cgroup.conf

NAME

cgroup.conf - Slurm configuration file for the cgroup support

DESCRIPTION

cgroup.conf is an ASCII file which defines parameters used by Slurm's Linux cgroup related plugins. The file will always be located in the same directory as the slurm.conf.

Parameter names are case insensitive. Any text following a "#" in the configuration file is treated as a comment through the end of that line. Changes to the configuration file take effect upon restart of Slurm daemons, daemon receipt of the SIGHUP signal, or execution of the command "scontrol reconfigure" unless otherwise noted.

For general Slurm cgroups information, see the Cgroups Guide at <https://slurm.schedmd.com/cgroups.html>.

The following cgroup.conf parameters are defined to control the general behavior of Slurm cgroup plugins.

CgroupAutomount=<yes|no>: In cgroup/v1 this parameter detects if /sys/fs/cgroup/<controller_name> is available, and if not it tries to mount the filesystem. In cgroup/v2 this parameter only takes effect if IgnoreSystemd is set, and enables the required controllers on slurmd and slurmstepd cgroup directories. This parameter is intended for development and testing with cgroup/v2.

CgroupMountpoint=PATH: Only intended for development and testing. Specifies the PATH under which cgroup controllers should be mounted. The default PATH is /sys/fs/cgroup.

CgroupPlugin=<cgroup/v1|cgroup/v2|autodetect>: Specify the plugin to be used when interacting with the cgroup subsystem. Supported values at the moment are "cgroup/v1" which supports the legacy interface of cgroup v1, "cgroup/v2" for unified architecture, or "autodetect" which tries to determine which cgroup version does your system provide. This is useful if nodes have support for different cgroup versions. The default value is "autodetect".

IgnoreSystemd=<yes|no>: Only for cgroup/v2 and for development and testing. It will avoid any call to dbus and contact with systemd, and instead will prepare all the cgroup hierarchy manually. This option is dangerous in systems with systemd since the cgroup can be modified by systemd and cause issues to jobs.

IgnoreSystemdOnFailure=<yes|no>: Only for cgroup/v2 and for development and testing. It has similar functionality to IgnoreSystemd but only in the case that a dbus call does not succeed.

TASK/CGROUP PLUGIN

The following cgroup.conf parameters are defined to control the behavior of this particular plugin:

AllowedKmemSpace=<number>: Only for cgroup/v1. Constrain the job cgroup kernel memory to this amount of the allocated memory, specified in bytes. The AllowedKmemSpace must be between the upper and lower memory limits, specified by MaxKmemPercent and MinKmemSpace, respectively. If AllowedKmemSpace goes beyond the upper or lower limit, it will be reset to that upper or lower limit, whichever has been exceeded.

AllowedRAMSpace=<number>: Constrain the job/step cgroup RAM to this percentage of the allocated memory. The percentage supplied may be expressed as floating point number, e.g. 101.5. Sets the cgroup soft memory limit at the allocated memory size and then sets the job/step hard memory limit at the (AllowedRAMSpace/100) * allocated memory. If the job/step exceeds the hard limit, then it might trigger Out Of Memory (OOM) events (including oom-kill) which will be logged to kernel log ring buffer (dmesg in Linux). Setting AllowedRAMSpace above 100 may cause system Out of Memory (OOM) events as it allows job/step to allocate more memory than configured to the nodes. Reducing configured node available memory to avoid system OOM events is suggested. Setting AllowedRAMSpace below 100 will result in jobs receiving less memory than allocated and soft memory limit will set to the same value as the hard limit. Also see ConstrainRAMSpace. The default value is 100.

AllowedSwapSpace=<number>: Constrain the job cgroup swap space to this percentage of the allocated memory. The default value is 0, which means that RAM+Swap will be limited to AllowedRAMSpace. The supplied percentage may be expressed as a floating point number, e.g. 50.5. If the limit is exceeded, the job steps will be killed and a warning message will be written to standard error. Also see ConstrainSwapSpace. NOTE: Setting AllowedSwapSpace to 0 does not restrict the Linux kernel from using swap space. To control how the kernel uses swap space, see MemorySwappiness.

ConstrainCores=<yes|no>: If configured to "yes" then constrain allowed cores to the subset of allocated resources. This functionality makes use of the cpuset subsystem. Due to a bug fixed in version 1.11.5 of HWLOC, the task/affinity plugin may be required in addition to task/cgroup for this to function properly. The default value is "no".

ConstrainDevices=<yes|no>: If configured to "yes" then constrain the job's allowed devices based on GRES allocated resources. It uses the devices subsystem for that. The default value is "no".

ConstrainKmemSpace=<yes|no>: Only for cgroup/v1. If configured to "yes" then constrain the job's Kmem RAM usage in addition to RAM usage. Only takes effect if ConstrainRAMSpace is set to "yes". If enabled, the job's Kmem limit will be assigned the value of AllowedKmemSpace or the value coming from MaxKmemPercent. The default value is "no" which will leave Kmem setting untouched by Slurm. Also see AllowedKmemSpace, MaxKmemPercent.

