Mercurial > hg > truffle
annotate src/share/vm/services/g1MemoryPool.hpp @ 1092:ed52bcc32739
6880903: G1: G1 reports incorrect Runtime.maxMemory()
Summary: G1 reports committed memory instead of reserved memory from the Runtime.maxMemory() method
Reviewed-by: ysr, jmasa
| author | tonyp |
|---|---|
| date | Fri, 04 Dec 2009 07:44:35 -0500 |
| parents | db0d5eba9d20 |
| children | afc30fccf324 |
| rev | line source |
|---|---|
| 1089 | 1 /* |
| 2 * Copyright (c) 2007 Sun Microsystems, Inc. All Rights Reserved. | |
| 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 * | |
| 19 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, | |
| 20 * CA 95054 USA or visit www.sun.com if you need additional information or | |
| 21 * have any questions. | |
| 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 | |
| 77 // the max size that each memory pool can grow to. Right now, we set | |
| 78 // that the committed size for the eden and the survivors and | |
| 79 // calculate the old gen max as follows (basically, it's a similar | |
| 80 // pattern to what we use for the committed space, as described | |
| 81 // above): | |
| 82 // | |
| 83 // old_gen_max = overall_max - eden_max - survivor_max | |
| 84 // | |
| 85 // 4) Now, there is a very subtle issue with all the above. The | |
| 86 // framework will call get_memory_usage() on the three pools | |
| 87 // asynchronously. As a result, each call might get a different value | |
| 88 // for, say, survivor_num which will yield inconsistent values for | |
| 89 // eden_used, survivor_used, and old_gen_used (as survivor_num is used | |
| 90 // in the calculation of all three). This would normally be | |
| 91 // ok. However, it's possible that this might cause the sum of | |
| 92 // eden_used, survivor_used, and old_gen_used to go over the max heap | |
| 93 // size and this seems to sometimes cause JConsole (and maybe other | |
| 94 // clients) to get confused. There's not a really an easy / clean | |
| 95 // solution to this problem, due to the asynchrounous nature of the | |
| 96 // framework. | |
| 97 | |
| 98 | |
| 99 // This class is shared by the three G1 memory pool classes | |
| 100 // (G1EdenPool, G1SurvivorPool, G1OldGenPool). Given that the way we | |
| 101 // calculate used / committed bytes for these three pools is related | |
| 102 // (see comment above), we put the calculations in this class so that | |
| 103 // we can easily share them among the subclasses. | |
| 104 class G1MemoryPoolSuper : public CollectedMemoryPool { | |
| 105 private: | |
| 106 G1CollectedHeap* _g1h; | |
| 107 | |
| 108 // It returns x - y if x > y, 0 otherwise. | |
| 109 // As described in the comment above, some of the inputs to the | |
| 110 // calculations we have to do are obtained concurrently and hence | |
| 111 // may be inconsistent with each other. So, this provides a | |
| 112 // defensive way of performing the subtraction and avoids the value | |
| 113 // going negative (which would mean a very large result, given that | |
| 114 // the parameter are size_t). | |
| 115 static size_t subtract_up_to_zero(size_t x, size_t y) { | |
| 116 if (x > y) { | |
| 117 return x - y; | |
| 118 } else { | |
| 119 return 0; | |
| 120 } | |
| 121 } | |
| 122 | |
| 123 protected: | |
| 124 // Would only be called from subclasses. | |
| 125 G1MemoryPoolSuper(G1CollectedHeap* g1h, | |
| 126 const char* name, | |
| 127 size_t init_size, | |
| 128 size_t max_size, | |
| 129 bool support_usage_threshold); | |
| 130 | |
| 131 // The reason why all the code is in static methods is so that it | |
| 132 // can be safely called from the constructors of the subclasses. | |
| 133 | |
