linux-kernel - Re: [PATCH 03/13] mm: Add generic p?d_large() macros

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Date:   Mon, 18 Feb 2019 11:14:23 +0000
From:   Mark Rutland <Mark.Rutland@....com>
To:     Steven Price <Steven.Price@....com>
CC:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "x86@...nel.org" <x86@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <Catalin.Marinas@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Will Deacon <Will.Deacon@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        James Morse <James.Morse@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 03/13] mm: Add generic p?d_large() macros

On Fri, Feb 15, 2019 at 05:02:24PM +0000, Steven Price wrote:
> From: James Morse <james.morse@....com>
>
> Exposing the pud/pgd levels of the page tables to walk_page_range() means
> we may come across the exotic large mappings that come with large areas
> of contiguous memory (such as the kernel's linear map).
>
> For architectures that don't provide p?d_large() macros, provided a
> does nothing default.
>
> Signed-off-by: James Morse <james.morse@....com>
> Signed-off-by: Steven Price <steven.price@....com>
> ---
>  include/asm-generic/pgtable.h | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
> index 05e61e6c843f..7630d663cd51 100644
> --- a/include/asm-generic/pgtable.h
> +++ b/include/asm-generic/pgtable.h
> @@ -1186,4 +1186,14 @@ static inline bool arch_has_pfn_modify_check(void)
>  #define mm_pmd_folded(mm)__is_defined(__PAGETABLE_PMD_FOLDED)
>  #endif
>
> +#ifndef pgd_large
> +#define pgd_large(x)0
> +#endif
> +#ifndef pud_large
> +#define pud_large(x)0
> +#endif
> +#ifndef pmd_large
> +#define pmd_large(x)0
> +#endif

It might be worth a comment defining the semantics of these, e.g. how
they differ from p?d_huge() and p?d_trans_huge().

Thanks,
Mark.

> +
>  #endif /* _ASM_GENERIC_PGTABLE_H */
> --
> 2.20.1
>
>
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