From owner-freebsd-hackers  Thu Jan 14 20:02:35 1999
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From: "John S. Dyson" <dyson@dyson.iquest.net>
Message-Id: <199901150401.XAA18990@dyson.iquest.net>
Subject: Re: Review and report of linux kernel VM
In-Reply-To: <199901142323.PAA07241@lestat.nas.nasa.gov> from Jason Thorpe at "Jan 14, 99 03:23:20 pm"
To: thorpej@nas.nasa.gov
Date: Thu, 14 Jan 1999 23:01:18 -0500 (EST)
Cc: dyson@dyson.iquest.net, dillon@apollo.backplane.com, root@dyson.iquest.net,
        dg@root.com, jkh@FreeBSD.ORG, hackers@FreeBSD.ORG
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> On Thu, 14 Jan 1999 17:57:57 -0500 (EST) 
>  "John S. Dyson" <dyson@dyson.iquest.net> wrote:
> 
>  > implementations, but also adds overhead.  It would be "nice" to be able
>  > for the upper level VM code to simply modify page table entries sometimes,
>  > wouldn't it?  One thing that I did in the FreeBSD code was to minimize the
> 
> It would?  What if your architecture doesn't use page tables, in the
> traditional sense?  (There are at least a couple modern RISC architectures
> for which this is the case...)
> 
In those cases, then they simulate the page table schemes.  (I am
VERY familiar with such, currently doing a port to such a machine.)
However, if you look at the VM code, the issues of the layer transitions
are significant.

It is clear that there is *something* wrong with the place where the
layering is between the upper and lower level VM code.  I am not sure
where to put it though.

John

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