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

[Justin Piszcz <jpiszcz@lucidpixels.com>]

On Thu, 5 Jul 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).
> >
> > This patch works around the problem by scanning the MTRRs at
> > boot and figuring out whether the current end_pfn value (setup
> > by early e820 code) goes beyond the highest WB MTRR range, and
> > if so, trimming it to match.  A fairly obnoxious KERN_WARNING
> > is printed too, letting the user know that not all of their
> > memory is available due to a likely BIOS bug.
> >
> > Something similar could be done on i386 if needed, but the boot
> > ordering would be slightly different, since the MTRR code on i386
> > depends on the boot_cpu_data structure being setup.
> >
> > This patch fixes a bug in the last patch that caused the code to
> > run on non-Intel machines (AMD machines apparently don't need it
> > and it's untested on other non-Intel machines, so best keep it
> > off).
> >
> > akpm -- this one should replace all the mtrr patches currently
> > in your tree.
> >
> > Yinghai, maybe you can test this on one of your AMD machines to
> > make sure I got the CPU code right?
>
> > +	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;
>
> I'd say using that many stars for KERN_WARNING printk is sign of
> mental illness or something...
> 							Pavel
> --
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Will this patch make it into 2.6.23?

Been patching manually for a while with each -rc for 2.6.22..

Justin.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/