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3289
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1 /*
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2 * Copyright (c) 2011, Oracle and/or its affiliates. All rights reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation.
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8 *
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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12 * version 2 for more details (a copy is included in the LICENSE file that
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13 * accompanied this code).
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14 *
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15 * You should have received a copy of the GNU General Public License version
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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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.
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22 *
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23 */
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24
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25 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1MONITORINGSUPPORT_HPP
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26 #define SHARE_VM_GC_IMPLEMENTATION_G1_G1MONITORINGSUPPORT_HPP
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27
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28 #include "gc_implementation/shared/hSpaceCounters.hpp"
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29
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30 class G1CollectedHeap;
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31 class G1SpaceMonitoringSupport;
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32
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33 // Class for monitoring logical spaces in G1.
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34 // G1 defines a set of regions as a young
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35 // collection (analogous to a young generation).
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36 // The young collection is a logical generation
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37 // with no fixed chunk (see space.hpp) reflecting
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38 // the address space for the generation. In addition
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39 // to the young collection there is its complement
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40 // the non-young collection that is simply the regions
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41 // not in the young collection. The non-young collection
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42 // is treated here as a logical old generation only
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43 // because the monitoring tools expect a generational
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44 // heap. The monitoring tools expect that a Space
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45 // (see space.hpp) exists that describe the
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46 // address space of young collection and non-young
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47 // collection and such a view is provided here.
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48 //
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49 // This class provides interfaces to access
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50 // the value of variables for the young collection
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51 // that include the "capacity" and "used" of the
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52 // young collection along with constant values
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53 // for the minimum and maximum capacities for
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54 // the logical spaces. Similarly for the non-young
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55 // collection.
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56 //
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57 // Also provided are counters for G1 concurrent collections
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58 // and stop-the-world full heap collecitons.
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59 //
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60 // Below is a description of how "used" and "capactiy"
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61 // (or committed) is calculated for the logical spaces.
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62 //
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63 // 1) The used space calculation for a pool is not necessarily
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64 // independent of the others. We can easily get from G1 the overall
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65 // used space in the entire heap, the number of regions in the young
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66 // generation (includes both eden and survivors), and the number of
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67 // survivor regions. So, from that we calculate:
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68 //
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69 // survivor_used = survivor_num * region_size
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70 // eden_used = young_region_num * region_size - survivor_used
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71 // old_gen_used = overall_used - eden_used - survivor_used
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72 //
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73 // Note that survivor_used and eden_used are upper bounds. To get the
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74 // actual value we would have to iterate over the regions and add up
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75 // ->used(). But that'd be expensive. So, we'll accept some lack of
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76 // accuracy for those two. But, we have to be careful when calculating
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77 // old_gen_used, in case we subtract from overall_used more then the
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78 // actual number and our result goes negative.
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79 //
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80 // 2) Calculating the used space is straightforward, as described
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81 // above. However, how do we calculate the committed space, given that
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82 // we allocate space for the eden, survivor, and old gen out of the
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83 // same pool of regions? One way to do this is to use the used value
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84 // as also the committed value for the eden and survivor spaces and
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85 // then calculate the old gen committed space as follows:
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86 //
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87 // old_gen_committed = overall_committed - eden_committed - survivor_committed
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88 //
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89 // Maybe a better way to do that would be to calculate used for eden
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90 // and survivor as a sum of ->used() over their regions and then
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91 // calculate committed as region_num * region_size (i.e., what we use
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92 // to calculate the used space now). This is something to consider
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93 // in the future.
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94 //
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95 // 3) Another decision that is again not straightforward is what is
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96 // the max size that each memory pool can grow to. One way to do this
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97 // would be to use the committed size for the max for the eden and
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98 // survivors and calculate the old gen max as follows (basically, it's
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99 // a similar pattern to what we use for the committed space, as
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100 // described above):
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101 //
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102 // old_gen_max = overall_max - eden_max - survivor_max
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103 //
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104 // Unfortunately, the above makes the max of each pool fluctuate over
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105 // time and, even though this is allowed according to the spec, it
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106 // broke several assumptions in the M&M framework (there were cases
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107 // where used would reach a value greater than max). So, for max we
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108 // use -1, which means "undefined" according to the spec.
