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 class ShenandoahResetUpdateRegionStateClosure : public ShenandoahHeapRegionClosure {
41 private:
42 ShenandoahHeap* _heap;
43 ShenandoahMarkingContext* const _ctx;
44 public:
45 ShenandoahResetUpdateRegionStateClosure() :
46 _heap(ShenandoahHeap::heap()),
47 _ctx(_heap->marking_context()) {}
48
49 void heap_region_do(ShenandoahHeapRegion* r) override {
50 if (_heap->is_bitmap_slice_committed(r)) {
51 _ctx->clear_bitmap(r);
52 }
53
54 if (r->is_active()) {
55 // Reset live data and set TAMS optimistically. We would recheck these under the pause
56 // anyway to capture any updates that happened since now.
57 _ctx->capture_top_at_mark_start(r);
58 r->clear_live_data();
59 }
60 }
61
62 bool is_thread_safe() override { return true; }
63 };
64
65 class ShenandoahResetBitmapTask : public ShenandoahHeapRegionClosure {
66 private:
67 ShenandoahHeap* _heap;
68 ShenandoahMarkingContext* const _ctx;
69 public:
70 ShenandoahResetBitmapTask() :
71 _heap(ShenandoahHeap::heap()),
72 _ctx(_heap->marking_context()) {}
73
74 void heap_region_do(ShenandoahHeapRegion* region) {
75 if (_heap->is_bitmap_slice_committed(region)) {
76 _ctx->clear_bitmap(region);
77 }
78 }
79
80 bool is_thread_safe() { return true; }
81 };
82
83 class ShenandoahMergeWriteTable: public ShenandoahHeapRegionClosure {
84 private:
85 ShenandoahHeap* _heap;
86 RememberedScanner* _scanner;
87 public:
88 ShenandoahMergeWriteTable() : _heap(ShenandoahHeap::heap()), _scanner(_heap->card_scan()) {}
89
90 virtual void heap_region_do(ShenandoahHeapRegion* r) override {
91 if (r->is_old()) {
92 _scanner->merge_write_table(r->bottom(), ShenandoahHeapRegion::region_size_words());
93 }
94 }
95
96 virtual bool is_thread_safe() override {
97 return true;
98 }
99 };
100
101 class ShenandoahSquirrelAwayCardTable: public ShenandoahHeapRegionClosure {
102 private:
103 ShenandoahHeap* _heap;
104 RememberedScanner* _scanner;
105 public:
106 ShenandoahSquirrelAwayCardTable() :
107 _heap(ShenandoahHeap::heap()),
108 _scanner(_heap->card_scan()) {}
109
110 void heap_region_do(ShenandoahHeapRegion* region) {
111 if (region->is_old()) {
112 _scanner->reset_remset(region->bottom(), ShenandoahHeapRegion::region_size_words());
113 }
114 }
115
116 bool is_thread_safe() { return true; }
117 };
118
119 void ShenandoahGeneration::confirm_heuristics_mode() {
120 if (_heuristics->is_diagnostic() && !UnlockDiagnosticVMOptions) {
121 vm_exit_during_initialization(
122 err_msg("Heuristics \"%s\" is diagnostic, and must be enabled via -XX:+UnlockDiagnosticVMOptions.",
123 _heuristics->name()));
124 }
125 if (_heuristics->is_experimental() && !UnlockExperimentalVMOptions) {
126 vm_exit_during_initialization(
127 err_msg("Heuristics \"%s\" is experimental, and must be enabled via -XX:+UnlockExperimentalVMOptions.",
128 _heuristics->name()));
129 }
130 }
131
132 ShenandoahHeuristics* ShenandoahGeneration::initialize_heuristics(ShenandoahMode* gc_mode) {
133 _heuristics = gc_mode->initialize_heuristics(this);
134 _heuristics->set_guaranteed_gc_interval(ShenandoahGuaranteedGCInterval);
135 confirm_heuristics_mode();
136 return _heuristics;
137 }
138
139 size_t ShenandoahGeneration::bytes_allocated_since_gc_start() {
140 return Atomic::load(&_bytes_allocated_since_gc_start);
141 }
142
143 void ShenandoahGeneration::reset_bytes_allocated_since_gc_start() {
144 Atomic::store(&_bytes_allocated_since_gc_start, (size_t)0);
145 }
146
147 void ShenandoahGeneration::increase_allocated(size_t bytes) {
148 Atomic::add(&_bytes_allocated_since_gc_start, bytes, memory_order_relaxed);
149 }
150
151 void ShenandoahGeneration::log_status(const char *msg) const {
152 typedef LogTarget(Info, gc, ergo) LogGcInfo;
153
154 if (!LogGcInfo::is_enabled()) {
155 return;
156 }
157
158 // Not under a lock here, so read each of these once to make sure
159 // byte size in proper unit and proper unit for byte size are consistent.
