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annotate src/share/vm/services/g1MemoryPool.hpp @ 3187:6ff76a1b8339
The benchmark tool should now print zero values to the csv file, if a benchmark fails
author | Josef Haider <josef.haider@khg.jku.at> |
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date | Thu, 07 Jul 2011 19:43:17 +0200 |
parents | f95d63e2154a |
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1089 | 1 /* |
1972 | 2 * Copyright (c) 2007, 2010, Oracle and/or its affiliates. All rights reserved. |
1089 | 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 | |
16 * 2 along with this work; if not, write to the Free Software Foundation, | |
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | |
18 * | |
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19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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20 * or visit www.oracle.com if you need additional information or have any |
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21 * questions. |
1089 | 22 * |
23 */ | |
24 | |
1972 | 25 #ifndef SHARE_VM_SERVICES_G1MEMORYPOOL_HPP |
26 #define SHARE_VM_SERVICES_G1MEMORYPOOL_HPP | |
27 | |
28 #ifndef SERIALGC | |
29 #include "services/memoryPool.hpp" | |
30 #include "services/memoryUsage.hpp" | |
31 #endif | |
32 | |
1089 | 33 class G1CollectedHeap; |
34 | |
35 // This file contains the three classes that represent the memory | |
36 // pools of the G1 spaces: G1EdenPool, G1SurvivorPool, and | |
37 // G1OldGenPool. In G1, unlike our other GCs, we do not have a | |
38 // physical space for each of those spaces. Instead, we allocate | |
39 // regions for all three spaces out of a single pool of regions (that | |
40 // pool basically covers the entire heap). As a result, the eden, | |
41 // survivor, and old gen are considered logical spaces in G1, as each | |
42 // is a set of non-contiguous regions. This is also reflected in the | |
43 // way we map them to memory pools here. The easiest way to have done | |
44 // this would have been to map the entire G1 heap to a single memory | |
45 // pool. However, it's helpful to show how large the eden and survivor | |
46 // get, as this does affect the performance and behavior of G1. Which | |
47 // is why we introduce the three memory pools implemented here. | |
48 // | |
49 // The above approach inroduces a couple of challenging issues in the | |
50 // implementation of the three memory pools: | |
51 // | |
52 // 1) The used space calculation for a pool is not necessarily | |
53 // independent of the others. We can easily get from G1 the overall | |
54 // used space in the entire heap, the number of regions in the young | |
55 // generation (includes both eden and survivors), and the number of | |
56 // survivor regions. So, from that we calculate: | |
57 // | |
58 // survivor_used = survivor_num * region_size | |
59 // eden_used = young_region_num * region_size - survivor_used | |
60 // old_gen_used = overall_used - eden_used - survivor_used | |
61 // | |
62 // Note that survivor_used and eden_used are upper bounds. To get the | |
63 // actual value we would have to iterate over the regions and add up | |
64 // ->used(). But that'd be expensive. So, we'll accept some lack of | |
65 // accuracy for those two. But, we have to be careful when calculating | |
66 // old_gen_used, in case we subtract from overall_used more then the | |
67 // actual number and our result goes negative. | |
68 // | |
69 // 2) Calculating the used space is straightforward, as described | |
70 // above. However, how do we calculate the committed space, given that | |
71 // we allocate space for the eden, survivor, and old gen out of the | |
72 // same pool of regions? One way to do this is to use the used value | |
73 // as also the committed value for the eden and survivor spaces and | |
74 // then calculate the old gen committed space as follows: | |
75 // | |
76 // old_gen_committed = overall_committed - eden_committed - survivor_committed | |
77 // | |
78 // Maybe a better way to do that would be to calculate used for eden | |
79 // and survivor as a sum of ->used() over their regions and then | |
80 // calculate committed as region_num * region_size (i.e., what we use | |
81 // to calculate the used space now). This is something to consider | |
82 // in the future. | |
83 // | |
84 // 3) Another decision that is again not straightforward is what is | |
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85 // the max size that each memory pool can grow to. One way to do this |
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86 // would be to use the committed size for the max for the eden and |
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87 // survivors and calculate the old gen max as follows (basically, it's |
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88 // a similar pattern to what we use for the committed space, as |
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89 // described above): |
1089 | 90 // |
91 // old_gen_max = overall_max - eden_max - survivor_max | |
92 // | |
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93 // Unfortunately, the above makes the max of each pool fluctuate over |
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94 // time and, even though this is allowed according to the spec, it |
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95 // broke several assumptions in the M&M framework (there were cases |
