1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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24
25 #ifndef SHARE_VM_GC_G1_G1MONITORINGSUPPORT_HPP
26 #define SHARE_VM_GC_G1_G1MONITORINGSUPPORT_HPP
27
28 #include "gc/shared/generationCounters.hpp"
29
30 class CollectorCounters;
31 class G1CollectedHeap;
32 class HSpaceCounters;
33
34 // Class for monitoring logical spaces in G1. It provides data for
35 // both G1's jstat counters as well as G1's memory pools.
36 //
37 // G1 splits the heap into heap regions and each heap region belongs
38 // to one of the following categories:
39 //
40 // * eden : regions that have been allocated since the last GC
41 // * survivors : regions with objects that survived the last few GCs
42 // * old : long-lived non-humongous regions
43 // * humongous : humongous regions
44 // * free : free regions
45 //
46 // The combination of eden and survivor regions form the equivalent of
47 // the young generation in the other GCs. The combination of old and
48 // humongous regions form the equivalent of the old generation in the
49 // other GCs. Free regions do not have a good equivalent in the other
50 // GCs given that they can be allocated as any of the other region types.
51 //
52 // The monitoring tools expect the heap to contain a number of
53 // generations (young, old, perm) and each generation to contain a
54 // number of spaces (young: eden, survivors, old). Given that G1 does
55 // not maintain those spaces physically (e.g., the set of
56 // non-contiguous eden regions can be considered as a "logical"
57 // space), we'll provide the illusion that those generations and
58 // spaces exist. In reality, each generation and space refers to a set
59 // of heap regions that are potentially non-contiguous.
60 //
61 // This class provides interfaces to access the min, current, and max
62 // capacity and current occupancy for each of G1's logical spaces and
63 // generations we expose to the monitoring tools. Also provided are
64 // counters for G1 concurrent collections and stop-the-world full heap
65 // collections.
66 //
67 // Below is a description of how the various sizes are calculated.
68 //
69 // * Current Capacity
70 //
71 // - heap_capacity = current heap capacity (e.g., current committed size)
72 // - young_gen_capacity = current max young gen target capacity
73 // (i.e., young gen target capacity + max allowed expansion capacity)
74 // - survivor_capacity = current survivor region capacity
75 // - eden_capacity = young_gen_capacity - survivor_capacity
76 // - old_capacity = heap_capacity - young_gen_capacity
77 //
78 // What we do in the above is to distribute the free regions among
79 // eden_capacity and old_capacity.
80 //
81 // * Occupancy
82 //
83 // - young_gen_used = current young region capacity
84 // - survivor_used = survivor_capacity
85 // - eden_used = young_gen_used - survivor_used
86 // - old_used = overall_used - young_gen_used
87 //
88 // Unfortunately, we currently only keep track of the number of
89 // currently allocated young and survivor regions + the overall used
90 // bytes in the heap, so the above can be a little inaccurate.
91 //
92 // * Min Capacity
93 //
94 // We set this to 0 for all spaces.
95 //
96 // * Max Capacity
97 //
98 // For jstat, we set the max capacity of all spaces to heap_capacity,
99 // given that we don't always have a reasonable upper bound on how big
100 // each space can grow. For the memory pools, we make the max
101 // capacity undefined with the exception of the old memory pool for
102 // which we make the max capacity same as the max heap capacity.
103 //
104 // If we had more accurate occupancy / capacity information per
105 // region set the above calculations would be greatly simplified and
106 // be made more accurate.
107 //
108 // We update all the above synchronously and we store the results in
109 // fields so that we just read said fields when needed. A subtle point
110 // is that all the above sizes need to be recalculated when the old
111 // gen changes capacity (after a GC or after a humongous allocation)
112 // but only the eden occupancy changes when a new eden region is
113 // allocated. So, in the latter case we have minimal recalculation to
114 // do which is important as we want to keep the eden region allocation
115 // path as low-overhead as possible.
116
117 class G1MonitoringSupport : public CHeapObj<mtGC> {
118 friend class VMStructs;
119
120 G1CollectedHeap* _g1h;
121
122 // jstat performance counters
123 // incremental collections both young and mixed
124 CollectorCounters* _incremental_collection_counters;
125 // full stop-the-world collections
126 CollectorCounters* _full_collection_counters;
127 // stop-the-world phases in G1
128 CollectorCounters* _conc_collection_counters;
129 // young collection set counters. The _eden_counters,
130 // _from_counters, and _to_counters are associated with
131 // this "generational" counter.
132 GenerationCounters* _young_collection_counters;
133 // old collection set counters. The _old_space_counters
134 // below are associated with this "generational" counter.
135 GenerationCounters* _old_collection_counters;
136 // Counters for the capacity and used for
137 // the whole heap
138 HSpaceCounters* _old_space_counters;
139 // the young collection
140 HSpaceCounters* _eden_counters;
141 // the survivor collection (only one, _to_counters, is actively used)
142 HSpaceCounters* _from_counters;
143 HSpaceCounters* _to_counters;
144
145 // When it's appropriate to recalculate the various sizes (at the
146 // end of a GC, when a new eden region is allocated, etc.) we store
147 // them here so that we can easily report them when needed and not
148 // have to recalculate them every time.
