From mboxrd@z Thu Jan 1 00:00:00 1970 Received: by rv-out-0910.google.com with SMTP id l15so1146884rvb.26 for ; Sat, 19 Jan 2008 17:31:43 -0800 (PST) Message-ID: <86802c440801191731h191ed4b3hb2e43ed95c60cb2b@mail.gmail.com> Date: Sat, 19 Jan 2008 17:31:43 -0800 From: "Yinghai Lu" Subject: Re: [PATCH 1/5] x86: Change size of node ids from u8 to u16 fixup In-Reply-To: <479298AF.8040806@sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <20080118183011.354965000@sgi.com> <20080118183011.527888000@sgi.com> <86802c440801182003vd94044ex7fb13e61e5f79c81@mail.gmail.com> <47926ACC.4060707@sgi.com> <479298AF.8040806@sgi.com> Sender: owner-linux-mm@kvack.org Return-Path: To: Mike Travis Cc: David Rientjes , Andrew Morton , Andi Kleen , mingo@elte.hu, Christoph Lameter , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Eric Dumazet List-ID: On Jan 19, 2008 4:41 PM, Mike Travis wrote: > 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. just use int for node id, and -1 will be NON_VALID... or s16? YH -- 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