Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755815AbZIVJcS (ORCPT ); Tue, 22 Sep 2009 05:32:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755794AbZIVJcQ (ORCPT ); Tue, 22 Sep 2009 05:32:16 -0400 Received: from gir.skynet.ie ([193.1.99.77]:51274 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754073AbZIVJcO (ORCPT ); Tue, 22 Sep 2009 05:32:14 -0400 Date: Tue, 22 Sep 2009 10:32:20 +0100 From: Mel Gorman To: Tejun Heo Cc: Nick Piggin , Pekka Enberg , Christoph Lameter , heiko.carstens@de.ibm.com, sachinp@in.ibm.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Benjamin Herrenschmidt Subject: Re: [PATCH 1/3] powerpc: Allocate per-cpu areas for node IDs for SLQB to use as per-node areas Message-ID: <20090922093220.GB12254@csn.ul.ie> References: <1253549426-917-1-git-send-email-mel@csn.ul.ie> <1253549426-917-2-git-send-email-mel@csn.ul.ie> <4AB813F3.8060102@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <4AB813F3.8060102@kernel.org> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2363 Lines: 64 On Tue, Sep 22, 2009 at 09:01:55AM +0900, Tejun Heo wrote: > Mel Gorman wrote: > > diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c > > index 1f68160..a5f52d4 100644 > > --- a/arch/powerpc/kernel/setup_64.c > > +++ b/arch/powerpc/kernel/setup_64.c > > @@ -588,6 +588,26 @@ void __init setup_per_cpu_areas(void) > > paca[i].data_offset = ptr - __per_cpu_start; > > memcpy(ptr, __per_cpu_start, __per_cpu_end - __per_cpu_start); > > } > > +#ifdef CONFIG_SLQB > > + /* > > + * SLQB abuses DEFINE_PER_CPU to setup a per-node area. This trick > > + * assumes that ever node ID will have a CPU of that ID to match. > > + * On systems with memoryless nodes, this may not hold true. Hence, > > + * we take a second pass initialising a "per-cpu" area for node-ids > > + * that SLQB can use > > + */ > > + for_each_node_state(i, N_NORMAL_MEMORY) { > > + > > + /* Skip node IDs that a valid CPU id exists for */ > > + if (paca[i].data_offset) > > + continue; > > + > > + ptr = alloc_bootmem_pages_node(NODE_DATA(cpu_to_node(i)), size); > > + > > + paca[i].data_offset = ptr - __per_cpu_start; > > + memcpy(ptr, __per_cpu_start, __per_cpu_end - __per_cpu_start); > > + } > > +#endif /* CONFIG_SLQB */ > > } > > #endif > > Eh... I don't know. This seems too hacky to me. I've come around to this opinion as well. There are probably too many other architectures and corners where this is gotten wrong and a more fundamental fix is needed for SLQB to be able to use this hack. > Why not just > allocate pointer array of MAX_NUMNODES and allocate per-node memory > there? That's what patch 1 from V1 did. I'll make it Patch 1 for V3. > This will be slightly more expensive but I doubt it will be > noticeable. The only extra overhead is the cachline footprint for the > extra array. > I'll compare the vmlinux's to quantify the exact penalty but basically, I don't think it can be avoided at this point. Thanks. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/