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

["zhenzhong.duan" <zhenzhong.duan@oracle.com>]

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