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

David Rientjes
2010-11-17T21:19:09Z

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?

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.

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.