1memsup(3) Erlang Module Definition memsup(3)
2
6 memsup - A Memory Supervisor Process
7
9 memsup is a process which supervises the memory usage for the system
10 and for individual processes. It is part of the OS_Mon application, see
11 os_mon(6). Available for Unix and Windows.
12 Periodically performs a memory check:
14 * If more than a certain amount of available system memory is allo‐
16 cated, as reported by the underlying operating system, the alarm
17 {system_memory_high_watermark, []} is set.
18 * If any Erlang process Pid in the system has allocated more than a
20 certain amount of total system memory, the alarm {process_mem‐
21 ory_high_watermark, Pid} is set.
22 Alarms are reported to the SASL alarm handler, see alarm_handler(3). To
24 set an alarm, alarm_handler:set_alarm(Alarm) is called where Alarm is
25 either of the alarms specified above.
26 The alarms are cleared automatically when the alarm cause is no longer
28 valid.
29 The function get_memory_data() can be used to retrieve the result of
31 the latest periodic memory check.
32 There is also a interface to system dependent memory data, get_sys‐
34 tem_memory_data(). The result is highly dependent on the underlying
35 operating system and the interface is targeted primarily for systems
36 without virtual memory. However, the output on other systems is still
37 valid, although sparse.
38 A call to get_system_memory_data/0 is more costly than a call to
40 get_memory_data/0 as data is collected synchronously when this function
41 is called.
42 The total system memory reported under UNIX is the number of physical
44 pages of memory times the page size, and the available memory is the
45 number of available physical pages times the page size. This is a rea‐
46 sonable measure as swapping should be avoided anyway, but the task of
47 defining total memory and available memory is difficult because of vir‐
48 tual memory and swapping.
49
51 The following configuration parameters can be used to change the
52 default values for time intervals and thresholds:
53 memory_check_interval = int()>0:
55 The time interval, in minutes, for the periodic memory check. The
56 default is one minute.
57 system_memory_high_watermark = float():
59 The threshold, as percentage of system memory, for how much system
60 memory can be allocated before the corresponding alarm is set. The
61 default is 0.80 (80%).
62 process_memory_high_watermark = float():
64 The threshold, as percentage of system memory, for how much system
65 memory can be allocated by one Erlang process before the corre‐
66 sponding alarm is set. The default is 0.05 (5%).
67 memsup_helper_timeout = int()>0:
69 A timeout, in seconds, for how long the memsup process should wait
70 for a result from a memory check. If the timeout expires, a warning
71 message "OS_MON (memsup) timeout" is issued via error_logger and
72 any pending, synchronous client calls will return a dummy value.
73 Normally, this situation should not occur. There have been cases on
74 Linux, however, where the pseudo file from which system data is
75 read is temporarily unavailable when the system is heavily loaded.
76 The default is 30 seconds.
78 memsup_system_only = bool():
80 Specifies whether the memsup process should only check system mem‐
81 ory usage (true) or not. The default is false, meaning that infor‐
82 mation regarding both system memory usage and Erlang process memory
83 usage is collected.
84 It is recommended to set this parameter to false on systems with
86 many concurrent processes, as each process memory check makes a
87 traversal of the entire list of processes.
88 memsup_improved_system_memory_data = bool():
90 Determines the behaviour of the get_system_memory_data() function.
91 When this configuration parameter is false, get_system_mem‐
92 ory_data() behaves as it has done up until the point of the intro‐
93 duction of the configuration parameter. When set to true new tagged
94 tuples are allowed in the result. Such new tuples may be introduced
95 at any time without prior notice. The classification of cached_mem‐
96 ory on Linux systems will also change so that more memory is clas‐
97 sified as cached_memory.
98 Note:
100 This configuration parameter defaults false and will do so up until
101 OTP 23. As of OTP 24 this configuration parameter will be removed and
102 get_system_memory_data() will begin behaving as it does now when the
103 configuration parameter has been set to true.
104 See config(4) for information about how to change the value of configu‐
107 ration parameters.
108
110 get_memory_data() -> {Total,Allocated,Worst}
111 Types:
113 Total = Allocated = int()
115 Worst = {Pid, PidAllocated} | undefined
116 Pid = pid()
117 PidAllocated = int()
118 Returns the result of the latest memory check, where Total is
120 the total memory size and Allocated the allocated memory size,
121 in bytes.
122 Worst is the pid and number of allocated bytes of the largest
124 Erlang process on the node. If memsup should not collect process
125 data, that is if the configuration parameter memsup_system_only
126 was set to true, Worst is undefined.
127 The function is normally asynchronous in the sense that it does
129 not invoke a memory check, but returns the latest available
130 value. The one exception if is the function is called before a
131 first memory check is finished, in which case it does not return
132 a value until the memory check is finished.
