Re: [RFC PATCH v2 00/30] 1GB PUD THP support on x86_64

[Michal Hocko]

On Fri 02-10-20 09:50:02, David Hildenbrand wrote:
> >>> - huge page sizes controllable by the userspace?
> >>
> >> It might be good to allow advanced users to choose the page sizes, so they
> >> have better control of their applications.
> > 
> > Could you elaborate more? Those advanced users can use hugetlb, right?
> > They get a very good control over page size and pool preallocation etc.
> > So they can get what they need - assuming there is enough memory.
> > 
> 
> I am still not convinced that 1G THP (TGP :) ) are really what we want
> to support. I can understand that there are some use cases that might
> benefit from it, especially:

Well, I would say that internal support for larger huge pages (e.g. 1GB)
that can transparently split under memory pressure is a useful
funtionality. I cannot really judge how complex that would be
consideting that 2MB THP have turned out to be quite a pain but
situation has settled over time. Maybe our current code base is prepared
for that much better.

Exposing that interface to the userspace is a different story of course.
I do agree that we likely do not want to be very explicit about that.
E.g. an interface for address space defragmentation without any more
specifics sounds like a useful feature to me. It will be up to the
kernel to decide which huge pages to use.
-- 
Michal Hocko
SUSE Labs