Messages in this thread | | | Date | Wed, 13 Jun 2007 12:19:31 -0400 | From | Dave Jones <> | Subject | Re: [PATCH] trim memory not covered by WB MTRRs |
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On Wed, Jun 13, 2007 at 08:52:23AM +0200, Bodo Eggert wrote: > Jesse Barnes <jesse.barnes@intel.com> 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. > > Wouldn't it be better to correct the MTRR, if possible? As far as I read > here (LKML), the BIOS did not merge the entries
The size/alignment constraints of MTRRs (must be a power of 2) means that the best-fit method of covering non power of 2 memory sizes is the, well.. best fit. There's nothing that can be merged.
Dave
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