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24
25#ifndef SHARE_GC_G1_G1MONITORINGSUPPORT_HPP
26#define SHARE_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
34class CollectorCounters;
35class G1CollectedHeap;
36class HSpaceCounters;
37class 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
122class G1MonitoringSupport : public CHeapObj<mtGC> {
123 friend class VMStructs;
124 friend class G1MonitoringScope;
125
126 G1CollectedHeap* _g1h;
127
128 // java.lang.management MemoryManager and MemoryPool support
129 GCMemoryManager _incremental_memory_manager;
130 GCMemoryManager _full_gc_memory_manager;
131
132 MemoryPool* _eden_space_pool;
133 MemoryPool* _survivor_space_pool;
134 MemoryPool* _old_gen_pool;
135
136 // jstat performance counters
137 // incremental collections both young and mixed
138 CollectorCounters* _incremental_collection_counters;
139 // full stop-the-world collections
140 CollectorCounters* _full_collection_counters;
141 // stop-the-world phases in G1
142 CollectorCounters* _conc_collection_counters;
143 // young collection set counters. The _eden_counters,
144 // _from_counters, and _to_counters are associated with
145 // this "generational" counter.
146 GenerationCounters* _young_gen_counters;
147 // old collection set counters. The _old_space_counters
148 // below are associated with this "generational" counter.
149 GenerationCounters* _old_gen_counters;
150 // Counters for the capacity and used for
151 // the whole heap
152 HSpaceCounters* _old_space_counters;
153 // the young collection
154 HSpaceCounters* _eden_space_counters;
155 // the survivor collection (only one, _to_counters, is actively used)
156 HSpaceCounters* _from_space_counters;
157 HSpaceCounters* _to_space_counters;
158
159 // When it's appropriate to recalculate the various sizes (at the
160 // end of a GC, when a new eden region is allocated, etc.) we store
161 // them here so that we can easily report them when needed and not
162 // have to recalculate them every time.
163
164 size_t _overall_committed;
165 size_t _overall_used;
166
167 size_t _young_gen_committed;
168 size_t _old_gen_committed;
169
170 size_t _eden_space_committed;
171 size_t _eden_space_used;
172 size_t _survivor_space_committed;
173 size_t _survivor_space_used;
174
175 size_t _old_gen_used;
176
177 // Recalculate all the sizes.
178 void recalculate_sizes();
179
180 void recalculate_eden_size();
181
182public:
183 G1MonitoringSupport(G1CollectedHeap* g1h);
184 ~G1MonitoringSupport();
185
186 void initialize_serviceability();
187
188 MemoryUsage memory_usage();
189 GrowableArray<GCMemoryManager*> memory_managers();
190 GrowableArray<MemoryPool*> memory_pools();
191
192 // Unfortunately, the jstat tool assumes that no space has 0
193 // capacity. In our case, given that each space is logical, it's
194 // possible that no regions will be allocated to it, hence to have 0
195 // capacity (e.g., if there are no survivor regions, the survivor
196 // space has 0 capacity). The way we deal with this is to always pad
197 // each capacity value we report to jstat by a very small amount to
198 // make sure that it's never zero. Given that we sometimes have to
199 // report a capacity of a generation that contains several spaces
200 // (e.g., young gen includes one eden, two survivor spaces), the
201 // mult parameter is provided in order to adding the appropriate
202 // padding multiple times so that the capacities add up correctly.
203 static size_t pad_capacity(size_t size_bytes, size_t mult = 1) {
204 return size_bytes + MinObjAlignmentInBytes * mult;
205 }
206
207 // Recalculate all the sizes from scratch and update all the jstat
208 // counters accordingly.
209 void update_sizes();
210
211 void update_eden_size();
212
213 CollectorCounters* conc_collection_counters() {
214 return _conc_collection_counters;
215 }
216
217 // Monitoring support used by
218 // MemoryService
219 // jstat counters
220 // Tracing
221 // Values may not be consistent wrt to each other.
222
223 size_t young_gen_committed() { return _young_gen_committed; }
224
225 size_t eden_space_used() { return _eden_space_used; }
226 size_t survivor_space_used() { return _survivor_space_used; }
227
228 size_t old_gen_committed() { return _old_gen_committed; }
229 size_t old_gen_used() { return _old_gen_used; }
230
231 // Monitoring support for MemoryPools. Values in the returned MemoryUsage are
232 // guaranteed to be consistent with each other.
233 MemoryUsage eden_space_memory_usage(size_t initial_size, size_t max_size);
234 MemoryUsage survivor_space_memory_usage(size_t initial_size, size_t max_size);
235
236 MemoryUsage old_gen_memory_usage(size_t initial_size, size_t max_size);
237};
238
239// Scope object for java.lang.management support.
240class G1MonitoringScope : public StackObj {
241 TraceCollectorStats _tcs;
242 TraceMemoryManagerStats _tms;
243public:
244 G1MonitoringScope(G1MonitoringSupport* g1mm, bool full_gc, bool all_memory_pools_affected);
245};
246
247#endif // SHARE_GC_G1_G1MONITORINGSUPPORT_HPP
248