1 /*
2 * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26
27 #include "gc/shenandoah/heuristics/shenandoahGlobalHeuristics.hpp"
28 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
29 #include "gc/shenandoah/shenandoahGlobalGeneration.hpp"
30 #include "gc/shenandoah/shenandoahGenerationalHeap.hpp"
31 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
32
33 #include "utilities/quickSort.hpp"
34
35 ShenandoahGlobalHeuristics::ShenandoahGlobalHeuristics(ShenandoahGlobalGeneration* generation)
36 : ShenandoahGenerationalHeuristics(generation) {
37 }
38
39
40 void ShenandoahGlobalHeuristics::choose_collection_set_from_regiondata(ShenandoahCollectionSet* cset,
41 RegionData* data, size_t size,
42 size_t actual_free) {
43 // The logic for cset selection in adaptive is as follows:
44 //
45 // 1. We cannot get cset larger than available free space. Otherwise we guarantee OOME
46 // during evacuation, and thus guarantee full GC. In practice, we also want to let
47 // application to allocate something. This is why we limit CSet to some fraction of
48 // available space. In non-overloaded heap, max_cset would contain all plausible candidates
49 // over garbage threshold.
50 //
51 // 2. We should not get cset too low so that free threshold would not be met right
52 // after the cycle. Otherwise we get back-to-back cycles for no reason if heap is
53 // too fragmented. In non-overloaded non-fragmented heap min_garbage would be around zero.
54 //
55 // Therefore, we start by sorting the regions by garbage. Then we unconditionally add the best candidates
56 // before we meet min_garbage. Then we add all candidates that fit with a garbage threshold before
57 // we hit max_cset. When max_cset is hit, we terminate the cset selection. Note that in this scheme,
58 // ShenandoahGarbageThreshold is the soft threshold which would be ignored until min_garbage is hit.
59
60 // In generational mode, the sort order within the data array is not strictly descending amounts of garbage. In
61 // particular, regions that have reached tenure age will be sorted into this array before younger regions that contain
62 // more garbage. This represents one of the reasons why we keep looking at regions even after we decide, for example,
63 // to exclude one of the regions because it might require evacuation of too much live data.
64
65
66
67 // Better select garbage-first regions
68 QuickSort::sort<RegionData>(data, (int) size, compare_by_garbage, false);
69
70 size_t cur_young_garbage = add_preselected_regions_to_collection_set(cset, data, size);
71
72 choose_global_collection_set(cset, data, size, actual_free, cur_young_garbage);
73
74 log_cset_composition(cset);
75 }
76
77
78 void ShenandoahGlobalHeuristics::choose_global_collection_set(ShenandoahCollectionSet* cset,
79 const ShenandoahHeuristics::RegionData* data,
80 size_t size, size_t actual_free,
81 size_t cur_young_garbage) const {
82 auto heap = ShenandoahGenerationalHeap::heap();
83 size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
84 size_t capacity = heap->young_generation()->max_capacity();
85 size_t garbage_threshold = region_size_bytes * ShenandoahGarbageThreshold / 100;
86 size_t ignore_threshold = region_size_bytes * ShenandoahIgnoreGarbageThreshold / 100;
87 const uint tenuring_threshold = heap->age_census()->tenuring_threshold();
88
89 size_t young_evac_reserve = heap->young_generation()->get_evacuation_reserve();
90 size_t old_evac_reserve = heap->old_generation()->get_evacuation_reserve();
91 size_t max_young_cset = (size_t) (young_evac_reserve / ShenandoahEvacWaste);
92 size_t young_cur_cset = 0;
93 size_t max_old_cset = (size_t) (old_evac_reserve / ShenandoahOldEvacWaste);
94 size_t old_cur_cset = 0;
95
96 // Figure out how many unaffiliated young regions are dedicated to mutator and to evacuator. Allow the young
97 // collector's unaffiliated regions to be transferred to old-gen if old-gen has more easily reclaimed garbage
98 // than young-gen. At the end of this cycle, any excess regions remaining in old-gen will be transferred back
99 // to young. Do not transfer the mutator's unaffiliated regions to old-gen. Those must remain available
100 // to the mutator as it needs to be able to consume this memory during concurrent GC.
