1 /*
2 * Copyright (c) 2011, 2018, Oracle and/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
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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20 * or visit www.oracle.com if you need additional information or have any
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23 */
24
25 #ifndef SHARE_VM_GC_G1_G1MONITORINGSUPPORT_HPP
26 #define SHARE_VM_GC_G1_G1MONITORINGSUPPORT_HPP
27
28 #include "gc/shared/collectorCounters.hpp"
29 #include "gc/shared/generationCounters.hpp"
30 #include "services/memoryManager.hpp"
31 #include "services/memoryService.hpp"
32
33 class CollectorCounters;
34 class G1CollectedHeap;
35 class HSpaceCounters;
36 class MemoryPool;
37
38 // Class for monitoring logical spaces in G1. It provides data for
39 // both G1's jstat counters as well as G1's memory pools.
40 //
41 // G1 splits the heap into heap regions and each heap region belongs
42 // to one of the following categories:
43 //
44 // * eden : regions that have been allocated since the last GC
45 // * survivors : regions with objects that survived the last few GCs
46 // * old : long-lived non-humongous regions
47 // * humongous : humongous regions
48 // * free : free regions
49 //
50 // The combination of eden and survivor regions form the equivalent of
51 // the young generation in the other GCs. The combination of old and
52 // humongous regions form the equivalent of the old generation in the
53 // other GCs. Free regions do not have a good equivalent in the other
54 // GCs given that they can be allocated as any of the other region types.
55 //
56 // The monitoring tools expect the heap to contain a number of
57 // generations (young, old, perm) and each generation to contain a
58 // number of spaces (young: eden, survivors, old). Given that G1 does
59 // not maintain those spaces physically (e.g., the set of
60 // non-contiguous eden regions can be considered as a "logical"
61 // space), we'll provide the illusion that those generations and
62 // spaces exist. In reality, each generation and space refers to a set
63 // of heap regions that are potentially non-contiguous.
64 //
65 // This class provides interfaces to access the min, current, and max
66 // capacity and current occupancy for each of G1's logical spaces and
67 // generations we expose to the monitoring tools. Also provided are
68 // counters for G1 concurrent collections and stop-the-world full heap
69 // collections.
70 //
71 // Below is a description of how the various sizes are calculated.
72 //
73 // * Current Capacity
74 //
75 // - heap_capacity = current heap capacity (e.g., current committed size)
76 // - young_gen_capacity = current max young gen target capacity
77 // (i.e., young gen target capacity + max allowed expansion capacity)
78 // - survivor_capacity = current survivor region capacity
79 // - eden_capacity = young_gen_capacity - survivor_capacity
80 // - old_capacity = heap_capacity - young_gen_capacity
81 //
82 // What we do in the above is to distribute the free regions among
83 // eden_capacity and old_capacity.
84 //
85 // * Occupancy
86 //
87 // - young_gen_used = current young region capacity
88 // - survivor_used = survivor_capacity
89 // - eden_used = young_gen_used - survivor_used
90 // - old_used = overall_used - young_gen_used
91 //
92 // Unfortunately, we currently only keep track of the number of
93 // currently allocated young and survivor regions + the overall used
94 // bytes in the heap, so the above can be a little inaccurate.
95 //
96 // * Min Capacity
97 //
98 // We set this to 0 for all spaces.
99 //
100 // * Max Capacity
101 //
102 // For jstat, we set the max capacity of all spaces to heap_capacity,
103 // given that we don't always have a reasonable upper bound on how big
104 // each space can grow. For the memory pools, we make the max
105 // capacity undefined with the exception of the old memory pool for
106 // which we make the max capacity same as the max heap capacity.
107 //
108 // If we had more accurate occupancy / capacity information per
109 // region set the above calculations would be greatly simplified and
110 // be made more accurate.
111 //
112 // We update all the above synchronously and we store the results in
113 // fields so that we just read said fields when needed. A subtle point
114 // is that all the above sizes need to be recalculated when the old
115 // gen changes capacity (after a GC or after a humongous allocation)
116 // but only the eden occupancy changes when a new eden region is
117 // allocated. So, in the latter case we have minimal recalculation to
118 // do which is important as we want to keep the eden region allocation
119 // path as low-overhead as possible.
