linux-kernel - Re: [rfc 08/45] cpu alloc: x86 support

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Message-ID: <Pine.LNX.4.64.0711201703570.29648@schroedinger.engr.sgi.com>
Date:	Tue, 20 Nov 2007 17:16:11 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Andi Kleen <ak@...e.de>
cc:	akpm@...ux-foundation.org, travis@....com,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	linux-kernel@...r.kernel.org
Subject: Re: [rfc 08/45] cpu alloc: x86 support

But one can subtract too... Hmmm... So the cpu area 0 could be put at
the beginning of the 2GB kernel area and then grow downwards from 
0xffffffff80000000. The cost in terms of code is one subtract
instruction for each per_cpu() or CPU_PTR()

The next thing doward from 0xffffffff80000000 is the vmemmap at 
0xffffe20000000000, so ~32TB. If we leave 16TB for the vmemmap
(a 16TB vmmemmap be able to map 2^(44 - 6 + 12) = 2^50 bytes 
more than currently supported by the processors)

then the remaining 16TB could be used to map 1GB per cpu for a 16k config. 
That is wildly overdoing it. Guess we could just do it with 1M anyways. 
Just to be safe we could do 128M. 128M x 16k = 2TB?

Would such a configuration be okay?

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