1 /*
2 * Copyright (c) 2018, 2020, Red Hat, Inc. All rights reserved.
3 *
4 * This code is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 only, as
6 * published by the Free Software Foundation.
7 *
8 * This code is distributed in the hope that it will be useful, but WITHOUT
9 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
10 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
11 * version 2 for more details (a copy is included in the LICENSE file that
12 * accompanied this code).
13 *
14 * You should have received a copy of the GNU General Public License version
15 * 2 along with this work; if not, write to the Free Software Foundation,
16 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
17 *
18 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
19 * or visit www.oracle.com if you need additional information or have any
20 * questions.
21 *
22 */
23
24 #include "precompiled.hpp"
25
26 #include "gc_interface/gcCause.hpp"
27 #include "gc_implementation/shenandoah/shenandoahCollectorPolicy.hpp"
28 #include "gc_implementation/shenandoah/shenandoahHeap.inline.hpp"
29 #include "gc_implementation/shenandoah/shenandoahHeapRegion.inline.hpp"
30 #include "gc_implementation/shenandoah/shenandoahMarkingContext.inline.hpp"
31 #include "gc_implementation/shenandoah/shenandoahUtils.hpp"
32 #include "gc_implementation/shenandoah/heuristics/shenandoahHeuristics.hpp"
33
34 int ShenandoahHeuristics::compare_by_garbage(RegionData a, RegionData b) {
35 if (a._garbage > b._garbage)
36 return -1;
37 else if (a._garbage < b._garbage)
38 return 1;
39 else return 0;
40 }
41
42 ShenandoahHeuristics::ShenandoahHeuristics() :
43 _region_data(NULL),
44 _degenerated_cycles_in_a_row(0),
45 _successful_cycles_in_a_row(0),
46 _cycle_start(os::elapsedTime()),
47 _last_cycle_end(0),
48 _gc_times_learned(0),
49 _gc_time_penalties(0),
50 _gc_time_history(new TruncatedSeq(5)),
51 _metaspace_oom()
52 {
53 // No unloading during concurrent mark? Communicate that to heuristics
54 if (!ClassUnloadingWithConcurrentMark) {
55 FLAG_SET_DEFAULT(ShenandoahUnloadClassesFrequency, 0);
56 }
57
58 size_t num_regions = ShenandoahHeap::heap()->num_regions();
59 assert(num_regions > 0, "Sanity");
60
61 _region_data = NEW_C_HEAP_ARRAY(RegionData, num_regions, mtGC);
62 }
63
64 ShenandoahHeuristics::~ShenandoahHeuristics() {
65 FREE_C_HEAP_ARRAY(RegionGarbage, _region_data, mtGC);
66 }
67
68 void ShenandoahHeuristics::choose_collection_set(ShenandoahCollectionSet* collection_set) {
69 assert(collection_set->count() == 0, "Must be empty");
70 start_choose_collection_set();
71
72 ShenandoahHeap* heap = ShenandoahHeap::heap();
73
74 // Check all pinned regions have updated status before choosing the collection set.
75 heap->assert_pinned_region_status();
76
77 // Step 1. Build up the region candidates we care about, rejecting losers and accepting winners right away.
78
79 size_t num_regions = heap->num_regions();
80
81 RegionData* candidates = _region_data;
82
83 size_t cand_idx = 0;
84
85 size_t total_garbage = 0;
86
87 size_t immediate_garbage = 0;
88 size_t immediate_regions = 0;
89
90 size_t free = 0;
91 size_t free_regions = 0;
92
93 ShenandoahMarkingContext* const ctx = heap->complete_marking_context();
94
95 for (size_t i = 0; i < num_regions; i++) {
96 ShenandoahHeapRegion* region = heap->get_region(i);
97
98 size_t garbage = region->garbage();
99 total_garbage += garbage;
100
101 if (region->is_empty()) {
102 free_regions++;
103 free += ShenandoahHeapRegion::region_size_bytes();
104 } else if (region->is_regular()) {
105 if (!region->has_live()) {
106 // We can recycle it right away and put it in the free set.
