1 /*
2 * Copyright (c) 2003, 2007, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 // Low Memory Detection Support
26 // Two memory alarms in the JDK (we called them sensors).
27 // - Heap memory sensor
28 // - Non-heap memory sensor
29 // When the VM detects if the memory usage of a memory pool has reached
30 // or exceeded its threshold, it will trigger the sensor for the type
31 // of the memory pool (heap or nonheap or both).
32 //
33 // If threshold == -1, no low memory detection is supported and
34 // the threshold value is not allowed to be changed.
35 // If threshold == 0, no low memory detection is performed for
36 // that memory pool. The threshold can be set to any non-negative
37 // value.
38 //
39 // The default threshold of the Hotspot memory pools are:
40 // Eden space -1
41 // Survivor space 1 -1
42 // Survivor space 2 -1
43 // Old generation 0
44 // Perm generation 0
45 // CodeCache 0
46 //
47 // For heap memory, detection will be performed when GC finishes
48 // and also in the slow path allocation.
49 // For Code cache, detection will be performed in the allocation
50 // and deallocation.
51 //
52 // May need to deal with hysteresis effect.
53 //
54
55 class LowMemoryDetectorThread;
56 class OopClosure;
57 class MemoryPool;
58
59 class ThresholdSupport : public CHeapObj {
60 private:
61 bool _support_high_threshold;
62 bool _support_low_threshold;
63 size_t _high_threshold;
64 size_t _low_threshold;
65 public:
66 ThresholdSupport(bool support_high, bool support_low) {
67 _support_high_threshold = support_high;
68 _support_low_threshold = support_low;
69 _high_threshold = 0;
70 _low_threshold= 0;
71 }
72
73 size_t high_threshold() const { return _high_threshold; }
74 size_t low_threshold() const { return _low_threshold; }
75 bool is_high_threshold_supported() { return _support_high_threshold; }
76 bool is_low_threshold_supported() { return _support_low_threshold; }
77
78 bool is_high_threshold_crossed(MemoryUsage usage) {
79 if (_support_high_threshold && _high_threshold > 0) {
80 return (usage.used() >= _high_threshold);
81 }
82 return false;
83 }
84 bool is_low_threshold_crossed(MemoryUsage usage) {
85 if (_support_low_threshold && _low_threshold > 0) {
86 return (usage.used() < _low_threshold);
87 }
88 return false;
89 }
90
91 size_t set_high_threshold(size_t new_threshold) {
92 assert(_support_high_threshold, "can only be set if supported");
93 assert(new_threshold >= _low_threshold, "new_threshold must be >= _low_threshold");
94 size_t prev = _high_threshold;
95 _high_threshold = new_threshold;
96 return prev;
97 }
98
99 size_t set_low_threshold(size_t new_threshold) {
100 assert(_support_low_threshold, "can only be set if supported");
101 assert(new_threshold <= _high_threshold, "new_threshold must be <= _high_threshold");
102 size_t prev = _low_threshold;
103 _low_threshold = new_threshold;
104 return prev;
105 }
106 };
107
108 class SensorInfo : public CHeapObj {
109 private:
110 instanceOop _sensor_obj;
111 bool _sensor_on;
112 size_t _sensor_count;
113
114 // before the actual sensor on flag and sensor count are set
115 // we maintain the number of pending triggers and clears.
116 // _pending_trigger_count means the number of pending triggers
117 // and the sensor count should be incremented by the same number.
118
119 int _pending_trigger_count;
120
121 // _pending_clear_count takes precedence if it's > 0 which
122 // indicates the resulting sensor will be off
123 // Sensor trigger requests will reset this clear count to
124 // indicate the resulting flag should be on.
125
126 int _pending_clear_count;
127
128 MemoryUsage _usage;
129
130 void clear(int count, TRAPS);
131 void trigger(int count, TRAPS);
132 public:
133 SensorInfo();
134 void set_sensor(instanceOop sensor) {
135 assert(_sensor_obj == NULL, "Should be set only once");
136 _sensor_obj = sensor;
137 }
138
139 bool has_pending_requests() {
140 return (_pending_trigger_count > 0 || _pending_clear_count > 0);
141 }
142
143 int pending_trigger_count() { return _pending_trigger_count; }
144 int pending_clear_count() { return _pending_clear_count; }
145
146 // When this method is used, the memory usage is monitored
147 // as a gauge attribute. High and low thresholds are designed
148 // to provide a hysteresis mechanism to avoid repeated triggering
149 // of notifications when the attribute value makes small oscillations
150 // around the high or low threshold value.
151 //
152 // The sensor will be triggered if:
153 // (1) the usage is crossing above the high threshold and
154 // the sensor is currently off and no pending
155 // trigger requests; or
156 // (2) the usage is crossing above the high threshold and
157 // the sensor will be off (i.e. sensor is currently on
158 // and has pending clear requests).
