linux-kernel - Re: [PATCH 3/5] mm, shmem: Add shmem

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Date:	Thu, 31 Jul 2014 22:03:52 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Jerome Marchand <jmarchan@...hat.com>
cc:	Oleg Nesterov <oleg@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	linux-doc@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux390@...ibm.com,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH 3/5] mm, shmem: Add shmem_vma() helper

On Tue, 22 Jul 2014, Jerome Marchand wrote:

> Add a simple helper to check if a vm area belongs to shmem.
> 
> Signed-off-by: Jerome Marchand <jmarchan@...hat.com>
> ---
>  include/linux/mm.h | 6 ++++++
>  mm/shmem.c         | 8 ++++++++
>  2 files changed, 14 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 34099fa..04a58d1 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1074,11 +1074,17 @@ int shmem_zero_setup(struct vm_area_struct *);
>  
>  extern int shmem_locate(struct vm_area_struct *vma, pgoff_t pgoff, int *count);
>  bool shmem_mapping(struct address_space *mapping);
> +bool shmem_vma(struct vm_area_struct *vma);
> +
>  #else
>  static inline bool shmem_mapping(struct address_space *mapping)
>  {
>  	return false;
>  }
> +static inline bool shmem_vma(struct vm_area_struct *vma)
> +{
> +	return false;
> +}
>  #endif

I would prefer include/linux/shmem_fs.h for this (and one of us clean
up where the declarations of shmem_zero_setup and shmem_mapping live).

But if 4/5 goes away, then there will only be one user of shmem_vma(),
so in that case better just declare it (using shmem_mapping()) there
in task_mmu.c in the smaps patch.

>  
>  extern int can_do_mlock(void);
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 8aa4892..7d16227 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1483,6 +1483,14 @@ bool shmem_mapping(struct address_space *mapping)
>  	return mapping->backing_dev_info == &shmem_backing_dev_info;
>  }
>  
> +bool shmem_vma(struct vm_area_struct *vma)
> +{
> +	return (vma->vm_file &&
> +		vma->vm_file->f_dentry->d_inode->i_mapping->backing_dev_info
> +		== &shmem_backing_dev_info);
> +

I agree with Oleg,
	vma->vm_file && shmem_mapping(file_inode(vma->vm_file)->i_mapping);
would be better,

Hugh
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