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src/hotspot/share/gc/shenandoah/heuristics/shenandoahHeuristics.cpp

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  1 /*
  2  * Copyright (c) 2018, 2020, Red Hat, Inc. 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/shared/gcCause.hpp"

 27 #include "gc/shenandoah/shenandoahCollectionSet.inline.hpp"
 28 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"

 29 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
 30 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
 31 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"


 32 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"

 33 #include "logging/log.hpp"
 34 #include "logging/logTag.hpp"
 35 #include "runtime/globals_extension.hpp"
 36 
 37 int ShenandoahHeuristics::compare_by_garbage(RegionData a, RegionData b) {
 38   if (a._garbage > b._garbage)
 39     return -1;
 40   else if (a._garbage < b._garbage)
 41     return 1;
 42   else return 0;
 43 }
 44 
 45 ShenandoahHeuristics::ShenandoahHeuristics() :

 46   _region_data(NULL),
 47   _degenerated_cycles_in_a_row(0),
 48   _successful_cycles_in_a_row(0),

 49   _cycle_start(os::elapsedTime()),
 50   _last_cycle_end(0),
 51   _gc_times_learned(0),
 52   _gc_time_penalties(0),
 53   _gc_time_history(new TruncatedSeq(10, ShenandoahAdaptiveDecayFactor)),


 54   _metaspace_oom()
 55 {
 56   // No unloading during concurrent mark? Communicate that to heuristics
 57   if (!ClassUnloadingWithConcurrentMark) {
 58     FLAG_SET_DEFAULT(ShenandoahUnloadClassesFrequency, 0);
 59   }
 60 
 61   size_t num_regions = ShenandoahHeap::heap()->num_regions();
 62   assert(num_regions > 0, "Sanity");
 63 
 64   _region_data = NEW_C_HEAP_ARRAY(RegionData, num_regions, mtGC);
 65 }
 66 
 67 ShenandoahHeuristics::~ShenandoahHeuristics() {
 68   FREE_C_HEAP_ARRAY(RegionGarbage, _region_data);
 69 }
 70 
 71 void ShenandoahHeuristics::choose_collection_set(ShenandoahCollectionSet* collection_set) {
 72   assert(collection_set->count() == 0, "Must be empty");
 73 
 74   ShenandoahHeap* heap = ShenandoahHeap::heap();
 75 



 76   // Check all pinned regions have updated status before choosing the collection set.
 77   heap->assert_pinned_region_status();
 78 
 79   // Step 1. Build up the region candidates we care about, rejecting losers and accepting winners right away.
 80 
 81   size_t num_regions = heap->num_regions();
 82 
 83   RegionData* candidates = _region_data;
 84 
 85   size_t cand_idx = 0;
 86 
 87   size_t total_garbage = 0;
 88 
 89   size_t immediate_garbage = 0;
 90   size_t immediate_regions = 0;
 91 
 92   size_t free = 0;
 93   size_t free_regions = 0;

 94 
 95   ShenandoahMarkingContext* const ctx = heap->complete_marking_context();
 96 

 97   for (size_t i = 0; i < num_regions; i++) {
 98     ShenandoahHeapRegion* region = heap->get_region(i);



 99 
100     size_t garbage = region->garbage();
101     total_garbage += garbage;
102 
103     if (region->is_empty()) {
104       free_regions++;
105       free += ShenandoahHeapRegion::region_size_bytes();
106     } else if (region->is_regular()) {
107       if (!region->has_live()) {
108         // We can recycle it right away and put it in the free set.
109         immediate_regions++;
110         immediate_garbage += garbage;
111         region->make_trash_immediate();
112       } else {



113         // This is our candidate for later consideration.
114         candidates[cand_idx]._region = region;






115         candidates[cand_idx]._garbage = garbage;
116         cand_idx++;
117       }
118     } else if (region->is_humongous_start()) {

