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
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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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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 #include "runtime/mutex.hpp"
33
34 class CollectorCounters;
35 class G1CollectedHeap;
36 class HSpaceCounters;
37 class MemoryPool;
38
39 // Class for monitoring logical spaces in G1. It provides data for
40 // both G1's jstat counters as well as G1's memory pools.
41 //
42 // G1 splits the heap into heap regions and each heap region belongs
43 // to one of the following categories:
44 //
45 // * eden : regions that have been allocated since the last GC
46 // * survivors : regions with objects that survived the last few GCs
47 // * old : long-lived non-humongous regions
48 // * humongous : humongous regions
49 // * free : free regions
50 //
51 // The combination of eden and survivor regions form the equivalent of
52 // the young generation in the other GCs. The combination of old and
53 // humongous regions form the equivalent of the old generation in the
54 // other GCs. Free regions do not have a good equivalent in the other
55 // GCs given that they can be allocated as any of the other region types.
56 //
57 // The monitoring tools expect the heap to contain a number of
58 // generations (young, old, perm) and each generation to contain a
59 // number of spaces (young: eden, survivors, old). Given that G1 does
60 // not maintain those spaces physically (e.g., the set of
61 // non-contiguous eden regions can be considered as a "logical"
62 // space), we'll provide the illusion that those generations and
63 // spaces exist. In reality, each generation and space refers to a set
64 // of heap regions that are potentially non-contiguous.
65 //
66 // This class provides interfaces to access the min, current, and max
67 // capacity and current occupancy for each of G1's logical spaces and
68 // generations we expose to the monitoring tools. Also provided are
69 // counters for G1 concurrent collections and stop-the-world full heap
70 // collections.
71 //
72 // Below is a description of how the various sizes are calculated.
73 //
74 // * Current Capacity
75 //
76 // - heap_capacity = current heap capacity (e.g., current committed size)
77 // - young_gen_capacity = current max young gen target capacity
78 // (i.e., young gen target capacity + max allowed expansion capacity)
79 // - survivor_capacity = current survivor region capacity
80 // - eden_capacity = young_gen_capacity - survivor_capacity
81 // - old_capacity = heap_capacity - young_gen_capacity
82 //
83 // What we do in the above is to distribute the free regions among
84 // eden_capacity and old_capacity.
85 //
86 // * Occupancy
87 //
88 // - young_gen_used = current young region capacity
89 // - survivor_used = survivor_capacity
90 // - eden_used = young_gen_used - survivor_used
91 // - old_used = overall_used - young_gen_used
92 //
93 // Unfortunately, we currently only keep track of the number of
94 // currently allocated young and survivor regions + the overall used
95 // bytes in the heap, so the above can be a little inaccurate.
96 //
97 // * Min Capacity
98 //
99 // We set this to 0 for all spaces.
100 //
101 // * Max Capacity
102 //
103 // For jstat, we set the max capacity of all spaces to heap_capacity,
104 // given that we don't always have a reasonable upper bound on how big
105 // each space can grow. For the memory pools, we make the max
106 // capacity undefined with the exception of the old memory pool for
107 // which we make the max capacity same as the max heap capacity.
108 //
109 // If we had more accurate occupancy / capacity information per
110 // region set the above calculations would be greatly simplified and
111 // be made more accurate.
112 //
113 // We update all the above synchronously and we store the results in
114 // fields so that we just read said fields when needed. A subtle point
115 // is that all the above sizes need to be recalculated when the old
116 // gen changes capacity (after a GC or after a humongous allocation)
117 // but only the eden occupancy changes when a new eden region is
118 // allocated. So, in the latter case we have minimal recalculation to
119 // do which is important as we want to keep the eden region allocation
120 // path as low-overhead as possible.
121
122 class G1MonitoringSupport : public CHeapObj<mtGC> {
123 friend class VMStructs;
124 friend class G1MonitoringScope;
125
126 G1CollectedHeap* _g1h;
127
128 Mutex _update_mutex;
129
130 // java.lang.management MemoryManager and MemoryPool support
131 GCMemoryManager _incremental_memory_manager;
132 GCMemoryManager _full_gc_memory_manager;
133
134 MemoryPool* _eden_pool;
135 MemoryPool* _survivor_pool;
136 MemoryPool* _old_pool;
137
138 // jstat performance counters
139 // incremental collections both young and mixed
140 CollectorCounters* _incremental_collection_counters;
141 // full stop-the-world collections
142 CollectorCounters* _full_collection_counters;
143 // stop-the-world phases in G1
144 CollectorCounters* _conc_collection_counters;
145 // young collection set counters. The _eden_counters,
146 // _from_counters, and _to_counters are associated with
147 // this "generational" counter.
