1 /*
2 * Copyright (c) 2018, 2019, 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/shenandoah/heuristics/shenandoahTraversalHeuristics.hpp"
27 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
28 #include "gc/shenandoah/shenandoahFreeSet.hpp"
29 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
30 #include "gc/shenandoah/shenandoahHeuristics.hpp"
31 #include "gc/shenandoah/shenandoahTraversalGC.hpp"
32 #include "logging/log.hpp"
33 #include "logging/logTag.hpp"
34 #include "utilities/quickSort.hpp"
35
36 ShenandoahTraversalHeuristics::ShenandoahTraversalHeuristics() : ShenandoahHeuristics(),
37 _last_cset_select(0)
38 {
39 FLAG_SET_DEFAULT(ShenandoahSATBBarrier, false);
40 FLAG_SET_DEFAULT(ShenandoahStoreValEnqueueBarrier, true);
41 FLAG_SET_DEFAULT(ShenandoahKeepAliveBarrier, false);
42 FLAG_SET_DEFAULT(ShenandoahAllowMixedAllocs, false);
43
44 SHENANDOAH_ERGO_OVERRIDE_DEFAULT(ShenandoahRefProcFrequency, 1);
45
46 // Adjust class unloading settings only if globally enabled.
47 if (ClassUnloadingWithConcurrentMark) {
48 SHENANDOAH_ERGO_OVERRIDE_DEFAULT(ShenandoahUnloadClassesFrequency, 1);
49 }
50
51 SHENANDOAH_ERGO_ENABLE_FLAG(ExplicitGCInvokesConcurrent);
52 SHENANDOAH_ERGO_ENABLE_FLAG(ShenandoahImplicitGCInvokesConcurrent);
53
54 // Final configuration checks
55 SHENANDOAH_CHECK_FLAG_SET(ShenandoahLoadRefBarrier);
56 SHENANDOAH_CHECK_FLAG_SET(ShenandoahStoreValEnqueueBarrier);
57 SHENANDOAH_CHECK_FLAG_SET(ShenandoahCASBarrier);
58 SHENANDOAH_CHECK_FLAG_SET(ShenandoahCloneBarrier);
59 }
60
61 bool ShenandoahTraversalHeuristics::should_start_normal_gc() const {
62 return false;
63 }
64
65 bool ShenandoahTraversalHeuristics::is_experimental() {
66 return true;
67 }
68
69 bool ShenandoahTraversalHeuristics::is_diagnostic() {
70 return false;
71 }
72
73 bool ShenandoahTraversalHeuristics::can_do_traversal_gc() {
74 return true;
75 }
76
77 const char* ShenandoahTraversalHeuristics::name() {
78 return "traversal";
79 }
80
81 void ShenandoahTraversalHeuristics::choose_collection_set(ShenandoahCollectionSet* collection_set) {
82 ShenandoahHeap* heap = ShenandoahHeap::heap();
83
84 ShenandoahTraversalGC* traversal_gc = heap->traversal_gc();
85
86 ShenandoahHeapRegionSet* traversal_set = traversal_gc->traversal_set();
87 traversal_set->clear();
88
89 RegionData *data = get_region_data_cache(heap->num_regions());
90 size_t cnt = 0;
91
92 // Step 0. Prepare all regions
93
94 for (size_t i = 0; i < heap->num_regions(); i++) {
95 ShenandoahHeapRegion* r = heap->get_region(i);
96 if (r->used() > 0) {
97 if (r->is_regular()) {
98 data[cnt]._region = r;
99 data[cnt]._garbage = r->garbage();
100 data[cnt]._seqnum_last_alloc = r->seqnum_last_alloc_mutator();
101 cnt++;
102 }
103 traversal_set->add_region(r);
104 }
105 }
106
107 // The logic for cset selection is similar to that of adaptive:
108 //
109 // 1. We cannot get cset larger than available free space. Otherwise we guarantee OOME
110 // during evacuation, and thus guarantee full GC. In practice, we also want to let
111 // application to allocate something. This is why we limit CSet to some fraction of
112 // available space. In non-overloaded heap, max_cset would contain all plausible candidates
113 // over garbage threshold.