119       // Reclaim humongous regions here, and count them as the immediate garbage
120 #ifdef ASSERT
121       bool reg_live = region->has_live();
122       bool bm_live = ctx->is_marked(cast_to_oop(region->bottom()));
123       assert(reg_live == bm_live,
124              "Humongous liveness and marks should agree. Region live: %s; Bitmap live: %s; Region Live Words: " SIZE_FORMAT,
125              BOOL_TO_STR(reg_live), BOOL_TO_STR(bm_live), region->get_live_data_words());
126 #endif
127       if (!region->has_live()) {
128         heap->trash_humongous_region_at(region);
129 
130         // Count only the start. Continuations would be counted on "trash" path
131         immediate_regions++;
132         immediate_garbage += garbage;


133       }
134     } else if (region->is_trash()) {
135       // Count in just trashed collection set, during coalesced CM-with-UR
136       immediate_regions++;
137       immediate_garbage += garbage;


138     }
139   }
140 


141   // Step 2. Look back at garbage statistics, and decide if we want to collect anything,
142   // given the amount of immediately reclaimable garbage. If we do, figure out the collection set.
143 
144   assert (immediate_garbage <= total_garbage,
145           "Cannot have more immediate garbage than total garbage: " SIZE_FORMAT "%s vs " SIZE_FORMAT "%s",
146           byte_size_in_proper_unit(immediate_garbage), proper_unit_for_byte_size(immediate_garbage),
147           byte_size_in_proper_unit(total_garbage),     proper_unit_for_byte_size(total_garbage));
148 
149   size_t immediate_percent = (total_garbage == 0) ? 0 : (immediate_garbage * 100 / total_garbage);
150 
151   if (immediate_percent <= ShenandoahImmediateThreshold) {




































































































152     choose_collection_set_from_regiondata(collection_set, candidates, cand_idx, immediate_garbage + free);




















































153   }
154 
155   size_t cset_percent = (total_garbage == 0) ? 0 : (collection_set->garbage() * 100 / total_garbage);


156 

157   size_t collectable_garbage = collection_set->garbage() + immediate_garbage;
158   size_t collectable_garbage_percent = (total_garbage == 0) ? 0 : (collectable_garbage * 100 / total_garbage);
159 
160   log_info(gc, ergo)("Collectable Garbage: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), "
161                      "Immediate: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), "
162                      "CSet: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%)",
163 
164                      byte_size_in_proper_unit(collectable_garbage),
165                      proper_unit_for_byte_size(collectable_garbage),
166                      collectable_garbage_percent,
167 
168                      byte_size_in_proper_unit(immediate_garbage),
169                      proper_unit_for_byte_size(immediate_garbage),
170                      immediate_percent,
171 
172                      byte_size_in_proper_unit(collection_set->garbage()),
173                      proper_unit_for_byte_size(collection_set->garbage()),
174                      cset_percent);
175 }
176 
177 void ShenandoahHeuristics::record_cycle_start() {
178   _cycle_start = os::elapsedTime();
179 }
180 
181 void ShenandoahHeuristics::record_cycle_end() {
182   _last_cycle_end = os::elapsedTime();
183 }
184 
185 bool ShenandoahHeuristics::should_start_gc() {
186   // Perform GC to cleanup metaspace
187   if (has_metaspace_oom()) {
188     // Some of vmTestbase/metaspace tests depend on following line to count GC cycles
189     log_info(gc)("Trigger: %s", GCCause::to_string(GCCause::_metadata_GC_threshold));
190     return true;
191   }
192 
193   if (ShenandoahGuaranteedGCInterval > 0) {
194     double last_time_ms = (os::elapsedTime() - _last_cycle_end) * 1000;
195     if (last_time_ms > ShenandoahGuaranteedGCInterval) {
196       log_info(gc)("Trigger: Time since last GC (%.0f ms) is larger than guaranteed interval (" UINTX_FORMAT " ms)",
197                    last_time_ms, ShenandoahGuaranteedGCInterval);
198       return true;
199     }
200   }
201 
202   return false;
203 }
204 
205 bool ShenandoahHeuristics::should_degenerate_cycle() {
206   return _degenerated_cycles_in_a_row <= ShenandoahFullGCThreshold;
207 }
208 
209 void ShenandoahHeuristics::adjust_penalty(intx step) {
210   assert(0 <= _gc_time_penalties && _gc_time_penalties <= 100,
211           "In range before adjustment: " INTX_FORMAT, _gc_time_penalties);
212 
213   intx new_val = _gc_time_penalties + step;
214   if (new_val < 0) {
215     new_val = 0;
216   }
217   if (new_val > 100) {
218     new_val = 100;
219   }
220   _gc_time_penalties = new_val;
221 
222   assert(0 <= _gc_time_penalties && _gc_time_penalties <= 100,
223           "In range after adjustment: " INTX_FORMAT, _gc_time_penalties);
224 }
225 
226 void ShenandoahHeuristics::record_success_concurrent() {
227   _degenerated_cycles_in_a_row = 0;
228   _successful_cycles_in_a_row++;
229 
230   _gc_time_history->add(time_since_last_gc());
231   _gc_times_learned++;


