in order to allow a quicker young-gen cycle (by avoiding the update-refs
301 // through ALL of old-gen). If there is some memory available in old-gen, we will use this for promotions as promotions
302 // do not add to the update-refs burden of GC.
303
304 size_t old_promo_reserve;
305 if (is_global()) {
306 // Global GC is typically triggered by user invocation of System.gc(), and typically indicates that there is lots
307 // of garbage to be reclaimed because we are starting a new phase of execution. Marking for global GC may take
308 // significantly longer than typical young marking because we must mark through all old objects. To expedite
309 // evacuation and update-refs, we give emphasis to reclaiming garbage first, wherever that garbage is found.
310 // Global GC will adjust generation sizes to accommodate the collection set it chooses.
311
312 // Set old_promo_reserve to enforce that no regions are preselected for promotion. Such regions typically
313 // have relatively high memory utilization. We still call select_aged_regions() because this will prepare for
314 // promotions in place, if relevant.
315 old_promo_reserve = 0;
316
317 // Dedicate all available old memory to old_evacuation reserve. This may be small, because old-gen is only
318 // expanded based on an existing mixed evacuation workload at the end of the previous GC cycle. We'll expand
319 // the budget for evacuation of old during GLOBAL cset selection.
320 old_evacuation_reserve = maximum_old_evacuation_reserve;
321 } else if (old_heuristics->unprocessed_old_collection_candidates() > 0) {
322 // We reserved all old-gen memory at end of previous GC to hold anticipated evacuations to old-gen. If this is
323 // mixed evacuation, reserve all of this memory for compaction of old-gen and do not promote. Prioritize compaction
324 // over promotion in order to defragment OLD so that it will be better prepared to efficiently receive promoted memory.
325 old_evacuation_reserve = maximum_old_evacuation_reserve;
326 old_promo_reserve = 0;
327 } else {
328 // Make all old-evacuation memory for promotion, but if we can't use it all for promotion, we'll allow some evacuation.
329 old_evacuation_reserve = 0;
330 old_promo_reserve = maximum_old_evacuation_reserve;
331 }
332
333 // We see too many old-evacuation failures if we force ourselves to evacuate into regions that are not initially empty.
334 // So we limit the old-evacuation reserve to unfragmented memory. Even so, old-evacuation is free to fill in nooks and
335 // crannies within existing partially used regions and it generally tries to do so.
336 size_t old_free_regions = old_generation->free_unaffiliated_regions();
337 size_t old_free_unfragmented = old_free_regions * region_size_bytes;
338 if (old_evacuation_reserve > old_free_unfragmented) {
339 size_t delta = old_evacuation_reserve - old_free_unfragmented;
340 old_evacuation_reserve -= delta;
341
342 // Let promo consume fragments of old-gen memory if not global
343 if (!is_global()) {
344 old_promo_reserve += delta;
345 }
346 }
347 collection_set->establish_preselected(preselected_regions);
348 consumed_by_advance_promotion = select_aged_regions(old_promo_reserve, num_regions, preselected_regions);
349 assert(consumed_by_advance_promotion <= maximum_old_evacuation_reserve, "Cannot promote more than available old-gen memory");
350
351 // Note that unused old_promo_reserve might not be entirely consumed_by_advance_promotion. Do not transfer this
352 // to old_evacuation_reserve because this memory is likely very fragmented, and we do not want to increase the likelihood
353 // of old evacuatino failure.
354
355 heap->set_young_evac_reserve(young_evacuation_reserve);
356 heap->set_old_evac_reserve(old_evacuation_reserve);
357 heap->set_promoted_reserve(consumed_by_advance_promotion);
358
359 // There is no need to expand OLD because all memory used here was set aside at end of previous GC, except in the
360 // case of a GLOBAL gc. During choose_collection_set() of GLOBAL, old will be expanded on demand.
361 }
362
363 // Having chosen the collection set, adjust the budgets for generational mode based on its composition. Note
364 // that young_generation->available() now knows about recently discovered immediate garbage.
365
366 void ShenandoahGeneration::adjust_evacuation_budgets(ShenandoahHeap* heap, ShenandoahCollectionSet* collection_set,
367 size_t consumed_by_advance_promotion) {
368 // We may find that old_evacuation_reserve and/or loaned_for_young_evacuation are not fully consumed, in which case we may
369 // be able to increase regions_available_to_loan
370
371 // The role of adjust_evacuation_budgets() is to compute the correct value of regions_available_to_loan and to make
372 // effective use of this memory, including the remnant memory within these regions that may result from rounding loan to
373 // integral number of regions. Excess memory that is available to be loaned is applied to an allocation supplement,
374 // which allows mutators to allocate memory beyond the current capacity of young-gen on the promise that the loan
375 // will be repaid as soon as we finish updating references for the recently evacuated collection set.
