Messages in this thread | | | Date | Tue, 15 Oct 2013 09:40:10 +0800 | From | Zhang Yanfei <> | Subject | Re: [PATCH part2 v2 0/8] Arrange hotpluggable memory as ZONE_MOVABLE |
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Hello tejun, peter and yinghai
On 10/15/2013 04:55 AM, Tejun Heo wrote: > Hello, > > On Mon, Oct 14, 2013 at 01:37:20PM -0700, Yinghai Lu wrote: >> The problem is how to define "amount necessary". If we can parse srat early, >> then we could just map RAM for all boot nodes one time, instead of try some >> small and then after SRAT table, expand it cover non-boot nodes. > > Wouldn't that amount be fairly static and restricted? If you wanna > chunk memory init anyway, there's no reason to init more than > necessary until smp stage is reached. The more you do early, the more > serialized you're, so wouldn't the goal naturally be initing the > minimum possible? > >> To keep non-boot numa node hot-removable. we need to page table (and other >> that we allocate during boot stage) on ram of non boot nodes, or their >> local node ram. (share page table always should be on boot nodes). > > The above assumes the followings, > > * 4k page mappings. It'd be nice to keep everything working for 4k > but just following SRAT isn't enough. What if the non-hotpluggable > boot node doesn't stretch high enough and page table reaches down > too far? This won't be an optional behavior, so it is actually > *likely* to happen on certain setups. > > * Memory hotplug is at NUMA node granularity instead of device. > >>> Optimizing NUMA boot just requires moving the heavy lifting to >>> appropriate NUMA nodes. It doesn't require that early boot phase >>> should strictly follow NUMA node boundaries. >> >> At end of day, I like to see all numa system (ram/cpu/pci) could have >> non boot nodes to be hot-removed logically. with any boot command >> line. > > I suppose you mean "without any boot command line"? Sure, but, first > of all, there is a clear performance trade-off, and, secondly, don't > we want something finer grained? Why would we want to that per-NUMA > node, which is extremely coarse? >
Both ways seem ok enough *currently*. But what tejun always emphasizes is the trade-off, or benefit / cost ratio.
Yinghai and peter insist on the long-term plan. But it seems currently no actual requirements and plans that *must* parse SRAT earlier comparing to the current approach in this patchset, right?
Should we follow "Make it work first and optimize/beautify it later"? I think if we have the scene that must parse SRAT earlier, I think tejun will have no objection to it.
-- Thanks. Zhang Yanfei
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