Subject: Re: [PATCH] fix spurious OOM kills
From: Thomas Gleixner <tglx@linutronix.de>
Reply-To: tglx@linutronix.de
To: Martin =?iso-8859-2?Q?MOKREJ=A9?= 
	<mmokrejs@ribosome.natur.cuni.cz>
Cc: Andrew Morton <akpm@osdl.org>, piggin@cyberone.com.au, chris@tebibyte.org,
       marcelo.tosatti@cyclades.com, andrea@novell.com,
       LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org,
       Rik van Riel <riel@redhat.com>
In-Reply-To: <41A08765.7030402@ribosome.natur.cuni.cz>
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Organization: linutronix
Date: Sun, 21 Nov 2004 14:57:49 +0100
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On Sun, 2004-11-21 at 13:17 +0100, Martin MOKREJ? wrote:
> Why can't the algorithm first find the asking for memory now.
> When found, kernel should kill first it's children, wait some time,
> then kill this process if still exists (it might exit itself when children
> get closed).
> You have said it's safer to kill that to send ENOMEM as happens
> in 2.4, but I still don't undertand why kernel first doesn't send
> ENOMEM, and only if that doesn't help it can start after those 5 seconds
> OOM killer, and try to kill the very same application.
> I don't get the idea why to kill immediately.

I see your concern. There are some more changes neccecary to make this
reliably work. I'm not sure if it can be done without really big
changes. I will look a bit deeper into this.

> As it has happened to me in the past, that random OOM selection has killed
> sshd or init, I believe the algorithm should be improved to not to try
> to kill these. First of all, sshd is well tested, so it will never
> be source of memleaks. Second, if the algorithm would really insist on
> killing either of these, I personally prefer it rather do clean reboot
> than a system in a state without sshd. I have to get to the console.
> Actually, it's several kilometers for me. :(

Yeah, I observed this too and therefor came up with the whom to kill and
reentrancy patch.

> It's a pitty no-one has time to at least figure out why those changes have
> exposed this stupid random part of the algorithm. Before 2.6.9-rc2
> OOM killer was also started in my tests, but it worked deterministically.
> I wouldn't prefer extra algorithm to check what we kill now, I'd rather look
> why we kill randomly since -rc2.

As I said before the random behaviour was _not_ introduced in -rc2. It
might have changed in -rc2. The random kill with overkill can also be
triggered in 2.6.7 and 2.6.8. I have not tried elder versions though.

tglx


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