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/shared/gcCause.hpp"
27 #include "gc/shenandoah/shenandoahCollectionSet.inline.hpp"
28 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
29 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
30 #include "gc/shenandoah/shenandoahHeapRegion.hpp"
31 #include "gc/shenandoah/shenandoahHeuristics.hpp"
32 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
33 #include "logging/log.hpp"
34 #include "logging/logTag.hpp"
35
36 int ShenandoahHeuristics::compare_by_garbage(RegionData a, RegionData b) {
37 if (a._garbage > b._garbage)
38 return -1;
39 else if (a._garbage < b._garbage)
40 return 1;
41 else return 0;
42 }
43
44 int ShenandoahHeuristics::compare_by_garbage_then_alloc_seq_ascending(RegionData a, RegionData b) {
45 int r = compare_by_garbage(a, b);
46 if (r != 0) {
47 return r;
48 }
49 return compare_by_alloc_seq_ascending(a, b);
50 }
51
52 int ShenandoahHeuristics::compare_by_alloc_seq_ascending(RegionData a, RegionData b) {
53 if (a._seqnum_last_alloc == b._seqnum_last_alloc)
54 return 0;
55 else if (a._seqnum_last_alloc < b._seqnum_last_alloc)
56 return -1;
57 else return 1;
58 }
59
60 int ShenandoahHeuristics::compare_by_alloc_seq_descending(RegionData a, RegionData b) {
61 return -compare_by_alloc_seq_ascending(a, b);
62 }
63
64 ShenandoahHeuristics::ShenandoahHeuristics() :
65 _update_refs_early(false),
66 _update_refs_adaptive(false),
67 _region_data(NULL),
68 _region_data_size(0),
69 _degenerated_cycles_in_a_row(0),
70 _successful_cycles_in_a_row(0),
71 _bytes_in_cset(0),
72 _cycle_start(os::elapsedTime()),
73 _last_cycle_end(0),
74 _gc_times_learned(0),
75 _gc_time_penalties(0),
76 _gc_time_history(new TruncatedSeq(5)),
77 _metaspace_oom()
78 {
79 if (strcmp(ShenandoahUpdateRefsEarly, "on") == 0 ||
80 strcmp(ShenandoahUpdateRefsEarly, "true") == 0 ) {
81 _update_refs_early = true;
82 } else if (strcmp(ShenandoahUpdateRefsEarly, "off") == 0 ||
83 strcmp(ShenandoahUpdateRefsEarly, "false") == 0 ) {
84 _update_refs_early = false;
85 } else if (strcmp(ShenandoahUpdateRefsEarly, "adaptive") == 0) {
86 _update_refs_adaptive = true;
87 _update_refs_early = true;
88 } else {
89 vm_exit_during_initialization("Unknown -XX:ShenandoahUpdateRefsEarly option: %s", ShenandoahUpdateRefsEarly);
90 }
91
92 // No unloading during concurrent mark? Communicate that to heuristics
93 if (!ClassUnloadingWithConcurrentMark) {
94 FLAG_SET_DEFAULT(ShenandoahUnloadClassesFrequency, 0);
95 }
96 }
97
98 ShenandoahHeuristics::~ShenandoahHeuristics() {
99 if (_region_data != NULL) {
100 FREE_C_HEAP_ARRAY(RegionGarbage, _region_data);
101 }
102 }
103
104 ShenandoahHeuristics::RegionData* ShenandoahHeuristics::get_region_data_cache(size_t num) {
105 RegionData* res = _region_data;
106 if (res == NULL) {
107 res = NEW_C_HEAP_ARRAY(RegionData, num, mtGC);
108 _region_data = res;
109 _region_data_size = num;
110 } else if (_region_data_size < num) {
111 res = REALLOC_C_HEAP_ARRAY(RegionData, _region_data, num, mtGC);
112 _region_data = res;
113 _region_data_size = num;
114 }
115 return res;
116 }
117
118 void ShenandoahHeuristics::choose_collection_set(ShenandoahCollectionSet* collection_set) {
119 assert(collection_set->count() == 0, "Must be empty");
120
121 ShenandoahHeap* heap = ShenandoahHeap::heap();
122
123 // Check all pinned regions have updated status before choosing the collection set.
124 heap->assert_pinned_region_status();
125
126 // Step 1. Build up the region candidates we care about, rejecting losers and accepting winners right away.