149
150 size_t _overall_reserved;
151 size_t _overall_committed;
152 size_t _overall_used;
153
154 uint _young_region_num;
155 size_t _young_gen_committed;
156 size_t _eden_committed;
157 size_t _eden_used;
158 size_t _survivor_committed;
159 size_t _survivor_used;
160
161 size_t _old_committed;
162 size_t _old_used;
163
164 // It returns x - y if x > y, 0 otherwise.
165 // As described in the comment above, some of the inputs to the
166 // calculations we have to do are obtained concurrently and hence
167 // may be inconsistent with each other. So, this provides a
168 // defensive way of performing the subtraction and avoids the value
169 // going negative (which would mean a very large result, given that
170 // the parameter are size_t).
171 static size_t subtract_up_to_zero(size_t x, size_t y) {
172 if (x > y) {
173 return x - y;
174 } else {
175 return 0;
176 }
177 }
178
179 // Recalculate all the sizes.
180 void recalculate_sizes();
181 // Recalculate only what's necessary when a new eden region is allocated.
182 void recalculate_eden_size();
183
184 public:
185 G1MonitoringSupport(G1CollectedHeap* g1h);
186
187 // Unfortunately, the jstat tool assumes that no space has 0
188 // capacity. In our case, given that each space is logical, it's
189 // possible that no regions will be allocated to it, hence to have 0
190 // capacity (e.g., if there are no survivor regions, the survivor
191 // space has 0 capacity). The way we deal with this is to always pad
192 // each capacity value we report to jstat by a very small amount to
193 // make sure that it's never zero. Given that we sometimes have to
194 // report a capacity of a generation that contains several spaces
195 // (e.g., young gen includes one eden, two survivor spaces), the
196 // mult parameter is provided in order to adding the appropriate
197 // padding multiple times so that the capacities add up correctly.
198 static size_t pad_capacity(size_t size_bytes, size_t mult = 1) {
199 return size_bytes + MinObjAlignmentInBytes * mult;
200 }
201
202 // Recalculate all the sizes from scratch and update all the jstat
203 // counters accordingly.
204 void update_sizes();
205 // Recalculate only what's necessary when a new eden region is
206 // allocated and update any jstat counters that need to be updated.
207 void update_eden_size();
208
209 CollectorCounters* incremental_collection_counters() {
210 return _incremental_collection_counters;
211 }
212 CollectorCounters* full_collection_counters() {
213 return _full_collection_counters;
214 }
215 CollectorCounters* conc_collection_counters() {
216 return _conc_collection_counters;
217 }
218 GenerationCounters* young_collection_counters() {
219 return _young_collection_counters;
220 }
221 GenerationCounters* old_collection_counters() {
222 return _old_collection_counters;
223 }
224 HSpaceCounters* old_space_counters() { return _old_space_counters; }
225 HSpaceCounters* eden_counters() { return _eden_counters; }
226 HSpaceCounters* from_counters() { return _from_counters; }
227 HSpaceCounters* to_counters() { return _to_counters; }
228
229 // Monitoring support used by
230 // MemoryService
231 // jstat counters
232 // Tracing
233
234 size_t overall_reserved() { return _overall_reserved; }
235 size_t overall_committed() { return _overall_committed; }
236 size_t overall_used() { return _overall_used; }
237
238 size_t young_gen_committed() { return _young_gen_committed; }
239 size_t young_gen_max() { return overall_reserved(); }
240 size_t eden_space_committed() { return _eden_committed; }
241 size_t eden_space_used() { return _eden_used; }
242 size_t survivor_space_committed() { return _survivor_committed; }
243 size_t survivor_space_used() { return _survivor_used; }
244
245 size_t old_gen_committed() { return old_space_committed(); }
246 size_t old_gen_max() { return overall_reserved(); }
247 size_t old_space_committed() { return _old_committed; }
248 size_t old_space_used() { return _old_used; }
249 };
250
251 class G1GenerationCounters: public GenerationCounters {
252 protected:
253 G1MonitoringSupport* _g1mm;
254
255 public:
256 G1GenerationCounters(G1MonitoringSupport* g1mm,
257 const char* name, int ordinal, int spaces,
258 size_t min_capacity, size_t max_capacity,
259 size_t curr_capacity);
260 };
261
262 class G1YoungGenerationCounters: public G1GenerationCounters {
263 public:
264 G1YoungGenerationCounters(G1MonitoringSupport* g1mm, const char* name);
265 virtual void update_all();
266 };
267
268 class G1OldGenerationCounters: public G1GenerationCounters {
269 public:
270 G1OldGenerationCounters(G1MonitoringSupport* g1mm, const char* name);
271 virtual void update_all();
272 };
273
274 #endif // SHARE_VM_GC_G1_G1MONITORINGSUPPORT_HPP