160 size_t v_used = used();
161 size_t v_used_regions = used_regions_size();
162 size_t v_soft_max_capacity = soft_max_capacity();
163 size_t v_max_capacity = max_capacity();
164 size_t v_available = available();
165 size_t v_humongous_waste = get_humongous_waste();
166 LogGcInfo::print("%s: %s generation used: " SIZE_FORMAT "%s, used regions: " SIZE_FORMAT "%s, "
167 "humongous waste: " SIZE_FORMAT "%s, soft capacity: " SIZE_FORMAT "%s, max capacity: " SIZE_FORMAT "%s, "
168 "available: " SIZE_FORMAT "%s", msg, name(),
169 byte_size_in_proper_unit(v_used), proper_unit_for_byte_size(v_used),
170 byte_size_in_proper_unit(v_used_regions), proper_unit_for_byte_size(v_used_regions),
171 byte_size_in_proper_unit(v_humongous_waste), proper_unit_for_byte_size(v_humongous_waste),
172 byte_size_in_proper_unit(v_soft_max_capacity), proper_unit_for_byte_size(v_soft_max_capacity),
173 byte_size_in_proper_unit(v_max_capacity), proper_unit_for_byte_size(v_max_capacity),
174 byte_size_in_proper_unit(v_available), proper_unit_for_byte_size(v_available));
175 }
176
177 void ShenandoahGeneration::reset_mark_bitmap() {
178 ShenandoahHeap* heap = ShenandoahHeap::heap();
179 heap->assert_gc_workers(heap->workers()->active_workers());
180
181 set_mark_incomplete();
182
183 ShenandoahResetBitmapTask task;
184 parallel_heap_region_iterate(&task);
185 }
186
187 // The ideal is to swap the remembered set so the safepoint effort is no more than a few pointer manipulations.
188 // However, limitations in the implementation of the mutator write-barrier make it difficult to simply change the
189 // location of the card table. So the interim implementation of swap_remembered_set will copy the write-table
190 // onto the read-table and will then clear the write-table.
191 void ShenandoahGeneration::swap_remembered_set() {
192 // Must be sure that marking is complete before we swap remembered set.
193 ShenandoahHeap* heap = ShenandoahHeap::heap();
194 heap->assert_gc_workers(heap->workers()->active_workers());
195 shenandoah_assert_safepoint();
196
197 // TODO: Eventually, we want replace this with a constant-time exchange of pointers.
198 ShenandoahSquirrelAwayCardTable task;
199 heap->old_generation()->parallel_heap_region_iterate(&task);
200 }
201
202 // If a concurrent cycle fails _after_ the card table has been swapped we need to update the read card
203 // table with any writes that have occurred during the transition to the degenerated cycle. Without this,
204 // newly created objects which are only referenced by old objects could be lost when the remembered set
205 // is scanned during the degenerated mark.
206 void ShenandoahGeneration::merge_write_table() {
207 // This should only happen for degenerated cycles
208 ShenandoahHeap* heap = ShenandoahHeap::heap();
209 heap->assert_gc_workers(heap->workers()->active_workers());
210 shenandoah_assert_safepoint();
211
212 ShenandoahMergeWriteTable task;
213 heap->old_generation()->parallel_heap_region_iterate(&task);
214 }
215
216 void ShenandoahGeneration::prepare_gc() {
217 // Invalidate the marking context
218 set_mark_incomplete();
219
220 // Capture Top At Mark Start for this generation (typically young) and reset mark bitmap.
221 ShenandoahResetUpdateRegionStateClosure cl;
222 parallel_heap_region_iterate(&cl);
223 }
224
225 void ShenandoahGeneration::compute_evacuation_budgets(ShenandoahHeap* heap, bool* preselected_regions,
226 ShenandoahCollectionSet* collection_set,
227 size_t &consumed_by_advance_promotion) {
228 size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
229 size_t regions_available_to_loan = 0;
230 size_t minimum_evacuation_reserve = ShenandoahOldCompactionReserve * region_size_bytes;
231 size_t old_regions_loaned_for_young_evac = 0;
232 consumed_by_advance_promotion = 0;
233
234 ShenandoahGeneration* old_generation = heap->old_generation();
235 ShenandoahYoungGeneration* young_generation = heap->young_generation();
236 size_t old_evacuation_reserve = 0;
237 size_t num_regions = heap->num_regions();
238
239 // During initialization and phase changes, it is more likely that fewer objects die young and old-gen
240 // memory is not yet full (or is in the process of being replaced). During these times especially, it
241 // is beneficial to loan memory from old-gen to young-gen during the evacuation and update-refs phases
242 // of execution.
243
244 // Calculate EvacuationReserve before PromotionReserve. Evacuation is more critical than promotion.
245 // If we cannot evacuate old-gen, we will not be able to reclaim old-gen memory. Promotions are less
246 // critical. If we cannot promote, there may be degradation of young-gen memory because old objects
247 // accumulate there until they can be promoted. This increases the young-gen marking and evacuation work.
