Re: [PATCH 0/2] resource control file system - aka containers on top of nsproxy!

[Srivatsa Vaddagiri]

On Fri, Mar 09, 2007 at 02:16:08AM +0100, Herbert Poetzl wrote:
> On Thu, Mar 08, 2007 at 05:00:54PM +0530, Srivatsa Vaddagiri wrote:
> > On Thu, Mar 08, 2007 at 01:50:01PM +1300, Sam Vilain wrote:
> > > 7. resource namespaces
> > 
> > It should be. Imagine giving 20% bandwidth to a user X. X wants to
> > divide this bandwidth further between multi-media (10%), kernel
> > compilation (5%) and rest (5%). So,
> 
> sounds quite nice, but ...
> 
> > > Is the subservient namespace's resource usage counting against ours too?
> > 
> > Yes, the resource usage of children should be accounted when capping
> > parent resource usage.
> 
> it will require to do accounting many times
> (and limit checks of course), which in itself
> might be a way to DoS the kernel by creating
> more and more resource groups

I was only pointing out the usefullness of the feature and not
necessarily saying it -should- be implemented! Ofcourse I understand it
will make the controller complicated and thats why probably none of the
recontrollers we are seeing posted on lkml don't support hierarchical
res mgmt.

> > > Can we dynamically alter the subservient namespace's resource
> > > allocations?
> > 
> > Should be possible yes. That lets user X completely manage his
> > allocation among whatever sub-groups he creates.
> 
> what happens if the parent changes, how is
> the resource change (if it was a reduction)
> propagated to the children?
>
> e.g. your guest has 1024 file handles, now
> you reduce it to 512, but the guest had two
> children, both with 256 file handles each ...

I believe CKRM handled this quite neatly (by defining child shares to be
relative to parent shares). 

In your example, 256+256 add up to 512 which is within the parent's new limit, 
so nothing happens :) You also picked an example of exhaustible/non-reclaimable 
resource, which makes it hard to define what should happen if parent's limit 
goes below 512. Either nothing happens or perhaps a task is killed,
don't know. In case of memory, I would say that some of child's pages may 
get kicked out and in case of cpu, child will start getting fewer
cycles.

> > The patches should give visibility to both nsproxy objects (by showing
> > what tasks share the same nsproxy objects and letting tasks move across
> > nsproxy objects if allowed) and the resource control objects pointed to
> > by nsproxy (struct cpuset, struct cpu_limit, struct rss_limit etc).
> 
> the nsproxy is not really relevant, as it
> is some kind of strange indirection, which
> does not necessarily depict the real relations,
> regardless wether you do the re-sharing of
> those nsproies or not .. 

So what are you recommending we do instead? My thought was whatever is
the fundamental unit to which resource management needs to be applied,
lets store resource parameters (or pointers to them) there (rather than 
duplicating the information in each task_struct).

-- 
Regards,
vatsa
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