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/shenandoah/heuristics/shenandoahAdaptiveHeuristics.hpp"
27 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
28 #include "gc/shenandoah/shenandoahFreeSet.hpp"
29 #include "gc/shenandoah/shenandoahHeapRegion.hpp"
30 #include "logging/log.hpp"
31 #include "logging/logTag.hpp"
32 #include "utilities/quickSort.hpp"
33
34 ShenandoahAdaptiveHeuristics::ShenandoahAdaptiveHeuristics() :
35 ShenandoahHeuristics(),
36 _cycle_gap_history(new TruncatedSeq(5)),
37 _conc_mark_duration_history(new TruncatedSeq(5)),
38 _conc_uprefs_duration_history(new TruncatedSeq(5)) {}
39
40 ShenandoahAdaptiveHeuristics::~ShenandoahAdaptiveHeuristics() {}
41
42 void ShenandoahAdaptiveHeuristics::choose_collection_set_from_regiondata(ShenandoahCollectionSet* cset,
43 RegionData* data, size_t size,
44 size_t actual_free) {
45 size_t garbage_threshold = ShenandoahHeapRegion::region_size_bytes() * ShenandoahGarbageThreshold / 100;
46
47 // The logic for cset selection in adaptive is as follows:
48 //
49 // 1. We cannot get cset larger than available free space. Otherwise we guarantee OOME
50 // during evacuation, and thus guarantee full GC. In practice, we also want to let
51 // application to allocate something. This is why we limit CSet to some fraction of
52 // available space. In non-overloaded heap, max_cset would contain all plausible candidates
53 // over garbage threshold.
54 //
55 // 2. We should not get cset too low so that free threshold would not be met right
56 // after the cycle. Otherwise we get back-to-back cycles for no reason if heap is
57 // too fragmented. In non-overloaded non-fragmented heap min_garbage would be around zero.
58 //
59 // Therefore, we start by sorting the regions by garbage. Then we unconditionally add the best candidates
60 // before we meet min_garbage. Then we add all candidates that fit with a garbage threshold before
61 // we hit max_cset. When max_cset is hit, we terminate the cset selection. Note that in this scheme,
62 // ShenandoahGarbageThreshold is the soft threshold which would be ignored until min_garbage is hit.
63
64 size_t capacity = ShenandoahHeap::heap()->max_capacity();
65 size_t free_target = capacity / 100 * ShenandoahMinFreeThreshold;
66 size_t min_garbage = free_target > actual_free ? (free_target - actual_free) : 0;
67 size_t max_cset = (size_t)((1.0 * capacity / 100 * ShenandoahEvacReserve) / ShenandoahEvacWaste);
68
69 log_info(gc, ergo)("Adaptive CSet Selection. Target Free: " SIZE_FORMAT "%s, Actual Free: "
70 SIZE_FORMAT "%s, Max CSet: " SIZE_FORMAT "%s, Min Garbage: " SIZE_FORMAT "%s",
71 byte_size_in_proper_unit(free_target), proper_unit_for_byte_size(free_target),
72 byte_size_in_proper_unit(actual_free), proper_unit_for_byte_size(actual_free),
73 byte_size_in_proper_unit(max_cset), proper_unit_for_byte_size(max_cset),
74 byte_size_in_proper_unit(min_garbage), proper_unit_for_byte_size(min_garbage));
75
76 // Better select garbage-first regions
77 QuickSort::sort<RegionData>(data, (int)size, compare_by_garbage, false);
78
79 size_t cur_cset = 0;
80 size_t cur_garbage = 0;
81 _bytes_in_cset = 0;
82
83 for (size_t idx = 0; idx < size; idx++) {
84 ShenandoahHeapRegion* r = data[idx]._region;
85
86 size_t new_cset = cur_cset + r->get_live_data_bytes();
87 size_t new_garbage = cur_garbage + r->garbage();
88
89 if (new_cset > max_cset) {
90 break;
91 }
92
93 if ((new_garbage < min_garbage) || (r->garbage() > garbage_threshold)) {
94 cset->add_region(r);
95 _bytes_in_cset += r->used();
96 cur_cset = new_cset;
97 cur_garbage = new_garbage;
98 }
99 }
100 }
101
102 void ShenandoahAdaptiveHeuristics::record_cycle_start() {
103 ShenandoahHeuristics::record_cycle_start();
104 double last_cycle_gap = (_cycle_start - _last_cycle_end);
105 _cycle_gap_history->add(last_cycle_gap);
106 }
107
108 void ShenandoahAdaptiveHeuristics::record_phase_time(ShenandoahPhaseTimings::Phase phase, double secs) {
109 if (phase == ShenandoahPhaseTimings::conc_mark) {
110 _conc_mark_duration_history->add(secs);
111 } else if (phase == ShenandoahPhaseTimings::conc_update_refs) {
112 _conc_uprefs_duration_history->add(secs);
113 } // Else ignore
114 }
115
116 bool ShenandoahAdaptiveHeuristics::should_start_gc() const {
117 ShenandoahHeap* heap = ShenandoahHeap::heap();
118 size_t capacity = heap->max_capacity();
119 size_t available = heap->free_set()->available();
120
121 // Check if we are falling below the worst limit, time to trigger the GC, regardless of
122 // anything else.
