1 /*
2 * Copyright (c) 2018, Red Hat, Inc. and/or its affiliates.
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 #include "gc_implementation/shenandoah/brooksPointer.hpp"
26 #include "gc_implementation/shenandoah/shenandoahCollectorPolicy.hpp"
27 #include "gc_implementation/shenandoah/shenandoahHeap.inline.hpp"
28 #include "gc_implementation/shenandoah/shenandoahHeapRegion.hpp"
29 #include "gc_implementation/shenandoah/shenandoahHeuristics.hpp"
30 #include "gc_implementation/shenandoah/shenandoahMarkingContext.inline.hpp"
31
32 int ShenandoahHeuristics::compare_by_garbage(RegionData a, RegionData b) {
33 if (a._garbage > b._garbage)
34 return -1;
35 else if (a._garbage < b._garbage)
36 return 1;
37 else return 0;
38 }
39
40 int ShenandoahHeuristics::compare_by_alloc_seq_ascending(RegionData a, RegionData b) {
41 if (a._seqnum_last_alloc == b._seqnum_last_alloc)
42 return 0;
43 else if (a._seqnum_last_alloc < b._seqnum_last_alloc)
44 return -1;
45 else return 1;
46 }
47
48 int ShenandoahHeuristics::compare_by_alloc_seq_descending(RegionData a, RegionData b) {
49 return -compare_by_alloc_seq_ascending(a, b);
50 }
51
52 ShenandoahHeuristics::ShenandoahHeuristics() :
53 _update_refs_early(false),
54 _update_refs_adaptive(false),
55 _region_data(NULL),
56 _region_data_size(0),
57 _degenerated_cycles_in_a_row(0),
58 _successful_cycles_in_a_row(0),
59 _bytes_in_cset(0),
60 _cycle_start(0),
61 _last_cycle_end(0),
62 _gc_times_learned(0),
63 _gc_time_penalties(0),
64 _gc_time_history(new TruncatedSeq(5))
65 {
66 if (strcmp(ShenandoahUpdateRefsEarly, "on") == 0 ||
67 strcmp(ShenandoahUpdateRefsEarly, "true") == 0 ) {
68 _update_refs_early = true;
69 } else if (strcmp(ShenandoahUpdateRefsEarly, "off") == 0 ||
70 strcmp(ShenandoahUpdateRefsEarly, "false") == 0 ) {
71 _update_refs_early = false;
72 } else if (strcmp(ShenandoahUpdateRefsEarly, "adaptive") == 0) {
73 _update_refs_adaptive = true;
74 _update_refs_early = true;
75 } else {
76 vm_exit_during_initialization("Unknown -XX:ShenandoahUpdateRefsEarly option: %s", ShenandoahUpdateRefsEarly);
77 }
78
79 // No unloading during concurrent mark? Communicate that to heuristics
80 if (!ClassUnloadingWithConcurrentMark) {
81 FLAG_SET_DEFAULT(ShenandoahUnloadClassesFrequency, 0);
82 }
83 }
84
85 ShenandoahHeuristics::~ShenandoahHeuristics() {
86 if (_region_data != NULL) {
87 FREE_C_HEAP_ARRAY(RegionGarbage, _region_data, mtGC);
88 }
89 }
90
91 ShenandoahHeuristics::RegionData* ShenandoahHeuristics::get_region_data_cache(size_t num) {
92 RegionData* res = _region_data;
93 if (res == NULL) {
94 res = NEW_C_HEAP_ARRAY(RegionData, num, mtGC);
95 _region_data = res;
96 _region_data_size = num;
97 } else if (_region_data_size < num) {
98 res = REALLOC_C_HEAP_ARRAY(RegionData, _region_data, num, mtGC);
99 _region_data = res;
100 _region_data_size = num;
101 }
102 return res;
103 }
104
105 void ShenandoahHeuristics::choose_collection_set(ShenandoahCollectionSet* collection_set) {
106 assert(collection_set->count() == 0, "Must be empty");
107 start_choose_collection_set();
108
109 ShenandoahHeap* heap = ShenandoahHeap::heap();
110
111 // Step 1. Build up the region candidates we care about, rejecting losers and accepting winners right away.
