cpuset - confine tasks to processor and memory node subsets
The cpuset file system is a pseudo-filesystem interface to the kernel
cpuset mechanism for controlling the processor and memory placement of
tasks. It is commonly mounted at /dev/cpuset.
A cpuset defines a list of CPUs and memory nodes. Cpusets are
represented as directories in a hierarchical virtual file system, where
the top directory in the hierarchy (/dev/cpuset) represents the entire
system (all online CPUs and memory nodes) and any cpuset that is the
child (descendant) of another parent cpuset contains a subset of that
parents CPUs and memory nodes. The directories and files representing
cpusets have normal file system permissions.
Every task in the system belongs to exactly one cpuset. A task is
confined to only run on the CPUs in the cpuset it belongs to, and to
allocate memory only on the memory nodes in that cpuset. When a task
forks, the child task is placed in the same cpuset as its parent. With
sufficient privilege, a task may be moved from one cpuset to another
and the allowed CPUs and memory nodes of an existing cpuset may be
When the system begins booting, only the top cpuset is defined and all
tasks are in that cpuset. During the boot process or later during
normal system operation, other cpusets may be created, as sub-
directories of the top cpuset under the control of the system
administrator and tasks may be placed in these other cpusets.
Cpusets are integrated with the sched_setaffinity(2) scheduling
affinity mechanism and the mbind(2) and set_mempolicy(2) memory
placement mechanisms in the kernel. Neither of these mechanisms let a
task make use of a CPU or memory node that is not allowed by cpusets.
If changes to a tasks cpuset placement conflict with these other
mechanisms, then cpuset placement is enforced even if it means
overriding these other mechanisms.
Typically, a cpuset is used to manage the CPU and memory node
confinement for the entire set of tasks in a job, and these other
mechanisms are used to manage the placement of individual tasks or
memory regions within a job.
Each directory below /dev/cpuset represents a cpuset and contains
several files describing the state of that cpuset.
New cpusets are created using the mkdir system call or shell command.
The properties of a cpuset, such as its flags, allowed CPUs and memory
nodes, and attached tasks, are queried and modified by reading or
writing to the appropriate file in that cpusets directory, as listed
The files in each cpuset directory are automatically created when the
cpuset is created, as a result of the mkdir invocation. It is not
allowed to add or remove files from a cpuset directory.
The files in each cpuset directory are small text files that may be
read and written using traditional shell utilities such as cat(1), and
echo(1), or using ordinary file access routines from programmatic
languages, such as open(2), read(2), write(2) and close(2) from the ’C’
library. These files represent internal kernel state and do not have
any persistent image on disk. Each of these per-cpuset files is listed
and described below.
List of the process IDs (PIDs) of the tasks in that cpuset. The
list is formatted as a series of ASCII decimal numbers, each
followed by a newline. A task may be added to a cpuset
(removing it from the cpuset previously containing it) by
writing its PID to that cpusets tasks file (with or without a
Beware that only one PID may be written to the tasks file at a
time. If a string is written that contains more than one PID,
only the first one will be considered.
Flag (0 or 1). If set (1), that cpuset will receive special
handling whenever its last using task and last child cpuset goes
away. See the Notify On Release section, below.
List of CPUs on which tasks in that cpuset are allowed to
execute. See List Format below for a description of the format
The CPUs allowed to a cpuset may be changed by writing a new
list to its cpus file. Note however, such a change does not
take affect until the PIDs of the tasks in the cpuset are
rewritten to the cpusets tasks file. See the WARNINGS section,
Flag (0 or 1). If set (1), the cpuset has exclusive use of its
CPUs (no sibling or cousin cpuset may overlap CPUs). By default
this is off (0). Newly created cpusets also initially default
this to off (0).
List of memory nodes on which tasks in that cpuset are allowed
to allocate memory. See List Format below for a description of
the format of mems.
