linux-kernel - Re: Suggestion: xtime as new inode attribute

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Date:	Fri, 18 Dec 2009 10:19:25 +0100
From:	Daniel Poelzleithner <poelzi@...lzi.org>
To:	Bryan Donlan <bdonlan@...il.com>
CC:	linux-kernel@...r.kernel.org, Simon Horman <horms@...ge.net.au>,
	Jeffrey Hundstad <jeffrey.hundstad@...u.edu>
Subject: Re: Suggestion: xtime as new inode attribute

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Bryan Donlan wrote:

> Why isn't atime sufficient? atime is updated when programs are
> executed, and it's uncommon for executable files to be accessed
> without being executed; for the purposes of determining whether a
> program is needed, it ought to be good enough.

Why atime is not useable is for example that full system backup would
distroy all data. Thinking about grepping for a string in /usr or
/usr/bin because you are searching for something will update all atime
stamps and therefore cause dataloss for this purpose.

> Note that many modern distros use relatime to reduce the (significant)
> overhead of atime; this may account for why you may not be seeing
> atime update for executables; try mounting with -o strictatime if you
> want to see it at work, but beware, as this will bring with it a major
> performance hit - which your proposal would as well :)

The performance impact is one reason of course. As executing is much
more seldom the impact of updating the xtime should be mild enough that
it could be done by default. I don't mount strictatime for this reason, too.

kindly regards
 Daniel

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