232 
233   adjust_penalty(Concurrent_Adjust);
234 }
235 
236 void ShenandoahHeuristics::record_success_degenerated() {
237   _degenerated_cycles_in_a_row++;
238   _successful_cycles_in_a_row = 0;
239 
240   adjust_penalty(Degenerated_Penalty);
241 }
242 
243 void ShenandoahHeuristics::record_success_full() {
244   _degenerated_cycles_in_a_row = 0;
245   _successful_cycles_in_a_row++;
246 
247   adjust_penalty(Full_Penalty);
248 }
249 
250 void ShenandoahHeuristics::record_allocation_failure_gc() {
251   // Do nothing.

271 }
272 
273 bool ShenandoahHeuristics::should_unload_classes() {
274   if (!can_unload_classes_normal()) return false;
275   if (has_metaspace_oom()) return true;
276   size_t cycle = ShenandoahHeap::heap()->shenandoah_policy()->cycle_counter();
277   // Unload classes every Nth GC cycle.
278   // This should not happen in the same cycle as process_references to amortize costs.
279   // Offsetting by one is enough to break the rendezvous when periods are equal.
280   // When periods are not equal, offsetting by one is just as good as any other guess.
281   return (cycle + 1) % ShenandoahUnloadClassesFrequency == 0;
282 }
283 
284 void ShenandoahHeuristics::initialize() {
285   // Nothing to do by default.
286 }
287 
288 double ShenandoahHeuristics::time_since_last_gc() const {
289   return os::elapsedTime() - _cycle_start;
290 }




















  1 /*
  2  * Copyright (c) 2018, 2021, Red Hat, Inc. 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/shared/gcCause.hpp"
 27 #include "gc/shenandoah/shenandoahAllocRequest.hpp"
 28 #include "gc/shenandoah/shenandoahCollectionSet.inline.hpp"
 29 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
 30 #include "gc/shenandoah/shenandoahGeneration.hpp"
 31 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
 32 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
 33 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
 34 #include "gc/shenandoah/shenandoahOldGeneration.hpp"
 35 #include "gc/shenandoah/shenandoahYoungGeneration.hpp"
 36 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
 37 #include "gc/shenandoah/mode/shenandoahMode.hpp"
 38 #include "logging/log.hpp"
 39 #include "logging/logTag.hpp"
 40 #include "runtime/globals_extension.hpp"
 41 
 42 int ShenandoahHeuristics::compare_by_garbage(RegionData a, RegionData b) {
 43   if (a._garbage > b._garbage)
 44     return -1;
 45   else if (a._garbage < b._garbage)
 46     return 1;
 47   else return 0;
 48 }
 49 
 50 ShenandoahHeuristics::ShenandoahHeuristics(ShenandoahGeneration* generation) :
 51   _generation(generation),
 52   _region_data(NULL),
 53   _degenerated_cycles_in_a_row(0),
 54   _successful_cycles_in_a_row(0),
 55   _guaranteed_gc_interval(0),
 56   _cycle_start(os::elapsedTime()),
 57   _last_cycle_end(0),
 58   _gc_times_learned(0),
 59   _gc_time_penalties(0),
 60   _gc_time_history(new TruncatedSeq(10, ShenandoahAdaptiveDecayFactor)),
 61   _live_memory_last_cycle(0),
 62   _live_memory_penultimate_cycle(0),
 63   _metaspace_oom()
 64 {
 65   // No unloading during concurrent mark? Communicate that to heuristics
 66   if (!ClassUnloadingWithConcurrentMark) {
 67     FLAG_SET_DEFAULT(ShenandoahUnloadClassesFrequency, 0);
 68   }
 69 
 70   size_t num_regions = ShenandoahHeap::heap()->num_regions();
 71   assert(num_regions > 0, "Sanity");
 72 
 73   _region_data = NEW_C_HEAP_ARRAY(RegionData, num_regions, mtGC);
 74 }
 75 
 76 ShenandoahHeuristics::~ShenandoahHeuristics() {
 77   FREE_C_HEAP_ARRAY(RegionGarbage, _region_data);
 78 }
 79 
 80 void ShenandoahHeuristics::choose_collection_set(ShenandoahCollectionSet* collection_set, ShenandoahOldHeuristics* old_heuristics) {

