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From: Rusty Russell <rusty@rustcorp.com.au>
To: Tejun Heo <tj@kernel.org>
Subject: Re: regarding the x86_64 zero-based percpu patches
Date: Thu, 15 Jan 2009 12:17:53 +1030
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Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
       Christoph Lameter <cl@linux-foundation.org>,
       Ingo Molnar <mingo@elte.hu>, travis@sgi.com,
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On Wednesday 14 January 2009 14:28:56 Tejun Heo wrote:
> The main problem is that the area needs to be congruent which
> basically mandates them to be contiguous.

I want to explore this assumption a little.  Logically, yes, if 50% of pages are free and we have 4096 cpus, the chance that a page is free on all CPUs is 1 in 2^4095.  But maybe such systems are fine with 2M pages for per-cpu areas at boot?  And can page mobility tricks help us make the odds reasonable here?
Only allowing movable pages in our expansion-of-percpu area?

Thanks,
Rusty.