Re: [PATCH v3] mm, oom: make the calculation of oom badness more accurate

[Yafang Shao]

On Mon, Jul 13, 2020 at 2:34 AM Naresh Kamboju
<naresh.kamboju@xxxxxxxxxx> wrote:
>
> On Fri, 10 Jul 2020 at 21:28, Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
> >
> > Recently we found an issue on our production environment that when memcg
> > oom is triggered the oom killer doesn't chose the process with largest
> > resident memory but chose the first scanned process. Note that all
> > processes in this memcg have the same oom_score_adj, so the oom killer
> > should chose the process with largest resident memory.
> >
> > Bellow is part of the oom info, which is enough to analyze this issue.
> > [7516987.983223] memory: usage 16777216kB, limit 16777216kB, failcnt 52843037
> > [7516987.983224] memory+swap: usage 16777216kB, limit 9007199254740988kB, failcnt 0
> > [7516987.983225] kmem: usage 301464kB, limit 9007199254740988kB, failcnt 0
> [...]
> > [7516987.984221] oom-kill:constraint=CONSTRAINT_MEMCG,nodemask=(null),cpuset=3aa16c9482ae3a6f6b78bda68a55d32c87c99b985e0f11331cddf05af6c4d753,mems_allowed=0-1,oom_memcg=/kubepods/podf1c273d3-9b36-11ea-b3df-246e9693c184,task_memcg=/kubepods/podf1c273d3-9b36-11ea-b3df-246e9693c184/1f246a3eeea8f70bf91141eeaf1805346a666e225f823906485ea0b6c37dfc3d,task=pause,pid=5740,uid=0
> > [7516987.984254] Memory cgroup out of memory: Killed process 5740 (pause) total-vm:1028kB, anon-rss:4kB, file-rss:0kB, shmem-rss:0kB
> > [7516988.092344] oom_reaper: reaped process 5740 (pause), now anon-rss:0kB, file-rss:0kB, shmem-rss:0kB
> >
> > We can find that the first scanned process 5740 (pause) was killed, but its
> > rss is only one page. That is because, when we calculate the oom badness in
> > oom_badness(), we always ignore the negtive point and convert all of these
> > negtive points to 1. Now as oom_score_adj of all the processes in this
> > targeted memcg have the same value -998, the points of these processes are
> > all negtive value. As a result, the first scanned process will be killed.
> >
> > The oom_socre_adj (-998) in this memcg is set by kubelet, because it is a
> > a Guaranteed pod, which has higher priority to prevent from being killed by
> > system oom.
> >
> > To fix this issue, we should make the calculation of oom point more
> > accurate. We can achieve it by convert the chosen_point from 'unsigned
> > long' to 'long'.
> >
> > [cai@xxxxxx: reported a issue in the previous version]
> > [mhocko@xxxxxxxx: fixed the issue reported by Cai]
> > [mhocko@xxxxxxxx: add the comment in proc_oom_score()]
> > Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> > Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> > Cc: David Rientjes <rientjes@xxxxxxxxxx>
> > Cc: Qian Cai <cai@xxxxxx>
> >
> > ---
> > v2 -> v3:
> > - fix the type of variable 'point' in oom_evaluate_task()
> > - initialize oom_control->chosen_points in select_bad_process() per Michal
> > - update the comment in proc_oom_score() per Michal
> >
> > Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
>
> Tested-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>
>
> I have noticed kernel panic with v2 patch while running LTP mm test suite.
>
> [ 63.451494] Out of memory and no killable processes...
> [ 63.456633] Kernel panic - not syncing: System is deadlocked on memory
>
> Then I have removed the v2 patch and applied this below v3 patch and re-tested.
> No regression noticed with v3 patch while running LTP mm on x86_64 and arm.
>
> OTOH,
> oom01 test case started with 100 iterations but runltp got killed after the
> 6th iteration [3]. I think this is expected.
>
> test steps:
>           - cd /opt/ltp
>           - ./runltp -s oom01 -I 100 || true
>
> [  209.052842] Out of memory: Killed process 519 (runltp)
> total-vm:10244kB, anon-rss:904kB, file-rss:4kB, shmem-rss:0kB, UID:0
> pgtables:60kB oom_score_adj:0
> [  209.066782] oom_reaper: reaped process 519 (runltp), now
> anon-rss:0kB, file-rss:0kB, shmem-rss:0kB
> /lava-1558245/0/tests/0_prep-tmp-disk/run.sh: line 21:   519 Killed
>               ./runltp -s oom01 -I 100
>
> > ---
> >  fs/proc/base.c      | 11 ++++++++++-
> >  include/linux/oom.h |  4 ++--
> >  mm/oom_kill.c       | 22 ++++++++++------------
> >  3 files changed, 22 insertions(+), 15 deletions(-)
>
>
> Reference test jobs,
> [1] https://lkft.validation.linaro.org/scheduler/job/1558246#L9189
> [2] https://lkft.validation.linaro.org/scheduler/job/1558247#L17213
> [3] https://lkft.validation.linaro.org/scheduler/job/1558245#L1407

Thanks for the test, Naresh.

-- 
Thanks
Yafang