Hello,

On Fri, Jun 22, 2018 at 11:00:03AM +0800, Waiman Long wrote:

On 06/21/2018 05:20 PM, Peter Zijlstra wrote:

quoted

quoted

As for the inconsistency between the real root and the container root,
this is true for almost all the controllers. So it is a generic problem.
One possible solution is to create a kind a pseudo root cgroup for the
container that looks and feels like a real root. But is there really a
need to do that?

I don't really know. I thought the idea was to make containers
indistinguishable from a real system. Now I know we're really rather far
away from that in reality, and I really have no clue how important all
that is.

That will certainly be the ideal.

Sure, ideal in theoretical sense; however, the practical cost-benefit
ratio of trying to make containers indistinguishible from system
doesn't seem enough to justify the effort.  Not yet anyway.  It'd be
nice to not paint ourselves into a corner where we can't get the
equivalence without major interface changes later but I think that's
about the extent we should go for now.

quoted

It all depends on how exactly this works; is it like I assumed, that
this file is owned by the parent instead of the current directory? And
that if you namespace this, you have an effective read-only file?

Yes, that is right.

quoted

Then fixing the inconsistency is trivial; simply provide a read-only
file for the actual root cgroup too.

And if the solution is trivial, I don't see a good reason not to do it.

Do you mean providing a flag like READONLY_AT_ROOT so that it will be
read-only at the real root? That is an cgroup architectural decision
that needs input from Tejun. Anyway, this issue is not specific to this
patchset and I would like to break it out as a separate discussion
independent of this patchset.

Yeah, it's a larger problem than cpuset and different controllers
trying it in different ways isn't a good idea anyway.  Let's shelve
this topic for now.

Thanks.

-- 
tejun
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