linux-kernel - Re: [PATCH 1/2] mm: Update generic gup implementation to handle hugepage directory

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Message-ID: <871tq8kpqb.fsf@linux.vnet.ibm.com>
Date:	Thu, 16 Oct 2014 20:48:20 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Steve Capper <steve.capper@...aro.org>
Cc:	akpm@...ux-foundation.org, Andrea Arcangeli <aarcange@...hat.com>,
	benh@...nel.crashing.org, mpe@...erman.id.au, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-arch@...r.kernel.org, will.deacon@....com,
	catalin.marinas@....com, linux@....linux.org.uk
Subject: Re: [PATCH 1/2] mm: Update generic gup implementation to handle hugepage directory

Steve Capper <steve.capper@...aro.org> writes:

> On Wed, Oct 15, 2014 at 10:04:47PM +0530, Aneesh Kumar K.V wrote:
>> Update generic gup implementation with powerpc specific details.
>> On powerpc at pmd level we can have hugepte, normal pmd pointer
>> or a pointer to the hugepage directory.
>> 
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
>
> Hi,
> This patch causes compiler errors on arm and arm64 due to pgd_huge
> being undefined. I've attached a fixup below, this fixup will require
> that #define pgd_huge(pgd) 0 be added back into:
> arch/powerpc/include/asm/page.h
> For the second patch in this series.
>
> Another avenue would be to do something like:
> #ifndef pgd_huge
> #define pgd_huge(pgd)	(0)
> #endif
>
> Then no changes would be required to arm and arm64 (or other
> architectures).
>
> To help with bisectability, could we please have a suitable fix applied
> to the two patches in the -mm tree:
> http://ozlabs.org/~akpm/mmots/broken-out/mm-update-generic-gup-implementation-to-handle-hugepage-directory.patch
> http://ozlabs.org/~akpm/mmots/broken-out/arch-powerpc-switch-to-generic-rcu-get_user_pages_fast.patch
>
> rather than applied afterwards?
>
> With pgd_huge(x) defined, this patch passes my futex test on arm
> (Arndale platform) and arm64(Juno).
>
> Cheers,
> -- 
> Steve
>
>
>
> From 2fb7b0308f0aca94c50611257ba82d656abb0768 Mon Sep 17 00:00:00 2001
> From: Steve Capper <steve.capper@...aro.org>
> Date: Thu, 16 Oct 2014 09:09:48 +0100
> Subject: [PATCH] Fixup for Update generic gup implementation
>
> The patch:
> mm: Update generic gup implementation to handle hugepage directory
>
> will not compile for arm or arm64 due to pgd_huge being undefined.
>
> Signed-off-by: Steve Capper <steve.capper@...aro.org>
> ---
>  arch/arm/include/asm/pgtable.h   | 2 ++
>  arch/arm64/include/asm/pgtable.h | 2 ++
>  include/linux/hugetlb.h          | 1 -
>  3 files changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
> index 90aa4583..46f81fb 100644
> --- a/arch/arm/include/asm/pgtable.h
> +++ b/arch/arm/include/asm/pgtable.h
> @@ -181,6 +181,8 @@ extern pgd_t swapper_pg_dir[PTRS_PER_PGD];
>  /* to find an entry in a kernel page-table-directory */
>  #define pgd_offset_k(addr)	pgd_offset(&init_mm, addr)
>
> +#define pgd_huge(pgd)		(0)
> +
>  #define pmd_none(pmd)		(!pmd_val(pmd))
>  #define pmd_present(pmd)	(pmd_val(pmd))
>
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 464c5ce..d4462ca 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -462,6 +462,8 @@ static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
>  extern pgd_t swapper_pg_dir[PTRS_PER_PGD];
>  extern pgd_t idmap_pg_dir[PTRS_PER_PGD];
>
> +#define pgd_huge(pgd)		(0)
> +
>  /*
>   * Encode and decode a swap entry:
>   *	bits 0-1:	present (must be zero)
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 65e12a2..6e6d338 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -138,7 +138,6 @@ static inline void hugetlb_show_meminfo(void)
>  #define prepare_hugepage_range(file, addr, len)	(-EINVAL)
>  #define pmd_huge(x)	0
>  #define pud_huge(x)	0
> -#define pgd_huge(x)	0
>  #define is_hugepage_only_range(mm, addr, len)	0
>  #define hugetlb_free_pgd_range(tlb, addr, end, floor, ceiling) ({BUG(); 0; })
>  #define hugetlb_fault(mm, vma, addr, flags)	({ BUG(); 0; })

don't do the last hunk, that will result in build failures on sub
platforms on ppc64. can you do the arm patch without making the change
to hugetlb.h ?

-aneesh

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