linux-kernel - Re: [PATCH, resend] relatime: Let relatime update atime at least once per day

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Date:	Sun, 28 Dec 2008 19:35:25 +0100 (CET)
From:	Jesper Juhl <jj@...osbits.net>
To:	Matthew Garrett <mjg@...hat.com>
cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH, resend] relatime: Let relatime update atime at least
 once per day

On Sun, 28 Dec 2008, Matthew Garrett wrote:

> Ensure relatime updates atime at least once per day
>     
> Allow atime to be updated once per day even with relatime. This lets
> utilities like tmpreaper (which delete files based on last access time)
> continue working.
>     
> Signed-off-by: Matthew Garrett <mjg@...hat.com>
> Reviewed-by: Matthew Wilcox <willy@...ux.intel.com>
> Acked-by: Valerie Aurora Henson <vaurora@...hat.com>
> Acked-by: Alan Cox <alan@...hat.com>
> Acked-by: Ingo Molnar <mingo@...e.hu>
> 

Overall I think the patch looks good.
Feel free to add
 Reviewed-by: Jesper Juhl <jj@...osbits.net>
if you like.

I only have a single pedantic comment below.

> ---
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 0487ddb..057c92b 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -1179,6 +1179,40 @@ sector_t bmap(struct inode * inode, sector_t block)
>  }
>  EXPORT_SYMBOL(bmap);
>  
> +/*
> + * With relative atime, only update atime if the previous atime is
> + * earlier than either the ctime or mtime or if at least a day has
> + * passed since the last atime update.
> + */
> +static int relatime_need_update(struct vfsmount *mnt, struct inode *inode,
> +			     struct timespec now)
> +{
> +
> +	if (!(mnt->mnt_flags & MNT_RELATIME))
> +		return 1;
> +	/*
> +	 * Is mtime younger than atime? If yes, update atime:
> +	 */
> +	if (timespec_compare(&inode->i_mtime, &inode->i_atime) >= 0)
> +		return 1;
> +	/*
> +	 * Is ctime younger than atime? If yes, update atime:
> +	 */
> +	if (timespec_compare(&inode->i_ctime, &inode->i_atime) >= 0)
> +		return 1;
> +
> +	/*
> +	 * Is the previous atime value older than a day? If yes,
> +	 * update atime:
> +	 */
> +	if ((long)(now.tv_sec - inode->i_atime.tv_sec) >= 24*60*60)
> +		return 1;

Not all days are 24*60*60 seconds long. Daylight savings time as well as 
leap seconds make this an inaccurate/incorrect constant for representing 
"one day".
I don't think we really care, but perhaps the comment above should 
acknowledge the fact that this is aproximately one day?

> +	/*
> +	 * Good, we can skip the atime update:
> +	 */
> +	return 0;
> +}
> +
>  /**
>   *	touch_atime	-	update the access time
>   *	@mnt: mount the inode is accessed on
> @@ -1206,17 +1240,12 @@ void touch_atime(struct vfsmount *mnt, struct dentry *dentry)
>  		goto out;
>  	if ((mnt->mnt_flags & MNT_NODIRATIME) && S_ISDIR(inode->i_mode))
>  		goto out;
> -	if (mnt->mnt_flags & MNT_RELATIME) {
> -		/*
> -		 * With relative atime, only update atime if the previous
> -		 * atime is earlier than either the ctime or mtime.
> -		 */
> -		if (timespec_compare(&inode->i_mtime, &inode->i_atime) < 0 &&
> -		    timespec_compare(&inode->i_ctime, &inode->i_atime) < 0)
> -			goto out;
> -	}
>  
>  	now = current_fs_time(inode->i_sb);
> +
> +	if (!relatime_need_update(mnt, inode, now))
> +		goto out;
> +
>  	if (timespec_equal(&inode->i_atime, &now))
>  		goto out;
> 

-- 
Jesper Juhl <jj@...osbits.net>
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