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

[Justin Piszcz <jpiszcz@lucidpixels.com>]

On Wed, 6 Jun 2007, Jesse Barnes wrote:

> 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.
>
> Justin, can you please test and make sure this patch works for
> you too?  It'll only work around the problem, but it's better
> than having to do mem= by hand or waiting for a fix from your
> BIOS vendor.
>
> Thanks,
> Jesse

Against what kernel version does this patch apply?

linux-2.6.21# patch -p1 < ../mtrr.patch
patching file arch/i386/kernel/cpu/mtrr/generic.c
Hunk #2 succeeded at 66 (offset -18 lines).
patching file arch/i386/kernel/cpu/mtrr/if.c
patching file arch/i386/kernel/cpu/mtrr/main.c
patching file arch/i386/kernel/cpu/mtrr/mtrr.h
can't find file to patch at input line 160
Perhaps you used the wrong -p or --strip option?
The text leading up to this was:
--------------------------
|diff --git a/arch/x86_64/kernel/bugs.c b/arch/x86_64/kernel/bugs.c
|index c3c6b91..c138eac 100644
|--- a/arch/x86_64/kernel/bugs.c
|+++ b/arch/x86_64/kernel/bugs.c
--------------------------
File to patch:

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