linux-kernel - Re: Linux kernel memory and split on 64-bit machines

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Message-ID: <20071029154801.GA31335@one.firstfloor.org>
Date:	Mon, 29 Oct 2007 16:48:01 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Yoav Artzi <yoavar@...ckpoint.com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org
Subject: Re: Linux kernel memory and split on 64-bit machines

On Mon, Oct 29, 2007 at 05:06:31PM +0200, Yoav Artzi wrote:
> I don't know what befell me. I realized the foolishness of the questions 
> a second after clicking the send button.
> 
> 
> Now, I just wonder what will happen when people will need more then 
> 2^46bytes of memory. Any idea?

The CPU needs to be extended then beyond 48bit VA.

(actually it could be extended to 2^46.5 or so) 


> 
> Another two issues:
> 
> 1. I see vmalloc() doesn't cover the entire possible space. Why is that?

It needs an reserved space for its virtual mappings.

> 
> 2. How come user space gets 47bits and kernel only gets 46bits in direct 
> mapping?

Half of the kernel space is reserved for special purposes 
(vmalloc, ioremap etc.) That is not fixed and could be varied.

-Andi

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