1 /*
2 * Copyright (c) 2018, 2021, Red Hat, Inc. 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 #include "gc/shared/gcCause.hpp"
27 #include "gc/shenandoah/shenandoahAllocRequest.hpp"
28 #include "gc/shenandoah/shenandoahCollectionSet.inline.hpp"
29 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
30 #include "gc/shenandoah/shenandoahGeneration.hpp"
31 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
32 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
33 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
34 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
35 #include "gc/shenandoah/mode/shenandoahMode.hpp"
36 #include "logging/log.hpp"
37 #include "logging/logTag.hpp"
38 #include "runtime/globals_extension.hpp"
39
40 int ShenandoahHeuristics::compare_by_garbage(RegionData a, RegionData b) {
41 if (a._garbage > b._garbage)
42 return -1;
43 else if (a._garbage < b._garbage)
44 return 1;
45 else return 0;
46 }
47
48 ShenandoahHeuristics::ShenandoahHeuristics(ShenandoahGeneration* generation) :
49 _generation(generation),
50 _region_data(NULL),
51 _degenerated_cycles_in_a_row(0),
52 _successful_cycles_in_a_row(0),
53 _guaranteed_gc_interval(0),
54 _cycle_start(os::elapsedTime()),
55 _last_cycle_end(0),
56 _gc_times_learned(0),
57 _gc_time_penalties(0),
58 _gc_time_history(new TruncatedSeq(10, ShenandoahAdaptiveDecayFactor)),
59 _metaspace_oom()
60 {
61 // No unloading during concurrent mark? Communicate that to heuristics
62 if (!ClassUnloadingWithConcurrentMark) {
63 FLAG_SET_DEFAULT(ShenandoahUnloadClassesFrequency, 0);
64 }
65
66 size_t num_regions = ShenandoahHeap::heap()->num_regions();
67 assert(num_regions > 0, "Sanity");
68
69 _region_data = NEW_C_HEAP_ARRAY(RegionData, num_regions, mtGC);
70 }
71
72 ShenandoahHeuristics::~ShenandoahHeuristics() {
73 FREE_C_HEAP_ARRAY(RegionGarbage, _region_data);
74 }
75
76 // Returns true iff the chosen collection set includes old-gen regions
77 bool ShenandoahHeuristics::choose_collection_set(ShenandoahCollectionSet* collection_set, ShenandoahOldHeuristics* old_heuristics) {
78 bool result = false;
79 ShenandoahHeap* heap = ShenandoahHeap::heap();
80
81 assert(collection_set->count() == 0, "Must be empty");
82 assert(_generation->generation_mode() != OLD, "Old GC invokes ShenandoahOldHeuristics::choose_collection_set()");
83
84 // Check all pinned regions have updated status before choosing the collection set.
85 heap->assert_pinned_region_status();
86
87 // Step 1. Build up the region candidates we care about, rejecting losers and accepting winners right away.
88
89 size_t num_regions = heap->num_regions();
90
91 RegionData* candidates = _region_data;
92
93 size_t cand_idx = 0;
94
95 size_t total_garbage = 0;
96
97 size_t immediate_garbage = 0;
98 size_t immediate_regions = 0;
99
100 size_t free = 0;
101 size_t free_regions = 0;
102
103 ShenandoahMarkingContext* const ctx = _generation->complete_marking_context();
104
105 for (size_t i = 0; i < num_regions; i++) {
106 ShenandoahHeapRegion* region = heap->get_region(i);
107 if (!in_generation(region)) {
108 continue;
109 }
110
111 size_t garbage = region->garbage();
112 total_garbage += garbage;
113
114 if (region->is_empty()) {
115 free_regions++;
116 free += ShenandoahHeapRegion::region_size_bytes();
117 } else if (region->is_regular()) {
118 if (!region->has_live()) {
119 // We can recycle it right away and put it in the free set.
120 immediate_regions++;
121 immediate_garbage += garbage;
122 region->make_trash_immediate();
123 } else {
124 assert (_generation->generation_mode() != OLD, "OLD is handled elsewhere");
125
126 // This is our candidate for later consideration.
