Re: [PATCH v2 2/6] mm/sparse-vmemmap: support device DAX in common vmemmap path

[Qi Zheng <qi.zheng@linux.dev>]

On 9/24/26 3:52 PM, Muchun Song wrote:
> The common vmemmap population path cannot yet handle optimized Device DAX
> mappings on its own. It uses pfn_to_zone() to find the shared tail page,
> but Device DAX populates its vmemmap at runtime before the ZONE_DEVICE span
> is initialized.
> 
> Teach the common path to use device_zone() for runtime optimized vmemmap
> population while retaining pfn_to_zone() for early boot. This allows the
> same path to support both early boot mappings and Device DAX.
> 
> The backing PFN supplied by the Device DAX-specific population path is no
> longer used, allowing the redundant lookup and population code to be
> removed later.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
> v2:
> - Expand comments around slab initialization to explain zone lookup and
>    page refcounting (suggested by Qi Zheng)
> ---
>   mm/sparse-vmemmap.c | 56 +++++++++++++++++++++++++--------------------
>   1 file changed, 31 insertions(+), 25 deletions(-)

Acked-by: Qi Zheng <qi.zheng@linux.dev>

Thanks,
Qi