1 /*
2 * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
27 #include "gc/shenandoah/shenandoahCollectionSetPreselector.hpp"
28 #include "gc/shenandoah/shenandoahFreeSet.hpp"
29 #include "gc/shenandoah/shenandoahGeneration.hpp"
30 #include "gc/shenandoah/shenandoahGenerationalHeap.hpp"
31 #include "gc/shenandoah/shenandoahHeapRegionClosures.hpp"
32 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
33 #include "gc/shenandoah/shenandoahOldGeneration.hpp"
34 #include "gc/shenandoah/shenandoahReferenceProcessor.hpp"
35 #include "gc/shenandoah/shenandoahScanRemembered.inline.hpp"
36 #include "gc/shenandoah/shenandoahTaskqueue.inline.hpp"
37 #include "gc/shenandoah/shenandoahUtils.hpp"
38 #include "gc/shenandoah/shenandoahVerifier.hpp"
39 #include "gc/shenandoah/shenandoahYoungGeneration.hpp"
40 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
41
42 #include "utilities/quickSort.hpp"
43
44 template <bool PREPARE_FOR_CURRENT_CYCLE, bool FULL_GC = false>
45 class ShenandoahResetBitmapClosure final : public ShenandoahHeapRegionClosure {
46 private:
47 ShenandoahHeap* _heap;
48 ShenandoahMarkingContext* _ctx;
49
50 public:
51 explicit ShenandoahResetBitmapClosure() :
52 ShenandoahHeapRegionClosure(), _heap(ShenandoahHeap::heap()), _ctx(_heap->marking_context()) {}
53
54 void heap_region_do(ShenandoahHeapRegion* region) override {
55 assert(!_heap->is_uncommit_in_progress(), "Cannot uncommit bitmaps while resetting them.");
56 if (PREPARE_FOR_CURRENT_CYCLE) {
57 if (region->need_bitmap_reset() && _heap->is_bitmap_slice_committed(region)) {
58 _ctx->clear_bitmap(region);
59 } else {
60 region->set_needs_bitmap_reset();
61 }
62 // Capture Top At Mark Start for this generation.
63 if (FULL_GC || region->is_active()) {
64 // Reset live data and set TAMS optimistically. We would recheck these under the pause
65 // anyway to capture any updates that happened since now.
66 _ctx->capture_top_at_mark_start(region);
67 region->clear_live_data();
68 }
69 } else {
70 if (_heap->is_bitmap_slice_committed(region)) {
71 _ctx->clear_bitmap(region);
72 region->unset_needs_bitmap_reset();
73 } else {
74 region->set_needs_bitmap_reset();
75 }
76 }
77 }
78
79 bool is_thread_safe() override { return true; }
80 };
81
82 // Copy the write-version of the card-table into the read-version, clearing the
83 // write-copy.
84 class ShenandoahMergeWriteTable: public ShenandoahHeapRegionClosure {
85 private:
86 ShenandoahScanRemembered* _scanner;
87 public:
88 ShenandoahMergeWriteTable(ShenandoahScanRemembered* scanner) : _scanner(scanner) {}
89
90 void heap_region_do(ShenandoahHeapRegion* r) override {
91 assert(r->is_old(), "Don't waste time doing this for non-old regions");
92 _scanner->merge_write_table(r->bottom(), ShenandoahHeapRegion::region_size_words());
93 }
94
95 bool is_thread_safe() override {
96 return true;
97 }
98 };
99
100 class ShenandoahCopyWriteCardTableToRead: public ShenandoahHeapRegionClosure {
101 private:
102 ShenandoahScanRemembered* _scanner;
103 public:
104 ShenandoahCopyWriteCardTableToRead(ShenandoahScanRemembered* scanner) : _scanner(scanner) {}
105
106 void heap_region_do(ShenandoahHeapRegion* region) override {
107 assert(region->is_old(), "Don't waste time doing this for non-old regions");
108 _scanner->reset_remset(region->bottom(), ShenandoahHeapRegion::region_size_words());
109 }
110
111 bool is_thread_safe() override { return true; }
112 };
113
114 // Add [TAMS, top) volume over young regions. Used to correct age 0 cohort census
115 // for adaptive tenuring when census is taken during marking.
116 // In non-product builds, for the purposes of verification, we also collect the total
117 // live objects in young regions as well.
118 class ShenandoahUpdateCensusZeroCohortClosure : public ShenandoahHeapRegionClosure {
119 private:
120 ShenandoahMarkingContext* const _ctx;
121 // Population size units are words (not bytes)
122 size_t _age0_pop; // running tally of age0 population size
123 size_t _total_pop; // total live population size
124 public:
125 explicit ShenandoahUpdateCensusZeroCohortClosure(ShenandoahMarkingContext* ctx)
126 : _ctx(ctx), _age0_pop(0), _total_pop(0) {}
127
128 void heap_region_do(ShenandoahHeapRegion* r) override {
129 if (_ctx != nullptr && r->is_active()) {
130 assert(r->is_young(), "Young regions only");
131 HeapWord* tams = _ctx->top_at_mark_start(r);
132 HeapWord* top = r->top();
133 if (top > tams) {
134 _age0_pop += pointer_delta(top, tams);
135 }
136 // TODO: check significance of _ctx != nullptr above, can that
137 // spoof _total_pop in some corner cases?
