.. _cgroup-v2:
================
Control Group v2
================
:Date: October, 2015
:Author: Tejun Heo <tj@kernel.org>
This is the authoritative documentation on the design, interface and
conventions of cgroup v2. It describes all userland-visible aspects
of cgroup including core and specific controller behaviors. All
future changes must be reflected in this document. Documentation for
v1 is available under :ref:`Documentation/admin-guide/cgroup-v1/index.rst <cgroup-v1>`.
.. CONTENTS
1. Introduction
1-1. Terminology
1-2. What is cgroup?
2. Basic Operations
2-1. Mounting
2-2. Organizing Processes and Threads
2-2-1. Processes
2-2-2. Threads
2-3. [Un]populated Notification
2-4. Controlling Controllers
2-4-1. Enabling and Disabling
2-4-2. Top-down Constraint
2-4-3. No Internal Process Constraint
2-5. Delegation
2-5-1. Model of Delegation
2-5-2. Delegation Containment
2-6. Guidelines
2-6-1. Organize Once and Control
2-6-2. Avoid Name Collisions
3. Resource Distribution Models
3-1. Weights
3-2. Limits
3-3. Protections
3-4. Allocations
4. Interface Files
4-1. Format
4-2. Conventions
4-3. Core Interface Files
5. Controllers
5-1. CPU
5-1-1. CPU Interface Files
5-2. Memory
5-2-1. Memory Interface Files
5-2-2. Usage Guidelines
5-2-3. Memory Ownership
5-3. IO
5-3-1. IO Interface Files
5-3-2. Writeback
5-3-3. IO Latency
5-3-3-1. How IO Latency Throttling Works
5-3-3-2. IO Latency Interface Files
5-3-4. IO Priority
5-4. PID
5-4-1. PID Interface Files
5-5. Cpuset
5.5-1. Cpuset Interface Files
5-6. Device
5-7. RDMA
5-7-1. RDMA Interface Files
5-8. DMEM
5-9. HugeTLB
5.9-1. HugeTLB Interface Files
5-10. Misc
5.10-1 Miscellaneous cgroup Interface Files
5.10-2 Migration and Ownership
5-11. Others
5-11-1. perf_event
5-N. Non-normative information
5-N-1. CPU controller root cgroup process behaviour
5-N-2. IO controller root cgroup process behaviour
6. Namespace
6-1. Basics
6-2. The Root and Views
6-3. Migration and setns(2)
6-4. Interaction with Other Namespaces
P. Information on Kernel Programming
P-1. Filesystem Support for Writeback
D. Deprecated v1 Core Features
R. Issues with v1 and Rationales for v2
R-1. Multiple Hierarchies
R-2. Thread Granularity
R-3. Competition Between Inner Nodes and Threads
R-4. Other Interface Issues
R-5. Controller Issues and Remedies
R-5-1. Memory
Introduction
============
Terminology
-----------
"cgroup" stands for "control group" and is never capitalized. The
singular form is used to designate the whole feature and also as a
qualifier as in "cgroup controllers". When explicitly referring to
multiple individual control groups, the plural form "cgroups" is used.
What is cgroup?
---------------
cgroup is a mechanism to organize processes hierarchically and
distribute system resources along the hierarchy in a controlled and
configurable manner.
cgroup is largely composed of two parts - the core and controllers.
cgroup core is primarily responsible for hierarchically organizing
processes. A cgroup controller is usually responsible for
distributing a specific type of system resource along the hierarchy
although there are utility controllers which serve purposes other than
resource distribution.
cgroups form a tree structure and every process in the system belongs
to one and only one cgroup. All threads of a process belong to the
same cgroup. On creation, all processes are put in the cgroup that
the parent process belongs to at the time. A process can be migrated
to another cgroup. Migration of a process doesn't affect already
existing descendant processes.
Following certain structural constraints, controllers may be enabled or
disabled selectively on a cgroup. All controller behaviors are
hierarchical - if a controller is enabled on a cgroup, it affects all
processes which belong to the cgroups consisting the inclusive
sub-hierarchy of the cgroup. When a controller is enabled on a nested
cgroup, it always restricts the resource distribution further. The
restrictions set closer to the root in the hierarchy can not be
overridden from further away.
Basic Operations
================
Mounting
--------
Unlike v1, cgroup v2 has only single hierarchy. The cgroup v2
hierarchy can be mounted with the following mount command::
# mount -t cgroup2 none $MOUNT_POINT
cgroup2 filesystem has the magic number 0x63677270 ("cgrp"). All
controllers which support v2 and are not bound to a v1 hierarchy are
automatically bound to the v2 hierarchy and show up at the root.
Controllers which are not in active use in the v2 hierarchy can be
bound to other hierarchies. This allows mixing v2 hierarchy with the
legacy v1 multiple hierarchies in a fully backward compatible way.
A controller can be moved across hierarchies only after the controller
is no longer referenced in its current hierarchy. Because per-cgroup
controller states are destroyed asynchronously and controllers may
have lingering references, a controller may not show up immediately on
the v2 hierarchy after the final umount of the previous hierarchy.
Similarly, a controller should be fully disabled to be moved out of
the unified hierarchy and it may take some time for the disabled
controller to become available for other hierarchies; furthermore, due
to inter-controller dependencies, other controllers may need to be
disabled too.
While useful for development and manual configurations, moving
controllers dynamically between the v2 and other hierarchies is
strongly discouraged for production use. It is recommended to decide
the hierarchies and controller associations before starting using the
controllers after system boot.
During transition to v2, system management software might still
automount the v1 cgroup filesystem and so hijack all controllers
during boot, before manual intervention is possible. To make testing
and experimenting easier, the kernel parameter cgroup_no_v1= allows
disabling controllers in v1 and make them always available in v2.
cgroup v2 currently supports the following mount options.
nsdelegate
Consider cgroup namespaces as delegation boundaries. This
option is system wide and can only be set on mount or modified
through remount from the init namespace. The mount option is
ignored on non-init namespace mounts. Please refer to the
Delegation section for details.
favordynmods
Reduce the latencies of dynamic cgroup modifications such as
task migrations and controller on/offs at the cost of making
hot path operations such as forks and exits more expensive.
The static usage pattern of creating a cgroup, enabling
controllers, and then seeding it with CLONE_INTO_CGROUP is
not affected by this option.
memory_localevents
Only populate memory.events with data for the current cgroup,
and not any subtrees. This is legacy behaviour, the default
behaviour without this option is to include subtree counts.
This option is system wide and can only be set on mount or
modified through remount from the init namespace. The mount
option is ignored on non-init namespace mounts.
memory_recursiveprot
Recursively apply memory.min and memory.low protection to
entire subtrees, without requiring explicit downward
propagation into leaf cgroups. This allows protecting entire
subtrees from one another, while retaining free competition
within those subtrees. This should have been the default
behavior but is a mount-option to avoid regressing setups
relying on the original semantics (e.g. specifying bogusly
high 'bypass' protection values at higher tree levels).
memory_hugetlb_accounting
Count HugeTLB memory usage towards the cgroup's overall
memory usage for the memory controller (for the purpose of
statistics reporting and memory protetion). This is a new
behavior that could regress existing setups, so it must be
explicitly opted in with this mount option.