107 immediate_regions++;
108 immediate_garbage += garbage;
109 region->make_trash_immediate();
110 } else {
111 // This is our candidate for later consideration.
112 candidates[cand_idx]._region = region;
113 candidates[cand_idx]._garbage = garbage;
114 cand_idx++;
115 }
116 } else if (region->is_humongous_start()) {
117 // Reclaim humongous regions here, and count them as the immediate garbage
118 #ifdef ASSERT
119 bool reg_live = region->has_live();
120 bool bm_live = ctx->is_marked(oop(region->bottom()));
121 assert(reg_live == bm_live,
122 err_msg("Humongous liveness and marks should agree. Region live: %s; Bitmap live: %s; Region Live Words: " SIZE_FORMAT,
123 BOOL_TO_STR(reg_live), BOOL_TO_STR(bm_live), region->get_live_data_words()));
124 #endif
125 if (!region->has_live()) {
126 heap->trash_humongous_region_at(region);
127
128 // Count only the start. Continuations would be counted on "trash" path
129 immediate_regions++;
130 immediate_garbage += garbage;
131 }
132 } else if (region->is_trash()) {
133 // Count in just trashed collection set, during coalesced CM-with-UR
134 immediate_regions++;
135 immediate_garbage += garbage;
136 }
137 }
138
139 // Step 2. Look back at garbage statistics, and decide if we want to collect anything,
140 // given the amount of immediately reclaimable garbage. If we do, figure out the collection set.
141
142 assert (immediate_garbage <= total_garbage,
143 err_msg("Cannot have more immediate garbage than total garbage: " SIZE_FORMAT "%s vs " SIZE_FORMAT "%s",
144 byte_size_in_proper_unit(immediate_garbage), proper_unit_for_byte_size(immediate_garbage),
145 byte_size_in_proper_unit(total_garbage), proper_unit_for_byte_size(total_garbage)));
146
147 size_t immediate_percent = (total_garbage == 0) ? 0 : (immediate_garbage * 100 / total_garbage);
148
149 if (immediate_percent <= ShenandoahImmediateThreshold) {
150 choose_collection_set_from_regiondata(collection_set, candidates, cand_idx, immediate_garbage + free);
151 }
152
153 size_t cset_percent = (total_garbage == 0) ? 0 : (collection_set->garbage() * 100 / total_garbage);
154
155 size_t collectable_garbage = collection_set->garbage() + immediate_garbage;
156 size_t collectable_garbage_percent = (total_garbage == 0) ? 0 : (collectable_garbage * 100 / total_garbage);
157
158 log_info(gc, ergo)("Collectable Garbage: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), "
159 "Immediate: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), "
160 "CSet: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%)",
161
162 byte_size_in_proper_unit(collectable_garbage),
163 proper_unit_for_byte_size(collectable_garbage),
164 collectable_garbage_percent,
165
166 byte_size_in_proper_unit(immediate_garbage),
167 proper_unit_for_byte_size(immediate_garbage),
168 immediate_percent,
169
170 byte_size_in_proper_unit(collection_set->garbage()),
171 proper_unit_for_byte_size(collection_set->garbage()),
172 cset_percent);
173 }
174
175 void ShenandoahHeuristics::record_cycle_start() {
176 _cycle_start = os::elapsedTime();
177 }
178
179 void ShenandoahHeuristics::record_cycle_end() {
180 _last_cycle_end = os::elapsedTime();
181 }
182
183 bool ShenandoahHeuristics::should_degenerate_cycle() {
184 return _degenerated_cycles_in_a_row <= ShenandoahFullGCThreshold;
185 }
186
187 void ShenandoahHeuristics::adjust_penalty(intx step) {
188 assert(0 <= _gc_time_penalties && _gc_time_penalties <= 100,
189 err_msg("In range before adjustment: " INTX_FORMAT, _gc_time_penalties));
190
191 intx new_val = _gc_time_penalties + step;
192 if (new_val < 0) {
193 new_val = 0;
194 }
195 if (new_val > 100) {
196 new_val = 100;
197 }
198 _gc_time_penalties = new_val;
199
200 assert(0 <= _gc_time_penalties && _gc_time_penalties <= 100,
201 err_msg("In range after adjustment: " INTX_FORMAT, _gc_time_penalties));
202 }
203
204 void ShenandoahHeuristics::record_success_concurrent() {
205 _degenerated_cycles_in_a_row = 0;
206 _successful_cycles_in_a_row++;
207
208 _gc_time_history->add(time_since_last_gc());
209 _gc_times_learned++;
210
211 adjust_penalty(Concurrent_Adjust);
212 }
213
214 void ShenandoahHeuristics::record_success_degenerated() {
215 _degenerated_cycles_in_a_row++;
216 _successful_cycles_in_a_row = 0;
217
218 adjust_penalty(Degenerated_Penalty);
219 }
220
221 void ShenandoahHeuristics::record_success_full() {
222 _degenerated_cycles_in_a_row = 0;
223 _successful_cycles_in_a_row++;
224
225 adjust_penalty(Full_Penalty);
226 }
227
228 void ShenandoahHeuristics::record_allocation_failure_gc() {
229 // Do nothing.
