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The memory subsystem generates automatic reports on memory resources used by the tasks in a control group, and sets limits on memory use by those tasks:
- memory.stat
-
reports a wide range of memory statistics, as described in the following table:
Table 3.1. Values reported by memory.stat
| Statistic |
Description |
cache |
page cache, including tmpfs (shmem), in bytes |
rss |
anonymous and swap cache, not including tmpfs (shmem), in bytes |
mapped_file |
size of memory-mapped mapped files, including tmpfs (shmem), in bytes |
pgpgin |
number of pages paged into memory |
pgpgout |
number of pages paged out of memory |
swap |
swap usage, in bytes |
active_anon |
anonymous and swap cache on active least-recently-used (LRU) list, including tmpfs (shmem), in bytes |
inactive_anon |
anonymous and swap cache on inactive LRU list, including tmpfs (shmem), in bytes |
active_file |
file-backed memory on active LRU list, in bytes |
inactive_file |
file-backed memory on inactive LRU list, in bytes |
unevictable |
memory that cannot be reclaimed, in bytes |
hierarchical_memory_limit |
memory limit for the hierarchy that contains the memory cgroup, in bytes |
hierarchical_memsw_limit |
memory plus swap limit for the hierarchy that contains the memory cgroup, in bytes |
Additionally, each of these files other than hierarchical_memory_limit and hierarchical_memsw_limit has a counterpart prefixed total_ that reports not only on the control group, but on all its children as well. For example, swap reports the swap usage by a control group and total_swap reports the total swap usage by the control group and all its child groups.
When you interpret the values reported by memory.stat, note how the various statistics inter-relate:
-
active_anon + inactive_anon = anonymous memory + file cache for tmpfs + swap cache
Therefore, active_anon + inactive_anon ≠ rss, because rss does not include tmpfs.
-
active_file + inactive_file = cache - size of tmpfs
- memory.usage_in_bytes
-
reports the total current memory usage by processes in the control group (in bytes).
- memory.memsw.usage_in_bytes
-
reports the sum of current memory usage plus swap space used by processes in the control group (in bytes).
- memory.max_usage_in_bytes
-
reports the maximum memory used by processes in the control group (in bytes).
- memory.memsw.max_usage_in_bytes
-
reports the maximum amount of memory and swap space used by processes in the control group (in bytes).
- memory.limit_in_bytes
-
sets the maximum amount of user memory (including file cache). If no units are specified, the value is interpreted as bytes. However, it is possible to use suffixes to represent larger units — k or K for kilobytes, m or M for Megabytes, and g or G for Gigabytes.
You cannot use memory.limit_in_bytes to limit the root control group; you can only apply values to groups lower in the hierarchy.
Write -1 to memory.limit_in_bytes to remove any existing limits.
- memory.memsw.limit_in_bytes
-
sets the maximum amount for the sum of memory and swap usage. If no units are specified, the value is interpreted as bytes. However, it is possible to use suffixes to represent larger units — k or K for kilobytes, m or M for Megabytes, and g or G for Gigabytes.
You cannot use memory.memsw.limit_in_bytes to limit the root control group; you can only apply values to groups lower in the hierarchy.
Write -1 to memory.memsw.limit_in_bytes to remove any existing limits.
- memory.failcnt
-
reports the number of times that the memory limit has reached the value set in memory.limit_in_bytes.
- memory.memsw.failcnt
-
reports the number of times that the memory plus swap space limit has reached the value set in memory.memsw.limit_in_bytes.
- memory.force_empty
-
when set to 0, empties memory of all pages used by tasks in this control group. This interface can only be used when the control group has no tasks. If memory cannot be freed, it is moved to a parent control group if possible. Use memory.force_empty before removing a control group to avoid moving out-of-use page caches to its parent control group.
- memory.swappiness
-
sets the tendency of the kernel to swap out process memory used by tasks in this control group instead of reclaiming pages from the page cache. This is the same tendency, calculated the same way, as set in /proc/sys/vm/swappiness for the system as a whole. The default value is 60. Values lower than 60 decrease the kernel's tendency to swap out process memory, values greater than 60 increase the kernel's tendency to swap out process memory, and values greater than 100 permit the kernel to swap out pages that are part of the address space of the processes in this control group.
Note that a value of 0 does not prevent process memory being swapped out; swap out might still happen when there is a shortage of system memory because the global virtual memory management logic does not read the cgroup value. To lock pages completely, use mlock() instead of cgroups.
You cannot change the swappiness of the following groups:
-
the root control group, which uses the swappiness set in /proc/sys/vm/swappiness.
-
a control group that has child groups below it.
- memory.use_hierarchy
-
contains a flag (0 or 1) that specifies whether memory usage should be accounted for throughout a hierarchy of control groups. If enabled (1), the memory controller reclaims memory from the children of and process that exceeds its memory limit. By default (0), the controller does not reclaim memory from a task's children.
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