Re: [LSF/MM ATTEND] Huge Page Futures

["Kirill A. Shutemov" <kirill@shutemov.name>]

On Thu, Jan 28, 2016 at 11:28:33AM -0800, Mike Kravetz wrote:
> On 01/28/2016 07:05 AM, Aneesh Kumar K.V wrote:
> > Mike Kravetz <mike.kravetz@oracle.com> writes:
> > 
> >> In a search of the archives, it appears huge page support in one form or
> >> another has been a discussion topic in almost every LSF/MM gathering. Based
> >> on patches submitted this past year, huge pages is still an area of active
> >> development.  And, it appears this level of activity will  continue in the
> >> coming year.
> >>
> >> I propose a "Huge Page Futures" session to discuss large works in progress
> >> as well as work people are considering for 2016.  Areas of discussion would
> >> minimally include:
> >>
> >> - Krill Shutemov's THP new refcounting code and the push for huge page
> >>   support in the page cache.
> > 
> > I am also interested in this discussion. We had some nice challenge
> > w.r.t to powerpc implementation of THP.
> > 
> >>
> >> - Matt Wilcox's huge page support in DAX enabled filesystems, but perhaps
> >>   more interesting is the desire for supporting PUD pages.  This seems to
> >>   beg the question of supporting transparent PUD pages elsewhere.
> >>
> > 
> > I am also looking at switching powerpc hugetlbfs to GENERAL_HUGETLB. To
> > support 16GB pages I would need hugepage at PUD/PGD. Can you elaborate
> > why supporting huge PUD page is a challenge ?
> 
> For hugetlbfs it should not be an issue.  However, page fault handling for
> hugetlbfs is already a special case today.  Is that what you were asking?
> 
> Matt's work adds THP for PUD sized huge pages to DAX mappings.  The thought
> that popped into my head is "Does it make sense to try and expand THP for
> PUD sized pages elsewhere?".  Perhaps that is nonsense and a silly question
> to ask.

I don't think it has much sense on x86-64. But if an architecture has more
reasonable page size on PUD level, who knows...

-- 
 Kirill A. Shutemov

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