Re: [PATCH v5 00/36] Private Memory NUMA Nodes

[Gregory Price <gourry@gourry.net>]

On Wed, Aug 12, 2026 at 02:01:12PM +0200, Pankaj Gupta wrote:
> >
> > Bonus Configuration: HBM device memory tiering
> > ==============================================
> > echo 1 > dax0.0/private       # make the node private
> > echo 0 > dax0.0/adistance     # highest tier
> > echo 1 > dax0.0/reclaim       # reclaim active
> > echo 1 > dax0.0/demotion      # may demote from the node
> > echo 1 > dax0.0/user_numa     # mbind()
> > echo online_movable > dax0.0/state
> > echo 1 > numa/demotion_enabled
> 
> I am bit confused by the HBM device example being discovered as a DAX
> device. Is it to
> only to showcase the use-case? Or we see HBM device is actually
> expected to be discovered as
> DAX device with N_MEMORY_PRIVATE?
> 

"actually expected to be" -> no.  there's no requirement HBM be
discovered and boudn to DAX, DAX is simply a convenient intermediary
to memory-hotplug.  This is at best a demonstration.

A device driver could very well just call memory-hotplug directly,
or its memory could be brought up as a private node via a boot
paremeter (which I have sculpted for v7).  The former is preferred,
but there's a bit of a chicken/egg scenario for bootstrapping.

Most of these UAPI extensions are going to be consolidated into a
debugfs interface for testing purposes only in v7.  I've been working
on aggressive Linux Test Project test expansion to ensure there is no
UAPI regressions.

~Gregory