138 NOT_PRODUCT(_total_pop += r->get_live_data_words();)
139 }
140 }
141
142 size_t get_age0_population() const { return _age0_pop; }
143 size_t get_total_population() const { return _total_pop; }
144 };
145
146 void ShenandoahGeneration::confirm_heuristics_mode() {
147 if (_heuristics->is_diagnostic() && !UnlockDiagnosticVMOptions) {
148 vm_exit_during_initialization(
149 err_msg("Heuristics \"%s\" is diagnostic, and must be enabled via -XX:+UnlockDiagnosticVMOptions.",
150 _heuristics->name()));
151 }
152 if (_heuristics->is_experimental() && !UnlockExperimentalVMOptions) {
153 vm_exit_during_initialization(
154 err_msg("Heuristics \"%s\" is experimental, and must be enabled via -XX:+UnlockExperimentalVMOptions.",
155 _heuristics->name()));
156 }
157 }
158
159 ShenandoahHeuristics* ShenandoahGeneration::initialize_heuristics(ShenandoahMode* gc_mode) {
160 _heuristics = gc_mode->initialize_heuristics(this);
161 _heuristics->set_guaranteed_gc_interval(ShenandoahGuaranteedGCInterval);
162 confirm_heuristics_mode();
163 return _heuristics;
164 }
165
166 size_t ShenandoahGeneration::bytes_allocated_since_gc_start() const {
167 return Atomic::load(&_bytes_allocated_since_gc_start);
168 }
169
170 void ShenandoahGeneration::reset_bytes_allocated_since_gc_start() {
171 Atomic::store(&_bytes_allocated_since_gc_start, (size_t)0);
172 }
173
174 void ShenandoahGeneration::increase_allocated(size_t bytes) {
175 Atomic::add(&_bytes_allocated_since_gc_start, bytes, memory_order_relaxed);
176 }
177
178 void ShenandoahGeneration::set_evacuation_reserve(size_t new_val) {
179 _evacuation_reserve = new_val;
180 }
181
182 size_t ShenandoahGeneration::get_evacuation_reserve() const {
183 return _evacuation_reserve;
184 }
185
186 void ShenandoahGeneration::augment_evacuation_reserve(size_t increment) {
187 _evacuation_reserve += increment;
188 }
189
190 void ShenandoahGeneration::log_status(const char *msg) const {
191 typedef LogTarget(Info, gc, ergo) LogGcInfo;
192
193 if (!LogGcInfo::is_enabled()) {
194 return;
195 }
196
197 // Not under a lock here, so read each of these once to make sure
198 // byte size in proper unit and proper unit for byte size are consistent.
199 const size_t v_used = used();
200 const size_t v_used_regions = used_regions_size();
201 const size_t v_soft_max_capacity = soft_max_capacity();
202 const size_t v_max_capacity = max_capacity();
203 const size_t v_available = available();
204 const size_t v_humongous_waste = get_humongous_waste();
205
206 const LogGcInfo target;
207 LogStream ls(target);
208 ls.print("%s: ", msg);
209 if (_type != NON_GEN) {
210 ls.print("%s generation ", name());
211 }
212
213 ls.print_cr("used: " PROPERFMT ", used regions: " PROPERFMT ", humongous waste: " PROPERFMT
214 ", soft capacity: " PROPERFMT ", max capacity: " PROPERFMT ", available: " PROPERFMT,
215 PROPERFMTARGS(v_used), PROPERFMTARGS(v_used_regions), PROPERFMTARGS(v_humongous_waste),
216 PROPERFMTARGS(v_soft_max_capacity), PROPERFMTARGS(v_max_capacity), PROPERFMTARGS(v_available));
217 }
218
219 template <bool PREPARE_FOR_CURRENT_CYCLE, bool FULL_GC>
220 void ShenandoahGeneration::reset_mark_bitmap() {
221 ShenandoahHeap* heap = ShenandoahHeap::heap();
222 heap->assert_gc_workers(heap->workers()->active_workers());
223
224 set_mark_incomplete();
225
226 ShenandoahResetBitmapClosure<PREPARE_FOR_CURRENT_CYCLE, FULL_GC> closure;
227 parallel_heap_region_iterate_free(&closure);
228 }
229 // Explicit specializations
230 template void ShenandoahGeneration::reset_mark_bitmap<true, false>();
231 template void ShenandoahGeneration::reset_mark_bitmap<true, true>();
232 template void ShenandoahGeneration::reset_mark_bitmap<false, false>();
233
234 // The ideal is to swap the remembered set so the safepoint effort is no more than a few pointer manipulations.
235 // However, limitations in the implementation of the mutator write-barrier make it difficult to simply change the
236 // location of the card table. So the interim implementation of swap_remembered_set will copy the write-table
237 // onto the read-table and will then clear the write-table.
238 void ShenandoahGeneration::swap_remembered_set() {
239 // Must be sure that marking is complete before we swap remembered set.
240 ShenandoahGenerationalHeap* heap = ShenandoahGenerationalHeap::heap();
241 heap->assert_gc_workers(heap->workers()->active_workers());
242 shenandoah_assert_safepoint();
243
244 ShenandoahOldGeneration* old_generation = heap->old_generation();
245 ShenandoahCopyWriteCardTableToRead task(old_generation->card_scan());
246 old_generation->parallel_heap_region_iterate(&task);
247 }
248
249 // Copy the write-version of the card-table into the read-version, clearing the
250 // write-version. The work is done at a safepoint and in parallel by the GC
251 // worker threads.
252 void ShenandoahGeneration::merge_write_table() {
253 // This should only happen for degenerated cycles
254 ShenandoahGenerationalHeap* heap = ShenandoahGenerationalHeap::heap();
255 heap->assert_gc_workers(heap->workers()->active_workers());
256 shenandoah_assert_safepoint();
257
258 ShenandoahOldGeneration* old_generation = heap->old_generation();
259 ShenandoahMergeWriteTable task(old_generation->card_scan());
260 old_generation->parallel_heap_region_iterate(&task);
261 }
262
263 void ShenandoahGeneration::prepare_gc() {
264 reset_mark_bitmap<true>();
265 }
266
267 void ShenandoahGeneration::parallel_heap_region_iterate_free(ShenandoahHeapRegionClosure* cl) {
268 ShenandoahHeap::heap()->parallel_heap_region_iterate(cl);
269 }
270
271 void ShenandoahGeneration::compute_evacuation_budgets(ShenandoahHeap* const heap) {
272 shenandoah_assert_generational();
273
274 ShenandoahOldGeneration* const old_generation = heap->old_generation();
275 ShenandoahYoungGeneration* const young_generation = heap->young_generation();
276
277 // During initialization and phase changes, it is more likely that fewer objects die young and old-gen
278 // memory is not yet full (or is in the process of being replaced). During these times especially, it
279 // is beneficial to loan memory from old-gen to young-gen during the evacuation and update-refs phases
280 // of execution.
281
282 // Calculate EvacuationReserve before PromotionReserve. Evacuation is more critical than promotion.
283 // If we cannot evacuate old-gen, we will not be able to reclaim old-gen memory. Promotions are less
284 // critical. If we cannot promote, there may be degradation of young-gen memory because old objects
285 // accumulate there until they can be promoted. This increases the young-gen marking and evacuation work.
286
287 // First priority is to reclaim the easy garbage out of young-gen.
