linux-kernel - Re: [PATCH 4/4] arm64: tlb: set huge page size to stride for hugepage

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Message-ID: <CAGsJ_4xvSyvskcKMptiwm+8eV-sgSWsJYgBEYpwQ2n=cHHNZ7Q@mail.gmail.com>
Date:   Mon, 31 Jul 2023 16:33:36 +0800
From:   Barry Song <21cnbao@...il.com>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        Mina Almasry <almasrymina@...gle.com>, kirill@...temov.name,
        joel@...lfernandes.org, william.kucharski@...cle.com,
        kaleshsingh@...gle.com, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] arm64: tlb: set huge page size to stride for hugepage

On Mon, Jul 31, 2023 at 4:14 PM Kefeng Wang <wangkefeng.wang@...wei.com> wrote:
>
> It is better to use huge_page_size() for hugepage(HugeTLB) instead of
> PAGE_SIZE for stride, which has been done in flush_pmd/pud_tlb_range(),
> it could reduce the loop in __flush_tlb_range().
>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
> ---
>  arch/arm64/include/asm/tlbflush.h | 21 +++++++++++----------
>  1 file changed, 11 insertions(+), 10 deletions(-)
>
> diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h
> index 412a3b9a3c25..25e35e6f8093 100644
> --- a/arch/arm64/include/asm/tlbflush.h
> +++ b/arch/arm64/include/asm/tlbflush.h
> @@ -360,16 +360,17 @@ static inline void __flush_tlb_range(struct vm_area_struct *vma,
>         dsb(ish);
>  }
>
> -static inline void flush_tlb_range(struct vm_area_struct *vma,
> -                                  unsigned long start, unsigned long end)
> -{
> -       /*
> -        * We cannot use leaf-only invalidation here, since we may be invalidating
> -        * table entries as part of collapsing hugepages or moving page tables.
> -        * Set the tlb_level to 0 because we can not get enough information here.
> -        */
> -       __flush_tlb_range(vma, start, end, PAGE_SIZE, false, 0);
> -}
> +/*
> + * We cannot use leaf-only invalidation here, since we may be invalidating
> + * table entries as part of collapsing hugepages or moving page tables.
> + * Set the tlb_level to 0 because we can not get enough information here.
> + */
> +#define flush_tlb_range(vma, start, end)                               \
> +       __flush_tlb_range(vma, start, end,                              \
> +                               ((vma)->vm_flags & VM_HUGETLB)          \
> +                               ? huge_page_size(hstate_vma(vma))       \
> +                               : PAGE_SIZE, false, 0)
> +

seems like a good idea.

I wonder if a better implementation will be MMU_GATHER_PAGE_SIZE,  in this case,
we are going to support stride for other large folios as well, such as thp.

>
>  static inline void flush_tlb_kernel_range(unsigned long start, unsigned long end)
>  {
> --
> 2.41.0
>

Thanks
Barry