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

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Message-ID: <20081228195921.GB19176@srcf.ucam.org>
Date:	Sun, 28 Dec 2008 19:59:21 +0000
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Éric Piel <E.A.B.Piel@...elft.nl>
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, Dec 28, 2008 at 08:04:50PM +0100, Éric Piel wrote:
> Matthew Garrett schreef:
> > 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.
> :
> Sorry, but I doubt it's a good idea. First, it breaks the simple
> semantic of relatime (mtime > atime?), mixing it with a rather arbitrary
> constant. Second, and most important, there are lots of workloads which
> will be strongly affected by this modification. For instance, running
> md5sum daily on the filesystem will cause a write for every file.

Yes. And? I can't think of a single case where something could 
absolutely depend on the current relatime semantics, so altering them to 
more usefully match the atime semantics doesn't seem likely to cause any 
trouble.

> I think that to solve the problem for your use case, it's better to use
> a different approach such as mounting separately /tmp (with the atime
> option).

The use case in this case is the significant body of currently installed 
machines that don't have /tmp on a separate filesystem. In the very 
common setup of tmpreaper being used, the current relatime semantics 
will result in undesired data loss. I think the proposed alteration 
makes the behaviour of relatime massively more useful without any 
obvious drawbacks.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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