A few caveats to keep in mind:
* There is no HugeTLB pool management involved in the memory
controller. The pre-allocated pool does not belong to anyone.
Specifically, when a new HugeTLB folio is allocated to
the pool, it is not accounted for from the perspective of the
memory controller. It is only charged to a cgroup when it is
actually used (for e.g at page fault time). Host memory
overcommit management has to consider this when configuring
hard limits. In general, HugeTLB pool management should be
done via other mechanisms (such as the HugeTLB controller).
* Failure to charge a HugeTLB folio to the memory controller
results in SIGBUS. This could happen even if the HugeTLB pool
still has pages available (but the cgroup limit is hit and
reclaim attempt fails).
* Charging HugeTLB memory towards the memory controller affects
memory protection and reclaim dynamics. Any userspace tuning
(of low, min limits for e.g) needs to take this into account.
* HugeTLB pages utilized while this option is not selected
will not be tracked by the memory controller (even if cgroup
v2 is remounted later on).
pids_localevents
The option restores v1-like behavior of pids.events:max, that is only
local (inside cgroup proper) fork failures are counted. Without this
option pids.events.max represents any pids.max enforcemnt across
cgroup's subtree.
Organizing Processes and Threads
--------------------------------
Processes
~~~~~~~~~
Initially, only the root cgroup exists to which all processes belong.
A child cgroup can be created by creating a sub-directory::
# mkdir $CGROUP_NAME
A given cgroup may have multiple child cgroups forming a tree
structure. Each cgroup has a read-writable interface file
"cgroup.procs". When read, it lists the PIDs of all processes which
belong to the cgroup one-per-line. The PIDs are not ordered and the
same PID may show up more than once if the process got moved to
another cgroup and then back or the PID got recycled while reading.
A process can be migrated into a cgroup by writing its PID to the
target cgroup's "cgroup.procs" file. Only one process can be migrated
on a single write(2) call. If a process is composed of multiple
threads, writing the PID of any thread migrates all threads of the
process.
When a process forks a child process, the new process is born into the
cgroup that the forking process belongs to at the time of the
operation. After exit, a process stays associated with the cgroup
that it belonged to at the time of exit until it's reaped; however, a
zombie process does not appear in "cgroup.procs" and thus can't be
moved to another cgroup.
A cgroup which doesn't have any children or live processes can be
destroyed by removing the directory. Note that a cgroup which doesn't
have any children and is associated only with zombie processes is
considered empty and can be removed::
# rmdir $CGROUP_NAME
"/proc/$PID/cgroup" lists a process's cgroup membership. If legacy
cgroup is in use in the system, this file may contain multiple lines,
one for each hierarchy. The entry for cgroup v2 is always in the
format "0::$PATH"::
# cat /proc/842/cgroup
...
0::/test-cgroup/test-cgroup-nested
If the process becomes a zombie and the cgroup it was associated with
is removed subsequently, " (deleted)" is appended to the path::
# cat /proc/842/cgroup
...
0::/test-cgroup/test-cgroup-nested (deleted)
Threads
~~~~~~~
cgroup v2 supports thread granularity for a subset of controllers to
support use cases requiring hierarchical resource distribution across
the threads of a group of processes. By default, all threads of a
process belong to the same cgroup, which also serves as the resource
domain to host resource consumptions which are not specific to a
process or thread. The thread mode allows threads to be spread across
a subtree while still maintaining the common resource domain for them.
Controllers which support thread mode are called threaded controllers.
The ones which don't are called domain controllers.
Marking a cgroup threaded makes it join the resource domain of its
parent as a threaded cgroup. The parent may be another threaded
cgroup whose resource domain is further up in the hierarchy. The root
of a threaded subtree, that is, the nearest ancestor which is not
threaded, is called threaded domain or thread root interchangeably and
serves as the resource domain for the entire subtree.
Inside a threaded subtree, threads of a process can be put in
different cgroups and are not subject to the no internal process
constraint - threaded controllers can be enabled on non-leaf cgroups
whether they have threads in them or not.
As the threaded domain cgroup hosts all the domain resource
consumptions of the subtree, it is considered to have internal
resource consumptions whether there are processes in it or not and
can't have populated child cgroups which aren't threaded. Because the
root cgroup is not subject to no internal process constraint, it can
serve both as a threaded domain and a parent to domain cgroups.
The current operation mode or type of the cgroup is shown in the
"cgroup.type" file which indicates whether the cgroup is a normal
domain, a domain which is serving as the domain of a threaded subtree,
or a threaded cgroup.
On creation, a cgroup is always a domain cgroup and can be made
threaded by writing "threaded" to the "cgroup.type" file. The
operation is single direction::
# echo threaded > cgroup.type
Once threaded, the cgroup can't be made a domain again. To enable the
thread mode, the following conditions must be met.
- As the cgroup will join the parent's resource domain. The parent
must either be a valid (threaded) domain or a threaded cgroup.
- When the parent is an unthreaded domain, it must not have any domain
controllers enabled or populated domain children. The root is
exempt from this requirement.
Topology-wise, a cgroup can be in an invalid state. Please consider
the following topology::
A (threaded domain) - B (threaded) - C (domain, just created)
C is created as a domain but isn't connected to a parent which can
host child domains. C can't be used until it is turned into a
threaded cgroup. "cgroup.type" file will report "domain (invalid)" in
these cases. Operations which fail due to invalid topology use
EOPNOTSUPP as the errno.
A domain cgroup is turned into a threaded domain when one of its child
cgroup becomes threaded or threaded controllers are enabled in the
"cgroup.subtree_control" file while there are processes in the cgroup.
A threaded domain reverts to a normal domain when the conditions
clear.
When read, "cgroup.threads" contains the list of the thread IDs of all
threads in the cgroup. Except that the operations are per-thread
instead of per-process, "cgroup.threads" has the same format and
behaves the same way as "cgroup.procs". While "cgroup.threads" can be
written to in any cgroup, as it can only move threads inside the same
threaded domain, its operations are confined inside each threaded
subtree.
The threaded domain cgroup serves as the resource domain for the whole
subtree, and, while the threads can be scattered across the subtree,
all the processes are considered to be in the threaded domain cgroup.
"cgroup.procs" in a threaded domain cgroup contains the PIDs of all
processes in the subtree and is not readable in the subtree proper.
However, "cgroup.procs" can be written to from anywhere in the subtree
to migrate all threads of the matching process to the cgroup.
Only threaded controllers can be enabled in a threaded subtree. When
a threaded controller is enabled inside a threaded subtree, it only
accounts for and controls resource consumptions associated with the
threads in the cgroup and its descendants. All consumptions which
aren't tied to a specific thread belong to the threaded domain cgroup.