120
121 class G1MonitoringSupport : public CHeapObj<mtGC> {
122 friend class VMStructs;
123 friend class G1MonitoringScope;
124
125 G1CollectedHeap* _g1h;
126
127 // java.lang.management MemoryManager and MemoryPool support
128 GCMemoryManager _incremental_memory_manager;
129 GCMemoryManager _full_gc_memory_manager;
130
131 MemoryPool* _eden_pool;
132 MemoryPool* _survivor_pool;
133 MemoryPool* _old_pool;
134
135 // jstat performance counters
136 // incremental collections both young and mixed
137 CollectorCounters* _incremental_collection_counters;
138 // full stop-the-world collections
139 CollectorCounters* _full_collection_counters;
140 // stop-the-world phases in G1
141 CollectorCounters* _conc_collection_counters;
142 // young collection set counters. The _eden_counters,
143 // _from_counters, and _to_counters are associated with
144 // this "generational" counter.
145 GenerationCounters* _young_gen_counters;
146 // old collection set counters. The _old_space_counters
147 // below are associated with this "generational" counter.
148 GenerationCounters* _old_gen_counters;
149 // Counters for the capacity and used for
150 // the whole heap
151 HSpaceCounters* _old_space_counters;
152 // the young collection
153 HSpaceCounters* _eden_space_counters;
154 // the survivor collection (only one, _to_counters, is actively used)
155 HSpaceCounters* _from_space_counters;
156 HSpaceCounters* _to_space_counters;
157
158 // When it's appropriate to recalculate the various sizes (at the
159 // end of a GC, when a new eden region is allocated, etc.) we store
160 // them here so that we can easily report them when needed and not
161 // have to recalculate them every time.
162
163 size_t _overall_committed;
164 size_t _overall_used;
165
166 size_t _young_gen_committed;
167 size_t _old_gen_committed;
168
169 size_t _eden_space_committed;
170 size_t _eden_space_used;
171 size_t _survivor_space_committed;
172 size_t _survivor_space_used;
173
174 size_t _old_gen_used;
175
176 // It returns x - y if x > y, 0 otherwise.
177 // As described in the comment above, some of the inputs to the
178 // calculations we have to do are obtained concurrently and hence
179 // may be inconsistent with each other. So, this provides a
180 // defensive way of performing the subtraction and avoids the value
181 // going negative (which would mean a very large result, given that
182 // the parameter are size_t).
183 static size_t subtract_up_to_zero(size_t x, size_t y) {
184 if (x > y) {
185 return x - y;
186 } else {
187 return 0;
188 }
189 }
190
191 // Recalculate all the sizes.
192 void recalculate_sizes();
193
194 void recalculate_eden_size();
195
196 public:
197 G1MonitoringSupport(G1CollectedHeap* g1h);
198 ~G1MonitoringSupport();
199
200 void initialize_serviceability();
201 GrowableArray<GCMemoryManager*> memory_managers();
202 GrowableArray<MemoryPool*> memory_pools();
203
204 // Unfortunately, the jstat tool assumes that no space has 0
205 // capacity. In our case, given that each space is logical, it's
206 // possible that no regions will be allocated to it, hence to have 0
207 // capacity (e.g., if there are no survivor regions, the survivor
208 // space has 0 capacity). The way we deal with this is to always pad
209 // each capacity value we report to jstat by a very small amount to
210 // make sure that it's never zero. Given that we sometimes have to
211 // report a capacity of a generation that contains several spaces
212 // (e.g., young gen includes one eden, two survivor spaces), the
213 // mult parameter is provided in order to adding the appropriate
214 // padding multiple times so that the capacities add up correctly.
215 static size_t pad_capacity(size_t size_bytes, size_t mult = 1) {
216 return size_bytes + MinObjAlignmentInBytes * mult;
217 }
218
219 // Recalculate all the sizes from scratch and update all the jstat
220 // counters accordingly.
221 void update_sizes();
222
223 void update_eden_size();
224
225 CollectorCounters* conc_collection_counters() {
226 return _conc_collection_counters;
227 }
228
229 // Monitoring support used by
230 // MemoryService
231 // jstat counters
232 // Tracing
233
234 size_t young_gen_committed() { return _young_gen_committed; }
235
236 size_t eden_space_committed() { return _eden_space_committed; }
237 size_t eden_space_used() { return _eden_space_used; }
238 size_t survivor_space_committed() { return _survivor_space_committed; }
239 size_t survivor_space_used() { return _survivor_space_used; }
240
241 size_t old_gen_committed() { return _old_gen_committed; }
242 size_t old_gen_used() { return _old_gen_used; }
243 };
244
245 // Scope object for java.lang.management support.
246 class G1MonitoringScope : public StackObj {
247 TraceCollectorStats _tcs;
248 TraceMemoryManagerStats _tms;
249 public:
250 G1MonitoringScope(G1MonitoringSupport* g1mm, bool full_gc, bool all_memory_pools_affected);
251 };
252
253 #endif // SHARE_VM_GC_G1_G1MONITORINGSUPPORT_HPP