148 GenerationCounters* _young_gen_counters;
149 // old collection set counters. The _old_space_counters
150 // below are associated with this "generational" counter.
151 GenerationCounters* _old_gen_counters;
152 // Counters for the capacity and used for
153 // the whole heap
154 HSpaceCounters* _old_space_counters;
155 // the young collection
156 HSpaceCounters* _eden_space_counters;
157 // the survivor collection (only one, _to_counters, is actively used)
158 HSpaceCounters* _from_space_counters;
159 HSpaceCounters* _to_space_counters;
160
161 // When it's appropriate to recalculate the various sizes (at the
162 // end of a GC, when a new eden region is allocated, etc.) we store
163 // them here so that we can easily report them when needed and not
164 // have to recalculate them every time.
165
166 size_t _overall_committed;
167 size_t _overall_used;
168
169 size_t _young_gen_committed;
170 size_t _old_gen_committed;
171
172 size_t _eden_space_committed;
173 size_t _eden_space_used;
174 size_t _survivor_space_committed;
175 size_t _survivor_space_used;
176
177 size_t _old_gen_used;
178
179 // It returns x - y if x > y, 0 otherwise.
180 // As described in the comment above, some of the inputs to the
181 // calculations we have to do are obtained concurrently and hence
182 // may be inconsistent with each other. So, this provides a
183 // defensive way of performing the subtraction and avoids the value
184 // going negative (which would mean a very large result, given that
185 // the parameter are size_t).
186 static size_t subtract_up_to_zero(size_t x, size_t y) {
187 if (x > y) {
188 return x - y;
189 } else {
190 return 0;
191 }
192 }
193
194 // Recalculate all the sizes.
195 void recalculate_sizes();
196
197 void recalculate_eden_size();
198
199 public:
200 G1MonitoringSupport(G1CollectedHeap* g1h);
201 ~G1MonitoringSupport();
202
203 void initialize_serviceability();
204
205 MemoryUsage memory_usage();
206 GrowableArray<GCMemoryManager*> memory_managers();
207 GrowableArray<MemoryPool*> memory_pools();
208
209 // Unfortunately, the jstat tool assumes that no space has 0
210 // capacity. In our case, given that each space is logical, it's
211 // possible that no regions will be allocated to it, hence to have 0
212 // capacity (e.g., if there are no survivor regions, the survivor
213 // space has 0 capacity). The way we deal with this is to always pad
214 // each capacity value we report to jstat by a very small amount to
215 // make sure that it's never zero. Given that we sometimes have to
216 // report a capacity of a generation that contains several spaces
217 // (e.g., young gen includes one eden, two survivor spaces), the
218 // mult parameter is provided in order to adding the appropriate
219 // padding multiple times so that the capacities add up correctly.
220 static size_t pad_capacity(size_t size_bytes, size_t mult = 1) {
221 return size_bytes + MinObjAlignmentInBytes * mult;
222 }
223
224 // Recalculate all the sizes from scratch and update all the jstat
225 // counters accordingly.
226 void update_sizes();
227
228 void update_eden_size();
229
230 CollectorCounters* conc_collection_counters() {
231 return _conc_collection_counters;
232 }
233
234 // Monitoring support used by
235 // MemoryService
236 // jstat counters
237 // Tracing
238 // Values may not be consistent wrt to each other.
239
240 size_t young_gen_committed() { return _young_gen_committed; }
241
242 size_t eden_space_used() { return _eden_space_used; }
243 size_t survivor_space_used() { return _survivor_space_used; }
244
245 size_t old_gen_committed() { return _old_gen_committed; }
246 size_t old_gen_used() { return _old_gen_used; }
247
248 // Monitoring support for MemoryPools. Values in the returned MemoryUsage are
249 // guaranteed to be consistent with each other.
250 MemoryUsage eden_space_memory_usage(size_t initial_size, size_t max_size);
251 MemoryUsage survivor_space_memory_usage(size_t initial_size, size_t max_size);
252
253 MemoryUsage old_gen_memory_usage(size_t initial_size, size_t max_size);
254 };
255
256 // Scope object for java.lang.management support.
257 class G1MonitoringScope : public StackObj {
258 TraceCollectorStats _tcs;
259 TraceMemoryManagerStats _tms;
260 public:
261 G1MonitoringScope(G1MonitoringSupport* g1mm, bool full_gc, bool all_memory_pools_affected);
262 };
263
264 #endif // SHARE_VM_GC_G1_G1MONITORINGSUPPORT_HPP