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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