linux-kernel - Re: [PATCH V2] Documentation: cgroups: Add notes on removing PIDs from tasks and cgroups requiring setup

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Message-ID: <AANLkTimRDfqm4wCRP1rw8FVbY81=by+V8p5jVEhCLL2G@mail.gmail.com>
Date:	Thu, 10 Mar 2011 19:00:09 -0800
From:	Paul Menage <menage@...gle.com>
To:	Eric B Munson <emunson@...bm.net>
Cc:	linux-doc@...r.kernel.org, containers@...ts.linux-foundation.org,
	rdunlap@...otime.net, linux-kernel@...r.kernel.org,
	kirill@...temov.name, mike@...rato.com
Subject: Re: [PATCH V2] Documentation: cgroups: Add notes on removing PIDs
 from tasks and cgroups requiring setup

On Thu, Mar 10, 2011 at 9:07 AM, Eric B Munson <emunson@...bm.net> wrote:
> The cgroup documentation does not specify how a process can be removed from a
> particular group.  This patch adds a note at the end of the simple example
> about how this is done.  Also, some cgroups (like cpusets) require user input
> before a new group can be used.  This is noted in the patch as well.
>
> Signed-off-by: Eric B Munson <emunson@...bm.net>

Acked-by: Paul Menage <menage@...gle.com>

> ---
> Changes from V1:
>  Rework the note about removing a process from a cgroup
>  Add note about ns cgroup causing failure when moving processes between groups
>
>  Documentation/cgroups/cgroups.txt |   12 ++++++++++++
>  1 files changed, 12 insertions(+), 0 deletions(-)
>
> diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
> index 44b8b7a..cbdfb7d 100644
> --- a/Documentation/cgroups/cgroups.txt
> +++ b/Documentation/cgroups/cgroups.txt
> @@ -349,6 +349,10 @@ To mount a cgroup hierarchy with all available subsystems, type:
>  The "xxx" is not interpreted by the cgroup code, but will appear in
>  /proc/mounts so may be any useful identifying string that you like.
>
> +Note: Some subsystems do not work without some user input first.  For instance,
> +if cpusets are enabled the user will have to populate the cpus and mems files
> +for each new cgroup created before that group can be used.
> +
>  To mount a cgroup hierarchy with just the cpuset and memory
>  subsystems, type:
>  # mount -t cgroup -o cpuset,memory hier1 /dev/cgroup
> @@ -426,6 +430,14 @@ You can attach the current shell task by echoing 0:
>
>  # echo 0 > tasks
>
> +Note: Since every task is always a member of exactly one cgroup in each
> +mounted hierarchy, to remove a task from its current cgroup you must
> +move it into a new cgroup (possibly the root cgroup) by writing to the
> +new cgroup's tasks file.
> +
> +Note: If the ns cgroup is active, moving a process to another cgroup can
> +fail.
> +
>  2.3 Mounting hierarchies by name
>  --------------------------------
>
> --
> 1.7.1
>
>
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