114 //
115 // 2. We should not get cset too low so that free threshold would not be met right
116 // after the cycle. Otherwise we get back-to-back cycles for no reason if heap is
117 // too fragmented. In non-overloaded non-fragmented heap min_garbage would be around zero.
118 //
119 // Therefore, we start by sorting the regions by garbage. Then we unconditionally add the best candidates
120 // before we meet min_garbage. Then we add all candidates that fit with a garbage threshold before
121 // we hit max_cset. When max_cset is hit, we terminate the cset selection. Note that in this scheme,
122 // ShenandoahGarbageThreshold is the soft threshold which would be ignored until min_garbage is hit.
123 //
124 // The significant complication is that liveness data was collected at the previous cycle, and only
125 // for those regions that were allocated before previous cycle started.
126
127 size_t capacity = heap->capacity();
128 size_t actual_free = heap->free_set()->available();
129 size_t free_target = ShenandoahMinFreeThreshold * capacity / 100;
130 size_t min_garbage = free_target > actual_free ? (free_target - actual_free) : 0;
131 size_t max_cset = (size_t)(1.0 * ShenandoahEvacReserve * capacity / 100 / ShenandoahEvacWaste);
132
133 log_info(gc, ergo)("Adaptive CSet Selection. Target Free: " SIZE_FORMAT "M, Actual Free: "
134 SIZE_FORMAT "M, Max CSet: " SIZE_FORMAT "M, Min Garbage: " SIZE_FORMAT "M",
135 free_target / M, actual_free / M, max_cset / M, min_garbage / M);
136
137 // Better select garbage-first regions, and then older ones
138 QuickSort::sort<RegionData>(data, (int) cnt, compare_by_garbage_then_alloc_seq_ascending, false);
139
140 size_t cur_cset = 0;
141 size_t cur_garbage = 0;
142
143 size_t garbage_threshold = ShenandoahHeapRegion::region_size_bytes() / 100 * ShenandoahGarbageThreshold;
144
145 // Step 1. Add trustworthy regions to collection set.
146 //
147 // We can trust live/garbage data from regions that were fully traversed during
148 // previous cycle. Even if actual liveness is different now, we can only have _less_
149 // live objects, because dead objects are not resurrected. Which means we can undershoot
150 // the collection set, but not overshoot it.
151
152 for (size_t i = 0; i < cnt; i++) {
153 if (data[i]._seqnum_last_alloc > _last_cset_select) continue;
154
155 ShenandoahHeapRegion* r = data[i]._region;
156 assert (r->is_regular(), "should have been filtered before");
157
158 size_t new_garbage = cur_garbage + r->garbage();
159 size_t new_cset = cur_cset + r->get_live_data_bytes();
160
161 if (new_cset > max_cset) {
162 break;
163 }
164
165 if ((new_garbage < min_garbage) || (r->garbage() > garbage_threshold)) {
166 assert(!collection_set->is_in(r), "must not yet be in cset");
167 collection_set->add_region(r);
168 cur_cset = new_cset;
169 cur_garbage = new_garbage;
170 }
171 }
172
173 // Step 2. Try to catch some recently allocated regions for evacuation ride.
174 //
175 // Pessimistically assume we are going to evacuate the entire region. While this
176 // is very pessimistic and in most cases undershoots the collection set when regions
177 // are mostly dead, it also provides more safety against running into allocation
178 // failure when newly allocated regions are fully live.