Flag (0 or 1). If set (1), the cpuset has exclusive use of its
memory nodes (no sibling or cousin may overlap). By default
this is off (0). Newly created cpusets also initially default
this to off (0).
Flag (0 or 1). If set (1), then memory migration is enabled.
See the Memory Migration section, below.
A measure of how much memory pressure the tasks in this cpuset
are causing. See the Memory Pressure section, below. Unless
memory_pressure_enabled is enabled, always has value zero (0).
This file is read-only. See the WARNINGS section, below.
Flag (0 or 1). This file is only present in the root cpuset,
normally /dev/cpuset. If set (1), the memory_pressure
calculations are enabled for all cpusets in the system. See the
Memory Pressure section, below.
Flag (0 or 1). If set (1), the kernel page cache (file system
buffers) are uniformly spread across the cpuset. See the Memory
Spread section, below.
Flag (0 or 1). If set (1), the kernel slab caches for file I/O
(directory and inode structures) are uniformly spread across the
cpuset. See the Memory Spread section, below.
In addition to the above special files in each directory below
/dev/cpuset, each task under /proc has an added file named cpuset,
displaying the cpuset name, as the path relative to the root of the
cpuset file system.
Also the /proc/<pid>/status file for each task has two added lines,
displaying the tasks cpus_allowed (on which CPUs it may be scheduled)
and mems_allowed (on which memory nodes it may obtain memory), in the
Mask Format (see below) as shown in the following example:
In addition to controlling which cpus and mems a task is allowed to
use, cpusets provide the following extended capabilities.
If a cpuset is marked cpu_exclusive or mem_exclusive, no other cpuset,
other than a direct ancestor or descendant, may share any of the same
CPUs or memory nodes.
A cpuset that is cpu_exclusive has a scheduler (sched) domain
associated with it. The sched domain consists of all CPUs in the
current cpuset that are not part of any exclusive child cpusets. This
ensures that the scheduler load balancing code only balances against
the CPUs that are in the sched domain as defined above and not all of
the CPUs in the system. This removes any overhead due to load balancing
code trying to pull tasks outside of the cpu_exclusive cpuset only to
be prevented by the tasks’ cpus_allowed mask.
A cpuset that is mem_exclusive restricts kernel allocations for page,
buffer and other data commonly shared by the kernel across multiple
users. All cpusets, whether mem_exclusive or not, restrict allocations
of memory for user space. This enables configuring a system so that
several independent jobs can share common kernel data, such as file
system pages, while isolating each jobs user allocation in its own
cpuset. To do this, construct a large mem_exclusive cpuset to hold all
the jobs, and construct child, non-mem_exclusive cpusets for each
individual job. Only a small amount of typical kernel memory, such as
requests from interrupt handlers, is allowed to be taken outside even a
Notify On Release
If the notify_on_release flag is enabled (1) in a cpuset, then whenever
the last task in the cpuset leaves (exits or attaches to some other
cpuset) and the last child cpuset of that cpuset is removed, the kernel
will run the command /sbin/cpuset_release_agent, supplying the pathname
(relative to the mount point of the cpuset file system) of the
abandoned cpuset. This enables automatic removal of abandoned cpusets.
The default value of notify_on_release in the root cpuset at system
boot is disabled (0). The default value of other cpusets at creation
is the current value of their parents notify_on_release setting.
The command /sbin/cpuset_release_agent is invoked, with the name
(/dev/cpuset relative path) of that cpuset in argv. This supports
automatic cleanup of abandoned cpusets.
The usual contents of the command /sbin/cpuset_release_agent is simply
the shell script:
By default, notify_on_release is off (0). Newly created cpusets
inherit their notify_on_release setting from their parent cpuset.
As with other flag values below, this flag can be changed by writing an
ASCII number 0 or 1 (with optional trailing newline) into the file, to
clear or set the flag, respectively.
