On Fri, Feb 26, 2021 at 8:42 AM Yang Shi <shy828301@xxxxxxxxx> wrote: > > On Thu, Feb 25, 2021 at 11:30 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > On Thu 25-02-21 18:12:54, Yang Shi wrote: > > > When debugging an oom issue, I found the oom_kill counter of memcg is > > > confusing. At the first glance without checking document, I thought it > > > just counts for memcg oom, but it turns out it counts both global and > > > memcg oom. > > > > Yes, this is the case indeed. The point of the counter was to count oom > > victims from the memcg rather than matching that to the source of the > > oom. Rememeber that this could have been a memcg oom up in the > > hierarchy as well. Counting victims on the oom origin could be equally > > Yes, it is updated hierarchically on v2, but not on v1. I'm supposed > this is because v1 may work in non-hierarchcal mode? If this is the > only reason we may be able to remove this to get aligned with v2 since > non-hierarchal mode is no longer supported. BTW, having the counter recorded hierarchically may help out one of our usecases. We want to monitor the oom_kill for some services, but systemd would wipe out the cgroup if the service is oom killed then restart the service from scratch (it means create a brand new cgroup with the same name). So this systemd behavior makes the counter useless if it is not recorded hierarchically. > > > confusing because in many cases there would be no victim counted for the > > above mentioned memcg ooms. > > > > > The cgroup v2 documents it, but the description is missed for cgroup v1. > > > > > > Signed-off-by: Yang Shi <shy828301@xxxxxxxxx> > > > > Acked-by: Michal Hocko <mhocko@xxxxxxxx> > > > > > --- > > > Documentation/admin-guide/cgroup-v1/memory.rst | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/Documentation/admin-guide/cgroup-v1/memory.rst b/Documentation/admin-guide/cgroup-v1/memory.rst > > > index 0936412e044e..44d5429636e2 100644 > > > --- a/Documentation/admin-guide/cgroup-v1/memory.rst > > > +++ b/Documentation/admin-guide/cgroup-v1/memory.rst > > > @@ -851,6 +851,9 @@ At reading, current status of OOM is shown. > > > (if 1, oom-killer is disabled) > > > - under_oom 0 or 1 > > > (if 1, the memory cgroup is under OOM, tasks may be stopped.) > > > + - oom_kill integer counter > > > + The number of processes belonging to this cgroup killed by any > > > + kind of OOM killer. > > > > > > 11. Memory Pressure > > > =================== > > > -- > > > 2.26.2 > > > > > > > -- > > Michal Hocko > > SUSE Labs