376
377 // We cannot recalculate regions_available_to_loan by simply dividing old_generation->available() by region_size_bytes
378 // because the available memory may be distributed between many partially occupied regions that are already holding old-gen
379 // objects. Memory in partially occupied regions is not "available" to be loaned. Note that an increase in old-gen
380 // available that results from a decrease in memory consumed by old evacuation is not necessarily available to be loaned
381 // to young-gen.
382
383 size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
384 ShenandoahOldGeneration* old_generation = heap->old_generation();
385 ShenandoahYoungGeneration* young_generation = heap->young_generation();
386
387 // Preselected regions have been inserted into the collection set, so we no longer need the preselected array.
388 collection_set->abandon_preselected();
389
390 size_t old_evacuated = collection_set->get_old_bytes_reserved_for_evacuation();
391 size_t old_evacuated_committed = (size_t) (ShenandoahOldEvacWaste * old_evacuated);
392 size_t old_evacuation_reserve = heap->get_old_evac_reserve();
393
394 if (old_evacuated_committed > old_evacuation_reserve) {
395 // This should only happen due to round-off errors when enforcing ShenandoahOldEvacWaste
396 assert(old_evacuated_committed <= (33 * old_evacuation_reserve) / 32,
397 "Round-off errors should be less than 3.125%%, committed: " SIZE_FORMAT ", reserved: " SIZE_FORMAT,
398 old_evacuated_committed, old_evacuation_reserve);
399 old_evacuated_committed = old_evacuation_reserve;
400 // Leave old_evac_reserve as previously configured
401 } else if (old_evacuated_committed < old_evacuation_reserve) {
402 // This happens if the old-gen collection consumes less than full budget.
403 old_evacuation_reserve = old_evacuated_committed;
404 heap->set_old_evac_reserve(old_evacuation_reserve);
405 }
406
407 size_t young_advance_promoted = collection_set->get_young_bytes_to_be_promoted();
408 size_t young_advance_promoted_reserve_used = (size_t) (ShenandoahPromoEvacWaste * young_advance_promoted);
409
410 size_t young_evacuated = collection_set->get_young_bytes_reserved_for_evacuation();
411 size_t young_evacuated_reserve_used = (size_t) (ShenandoahEvacWaste * young_evacuated);
412
413 size_t total_young_available = young_generation->available_with_reserve();
414 assert(young_evacuated_reserve_used <= total_young_available, "Cannot evacuate more than is available in young");
415 heap->set_young_evac_reserve(young_evacuated_reserve_used);
416
417 size_t old_available = old_generation->available();
418 // Now that we've established the collection set, we know how much memory is really required by old-gen for evacuation
419 // and promotion reserves. Try shrinking OLD now in case that gives us a bit more runway for mutator allocations during
420 // evac and update phases.
421 size_t old_consumed = old_evacuated_committed + young_advance_promoted_reserve_used;
422
423 if (old_available < old_consumed) {
424 // This can happen due to round-off errors when adding the results of truncated integer arithmetic.
425 // We've already truncated old_evacuated_committed. Truncate young_advance_promoted_reserve_used here.
426 assert(young_advance_promoted_reserve_used <= (33 * (old_available - old_evacuated_committed)) / 32,
427 "Round-off errors should be less than 3.125%%, committed: " SIZE_FORMAT ", reserved: " SIZE_FORMAT,
428 young_advance_promoted_reserve_used, old_available - old_evacuated_committed);
429 young_advance_promoted_reserve_used = old_available - old_evacuated_committed;
430 old_consumed = old_evacuated_committed + young_advance_promoted_reserve_used;
431 }
432
433 assert(old_available >= old_consumed, "Cannot consume (" SIZE_FORMAT ") more than is available (" SIZE_FORMAT ")",
434 old_consumed, old_available);
435 size_t excess_old = old_available - old_consumed;
436 size_t unaffiliated_old_regions = old_generation->free_unaffiliated_regions();
437 size_t unaffiliated_old = unaffiliated_old_regions * region_size_bytes;
438 assert(old_available >= unaffiliated_old, "Unaffiliated old is a subset of old available");
439
440 // Make sure old_evac_committed is unaffiliated
441 if (old_evacuated_committed > 0) {
442 if (unaffiliated_old > old_evacuated_committed) {
443 size_t giveaway = unaffiliated_old - old_evacuated_committed;
444 size_t giveaway_regions = giveaway / region_size_bytes; // round down
445 if (giveaway_regions > 0) {
446 excess_old = MIN2(excess_old, giveaway_regions * region_size_bytes);
447 } else {
448 excess_old = 0;
449 }
450 } else {
451 excess_old = 0;
452 }
453 }
454
455 // If we find that OLD has excess regions, give them back to YOUNG now to reduce likelihood we run out of allocation
456 // runway during evacuation and update-refs.
