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 // Final configuration checks
44 SHENANDOAH_CHECK_FLAG_SET(ShenandoahSATBBarrier);
45 SHENANDOAH_CHECK_FLAG_SET(ShenandoahReadBarrier);
46 SHENANDOAH_CHECK_FLAG_SET(ShenandoahWriteBarrier);
47 SHENANDOAH_CHECK_FLAG_SET(ShenandoahStoreValReadBarrier);
48 SHENANDOAH_CHECK_FLAG_SET(ShenandoahKeepAliveBarrier);
49 SHENANDOAH_CHECK_FLAG_SET(ShenandoahCASBarrier);
50 SHENANDOAH_CHECK_FLAG_SET(ShenandoahAcmpBarrier);
51 SHENANDOAH_CHECK_FLAG_SET(ShenandoahCloneBarrier);
52 }
53
54 ShenandoahAdaptiveHeuristics::~ShenandoahAdaptiveHeuristics() {}
55
56 void ShenandoahAdaptiveHeuristics::choose_collection_set_from_regiondata(ShenandoahCollectionSet* cset,
57 RegionData* data, size_t size,
58 size_t actual_free) {
59 size_t garbage_threshold = ShenandoahHeapRegion::region_size_bytes() * ShenandoahGarbageThreshold / 100;
60
61 // The logic for cset selection in adaptive is as follows:
62 //
63 // 1. We cannot get cset larger than available free space. Otherwise we guarantee OOME
64 // during evacuation, and thus guarantee full GC. In practice, we also want to let
65 // application to allocate something. This is why we limit CSet to some fraction of
66 // available space. In non-overloaded heap, max_cset would contain all plausible candidates
67 // over garbage threshold.
68 //
69 // 2. We should not get cset too low so that free threshold would not be met right
70 // after the cycle. Otherwise we get back-to-back cycles for no reason if heap is
71 // too fragmented. In non-overloaded non-fragmented heap min_garbage would be around zero.
72 //
73 // Therefore, we start by sorting the regions by garbage. Then we unconditionally add the best candidates
74 // before we meet min_garbage. Then we add all candidates that fit with a garbage threshold before
75 // we hit max_cset. When max_cset is hit, we terminate the cset selection. Note that in this scheme,
76 // ShenandoahGarbageThreshold is the soft threshold which would be ignored until min_garbage is hit.
77
78 size_t capacity = ShenandoahHeap::heap()->capacity();
79 size_t free_target = ShenandoahMinFreeThreshold * capacity / 100;
80 size_t min_garbage = free_target > actual_free ? (free_target - actual_free) : 0;
81 size_t max_cset = (size_t)(1.0 * ShenandoahEvacReserve * capacity / 100 / ShenandoahEvacWaste);
82
83 log_info(gc, ergo)("Adaptive CSet Selection. Target Free: " SIZE_FORMAT "M, Actual Free: "
84 SIZE_FORMAT "M, Max CSet: " SIZE_FORMAT "M, Min Garbage: " SIZE_FORMAT "M",
85 free_target / M, actual_free / M, max_cset / M, min_garbage / M);
86
87 // Better select garbage-first regions
88 QuickSort::sort<RegionData>(data, (int)size, compare_by_garbage, false);
89
90 size_t cur_cset = 0;
91 size_t cur_garbage = 0;
92 _bytes_in_cset = 0;
93
94 for (size_t idx = 0; idx < size; idx++) {
95 ShenandoahHeapRegion* r = data[idx]._region;
96
97 size_t new_cset = cur_cset + r->get_live_data_bytes();
98 size_t new_garbage = cur_garbage + r->garbage();
99
100 if (new_cset > max_cset) {
101 break;
102 }
103
104 if ((new_garbage < min_garbage) || (r->garbage() > garbage_threshold)) {
105 cset->add_region(r);
106 _bytes_in_cset += r->used();
107 cur_cset = new_cset;
108 cur_garbage = new_garbage;
109 }
110 }
111 }
112
113 void ShenandoahAdaptiveHeuristics::record_cycle_start() {
114 ShenandoahHeuristics::record_cycle_start();
115 double last_cycle_gap = (_cycle_start - _last_cycle_end);
116 _cycle_gap_history->add(last_cycle_gap);
117 }
118
119 void ShenandoahAdaptiveHeuristics::record_phase_time(ShenandoahPhaseTimings::Phase phase, double secs) {
120 if (phase == ShenandoahPhaseTimings::conc_mark) {
121 _conc_mark_duration_history->add(secs);
122 } else if (phase == ShenandoahPhaseTimings::conc_update_refs) {
123 _conc_uprefs_duration_history->add(secs);
124 } // Else ignore
125 }
126
127 bool ShenandoahAdaptiveHeuristics::should_start_normal_gc() const {
128 ShenandoahHeap* heap = ShenandoahHeap::heap();
129 size_t capacity = heap->capacity();
130 size_t available = heap->free_set()->available();
131
132 // Check if we are falling below the worst limit, time to trigger the GC, regardless of
133 // anything else.
