linux-kernel - Re: [PATCH] Allow relatime to update atime once a day

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Message-ID: <20090326175629.GA13742@x200.localdomain>
Date:	Thu, 26 Mar 2009 20:56:29 +0300
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Matthew Garrett <mjg@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frans Pop <elendil@...net.nl>, mingo@...e.hu, tytso@....edu,
	jack@...e.cz, alan@...rguk.ukuu.org.uk, arjan@...radead.org,
	a.p.zijlstra@...llo.nl, npiggin@...e.de, jens.axboe@...cle.com,
	drees76@...il.com, jesper@...gh.cc, linux-kernel@...r.kernel.org,
	oleg@...hat.com, roland@...hat.com, willy@...ux.intel.com,
	vaurora@...hat.com
Subject: Re: [PATCH] Allow relatime to update atime once a day

On Thu, Mar 26, 2009 at 05:32:14PM +0000, Matthew Garrett wrote:
> 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, making relatime a plausible default for distributions.

> +/*
> + * 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;
> +	/*
> +	 * Good, we can skip the atime update:
> +	 */
> +	return 0;
> +}

Good example of overcommented code.
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