Re: [RFC][PATCH] NOOP cgroup subsystem

[Li Zefan <lizf@cn.fujitsu.com>]

KAMEZAWA Hiroyuki wrote:
> How about this idea ? Any comments are welcome.
> 
> -Kame
> 
> ==
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> 
> Add an NO OPERATION cgroup subsystem.
> 
> Cgroup itself is providing a feature to attach a task(PID) to some class.
> This feature itself is very useful but "no operation" cgroup is not supported
> now other than debug cgroup. (But debug cgroup should be for DEBUG. distro
> may not configure it.)
> 

Then how can we make sure distro will configure this noop subsys. :)

Or we can make the debug subsys always configured if CONFIG_CGROUP=y ?
The debug system adds no runtime overhead, and it's about 100 lines
of code only.

> Motivation: Simply classify Applications by cgroup
>   When using cgroup for classifying applications, some kind of "control" or
>   "account" subsys must be used. For flexible use of cgroup's nature of
>   classifying applications, NOOP is useful. It can be used regardless of
>   resource accounting unit or name spaces or some controls.
>   IOW, NOOP cgroup allows users to tie PIDs with some nickname.
> 
> After this, application can be checked whether it's still alive or not by
> 
> 	mount -t cgroup none /var/apps noop
> 	mkdir /var/apps/mydaemon
> 	echo 0 > /var/apps/mydaemon
> 	/etc/init.d/mydaemon start
> 	exit
> 
> This can be used as the same technique of "recording pid into /var/run/xxx.pid"
> and not necessary to remove stale files. If mydaemon dies, tasks file will
> be empty and notify_on_release handler can be used.
> 
> I myself want to use this for replacement of "ps -elf | grep" if libcgroup supports
> ps under cgroup.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>