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

From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Ingo Molnar <mingo@elte.hu>
Cc: J??rn Engel <joern@logfs.org>, Jeff Garzik <jeff@garzik.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	linux-mm@kvack.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	miklos@szeredi.hu, akpm@linux-foundation.org, neilb@suse.de,
	dgc@sgi.com, tomoki.sekiyama.qu@hitachi.com,
	nikita@clusterfs.com, trond.myklebust@fys.uio.no,
	yingchao.zhou@gmail.com, richard@rsk.demon.co.uk, david@lang.hm
Subject: Re: [PATCH 00/23] per device dirty throttling -v8
Date: Sun, 5 Aug 2007 20:11:46 +0100	[thread overview]
Message-ID: <20070805201146.1082f8c0@the-village.bc.nu> (raw)
In-Reply-To: <20070805180826.GD3244@elte.hu>

On Sun, 5 Aug 2007 20:08:26 +0200
Ingo Molnar <mingo@elte.hu> wrote:

> 
> * Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:
> 
> > And you honestly think that putting it in Kconfig as well as allowing 
> > users to screw up horribly and creating incompatible defaults you
> 
> So far you've not offered one realistic scenario of "screw up horribly". 
> People have been using noatime for a long time and there are no horror 
> stories about that. _Which_ OSS HSM software relies on atime?

Whats this about "OSS". OSS or proprietary. And you've been given one
example already - tmpwatch. Although its more of a trash compactor than
HSM.

> > can't test for in a user space app where it matters is going to 
> > *change* this.
> 
> The patch i posted today adds /proc/sys/kernel/mount_with_atime. That 
> can be tested by user-space, if it truly cares about atime.

We have an existing API and ABI thank you. See man mount.

> > Do you really think anyone who said "noatime, compatibility, umm errr" 
> > is going to say "noatime, compatibility, but hey its in Kconfig lets 
> > do it". You argument doesn't hold up to minimal rational 
> > consideration. Posting to the distribution devel list with: "Its a 50% 
> > performance win, we need to fix these corner cases, here's a tmpwatch 
> > patch" is *exactly* what is needed to change it, and Kconfig options 
> > are irrelevant to that.
> 
> i did exactly that 6 months ago, check your email folders. I went by the 
> "process". But it doesnt really matter anymore, Ubuntu has done the step 

And your Kconfig argument is still not rational. A question I note you
chose not to answer. Anyway if Ubuntu has switched to noatime by default
(or relatime) and hasn't used a Kconfig line that proves my whole point -
we don't need one and its pointless to add so.

> we really have to ask ourselves whether the "process" is correct if 
> advantages to the user of this order of magnitude can be brushed aside 
> with simple "this breaks binary-only HSM" and "it's not standards 
> compliant" arguments.

Thats a discussion to have with your distribution development team. The
kernel provides the required facilities already. Open source means
everyone can do cool stuff as they see fit and natural selection will do
the rest.

Look I agree entirely with you that relatime, or noatime + minor package
patches is the right thing to do for FC8. I've also pointed out you can
build and release tuning packages for FC 7 and they'll make the
distribution. FC8 beta 1 approaches so now is the time to be talking to
the distribution people and to the ever kernel building Dave Jones about
it.

But none of this makes stupid Kconfig hacks the right answer.

Alan