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/shenandoahGenerationalHeuristics.hpp"
28 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
29 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
30 #include "gc/shenandoah/shenandoahGeneration.hpp"
31 #include "gc/shenandoah/shenandoahGenerationalHeap.hpp"
32 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
33 #include "gc/shenandoah/shenandoahOldGeneration.hpp"
34
35 #include "logging/log.hpp"
36
37 ShenandoahGenerationalHeuristics::ShenandoahGenerationalHeuristics(ShenandoahGeneration* generation)
38 : ShenandoahAdaptiveHeuristics(generation), _generation(generation) {
39 }
40
41 void ShenandoahGenerationalHeuristics::choose_collection_set(ShenandoahCollectionSet* collection_set) {
42 assert(collection_set->is_empty(), "Must be empty");
43
44 auto heap = ShenandoahGenerationalHeap::heap();
45 size_t region_size_bytes = ShenandoahHeapRegion::region_size_bytes();
46
47
48 // Check all pinned regions have updated status before choosing the collection set.
49 heap->assert_pinned_region_status();
50
51 // Step 1. Build up the region candidates we care about, rejecting losers and accepting winners right away.
52
53 size_t num_regions = heap->num_regions();
54
55 RegionData* candidates = _region_data;
56
57 size_t cand_idx = 0;
58 size_t preselected_candidates = 0;
59
60 size_t total_garbage = 0;
61
62 size_t immediate_garbage = 0;
63 size_t immediate_regions = 0;
64
65 size_t free = 0;
66 size_t free_regions = 0;
67
68 const uint tenuring_threshold = heap->age_census()->tenuring_threshold();
69
70 // This counts number of humongous regions that we intend to promote in this cycle.
71 size_t humongous_regions_promoted = 0;
72 // This counts number of regular regions that will be promoted in place.
73 size_t regular_regions_promoted_in_place = 0;
74 // This counts bytes of memory used by regular regions to be promoted in place.
75 size_t regular_regions_promoted_usage = 0;
76
77 for (size_t i = 0; i < num_regions; i++) {
78 ShenandoahHeapRegion* region = heap->get_region(i);
79 if (!_generation->contains(region)) {
80 continue;
81 }
82 size_t garbage = region->garbage();
83 total_garbage += garbage;
84 if (region->is_empty()) {
85 free_regions++;
86 free += region_size_bytes;
87 } else if (region->is_regular()) {
88 if (!region->has_live()) {
89 // We can recycle it right away and put it in the free set.
90 immediate_regions++;
91 immediate_garbage += garbage;
92 region->make_trash_immediate();
93 } else {
94 bool is_candidate;
95 // This is our candidate for later consideration.
96 if (collection_set->is_preselected(i)) {
97 assert(region->age() >= tenuring_threshold, "Preselection filter");
98 is_candidate = true;
99 preselected_candidates++;
100 // Set garbage value to maximum value to force this into the sorted collection set.
101 garbage = region_size_bytes;
102 } else if (region->is_young() && (region->age() >= tenuring_threshold)) {
103 // Note that for GLOBAL GC, region may be OLD, and OLD regions do not qualify for pre-selection
104
105 // This region is old enough to be promoted but it was not preselected, either because its garbage is below
106 // ShenandoahOldGarbageThreshold so it will be promoted in place, or because there is not sufficient room
107 // in old gen to hold the evacuated copies of this region's live data. In both cases, we choose not to
108 // place this region into the collection set.