112
113 size_t num_regions = heap->num_regions();
114
115 RegionData* candidates = get_region_data_cache(num_regions);
116
117 size_t cand_idx = 0;
118
119 size_t total_garbage = 0;
120
121 size_t immediate_garbage = 0;
122 size_t immediate_regions = 0;
123
124 size_t free = 0;
125 size_t free_regions = 0;
126
127 ShenandoahMarkingContext* const ctx = heap->complete_marking_context();
128
129 for (size_t i = 0; i < num_regions; i++) {
130 ShenandoahHeapRegion* region = heap->get_region(i);
131
132 size_t garbage = region->garbage();
133 total_garbage += garbage;
134
135 if (region->is_empty()) {
136 free_regions++;
137 free += ShenandoahHeapRegion::region_size_bytes();
138 } else if (region->is_regular()) {
139 if (!region->has_live()) {
140 // We can recycle it right away and put it in the free set.
141 immediate_regions++;
142 immediate_garbage += garbage;
143 region->make_trash();
144 } else {
145 // This is our candidate for later consideration.
146 candidates[cand_idx]._region = region;
147 candidates[cand_idx]._garbage = garbage;
148 cand_idx++;
149 }
150 } else if (region->is_humongous_start()) {
151 // Reclaim humongous regions here, and count them as the immediate garbage
152 #ifdef ASSERT
153 bool reg_live = region->has_live();
154 bool bm_live = ctx->is_marked(oop(region->bottom() + BrooksPointer::word_size()));
155 assert(reg_live == bm_live,
156 err_msg("Humongous liveness and marks should agree. Region live: %s; Bitmap live: %s; Region Live Words: " SIZE_FORMAT,
157 BOOL_TO_STR(reg_live), BOOL_TO_STR(bm_live), region->get_live_data_words()));
158 #endif
159 if (!region->has_live()) {
160 heap->trash_humongous_region_at(region);
161
162 // Count only the start. Continuations would be counted on "trash" path
163 immediate_regions++;
164 immediate_garbage += garbage;
165 }
166 } else if (region->is_trash()) {
167 // Count in just trashed collection set, during coalesced CM-with-UR
168 immediate_regions++;
169 immediate_garbage += garbage;
170 }
171 }
172
173 // Step 2. Look back at garbage statistics, and decide if we want to collect anything,
174 // given the amount of immediately reclaimable garbage. If we do, figure out the collection set.
175
176 assert (immediate_garbage <= total_garbage,
177 err_msg("Cannot have more immediate garbage than total garbage: " SIZE_FORMAT "M vs " SIZE_FORMAT "M",
178 immediate_garbage / M, total_garbage / M));
179
180 size_t immediate_percent = total_garbage == 0 ? 0 : (immediate_garbage * 100 / total_garbage);
181
182 if (immediate_percent <= ShenandoahImmediateThreshold) {
183 choose_collection_set_from_regiondata(collection_set, candidates, cand_idx, immediate_garbage + free);
184 collection_set->update_region_status();
185
186 size_t cset_percent = total_garbage == 0 ? 0 : (collection_set->garbage() * 100 / total_garbage);
187 log_info(gc, ergo)("Collectable Garbage: " SIZE_FORMAT "M (" SIZE_FORMAT "%% of total), " SIZE_FORMAT "M CSet, " SIZE_FORMAT " CSet regions",
188 collection_set->garbage() / M, cset_percent, collection_set->live_data() / M, collection_set->count());
189 }
190 end_choose_collection_set();
191
192 log_info(gc, ergo)("Immediate Garbage: " SIZE_FORMAT "M (" SIZE_FORMAT "%% of total), " SIZE_FORMAT " regions",