248
249 // Do not fill up old-gen memory with promotions. Reserve some amount of memory for compaction purposes.
250 size_t young_evac_reserve_max = 0;
251
252 // First priority is to reclaim the easy garbage out of young-gen.
253
254 // maximum_young_evacuation_reserve is upper bound on memory to be evacuated out of young
255 size_t maximum_young_evacuation_reserve = (young_generation->max_capacity() * ShenandoahEvacReserve) / 100;
256 size_t young_evacuation_reserve = maximum_young_evacuation_reserve;
257 size_t excess_young;
258 if (young_generation->available() > young_evacuation_reserve) {
259 excess_young = young_generation->available() - young_evacuation_reserve;
260 } else {
261 young_evacuation_reserve = young_generation->available();
262 excess_young = 0;
263 }
264 size_t unaffiliated_young = young_generation->free_unaffiliated_regions() * region_size_bytes;
265 if (excess_young > unaffiliated_young) {
266 excess_young = unaffiliated_young;
267 } else {
268 // round down to multiple of region size
269 excess_young /= region_size_bytes;
270 excess_young *= region_size_bytes;
271 }
272 // excess_young is available to be transferred to OLD. Assume that OLD will not request any more than had
273 // already been set aside for its promotion and evacuation needs at the end of previous GC. No need to
274 // hold back memory for allocation runway.
275
276 ShenandoahOldHeuristics* old_heuristics = heap->old_heuristics();
277
278 // maximum_old_evacuation_reserve is an upper bound on memory evacuated from old and evacuated to old (promoted).
279 size_t maximum_old_evacuation_reserve =
280 maximum_young_evacuation_reserve * ShenandoahOldEvacRatioPercent / (100 - ShenandoahOldEvacRatioPercent);
281 // Here's the algebra:
282 // TotalEvacuation = OldEvacuation + YoungEvacuation
283 // OldEvacuation = TotalEvacuation * (ShenandoahOldEvacRatioPercent/100)
284 // OldEvacuation = YoungEvacuation * (ShenandoahOldEvacRatioPercent/100)/(1 - ShenandoahOldEvacRatioPercent/100)
285 // OldEvacuation = YoungEvacuation * ShenandoahOldEvacRatioPercent/(100 - ShenandoahOldEvacRatioPercent)
286
287 if (maximum_old_evacuation_reserve > old_generation->available()) {
288 maximum_old_evacuation_reserve = old_generation->available();
289 }
290
291 // Second priority is to reclaim garbage out of old-gen if there are old-gen collection candidates. Third priority
292 // is to promote as much as we have room to promote. However, if old-gen memory is in short supply, this means young
293 // GC is operating under "duress" and was unable to transfer the memory that we would normally expect. In this case,
294 // old-gen will refrain from compacting itself in order to allow a quicker young-gen cycle (by avoiding the update-refs
295 // through ALL of old-gen). If there is some memory available in old-gen, we will use this for promotions as promotions
296 // do not add to the update-refs burden of GC.
297
298 size_t old_promo_reserve;
299 if (old_heuristics->unprocessed_old_collection_candidates() > 0) {
300 // We reserved all old-gen memory at end of previous GC to hold anticipated evacuations to old-gen. If this is
301 // mixed evacuation, reserve all of this memory for compaction of old-gen and do not promote. Prioritize compaction
302 // over promotion in order to defragment OLD so that it will be better prepared to efficiently receive promoted memory.
303 old_evacuation_reserve = maximum_old_evacuation_reserve;
304 old_promo_reserve = 0;
305 } else {
306 // Make all old-evacuation memory for promotion, but if we can't use it all for promotion, we'll allow some evacuation.
307 old_evacuation_reserve = 0;
308 old_promo_reserve = maximum_old_evacuation_reserve;
309 }
310
311 // We see too many old-evacuation failures if we force ourselves to evacuate into regions that are not initially empty.
312 // So we limit the old-evacuation reserve to unfragmented memory. Even so, old-evacuation is free to fill in nooks and
313 // crannies within existing partially used regions and it generally tries to do so.
314 size_t old_free_regions = old_generation->free_unaffiliated_regions();
315 size_t old_free_unfragmented = old_free_regions * region_size_bytes;
316 if (old_evacuation_reserve > old_free_unfragmented) {
317 size_t delta = old_evacuation_reserve - old_free_unfragmented;
318 old_evacuation_reserve -= delta;
319
320 // Let promo consume fragments of old-gen memory.
