Re: [PATCH] mm/oom_kill: count global and memory cgroup oom kills

[Konstantin Khlebnikov]

On 19.05.2017 19:34, Roman Guschin wrote:
> 2017-05-19 15:22 GMT+01:00 Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>:
> > Show count of global oom killer invocations in /proc/vmstat and
> > count of oom kills inside memory cgroup in knob "memory.events"
> > (in memory.oom_control for v1 cgroup).
> >
> > Also describe difference between "oom" and "oom_kill" in memory
> > cgroup documentation. Currently oom in memory cgroup kills tasks
> > iff shortage has happened inside page fault.
> >
> > These counters helps in monitoring oom kills - for now
> > the only way is grepping for magic words in kernel log.
> >
> > Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
> > ---
> >   Documentation/cgroup-v2.txt   |   12 +++++++++++-
> >   include/linux/memcontrol.h    |    1 +
> >   include/linux/vm_event_item.h |    1 +
> >   mm/memcontrol.c               |    2 ++
> >   mm/oom_kill.c                 |    6 ++++++
> >   mm/vmstat.c                   |    1 +
> >   6 files changed, 22 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
> > index dc5e2dcdbef4..a742008d76aa 100644
> > --- a/Documentation/cgroup-v2.txt
> > +++ b/Documentation/cgroup-v2.txt
> > @@ -830,9 +830,19 @@ PAGE_SIZE multiple when read back.
> >
> >            oom
> >
> > +               The number of time the cgroup's memory usage was
> > +               reached the limit and allocation was about to fail.
> > +               Result could be oom kill, -ENOMEM from any syscall or
> > +               completely ignored in cases like disk readahead.
> > +               For now oom in memory cgroup kills tasks iff shortage
> > +               has happened inside page fault.
>
>  From a user's point of view the difference between "oom" and "max"
> becomes really vague here,
> assuming that "max" is described almost in the same words:
>
> "The number of times the cgroup's memory usage was
> about to go over the max boundary.  If direct reclaim
> fails to bring it down, the OOM killer is invoked."
>
> I wonder, if it's better to fix the existing "oom" value  to show what
> it has to show, according to docs,
> rather than to introduce a new one?

Nope, they are different. I think we should rephase documentation somehow

low - count of reclaims below low level
high - count of post-allocation reclaims above high level
max - count of direct reclaims
oom - count of failed direct reclaims
oom_kill - count of oom killer invocations and killed processes

> > +
> > +         oom_kill
> > +
> >                  The number of times the OOM killer has been invoked in
> >                  the cgroup.  This may not exactly match the number of
> > -               processes killed but should generally be close.
> > +               processes killed but should generally be close: each
> > +               invocation could kill several processes at once.
> >
> >     memory.stat