127
128 size_t num_regions = heap->num_regions();
129
130 RegionData* candidates = get_region_data_cache(num_regions);
131
132 size_t cand_idx = 0;
133
134 size_t total_garbage = 0;
135
136 size_t immediate_garbage = 0;
137 size_t immediate_regions = 0;
138
139 size_t free = 0;
140 size_t free_regions = 0;
141
142 ShenandoahMarkingContext* const ctx = heap->complete_marking_context();
143
144 for (size_t i = 0; i < num_regions; i++) {
145 ShenandoahHeapRegion* region = heap->get_region(i);
146
147 size_t garbage = region->garbage();
148 total_garbage += garbage;
149
150 if (region->is_empty()) {
151 free_regions++;
152 free += ShenandoahHeapRegion::region_size_bytes();
153 } else if (region->is_regular()) {
154 if (!region->has_live()) {
155 // We can recycle it right away and put it in the free set.
156 immediate_regions++;
157 immediate_garbage += garbage;
158 region->make_trash_immediate();
159 } else {
160 // This is our candidate for later consideration.
161 candidates[cand_idx]._region = region;
162 candidates[cand_idx]._garbage = garbage;
163 cand_idx++;
164 }
165 } else if (region->is_humongous_start()) {
166 // Reclaim humongous regions here, and count them as the immediate garbage
167 #ifdef ASSERT
168 bool reg_live = region->has_live();
169 bool bm_live = ctx->is_marked(oop(region->bottom()));
170 assert(reg_live == bm_live,
171 "Humongous liveness and marks should agree. Region live: %s; Bitmap live: %s; Region Live Words: " SIZE_FORMAT,
172 BOOL_TO_STR(reg_live), BOOL_TO_STR(bm_live), region->get_live_data_words());
173 #endif
174 if (!region->has_live()) {
175 heap->trash_humongous_region_at(region);
176
177 // Count only the start. Continuations would be counted on "trash" path
178 immediate_regions++;
179 immediate_garbage += garbage;
180 }
181 } else if (region->is_trash()) {
182 // Count in just trashed collection set, during coalesced CM-with-UR
183 immediate_regions++;
184 immediate_garbage += garbage;
185 }
186 }
187
188 // Step 2. Look back at garbage statistics, and decide if we want to collect anything,
189 // given the amount of immediately reclaimable garbage. If we do, figure out the collection set.
190
191 assert (immediate_garbage <= total_garbage,
192 "Cannot have more immediate garbage than total garbage: " SIZE_FORMAT "%s vs " SIZE_FORMAT "%s",
193 byte_size_in_proper_unit(immediate_garbage), proper_unit_for_byte_size(immediate_garbage),
194 byte_size_in_proper_unit(total_garbage), proper_unit_for_byte_size(total_garbage));
195
196 size_t immediate_percent = total_garbage == 0 ? 0 : (immediate_garbage * 100 / total_garbage);
197
198 if (immediate_percent <= ShenandoahImmediateThreshold) {
199 choose_collection_set_from_regiondata(collection_set, candidates, cand_idx, immediate_garbage + free);
200 collection_set->update_region_status();
201
202 size_t cset_percent = total_garbage == 0 ? 0 : (collection_set->garbage() * 100 / total_garbage);
203 log_info(gc, ergo)("Collectable Garbage: " SIZE_FORMAT "%s (" SIZE_FORMAT "%% of total), " SIZE_FORMAT "%s CSet, " SIZE_FORMAT " CSet regions",
204 byte_size_in_proper_unit(collection_set->garbage()), proper_unit_for_byte_size(collection_set->garbage()),
205 cset_percent,
206 byte_size_in_proper_unit(collection_set->live_data()), proper_unit_for_byte_size(collection_set->live_data()),
207 collection_set->count());
208 }
209
210 log_info(gc, ergo)("Immediate Garbage: " SIZE_FORMAT "%s (" SIZE_FORMAT "%% of total), " SIZE_FORMAT " regions",
211 byte_size_in_proper_unit(immediate_garbage), proper_unit_for_byte_size(immediate_garbage),
212 immediate_percent, immediate_regions);
213 }
214
215 void ShenandoahHeuristics::record_gc_start() {
216 // Do nothing
217 }
218
219 void ShenandoahHeuristics::record_gc_end() {
220 // Do nothing
221 }
222
223 void ShenandoahHeuristics::record_cycle_start() {
224 _cycle_start = os::elapsedTime();
225 }
226