109 if (region->get_top_before_promote() != nullptr) {
110 // Region was included for promotion-in-place
111 regular_regions_promoted_in_place++;
112 regular_regions_promoted_usage += region->used_before_promote();
113 }
114 is_candidate = false;
115 } else {
116 is_candidate = true;
117 }
118 if (is_candidate) {
119 candidates[cand_idx]._region = region;
120 candidates[cand_idx]._u._garbage = garbage;
121 cand_idx++;
122 }
123 }
124 } else if (region->is_humongous_start()) {
125 // Reclaim humongous regions here, and count them as the immediate garbage
126 #ifdef ASSERT
127 bool reg_live = region->has_live();
128 bool bm_live = heap->complete_marking_context()->is_marked(cast_to_oop(region->bottom()));
129 assert(reg_live == bm_live,
130 "Humongous liveness and marks should agree. Region live: %s; Bitmap live: %s; Region Live Words: " SIZE_FORMAT,
131 BOOL_TO_STR(reg_live), BOOL_TO_STR(bm_live), region->get_live_data_words());
132 #endif
133 if (!region->has_live()) {
134 heap->trash_humongous_region_at(region);
135
136 // Count only the start. Continuations would be counted on "trash" path
137 immediate_regions++;
138 immediate_garbage += garbage;
139 } else {
140 if (region->is_young() && region->age() >= tenuring_threshold) {
141 oop obj = cast_to_oop(region->bottom());
142 size_t humongous_regions = ShenandoahHeapRegion::required_regions(obj->size() * HeapWordSize);
143 humongous_regions_promoted += humongous_regions;
144 }
145 }
146 } else if (region->is_trash()) {
147 // Count in just trashed collection set, during coalesced CM-with-UR
148 immediate_regions++;
149 immediate_garbage += garbage;
150 }
151 }
152 heap->old_generation()->set_expected_humongous_region_promotions(humongous_regions_promoted);
153 heap->old_generation()->set_expected_regular_region_promotions(regular_regions_promoted_in_place);
154 log_info(gc, ergo)("Planning to promote in place " SIZE_FORMAT " humongous regions and " SIZE_FORMAT
155 " regular regions, spanning a total of " SIZE_FORMAT " used bytes",
156 humongous_regions_promoted, regular_regions_promoted_in_place,
157 humongous_regions_promoted * ShenandoahHeapRegion::region_size_bytes() +
158 regular_regions_promoted_usage);
159
160 // Step 2. Look back at garbage statistics, and decide if we want to collect anything,
161 // given the amount of immediately reclaimable garbage. If we do, figure out the collection set.
162
163 assert (immediate_garbage <= total_garbage,
164 "Cannot have more immediate garbage than total garbage: " SIZE_FORMAT "%s vs " SIZE_FORMAT "%s",
165 byte_size_in_proper_unit(immediate_garbage), proper_unit_for_byte_size(immediate_garbage),
166 byte_size_in_proper_unit(total_garbage), proper_unit_for_byte_size(total_garbage));
167
168 size_t immediate_percent = (total_garbage == 0) ? 0 : (immediate_garbage * 100 / total_garbage);
169
170 bool doing_promote_in_place = (humongous_regions_promoted + regular_regions_promoted_in_place > 0);
171 if (doing_promote_in_place || (preselected_candidates > 0) || (immediate_percent <= ShenandoahImmediateThreshold)) {
172 // Only young collections need to prime the collection set.
173 if (_generation->is_young()) {
174 heap->old_generation()->heuristics()->prime_collection_set(collection_set);
175 }
176
177 // Call the subclasses to add young-gen regions into the collection set.
