linux-kernel - Re: [take2] OOM documentation update [was: Linux killed Kenny, bastard!]

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Date:	Wed, 14 Jan 2009 13:34:44 -0800
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Evgeniy Polyakov <zbr@...emap.net>
Cc:	linux-kernel@...r.kernel.org, David Rientjes <rientjes@...gle.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Dave Jones <davej@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Theodore Tso <tytso@....edu>,
	Matthias Andree <matthias.andree@....de>
Subject: Re: [take2] OOM documentation update [was: Linux killed Kenny,
 bastard!]

On Wed, 14 Jan 2009 20:06:06 +0300 Evgeniy Polyakov wrote:

> Updated version fixes some errors and extends description by adding
> swapping and children relation explaintaion.
> 
> Signed.

??

> diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
> index d105eb4..4aa1918 100644
> --- a/Documentation/filesystems/proc.txt
> +++ b/Documentation/filesystems/proc.txt
> @@ -2311,6 +2311,33 @@ increase the likelihood of this process being killed by the oom-killer.  Valid
>  values are in the range -16 to +15, plus the special value -17, which disables
>  oom-killing altogether for this process.
>  
> +The process to be killed in an out-of-memory situation is selected among all others
> +based on its badness score. This value equals the original memory size of the process
> +originally and is then updated according to its CPU time (utime + stime) and the

drop "originally" since earlier part of sentence says "original memory size".

> +run time (uptime - start time). The longer it runs the smaller is the score.
> +Badness score is divided by the square root of the cpu time and then by

                                                      CPU

> +the double square root of the run time.
> +
> +Swapped out tasks are killed first. Half of each child's memory size is added to
> +the parent's score if they do not share the same memory. Thus forking servers
> +are the prime candidates to be killed. Having only one 'hungry' child will make
> +parent less preferable than the child.
> +
> +/proc/<pid>/oom_score shows process' current badness score.
> +
> +The following heuristics are then applied:
> + * if the task was reniced, its score doubles
> + * superuser or direct hardware access tasks (CAP_SYS_ADMIN, CAP_SYS_RESOURCE
> + 	or CAP_SYS_RAWIO) have their score divided by 4
> + * if oom condition happened in one cpuset and checked task does not belong
> + 	to it, its score is divided by 8
> + * resulted score is multiplied by the two in the power of oom_adj when it is

confusing.  Is this:    multiplied by two to the power of oom_adj when it is ... ?

> + 	positive, and divided otherwise, i.e.
> +	points <<= oom_adj when it is positive and
> +	points >>= oom_adj otherwise
> +
> +The task with the highest badness score is then killed.
> +
>  2.13 /proc/<pid>/oom_score - Display current oom-killer score
>  -------------------------------------------------------------


---
~Randy
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