linux-kernel - Re: Memory overcommit

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Date:	Wed, 28 Oct 2009 11:47:55 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Hugh Dickins <hugh.dickins@...cali.co.uk>
Cc:	kosaki.motohiro@...fujitsu.com,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	vedran.furac@...il.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, minchan.kim@...il.com,
	akpm@...ux-foundation.org, rientjes@...gle.com, aarcange@...hat.com
Subject: Re: Memory overcommit

> 2.  I started out running my mlock test program as root (later
> switched to use "ulimit -l unlimited" first).  But badness() reckons
> CAP_SYS_ADMIN or CAP_SYS_RESOURCE is a reason to quarter your points;
> and CAP_SYS_RAWIO another reason to quarter your points: so running
> as root makes you sixteen times less likely to be killed.  Quartering
> is anyway debatable, but sixteenthing seems utterly excessive to me.
> 
> I moved the CAP_SYS_RAWIO test in with the others, so it does no
> more than quartering; but is quartering appropriate anyway?  I did
> wonder if I was right to be "subverting" the fine-grained CAPs in
> this way, but have since seen unrelated mail from one who knows
> better, implying they're something of a fantasy, that su and sudo
> are indeed what's used in the real world.  Maybe this patch was okay.

I agree quartering is debatable.
At least, killing quartering is worth for any user, and it can be push into -stable.




>From 27331555366c908a93c2cdd780b77e421869c5af Mon Sep 17 00:00:00 2001
From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Date: Wed, 28 Oct 2009 11:28:39 +0900
Subject: [PATCH] oom: Mitigate suer-user's bonus of oom-score

Currently, badness calculation code of oom contemplate following bonus.
 - Super-user have quartering oom-score
 - CAP_SYS_RAWIO process (e.g. database) also have quartering oom-score

The problem is, Super-users have CAP_SYS_RAWIO too. Then, they have
sixteenthing bonus. it's obviously too excessive and meaningless.

This patch fixes it.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
---
 mm/oom_kill.c |   13 +++++--------
 1 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index ea2147d..40d323d 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -152,18 +152,15 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
 	/*
 	 * Superuser processes are usually more important, so we make it
 	 * less likely that we kill those.
-	 */
-	if (has_capability_noaudit(p, CAP_SYS_ADMIN) ||
-	    has_capability_noaudit(p, CAP_SYS_RESOURCE))
-		points /= 4;
-
-	/*
-	 * We don't want to kill a process with direct hardware access.
+	 *
+	 * Plus, We don't want to kill a process with direct hardware access.
 	 * Not only could that mess up the hardware, but usually users
 	 * tend to only have this flag set on applications they think
 	 * of as important.
 	 */
-	if (has_capability_noaudit(p, CAP_SYS_RAWIO))
+	if (has_capability_noaudit(p, CAP_SYS_ADMIN) ||
+	    has_capability_noaudit(p, CAP_SYS_RESOURCE) ||
+	    has_capability_noaudit(p, CAP_SYS_RAWIO))
 		points /= 4;
 
 	/*
-- 
1.6.2.5




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