1 /*
   2  * Copyright (c) 2018, Red Hat, Inc. All rights reserved.
   3  *
   4  * This code is free software; you can redistribute it and/or modify it
   5  * under the terms of the GNU General Public License version 2 only, as
   6  * published by the Free Software Foundation.
   7  *
   8  * This code is distributed in the hope that it will be useful, but WITHOUT
   9  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  10  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  11  * version 2 for more details (a copy is included in the LICENSE file that
  12  * accompanied this code).
  13  *
  14  * You should have received a copy of the GNU General Public License version
  15  * 2 along with this work; if not, write to the Free Software Foundation,
  16  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  17  *
  18  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  19  * or visit www.oracle.com if you need additional information or have any
  20  * questions.
  21  *
  22  */
  23 
  24 #include "precompiled.hpp"
  25 
  26 #include "gc_implementation/shenandoah/heuristics/shenandoahAdaptiveHeuristics.hpp"
  27 #include "gc_implementation/shenandoah/shenandoahCollectionSet.hpp"
  28 #include "gc_implementation/shenandoah/shenandoahFreeSet.hpp"
  29 #include "gc_implementation/shenandoah/shenandoahHeapRegion.hpp"
  30 #include "gc_implementation/shenandoah/shenandoahLogging.hpp"
  31 #include "utilities/quickSort.hpp"
  32 
  33 ShenandoahAdaptiveHeuristics::ShenandoahAdaptiveHeuristics() :
  34   ShenandoahHeuristics(),
  35   _cycle_gap_history(new TruncatedSeq(5)),
  36   _conc_mark_duration_history(new TruncatedSeq(5)),
  37   _conc_uprefs_duration_history(new TruncatedSeq(5)) {}
  38 
  39 ShenandoahAdaptiveHeuristics::~ShenandoahAdaptiveHeuristics() {}
  40 
  41 void ShenandoahAdaptiveHeuristics::choose_collection_set_from_regiondata(ShenandoahCollectionSet* cset,
  42                                                                          RegionData* data, size_t size,
  43                                                                          size_t actual_free) {
  44   size_t garbage_threshold = ShenandoahHeapRegion::region_size_bytes() * ShenandoahGarbageThreshold / 100;
  45 
  46   // The logic for cset selection in adaptive is as follows:
  47   //
  48   //   1. We cannot get cset larger than available free space. Otherwise we guarantee OOME
  49   //      during evacuation, and thus guarantee full GC. In practice, we also want to let
  50   //      application to allocate something. This is why we limit CSet to some fraction of
  51   //      available space. In non-overloaded heap, max_cset would contain all plausible candidates
  52   //      over garbage threshold.
  53   //
  54   //   2. We should not get cset too low so that free threshold would not be met right
  55   //      after the cycle. Otherwise we get back-to-back cycles for no reason if heap is
  56   //      too fragmented. In non-overloaded non-fragmented heap min_garbage would be around zero.
  57   //
  58   // Therefore, we start by sorting the regions by garbage. Then we unconditionally add the best candidates
  59   // before we meet min_garbage. Then we add all candidates that fit with a garbage threshold before
  60   // we hit max_cset. When max_cset is hit, we terminate the cset selection. Note that in this scheme,
  61   // ShenandoahGarbageThreshold is the soft threshold which would be ignored until min_garbage is hit.
  62 
  63   size_t capacity    = ShenandoahHeap::heap()->max_capacity();
  64   size_t free_target = capacity / 100 * ShenandoahMinFreeThreshold;
  65   size_t min_garbage = free_target > actual_free ? (free_target - actual_free) : 0;
  66   size_t max_cset    = (size_t)((1.0 * capacity / 100 * ShenandoahEvacReserve) / ShenandoahEvacWaste);
  67 
  68   log_info(gc, ergo)("Adaptive CSet Selection. Target Free: " SIZE_FORMAT "%s, Actual Free: "
  69                      SIZE_FORMAT "%s, Max CSet: " SIZE_FORMAT "%s, Min Garbage: " SIZE_FORMAT "%s",
  70                      byte_size_in_proper_unit(free_target), proper_unit_for_byte_size(free_target),
  71                      byte_size_in_proper_unit(actual_free), proper_unit_for_byte_size(actual_free),
  72                      byte_size_in_proper_unit(max_cset),    proper_unit_for_byte_size(max_cset),
  73                      byte_size_in_proper_unit(min_garbage), proper_unit_for_byte_size(min_garbage));
  74 
  75   // Better select garbage-first regions
  76   QuickSort::sort<RegionData>(data, (int)size, compare_by_garbage, false);
  77 
  78   size_t cur_cset = 0;
  79   size_t cur_garbage = 0;
  80   _bytes_in_cset = 0;
  81 
  82   for (size_t idx = 0; idx < size; idx++) {
  83     ShenandoahHeapRegion* r = data[idx]._region;
  84 
  85     size_t new_cset    = cur_cset + r->get_live_data_bytes();
  86     size_t new_garbage = cur_garbage + r->garbage();
  87 
  88     if (new_cset > max_cset) {
  89       break;
  90     }
  91 
  92     if ((new_garbage < min_garbage) || (r->garbage() > garbage_threshold)) {
  93       cset->add_region(r);
  94       _bytes_in_cset += r->used();
  95       cur_cset = new_cset;
  96       cur_garbage = new_garbage;
  97     }
  98   }
  99 }
 100 
 101 void ShenandoahAdaptiveHeuristics::record_cycle_start() {
 102   ShenandoahHeuristics::record_cycle_start();
 103   double last_cycle_gap = (_cycle_start - _last_cycle_end);
 104   _cycle_gap_history->add(last_cycle_gap);
 105 }
 106 
 107 void ShenandoahAdaptiveHeuristics::record_phase_time(ShenandoahPhaseTimings::Phase phase, double secs) {
 108   if (phase == ShenandoahPhaseTimings::conc_mark) {
 109     _conc_mark_duration_history->add(secs);
 110   } else if (phase == ShenandoahPhaseTimings::conc_update_refs) {
 111     _conc_uprefs_duration_history->add(secs);
 112   } // Else ignore
 113 }
 114 
 115 bool ShenandoahAdaptiveHeuristics::should_start_gc() const {
 116   ShenandoahHeap* heap = ShenandoahHeap::heap();
 117   size_t capacity = heap->max_capacity();
 118   size_t available = heap->free_set()->available();
 119 
 120   // Check if we are falling below the worst limit, time to trigger the GC, regardless of
 121   // anything else.
