linux-kernel - Re: [PATCH v2 16/46] hugetlb: make default arch_make_huge

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Message-ID: <CAHS8izP9qVOV4ZvDT4vRS0-xvJ2yiQu9Uze-TSJO1f0Oec95hA@mail.gmail.com>
Date:   Wed, 22 Feb 2023 13:17:57 -0800
From:   Mina Almasry <almasrymina@...gle.com>
To:     James Houghton <jthoughton@...gle.com>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Peter Xu <peterx@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        "Zach O'Keefe" <zokeefe@...gle.com>,
        Manish Mishra <manish.mishra@...anix.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Yang Shi <shy828301@...il.com>,
        Frank van der Linden <fvdl@...gle.com>,
        Jiaqi Yan <jiaqiyan@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 16/46] hugetlb: make default arch_make_huge_pte
 understand small mappings

On Fri, Feb 17, 2023 at 4:28 PM James Houghton <jthoughton@...gle.com> wrote:
>
> This is a simple change: don't create a "huge" PTE if we are making a
> regular, PAGE_SIZE PTE. All architectures that want to implement HGM
> likely need to be changed in a similar way if they implement their own
> version of arch_make_huge_pte.
>
> Signed-off-by: James Houghton <jthoughton@...gle.com>
>
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 726d581158b1..b767b6889dea 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -899,7 +899,7 @@ static inline void arch_clear_hugepage_flags(struct page *page) { }
>  static inline pte_t arch_make_huge_pte(pte_t entry, unsigned int shift,
>                                        vm_flags_t flags)
>  {
> -       return pte_mkhuge(entry);
> +       return shift > PAGE_SHIFT ? pte_mkhuge(entry) : entry;
>  }
>  #endif
>

How are contig_pte's handled here? Will shift show that it's actually
a contig_pte and not just PAGE_SHIFT? Or is that arm64 specific so it
exists only in the arm64 version of this function? Do we need to worry
about it here?

> --
> 2.39.2.637.g21b0678d19-goog
>