Fri, 23 Sep 2011 16:07:49 -0400
7075646: G1: fix inconsistencies in the monitoring data
Summary: Fixed a few inconsistencies in the monitoring data, in particular when reported from jstat.
Reviewed-by: jmasa, brutisso, johnc
1 /*
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25 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1MONITORINGSUPPORT_HPP
26 #define SHARE_VM_GC_IMPLEMENTATION_G1_G1MONITORINGSUPPORT_HPP
28 #include "gc_implementation/shared/hSpaceCounters.hpp"
30 class G1CollectedHeap;
32 // Class for monitoring logical spaces in G1. It provides data for
33 // both G1's jstat counters as well as G1's memory pools.
34 //
35 // G1 splits the heap into heap regions and each heap region belongs
36 // to one of the following categories:
37 //
38 // * eden : regions that have been allocated since the last GC
39 // * survivors : regions with objects that survived the last few GCs
40 // * old : long-lived non-humongous regions
41 // * humongous : humongous regions
42 // * free : free regions
43 //
44 // The combination of eden and survivor regions form the equivalent of
45 // the young generation in the other GCs. The combination of old and
46 // humongous regions form the equivalent of the old generation in the
47 // other GCs. Free regions do not have a good equivalent in the other
48 // GCs given that they can be allocated as any of the other region types.
49 //
50 // The monitoring tools expect the heap to contain a number of
51 // generations (young, old, perm) and each generation to contain a
52 // number of spaces (young: eden, survivors, old). Given that G1 does
53 // not maintain those spaces physically (e.g., the set of
54 // non-contiguous eden regions can be considered as a "logical"
55 // space), we'll provide the illusion that those generations and
56 // spaces exist. In reality, each generation and space refers to a set
57 // of heap regions that are potentially non-contiguous.
58 //
59 // This class provides interfaces to access the min, current, and max
60 // capacity and current occupancy for each of G1's logical spaces and
61 // generations we expose to the monitoring tools. Also provided are
62 // counters for G1 concurrent collections and stop-the-world full heap
63 // collections.
64 //
65 // Below is a description of how the various sizes are calculated.
66 //
67 // * Current Capacity
68 //
69 // - heap_capacity = current heap capacity (e.g., current committed size)
70 // - young_gen_capacity = current max young gen target capacity
71 // (i.e., young gen target capacity + max allowed expansion capacity)
72 // - survivor_capacity = current survivor region capacity
73 // - eden_capacity = young_gen_capacity - survivor_capacity
74 // - old_capacity = heap_capacity - young_gen_capacity
75 //
76 // What we do in the above is to distribute the free regions among
77 // eden_capacity and old_capacity.
78 //
79 // * Occupancy
80 //
81 // - young_gen_used = current young region capacity
82 // - survivor_used = survivor_capacity
83 // - eden_used = young_gen_used - survivor_used
84 // - old_used = overall_used - young_gen_used
85 //
86 // Unfortunately, we currently only keep track of the number of
87 // currently allocated young and survivor regions + the overall used
88 // bytes in the heap, so the above can be a little inaccurate.
89 //
90 // * Min Capacity
91 //
92 // We set this to 0 for all spaces. We could consider setting the old
93 // min capacity to the min capacity of the heap (see 7078465).
94 //
95 // * Max Capacity
96 //
97 // For jstat, we set the max capacity of all spaces to heap_capacity,
98 // given that we don't always have a reasonably upper bound on how big
99 // each space can grow. For the memory pools, we actually make the max
100 // capacity undefined. We could consider setting the old max capacity
101 // to the max capacity of the heap (see 7078465).
102 //
103 // If we had more accurate occupancy / capacity information per
104 // region set the above calculations would be greatly simplified and
105 // be made more accurate.
106 //
107 // We update all the above synchronously and we store the results in
108 // fields so that we just read said fields when needed. A subtle point
109 // is that all the above sizes need to be recalculated when the old
110 // gen changes capacity (after a GC or after a humongous allocation)
111 // but only the eden occupancy changes when a new eden region is
112 // allocated. So, in the latter case we have minimal recalcuation to
113 // do which is important as we want to keep the eden region allocation
114 // path as low-overhead as possible.
116 class G1MonitoringSupport : public CHeapObj {
117 G1CollectedHeap* _g1h;
119 // jstat performance counters
120 // incremental collections both fully and partially young
121 CollectorCounters* _incremental_collection_counters;
122 // full stop-the-world collections
123 CollectorCounters* _full_collection_counters;
124 // young collection set counters. The _eden_counters,
125 // _from_counters, and _to_counters are associated with
126 // this "generational" counter.
127 GenerationCounters* _young_collection_counters;
128 // old collection set counters. The _old_space_counters
129 // below are associated with this "generational" counter.
