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

[Ingo Molnar]

* Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> 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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