linux-kernel - Re: physical memory limit of 64-bit linux

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Message-ID: <20081216164443.GY25779@one.firstfloor.org>
Date:	Tue, 16 Dec 2008 17:44:43 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Martin Steigerwald <ms@...mix.de>, linux-kernel@...r.kernel.org,
	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: physical memory limit of 64-bit linux

On Tue, Dec 16, 2008 at 04:54:16PM +0100, Rafael J. Wysocki wrote:
> On Tuesday, 16 of December 2008, Martin Steigerwald wrote:
> > 
> > Hi!
> > 
> > What is the physical memory limit for 64-bit Linux? I read about 40 bit 
> > address bus for AMD Athlon X2 (1 TB) and 48 bit for Barcelona X4 (256 TB).
> > 
> > Is 64-bit linux able to use that amount - provided that one would manage to 
> > build it into a machine? Or does it have a lower limit?

It depends on which 64bit Linux; e.g. IA64 has larger limits.

> > Looking into the Google crystal ball gives unclear pictures... I tend to 
> > assume that Linux would handle it, but I am not sure.
> 
> IIRC, the current maximal virtual memory space size of the kernel on x86_64 is 2^46.

Correct.

-Andi

-- 
ak@...ux.intel.com
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