linux-kernel - Re: [PATCH 3/5] oom: oom-killer don't use proportion of system-ram internally

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Date:	Mon, 23 May 2011 15:28:29 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, caiqian@...hat.com, hughd@...gle.com,
	kamezawa.hiroyu@...fujitsu.com, minchan.kim@...il.com,
	oleg@...hat.com
Subject: Re: [PATCH 3/5] oom: oom-killer don't use proportion of system-ram
 internally

On Fri, 20 May 2011, KOSAKI Motohiro wrote:

> CAI Qian reported his kernel did hang-up if he ran fork intensive
> workload and then invoke oom-killer.
> 
> The problem is, current oom calculation uses 0-1000 normalized value
> (The unit is a permillage of system-ram). Its low precision make
> a lot of same oom score. IOW, in his case, all processes have smaller
> oom score than 1 and internal calculation round it to 1.
> 
> Thus oom-killer kill ineligible process. This regression is caused by
> commit a63d83f427 (oom: badness heuristic rewrite).
> 
> The solution is, the internal calculation just use number of pages
> instead of permillage of system-ram. And convert it to permillage
> value at displaying time.
> 
> This patch doesn't change any ABI (included  /proc/<pid>/oom_score_adj)
> even though current logic has a lot of my dislike thing.
> 

Same response as when you initially proposed this patch: 
http://marc.info/?l=linux-kernel&m=130507086613317 -- you never replied to 
that.

The changelog doesn't accurately represent CAI Qian's problem; the issue 
is that root processes are given too large of a bonus in comparison to 
other threads that are using at most 1.9% of available memory.  That can 
be fixed, as I suggested by giving 1% bonus per 10% of memory used so that 
the process would have to be using 10% before it even receives a bonus.

I already suggested an alternative patch to CAI Qian to greatly increase 
the granularity of the oom score from a range of 0-1000 to 0-10000 to 
differentiate between tasks within 0.01% of available memory (16MB on CAI 
Qian's 16GB system).  I'll propose this officially in a separate email.

This patch also includes undocumented changes such as changing the bonus 
given to root processes.
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