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