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Date:   Thu, 18 Feb 2021 13:25:00 -0400
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Zi Yan <ziy@nvidia.com>, Davidlohr Bueso <dbueso@suse.de>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Oscar Salvador <osalvador@suse.de>,
        Joao Martins <joao.m.martins@oracle.com>,
        stable@vger.kernel.org
Subject: Re: [PATCH 1/2] hugetlb: fix update_and_free_page contig page struct
 assumption
Message-ID: <20210218172500.GA4718@ziepe.ca>
References: <20210217184926.33567-1-mike.kravetz@oracle.com>
 <20210217110252.185c7f5cd5a87c3f7b0c0144@linux-foundation.org>
 <20210218144554.GS2858050@casper.infradead.org>
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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@oracle.com> 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