457 size_t regions_to_xfer = 0;
458 if (excess_old > unaffiliated_old) {
459 // we can give back unaffiliated_old (all of unaffiliated is excess)
460 if (unaffiliated_old_regions > 0) {
461 regions_to_xfer = unaffiliated_old_regions;
462 }
463 } else if (unaffiliated_old_regions > 0) {
464 // excess_old < unaffiliated old: we can give back MIN(excess_old/region_size_bytes, unaffiliated_old_regions)
465 size_t excess_regions = excess_old / region_size_bytes;
466 size_t regions_to_xfer = MIN2(excess_regions, unaffiliated_old_regions);
467 }
468
469 if (regions_to_xfer > 0) {
470 bool result = heap->generation_sizer()->transfer_to_young(regions_to_xfer);
471 assert(excess_old > regions_to_xfer * region_size_bytes, "Cannot xfer more than excess old");
472 excess_old -= regions_to_xfer * region_size_bytes;
473 log_info(gc, ergo)("%s transferred " SIZE_FORMAT " excess regions to young before start of evacuation",
474 result? "Successfully": "Unsuccessfully", regions_to_xfer);
475 }
476
477 // Add in the excess_old memory to hold unanticipated promotions, if any. If there are more unanticipated
478 // promotions than fit in reserved memory, they will be deferred until a future GC pass.
479 size_t total_promotion_reserve = young_advance_promoted_reserve_used + excess_old;
480 heap->set_promoted_reserve(total_promotion_reserve);
481 heap->reset_promoted_expended();
482 }
483
484 typedef struct {
485 ShenandoahHeapRegion* _region;
486 size_t _live_data;
487 } AgedRegionData;
488
489 static int compare_by_aged_live(AgedRegionData a, AgedRegionData b) {
490 if (a._live_data < b._live_data)
491 return -1;
492 else if (a._live_data > b._live_data)
493 return 1;
494 else return 0;
495 }
496
497 inline void assert_no_in_place_promotions() {
498 #ifdef ASSERT
499 class ShenandoahNoInPlacePromotions : public ShenandoahHeapRegionClosure {
500 public:
501 void heap_region_do(ShenandoahHeapRegion *r) override {
502 assert(r->get_top_before_promote() == nullptr,
503 "Region " SIZE_FORMAT " should not be ready for in-place promotion", r->index());
504 }
505 } cl;
506 ShenandoahHeap::heap()->heap_region_iterate(&cl);
507 #endif
508 }
509
510 // Preselect for inclusion into the collection set regions whose age is at or above tenure age which contain more than
511 // ShenandoahOldGarbageThreshold amounts of garbage. We identify these regions by setting the appropriate entry of
512 // candidate_regions_for_promotion_by_copy[] to true. All entries are initialized to false before calling this
513 // function.
514 //
515 // During the subsequent selection of the collection set, we give priority to these promotion set candidates.
516 // Without this prioritization, we found that the aged regions tend to be ignored because they typically have
517 // much less garbage and much more live data than the recently allocated "eden" regions. When aged regions are
518 // repeatedly excluded from the collection set, the amount of live memory within the young generation tends to
519 // accumulate and this has the undesirable side effect of causing young-generation collections to require much more
520 // CPU and wall-clock time.
521 //
522 // A second benefit of treating aged regions differently than other regions during collection set selection is
523 // that this allows us to more accurately budget memory to hold the results of evacuation. Memory for evacuation
524 // of aged regions must be reserved in the old generations. Memory for evacuation of all other regions must be
525 // reserved in the young generation.
526 size_t ShenandoahGeneration::select_aged_regions(size_t old_available, size_t num_regions,
527 bool candidate_regions_for_promotion_by_copy[]) {
528
529 // There should be no regions configured for subsequent in-place-promotions carried over from the previous cycle.
530 assert_no_in_place_promotions();
531
532 ShenandoahHeap* heap = ShenandoahHeap::heap();
533 assert(heap->mode()->is_generational(), "Only in generational mode");
534 ShenandoahMarkingContext* const ctx = heap->marking_context();
535
536 const uint tenuring_threshold = heap->age_census()->tenuring_threshold();
537
538 size_t old_consumed = 0;
539 size_t promo_potential = 0;
540
541 heap->clear_promotion_potential();
542 size_t candidates = 0;
543 size_t candidates_live = 0;
544 size_t old_garbage_threshold = (ShenandoahHeapRegion::region_size_bytes() * ShenandoahOldGarbageThreshold) / 100;
545 size_t promote_in_place_regions = 0;
546 size_t promote_in_place_live = 0;
547 size_t promote_in_place_pad = 0;
548 size_t anticipated_candidates = 0;
549 size_t anticipated_promote_in_place_regions = 0;
550
551 // Sort the promotion-eligible regions according to live-data-bytes so that we can first reclaim regions that require
552 // less evacuation effort. This prioritizes garbage first, expanding the allocation pool before we begin the work of
553 // reclaiming regions that require more effort.
