Re: [LSF/MM/BPF TOPIC] Beyond 2MB: Why Terabyte-Scale Machines Need 1GB Transparent Huge Pages

[Zi Yan <ziy@nvidia.com>]

On 24 Feb 2026, at 14:03, Johannes Weiner wrote:

> On Thu, Feb 19, 2026 at 03:53:35PM +0000, Usama Arif wrote:
>> Why 1G THP over hugetlbfs?
>> ==========================
>
> I know this isn't your intention, but one interesting aspect of
> supporting PUD mapped folios natively is that it could open the door
> to simplifying hugetlb as well.
>
> We currently have all kinds of huge_vma checks scattered over the page
> table code, and entirely parallel paths for unmapping etc. With native
> PUD mappings, this could allow pushing the special casing out of the
> virtual memory layer and into where we deal with the page objects.
>
> You might be able to take it as far as the only thing left of hugetlb
> is the reservation pool. Such that a naive application does mmap() as
> per usual, and it comes down to a separate allocation policy how the
> backing pages are served (buddy, CMA, boot-time reservations, ...)
>
> Approaching it this way could help separate out the discussion on code
> impact and tech debt of PUD mappings, from the allocation technique
> question, which in itself is a fairly large topic.

I agree with this 100%. Adding 1GB folio support first, we then can think
about what other THP features, e.g., split, migration, PMD/PTE mapping, are
really needed and add them one by one. It is also going to be a good way
of retiring hugetlb special code.

Best Regards,
Yan, Zi