Re: [PATCH v3 0/6] mm: Unify device DAX and HugeTLB vmemmap population paths

[Muchun Song <muchun.song@linux.dev>]

> On Sep 30, 2026, at 05:32, Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> On Tue, 29 Sep 2026 13:32:25 +0800 Muchun Song <songmuchun@bytedance.com> wrote:
> 
>> This v3 is based on mm-new commit 2ddb90ee544a, which contains v5 of
>> "mm: Switch device DAX to section-based vmemmap optimization" [1].
>> 
>> This series is split out from the earlier, larger series "mm: Generalize
>> HVO for HugeTLB and device DAX" [2]. While the parent series generalizes
>> vmemmap optimization across HugeTLB and device DAX, this subset addresses
>> a single, self-contained step: unifying their vmemmap population paths.
>> 
>> After the preceding Device DAX conversion, both HugeTLB and Device DAX
>> describe optimized vmemmap mappings through memory-section metadata and
>> use per-zone shared tail vmemmap pages. The generic code, however, still
>> carries a Device DAX-specific population flag and compound-page population
>> path, along with arguments and helpers needed only by that path.
>> 
>> This series first removes VMEMMAP_POPULATE_DAX and moves selection and
>> reference handling for the shared tail page into the common vmemmap
>> population path. It then removes the generic Device DAX-specific
>> compound-page population path and routes section vmemmap population
>> through vmemmap_populate(). The powerpc radix path continues to use its
>> architecture-specific compound-page population implementation for
>> optimizable sections.
>> 
>> The remaining patches remove the unused ptpfn argument, open-code
>> vmemmap_populate_address() now that no caller needs its returned PTE, and
>> add a warning for inconsistent zone initialization of shared tail vmemmap
>> pages.
>> 
>> This is the fourth smaller step toward the broader HVO generalization.
>> After this series, HugeTLB and Device DAX use the same population model
>> instead of parallel generic paths, while powerpc keeps its
>> architecture-specific implementation.
> 
> afaict the whole series is "no functional changes intended".  Apart
> from [6/6]'s new WARN_ON.

Yes.

> 
> And [3/6] is the one which could cause unintended fuctional changes!

Understood. However, the resulting vmemmap layout is intended to remain
unchanged.

> 
> Thanks.  I'll queue it.  Reluctantly.  We're up to 688 MM patches this
> cycle and it's time to stop.

Thanks for taking it despite the load.

Muchun,
Thanks.