Re: [RFC 00/12] mm: PUD (1GB) THP implementation

[David Hildenbrand (arm)]

On 2/2/26 05:00, Matthew Wilcox wrote:
> On Sun, Feb 01, 2026 at 04:50:17PM -0800, Usama Arif wrote:
> > This is an RFC series to implement 1GB PUD-level THPs, allowing
> > applications to benefit from reduced TLB pressure without requiring
> > hugetlbfs. The patches are based on top of
> > f9b74c13b773b7c7e4920d7bc214ea3d5f37b422 from mm-stable (6.19-rc6).
>
> I suggest this has not had enough testing.  There are dozens of places
> in the MM which assume that if a folio is at leaast PMD size then it is
> exactly PMD size.  Everywhere that calls folio_test_pmd_mappable() needs
> to be audited to make sure that it will work properly if the folio is
> larger than PMD size.

I think the hack (ehm trick) in this patch set is to do it just like dax 
PUDs: only map through a PUD or through PTEs, not through PMDs.

That also avoids dealing with mapcounts until I sorted that out.

--
Cheers

David