554 AgedRegionData* sorted_regions = (AgedRegionData*) alloca(num_regions * sizeof(AgedRegionData));
555 for (size_t i = 0; i < num_regions; i++) {
556 ShenandoahHeapRegion* r = heap->get_region(i);
557 if (r->is_empty() || !r->has_live() || !r->is_young() || !r->is_regular()) {
558 continue;
559 }
560 if (r->age() >= tenuring_threshold) {
561 if ((r->garbage() < old_garbage_threshold)) {
562 HeapWord* tams = ctx->top_at_mark_start(r);
563 HeapWord* original_top = r->top();
564 if (tams == original_top) {
565 // No allocations from this region have been made during concurrent mark. It meets all the criteria
566 // for in-place-promotion. Though we only need the value of top when we fill the end of the region,
567 // we use this field to indicate that this region should be promoted in place during the evacuation
568 // phase.
569 r->save_top_before_promote();
570
571 size_t remnant_size = r->free() / HeapWordSize;
572 if (remnant_size > ShenandoahHeap::min_fill_size()) {
573 ShenandoahHeap::fill_with_object(original_top, remnant_size);
574 // Fill the remnant memory within this region to assure no allocations prior to promote in place. Otherwise,
575 // newly allocated objects will not be parseable when promote in place tries to register them. Furthermore, any
576 // new allocations would not necessarily be eligible for promotion. This addresses both issues.
577 r->set_top(r->end());
578 promote_in_place_pad += remnant_size * HeapWordSize;
579 } else {
580 // Since the remnant is so small that it cannot be filled, we don't have to worry about any accidental
581 // allocations occurring within this region before the region is promoted in place.
582 }
583 promote_in_place_regions++;
584 promote_in_place_live += r->get_live_data_bytes();
585 }
586 // Else, we do not promote this region (either in place or by copy) because it has received new allocations.
587
588 // During evacuation, we exclude from promotion regions for which age > tenure threshold, garbage < garbage-threshold,
589 // and get_top_before_promote() != tams
590 } else {
591 // After sorting and selecting best candidates below, we may decide to exclude this promotion-eligible region
592 // from the current collection sets. If this happens, we will consider this region as part of the anticipated
593 // promotion potential for the next GC pass.
594 size_t live_data = r->get_live_data_bytes();
595 candidates_live += live_data;
596 sorted_regions[candidates]._region = r;
597 sorted_regions[candidates++]._live_data = live_data;
598 }
599 } else {
600 // We only anticipate to promote regular regions if garbage() is above threshold. Tenure-aged regions with less
601 // garbage are promoted in place. These take a different path to old-gen. Note that certain regions that are
602 // excluded from anticipated promotion because their garbage content is too low (causing us to anticipate that
603 // the region would be promoted in place) may be eligible for evacuation promotion by the time promotion takes
604 // place during a subsequent GC pass because more garbage is found within the region between now and then. This
605 // should not happen if we are properly adapting the tenure age. The theory behind adaptive tenuring threshold
606 // is to choose the youngest age that demonstrates no "significant" futher loss of population since the previous
607 // age. If not this, we expect the tenure age to demonstrate linear population decay for at least two population
608 // samples, whereas we expect to observe exponetial population decay for ages younger than the tenure age.
609 //
610 // In the case that certain regions which were anticipated to be promoted in place need to be promoted by
611 // evacuation, it may be the case that there is not sufficient reserve within old-gen to hold evacuation of
612 // these regions. The likely outcome is that these regions will not be selected for evacuation or promotion
613 // in the current cycle and we will anticipate that they will be promoted in the next cycle. This will cause
614 // us to reserve more old-gen memory so that these objects can be promoted in the subsequent cycle.
615 //
616 // TODO:
617 // If we are auto-tuning the tenure age and regions that were anticipated to be promoted in place end up
618 // being promoted by evacuation, this event should feed into the tenure-age-selection heuristic so that
619 // the tenure age can be increased.
620 if (heap->is_aging_cycle() && (r->age() + 1 == tenuring_threshold)) {
621 if (r->garbage() >= old_garbage_threshold) {
622 anticipated_candidates++;
623 promo_potential += r->get_live_data_bytes();
624 }
625 else {
626 anticipated_promote_in_place_regions++;
627 }
628 }
629 }
630 // Note that we keep going even if one region is excluded from selection.
631 // Subsequent regions may be selected if they have smaller live data.
632 }
633 // Sort in increasing order according to live data bytes. Note that candidates represents the number of regions
634 // that qualify to be promoted by evacuation.
635 if (candidates > 0) {
636 size_t selected_regions = 0;
637 size_t selected_live = 0;
638 QuickSort::sort<AgedRegionData>(sorted_regions, candidates, compare_by_aged_live, false);
639 for (size_t i = 0; i < candidates; i++) {
640 size_t region_live_data = sorted_regions[i]._live_data;
641 size_t promotion_need = (size_t) (region_live_data * ShenandoahPromoEvacWaste);
642 if (old_consumed + promotion_need <= old_available) {
643 ShenandoahHeapRegion* region = sorted_regions[i]._region;
644 old_consumed += promotion_need;
645 candidate_regions_for_promotion_by_copy[region->index()] = true;
646 selected_regions++;
647 selected_live += region_live_data;
648 } else {
649 // We rejected this promotable region from the collection set because we had no room to hold its copy.
