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

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Date:	Tue, 12 Jun 2007 08:29:21 -0700
From:	Jesse Barnes <jesse.barnes@...el.com>
To:	Pavel Machek <pavel@....cz>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	Justin Piszcz <jpiszcz@...idpixels.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH] trim memory not covered by WB MTRRs

On Tuesday, June 12, 2007 7:50:08 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...

Jesse
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