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 op‐
35 erating 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 de‐
52 fault 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 currently can
130 be one of 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 available_memory:
138 Informs about the amount memory that is available for in‐
139 creased usage if there is an increased memory need. This
140 value is not based on a calculation of the other provided
141 values and should give a better value of the amount of mem‐
142 ory that actually is available than calculating a value
143 based on the other values reported. This value is currently
144 only present on newer Linux kernels. If this value is not
145 available on Linux, you can use the sum of cached_memory,
146 buffered_memory, and free_memory as an approximation.
147 free_memory:
149 The amount of free memory available to the Erlang emulator
150 for allocation.
151 system_total_memory:
153 The amount of memory available to the whole operating sys‐
154 tem. This may well be equal to total_memory but not neces‐
155 sarily.
156 buffered_memory:
158 The amount of memory the system uses for temporary storing
159 raw disk blocks.
160 cached_memory:
162 The amount of memory the system uses for cached files read
163 from disk. On Linux, also memory marked as reclaimable in
164 the kernel slab allocator will be added to this value.
165 total_swap:
167 The amount of total amount of memory the system has avail‐
168 able for disk swap.
169 free_swap:
171 The amount of memory the system has available for disk
172 swap.
173 Note:
175 Note that new tagged tuples may be introduced in the result at
176 any time without prior notice
177 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 get_os_wordsize() -> Wordsize
188 Types:
190 Wordsize = 32 | 64 | unsupported_os
192 Returns the wordsize of the current running operating system.
194 get_check_interval() -> MS
196 Types:
198 MS = int()
200 Returns the time interval, in milliseconds, for the periodic
202 memory check.
203 set_check_interval(Minutes) -> ok
205 Types:
207 Minutes = int()>0
209 Changes the time interval, given in minutes, for the periodic
211 memory check.
212 The change will take effect after the next memory check and is
214 non-persistent. That is, in case of a process restart, this
215 value is forgotten and the default value will be used. See Con‐
216 figuration above.
217 get_procmem_high_watermark() -> int()
219 Returns the threshold, in percent, for process memory alloca‐
221 tion.
222 set_procmem_high_watermark(Float) -> ok
224 Changes the threshold, given as a float, for process memory al‐
226 location.
227 The change will take effect during the next periodic memory
229 check and is non-persistent. That is, in case of a process
230 restart, this value is forgotten and the default value will be
231 used. See Configuration above.
232 get_sysmem_high_watermark() -> int()
234 Returns the threshold, in percent, for system memory allocation.
236 set_sysmem_high_watermark(Float) -> ok
238 Changes the threshold, given as a float, for system memory allo‐
240 cation.
241 The change will take effect during the next periodic memory
243 check and is non-persistent. That is, in case of a process
244 restart, this value is forgotten and the default value will be
245 used. See Configuration above.
246 get_helper_timeout() -> Seconds
248 Types:
250 Seconds = int()
252 Returns the timeout value, in seconds, for memory checks.
254 set_helper_timeout(Seconds) -> ok
256 Types:
258 Seconds = int() (>= 1)
260 Changes the timeout value, given in seconds, for memory checks.
262 The change will take effect for the next memory check and is
264 non-persistent. That is, in the case of a process restart, this
265 value is forgotten and the default value will be used. See Con‐
266 figuration above.
267
269 alarm_handler(3), os_mon(3)
270Ericsson AB os_mon 2.8 memsup(3)