321 old_promo_reserve += delta;
322 }
323 collection_set->establish_preselected(preselected_regions);
324 consumed_by_advance_promotion = _heuristics->select_aged_regions(old_promo_reserve, num_regions, preselected_regions);
325 assert(consumed_by_advance_promotion <= maximum_old_evacuation_reserve, "Cannot promote more than available old-gen memory");
326 if (consumed_by_advance_promotion < old_promo_reserve) {
327 // If we're in a global collection, this memory can be used for old evacuations
328 old_evacuation_reserve += old_promo_reserve - consumed_by_advance_promotion;
329 }
330 heap->set_young_evac_reserve(young_evacuation_reserve);
331 heap->set_old_evac_reserve(old_evacuation_reserve);
332 heap->set_promoted_reserve(consumed_by_advance_promotion);
333
334 // There is no need to expand OLD because all memory used here was set aside at end of previous GC
335 }
336
337 // Having chosen the collection set, adjust the budgets for generational mode based on its composition. Note
338 // that young_generation->available() now knows about recently discovered immediate garbage.
339
340 void ShenandoahGeneration::adjust_evacuation_budgets(ShenandoahHeap* heap, ShenandoahCollectionSet* collection_set,
341 size_t consumed_by_advance_promotion) {
342 // We may find that old_evacuation_reserve and/or loaned_for_young_evacuation are not fully consumed, in which case we may
343 // be able to increase regions_available_to_loan
344
345 // The role of adjust_evacuation_budgets() is to compute the correct value of regions_available_to_loan and to make
346 // effective use of this memory, including the remnant memory within these regions that may result from rounding loan to
347 // integral number of regions. Excess memory that is available to be loaned is applied to an allocation supplement,
348 // which allows mutators to allocate memory beyond the current capacity of young-gen on the promise that the loan
349 // will be repaid as soon as we finish updating references for the recently evacuated collection set.
350
351 // We cannot recalculate regions_available_to_loan by simply dividing old_generation->available() by region_size_bytes
352 // because the available memory may be distributed between many partially occupied regions that are already holding old-gen
353 // objects. Memory in partially occupied regions is not "available" to be loaned. Note that an increase in old-gen
354 // available that results from a decrease in memory consumed by old evacuation is not necessarily available to be loaned
355 // to young-gen.
356
357 size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
358 ShenandoahOldGeneration* old_generation = heap->old_generation();
359 ShenandoahYoungGeneration* young_generation = heap->young_generation();
360
361 // Preselected regions have been inserted into the collection set, so we no longer need the preselected array.
362 collection_set->abandon_preselected();
363
364 size_t old_evacuated = collection_set->get_old_bytes_reserved_for_evacuation();
365 size_t old_evacuated_committed = (size_t) (ShenandoahOldEvacWaste * old_evacuated);
366 size_t old_evacuation_reserve = heap->get_old_evac_reserve();
367
368 if (old_evacuated_committed > old_evacuation_reserve) {
369 // This should only happen due to round-off errors when enforcing ShenandoahOldEvacWaste
370 assert(old_evacuated_committed <= (33 * old_evacuation_reserve) / 32,
371 "Round-off errors should be less than 3.125%%, committed: " SIZE_FORMAT ", reserved: " SIZE_FORMAT,
372 old_evacuated_committed, old_evacuation_reserve);
373 old_evacuated_committed = old_evacuation_reserve;
374 // Leave old_evac_reserve as previously configured
375 } else if (old_evacuated_committed < old_evacuation_reserve) {
376 // This happens if the old-gen collection consumes less than full budget.
377 old_evacuation_reserve = old_evacuated_committed;
378 heap->set_old_evac_reserve(old_evacuation_reserve);
379 }
380
381 size_t young_advance_promoted = collection_set->get_young_bytes_to_be_promoted();
382 size_t young_advance_promoted_reserve_used = (size_t) (ShenandoahPromoEvacWaste * young_advance_promoted);
383
384 size_t young_evacuated = collection_set->get_young_bytes_reserved_for_evacuation();
385 size_t young_evacuated_reserve_used = (size_t) (ShenandoahEvacWaste * young_evacuated);
386
387 assert(young_evacuated_reserve_used <= young_generation->available(), "Cannot evacuate more than is available in young");
388 heap->set_young_evac_reserve(young_evacuated_reserve_used);
389
390 size_t old_available = old_generation->available();
391 // Now that we've established the collection set, we know how much memory is really required by old-gen for evacuation
392 // and promotion reserves. Try shrinking OLD now in case that gives us a bit more runway for mutator allocations during
393 // evac and update phases.
394 size_t old_consumed = old_evacuated_committed + young_advance_promoted_reserve_used;
395 assert(old_available >= old_consumed, "Cannot consume more than is available");
396 size_t excess_old = old_available - old_consumed;
397 size_t unaffiliated_old_regions = old_generation->free_unaffiliated_regions();
398 size_t unaffiliated_old = unaffiliated_old_regions * region_size_bytes;
399 assert(old_available >= unaffiliated_old, "Unaffiliated old is a subset of old available");
400
401 // Make sure old_evac_committed is unaffiliated
402 if (old_evacuated_committed > 0) {
403 if (unaffiliated_old > old_evacuated_committed) {
404 size_t giveaway = unaffiliated_old - old_evacuated_committed;
405 size_t giveaway_regions = giveaway / region_size_bytes; // round down
406 if (giveaway_regions > 0) {
407 excess_old = MIN2(excess_old, giveaway_regions * region_size_bytes);
408 } else {
409 excess_old = 0;
410 }
411 } else {
412 excess_old = 0;
413 }
414 }
415
416 // If we find that OLD has excess regions, give them back to YOUNG now to reduce likelihood we run out of allocation
417 // runway during evacuation and update-refs.