Because a threaded subtree is exempt from no internal process
constraint, a threaded controller must be able to handle competition
between threads in a non-leaf cgroup and its child cgroups. Each
threaded controller defines how such competitions are handled.
Currently, the following controllers are threaded and can be enabled
in a threaded cgroup::
- cpu
- cpuset
- perf_event
- pids
[Un]populated Notification
--------------------------
Each non-root cgroup has a "cgroup.events" file which contains
"populated" field indicating whether the cgroup's sub-hierarchy has
live processes in it. Its value is 0 if there is no live process in
the cgroup and its descendants; otherwise, 1. poll and [id]notify
events are triggered when the value changes. This can be used, for
example, to start a clean-up operation after all processes of a given
sub-hierarchy have exited. The populated state updates and
notifications are recursive. Consider the following sub-hierarchy
where the numbers in the parentheses represent the numbers of processes
in each cgroup::
A(4) - B(0) - C(1)
\ D(0)
A, B and C's "populated" fields would be 1 while D's 0. After the one
process in C exits, B and C's "populated" fields would flip to "0" and
file modified events will be generated on the "cgroup.events" files of
both cgroups.
Controlling Controllers
-----------------------
Availability
~~~~~~~~~~~~
A controller is available in a cgroup when it is supported by the kernel (i.e.,
compiled in, not disabled and not attached to a v1 hierarchy) and listed in the
"cgroup.controllers" file. Availability means the controller's interface files
are exposed in the cgroup’s directory, allowing the distribution of the target
resource to be observed or controlled within that cgroup.
Enabling and Disabling
~~~~~~~~~~~~~~~~~~~~~~
Each cgroup has a "cgroup.controllers" file which lists all
controllers available for the cgroup to enable::
# cat cgroup.controllers
cpu io memory
No controller is enabled by default. Controllers can be enabled and
disabled by writing to the "cgroup.subtree_control" file::
# echo "+cpu +memory -io" > cgroup.subtree_control
Only controllers which are listed in "cgroup.controllers" can be
enabled. When multiple operations are specified as above, either they
all succeed or fail. If multiple operations on the same controller
are specified, the last one is effective.
Enabling a controller in a cgroup indicates that the distribution of
the target resource across its immediate children will be controlled.
Consider the following sub-hierarchy. The enabled controllers are
listed in parentheses::
A(cpu,memory) - B(memory) - C()
\ D()
As A has "cpu" and "memory" enabled, A will control the distribution
of CPU cycles and memory to its children, in this case, B. As B has
"memory" enabled but not "CPU", C and D will compete freely on CPU
cycles but their division of memory available to B will be controlled.
As a controller regulates the distribution of the target resource to
the cgroup's children, enabling it creates the controller's interface
files in the child cgroups. In the above example, enabling "cpu" on B
would create the "cpu." prefixed controller interface files in C and
D. Likewise, disabling "memory" from B would remove the "memory."
prefixed controller interface files from C and D. This means that the
controller interface files - anything which doesn't start with
"cgroup." are owned by the parent rather than the cgroup itself.
Top-down Constraint
~~~~~~~~~~~~~~~~~~~
Resources are distributed top-down and a cgroup can further distribute
a resource only if the resource has been distributed to it from the
parent. This means that all non-root "cgroup.subtree_control" files
can only contain controllers which are enabled in the parent's
"cgroup.subtree_control" file. A controller can be enabled only if
the parent has the controller enabled and a controller can't be
disabled if one or more children have it enabled.
No Internal Process Constraint
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Non-root cgroups can distribute domain resources to their children
only when they don't have any processes of their own. In other words,
only domain cgroups which don't contain any processes can have domain
controllers enabled in their "cgroup.subtree_control" files.
This guarantees that, when a domain controller is looking at the part
of the hierarchy which has it enabled, processes are always only on
the leaves. This rules out situations where child cgroups compete
against internal processes of the parent.
The root cgroup is exempt from this restriction. Root contains
processes and anonymous resource consumption which can't be associated
with any other cgroups and requires special treatment from most
controllers. How resource consumption in the root cgroup is governed
is up to each controller (for more information on this topic please
refer to the Non-normative information section in the Controllers
chapter).
Note that the restriction doesn't get in the way if there is no
enabled controller in the cgroup's "cgroup.subtree_control". This is
important as otherwise it wouldn't be possible to create children of a
populated cgroup. To control resource distribution of a cgroup, the
cgroup must create children and transfer all its processes to the
children before enabling controllers in its "cgroup.subtree_control"
file.
Delegation
----------
Model of Delegation
~~~~~~~~~~~~~~~~~~~
A cgroup can be delegated in two ways. First, to a less privileged
user by granting write access of the directory and its "cgroup.procs",
"cgroup.threads" and "cgroup.subtree_control" files to the user.
Second, if the "nsdelegate" mount option is set, automatically to a
cgroup namespace on namespace creation.
Because the resource control interface files in a given directory
control the distribution of the parent's resources, the delegatee
shouldn't be allowed to write to them. For the first method, this is
achieved by not granting access to these files. For the second, files
outside the namespace should be hidden from the delegatee by the means
of at least mount namespacing, and the kernel rejects writes to all
files on a namespace root from inside the cgroup namespace, except for
those files listed in "/sys/kernel/cgroup/delegate" (including
"cgroup.procs", "cgroup.threads", "cgroup.subtree_control", etc.).
The end results are equivalent for both delegation types. Once
delegated, the user can build sub-hierarchy under the directory,
organize processes inside it as it sees fit and further distribute the
resources it received from the parent. The limits and other settings
of all resource controllers are hierarchical and regardless of what
happens in the delegated sub-hierarchy, nothing can escape the
resource restrictions imposed by the parent.
Currently, cgroup doesn't impose any restrictions on the number of
cgroups in or nesting depth of a delegated sub-hierarchy; however,
this may be limited explicitly in the future.
Delegation Containment
~~~~~~~~~~~~~~~~~~~~~~
A delegated sub-hierarchy is contained in the sense that processes
can't be moved into or out of the sub-hierarchy by the delegatee.
For delegations to a less privileged user, this is achieved by
requiring the following conditions for a process with a non-root euid
to migrate a target process into a cgroup by writing its PID to the
"cgroup.procs" file.
- The writer must have write access to the "cgroup.procs" file.
- The writer must have write access to the "cgroup.procs" file of the
common ancestor of the source and destination cgroups.
The above two constraints ensure that while a delegatee may migrate
processes around freely in the delegated sub-hierarchy it can't pull
in from or push out to outside the sub-hierarchy.