101
102 size_t unaffiliated_young_regions = heap->young_generation()->free_unaffiliated_regions();
103 size_t unaffiliated_young_memory = unaffiliated_young_regions * region_size_bytes;
104
105 if (unaffiliated_young_memory > max_young_cset) {
106 size_t unaffiliated_mutator_memory = unaffiliated_young_memory - max_young_cset;
107 unaffiliated_young_memory -= unaffiliated_mutator_memory;
108 unaffiliated_young_regions = unaffiliated_young_memory / region_size_bytes; // round down
109 unaffiliated_young_memory = unaffiliated_young_regions * region_size_bytes;
110 }
111
112 // We'll affiliate these unaffiliated regions with either old or young, depending on need.
113 max_young_cset -= unaffiliated_young_memory;
114
115 // Keep track of how many regions we plan to transfer from young to old.
116 size_t regions_transferred_to_old = 0;
117
118 size_t free_target = (capacity * ShenandoahMinFreeThreshold) / 100 + max_young_cset;
119 size_t min_garbage = (free_target > actual_free) ? (free_target - actual_free) : 0;
120
121 log_info(gc, ergo)("Adaptive CSet Selection for GLOBAL. Max Young Evacuation: " SIZE_FORMAT
122 "%s, Max Old Evacuation: " SIZE_FORMAT "%s, Actual Free: " SIZE_FORMAT "%s.",
123 byte_size_in_proper_unit(max_young_cset), proper_unit_for_byte_size(max_young_cset),
124 byte_size_in_proper_unit(max_old_cset), proper_unit_for_byte_size(max_old_cset),
125 byte_size_in_proper_unit(actual_free), proper_unit_for_byte_size(actual_free));
126
127 for (size_t idx = 0; idx < size; idx++) {
128 ShenandoahHeapRegion* r = data[idx]._region;
129 if (cset->is_preselected(r->index())) {
130 fatal("There should be no preselected regions during GLOBAL GC");
131 continue;
132 }
133 bool add_region = false;
134 if (r->is_old() || (r->age() >= tenuring_threshold)) {
135 size_t new_cset = old_cur_cset + r->get_live_data_bytes();
136 if ((r->garbage() > garbage_threshold)) {
137 while ((new_cset > max_old_cset) && (unaffiliated_young_regions > 0)) {
138 unaffiliated_young_regions--;
139 regions_transferred_to_old++;
140 max_old_cset += region_size_bytes / ShenandoahOldEvacWaste;
141 }
142 }
143 if ((new_cset <= max_old_cset) && (r->garbage() > garbage_threshold)) {
144 add_region = true;
145 old_cur_cset = new_cset;
146 }
147 } else {
148 assert(r->is_young() && (r->age() < tenuring_threshold), "DeMorgan's law (assuming r->is_affiliated)");
149 size_t new_cset = young_cur_cset + r->get_live_data_bytes();
150 size_t region_garbage = r->garbage();
151 size_t new_garbage = cur_young_garbage + region_garbage;
152 bool add_regardless = (region_garbage > ignore_threshold) && (new_garbage < min_garbage);
153
154 if (add_regardless || (r->garbage() > garbage_threshold)) {
155 while ((new_cset > max_young_cset) && (unaffiliated_young_regions > 0)) {
156 unaffiliated_young_regions--;
157 max_young_cset += region_size_bytes / ShenandoahEvacWaste;
158 }
159 }
160 if ((new_cset <= max_young_cset) && (add_regardless || (region_garbage > garbage_threshold))) {
161 add_region = true;
162 young_cur_cset = new_cset;
163 cur_young_garbage = new_garbage;
164 }
165 }
166 if (add_region) {
167 cset->add_region(r);
168 }
169 }
170
171 if (regions_transferred_to_old > 0) {
172 heap->generation_sizer()->force_transfer_to_old(regions_transferred_to_old);
173 heap->young_generation()->set_evacuation_reserve(young_evac_reserve - regions_transferred_to_old * region_size_bytes);
174 heap->old_generation()->set_evacuation_reserve(old_evac_reserve + regions_transferred_to_old * region_size_bytes);
175 }
176 }