linux-kernel - Re: [RFC] x86: mtrr: Constrain WB MTRR to max phys mem prior to cleanup

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Message-ID: <504D6490.2060606@oracle.com>
Date:	Mon, 10 Sep 2012 11:54:56 +0800
From:	"zhenzhong.duan" <zhenzhong.duan@...cle.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Peter Hurley <peter@...leysoftware.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] x86: mtrr: Constrain WB MTRR to max phys mem prior to cleanup



于 2012-09-08 02:40, H. Peter Anvin 写道:
> On 09/07/2012 10:44 AM, Peter Hurley wrote:
> \>
>> diff --git a/arch/x86/kernel/cpu/mtrr/cleanup.c 
>> b/arch/x86/kernel/cpu/mtrr/cleanup.c
>
> I really don't like it as it introduces yet another user of max_pfn, 
> which should be going away.  Furthermore, the better question is what 
> remaining needs there are for MTRR cleanup; historically the reason 
> was that it prevented the display from being mapped WC via MTRR due to 
> the MTRR conflict resolution rules favoring UC.
For a large memory system, mtrr_cleanup offten fail in most case. Even 
if it succeed, it often occupy all of MTRR entrys.
How was display mapped as WC in above case?
Why did bios give a lot of space then real mem, for hotplug?
>
> However, the right way to fix that is to use the PAT interfaces, which 
> doesn't have this drawback -- then MTRR cleanup becomes entirely 
> superfluous and the problem goes away.
Do you mean disable MTRR totally here?
Regards
zduan
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