From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <479298AF.8040806@sgi.com> Date: Sat, 19 Jan 2008 16:41:19 -0800 From: Mike Travis MIME-Version: 1.0 Subject: Re: [PATCH 1/5] x86: Change size of node ids from u8 to u16 fixup References: <20080118183011.354965000@sgi.com> <20080118183011.527888000@sgi.com> <86802c440801182003vd94044ex7fb13e61e5f79c81@mail.gmail.com> <47926ACC.4060707@sgi.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: David Rientjes Cc: Yinghai Lu , Andrew Morton , Andi Kleen , mingo@elte.hu, Christoph Lameter , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Eric Dumazet List-ID: David Rientjes wrote: > 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. Perhaps numanode_t should be set to u16 if MAX_NUMNODES > 255 to allow for an invalid value of 255? #if MAX_NUMNODES > 255 typedef u16 numanode_t; #else typedef u8 numanode_t; #endif > >> if (node != NUMA_NO_NODE) { > > Wrong, this should be > > node == NUMA_NO_NODE Oops, yes you're right. >>>> 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. Yes, I agree. I'll do the changes you're suggesting. > 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. So are you saying that I should just use u16 for all node ids whether CONFIG_NODES_SHIFT > 7 or not? Othersise, I would think that defining a typedef is a fairly clean solution. A quick grep shows that there are 35 arrays defined by MAX_NUMNODES in x86_64, 38 in X86_32 (not verified.) So it's not exactly a trivial amount of memory. > >> 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. Thanks for the info. I wasn't sure exactly what the PXM value represents. > > David Thanks again, Mike -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org