Re: [PATCH] docs/cxl: Add serial number for persistent-memdev

[Dan Williams <dan.j.williams@intel.com>]

Jonathan Cameron wrote:
> On Wed, 5 Mar 2025 18:35:40 +0800
> Yuquan Wang <wangyuquan1236@phytium.com.cn> wrote:
> 
> > > 
> > > On Tue, 4 Mar 2025 14:22:48 +0800
> > > Yuquan Wang <wangyuquan1236@phytium.com.cn> wrote:
> > >   
> > > > > 
> > > > > On Thu, Feb 20, 2025 at 04:12:13PM +0000, Jonathan Cameron wrote:    
> > > > > > On Mon, 17 Feb 2025 19:20:39 +0800
> > > > > > Yuquan Wang <wangyuquan1236@phytium.com.cn> wrote:
> > > > > >     
> > > > > > > Add serial number parameter in the cxl persistent examples.
> > > > > > > 
> > > > > > > Signed-off-by: Yuquan Wang <wangyuquan1236@phytium.com.cn>    
> > > > > > Looks good.  I've queued it up on my gitlab staging tree, but
> > > > > > Michael if you want to pick this one directly that's fine as well.    
> > > > > 
> > > > > See no reason to, I was not even CC'd.    
> > > > 
> > > > Hi, Michael
> > > > 
> > > > I'm sorry, this is my fault. I used "get_maintainer.pl" to check this
> > > > patch's maintainers but it shows "No maintainers found, printing recent
> > > > contributors". 
> > > >   
> > > I usually stage up multiple series together and send on to Michael.
> > > So it was be being lazy for a minor change rather than anything much
> > > that you did wrong.
> > > 
> > > If I get time I'll post a series with this a few other patches
> > > later today.  
> > > 
> > > Jonathan
> > >   
> > Thank you!
> > 
> > BTW, I found a corner case in CXL numa node creation.
> > 
> > Condition: 
> > 1) A UMA/NUMA system without SRAT, but with CEDT.CFMWS
> > 2）Enable CONFIG_ACPI_NUMA
> > 
> > Results:
> > 1) acpi_numa_init: the fake_pxm will be 0 and send to acpi_parse_cfmws()
> > 2）If dynamically create cxl ram region, the cxl memory would be assigned
> > to node0 rather than a new node
> > 
> > Confusions:
> > 1) Is a numa system a requirement for CXL memory usage?
> 
> Obviously discussion has gone on elsewhere, but I'd say in general it
> would be a bad idea to not have an SRAT because the moment we add CXL
> it is definitely a NUMA system and we want the Generic Port entry to
> allow us to get perf information.
> 
> So I wouldn't mind if we fail CXL init in this case, but maybe
> it is worth papering over things.

I think that is too severe. If a driver has a path to advertise
resources, even in a less than ideal way, it should make every effort to
do that. There are plenty of ways for the NUMA information to fail, that
does not mean the memory needs to be prevented from coming online. Let
the end user decide if lack of performance information is fatal.