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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(nullptr),
 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.
252 }
253 
254 void ShenandoahHeuristics::record_requested_gc() {
255   // Assume users call System.gc() when external state changes significantly,
256   // which forces us to re-learn the GC timings and allocation rates.




257   _gc_times_learned = 0;
258 }
259 
260 bool ShenandoahHeuristics::can_unload_classes() {
261   if (!ClassUnloading) return false;
262   return true;
263 }
264 
265 bool ShenandoahHeuristics::can_unload_classes_normal() {
266   if (!can_unload_classes()) return false;
267   if (has_metaspace_oom()) return true;
268   if (!ClassUnloadingWithConcurrentMark) return false;
269   if (ShenandoahUnloadClassesFrequency == 0) return false;
270   return true;
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(nullptr),
 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_cycle_time_history(new TruncatedSeq(Moving_Average_Samples, ShenandoahAdaptiveDecayFactor)),
 61   _metaspace_oom()
 62 {
 63   // No unloading during concurrent mark? Communicate that to heuristics
 64   if (!ClassUnloadingWithConcurrentMark) {
 65     FLAG_SET_DEFAULT(ShenandoahUnloadClassesFrequency, 0);
 66   }
 67 
 68   size_t num_regions = ShenandoahHeap::heap()->num_regions();
 69   assert(num_regions > 0, "Sanity");
 70 
 71   _region_data = NEW_C_HEAP_ARRAY(RegionData, num_regions, mtGC);
 72 }
 73 
 74 ShenandoahHeuristics::~ShenandoahHeuristics() {
 75   FREE_C_HEAP_ARRAY(RegionGarbage, _region_data);
 76 }
 77 
 78 size_t ShenandoahHeuristics::select_aged_regions(size_t old_available, size_t num_regions, bool preselected_regions[]) {
 79   ShenandoahHeap* heap = ShenandoahHeap::heap();
 80   size_t old_consumed = 0;
 81   if (heap->mode()->is_generational()) {
 82     for (size_t i = 0; i < num_regions; i++) {
 83       ShenandoahHeapRegion* region = heap->get_region(i);
 84       if (in_generation(region) && !region->is_empty() && region->is_regular() && (region->age() >= InitialTenuringThreshold)) {
 85         size_t promotion_need = (size_t) (region->get_live_data_bytes() * ShenandoahEvacWaste);
 86         if (old_consumed + promotion_need < old_available) {
 87           old_consumed += promotion_need;
 88           preselected_regions[i] = true;
 89         }
 90         // Note that we keep going even if one region is excluded from selection.  Subsequent regions may be selected
 91         // if they have smaller live data.
 92       }
 93     }
 94   }
 95   return old_consumed;
 96 }
 97 
 98 void ShenandoahHeuristics::choose_collection_set(ShenandoahCollectionSet* collection_set, ShenandoahOldHeuristics* old_heuristics) {
 99   ShenandoahHeap* heap = ShenandoahHeap::heap();
100   bool is_generational = heap->mode()->is_generational();
101 
102   assert(collection_set->count() == 0, "Must be empty");
103   assert(_generation->generation_mode() != OLD, "Old GC invokes ShenandoahOldHeuristics::choose_collection_set()");
104 
105   // Check all pinned regions have updated status before choosing the collection set.
106   heap->assert_pinned_region_status();
107 
108   // Step 1. Build up the region candidates we care about, rejecting losers and accepting winners right away.
109 
110   size_t num_regions = heap->num_regions();
111 
112   RegionData* candidates = _region_data;
113 
114   size_t cand_idx = 0;
115 
116   size_t total_garbage = 0;
117 
118   size_t immediate_garbage = 0;
119   size_t immediate_regions = 0;
120 
121   size_t free = 0;
122   size_t free_regions = 0;
123   size_t live_memory = 0;

124 
125   for (size_t i = 0; i < num_regions; i++) {
126     ShenandoahHeapRegion* region = heap->get_region(i);
127     if (is_generational && !in_generation(region)) {
128       continue;
129     }
130 
131     size_t garbage = region->garbage();
132     total_garbage += garbage;

133     if (region->is_empty()) {
134       free_regions++;
135       free += ShenandoahHeapRegion::region_size_bytes();
136     } else if (region->is_regular()) {
137       if (!region->has_live()) {
138         // We can recycle it right away and put it in the free set.