133 Returns {0,0,{pid(),0}} or {0,0,undefined} if memsup is not
135 available, or if all memory checks so far have timed out.
136 get_system_memory_data() -> MemDataList
138 Types:
140 MemDataList = [{Tag, Size}]
142 Tag = atom()
143 Size = int()
144 Invokes a memory check and returns the resulting, system depen‐
146 dent, data as a list of tagged tuples, where Tag can be one of
147 the following:
148 total_memory:
150 The total amount of memory available to the Erlang emulator,
151 allocated and free. May or may not be equal to the amount of
152 memory configured in the system.
153 free_memory:
155 The amount of free memory available to the Erlang emulator
156 for allocation.
157 system_total_memory:
159 The amount of memory available to the whole operating sys‐
160 tem. This may well be equal to total_memory but not neces‐
161 sarily.
162 buffered_memory:
164 The amount of memory the system uses for temporary storing
165 raw disk blocks.
166 cached_memory:
168 The amount of memory the system uses for cached files read
169 from disk.
170 total_swap:
172 The amount of total amount of memory the system has avail‐
173 able for disk swap.
174 free_swap:
176 The amount of memory the system has available for disk
177 swap.
178 Note that the order of the tuples in the resulting list is unde‐
180 fined and may change at any time.
181 All memory sizes are presented as number of bytes.
183 Returns the empty list [] if memsup is not available, or if the
185 memory check times out.
186 Note:
188 On Linux the memory available to the emulator is cached_memory
189 and buffered_memory in addition to free_memory.
190 The above describes how it works if the configuration parameter
193 memsup_improved_system_memory_data has been set to false which
194 currently also is the default behavior. If the configuration
195 parameter is set to true the behavior is slightly changed:
196 * New tagged tuples may be added in the resulting list at any
198 time.
199 * On Linux systems the following changes will be made:
201 * A new tuple with the tag available_memory will be added to
203 the result when this value is provided by the kernel. The
204 available_memory value informs about the amount memory
205 that is available for use if there is an increased memory
206 need. This value is not based on a calculation of the
207 other provided values and should give a better value of
208 the amount of memory that actually is available than cal‐
209 culating a value based on the other values reported.
210 * The classification of cached_memory is changed. Also mem‐
212 ory marked as reclaimable in the kernel slab allocator
213 will be added to the value presented as cached_memory.
214 Note:
216 As of OTP 24 memsup_improved_system_memory_data configuration
217 parameter will be removed and get_system_memory_data() will
218 begin behaving as it does now when the configuration parameter
219 has been set to true.
220 get_os_wordsize() -> Wordsize
223 Types:
225 Wordsize = 32 | 64 | unsupported_os
227 Returns the wordsize of the current running operating system.
229 get_check_interval() -> MS
231 Types:
233 MS = int()
235 Returns the time interval, in milliseconds, for the periodic
237 memory check.
238 set_check_interval(Minutes) -> ok
240 Types:
242 Minutes = int()>0
244 Changes the time interval, given in minutes, for the periodic
246 memory check.
247 The change will take effect after the next memory check and is
249 non-persistent. That is, in case of a process restart, this
250 value is forgotten and the default value will be used. See Con‐
251 figuration above.
252 get_procmem_high_watermark() -> int()
254 Returns the threshold, in percent, for process memory alloca‐
256 tion.
257 set_procmem_high_watermark(Float) -> ok
259 Changes the threshold, given as a float, for process memory
261 allocation.
262 The change will take effect during the next periodic memory
264 check and is non-persistent. That is, in case of a process
265 restart, this value is forgotten and the default value will be
266 used. See Configuration above.
267 get_sysmem_high_watermark() -> int()
269 Returns the threshold, in percent, for system memory allocation.
271 set_sysmem_high_watermark(Float) -> ok
273 Changes the threshold, given as a float, for system memory allo‐
275 cation.
276 The change will take effect during the next periodic memory
278 check and is non-persistent. That is, in case of a process
279 restart, this value is forgotten and the default value will be
280 used. See Configuration above.
281 get_helper_timeout() -> Seconds
283 Types:
285 Seconds = int()
287 Returns the timeout value, in seconds, for memory checks.
289 set_helper_timeout(Seconds) -> ok
291 Types:
293 Seconds = int() (>= 1)
295 Changes the timeout value, given in seconds, for memory checks.
297 The change will take effect for the next memory check and is
299 non-persistent. That is, in the case of a process restart, this
300 value is forgotten and the default value will be used. See Con‐
301 figuration above.
302
304 alarm_handler(3), os_mon(3)
305Ericsson AB os_mon 2.6.1 memsup(3)