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

[David Hildenbrand]

> > > 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. For larger folios, it won't really work/be desirable, though.

--
Cheers,

David / dhildenb