1 /*
2 * Copyright (c) 2018, 2020, 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
27 #include "gc/shared/gcCause.hpp"
28 #include "gc/shenandoah/shenandoahCollectionSet.inline.hpp"
29 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
30 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
31 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
32 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
33 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
34 #include "logging/log.hpp"
35 #include "logging/logTag.hpp"
36
37 int ShenandoahHeuristics::compare_by_garbage(RegionData a, RegionData b) {
38 if (a._garbage > b._garbage)
39 return -1;
40 else if (a._garbage < b._garbage)
41 return 1;
42 else return 0;
43 }
44
45 ShenandoahHeuristics::ShenandoahHeuristics() :
46 _region_data(NULL),
47 _degenerated_cycles_in_a_row(0),
48 _successful_cycles_in_a_row(0),
49 _cycle_start(os::elapsedTime()),
50 _last_cycle_end(0),
51 _gc_times_learned(0),
52 _gc_time_penalties(0),
53 _gc_time_history(new TruncatedSeq(5)),
54 _metaspace_oom()
55 {
56 // No unloading during concurrent mark? Communicate that to heuristics
57 if (!ClassUnloadingWithConcurrentMark) {
58 FLAG_SET_DEFAULT(ShenandoahUnloadClassesFrequency, 0);
59 }
60
61 size_t num_regions = ShenandoahHeap::heap()->num_regions();
62 assert(num_regions > 0, "Sanity");
63
64 _region_data = NEW_C_HEAP_ARRAY(RegionData, num_regions, mtGC);
65 }
66
67 ShenandoahHeuristics::~ShenandoahHeuristics() {
68 FREE_C_HEAP_ARRAY(RegionGarbage, _region_data);
69 }
70
71 void ShenandoahHeuristics::choose_collection_set(ShenandoahCollectionSet* collection_set) {
72 assert(collection_set->count() == 0, "Must be empty");
73
74 ShenandoahHeap* heap = ShenandoahHeap::heap();
75
76 // Check all pinned regions have updated status before choosing the collection set.
77 heap->assert_pinned_region_status();
78
79 // Step 1. Build up the region candidates we care about, rejecting losers and accepting winners right away.
80
81 size_t num_regions = heap->num_regions();
82
83 RegionData* candidates = _region_data;
84
85 size_t cand_idx = 0;
86
87 size_t total_garbage = 0;
88
89 size_t immediate_garbage = 0;
90 size_t immediate_regions = 0;
91
92 size_t free = 0;
93 size_t free_regions = 0;
94
95 ShenandoahMarkingContext* const ctx = heap->complete_marking_context();
96
97 for (size_t i = 0; i < num_regions; i++) {
98 ShenandoahHeapRegion* region = heap->get_region(i);
99
100 size_t garbage = region->garbage();
101 total_garbage += garbage;
102
103 if (region->is_empty()) {
104 free_regions++;
105 free += ShenandoahHeapRegion::region_size_bytes();
106 } else if (region->is_regular()) {
107 if (!region->has_live()) {
108 // We can recycle it right away and put it in the free set.
109 immediate_regions++;
110 immediate_garbage += garbage;
111 region->make_trash_immediate();
112 } else {
113 // This is our candidate for later consideration.
114 candidates[cand_idx]._region = region;
115 candidates[cand_idx]._garbage = garbage;
116 cand_idx++;
117 }
118 } else if (region->is_humongous_start()) {
119 // Reclaim humongous regions here, and count them as the immediate garbage
120 #ifdef ASSERT
121 bool reg_live = region->has_live();
122 bool bm_live = ctx->is_marked(oop(region->bottom()));
123 assert(reg_live == bm_live,
124 "Humongous liveness and marks should agree. Region live: %s; Bitmap live: %s; Region Live Words: " SIZE_FORMAT,
125 BOOL_TO_STR(reg_live), BOOL_TO_STR(bm_live), region->get_live_data_words());
126 #endif
127 if (!region->has_live()) {
128 heap->trash_humongous_region_at(region);
129
130 // Count only the start. Continuations would be counted on "trash" path
131 immediate_regions++;
132 immediate_garbage += garbage;
133 }
134 } else if (region->is_trash()) {
135 // Count in just trashed collection set, during coalesced CM-with-UR
136 immediate_regions++;
137 immediate_garbage += garbage;
138 }
139 }
140
141 // Step 2. Look back at garbage statistics, and decide if we want to collect anything,
142 // given the amount of immediately reclaimable garbage. If we do, figure out the collection set.