127 candidates[cand_idx]._region = region;
128 if (heap->mode()->is_generational() && (region->age() >= InitialTenuringThreshold)) {
129 // Bias selection of regions that have reached tenure age
130 for (int i = region->age() - InitialTenuringThreshold; i >= 0; i--) {
131 // Avoid floating-point math with integer multiply and shift.
132 garbage = (garbage * ShenandoahTenuredRegionUsageBias) >> ShenandoahTenuredRegionUsageBiasLogBase2;
133 }
134 }
135 candidates[cand_idx]._garbage = garbage;
136 cand_idx++;
137 }
138 } else if (region->is_humongous_start()) {
139
140 // Reclaim humongous regions here, and count them as the immediate garbage
141 #ifdef ASSERT
142 bool reg_live = region->has_live();
143 bool bm_live = ctx->is_marked(cast_to_oop(region->bottom()));
144 assert(reg_live == bm_live,
145 "Humongous liveness and marks should agree. Region live: %s; Bitmap live: %s; Region Live Words: " SIZE_FORMAT,
146 BOOL_TO_STR(reg_live), BOOL_TO_STR(bm_live), region->get_live_data_words());
147 #endif
148 if (!region->has_live()) {
149 heap->trash_humongous_region_at(region);
150
151 // Count only the start. Continuations would be counted on "trash" path
152 immediate_regions++;
153 immediate_garbage += garbage;
154 }
155 } else if (region->is_trash()) {
156 // Count in just trashed collection set, during coalesced CM-with-UR
157 immediate_regions++;
158 immediate_garbage += garbage;
159 }
160 }
161
162 // Step 2. Look back at garbage statistics, and decide if we want to collect anything,
163 // given the amount of immediately reclaimable garbage. If we do, figure out the collection set.
164
165 assert (immediate_garbage <= total_garbage,
166 "Cannot have more immediate garbage than total garbage: " SIZE_FORMAT "%s vs " SIZE_FORMAT "%s",
167 byte_size_in_proper_unit(immediate_garbage), proper_unit_for_byte_size(immediate_garbage),
168 byte_size_in_proper_unit(total_garbage), proper_unit_for_byte_size(total_garbage));
169
170 size_t immediate_percent = (total_garbage == 0) ? 0 : (immediate_garbage * 100 / total_garbage);
171
172 if (immediate_percent <= ShenandoahImmediateThreshold) {
173
174 if (old_heuristics != NULL) {
175 if (old_heuristics->prime_collection_set(collection_set)) {
176 result = true;
177 }
178 }
179 // else, this is global collection and doesn't need to prime_collection_set
180
181 // Add young-gen regions into the collection set. This is a virtual call, implemented differently by each
182 // of the heuristics subclasses.
183 choose_collection_set_from_regiondata(collection_set, candidates, cand_idx, immediate_garbage + free);
184 }
185
186 size_t cset_percent = (total_garbage == 0) ? 0 : (collection_set->garbage() * 100 / total_garbage);
187
188 size_t collectable_garbage = collection_set->garbage() + immediate_garbage;
189 size_t collectable_garbage_percent = (total_garbage == 0) ? 0 : (collectable_garbage * 100 / total_garbage);
190
191 log_info(gc, ergo)("Collectable Garbage: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), "
192 "Immediate: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), "
193 "CSet: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%)",
194
195 byte_size_in_proper_unit(collectable_garbage),
196 proper_unit_for_byte_size(collectable_garbage),
197 collectable_garbage_percent,
198
199 byte_size_in_proper_unit(immediate_garbage),
200 proper_unit_for_byte_size(immediate_garbage),
201 immediate_percent,
202
203 byte_size_in_proper_unit(collection_set->garbage()),
204 proper_unit_for_byte_size(collection_set->garbage()),
205 cset_percent);
206 return result;
207 }
208
209 void ShenandoahHeuristics::record_cycle_start() {
210 _cycle_start = os::elapsedTime();
211 }
212
213 void ShenandoahHeuristics::record_cycle_end() {
214 _last_cycle_end = os::elapsedTime();
215 }
216
217 bool ShenandoahHeuristics::should_start_gc() {
