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