1 /*
2 * Copyright (c) 2018, 2020, Red Hat, Inc. All rights reserved.
3 * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
5 *
6 * This code is free software; you can redistribute it and/or modify it
7 * under the terms of the GNU General Public License version 2 only, as
8 * published by the Free Software Foundation.
9 *
10 * This code is distributed in the hope that it will be useful, but WITHOUT
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
17 * 2 along with this work; if not, write to the Free Software Foundation,
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 * or visit www.oracle.com if you need additional information or have any
22 * questions.
23 *
24 */
25
26 #include "precompiled.hpp"
27 #include "gc/shared/gcCause.hpp"
28 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
29 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
30 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
31 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
32 #include "logging/log.hpp"
33 #include "logging/logTag.hpp"
34 #include "runtime/globals_extension.hpp"
35 #include "utilities/quickSort.hpp"
36
37 // sort by decreasing garbage (so most garbage comes first)
38 int ShenandoahHeuristics::compare_by_garbage(RegionData a, RegionData b) {
39 if (a._u._garbage > b._u._garbage)
40 return -1;
41 else if (a._u._garbage < b._u._garbage)
42 return 1;
43 else return 0;
44 }
45
46 ShenandoahHeuristics::ShenandoahHeuristics(ShenandoahSpaceInfo* space_info) :
47 _space_info(space_info),
48 _region_data(nullptr),
49 _guaranteed_gc_interval(0),
50 _cycle_start(os::elapsedTime()),
51 _last_cycle_end(0),
52 _gc_times_learned(0),
53 _gc_time_penalties(0),
54 _gc_cycle_time_history(new TruncatedSeq(Moving_Average_Samples, ShenandoahAdaptiveDecayFactor)),
55 _metaspace_oom()
56 {
57 // No unloading during concurrent mark? Communicate that to heuristics
58 if (!ClassUnloadingWithConcurrentMark) {
59 FLAG_SET_DEFAULT(ShenandoahUnloadClassesFrequency, 0);
60 }
61
62 size_t num_regions = ShenandoahHeap::heap()->num_regions();
63 assert(num_regions > 0, "Sanity");
64
65 _region_data = NEW_C_HEAP_ARRAY(RegionData, num_regions, mtGC);
66 }
67
68 ShenandoahHeuristics::~ShenandoahHeuristics() {
69 FREE_C_HEAP_ARRAY(RegionGarbage, _region_data);
70 }
71
72 void ShenandoahHeuristics::choose_collection_set(ShenandoahCollectionSet* collection_set) {
73 assert(collection_set->is_empty(), "Must be empty");
74
75 ShenandoahHeap* heap = ShenandoahHeap::heap();
76
77 // Check all pinned regions have updated status before choosing the collection set.
78 heap->assert_pinned_region_status();
79
80 // Step 1. Build up the region candidates we care about, rejecting losers and accepting winners right away.
81
82 size_t num_regions = heap->num_regions();
83
84 RegionData* candidates = _region_data;
85
86 size_t cand_idx = 0;
87
88 size_t total_garbage = 0;
89
90 size_t immediate_garbage = 0;
91 size_t immediate_regions = 0;
92
93 size_t free = 0;
94 size_t free_regions = 0;
95
96 ShenandoahMarkingContext* const ctx = heap->complete_marking_context();
97
98 for (size_t i = 0; i < num_regions; i++) {
99 ShenandoahHeapRegion* region = heap->get_region(i);
100
101 size_t garbage = region->garbage();
102 total_garbage += garbage;
103
104 if (region->is_empty()) {
105 free_regions++;
106 free += ShenandoahHeapRegion::region_size_bytes();
107 } else if (region->is_regular()) {
108 if (!region->has_live()) {
109 // We can recycle it right away and put it in the free set.
110 immediate_regions++;
111 immediate_garbage += garbage;
112 region->make_trash_immediate();
113 } else {
114 // This is our candidate for later consideration.
115 candidates[cand_idx]._region = region;
116 candidates[cand_idx]._u._garbage = garbage;
117 cand_idx++;
118 }
119 } else if (region->is_humongous_start()) {
120 // Reclaim humongous regions here, and count them as the immediate garbage
121 #ifdef ASSERT
122 bool reg_live = region->has_live();
123 bool bm_live = ctx->is_marked(cast_to_oop(region->bottom()));
124 assert(reg_live == bm_live,
125 "Humongous liveness and marks should agree. Region live: %s; Bitmap live: %s; Region Live Words: " SIZE_FORMAT,
126 BOOL_TO_STR(reg_live), BOOL_TO_STR(bm_live), region->get_live_data_words());
127 #endif
128 if (!region->has_live()) {
129 heap->trash_humongous_region_at(region);
130
131 // Count only the start. Continuations would be counted on "trash" path
132 immediate_regions++;
133 immediate_garbage += garbage;
134 }
135 } else if (region->is_trash()) {
136 // Count in just trashed collection set, during coalesced CM-with-UR
137 immediate_regions++;
138 immediate_garbage += garbage;
139 }
140 }
141
142 // Step 2. Look back at garbage statistics, and decide if we want to collect anything,
143 // given the amount of immediately reclaimable garbage. If we do, figure out the collection set.
