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.
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 23  */
 24 
 25 #include "precompiled.hpp"
 26 
 27 #include "gc/shenandoah/heuristics/shenandoahOldHeuristics.hpp"
 28 #include "gc/shenandoah/heuristics/shenandoahYoungHeuristics.hpp"
 29 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
 30 #include "gc/shenandoah/shenandoahGenerationalHeap.hpp"
 31 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
 32 #include "gc/shenandoah/shenandoahOldGeneration.hpp"
 33 #include "gc/shenandoah/shenandoahYoungGeneration.hpp"
 34 
 35 #include "utilities/quickSort.hpp"
 36 
 37 ShenandoahYoungHeuristics::ShenandoahYoungHeuristics(ShenandoahYoungGeneration* generation)
 38         : ShenandoahGenerationalHeuristics(generation) {
 39 }
 40 
 41 
 42 void ShenandoahYoungHeuristics::choose_collection_set_from_regiondata(ShenandoahCollectionSet* cset,
 43                                                                       RegionData* data, size_t size,
 44                                                                       size_t actual_free) {
 45   // See comments in ShenandoahAdaptiveHeuristics::choose_collection_set_from_regiondata():
 46   // we do the same here, but with the following adjustments for generational mode:
 47   //
 48   // In generational mode, the sort order within the data array is not strictly descending amounts
 49   // of garbage. In particular, regions that have reached tenure age will be sorted into this
 50   // array before younger regions that typically contain more garbage. This is one reason why,
 51   // for example, we continue examining regions even after rejecting a region that has
 52   // more live data than we can evacuate.
 53 
 54   // Better select garbage-first regions
 55   QuickSort::sort<RegionData>(data, (int) size, compare_by_garbage);
 56 
 57   size_t cur_young_garbage = add_preselected_regions_to_collection_set(cset, data, size);
 58 
 59   choose_young_collection_set(cset, data, size, actual_free, cur_young_garbage);
 60 
 61   log_cset_composition(cset);
 62 }
 63 
 64 void ShenandoahYoungHeuristics::choose_young_collection_set(ShenandoahCollectionSet* cset,
 65                                                             const RegionData* data,
 66                                                             size_t size, size_t actual_free,
 67                                                             size_t cur_young_garbage) const {
 68 
 69   auto heap = ShenandoahGenerationalHeap::heap();
 70 
 71   size_t capacity = heap->young_generation()->max_capacity();
 72   size_t garbage_threshold = ShenandoahHeapRegion::region_size_bytes() * ShenandoahGarbageThreshold / 100;
 73   size_t ignore_threshold = ShenandoahHeapRegion::region_size_bytes() * ShenandoahIgnoreGarbageThreshold / 100;
 74   const uint tenuring_threshold = heap->age_census()->tenuring_threshold();
 75 
 76   // This is young-gen collection or a mixed evacuation.
 77   // If this is mixed evacuation, the old-gen candidate regions have already been added.
 78   size_t max_cset = (size_t) (heap->young_generation()->get_evacuation_reserve() / ShenandoahEvacWaste);
 79   size_t cur_cset = 0;
 80   size_t free_target = (capacity * ShenandoahMinFreeThreshold) / 100 + max_cset;
 81   size_t min_garbage = (free_target > actual_free) ? (free_target - actual_free) : 0;
 82 
 83 
 84   log_info(gc, ergo)(
 85           "Adaptive CSet Selection for YOUNG. Max Evacuation: " SIZE_FORMAT "%s, Actual Free: " SIZE_FORMAT "%s.",
 86           byte_size_in_proper_unit(max_cset), proper_unit_for_byte_size(max_cset),
 87           byte_size_in_proper_unit(actual_free), proper_unit_for_byte_size(actual_free));
 88 
 89   for (size_t idx = 0; idx < size; idx++) {
 90     ShenandoahHeapRegion* r = data[idx].get_region();
 91     if (cset->is_preselected(r->index())) {
 92       continue;
 93     }
 94     if (r->age() < tenuring_threshold) {
 95       size_t new_cset = cur_cset + r->get_live_data_bytes();
 96       size_t region_garbage = r->garbage();
 97       size_t new_garbage = cur_young_garbage + region_garbage;
 98       bool add_regardless = (region_garbage > ignore_threshold) && (new_garbage < min_garbage);
 99       assert(r->is_young(), "Only young candidates expected in the data array");
100       if ((new_cset <= max_cset) && (add_regardless || (region_garbage > garbage_threshold))) {
101         cur_cset = new_cset;
102         cur_young_garbage = new_garbage;
103         cset->add_region(r);
104       }
105     }
106     // Note that we do not add aged regions if they were not pre-selected.  The reason they were not preselected
107     // is because there is not sufficient room in old-gen to hold their to-be-promoted live objects or because
108     // they are to be promoted in place.
109   }
110 }
111 
112 
113 bool ShenandoahYoungHeuristics::should_start_gc() {
114   auto heap = ShenandoahGenerationalHeap::heap();
115   ShenandoahOldHeuristics* old_heuristics = heap->old_generation()->heuristics();
116 
117   // Checks that an old cycle has run for at least ShenandoahMinimumOldMarkTimeMs before allowing a young cycle.
118   if (ShenandoahMinimumOldMarkTimeMs > 0 && heap->is_concurrent_old_mark_in_progress()) {
119     size_t old_mark_elapsed = size_t(old_heuristics->elapsed_cycle_time() * 1000);
120     if (old_mark_elapsed < ShenandoahMinimumOldMarkTimeMs) {
121       return false;
122     }
123   }
124 
125   // inherited triggers have already decided to start a cycle, so no further evaluation is required
126   if (ShenandoahAdaptiveHeuristics::should_start_gc()) {
127     return true;
128   }
129 
130   // Get through promotions and mixed evacuations as quickly as possible.  These cycles sometimes require significantly
131   // more time than traditional young-generation cycles so start them up as soon as possible.  This is a "mitigation"
132   // for the reality that old-gen and young-gen activities are not truly "concurrent".  If there is old-gen work to
133   // be done, we start up the young-gen GC threads so they can do some of this old-gen work.  As implemented, promotion
134   // gets priority over old-gen marking.
