Re: [PATCH] numa: add 'spm' option for special purpose memory

[David Hildenbrand <david@redhat.com>]

On 02.10.25 16:11, Igor Mammedov wrote:
> On Wed, 24 Sep 2025 18:33:23 +0800
> fanhuang <FangSheng.Huang@amd.com> wrote:
> 
>> Hi David,
>>
>> I hope this email finds you well. It's been several months since Zhigang last discussion about the Special Purpose Memory (SPM) implementation in QEMU with you, and I wanted to provide some background context before presenting the new patch based on your valuable suggestions.
>>
>> Previous Discussion Summary
>> ===========================
>> Back in December 2024, we had an extensive discussion regarding my original patch that added the `hmem` option to `memory-backend-file`. During that conversation, you raised several important concerns about the design approach:
>>
>> Original Approach (December 2024)
>> ----------------------------------
>> - Zhigang's patch: Added `hmem=on` option to `memory-backend-file`
>> - QEMU cmdline example:
>>    -object memory-backend-file,size=16G,id=m1,mem-path=/dev/dax0.0,prealloc=on,align=1G,hmem=on
>>    -numa node,nodeid=1,memdev=m1
>>
>> Your Concerns and Suggestions
>> -----------------------------
>> You correctly identified some issues with the original approach:
>> - Configuration Safety: Users could create problematic configurations like:
>>     -object memory-backend-file,size=16G,id=unused,mem-path=whatever,hmem=on
>>
>> - Your Recommendation: You proposed a cleaner approach using NUMA node configuration:
>>     -numa node,nodeid=1,memdev=m1,spm=on
> 
> that seems to me a bit backwards,
> aka it's just a particular case where node would have SPM memory only,
> which (spm) is not a property of numa node, but rather of memory device attached to it.

The problem is that boot memory is not modeled as a memory device.

-- 
Cheers

David / dhildenb