The memory_pressure of a cpuset provides a simple per-cpuset metric of
the rate that the tasks in a cpuset are attempting to free up in use
memory on the nodes of the cpuset to satisfy additional memory
This enables batch managers monitoring jobs running in dedicated
cpusets to efficiently detect what level of memory pressure that job is
This is useful both on tightly managed systems running a wide mix of
submitted jobs, which may choose to terminate or re-prioritize jobs
that are trying to use more memory than allowed on the nodes assigned
them, and with tightly coupled, long running, massively parallel
scientific computing jobs that will dramatically fail to meet required
performance goals if they start to use more memory than allowed to
This mechanism provides a very economical way for the batch manager to
monitor a cpuset for signs of memory pressure. It’s up to the batch
manager or other user code to decide what to do about it and take
Unless memory pressure calculation is enabled by setting the special
file /dev/cpuset/memory_pressure_enabled, it is not computed for any
cpuset, and always reads a value of zero. See the WARNINGS section,
Why a per-cpuset, running average:
Because this meter is per-cpuset rather than per-task or mm, the
system load imposed by a batch scheduler monitoring this metric is
sharply reduced on large systems, because a scan of the tasklist can
be avoided on each set of queries.
Because this meter is a running average rather than an accumulating
counter, a batch scheduler can detect memory pressure with a single
read, instead of having to read and accumulate results for a period
Because this meter is per-cpuset rather than per-task or mm, the
batch scheduler can obtain the key information, memory pressure in a
cpuset, with a single read, rather than having to query and
accumulate results over all the (dynamically changing) set of tasks
in the cpuset.
A per-cpuset simple digital filter is kept within the kernel, and
updated by any task attached to that cpuset, if it enters the
synchronous (direct) page reclaim code.
A per-cpuset file provides an integer number representing the recent
(half-life of 10 seconds) rate of direct page reclaims caused by the
tasks in the cpuset, in units of reclaims attempted per second, times
There are two Boolean flag files per cpuset that control where the
kernel allocates pages for the file system buffers and related in
kernel data structures. They are called memory_spread_page and
If the per-cpuset Boolean flag file memory_spread_page is set, then the
kernel will spread the file system buffers (page cache) evenly over all
the nodes that the faulting task is allowed to use, instead of
preferring to put those pages on the node where the task is running.
If the per-cpuset Boolean flag file memory_spread_slab is set, then the
kernel will spread some file system related slab caches, such as for
inodes and directory entries evenly over all the nodes that the
faulting task is allowed to use, instead of preferring to put those
pages on the node where the task is running.
The setting of these flags does not affect anonymous data segment or
stack segment pages of a task.
By default, both kinds of memory spreading are off and the kernel
prefers to allocate memory pages on the node local to where the
requesting task is running. If that node is not allowed by the tasks
NUMA mempolicy or cpuset configuration or if there are insufficient
free memory pages on that node, then the kernel looks for the nearest
node that is allowed and does have sufficient free memory.
When new cpusets are created, they inherit the memory spread settings
of their parent.
Setting memory spreading causes allocations for the affected page or
slab caches to ignore the tasks NUMA mempolicy and be spread instead.
Tasks using mbind() or set_mempolicy() calls to set NUMA mempolicies
will not notice any change in these calls as a result of their
containing tasks memory spread settings. If memory spreading is turned
off, the currently specified NUMA mempolicy once again applies to
memory page allocations.
Both memory_spread_page and memory_spread_slab are Boolean flag files.
By default they contain "0", meaning that the feature is off for that
cpuset. If a "1" is written to that file, that turns the named feature
This memory placement policy is also known (in other contexts) as
round-robin or interleave.