288
289 // maximum_young_evacuation_reserve is upper bound on memory to be evacuated out of young
290 const size_t maximum_young_evacuation_reserve = (young_generation->max_capacity() * ShenandoahEvacReserve) / 100;
291 const size_t young_evacuation_reserve = MIN2(maximum_young_evacuation_reserve, young_generation->available_with_reserve());
292
293 // maximum_old_evacuation_reserve is an upper bound on memory evacuated from old and evacuated to old (promoted),
294 // clamped by the old generation space available.
295 //
296 // Here's the algebra.
297 // Let SOEP = ShenandoahOldEvacRatioPercent,
298 // OE = old evac,
299 // YE = young evac, and
300 // TE = total evac = OE + YE
301 // By definition:
302 // SOEP/100 = OE/TE
303 // = OE/(OE+YE)
304 // => SOEP/(100-SOEP) = OE/((OE+YE)-OE) // componendo-dividendo: If a/b = c/d, then a/(b-a) = c/(d-c)
305 // = OE/YE
306 // => OE = YE*SOEP/(100-SOEP)
307
308 // We have to be careful in the event that SOEP is set to 100 by the user.
309 assert(ShenandoahOldEvacRatioPercent <= 100, "Error");
310 const size_t old_available = old_generation->available();
311 const size_t maximum_old_evacuation_reserve = (ShenandoahOldEvacRatioPercent == 100) ?
312 old_available : MIN2((maximum_young_evacuation_reserve * ShenandoahOldEvacRatioPercent) / (100 - ShenandoahOldEvacRatioPercent),
313 old_available);
314
315
316 // Second priority is to reclaim garbage out of old-gen if there are old-gen collection candidates. Third priority
317 // is to promote as much as we have room to promote. However, if old-gen memory is in short supply, this means young
318 // GC is operating under "duress" and was unable to transfer the memory that we would normally expect. In this case,
319 // old-gen will refrain from compacting itself in order to allow a quicker young-gen cycle (by avoiding the update-refs
320 // through ALL of old-gen). If there is some memory available in old-gen, we will use this for promotions as promotions
321 // do not add to the update-refs burden of GC.
322
323 size_t old_evacuation_reserve, old_promo_reserve;
324 if (is_global()) {
325 // Global GC is typically triggered by user invocation of System.gc(), and typically indicates that there is lots
326 // of garbage to be reclaimed because we are starting a new phase of execution. Marking for global GC may take
327 // significantly longer than typical young marking because we must mark through all old objects. To expedite
328 // evacuation and update-refs, we give emphasis to reclaiming garbage first, wherever that garbage is found.
329 // Global GC will adjust generation sizes to accommodate the collection set it chooses.
330
331 // Set old_promo_reserve to enforce that no regions are preselected for promotion. Such regions typically
332 // have relatively high memory utilization. We still call select_aged_regions() because this will prepare for
333 // promotions in place, if relevant.
334 old_promo_reserve = 0;
335
336 // Dedicate all available old memory to old_evacuation reserve. This may be small, because old-gen is only
337 // expanded based on an existing mixed evacuation workload at the end of the previous GC cycle. We'll expand
338 // the budget for evacuation of old during GLOBAL cset selection.
339 old_evacuation_reserve = maximum_old_evacuation_reserve;
340 } else if (old_generation->has_unprocessed_collection_candidates()) {
341 // We reserved all old-gen memory at end of previous GC to hold anticipated evacuations to old-gen. If this is
342 // mixed evacuation, reserve all of this memory for compaction of old-gen and do not promote. Prioritize compaction
343 // over promotion in order to defragment OLD so that it will be better prepared to efficiently receive promoted memory.
344 old_evacuation_reserve = maximum_old_evacuation_reserve;
345 old_promo_reserve = 0;
346 } else {
347 // Make all old-evacuation memory for promotion, but if we can't use it all for promotion, we'll allow some evacuation.
348 old_evacuation_reserve = 0;
349 old_promo_reserve = maximum_old_evacuation_reserve;
350 }
351 assert(old_evacuation_reserve <= old_available, "Error");
352
353 // We see too many old-evacuation failures if we force ourselves to evacuate into regions that are not initially empty.
354 // So we limit the old-evacuation reserve to unfragmented memory. Even so, old-evacuation is free to fill in nooks and
355 // crannies within existing partially used regions and it generally tries to do so.
356 const size_t old_free_unfragmented = old_generation->free_unaffiliated_regions() * ShenandoahHeapRegion::region_size_bytes();
357 if (old_evacuation_reserve > old_free_unfragmented) {
358 const size_t delta = old_evacuation_reserve - old_free_unfragmented;
359 old_evacuation_reserve -= delta;
360 // Let promo consume fragments of old-gen memory if not global
361 if (!is_global()) {
362 old_promo_reserve += delta;
363 }
364 }
365
366 // Preselect regions for promotion by evacuation (obtaining the live data to seed promoted_reserve),
367 // and identify regions that will promote in place. These use the tenuring threshold.
368 const size_t consumed_by_advance_promotion = select_aged_regions(old_promo_reserve);
369 assert(consumed_by_advance_promotion <= maximum_old_evacuation_reserve, "Cannot promote more than available old-gen memory");
370
371 // Note that unused old_promo_reserve might not be entirely consumed_by_advance_promotion. Do not transfer this
372 // to old_evacuation_reserve because this memory is likely very fragmented, and we do not want to increase the likelihood
373 // of old evacuation failure.
374 young_generation->set_evacuation_reserve(young_evacuation_reserve);
375 old_generation->set_evacuation_reserve(old_evacuation_reserve);
376 old_generation->set_promoted_reserve(consumed_by_advance_promotion);
377
378 // There is no need to expand OLD because all memory used here was set aside at end of previous GC, except in the
379 // case of a GLOBAL gc. During choose_collection_set() of GLOBAL, old will be expanded on demand.
380 }
381
382 // Having chosen the collection set, adjust the budgets for generational mode based on its composition. Note
383 // that young_generation->available() now knows about recently discovered immediate garbage.
384 //
385 void ShenandoahGeneration::adjust_evacuation_budgets(ShenandoahHeap* const heap, ShenandoahCollectionSet* const collection_set) {
386 shenandoah_assert_generational();
387 // We may find that old_evacuation_reserve and/or loaned_for_young_evacuation are not fully consumed, in which case we may
388 // be able to increase regions_available_to_loan
389
390 // The role of adjust_evacuation_budgets() is to compute the correct value of regions_available_to_loan and to make
391 // effective use of this memory, including the remnant memory within these regions that may result from rounding loan to
392 // integral number of regions. Excess memory that is available to be loaned is applied to an allocation supplement,
393 // which allows mutators to allocate memory beyond the current capacity of young-gen on the promise that the loan
394 // will be repaid as soon as we finish updating references for the recently evacuated collection set.