418 size_t regions_to_xfer = 0;
419 if (excess_old > unaffiliated_old) {
420 // we can give back unaffiliated_old (all of unaffiliated is excess)
421 if (unaffiliated_old_regions > 0) {
422 regions_to_xfer = unaffiliated_old_regions;
423 }
424 } else if (unaffiliated_old_regions > 0) {
425 // excess_old < unaffiliated old: we can give back MIN(excess_old/region_size_bytes, unaffiliated_old_regions)
426 size_t excess_regions = excess_old / region_size_bytes;
427 size_t regions_to_xfer = MIN2(excess_regions, unaffiliated_old_regions);
428 }
429
430 if (regions_to_xfer > 0) {
431 bool result = heap->generation_sizer()->transfer_to_young(regions_to_xfer);
432 assert(excess_old > regions_to_xfer * region_size_bytes, "Cannot xfer more than excess old");
433 excess_old -= regions_to_xfer * region_size_bytes;
434 log_info(gc, ergo)("%s transferred " SIZE_FORMAT " excess regions to young before start of evacuation",
435 result? "Successfully": "Unsuccessfully", regions_to_xfer);
436 }
437
438 // Add in the excess_old memory to hold unanticipated promotions, if any. If there are more unanticipated
439 // promotions than fit in reserved memory, they will be deferred until a future GC pass.
440 size_t total_promotion_reserve = young_advance_promoted_reserve_used + excess_old;
441 heap->set_promoted_reserve(total_promotion_reserve);
442 heap->reset_promoted_expended();
443 }
444
445 void ShenandoahGeneration::prepare_regions_and_collection_set(bool concurrent) {
446 ShenandoahHeap* heap = ShenandoahHeap::heap();
447 ShenandoahCollectionSet* collection_set = heap->collection_set();
448
449 assert(!heap->is_full_gc_in_progress(), "Only for concurrent and degenerated GC");
450 assert(!is_old(), "Only YOUNG and GLOBAL GC perform evacuations");
451 {
452 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::final_update_region_states :
453 ShenandoahPhaseTimings::degen_gc_final_update_region_states);
454 ShenandoahFinalMarkUpdateRegionStateClosure cl(complete_marking_context());
455 parallel_heap_region_iterate(&cl);
456
457 if (is_young()) {
458 // We always need to update the watermark for old regions. If there
459 // are mixed collections pending, we also need to synchronize the
460 // pinned status for old regions. Since we are already visiting every
461 // old region here, go ahead and sync the pin status too.
462 ShenandoahFinalMarkUpdateRegionStateClosure old_cl(nullptr);
463 heap->old_generation()->parallel_heap_region_iterate(&old_cl);
464 }
465 }
466
467 {
468 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::choose_cset :
469 ShenandoahPhaseTimings::degen_gc_choose_cset);
470
471 collection_set->clear();
472 ShenandoahHeapLocker locker(heap->lock());
473 if (heap->mode()->is_generational()) {
474 size_t consumed_by_advance_promotion;
475 bool* preselected_regions = (bool*) alloca(heap->num_regions() * sizeof(bool));
476 for (unsigned int i = 0; i < heap->num_regions(); i++) {
477 preselected_regions[i] = false;
478 }
479
480 // TODO: young_available can include available (between top() and end()) within each young region that is not
481 // part of the collection set. Making this memory available to the young_evacuation_reserve allows a larger
482 // young collection set to be chosen when available memory is under extreme pressure. Implementing this "improvement"
483 // is tricky, because the incremental construction of the collection set actually changes the amount of memory
484 // available to hold evacuated young-gen objects. As currently implemented, the memory that is available within
485 // non-empty regions that are not selected as part of the collection set can be allocated by the mutator while
486 // GC is evacuating and updating references.
487
488 // Budgeting parameters to compute_evacuation_budgets are passed by reference.
489 compute_evacuation_budgets(heap, preselected_regions, collection_set, consumed_by_advance_promotion);
490 _heuristics->choose_collection_set(collection_set, heap->old_heuristics());
491 if (!collection_set->is_empty()) {
492 // only make use of evacuation budgets when we are evacuating
493 adjust_evacuation_budgets(heap, collection_set, consumed_by_advance_promotion);
494 }
495 } else {
496 _heuristics->choose_collection_set(collection_set, heap->old_heuristics());
497 }
498 }
499
500 // Freeset construction uses reserve quantities if they are valid
501 heap->set_evacuation_reserve_quantities(true);
502 {
503 ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::final_rebuild_freeset :
504 ShenandoahPhaseTimings::degen_gc_final_rebuild_freeset);
505 ShenandoahHeapLocker locker(heap->lock());
506 size_t young_cset_regions, old_cset_regions;
507
508 // We are preparing for evacuation. At this time, we ignore cset region tallies.