For an example, let's assume cgroups C0 and C1 have been delegated to
user U0 who created C00, C01 under C0 and C10 under C1 as follows and
all processes under C0 and C1 belong to U0::
~~~~~~~~~~~~~ - C0 - C00
~ cgroup ~ \ C01
~ hierarchy ~
~~~~~~~~~~~~~ - C1 - C10
Let's also say U0 wants to write the PID of a process which is
currently in C10 into "C00/cgroup.procs". U0 has write access to the
file; however, the common ancestor of the source cgroup C10 and the
destination cgroup C00 is above the points of delegation and U0 would
not have write access to its "cgroup.procs" files and thus the write
will be denied with -EACCES.
For delegations to namespaces, containment is achieved by requiring
that both the source and destination cgroups are reachable from the
namespace of the process which is attempting the migration. If either
is not reachable, the migration is rejected with -ENOENT.
Guidelines
----------
Organize Once and Control
~~~~~~~~~~~~~~~~~~~~~~~~~
Migrating a process across cgroups is a relatively expensive operation
and stateful resources such as memory are not moved together with the
process. This is an explicit design decision as there often exist
inherent trade-offs between migration and various hot paths in terms
of synchronization cost.
As such, migrating processes across cgroups frequently as a means to
apply different resource restrictions is discouraged. A workload
should be assigned to a cgroup according to the system's logical and
resource structure once on start-up. Dynamic adjustments to resource
distribution can be made by changing controller configuration through
the interface files.
Avoid Name Collisions
~~~~~~~~~~~~~~~~~~~~~
Interface files for a cgroup and its children cgroups occupy the same
directory and it is possible to create children cgroups which collide
with interface files.
All cgroup core interface files are prefixed with "cgroup." and each
controller's interface files are prefixed with the controller name and
a dot. A controller's name is composed of lower case alphabets and
'_'s but never begins with an '_' so it can be used as the prefix
character for collision avoidance. Also, interface file names won't
start or end with terms which are often used in categorizing workloads
such as job, service, slice, unit or workload.
cgroup doesn't do anything to prevent name collisions and it's the
user's responsibility to avoid them.
Resource Distribution Models
============================
cgroup controllers implement several resource distribution schemes
depending on the resource type and expected use cases. This section
describes major schemes in use along with their expected behaviors.
Weights
-------
A parent's resource is distributed by adding up the weights of all
active children and giving each the fraction matching the ratio of its
weight against the sum. As only children which can make use of the
resource at the moment participate in the distribution, this is
work-conserving. Due to the dynamic nature, this model is usually
used for stateless resources.
All weights are in the range [1, 10000] with the default at 100. This
allows symmetric multiplicative biases in both directions at fine
enough granularity while staying in the intuitive range.
As long as the weight is in range, all configuration combinations are
valid and there is no reason to reject configuration changes or
process migrations.
"cpu.weight" proportionally distributes CPU cycles to active children
and is an example of this type.
.. _cgroupv2-limits-distributor:
Limits
------
A child can only consume up to the configured amount of the resource.
Limits can be over-committed - the sum of the limits of children can
exceed the amount of resource available to the parent.
Limits are in the range [0, max] and defaults to "max", which is noop.
As limits can be over-committed, all configuration combinations are
valid and there is no reason to reject configuration changes or
process migrations.
"io.max" limits the maximum BPS and/or IOPS that a cgroup can consume
on an IO device and is an example of this type.
.. _cgroupv2-protections-distributor:
Protections
-----------
A cgroup is protected up to the configured amount of the resource
as long as the usages of all its ancestors are under their
protected levels. Protections can be hard guarantees or best effort
soft boundaries. Protections can also be over-committed in which case
only up to the amount available to the parent is protected among
children.
Protections are in the range [0, max] and defaults to 0, which is
noop.
As protections can be over-committed, all configuration combinations
are valid and there is no reason to reject configuration changes or
process migrations.
"memory.low" implements best-effort memory protection and is an
example of this type.
Allocations
-----------
A cgroup is exclusively allocated a certain amount of a finite
resource. Allocations can't be over-committed - the sum of the
allocations of children can not exceed the amount of resource
available to the parent.
Allocations are in the range [0, max] and defaults to 0, which is no
resource.
As allocations can't be over-committed, some configuration
combinations are invalid and should be rejected. Also, if the
resource is mandatory for execution of processes, process migrations
may be rejected.
"cpu.rt.max" hard-allocates realtime slices and is an example of this
type.
Interface Files
===============
Format
------
All interface files should be in one of the following formats whenever
possible::
New-line separated values
(when only one value can be written at once)
VAL0\n
VAL1\n
...
Space separated values
(when read-only or multiple values can be written at once)
VAL0 VAL1 ...\n
Flat keyed
KEY0 VAL0\n
KEY1 VAL1\n
...
Nested keyed
KEY0 SUB_KEY0=VAL00 SUB_KEY1=VAL01...
KEY1 SUB_KEY0=VAL10 SUB_KEY1=VAL11...
...
For a writable file, the format for writing should generally match
reading; however, controllers may allow omitting later fields or
implement restricted shortcuts for most common use cases.
For both flat and nested keyed files, only the values for a single key
can be written at a time. For nested keyed files, the sub key pairs
may be specified in any order and not all pairs have to be specified.
Conventions
-----------
- Settings for a single feature should be contained in a single file.
- The root cgroup should be exempt from resource control and thus
shouldn't have resource control interface files.
- The default time unit is microseconds. If a different unit is ever
used, an explicit unit suffix must be present.
- A parts-per quantity should use a percentage decimal with at least
two digit fractional part - e.g. 13.40.
- If a controller implements weight based resource distribution, its
interface file should be named "weight" and have the range [1,
10000] with 100 as the default. The values are chosen to allow
enough and symmetric bias in both directions while keeping it
intuitive (the default is 100%).
- If a controller implements an absolute resource guarantee and/or
limit, the interface files should be named "min" and "max"
respectively. If a controller implements best effort resource
guarantee and/or limit, the interface files should be named "low"
and "high" respectively.
In the above four control files, the special token "max" should be
used to represent upward infinity for both reading and writing.
- If a setting has a configurable default value and keyed specific
overrides, the default entry should be keyed with "default" and
appear as the first entry in the file.
The default value can be updated by writing either "default $VAL" or
"$VAL".
When writing to update a specific override, "default" can be used as
the value to indicate removal of the override. Override entries
with "default" as the value must not appear when read.
For example, a setting which is keyed by major:minor device numbers
with integer values may look like the following::
# cat cgroup-example-interface-file
default 150
8:0 300
The default value can be updated by::
# echo 125 > cgroup-example-interface-file
or::
# echo "default 125" > cgroup-example-interface-file
An override can be set by::
# echo "8:16 170" > cgroup-example-interface-file
and cleared by::
# echo "8:0 default" > cgroup-example-interface-file
# cat cgroup-example-interface-file
default 125
8:16 170
- For events which are not very high frequency, an interface file
"events" should be created which lists event key value pairs.
Whenever a notifiable event happens, file modified event should be
generated on the file.