395
396 // We cannot recalculate regions_available_to_loan by simply dividing old_generation->available() by region_size_bytes
397 // because the available memory may be distributed between many partially occupied regions that are already holding old-gen
398 // objects. Memory in partially occupied regions is not "available" to be loaned. Note that an increase in old-gen
399 // available that results from a decrease in memory consumed by old evacuation is not necessarily available to be loaned
400 // to young-gen.
401
402 size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
403 ShenandoahOldGeneration* const old_generation = heap->old_generation();
404 ShenandoahYoungGeneration* const young_generation = heap->young_generation();
405
406 size_t old_evacuated = collection_set->get_old_bytes_reserved_for_evacuation();
407 size_t old_evacuated_committed = (size_t) (ShenandoahOldEvacWaste * double(old_evacuated));
408 size_t old_evacuation_reserve = old_generation->get_evacuation_reserve();
409
410 if (old_evacuated_committed > old_evacuation_reserve) {
411 // This should only happen due to round-off errors when enforcing ShenandoahOldEvacWaste
412 assert(old_evacuated_committed <= (33 * old_evacuation_reserve) / 32,
413 "Round-off errors should be less than 3.125%%, committed: " SIZE_FORMAT ", reserved: " SIZE_FORMAT,
414 old_evacuated_committed, old_evacuation_reserve);
415 old_evacuated_committed = old_evacuation_reserve;
416 // Leave old_evac_reserve as previously configured
417 } else if (old_evacuated_committed < old_evacuation_reserve) {
418 // This happens if the old-gen collection consumes less than full budget.
419 old_evacuation_reserve = old_evacuated_committed;
420 old_generation->set_evacuation_reserve(old_evacuation_reserve);
421 }
422
423 size_t young_advance_promoted = collection_set->get_young_bytes_to_be_promoted();
424 size_t young_advance_promoted_reserve_used = (size_t) (ShenandoahPromoEvacWaste * double(young_advance_promoted));
425
426 size_t young_evacuated = collection_set->get_young_bytes_reserved_for_evacuation();
427 size_t young_evacuated_reserve_used = (size_t) (ShenandoahEvacWaste * double(young_evacuated));
428
429 size_t total_young_available = young_generation->available_with_reserve();
430 assert(young_evacuated_reserve_used <= total_young_available, "Cannot evacuate more than is available in young");
431 young_generation->set_evacuation_reserve(young_evacuated_reserve_used);
432
433 size_t old_available = old_generation->available();
434 // Now that we've established the collection set, we know how much memory is really required by old-gen for evacuation
435 // and promotion reserves. Try shrinking OLD now in case that gives us a bit more runway for mutator allocations during
436 // evac and update phases.
437 size_t old_consumed = old_evacuated_committed + young_advance_promoted_reserve_used;
438
439 if (old_available < old_consumed) {
440 // This can happen due to round-off errors when adding the results of truncated integer arithmetic.
441 // We've already truncated old_evacuated_committed. Truncate young_advance_promoted_reserve_used here.
442 assert(young_advance_promoted_reserve_used <= (33 * (old_available - old_evacuated_committed)) / 32,
443 "Round-off errors should be less than 3.125%%, committed: " SIZE_FORMAT ", reserved: " SIZE_FORMAT,
444 young_advance_promoted_reserve_used, old_available - old_evacuated_committed);
445 young_advance_promoted_reserve_used = old_available - old_evacuated_committed;
446 old_consumed = old_evacuated_committed + young_advance_promoted_reserve_used;
447 }
448
449 assert(old_available >= old_consumed, "Cannot consume (" SIZE_FORMAT ") more than is available (" SIZE_FORMAT ")",
450 old_consumed, old_available);
451 size_t excess_old = old_available - old_consumed;
452 size_t unaffiliated_old_regions = old_generation->free_unaffiliated_regions();
453 size_t unaffiliated_old = unaffiliated_old_regions * region_size_bytes;
454 assert(old_available >= unaffiliated_old, "Unaffiliated old is a subset of old available");
455
456 // Make sure old_evac_committed is unaffiliated
457 if (old_evacuated_committed > 0) {
458 if (unaffiliated_old > old_evacuated_committed) {
459 size_t giveaway = unaffiliated_old - old_evacuated_committed;
460 size_t giveaway_regions = giveaway / region_size_bytes; // round down
461 if (giveaway_regions > 0) {
462 excess_old = MIN2(excess_old, giveaway_regions * region_size_bytes);
463 } else {
464 excess_old = 0;
465 }
466 } else {
467 excess_old = 0;
468 }
469 }
470
471 // If we find that OLD has excess regions, give them back to YOUNG now to reduce likelihood we run out of allocation
472 // runway during evacuation and update-refs.
473 size_t regions_to_xfer = 0;
474 if (excess_old > unaffiliated_old) {
475 // we can give back unaffiliated_old (all of unaffiliated is excess)
476 if (unaffiliated_old_regions > 0) {
477 regions_to_xfer = unaffiliated_old_regions;
478 }
479 } else if (unaffiliated_old_regions > 0) {
480 // excess_old < unaffiliated old: we can give back MIN(excess_old/region_size_bytes, unaffiliated_old_regions)
481 size_t excess_regions = excess_old / region_size_bytes;
482 regions_to_xfer = MIN2(excess_regions, unaffiliated_old_regions);
483 }
484
485 if (regions_to_xfer > 0) {
486 bool result = ShenandoahGenerationalHeap::cast(heap)->generation_sizer()->transfer_to_young(regions_to_xfer);
487 assert(excess_old >= regions_to_xfer * region_size_bytes,
488 "Cannot transfer (" SIZE_FORMAT ", " SIZE_FORMAT ") more than excess old (" SIZE_FORMAT ")",
489 regions_to_xfer, region_size_bytes, excess_old);
490 excess_old -= regions_to_xfer * region_size_bytes;
491 log_debug(gc, ergo)("%s transferred " SIZE_FORMAT " excess regions to young before start of evacuation",
492 result? "Successfully": "Unsuccessfully", regions_to_xfer);
493 }
494
495 // Add in the excess_old memory to hold unanticipated promotions, if any. If there are more unanticipated
496 // promotions than fit in reserved memory, they will be deferred until a future GC pass.
