Re: #tj-percpu has been rebased

From: "H. Peter Anvin" <hpa@zytor.com>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: Tejun Heo <tj@kernel.org>, Ingo Molnar <mingo@elte.hu>,
	Thomas Gleixner <tglx@linutronix.de>,
	x86@kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Jeremy Fitzhardinge <jeremy@goop.org>,
	cpw@sgi.com
Subject: Re: #tj-percpu has been rebased
Date: Tue, 17 Feb 2009 22:40:20 -0800	[thread overview]
Message-ID: <499BAD54.3050108@zytor.com> (raw)
In-Reply-To: <200902181455.11572.rusty@rustcorp.com.au>

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.