linux-kernel - Re: [patch 2/3] mm: memory: remove ->vm

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Date:	Tue, 2 Dec 2014 09:58:25 +0100
From:	Jan Kara <jack@...e.cz>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, Hugh Dickins <hughd@...gle.com>,
	Michel Lespinasse <walken@...gle.com>, Jan Kara <jack@...e.cz>,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 2/3] mm: memory: remove ->vm_file check on shared
 writable vmas

On Mon 01-12-14 17:58:01, Johannes Weiner wrote:
> The only way a VMA can have shared and writable semantics is with a
> backing file.
  OK, one always learns :) After some digging I found that MAP_SHARED |
MAP_ANONYMOUS mappings are in fact mappings of a temporary file in tmpfs.
It would be worth to mention this in the changelog I believe. Otherwise
feel free to add:
  Reviewed-by: Jan Kara <jack@...e.cz>

								Honza
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> ---
>  mm/memory.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index 73220eb6e9e3..2a2e3648ed65 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2167,9 +2167,7 @@ reuse:
>  				balance_dirty_pages_ratelimited(mapping);
>  			}
>  
> -			/* file_update_time outside page_lock */
> -			if (vma->vm_file)
> -				file_update_time(vma->vm_file);
> +			file_update_time(vma->vm_file);
>  		}
>  		put_page(dirty_page);
>  		if (page_mkwrite) {
> @@ -3025,8 +3023,7 @@ static int do_shared_fault(struct mm_struct *mm, struct vm_area_struct *vma,
>  		balance_dirty_pages_ratelimited(mapping);
>  	}
>  
> -	/* file_update_time outside page_lock */
> -	if (vma->vm_file && !vma->vm_ops->page_mkwrite)
> +	if (!vma->vm_ops->page_mkwrite)
>  		file_update_time(vma->vm_file);
>  
>  	return ret;
> -- 
> 2.1.3
> 
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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