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annotate src/share/vm/services/g1MemoryPool.hpp @ 1923:2db84614f61d
6998737: JSR 292: Remove the plug guarding the use of compressed oops
Summary: The plug that guards the use of compressed oops with invokedynamic needs to be removed
Reviewed-by: twisti, kvn
| author | iveresov |
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| date | Tue, 09 Nov 2010 15:12:15 -0800 |
| parents | e967bad2a9ab |
| children | f95d63e2154a |
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| 1089 | 1 /* |
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2 * Copyright (c) 2007, 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 | |
| 25 class G1CollectedHeap; | |
| 26 | |
| 27 // This file contains the three classes that represent the memory | |
| 28 // pools of the G1 spaces: G1EdenPool, G1SurvivorPool, and | |
| 29 // G1OldGenPool. In G1, unlike our other GCs, we do not have a | |
| 30 // physical space for each of those spaces. Instead, we allocate | |
| 31 // regions for all three spaces out of a single pool of regions (that | |
| 32 // pool basically covers the entire heap). As a result, the eden, | |
| 33 // survivor, and old gen are considered logical spaces in G1, as each | |
| 34 // is a set of non-contiguous regions. This is also reflected in the | |
| 35 // way we map them to memory pools here. The easiest way to have done | |
| 36 // this would have been to map the entire G1 heap to a single memory | |
| 37 // pool. However, it's helpful to show how large the eden and survivor | |
| 38 // get, as this does affect the performance and behavior of G1. Which | |
| 39 // is why we introduce the three memory pools implemented here. | |
| 40 // | |
| 41 // The above approach inroduces a couple of challenging issues in the | |
| 42 // implementation of the three memory pools: | |
| 43 // | |
| 44 // 1) The used space calculation for a pool is not necessarily | |
| 45 // independent of the others. We can easily get from G1 the overall | |
| 46 // used space in the entire heap, the number of regions in the young | |
| 47 // generation (includes both eden and survivors), and the number of | |
| 48 // survivor regions. So, from that we calculate: | |
| 49 // | |
| 50 // survivor_used = survivor_num * region_size | |
| 51 // eden_used = young_region_num * region_size - survivor_used | |
| 52 // old_gen_used = overall_used - eden_used - survivor_used | |
| 53 // | |
| 54 // Note that survivor_used and eden_used are upper bounds. To get the | |
| 55 // actual value we would have to iterate over the regions and add up | |
| 56 // ->used(). But that'd be expensive. So, we'll accept some lack of | |
| 57 // accuracy for those two. But, we have to be careful when calculating | |
| 58 // old_gen_used, in case we subtract from overall_used more then the | |
| 59 // actual number and our result goes negative. | |
| 60 // | |
| 61 // 2) Calculating the used space is straightforward, as described | |
| 62 // above. However, how do we calculate the committed space, given that | |
| 63 // we allocate space for the eden, survivor, and old gen out of the | |
| 64 // same pool of regions? One way to do this is to use the used value | |
| 65 // as also the committed value for the eden and survivor spaces and | |
| 66 // then calculate the old gen committed space as follows: | |
| 67 // | |
| 68 // old_gen_committed = overall_committed - eden_committed - survivor_committed | |
| 69 // | |
| 70 // Maybe a better way to do that would be to calculate used for eden | |
| 71 // and survivor as a sum of ->used() over their regions and then | |
| 72 // calculate committed as region_num * region_size (i.e., what we use | |
| 73 // to calculate the used space now). This is something to consider | |
| 74 // in the future. | |
| 75 // | |
| 76 // 3) Another decision that is again not straightforward is what is | |
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77 // the max size that each memory pool can grow to. One way to do this |
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78 // would be to use the committed size for the max for the eden and |
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79 // survivors and calculate the old gen max as follows (basically, it's |
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80 // a similar pattern to what we use for the committed space, as |
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81 // described above): |
| 1089 | 82 // |
| 83 // old_gen_max = overall_max - eden_max - survivor_max | |
| 84 // | |
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85 // Unfortunately, the above makes the max of each pool fluctuate over |
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86 // time and, even though this is allowed according to the spec, it |
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87 // broke several assumptions in the M&M framework (there were cases |
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88 // where used would reach a value greater than max). So, for max we |
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89 // use -1, which means "undefined" according to the spec. |
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90 // |