This policy can provide substantial improvements for jobs that need to
place thread local data on the corresponding node, but that need to
access large file system data sets that need to be spread across the
several nodes in the jobs cpuset in order to fit. Without this policy,
especially for jobs that might have one thread reading in the data set,
the memory allocation across the nodes in the jobs cpuset can become
Normally, under the default setting (disabled) of memory_migrate, once
a page is allocated (given a physical page of main memory) then that
page stays on whatever node it was allocated, so long as it remains
allocated, even if the cpusets memory placement policy mems
When memory migration is enabled in a cpuset, if the mems setting of
the cpuset is changed, then any memory page in use by any task in the
cpuset that is on a memory node no longer allowed will be migrated to a
memory node that is allowed.
Also if a task is moved into a cpuset with memory_migrate enabled, any
memory pages it uses that were on memory nodes allowed in its previous
cpuset, but which are not allowed in its new cpuset, will be migrated
to a memory node allowed in the new cpuset.
The relative placement of a migrated page within the cpuset is
preserved during these migration operations if possible. For example,
if the page was on the second valid node of the prior cpuset, then the
page will be placed on the second valid node of the new cpuset, if
The following formats are used to represent sets of CPUs and memory
The Mask Format is used to represent CPU and memory node bitmasks in
the /proc/<pid>/status file.
It is hexadecimal, using ASCII characters "0" - "9" and "a" - "f". This
format displays each 32-bit word in hex (zero filled) and for masks
longer than one word uses a comma separator between words. Words are
displayed in big-endian order most significant first. And hex digits
within a word are also in big-endian order.
The number of 32-bit words displayed is the minimum number needed to
display all bits of the bitmask, based on the size of the bitmask.
Examples of the Mask Format:
00000001 # just bit 0 set
80000000,00000000,00000000 # just bit 95 set
00000001,00000000,00000000 # just bit 64 set
000000ff,00000000 # bits 32-39 set
00000000,000E3862 # 1,5,6,11-13,17-19 set
A mask with bits 0, 1, 2, 4, 8, 16, 32 and 64 set displays as
"00000001,00000001,00010117". The first "1" is for bit 64, the second
for bit 32, the third for bit 16, the fourth for bit 8, the fifth for
bit 4, and the "7" is for bits 2, 1 and 0.
The List Format for cpus and mems is a comma separated list of CPU or
memory node numbers and ranges of numbers, in ASCII decimal.
Examples of the List Format:
0-4,9 # bits 0, 1, 2, 3, 4 and 9 set
0-2,7,12-14 # bits 0, 1, 2, 7, 12, 13 and 14 set
The following rules apply to each cpuset:
* Its CPUs and memory nodes must be a (possibly equal) subset of its
* It can only be marked cpu_exclusive if its parent is.
* It can only be marked mem_exclusive if its parent is.
* If it is cpu_exclusive, its CPUs may not overlap any sibling.
* If it is memory_exclusive, its memory nodes may not overlap any
The permissions of a cpuset are determined by the permissions of the
special files and directories in the cpuset file system, normally
mounted at /dev/cpuset.
For instance, a task can put itself in some other cpuset (than its
current one) if it can write the tasks file for that cpuset (requires
execute permission on the encompassing directories and write permission
on that tasks file).
An additional constraint is applied to requests to place some other
task in a cpuset. One task may not attach another to a cpuset unless
it would have permission to send that task a signal.
A task may create a child cpuset if it can access and write the parent
cpuset directory. It can modify the CPUs or memory nodes in a cpuset
if it can access that cpusets directory (execute permissions on the
encompassing directories) and write the corresponding cpus or mems
Note however that since changes to the CPUs of a cpuset don’t apply to
any task in that cpuset until said task is reattached to that cpuset,
it would normally not be a good idea to arrange the permissions on a
cpuset so that some task could write the cpus file unless it could also
write the tasks file to reattach the tasks therein.
