From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rusty Russell Subject: Re: [patch 04/41] cpu ops: Core piece for generic atomic per cpu operations Date: Fri, 13 Jun 2008 10:38:12 +1000 Message-ID: <200806131038.12987.rusty@rustcorp.com.au> References: <20080530035620.587204923@sgi.com> <200806122121.09835.nickpiggin@yahoo.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Return-path: Received: from ozlabs.org ([203.10.76.45]:33268 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756349AbYFMAi2 (ORCPT ); Thu, 12 Jun 2008 20:38:28 -0400 In-Reply-To: Content-Disposition: inline Sender: linux-arch-owner@vger.kernel.org List-ID: To: Christoph Lameter Cc: Nick Piggin , Martin Peschke , Andrew Morton , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, David Miller , Eric Dumazet , Peter Zijlstra , Mike Travis On Friday 13 June 2008 03:19:51 Christoph Lameter wrote: > Populating the per cpu areas on demand is a good thing especially for > configurations with a large number of processors. If we really go to > support 4k processor by default then we need to allocate the smallest > amount of per cpu structures necessary. Maybe ACPI or so can tell us how > many processors are possible and we only allocate those. But it would be > best if the percpu structures are only allocated for actually active > processors. cpu_possible_map should definitely be minimal, but your point is well made: dynamic percpu could actually cut memory allocation. If we go for a hybrid scheme where static percpu is always allocated from the initial chunk, however, we still need the current pessimistic overallocation. Mike's a clever guy, I'm sure he'll think of something :) Rusty.