509 heap->free_set()->prepare_to_rebuild(young_cset_regions, old_cset_regions);
510 heap->free_set()->rebuild(young_cset_regions, old_cset_regions);
511 }
512 heap->set_evacuation_reserve_quantities(false);
513 }
514
515 bool ShenandoahGeneration::is_bitmap_clear() {
516 ShenandoahHeap* heap = ShenandoahHeap::heap();
517 ShenandoahMarkingContext* context = heap->marking_context();
518 size_t num_regions = heap->num_regions();
519 for (size_t idx = 0; idx < num_regions; idx++) {
520 ShenandoahHeapRegion* r = heap->get_region(idx);
521 if (contains(r) && r->is_affiliated()) {
522 if (heap->is_bitmap_slice_committed(r) && (context->top_at_mark_start(r) > r->bottom()) &&
523 !context->is_bitmap_clear_range(r->bottom(), r->end())) {
524 return false;
525 }
526 }
527 }
528 return true;
529 }
530
531 bool ShenandoahGeneration::is_mark_complete() {
532 return _is_marking_complete.is_set();
533 }
534
535 void ShenandoahGeneration::set_mark_complete() {
536 _is_marking_complete.set();
537 }
538
539 void ShenandoahGeneration::set_mark_incomplete() {
540 _is_marking_complete.unset();
541 }
542
543 ShenandoahMarkingContext* ShenandoahGeneration::complete_marking_context() {
544 assert(is_mark_complete(), "Marking must be completed.");
545 return ShenandoahHeap::heap()->marking_context();
546 }
547
548 void ShenandoahGeneration::cancel_marking() {
549 log_info(gc)("Cancel marking: %s", name());
550 if (is_concurrent_mark_in_progress()) {
551 set_mark_incomplete();
552 }
553 _task_queues->clear();
554 ref_processor()->abandon_partial_discovery();
555 set_concurrent_mark_in_progress(false);
556 }
557
558 ShenandoahGeneration::ShenandoahGeneration(ShenandoahGenerationType type,
559 uint max_workers,
560 size_t max_capacity,
561 size_t soft_max_capacity) :
562 _type(type),
563 _task_queues(new ShenandoahObjToScanQueueSet(max_workers)),
564 _ref_processor(new ShenandoahReferenceProcessor(MAX2(max_workers, 1U))),
565 _collection_thread_time_s(0.0),
566 _affiliated_region_count(0), _humongous_waste(0), _used(0), _bytes_allocated_since_gc_start(0),
567 _max_capacity(max_capacity), _soft_max_capacity(soft_max_capacity),
568 _heuristics(nullptr) {
569 _is_marking_complete.set();
570 assert(max_workers > 0, "At least one queue");
571 for (uint i = 0; i < max_workers; ++i) {
572 ShenandoahObjToScanQueue* task_queue = new ShenandoahObjToScanQueue();
573 _task_queues->register_queue(i, task_queue);
574 }
575 }
576
577 ShenandoahGeneration::~ShenandoahGeneration() {
578 for (uint i = 0; i < _task_queues->size(); ++i) {
579 ShenandoahObjToScanQueue* q = _task_queues->queue(i);
580 delete q;
581 }
582 delete _task_queues;
583 }
584
585 void ShenandoahGeneration::reserve_task_queues(uint workers) {
586 _task_queues->reserve(workers);
587 }
588
589 ShenandoahObjToScanQueueSet* ShenandoahGeneration::old_gen_task_queues() const {
590 return nullptr;
591 }
592
593 void ShenandoahGeneration::scan_remembered_set(bool is_concurrent) {
594 assert(is_young(), "Should only scan remembered set for young generation.");
595
596 ShenandoahHeap* const heap = ShenandoahHeap::heap();
597 uint nworkers = heap->workers()->active_workers();
598 reserve_task_queues(nworkers);
599
600 ShenandoahReferenceProcessor* rp = ref_processor();
601 ShenandoahRegionChunkIterator work_list(nworkers);
602 ShenandoahScanRememberedTask task(task_queues(), old_gen_task_queues(), rp, &work_list, is_concurrent);
603 heap->assert_gc_workers(nworkers);
604 heap->workers()->run_task(&task);
605 if (ShenandoahEnableCardStats) {
606 assert(heap->card_scan() != nullptr, "Not generational");
607 heap->card_scan()->log_card_stats(nworkers, CARD_STAT_SCAN_RS);
608 }
609 }
610
611 size_t ShenandoahGeneration::increment_affiliated_region_count() {
612 shenandoah_assert_heaplocked_or_fullgc_safepoint();
613 // During full gc, multiple GC worker threads may change region affiliations without a lock. No lock is enforced
614 // on read and write of _affiliated_region_count. At the end of full gc, a single thread overwrites the count with
615 // a coherent value.