 81 
 82   ShenandoahHeap* heap = ShenandoahHeap::heap();
 83 
 84   assert(collection_set->count() == 0, "Must be empty");
 85   assert(_generation->generation_mode() != OLD, "Old GC invokes ShenandoahOldHeuristics::choose_collection_set()");
 86 
 87   // Check all pinned regions have updated status before choosing the collection set.
 88   heap->assert_pinned_region_status();
 89 
 90   // Step 1. Build up the region candidates we care about, rejecting losers and accepting winners right away.
 91 
 92   size_t num_regions = heap->num_regions();
 93 
 94   RegionData* candidates = _region_data;
 95 
 96   size_t cand_idx = 0;
 97 
 98   size_t total_garbage = 0;
 99 
100   size_t immediate_garbage = 0;
101   size_t immediate_regions = 0;
102 
103   size_t free = 0;
104   size_t free_regions = 0;
105   size_t live_memory = 0;
106 
107   ShenandoahMarkingContext* const ctx = _generation->complete_marking_context();
108 
109   size_t remnant_available = 0;
110   for (size_t i = 0; i < num_regions; i++) {
111     ShenandoahHeapRegion* region = heap->get_region(i);
112     if (!in_generation(region)) {
113       continue;
114     }
115 
116     size_t garbage = region->garbage();
117     total_garbage += garbage;
118 
119     if (region->is_empty()) {
120       free_regions++;
121       free += ShenandoahHeapRegion::region_size_bytes();
122     } else if (region->is_regular()) {
123       if (!region->has_live()) {
124         // We can recycle it right away and put it in the free set.
125         immediate_regions++;
126         immediate_garbage += garbage;
127         region->make_trash_immediate();
128       } else {
129         assert (_generation->generation_mode() != OLD, "OLD is handled elsewhere");
130 
131         live_memory += region->get_live_data_bytes();
132         // This is our candidate for later consideration.
133         candidates[cand_idx]._region = region;
134         if (heap->mode()->is_generational() && (region->age() >= InitialTenuringThreshold)) {
135           // Bias selection of regions that have reached tenure age
136           for (uint j = region->age() - InitialTenuringThreshold; j > 0; j--) {
137             garbage = (garbage + ShenandoahTenuredRegionUsageBias) * ShenandoahTenuredRegionUsageBias;
138           }
139         }
140         candidates[cand_idx]._garbage = garbage;
141         cand_idx++;
142       }
143     } else if (region->is_humongous_start()) {
144 
145       // Reclaim humongous regions here, and count them as the immediate garbage
146 #ifdef ASSERT
147       bool reg_live = region->has_live();
148       bool bm_live = ctx->is_marked(cast_to_oop(region->bottom()));
149       assert(reg_live == bm_live,
150              "Humongous liveness and marks should agree. Region live: %s; Bitmap live: %s; Region Live Words: " SIZE_FORMAT,
151              BOOL_TO_STR(reg_live), BOOL_TO_STR(bm_live), region->get_live_data_words());
152 #endif
153       if (!region->has_live()) {
154         heap->trash_humongous_region_at(region);
155 
156         // Count only the start. Continuations would be counted on "trash" path
157         immediate_regions++;
158         immediate_garbage += garbage;
159       } else {
160         live_memory += region->get_live_data_bytes();
161       }
162     } else if (region->is_trash()) {
163       // Count in just trashed collection set, during coalesced CM-with-UR
164       immediate_regions++;
165       immediate_garbage += garbage;
166     } else {                      // region->is_humongous_cont() and !region->is_trash()
167       live_memory += region->get_live_data_bytes();
168     }
169   }
170 
171   save_last_live_memory(live_memory);
172 
173   // Step 2. Look back at garbage statistics, and decide if we want to collect anything,
174   // given the amount of immediately reclaimable garbage. If we do, figure out the collection set.
175 
176   assert (immediate_garbage <= total_garbage,
177           "Cannot have more immediate garbage than total garbage: " SIZE_FORMAT "%s vs " SIZE_FORMAT "%s",
178           byte_size_in_proper_unit(immediate_garbage), proper_unit_for_byte_size(immediate_garbage),
179           byte_size_in_proper_unit(total_garbage),     proper_unit_for_byte_size(total_garbage));
180 
181   size_t immediate_percent = (total_garbage == 0) ? 0 : (immediate_garbage * 100 / total_garbage);
182 
183   if (immediate_percent <= ShenandoahImmediateThreshold) {
184 
185     if (old_heuristics != NULL) {
186       old_heuristics->prime_collection_set(collection_set);
187 
188       size_t bytes_reserved_for_old_evacuation = collection_set->get_old_bytes_reserved_for_evacuation();
189       if (bytes_reserved_for_old_evacuation * ShenandoahEvacWaste < heap->get_old_evac_reserve()) {
190         size_t old_evac_reserve = (size_t) (bytes_reserved_for_old_evacuation * ShenandoahEvacWaste);
