Re: [PATCH v2] mm: prohibit the last subpage from reusing the entire large folio

[David Hildenbrand]

On 08.03.24 14:45, Ryan Roberts wrote:
> On 08/03/2024 13:24, David Hildenbrand wrote:
> > > > > This patch migrates the last subpage to a small folio and immediately
> > > > > returns the large folio to the system. It benefits both memory availability
> > > > > and anti-fragmentation.
> > > >
> > > > It might be controversial optimization, and as Ryan said, there, are likely
> > > > other cases where we'd want to migrate off-of a thp if possible earlier.
> > >
> > > Personally, I think there might also be cases where you want to copy/reuse the
> > > entire large folio. If you're application is using 16K THPs perhaps it's a
> > > bigger win to just treat it like a base page? I expect the cost/benefit will
> > > change as the THP size increases?
> >
> > Yes, I think for small folios (i.e., 16KiB) it will be rather easy to make a
> > decision. The larger the folio, the larger the page fault latency due to
> > scanning, copying, modifying, which can easily turn undesirable.
> >
> > At least when it comes to page reuse, I have some simple backup plans for small
> > folios if I won't be able to make progress with my other approach.
>
> Do you mean "small large folios" here? i.e. order >= 1? If so, great!

*smaller*, yes :)

--
Cheers,

David / dhildenb