Re: [RFC PATCH 0/3] Add Support for Multiple DC Regions

[Alireza Sanaee <alireza.sanaee@huawei.com>]

On Mon, 12 Jan 2026 14:23:55 -0800
Anisa Su <anisa.su887@gmail.com> wrote:

Hi Anisa,

> On Fri, Dec 12, 2025 at 04:07:32PM -0600, Ira Weiny wrote:
> > Anisa Su wrote:  
> > > On Thu, Dec 04, 2025 at 11:28:40AM -0600, Ira Weiny wrote:  
> > > > anisa.su887@ wrote:  
> > > > > From: Anisa Su <anisa.su@samsung.com>
> > > > >   
> [snip] 
> > > > Unfortunately none of the details presented in this cover letter really
> > > > show why the kernel needs this additional complexity.
> > > > 
> > > > Can you go into more details on the use cases of multiple partitions?
> > > >   
> > > From what I understand, the motivation for DCD as a whole has always been a
> > > blocker for the entire series. However, this year we've seen multiple vendors
> > > demo memory pooling/sharing at SC,25[1], as well as the development of a 
> > > controller that supports "memory pooling and sharing across 
> > > multiple hosts" from Montage[2].  
> > 
> > That is great!  Do we know if they used the patches which have been
> > submitted?  Do we know if the user interfaces were sufficient?  
> 
> Sorry for the delay! While I don't know the details of the software
> stack used in those demos, I think the root of the question "Do we know
> if the user interfaces were sufficient" goes back to the missing use
> case for DCD.
> 
> So then, can I ask: how can I demonstrate a reasonable use case?
> Ex: bringing up Kubernetes pods using this patchset on real hw?
> Or something else?
> ^ This is also a question for the community, so everyone please chime in :)
> >  
> > How will this memory be presented with the new DAX changes being proposed?
> >  
> From the call today, there seemed to be general agreement that the changes
> proposed by Gregory's patches are a promising direction for DCD, bc it
> allows hotplug/unplug capabilities without needing to route it through
> the DAX subsystem.
> I haven't looked at those patches yet, but from what was
> discussed today, plan to move forward based on that. Are those the changes
> you were referring to? Or the special famfs dax type you mentioned
> below?
> > > 
> > > The flexibility and control provided by multiple partitions is
> > > an important capability of DCD for enabling composable memory 
> > > infrastructures. IMO, adding multi-partition support back in from v8 or
> > > picking up this patchset would strengthen the series.
> > > 
> > > Let me know if this proposal sounds fair? Otherwise I can
> > > separate out the 2 patches that are bug fixes.  
> > 
> > After RC1 could you rebase the series and fold the bug fixes in?
> >   
> Yep, working on rebasing the series now and will send RC2 with the bug
> fixes.
> > Before we get to multiple DCD partitions the interface for DAX devices
> > needs to be settled.  In the last community call we were discussing a
> > special famfs dax type I believe.  Has any work been done on that?
> >  
> That makes sense to me; I missed that call, so I'm not familiar with the
> famfs dax type, but as I mentioned above, it sounds like Gregory's
> patch set is a good solution to this, so I'll explore how to integrate
> with that first.
> 
> > For multi-partitions we need some review on the partition (region) names
> > because you made a change which would be incompatible with the base
> > series.  But it would be good to get single partitions landed and then
> > multiple partitions as you have added.
> >   
> Sounds good. For RC2, I'll keep it simple and just rebase + bug fixes.
Thanks Anisa. I was also about to look into the rebasing as well.
> > > Also, apologies if these points have already been discussed. I've not been
> > > following this series for very long, so forgive the ignorance as I try to
> > > catch up. If you can think of any materials/documentation outside of the
> > > mailing list or open collab sync notes that would help fill in the gaps,
> > > please let me know :)  
> > 
> > NP this has been a while.  I've been looking for someone to take the
> > series who is more familiar with the use cases.
> > 
> > I look forward to you posting a new series with the support you feel you
> > need.
> > 
> > Ira
> >   
> Thanks Ira, I will definitely have to keep bothering you, though I'll
> try to keep it to a minimum.
> 
> Thanks,
> Anisa
> 
> [snip]