Sidebar
manual:appendix:items:vm.memory.size_params
Table of Contents
2 vm.memory.size parameters
Overview
This section provides more details and platform-specific information on the parameters of the vm.memory.size[<mode>] agent item.
Parameters
The following parameters are available for this item:
- active - memory currently in use or very recently used, and so it is in RAM
- anon - memory not associated with a file (cannot be re-read from it)
- available - available memory, calculated differently depending on the platform (see the table below)
- buffers - cache for things like file system metadata
- cached - cache for various things
- exec - executable code, typically from a (program) file
- file - cache for contents of recently accessed files
- free - memory that is readily available to any entity requesting memory
- inactive - memory that is marked as not used
- pavailable - 'available' memory as percentage of 'total' (calculated as
available/total*100) - pinned - same as 'wired'
- pused - 'used' memory as percentage of 'total' (calculated as
used/total*100) - shared - memory that may be simultaneously accessed by multiple processes
- slab - total amount of memory used by the kernel to cache data structures for its own use
- total - total physical memory available
- used - used memory, calculated differently depending on the platform (see the table below)
- wired - memory that is marked to always stay in RAM. It is never moved to disk.
Some of these parameters are platform-specific and might not be available on your platform. Please refer to this page for details.
Platform-specific calculation of available and used:
| Platform | “available” | “used” |
|---|---|---|
| AIX | free + cached | real memory in use |
| FreeBSD | inactive + cached + free | active + wired + cached |
| HP UX | free | total - free |
| Linux<3.14 | free + buffers + cached | total - free |
| Linux 3.14+ (also backported to 3.10 on RHEL 7) | /proc/meminfo, see "MemAvailable" in Linux kernel documentation for details. Note that free + buffers + cached is no longer equal to 'available' due to not all the page cache can be freed and low watermark being used in calculation. | total - free |
| NetBSD | inactive + execpages + file + free | total - free |
| OpenBSD | inactive + free + cached | active + wired |
| OSX | inactive + free | active + wired |
| Solaris | free | total - free |
| Win32 | free | total - free |
The sum of vm.memory.size[used] and vm.memory.size[available] does not necessarily equal total. For instance, on FreeBSD:
* Active, inactive, wired, cached memories are considered used, because they store some useful information.
* At the same time inactive, cached, free memories are considered available, because these kinds of memories can be given instantly to processes that request more memory.
So inactive memory is both used and available simultaneously. Because of this, the vm.memory.size[used] item is designed for informational purposes only, while vm.memory.size[available] is designed to be used in triggers.
* Active, inactive, wired, cached memories are considered used, because they store some useful information.
* At the same time inactive, cached, free memories are considered available, because these kinds of memories can be given instantly to processes that request more memory.
So inactive memory is both used and available simultaneously. Because of this, the vm.memory.size[used] item is designed for informational purposes only, while vm.memory.size[available] is designed to be used in triggers.
See the "See also" section at the bottom of this page to find more detailed information about memory calculation in different OS.
Platform-specific notes
- on Linux shared works only on kernel 2.4