144
145 assert (immediate_garbage <= total_garbage,
146 "Cannot have more immediate garbage than total garbage: " SIZE_FORMAT "%s vs " SIZE_FORMAT "%s",
147 byte_size_in_proper_unit(immediate_garbage), proper_unit_for_byte_size(immediate_garbage),
148 byte_size_in_proper_unit(total_garbage), proper_unit_for_byte_size(total_garbage));
149
150 size_t immediate_percent = (total_garbage == 0) ? 0 : (immediate_garbage * 100 / total_garbage);
151
152 if (immediate_percent <= ShenandoahImmediateThreshold) {
153 choose_collection_set_from_regiondata(collection_set, candidates, cand_idx, immediate_garbage + free);
154 }
155
156 size_t cset_percent = (total_garbage == 0) ? 0 : (collection_set->garbage() * 100 / total_garbage);
157 size_t collectable_garbage = collection_set->garbage() + immediate_garbage;
158 size_t collectable_garbage_percent = (total_garbage == 0) ? 0 : (collectable_garbage * 100 / total_garbage);
159
160 log_info(gc, ergo)("Collectable Garbage: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), "
161 "Immediate: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), " SIZE_FORMAT " regions, "
162 "CSet: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), " SIZE_FORMAT " regions",
163
164 byte_size_in_proper_unit(collectable_garbage),
165 proper_unit_for_byte_size(collectable_garbage),
166 collectable_garbage_percent,
167
168 byte_size_in_proper_unit(immediate_garbage),
169 proper_unit_for_byte_size(immediate_garbage),
170 immediate_percent,
171 immediate_regions,
172
173 byte_size_in_proper_unit(collection_set->garbage()),
174 proper_unit_for_byte_size(collection_set->garbage()),
175 cset_percent,
176 collection_set->count());
177 }
178
179 void ShenandoahHeuristics::record_cycle_start() {
180 _cycle_start = os::elapsedTime();
181 }
182
183 void ShenandoahHeuristics::record_cycle_end() {
184 _last_cycle_end = os::elapsedTime();
185 }
186
187 bool ShenandoahHeuristics::should_start_gc() {
188 // Perform GC to cleanup metaspace
189 if (has_metaspace_oom()) {
190 // Some of vmTestbase/metaspace tests depend on following line to count GC cycles
191 log_info(gc)("Trigger: %s", GCCause::to_string(GCCause::_metadata_GC_threshold));
192 return true;
193 }
194
195 if (_guaranteed_gc_interval > 0) {
196 double last_time_ms = (os::elapsedTime() - _last_cycle_end) * 1000;
197 if (last_time_ms > _guaranteed_gc_interval) {
198 log_info(gc)("Trigger (%s): Time since last GC (%.0f ms) is larger than guaranteed interval (" UINTX_FORMAT " ms)",
199 _space_info->name(), last_time_ms, _guaranteed_gc_interval);
200 return true;
201 }
202 }
203
204 return false;
205 }
206
207 bool ShenandoahHeuristics::should_degenerate_cycle() {
208 return ShenandoahHeap::heap()->shenandoah_policy()->consecutive_degenerated_gc_count() <= ShenandoahFullGCThreshold;
209 }
210
211 void ShenandoahHeuristics::adjust_penalty(intx step) {
212 assert(0 <= _gc_time_penalties && _gc_time_penalties <= 100,
213 "In range before adjustment: " INTX_FORMAT, _gc_time_penalties);
214
215 intx new_val = _gc_time_penalties + step;
216 if (new_val < 0) {
217 new_val = 0;
218 }
219 if (new_val > 100) {
220 new_val = 100;
221 }
222 _gc_time_penalties = new_val;
223
224 assert(0 <= _gc_time_penalties && _gc_time_penalties <= 100,
225 "In range after adjustment: " INTX_FORMAT, _gc_time_penalties);
226 }
227
228 void ShenandoahHeuristics::record_success_concurrent(bool abbreviated) {
229 _gc_times_learned++;
230
231 adjust_penalty(Concurrent_Adjust);
232
233 if (_gc_times_learned <= ShenandoahLearningSteps || !(abbreviated && ShenandoahAdaptiveIgnoreShortCycles)) {
234 _gc_cycle_time_history->add(elapsed_cycle_time());
235 }
236 }
237
238 void ShenandoahHeuristics::record_success_degenerated() {
239 adjust_penalty(Degenerated_Penalty);
240 }
241
242 void ShenandoahHeuristics::record_success_full() {
243 adjust_penalty(Full_Penalty);
244 }
245
246 void ShenandoahHeuristics::record_allocation_failure_gc() {
247 // Do nothing.
248 }
249
250 void ShenandoahHeuristics::record_requested_gc() {
251 // Assume users call System.gc() when external state changes significantly,
252 // which forces us to re-learn the GC timings and allocation rates.
253 _gc_times_learned = 0;
254 }
255
256 bool ShenandoahHeuristics::can_unload_classes() {
257 if (!ClassUnloading) return false;
258 return true;
259 }
260
261 bool ShenandoahHeuristics::can_unload_classes_normal() {
262 if (!can_unload_classes()) return false;
263 if (has_metaspace_oom()) return true;
264 if (!ClassUnloadingWithConcurrentMark) return false;
265 if (ShenandoahUnloadClassesFrequency == 0) return false;
266 return true;
267 }
268
269 bool ShenandoahHeuristics::should_unload_classes() {
270 if (!can_unload_classes_normal()) return false;
271 if (has_metaspace_oom()) return true;
272 size_t cycle = ShenandoahHeap::heap()->shenandoah_policy()->cycle_counter();
273 // Unload classes every Nth GC cycle.
274 // This should not happen in the same cycle as process_references to amortize costs.
275 // Offsetting by one is enough to break the rendezvous when periods are equal.
276 // When periods are not equal, offsetting by one is just as good as any other guess.
277 return (cycle + 1) % ShenandoahUnloadClassesFrequency == 0;
278 }
279
280 void ShenandoahHeuristics::initialize() {
281 // Nothing to do by default.
282 }
283
284 double ShenandoahHeuristics::elapsed_cycle_time() const {
285 return os::elapsedTime() - _cycle_start;
286 }