1 /*
2 * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #ifndef SHARE_GC_SHENANDOAH_SHENANDOAHAGECENSUS_HPP
26 #define SHARE_GC_SHENANDOAH_SHENANDOAHAGECENSUS_HPP
27
28 #include "gc/shared/ageTable.hpp"
29
30 #ifndef PRODUCT
31 // Enable noise instrumentation
32 #define SHENANDOAH_CENSUS_NOISE 1
33 #endif // PRODUCT
34
35 #ifdef SHENANDOAH_CENSUS_NOISE
36
37 #define CENSUS_NOISE(x) x
38 #define NO_CENSUS_NOISE(x)
39
40 struct ShenandoahNoiseStats {
41 size_t skipped; // Volume of objects skipped
42 size_t aged; // Volume of objects from aged regions
43 size_t clamped; // Volume of objects whose ages were clamped
44 size_t young; // Volume of (rejuvenated) objects of retrograde age
45
46 ShenandoahNoiseStats() {
47 clear();
48 }
49
50 void clear() {
51 skipped = 0;
52 aged = 0;
53 clamped = 0;
54 young = 0;
55 }
56
57 #ifndef PRODUCT
58 bool is_clear() {
59 return (skipped + aged + clamped + young) == 0;
60 }
61 #endif // !PRODUCT
62
63 void merge(ShenandoahNoiseStats& other) {
64 skipped += other.skipped;
65 aged += other.aged;
66 clamped += other.clamped;
67 young += other.young;
68 }
69
70 void print(size_t total);
71 };
72 #else // SHENANDOAH_CENSUS_NOISE
73 #define CENSUS_NOISE(x)
74 #define NO_CENSUS_NOISE(x) x
75 #endif // SHENANDOAH_CENSUS_NOISE
76
77 // A class for tracking a sequence of cohort population vectors (or,
78 // interchangeably, age tables) for up to C=MAX_COHORTS age cohorts, where a cohort
79 // represents the set of objects allocated during a specific inter-GC epoch.
80 // Epochs are demarcated by GC cycles, with those surviving a cycle aging by
81 // an epoch. The census tracks the historical variation of cohort demographics
82 // across N=MAX_SNAPSHOTS recent epochs. Since there are at most C age cohorts in
83 // the population, we need only track at most N=C epochal snapshots to track a
84 // maximal longitudinal demographics of every object's longitudinal cohort in
85 // the young generation. The _global_age_table is thus, currently, a C x N (row-major)
86 // matrix, with C=16, and, for now N=C=16, currently.
87 // In theory, we might decide to track even longer (N=MAX_SNAPSHOTS) demographic
88 // histories, but that isn't the case today. In particular, the current tenuring
89 // threshold algorithm uses only 2 most recent snapshots, with the remaining
90 // MAX_SNAPSHOTS-2=14 reserved for research purposes.
91 //
92 // In addition, this class also maintains per worker population vectors into which
93 // census for the current minor GC is accumulated (during marking or, optionally, during
94 // evacuation). These are cleared after each marking (resectively, evacuation) cycle,
95 // once the per-worker data is consolidated into the appropriate population vector
96 // per minor collection. The _local_age_table is thus C x N, for N GC workers.
97 class ShenandoahAgeCensus: public CHeapObj<mtGC> {
98 AgeTable** _global_age_table; // Global age table used for adapting tenuring threshold, one per snapshot
99 AgeTable** _local_age_table; // Local scratch age tables to track object ages, one per worker
100
101 #ifdef SHENANDOAH_CENSUS_NOISE
102 ShenandoahNoiseStats* _global_noise; // Noise stats, one per snapshot
103 ShenandoahNoiseStats* _local_noise; // Local scratch table for noise stats, one per worker
104
105 size_t _skipped; // net size of objects encountered, but skipped during census,
106 // because their age was indeterminate
107 #endif // SHENANDOAH_CENSUS_NOISE
108
109 #ifndef PRODUCT
110 size_t _counted; // net size of objects counted in census
111 size_t _total; // net size of objects encountered (counted or skipped) in census
112 #endif
113
114 uint _epoch; // Current epoch (modulo max age)
115 uint *_tenuring_threshold; // An array of the last N tenuring threshold values we
116 // computed.
117
118 // Mortality rate of a cohort, given its population in
119 // previous and current epochs
120 double mortality_rate(size_t prev_pop, size_t cur_pop);
121
122 // Update to a new epoch, creating a slot for new census.
