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, Windows and VxWorks.
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 (e.g. VxWorks). The output on other systems is
37 however still 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 See config(4) for information about how to change the value of configu‐
90 ration parameters.
91
93 get_memory_data() -> {Total,Allocated,Worst}
94 Types:
96 Total = Allocated = int()
98 Worst = {Pid, PidAllocated} | undefined
99 Pid = pid()
100 PidAllocated = int()
101 Returns the result of the latest memory check, where Total is
103 the total memory size and Allocated the allocated memory size,
104 in bytes.
105 Worst is the pid and number of allocated bytes of the largest
107 Erlang process on the node. If memsup should not collect process
108 data, that is if the configuration parameter memsup_system_only
109 was set to true, Worst is undefined.
110 The function is normally asynchronous in the sense that it does
112 not invoke a memory check, but returns the latest available
113 value. The one exception if is the function is called before a
114 first memory check is finished, in which case it does not return
115 a value until the memory check is finished.
116 Returns {0,0,{pid(),0}} or {0,0,undefined} if memsup is not
118 available, or if all memory checks so far have timed out.
119 get_system_memory_data() -> MemDataList
121 Types:
123 MemDataList = [{Tag, Size}]
125 Tag = atom()
126 Size = int()
127 Invokes a memory check and returns the resulting, system depen‐
129 dent, data as a list of tagged tuples, where Tag can be one of
130 the following:
131 total_memory:
133 The total amount of memory available to the Erlang emulator,
134 allocated and free. May or may not be equal to the amount of
135 memory configured in the system.
136 free_memory:
138 The amount of free memory available to the Erlang emulator
139 for allocation.
140 system_total_memory:
142 The amount of memory available to the whole operating sys‐
143 tem. This may well be equal to total_memory but not neces‐
144 sarily.
145 largest_free:
147 The size of the largest contiguous free memory block avail‐
148 able to the Erlang emulator.
149 number_of_free:
151 The number of free blocks available to the Erlang runtime
152 system. This gives a fair indication of how fragmented the
153 memory is.
154 buffered_memory:
156 The amount of memory the system uses for temporary storing
157 raw disk blocks.
158 cached_memory:
160 The amount of memory the system uses for cached files read
161 from disk.
162 total_swap:
164 The amount of total amount of memory the system has avail‐
165 able for disk swap.
166 free_swap:
168 The amount of memory the system has available for disk
169 swap.
170 All memory sizes are presented as number of bytes.
172 The largest_free and number_of_free tags are currently only
174 returned on a VxWorks system.
175 Returns the empty list [] if memsup is not available, or if the
177 memory check times out.
178 Note:
180 On linux the memory available to the emulator is cached_memory
181 and buffered_memory in addition to free_memory.
182 get_os_wordsize() -> Wordsize
185 Types:
187 Wordsize = 32 | 64 | unsupported_os
189 Returns the wordsize of the current running operating system.
191 get_check_interval() -> MS
193 Types:
195 MS = int()
197 Returns the time interval, in milliseconds, for the periodic
199 memory check.
200 set_check_interval(Minutes) -> ok
202 Types:
204 Minutes = int()>0
206 Changes the time interval, given in minutes, for the periodic
208 memory check.
209 The change will take effect after the next memory check and is
211 non-persistent. That is, in case of a process restart, this
212 value is forgotten and the default value will be used. See Con‐
213 figuration above.
214 get_procmem_high_watermark() -> int()
216 Returns the threshold, in percent, for process memory alloca‐
218 tion.
219 set_procmem_high_watermark(Float) -> ok
221 Changes the threshold, given as a float, for process memory
223 allocation.
224 The change will take effect during the next periodic memory
226 check and is non-persistent. That is, in case of a process
227 restart, this value is forgotten and the default value will be
228 used. See Configuration above.
229 get_sysmem_high_watermark() -> int()
231 Returns the threshold, in percent, for system memory allocation.
233 set_sysmem_high_watermark(Float) -> ok
235 Changes the threshold, given as a float, for system memory allo‐
237 cation.
238 The change will take effect during the next periodic memory
240 check and is non-persistent. That is, in case of a process
241 restart, this value is forgotten and the default value will be
242 used. See Configuration above.
243 get_helper_timeout() -> Seconds
245 Types:
247 Seconds = int()
249 Returns the timeout value, in seconds, for memory checks.
251 set_helper_timeout(Seconds) -> ok
253 Types:
255 Seconds = int() (>= 1)
257 Changes the timeout value, given in seconds, for memory checks.
259 The change will take effect for the next memory check and is
261 non-persistent. That is, in the case of a process restart, this
262 value is forgotten and the default value will be used. See Con‐
263 figuration above.
264
266 alarm_handler(3), os_mon(3)
267Ericsson AB os_mon 2.4.4 memsup(3)