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/shenandoahHeap.inline.hpp"
30 #include "gc_implementation/shenandoah/shenandoahHeapRegion.inline.hpp"
31 #include "gc_implementation/shenandoah/shenandoahLogging.hpp"
32 #include "utilities/quickSort.hpp"
33
34 ShenandoahAdaptiveHeuristics::ShenandoahAdaptiveHeuristics() :
35 ShenandoahHeuristics() {}
36
37 ShenandoahAdaptiveHeuristics::~ShenandoahAdaptiveHeuristics() {}
38
39 void ShenandoahAdaptiveHeuristics::choose_collection_set_from_regiondata(ShenandoahCollectionSet* cset,
40 RegionData* data, size_t size,
41 size_t actual_free) {
42 size_t garbage_threshold = ShenandoahHeapRegion::region_size_bytes() * ShenandoahGarbageThreshold / 100;
43
44 // The logic for cset selection in adaptive is as follows:
45 //
46 // 1. We cannot get cset larger than available free space. Otherwise we guarantee OOME
47 // during evacuation, and thus guarantee full GC. In practice, we also want to let
48 // application to allocate something. This is why we limit CSet to some fraction of
49 // available space. In non-overloaded heap, max_cset would contain all plausible candidates
50 // over garbage threshold.
51 //
52 // 2. We should not get cset too low so that free threshold would not be met right
53 // after the cycle. Otherwise we get back-to-back cycles for no reason if heap is
54 // too fragmented. In non-overloaded non-fragmented heap min_garbage would be around zero.
55 //
56 // Therefore, we start by sorting the regions by garbage. Then we unconditionally add the best candidates
57 // before we meet min_garbage. Then we add all candidates that fit with a garbage threshold before
58 // we hit max_cset. When max_cset is hit, we terminate the cset selection. Note that in this scheme,
59 // ShenandoahGarbageThreshold is the soft threshold which would be ignored until min_garbage is hit.
60
61 size_t capacity = ShenandoahHeap::heap()->soft_max_capacity();
62 size_t max_cset = (size_t)((1.0 * capacity / 100 * ShenandoahEvacReserve) / ShenandoahEvacWaste);
63 size_t free_target = (capacity / 100 * ShenandoahMinFreeThreshold) + max_cset;
64 size_t min_garbage = (free_target > actual_free ? (free_target - actual_free) : 0);
65
66 log_info(gc, ergo)("Adaptive CSet Selection. Target Free: " SIZE_FORMAT "%s, Actual Free: "
67 SIZE_FORMAT "%s, Max CSet: " SIZE_FORMAT "%s, Min Garbage: " SIZE_FORMAT "%s",
68 byte_size_in_proper_unit(free_target), proper_unit_for_byte_size(free_target),
69 byte_size_in_proper_unit(actual_free), proper_unit_for_byte_size(actual_free),
70 byte_size_in_proper_unit(max_cset), proper_unit_for_byte_size(max_cset),
71 byte_size_in_proper_unit(min_garbage), proper_unit_for_byte_size(min_garbage));
72
73 // Better select garbage-first regions
74 QuickSort::sort<RegionData>(data, (int)size, compare_by_garbage, false);
75
76 size_t cur_cset = 0;
77 size_t cur_garbage = 0;
78
79 for (size_t idx = 0; idx < size; idx++) {
80 ShenandoahHeapRegion* r = data[idx]._region;
81
82 size_t new_cset = cur_cset + r->get_live_data_bytes();
83 size_t new_garbage = cur_garbage + r->garbage();
84
85 if (new_cset > max_cset) {
86 break;
87 }
88
89 if ((new_garbage < min_garbage) || (r->garbage() > garbage_threshold)) {
90 cset->add_region(r);
91 cur_cset = new_cset;
92 cur_garbage = new_garbage;
93 }
94 }
95 }
96
97 void ShenandoahAdaptiveHeuristics::record_cycle_start() {
98 ShenandoahHeuristics::record_cycle_start();
99 }
100
101 bool ShenandoahAdaptiveHeuristics::should_start_gc() const {
102 ShenandoahHeap* heap = ShenandoahHeap::heap();
103 size_t max_capacity = heap->max_capacity();
104 size_t capacity = heap->soft_max_capacity();
105 size_t available = heap->free_set()->available();
106
107 // Make sure the code below treats available without the soft tail.
108 size_t soft_tail = max_capacity - capacity;
109 available = (available > soft_tail) ? (available - soft_tail) : 0;
110
111 // Check if we are falling below the worst limit, time to trigger the GC, regardless of
112 // anything else.
113 size_t min_threshold = capacity / 100 * ShenandoahMinFreeThreshold;
114 if (available < min_threshold) {
115 log_info(gc)("Trigger: Free (" SIZE_FORMAT "%s) is below minimum threshold (" SIZE_FORMAT "%s)",
116 byte_size_in_proper_unit(available), proper_unit_for_byte_size(available),
117 byte_size_in_proper_unit(min_threshold), proper_unit_for_byte_size(min_threshold));
118 return true;
119 }
120
121 // Check if are need to learn a bit about the application
122 const size_t max_learn = ShenandoahLearningSteps;
123 if (_gc_times_learned < max_learn) {
124 size_t init_threshold = capacity / 100 * ShenandoahInitFreeThreshold;
125 if (available < init_threshold) {
126 log_info(gc)("Trigger: Learning " SIZE_FORMAT " of " SIZE_FORMAT ". Free (" SIZE_FORMAT "%s) is below initial threshold (" SIZE_FORMAT "%s)",
127 _gc_times_learned + 1, max_learn,
128 byte_size_in_proper_unit(available), proper_unit_for_byte_size(available),
129 byte_size_in_proper_unit(init_threshold), proper_unit_for_byte_size(init_threshold));
130 return true;
131 }
132 }
133
134 // Check if allocation headroom is still okay. This also factors in:
135 // 1. Some space to absorb allocation spikes
136 // 2. Accumulated penalties from Degenerated and Full GC
137
138 size_t allocation_headroom = available;
139
140 size_t spike_headroom = capacity / 100 * ShenandoahAllocSpikeFactor;
141 size_t penalties = capacity / 100 * _gc_time_penalties;
142
143 allocation_headroom -= MIN2(allocation_headroom, spike_headroom);
144 allocation_headroom -= MIN2(allocation_headroom, penalties);
145
146 // TODO: Allocation rate is way too averaged to be useful during state changes
147
148 double average_gc = _gc_time_history->avg();
149 double time_since_last = time_since_last_gc();
150 double allocation_rate = heap->bytes_allocated_since_gc_start() / time_since_last;
151
152 if (average_gc > allocation_headroom / allocation_rate) {
153 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)",
154 average_gc * 1000,
155 byte_size_in_proper_unit(allocation_rate), proper_unit_for_byte_size(allocation_rate),
156 byte_size_in_proper_unit(allocation_headroom), proper_unit_for_byte_size(allocation_headroom));
157 log_info(gc, ergo)("Free headroom: " SIZE_FORMAT "%s (free) - " SIZE_FORMAT "%s (spike) - " SIZE_FORMAT "%s (penalties) = " SIZE_FORMAT "%s",
158 byte_size_in_proper_unit(available), proper_unit_for_byte_size(available),
159 byte_size_in_proper_unit(spike_headroom), proper_unit_for_byte_size(spike_headroom),
160 byte_size_in_proper_unit(penalties), proper_unit_for_byte_size(penalties),
161 byte_size_in_proper_unit(allocation_headroom), proper_unit_for_byte_size(allocation_headroom));
162 return true;
163 }
164
165 return ShenandoahHeuristics::should_start_gc();
166 }