123 void prepare_for_census_update();
124
125 // Update the tenuring threshold, calling
126 // compute_tenuring_threshold() to calculate the new
127 // value
128 void update_tenuring_threshold();
129
130 // Use _global_age_table and the current _epoch to compute a new tenuring
131 // threshold, which will be remembered until the next invocation of
132 // compute_tenuring_threshold.
133 uint compute_tenuring_threshold();
134
135 // Return the tenuring threshold computed for the previous epoch
136 uint previous_tenuring_threshold() const {
137 assert(_epoch < MAX_SNAPSHOTS, "Error");
138 uint prev = _epoch - 1;
139 if (prev >= MAX_SNAPSHOTS) {
140 // _epoch is 0
141 assert(_epoch == 0, "Error");
142 prev = MAX_SNAPSHOTS - 1;
143 }
144 return _tenuring_threshold[prev];
145 }
146
147 #ifndef PRODUCT
148 // Return the sum of size of objects of all ages recorded in the
149 // census at snapshot indexed by snap.
150 size_t get_all_ages(uint snap);
151
152 // Return the size of all objects that were encountered, but skipped,
153 // during the census, because their age was indeterminate.
154 size_t get_skipped(uint snap);
155
156 // Update the total size of objects counted or skipped at the census for
157 // the most recent epoch.
158 void update_total();
159 #endif // !PRODUCT
160
161 public:
162 enum {
163 MAX_COHORTS = AgeTable::table_size, // = markWord::max_age + 1
164 MAX_SNAPSHOTS = MAX_COHORTS // May change in the future
165 };
166
167 ShenandoahAgeCensus();
168
169 // Return the local age table (population vector) for worker_id.
170 // Only used in the case of (ShenandoahGenerationalAdaptiveTenuring && !ShenandoahGenerationalCensusAtEvac)
171 AgeTable* get_local_age_table(uint worker_id) {
172 return (AgeTable*) _local_age_table[worker_id];
173 }
174
175 // Update the local age table for worker_id by size for
176 // given obj_age, region_age, and region_youth
177 CENSUS_NOISE(void add(uint obj_age, uint region_age, uint region_youth, size_t size, uint worker_id);)
178 NO_CENSUS_NOISE(void add(uint obj_age, uint region_age, size_t size, uint worker_id);)
179
180 #ifdef SHENANDOAH_CENSUS_NOISE
181 // Update the local skip table for worker_id by size
182 void add_skipped(size_t size, uint worker_id);
183 // Update the local aged region volume table for worker_id by size
184 void add_aged(size_t size, uint worker_id);
185 // Update the local clamped object volume table for worker_id by size
186 void add_clamped(size_t size, uint worker_id);
187 // Update the local (rejuvenated) object volume (retrograde age) for worker_id by size
188 void add_young(size_t size, uint worker_id);
189 #endif // SHENANDOAH_CENSUS_NOISE
190
191 // Update the census data, and compute the new tenuring threshold.
192 // This method should be called at the end of each marking (or optionally
193 // evacuation) cycle to update the tenuring threshold to be used in
194 // the next cycle.
195 // age0_pop is the population of Cohort 0 that may have been missed in
196 // the regular census during the marking cycle, corresponding to objects
197 // allocated when the concurrent marking was in progress.
198 // Optional parameters, pv1 and pv2 are population vectors that together
199 // provide object census data (only) for the case when
200 // ShenandoahGenerationalCensusAtEvac. In this case, the age0_pop
201 // is 0, because the evacuated objects have all had their ages incremented.
202 void update_census(size_t age0_pop, AgeTable* pv1 = nullptr, AgeTable* pv2 = nullptr);
203
204 // Return the most recently computed tenuring threshold
205 uint tenuring_threshold() const { return _tenuring_threshold[_epoch]; }
206
207 // Reset the epoch, clearing accumulated census history
208 // Note: this isn't currently used, but reserved for planned
209 // future usage.
210 void reset_global();
211
212 // Reset any (potentially partial) census information in worker-local age tables
213 void reset_local();
214
215 #ifndef PRODUCT
216 // Check whether census information is clear
217 bool is_clear_global();
218 bool is_clear_local();
219
220 // Return the net size of objects encountered (counted or skipped) in census
221 // at most recent epoch.
222 size_t get_total() { return _total; }
223 #endif // !PRODUCT
224
225 // Print the age census information
226 void print();
227 };
228
229 #endif // SHARE_GC_SHENANDOAH_SHENANDOAHAGECENSUS_HPP