1 /*
2 * Copyright (c) 2018, 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.hpp"
30 #include "gc_implementation/shenandoah/shenandoahHeuristics.hpp"
31 #include "gc_implementation/shenandoah/shenandoahMarkingContext.inline.hpp"
32 #include "gc_implementation/shenandoah/shenandoahUtils.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 int ShenandoahHeuristics::compare_by_alloc_seq_ascending(RegionData a, RegionData b) {
43 if (a._seqnum_last_alloc == b._seqnum_last_alloc)
44 return 0;
45 else if (a._seqnum_last_alloc < b._seqnum_last_alloc)
46 return -1;
47 else return 1;
48 }
49
50 int ShenandoahHeuristics::compare_by_alloc_seq_descending(RegionData a, RegionData b) {
51 return -compare_by_alloc_seq_ascending(a, b);
52 }
53
54 ShenandoahHeuristics::ShenandoahHeuristics() :
55 _update_refs_early(false),
56 _update_refs_adaptive(false),
57 _region_data(NULL),
58 _region_data_size(0),
59 _degenerated_cycles_in_a_row(0),
60 _successful_cycles_in_a_row(0),
61 _bytes_in_cset(0),
62 _cycle_start(os::elapsedTime()),
63 _last_cycle_end(0),
64 _gc_times_learned(0),
65 _gc_time_penalties(0),
66 _gc_time_history(new TruncatedSeq(5)),
67 _metaspace_oom()
68 {
69 if (strcmp(ShenandoahUpdateRefsEarly, "on") == 0 ||
70 strcmp(ShenandoahUpdateRefsEarly, "true") == 0 ) {
71 _update_refs_early = true;
72 } else if (strcmp(ShenandoahUpdateRefsEarly, "off") == 0 ||
73 strcmp(ShenandoahUpdateRefsEarly, "false") == 0 ) {
74 _update_refs_early = false;
75 } else if (strcmp(ShenandoahUpdateRefsEarly, "adaptive") == 0) {
76 _update_refs_adaptive = true;
77 _update_refs_early = true;
78 } else {
79 vm_exit_during_initialization("Unknown -XX:ShenandoahUpdateRefsEarly option: %s", ShenandoahUpdateRefsEarly);
80 }
81
82 // No unloading during concurrent mark? Communicate that to heuristics
83 if (!ClassUnloadingWithConcurrentMark) {
84 FLAG_SET_DEFAULT(ShenandoahUnloadClassesFrequency, 0);
85 }
86 }
87
88 ShenandoahHeuristics::~ShenandoahHeuristics() {
89 if (_region_data != NULL) {
90 FREE_C_HEAP_ARRAY(RegionGarbage, _region_data, mtGC);
91 }
92 }
93
94 ShenandoahHeuristics::RegionData* ShenandoahHeuristics::get_region_data_cache(size_t num) {
95 RegionData* res = _region_data;
96 if (res == NULL) {
97 res = NEW_C_HEAP_ARRAY(RegionData, num, mtGC);
98 _region_data = res;
99 _region_data_size = num;
100 } else if (_region_data_size < num) {
101 res = REALLOC_C_HEAP_ARRAY(RegionData, _region_data, num, mtGC);
102 _region_data = res;
103 _region_data_size = num;
104 }
105 return res;
106 }
107
108 void ShenandoahHeuristics::choose_collection_set(ShenandoahCollectionSet* collection_set) {
109 assert(collection_set->count() == 0, "Must be empty");
110 start_choose_collection_set();
111
112 ShenandoahHeap* heap = ShenandoahHeap::heap();
113
114 // Check all pinned regions have updated status before choosing the collection set.
115 heap->assert_pinned_region_status();
116
117 // Step 1. Build up the region candidates we care about, rejecting losers and accepting winners right away.
118
119 size_t num_regions = heap->num_regions();
120
121 RegionData* candidates = get_region_data_cache(num_regions);
122
123 size_t cand_idx = 0;
124
125 size_t total_garbage = 0;
126
127 size_t immediate_garbage = 0;
128 size_t immediate_regions = 0;
129
130 size_t free = 0;
131 size_t free_regions = 0;
132
133 ShenandoahMarkingContext* const ctx = heap->complete_marking_context();
134
135 for (size_t i = 0; i < num_regions; i++) {
136 ShenandoahHeapRegion* region = heap->get_region(i);
137
138 size_t garbage = region->garbage();
139 total_garbage += garbage;
140
141 if (region->is_empty()) {
142 free_regions++;
143 free += ShenandoahHeapRegion::region_size_bytes();
144 } else if (region->is_regular()) {
145 if (!region->has_live()) {
146 // We can recycle it right away and put it in the free set.
