Re: [PATCH v3 1/6] mm/sparse-vmemmap: drop VMEMMAP_POPULATE_DAX

[Lance Yang]

On Tue, Sep 29, 2026 at 01:32:26PM +0800, Muchun Song wrote:
>VMEMMAP_POPULATE_DAX currently distinguishes DAX vmemmap population in
>two places: it keeps allocations on the normal path and takes a reference
>when a backing page is supplied for reuse.
>
>After Device DAX switched to the common per-zone shared tail page, both
>conditions can be determined locally. DAX supplies ptpfn for every shared
>tail mapping and requests an allocation only for compound head mappings,
>whose PFNs are not optimizable. Therefore, vmemmap_optimizable_pfn() alone
>selects the correct allocation path.
>
>When ptpfn is supplied, the caller is reusing an existing backing page.
>Once the slab allocator is available, take a reference for each reused
>mapping to balance the release performed by vmemmap_free(). Although the
>buddy allocator is available before slab, no vmemmap population occurs in
>that interval. Earlier mappings are backed by memblock/reserved memory and
>do not need page reference accounting.
>
>Remove VMEMMAP_POPULATE_DAX and the flags argument from the vmemmap
>population helpers.
>
>Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
>Acked-by: Qi Zheng <qi.zheng@xxxxxxxxx>
>---

LGTM! Feel free to add:

Reviewed-by: Lance Yang <lance.yang@xxxxxxxxx>