On Fri 24-02-23 13:07:57, Suren Baghdasaryan wrote: > On Fri, Feb 24, 2023 at 4:47 AM Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > On Tue 14-02-23 11:34:30, Suren Baghdasaryan wrote: > > [...] > > > Your suggestion to have this limit configurable sounds like obvious > > > solution. I would like to get some opinions from other maintainers. > > > Johannes, WDYT? CC'ing Michal to chime in as well since this is mostly > > > related to memory stalls. > > > > I do not think that making this configurable helps much. Many users will > > be bound to distribution config and also it would be hard to experiment > > with a recompile cycle every time. This seems just too impractical. > > > > Is there any reason why we shouldn't allow any timeout? Shorter > > timeouts could be restricted to a priviledged context to avoid an easy > > way to swamp system by too frequent polling. > > Hmm, ok. Maybe then we just ensure that only privileged users can set > triggers and remove the min limit (use a >0 check)? This could break existing userspace which is not privileged. I would just go with CAP_SYS_NICE or similar with small (sub min) timeouts. > > Btw. it seems that there is is only a limit on a single trigger per fd > > but no limits per user so it doesn't sound too hard to end up with too > > much polling even with a larger timeouts. To me it seems like we need to > > contain the polling thread to be bound by the cpu controller. > > Hmm. We have one "psimon" thread per cgroup (+1 system-level one) and > poll_min_period for each thread is chosen as the min() of polling > periods between triggers created in that group. So, a bad trigger that > causes overly aggressive polling and polling thread being throttled, > might affect other triggers in that cgroup. Yes, and why that would be a problem? -- Michal Hocko SUSE Labs
