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On Thu, 7 Jun 2007, Jesse Barnes wrote: > On Thursday, June 7, 2007 1:16 am Andi Kleen wrote: >> On Wed, Jun 06, 2007 at 12:29:23PM -0700, 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). >> >> In theory -- while not recommended -- a BIOS could also >> use a default fallback MTRR for cached and use explicit MTRRs to >> map the non existing ranges uncached. Would it make sense to handle >> this case? > > Probably. I could just check the default memory type and bail out if > it's cacheable. > >> Should also probably have some command line option >> to disable the check in case something bad happens with it. > > Sure. > >> Another thing that might be sense to investigate in relationship >> to this patch is large page mappings with MTRRs. iirc P4 and also K8 >> splits pages internally with MTRR boundaries and might have some >> other bad side effects. Should we use this as hints to use 4K pages >> for the boundary areas? > > Or I could trim to the nearest large page boundary... We'd lose a > little more memory but it would keep things simple. > > Jesse > How much more memory are we going to lose? Is mem= a better option if its going to keep decreasing? - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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