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