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/shenandoah/heuristics/shenandoahTraversalHeuristics.hpp"
27 #include "gc/shenandoah/shenandoahFreeSet.hpp"
28 #include "gc/shenandoah/shenandoahHeuristics.hpp"
29 #include "gc/shenandoah/shenandoahTraversalGC.hpp"
30 #include "logging/log.hpp"
31 #include "logging/logTag.hpp"
32 #include "utilities/quickSort.hpp"
33
34 ShenandoahTraversalHeuristics::ShenandoahTraversalHeuristics() : ShenandoahHeuristics(),
35 _last_cset_select(0)
36 {
37 FLAG_SET_DEFAULT(ShenandoahSATBBarrier, false);
38 FLAG_SET_DEFAULT(ShenandoahStoreValReadBarrier, false);
39 FLAG_SET_DEFAULT(ShenandoahStoreValEnqueueBarrier, true);
40 FLAG_SET_DEFAULT(ShenandoahKeepAliveBarrier, false);
41 FLAG_SET_DEFAULT(ShenandoahAllowMixedAllocs, false);
42
43 SHENANDOAH_ERGO_OVERRIDE_DEFAULT(ShenandoahRefProcFrequency, 1);
44
45 // Adjust class unloading settings only if globally enabled.
46 if (ClassUnloadingWithConcurrentMark) {
47 SHENANDOAH_ERGO_OVERRIDE_DEFAULT(ShenandoahUnloadClassesFrequency, 1);
48 }
49
50 SHENANDOAH_ERGO_ENABLE_FLAG(ExplicitGCInvokesConcurrent);
51 SHENANDOAH_ERGO_ENABLE_FLAG(ShenandoahImplicitGCInvokesConcurrent);
52
53 // Final configuration checks
54 SHENANDOAH_CHECK_FLAG_SET(ShenandoahReadBarrier);
55 SHENANDOAH_CHECK_FLAG_SET(ShenandoahWriteBarrier);
56 SHENANDOAH_CHECK_FLAG_SET(ShenandoahStoreValEnqueueBarrier);
57 SHENANDOAH_CHECK_FLAG_SET(ShenandoahCASBarrier);
58 SHENANDOAH_CHECK_FLAG_SET(ShenandoahAcmpBarrier);
59 SHENANDOAH_CHECK_FLAG_SET(ShenandoahCloneBarrier);
60 }
61
62 bool ShenandoahTraversalHeuristics::should_start_normal_gc() const {
63 return false;
64 }
65
66 bool ShenandoahTraversalHeuristics::is_experimental() {
67 return true;
68 }
69
70 bool ShenandoahTraversalHeuristics::is_diagnostic() {
71 return false;
72 }
73
74 bool ShenandoahTraversalHeuristics::can_do_traversal_gc() {
75 return true;
76 }
77
78 const char* ShenandoahTraversalHeuristics::name() {
79 return "traversal";
80 }
81
82 void ShenandoahTraversalHeuristics::choose_collection_set(ShenandoahCollectionSet* collection_set) {
83 ShenandoahHeap* heap = ShenandoahHeap::heap();
84
85 ShenandoahTraversalGC* traversal_gc = heap->traversal_gc();
86
87 ShenandoahHeapRegionSet* traversal_set = traversal_gc->traversal_set();
88 traversal_set->clear();
89
90 RegionData *data = get_region_data_cache(heap->num_regions());
91 size_t cnt = 0;
92
93 // Step 0. Prepare all regions
94
95 for (size_t i = 0; i < heap->num_regions(); i++) {
96 ShenandoahHeapRegion* r = heap->get_region(i);
97 if (r->used() > 0) {
98 if (r->is_regular()) {
99 data[cnt]._region = r;
100 data[cnt]._garbage = r->garbage();
101 data[cnt]._seqnum_last_alloc = r->seqnum_last_alloc_mutator();
102 cnt++;
103 }
104 traversal_set->add_region(r);
105 }
106 }
107
108 // The logic for cset selection is similar to that of adaptive:
109 //
110 // 1. We cannot get cset larger than available free space. Otherwise we guarantee OOME
111 // during evacuation, and thus guarantee full GC. In practice, we also want to let
112 // application to allocate something. This is why we limit CSet to some fraction of
113 // available space. In non-overloaded heap, max_cset would contain all plausible candidates
114 // over garbage threshold.
