Re: [PATCH 04/11] mm/sparse-vmemmap: prepare DAX vmemmap population for section orders

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

On 8/31/26 3:53 PM, Muchun Song wrote:
> Device DAX still uses vmemmap_populate_compound_pages() to populate its
> compound-page vmemmap mappings. That helper allocates the head and first
> tail vmemmap pages explicitly, then reuses the first tail page for the
> remaining tail page mappings.
> 
> Device DAX is being moved to the section-based vmemmap optimization
> infrastructure, but it cannot switch to the generic section-based
> population path yet. Once a later patch records the DAX compound-page
> geometry in the section order, DAX head and first-tail PFNs can look
> optimizable to the generic helpers as well.
> 
> Add a DAX-specific population flag for this transition. It keeps DAX
> head/first-tail allocations on the normal vmemmap allocation path, while
> preserving the existing page reference for reused DAX tail mappings.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
>   mm/sparse-vmemmap.c | 27 +++++++++++++++------------
>   1 file changed, 15 insertions(+), 12 deletions(-)
> 

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

Thanks,
Qi