497 size_t total_promotion_reserve = young_advance_promoted_reserve_used + excess_old;
498 old_generation->set_promoted_reserve(total_promotion_reserve);
499 old_generation->reset_promoted_expended();
500 }
501
502 typedef struct {
503 ShenandoahHeapRegion* _region;
504 size_t _live_data;
505 } AgedRegionData;
506
507 static int compare_by_aged_live(AgedRegionData a, AgedRegionData b) {
508 if (a._live_data < b._live_data)
509 return -1;
510 else if (a._live_data > b._live_data)
511 return 1;
512 else return 0;
513 }
514
515 inline void assert_no_in_place_promotions() {
516 #ifdef ASSERT
517 class ShenandoahNoInPlacePromotions : public ShenandoahHeapRegionClosure {
518 public:
519 void heap_region_do(ShenandoahHeapRegion *r) override {
520 assert(r->get_top_before_promote() == nullptr,
521 "Region " SIZE_FORMAT " should not be ready for in-place promotion", r->index());
522 }
523 } cl;
524 ShenandoahHeap::heap()->heap_region_iterate(&cl);
525 #endif
526 }
527
528 // Preselect for inclusion into the collection set regions whose age is at or above tenure age which contain more than
529 // ShenandoahOldGarbageThreshold amounts of garbage. We identify these regions by setting the appropriate entry of
530 // the collection set's preselected regions array to true. All entries are initialized to false before calling this
531 // function.
532 //
533 // During the subsequent selection of the collection set, we give priority to these promotion set candidates.
534 // Without this prioritization, we found that the aged regions tend to be ignored because they typically have
535 // much less garbage and much more live data than the recently allocated "eden" regions. When aged regions are
536 // repeatedly excluded from the collection set, the amount of live memory within the young generation tends to
537 // accumulate and this has the undesirable side effect of causing young-generation collections to require much more
538 // CPU and wall-clock time.
539 //
540 // A second benefit of treating aged regions differently than other regions during collection set selection is
541 // that this allows us to more accurately budget memory to hold the results of evacuation. Memory for evacuation
542 // of aged regions must be reserved in the old generation. Memory for evacuation of all other regions must be
543 // reserved in the young generation.
544 size_t ShenandoahGeneration::select_aged_regions(size_t old_available) {
545
546 // There should be no regions configured for subsequent in-place-promotions carried over from the previous cycle.
547 assert_no_in_place_promotions();
548
549 auto const heap = ShenandoahGenerationalHeap::heap();
550 bool* const candidate_regions_for_promotion_by_copy = heap->collection_set()->preselected_regions();
551 ShenandoahMarkingContext* const ctx = heap->marking_context();
552
553 const uint tenuring_threshold = heap->age_census()->tenuring_threshold();
554 const size_t old_garbage_threshold = (ShenandoahHeapRegion::region_size_bytes() * ShenandoahOldGarbageThreshold) / 100;
555
556 size_t old_consumed = 0;
557 size_t promo_potential = 0;
558 size_t candidates = 0;
559
560 // Tracks the padding of space above top in regions eligible for promotion in place
561 size_t promote_in_place_pad = 0;
562
563 // Sort the promotion-eligible regions in order of increasing live-data-bytes so that we can first reclaim regions that require
564 // less evacuation effort. This prioritizes garbage first, expanding the allocation pool early before we reclaim regions that
565 // have more live data.
566 const size_t num_regions = heap->num_regions();
567
568 ResourceMark rm;
569 AgedRegionData* sorted_regions = NEW_RESOURCE_ARRAY(AgedRegionData, num_regions);
570
571 for (size_t i = 0; i < num_regions; i++) {
572 ShenandoahHeapRegion* const r = heap->get_region(i);
573 if (r->is_empty() || !r->has_live() || !r->is_young() || !r->is_regular()) {
574 // skip over regions that aren't regular young with some live data
575 continue;
576 }
577 if (r->age() >= tenuring_threshold) {
578 if ((r->garbage() < old_garbage_threshold)) {
579 // This tenure-worthy region has too little garbage, so we do not want to expend the copying effort to
580 // reclaim the garbage; instead this region may be eligible for promotion-in-place to the
581 // old generation.
582 HeapWord* tams = ctx->top_at_mark_start(r);
583 HeapWord* original_top = r->top();
584 if (!heap->is_concurrent_old_mark_in_progress() && tams == original_top) {
585 // No allocations from this region have been made during concurrent mark. It meets all the criteria
586 // for in-place-promotion. Though we only need the value of top when we fill the end of the region,
587 // we use this field to indicate that this region should be promoted in place during the evacuation
588 // phase.
589 r->save_top_before_promote();
590
591 size_t remnant_size = r->free() / HeapWordSize;
592 if (remnant_size > ShenandoahHeap::min_fill_size()) {
593 ShenandoahHeap::fill_with_object(original_top, remnant_size);
594 // Fill the remnant memory within this region to assure no allocations prior to promote in place. Otherwise,
595 // newly allocated objects will not be parsable when promote in place tries to register them. Furthermore, any
596 // new allocations would not necessarily be eligible for promotion. This addresses both issues.
597 r->set_top(r->end());
598 promote_in_place_pad += remnant_size * HeapWordSize;
599 } else {
600 // Since the remnant is so small that it cannot be filled, we don't have to worry about any accidental
601 // allocations occurring within this region before the region is promoted in place.
602 }
603 }
604 // Else, we do not promote this region (either in place or by copy) because it has received new allocations.
605
606 // During evacuation, we exclude from promotion regions for which age > tenure threshold, garbage < garbage-threshold,
607 // and get_top_before_promote() != tams
608 } else {
609 // Record this promotion-eligible candidate region. After sorting and selecting the best candidates below,
610 // we may still decide to exclude this promotion-eligible region from the current collection set. If this
611 // happens, we will consider this region as part of the anticipated promotion potential for the next GC
612 // pass; see further below.
613 sorted_regions[candidates]._region = r;
614 sorted_regions[candidates++]._live_data = r->get_live_data_bytes();
615 }
616 } else {
617 // We only evacuate & promote objects from regular regions whose garbage() is above old-garbage-threshold.
