"Zhijian Li (Fujitsu)" <lizhijian@xxxxxxxxxxx> writes: > 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? I have no object to print some demotion information in dmesg. -- Best Regards, Huang, Ying > >> >> 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.
