Re: [PATCH v2 2/5] powerpc/mm: drop powerpc vmemmap_can_optimize()

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

> On Nov 5, 2026, at 16:02, Lance Yang <lance.yang@linux.dev> wrote:
> 
> 
> On Thu, Nov 05, 2026 at 07:16:48AM +0000, sashiko-bot@kernel.org wrote:
>> Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
>> - [Low] mm: undeclared vmemmap in section_vmemmap_optimization_disable()
>> - [Low] mm: define vmemmap_optimizable_order() before section_vmemmap_optimizable()
>> --
> 
> IIUC, on LoongArch, asm/pgtable.h includes vmemmap-optimization.h before
> defining vmemmap.

Yeah. Really nasty.

> 
> How about taking a PFN and page count instead, and leaving the conversion
> to the callers?

However, although this can solve the compilation problem, for the caller,
it is not very straightforward because they need to calculate nr_pages.
section_vmemmap_optimization_disable is only supposed to be used in the
vmemmap population path, and in these paths, the most direct parameters
are start and end. I think this function could be moved to
mm/sparse-vmemmap.c, and that way the compilation dependency problem
would be solved.

What do you think?

Thanks,
Muchun

> 
> ---8<---
> diff --git a/arch/loongarch/mm/init.c b/arch/loongarch/mm/init.c
> index c91afce46136..5a3a225135be 100644
> --- a/arch/loongarch/mm/init.c
> +++ b/arch/loongarch/mm/init.c
> @@ -143,7 +143,8 @@ void __meminit vmemmap_set_pmd(pmd_t *pmd, void *p, int node,
> int __meminit vmemmap_populate(unsigned long start, unsigned long end,
> 			       int node, struct vmem_altmap *altmap)
> {
> -	section_vmemmap_optimization_disable(start, end);
> +	section_vmemmap_optimization_disable(page_to_pfn((struct page *)start),
> +					     (end - start) / sizeof(struct page));
> #if CONFIG_PGTABLE_LEVELS == 2
> 	return vmemmap_populate_basepages(start, end, node, NULL);
> #else
> diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
> index 4d6928f717cf..43c98aec29aa 100644
> --- a/arch/powerpc/mm/init_64.c
> +++ b/arch/powerpc/mm/init_64.c
> @@ -283,7 +283,8 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
> 		return radix__vmemmap_populate(start, end, node, altmap);
> #endif
> 
> -	section_vmemmap_optimization_disable(start, end);
> +	section_vmemmap_optimization_disable(page_to_pfn((struct page *)start),
> +					     (end - start) / sizeof(struct page));
> 	return __vmemmap_populate(start, end, node, altmap);
> }
> 
> diff --git a/include/linux/vmemmap-optimization.h b/include/linux/vmemmap-optimization.h
> index 9d9f7a67d195..0501234ab16b 100644
> --- a/include/linux/vmemmap-optimization.h
> +++ b/include/linux/vmemmap-optimization.h
> @@ -76,11 +76,9 @@ static inline bool section_vmemmap_optimizable(const struct mem_section *section
> 	return vmemmap_optimizable_order(section_compound_order(section));
> }
> 
> -static inline void section_vmemmap_optimization_disable(unsigned long start,
> -		unsigned long end)
> +static inline void section_vmemmap_optimization_disable(unsigned long pfn,
> +							unsigned long nr_pages)
> {
> -	unsigned long pfn = page_to_pfn((struct page *)start);
> -	unsigned long nr_pages = (end - start) / sizeof(struct page);
> 	struct mem_section *section = __pfn_to_section(pfn);
> 
> 	if (nr_pages < PAGES_PER_SECTION) {
> @@ -119,8 +117,8 @@ static inline bool section_vmemmap_optimizable(const struct mem_section *section
> 	return false;
> }
> 
> -static inline void section_vmemmap_optimization_disable(unsigned long start,
> -		unsigned long end)
> +static inline void section_vmemmap_optimization_disable(unsigned long pfn,
> +							unsigned long nr_pages)
> {
> }
> 
> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> index 5777f2e29684..64bc346d0fc5 100644
> --- a/mm/sparse-vmemmap.c
> +++ b/mm/sparse-vmemmap.c
> @@ -474,7 +474,7 @@ struct page * __meminit __populate_section_memmap(unsigned long pfn,
> 
> 	/* Altmap-backed vmemmap pages cannot be optimized. */
> 	if (altmap)
> -		section_vmemmap_optimization_disable(start, end);
> +		section_vmemmap_optimization_disable(pfn, nr_pages);
> 	r = vmemmap_populate(start, end, nid, altmap);
> 	if (r < 0)
> 		return NULL;
> ---
> 
> Cheers, Lance