Re: [RFC] How to handle the rules engine for cgroups

[KAMEZAWA Hiroyuki]

On Tue, 1 Jul 2008 15:11:26 -0400
Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:

> Hi,
> 
> While development is going on for cgroup and various controllers, we also
> need a facility so that an admin/user can specify the group creation and
> also specify the rules based on which tasks should be placed in respective
> groups. Group creation part will be handled by libcg which is already
> under development. We still need to tackle the issue of how to specify
> the rules and how these rules are enforced (rules engine).
> 
> I have gathered few views, with regards to how rule engine can possibly be
> implemented, I am listing these down.
> 
> Proposal 1
> ==========
> Let user space daemon hanle all that. Daemon will open a netlink socket
> and receive the notifications for various kernel events. Daemon will
> also parse appropriate admin specified rules config file and place the
> processes in right cgroup based on rules as and when events happen.
> 
> I have written a prototype user space program which does that. Program 
> can be found here. Currently it is in very crude shape.
> 
> http://people.redhat.com/vgoyal/misc/rules-engine-daemon/user-id-based-namespaces.patch
> 
> Various people have raised two main issues with this approach.
> 
> - netlink is not a reliable protocol.
> 	- Messages can be dropped and one can loose message. That means a
> 	  newly forked process might never go into right group as meant.
> 
> - How to handle delays in rule exectuion?
> 	- For example, if an "exec" happens and by the time process is moved to
> 	 right group, it might have forked off few more processes or might
> 	 have done quite some amount of memory allocation which will be
>    	 charged to the wring group. Or, newly exec process might get
>  	 killed in existing cgroup because of lack of memory (despite the
> 	 fact that destination cgroup has sufficient memory).
> 
Hmm, can't we rework the process event connector to use some reliable
fast interface besides netlink ? (I mean an interface like eventpoll.)
(Or enhance netlink ? ;)

Because "a child inherits parent's" rule is very strong, I think the amount
of events we have to check is much less than we get report. Can't we add some
filter/assumption here ?

BTW, the placement of proc_exec_connector() is not too late ? It seems memory for
creating exec-image is charged to original group...

Thanks,
-Kame

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