Re: [PATCH] mmap : save some cycles for the shared anonymous mapping

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 11 Sep 2009 09:52:46 +0800
Huang Shijie <shijie8@gmail.com> wrote:

> The shmem_zere_setup() does not change vm_start, pgoff or vm_flags,
> only some drivers change them (such as /driver/video/bfin-t350mcqb-fb.c).
> 
> Moving these codes to a more proper place to save cycles for shared anonymous mapping.
> 
> Signed-off-by: Huang Shijie <shijie8@gmail.com>
> ---
>  mm/mmap.c |   18 +++++++++---------
>  1 files changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 8101de4..840e91e 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1195,21 +1195,21 @@ munmap_back:
>  			goto unmap_and_free_vma;
>  		if (vm_flags & VM_EXECUTABLE)
>  			added_exe_file_vma(mm);
> +
> +		/* Can addr have changed??
> +		 *
> +		 * Answer: Yes, several device drivers can do it in their
> +		 *         f_op->mmap method. -DaveM
> +		 */
> +		addr = vma->vm_start;
> +		pgoff = vma->vm_pgoff;
> +		vm_flags = vma->vm_flags;
>  	} else if (vm_flags & VM_SHARED) {
>  		error = shmem_zero_setup(vma);
>  		if (error)
>  			goto free_vma;
>  	}
>  
> -	/* Can addr have changed??
> -	 *
> -	 * Answer: Yes, several device drivers can do it in their
> -	 *         f_op->mmap method. -DaveM
> -	 */
> -	addr = vma->vm_start;
> -	pgoff = vma->vm_pgoff;
> -	vm_flags = vma->vm_flags;
> -
>  	if (vma_wants_writenotify(vma))
>  		vma->vm_page_prot = vm_get_page_prot(vm_flags & ~VM_SHARED);
>  

hm, maybe we should nuke those locals and just use vma->foo everywhere.

Local variable pgoff never gets used again anyway.

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