Re: [PATCH 21/46] hugetlb: use struct hugetlb_pte for walk_hugetlb_range

[David Hildenbrand]

On 12.01.23 22:33, Peter Xu wrote:
> On Thu, Jan 12, 2023 at 04:17:52PM -0500, James Houghton wrote:
> > I'll look into it, but doing it this way will use _mapcount, so we
> > won't be able to use the vmemmap optimization. I think even if we do
> > use Hugh's approach, refcount is still being kept on the head page, so
> > there's still an overflow risk there (but maybe I am
> > misunderstanding).
>
> Could you remind me what's the issue if using refcount on the small pages
> rather than the head (assuming vmemmap still can be disabled)?

The THP-way of doing things is refcounting on the head page. All folios 
use a single refcount on the head.

There has to be a pretty good reason to do it differently.

--
Thanks,

David / dhildenb