CGroup introduction

This paper deals with linux Provided cgroup Ability , The following has been expected to be explained ：

• What is? cgroups ?

• Why cgroups ?

• cgroups How did it happen ?

• How to use cgroups ?

1  What is? cgroups ?

CGroups Provides a set of management processes （ Subprocesses ） Resource control mechanism .

The following technical terms are defined :cgroup： Use one or more subsystems To control a set of tasks .subsystem：subsystem It is a resource controller provided by the kernel to manage specific resources .hierarchy：hierarchy It 's a logical concept ,cgroup according to subsystem To classify , Form a series of cgroups, And tree The structure of ,hierarchy This means something like tree Hierarchy . Every hierarchy The hierarchy can be mapped to the virtual file system in the operating system , Every subsystem Map to a cgroup tree.

User mode programs will use cgroup Virtual file system corresponding to the name to create 、 Delete cgroup example 、 Set or query the task cgroup. These operations only affect cgroup Associated in the file system cgroup Instance hierarchy.

2  Why cgroups?

Linux The kernel uses a variety of technologies （cpusets, CKRM/ResGroups, UserBeanCounters,  as well as virtual servernamespaces） Management process . These technologies require grouping processes / Partition .

kernel-provided cgroup Provides a set of kernel mechanisms . for instance ：

echo pid > /sys/fs/cgroup/network/<new_class>/tasks

Just write the management tasks into , You can control a certain resource （ Such as network）.

3 cgroup How is it realized ?

cgroups The kernel is extended with the following :

• Each task points to a css_set Structure pointer .

• One css_set  Contains a series of points cgroup_subsys_state Pointer to structure ,  Every cgroup_subsys_state Corresponding to one cgroup subsystem.

• cgroup hierarchy  Files can be mounted and browsed 、 Execute user mode operation .

• see cgroup Under all the tasks PID.

Specifically, how to pass in the kernel css_set Management is beyond the scope of this article .

In the folder Directory , You can see cgroup Contains the following folder contents :

• tasks:  A series of pids.  Process ID Writing this file will move it to this cgroup.

• cgroup.procs:  A series of process groups IDs. Group processes ID Writing this file will move it to this cgroup.

• notify_on_release flag:  Whether to run release agent?

• release_agent:  The path used to publish the notification （ This file exists only at the top  cgroup）

cgroups have access to mkdir System call or shell Command to create ,cgroup The attribute of can be modified by modifying the corresponding file content .

Meituan has a drawing of this architecture , As shown in the figure .

4  How to use cgroups ?

With a httpd Program pid=51656 Program, for example , Need to limit httpd cpu Use 2,3, mem Use 1 Limit ,net Restricted use cg3 Existing configuration content in . The schematic diagram is as shown in the figure

 ##  Limit cpu、mem Use
 cd /sys/fs/cgroup/cpu_mem_cg
 mkdir cg2
 cd cg2
 /bin/echo 2-3 > cpuset.cpus
 /bin/echo 1 > cpuset.mems
 /bin/echo 51565 > tasks
 ##  Limit net Use
 cd /sys/fs/cgroup/net/cg3
 /bin/echo 51565 > tasks


reference

linux Resource management cgroups brief introduction

Linux kernel cgroups-v1