linux-kernel - Re: [PATCH] Revert oom rewrite series

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Date:	Sat, 27 Nov 2010 17:45:36 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ying Han <yinghan@...gle.com>, Bodo Eggert <7eggert@....de>,
	Mandeep Singh Baines <msb@...gle.com>,
	"Figo.zhang" <figo1802@...il.com>
Subject: Re: [PATCH] Revert oom rewrite series

On Tue, 23 Nov 2010, KOSAKI Motohiro wrote:

> > You may remember that the initial version of my rewrite replaced oom_adj 
> > entirely with the new oom_score_adj semantics.  Others suggested that it 
> > be seperated into a new tunable and the old tunable deprecated for a 
> > lengthy period of time.  I accepted that criticism and understood the 
> > drawbacks of replacing the tunable immediately and followed those 
> > suggestions.  I disagree with you that the deprecation of oom_adj for a 
> > period of two years is as dramatic as you imply and I disagree that users 
> > are experiencing problems with the linear scale that it now operates on 
> > versus the old exponential scale.
> 
> Yes and No. People wanted to separate AND don't break old one.
> 

You're arguing on the behalf of applications that don't exist.

> > > 1) About two month ago, Dave hansen observed strange OOM issue because he
> > >    has a big machine and ALL process are not so big. thus, eventually all 
> > >    process got oom-score=0 and oom-killer didn't work.
> > > 
> > >    https://kerneltrap.org/mailarchive/linux-driver-devel/2010/9/9/6886383
> > > 
> > >    DavidR changed oom-score to +1 in such situation. 
> > > 
> > >    http://kerneltrap.org/mailarchive/linux-kernel/2010/9/9/4617455
> > > 
> > >    But it is completely bognus. If all process have score=1, oom-killer fall
> > >    back to purely random killer. I expected and explained his patch has
> > >    its problem at half years ago. but he didn't fix yet.
> > > 
> > 
> > The resolution with which the oom killer considers memory is at 0.1% of 
> > system RAM at its highest (smaller when you have a memory controller, 
> > cpuset, or mempolicy constrained oom).  It considers a task within 0.1% of 
> > memory of another task to have equal "badness" to kill, we don't break 
> > ties in between that resolution -- it all depends on which one shows up in 
> > the tasklist first.  If you disagree with that resolution, which I support 
> > as being high enough, then you may certainly propose a patch to make it 
> > even finer at 0.01%, 0.001%, etc.  It would only change oom_badness() to 
> > range between [0,10000], [0,100000], etc.
> 
> No.
> Think Moore's Law. rational value will be not able to work in future anyway.
> 10 years ago, I used 20M bytes memory desktop machine and I'm now using 2GB.
> memory amount is growing and growing. and bash size doesn't grwoing so fast.
> 

If you'd like to suggest an increase to the upper-bound of the badness 
score, please do so, although I don't think we need to break ties amongst 
tasks that differ by at most <0.1% of the system's capacity.
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