Core Interface Files
--------------------
All cgroup core files are prefixed with "cgroup."
cgroup.type
A read-write single value file which exists on non-root
cgroups.
When read, it indicates the current type of the cgroup, which
can be one of the following values.
- "domain" : A normal valid domain cgroup.
- "domain threaded" : A threaded domain cgroup which is
serving as the root of a threaded subtree.
- "domain invalid" : A cgroup which is in an invalid state.
It can't be populated or have controllers enabled. It may
be allowed to become a threaded cgroup.
- "threaded" : A threaded cgroup which is a member of a
threaded subtree.
A cgroup can be turned into a threaded cgroup by writing
"threaded" to this file.
cgroup.procs
A read-write new-line separated values file which exists on
all cgroups.
When read, it lists the PIDs of all processes which belong to
the cgroup one-per-line. The PIDs are not ordered and the
same PID may show up more than once if the process got moved
to another cgroup and then back or the PID got recycled while
reading.
A PID can be written to migrate the process associated with
the PID to the cgroup. The writer should match all of the
following conditions.
- It must have write access to the "cgroup.procs" file.
- It must have write access to the "cgroup.procs" file of the
common ancestor of the source and destination cgroups.
When delegating a sub-hierarchy, write access to this file
should be granted along with the containing directory.
In a threaded cgroup, reading this file fails with EOPNOTSUPP
as all the processes belong to the thread root. Writing is
supported and moves every thread of the process to the cgroup.
cgroup.threads
A read-write new-line separated values file which exists on
all cgroups.
When read, it lists the TIDs of all threads which belong to
the cgroup one-per-line. The TIDs are not ordered and the
same TID may show up more than once if the thread got moved to
another cgroup and then back or the TID got recycled while
reading.
A TID can be written to migrate the thread associated with the
TID to the cgroup. The writer should match all of the
following conditions.
- It must have write access to the "cgroup.threads" file.
- The cgroup that the thread is currently in must be in the
same resource domain as the destination cgroup.
- It must have write access to the "cgroup.procs" file of the
common ancestor of the source and destination cgroups.
When delegating a sub-hierarchy, write access to this file
should be granted along with the containing directory.
cgroup.controllers
A read-only space separated values file which exists on all
cgroups.
It shows space separated list of all controllers available to
the cgroup. The controllers are not ordered.
cgroup.subtree_control
A read-write space separated values file which exists on all
cgroups. Starts out empty.
When read, it shows space separated list of the controllers
which are enabled to control resource distribution from the
cgroup to its children.
Space separated list of controllers prefixed with '+' or '-'
can be written to enable or disable controllers. A controller
name prefixed with '+' enables the controller and '-'
disables. If a controller appears more than once on the list,
the last one is effective. When multiple enable and disable
operations are specified, either all succeed or all fail.
cgroup.events
A read-only flat-keyed file which exists on non-root cgroups.
The following entries are defined. Unless specified
otherwise, a value change in this file generates a file
modified event.
populated
1 if the cgroup or its descendants contains any live
processes; otherwise, 0.
frozen
1 if the cgroup is frozen; otherwise, 0.
cgroup.max.descendants
A read-write single value files. The default is "max".
Maximum allowed number of descent cgroups.
If the actual number of descendants is equal or larger,
an attempt to create a new cgroup in the hierarchy will fail.
cgroup.max.depth
A read-write single value files. The default is "max".
Maximum allowed descent depth below the current cgroup.
If the actual descent depth is equal or larger,
an attempt to create a new child cgroup will fail.
cgroup.stat
A read-only flat-keyed file with the following entries:
nr_descendants
Total number of visible descendant cgroups.
nr_dying_descendants
Total number of dying descendant cgroups. A cgroup becomes
dying after being deleted by a user. The cgroup will remain
in dying state for some time undefined time (which can depend
on system load) before being completely destroyed.
A process can't enter a dying cgroup under any circumstances,
a dying cgroup can't revive.
A dying cgroup can consume system resources not exceeding
limits, which were active at the moment of cgroup deletion.
nr_subsys_<cgroup_subsys>
Total number of live cgroup subsystems (e.g memory
cgroup) at and beneath the current cgroup.
nr_dying_subsys_<cgroup_subsys>
Total number of dying cgroup subsystems (e.g. memory
cgroup) at and beneath the current cgroup.
cgroup.freeze
A read-write single value file which exists on non-root cgroups.
Allowed values are "0" and "1". The default is "0".
Writing "1" to the file causes freezing of the cgroup and all
descendant cgroups. This means that all belonging processes will
be stopped and will not run until the cgroup will be explicitly
unfrozen. Freezing of the cgroup may take some time; when this action
is completed, the "frozen" value in the cgroup.events control file
will be updated to "1" and the corresponding notification will be
issued.
A cgroup can be frozen either by its own settings, or by settings
of any ancestor cgroups. If any of ancestor cgroups is frozen, the
cgroup will remain frozen.
Processes in the frozen cgroup can be killed by a fatal signal.
They also can enter and leave a frozen cgroup: either by an explicit
move by a user, or if freezing of the cgroup races with fork().
If a process is moved to a frozen cgroup, it stops. If a process is
moved out of a frozen cgroup, it becomes running.
Frozen status of a cgroup doesn't affect any cgroup tree operations:
it's possible to delete a frozen (and empty) cgroup, as well as
create new sub-cgroups.
cgroup.kill
A write-only single value file which exists in non-root cgroups.
The only allowed value is "1".
Writing "1" to the file causes the cgroup and all descendant cgroups to
be killed. This means that all processes located in the affected cgroup
tree will be killed via SIGKILL.
Killing a cgroup tree will deal with concurrent forks appropriately and
is protected against migrations.
In a threaded cgroup, writing this file fails with EOPNOTSUPP as
killing cgroups is a process directed operation, i.e. it affects
the whole thread-group.
cgroup.pressure
A read-write single value file that allowed values are "0" and "1".
The default is "1".
Writing "0" to the file will disable the cgroup PSI accounting.
Writing "1" to the file will re-enable the cgroup PSI accounting.
This control attribute is not hierarchical, so disable or enable PSI
accounting in a cgroup does not affect PSI accounting in descendants
and doesn't need pass enablement via ancestors from root.
The reason this control attribute exists is that PSI accounts stalls for
each cgroup separately and aggregates it at each level of the hierarchy.
This may cause non-negligible overhead for some workloads when under
deep level of the hierarchy, in which case this control attribute can
be used to disable PSI accounting in the non-leaf cgroups.
irq.pressure
A read-write nested-keyed file.
Shows pressure stall information for IRQ/SOFTIRQ. See
:ref:`Documentation/accounting/psi.rst <psi>` for details.
Controllers
===========
.. _cgroup-v2-cpu:
CPU
---
The "cpu" controllers regulates distribution of CPU cycles. This
controller implements weight and absolute bandwidth limit models for
normal scheduling policy and absolute bandwidth allocation model for
realtime scheduling policy.