191         heap->set_old_evac_reserve(old_evac_reserve);
192       }
193     }
194     // else, this is global collection and doesn't need to prime_collection_set
195 
196     ShenandoahYoungGeneration* young_generation = heap->young_generation();
197     size_t young_evacuation_reserve = (young_generation->soft_max_capacity() * ShenandoahEvacReserve) / 100;
198 
199     // At this point, young_generation->available() does not know about recently discovered immediate garbage.
200     // What memory it does think to be available is not entirely trustworthy because any available memory associated
201     // with a region that is placed into the collection set becomes unavailable when the region is chosen
202     // for the collection set.  We'll compute an approximation of young available.  If young_available is zero,
203     // we'll need to borrow from old-gen in order to evacuate.  If there's nothing to borrow, we're going to
204     // degenerate to full GC.
205 
206     // TODO: young_available can include available (between top() and end()) within each young region that is not
207     // part of the collection set.  Making this memory available to the young_evacuation_reserve allows a larger
208     // young collection set to be chosen when available memory is under extreme pressure.  Implementing this "improvement"
209     // is tricky, because the incremental construction of the collection set actually changes the amount of memory
210     // available to hold evacuated young-gen objects.  As currently implemented, the memory that is available within
211     // non-empty regions that are not selected as part of the collection set can be allocated by the mutator while
212     // GC is evacuating and updating references.
213 
214     size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
215     size_t free_affiliated_regions = immediate_regions + free_regions;
216     size_t young_available = (free_affiliated_regions + young_generation->free_unaffiliated_regions()) * region_size_bytes;
217 
218     size_t regions_available_to_loan = 0;
219 
220     if (heap->mode()->is_generational()) {
221       //  Now that we've primed the collection set, we can figure out how much memory to reserve for evacuation
222       //  of young-gen objects.
223       //
224       //  YoungEvacuationReserve for young generation: how much memory are we reserving to hold the results
225       //     of evacuating young collection set regions?  This is typically smaller than the total amount
226       //     of available memory, and is also smaller than the total amount of marked live memory within
227       //     young-gen.  This value is the minimum of:
228       //       1. young_gen->available() + (old_gen->available - (OldEvacuationReserve + PromotionReserve))
229       //       2. young_gen->capacity() * ShenandoahEvacReserve
230       //
231       //     Note that any region added to the collection set will be completely evacuated and its memory will
232       //     be completely recycled at the end of GC.  The recycled memory will be at least as great as the
233       //     memory borrowed from old-gen.  Enforce that the amount borrowed from old-gen for YoungEvacuationReserve
234       //     is an integral number of entire heap regions.
235       //
236       young_evacuation_reserve -= heap->get_old_evac_reserve();
237 
238       // Though we cannot know the evacuation_supplement until after we have computed the collection set, we do
239       // know that every young-gen region added to the collection set will have a net positive impact on available
240       // memory within young-gen, since each contributes a positive amount of garbage to available.  Thus, even
241       // without knowing the exact composition of the collection set, we can allow young_evacuation_reserve to
242       // exceed young_available if there are empty regions available within old-gen to hold the results of evacuation.
243 
244       ShenandoahGeneration* old_generation = heap->old_generation();
245 
246       // Not all of what is currently available within young-gen can be reserved to hold the results of young-gen
247       // evacuation.  This is because memory available within any heap region that is placed into the collection set
248       // is not available to be allocated during evacuation.  To be safe, we assure that all memory required for evacuation
249       // is available within "virgin" heap regions.
250 
251       const size_t available_young_regions = free_regions + immediate_regions + young_generation->free_unaffiliated_regions();
252       const size_t available_old_regions = old_generation->free_unaffiliated_regions();
253       size_t already_reserved_old_bytes = heap->get_old_evac_reserve() + heap->get_promotion_reserve();