123 size_t min_threshold = capacity / 100 * ShenandoahMinFreeThreshold;
124 if (available < min_threshold) {
125 log_info(gc)("Trigger: Free (" SIZE_FORMAT "%s) is below minimum threshold (" SIZE_FORMAT "%s)",
126 byte_size_in_proper_unit(available), proper_unit_for_byte_size(available),
127 byte_size_in_proper_unit(min_threshold), proper_unit_for_byte_size(min_threshold));
128 return true;
129 }
130
131 // Check if are need to learn a bit about the application
132 const size_t max_learn = ShenandoahLearningSteps;
133 if (_gc_times_learned < max_learn) {
134 size_t init_threshold = capacity / 100 * ShenandoahInitFreeThreshold;
135 if (available < init_threshold) {
136 log_info(gc)("Trigger: Learning " SIZE_FORMAT " of " SIZE_FORMAT ". Free (" SIZE_FORMAT "%s) is below initial threshold (" SIZE_FORMAT "%s)",
137 _gc_times_learned + 1, max_learn,
138 byte_size_in_proper_unit(available), proper_unit_for_byte_size(available),
139 byte_size_in_proper_unit(init_threshold), proper_unit_for_byte_size(init_threshold));
140 return true;
141 }
142 }
143
144 // Check if allocation headroom is still okay. This also factors in:
145 // 1. Some space to absorb allocation spikes
146 // 2. Accumulated penalties from Degenerated and Full GC
147
148 size_t allocation_headroom = available;
149
150 size_t spike_headroom = capacity / 100 * ShenandoahAllocSpikeFactor;
151 size_t penalties = capacity / 100 * _gc_time_penalties;
152
153 allocation_headroom -= MIN2(allocation_headroom, spike_headroom);
154 allocation_headroom -= MIN2(allocation_headroom, penalties);
155
156 // TODO: Allocation rate is way too averaged to be useful during state changes
157
158 double average_gc = _gc_time_history->avg();
159 double time_since_last = time_since_last_gc();
160 double allocation_rate = heap->bytes_allocated_since_gc_start() / time_since_last;
161
162 if (average_gc > allocation_headroom / allocation_rate) {
163 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)",
164 average_gc * 1000,
165 byte_size_in_proper_unit(allocation_rate), proper_unit_for_byte_size(allocation_rate),
166 byte_size_in_proper_unit(allocation_headroom), proper_unit_for_byte_size(allocation_headroom));
167 log_info(gc, ergo)("Free headroom: " SIZE_FORMAT "%s (free) - " SIZE_FORMAT "%s (spike) - " SIZE_FORMAT "%s (penalties) = " SIZE_FORMAT "%s",
168 byte_size_in_proper_unit(available), proper_unit_for_byte_size(available),
169 byte_size_in_proper_unit(spike_headroom), proper_unit_for_byte_size(spike_headroom),
170 byte_size_in_proper_unit(penalties), proper_unit_for_byte_size(penalties),
171 byte_size_in_proper_unit(allocation_headroom), proper_unit_for_byte_size(allocation_headroom));
172 return true;
173 }
174
175 return ShenandoahHeuristics::should_start_gc();
176 }
177
178 bool ShenandoahAdaptiveHeuristics::should_start_update_refs() {
179 if (! _update_refs_adaptive) {
180 return _update_refs_early;
181 }
182
183 double cycle_gap_avg = _cycle_gap_history->avg();
184 double conc_mark_avg = _conc_mark_duration_history->avg();
185 double conc_uprefs_avg = _conc_uprefs_duration_history->avg();
186
187 if (_update_refs_early) {
188 double threshold = ShenandoahMergeUpdateRefsMinGap / 100.0;
189 if (conc_mark_avg + conc_uprefs_avg > cycle_gap_avg * threshold) {
190 _update_refs_early = false;
191 }
192 } else {
193 double threshold = ShenandoahMergeUpdateRefsMaxGap / 100.0;
194 if (conc_mark_avg + conc_uprefs_avg < cycle_gap_avg * threshold) {
195 _update_refs_early = true;
196 }
197 }
198 return _update_refs_early;
199 }
200
201 const char* ShenandoahAdaptiveHeuristics::name() {
202 return "adaptive";
203 }
204
205 bool ShenandoahAdaptiveHeuristics::is_diagnostic() {
206 return false;
207 }
208
209 bool ShenandoahAdaptiveHeuristics::is_experimental() {
210 return false;
211 }