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109 //
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110 // 4) Now, there is a very subtle issue with all the above. The
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111 // framework will call get_memory_usage() on the three pools
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112 // asynchronously. As a result, each call might get a different value
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113 // for, say, survivor_num which will yield inconsistent values for
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114 // eden_used, survivor_used, and old_gen_used (as survivor_num is used
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115 // in the calculation of all three). This would normally be
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116 // ok. However, it's possible that this might cause the sum of
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117 // eden_used, survivor_used, and old_gen_used to go over the max heap
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118 // size and this seems to sometimes cause JConsole (and maybe other
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119 // clients) to get confused. There's not a really an easy / clean
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120 // solution to this problem, due to the asynchrounous nature of the
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121 // framework.
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122
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123 class G1MonitoringSupport : public CHeapObj {
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124 G1CollectedHeap* _g1h;
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125 VirtualSpace* _g1_storage_addr;
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126
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127 // jstat performance counters
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128 // incremental collections both fully and partially young
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129 CollectorCounters* _incremental_collection_counters;
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130 // full stop-the-world collections
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131 CollectorCounters* _full_collection_counters;
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132 // young collection set counters. The _eden_counters,
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133 // _from_counters, and _to_counters are associated with
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134 // this "generational" counter.
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135 GenerationCounters* _young_collection_counters;
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136 // non-young collection set counters. The _old_space_counters
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137 // below are associated with this "generational" counter.
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138 GenerationCounters* _non_young_collection_counters;
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139 // Counters for the capacity and used for
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140 // the whole heap
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141 HSpaceCounters* _old_space_counters;
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142 // the young collection
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143 HSpaceCounters* _eden_counters;
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144 // the survivor collection (only one, _to_counters, is actively used)
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145 HSpaceCounters* _from_counters;
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146 HSpaceCounters* _to_counters;
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147
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148 // It returns x - y if x > y, 0 otherwise.
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149 // As described in the comment above, some of the inputs to the
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150 // calculations we have to do are obtained concurrently and hence
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151 // may be inconsistent with each other. So, this provides a
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152 // defensive way of performing the subtraction and avoids the value
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153 // going negative (which would mean a very large result, given that
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154 // the parameter are size_t).
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155 static size_t subtract_up_to_zero(size_t x, size_t y) {
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156 if (x > y) {
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157 return x - y;
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158 } else {
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159 return 0;
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160 }
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161 }
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162
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163 public:
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164 G1MonitoringSupport(G1CollectedHeap* g1h, VirtualSpace* g1_storage_addr);
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165
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166 G1CollectedHeap* g1h() { return _g1h; }
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167 VirtualSpace* g1_storage_addr() { return _g1_storage_addr; }
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168
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169 // Performance Counter accessors
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170 void update_counters();
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171 void update_eden_counters();
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172
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173 CollectorCounters* incremental_collection_counters() {
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174 return _incremental_collection_counters;
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175 }
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176 CollectorCounters* full_collection_counters() {
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177 return _full_collection_counters;
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178 }
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179 GenerationCounters* non_young_collection_counters() {
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180 return _non_young_collection_counters;
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181 }
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182 HSpaceCounters* old_space_counters() { return _old_space_counters; }
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183 HSpaceCounters* eden_counters() { return _eden_counters; }
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184 HSpaceCounters* from_counters() { return _from_counters; }
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185 HSpaceCounters* to_counters() { return _to_counters; }
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186
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187 // Monitoring support used by
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188 // MemoryService
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189 // jstat counters
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190 size_t overall_committed();
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191 size_t overall_used();
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192
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193 size_t eden_space_committed();
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194 size_t eden_space_used();
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195
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196 size_t survivor_space_committed();
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197 size_t survivor_space_used();
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198
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199 size_t old_space_committed();
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200 size_t old_space_used();
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201 };
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202
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203 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1MONITORINGSUPPORT_HPP
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