254       size_t regions_reserved_for_evac_and_promotion = (already_reserved_old_bytes + region_size_bytes - 1) / region_size_bytes;
255       regions_available_to_loan = available_old_regions - regions_reserved_for_evac_and_promotion;
256 
257       if (available_young_regions * region_size_bytes < young_evacuation_reserve) {
258         // Try to borrow old-gen regions in order to avoid shrinking young_evacuation_reserve
259         size_t loan_request = young_evacuation_reserve - available_young_regions * region_size_bytes;
260         size_t loaned_region_request = (loan_request + region_size_bytes - 1) / region_size_bytes;
261         if (loaned_region_request > regions_available_to_loan) {
262           // Scale back young_evacuation_reserve to consume all available young and old regions.  After the
263           // collection set is chosen, we may get some of this memory back for pacing allocations during evacuation
264           // and update refs.
265           loaned_region_request = regions_available_to_loan;
266           young_evacuation_reserve = (available_young_regions + loaned_region_request) * region_size_bytes;
267         } else {
268           // No need to scale back young_evacuation_reserve.
269         }
270       } else {
271         // No need scale back young_evacuation_reserve and no need to borrow from old-gen.  We may even have some
272         // available_young_regions to support allocation pacing.
273       }
274 
275     } else if (young_evacuation_reserve > young_available) {
276       // In non-generational mode, there's no old-gen memory to borrow from
277       young_evacuation_reserve = young_available;
278     }
279 
280     heap->set_young_evac_reserve(young_evacuation_reserve);
281 
282     // Add young-gen regions into the collection set.  This is a virtual call, implemented differently by each
283     // of the heuristics subclasses.
284     choose_collection_set_from_regiondata(collection_set, candidates, cand_idx, immediate_garbage + free);
285 
286     // Now compute the evacuation supplement, which is extra memory borrowed from old-gen that can be allocated
287     // by mutators while GC is working on evacuation and update-refs.
288 
289     // During evacuation and update refs, we will be able to allocate any memory that is currently available
290     // plus any memory that can be borrowed on the collateral of the current collection set, reserving a certain
291     // percentage of the anticipated replenishment from collection set memory to be allocated during the subsequent
292     // concurrent marking effort.  This is how much I can repay.
293     size_t potential_supplement_regions = collection_set->get_young_region_count();
294 
295     // Though I can repay potential_supplement_regions, I can't borrow them unless they are available in old-gen.
296     if (potential_supplement_regions > regions_available_to_loan) {
297       potential_supplement_regions = regions_available_to_loan;
298     }
299 
300     size_t potential_evac_supplement;
301 
302     // How much of the potential_supplement_regions will be consumed by young_evacuation_reserve: borrowed_evac_regions.
303     const size_t available_unaffiliated_young_regions = young_generation->free_unaffiliated_regions();
304     const size_t available_affiliated_regions = free_regions + immediate_regions;
305     const size_t available_young_regions = available_unaffiliated_young_regions + available_affiliated_regions;
306     size_t young_evac_regions = (young_evacuation_reserve + region_size_bytes - 1) / region_size_bytes;
307     size_t borrowed_evac_regions = (young_evac_regions > available_young_regions)? young_evac_regions - available_young_regions: 0;
308 
309     potential_supplement_regions -= borrowed_evac_regions;
310     potential_evac_supplement = potential_supplement_regions * region_size_bytes;
311 
312     // Leave some allocation runway for subsequent concurrent mark phase.
313     potential_evac_supplement = (potential_evac_supplement * ShenandoahBorrowPercent) / 100;
314 
315     heap->set_alloc_supplement_reserve(potential_evac_supplement);
316 
317     size_t promotion_budget = heap->get_promotion_reserve();
318     size_t old_evac_budget = heap->get_old_evac_reserve();
319     size_t alloc_budget_evac_and_update = potential_evac_supplement + young_available;
320 
321     // TODO: young_available, which feeds into alloc_budget_evac_and_update is lacking memory available within
322     // existing young-gen regions that were not selected for the collection set.  Add this in and adjust the
323     // log message (where it says "empty-region allocation budget").
324 
325     log_info(gc, ergo)("Memory reserved for evacuation and update-refs includes promotion budget: " SIZE_FORMAT
326                        "%s, young evacuation budget: " SIZE_FORMAT "%s, old evacuation budget: " SIZE_FORMAT
