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/shenandoahHeap.inline.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 ShenandoahHeap* heap = ShenandoahHeap::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 max_young_cset = (size_t) (heap->get_young_evac_reserve() / ShenandoahEvacWaste);
90 size_t young_cur_cset = 0;
91 size_t max_old_cset = (size_t) (heap->get_old_evac_reserve() / ShenandoahOldEvacWaste);
92 size_t old_cur_cset = 0;
93
94 // Figure out how many unaffiliated young regions are dedicated to mutator and to evacuator. Allow the young
95 // collector's unaffiliated regions to be transferred to old-gen if old-gen has more easily reclaimed garbage
96 // than young-gen. At the end of this cycle, any excess regions remaining in old-gen will be transferred back
97 // to young. Do not transfer the mutator's unaffiliated regions to old-gen. Those must remain available
98 // to the mutator as it needs to be able to consume this memory during concurrent GC.
99
100 size_t unaffiliated_young_regions = heap->young_generation()->free_unaffiliated_regions();
101 size_t unaffiliated_young_memory = unaffiliated_young_regions * region_size_bytes;
102
103 if (unaffiliated_young_memory > max_young_cset) {
104 size_t unaffiliated_mutator_memory = unaffiliated_young_memory - max_young_cset;
105 unaffiliated_young_memory -= unaffiliated_mutator_memory;
106 unaffiliated_young_regions = unaffiliated_young_memory / region_size_bytes; // round down
107 unaffiliated_young_memory = unaffiliated_young_regions * region_size_bytes;
108 }
109
110 // We'll affiliate these unaffiliated regions with either old or young, depending on need.
111 max_young_cset -= unaffiliated_young_memory;
112
113 // Keep track of how many regions we plan to transfer from young to old.
114 size_t regions_transferred_to_old = 0;
115
116 size_t free_target = (capacity * ShenandoahMinFreeThreshold) / 100 + max_young_cset;
117 size_t min_garbage = (free_target > actual_free) ? (free_target - actual_free) : 0;
118
119 log_info(gc, ergo)("Adaptive CSet Selection for GLOBAL. Max Young Evacuation: " SIZE_FORMAT
120 "%s, Max Old Evacuation: " SIZE_FORMAT "%s, Actual Free: " SIZE_FORMAT "%s.",
121 byte_size_in_proper_unit(max_young_cset), proper_unit_for_byte_size(max_young_cset),
122 byte_size_in_proper_unit(max_old_cset), proper_unit_for_byte_size(max_old_cset),
123 byte_size_in_proper_unit(actual_free), proper_unit_for_byte_size(actual_free));
124
125 for (size_t idx = 0; idx < size; idx++) {
126 ShenandoahHeapRegion* r = data[idx]._region;
127 if (cset->is_preselected(r->index())) {
128 fatal("There should be no preselected regions during GLOBAL GC");
129 continue;
130 }
131 bool add_region = false;
132 if (r->is_old() || (r->age() >= tenuring_threshold)) {
133 size_t new_cset = old_cur_cset + r->get_live_data_bytes();
134 if ((r->garbage() > garbage_threshold)) {
135 while ((new_cset > max_old_cset) && (unaffiliated_young_regions > 0)) {
136 unaffiliated_young_regions--;
137 regions_transferred_to_old++;
138 max_old_cset += region_size_bytes / ShenandoahOldEvacWaste;
139 }
140 }
141 if ((new_cset <= max_old_cset) && (r->garbage() > garbage_threshold)) {
142 add_region = true;
143 old_cur_cset = new_cset;
144 }
145 } else {
146 assert(r->is_young() && (r->age() < tenuring_threshold), "DeMorgan's law (assuming r->is_affiliated)");
147 size_t new_cset = young_cur_cset + r->get_live_data_bytes();
148 size_t region_garbage = r->garbage();
149 size_t new_garbage = cur_young_garbage + region_garbage;
150 bool add_regardless = (region_garbage > ignore_threshold) && (new_garbage < min_garbage);
151
152 if (add_regardless || (r->garbage() > garbage_threshold)) {
153 while ((new_cset > max_young_cset) && (unaffiliated_young_regions > 0)) {
154 unaffiliated_young_regions--;
155 max_young_cset += region_size_bytes / ShenandoahEvacWaste;
156 }
157 }
158 if ((new_cset <= max_young_cset) && (add_regardless || (region_garbage > garbage_threshold))) {
159 add_region = true;
160 young_cur_cset = new_cset;
161 cur_young_garbage = new_garbage;
162 }
163 }
164 if (add_region) {
165 cset->add_region(r);
166 }
167 }
168
169 if (regions_transferred_to_old > 0) {
170 heap->generation_sizer()->force_transfer_to_old(regions_transferred_to_old);
171 heap->set_young_evac_reserve(heap->get_young_evac_reserve() - regions_transferred_to_old * region_size_bytes);
172 heap->set_old_evac_reserve(heap->get_old_evac_reserve() + regions_transferred_to_old * region_size_bytes);
173 }
174 }