135   size_t promo_expedite_threshold = percent_of(heap->young_generation()->max_capacity(), ShenandoahExpeditePromotionsThreshold);
136   size_t promo_potential = heap->old_generation()->get_promotion_potential();
137   if (promo_potential > promo_expedite_threshold) {
138     // Detect unsigned arithmetic underflow
139     assert(promo_potential < heap->capacity(), "Sanity");
140     log_info(gc)("Trigger (%s): expedite promotion of " SIZE_FORMAT "%s",
141                  _space_info->name(),
142                  byte_size_in_proper_unit(promo_potential),
143                  proper_unit_for_byte_size(promo_potential));
144     return true;
145   }
146 
147   size_t mixed_candidates = old_heuristics->unprocessed_old_collection_candidates();
148   if (mixed_candidates > ShenandoahExpediteMixedThreshold && !heap->is_concurrent_weak_root_in_progress()) {
149     // We need to run young GC in order to open up some free heap regions so we can finish mixed evacuations.
150     // If concurrent weak root processing is in progress, it means the old cycle has chosen mixed collection
151     // candidates, but has not completed. There is no point in trying to start the young cycle before the old
152     // cycle completes.
153     log_info(gc)("Trigger (%s): expedite mixed evacuation of " SIZE_FORMAT " regions",
154                  _space_info->name(), mixed_candidates);
155     return true;
156   }
157 
158   return false;
159 }
160 
161 // Return a conservative estimate of how much memory can be allocated before we need to start GC. The estimate is based
162 // on memory that is currently available within young generation plus all of the memory that will be added to the young
163 // generation at the end of the current cycle (as represented by young_regions_to_be_reclaimed) and on the anticipated
164 // amount of time required to perform a GC.
165 size_t ShenandoahYoungHeuristics::bytes_of_allocation_runway_before_gc_trigger(size_t young_regions_to_be_reclaimed) {
166   size_t capacity = _space_info->max_capacity();
167   size_t usage = _space_info->used();
168   size_t available = (capacity > usage)? capacity - usage: 0;
169   size_t allocated = _space_info->bytes_allocated_since_gc_start();
170 
171   size_t available_young_collected = ShenandoahHeap::heap()->collection_set()->get_young_available_bytes_collected();
172   size_t anticipated_available =
173           available + young_regions_to_be_reclaimed * ShenandoahHeapRegion::region_size_bytes() - available_young_collected;
174   size_t spike_headroom = capacity * ShenandoahAllocSpikeFactor / 100;
175   size_t penalties      = capacity * _gc_time_penalties / 100;
176 
177   double rate = _allocation_rate.sample(allocated);
178 
179   // At what value of available, would avg and spike triggers occur?
180   //  if allocation_headroom < avg_cycle_time * avg_alloc_rate, then we experience avg trigger
181   //  if allocation_headroom < avg_cycle_time * rate, then we experience spike trigger if is_spiking
182   //
183   // allocation_headroom =
184   //     0, if penalties > available or if penalties + spike_headroom > available
185   //     available - penalties - spike_headroom, otherwise
186   //
187   // so we trigger if available - penalties - spike_headroom < avg_cycle_time * avg_alloc_rate, which is to say
188   //                  available < avg_cycle_time * avg_alloc_rate + penalties + spike_headroom
189   //            or if available < penalties + spike_headroom
190   //
191   // since avg_cycle_time * avg_alloc_rate > 0, the first test is sufficient to test both conditions
192   //
193   // thus, evac_slack_avg is MIN2(0,  available - avg_cycle_time * avg_alloc_rate + penalties + spike_headroom)
194   //
195   // similarly, evac_slack_spiking is MIN2(0, available - avg_cycle_time * rate + penalties + spike_headroom)
196   // but evac_slack_spiking is only relevant if is_spiking, as defined below.
197 
198   double avg_cycle_time = _gc_cycle_time_history->davg() + (_margin_of_error_sd * _gc_cycle_time_history->dsd());
199   double avg_alloc_rate = _allocation_rate.upper_bound(_margin_of_error_sd);
200   size_t evac_slack_avg;
201   if (anticipated_available > avg_cycle_time * avg_alloc_rate + penalties + spike_headroom) {
202     evac_slack_avg = anticipated_available - (avg_cycle_time * avg_alloc_rate + penalties + spike_headroom);
203   } else {
204     // we have no slack because it's already time to trigger
205     evac_slack_avg = 0;
206   }
207 
208   bool is_spiking = _allocation_rate.is_spiking(rate, _spike_threshold_sd);
209   size_t evac_slack_spiking;
210   if (is_spiking) {
211     if (anticipated_available > avg_cycle_time * rate + penalties + spike_headroom) {
212       evac_slack_spiking = anticipated_available - (avg_cycle_time * rate + penalties + spike_headroom);
213     } else {
214       // we have no slack because it's already time to trigger
215       evac_slack_spiking = 0;
216     }
217   } else {
218     evac_slack_spiking = evac_slack_avg;
219   }
220 
221   size_t threshold = min_free_threshold();
222   size_t evac_min_threshold = (anticipated_available > threshold)? anticipated_available - threshold: 0;
223   return MIN3(evac_slack_spiking, evac_slack_avg, evac_min_threshold);
224 }
225