159 //
160 // Subsequent crossings of the high threshold value do not cause
161 // any triggers unless the usage becomes less than the low threshold.
162 //
163 // The sensor will be cleared if:
164 // (1) the usage is crossing below the low threshold and
165 // the sensor is currently on and no pending
166 // clear requests; or
167 // (2) the usage is crossing below the low threshold and
168 // the sensor will be on (i.e. sensor is currently off
169 // and has pending trigger requests).
170 //
171 // Subsequent crossings of the low threshold value do not cause
172 // any clears unless the usage becomes greater than or equal
173 // to the high threshold.
174 //
175 // If the current level is between high and low threhsold, no change.
176 //
177 void set_gauge_sensor_level(MemoryUsage usage, ThresholdSupport* high_low_threshold);
178
179 // When this method is used, the memory usage is monitored as a
180 // simple counter attribute. The sensor will be triggered
181 // whenever the usage is crossing the threshold to keep track
182 // of the number of times the VM detects such a condition occurs.
183 //
184 // The sensor will be triggered if:
185 // - the usage is crossing above the high threshold regardless
186 // of the current sensor state.
187 //
188 // The sensor will be cleared if:
189 // (1) the usage is crossing below the low threshold and
190 // the sensor is currently on; or
191 // (2) the usage is crossing below the low threshold and
192 // the sensor will be on (i.e. sensor is currently off
193 // and has pending trigger requests).
194 //
195 void set_counter_sensor_level(MemoryUsage usage, ThresholdSupport* counter_threshold);
196
197 void process_pending_requests(TRAPS);
198 void oops_do(OopClosure* f);
199
200 #ifndef PRODUCT
201 // printing on default output stream;
202 void print();
203 #endif // PRODUCT
204 };
205
206 class LowMemoryDetector : public AllStatic {
207 friend class LowMemoryDetectorDisabler;
208 private:
209 // true if any collected heap has low memory detection enabled
210 static volatile bool _enabled_for_collected_pools;
211 // > 0 if temporary disabed
212 static volatile jint _disabled_count;
213
214 static LowMemoryDetectorThread* _detector_thread;
215 static void low_memory_detector_thread_entry(JavaThread* thread, TRAPS);
216 static void check_memory_usage();
217 static bool has_pending_requests();
218 static bool temporary_disabled() { return _disabled_count > 0; }
219 static void disable() { Atomic::inc(&_disabled_count); }
220 static void enable() { Atomic::dec(&_disabled_count); }
221
222 public:
223 static void initialize();
224 static void detect_low_memory();
225 static void detect_low_memory(MemoryPool* pool);
226 static void detect_after_gc_memory(MemoryPool* pool);
227
228 static bool is_enabled(MemoryPool* pool) {
229 // low memory detection is enabled for collected memory pools
230 // iff one of the collected memory pool has a sensor and the
231 // threshold set non-zero
232 if (pool->usage_sensor() == NULL) {
233 return false;
234 } else {
235 ThresholdSupport* threshold_support = pool->usage_threshold();
236 return (threshold_support->is_high_threshold_supported() ?
237 (threshold_support->high_threshold() > 0) : false);
238 }
239 }
240
241 // indicates if low memory detection is enabled for any collected
242 // memory pools
243 static inline bool is_enabled_for_collected_pools() {
244 return !temporary_disabled() && _enabled_for_collected_pools;
245 }
246
247 // recompute enabled flag
248 static void recompute_enabled_for_collected_pools();
249
250 // low memory detection for collected memory pools.
251 static inline void detect_low_memory_for_collected_pools() {
252 // no-op if low memory detection not enabled
253 if (!is_enabled_for_collected_pools()) {
254 return;
255 }
256 int num_memory_pools = MemoryService::num_memory_pools();
257 for (int i=0; i<num_memory_pools; i++) {
258 MemoryPool* pool = MemoryService::get_memory_pool(i);
259
260 // if low memory detection is enabled then check if the
261 // current used exceeds the high threshold
262 if (pool->is_collected_pool() && is_enabled(pool)) {
263 size_t used = pool->used_in_bytes();
264 size_t high = pool->usage_threshold()->high_threshold();
265 if (used > high) {
266 detect_low_memory(pool);
267 }
268 }
269 }
270 }
271
272 };
273
274 class LowMemoryDetectorDisabler: public StackObj {
275 public:
276 LowMemoryDetectorDisabler()
277 {
278 LowMemoryDetector::disable();
279 }
280 ~LowMemoryDetectorDisabler()
281 {
282 assert(LowMemoryDetector::temporary_disabled(), "should be disabled!");
283 LowMemoryDetector::enable();
284 }
285 };