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


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.
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