618 // Objects in tenure-worthy regions with less garbage are promoted in place. These take a different path to
619 // old-gen. Regions excluded from promotion because their garbage content is too low (causing us to anticipate that
620 // the region would be promoted in place) may be eligible for evacuation promotion by the time promotion takes
621 // place during a subsequent GC pass because more garbage is found within the region between now and then. This
622 // should not happen if we are properly adapting the tenure age. The theory behind adaptive tenuring threshold
623 // is to choose the youngest age that demonstrates no "significant" further loss of population since the previous
624 // age. If not this, we expect the tenure age to demonstrate linear population decay for at least two population
625 // samples, whereas we expect to observe exponential population decay for ages younger than the tenure age.
626 //
627 // In the case that certain regions which were anticipated to be promoted in place need to be promoted by
628 // evacuation, it may be the case that there is not sufficient reserve within old-gen to hold evacuation of
629 // these regions. The likely outcome is that these regions will not be selected for evacuation or promotion
630 // in the current cycle and we will anticipate that they will be promoted in the next cycle. This will cause
631 // us to reserve more old-gen memory so that these objects can be promoted in the subsequent cycle.
632 if (heap->is_aging_cycle() && (r->age() + 1 == tenuring_threshold)) {
633 if (r->garbage() >= old_garbage_threshold) {
634 promo_potential += r->get_live_data_bytes();
635 }
636 }
637 }
638 // Note that we keep going even if one region is excluded from selection.
639 // Subsequent regions may be selected if they have smaller live data.
640 }
641 // Sort in increasing order according to live data bytes. Note that candidates represents the number of regions
642 // that qualify to be promoted by evacuation.
643 if (candidates > 0) {
644 size_t selected_regions = 0;
645 size_t selected_live = 0;
646 QuickSort::sort<AgedRegionData>(sorted_regions, candidates, compare_by_aged_live, false);
647 for (size_t i = 0; i < candidates; i++) {
648 ShenandoahHeapRegion* const region = sorted_regions[i]._region;
649 size_t region_live_data = sorted_regions[i]._live_data;
650 size_t promotion_need = (size_t) (region_live_data * ShenandoahPromoEvacWaste);
651 if (old_consumed + promotion_need <= old_available) {
652 old_consumed += promotion_need;
653 candidate_regions_for_promotion_by_copy[region->index()] = true;
654 selected_regions++;
655 selected_live += region_live_data;
656 } else {
657 // We rejected this promotable region from the collection set because we had no room to hold its copy.
658 // Add this region to promo potential for next GC.
659 promo_potential += region_live_data;
660 assert(!candidate_regions_for_promotion_by_copy[region->index()], "Shouldn't be selected");
661 }
662 // We keep going even if one region is excluded from selection because we need to accumulate all eligible
663 // regions that are not preselected into promo_potential
664 }
665 log_debug(gc)("Preselected " SIZE_FORMAT " regions containing " SIZE_FORMAT " live bytes,"
666 " consuming: " SIZE_FORMAT " of budgeted: " SIZE_FORMAT,
667 selected_regions, selected_live, old_consumed, old_available);
668 }
669
670 heap->old_generation()->set_pad_for_promote_in_place(promote_in_place_pad);
671 heap->old_generation()->set_promotion_potential(promo_potential);
672 return old_consumed;
673 }
674
675 void ShenandoahGeneration::prepare_regions_and_collection_set(bool concurrent) {
676 ShenandoahHeap* heap = ShenandoahHeap::heap();
677 ShenandoahCollectionSet* collection_set = heap->collection_set();
678 bool is_generational = heap->mode()->is_generational();
679
680 assert(!heap->is_full_gc_in_progress(), "Only for concurrent and degenerated GC");
681 assert(!is_old(), "Only YOUNG and GLOBAL GC perform evacuations");
682 {
683 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::final_update_region_states :
684 ShenandoahPhaseTimings::degen_gc_final_update_region_states);
685 ShenandoahFinalMarkUpdateRegionStateClosure cl(complete_marking_context());
686 parallel_heap_region_iterate(&cl);
687
688 if (is_young()) {
689 // We always need to update the watermark for old regions. If there
690 // are mixed collections pending, we also need to synchronize the
691 // pinned status for old regions. Since we are already visiting every
692 // old region here, go ahead and sync the pin status too.
693 ShenandoahFinalMarkUpdateRegionStateClosure old_cl(nullptr);
694 heap->old_generation()->parallel_heap_region_iterate(&old_cl);
695 }
696 }
697
698 // Tally the census counts and compute the adaptive tenuring threshold
699 if (is_generational && ShenandoahGenerationalAdaptiveTenuring && !ShenandoahGenerationalCensusAtEvac) {
700 // Objects above TAMS weren't included in the age census. Since they were all
701 // allocated in this cycle they belong in the age 0 cohort. We walk over all
702 // young regions and sum the volume of objects between TAMS and top.
703 ShenandoahUpdateCensusZeroCohortClosure age0_cl(complete_marking_context());
704 heap->young_generation()->heap_region_iterate(&age0_cl);
705 size_t age0_pop = age0_cl.get_age0_population();
706
707 // Update the global census, including the missed age 0 cohort above,
708 // along with the census done during marking, and compute the tenuring threshold.
709 ShenandoahAgeCensus* census = ShenandoahGenerationalHeap::heap()->age_census();
710 census->update_census(age0_pop);
711 #ifndef PRODUCT
712 size_t total_pop = age0_cl.get_total_population();
713 size_t total_census = census->get_total();
714 // Usually total_pop > total_census, but not by too much.
715 // We use integer division so anything up to just less than 2 is considered
716 // reasonable, and the "+1" is to avoid divide-by-zero.
717 assert((total_pop+1)/(total_census+1) == 1, "Extreme divergence: "
718 SIZE_FORMAT "/" SIZE_FORMAT, total_pop, total_census);
719 #endif
720 }
721
722 {
723 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::choose_cset :
724 ShenandoahPhaseTimings::degen_gc_choose_cset);
725
726 collection_set->clear();
727 ShenandoahHeapLocker locker(heap->lock());
728 if (is_generational) {
729 // Seed the collection set with resource area-allocated
730 // preselected regions, which are removed when we exit this scope.
731 ShenandoahCollectionSetPreselector preselector(collection_set, heap->num_regions());
732
733 // Find the amount that will be promoted, regions that will be promoted in
734 // place, and preselect older regions that will be promoted by evacuation.
735 compute_evacuation_budgets(heap);
736
737 // Choose the collection set, including the regions preselected above for
738 // promotion into the old generation.