There is one minor difference between the manner in which these
permissions are evaluated and the manner in which normal file system
operation permissions are evaluated. The kernel evaluates relative
pathnames starting at a tasks current working directory. Even if one
is operating on a cpuset file, relative pathnames are evaluated
relative to the current working directory, not relative to a tasks
current cpuset. The only ways that cpuset paths relative to a tasks
current cpuset can be used are if either the tasks current working
directory is its cpuset (it first did a cd or chdir to its cpuset
directory beneath /dev/cpuset, which is a bit unusual) or if some user
code converts the relative cpuset path to a full file system path.
Updating a cpusets cpus
Changes to a cpusets cpus file do not take affect for any task in that
cpuset until that tasks process ID (PID) is rewritten to the cpusets
tasks file. This unusual requirement is needed to optimize a critical
code path in the Linux kernel. Beware that only one PID can be written
at a time to a cpusets tasks file. Additional PIDs on a single
write(2) system call are ignored. One (unobvious) way to satisfy this
requirement to rewrite the tasks file after updating the cpus file is
to use the -u unbuffered option to the sed(1) command, as in the
cd /dev/cpuset/foo # /foo is an existing cpuset
/bin/echo 3 > cpus # change /foo’s cpus
sed -un p < tasks > tasks # rewrite /foo’s tasks file
If one examines the Cpus_allowed value in the /proc/<pid>/status file
for one of the tasks in cpuset /foo in the above scenario, one will
notice that the value does not change when the cpus file is written
(the echo command), but only later, after the tasks file is rewritten
(the sed command).
By default, the per-cpuset file memory_pressure always contains zero
(0). Unless this feature is enabled by writing "1" to the special file
/dev/cpuset/memory_pressure_enabled, the kernel does not compute per-
Using the echo command
When using the echo command at the shell prompt to change the values of
cpuset files, beware that most shell built-in echo commands to not
display an error message if the write(2) system call fails. For
example, if the command:
echo 19 > mems
failed because memory node 19 was not allowed (perhaps the current
system does not have a memory node 19), then the above echo command
would not display any error. It is better to use the /bin/echo
external command to change cpuset file settings, as this command will
display write(2) errors, as in the example:
/bin/echo 19 > mems
/bin/echo: write error: No space left on device
Not all allocations of system memory are constrained by cpusets, for
the following reasons.
If hot-plug functionality is used to remove all the CPUs that are
currently assigned to a cpuset, then the kernel will automatically
update the cpus_allowed of all tasks attached to CPUs in that cpuset to
allow all CPUs. When memory hot-plug functionality for removing memory
nodes is available, a similar exception is expected to apply there as
well. In general, the kernel prefers to violate cpuset placement, over
starving a task that has had all its allowed CPUs or memory nodes taken
offline. User code should reconfigure cpusets to only refer to online
CPUs and memory nodes when using hot-plug to add or remove such
A few kernel critical internal memory allocation requests, marked
GFP_ATOMIC, must be satisfied, immediately. The kernel may drop some
request or malfunction if one of these allocations fail. If such a
request cannot be satisfied within the current tasks cpuset, then we
relax the cpuset, and look for memory anywhere we can find it. It’s
better to violate the cpuset than stress the kernel.
Allocations of memory requested by kernel drivers while processing an
interrupt lack any relevant task context, and are not confined by
Kernel limitations updating cpusets
In order to minimize the impact of cpusets on critical kernel code,
such as the scheduler, and due to the fact that the kernel does not
support one task updating the memory placement of another task
directly, the impact on a task of changing its cpuset CPU or memory
node placement, or of changing to which cpuset a task is attached, is
If a cpuset has its memory nodes modified, then for each task attached
to that cpuset, the next time that the kernel attempts to allocate a
page of memory for that task, the kernel will notice the change in the
tasks cpuset, and update its per-task memory placement to remain within
the new cpusets memory placement. If the task was using mempolicy
MPOL_BIND, and the nodes to which it was bound overlap with its new
cpuset, then the task will continue to use whatever subset of MPOL_BIND
nodes are still allowed in the new cpuset. If the task was using
MPOL_BIND and now none of its MPOL_BIND nodes are allowed in the new
cpuset, then the task will be essentially treated as if it was
MPOL_BIND bound to the new cpuset (even though its NUMA placement, as
queried by get_mempolicy(), doesn’t change). If a task is moved from
one cpuset to another, then the kernel will adjust the tasks memory
placement, as above, the next time that the kernel attempts to allocate
a page of memory for that task.