| 1089 | 91 // 4) Now, there is a very subtle issue with all the above. The |
| 92 // framework will call get_memory_usage() on the three pools | |
| 93 // asynchronously. As a result, each call might get a different value | |
| 94 // for, say, survivor_num which will yield inconsistent values for | |
| 95 // eden_used, survivor_used, and old_gen_used (as survivor_num is used | |
| 96 // in the calculation of all three). This would normally be | |
| 97 // ok. However, it's possible that this might cause the sum of | |
| 98 // eden_used, survivor_used, and old_gen_used to go over the max heap | |
| 99 // size and this seems to sometimes cause JConsole (and maybe other | |
| 100 // clients) to get confused. There's not a really an easy / clean | |
| 101 // solution to this problem, due to the asynchrounous nature of the | |
| 102 // framework. | |
| 103 | |
| 104 | |
| 105 // This class is shared by the three G1 memory pool classes | |
| 106 // (G1EdenPool, G1SurvivorPool, G1OldGenPool). Given that the way we | |
| 107 // calculate used / committed bytes for these three pools is related | |
| 108 // (see comment above), we put the calculations in this class so that | |
| 109 // we can easily share them among the subclasses. | |
| 110 class G1MemoryPoolSuper : public CollectedMemoryPool { | |
| 111 private: | |
| 112 // It returns x - y if x > y, 0 otherwise. | |
| 113 // As described in the comment above, some of the inputs to the | |
| 114 // calculations we have to do are obtained concurrently and hence | |
| 115 // may be inconsistent with each other. So, this provides a | |
| 116 // defensive way of performing the subtraction and avoids the value | |
| 117 // going negative (which would mean a very large result, given that | |
| 118 // the parameter are size_t). | |
| 119 static size_t subtract_up_to_zero(size_t x, size_t y) { | |
| 120 if (x > y) { | |
| 121 return x - y; | |
| 122 } else { | |
| 123 return 0; | |
| 124 } | |
| 125 } | |
| 126 | |
| 127 protected: | |
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128 G1CollectedHeap* _g1h; |
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129 |
| 1089 | 130 // Would only be called from subclasses. |
| 131 G1MemoryPoolSuper(G1CollectedHeap* g1h, | |
| 132 const char* name, | |
| 133 size_t init_size, | |
| 134 bool support_usage_threshold); | |
| 135 | |
| 136 // The reason why all the code is in static methods is so that it | |
| 137 // can be safely called from the constructors of the subclasses. | |
| 138 | |
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139 static size_t undefined_max() { |
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140 return (size_t) -1; |
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141 } |
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142 |
| 1089 | 143 static size_t overall_committed(G1CollectedHeap* g1h) { |
| 144 return g1h->capacity(); | |
| 145 } | |
| 146 static size_t overall_used(G1CollectedHeap* g1h) { | |
| 147 return g1h->used_unlocked(); | |
| 148 } | |
| 149 | |
| 150 static size_t eden_space_committed(G1CollectedHeap* g1h); | |
| 151 static size_t eden_space_used(G1CollectedHeap* g1h); | |
| 152 | |
| 153 static size_t survivor_space_committed(G1CollectedHeap* g1h); | |
| 154 static size_t survivor_space_used(G1CollectedHeap* g1h); | |
| 155 | |
| 156 static size_t old_space_committed(G1CollectedHeap* g1h); | |
| 157 static size_t old_space_used(G1CollectedHeap* g1h); | |
| 158 }; | |
| 159 | |
| 160 // Memory pool that represents the G1 eden. | |
| 161 class G1EdenPool : public G1MemoryPoolSuper { | |
| 162 public: | |
| 163 G1EdenPool(G1CollectedHeap* g1h); | |
| 164 | |
| 165 size_t used_in_bytes() { | |
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166 return eden_space_used(_g1h); |
| 1089 | 167 } |
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168 size_t max_size() const { |
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169 return undefined_max(); |
| 1089 | 170 } |
| 171 MemoryUsage get_memory_usage(); | |
| 172 }; | |
| 173 | |
| 174 // Memory pool that represents the G1 survivor. | |
| 175 class G1SurvivorPool : public G1MemoryPoolSuper { | |
| 176 public: | |
| 177 G1SurvivorPool(G1CollectedHeap* g1h); | |
| 178 | |
| 179 size_t used_in_bytes() { | |
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180 return survivor_space_used(_g1h); |
| 1089 | 181 } |
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182 size_t max_size() const { |
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183 return undefined_max(); |
| 1089 | 184 } |
| 185 MemoryUsage get_memory_usage(); | |
| 186 }; | |
| 187 | |
| 188 // Memory pool that represents the G1 old gen. | |
| 189 class G1OldGenPool : public G1MemoryPoolSuper { | |
| 190 public: | |
| 191 G1OldGenPool(G1CollectedHeap* g1h); | |
| 192 | |
| 193 size_t used_in_bytes() { | |
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194 return old_space_used(_g1h); |
| 1089 | 195 } |
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196 size_t max_size() const { |
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197 return undefined_max(); |
| 1089 | 198 } |
| 199 MemoryUsage get_memory_usage(); | |
| 200 }; |