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Chapter 4. Control Group Application Examples
cgroups to be created:
mount {
cpu = /cgroup/cpu_and_mem;
cpuacct = /cgroup/cpu_and_mem;
memory = /cgroup/cpu_and_mem;
}
group finance {
cpu {
cpu.shares="250";
}
cpuacct {
cpuacct.usage="0";
}
memory {
memory.limit_in_bytes="2G";
memory.memsw.limit_in_bytes="3G";
}
}
group sales {
cpu {
cpu.shares="250";
}
cpuacct {
cpuacct.usage="0";
}
memory {
memory.limit_in_bytes="4G";
memory.memsw.limit_in_bytes="6G";
}
}
group engineering {
cpu {
cpu.shares="500";
}
cpuacct {
cpuacct.usage="0";
}
memory {
memory.limit_in_bytes="8G";
memory.memsw.limit_in_bytes="16G";
}
}
When loaded, the above configuration file mounts the cpu, cpuacct, and memory subsystems to
a single cpu_and_mem cgroup. For more information on these subsystems, refer to Chapter 3,
Subsystems and Tunable Parameters. Next, it creates a hierarchy in cpu_and_mem which
contains three cgroups: sales, finance, and engineering. In each of these cgroups, custom
parameters are set for each subsystem:
cpu the cpu.shares parameter determines the share of CPU resources available to each
process in all cgroups. Setting the parameter to 250, 250, and 500 in the finance, sales, and
engineering cgroups respectively means that processes started in these groups will split the
resources with a 1:1:2 ratio. Note that when a single process is running, it consumes as much
CPU as necessary no matter which cgroup it is placed in. The CPU limitation only comes into
effect when two or more processes compete for CPU resources.
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cpuacct the cpuacct.usage="0" parameter is used to reset values stored in the
cpuacct.usage and cpuacct.usage_percpu files. These files report total CPU time (in
nanoseconds) consumed by all processes in a cgroup.
memory the memory.limit_in_bytes parameter represents the amount of memory that is
made available to all processes within a certain cgroup. In our example, processes started in
the finance cgroup have 2 GB of memory available, processes in the sales group have 4 GB of
memory available, and processes in the engineering group have 8 GB of memory available.
The memory.memsw.limit_in_bytes parameter specifies the total amount of memory and
swap space processes may use. Should a process in the finance cgroup hit the 2 GB memory
limit, it is allowed to use another 1 GB of swap space, thus totaling the configured 3 GB.
2. To define the rules which the cgrulesengd daemon uses to move processes to specific
cgroups, configure the /etc/cgrules.conf in the following way:
#
@finance cpu,cpuacct,memory finance
@sales cpu,cpuacct,memory sales
@engineering cpu,cpuacct,memory engineering
The above configuration creates rules that assign a specific system group (for example,
@finance) the resource controllers it may use (for example, cpu, cpuacct, memory) and a
cgroup (for example, finance) which contains all processes originating from that system group.
In our example, when the cgrulesengd daemon, started via the service cgred start
command, detects a process that is started by a user that belongs to the finance system group
(for example, jenn), that process is automatically moved to the
/cgroup/cpu_and_mem/finance/tasks file and is subjected to the resource limitations set
in the finance cgroup.
3. Start the cgconfig service to create the hierarchy of cgroups and set the needed parameters in
all created cgroups:
~]# service cgconfig start
Starting cgconfig service: [ OK ]
Start the cgred service to let the cgrulesengd daemon detect any processes started in system
groups configured in the /etc/cgrules.conf file:
~]# service cgred start
Starting CGroup Rules Engine Daemon: [ OK ]
Note that cgred is the name of the service that starts the cgrulesengd daemon.
4. To make all of the changes above persistent across reboots, configure the cgconfig and
cgred services to be started by default:
~]# chkconfig cgconfig on
~]# chkconfig cgred on
To test whether this setup works, execute a CPU or memory intensive process and observe the results,
for example, using the top utility. To test the CPU resource management, execute the following dd
command under each user:
~]$ dd if=/dev/zero of=/dev/null bs=1024k
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Chapter 4. Control Group Application Examples
The above command reads the /dev/zero and outputs it to the /dev/null in chunks of 1024 KB.
