1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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7 * published by the Free Software Foundation.
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12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
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24
25 #ifndef SHARE_SERVICES_LOWMEMORYDETECTOR_HPP
26 #define SHARE_SERVICES_LOWMEMORYDETECTOR_HPP
27
28 #include "memory/allocation.hpp"
29 #include "services/memoryPool.hpp"
30 #include "services/memoryService.hpp"
31 #include "services/memoryUsage.hpp"
32
33 // Low Memory Detection Support
34 // Two memory alarms in the JDK (we called them sensors).
35 // - Heap memory sensor
36 // - Non-heap memory sensor
37 // When the VM detects if the memory usage of a memory pool has reached
38 // or exceeded its threshold, it will trigger the sensor for the type
39 // of the memory pool (heap or nonheap or both).
40 //
41 // If threshold == -1, no low memory detection is supported and
42 // the threshold value is not allowed to be changed.
43 // If threshold == 0, no low memory detection is performed for
44 // that memory pool. The threshold can be set to any non-negative
45 // value.
46 //
47 // The default threshold of the Hotspot memory pools are:
48 // Eden space -1
49 // Survivor space 1 -1
50 // Survivor space 2 -1
51 // Old generation 0
52 // Perm generation 0
53 // CodeCache 0
54 //
55 // For heap memory, detection will be performed when GC finishes
56 // and also in the slow path allocation.
57 // For Code cache, detection will be performed in the allocation
58 // and deallocation.
59 //
60 // May need to deal with hysteresis effect.
61 //
62 // Memory detection code runs in the Notification thread or
63 // ServiceThread depending on UseNotificationThread flag.
64
65 class OopClosure;
66 class MemoryPool;
67
68 class ThresholdSupport : public CHeapObj<mtInternal> {
69 private:
70 bool _support_high_threshold;
71 bool _support_low_threshold;
72 size_t _high_threshold;
73 size_t _low_threshold;
74 public:
75 ThresholdSupport(bool support_high, bool support_low) {
76 _support_high_threshold = support_high;
77 _support_low_threshold = support_low;
78 _high_threshold = 0;
79 _low_threshold= 0;
80 }
81
82 size_t high_threshold() const { return _high_threshold; }
83 size_t low_threshold() const { return _low_threshold; }
84 bool is_high_threshold_supported() { return _support_high_threshold; }
85 bool is_low_threshold_supported() { return _support_low_threshold; }
86
87 bool is_high_threshold_crossed(MemoryUsage usage) {
88 if (_support_high_threshold && _high_threshold > 0) {
89 return (usage.used() >= _high_threshold);
90 }
91 return false;
92 }
93 bool is_low_threshold_crossed(MemoryUsage usage) {
94 if (_support_low_threshold && _low_threshold > 0) {
95 return (usage.used() < _low_threshold);
96 }
97 return false;
98 }
99
100 size_t set_high_threshold(size_t new_threshold) {
101 assert(_support_high_threshold, "can only be set if supported");
102 assert(new_threshold >= _low_threshold, "new_threshold must be >= _low_threshold");
103 size_t prev = _high_threshold;
104 _high_threshold = new_threshold;
105 return prev;
106 }
107
108 size_t set_low_threshold(size_t new_threshold) {
109 assert(_support_low_threshold, "can only be set if supported");
110 assert(new_threshold <= _high_threshold, "new_threshold must be <= _high_threshold");
111 size_t prev = _low_threshold;
112 _low_threshold = new_threshold;
113 return prev;
114 }
115 };
116
117 class SensorInfo : public CHeapObj<mtInternal> {
118 private:
119 instanceOop _sensor_obj;
120 bool _sensor_on;
121 size_t _sensor_count;
122
123 // before the actual sensor on flag and sensor count are set
124 // we maintain the number of pending triggers and clears.
125 // _pending_trigger_count means the number of pending triggers
126 // and the sensor count should be incremented by the same number.
127
128 int _pending_trigger_count;
129
130 // _pending_clear_count takes precedence if it's > 0 which
131 // indicates the resulting sensor will be off
132 // Sensor trigger requests will reset this clear count to
133 // indicate the resulting flag should be on.
134
135 int _pending_clear_count;
136
137 MemoryUsage _usage;
138
139 void clear(int count, TRAPS);
140 void trigger(int count, TRAPS);
141 public:
142 SensorInfo();
143 void set_sensor(instanceOop sensor) {
144 assert(_sensor_obj == NULL, "Should be set only once");
145 _sensor_obj = sensor;
146 }
147
148 bool has_pending_requests() {
149 return (_pending_trigger_count > 0 || _pending_clear_count > 0);
150 }
151
152 int pending_trigger_count() { return _pending_trigger_count; }
153 int pending_clear_count() { return _pending_clear_count; }
154
155 // When this method is used, the memory usage is monitored
156 // as a gauge attribute. High and low thresholds are designed
157 // to provide a hysteresis mechanism to avoid repeated triggering
158 // of notifications when the attribute value makes small oscillations
159 // around the high or low threshold value.
