linux-kernel - Re: The 3G (or nG) Kernel Memory Space Offset

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Message-ID: <Pine.LNX.4.61.0608291828540.8682@yvahk01.tjqt.qr>
Date:	Tue, 29 Aug 2006 18:30:19 +0200 (MEST)
From:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
To:	Arjan van de Ven <arjan@...radead.org>
cc:	Dong Feng <middle.fengdong@...il.com>, Andi Kleen <ak@...e.de>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Paul Mackerras <paulus@...ba.org>,
	Christoph Lameter <clameter@....com>,
	David Howells <dhowells@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: The 3G (or nG) Kernel Memory Space Offset

>> 
>> Sorry for my typo. I actually means "0-1G physical memory space." My
>> question is actually why there is a 3G offset from linear kernel to
>> physical kernel. Why not simply have kernel memory linear space
>> located on 0-1G linear address, and therefore the physical kernel and
>> linear kernel just coincide?
>
>the price for that would be that you would have to flush all the tlb's
>on each syscall. That's seen as a quite hefty price by many kernel
>developers.

Since it's all just virtual addresses, is the TLB flush really that much 
different when kernelspace runs from (virtual) 0x00000000-0x3FFFFFFF rather 
than (virtual)0xC000000-0xFFFFFFFF?


Jan Engelhardt
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