In all the above models, cycles distribution is defined only on a temporal
base and it does not account for the frequency at which tasks are executed.
The (optional) utilization clamping support allows to hint the schedutil
cpufreq governor about the minimum desired frequency which should always be
provided by a CPU, as well as the maximum desired frequency, which should not
be exceeded by a CPU.
WARNING: cgroup2 cpu controller doesn't yet support the (bandwidth) control of
realtime processes. For a kernel built with the CONFIG_RT_GROUP_SCHED option
enabled for group scheduling of realtime processes, the cpu controller can only
be enabled when all RT processes are in the root cgroup. Be aware that system
management software may already have placed RT processes into non-root cgroups
during the system boot process, and these processes may need to be moved to the
root cgroup before the cpu controller can be enabled with a
CONFIG_RT_GROUP_SCHED enabled kernel.
With CONFIG_RT_GROUP_SCHED disabled, this limitation does not apply and some of
the interface files either affect realtime processes or account for them. See
the following section for details. Only the cpu controller is affected by
CONFIG_RT_GROUP_SCHED. Other controllers can be used for the resource control of
realtime processes irrespective of CONFIG_RT_GROUP_SCHED.
CPU Interface Files
~~~~~~~~~~~~~~~~~~~
The interaction of a process with the cpu controller depends on its scheduling
policy and the underlying scheduler. From the point of view of the cpu controller,
processes can be categorized as follows:
* Processes under the fair-class scheduler
* Processes under a BPF scheduler with the ``cgroup_set_weight`` callback
* Everything else: ``SCHED_{FIFO,RR,DEADLINE}`` and processes under a BPF scheduler
without the ``cgroup_set_weight`` callback
For details on when a process is under the fair-class scheduler or a BPF scheduler,
check out :ref:`Documentation/scheduler/sched-ext.rst <sched-ext>`.
For each of the following interface files, the above categories
will be referred to. All time durations are in microseconds.
cpu.stat
A read-only flat-keyed file.
This file exists whether the controller is enabled or not.
It always reports the following three stats, which account for all the
processes in the cgroup:
- usage_usec
- user_usec
- system_usec
and the following five when the controller is enabled, which account for
only the processes under the fair-class scheduler:
- nr_periods
- nr_throttled
- throttled_usec
- nr_bursts
- burst_usec
cpu.weight
A read-write single value file which exists on non-root
cgroups. The default is "100".
For non idle groups (cpu.idle = 0), the weight is in the
range [1, 10000].
If the cgroup has been configured to be SCHED_IDLE (cpu.idle = 1),
then the weight will show as a 0.
This file affects only processes under the fair-class scheduler and a BPF
scheduler with the ``cgroup_set_weight`` callback depending on what the
callback actually does.
cpu.weight.nice
A read-write single value file which exists on non-root
cgroups. The default is "0".
The nice value is in the range [-20, 19].
This interface file is an alternative interface for
"cpu.weight" and allows reading and setting weight using the
same values used by nice(2). Because the range is smaller and
granularity is coarser for the nice values, the read value is
the closest approximation of the current weight.
This file affects only processes under the fair-class scheduler and a BPF
scheduler with the ``cgroup_set_weight`` callback depending on what the
callback actually does.
cpu.max
A read-write two value file which exists on non-root cgroups.
The default is "max 100000".
The maximum bandwidth limit. It's in the following format::
$MAX $PERIOD
which indicates that the group may consume up to $MAX in each
$PERIOD duration. "max" for $MAX indicates no limit. If only
one number is written, $MAX is updated.
This file affects only processes under the fair-class scheduler.
cpu.max.burst
A read-write single value file which exists on non-root
cgroups. The default is "0".
The burst in the range [0, $MAX].
This file affects only processes under the fair-class scheduler.
cpu.pressure
A read-write nested-keyed file.
Shows pressure stall information for CPU. See
:ref:`Documentation/accounting/psi.rst <psi>` for details.
This file accounts for all the processes in the cgroup.
cpu.uclamp.min
A read-write single value file which exists on non-root cgroups.
The default is "0", i.e. no utilization boosting.
The requested minimum utilization (protection) as a percentage
rational number, e.g. 12.34 for 12.34%.
This interface allows reading and setting minimum utilization clamp
values similar to the sched_setattr(2). This minimum utilization
value is used to clamp the task specific minimum utilization clamp,
including those of realtime processes.
The requested minimum utilization (protection) is always capped by
the current value for the maximum utilization (limit), i.e.
`cpu.uclamp.max`.
This file affects all the processes in the cgroup.
cpu.uclamp.max
A read-write single value file which exists on non-root cgroups.
The default is "max". i.e. no utilization capping
The requested maximum utilization (limit) as a percentage rational
number, e.g. 98.76 for 98.76%.
This interface allows reading and setting maximum utilization clamp
values similar to the sched_setattr(2). This maximum utilization
value is used to clamp the task specific maximum utilization clamp,
including those of realtime processes.
This file affects all the processes in the cgroup.
cpu.idle
A read-write single value file which exists on non-root cgroups.
The default is 0.
This is the cgroup analog of the per-task SCHED_IDLE sched policy.
Setting this value to a 1 will make the scheduling policy of the
cgroup SCHED_IDLE. The threads inside the cgroup will retain their
own relative priorities, but the cgroup itself will be treated as
very low priority relative to its peers.
This file affects only processes under the fair-class scheduler.
Memory
------
The "memory" controller regulates distribution of memory. Memory is
stateful and implements both limit and protection models. Due to the
intertwining between memory usage and reclaim pressure and the
stateful nature of memory, the distribution model is relatively
complex.
While not completely water-tight, all major memory usages by a given
cgroup are tracked so that the total memory consumption can be
accounted and controlled to a reasonable extent. Currently, the
following types of memory usages are tracked.
- Userland memory - page cache and anonymous memory.
- Kernel data structures such as dentries and inodes.
- TCP socket buffers.
The above list may expand in the future for better coverage.
Memory Interface Files
~~~~~~~~~~~~~~~~~~~~~~
All memory amounts are in bytes. If a value which is not aligned to
PAGE_SIZE is written, the value may be rounded up to the closest
PAGE_SIZE multiple when read back.
memory.current
A read-only single value file which exists on non-root
cgroups.
The total amount of memory currently being used by the cgroup
and its descendants.
memory.min
A read-write single value file which exists on non-root
cgroups. The default is "0".
Hard memory protection. If the memory usage of a cgroup
is within its effective min boundary, the cgroup's memory
won't be reclaimed under any conditions. If there is no
unprotected reclaimable memory available, OOM killer
is invoked. Above the effective min boundary (or
effective low boundary if it is higher), pages are reclaimed
proportionally to the overage, reducing reclaim pressure for
smaller overages.
Effective min boundary is limited by memory.min values of
all ancestor cgroups. If there is memory.min overcommitment
(child cgroup or cgroups are requiring more protected memory
than parent will allow), then each child cgroup will get
the part of parent's protection proportional to its
actual memory usage below memory.min.
