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

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Sun, Feb 01, 2026 at 09:44:12PM -0500, Rik van Riel wrote:
> On Sun, 2026-02-01 at 16:50 -0800, Usama Arif wrote:
> >
> > 1. Static Reservation: hugetlbfs requires pre-allocating huge pages
> > at boot
> >    or runtime, taking memory away. This requires capacity planning,
> >    administrative overhead, and makes workload orchastration much
> > much more
> >    complex, especially colocating with workloads that don't use
> > hugetlbfs.
> >
> To address the obvious objection "but how could we
> possibly allocate 1GB huge pages while the workload
> is running?", I am planning to pick up the CMA balancing
> patch series (thank you, Frank) and get that in an
> upstream ready shape soon.
>
> https://lkml.org/2025/9/15/1735

That link doesn't work?

Did a quick search for CMA balancing on lore, couldn't find anything, could you
provide a lore link?

>
> That patch set looks like another case where no
> amount of internal testing will find every single
> corner case, and we'll probably just want to
> merge it upstream, deploy it experimentally, and
> aggressively deal with anything that might pop up.

I'm not really in favour of this kind of approach. There's plenty of things that
were considered 'temporary' upstream that became rather permanent :)

Maybe we can't cover all corner-cases, but we need to make sure whatever we do
send upstream is maintainable, conceptually sensible and doesn't paint us into
any corners, etc.

>
> With CMA balancing, it would be possibly to just
> have half (or even more) of system memory for
> movable allocations only, which would make it possible
> to allocate 1GB huge pages dynamically.

Could you expand on that?

>
> --
> All Rights Reversed.

Thanks, Lorenzo