On 31/01/2024 11:17, Li Zhijian wrote: >>> node[0].preferred = 2 >>> node[0].demotion_targets = 2-5 >>> node[1].preferred = 5 >>> node[1].demotion_targets = 2-5 >>> node[2].preferred = 4 >>> node[2].demotion_targets = 3-4 >>> node[3].preferred = <empty> >>> node[3].demotion_targets = <empty> >>> node[4].preferred = <empty> >>> node[4].demotion_targets = <empty> >>> node[5].preferred = 3 >>> node[5].demotion_targets = 3-4 >>> But >>> this demotion path is not explicitly known to administrator. And with >>> the >>> feedback from our customers, they also think it is helpful to know demotion >>> path built by kernel to understand the demotion behaviors. >>> >>> So i think we should have 2 new interfaces for each node: >>> >>> /sys/devices/system/node/nodeN/demotion_allowed_nodes >>> /sys/devices/system/node/nodeN/demotion_preferred_nodes >>> >>> I value your opinion, and I'd like to know what you think about... >> >> Per my understanding, we will not expose everything inside kernel to >> user space. For page placement in a tiered memory system, demotion is >> just a part of the story. For example, if the DRAM of a system becomes >> full, new page allocation will fall back to the CXL memory. Have we >> exposed the default page allocation fallback order to user space? Back to our initial requirement: When demotion is enabled, what's the demotion path, especially the preferred node? are they consistent with administrator's expectations?" It seems there is no a direct answer. But actually, kernel have already known this information, IMHO, exposing them to users is not a bad choice. This information is able to help them adjust/tune the machine before really deploy their workloads. If the sysfs approach isn't better enough, is it possible to have another more user-friendly way to convey this information? like the allocation fallback order does, simply print them to dmesg? Thanks Zhijian > > Good question, I have no answer yet, but I think we can get the fallback order > from the dmesg now. > > The further action for us is that we will also try improve the use space tool, > such as numactl to show the demotion path with the help of this exposed information.