218 // Perform GC to cleanup metaspace
219 if (has_metaspace_oom()) {
220 // Some of vmTestbase/metaspace tests depend on following line to count GC cycles
221 log_info(gc)("Trigger: %s", GCCause::to_string(GCCause::_metadata_GC_threshold));
222 return true;
223 }
224
225 if (_guaranteed_gc_interval > 0) {
226 double last_time_ms = (os::elapsedTime() - _last_cycle_end) * 1000;
227 if (last_time_ms > _guaranteed_gc_interval) {
228 log_info(gc)("Trigger (%s): Time since last GC (%.0f ms) is larger than guaranteed interval (" UINTX_FORMAT " ms)",
229 _generation->name(), last_time_ms, _guaranteed_gc_interval);
230 return true;
231 }
232 }
233
234 return false;
235 }
236
237 bool ShenandoahHeuristics::should_degenerate_cycle() {
238 return _degenerated_cycles_in_a_row <= ShenandoahFullGCThreshold;
239 }
240
241 void ShenandoahHeuristics::adjust_penalty(intx step) {
242 assert(0 <= _gc_time_penalties && _gc_time_penalties <= 100,
243 "In range before adjustment: " INTX_FORMAT, _gc_time_penalties);
244
245 intx new_val = _gc_time_penalties + step;
246 if (new_val < 0) {
247 new_val = 0;
248 }
249 if (new_val > 100) {
250 new_val = 100;
251 }
252 _gc_time_penalties = new_val;
253
254 assert(0 <= _gc_time_penalties && _gc_time_penalties <= 100,
255 "In range after adjustment: " INTX_FORMAT, _gc_time_penalties);
256 }
257
258 void ShenandoahHeuristics::record_success_concurrent() {
259 _degenerated_cycles_in_a_row = 0;
260 _successful_cycles_in_a_row++;
261
262 _gc_time_history->add(time_since_last_gc());
263 _gc_times_learned++;
264
265 adjust_penalty(Concurrent_Adjust);
266 }
267
268 void ShenandoahHeuristics::record_success_degenerated() {
269 _degenerated_cycles_in_a_row++;
270 _successful_cycles_in_a_row = 0;
271
272 adjust_penalty(Degenerated_Penalty);
273 }
274
275 void ShenandoahHeuristics::record_success_full() {
276 _degenerated_cycles_in_a_row = 0;
277 _successful_cycles_in_a_row++;
278
279 adjust_penalty(Full_Penalty);
280 }
281
282 void ShenandoahHeuristics::record_allocation_failure_gc() {
283 // Do nothing.
284 }
285
286 void ShenandoahHeuristics::record_requested_gc() {
287 // Assume users call System.gc() when external state changes significantly,
288 // which forces us to re-learn the GC timings and allocation rates.
289 _gc_times_learned = 0;
290 }
291
292 bool ShenandoahHeuristics::can_unload_classes() {
293 if (!ClassUnloading) return false;
294 return true;
295 }
296
297 bool ShenandoahHeuristics::can_unload_classes_normal() {
298 if (!can_unload_classes()) return false;
299 if (has_metaspace_oom()) return true;
300 if (!ClassUnloadingWithConcurrentMark) return false;
301 if (ShenandoahUnloadClassesFrequency == 0) return false;
302 return true;
303 }
304
305 bool ShenandoahHeuristics::should_unload_classes() {
306 if (!can_unload_classes_normal()) return false;
307 if (has_metaspace_oom()) return true;
308 size_t cycle = ShenandoahHeap::heap()->shenandoah_policy()->cycle_counter();
309 // Unload classes every Nth GC cycle.
310 // This should not happen in the same cycle as process_references to amortize costs.
311 // Offsetting by one is enough to break the rendezvous when periods are equal.
312 // When periods are not equal, offsetting by one is just as good as any other guess.
313 return (cycle + 1) % ShenandoahUnloadClassesFrequency == 0;
314 }
315
316 void ShenandoahHeuristics::initialize() {
317 // Nothing to do by default.
318 }
319
320 double ShenandoahHeuristics::time_since_last_gc() const {
321 return os::elapsedTime() - _cycle_start;
322 }
323
324 bool ShenandoahHeuristics::in_generation(ShenandoahHeapRegion* region) {
325 return ((_generation->generation_mode() == GLOBAL)
326 || (_generation->generation_mode() == YOUNG && region->affiliation() == YOUNG_GENERATION)
327 || (_generation->generation_mode() == OLD && region->affiliation() == OLD_GENERATION));
328 }
329