Re: [RFC v2 0/3] Decoupling large folios dependency on THP

[Zi Yan]

On 9 Dec 2025, at 23:27, Matthew Wilcox wrote:

> On Tue, Dec 09, 2025 at 11:03:23AM -0500, Zi Yan wrote:
>> I wonder if core-mm should move mTHP code out of CONFIG_TRANSPARENT_HUGEPAGE
>> and mTHP might just work. Hmm, folio split might need to be moved out of
>> mm/huge_memory.c in that case. khugepaged should work for mTHP without
>> CONFIG_TRANSPARENT_HUGEPAGE as well. OK, for anon folios, the changes might
>> be more involved.
>
> I think this is the key question to be discussed at LPC.  How much of

I am not going, so would like to get a summary afterwards. :)

> the current THP code should we say "OK, this is large folio support
> and everybody needs it" and how much is "This is PMD (or mTHP) support;
> this architecture doesn't have it, we don't need to compile it in".

I agree with most of it, except mTHP part. mTHP should be part of large
folio, since I see mTHP is anon equivalent to file backed large folio.
Both are a >0 order folio mapped by PTEs (ignoring to-be-implemented
multi-PMD mapped large folios for now).

Best Regards,
Yan, Zi