Re: [PATCH 7/8] dax/kmem: add sysfs interface for runtime hotplug state control

["David Hildenbrand (Red Hat)" <david@kernel.org>]

On 1/23/26 01:43, Gregory Price wrote:
> On Thu, Jan 22, 2026 at 11:49:48PM +0100, David Hildenbrand (Red Hat) wrote:
>>
>> I'm merely wondering why, in the new world, you would even want the offline
>> state.
>>
>> So what are the use cases for that?
>>
> 
> I don't have one, and in the 5-patch series I killed it.  You are right,
> it makes no sense.
> 
> However:
> 
>> Why would user space possibly want that? [plugged-in offline blocks]
>>
> 
> I don't think anyone does.
> 
> This is baggage.
> 
> The CXL driver auto-creates dax_kmem w/ offline memory blocks
> 
> Changing this behavior breaks existing systems :[
> 
>> Can't ndctl just use the old (existing) interface if such an operation is
>> requested, and the new one (you want to add) when we want to do something
>> reasonable (actually use system ram? :) ).
> 
> I think we're in agreement, I think I'm doing a poor job of explaining
> the interconnected issues.
> 
> summarizing the long email:
> 
>     cxl/region + dax/cxl.c + dax/bus.c auto-probe baggage for
>     BIOS-configured regions prevents any userland policy from
>     from being plumbed from cxl to dax.  There's no interposition step.
> 
> So yes - new interfaces would resolve this and the old interfaces
> could be left for compat.

Great!

-- 
Cheers

David