linux-kernel - Re: [RFC PATCH v2 14/47] hugetlb: make default arch_make_huge

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Message-ID: <Y5pLcoxp2qVZtOq9@monkey>
Date:   Wed, 14 Dec 2022 14:17:22 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     James Houghton <jthoughton@...gle.com>
Cc:     Muchun Song <songmuchun@...edance.com>,
        Peter Xu <peterx@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Mina Almasry <almasrymina@...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>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 14/47] hugetlb: make default arch_make_huge_pte
 understand small mappings

On 10/21/22 16:36, James Houghton 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.

Nothing wrong with this patch.

However, I wish there was some way we could flag this requirement in
arch specific code.  Just seems like something that would be easy to
overlook.

-- 
Mike Kravetz

> Signed-off-by: James Houghton <jthoughton@...gle.com>
> ---
>  include/linux/hugetlb.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 4b1548adecde..d305742e9d44 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -907,7 +907,7 @@ 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
>  
> -- 
> 2.38.0.135.g90850a2211-goog
>