Putting more memory than generally available under this
protection is discouraged and may lead to constant OOMs.
If a memory cgroup is not populated with processes,
its memory.min is ignored.
memory.low
A read-write single value file which exists on non-root
cgroups. The default is "0".
Best-effort memory protection. If the memory usage of a
cgroup is within its effective low boundary, the cgroup's
memory won't be reclaimed unless there is no reclaimable
memory available in unprotected cgroups.
Above the effective low boundary (or
effective min boundary if it is higher), pages are reclaimed
proportionally to the overage, reducing reclaim pressure for
smaller overages.
Effective low boundary is limited by memory.low values of
all ancestor cgroups. If there is memory.low overcommitment
(child cgroup or cgroups are requiring more protected memory
than parent will allow), then each child cgroup will get
the part of parent's protection proportional to its
actual memory usage below memory.low.
Putting more memory than generally available under this
protection is discouraged.
memory.high
A read-write single value file which exists on non-root
cgroups. The default is "max".
Memory usage throttle limit. If a cgroup's usage goes
over the high boundary, the processes of the cgroup are
throttled and put under heavy reclaim pressure.
Going over the high limit never invokes the OOM killer and
under extreme conditions the limit may be breached. The high
limit should be used in scenarios where an external process
monitors the limited cgroup to alleviate heavy reclaim
pressure.
If memory.high is opened with O_NONBLOCK then the synchronous
reclaim is bypassed. This is useful for admin processes that
need to dynamically adjust the job's memory limits without
expending their own CPU resources on memory reclamation. The
job will trigger the reclaim and/or get throttled on its
next charge request.
Please note that with O_NONBLOCK, there is a chance that the
target memory cgroup may take indefinite amount of time to
reduce usage below the limit due to delayed charge request or
busy-hitting its memory to slow down reclaim.
memory.max
A read-write single value file which exists on non-root
cgroups. The default is "max".
Memory usage hard limit. This is the main mechanism to limit
memory usage of a cgroup. If a cgroup's memory usage reaches
this limit and can't be reduced, the OOM killer is invoked in
the cgroup. Under certain circumstances, the usage may go
over the limit temporarily.
In default configuration regular 0-order allocations always
succeed unless OOM killer chooses current task as a victim.
Some kinds of allocations don't invoke the OOM killer.
Caller could retry them differently, return into userspace
as -ENOMEM or silently ignore in cases like disk readahead.
If memory.max is opened with O_NONBLOCK, then the synchronous
reclaim and oom-kill are bypassed. This is useful for admin
processes that need to dynamically adjust the job's memory limits
without expending their own CPU resources on memory reclamation.
The job will trigger the reclaim and/or oom-kill on its next
charge request.
Please note that with O_NONBLOCK, there is a chance that the
target memory cgroup may take indefinite amount of time to
reduce usage below the limit due to delayed charge request or
busy-hitting its memory to slow down reclaim.
memory.reclaim
A write-only nested-keyed file which exists for all cgroups.
This is a simple interface to trigger memory reclaim in the
target cgroup.
Example::
echo "1G" > memory.reclaim
Please note that the kernel can over or under reclaim from
the target cgroup. If less bytes are reclaimed than the
specified amount, -EAGAIN is returned.
Please note that the proactive reclaim (triggered by this
interface) is not meant to indicate memory pressure on the
memory cgroup. Therefore socket memory balancing triggered by
the memory reclaim normally is not exercised in this case.
This means that the networking layer will not adapt based on
reclaim induced by memory.reclaim.
The following nested keys are defined.
========== ================================
swappiness Swappiness value to reclaim with
========== ================================
Specifying a swappiness value instructs the kernel to perform
the reclaim with that swappiness value. Note that this has the
same semantics as vm.swappiness applied to memcg reclaim with
all the existing limitations and potential future extensions.
The valid range for swappiness is [0-200, max], setting
swappiness=max exclusively reclaims anonymous memory.
memory.peak
A read-write single value file which exists on non-root cgroups.
The max memory usage recorded for the cgroup and its descendants since
either the creation of the cgroup or the most recent reset for that FD.
A write of any non-empty string to this file resets it to the
current memory usage for subsequent reads through the same
file descriptor.
memory.oom.group
A read-write single value file which exists on non-root
cgroups. The default value is "0".
Determines whether the cgroup should be treated as
an indivisible workload by the OOM killer. If set,
all tasks belonging to the cgroup or to its descendants
(if the memory cgroup is not a leaf cgroup) are killed
together or not at all. This can be used to avoid
partial kills to guarantee workload integrity.
Tasks with the OOM protection (oom_score_adj set to -1000)
are treated as an exception and are never killed.
If the OOM killer is invoked in a cgroup, it's not going
to kill any tasks outside of this cgroup, regardless
memory.oom.group values of ancestor cgroups.
memory.events
A read-only flat-keyed file which exists on non-root cgroups.
The following entries are defined. Unless specified
otherwise, a value change in this file generates a file
modified event.
Note that all fields in this file are hierarchical and the
file modified event can be generated due to an event down the
hierarchy. For the local events at the cgroup level see
memory.events.local.
low
The number of times the cgroup is reclaimed due to
high memory pressure even though its usage is under
the low boundary. This usually indicates that the low
boundary is over-committed.
high
The number of times processes of the cgroup are
throttled and routed to perform direct memory reclaim
because the high memory boundary was exceeded. For a
cgroup whose memory usage is capped by the high limit
rather than global memory pressure, this event's
occurrences are expected.
max
The number of times the cgroup's memory usage was
about to go over the max boundary. If direct reclaim
fails to bring it down, the cgroup goes to OOM state.
oom
The number of time the cgroup's memory usage was
reached the limit and allocation was about to fail.
This event is not raised if the OOM killer is not
considered as an option, e.g. for failed high-order
allocations or if caller asked to not retry attempts.
oom_kill
The number of processes belonging to this cgroup
killed by any kind of OOM killer.
oom_group_kill
The number of times a group OOM has occurred.
memory.events.local
Similar to memory.events but the fields in the file are local
to the cgroup i.e. not hierarchical. The file modified event
generated on this file reflects only the local events.
memory.stat
A read-only flat-keyed file which exists on non-root cgroups.
This breaks down the cgroup's memory footprint into different
types of memory, type-specific details, and other information
on the state and past events of the memory management system.
All memory amounts are in bytes.
The entries are ordered to be human readable, and new entries
can show up in the middle. Don't rely on items remaining in a
fixed position; use the keys to look up specific values!