143
144 assert (immediate_garbage <= total_garbage,
145 "Cannot have more immediate garbage than total garbage: " SIZE_FORMAT "%s vs " SIZE_FORMAT "%s",
146 byte_size_in_proper_unit(immediate_garbage), proper_unit_for_byte_size(immediate_garbage),
147 byte_size_in_proper_unit(total_garbage), proper_unit_for_byte_size(total_garbage));
148
149 size_t immediate_percent = (total_garbage == 0) ? 0 : (immediate_garbage * 100 / total_garbage);
150
151 if (immediate_percent <= ShenandoahImmediateThreshold) {
152 choose_collection_set_from_regiondata(collection_set, candidates, cand_idx, immediate_garbage + free);
153 }
154
155 size_t cset_percent = (total_garbage == 0) ? 0 : (collection_set->garbage() * 100 / total_garbage);
156
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 "%%), "
162 "CSet: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%)",
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
172 byte_size_in_proper_unit(collection_set->garbage()),
173 proper_unit_for_byte_size(collection_set->garbage()),
174 cset_percent);
175 }
176
177 void ShenandoahHeuristics::record_cycle_start() {
178 _cycle_start = os::elapsedTime();
179 }
180
181 void ShenandoahHeuristics::record_cycle_end() {
182 _last_cycle_end = os::elapsedTime();
183 }
184
185 bool ShenandoahHeuristics::should_start_gc() const {
186 // Perform GC to cleanup metaspace
187 if (has_metaspace_oom()) {
188 // Some of vmTestbase/metaspace tests depend on following line to count GC cycles
189 log_info(gc)("Trigger: %s", GCCause::to_string(GCCause::_metadata_GC_threshold));
190 return true;
191 }
192
193 if (ShenandoahGuaranteedGCInterval > 0) {
194 double last_time_ms = (os::elapsedTime() - _last_cycle_end) * 1000;
195 if (last_time_ms > ShenandoahGuaranteedGCInterval) {
196 log_info(gc)("Trigger: Time since last GC (%.0f ms) is larger than guaranteed interval (" UINTX_FORMAT " ms)",
197 last_time_ms, ShenandoahGuaranteedGCInterval);
198 return true;
199 }
200 }
201
202 return false;
203 }
204
205 bool ShenandoahHeuristics::should_degenerate_cycle() {
206 return _degenerated_cycles_in_a_row <= ShenandoahFullGCThreshold;
207 }
208
209 void ShenandoahHeuristics::adjust_penalty(intx step) {
210 assert(0 <= _gc_time_penalties && _gc_time_penalties <= 100,
211 "In range before adjustment: " INTX_FORMAT, _gc_time_penalties);
212
213 intx new_val = _gc_time_penalties + step;
214 if (new_val < 0) {
215 new_val = 0;
216 }
217 if (new_val > 100) {
218 new_val = 100;
219 }
220 _gc_time_penalties = new_val;
221
222 assert(0 <= _gc_time_penalties && _gc_time_penalties <= 100,
223 "In range after adjustment: " INTX_FORMAT, _gc_time_penalties);
224 }
225
226 void ShenandoahHeuristics::record_success_concurrent() {
227 _degenerated_cycles_in_a_row = 0;
228 _successful_cycles_in_a_row++;
229
230 _gc_time_history->add(time_since_last_gc());
231 _gc_times_learned++;
232
233 adjust_penalty(Concurrent_Adjust);
234 }
235
236 void ShenandoahHeuristics::record_success_degenerated() {
237 _degenerated_cycles_in_a_row++;
238 _successful_cycles_in_a_row = 0;
239
240 adjust_penalty(Degenerated_Penalty);
241 }
242
243 void ShenandoahHeuristics::record_success_full() {
244 _degenerated_cycles_in_a_row = 0;
245 _successful_cycles_in_a_row++;
246
247 adjust_penalty(Full_Penalty);
248 }
249
250 void ShenandoahHeuristics::record_allocation_failure_gc() {
251 // Do nothing.
252 }
253
254 void ShenandoahHeuristics::record_requested_gc() {
255 // Assume users call System.gc() when external state changes significantly,
256 // which forces us to re-learn the GC timings and allocation rates.
257 _gc_times_learned = 0;
258 }
259
260 bool ShenandoahHeuristics::can_process_references() {
261 if (ShenandoahRefProcFrequency == 0) return false;
262 return true;
263 }
264
265 bool ShenandoahHeuristics::should_process_references() {
266 if (!can_process_references()) return false;
267 size_t cycle = ShenandoahHeap::heap()->shenandoah_policy()->cycle_counter();
268 // Process references every Nth GC cycle.
269 return cycle % ShenandoahRefProcFrequency == 0;
270 }
271
272 bool ShenandoahHeuristics::can_unload_classes() {
273 if (!ClassUnloading) return false;
274 return true;
275 }
276
277 bool ShenandoahHeuristics::can_unload_classes_normal() {
278 if (!can_unload_classes()) return false;
279 if (has_metaspace_oom()) return true;
280 if (!ClassUnloadingWithConcurrentMark) return false;
281 if (ShenandoahUnloadClassesFrequency == 0) return false;
282 return true;
283 }
284
285 bool ShenandoahHeuristics::should_unload_classes() {
286 if (!can_unload_classes_normal()) return false;
287 if (has_metaspace_oom()) return true;
288 size_t cycle = ShenandoahHeap::heap()->shenandoah_policy()->cycle_counter();
289 // Unload classes every Nth GC cycle.
290 // This should not happen in the same cycle as process_references to amortize costs.
291 // Offsetting by one is enough to break the rendezvous when periods are equal.
292 // When periods are not equal, offsetting by one is just as good as any other guess.
293 return (cycle + 1) % ShenandoahUnloadClassesFrequency == 0;
294 }
295
296 void ShenandoahHeuristics::initialize() {
297 // Nothing to do by default.
298 }
299
300 double ShenandoahHeuristics::time_since_last_gc() const {
301 return os::elapsedTime() - _cycle_start;
302 }