139         immediate_regions++;
140         immediate_garbage += garbage;
141         region->make_trash_immediate();
142       } else {
143         assert (_generation->generation_mode() != OLD, "OLD is handled elsewhere");
144         live_memory += region->get_live_data_bytes();
145         // This is our candidate for later consideration.
146         candidates[cand_idx]._region = region;
147         if (is_generational && collection_set->is_preselected(i)) {
148           // If region is preselected, we know mode()->is_generational() and region->age() >= InitialTenuringThreshold)
149           garbage = ShenandoahHeapRegion::region_size_bytes();
150         }
151         candidates[cand_idx]._garbage = garbage;
152         cand_idx++;
153       }
154     } else if (region->is_humongous_start()) {
155 
156       // Reclaim humongous regions here, and count them as the immediate garbage
157 #ifdef ASSERT
158       bool reg_live = region->has_live();
159       bool bm_live = heap->complete_marking_context()->is_marked(cast_to_oop(region->bottom()));
160       assert(reg_live == bm_live,
161              "Humongous liveness and marks should agree. Region live: %s; Bitmap live: %s; Region Live Words: " SIZE_FORMAT,
162              BOOL_TO_STR(reg_live), BOOL_TO_STR(bm_live), region->get_live_data_words());
163 #endif
164       if (!region->has_live()) {
165         heap->trash_humongous_region_at(region);
166 
167         // Count only the start. Continuations would be counted on "trash" path
168         immediate_regions++;
169         immediate_garbage += garbage;
170       } else {
171         live_memory += region->get_live_data_bytes();
172       }
173     } else if (region->is_trash()) {
174       // Count in just trashed collection set, during coalesced CM-with-UR
175       immediate_regions++;
176       immediate_garbage += garbage;
177     } else {                      // region->is_humongous_cont() and !region->is_trash()
178       live_memory += region->get_live_data_bytes();
179     }
180   }
181 
182   // Step 2. Look back at garbage statistics, and decide if we want to collect anything,
183   // given the amount of immediately reclaimable garbage. If we do, figure out the collection set.
184 
185   assert (immediate_garbage <= total_garbage,
186           "Cannot have more immediate garbage than total garbage: " SIZE_FORMAT "%s vs " SIZE_FORMAT "%s",
187           byte_size_in_proper_unit(immediate_garbage), proper_unit_for_byte_size(immediate_garbage),
188           byte_size_in_proper_unit(total_garbage),     proper_unit_for_byte_size(total_garbage));
189 
190   size_t immediate_percent = (total_garbage == 0) ? 0 : (immediate_garbage * 100 / total_garbage);
191   collection_set->set_immediate_trash(immediate_garbage);
192 
193   if (immediate_percent <= ShenandoahImmediateThreshold) {
194     if (old_heuristics != nullptr) {
195       old_heuristics->prime_collection_set(collection_set);
196     }
197     // else, this is global collection and doesn't need to prime_collection_set
198 
199     // Add young-gen regions into the collection set.  This is a virtual call, implemented differently by each
200     // of the heuristics subclasses.
201     choose_collection_set_from_regiondata(collection_set, candidates, cand_idx, immediate_garbage + free);
202   } else {
203     // we're going to skip evacuation and update refs because we reclaimed sufficient amounts of immediate garbage.
