[Pmem] Re: [PATCH] anolis: mm: Add page promotion throttle statistic

( 2/23/2022 4:44 PM, Huang, Ying S: > Baolin Wang <baolin.wang(a)linux.alibaba.com> writes: > >> ( 2/23/2022 3:51 PM, Huang, Ying S: >>> Baolin Wang <baolin.wang(a)linux.alibaba.com> writes: >>> >>>> ANBZ: #80 >>>> >>>> Add page promotion throttle statistic, which can be used to check >>>> how many cold pages were trying to be prmoted to DRAM, and help >>>> to tuning the latency threhold. >>> Can this be calculated via the following formula? >>> numa_hint_faults - pgpromote_candidate >> >> They are not same. Since numa_hint_faults will not contain file page >> promotion statistics, while the should_numa_migrate_memory() will >> check the file pages latency before promotion. Here some statistics I >> observed: >> >> pgpromote_candidate 3890100 >> pgpromote_cold_throttle 50342001 >> numa_hint_faults 35341839 > Then how about adding a counter for unmapped pages accesses we > checked? > And I think these kind of counters are for debugging only at least > for > now. Should we merge them formally? > Do you have an example about how to use this new counter or similar > one? We can add a counter for unmapped pages, but it still be little clear for these cold throttling counter. Please also considering numa_hint_faults will contain local faults, and some page promotion counts if the DRAM is free enough. I think the cold throttling counter is not only for debugging, but also for doing some decision in future. We can know how many cold pages are accessed, and we can measure the cold and hot memory distribution for this workdload to decide if the workload is suitable for the tiered-memory. So a clear and accurate cold throttling counter will be helpful. How do you think?