On Thu 05-09-13 13:47:02, azurIt wrote: > >On Thu 05-09-13 12:17:00, azurIt wrote: > >> >[...] > >> >> My script detected another freezed cgroup today, sending stacks. Is > >> >> there anything interesting? > >> > > >> >3 tasks are sleeping and waiting for somebody to take an action to > >> >resolve memcg OOM. The memcg oom killer is enabled for that group? If > >> >yes, which task has been selected to be killed? You can find that in oom > >> >report in dmesg. > >> > > >> >I can see a way how this might happen. If the killed task happened to > >> >allocate a memory while it is exiting then it would get to the oom > >> >condition again without freeing any memory so nobody waiting on the > >> >memcg_oom_waitq gets woken. We have a report like that: > >> >https://lkml.org/lkml/2013/7/31/94 > >> > > >> >The issue got silent in the meantime so it is time to wake it up. > >> >It would be definitely good to see what happened in your case though. > >> >If any of the bellow tasks was the oom victim then it is very probable > >> >this is the same issue. > >> > >> Here it is: > >> http://watchdog.sk/lkml/kern5.log > > > >$ grep "Killed process \<103[168]\>" kern5.log > >$ > > > >So none of the sleeping tasks has been killed previously. > > > >> Processes were killed by my script > > > >OK, I am really confused now. The log contains a lot of in-kernel memcg > >oom killer messages: > >$ grep "Memory cgroup out of memory:" kern5.log | wc -l > >809 > > > >This suggests that the oom killer is not disabled. What exactly has you > >script done? > > > >> at about 11:05:35. > > > >There is an oom killer striking at 11:05:35: > >Sep 5 11:05:35 server02 kernel: [1751856.433101] Task in /1066/uid killed as a result of limit of /1066 > >[...] > >Sep 5 11:05:35 server02 kernel: [1751856.539356] [ pid ] uid tgid total_vm rss cpu oom_adj oom_score_adj name > >Sep 5 11:05:35 server02 kernel: [1751856.539745] [ 1046] 1066 1046 228537 95491 3 0 0 apache2 > >Sep 5 11:05:35 server02 kernel: [1751856.539894] [ 1047] 1066 1047 228604 95488 6 0 0 apache2 > >Sep 5 11:05:35 server02 kernel: [1751856.540043] [ 1050] 1066 1050 228470 95452 5 0 0 apache2 > >Sep 5 11:05:35 server02 kernel: [1751856.540191] [ 1051] 1066 1051 228592 95521 6 0 0 apache2 > >Sep 5 11:05:35 server02 kernel: [1751856.540340] [ 1052] 1066 1052 228594 95546 5 0 0 apache2 > >Sep 5 11:05:35 server02 kernel: [1751856.540489] [ 1054] 1066 1054 228470 95453 5 0 0 apache2 > >Sep 5 11:05:35 server02 kernel: [1751856.540646] Memory cgroup out of memory: Kill process 1046 (apache2) score 1000 or sacrifice child > > > >And this doesn't list any of the tasks sleeping and waiting for oom > >resolving so they must have been created after this OOM. Is this the > >same group? > > cgroup was 1066. My script is doing this: > 1.) It checks memory usage of all cgroups and is searching for those whos memory usage is >= 99% of their limit. > 2.) If any are found, they are saved in an array of 'candidates for killing'. > 3.) It sleep for 30 seconds. > 4.) Do (1) and if any of found cgorups were also found in (2), it kills all processes inside it. > 5.) Clear array of saved cgroups and continue. This is racy and doesn't really tell you anything about any group being frozen. [...] > But, of course, i cannot guarantee that the killed cgroup was really > freezed (because of bug in linux kernel), there could be some false > positives - for example, cgroup has 99% usage of memory, my script > detected it, OOM successfully resolved the problem and, after 30 > seconds, the same cgroup has again 99% usage of it's memory and my > script detected it again. Exactly > This is why i'm sending stacks here, i simply cannot tell if > there was or wasn't a problem. On the other hand if those processes would be stuck waiting for somebody to resolve the OOM for a long time without any change then yes we have a problem. Just to be sure I got you right. You have killed all the processes from the group you have sent stacks for, right? If that is the case I am really curious about processes sitting in sleep_on_page_killable because those are killable by definition. > I can disable the script and wait until the problem really occurs but > when it happens, our services will go down. I definitely do not want to encourage you to let your services down... > Hope i was clear enough - if not, i can post the source code of that > script. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>