linux-kernel - Re: [Xen-devel] Re: [PATCH 00 of 36] x86/paravirt: groundwork for 64-bit Xen support

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Message-ID: <20080625191315.GD6708@one.firstfloor.org>
Date:	Wed, 25 Jun 2008 21:13:15 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Keir Fraser <keir.fraser@...citrix.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Mark McLoughlin <markmc@...hat.com>,
	xen-devel <xen-devel@...ts.xensource.com>,
	Eduardo Habkost <ehabkost@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Stephen Tweedie <sct@...hat.com>
Subject: Re: [Xen-devel] Re: [PATCH 00 of 36] x86/paravirt: groundwork for 64-bit Xen support

> What does Linux expect to scale up to? Reserving 16 PML4 entries leaves the
> kernel with 120TB of available 'negative' address space. Should be plenty, I
> would think.

There are already (ok non x86-64) systems shipping today with 10+TB of 
addressable memory. 100+TB is not that far away with typical
growth rates. Besides there has to be much more in the negative address
space than just direct mapping.

So far we always that 64bit Linux can support upto 1/4*max VA memory.
With your change that formula would be not true anymore.

-Andi 


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