linux-kernel - Re: Maximum size of a swap partition

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Message-Id: <20090529160607.db4d55b6.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 29 May 2009 16:06:07 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Christoph Pleger <Christoph.Pleger@...tu-dortmund.de>,
	linux-kernel@...r.kernel.org
Subject: Re: Maximum size of a swap partition

On Fri, 29 May 2009 15:47:01 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> I'm not sure whether there are other limitations. But maybe enough big.
> 
I missed the another story.

For managing swap, the kernel uses 2bytes per 1 swap entry.
Then, if swap parttion is 1Gbytes, the kernel uses 512k bytes of memory.

in x86, this memory is allocated from vmalloc() area (you can see it in meminfo)
and it has only 80?MB. And there are other users of this area.

Then, in real x86-32bit world, you can't use verrrrry big swap device.

Then, 16GB=8MB in the kernel (or some more) is realistic limitation for usual
users.

Thanks,
-Kame

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