147 immediate_regions++;
148 immediate_garbage += garbage;
149 region->make_trash_immediate();
150 } else {
151 // This is our candidate for later consideration.
152 candidates[cand_idx]._region = region;
153 candidates[cand_idx]._garbage = garbage;
154 cand_idx++;
155 }
156 } else if (region->is_humongous_start()) {
157 // Reclaim humongous regions here, and count them as the immediate garbage
158 #ifdef ASSERT
159 bool reg_live = region->has_live();
160 bool bm_live = ctx->is_marked(oop(region->bottom()));
161 assert(reg_live == bm_live,
162 err_msg("Humongous liveness and marks should agree. Region live: %s; Bitmap live: %s; Region Live Words: " SIZE_FORMAT,
163 BOOL_TO_STR(reg_live), BOOL_TO_STR(bm_live), region->get_live_data_words()));
164 #endif
165 if (!region->has_live()) {
166 heap->trash_humongous_region_at(region);
167
168 // Count only the start. Continuations would be counted on "trash" path
169 immediate_regions++;
170 immediate_garbage += garbage;
171 }
172 } else if (region->is_trash()) {
173 // Count in just trashed collection set, during coalesced CM-with-UR
174 immediate_regions++;
175 immediate_garbage += garbage;
176 }
177 }
178
179 // Step 2. Look back at garbage statistics, and decide if we want to collect anything,
180 // given the amount of immediately reclaimable garbage. If we do, figure out the collection set.
181
182 assert (immediate_garbage <= total_garbage,
183 err_msg("Cannot have more immediate garbage than total garbage: " SIZE_FORMAT "%s vs " SIZE_FORMAT "%s",
184 byte_size_in_proper_unit(immediate_garbage), proper_unit_for_byte_size(immediate_garbage),
185 byte_size_in_proper_unit(total_garbage), proper_unit_for_byte_size(total_garbage)));
186
187 size_t immediate_percent = total_garbage == 0 ? 0 : (immediate_garbage * 100 / total_garbage);
188
189 if (immediate_percent <= ShenandoahImmediateThreshold) {
190 choose_collection_set_from_regiondata(collection_set, candidates, cand_idx, immediate_garbage + free);
191 collection_set->update_region_status();
192
193 size_t cset_percent = total_garbage == 0 ? 0 : (collection_set->garbage() * 100 / total_garbage);
194 log_info(gc, ergo)("Collectable Garbage: " SIZE_FORMAT "%s (" SIZE_FORMAT "%% of total), " SIZE_FORMAT "%s CSet, " SIZE_FORMAT " CSet regions",
195 byte_size_in_proper_unit(collection_set->garbage()), proper_unit_for_byte_size(collection_set->garbage()),
196 cset_percent,
197 byte_size_in_proper_unit(collection_set->live_data()), proper_unit_for_byte_size(collection_set->live_data()),
198 collection_set->count());
199 }
200 end_choose_collection_set();
201
202 log_info(gc, ergo)("Immediate Garbage: " SIZE_FORMAT "%s (" SIZE_FORMAT "%% of total), " SIZE_FORMAT " regions",
203 byte_size_in_proper_unit(immediate_garbage), proper_unit_for_byte_size(immediate_garbage),
204 immediate_percent, immediate_regions);
205 }
206
207 void ShenandoahHeuristics::record_gc_start() {
208 // Do nothing
209 }
210
211 void ShenandoahHeuristics::record_gc_end() {
212 // Do nothing
213 }
214
215 void ShenandoahHeuristics::record_cycle_start() {
216 _cycle_start = os::elapsedTime();
217 }
218
219 void ShenandoahHeuristics::record_cycle_end() {
220 _last_cycle_end = os::elapsedTime();
221 }
222
223 void ShenandoahHeuristics::record_phase_time(ShenandoahPhaseTimings::Phase phase, double secs) {
224 // Do nothing
225 }
226
227 bool ShenandoahHeuristics::should_start_update_refs() {
228 return _update_refs_early;
229 }
230
231 bool ShenandoahHeuristics::should_degenerate_cycle() {