134 size_t min_threshold = ShenandoahMinFreeThreshold * heap->capacity() / 100;
135 if (available < min_threshold) {
136 log_info(gc)("Trigger: Free (" SIZE_FORMAT "M) is below minimum threshold (" SIZE_FORMAT "M)",
137 available / M, min_threshold / M);
138 return true;
139 }
140
141 // Check if are need to learn a bit about the application
142 const size_t max_learn = ShenandoahLearningSteps;
143 if (_gc_times_learned < max_learn) {
144 size_t init_threshold = ShenandoahInitFreeThreshold * heap->capacity() / 100;
145 if (available < init_threshold) {
146 log_info(gc)("Trigger: Learning " SIZE_FORMAT " of " SIZE_FORMAT ". Free (" SIZE_FORMAT "M) is below initial threshold (" SIZE_FORMAT "M)",
147 _gc_times_learned + 1, max_learn, available / M, init_threshold / M);
148 return true;
149 }
150 }
151
152 // Check if allocation headroom is still okay. This also factors in:
153 // 1. Some space to absorb allocation spikes
154 // 2. Accumulated penalties from Degenerated and Full GC
155
156 size_t allocation_headroom = available;
157
158 size_t spike_headroom = ShenandoahAllocSpikeFactor * capacity / 100;
159 size_t penalties = _gc_time_penalties * capacity / 100;
160
161 allocation_headroom -= MIN2(allocation_headroom, spike_headroom);
162 allocation_headroom -= MIN2(allocation_headroom, penalties);
163
164 // TODO: Allocation rate is way too averaged to be useful during state changes
165
166 double average_gc = _gc_time_history->avg();
167 double time_since_last = time_since_last_gc();
168 double allocation_rate = heap->bytes_allocated_since_gc_start() / time_since_last;
169
170 if (average_gc > allocation_headroom / allocation_rate) {
171 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)",
172 average_gc * 1000, allocation_rate / M, allocation_headroom / M);
173 log_info(gc, ergo)("Free headroom: " SIZE_FORMAT "M (free) - " SIZE_FORMAT "M (spike) - " SIZE_FORMAT "M (penalties) = " SIZE_FORMAT "M",
174 available / M, spike_headroom / M, penalties / M, allocation_headroom / M);
175 return true;
176 }
177
178 return ShenandoahHeuristics::should_start_normal_gc();
179 }
180
181 bool ShenandoahAdaptiveHeuristics::should_start_update_refs() {
182 if (! _update_refs_adaptive) {
183 return _update_refs_early;
184 }
185
186 double cycle_gap_avg = _cycle_gap_history->avg();
187 double conc_mark_avg = _conc_mark_duration_history->avg();
188 double conc_uprefs_avg = _conc_uprefs_duration_history->avg();
189
190 if (_update_refs_early) {
191 double threshold = ShenandoahMergeUpdateRefsMinGap / 100.0;
192 if (conc_mark_avg + conc_uprefs_avg > cycle_gap_avg * threshold) {
193 _update_refs_early = false;
194 }
195 } else {
196 double threshold = ShenandoahMergeUpdateRefsMaxGap / 100.0;
197 if (conc_mark_avg + conc_uprefs_avg < cycle_gap_avg * threshold) {
198 _update_refs_early = true;
199 }
200 }
201 return _update_refs_early;
202 }
203
204 const char* ShenandoahAdaptiveHeuristics::name() {
205 return "adaptive";
206 }
207
208 bool ShenandoahAdaptiveHeuristics::is_diagnostic() {
209 return false;
210 }
211
212 bool ShenandoahAdaptiveHeuristics::is_experimental() {
213 return false;
214 }