Messages in this thread | | | Date | Wed, 25 Jun 2008 20:22:58 +0100 | Subject | Re: [Xen-devel] Re: [PATCH 00 of 36] x86/paravirt: groundwork for 64-bit Xen support | From | Keir Fraser <> |
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On 25/6/08 20:13, "Andi Kleen" <andi@firstfloor.org> wrote:
>> What does Linux expect to scale up to? Reserving 16 PML4 entries leaves the >> kernel with 120TB of available 'negative' address space. Should be plenty, I >> would think. > > There are already (ok non x86-64) systems shipping today with 10+TB of > addressable memory. 100+TB is not that far away with typical > growth rates. Besides there has to be much more in the negative address > space than just direct mapping.
There are obviously no x64 boxes around at the moment with >1TB of regular shared memory, since no CPUs have more than 40 address lines. 100+TB RAM is surely years away.
If this is a blocker issue, we could just keep PAGE_OFFSET as it is when Xen support is not configured into the kernel. Then those who are concerned about 5% extra headroom at 100TB RAM sizes can configure their kernel appropriately.
> So far we always that 64bit Linux can support upto 1/4*max VA memory. > With your change that formula would be not true anymore.
Does the formula have any practical significance?
-- Keir
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