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

[Pankaj Raghav]

On 2/27/2026 6:31 AM, Matthew Wilcox wrote:
> On Sat, Dec 06, 2025 at 04:08:55AM +0100, Pankaj Raghav wrote:
> > There are multiple solutions to solve this problem and this is one of
> > them with minimal changes. I plan on discussing possible other solutions
> > at the talk.
>
> Here's an argument.  The one remaining caller of add_to_page_cache_lru()
> is ramfs_nommu_expand_for_mapping().  Attached is a patch which
> eliminates it ... but it doesn't compile because folio_split() is
> undefined on nommu.
>
> So either we need to reimplement all the good stuff that folio_split()
> does for us, or we need to make folio_split() available on nommu.

I had a question, one conclusion I came to was: folio splitting depends on THP, 
so we either need to implement the split logic without THP dependency or just 
make sure we don't split a large folio at all when we use large folio (what I 
did in this RFC but not a great long term solution).

So even if we implement folio_split without any dependency on THP, do we need to 
re-implement or make folio_split available for nommu? I am also wondering how 
nommu code is related to removing large folios dependency on THP.

--
Pankaj