From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758822AbYASWeT (ORCPT ); Sat, 19 Jan 2008 17:34:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753007AbYASWeG (ORCPT ); Sat, 19 Jan 2008 17:34:06 -0500 Received: from smtp-out.google.com ([216.239.33.17]:40512 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751634AbYASWeF (ORCPT ); Sat, 19 Jan 2008 17:34:05 -0500 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=received:date:from:x-x-sender:to:cc:subject:in-reply-to: message-id:references:mime-version:content-type; b=acoUMKqKYe6zODlF0bEGwEBtPc+7BalGg/oaoHezohVo13Hwkjf2hJelbtHSa2xT6 AW8qys4B4n8UVl34vDVNA== Date: Sat, 19 Jan 2008 14:33:04 -0800 (PST) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Mike Travis cc: Yinghai Lu , Andrew Morton , Andi Kleen , mingo@elte.hu, Christoph Lameter , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Eric Dumazet Subject: Re: [PATCH 1/5] x86: Change size of node ids from u8 to u16 fixup In-Reply-To: <47926ACC.4060707@sgi.com> Message-ID: References: <20080118183011.354965000@sgi.com> <20080118183011.527888000@sgi.com> <86802c440801182003vd94044ex7fb13e61e5f79c81@mail.gmail.com> <47926ACC.4060707@sgi.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 19 Jan 2008, Mike Travis wrote: > > Yeah, NID_INVAL is negative so no unsigned type will work here, > > unfortunately. And that reduces the intended savings of your change since > > the smaller type can only be used with a smaller CONFIG_NODES_SHIFT. > > > > Excuse my ignorance but why wouldn't this work: > > static numanode_t pxm_to_node_map[MAX_PXM_DOMAINS] > = { [0 ... MAX_PXM_DOMAINS - 1] = NUMA_NO_NODE }; > ... > >> int acpi_map_pxm_to_node(int pxm) > >> { > > int node = pxm_to_node_map[pxm]; > > > > if (node < 0) > > numanode_t node = pxm_to_node_map[pxm]; > Because NUMA_NO_NODE is 0xff on x86. That's a valid node id for configurations with CONFIG_NODES_SHIFT equal to or greater than 8. > if (node != NUMA_NO_NODE) { Wrong, this should be node == NUMA_NO_NODE > >> if (nodes_weight(nodes_found_map) >= MAX_NUMNODES) > >> return NID_INVAL; > >> node = first_unset_node(nodes_found_map); > >> __acpi_map_pxm_to_node(pxm, node); > >> node_set(node, nodes_found_map); > >> } > The net result of this is that if a proximity domain is looked up through acpi_map_pxm_to_node() and already has a mapping to node 255 (legal with CONFIG_NODES_SHIFT == 8), this function will return NID_INVAL since the weight of nodes_found_map is equal to MAX_NUMNODES. You simply can't use valid node id's to signify invalid or unused node ids. > or change: > #define NID_INVAL (-1) > to > #define NID_INVAL ((numanode_t)(-1)) > ... > if (node != NID_INVAL) { You mean node == NID_INVAL > >> if (nodes_weight(nodes_found_map) >= MAX_NUMNODES) > >> return NID_INVAL; > >> node = first_unset_node(nodes_found_map); > >> __acpi_map_pxm_to_node(pxm, node); > >> node_set(node, nodes_found_map); > >> } > That's the equivalent of your NUMA_NO_NODE code above. The fact remains that (numanode_t)-1 is still a valid node id for MAX_NUMNODES >= 256. So, as I said in my initial reply, the only way to get the savings you're looking for is to use u8 for CONFIG_NODES_SHIFT <= 7 and then convert all NID_INVAL users to use NUMA_NO_NODE. Additionally, Linux has always discouraged typedefs when they do not define an architecture-specific size. The savings from your patch for CONFIG_NODES_SHIFT == 7 would be 256 bytes for this mapping. It's simply not worth it. > And btw, shouldn't the pxm value be sized to numanode_t size as well? > Will it ever be larger than the largest node id? > Section 6.2.9 of ACPI 2.0 states that PXM's return an integer, so that would be non-conforming to the standard. Additionally, PXM's are not nodes, so casting them to anything called numanode_t shows the semantic flaw in your patch. David