path: root/Documentation
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authorJesse Barnes <jesse.barnes@intel.com>2008-01-30 13:33:18 +0100
committerIngo Molnar <mingo@elte.hu>2008-01-30 13:33:18 +0100
commit99fc8d424bc5d803fe92cad56c068fe64e73747a (patch)
tree983f615ed69b98c614f38b7240c343c9d7f9418d /Documentation
parent03252919b79891063cf99145612360efbdf9500b (diff)
x86, 32-bit: trim memory not covered by wb mtrrs
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). Further enhancements and fixes from: Yinghai Lu <Yinghai.Lu@Sun.COM> Andi Kleen <ak@suse.de> Signed-off-by: Jesse Barnes <jesse.barnes@intel.com> Tested-by: Justin Piszcz <jpiszcz@lucidpixels.com> Cc: Andi Kleen <andi@firstfloor.org> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Yinghai Lu <yhlu.kernel@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'Documentation')
1 files changed, 6 insertions, 0 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 860a9087549..b8fadf5f75a 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -570,6 +570,12 @@ and is between 256 and 4096 characters. It is defined in the file
See drivers/char/README.epca and
+ disable_mtrr_trim [X86-64, Intel only]
+ By default the kernel will trim any uncacheable
+ memory out of your available memory pool based on
+ MTRR settings. This parameter disables that behavior,
+ possibly causing your machine to run very slowly.
dmasound= [HW,OSS] Sound subsystem buffers
dscc4.setup= [NET]