From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <45F5E84B.9010901@google.com> Date: Mon, 12 Mar 2007 16:54:51 -0700 From: Ethan Solomita MIME-Version: 1.0 Subject: Re: [PATCH 1/1] mm: Inconsistent use of node IDs References: <45F5D974.2050702@google.com> <200703130019.30953.ak@suse.de> In-Reply-To: <200703130019.30953.ak@suse.de> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Andi Kleen Cc: akpm@osdl.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: Andi Kleen wrote: > On Monday 12 March 2007 23:51, Ethan Solomita wrote: >> This patch corrects inconsistent use of node numbers (variously "nid" or >> "node") in the presence of fake NUMA. > > I think it's very consistent -- your patch would make it inconsistent though. It's consistent to call node_online() with a physical node ID when the online node mask is composed of fake nodes? > Sorry, but when you ask for NUMA emulation you will get it. I don't see > any point in a "half way only for some subsystems I like" NUMA emulation. > It's unlikely that your ideas of where it is useful and where is not > matches other NUMA emulation user's ideas too. I don't understand your comments. My code is intended to work for all systems. If the system is non-NUMA by nature, then all CPUs map to fake node 0. As an example, on a two chip dual-core AMD opteron system, there are 4 "cpus" where CPUs 0 and 1 are close to the first half of memory, and CPUs 2 and 3 are close to the second half. Without this change CPUs 2 and 3 are mapped to fake node 1. This results in awful performance. With this change, CPUs 2 and 3 are mapped to (roughly) 1/2 the fake node count. Their zonelists[] are ordered to do allocations preferentially from zones that are local to CPUs 2 and 3. Can you tell me the scenario where my code makes things worse? > Besides adding such a secondary node space would be likely a huge long term > mainteance issue. I just can it see breaking with every non trivial change. I'm adding no data structures to do this. The current code already has get_phys_node. My changes use the existing information about node layout, both the physical and fake, and defines a mapping. The current mapping just takes a physical node and says "it's the fake node too". > NACK. I wish you would include some specifics as to why you think what you do. You're suggesting we leave in place a system that destroys NUMA locality when using fake numa, and passes around physical node ids as an index into nodes[] whihc is indexed by fake nodes. My change has no effect without fake numa, and harms no one with fake numa. -- Ethan -- 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