Jesse Barnes <[EMAIL PROTECTED]> writes: > 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.
A quick update. This patch is horribly incorrect on a socket F opteron/Athlon 64 with memory above 4GB. In particular those cpus are capable of mapping all of memory above 4GB as write back without using a single MTRR. So examining MTRRs is insufficient. Eric - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
