[Devel] Re: Fw: cgroups and dbus

[Li Zefan]

>> It seems what you asked was an example of cgroup.
>> Maybe the simplest cgroup in the kernel is CONFIG_CGROUP_CPUACCT. 
>> (kernel/sched.c) The next one is CGROUP_DEVICE (security/device_cgroup.c)
>>
>> Documentation under Documentation/cgroups/ is always taken care to be updated.
>> If you notice some description is unclear or obsolete, please report it.
> 
> I found my problem with the example there,
> 
> my machine has no RAM on node 0.
> 
> Can I suggest that the example might be better if it uses node 0 ? or had a
> note saying that if you have no memory on node 1 that it will fail with:
> "/bin/echo: write error: No space left on device" ?
> 
> Also it would be a good idea if the example pointed out that the parent to
> 'sh' is in the cgroup Charlie also.
> 
> Heres a patch:
> 
>>From e6e430d3c3e865f21dffc75ff090bb283a4f32a0 Mon Sep 17 00:00:00 2001
> From: Ian Molton <ian.molton at collabora.co.uk>
> Date: Tue, 22 Dec 2009 10:31:20 +0000
> Subject: [PATCH] cgroup: Clarify documentation
> 
>         This patch clarifies the cgroup documentation, giving some info on why
> the example given may fail, and a little more detail on its expected behaviour.
> 
> Signed-off-by: Ian Molton <ian.molton at collabora.co.uk>
> ---
>  Documentation/cgroups/cgroups.txt |    9 ++++++++-
>  1 files changed, 8 insertions(+), 1 deletions(-)
> 
> diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
> index 0b33bfe..8ac8615 100644
> --- a/Documentation/cgroups/cgroups.txt
> +++ b/Documentation/cgroups/cgroups.txt
> @@ -309,7 +309,9 @@ the "cpuset" cgroup subsystem, the steps are something like:
> 
>  For example, the following sequence of commands will setup a cgroup
>  named "Charlie", containing just CPUs 2 and 3, and Memory Node 1,
> -and then start a subshell 'sh' in that cgroup:
> +and then start a subshell 'sh' in that cgroup. Note that if you have no RAM
> +on node 1 or dont have 4 CPUs you will want to modify the example
> +accordingly:
> 
>    mount -t cgroup cpuset -ocpuset /dev/cgroup
>    cd /dev/cgroup
> @@ -317,7 +319,12 @@ and then start a subshell 'sh' in that cgroup:
>    cd Charlie
>    /bin/echo 2-3 > cpuset.cpus
>    /bin/echo 1 > cpuset.mems
> +  # If you have no RAM on Node 0 the next command will return an error, eg.
> +  # write error: No space left on device

Please patch Documentation/cgroups/cpusets.txt instead, and CC
the maintainers.

>    /bin/echo $$ > tasks
> +  # The current shell is now in cgroup Charlie. You can check this with:
> +  cat /proc/self/cgroup

This is a duplicate. The documenation just below has showed
the use of /proc/self/cgroup.

> +  # Now launch a subshell which should inherit the cgroup:
>    sh
>    # The subshell 'sh' is now running in cgroup Charlie
>    # The next line should display '/Charlie'
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