linux-kernel - Re: relatime: update once per day patches (was: ext3 IO latency measurements)

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Date:	Thu, 26 Mar 2009 09:24:54 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Frans Pop <elendil@...net.nl>, mingo@...e.hu, tytso@....edu,
	jack@...e.cz, alan@...rguk.ukuu.org.uk, arjan@...radead.org,
	a.p.zijlstra@...llo.nl, npiggin@...e.de, jens.axboe@...cle.com,
	drees76@...il.com, jesper@...gh.cc, linux-kernel@...r.kernel.org,
	oleg@...hat.com, roland@...hat.com
Subject: Re: relatime: update once per day patches (was: ext3 IO latency
 measurements)

On Thu, 26 Mar 2009 09:14:28 -0700 (PDT) Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> 
> 
> On Thu, 26 Mar 2009, Andrew Morton wrote:
> > 
> > Hard-wiring a 24-hour interval into the core VFS for all mounted
> > filesystems is dumb.
> 
> Umm. 
> 
> I generally agree witht he "leave policy to user space" people, but this 
> is an area where (a) user space has shown itself to not get it right (ie 
> people don't do even the existing relatime because distros don't) and (b) 
> what's the alternative?
> 
> > I (and others) pointed out that it would be better to implement this as
> > a mount option.  That suggestion was met with varying sillinesses and
> > that is where things stand.
> 
> I'd suggest first just doing the 24 hour thing, and then, IF user space 
> actually ever gets its act together, and people care, and they _ask_ for a 
> mount option, that's when it's worth doing.
> 

We wouldn't normally just enable the new feature by default because it
changes kernel behaviour.  Userspace needs to be changed in some manner to
opt-in.  One way it's `mount -o remount', the other way it's a poke in
/proc.



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