On Mon, May 4, 2020 at 7:11 AM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > On Mon 04-05-20 06:54:40, Shakeel Butt wrote: > > On Sun, May 3, 2020 at 11:56 PM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > > > On Thu 30-04-20 11:27:12, Shakeel Butt wrote: > > > > Lowering memory.max can trigger an oom-kill if the reclaim does not > > > > succeed. However if oom-killer does not find a process for killing, it > > > > dumps a lot of warnings. > > > > > > It shouldn't dump much more than the regular OOM report AFAICS. Sure > > > there is "Out of memory and no killable processes..." message printed as > > > well but is that a real problem? > > > > > > > Deleting a memcg does not reclaim memory from it and the memory can > > > > linger till there is a memory pressure. One normal way to proactively > > > > reclaim such memory is to set memory.max to 0 just before deleting the > > > > memcg. However if some of the memcg's memory is pinned by others, this > > > > operation can trigger an oom-kill without any process and thus can log a > > > > lot un-needed warnings. So, ignore all such warnings from memory.max. > > > > > > OK, I can see why you might want to use memory.max for that purpose but > > > I do not really understand why the oom report is a problem here. > > > > It may not be a problem for an individual or small scale deployment > > but when "sweep before tear down" is the part of the workflow for > > thousands of machines cycling through hundreds of thousands of cgroups > > then we can potentially flood the logs with not useful dumps and may > > hide (or overflow) any useful information in the logs. > > If you are doing this in a large scale and the oom report is really a > problem then you shouldn't be resetting hard limit to 0 in the first > place. > I think I have pretty clearly described why we want to reset the hard limit to 0, so, unless there is an alternative I don't see why we should not be doing this. > > > memory.max can trigger the oom kill and user should be expecting the oom > > > report under that condition. Why is "no eligible task" so special? Is it > > > because you know that there won't be any tasks for your particular case? > > > What about other use cases where memory.max is not used as a "sweep > > > before tear down"? > > > > What other such use-cases would be? The only use-case I can envision > > of adjusting limits dynamically of a live cgroup are resource > > managers. However for cgroup v2, memory.high is the recommended way to > > limit the usage, so, why would resource managers be changing > > memory.max instead of memory.high? I am not sure. What do you think? > > There are different reasons to use the hard limit. Mostly to contain > potential runaways. While high limit might be a sufficient measure to > achieve that as well the hard limit is the last resort. And it clearly > has the oom killer semantic so I am not really sure why you are > comparing the two. > I am trying to see if "no eligible task" is really an issue and should be warned for the "other use cases". The only real use-case I can think of are resource managers adjusting the limit dynamically. I don't see "no eligible task" a concerning reason for such use-case. If you have some other use-case please do tell. Shakeel
