Re: [PATCH 1/2] mm/mm_init: factor out memmap_init_page_from_template()

[Balbir Singh <balbirs@nvidia.com>]

On Thu, Nov 05, 2026 at 08:06:14PM +0800, Li Zhe wrote:
> ZONE_DEVICE memmap initialization already uses a reusable struct page
> template when initializing compound tail pages.  The template mostly
> contains invariant state, but a few fields still depend on the target
> PFN and must be refreshed before copying the template into each
> destination struct page.
> 
> Factor that operation into memmap_init_page_from_template() so other
> boot-time memmap initialization paths can reuse the same helper.
> 
> No functional change intended.
> 
> Signed-off-by: Li Zhe <lizhe.67@bytedance.com>
> ---
>  mm/mm_init.c | 29 +++++++++++++++--------------
>  mm/mm_init.h |  2 ++
>  2 files changed, 17 insertions(+), 14 deletions(-)
> 
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index 2a0e782a151d..495e20fbdec0 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -625,6 +625,17 @@ void __meminit __init_single_page(struct page *page, unsigned long pfn,
>  	vmemmap_optimization_verify_zone(page);
>  }
>  
> +void __meminit memmap_init_page_from_template(struct page *page,
> +		unsigned long pfn, unsigned long zone, struct page *template)
> +{
> +	set_page_section_from_pfn(template, pfn);
> +#ifdef WANT_PAGE_VIRTUAL
> +	if (!is_highmem_idx(zone))
> +		set_page_address(template, __va(pfn << PAGE_SHIFT));
> +#endif
> +	memcpy_nontemporal(page, template, sizeof(*page));
> +}
> +

Can we make the template a const? Why can't we do

void __meminit memmap_init_page_from_template(struct page *page,
		unsigned long pfn, unsigned long zone,
		const struct page *template)
{
	memcpy_nontemporal(page, template, sizeof(*page));

	set_page_section_from_pfn(page, pfn);
#ifdef WANT_PAGE_VIRTUAL
	if (!is_highmem_idx(zone))
		set_page_address(page, __va(pfn << PAGE_SHIFT));
#endif

That way we don't update template once it is set, if template is r/o,
then we don't need both first page and template in the caller to
be different.


>  #ifdef CONFIG_NUMA
>  /*
>   * During memory init memblocks map pfns to nids. The search is expensive and
> @@ -1073,17 +1084,6 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
>  	}
>  }
>  
> -static void zone_device_page_init_from_template(struct page *page,
> -		unsigned long pfn, struct page *template)
> -{
> -	set_page_section_from_pfn(template, pfn);
> -#ifdef WANT_PAGE_VIRTUAL
> -	if (!is_highmem_idx(ZONE_DEVICE))
> -		set_page_address(template, __va(pfn << PAGE_SHIFT));
> -#endif
> -	memcpy_nontemporal(page, template, sizeof(*page));
> -}
> -
>  /*
>   * With compound page geometry and when struct pages are stored in ram most
>   * tail pages are reused. Consequently, the amount of unique struct pages to
> @@ -1136,8 +1136,8 @@ static void __ref memmap_init_compound(struct page *head,
>  
>  	/* Initialize the remaining tail pages from template. */
>  	for (pfn = head_pfn + 2; pfn < end_pfn; pfn++)
> -		zone_device_page_init_from_template(pfn_to_page(pfn), pfn,
> -						    &template);
> +		memmap_init_page_from_template(pfn_to_page(pfn), pfn,
> +					       ZONE_DEVICE, &template);
>  	prep_compound_head(head, order);
>  }
>  
> @@ -1192,7 +1192,8 @@ void __ref memmap_init_zone_device(struct zone *zone,
>  	for (; pfn < end_pfn; pfn += pfns_per_compound) {
>  		page = pfn_to_page(pfn);
>  
> -		zone_device_page_init_from_template(page, pfn, &template);
> +		memmap_init_page_from_template(page, pfn, ZONE_DEVICE,
> +					       &template);
>  
>  		if (IS_ALIGNED(pfn, PAGES_PER_SECTION))
>  			cond_resched();
> diff --git a/mm/mm_init.h b/mm/mm_init.h
> index 0034e37dbabd..22c465122b47 100644
> --- a/mm/mm_init.h
> +++ b/mm/mm_init.h
> @@ -111,5 +111,7 @@ void memblock_free_all(void);
>  
>  void __meminit __init_single_page(struct page *page, unsigned long pfn,
>  				unsigned long zone, int nid);
> +void __meminit memmap_init_page_from_template(struct page *page,
> +		unsigned long pfn, unsigned long zone, struct page *template);
>  
>  #endif /* __MM_MM_INIT_H */
> -- 


Balbir