Re: [PATCH] mm/sparse: fix BUILD_BUG_ON check for section map alignment

David Hildenbrand (Arm)
2026-04-01T07:26:58Z

On 4/1/26 09:23, Muchun Song wrote:
>
>
>> On Apr 1, 2026, at 15:08, David Hildenbrand (Arm) <david@kernel.org> wrote:
>>
>> On 4/1/26 06:01, Muchun Song wrote:
>>>
>>>
>>>
>>> Sorry, I misread it earlier — I thought it was about the memory
>>> section size, but it's actually about the memmap size. Let me respond
>>> again to your question. On the powerpc architecture, when PFN_SECTION_SHIFT
>>> is 6 and PAGE_SHIFT is 18, it does seem that the memmap of a memory
>>> section would be smaller than a single page.
>>
>> Right, and I am saying we don't care about that and do not support it.
>>
>> For example, most vmemmap code I am aware of relies on a single section
>> covering full pages.
>>
>> So I don't think this patch here adds any value, except faking that we
>> might be supporting something we don't?
>
> Got it.
>
> My original motivation was simply that when I read this part of the code,
> the comment felt a bit off to me, so I just fixed it casually. But if it
> ends up creating the impression that "we might be supporting something
> we don't," as you said, then I'm fine with dropping this patch.

Can you rework your patch to only simplify the comment, and to clarify
that we always expect a single section to cover full pages?

--
Cheers,

David