160 //
161 // The sensor will be triggered if:
162 // (1) the usage is crossing above the high threshold and
163 // the sensor is currently off and no pending
164 // trigger requests; or
165 // (2) the usage is crossing above the high threshold and
166 // the sensor will be off (i.e. sensor is currently on
167 // and has pending clear requests).
168 //
169 // Subsequent crossings of the high threshold value do not cause
170 // any triggers unless the usage becomes less than the low threshold.
171 //
172 // The sensor will be cleared if:
173 // (1) the usage is crossing below the low threshold and
174 // the sensor is currently on and no pending
175 // clear requests; or
176 // (2) the usage is crossing below the low threshold and
177 // the sensor will be on (i.e. sensor is currently off
178 // and has pending trigger requests).
179 //
180 // Subsequent crossings of the low threshold value do not cause
181 // any clears unless the usage becomes greater than or equal
182 // to the high threshold.
183 //
184 // If the current level is between high and low threshold, no change.
185 //
186 void set_gauge_sensor_level(MemoryUsage usage, ThresholdSupport* high_low_threshold);
187
188 // When this method is used, the memory usage is monitored as a
189 // simple counter attribute. The sensor will be triggered
190 // whenever the usage is crossing the threshold to keep track
191 // of the number of times the VM detects such a condition occurs.
192 //
193 // The sensor will be triggered if:
194 // - the usage is crossing above the high threshold regardless
195 // of the current sensor state.
196 //
197 // The sensor will be cleared if:
198 // (1) the usage is crossing below the low threshold and
199 // the sensor is currently on; or
200 // (2) the usage is crossing below the low threshold and
201 // the sensor will be on (i.e. sensor is currently off
202 // and has pending trigger requests).
203 //
204 void set_counter_sensor_level(MemoryUsage usage, ThresholdSupport* counter_threshold);
205
206 void process_pending_requests(TRAPS);
207 void oops_do(OopClosure* f);
208
209 #ifndef PRODUCT
210 // printing on default output stream;
211 void print();
212 #endif // PRODUCT
213 };
214
215 class LowMemoryDetector : public AllStatic {
216 friend class LowMemoryDetectorDisabler;
217 friend class ServiceThread;
218 friend class NotificationThread;
219 private:
220 // true if any collected heap has low memory detection enabled
221 static volatile bool _enabled_for_collected_pools;
222 // > 0 if temporary disabed
223 static volatile jint _disabled_count;
224
225 static void check_memory_usage();
226 static bool has_pending_requests();
227 static bool temporary_disabled() { return _disabled_count > 0; }
228 static void disable() { Atomic::inc(&_disabled_count); }
229 static void enable() { Atomic::dec(&_disabled_count); }
230 static void process_sensor_changes(TRAPS);
231
232 public:
233 static void detect_low_memory();
234 static void detect_low_memory(MemoryPool* pool);
235 static void detect_after_gc_memory(MemoryPool* pool);
236
237 static bool is_enabled(MemoryPool* pool) {
238 // low memory detection is enabled for collected memory pools
239 // iff one of the collected memory pool has a sensor and the
240 // threshold set non-zero
241 if (pool->usage_sensor() == NULL) {
242 return false;
243 } else {
244 ThresholdSupport* threshold_support = pool->usage_threshold();
245 return (threshold_support->is_high_threshold_supported() ?
246 (threshold_support->high_threshold() > 0) : false);
247 }
248 }
249
250 // indicates if low memory detection is enabled for any collected
251 // memory pools
252 static inline bool is_enabled_for_collected_pools() {
253 return !temporary_disabled() && _enabled_for_collected_pools;
254 }
255
256 // recompute enabled flag
257 static void recompute_enabled_for_collected_pools();
258
259 // low memory detection for collected memory pools.
260 static inline void detect_low_memory_for_collected_pools() {
261 // no-op if low memory detection not enabled
262 if (!is_enabled_for_collected_pools()) {
263 return;
264 }
265 int num_memory_pools = MemoryService::num_memory_pools();
266 for (int i=0; i<num_memory_pools; i++) {
267 MemoryPool* pool = MemoryService::get_memory_pool(i);
268
269 // if low memory detection is enabled then check if the
270 // current used exceeds the high threshold
271 if (pool->is_collected_pool() && is_enabled(pool)) {
272 size_t used = pool->used_in_bytes();
273 size_t high = pool->usage_threshold()->high_threshold();
274 if (used > high) {
275 detect_low_memory(pool);
276 }
277 }
278 }
279 }
280 };
281
282 class LowMemoryDetectorDisabler: public StackObj {
283 public:
284 LowMemoryDetectorDisabler()
285 {
286 LowMemoryDetector::disable();
287 }
288 ~LowMemoryDetectorDisabler()
289 {
290 assert(LowMemoryDetector::temporary_disabled(), "should be disabled!");
291 LowMemoryDetector::enable();
292 }
293 };
294
295 #endif // SHARE_SERVICES_LOWMEMORYDETECTOR_HPP