Re: [v3 00/24] mm: thp: lazy PTE page table allocation at PMD split time

Matthew Wilcox
2026-04-08T19:50:08Z

On Wed, Apr 08, 2026 at 04:06:29PM +0100, Usama Arif wrote:
> On 06/04/2026 00:34, Hugh Dickins wrote:
> > What would help a lot would be the implementation of swap entries
> > at the PMD level. Whether that would help enough, I'm sceptical:
> > I do think it's foolish to depend upon the availability of huge
> > contiguous swap extents, whatever the recent improvements there;
> > but it would at least be an arguable justification.
> >
> Thanks for pointing this out. I should have thought of this as I
> have been thinking about fork a lot for 1G THP and for this series.
>
> I am working on trying to make PMD level swap entires work. I hope
> to have a RFC soon.

I think you may have missed Hugh's point a little bit. If we do
support PMD-level swap entries, that means we have to be able to find
contiguous space in the swap space for 512 entries. I don't know how
hard that will be, but I can imagine it's not that easy.