Re: [7/8,v3] NUMA Hotplug Emulator: extend memory probe interface to support NUMA

Shaohui Zheng
2010-11-18T06:09:56Z

On Wed, Nov 17, 2010 at 01:18:50PM -0800, David Rientjes wrote:
> On Wed, 17 Nov 2010, Dave Hansen wrote:
>
> > The other thing that Greg suggested was to use configfs. Looking back
> > on it, that makes a lot of sense. We can do better than these "probe"
> > files.
> >
> > In your case, it might be useful to tell the kernel to be able to add
> > memory in a node and add the node all in one go. That'll probably be
> > closer to what the hardware will do, and will exercise different code
> > paths that the separate "add node", "then add memory" steps that you're
> > using here.
> >
>
> That seems like a seperate issue of moving the memory hotplug interface
> over to configfs and that seems like it will cause a lot of userspace
> breakage. The memory hotplug interface can already add memory to a node
> without using the ACPI notifier, so what does it have to do with this
> patchset?

Agree with you, I do not suggest to implement it in this patchset.

>
> I think what this patchset really wants to do is map offline hot-added
> memory to a different node id before it is onlined. It needs no
> additional command-line interface or kconfig options, users just need to
> physically hot-add memory at runtime or use mem= when booting to reserve
> present memory from being used.

I already send out the implementation in another email, you can help to do
a review.

>
> Then, export the amount of memory that is actually physically present in
> the e820 but was truncated by mem= and allow users to hot-add the memory
> via the probe interface. Add a writeable 'node' file to offlined memory
> section directories and allow it to be changed prior to online.

for memory offlining, it is a known diffcult thing, and it is not supported
well in current kernel, so I do not suggest to provide the offline interface
in the emulator, it just take more pains. We can consider to add it when
the memory offlining works well.

--
Thanks & Regards,
Shaohui