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SubjectRe: [RFC] How to handle the rules engine for cgroups
On Mon, Jul 14, 2008 at 10:44:43AM -0400, David Collier-Brown wrote:
> Vivek Goyal wrote:
>> If admin has decided to group applications and has written the rules for
>> it then applications should not know anything about grouping. So I think
>> application writing an script for being placed into the right group should
>> be out of question. Now how does an admin write a wrapper around existing
>> application without breaking anything else.
>
> In the Solaris world, processes are placed into cgroups (projects) by
> one of two mechanisms:
>
> 1) inheritance, with everything I create in my existing project.
> To get this started, there is a mechanism under login/getty/whatever
> reading the /etc/projects file and, for example, tossing user davecb
> into a "user.davecb" project.
>

Placing the login sessions in right cgroup based on uid/gid rules is
probably easy as check needs to be placed only on system entry upon login
(Pam plugin should do). And after that any job started by the user
will automatically start in the same cgroup.

> 2) explicit placement with newtask, which starts a program or moves
> a process into a project/cgroup
>

explicit placement of task based on application type will be tricky.

> I have a "bg" project which I use for limiting resource consumption of
> background jobs, and a background command which either starts or moves
> jobs, thusly:
>
> case "$1" in
> [0-9]*) # It's a pid
> newtask -p bg -c $1

Ok, this is moving of tasks from one cgroup to other based on pid. This
is really easy to do through cgroup file system. Just a matter of writing
to task file.

> ;;
> *) # It's a command-line
> newtask -p bg "$@" &
> ;;

So here a user explicitly invokes the wrapper passing it the targeted
cgroup and the application to be launched in that cgroup. This should work
if there is a facility if user has created its own cgroups (lets say
under user controlled cgroup dir in the hierarchy) and user explicitly
wants to control the resources of applications under its dir. For example,

/mnt/cgroup
| |
gid1 gid2
| | | |
uid1 uid2 uid3 uid4
| |
proj1 proj2

Here probably admin can write the rules for how users are allocated the
resources and give ability to users to create subdirs under their cgroups
where users can create more cgroups and can do their own resource
management based on application tasks and place applications in the right
cgroup by writing wrappers as mentioned by you "newtask".

But here there is no discrimination of application type by admin. Admin
controls resource divisions only based on uid/gid. And users can manage
applications within their user groups. In fact I am having hard time thinking
in what kind of scenarios, there is a need for an admin to control
resource based on application type? Do we really need setups like, on
a system databases should get network bandwidth of 30%. If yes, then
it becomes tricky where admin need to write a wrapper to place the task
in right cgroup without application/user knowing it.

Thanks
Vivek


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