Date:	Sun, 14 Nov 2010 14:07:11 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [resend][PATCH 2/4] Revert "oom: deprecate oom_adj tunable"

> On Tue, 9 Nov 2010, KOSAKI Motohiro wrote:
> 
> > > > > The new tunable added in 2.6.36, /proc/pid/oom_score_adj, is necessary for 
> > > > > the units that the badness score now uses.  We need a tunable with a much 
> > > > 
> > > > Who we?
> > > > 
> > > 
> > > Linux users who care about prioritizing tasks for oom kill with a tunable 
> > > that (1) has a unit, (2) has a higher resolution, and (3) is linear and 
> > > not exponential.  
> > 
> > No. Majority user don't care. You only talk about your case. Don't ignore
> > end user.
> 
> If they don't care, then they won't be using oom_adj, so you're point 
> about it's deprecation is irrelevant.

No irrelevant. Your patch break their environment even though
they don't use oom_adj explicitly. because their application are using it.


> 
> Other users do want a more powerful userspace interface with a unit and 
> higher resolution (I am one of them), there's no requirement that those 
> users need to be in the majority.

But, they only live in your DREAM. you coldn't show who necessary.


>
> > > Memcg doesn't solve this issue without incurring a 1% 
> > > memory cost.
> > 
> > Look at a real.
> > All major distributions has already turn on memcg. End user don't need
> > to pay additional cost.
> 
> Memcg also has a command-line disabling option to avoid incurring this 1% 
> memory cost when you're not going to be using it.

Look at real. who use it?



> > > No, it doesn't, and you completely and utterly failed to show a single 
> > > usecase that broke as a result of this because nobody can currently use 
> > > oom_adj for anything other than polarization.  Thus, there's no backwards 
> > > compatibility issue.
> > 
> > No. I showed. 
> > 1) Google code search showed some application are using this feature.
> > 	http://www.google.com/codesearch?as_q=oom_adj&btnG=Search+Code&hl=ja&as_package=&as_lang=&as_filename=&as_class=&as_function=&as_license=&as_case=
> > 
> 
> oom_adj isn't removed, it's deprecated.  These users are using a 
> deprecated interface and have a few years to convert to using the new 
> interface (if it ever is actually removed).

No. there is no reason to enforce rewrite tons applicatin.



> 
> > 2) Not body use oom_adj other than polarization even though there are a few.
> >    example, kde are using.
> > 	http://www.google.com/codesearch/p?hl=ja#MPJuLvSvNYM/pub/kde/unstable/snapshots/kdelibs.tar.bz2%7CWClmGVN5niU/kdelibs-1164923/kinit/start_kdeinit.c&q=oom_adj%20kde%205
> > 
> > When you are talking polarization issue, you blind a real. Don't talk your dream.
> > 
> 
> I don't understand what you're trying to say here, but the current users 
> of oom_adj that aren't +15 or -16 (or OOM_DISABLE) are arbitrary based 
> relative to other tasks such as +5, +10, etc.  They don't have any 
> semantics other than being arbitrarily relative because it doesn't work in 
> a linear way or with a scale.

Even if you don't understand, they are IN THE WORLD. you don't have to
ignore a real.


> > 3) udev are using this feature. It's one of major linux component and you broke.
> > 
> > http://www.google.com/codesearch/p?hl=ja#KVTjzuVpblQ/pub/linux/utils/kernel/hotplug/udev-072.tar.bz2%7CwUSE-Ay3lLI/udev-072/udevd.c&q=oom_adj
> > 
> > You don't have to break our userland. you can't rewrite or deprecate 
> > old one. It's used! You can only add orthogonal new knob.
> > 
> 
> That's incorrect, I didn't break anything by deprecating a tunable for a 
> few years.  oom_adj gets converted roughly into an equivalent (but linear) 
> oom_score_adj.
> 
> Unfortunately for your argument, you can't show a single example of a 
> current oom_adj user that has a scientific calculation behind its value 
> that is now broken on the linear scale.

you are talking unrelated thing.

> 
> > > Yes, I've tested it, and it deprecates the tunable as expected.  A single 
> > > warning message serves the purpose well: let users know one time without 
> > > being overly verbose that the tunable is deprecated and give them 
> > > sufficient time (2 years) to start using the new tunable.  That's how 
> > > deprecation is done.
> > 
> > no sense.
> > 
> > Why do their application need to rewrite for *YOU*? Okey, you will got
> > benefit from your new knob. But NOBDOY use the new one. and People need
> > to rewrite their application even though no benefit. 
> > 
> > Don't do selfish userland breakage!
> > 
> 
> It's deprecated for a few years so users can gradually convert to the new 
> tunable, it wasn't removed when the new one was introduced.  A higher 
> resolution tunable that scales linearly with a unit is an advantage for 
> Linux (for the minority of users who care about oom killing priority 
> beyond the heuristic) and I think a few years is enough time for users to 
> do a simple conversion to the new tunable.

no sense.



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