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1 /* |
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2 * Copyright 2003-2007 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
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20 * CA 95054 USA or visit www.sun.com if you need additional information or |
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21 * have any questions. |
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22 * |
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23 */ |
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24 |
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25 // Low Memory Detection Support |
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26 // Two memory alarms in the JDK (we called them sensors). |
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27 // - Heap memory sensor |
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28 // - Non-heap memory sensor |
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29 // When the VM detects if the memory usage of a memory pool has reached |
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30 // or exceeded its threshold, it will trigger the sensor for the type |
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31 // of the memory pool (heap or nonheap or both). |
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32 // |
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33 // If threshold == -1, no low memory detection is supported and |
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34 // the threshold value is not allowed to be changed. |
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35 // If threshold == 0, no low memory detection is performed for |
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36 // that memory pool. The threshold can be set to any non-negative |
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37 // value. |
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38 // |
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39 // The default threshold of the Hotspot memory pools are: |
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40 // Eden space -1 |
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41 // Survivor space 1 -1 |
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42 // Survivor space 2 -1 |
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43 // Old generation 0 |
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44 // Perm generation 0 |
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45 // CodeCache 0 |
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46 // |
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47 // For heap memory, detection will be performed when GC finishes |
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48 // and also in the slow path allocation. |
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49 // For Code cache, detection will be performed in the allocation |
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50 // and deallocation. |
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51 // |
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52 // May need to deal with hysteresis effect. |
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53 // |
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54 |
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55 class LowMemoryDetectorThread; |
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56 class OopClosure; |
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57 class MemoryPool; |
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58 |
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59 class ThresholdSupport : public CHeapObj { |
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60 private: |
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61 bool _support_high_threshold; |
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62 bool _support_low_threshold; |
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63 size_t _high_threshold; |
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64 size_t _low_threshold; |
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65 public: |
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66 ThresholdSupport(bool support_high, bool support_low) { |
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67 _support_high_threshold = support_high; |
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68 _support_low_threshold = support_low; |
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69 _high_threshold = 0; |
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70 _low_threshold= 0; |
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71 } |
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72 |
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73 size_t high_threshold() const { return _high_threshold; } |
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74 size_t low_threshold() const { return _low_threshold; } |
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75 bool is_high_threshold_supported() { return _support_high_threshold; } |
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76 bool is_low_threshold_supported() { return _support_low_threshold; } |
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77 |
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78 bool is_high_threshold_crossed(MemoryUsage usage) { |
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79 if (_support_high_threshold && _high_threshold > 0) { |
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80 return (usage.used() >= _high_threshold); |
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81 } |
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82 return false; |
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83 } |
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84 bool is_low_threshold_crossed(MemoryUsage usage) { |
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85 if (_support_low_threshold && _low_threshold > 0) { |
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86 return (usage.used() < _low_threshold); |
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87 } |
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88 return false; |
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89 } |
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90 |
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91 size_t set_high_threshold(size_t new_threshold) { |
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92 assert(_support_high_threshold, "can only be set if supported"); |
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93 assert(new_threshold >= _low_threshold, "new_threshold must be >= _low_threshold"); |
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94 size_t prev = _high_threshold; |
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95 _high_threshold = new_threshold; |
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96 return prev; |
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97 } |
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98 |
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99 size_t set_low_threshold(size_t new_threshold) { |
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100 assert(_support_low_threshold, "can only be set if supported"); |
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101 assert(new_threshold <= _high_threshold, "new_threshold must be <= _high_threshold"); |
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102 size_t prev = _low_threshold; |
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103 _low_threshold = new_threshold; |
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104 return prev; |
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105 } |
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106 }; |
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107 |
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108 class SensorInfo : public CHeapObj { |
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109 private: |
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110 instanceOop _sensor_obj; |
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111 bool _sensor_on; |
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112 size_t _sensor_count; |
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113 |
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114 // before the actual sensor on flag and sensor count are set |
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115 // we maintain the number of pending triggers and clears. |
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116 // _pending_trigger_count means the number of pending triggers |
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117 // and the sensor count should be incremented by the same number. |
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118 |
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119 int _pending_trigger_count; |
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120 |
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121 // _pending_clear_count takes precedence if it's > 0 which |
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122 // indicates the resulting sensor will be off |
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123 // Sensor trigger requests will reset this clear count to |
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124 // indicate the resulting flag should be on. |
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125 |
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126 int _pending_clear_count; |
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127 |
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128 MemoryUsage _usage; |
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129 |
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130 void clear(int count, TRAPS); |
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131 void trigger(int count, TRAPS); |
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132 public: |
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133 SensorInfo(); |
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134 void set_sensor(instanceOop sensor) { |
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135 assert(_sensor_obj == NULL, "Should be set only once"); |
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136 _sensor_obj = sensor; |
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137 } |
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138 |
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139 bool has_pending_requests() { |
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140 return (_pending_trigger_count > 0 || _pending_clear_count > 0); |
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141 } |
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142 |
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143 int pending_trigger_count() { return _pending_trigger_count; } |
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144 int pending_clear_count() { return _pending_clear_count; } |
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145 |
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146 // When this method is used, the memory usage is monitored |
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147 // as a gauge attribute. High and low thresholds are designed |
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148 // to provide a hysteresis mechanism to avoid repeated triggering |
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149 // of notifications when the attribute value makes small oscillations |
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150 // around the high or low threshold value. |
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151 // |
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152 // The sensor will be triggered if: |
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153 // (1) the usage is crossing above the high threshold and |