232 return _degenerated_cycles_in_a_row <= ShenandoahFullGCThreshold;
233 }
234
235 void ShenandoahHeuristics::record_success_concurrent() {
236 _degenerated_cycles_in_a_row = 0;
237 _successful_cycles_in_a_row++;
238
239 _gc_time_history->add(time_since_last_gc());
240 _gc_times_learned++;
241 _gc_time_penalties -= MIN2<size_t>(_gc_time_penalties, Concurrent_Adjust);
242 }
243
244 void ShenandoahHeuristics::record_success_degenerated() {
245 _degenerated_cycles_in_a_row++;
246 _successful_cycles_in_a_row = 0;
247 _gc_time_penalties += Degenerated_Penalty;
248 }
249
250 void ShenandoahHeuristics::record_success_full() {
251 _degenerated_cycles_in_a_row = 0;
252 _successful_cycles_in_a_row++;
253 _gc_time_penalties += Full_Penalty;
254 }
255
256 void ShenandoahHeuristics::record_allocation_failure_gc() {
257 _bytes_in_cset = 0;
258 }
259
260 void ShenandoahHeuristics::record_requested_gc() {
261 _bytes_in_cset = 0;
262
263 // Assume users call System.gc() when external state changes significantly,
264 // which forces us to re-learn the GC timings and allocation rates.
265 _gc_times_learned = 0;
266 }
267
268 bool ShenandoahHeuristics::can_process_references() {
269 if (ShenandoahRefProcFrequency == 0) return false;
270 return true;
271 }
272
273 bool ShenandoahHeuristics::should_process_references() {
274 if (!can_process_references()) return false;
275 size_t cycle = ShenandoahHeap::heap()->shenandoah_policy()->cycle_counter();
276 // Process references every Nth GC cycle.
277 return cycle % ShenandoahRefProcFrequency == 0;
278 }
279
280 bool ShenandoahHeuristics::can_unload_classes() {
281 if (!ClassUnloading) return false;
282 return true;
283 }
284
285 bool ShenandoahHeuristics::can_unload_classes_normal() {
286 if (!can_unload_classes()) return false;
287 if (has_metaspace_oom()) return true;
288 if (!ClassUnloadingWithConcurrentMark) return false;
289 if (ShenandoahUnloadClassesFrequency == 0) return false;
290 return true;
291 }
292
293 bool ShenandoahHeuristics::should_unload_classes() {
294 if (!can_unload_classes_normal()) return false;
295 if (has_metaspace_oom()) return true;
296 size_t cycle = ShenandoahHeap::heap()->shenandoah_policy()->cycle_counter();
297 // Unload classes every Nth GC cycle.
298 // This should not happen in the same cycle as process_references to amortize costs.
299 // Offsetting by one is enough to break the rendezvous when periods are equal.
300 // When periods are not equal, offsetting by one is just as good as any other guess.
301 return (cycle + 1) % ShenandoahUnloadClassesFrequency == 0;
302 }
303
304 void ShenandoahHeuristics::initialize() {
305 // Nothing to do by default.
306 }
307
308 double ShenandoahHeuristics::time_since_last_gc() const {
309 return os::elapsedTime() - _cycle_start;
310 }
311
312 bool ShenandoahHeuristics::should_start_gc() const {
313 // Perform GC to cleanup metaspace
314 if (has_metaspace_oom()) {
315 // Some of vmTestbase/metaspace tests depend on following line to count GC cycles
316 log_info(gc)("Trigger: %s", GCCause::to_string(GCCause::_metadata_GC_threshold));
317 return true;
318 }
319
320 double last_time_ms = (os::elapsedTime() - _last_cycle_end) * 1000;
321 bool periodic_gc = (last_time_ms > ShenandoahGuaranteedGCInterval);
322 if (periodic_gc) {
323 log_info(gc)("Trigger: Time since last GC (%.0f ms) is larger than guaranteed interval (" UINTX_FORMAT " ms)",
324 last_time_ms, ShenandoahGuaranteedGCInterval);
325 }
326 return periodic_gc;
327 }