| 134 static size_t overall_committed(G1CollectedHeap* g1h) { | |
| 135 return g1h->capacity(); | |
| 136 } | |
| 137 static size_t overall_used(G1CollectedHeap* g1h) { | |
| 138 return g1h->used_unlocked(); | |
| 139 } | |
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6880903: G1: G1 reports incorrect Runtime.maxMemory()
tonyp
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140 static size_t overall_max(G1CollectedHeap* g1h) { |
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6880903: G1: G1 reports incorrect Runtime.maxMemory()
tonyp
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141 return g1h->g1_reserved_obj_bytes(); |
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6880903: G1: G1 reports incorrect Runtime.maxMemory()
tonyp
parents:
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142 } |
| 1089 | 143 |
| 144 static size_t eden_space_committed(G1CollectedHeap* g1h); | |
| 145 static size_t eden_space_used(G1CollectedHeap* g1h); | |
| 146 static size_t eden_space_max(G1CollectedHeap* g1h); | |
| 147 | |
| 148 static size_t survivor_space_committed(G1CollectedHeap* g1h); | |
| 149 static size_t survivor_space_used(G1CollectedHeap* g1h); | |
| 150 static size_t survivor_space_max(G1CollectedHeap* g1h); | |
| 151 | |
| 152 static size_t old_space_committed(G1CollectedHeap* g1h); | |
| 153 static size_t old_space_used(G1CollectedHeap* g1h); | |
| 154 static size_t old_space_max(G1CollectedHeap* g1h); | |
| 155 | |
| 156 // The non-static versions are included for convenience. | |
| 157 | |
| 158 size_t eden_space_committed() { | |
| 159 return eden_space_committed(_g1h); | |
| 160 } | |
| 161 size_t eden_space_used() { | |
| 162 return eden_space_used(_g1h); | |
| 163 } | |
| 164 size_t eden_space_max() { | |
| 165 return eden_space_max(_g1h); | |
| 166 } | |
| 167 | |
| 168 size_t survivor_space_committed() { | |
| 169 return survivor_space_committed(_g1h); | |
| 170 } | |
| 171 size_t survivor_space_used() { | |
| 172 return survivor_space_used(_g1h); | |
| 173 } | |
| 174 size_t survivor_space_max() { | |
| 175 return survivor_space_max(_g1h); | |
| 176 } | |
| 177 | |
| 178 size_t old_space_committed() { | |
| 179 return old_space_committed(_g1h); | |
| 180 } | |
| 181 size_t old_space_used() { | |
| 182 return old_space_used(_g1h); | |
| 183 } | |
| 184 size_t old_space_max() { | |
| 185 return old_space_max(_g1h); | |
| 186 } | |
| 187 }; | |
| 188 | |
| 189 // Memory pool that represents the G1 eden. | |
| 190 class G1EdenPool : public G1MemoryPoolSuper { | |
| 191 public: | |
| 192 G1EdenPool(G1CollectedHeap* g1h); | |
| 193 | |
| 194 size_t used_in_bytes() { | |
| 195 return eden_space_used(); | |
| 196 } | |
| 197 size_t max_size() { | |
| 198 return eden_space_max(); | |
| 199 } | |
| 200 MemoryUsage get_memory_usage(); | |
| 201 }; | |
| 202 | |
| 203 // Memory pool that represents the G1 survivor. | |
| 204 class G1SurvivorPool : public G1MemoryPoolSuper { | |
| 205 public: | |
| 206 G1SurvivorPool(G1CollectedHeap* g1h); | |
| 207 | |
| 208 size_t used_in_bytes() { | |
| 209 return survivor_space_used(); | |
| 210 } | |
| 211 size_t max_size() { | |
| 212 return survivor_space_max(); | |
| 213 } | |
| 214 MemoryUsage get_memory_usage(); | |
| 215 }; | |
| 216 | |
| 217 // Memory pool that represents the G1 old gen. | |
| 218 class G1OldGenPool : public G1MemoryPoolSuper { | |
| 219 public: | |
| 220 G1OldGenPool(G1CollectedHeap* g1h); | |
| 221 | |
| 222 size_t used_in_bytes() { | |
| 223 return old_space_used(); | |
| 224 } | |
| 225 size_t max_size() { | |
| 226 return old_space_max(); | |
| 227 } | |
| 228 MemoryUsage get_memory_usage(); | |
| 229 }; |