650 // Add this region to promo potential for next GC.
651 promo_potential += region_live_data;
652 }
653 // We keep going even if one region is excluded from selection because we need to accumulate all eligible
654 // regions that are not preselected into promo_potential
655 }
656 log_info(gc)("Preselected " SIZE_FORMAT " regions containing " SIZE_FORMAT " live bytes,"
657 " consuming: " SIZE_FORMAT " of budgeted: " SIZE_FORMAT,
658 selected_regions, selected_live, old_consumed, old_available);
659 }
660 heap->set_pad_for_promote_in_place(promote_in_place_pad);
661 heap->set_promotion_potential(promo_potential);
662 return old_consumed;
663 }
664
665 void ShenandoahGeneration::prepare_regions_and_collection_set(bool concurrent) {
666 ShenandoahHeap* heap = ShenandoahHeap::heap();
667 ShenandoahCollectionSet* collection_set = heap->collection_set();
668 bool is_generational = heap->mode()->is_generational();
669
670 assert(!heap->is_full_gc_in_progress(), "Only for concurrent and degenerated GC");
671 assert(!is_old(), "Only YOUNG and GLOBAL GC perform evacuations");
672 {
673 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::final_update_region_states :
674 ShenandoahPhaseTimings::degen_gc_final_update_region_states);
675 ShenandoahFinalMarkUpdateRegionStateClosure cl(complete_marking_context());
676 parallel_heap_region_iterate(&cl);
677
678 if (is_young()) {
679 // We always need to update the watermark for old regions. If there
680 // are mixed collections pending, we also need to synchronize the
681 // pinned status for old regions. Since we are already visiting every
682 // old region here, go ahead and sync the pin status too.
683 ShenandoahFinalMarkUpdateRegionStateClosure old_cl(nullptr);
684 heap->old_generation()->parallel_heap_region_iterate(&old_cl);
685 }
686 }
687
688 // Tally the census counts and compute the adaptive tenuring threshold
689 if (is_generational && ShenandoahGenerationalAdaptiveTenuring && !ShenandoahGenerationalCensusAtEvac) {
690 // Objects above TAMS weren't included in the age census. Since they were all
691 // allocated in this cycle they belong in the age 0 cohort. We walk over all
692 // young regions and sum the volume of objects between TAMS and top.
693 ShenandoahUpdateCensusZeroCohortClosure age0_cl(complete_marking_context());
694 heap->young_generation()->heap_region_iterate(&age0_cl);
695 size_t age0_pop = age0_cl.get_population();
696
697 // Age table updates
698 ShenandoahAgeCensus* census = heap->age_census();
699 census->prepare_for_census_update();
700 // Update the global census, including the missed age 0 cohort above,
701 // along with the census during marking, and compute the tenuring threshold
702 census->update_census(age0_pop);
703 }
704
705 {
706 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::choose_cset :
707 ShenandoahPhaseTimings::degen_gc_choose_cset);
708
709 collection_set->clear();
710 ShenandoahHeapLocker locker(heap->lock());
711 if (is_generational) {
712 size_t consumed_by_advance_promotion;
713 bool* preselected_regions = (bool*) alloca(heap->num_regions() * sizeof(bool));
714 for (unsigned int i = 0; i < heap->num_regions(); i++) {
715 preselected_regions[i] = false;
716 }
717
718 // TODO: young_available can include available (between top() and end()) within each young region that is not
719 // part of the collection set. Making this memory available to the young_evacuation_reserve allows a larger
720 // young collection set to be chosen when available memory is under extreme pressure. Implementing this "improvement"
721 // is tricky, because the incremental construction of the collection set actually changes the amount of memory
722 // available to hold evacuated young-gen objects. As currently implemented, the memory that is available within
723 // non-empty regions that are not selected as part of the collection set can be allocated by the mutator while
724 // GC is evacuating and updating references.
725
726 // Budgeting parameters to compute_evacuation_budgets are passed by reference.
727 compute_evacuation_budgets(heap, preselected_regions, collection_set, consumed_by_advance_promotion);
728 _heuristics->choose_collection_set(collection_set);
729 if (!collection_set->is_empty()) {
730 // only make use of evacuation budgets when we are evacuating
731 adjust_evacuation_budgets(heap, collection_set, consumed_by_advance_promotion);
732 }
733
734 if (is_global()) {
735 // We have just chosen a collection set for a global cycle. The mark bitmap covering old regions is complete, so
736 // the remembered set scan can use that to avoid walking into garbage. When the next old mark begins, we will
737 // use the mark bitmap to make the old regions parseable by coalescing and filling any unmarked objects. Thus,
738 // we prepare for old collections by remembering which regions are old at this time. Note that any objects
739 // promoted into old regions will be above TAMS, and so will be considered marked. However, free regions that
740 // become old after this point will not be covered correctly by the mark bitmap, so we must be careful not to
741 // coalesce those regions. Only the old regions which are not part of the collection set at this point are
742 // eligible for coalescing. As implemented now, this has the side effect of possibly initiating mixed-evacuations
743 // after a global cycle for old regions that were not included in this collection set.