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96 // where used would reach a value greater than max). So, for max we |
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97 // use -1, which means "undefined" according to the spec. |
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98 // |
1089 | 99 // 4) Now, there is a very subtle issue with all the above. The |
100 // framework will call get_memory_usage() on the three pools | |
101 // asynchronously. As a result, each call might get a different value | |
102 // for, say, survivor_num which will yield inconsistent values for | |
103 // eden_used, survivor_used, and old_gen_used (as survivor_num is used | |
104 // in the calculation of all three). This would normally be | |
105 // ok. However, it's possible that this might cause the sum of | |
106 // eden_used, survivor_used, and old_gen_used to go over the max heap | |
107 // size and this seems to sometimes cause JConsole (and maybe other | |
108 // clients) to get confused. There's not a really an easy / clean | |
109 // solution to this problem, due to the asynchrounous nature of the | |
110 // framework. | |
111 | |
112 | |
113 // This class is shared by the three G1 memory pool classes | |
114 // (G1EdenPool, G1SurvivorPool, G1OldGenPool). Given that the way we | |
115 // calculate used / committed bytes for these three pools is related | |
116 // (see comment above), we put the calculations in this class so that | |
117 // we can easily share them among the subclasses. | |
118 class G1MemoryPoolSuper : public CollectedMemoryPool { | |
119 private: | |
120 // It returns x - y if x > y, 0 otherwise. | |
121 // As described in the comment above, some of the inputs to the | |
122 // calculations we have to do are obtained concurrently and hence | |
123 // may be inconsistent with each other. So, this provides a | |
124 // defensive way of performing the subtraction and avoids the value | |
125 // going negative (which would mean a very large result, given that | |
126 // the parameter are size_t). | |
127 static size_t subtract_up_to_zero(size_t x, size_t y) { | |
128 if (x > y) { | |
129 return x - y; | |
130 } else { | |
131 return 0; | |
132 } | |
133 } | |
134 | |
135 protected: | |
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136 G1CollectedHeap* _g1h; |
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137 |
1089 | 138 // Would only be called from subclasses. |
139 G1MemoryPoolSuper(G1CollectedHeap* g1h, | |
140 const char* name, | |
141 size_t init_size, | |
142 bool support_usage_threshold); | |
143 | |
144 // The reason why all the code is in static methods is so that it | |
145 // can be safely called from the constructors of the subclasses. | |
146 | |
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147 static size_t undefined_max() { |
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148 return (size_t) -1; |
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149 } |
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150 |
1089 | 151 static size_t overall_committed(G1CollectedHeap* g1h) { |
152 return g1h->capacity(); | |
153 } | |
154 static size_t overall_used(G1CollectedHeap* g1h) { | |
155 return g1h->used_unlocked(); | |
156 } | |
157 | |
158 static size_t eden_space_committed(G1CollectedHeap* g1h); | |
159 static size_t eden_space_used(G1CollectedHeap* g1h); | |
160 | |
161 static size_t survivor_space_committed(G1CollectedHeap* g1h); | |
162 static size_t survivor_space_used(G1CollectedHeap* g1h); | |
163 | |
164 static size_t old_space_committed(G1CollectedHeap* g1h); | |
165 static size_t old_space_used(G1CollectedHeap* g1h); | |
166 }; | |
167 | |
168 // Memory pool that represents the G1 eden. | |
169 class G1EdenPool : public G1MemoryPoolSuper { | |
170 public: | |
171 G1EdenPool(G1CollectedHeap* g1h); | |
172 | |
173 size_t used_in_bytes() { | |
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174 return eden_space_used(_g1h); |
1089 | 175 } |
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176 size_t max_size() const { |
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177 return undefined_max(); |
1089 | 178 } |
179 MemoryUsage get_memory_usage(); | |
180 }; | |
181 | |
182 // Memory pool that represents the G1 survivor. | |
183 class G1SurvivorPool : public G1MemoryPoolSuper { | |
184 public: | |
185 G1SurvivorPool(G1CollectedHeap* g1h); | |
186 | |
187 size_t used_in_bytes() { | |
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188 return survivor_space_used(_g1h); |
1089 | 189 } |
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190 size_t max_size() const { |
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191 return undefined_max(); |
1089 | 192 } |
193 MemoryUsage get_memory_usage(); | |
194 }; | |
195 | |
196 // Memory pool that represents the G1 old gen. | |
197 class G1OldGenPool : public G1MemoryPoolSuper { | |
198 public: | |
199 G1OldGenPool(G1CollectedHeap* g1h); | |
200 | |
201 size_t used_in_bytes() { | |
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202 return old_space_used(_g1h); |
1089 | 203 } |
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204 size_t max_size() const { |
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205 return undefined_max(); |
1089 | 206 } |
207 MemoryUsage get_memory_usage(); | |
208 }; | |
1972 | 209 |
210 #endif // SHARE_VM_SERVICES_G1MEMORYPOOL_HPP |