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| author | Michael Kerrisk <mtk.manpages@gmail.com> | 2016-10-05 14:28:25 +0200 |
|---|---|---|
| committer | Michael Kerrisk <mtk.manpages@gmail.com> | 2016-10-07 23:01:34 +0200 |
| commit | 8bff71400e8d794f6133230aac5c255c6f32827e (patch) | |
| tree | 81417fca78d9bdc07c22ad9360d64977dffe3b4b | |
| parent | 28bcfee96db682637fab704e0e74dcbe5e1ee9cc (diff) | |
| download | man-pages-8bff71400e8d794f6133230aac5c255c6f32827e.tar.gz | |
cgroups.7: Rework intro text a little
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
| -rw-r--r-- | man7/cgroups.7 | 82 |
1 files changed, 43 insertions, 39 deletions
diff --git a/man7/cgroups.7 b/man7/cgroups.7 index 48f4682244..067bbfbdcb 100644 --- a/man7/cgroups.7 +++ b/man7/cgroups.7 @@ -28,48 +28,14 @@ cgroups \- Linux control groups .SH DESCRIPTION Control cgroups, usually referred to as cgroups, -are a Linux kernel feature which provides for grouping of processes and -resource tracking and limitations for those groups. -While several systems have been introduced to help in configuring and -managing cgroups, the kernel's cgroup interface is provided through +are a Linux kernel feature which which allow processes to +be organized into hierarchical groups whose usage of +various types of resources can then be limited and monitored. +The kernel's cgroup interface is provided through a pseudo-filesystem called cgroupfs. Grouping is implemented in the core cgroup kernel code, while resource tracking and limits are implemented in -a set of per-resource-type subsystems (memory, CPU, and so on) which may be -enabled as separate hierarchies, or joined into comounted hierarchies. - -Each hierarchy constitutes a separate mount of the cgroup filesystem, -with the subsystems enabled in that hierarchy listed in the mount options. -For each mounted hierarchy, -the directory tree mirrors the control group hierarchy. -Each control group is represented by a directory, with each of its child -control cgroups represented as a child directory. -For instance, -.IR /user/joe/1.session -represents control group -.IR 1.session , -which is a child of cgroup -.IR joe , -which is a child of -.IR /user . -Under each cgroup directory is a set of files which can be read or -written to, reflecting resource limits and a few general cgroup -properties. - -In general, cgroup limits are hierarchical, meaning that the limits placed on -.IR /user/joe -cannot be exceeded by -.IR /usr/joe/1.session . -There are currently exceptions to this rule, -but stricter adherence is a goal as cgroups are being largely reworked. - -In addition, cgroups can be mounted with no bound subsystem, in which case -they serve only to track processes. -An example of this is the -.I name=systemd -cgroup which is used by -.BR systemd (1) -to track services and user sessions. +a set of per-resource-type subsystems (memory, CPU, and so on). .\" .SS Terminology A @@ -96,6 +62,11 @@ renaming subdirectories within the cgroup filesystem. At each level of the hierarchy, attributes (e.g., limits) can be defined; these attributes may govern or propagate to child cgroups and their descendants in the hierarchy. + +The limits, control, and accounting provided by cgroups are hierarchical. +Thus, for example, the limits placed on +a cgroup at a higher level in the hierarchy cannot be exceeded +by descendant cgroups. .\" .SS Cgroups version 1 and version 2 The initial release of the cgroups implementation was in Linux 2.6.24. @@ -130,6 +101,39 @@ that are supported under version 2, while also using version 1 controllers where version 2 does not yet support those controllers. .\" +.SS Cgroups version 1 +Under cgroups v1, each controller may be mounted against a separate +cgroup filesystem that provides its own hierarchical organization of the +processes on the system. +It is also possible comount multiple (or even all) cgroups v1 controllers +against the same cgroup filesystem, meaning that the comounted controllers +manage the same hierarchical organization of processes. + +For each mounted hierarchy, +the directory tree mirrors the control group hierarchy. +Each control group is represented by a directory, with each of its child +control cgroups represented as a child directory. +For instance, +.IR /user/joe/1.session +represents control group +.IR 1.session , +which is a child of cgroup +.IR joe , +which is a child of +.IR /user . +Under each cgroup directory is a set of files which can be read or +written to, reflecting resource limits and a few general cgroup +properties. + +In addition, in cgroups v1, +cgroups can be mounted with no bound subsystem, in which case +they serve only to track processes. +An example of this is the +.I name=systemd +cgroup which is used by +.BR systemd (1) +to track services and user sessions. +.\" .SS Tasks (threads) versus processes In cgroups v1, a distinction is drawn between .I processes |