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