From: Andi Kleen <andi@firstfloor.org>
To: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Ingo Molnar <mingo@elte.hu>,
x86@kernel.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Jan Beulich <jbeulich@novell.com>,
Stable Kernel <stable@kernel.org>
Subject: Re: [PATCH] x86: set PAE PHYSICAL_MASK_SHIFT to match 64-bit
Date: Fri, 06 Jun 2008 03:40:24 +0200 [thread overview]
Message-ID: <87ve0ntk6v.fsf@basil.nowhere.org> (raw)
In-Reply-To: <4848046A.5060006@goop.org> (Jeremy Fitzhardinge's message of "Thu, 05 Jun 2008 16:21:14 +0100")
Jeremy Fitzhardinge <jeremy@goop.org> writes:
>
> The 46-bit mask used in 64-bit seems pretty arbitrary.
The rationale for the 46 bits is that the kernel needs roughly 4x as
much virtual space as physical space and the virtual space is limited
to 48bits.
To be exact 47 bits is always user space and the 47 bits remaining
for the kernel are split into half, with one half for the direct mapping
and the other half for random mappings. With some pushing you could
extend it to 46.5 bits or so, but beyond that you'll be in trouble.
It's not arbitrary at all.
-Andi
next prev parent reply other threads:[~2008-06-06 1:40 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-06-05 15:21 [PATCH] x86: set PAE PHYSICAL_MASK_SHIFT to match 64-bit Jeremy Fitzhardinge
2008-06-05 15:34 ` Jan Beulich
2008-06-05 15:42 ` Jeremy Fitzhardinge
2008-06-05 16:45 ` H. Peter Anvin
2008-06-05 21:14 ` Jeremy Fitzhardinge
2008-06-07 18:35 ` H. Peter Anvin
2008-06-06 9:21 ` [PATCH UPDATED] x86: set PAE PHYSICAL_MASK_SHIFT to 44 bits Jeremy Fitzhardinge
2008-06-06 9:58 ` Jan Beulich
2008-06-06 13:15 ` Andi Kleen
2008-06-06 13:50 ` Jeremy Fitzhardinge
2008-06-10 10:31 ` Ingo Molnar
2008-06-10 13:06 ` Jeremy Fitzhardinge
2008-06-13 7:24 ` Ingo Molnar
2008-06-06 1:40 ` Andi Kleen [this message]
2008-06-06 7:14 ` [PATCH] x86: set PAE PHYSICAL_MASK_SHIFT to match 64-bit Jan Beulich
2008-06-06 7:59 ` Jeremy Fitzhardinge
2008-06-06 8:14 ` Jan Beulich
2008-06-06 8:15 ` Jeremy Fitzhardinge
2008-06-07 18:39 ` H. Peter Anvin
2008-06-06 4:45 ` Arjan van de Ven
2008-06-06 8:08 ` Jeremy Fitzhardinge
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