linux-kernel - Re: [PATCH] x86: trim ram need to check if mtrr is there v3

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Date:	Fri, 25 Jan 2008 07:57:07 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Andi Kleen <andi@...stfloor.org>, Yinghai Lu <Yinghai.Lu@....COM>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: trim ram need to check if mtrr is there v3

Ingo Molnar wrote:
> 
> no, to be fully generic it would have to be able to 'split' e820 entries 
> up and punch holes into them - but we dont want to go that far i think. 
> The most common problem is mismatch at the end of a range.
> 

For what it's worth, I have a set of code to do this, written in order 
to canonicalize and modify e820 data structures for memdisk.

The key to it is the observation that the e820-delivered (address, len, 
type) tuples isn't actually the data structure you want -- what you want 
is an ordered list of (address, type) tuples, where type may includes 
undefined (the e820 default type - i.e. unused, available address space).

In addition to the attached code, to do this right, we probably want a 
function to do filtering (only clobber entries of a specfic type, in 
this case type 1) as opposed to blind clobber; with an ordered array 
this is quite trivial.

	-hpa

View attachment "e820.h" of type "text/x-chdr" (1000 bytes)

View attachment "e820func.c" of type "text/x-csrc" (2504 bytes)