Re: [RFC PATCH 0/4] cxl/extent: Enable and validate multi-extent DCDs

[Gregory Price]

On Fri, May 01, 2026 at 03:00:07PM -0700, Anisa Su wrote:
> 
> 4. If we allow non-tagged extents (as this patchset allows):
> 	- can non-tagged extents be partially claimed by a DAX device that
> 	  doesn't have a specified tag?
> 
> Ira's original patchset introduced minimal changes to DAX logic. Introducing
> tag-awareness to
> DAX resize logic may require adding more conditional statements, 
> especially if we allow both NULL and non-NULL tags (but there might be a nice
> way to do it;
> This is just my initial impression, I haven't tried implementing it, and I could
> certainly look into it more)
>

There is a lot of confusion built around tagged vs untagged.

Can we at least agree if a DC Extent has a NULL tag:

    1 extent = 1 DAX device

And we just denote that a NULL UUID is a sentinel value ("Unknown").

e.g.:  there's no such thing as a "partial claim by a dax device".
       either the extent is tagged (part of a set), or it is its own
       thing without any identifying data around it (probably intended
       to be hotplugged as system ram or something, userland problem).

alternatively:  do not allow untagged extents, because we can't make
sense of what to do with it.

~Gregory