130 GenerationCounters* _old_collection_counters;
131 // Counters for the capacity and used for
132 // the whole heap
133 HSpaceCounters* _old_space_counters;
134 // the young collection
135 HSpaceCounters* _eden_counters;
136 // the survivor collection (only one, _to_counters, is actively used)
137 HSpaceCounters* _from_counters;
138 HSpaceCounters* _to_counters;
140 // When it's appropriate to recalculate the various sizes (at the
141 // end of a GC, when a new eden region is allocated, etc.) we store
142 // them here so that we can easily report them when needed and not
143 // have to recalculate them every time.
145 size_t _overall_reserved;
146 size_t _overall_committed;
147 size_t _overall_used;
149 size_t _young_region_num;
150 size_t _young_gen_committed;
151 size_t _eden_committed;
152 size_t _eden_used;
153 size_t _survivor_committed;
154 size_t _survivor_used;
156 size_t _old_committed;
157 size_t _old_used;
159 G1CollectedHeap* g1h() { return _g1h; }
161 // It returns x - y if x > y, 0 otherwise.
162 // As described in the comment above, some of the inputs to the
163 // calculations we have to do are obtained concurrently and hence
164 // may be inconsistent with each other. So, this provides a
165 // defensive way of performing the subtraction and avoids the value
166 // going negative (which would mean a very large result, given that
167 // the parameter are size_t).
168 static size_t subtract_up_to_zero(size_t x, size_t y) {
169 if (x > y) {
170 return x - y;
171 } else {
172 return 0;
173 }
174 }
176 // Recalculate all the sizes.
177 void recalculate_sizes();
178 // Recalculate only what's necessary when a new eden region is allocated.
179 void recalculate_eden_size();
181 public:
182 G1MonitoringSupport(G1CollectedHeap* g1h);
184 // Unfortunately, the jstat tool assumes that no space has 0
185 // capacity. In our case, given that each space is logical, it's
186 // possible that no regions will be allocated to it, hence to have 0
187 // capacity (e.g., if there are no survivor regions, the survivor
188 // space has 0 capacity). The way we deal with this is to always pad
189 // each capacity value we report to jstat by a very small amount to
190 // make sure that it's never zero. Given that we sometimes have to
191 // report a capacity of a generation that contains several spaces
192 // (e.g., young gen includes one eden, two survivor spaces), the
193 // mult parameter is provided in order to adding the appropriate
194 // padding multiple times so that the capacities add up correctly.
195 static size_t pad_capacity(size_t size_bytes, size_t mult = 1) {
196 return size_bytes + MinObjAlignmentInBytes * mult;
197 }
199 // Recalculate all the sizes from scratch and update all the jstat
200 // counters accordingly.
201 void update_sizes();
202 // Recalculate only what's necessary when a new eden region is
203 // allocated and update any jstat counters that need to be updated.
204 void update_eden_size();
206 CollectorCounters* incremental_collection_counters() {
207 return _incremental_collection_counters;
208 }
209 CollectorCounters* full_collection_counters() {
210 return _full_collection_counters;
211 }
212 GenerationCounters* young_collection_counters() {
213 return _young_collection_counters;
214 }
215 GenerationCounters* old_collection_counters() {
216 return _old_collection_counters;
217 }
218 HSpaceCounters* old_space_counters() { return _old_space_counters; }
219 HSpaceCounters* eden_counters() { return _eden_counters; }
220 HSpaceCounters* from_counters() { return _from_counters; }
221 HSpaceCounters* to_counters() { return _to_counters; }
223 // Monitoring support used by
224 // MemoryService
225 // jstat counters
227 size_t overall_reserved() { return _overall_reserved; }
228 size_t overall_committed() { return _overall_committed; }
229 size_t overall_used() { return _overall_used; }
231 size_t young_gen_committed() { return _young_gen_committed; }
232 size_t young_gen_max() { return overall_reserved(); }
233 size_t eden_space_committed() { return _eden_committed; }
234 size_t eden_space_used() { return _eden_used; }
235 size_t survivor_space_committed() { return _survivor_committed; }
236 size_t survivor_space_used() { return _survivor_used; }
238 size_t old_gen_committed() { return old_space_committed(); }
239 size_t old_gen_max() { return overall_reserved(); }
240 size_t old_space_committed() { return _old_committed; }
241 size_t old_space_used() { return _old_used; }
242 };
244 class G1GenerationCounters: public GenerationCounters {
245 protected:
246 G1MonitoringSupport* _g1mm;
248 public:
249 G1GenerationCounters(G1MonitoringSupport* g1mm,
250 const char* name, int ordinal, int spaces,
251 size_t min_capacity, size_t max_capacity,
252 size_t curr_capacity);
253 };
255 class G1YoungGenerationCounters: public G1GenerationCounters {
256 public:
257 G1YoungGenerationCounters(G1MonitoringSupport* g1mm, const char* name);
258 virtual void update_all();
259 };
261 class G1OldGenerationCounters: public G1GenerationCounters {
262 public:
263 G1OldGenerationCounters(G1MonitoringSupport* g1mm, const char* name);
264 virtual void update_all();
265 };
267 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1MONITORINGSUPPORT_HPP