739 _heuristics->choose_collection_set(collection_set);
740 if (!collection_set->is_empty()) {
741 // only make use of evacuation budgets when we are evacuating
742 adjust_evacuation_budgets(heap, collection_set);
743 }
744
745 if (is_global()) {
746 // We have just chosen a collection set for a global cycle. The mark bitmap covering old regions is complete, so
747 // the remembered set scan can use that to avoid walking into garbage. When the next old mark begins, we will
748 // use the mark bitmap to make the old regions parsable by coalescing and filling any unmarked objects. Thus,
749 // we prepare for old collections by remembering which regions are old at this time. Note that any objects
750 // promoted into old regions will be above TAMS, and so will be considered marked. However, free regions that
751 // become old after this point will not be covered correctly by the mark bitmap, so we must be careful not to
752 // coalesce those regions. Only the old regions which are not part of the collection set at this point are
753 // eligible for coalescing. As implemented now, this has the side effect of possibly initiating mixed-evacuations
754 // after a global cycle for old regions that were not included in this collection set.
755 heap->old_generation()->prepare_for_mixed_collections_after_global_gc();
756 }
757 } else {
758 _heuristics->choose_collection_set(collection_set);
759 }
760 }
761
762
763 {
764 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::final_rebuild_freeset :
765 ShenandoahPhaseTimings::degen_gc_final_rebuild_freeset);
766 ShenandoahHeapLocker locker(heap->lock());
767 size_t young_cset_regions, old_cset_regions;
768
769 // We are preparing for evacuation. At this time, we ignore cset region tallies.
770 size_t first_old, last_old, num_old;
771 heap->free_set()->prepare_to_rebuild(young_cset_regions, old_cset_regions, first_old, last_old, num_old);
772 // Free set construction uses reserve quantities, because they are known to be valid here
773 heap->free_set()->finish_rebuild(young_cset_regions, old_cset_regions, num_old, true);
774 }
775 }
776
777 bool ShenandoahGeneration::is_bitmap_clear() {
778 ShenandoahHeap* heap = ShenandoahHeap::heap();
779 ShenandoahMarkingContext* context = heap->marking_context();
780 const size_t num_regions = heap->num_regions();
781 for (size_t idx = 0; idx < num_regions; idx++) {
782 ShenandoahHeapRegion* r = heap->get_region(idx);
783 if (contains(r) && r->is_affiliated()) {
784 if (heap->is_bitmap_slice_committed(r) && (context->top_at_mark_start(r) > r->bottom()) &&
785 !context->is_bitmap_range_within_region_clear(r->bottom(), r->end())) {
786 return false;
787 }
788 }
789 }
790 return true;
791 }
792
793 bool ShenandoahGeneration::is_mark_complete() {
794 return _is_marking_complete.is_set();
795 }
796
797 void ShenandoahGeneration::set_mark_complete() {
798 _is_marking_complete.set();
799 }
800
801 void ShenandoahGeneration::set_mark_incomplete() {
802 _is_marking_complete.unset();
803 }
804
805 ShenandoahMarkingContext* ShenandoahGeneration::complete_marking_context() {
806 assert(is_mark_complete(), "Marking must be completed.");
807 return ShenandoahHeap::heap()->marking_context();
808 }
809
810 void ShenandoahGeneration::cancel_marking() {
811 log_info(gc)("Cancel marking: %s", name());
812 if (is_concurrent_mark_in_progress()) {
813 set_mark_incomplete();
814 }
815 _task_queues->clear();
816 ref_processor()->abandon_partial_discovery();
817 set_concurrent_mark_in_progress(false);
818 }
819
820 ShenandoahGeneration::ShenandoahGeneration(ShenandoahGenerationType type,
821 uint max_workers,
822 size_t max_capacity,
823 size_t soft_max_capacity) :
824 _type(type),
825 _task_queues(new ShenandoahObjToScanQueueSet(max_workers)),
826 _ref_processor(new ShenandoahReferenceProcessor(MAX2(max_workers, 1U))),
827 _affiliated_region_count(0), _humongous_waste(0), _evacuation_reserve(0),
828 _used(0), _bytes_allocated_since_gc_start(0),
829 _max_capacity(max_capacity), _soft_max_capacity(soft_max_capacity),
830 _heuristics(nullptr)
831 {
832 _is_marking_complete.set();
833 assert(max_workers > 0, "At least one queue");
834 for (uint i = 0; i < max_workers; ++i) {
835 ShenandoahObjToScanQueue* task_queue = new ShenandoahObjToScanQueue();
836 _task_queues->register_queue(i, task_queue);
837 }
838 }
839
840 ShenandoahGeneration::~ShenandoahGeneration() {
841 for (uint i = 0; i < _task_queues->size(); ++i) {
842 ShenandoahObjToScanQueue* q = _task_queues->queue(i);
843 delete q;
844 }
845 delete _task_queues;
846 }
847
848 void ShenandoahGeneration::reserve_task_queues(uint workers) {
849 _task_queues->reserve(workers);
850 }
851
852 ShenandoahObjToScanQueueSet* ShenandoahGeneration::old_gen_task_queues() const {
853 return nullptr;
854 }
855
856 void ShenandoahGeneration::scan_remembered_set(bool is_concurrent) {
857 assert(is_young(), "Should only scan remembered set for young generation.");
858
859 ShenandoahGenerationalHeap* const heap = ShenandoahGenerationalHeap::heap();
860 uint nworkers = heap->workers()->active_workers();
861 reserve_task_queues(nworkers);
862
863 ShenandoahReferenceProcessor* rp = ref_processor();
864 ShenandoahRegionChunkIterator work_list(nworkers);
865 ShenandoahScanRememberedTask task(task_queues(), old_gen_task_queues(), rp, &work_list, is_concurrent);
866 heap->assert_gc_workers(nworkers);
867 heap->workers()->run_task(&task);
868 if (ShenandoahEnableCardStats) {
869 ShenandoahScanRemembered* scanner = heap->old_generation()->card_scan();
870 assert(scanner != nullptr, "Not generational");
871 scanner->log_card_stats(nworkers, CARD_STAT_SCAN_RS);
872 }
873 }
874
875 size_t ShenandoahGeneration::increment_affiliated_region_count() {
876 shenandoah_assert_heaplocked_or_safepoint();
877 // During full gc, multiple GC worker threads may change region affiliations without a lock. No lock is enforced
878 // on read and write of _affiliated_region_count. At the end of full gc, a single thread overwrites the count with
879 // a coherent value.
