linux-kernel - Re: [PATCH v4 07/10] powerpc/mm: Use generic_hugetlb_get_unmapped

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Message-Id: <1639043741.e2zqhea1ix.astroid@bobo.none>
Date:   Thu, 09 Dec 2021 20:02:03 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     "alex@...ti.fr" <alex@...ti.fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>
Cc:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v4 07/10] powerpc/mm: Use
 generic_hugetlb_get_unmapped_area()

Excerpts from Christophe Leroy's message of December 9, 2021 3:18 am:
> Use the generic version of arch_hugetlb_get_unmapped_area()
> which is now available at all time.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>  arch/powerpc/include/asm/book3s/64/hugetlb.h |  4 --
>  arch/powerpc/mm/book3s64/radix_hugetlbpage.c | 55 --------------------
>  arch/powerpc/mm/hugetlbpage.c                |  4 +-
>  3 files changed, 1 insertion(+), 62 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/book3s/64/hugetlb.h b/arch/powerpc/include/asm/book3s/64/hugetlb.h
> index 12e150e615b7..b37a28f62cf6 100644
> --- a/arch/powerpc/include/asm/book3s/64/hugetlb.h
> +++ b/arch/powerpc/include/asm/book3s/64/hugetlb.h
> @@ -8,10 +8,6 @@
>   */
>  void radix__flush_hugetlb_page(struct vm_area_struct *vma, unsigned long vmaddr);
>  void radix__local_flush_hugetlb_page(struct vm_area_struct *vma, unsigned long vmaddr);
> -extern unsigned long
> -radix__hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
> -				unsigned long len, unsigned long pgoff,
> -				unsigned long flags);
>  
>  extern void radix__huge_ptep_modify_prot_commit(struct vm_area_struct *vma,
>  						unsigned long addr, pte_t *ptep,
> diff --git a/arch/powerpc/mm/book3s64/radix_hugetlbpage.c b/arch/powerpc/mm/book3s64/radix_hugetlbpage.c
> index 23d3e08911d3..d2fb776febb4 100644
> --- a/arch/powerpc/mm/book3s64/radix_hugetlbpage.c
> +++ b/arch/powerpc/mm/book3s64/radix_hugetlbpage.c
> @@ -41,61 +41,6 @@ void radix__flush_hugetlb_tlb_range(struct vm_area_struct *vma, unsigned long st
>  		radix__flush_tlb_range_psize(vma->vm_mm, start, end, psize);
>  }
>  
> -/*
> - * A vairant of hugetlb_get_unmapped_area doing topdown search
> - * FIXME!! should we do as x86 does or non hugetlb area does ?
> - * ie, use topdown or not based on mmap_is_legacy check ?
> - */
> -unsigned long
> -radix__hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
> -				unsigned long len, unsigned long pgoff,
> -				unsigned long flags)
> -{
> -	struct mm_struct *mm = current->mm;
> -	struct vm_area_struct *vma;
> -	struct hstate *h = hstate_file(file);
> -	int fixed = (flags & MAP_FIXED);
> -	unsigned long high_limit;
> -	struct vm_unmapped_area_info info;
> -
> -	high_limit = DEFAULT_MAP_WINDOW;
> -	if (addr >= high_limit || (fixed && (addr + len > high_limit)))
> -		high_limit = TASK_SIZE;

I wonder if generic hugetlb_get_unmapped_area needs to have the
arch_get_mmap_end() added.

arm64 has arch_get_mmap_end() and !HAVE_ARCH_HUGETLB_UNMAPPED_AREA so
it looks like it has broken large address hint logic for hugetlbfs
mappings? x86-64 defines their own and does the same hinting for
normal and hugetlbfs mmap.

If we had that and defied arch_get_mmap_end(), then this patch should
work.

Thanks,
Nick