linux-kernel - Re: [PATCH 00/23] per device dirty throttling -v8

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Date:	Sun, 5 Aug 2007 09:28:05 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Claudio Martins <ctpm@....utl.pt>, Jeff Garzik <jeff@...zik.org>,
	Jörn Engel <joern@...fs.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-mm@...ck.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	miklos@...redi.hu, akpm@...ux-foundation.org, neilb@...e.de,
	dgc@....com, tomoki.sekiyama.qu@...achi.com, nikita@...sterfs.com,
	trond.myklebust@....uio.no, yingchao.zhou@...il.com,
	richard@....demon.co.uk, david@...g.hm
Subject: Re: [PATCH 00/23] per device dirty throttling -v8


* Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

> >  Can you give examples of backup solutions that rely on atime being 
> > updated? I can understand backup tools using mtime/ctime for 
> > incremental backups (like tar + Amanda, etc), but I'm having trouble 
> > figuring out why someone would want to use atime for that.
> 
> HSM is the usual one, and to a large extent probably why Unix 
> originally had atime. Basically migrating less used files away so as 
> to keep the system disks tidy.

atime is used as a _hint_, at most and HSM sure works just fine on an 
atime-incapable filesystem too. So it's the same deal as "add user_xattr 
mount option to the filesystem to make Beagle index faster". It's now: 
"if you use HSM storage add the atime mount option to make it slightly 
more intelligent. Expect huge IO slowdowns though."

The only remotely valid compatibility argument would be Mutt - but even 
that handles it just fine. (we broke way more software via noexec)

	Ingo
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