Re: [RFC][PATCH 2/3] memcg:: seq_ops support for cgroup

[Hirokazu Takahashi <taka@valinux.co.jp>]

Hi,

> > With current interface, my concern is hotplug.
> >
> > File-per-node method requires delete/add files at hotplug.
> > A file for all nodes with _maps_ method cannot be used because
> > maps file says
> > ==
> > The key/value pairs (and their ordering) should not
> >         * change between reboots.
> > ==
> 
> OK, so we may need to extend the interface ...

I also hope it!

Now I'm working on dm-ioband --- I/O bandwidth controller --- and
making it be able to work under cgroups.
I realized it is quite hard to set some specific value to each block
device because each machine has various number of devices and then
some of them are hot-added or hot-removed.

So I hope CGROUP will support some method to handle hot-pluggable
resources.

> The main reason for that restriction (not allowing the set of keys to
> change) was to simplify and speed up userspace parsing and make any
> future binary API simpler. But if it's not going to work, we can maybe
> make that optional instead.
> >
> > And (*read) method isn't useful ;)
> >
> > Can we add new stat file dynamically ?
> 
> Yes, there's no reason we can't do that. Right now it's not possible
> to remove a control file without deleting the cgroup, but I have a
> patch that supports removal.
> 
> The question is whether it's better to have one file per CPU/node or
> one large complex file.
> 
> Paul
> 
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