Re: [PATCH 1/2] hugetlb: fix update_and_free_page contig page struct assumption

[Jason Gunthorpe]

On Thu, Feb 18, 2021 at 02:45:54PM +0000, Matthew Wilcox wrote:
> On Wed, Feb 17, 2021 at 11:02:52AM -0800, Andrew Morton wrote:
> > On Wed, 17 Feb 2021 10:49:25 -0800 Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote:
> > > page structs are not guaranteed to be contiguous for gigantic pages.  The
> >
> > June 2014.  That's a long lurk time for a bug.  I wonder if some later
> > commit revealed it.
> 
> I would suggest that gigantic pages have not seen much use.  Certainly
> performance with Intel CPUs on benchmarks that I've been involved with
> showed lower performance with 1GB pages than with 2MB pages until quite
> recently.

I suggested in another thread that maybe it is time to consider
dropping this "feature"

If it has been slightly broken for 7 years it seems a good bet it
isn't actually being used.

The cost to fix GUP to be compatible with this will hurt normal
GUP performance - and again, that nobody has hit this bug in GUP
further suggests the feature isn't used..

Jason