linux-ext4 - Re: [PATCH] Update atime from future.

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Date:	Thu, 13 Jan 2011 14:18:57 +0000
From:	Steven Whitehouse <swhiteho@...hat.com>
To:	Pavel Machek <pavel@....cz>
Cc:	yangsheng <sickamd@...il.com>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, adilger.kernel@...ger.ca,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] Update atime from future.

Hi,

On Tue, 2011-01-11 at 14:33 +0100, Pavel Machek wrote:
> 	return 1;
> > > +	/*
> > > +	 * Is the previous atime value old than a day? If yes,
> > >  	 * update atime:
> > >  	 */
> > >  	if ((long)(now.tv_sec - inode->i_atime.tv_sec) >= 24*60*60)
> > 
> > I don't think this is a good plan for cluster filesystems, since if the
> > times on the nodes are not exactly synchronised (we do highly recommend
> > people run ntp or similar) then this might lead to excessive atime
> > updating. The current behaviour is to ignore atimes which are in the
> > future for exactly this reason,
> 
> Well, would these "update storms" really be a problem?
> 
> AFAICT they should be fairly non-frequent, and worst thing that can
> happen is that you'll do as many updates as different time settings,
> settling for the lowest value...?
> 									Pavel

Sorry for the delay in replying. It has been a problem in the past,
certainly. I think it is best to be cautious in this case, since that
way we can be sure it won't be a problem. The chosen solution looks ok
to me,

Steve.


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