227 void ShenandoahHeuristics::record_cycle_end() {
228 _last_cycle_end = os::elapsedTime();
229 }
230
231 void ShenandoahHeuristics::record_phase_time(ShenandoahPhaseTimings::Phase phase, double secs) {
232 // Do nothing
233 }
234
235 bool ShenandoahHeuristics::should_start_update_refs() {
236 return _update_refs_early;
237 }
238
239 bool ShenandoahHeuristics::should_start_gc() const {
240 // Perform GC to cleanup metaspace
241 if (has_metaspace_oom()) {
242 // Some of vmTestbase/metaspace tests depend on following line to count GC cycles
243 log_info(gc)("Trigger: %s", GCCause::to_string(GCCause::_metadata_GC_threshold));
244 return true;
245 }
246
247 if (ShenandoahGuaranteedGCInterval > 0) {
248 double last_time_ms = (os::elapsedTime() - _last_cycle_end) * 1000;
249 if (last_time_ms > ShenandoahGuaranteedGCInterval) {
250 log_info(gc)("Trigger: Time since last GC (%.0f ms) is larger than guaranteed interval (" UINTX_FORMAT " ms)",
251 last_time_ms, ShenandoahGuaranteedGCInterval);
252 return true;
253 }
254 }
255
256 return false;
257 }
258
259 bool ShenandoahHeuristics::should_degenerate_cycle() {
260 return _degenerated_cycles_in_a_row <= ShenandoahFullGCThreshold;
261 }
262
263 void ShenandoahHeuristics::record_success_concurrent() {
264 _degenerated_cycles_in_a_row = 0;
265 _successful_cycles_in_a_row++;
266
267 _gc_time_history->add(time_since_last_gc());
268 _gc_times_learned++;
269 _gc_time_penalties -= MIN2<size_t>(_gc_time_penalties, Concurrent_Adjust);
270 }
271
272 void ShenandoahHeuristics::record_success_degenerated() {
273 _degenerated_cycles_in_a_row++;
274 _successful_cycles_in_a_row = 0;
275 _gc_time_penalties += Degenerated_Penalty;
276 }
277
278 void ShenandoahHeuristics::record_success_full() {
279 _degenerated_cycles_in_a_row = 0;
280 _successful_cycles_in_a_row++;
281 _gc_time_penalties += Full_Penalty;
282 }
283
284 void ShenandoahHeuristics::record_allocation_failure_gc() {
285 _bytes_in_cset = 0;
286 }
287
288 void ShenandoahHeuristics::record_requested_gc() {
289 _bytes_in_cset = 0;
290
291 // Assume users call System.gc() when external state changes significantly,
292 // which forces us to re-learn the GC timings and allocation rates.
293 _gc_times_learned = 0;
294 }
295
296 bool ShenandoahHeuristics::can_process_references() {
297 if (ShenandoahRefProcFrequency == 0) return false;
298 return true;
299 }
300
301 bool ShenandoahHeuristics::should_process_references() {
302 if (!can_process_references()) return false;
303 size_t cycle = ShenandoahHeap::heap()->shenandoah_policy()->cycle_counter();
304 // Process references every Nth GC cycle.
305 return cycle % ShenandoahRefProcFrequency == 0;
306 }
307
308 bool ShenandoahHeuristics::can_unload_classes() {
309 if (!ClassUnloading) return false;
310 return true;
311 }
312
313 bool ShenandoahHeuristics::can_unload_classes_normal() {
314 if (!can_unload_classes()) return false;
315 if (has_metaspace_oom()) return true;
316 if (!ClassUnloadingWithConcurrentMark) return false;
317 if (ShenandoahUnloadClassesFrequency == 0) return false;
318 return true;
319 }
320
321 bool ShenandoahHeuristics::should_unload_classes() {
322 if (!can_unload_classes_normal()) return false;
323 if (has_metaspace_oom()) return true;
324 size_t cycle = ShenandoahHeap::heap()->shenandoah_policy()->cycle_counter();
325 // Unload classes every Nth GC cycle.
326 // This should not happen in the same cycle as process_references to amortize costs.
327 // Offsetting by one is enough to break the rendezvous when periods are equal.
328 // When periods are not equal, offsetting by one is just as good as any other guess.
329 return (cycle + 1) % ShenandoahUnloadClassesFrequency == 0;
330 }
331
332 void ShenandoahHeuristics::initialize() {
333 // Nothing to do by default.
334 }
335
336 double ShenandoahHeuristics::time_since_last_gc() const {
337 return os::elapsedTime() - _cycle_start;
338 }