If a cpuset has its CPUs modified, each task using that cpuset does
_not_ change its behavior automatically. In order to minimize the
impact on the critical scheduling code in the kernel, tasks will
continue to use their prior CPU placement until they are rebound to
their cpuset, by rewriting their PID to the ’tasks’ file of their
cpuset. If a task had been bound to some subset of its cpuset using
the sched_setaffinity() call, and if any of that subset is still
allowed in its new cpuset settings, then the task will be restricted to
the intersection of the CPUs it was allowed on before, and its new
cpuset CPU placement. If, on the other hand, there is no overlap
between a tasks prior placement and its new cpuset CPU placement, then
the task will be allowed to run on any CPU allowed in its new cpuset.
If a task is moved from one cpuset to another, its CPU placement is
updated in the same way as if the tasks PID is rewritten to the ’tasks’
file of its current cpuset.
In summary, the memory placement of a task whose cpuset is changed is
updated by the kernel, on the next allocation of a page for that task,
but the processor placement is not updated, until that tasks PID is
rewritten to the ’tasks’ file of its cpuset. This is done to avoid
impacting the scheduler code in the kernel with a check for changes in
a tasks processor placement.
You can use the rename(2) system call to rename cpusets. Only simple
renaming is supported, changing the name of a cpuset directory while
keeping its same parent.
Despite its name, the pid parameter is actually a thread id, and each
thread in a threaded group can be attached to a different cpuset. The
value returned from a call to gettid(2) can be passed in the argument
The following examples demonstrate querying and setting cpuset options
using shell commands.
Creating and attaching to a cpuset.
To create a new cpuset and attach the current command shell to it, the
1) mkdir /dev/cpuset (if not already done)
2) mount -t cpuset none /dev/cpuset (if not already done)
3) Create the new cpuset using mkdir(1).
4) Assign CPUs and memory nodes to the new cpuset.
5) Attach the shell to the new cpuset.
For example, the following sequence of commands will setup a cpuset
named "Charlie", containing just CPUs 2 and 3, and memory node 1, and
then attach the current shell to that cpuset.
mount -t cpuset cpuset /dev/cpuset
/bin/echo 2-3 > cpus
/bin/echo 1 > mems
/bin/echo $$ > tasks
# The current shell is now running in cpuset Charlie
# The next line should display ’/Charlie’
Migrating a job to different memory nodes.
To migrate a job (the set of tasks attached to a cpuset) to different
CPUs and memory nodes in the system, including moving the memory pages
currently allocated to that job, perform the following steps.
1) Lets say we want to move the job in cpuset alpha (CPUs 4-7 and
memory nodes 2-3) to a new cpuset beta (CPUs 16-19 and memory
2) First create the new cpuset beta.
3) Then allow CPUs 16-19 and memory nodes 8-9 in beta.
4) Then enable memory_migration in beta.
5) Then move each task from alpha to beta.
The following sequence of commands accomplishes this.
/bin/echo 16-19 > cpus
/bin/echo 8-9 > mems
/bin/echo 1 > memory_migrate
while read i; do /bin/echo $i; done < ../alpha/tasks > tasks
The above should move any tasks in alpha to beta, and any memory held
by these tasks on memory nodes 2-3 to memory nodes 8-9, respectively.
Notice that the last step of the above sequence did not do:
cp ../alpha/tasks tasks
The while loop, rather than the seemingly easier use of the cp(1)
command, was necessary because only one task PID at a time may be
written to the tasks file.
