On 11/9/10 9:04 AM, Bakul Shah wrote:
On Tue, 09 Nov 2010 08:45:14 PST Julian Elischer<jul...@freebsd.org> wrote:
During the discussion at MeetBSD the question came up as to what the real
limiting factors were with regard to how much RAM a system could have.
it was put to us that the limit was currently around 512 GB, though no-one
at teh discussion knew what the mechanism of the limitation was or
what might ligh beyond it.
Could anyone who knows, pipe upt and let use know what the factors are,
and if the current limit is overcome, what the next one after that will be?
You mean beyond architectural limits?
no, though of course they are relevant.
I was thinking more of details like limits to the KVM space or
any limitations there may be on the size of the direct-map region,
or maybe some limit on some data structure size in the kernel.
Since I don 't know the details, this is exactly the question..
what IS the limit?
> From Wikipedia:
Larger physical address space: The original
implementation of the AMD64 architecture implemented
40-bit physical addresses and so could address up to 1 TB
(2^40 bytes) of RAM. Current implementations of the AMD64
architecture (starting from AMD 10h microarchitecture)
extend this to 48-bit physical addresses and therefore
can address up to 256 TB of RAM. The architecture permits
extending this to 52 bits in the future (limited by the
page table entry format); this would allow addressing of
up to 4 PB of RAM.
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