327                        "%s, empty-region allocation budget: " SIZE_FORMAT "%s, including supplement: " SIZE_FORMAT "%s",
328                        byte_size_in_proper_unit(promotion_budget), proper_unit_for_byte_size(promotion_budget),
329                        byte_size_in_proper_unit(young_evacuation_reserve), proper_unit_for_byte_size(young_evacuation_reserve),
330                        byte_size_in_proper_unit(old_evac_budget), proper_unit_for_byte_size(old_evac_budget),
331                        byte_size_in_proper_unit(alloc_budget_evac_and_update),
332                        proper_unit_for_byte_size(alloc_budget_evac_and_update),
333                        byte_size_in_proper_unit(potential_evac_supplement), proper_unit_for_byte_size(potential_evac_supplement));
334   } else {
335     // we're going to skip evacuation and update refs because we reclaimed sufficient amounts of immediate garbage.
336     heap->shenandoah_policy()->record_abbreviated_cycle();
337   }
338 
339   if (collection_set->has_old_regions()) {
340     heap->shenandoah_policy()->record_mixed_cycle();
341   }
342 
343   size_t cset_percent = (total_garbage == 0) ? 0 : (collection_set->garbage() * 100 / total_garbage);
344   size_t collectable_garbage = collection_set->garbage() + immediate_garbage;
345   size_t collectable_garbage_percent = (total_garbage == 0) ? 0 : (collectable_garbage * 100 / total_garbage);
346 
347   log_info(gc, ergo)("Collectable Garbage: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), "
348                      "Immediate: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), "
349                      "CSet: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%)",
350 
351                      byte_size_in_proper_unit(collectable_garbage),
352                      proper_unit_for_byte_size(collectable_garbage),
353                      collectable_garbage_percent,
354 
355                      byte_size_in_proper_unit(immediate_garbage),
356                      proper_unit_for_byte_size(immediate_garbage),
357                      immediate_percent,
358 
359                      byte_size_in_proper_unit(collection_set->garbage()),
360                      proper_unit_for_byte_size(collection_set->garbage()),
361                      cset_percent);
362 }
363 
364 void ShenandoahHeuristics::record_cycle_start() {
365   _cycle_start = os::elapsedTime();
366 }
367 
368 void ShenandoahHeuristics::record_cycle_end() {
369   _last_cycle_end = os::elapsedTime();
370 }
371 
372 bool ShenandoahHeuristics::should_start_gc() {
373   // Perform GC to cleanup metaspace
374   if (has_metaspace_oom()) {
375     // Some of vmTestbase/metaspace tests depend on following line to count GC cycles
376     log_info(gc)("Trigger: %s", GCCause::to_string(GCCause::_metadata_GC_threshold));
377     return true;
378   }
379 
380   if (_guaranteed_gc_interval > 0) {
381     double last_time_ms = (os::elapsedTime() - _last_cycle_end) * 1000;
382     if (last_time_ms > _guaranteed_gc_interval) {
383       log_info(gc)("Trigger (%s): Time since last GC (%.0f ms) is larger than guaranteed interval (" UINTX_FORMAT " ms)",
384                    _generation->name(), last_time_ms, _guaranteed_gc_interval);
385       return true;
386     }
387   }
388 
389   return false;
390 }
391 
392 bool ShenandoahHeuristics::should_degenerate_cycle() {
393   return _degenerated_cycles_in_a_row <= ShenandoahFullGCThreshold;
394 }
395 
396 void ShenandoahHeuristics::adjust_penalty(intx step) {
397   assert(0 <= _gc_time_penalties && _gc_time_penalties <= 100,
398          "In range before adjustment: " INTX_FORMAT, _gc_time_penalties);
399 
400   intx new_val = _gc_time_penalties + step;
401   if (new_val < 0) {
402     new_val = 0;
403   }
404   if (new_val > 100) {
405     new_val = 100;
406   }
407   _gc_time_penalties = new_val;
408 
409   assert(0 <= _gc_time_penalties && _gc_time_penalties <= 100,
410          "In range after adjustment: " INTX_FORMAT, _gc_time_penalties);
411 }
412 
413 void ShenandoahHeuristics::record_success_concurrent(bool abbreviated) {
414   _degenerated_cycles_in_a_row = 0;
415   _successful_cycles_in_a_row++;
416 
417   if (!(abbreviated && ShenandoahAdaptiveIgnoreShortCycles)) {
418     _gc_time_history->add(time_since_last_gc());
419     _gc_times_learned++;
420   }
421 
422   adjust_penalty(Concurrent_Adjust);
423 }
424 
425 void ShenandoahHeuristics::record_success_degenerated() {
426   _degenerated_cycles_in_a_row++;
427   _successful_cycles_in_a_row = 0;
428 
429   adjust_penalty(Degenerated_Penalty);
430 }
431 
432 void ShenandoahHeuristics::record_success_full() {
433   _degenerated_cycles_in_a_row = 0;
434   _successful_cycles_in_a_row++;
435 
436   adjust_penalty(Full_Penalty);
437 }
438 
439 void ShenandoahHeuristics::record_allocation_failure_gc() {
440   // Do nothing.

