Subject: Re: [PATCH 1/2] mm: Introducing arch_remap hook

From: Ingo Molnar <[email-masked]>
Date: Mon, 23 Mar 2015 09:52:09 +0100

* Laurent Dufour <[email-masked]> wrote:

> Some architecture would like to be triggered when a memory area is moved
> through the mremap system call.
> 
> This patch is introducing a new arch_remap mm hook which is placed in the
> path of mremap, and is called before the old area is unmapped (and the
> arch_unmap hook is called).
> 
> To no break the build, this patch adds the empty hook definition to the
> architectures that were not using the generic hook's definition.
> 
> Signed-off-by: Laurent Dufour <[email-masked]>
> ---
>  arch/s390/include/asm/mmu_context.h      | 6 ++++++
>  arch/um/include/asm/mmu_context.h        | 5 +++++
>  arch/unicore32/include/asm/mmu_context.h | 6 ++++++
>  arch/x86/include/asm/mmu_context.h       | 6 ++++++
>  include/asm-generic/mm_hooks.h           | 6 ++++++
>  mm/mremap.c                              | 9 +++++++--
>  6 files changed, 36 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_context.h
> index 8fb3802f8fad..ddd861a490ba 100644
> --- a/arch/s390/include/asm/mmu_context.h
> +++ b/arch/s390/include/asm/mmu_context.h
> @@ -131,4 +131,10 @@ static inline void arch_bprm_mm_init(struct mm_struct *mm,
>  {
>  }
>  
> +static inline void arch_remap(struct mm_struct *mm,
> +			      unsigned long old_start, unsigned long old_end,
> +			      unsigned long new_start, unsigned long new_end)
> +{
> +}
> +
>  #endif /* __S390_MMU_CONTEXT_H */
> diff --git a/arch/um/include/asm/mmu_context.h b/arch/um/include/asm/mmu_context.h
> index 941527e507f7..f499b017c1f9 100644
> --- a/arch/um/include/asm/mmu_context.h
> +++ b/arch/um/include/asm/mmu_context.h
> @@ -27,6 +27,11 @@ static inline void arch_bprm_mm_init(struct mm_struct *mm,
>  				     struct vm_area_struct *vma)
>  {
>  }
> +static inline void arch_remap(struct mm_struct *mm,
> +			      unsigned long old_start, unsigned long old_end,
> +			      unsigned long new_start, unsigned long new_end)
> +{
> +}
>  /*
>   * end asm-generic/mm_hooks.h functions
>   */
> diff --git a/arch/unicore32/include/asm/mmu_context.h b/arch/unicore32/include/asm/mmu_context.h
> index 1cb5220afaf9..39a0a553172e 100644
> --- a/arch/unicore32/include/asm/mmu_context.h
> +++ b/arch/unicore32/include/asm/mmu_context.h
> @@ -97,4 +97,10 @@ static inline void arch_bprm_mm_init(struct mm_struct *mm,
>  {
>  }
>  
> +static inline void arch_remap(struct mm_struct *mm,
> +			      unsigned long old_start, unsigned long old_end,
> +			      unsigned long new_start, unsigned long new_end)
> +{
> +}
> +
>  #endif
> diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
> index 883f6b933fa4..75cb71f4be1e 100644
> --- a/arch/x86/include/asm/mmu_context.h
> +++ b/arch/x86/include/asm/mmu_context.h
> @@ -172,4 +172,10 @@ static inline void arch_unmap(struct mm_struct *mm, struct vm_area_struct *vma,
>  		mpx_notify_unmap(mm, vma, start, end);
>  }
>  
> +static inline void arch_remap(struct mm_struct *mm,
> +			      unsigned long old_start, unsigned long old_end,
> +			      unsigned long new_start, unsigned long new_end)
> +{
> +}
> +
>  #endif /* _ASM_X86_MMU_CONTEXT_H */

So instead of spreading these empty prototypes around mmu_context.h 
files, why not add something like this to the PPC definition:

 #define __HAVE_ARCH_REMAP

and define the empty prototype for everyone else? It's a bit like how 
the __HAVE_ARCH_PTEP_* namespace works.

That should shrink this patch considerably.

Thanks,

	Ingo