115 //
116 // 2. We should not get cset too low so that free threshold would not be met right
117 // after the cycle. Otherwise we get back-to-back cycles for no reason if heap is
118 // too fragmented. In non-overloaded non-fragmented heap min_garbage would be around zero.
119 //
120 // Therefore, we start by sorting the regions by garbage. Then we unconditionally add the best candidates
121 // before we meet min_garbage. Then we add all candidates that fit with a garbage threshold before
122 // we hit max_cset. When max_cset is hit, we terminate the cset selection. Note that in this scheme,
123 // ShenandoahGarbageThreshold is the soft threshold which would be ignored until min_garbage is hit.
124 //
125 // The significant complication is that liveness data was collected at the previous cycle, and only
126 // for those regions that were allocated before previous cycle started.
127
128 size_t capacity = heap->capacity();
129 size_t actual_free = heap->free_set()->available();
130 size_t free_target = ShenandoahMinFreeThreshold * capacity / 100;
131 size_t min_garbage = free_target > actual_free ? (free_target - actual_free) : 0;
132 size_t max_cset = (size_t)(1.0 * ShenandoahEvacReserve * capacity / 100 / ShenandoahEvacWaste);
133
134 log_info(gc, ergo)("Adaptive CSet Selection. Target Free: " SIZE_FORMAT "M, Actual Free: "
135 SIZE_FORMAT "M, Max CSet: " SIZE_FORMAT "M, Min Garbage: " SIZE_FORMAT "M",
136 free_target / M, actual_free / M, max_cset / M, min_garbage / M);
137
138 // Better select garbage-first regions, and then older ones
139 QuickSort::sort<RegionData>(data, (int) cnt, compare_by_garbage_then_alloc_seq_ascending, false);
140
141 size_t cur_cset = 0;
142 size_t cur_garbage = 0;
143
144 size_t garbage_threshold = ShenandoahHeapRegion::region_size_bytes() / 100 * ShenandoahGarbageThreshold;
145
146 // Step 1. Add trustworthy regions to collection set.
147 //
148 // We can trust live/garbage data from regions that were fully traversed during
149 // previous cycle. Even if actual liveness is different now, we can only have _less_
150 // live objects, because dead objects are not resurrected. Which means we can undershoot
151 // the collection set, but not overshoot it.
152
153 for (size_t i = 0; i < cnt; i++) {
154 if (data[i]._seqnum_last_alloc > _last_cset_select) continue;
155
156 ShenandoahHeapRegion* r = data[i]._region;
157 assert (r->is_regular(), "should have been filtered before");
158
159 size_t new_garbage = cur_garbage + r->garbage();
160 size_t new_cset = cur_cset + r->get_live_data_bytes();
161
162 if (new_cset > max_cset) {
163 break;
164 }
165
166 if ((new_garbage < min_garbage) || (r->garbage() > garbage_threshold)) {
167 assert(!collection_set->is_in(r), "must not yet be in cset");
168 collection_set->add_region(r);
169 cur_cset = new_cset;
170 cur_garbage = new_garbage;
171 }
172 }
173
174 // Step 2. Try to catch some recently allocated regions for evacuation ride.
175 //
176 // Pessimistically assume we are going to evacuate the entire region. While this
177 // is very pessimistic and in most cases undershoots the collection set when regions
178 // are mostly dead, it also provides more safety against running into allocation
179 // failure when newly allocated regions are fully live.