If the entry has no per-node counter (or not show in the
memory.numa_stat). We use 'npn' (non-per-node) as the tag
to indicate that it will not show in the memory.numa_stat.
anon
Amount of memory used in anonymous mappings such as
brk(), sbrk(), and mmap(MAP_ANONYMOUS). Note that
some kernel configurations might account complete larger
allocations (e.g., THP) if only some, but not all the
memory of such an allocation is mapped anymore.
file
Amount of memory used to cache filesystem data,
including tmpfs and shared memory.
kernel (npn)
Amount of total kernel memory, including
(kernel_stack, pagetables, percpu, vmalloc, slab) in
addition to other kernel memory use cases.
kernel_stack
Amount of memory allocated to kernel stacks.
pagetables
Amount of memory allocated for page tables.
sec_pagetables
Amount of memory allocated for secondary page tables,
this currently includes KVM mmu allocations on x86
and arm64 and IOMMU page tables.
percpu (npn)
Amount of memory used for storing per-cpu kernel
data structures.
sock (npn)
Amount of memory used in network transmission buffers
vmalloc (npn)
Amount of memory used for vmap backed memory.
shmem
Amount of cached filesystem data that is swap-backed,
such as tmpfs, shm segments, shared anonymous mmap()s
zswap
Amount of memory consumed by the zswap compression backend.
zswapped
Amount of application memory swapped out to zswap.
file_mapped
Amount of cached filesystem data mapped with mmap(). Note
that some kernel configurations might account complete
larger allocations (e.g., THP) if only some, but not
not all the memory of such an allocation is mapped.
file_dirty
Amount of cached filesystem data that was modified but
not yet written back to disk
file_writeback
Amount of cached filesystem data that was modified and
is currently being written back to disk
swapcached
Amount of swap cached in memory. The swapcache is accounted
against both memory and swap usage.
anon_thp
Amount of memory used in anonymous mappings backed by
transparent hugepages
file_thp
Amount of cached filesystem data backed by transparent
hugepages
shmem_thp
Amount of shm, tmpfs, shared anonymous mmap()s backed by
transparent hugepages
inactive_anon, active_anon, inactive_file, active_file, unevictable
Amount of memory, swap-backed and filesystem-backed,
on the internal memory management lists used by the
page reclaim algorithm.
As these represent internal list state (eg. shmem pages are on anon
memory management lists), inactive_foo + active_foo may not be equal to
the value for the foo counter, since the foo counter is type-based, not
list-based.
slab_reclaimable
Part of "slab" that might be reclaimed, such as
dentries and inodes.
slab_unreclaimable
Part of "slab" that cannot be reclaimed on memory
pressure.
slab (npn)
Amount of memory used for storing in-kernel data
structures.
workingset_refault_anon
Number of refaults of previously evicted anonymous pages.
workingset_refault_file
Number of refaults of previously evicted file pages.
workingset_activate_anon
Number of refaulted anonymous pages that were immediately
activated.
workingset_activate_file
Number of refaulted file pages that were immediately activated.
workingset_restore_anon
Number of restored anonymous pages which have been detected as
an active workingset before they got reclaimed.
workingset_restore_file
Number of restored file pages which have been detected as an
active workingset before they got reclaimed.
workingset_nodereclaim
Number of times a shadow node has been reclaimed
pswpin (npn)
Number of pages swapped into memory
pswpout (npn)
Number of pages swapped out of memory
pgscan (npn)
Amount of scanned pages (in an inactive LRU list)
pgsteal (npn)
Amount of reclaimed pages
pgscan_kswapd (npn)
Amount of scanned pages by kswapd (in an inactive LRU list)
pgscan_direct (npn)
Amount of scanned pages directly (in an inactive LRU list)
pgscan_khugepaged (npn)
Amount of scanned pages by khugepaged (in an inactive LRU list)
pgscan_proactive (npn)
Amount of scanned pages proactively (in an inactive LRU list)
pgsteal_kswapd (npn)
Amount of reclaimed pages by kswapd
pgsteal_direct (npn)
Amount of reclaimed pages directly
pgsteal_khugepaged (npn)
Amount of reclaimed pages by khugepaged
pgsteal_proactive (npn)
Amount of reclaimed pages proactively
pgfault (npn)
Total number of page faults incurred
pgmajfault (npn)
Number of major page faults incurred
pgrefill (npn)
Amount of scanned pages (in an active LRU list)
pgactivate (npn)
Amount of pages moved to the active LRU list
pgdeactivate (npn)
Amount of pages moved to the inactive LRU list
pglazyfree (npn)
Amount of pages postponed to be freed under memory pressure
pglazyfreed (npn)
Amount of reclaimed lazyfree pages
swpin_zero
Number of pages swapped into memory and filled with zero, where I/O
was optimized out because the page content was detected to be zero
during swapout.
swpout_zero
Number of zero-filled pages swapped out with I/O skipped due to the
content being detected as zero.
zswpin
Number of pages moved in to memory from zswap.
zswpout
Number of pages moved out of memory to zswap.
zswpwb
Number of pages written from zswap to swap.
thp_fault_alloc (npn)
Number of transparent hugepages which were allocated to satisfy
a page fault. This counter is not present when CONFIG_TRANSPARENT_HUGEPAGE
is not set.
thp_collapse_alloc (npn)
Number of transparent hugepages which were allocated to allow
collapsing an existing range of pages. This counter is not
present when CONFIG_TRANSPARENT_HUGEPAGE is not set.
thp_swpout (npn)
Number of transparent hugepages which are swapout in one piece
without splitting.
thp_swpout_fallback (npn)
Number of transparent hugepages which were split before swapout.
Usually because failed to allocate some continuous swap space
for the huge page.
numa_pages_migrated (npn)
Number of pages migrated by NUMA balancing.
numa_pte_updates (npn)
Number of pages whose page table entries are modified by
NUMA balancing to produce NUMA hinting faults on access.
numa_hint_faults (npn)
Number of NUMA hinting faults.
pgdemote_kswapd
Number of pages demoted by kswapd.
pgdemote_direct
Number of pages demoted directly.
pgdemote_khugepaged
Number of pages demoted by khugepaged.
pgdemote_proactive
Number of pages demoted by proactively.
hugetlb
Amount of memory used by hugetlb pages. This metric only shows
up if hugetlb usage is accounted for in memory.current (i.e.
cgroup is mounted with the memory_hugetlb_accounting option).
memory.numa_stat
A read-only nested-keyed file which exists on non-root cgroups.
This breaks down the cgroup's memory footprint into different
types of memory, type-specific details, and other information
per node on the state of the memory management system.
This is useful for providing visibility into the NUMA locality
information within an memcg since the pages are allowed to be
allocated from any physical node. One of the use case is evaluating
application performance by combining this information with the
application's CPU allocation.
All memory amounts are in bytes.
The output format of memory.numa_stat is::
type N0=<bytes in node 0> N1=<bytes in node 1> ...
The entries are ordered to be human readable, and new entries
can show up in the middle. Don't rely on items remaining in a
fixed position; use the keys to look up specific values!
The entries can refer to the memory.stat.
memory.swap.current
--> --------------------
--> maximum size reached
--> --------------------