When the top utility is launched, you can see results similar to these:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
8201 peter 20 0 103m 1676 556 R 24.9 0.2 0:04.18 dd
8202 mike 20 0 103m 1672 556 R 24.9 0.2 0:03.47 dd
8199 jenn 20 0 103m 1676 556 R 12.6 0.2 0:02.87 dd
8200 john 20 0 103m 1676 556 R 12.6 0.2 0:02.20 dd
8197 martin 20 0 103m 1672 556 R 12.6 0.2 0:05.56 dd
8198 mark 20 0 103m 1672 556 R 12.3 0.2 0:04.28 dd
î"
All processes have been correctly assigned to their cgroups and are only allowed to consume CPU
resource made available to them. If all but two processes, which belong to the finance and engineering
cgroups, are stopped, the remaining resources are evenly split between both processes:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
8202 mike 20 0 103m 1676 556 R 66.4 0.2 0:06.35 dd
8200 john 20 0 103m 1672 556 R 33.2 0.2 0:05.08 dd
î"
Alternative method
Because the cgrulesengd daemon moves a process to a cgroup only after the appropriate conditions
set by the rules in /etc/cgrules.conf have been fulfilled, that process may be running for a few
milliseconds in an incorrect cgroup. An alternative way to move processes to their specified cgroups is
to use the pam_cgroup.so PAM module. This module moves processes to available cgroups
according to rules defined in the /etc/cgrules.conf file. Follow the steps in Procedure 4.4, Using a
PAM module to move processes to cgroups to configure the pam_cgroup.so PAM module.
Procedure 4 .4 . Using a PAM module to move processes to cgroups
1. Install the libcgroup-pam package from the optional Red Hat Enterprise Linux Yum repository:
~]# yum install libcgroup-pam --enablerepo=rhel-6-server-optional-rpms
2. Ensure that the PAM module has been installed and exists:
~]# ls /lib64/security/pam_cgroup.so
/lib64/security/pam_cgroup.so
Note that on 32-bit systems, the module is placed in the /lib/security directory.
3. Add the following line to the /etc/pam.d/su file to use the pam_cgroup.so module each time
the su command is executed:
session optional pam_cgroup.so
4. Configure the /etc/cgconfig.conf and /etc/cgrules.conf files as in Procedure 4.4,
Using a PAM module to move processes to cgroups .
5. Log out all users that are affected by the cgroup settings in the /etc/cgrules.conf file to
apply the above configuration.
When using the pam_cgroup.so PAM module, you may disable the cgred service.
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Red Hat Enterprise Linux 6 Resource Management Guide
Revision History
Revision 1.0-22.4 05 Mon Nov 25 2013 Rüdiger Landmann
Rebuild with Publican 4.0.0
Revision 1.0-22 Tue Nov 19 2013 Yoana Ruseva
Version for 6.5 GA release
Revision 1.0-16 Thu Feb 21 2013 Martin Prpi%0Å„
Red Hat Enterprise Linux 6.4 GA release of the Resource Management Guide. Includes various fixes
and new content:
- Final use case scenarios 584631
- Documentation for the perf_event controller 807326
- Documentation for common cgroup files 807329
- Documentation for OOM control and the notification API 822400, 822401
- CPU ceiling enforcement documentation 828991
Revision 1.0-7 Wed Jun 20 2012 Martin Prpi%0Å„
Red Hat Enterprise Linux 6.3 GA release of the Resource Management Guide.
- Added two use cases.
- Added documentation for the net_prio subsystem.
Revision 1.0-6 Tue Dec 6 2011 Martin Prpi%0Å„
Red Hat Enterprise Linux 6.2 GA release of the Resource Management Guide.
Revision 1.0-5 Thu May 19 2011 Martin Prpi%0Å„
Red Hat Enterprise Linux 6.1 GA release of the Resource Management Guide.
Revision 1.0-4 Tue Mar 1 2011 Martin Prpi%0Å„
- Fixed multiple examples BZ#667623, BZ#667676, BZ#667699
- Clarification of the cgclear command BZ#577101
- Clarification of the lssubsystem command BZ#678517
- Freezing a process BZ#677548
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