744 assert(heap->old_generation()->is_mark_complete(), "Expected old generation mark to be complete after global cycle.");
745 heap->old_heuristics()->prepare_for_old_collections();
746 log_info(gc)("After choosing global collection set, mixed candidates: " UINT32_FORMAT ", coalescing candidates: " SIZE_FORMAT,
747 heap->old_heuristics()->unprocessed_old_collection_candidates(),
748 heap->old_heuristics()->coalesce_and_fill_candidates_count());
749 }
750 } else {
751 _heuristics->choose_collection_set(collection_set);
752 }
753 }
754
755 // Freeset construction uses reserve quantities if they are valid
756 heap->set_evacuation_reserve_quantities(true);
757 {
758 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::final_rebuild_freeset :
759 ShenandoahPhaseTimings::degen_gc_final_rebuild_freeset);
760 ShenandoahHeapLocker locker(heap->lock());
761 size_t young_cset_regions, old_cset_regions;
762
763 // We are preparing for evacuation. At this time, we ignore cset region tallies.
764 heap->free_set()->prepare_to_rebuild(young_cset_regions, old_cset_regions);
765 heap->free_set()->rebuild(young_cset_regions, old_cset_regions);
766 }
767 heap->set_evacuation_reserve_quantities(false);
768 }
769
770 bool ShenandoahGeneration::is_bitmap_clear() {
771 ShenandoahHeap* heap = ShenandoahHeap::heap();
772 ShenandoahMarkingContext* context = heap->marking_context();
773 size_t num_regions = heap->num_regions();
774 for (size_t idx = 0; idx < num_regions; idx++) {
775 ShenandoahHeapRegion* r = heap->get_region(idx);
776 if (contains(r) && r->is_affiliated()) {
777 if (heap->is_bitmap_slice_committed(r) && (context->top_at_mark_start(r) > r->bottom()) &&
778 !context->is_bitmap_clear_range(r->bottom(), r->end())) {
779 return false;
780 }
781 }
782 }
783 return true;
784 }
785
786 bool ShenandoahGeneration::is_mark_complete() {
787 return _is_marking_complete.is_set();
788 }
789
790 void ShenandoahGeneration::set_mark_complete() {
791 _is_marking_complete.set();
792 }
793
794 void ShenandoahGeneration::set_mark_incomplete() {
795 _is_marking_complete.unset();
796 }
797
798 ShenandoahMarkingContext* ShenandoahGeneration::complete_marking_context() {
799 assert(is_mark_complete(), "Marking must be completed.");
800 return ShenandoahHeap::heap()->marking_context();
801 }
802
803 void ShenandoahGeneration::cancel_marking() {
804 log_info(gc)("Cancel marking: %s", name());
805 if (is_concurrent_mark_in_progress()) {
806 set_mark_incomplete();
807 }
808 _task_queues->clear();
809 ref_processor()->abandon_partial_discovery();
810 set_concurrent_mark_in_progress(false);
811 }
812
813 ShenandoahGeneration::ShenandoahGeneration(ShenandoahGenerationType type,
814 uint max_workers,
815 size_t max_capacity,
816 size_t soft_max_capacity) :
817 _type(type),
818 _task_queues(new ShenandoahObjToScanQueueSet(max_workers)),
819 _ref_processor(new ShenandoahReferenceProcessor(MAX2(max_workers, 1U))),
820 _affiliated_region_count(0), _humongous_waste(0), _used(0), _bytes_allocated_since_gc_start(0),
821 _max_capacity(max_capacity), _soft_max_capacity(soft_max_capacity),
822 _heuristics(nullptr) {
823 _is_marking_complete.set();
824 assert(max_workers > 0, "At least one queue");
825 for (uint i = 0; i < max_workers; ++i) {
826 ShenandoahObjToScanQueue* task_queue = new ShenandoahObjToScanQueue();
827 _task_queues->register_queue(i, task_queue);
828 }
829 }
830
831 ShenandoahGeneration::~ShenandoahGeneration() {
832 for (uint i = 0; i < _task_queues->size(); ++i) {
833 ShenandoahObjToScanQueue* q = _task_queues->queue(i);
834 delete q;
835 }
836 delete _task_queues;
837 }
838
839 void ShenandoahGeneration::reserve_task_queues(uint workers) {
840 _task_queues->reserve(workers);
841 }
842
843 ShenandoahObjToScanQueueSet* ShenandoahGeneration::old_gen_task_queues() const {
844 return nullptr;
845 }
846
847 void ShenandoahGeneration::scan_remembered_set(bool is_concurrent) {
848 assert(is_young(), "Should only scan remembered set for young generation.");
849
850 ShenandoahHeap* const heap = ShenandoahHeap::heap();
851 uint nworkers = heap->workers()->active_workers();
852 reserve_task_queues(nworkers);
853
854 ShenandoahReferenceProcessor* rp = ref_processor();
855 ShenandoahRegionChunkIterator work_list(nworkers);
856 ShenandoahScanRememberedTask task(task_queues(), old_gen_task_queues(), rp, &work_list, is_concurrent);
857 heap->assert_gc_workers(nworkers);
858 heap->workers()->run_task(&task);
859 if (ShenandoahEnableCardStats) {
860 assert(heap->card_scan() != nullptr, "Not generational");
861 heap->card_scan()->log_card_stats(nworkers, CARD_STAT_SCAN_RS);
862 }
863 }
864
865 size_t ShenandoahGeneration::increment_affiliated_region_count() {
866 shenandoah_assert_heaplocked_or_fullgc_safepoint();
867 // During full gc, multiple GC worker threads may change region affiliations without a lock. No lock is enforced
868 // on read and write of _affiliated_region_count. At the end of full gc, a single thread overwrites the count with
869 // a coherent value.
