linux-kernel - Re: Out of memory and no killable processes: 2.6.22-2-686-bigmem

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Date:	Wed, 19 Dec 2007 03:56:46 -0500 (EST)
From:	Parag Warudkar <parag.warudkar@...il.com>
To:	Nico Schottelius <nico-kernel-20071219@...ottelius.org>
cc:	Robert Hancock <hancockr@...w.ca>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Out of memory and no killable processes: 2.6.22-2-686-bigmem

On Wed, 19 Dec 2007, Nico Schottelius wrote:

>> If you're running tons of memory, it
>> really is better to run a 64-bit kernel if possible.
>
> Sure? Afaik that results in a bit slower access to memory and appart
> from being able to address MUCH more memory doesn't change the
> situation.

No, generally 64-bit x86 does not slow down things - it might speed things 
up a bit due to more accessible registers in 64-bit mode. And it does 
change the situation from VM PoV a lot. In (bearded) God's own words - 
"... run a 64bit kernel and then the kernel isn't trying the software equivalent of 
managing a filing cabinet through the keyhole."

You will find this recent thread on same topic useful - 
http://lkml.org/lkml/2007/12/17/7 .

> Perhaps I missed something.
>
> And updating to 64 Bit kernel also implies changing the userland, so
> a reinstall would be necessary, wouldn't it?

May not be necessary - I recently tried installing Fedora 8 32-bit/PAE on 
a 8Gb Core 2 box and then upgrading just the kernel to 64-bit and it worked 
fine except for the 32-bit iptables service having problems running on 
64-bit kernel. [Also I hear the closed source nVidia binaries will not 
work on this setup - so if you don't need such things you will be able to 
go to a 64-bit kernel w/o reinstalling userspace.]

>> I believe there are
>> some cases where low memory can be pretty easily exhausted on machines with
>> lots of high memory.
>
> Some minutes ago the third machine of that type freezed.
> with 7 GiB of *free* memory, before getting oom+panic.
>
> Is it possible to debug this issue somehow?

Like said in the above thread I referred to you might have better luck 
with RHEL/CentOS or other "Enterprise" kernels if you want to stick to 
32-bit. But the pain is not worthwhile - give 64-bit kernel a shot.

HTH

Parag
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