 122   size_t min_threshold = capacity / 100 * ShenandoahMinFreeThreshold;
 123   if (available < min_threshold) {
 124     log_info(gc)("Trigger: Free (" SIZE_FORMAT "%s) is below minimum threshold (" SIZE_FORMAT "%s)",
 125                  byte_size_in_proper_unit(available),     proper_unit_for_byte_size(available),
 126                  byte_size_in_proper_unit(min_threshold), proper_unit_for_byte_size(min_threshold));
 127     return true;
 128   }
 129 
 130   // Check if are need to learn a bit about the application
 131   const size_t max_learn = ShenandoahLearningSteps;
 132   if (_gc_times_learned < max_learn) {
 133     size_t init_threshold = capacity / 100 * ShenandoahInitFreeThreshold;
 134     if (available < init_threshold) {
 135       log_info(gc)("Trigger: Learning " SIZE_FORMAT " of " SIZE_FORMAT ". Free (" SIZE_FORMAT "%s) is below initial threshold (" SIZE_FORMAT "%s)",
 136                    _gc_times_learned + 1, max_learn,
 137                    byte_size_in_proper_unit(available),      proper_unit_for_byte_size(available),
 138                    byte_size_in_proper_unit(init_threshold), proper_unit_for_byte_size(init_threshold));
 139       return true;
 140     }
 141   }
 142 
 143   // Check if allocation headroom is still okay. This also factors in:
 144   //   1. Some space to absorb allocation spikes
 145   //   2. Accumulated penalties from Degenerated and Full GC
 146 
 147   size_t allocation_headroom = available;
 148 
 149   size_t spike_headroom = capacity / 100 * ShenandoahAllocSpikeFactor;
 150   size_t penalties      = capacity / 100 * _gc_time_penalties;
 151 
 152   allocation_headroom -= MIN2(allocation_headroom, spike_headroom);
 153   allocation_headroom -= MIN2(allocation_headroom, penalties);
 154 
 155   // TODO: Allocation rate is way too averaged to be useful during state changes
 156 
 157   double average_gc = _gc_time_history->avg();
 158   double time_since_last = time_since_last_gc();
 159   double allocation_rate = heap->bytes_allocated_since_gc_start() / time_since_last;
 160 
 161   if (average_gc > allocation_headroom / allocation_rate) {
 162     log_info(gc)("Trigger: Average GC time (%.2f ms) is above the time for allocation rate (%.0f %sB/s) to deplete free headroom (" SIZE_FORMAT "%s)",
 163                  average_gc * 1000,
 164                  byte_size_in_proper_unit(allocation_rate),     proper_unit_for_byte_size(allocation_rate),
 165                  byte_size_in_proper_unit(allocation_headroom), proper_unit_for_byte_size(allocation_headroom));
 166     log_info(gc, ergo)("Free headroom: " SIZE_FORMAT "%s (free) - " SIZE_FORMAT "%s (spike) - " SIZE_FORMAT "%s (penalties) = " SIZE_FORMAT "%s",
 167                  byte_size_in_proper_unit(available),           proper_unit_for_byte_size(available),
 168                  byte_size_in_proper_unit(spike_headroom),      proper_unit_for_byte_size(spike_headroom),
 169                  byte_size_in_proper_unit(penalties),           proper_unit_for_byte_size(penalties),
 170                  byte_size_in_proper_unit(allocation_headroom), proper_unit_for_byte_size(allocation_headroom));
 171     return true;
 172   }
 173 
 174   return ShenandoahHeuristics::should_start_gc();
 175 }
 176 
 177 bool ShenandoahAdaptiveHeuristics::should_start_update_refs() {
 178   if (! _update_refs_adaptive) {
 179     return _update_refs_early;
 180   }
 181 
 182   double cycle_gap_avg = _cycle_gap_history->avg();
 183   double conc_mark_avg = _conc_mark_duration_history->avg();
 184   double conc_uprefs_avg = _conc_uprefs_duration_history->avg();
 185 
 186   if (_update_refs_early) {
 187     double threshold = ShenandoahMergeUpdateRefsMinGap / 100.0;
 188     if (conc_mark_avg + conc_uprefs_avg > cycle_gap_avg * threshold) {
 189       _update_refs_early = false;
 190     }
 191   } else {
 192     double threshold = ShenandoahMergeUpdateRefsMaxGap / 100.0;
 193     if (conc_mark_avg + conc_uprefs_avg < cycle_gap_avg * threshold) {
 194       _update_refs_early = true;
 195     }
 196   }
 197   return _update_refs_early;
 198 }
 199 
 200 const char* ShenandoahAdaptiveHeuristics::name() {
 201   return "adaptive";
 202 }
 203 
 204 bool ShenandoahAdaptiveHeuristics::is_diagnostic() {
 205   return false;
 206 }
 207 
 208 bool ShenandoahAdaptiveHeuristics::is_experimental() {
 209   return false;
 210 }