204     heap->shenandoah_policy()->record_abbreviated_cycle();
205   }
206 
207   if (collection_set->has_old_regions()) {
208     heap->shenandoah_policy()->record_mixed_cycle();
209   }
210 
211   size_t cset_percent = (total_garbage == 0) ? 0 : (collection_set->garbage() * 100 / total_garbage);
212   size_t collectable_garbage = collection_set->garbage() + immediate_garbage;
213   size_t collectable_garbage_percent = (total_garbage == 0) ? 0 : (collectable_garbage * 100 / total_garbage);
214 
215   log_info(gc, ergo)("Collectable Garbage: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), "
216                      "Immediate: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%) R: " SIZE_FORMAT ", "
217                      "CSet: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%) R: " SIZE_FORMAT,
218 
219                      byte_size_in_proper_unit(collectable_garbage),
220                      proper_unit_for_byte_size(collectable_garbage),
221                      collectable_garbage_percent,
222 
223                      byte_size_in_proper_unit(immediate_garbage),
224                      proper_unit_for_byte_size(immediate_garbage),
225                      immediate_percent,
226                      immediate_regions,
227 
228                      byte_size_in_proper_unit(collection_set->garbage()),
229                      proper_unit_for_byte_size(collection_set->garbage()),
230                      cset_percent,
231                      collection_set->count());
232 
233   if (collection_set->garbage() > 0) {
234     size_t young_evac_bytes = collection_set->get_young_bytes_reserved_for_evacuation();
235     size_t promote_evac_bytes = collection_set->get_young_bytes_to_be_promoted();
236     size_t old_evac_bytes = collection_set->get_old_bytes_reserved_for_evacuation();
237     size_t total_evac_bytes = young_evac_bytes + promote_evac_bytes + old_evac_bytes;
238     log_info(gc, ergo)("Evacuation Targets: YOUNG: " SIZE_FORMAT "%s, "
239                        "PROMOTE: " SIZE_FORMAT "%s, "
240                        "OLD: " SIZE_FORMAT "%s, "
241                        "TOTAL: " SIZE_FORMAT "%s",
242                        byte_size_in_proper_unit(young_evac_bytes), proper_unit_for_byte_size(young_evac_bytes),
243                        byte_size_in_proper_unit(promote_evac_bytes), proper_unit_for_byte_size(promote_evac_bytes),
244                        byte_size_in_proper_unit(old_evac_bytes), proper_unit_for_byte_size(old_evac_bytes),
245                        byte_size_in_proper_unit(total_evac_bytes), proper_unit_for_byte_size(total_evac_bytes));
246   }
247 }
248 
249 void ShenandoahHeuristics::record_cycle_start() {
250   _cycle_start = os::elapsedTime();
251 }
252 
253 void ShenandoahHeuristics::record_cycle_end() {
254   _last_cycle_end = os::elapsedTime();
255 }
256 
257 bool ShenandoahHeuristics::should_start_gc() {
258   // Perform GC to cleanup metaspace
259   if (has_metaspace_oom()) {
260     // Some of vmTestbase/metaspace tests depend on following line to count GC cycles
261     log_info(gc)("Trigger: %s", GCCause::to_string(GCCause::_metadata_GC_threshold));
262     return true;
263   }
264 
265   if (_guaranteed_gc_interval > 0) {
266     double last_time_ms = (os::elapsedTime() - _last_cycle_end) * 1000;
267     if (last_time_ms > _guaranteed_gc_interval) {
268       log_info(gc)("Trigger (%s): Time since last GC (%.0f ms) is larger than guaranteed interval (" UINTX_FORMAT " ms)",
269                    _generation->name(), last_time_ms, _guaranteed_gc_interval);
270       return true;
271     }
272   }
273 
274   return false;
275 }
276 
277 bool ShenandoahHeuristics::should_degenerate_cycle() {
278   return _degenerated_cycles_in_a_row <= ShenandoahFullGCThreshold;