880 return Atomic::add(&_affiliated_region_count, (size_t) 1);
881 }
882
883 size_t ShenandoahGeneration::decrement_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 auto affiliated_region_count = Atomic::sub(&_affiliated_region_count, (size_t) 1);
889 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
890 (used() + _humongous_waste <= affiliated_region_count * ShenandoahHeapRegion::region_size_bytes()),
891 "used + humongous cannot exceed regions");
892 return affiliated_region_count;
893 }
894
895 size_t ShenandoahGeneration::decrement_affiliated_region_count_without_lock() {
896 return Atomic::sub(&_affiliated_region_count, (size_t) 1);
897 }
898
899 size_t ShenandoahGeneration::increase_affiliated_region_count(size_t delta) {
900 shenandoah_assert_heaplocked_or_safepoint();
901 return Atomic::add(&_affiliated_region_count, delta);
902 }
903
904 size_t ShenandoahGeneration::decrease_affiliated_region_count(size_t delta) {
905 shenandoah_assert_heaplocked_or_safepoint();
906 assert(Atomic::load(&_affiliated_region_count) >= delta, "Affiliated region count cannot be negative");
907
908 auto const affiliated_region_count = Atomic::sub(&_affiliated_region_count, delta);
909 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
910 (_used + _humongous_waste <= affiliated_region_count * ShenandoahHeapRegion::region_size_bytes()),
911 "used + humongous cannot exceed regions");
912 return affiliated_region_count;
913 }
914
915 void ShenandoahGeneration::establish_usage(size_t num_regions, size_t num_bytes, size_t humongous_waste) {
916 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
917 Atomic::store(&_affiliated_region_count, num_regions);
918 Atomic::store(&_used, num_bytes);
919 _humongous_waste = humongous_waste;
920 }
921
922 void ShenandoahGeneration::increase_used(size_t bytes) {
923 Atomic::add(&_used, bytes);
924 }
925
926 void ShenandoahGeneration::increase_humongous_waste(size_t bytes) {
927 if (bytes > 0) {
928 Atomic::add(&_humongous_waste, bytes);
929 }
930 }
931
932 void ShenandoahGeneration::decrease_humongous_waste(size_t bytes) {
933 if (bytes > 0) {
934 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() || (_humongous_waste >= bytes),
935 "Waste (" SIZE_FORMAT ") cannot be negative (after subtracting " SIZE_FORMAT ")", _humongous_waste, bytes);
936 Atomic::sub(&_humongous_waste, bytes);
937 }
938 }
939
940 void ShenandoahGeneration::decrease_used(size_t bytes) {
941 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
942 (_used >= bytes), "cannot reduce bytes used by generation below zero");
943 Atomic::sub(&_used, bytes);
944 }
945
946 size_t ShenandoahGeneration::used_regions() const {
947 return Atomic::load(&_affiliated_region_count);
948 }
949
950 size_t ShenandoahGeneration::free_unaffiliated_regions() const {
951 size_t result = max_capacity() / ShenandoahHeapRegion::region_size_bytes();
952 auto const used_regions = this->used_regions();
953 if (used_regions > result) {
954 result = 0;
955 } else {
956 result -= used_regions;
957 }
958 return result;
959 }
960
961 size_t ShenandoahGeneration::used_regions_size() const {
962 return used_regions() * ShenandoahHeapRegion::region_size_bytes();
963 }
964
965 size_t ShenandoahGeneration::available() const {
966 return available(max_capacity());
967 }
968
969 // For ShenandoahYoungGeneration, Include the young available that may have been reserved for the Collector.
970 size_t ShenandoahGeneration::available_with_reserve() const {
971 return available(max_capacity());
972 }
973
974 size_t ShenandoahGeneration::soft_available() const {
975 return available(soft_max_capacity());
976 }
977
978 size_t ShenandoahGeneration::available(size_t capacity) const {
979 size_t in_use = used() + get_humongous_waste();
980 return in_use > capacity ? 0 : capacity - in_use;
981 }
982
983 size_t ShenandoahGeneration::increase_capacity(size_t increment) {
984 shenandoah_assert_heaplocked_or_safepoint();
985
986 // We do not enforce that new capacity >= heap->max_size_for(this). The maximum generation size is treated as a rule of thumb
987 // which may be violated during certain transitions, such as when we are forcing transfers for the purpose of promoting regions
988 // in place.
989 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
990 (_max_capacity + increment <= ShenandoahHeap::heap()->max_capacity()), "Generation cannot be larger than heap size");
991 assert(increment % ShenandoahHeapRegion::region_size_bytes() == 0, "Generation capacity must be multiple of region size");
992 _max_capacity += increment;
993
994 // This detects arithmetic wraparound on _used
995 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
996 (used_regions_size() >= used()),
997 "Affiliated regions must hold more than what is currently used");
998 return _max_capacity;
999 }
1000
1001 size_t ShenandoahGeneration::set_capacity(size_t byte_size) {
1002 shenandoah_assert_heaplocked_or_safepoint();
1003 _max_capacity = byte_size;
1004 return _max_capacity;
1005 }
1006
1007 size_t ShenandoahGeneration::decrease_capacity(size_t decrement) {
1008 shenandoah_assert_heaplocked_or_safepoint();
1009
1010 // We do not enforce that new capacity >= heap->min_size_for(this). The minimum generation size is treated as a rule of thumb
1011 // which may be violated during certain transitions, such as when we are forcing transfers for the purpose of promoting regions
1012 // in place.
1013 assert(decrement % ShenandoahHeapRegion::region_size_bytes() == 0, "Generation capacity must be multiple of region size");
1014 assert(_max_capacity >= decrement, "Generation capacity cannot be negative");
1015
1016 _max_capacity -= decrement;
1017
1018 // This detects arithmetic wraparound on _used
1019 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
1020 (used_regions_size() >= used()),
1021 "Affiliated regions must hold more than what is currently used");
1022 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
1023 (_used <= _max_capacity), "Cannot use more than capacity");
1024 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() ||
1025 (used_regions_size() <= _max_capacity),
1026 "Cannot use more than capacity");
1027 return _max_capacity;
1028 }
1029
1030 void ShenandoahGeneration::record_success_concurrent(bool abbreviated) {
1031 heuristics()->record_success_concurrent();
1032 ShenandoahHeap::heap()->shenandoah_policy()->record_success_concurrent(is_young(), abbreviated);
1033 }