179
180 for (size_t i = 0; i < cnt; i++) {
181 if (data[i]._seqnum_last_alloc <= _last_cset_select) continue;
182
183 ShenandoahHeapRegion* r = data[i]._region;
184 assert (r->is_regular(), "should have been filtered before");
185
186 // size_t new_garbage = cur_garbage + 0; (implied)
187 size_t new_cset = cur_cset + r->used();
188
189 if (new_cset > max_cset) {
190 break;
191 }
192
193 assert(!collection_set->is_in(r), "must not yet be in cset");
194 collection_set->add_region(r);
195 cur_cset = new_cset;
196 }
197
198 // Step 3. Clear liveness data
199 // TODO: Merge it with step 0, but save live data in RegionData before.
200 for (size_t i = 0; i < heap->num_regions(); i++) {
201 ShenandoahHeapRegion* r = heap->get_region(i);
202 if (r->used() > 0) {
203 r->clear_live_data();
204 }
205 }
206
207 collection_set->update_region_status();
208
209 _last_cset_select = ShenandoahHeapRegion::seqnum_current_alloc();
210 }
211
212 bool ShenandoahTraversalHeuristics::should_start_traversal_gc() {
213 ShenandoahHeap* heap = ShenandoahHeap::heap();
214 assert(!heap->has_forwarded_objects(), "no forwarded objects here");
215
216 size_t capacity = heap->capacity();
217 size_t available = heap->free_set()->available();
218
219 // Check if we are falling below the worst limit, time to trigger the GC, regardless of
220 // anything else.
221 size_t min_threshold = ShenandoahMinFreeThreshold * heap->capacity() / 100;
222 if (available < min_threshold) {
223 log_info(gc)("Trigger: Free (" SIZE_FORMAT "M) is below minimum threshold (" SIZE_FORMAT "M)",
224 available / M, min_threshold / M);
225 return true;
226 }
227
228 // Check if are need to learn a bit about the application
229 const size_t max_learn = ShenandoahLearningSteps;
230 if (_gc_times_learned < max_learn) {
231 size_t init_threshold = ShenandoahInitFreeThreshold * heap->capacity() / 100;
232 if (available < init_threshold) {
233 log_info(gc)("Trigger: Learning " SIZE_FORMAT " of " SIZE_FORMAT ". Free (" SIZE_FORMAT "M) is below initial threshold (" SIZE_FORMAT "M)",
234 _gc_times_learned + 1, max_learn, available / M, init_threshold / M);
235 return true;
236 }
237 }
238
239 // Check if allocation headroom is still okay. This also factors in:
240 // 1. Some space to absorb allocation spikes
241 // 2. Accumulated penalties from Degenerated and Full GC
242
243 size_t allocation_headroom = available;
244
245 size_t spike_headroom = ShenandoahAllocSpikeFactor * capacity / 100;
246 size_t penalties = _gc_time_penalties * capacity / 100;
247
248 allocation_headroom -= MIN2(allocation_headroom, spike_headroom);
249 allocation_headroom -= MIN2(allocation_headroom, penalties);
250
251 double average_gc = _gc_time_history->avg();
252 double time_since_last = time_since_last_gc();
253 double allocation_rate = heap->bytes_allocated_since_gc_start() / time_since_last;
254
255 if (average_gc > allocation_headroom / allocation_rate) {
256 log_info(gc)("Trigger: Average GC time (%.2f ms) is above the time for allocation rate (%.2f MB/s) to deplete free headroom (" SIZE_FORMAT "M)",
257 average_gc * 1000, allocation_rate / M, allocation_headroom / M);
258 log_info(gc, ergo)("Free headroom: " SIZE_FORMAT "M (free) - " SIZE_FORMAT "M (spike) - " SIZE_FORMAT "M (penalties) = " SIZE_FORMAT "M",
259 available / M, spike_headroom / M, penalties / M, allocation_headroom / M);
260 return true;
261 } else if (ShenandoahHeuristics::should_start_normal_gc()) {
262 return true;
263 }
264
265 return false;
266 }
267
268 void ShenandoahTraversalHeuristics::choose_collection_set_from_regiondata(ShenandoahCollectionSet* set,
269 RegionData* data, size_t data_size,
270 size_t free) {
271 ShouldNotReachHere();
272 }