180
181 for (size_t i = 0; i < cnt; i++) {
182 if (data[i]._seqnum_last_alloc <= _last_cset_select) continue;
183
184 ShenandoahHeapRegion* r = data[i]._region;
185 assert (r->is_regular(), "should have been filtered before");
186
187 // size_t new_garbage = cur_garbage + 0; (implied)
188 size_t new_cset = cur_cset + r->used();
189
190 if (new_cset > max_cset) {
191 break;
192 }
193
194 assert(!collection_set->is_in(r), "must not yet be in cset");
195 collection_set->add_region(r);
196 cur_cset = new_cset;
197 }
198
199 // Step 3. Clear liveness data
200 // TODO: Merge it with step 0, but save live data in RegionData before.
201 for (size_t i = 0; i < heap->num_regions(); i++) {
202 ShenandoahHeapRegion* r = heap->get_region(i);
203 if (r->used() > 0) {
204 r->clear_live_data();
205 }
206 }
207
208 collection_set->update_region_status();
209
210 _last_cset_select = ShenandoahHeapRegion::seqnum_current_alloc();
211 }
212
213 bool ShenandoahTraversalHeuristics::should_start_traversal_gc() {
214 ShenandoahHeap* heap = ShenandoahHeap::heap();
215 assert(!heap->has_forwarded_objects(), "no forwarded objects here");
216
217 size_t capacity = heap->capacity();
218 size_t available = heap->free_set()->available();
219
220 // Check if we are falling below the worst limit, time to trigger the GC, regardless of
221 // anything else.
222 size_t min_threshold = ShenandoahMinFreeThreshold * heap->capacity() / 100;
223 if (available < min_threshold) {
224 log_info(gc)("Trigger: Free (" SIZE_FORMAT "M) is below minimum threshold (" SIZE_FORMAT "M)",
225 available / M, min_threshold / M);
226 return true;
227 }
228
229 // Check if are need to learn a bit about the application
230 const size_t max_learn = ShenandoahLearningSteps;
231 if (_gc_times_learned < max_learn) {
232 size_t init_threshold = ShenandoahInitFreeThreshold * heap->capacity() / 100;
233 if (available < init_threshold) {
234 log_info(gc)("Trigger: Learning " SIZE_FORMAT " of " SIZE_FORMAT ". Free (" SIZE_FORMAT "M) is below initial threshold (" SIZE_FORMAT "M)",
235 _gc_times_learned + 1, max_learn, available / M, init_threshold / M);
236 return true;
237 }
238 }
239
240 // Check if allocation headroom is still okay. This also factors in:
241 // 1. Some space to absorb allocation spikes
242 // 2. Accumulated penalties from Degenerated and Full GC
243
244 size_t allocation_headroom = available;
245
246 size_t spike_headroom = ShenandoahAllocSpikeFactor * capacity / 100;
247 size_t penalties = _gc_time_penalties * capacity / 100;
248
249 allocation_headroom -= MIN2(allocation_headroom, spike_headroom);
250 allocation_headroom -= MIN2(allocation_headroom, penalties);
251
252 double average_gc = _gc_time_history->avg();
253 double time_since_last = time_since_last_gc();
254 double allocation_rate = heap->bytes_allocated_since_gc_start() / time_since_last;
255
256 if (average_gc > allocation_headroom / allocation_rate) {
257 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)",
258 average_gc * 1000, allocation_rate / M, allocation_headroom / M);
259 log_info(gc, ergo)("Free headroom: " SIZE_FORMAT "M (free) - " SIZE_FORMAT "M (spike) - " SIZE_FORMAT "M (penalties) = " SIZE_FORMAT "M",
260 available / M, spike_headroom / M, penalties / M, allocation_headroom / M);
261 return true;
262 } else if (ShenandoahHeuristics::should_start_normal_gc()) {
263 return true;
264 }
265
266 return false;
267 }
268
269 void ShenandoahTraversalHeuristics::choose_collection_set_from_regiondata(ShenandoahCollectionSet* set,
270 RegionData* data, size_t data_size,
271 size_t free) {
272 ShouldNotReachHere();
273 }