870 _affiliated_region_count++;
871 return _affiliated_region_count;
872 }
873
874 size_t ShenandoahGeneration::decrement_affiliated_region_count() {
875 shenandoah_assert_heaplocked_or_fullgc_safepoint();
876 // During full gc, multiple GC worker threads may change region affiliations without a lock. No lock is enforced
877 // on read and write of _affiliated_region_count. At the end of full gc, a single thread overwrites the count with
878 // a coherent value.
879 _affiliated_region_count--;
880 // TODO: REMOVE IS_GLOBAL() QUALIFIER AFTER WE FIX GLOBAL AFFILIATED REGION ACCOUNTING
881 assert(is_global() || ShenandoahHeap::heap()->is_full_gc_in_progress() ||
882 (_used + _humongous_waste <= _affiliated_region_count * ShenandoahHeapRegion::region_size_bytes()),
883 "used + humongous cannot exceed regions");
884 return _affiliated_region_count;
885 }
886
887 size_t ShenandoahGeneration::increase_affiliated_region_count(size_t delta) {
888 shenandoah_assert_heaplocked_or_fullgc_safepoint();
889 _affiliated_region_count += delta;
890 return _affiliated_region_count;
891 }
892
893 size_t ShenandoahGeneration::decrease_affiliated_region_count(size_t delta) {
894 shenandoah_assert_heaplocked_or_fullgc_safepoint();
895 assert(_affiliated_region_count >= delta, "Affiliated region count cannot be negative");
896
897 _affiliated_region_count -= delta;
898 // TODO: REMOVE IS_GLOBAL() QUALIFIER AFTER WE FIX GLOBAL AFFILIATED REGION ACCOUNTING
899 assert(is_global() || ShenandoahHeap::heap()->is_full_gc_in_progress() ||
900 (_used + _humongous_waste <= _affiliated_region_count * ShenandoahHeapRegion::region_size_bytes()),
901 "used + humongous cannot exceed regions");
902 return _affiliated_region_count;
903 }
904
905 void ShenandoahGeneration::establish_usage(size_t num_regions, size_t num_bytes, size_t humongous_waste) {
906 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
907 _affiliated_region_count = num_regions;
908 _used = num_bytes;
909 _humongous_waste = humongous_waste;
910 }
911
912 void ShenandoahGeneration::increase_used(size_t bytes) {
913 Atomic::add(&_used, bytes);
914 }
915
916 void ShenandoahGeneration::increase_humongous_waste(size_t bytes) {
917 if (bytes > 0) {
918 Atomic::add(&_humongous_waste, bytes);
919 }
920 }
921
922 void ShenandoahGeneration::decrease_humongous_waste(size_t bytes) {
923 if (bytes > 0) {
924 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() || (_humongous_waste >= bytes),
925 "Waste (" SIZE_FORMAT ") cannot be negative (after subtracting " SIZE_FORMAT ")", _humongous_waste, bytes);
926 Atomic::sub(&_humongous_waste, bytes);
927 }
928 }
929
930 void ShenandoahGeneration::decrease_used(size_t bytes) {
931 // TODO: REMOVE IS_GLOBAL() QUALIFIER AFTER WE FIX GLOBAL AFFILIATED REGION ACCOUNTING
932 assert(is_global() || ShenandoahHeap::heap()->is_full_gc_in_progress() ||
933 (_used >= bytes), "cannot reduce bytes used by generation below zero");
934 Atomic::sub(&_used, bytes);
935 }
936
937 size_t ShenandoahGeneration::used_regions() const {
938 return _affiliated_region_count;
939 }
940
941 size_t ShenandoahGeneration::free_unaffiliated_regions() const {
942 size_t result = max_capacity() / ShenandoahHeapRegion::region_size_bytes();
943 if (_affiliated_region_count > result) {
944 result = 0;
945 } else {
946 result -= _affiliated_region_count;
947 }
948 return result;
949 }
950
951 size_t ShenandoahGeneration::used_regions_size() const {
952 return _affiliated_region_count * ShenandoahHeapRegion::region_size_bytes();
953 }
954
955 size_t ShenandoahGeneration::available() const {
956 return available(max_capacity());
957 }
958
959 // For ShenandoahYoungGeneration, Include the young available that may have been reserved for the Collector.