The same affect (writing one pid at a time) as the while loop can be
accomplished more efficiently, in fewer keystrokes and in syntax that
works on any shell, but alas more obscurely, by using the sed -u
sed -un p < ../alpha/tasks > tasks
The Linux kernel implementation of cpusets sets errno to specify the
reason for a failed system call affecting cpusets.
The possible errno settings and their meaning when set on a failed
cpuset call are as listed below.
ENOMEM Insufficient memory is available.
EBUSY Attempted to remove a cpuset with attached tasks.
EBUSY Attempted to remove a cpuset with child cpusets.
ENOENT Attempted to create a cpuset in a parent cpuset that doesn’t
ENOENT Attempted to access a non-existent file in a cpuset directory.
EEXIST Attempted to create a cpuset that already exists.
EEXIST Attempted to rename(2) a cpuset to a name that already exists.
Attempted to rename(2) a non-existent cpuset.
E2BIG Attempted a write(2) system call on a special cpuset file with
a length larger than some kernel determined upper limit on the
length of such writes.
ESRCH Attempted to write the process ID (PID) of a non-existent task
to a cpuset tasks file.
EACCES Attempted to write the process ID (PID) of a task to a cpuset
tasks file when one lacks permission to move that task.
Attempted to write(2) a memory_pressure file.
ENOSPC Attempted to write the process ID (PID) of a task to a cpuset
tasks file when the cpuset had an empty cpus or empty mems
EINVAL Attempted to change a cpuset in a way that would violate a
cpu_exclusive or mem_exclusive attribute of that cpuset or any
of its siblings.
EINVAL Attempted to write(2) an empty cpus or mems list to the kernel.
The kernel creates new cpusets (via mkdir(2)) with empty cpus
and mems. But the kernel will not allow an empty list to be
written to the special cpus or mems files of a cpuset.
EIO Attempted to write(2) a string to a cpuset tasks file that does
not begin with an ASCII decimal integer.
EIO Attempted to rename(2) a cpuset outside of its current
ENOSPC Attempted to write(2) a list to a cpus file that did not include
any online CPUs.
ENOSPC Attempted to write(2) a list to a mems file that did not include
any online memory nodes.
ENODEV The cpuset was removed by another task at the same time as a
write(2) was attempted on one of the special files in the cpuset
EACCES Attempted to add a CPU or memory node to a cpuset that is not
already in its parent.
EACCES Attempted to set cpu_exclusive or mem_exclusive on a cpuset
whose parent lacks the same setting.
EBUSY Attempted to remove a CPU or memory node from a cpuset that is
also in a child of that cpuset.
EFAULT Attempted to read(2) or write(2) a cpuset file using a buffer
that is outside your accessible address space.
Attempted to read a /proc/<pid>/cpuset file for a cpuset path
that is longer than the kernel page size.
Attempted to create a cpuset whose base directory name is longer
than 255 characters.
Attempted to create a cpuset whose full pathname including the
"/dev/cpuset/" prefix is longer than 4095 characters.
EINVAL Specified a cpus or mems list to the kernel which included a
range with the second number smaller than the first number.
EINVAL Specified a cpus or mems list to the kernel which included an
invalid character in the string.
ERANGE Specified a cpus or mems list to the kernel which included a
number too large for the kernel to set in its bitmasks.
cat(1), echo(1), ls(1), mkdir(1), rmdir(1), sed(1), taskset(1),
close(2), get_mempolicy(2), mbind(2), mkdir(2), open(2), read(2)
rmdir(2), sched_getaffinity(2), sched_setaffinity(2), set_mempolicy(2),
sched_setscheduler(2), taskset(2), write(2), libbitmask(3), proc(5),
Cpusets appeared in version 2.6.13 of the Linux kernel.
memory_pressure cpuset files can be opened for writing, creation or
truncation, but then the write(2) fails with errno == EACCESS, and the
creation and truncation options on open(2) have no affect.
This man page was written by Paul Jackson.