279 }
280 
281 void ShenandoahHeuristics::adjust_penalty(intx step) {
282   assert(0 <= _gc_time_penalties && _gc_time_penalties <= 100,
283          "In range before adjustment: " INTX_FORMAT, _gc_time_penalties);
284 
285   intx new_val = _gc_time_penalties + step;
286   if (new_val < 0) {
287     new_val = 0;
288   }
289   if (new_val > 100) {
290     new_val = 100;
291   }
292   _gc_time_penalties = new_val;
293 
294   assert(0 <= _gc_time_penalties && _gc_time_penalties <= 100,
295          "In range after adjustment: " INTX_FORMAT, _gc_time_penalties);
296 }
297 
298 void ShenandoahHeuristics::record_success_concurrent(bool abbreviated) {
299   _degenerated_cycles_in_a_row = 0;
300   _successful_cycles_in_a_row++;
301 
302   if (!(abbreviated && ShenandoahAdaptiveIgnoreShortCycles)) {
303     _gc_cycle_time_history->add(elapsed_cycle_time());
304     _gc_times_learned++;
305   }
306 
307   adjust_penalty(Concurrent_Adjust);
308 }
309 
310 void ShenandoahHeuristics::record_success_degenerated() {
311   _degenerated_cycles_in_a_row++;
312   _successful_cycles_in_a_row = 0;
313 
314   adjust_penalty(Degenerated_Penalty);
315 }
316 
317 void ShenandoahHeuristics::record_success_full() {
318   _degenerated_cycles_in_a_row = 0;
319   _successful_cycles_in_a_row++;
320 
321   adjust_penalty(Full_Penalty);
322 }
323 
324 void ShenandoahHeuristics::record_allocation_failure_gc() {
325   // Do nothing.
326 }
327 
328 void ShenandoahHeuristics::record_requested_gc() {
329   // Assume users call System.gc() when external state changes significantly,
330   // which forces us to re-learn the GC timings and allocation rates.
331   reset_gc_learning();
332 }
333 
334 void ShenandoahHeuristics::reset_gc_learning() {
335   _gc_times_learned = 0;
336 }
337 
338 bool ShenandoahHeuristics::can_unload_classes() {
339   if (!ClassUnloading) return false;
340   return true;
341 }
342 
343 bool ShenandoahHeuristics::can_unload_classes_normal() {
344   if (!can_unload_classes()) return false;
345   if (has_metaspace_oom()) return true;
346   if (!ClassUnloadingWithConcurrentMark) return false;
347   if (ShenandoahUnloadClassesFrequency == 0) return false;
348   return true;
349 }
350 
351 bool ShenandoahHeuristics::should_unload_classes() {
352   if (!can_unload_classes_normal()) return false;
353   if (has_metaspace_oom()) return true;
354   size_t cycle = ShenandoahHeap::heap()->shenandoah_policy()->cycle_counter();
355   // Unload classes every Nth GC cycle.
356   // This should not happen in the same cycle as process_references to amortize costs.
357   // Offsetting by one is enough to break the rendezvous when periods are equal.
358   // When periods are not equal, offsetting by one is just as good as any other guess.
359   return (cycle + 1) % ShenandoahUnloadClassesFrequency == 0;
360 }
361 
362 void ShenandoahHeuristics::initialize() {
363   // Nothing to do by default.
364 }
365 
366 double ShenandoahHeuristics::elapsed_cycle_time() const {
367   return os::elapsedTime() - _cycle_start;
368 }
369 
370 bool ShenandoahHeuristics::in_generation(ShenandoahHeapRegion* region) {
371   return ((_generation->generation_mode() == GLOBAL)
372           || (_generation->generation_mode() == YOUNG && region->affiliation() == YOUNG_GENERATION)
373           || (_generation->generation_mode() == OLD && region->affiliation() == OLD_GENERATION));
374 }
375 
376 size_t ShenandoahHeuristics::min_free_threshold() {
377   size_t min_free_threshold =
378       _generation->generation_mode() == GenerationMode::OLD
379           ? ShenandoahOldMinFreeThreshold
380           : ShenandoahMinFreeThreshold;
381   return _generation->soft_max_capacity() / 100 * min_free_threshold;
382 }
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