[PATCH v1 0/2] udmabuf: Add back support for mapping hugetlb pages

[Jason Gunthorpe]

On Mon, Jun 26, 2023 at 03:04:21PM -0400, Peter Xu wrote:
> On Mon, Jun 26, 2023 at 03:18:48PM -0300, Jason Gunthorpe wrote:
> > On Mon, Jun 26, 2023 at 08:14:27PM +0200, David Hildenbrand wrote:
> > 
> > > So we might have to implement the same page migration as gup does on
> > > FOLL_LONGTERM here ... maybe there are more such cases/drivers that actually
> > > require that handling when simply taking pages out of the memfd, believing
> > > they can hold on to them forever.
> > 
> > In general I would like to see an interface to FOLL_LONGTERM pin pages
> > from a memfd. I would quite happily use that in iommufd as well.
> > 
> > It solves some problems we have there with fork/exec/etc if the pages
> > are not linked to a mm_struct.
> 
> Afaiu any fd based approach should mean it'll never work with private
> memories, while mm-based should be able to work on any kind.  

Is there a significant use case to open a memfd and then use
MAP_PRIVATE? Why would anyone want to do that instead of just using
normal mmap anonymous memory?

Jason