178 choose_collection_set_from_regiondata(collection_set, candidates, cand_idx, immediate_garbage + free);
179 }
180
181 if (collection_set->has_old_regions()) {
182 heap->shenandoah_policy()->record_mixed_cycle();
183 }
184
185 size_t cset_percent = (total_garbage == 0) ? 0 : (collection_set->garbage() * 100 / total_garbage);
186 size_t collectable_garbage = collection_set->garbage() + immediate_garbage;
187 size_t collectable_garbage_percent = (total_garbage == 0) ? 0 : (collectable_garbage * 100 / total_garbage);
188
189 log_info(gc, ergo)("Collectable Garbage: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), "
190 "Immediate: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), " SIZE_FORMAT " regions, "
191 "CSet: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), " SIZE_FORMAT " regions",
192
193 byte_size_in_proper_unit(collectable_garbage),
194 proper_unit_for_byte_size(collectable_garbage),
195 collectable_garbage_percent,
196
197 byte_size_in_proper_unit(immediate_garbage),
198 proper_unit_for_byte_size(immediate_garbage),
199 immediate_percent,
200 immediate_regions,
201
202 byte_size_in_proper_unit(collection_set->garbage()),
203 proper_unit_for_byte_size(collection_set->garbage()),
204 cset_percent,
205 collection_set->count());
206
207 if (collection_set->garbage() > 0) {
208 size_t young_evac_bytes = collection_set->get_young_bytes_reserved_for_evacuation();
209 size_t promote_evac_bytes = collection_set->get_young_bytes_to_be_promoted();
210 size_t old_evac_bytes = collection_set->get_old_bytes_reserved_for_evacuation();
211 size_t total_evac_bytes = young_evac_bytes + promote_evac_bytes + old_evac_bytes;
212 log_info(gc, ergo)("Evacuation Targets: YOUNG: " SIZE_FORMAT "%s, "
213 "PROMOTE: " SIZE_FORMAT "%s, "
214 "OLD: " SIZE_FORMAT "%s, "
215 "TOTAL: " SIZE_FORMAT "%s",
216 byte_size_in_proper_unit(young_evac_bytes), proper_unit_for_byte_size(young_evac_bytes),
217 byte_size_in_proper_unit(promote_evac_bytes), proper_unit_for_byte_size(promote_evac_bytes),
218 byte_size_in_proper_unit(old_evac_bytes), proper_unit_for_byte_size(old_evac_bytes),
219 byte_size_in_proper_unit(total_evac_bytes), proper_unit_for_byte_size(total_evac_bytes));
220 }
221 }
222
223
224 size_t ShenandoahGenerationalHeuristics::add_preselected_regions_to_collection_set(ShenandoahCollectionSet* cset,
225 const RegionData* data,
226 size_t size) const {
227 #ifdef ASSERT
228 const uint tenuring_threshold = ShenandoahHeap::heap()->age_census()->tenuring_threshold();
229 #endif
230
231 // cur_young_garbage represents the amount of memory to be reclaimed from young-gen. In the case that live objects
232 // are known to be promoted out of young-gen, we count this as cur_young_garbage because this memory is reclaimed
233 // from young-gen and becomes available to serve future young-gen allocation requests.
234 size_t cur_young_garbage = 0;
235 for (size_t idx = 0; idx < size; idx++) {
236 ShenandoahHeapRegion* r = data[idx]._region;
237 if (cset->is_preselected(r->index())) {
238 assert(r->age() >= tenuring_threshold, "Preselected regions must have tenure age");
239 // Entire region will be promoted, This region does not impact young-gen or old-gen evacuation reserve.
240 // This region has been pre-selected and its impact on promotion reserve is already accounted for.
241
242 // r->used() is r->garbage() + r->get_live_data_bytes()
243 // Since all live data in this region is being evacuated from young-gen, it is as if this memory
244 // is garbage insofar as young-gen is concerned. Counting this as garbage reduces the need to
245 // reclaim highly utilized young-gen regions just for the sake of finding min_garbage to reclaim
246 // within young-gen memory.
247
248 cur_young_garbage += r->garbage();
249 cset->add_region(r);
250 }
251 }
252 return cur_young_garbage;
253 }
254
255 void ShenandoahGenerationalHeuristics::log_cset_composition(ShenandoahCollectionSet* cset) const {
256 size_t collected_old = cset->get_old_bytes_reserved_for_evacuation();
257 size_t collected_promoted = cset->get_young_bytes_to_be_promoted();
258 size_t collected_young = cset->get_young_bytes_reserved_for_evacuation();
259
260 log_info(gc, ergo)(
261 "Chosen CSet evacuates young: " SIZE_FORMAT "%s (of which at least: " SIZE_FORMAT "%s are to be promoted), "
262 "old: " SIZE_FORMAT "%s",
263 byte_size_in_proper_unit(collected_young), proper_unit_for_byte_size(collected_young),
264 byte_size_in_proper_unit(collected_promoted), proper_unit_for_byte_size(collected_promoted),
265 byte_size_in_proper_unit(collected_old), proper_unit_for_byte_size(collected_old));
266 }