193 immediate_garbage / M, immediate_percent, immediate_regions);
194 }
195
196 void ShenandoahHeuristics::record_gc_start() {
197 // Do nothing
198 }
199
200 void ShenandoahHeuristics::record_gc_end() {
201 // Do nothing
202 }
203
204 void ShenandoahHeuristics::record_cycle_start() {
205 _cycle_start = os::elapsedTime();
206 }
207
208 void ShenandoahHeuristics::record_cycle_end() {
209 _last_cycle_end = os::elapsedTime();
210 }
211
212 void ShenandoahHeuristics::record_phase_time(ShenandoahPhaseTimings::Phase phase, double secs) {
213 // Do nothing
214 }
215
216 bool ShenandoahHeuristics::should_start_update_refs() {
217 return _update_refs_early;
218 }
219
220 bool ShenandoahHeuristics::should_degenerate_cycle() {
221 return _degenerated_cycles_in_a_row <= ShenandoahFullGCThreshold;
222 }
223
224 void ShenandoahHeuristics::record_success_concurrent() {
225 _degenerated_cycles_in_a_row = 0;
226 _successful_cycles_in_a_row++;
227
228 double duration = (os::elapsedTime() - _cycle_start);
229 _gc_time_history->add(duration);
230 _gc_times_learned++;
231 _gc_time_penalties -= MIN2<size_t>(_gc_time_penalties, Concurrent_Adjust);
232 }
233
234 void ShenandoahHeuristics::record_success_degenerated() {
235 _degenerated_cycles_in_a_row++;
236 _successful_cycles_in_a_row = 0;
237 _gc_time_penalties += Degenerated_Penalty;
238 }
239
240 void ShenandoahHeuristics::record_success_full() {
241 _degenerated_cycles_in_a_row = 0;
242 _successful_cycles_in_a_row++;
243 _gc_time_penalties += Full_Penalty;
244 }
245
246 void ShenandoahHeuristics::record_allocation_failure_gc() {
247 _bytes_in_cset = 0;
248 }
249
250 void ShenandoahHeuristics::record_explicit_gc() {
251 _bytes_in_cset = 0;
252
253 // Assume users call System.gc() when external state changes significantly,
254 // which forces us to re-learn the GC timings and allocation rates.
255 _gc_times_learned = 0;
256 }
257
258 bool ShenandoahHeuristics::should_process_references() {
259 if (ShenandoahRefProcFrequency == 0) return false;
260 size_t cycle = ShenandoahHeap::heap()->shenandoahPolicy()->cycle_counter();
261 // Process references every Nth GC cycle.
262 return cycle % ShenandoahRefProcFrequency == 0;
263 }
264
265 bool ShenandoahHeuristics::should_unload_classes() {
266 if (ShenandoahUnloadClassesFrequency == 0) return false;
267 size_t cycle = ShenandoahHeap::heap()->shenandoahPolicy()->cycle_counter();
268 // Unload classes every Nth GC cycle.
269 // This should not happen in the same cycle as process_references to amortize costs.
270 // Offsetting by one is enough to break the rendezvous when periods are equal.
271 // When periods are not equal, offsetting by one is just as good as any other guess.
272 return (cycle + 1) % ShenandoahUnloadClassesFrequency == 0;
273 }
274
275 void ShenandoahHeuristics::initialize() {
276 // Nothing to do by default.
277 }
278
279 bool ShenandoahHeuristics::should_start_normal_gc() const {
280 double last_time_ms = (os::elapsedTime() - _last_cycle_end) * 1000;
281 bool periodic_gc = (last_time_ms > ShenandoahGuaranteedGCInterval);
282 if (periodic_gc) {
283 log_info(gc)("Trigger: Time since last GC (%.0f ms) is larger than guaranteed interval (" UINTX_FORMAT " ms)",
284 last_time_ms, ShenandoahGuaranteedGCInterval);
285 }
286 return periodic_gc;
287 }