linux-kernel - Re: #tj-percpu has been rebased

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Message-ID: <499BAD54.3050108@zytor.com>
Date:	Tue, 17 Feb 2009 22:40:20 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	Tejun Heo <tj@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>, cpw@....com
Subject: Re: #tj-percpu has been rebased

Rusty Russell wrote:
>>>
>> num_possible_cpus() can be very large though, so in many cases the
>> likelihood of finding that many pages approach zero.  Furthermore,
>> num_possible_cpus() may be quite a bit larger than the actual number of
>> CPUs in the system.
> 
> Sure, so we end up at vmalloc.  No worse, but simpler and much better if we
> *can* do it.
> 

If the likelihood is near zero, then you're wasting opportunities to do
it better.  If we have compact per-cpu virtual areas then we can use
large pages if we know we'll have large percpu areas.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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