616 _affiliated_region_count++;
617 return _affiliated_region_count;
618 }
619
620 size_t ShenandoahGeneration::decrement_affiliated_region_count() {
621 shenandoah_assert_heaplocked_or_fullgc_safepoint();
622 // During full gc, multiple GC worker threads may change region affiliations without a lock. No lock is enforced
623 // on read and write of _affiliated_region_count. At the end of full gc, a single thread overwrites the count with
624 // a coherent value.
625 _affiliated_region_count--;
626 // TODO: REMOVE IS_GLOBAL() QUALIFIER AFTER WE FIX GLOBAL AFFILIATED REGION ACCOUNTING
627 assert(is_global() || ShenandoahHeap::heap()->is_full_gc_in_progress() ||
628 (_used + _humongous_waste <= _affiliated_region_count * ShenandoahHeapRegion::region_size_bytes()),
629 "used + humongous cannot exceed regions");
630 return _affiliated_region_count;
631 }
632
633 size_t ShenandoahGeneration::increase_affiliated_region_count(size_t delta) {
634 shenandoah_assert_heaplocked_or_fullgc_safepoint();
635 _affiliated_region_count += delta;
636 return _affiliated_region_count;
637 }
638
639 size_t ShenandoahGeneration::decrease_affiliated_region_count(size_t delta) {
640 shenandoah_assert_heaplocked_or_fullgc_safepoint();
641 assert(_affiliated_region_count > delta, "Affiliated region count cannot be negative");
642
643 _affiliated_region_count -= delta;
644 // TODO: REMOVE IS_GLOBAL() QUALIFIER AFTER WE FIX GLOBAL AFFILIATED REGION ACCOUNTING
645 assert(is_global() || ShenandoahHeap::heap()->is_full_gc_in_progress() ||
646 (_used + _humongous_waste <= _affiliated_region_count * ShenandoahHeapRegion::region_size_bytes()),
647 "used + humongous cannot exceed regions");
648 return _affiliated_region_count;
649 }
650
651 void ShenandoahGeneration::establish_usage(size_t num_regions, size_t num_bytes, size_t humongous_waste) {
652 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
653 _affiliated_region_count = num_regions;
654 _used = num_bytes;
655 _humongous_waste = humongous_waste;
656 }
657
658 void ShenandoahGeneration::increase_used(size_t bytes) {
659 Atomic::add(&_used, bytes);
660 // This detects arithmetic wraparound on _used. Non-generational mode does not keep track of _affiliated_region_count
661 // TODO: REMOVE IS_GLOBAL() QUALIFIER AFTER WE FIX GLOBAL AFFILIATED REGION ACCOUNTING
662 assert(is_global() || ShenandoahHeap::heap()->is_full_gc_in_progress() ||
663 (_used + _humongous_waste <= _affiliated_region_count * ShenandoahHeapRegion::region_size_bytes()),
664 "used cannot exceed regions");
665 }
666
667 void ShenandoahGeneration::increase_humongous_waste(size_t bytes) {
668 if (bytes > 0) {
669 Atomic::add(&_humongous_waste, bytes);
670 }
671 }
672
673 void ShenandoahGeneration::decrease_humongous_waste(size_t bytes) {
674 if (bytes > 0) {
675 assert(ShenandoahHeap::heap()->is_full_gc_in_progress() || (_humongous_waste >= bytes),
676 "Waste (" SIZE_FORMAT ") cannot be negative (after subtracting " SIZE_FORMAT ")", _humongous_waste, bytes);
677 Atomic::sub(&_humongous_waste, bytes);
678 }
679 }
680
681 void ShenandoahGeneration::decrease_used(size_t bytes) {
682 // TODO: REMOVE IS_GLOBAL() QUALIFIER AFTER WE FIX GLOBAL AFFILIATED REGION ACCOUNTING
683 assert(is_global() || ShenandoahHeap::heap()->is_full_gc_in_progress() ||
684 (_used >= bytes), "cannot reduce bytes used by generation below zero");
685 Atomic::sub(&_used, bytes);
686
687 // Non-generational mode does not maintain affiliated region counts
688 // TODO: REMOVE IS_GLOBAL() QUALIFIER AFTER WE FIX GLOBAL AFFILIATED REGION ACCOUNTING
689 assert(is_global() || ShenandoahHeap::heap()->is_full_gc_in_progress() ||
690 (_affiliated_region_count * ShenandoahHeapRegion::region_size_bytes() >= _used),
691 "Affiliated regions must hold more than what is currently used");
692 }
693
694 size_t ShenandoahGeneration::used_regions() const {
695 return _affiliated_region_count;
696 }
697
698 size_t ShenandoahGeneration::free_unaffiliated_regions() const {
699 size_t result = max_capacity() / ShenandoahHeapRegion::region_size_bytes();
700 if (_affiliated_region_count > result) {
701 result = 0;
702 } else {
703 result -= _affiliated_region_count;
704 }
705 return result;
706 }
707
708 size_t ShenandoahGeneration::used_regions_size() const {
709 return _affiliated_region_count * ShenandoahHeapRegion::region_size_bytes();
710 }
711
712 size_t ShenandoahGeneration::available() const {
713 size_t in_use = used() + get_humongous_waste();
714 size_t capacity = max_capacity();
715 return in_use > capacity ? 0 : capacity - in_use;
716 }
717
718 size_t ShenandoahGeneration::soft_available() const {
719 size_t in_use = used() + get_humongous_waste();
720 size_t soft_capacity = soft_max_capacity();
721 return in_use > soft_capacity ? 0 : soft_capacity - in_use;
722 }
723
724 void ShenandoahGeneration::increase_capacity(size_t increment) {
725 shenandoah_assert_heaplocked_or_safepoint();
726
727 // We do not enforce that new capacity >= heap->max_size_for(this). The maximum generation size is treated as a rule of thumb
728 // which may be violated during certain transitions, such as when we are forcing transfers for the purpose of promoting regions
729 // in place.