ConstrainRAMSpace=<yes|no>: If configured to "yes" then constrain the job's RAM usage by setting the memory soft limit to the allocated memory and the hard limit to the allocated memory * AllowedRAMSpace. The default value is "no", in which case the job's RAM limit will be set to its swap space limit if ConstrainSwapSpace is set to "yes". Also see AllowedSwapSpace, AllowedRAMSpace and ConstrainSwapSpace. NOTE: When using ConstrainRAMSpace, if the combined memory used by all processes in a step is greater than the limit, then the kernel will trigger an OOM event, killing one or more of the processes in the step. The step state will be marked as OOM, but the step itself will keep running and other processes in the step may continue to run as well. This differs from the behavior of OverMemoryKill, where the whole step will be killed/cancelled. NOTE: When enabled, ConstrainRAMSpace can lead to a noticeable decline in per-node job throughout. Sites with high-throughput requirements should carefully weigh the tradeoff between per-node throughput, versus potential problems that can arise from unconstrained memory usage on the node. See <https://slurm.schedmd.com/high_throughput.html> for further discussion.

ConstrainSwapSpace=<yes|no>: If configured to "yes" then constrain the job's swap space usage. The default value is "no". Note that when set to "yes" and ConstrainRAMSpace is set to "no", AllowedRAMSpace is automatically set to 100% in order to limit the RAM+Swap amount to 100% of job's requirement plus the percent of allowed swap space. This amount is thus set to both RAM and RAM+Swap limits. This means that in that particular case, ConstrainRAMSpace is automatically enabled with the same limit as the one used to constrain swap space. Also see AllowedSwapSpace.

MaxRAMPercent=PERCENT: Set an upper bound in percent of total RAM on the RAM constraint for a job. This will be the memory constraint applied to jobs that are not explicitly allocated memory by Slurm (i.e. Slurm's select plugin is not configured to manage memory allocations). The PERCENT may be an arbitrary floating point number. The default value is 100.

MaxSwapPercent=PERCENT: Set an upper bound (in percent of total RAM) on the amount of RAM+Swap that may be used for a job. This will be the swap limit applied to jobs on systems where memory is not being explicitly allocated to job. The PERCENT may be an arbitrary floating point number between 0 and 100. The default value is 100.

MaxKmemPercent=PERCENT: Only for cgroup/v1. Set an upper bound in percent of total RAM as the maximum Kmem for a job. The PERCENT may be an arbitrary floating point number, however, the product of MaxKmemPercent and job requested memory has to fall between MinKmemSpace and job requested memory, otherwise the boundary value is used. The default value is 100.

MemorySwappiness=<number>: Only for cgroup/v1. Configure the kernel's priority for swapping out anonymous pages (such as program data) verses file cache pages for the job cgroup. Valid values are between 0 and 100, inclusive. A value of 0 prevents the kernel from swapping out program data. A value of 100 gives equal priority to swapping out file cache or anonymous pages. If not set, then the kernel's default swappiness value will be used. ConstrainSwapSpace must be set to yes in order for this parameter to be applied.

MinKmemSpace=<number>: Only for cgroup/v1. Set a lower bound (in MB) on the memory limits defined by AllowedKmemSpace. The default limit is 30M.

MinRAMSpace=<number>: Set a lower bound (in MB) on the memory limits defined by AllowedRAMSpace and AllowedSwapSpace. This prevents accidentally creating a memory cgroup with such a low limit that slurmstepd is immediately killed due to lack of RAM. The default limit is 30M.

DISTRIBUTION-SPECIFIC NOTES

Debian and derivatives (e.g. Ubuntu) usually exclude the memory and memsw (swap) cgroups by default. To include them, add the following parameters to the kernel command line: cgroup_enable=memory swapaccount=1

This can usually be placed in /etc/default/grub inside the GRUB_CMDLINE_LINUX variable. A command such as update-grub must be run after updating the file.

EXAMPLE

/etc/slurm/cgroup.conf:: This example cgroup.conf file shows a configuration that enables the more commonly used cgroup enforcement mechanisms.

###
# Slurm cgroup support configuration file.
###
CgroupAutomount=yes
CgroupMountpoint=/sys/fs/cgroup
ConstrainCores=yes
ConstrainDevices=yes
ConstrainKmemSpace=no        #avoid known Kernel issues
ConstrainRAMSpace=yes
ConstrainSwapSpace=yes

/etc/slurm/slurm.conf:: These are the entries required in slurm.conf to activate the cgroup enforcement mechanisms. Make sure that the node definitions in your slurm.conf closely match the configuration as shown by " slurmd -C". Either MemSpecLimit should be set or RealMemory should be defined with less than the actual amount of memory for a node to ensure that all system/non-job processes will have sufficient memory at all times. Sites should also configure pam_slurm_adopt to ensure users can not escape the cgroups via ssh.

###
# Slurm configuration entries for cgroups
###
ProctrackType=proctrack/cgroup
TaskPlugin=task/cgroup,task/affinity
JobAcctGatherType=jobacct_gather/cgroup #optional for gathering metrics
PrologFlags=Contain                     #X11 flag is also suggested

COPYING

This file is part of Slurm, a resource management program. For details, see <https://slurm.schedmd.com/>.

Slurm is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

Slurm is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.