Re: [PATCH v2 03/17] mm/mm_init: skip initializing shared vmemmap tail pages

[Muchun Song]

> On Aug 3, 2026, at 14:38, Mike Rapoport <rppt@xxxxxxxxxx> wrote:
> 
> On Fri, Jul 31, 2026 at 10:13:43AM +0800, Muchun Song wrote:
>>> On Jul 30, 2026, at 22:32, Mike Rapoport <rppt@xxxxxxxxxx> wrote:
>>>> 
>>>> Since we also use __pfn_to_section in the patch 14 in this series for
>>>> !SPARSEMEM, we need to make corresponding adjustments—specifically, by using
>>>> pfn_to_section_order to determine whether the vmemmap of a given section is
>>>> optimizable. This new helper will be called from several places, so I'm afraid
>>>> its introduction is unavoidable.
>>> 
>>> Do you mean that section_vmemmap_optimizable() will receive pfn as a
>>> parameter and use pfn_to_section_order() internally?
>> 
>> I was originally planning to go with the this approach, but now I've come across
>> something that feels a bit unusual to me: a function whose name starts with section
>> takes a pfn as its argument instead of a mem_section.
>> 
>> So I started thinking about an alternative. How about we keep section_vmemmap_optimizable()
>> as it is, but introduce a new helper like this:
>> 
>> static inline bool order_vmemmap_optimizable(unsigned int order)
>> {
>> 	return order >= OPTIMIZABLE_FOLIO_MIN_ORDER;
>> }
> 
> Maybe name it vmemmap_optimizable_order() so it'll belong to vmemmap
> namespace, order_ can be really a lot of things.

Make sense.

> 
> I think it makes sense. Let's see how it fits in the end in the new
> version :)

I'll update it as soon as possible.

Muchun,
Thanks.

> 
> -- 
> Sincerely yours,
> Mike.