On Mon, 2019-04-08 at 17:22 +0200, Helge Deller wrote: > On 08.04.19 16:29, James Bottomley wrote: > > On Mon, 2019-04-08 at 10:52 +0100, Mel Gorman wrote: > > > First, if pa-risc is !NUMA then why are separate local ranges > > > represented as separate nodes? Is it because of DISCONTIGMEM or > > > something else? DISCONTIGMEM is before my time so I'm not > > > familiar with it and I consider it "essentially dead" but the > > > arch init code seems to setup pgdats for each physical contiguous > > > range so it's a possibility. The most likely explanation is pa- > > > risc does not have hardware with addressing limitations smaller > > > than the CPUs physical address limits and it's possible to have > > > more ranges than available zones but clarification would be nice. > > > > Let me try, since I remember the ancient history. In the early > > days, there had to be a single mem_map array covering all of > > physical memory. Some pa-risc systems had huge gaps in the > > physical memory; I think one gap was somewhere around 1GB, so this > > lead us to wasting huge amounts of space in mem_map on non-existent > > memory. What CONFIG_DISCONTIGMEM did was allow you to represent > > this discontinuity on a non-NUMA system using numa nodes, so we > > effectively got one node per discontiguous range. It's hacky, but > > it worked. I thought we finally got converted to sparsemem by the > > NUMA people, but I can't find the commit. > > James, you tried once: > https://patchwork.kernel.org/patch/729441/ Ah, so what I was remembering as someone else's problem was, in fact, my problem? Hey, I should bottle my memory recall algorithms and sell them as executive training courses. > It seems we better should move over to sparsemem now? I think so. The basics of the patch likely apply and hopefully in the intervening 8 years some of the problems I identified have been fixed. James