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154 // the sensor is currently off and no pending |
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155 // trigger requests; or |
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156 // (2) the usage is crossing above the high threshold and |
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157 // the sensor will be off (i.e. sensor is currently on |
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158 // and has pending clear requests). |
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159 // |
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160 // Subsequent crossings of the high threshold value do not cause |
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161 // any triggers unless the usage becomes less than the low threshold. |
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162 // |
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163 // The sensor will be cleared if: |
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164 // (1) the usage is crossing below the low threshold and |
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165 // the sensor is currently on and no pending |
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166 // clear requests; or |
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167 // (2) the usage is crossing below the low threshold and |
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168 // the sensor will be on (i.e. sensor is currently off |
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169 // and has pending trigger requests). |
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170 // |
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171 // Subsequent crossings of the low threshold value do not cause |
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172 // any clears unless the usage becomes greater than or equal |
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173 // to the high threshold. |
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174 // |
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175 // If the current level is between high and low threhsold, no change. |
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176 // |
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177 void set_gauge_sensor_level(MemoryUsage usage, ThresholdSupport* high_low_threshold); |
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178 |
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179 // When this method is used, the memory usage is monitored as a |
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180 // simple counter attribute. The sensor will be triggered |
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181 // whenever the usage is crossing the threshold to keep track |
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182 // of the number of times the VM detects such a condition occurs. |
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183 // |
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184 // The sensor will be triggered if: |
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185 // - the usage is crossing above the high threshold regardless |
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186 // of the current sensor state. |
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187 // |
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188 // The sensor will be cleared if: |
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189 // (1) the usage is crossing below the low threshold and |
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190 // the sensor is currently on; or |
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191 // (2) the usage is crossing below the low threshold and |
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192 // the sensor will be on (i.e. sensor is currently off |
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193 // and has pending trigger requests). |
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194 // |
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195 void set_counter_sensor_level(MemoryUsage usage, ThresholdSupport* counter_threshold); |
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196 |
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197 void process_pending_requests(TRAPS); |
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198 void oops_do(OopClosure* f); |
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199 |
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200 #ifndef PRODUCT |
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201 // printing on default output stream; |
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202 void print(); |
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203 #endif // PRODUCT |
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204 }; |
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205 |
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206 class LowMemoryDetector : public AllStatic { |
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207 friend class LowMemoryDetectorDisabler; |
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208 private: |
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209 // true if any collected heap has low memory detection enabled |
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210 static volatile bool _enabled_for_collected_pools; |
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211 // > 0 if temporary disabed |
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212 static volatile jint _disabled_count; |
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213 |
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214 static LowMemoryDetectorThread* _detector_thread; |
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215 static void low_memory_detector_thread_entry(JavaThread* thread, TRAPS); |
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216 static void check_memory_usage(); |
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217 static bool has_pending_requests(); |
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218 static bool temporary_disabled() { return _disabled_count > 0; } |
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219 static void disable() { Atomic::inc(&_disabled_count); } |
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220 static void enable() { Atomic::dec(&_disabled_count); } |
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221 |
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222 public: |
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223 static void initialize(); |
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224 static void detect_low_memory(); |
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225 static void detect_low_memory(MemoryPool* pool); |
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226 static void detect_after_gc_memory(MemoryPool* pool); |
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227 |
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228 static bool is_enabled(MemoryPool* pool) { |
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229 // low memory detection is enabled for collected memory pools |
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230 // iff one of the collected memory pool has a sensor and the |
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231 // threshold set non-zero |
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232 if (pool->usage_sensor() == NULL) { |
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233 return false; |
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234 } else { |
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235 ThresholdSupport* threshold_support = pool->usage_threshold(); |
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236 return (threshold_support->is_high_threshold_supported() ? |
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237 (threshold_support->high_threshold() > 0) : false); |
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238 } |
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239 } |
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240 |
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241 // indicates if low memory detection is enabled for any collected |
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242 // memory pools |
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243 static inline bool is_enabled_for_collected_pools() { |
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244 return !temporary_disabled() && _enabled_for_collected_pools; |
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245 } |
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246 |
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247 // recompute enabled flag |
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248 static void recompute_enabled_for_collected_pools(); |
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249 |
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250 // low memory detection for collected memory pools. |
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251 static inline void detect_low_memory_for_collected_pools() { |
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252 // no-op if low memory detection not enabled |
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253 if (!is_enabled_for_collected_pools()) { |
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254 return; |
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255 } |
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256 int num_memory_pools = MemoryService::num_memory_pools(); |
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257 for (int i=0; i<num_memory_pools; i++) { |
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258 MemoryPool* pool = MemoryService::get_memory_pool(i); |
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259 |
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260 // if low memory detection is enabled then check if the |
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261 // current used exceeds the high threshold |
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262 if (pool->is_collected_pool() && is_enabled(pool)) { |
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263 size_t used = pool->used_in_bytes(); |
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264 size_t high = pool->usage_threshold()->high_threshold(); |
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265 if (used > high) { |
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266 detect_low_memory(pool); |
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267 } |
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268 } |
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269 } |
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270 } |
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271 |
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272 }; |
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273 |
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274 class LowMemoryDetectorDisabler: public StackObj { |
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275 public: |
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276 LowMemoryDetectorDisabler() |
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277 { |
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278 LowMemoryDetector::disable(); |
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279 } |
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280 ~LowMemoryDetectorDisabler() |
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281 { |
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282 assert(LowMemoryDetector::temporary_disabled(), "should be disabled!"); |
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283 LowMemoryDetector::enable(); |
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284 } |
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285 }; |