linux-kernel - Re: [PATCH] trim memory not covered by WB MTRRs

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Message-ID: <Pine.LNX.4.64.0706121731250.7526@p34.internal.lan>
Date:	Tue, 12 Jun 2007 17:31:44 -0400 (EDT)
From:	Justin Piszcz <jpiszcz@...idpixels.com>
To:	Pavel Machek <pavel@....cz>
cc:	Jesse Barnes <jesse.barnes@...el.com>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH] trim memory not covered by WB MTRRs



On Tue, 12 Jun 2007, Pavel Machek wrote:

> Hi!
>
>>>> On some machines, buggy BIOSes don't properly setup WB MTRRs to
>>>> cover all available RAM, meaning the last few megs (or even gigs)
>>>> of memory will be marked uncached.  Since Linux tends to allocate
>>>> from high memory addresses first, this causes the machine to be
>>>> unusably slow as soon as the kernel starts really using memory
>>>> (i.e. right around init time).
>>>>
>>>> +	if ((highest_addr >> PAGE_SHIFT) != end_pfn) {
>>>> +		printk(KERN_WARNING "***************\n");
>>>> +		printk(KERN_WARNING "**** WARNING: likely BIOS bug\n");
>>>> +		printk(KERN_WARNING "**** MTRRs don't cover all of "
>>>> +		       "memory, trimmed %ld pages\n", end_pfn -
>>>> +		       (highest_addr >> PAGE_SHIFT));
>>>> +		printk(KERN_WARNING "***************\n");
>>>> +		end_pfn = highest_addr >> PAGE_SHIFT;
>>>
>>> Missing 4K of memory is not worth 4K of junk in syslog per boot. Can
>>> you drop the stars and stop shouting?
>>
>> How missing about 1G of memory?  We already discussed this, and Andi and
>> Venki felt that either a panic or a really obnoxious message was the
>> way to go...
>
> Just use panic, then.
> 									Pavel,
> 	who still thinks anyone missing 1GB of ram will not miss
> 	friendly notice in dmesg, even if it goes without 20 stars.
>
> -- 
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
>

What is wrong with Jesse's patch?  I've been using it for quite a few days 
now, no issues.

Justin.
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