On Mon 26-01-26 11:39:33, Mathieu Desnoyers wrote: > On 2026-01-16 16:55, Michal Hocko wrote: > > On Wed 14-01-26 14:36:44, Mathieu Desnoyers wrote: > > > On 2026-01-14 12:06, Michal Hocko wrote: > > > > On Wed 14-01-26 09:59:15, Mathieu Desnoyers wrote: > > [...] > > Thanks to those clarifications > > > > My overall impression is that the implementation is really involved and > > > > at this moment I do not really see a big benefit of all the complexity. > > > > > > Note that we can get the proc ABI RSS accuracy improvements with the > > > previous 2 patches without this 2-pass algo. Do you see more value in > > > the RSS accuracy improvements than in the oom killer latency reduction ? > > > > Yes, TBH I do not see oom latency as a big problem. As already mention > > this is a slow path and we are not talking about a huge latency anyway. > > proc numbers are much more sensitive to latency as they are regularly > > read by user space tools and accuracy for those matters as well (being > > off by 100s MB or GBs is simply making those numbers completely bogus). > > It makes sense. > > > > > It would help to explicitly mention what is the the overall imprecision > > > > of the oom victim selection with the new data structure (maybe this is > > > > good enough[*]). What if we go with exact precision with the new data > > > > structure comparing to the original pcp counters. > > > > > > Do you mean comparing using approximate sums with the new data > > > structure (which has a bounded accuracy of O(nr_cpus*log(nr_cpus))) > > > compared to the old data structure which had an inaccuracy of > > > O(nr_cpus^2) ? So if the inaccuracy provided by the new data structure > > > is good enough for OOM task selection, we could go from precise sum > > > back to an approximation and just use that with the new data > > > structure. > > > > Exactly! > OK, so based on your feedback, I plan to remove this 2-pass algo > from the series, and simply keep using the precise sum for the OOM > killer. If people complain about its latency, then we can eventually > use the approximation provided by the hierarchical counters. But let's > wait until someone asks for it rather than add this complexity when > there is no need. > > The hierarchical counters are still useful as they increase the > accuracy of approximations exported through /proc. > > How does that sound ?
Works for me. Thanks! -- Michal Hocko SUSE Labs
