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

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Message-ID: <20070612213020.GA13747@elf.ucw.cz>
Date:	Tue, 12 Jun 2007 23:30:20 +0200
From:	Pavel Machek <pavel@....cz>
To:	Jesse Barnes <jesse.barnes@...el.com>
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

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
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