memsup - Erlang 23 Documentation

Module

memsup

Module Summary

A Memory Supervisor Process

Description

memsup is a process which supervises the memory usage for the system and for individual processes. It is part of the OS_Mon application, see os_mon(6). Available for Unix and Windows.

Periodically performs a memory check:

If more than a certain amount of available system memory is allocated, as reported by the underlying operating system, the alarm {system_memory_high_watermark, []} is set.
If any Erlang process Pid in the system has allocated more than a certain amount of total system memory, the alarm {process_memory_high_watermark, Pid} is set.

Alarms are reported to the SASL alarm handler, see alarm_handler(3). To set an alarm, alarm_handler:set_alarm(Alarm) is called where Alarm is either of the alarms specified above.

The alarms are cleared automatically when the alarm cause is no longer valid.

The function get_memory_data() can be used to retrieve the result of the latest periodic memory check.

There is also a interface to system dependent memory data, get_system_memory_data(). The result is highly dependent on the underlying operating system and the interface is targeted primarily for systems without virtual memory. However, the output on other systems is still valid, although sparse.

A call to get_system_memory_data/0 is more costly than a call to get_memory_data/0 as data is collected synchronously when this function is called.

The total system memory reported under UNIX is the number of physical pages of memory times the page size, and the available memory is the number of available physical pages times the page size. This is a reasonable measure as swapping should be avoided anyway, but the task of defining total memory and available memory is difficult because of virtual memory and swapping.

Configuration

The following configuration parameters can be used to change the default values for time intervals and thresholds:

memory_check_interval = int()>0

The time interval, in minutes, for the periodic memory check. The default is one minute.

system_memory_high_watermark = float()

The threshold, as percentage of system memory, for how much system memory can be allocated before the corresponding alarm is set. The default is 0.80 (80%).

process_memory_high_watermark = float()

The threshold, as percentage of system memory, for how much system memory can be allocated by one Erlang process before the corresponding alarm is set. The default is 0.05 (5%).

memsup_helper_timeout = int()>0

A timeout, in seconds, for how long the memsup process should wait for a result from a memory check. If the timeout expires, a warning message "OS_MON (memsup) timeout" is issued via error_logger and any pending, synchronous client calls will return a dummy value. Normally, this situation should not occur. There have been cases on Linux, however, where the pseudo file from which system data is read is temporarily unavailable when the system is heavily loaded.

The default is 30 seconds.

memsup_system_only = bool()

Specifies whether the memsup process should only check system memory usage (true) or not. The default is false, meaning that information regarding both system memory usage and Erlang process memory usage is collected.

It is recommended to set this parameter to false on systems with many concurrent processes, as each process memory check makes a traversal of the entire list of processes.

memsup_improved_system_memory_data = bool()

Determines the behaviour of the get_system_memory_data() function. When this configuration parameter is false, get_system_memory_data() behaves as it has done up until the point of the introduction of the configuration parameter. When set to true new tagged tuples are allowed in the result. Such new tuples may be introduced at any time without prior notice. The classification of cached_memory on Linux systems will also change so that more memory is classified as cached_memory.

Note

This configuration parameter defaults false and will do so up until OTP 23. As of OTP 24 this configuration parameter will be removed and get_system_memory_data() will begin behaving as it does now when the configuration parameter has been set to true.

See config(4) for information about how to change the value of configuration parameters.

Exports

get_memory_data() -> {Total,Allocated,Worst}

Types

Returns the result of the latest memory check, where Total is the total memory size and Allocated the allocated memory size, in bytes.

Worst is the pid and number of allocated bytes of the largest Erlang process on the node. If memsup should not collect process data, that is if the configuration parameter memsup_system_only was set to true, Worst is undefined.

The function is normally asynchronous in the sense that it does not invoke a memory check, but returns the latest available value. The one exception if is the function is called before a first memory check is finished, in which case it does not return a value until the memory check is finished.

Returns {0,0,{pid(),0}} or {0,0,undefined} if memsup is not available, or if all memory checks so far have timed out.

get_system_memory_data() -> MemDataList

Types

Invokes a memory check and returns the resulting, system dependent, data as a list of tagged tuples, where Tag can be one of the following:

total_memory: The total amount of memory available to the Erlang emulator, allocated and free. May or may not be equal to the amount of memory configured in the system.
free_memory: The amount of free memory available to the Erlang emulator for allocation.
system_total_memory: The amount of memory available to the whole operating system. This may well be equal to total_memory but not necessarily.
buffered_memory: The amount of memory the system uses for temporary storing raw disk blocks.
cached_memory: The amount of memory the system uses for cached files read from disk.
total_swap: The amount of total amount of memory the system has available for disk swap.
free_swap: The amount of memory the system has available for disk swap.

Note that the order of the tuples in the resulting list is undefined and may change at any time.

All memory sizes are presented as number of bytes.

Returns the empty list [] if memsup is not available, or if the memory check times out.

Note

On Linux the memory available to the emulator is cached_memory and buffered_memory in addition to free_memory.

The above describes how it works if the configuration parameter memsup_improved_system_memory_data has been set to false which currently also is the default behavior. If the configuration parameter is set to true the behavior is slightly changed:

New tagged tuples may be added in the resulting list at any time.
On Linux systems the following changes will be made:
- A new tuple with the tag available_memory will be added to the result when this value is provided by the kernel. The available_memory value informs about the amount memory that is available for use if there is an increased memory need. This value is not based on a calculation of the other provided values and should give a better value of the amount of memory that actually is available than calculating a value based on the other values reported.
- The classification of cached_memory is changed. Also memory marked as reclaimable in the kernel slab allocator will be added to the value presented as cached_memory.

Note

As of OTP 24 memsup_improved_system_memory_data configuration parameter will be removed and get_system_memory_data() will begin behaving as it does now when the configuration parameter has been set to true.

get_os_wordsize() -> Wordsize

Types

Returns the wordsize of the current running operating system.

get_check_interval() -> MS

Types

Returns the time interval, in milliseconds, for the periodic memory check.

set_check_interval(Minutes) -> ok

Types

Changes the time interval, given in minutes, for the periodic memory check.

The change will take effect after the next memory check and is non-persistent. That is, in case of a process restart, this value is forgotten and the default value will be used. See Configuration above.

get_procmem_high_watermark() -> int()

Returns the threshold, in percent, for process memory allocation.

set_procmem_high_watermark(Float) -> ok

Changes the threshold, given as a float, for process memory allocation.

The change will take effect during the next periodic memory check and is non-persistent. That is, in case of a process restart, this value is forgotten and the default value will be used. See Configuration above.

get_sysmem_high_watermark() -> int()

Returns the threshold, in percent, for system memory allocation.

set_sysmem_high_watermark(Float) -> ok

Changes the threshold, given as a float, for system memory allocation.

get_helper_timeout() -> Seconds

Types

Returns the timeout value, in seconds, for memory checks.

set_helper_timeout(Seconds) -> ok

Types

Changes the timeout value, given in seconds, for memory checks.

The change will take effect for the next memory check and is non-persistent. That is, in the case of a process restart, this value is forgotten and the default value will be used. See Configuration above.

Module

Module Summary

Description

Configuration

Exports

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