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Date: Mon, 12 Mar 2007 16:54:51 -0700 From: Ethan Solomita <solo@...gle.com> To: Andi Kleen <ak@...e.de> CC: akpm@...l.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org Subject: Re: [PATCH 1/1] mm: Inconsistent use of node IDs 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 from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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