960 size_t ShenandoahGeneration::available_with_reserve() const {
961 return available(max_capacity());
962 }
963
964 size_t ShenandoahGeneration::soft_available() const {
965 return available(soft_max_capacity());
966 }
967
968 size_t ShenandoahGeneration::available(size_t capacity) const {
969 size_t in_use = used() + get_humongous_waste();
970 return in_use > capacity ? 0 : capacity - in_use;
971 }
972
973 void ShenandoahGeneration::increase_capacity(size_t increment) {
974 shenandoah_assert_heaplocked_or_safepoint();
975
976 // We do not enforce that new capacity >= heap->max_size_for(this). The maximum generation size is treated as a rule of thumb
977 // which may be violated during certain transitions, such as when we are forcing transfers for the purpose of promoting regions
978 // in place.
979 // TODO: REMOVE IS_GLOBAL() QUALIFIER AFTER WE FIX GLOBAL AFFILIATED REGION ACCOUNTING
980 assert(is_global() || ShenandoahHeap::heap()->is_full_gc_in_progress() ||
981 (_max_capacity + increment <= ShenandoahHeap::heap()->max_capacity()), "Generation cannot be larger than heap size");
982 assert(increment % ShenandoahHeapRegion::region_size_bytes() == 0, "Generation capacity must be multiple of region size");
983 _max_capacity += increment;
984
985 // This detects arithmetic wraparound on _used
986 // TODO: REMOVE IS_GLOBAL() QUALIFIER AFTER WE FIX GLOBAL AFFILIATED REGION ACCOUNTING
987 assert(is_global() || ShenandoahHeap::heap()->is_full_gc_in_progress() ||
988 (_affiliated_region_count * ShenandoahHeapRegion::region_size_bytes() >= _used),
989 "Affiliated regions must hold more than what is currently used");
990 }
991
992 void ShenandoahGeneration::decrease_capacity(size_t decrement) {
993 shenandoah_assert_heaplocked_or_safepoint();
994
995 // We do not enforce that new capacity >= heap->min_size_for(this). The minimum generation size is treated as a rule of thumb
996 // which may be violated during certain transitions, such as when we are forcing transfers for the purpose of promoting regions
997 // in place.
998 assert(decrement % ShenandoahHeapRegion::region_size_bytes() == 0, "Generation capacity must be multiple of region size");
999 assert(_max_capacity >= decrement, "Generation capacity cannot be negative");
1000
1001 _max_capacity -= decrement;
1002
1003 // This detects arithmetic wraparound on _used
1004 // TODO: REMOVE IS_GLOBAL() QUALIFIER AFTER WE FIX GLOBAL AFFILIATED REGION ACCOUNTING
1005 assert(is_global() || ShenandoahHeap::heap()->is_full_gc_in_progress() ||
1006 (_affiliated_region_count * ShenandoahHeapRegion::region_size_bytes() >= _used),
1007 "Affiliated regions must hold more than what is currently used");
1008 // TODO: REMOVE IS_GLOBAL() QUALIFIER AFTER WE FIX GLOBAL AFFILIATED REGION ACCOUNTING
1009 assert(is_global() || ShenandoahHeap::heap()->is_full_gc_in_progress() ||
1010 (_used <= _max_capacity), "Cannot use more than capacity");
1011 // TODO: REMOVE IS_GLOBAL() QUALIFIER AFTER WE FIX GLOBAL AFFILIATED REGION ACCOUNTING
1012 assert(is_global() || ShenandoahHeap::heap()->is_full_gc_in_progress() ||
1013 (_affiliated_region_count * ShenandoahHeapRegion::region_size_bytes() <= _max_capacity),
1014 "Cannot use more than capacity");
1015 }
1016
1017 void ShenandoahGeneration::record_success_concurrent(bool abbreviated) {
1018 heuristics()->record_success_concurrent(abbreviated);
1019 ShenandoahHeap::heap()->shenandoah_policy()->record_success_concurrent();
1020 }
1021
1022 void ShenandoahGeneration::record_success_degenerated() {
1023 heuristics()->record_success_degenerated();
1024 ShenandoahHeap::heap()->shenandoah_policy()->record_success_degenerated();
1025 }