460 }
461 
462 bool ShenandoahHeuristics::should_unload_classes() {
463   if (!can_unload_classes_normal()) return false;
464   if (has_metaspace_oom()) return true;
465   size_t cycle = ShenandoahHeap::heap()->shenandoah_policy()->cycle_counter();
466   // Unload classes every Nth GC cycle.
467   // This should not happen in the same cycle as process_references to amortize costs.
468   // Offsetting by one is enough to break the rendezvous when periods are equal.
469   // When periods are not equal, offsetting by one is just as good as any other guess.
470   return (cycle + 1) % ShenandoahUnloadClassesFrequency == 0;
471 }
472 
473 void ShenandoahHeuristics::initialize() {
474   // Nothing to do by default.
475 }
476 
477 double ShenandoahHeuristics::time_since_last_gc() const {
478   return os::elapsedTime() - _cycle_start;
479 }
480 
481 bool ShenandoahHeuristics::in_generation(ShenandoahHeapRegion* region) {
482   return ((_generation->generation_mode() == GLOBAL)
483           || (_generation->generation_mode() == YOUNG && region->affiliation() == YOUNG_GENERATION)
484           || (_generation->generation_mode() == OLD && region->affiliation() == OLD_GENERATION));
485 }
486 
487 void ShenandoahHeuristics::save_last_live_memory(size_t live_memory) {
488   _live_memory_penultimate_cycle = _live_memory_last_cycle;
489   _live_memory_last_cycle = live_memory;
490 }
491 
492 size_t ShenandoahHeuristics::get_last_live_memory() {
493   return _live_memory_last_cycle;
494 }
495 
496 size_t ShenandoahHeuristics::get_penultimate_live_memory() {
497   return _live_memory_penultimate_cycle;
498 }
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