730 // TODO: REMOVE IS_GLOBAL() QUALIFIER AFTER WE FIX GLOBAL AFFILIATED REGION ACCOUNTING
731 assert(is_global() || ShenandoahHeap::heap()->is_full_gc_in_progress() ||
732 (_max_capacity + increment <= ShenandoahHeap::heap()->max_capacity()), "Generation cannot be larger than heap size");
733 assert(increment % ShenandoahHeapRegion::region_size_bytes() == 0, "Generation capacity must be multiple of region size");
734 _max_capacity += increment;
735
736 // This detects arithmetic wraparound on _used
737 // TODO: REMOVE IS_GLOBAL() QUALIFIER AFTER WE FIX GLOBAL AFFILIATED REGION ACCOUNTING
738 assert(is_global() || ShenandoahHeap::heap()->is_full_gc_in_progress() ||
739 (_affiliated_region_count * ShenandoahHeapRegion::region_size_bytes() >= _used),
740 "Affiliated regions must hold more than what is currently used");
741 }
742
743 void ShenandoahGeneration::decrease_capacity(size_t decrement) {
744 shenandoah_assert_heaplocked_or_safepoint();
745
746 // We do not enforce that new capacity >= heap->min_size_for(this). The minimum generation size is treated as a rule of thumb
747 // which may be violated during certain transitions, such as when we are forcing transfers for the purpose of promoting regions
748 // in place.
749 assert(decrement % ShenandoahHeapRegion::region_size_bytes() == 0, "Generation capacity must be multiple of region size");
750 assert(_max_capacity >= decrement, "Generation capacity cannot be negative");
751
752 _max_capacity -= decrement;
753
754 // This detects arithmetic wraparound on _used
755 // TODO: REMOVE IS_GLOBAL() QUALIFIER AFTER WE FIX GLOBAL AFFILIATED REGION ACCOUNTING
756 assert(is_global() || ShenandoahHeap::heap()->is_full_gc_in_progress() ||
757 (_affiliated_region_count * ShenandoahHeapRegion::region_size_bytes() >= _used),
758 "Affiliated regions must hold more than what is currently used");
759 // TODO: REMOVE IS_GLOBAL() QUALIFIER AFTER WE FIX GLOBAL AFFILIATED REGION ACCOUNTING
760 assert(is_global() || ShenandoahHeap::heap()->is_full_gc_in_progress() ||
761 (_used <= _max_capacity), "Cannot use more than capacity");
762 // TODO: REMOVE IS_GLOBAL() QUALIFIER AFTER WE FIX GLOBAL AFFILIATED REGION ACCOUNTING
763 assert(is_global() || ShenandoahHeap::heap()->is_full_gc_in_progress() ||
764 (_affiliated_region_count * ShenandoahHeapRegion::region_size_bytes() <= _max_capacity),
765 "Cannot use more than capacity");
766 }
767
768 void ShenandoahGeneration::record_success_concurrent(bool abbreviated) {
769 heuristics()->record_success_concurrent(abbreviated);
770 ShenandoahHeap::heap()->shenandoah_policy()->record_success_concurrent();
771 }
772
773 void ShenandoahGeneration::record_success_degenerated() {
774 heuristics()->record_success_degenerated();
775 ShenandoahHeap::heap()->shenandoah_policy()->record_success_degenerated();
776 }
777
778 void ShenandoahGeneration::add_collection_time(double time_seconds) {
779 shenandoah_assert_control_or_vm_thread();
780 _collection_thread_time_s += time_seconds;
781 }
782
783 double ShenandoahGeneration::reset_collection_time() {
784 double t = _collection_thread_time_s;
785 _collection_thread_time_s = 0.0;
786 return t;
787 }
788