230 }
231
232 void ShenandoahHeuristics::record_requested_gc() {
233 // Assume users call System.gc() when external state changes significantly,
234 // which forces us to re-learn the GC timings and allocation rates.
235 _gc_times_learned = 0;
236 }
237
238 bool ShenandoahHeuristics::can_process_references() {
239 if (ShenandoahRefProcFrequency == 0) return false;
240 return true;
241 }
242
243 bool ShenandoahHeuristics::should_process_references() {
244 if (!can_process_references()) return false;
245 size_t cycle = ShenandoahHeap::heap()->shenandoah_policy()->cycle_counter();
246 // Process references every Nth GC cycle.
247 return cycle % ShenandoahRefProcFrequency == 0;
248 }
249
250 bool ShenandoahHeuristics::can_unload_classes() {
251 if (!ClassUnloading) return false;
252 return true;
253 }
254
255 bool ShenandoahHeuristics::can_unload_classes_normal() {
256 if (!can_unload_classes()) return false;
257 if (has_metaspace_oom()) return true;
258 if (!ClassUnloadingWithConcurrentMark) return false;
259 if (ShenandoahUnloadClassesFrequency == 0) return false;
260 return true;
261 }
262
263 bool ShenandoahHeuristics::should_unload_classes() {
264 if (!can_unload_classes_normal()) return false;
265 if (has_metaspace_oom()) return true;
266 size_t cycle = ShenandoahHeap::heap()->shenandoah_policy()->cycle_counter();
267 // Unload classes every Nth GC cycle.
268 // This should not happen in the same cycle as process_references to amortize costs.
269 // Offsetting by one is enough to break the rendezvous when periods are equal.
270 // When periods are not equal, offsetting by one is just as good as any other guess.
271 return (cycle + 1) % ShenandoahUnloadClassesFrequency == 0;
272 }
273
274 void ShenandoahHeuristics::initialize() {
275 // Nothing to do by default.
276 }
277
278 double ShenandoahHeuristics::time_since_last_gc() const {
279 return os::elapsedTime() - _cycle_start;
280 }
281
282 bool ShenandoahHeuristics::should_start_gc() const {
283 // Perform GC to cleanup metaspace
284 if (has_metaspace_oom()) {
285 // Some of vmTestbase/metaspace tests depend on following line to count GC cycles
286 log_info(gc)("Trigger: %s", GCCause::to_string(GCCause::_metadata_GC_threshold));
287 return true;
288 }
289
290 if (ShenandoahGuaranteedGCInterval > 0) {
291 double last_time_ms = (os::elapsedTime() - _last_cycle_end) * 1000;
292 if (last_time_ms > ShenandoahGuaranteedGCInterval) {
293 log_info(gc)("Trigger: Time since last GC (%.0f ms) is larger than guaranteed interval (" UINTX_FORMAT " ms)",
294 last_time_ms, ShenandoahGuaranteedGCInterval);
295 return true;
296 }
297 }
298
299 return false;
300 }