linux-kernel - Re: How much kernel memory is in 64-bit OS ?

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Date:	Mon, 18 Sep 2006 15:39:36 +0200
From:	Helge Hafting <helge.hafting@...el.hist.no>
To:	yogeshwar sonawane <yogyas@...il.com>
CC:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: How much kernel memory is in 64-bit OS ?

yogeshwar sonawane wrote:
> On 9/16/06, yogeshwar sonawane <yogyas@...il.com> wrote:
>> Hi all,
>>
>> We all know that in 32-bit OS, total 4GB memory space is divided in
>> 3(user) + 1(kernel) space.
>>
>> Similarly, what is the division/scenario in case of 64-bit OS ?
>>
>> Any reference/explanation will be helpful.
>>
>> thanks in advance.
>>
>>
>> Yogeshwar
>>
>
> On similar lines, some time back, i read that, to accomodate large
> physical memory ,
> the 3G/1G layout is modified to have 4G/4G partition. But if somebody
> can focus the light on following things, it will be helpful.
> 1) what was the requirement of 4G/4G layout ?
It offers more memory than 3G/1G.  This is an improvement, so of
course it is the chosen way. It was not required - you sure can use
a 3G/1G split on a 64-bit processor - but why introduce an artifical
limitation?

The requirement for using a 4G/4G split is to have a processor
that support 64-bit adressing as well as 32-bit backward compatibility.
> 2) how it is managed ?
The kernel runs in 64-bit mode, offering the 4G/4G stuff for 32-bit 
processes.

> 3) how HIGH_MEMORY concept is related here.
high memory is a quirky way of supporting more than 4G on a 32-bit
processor.  A 64-bit processor support much more than 4G, so no need
for tricks that work around the limitations of 32-bit processors.


Helge Hafting
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