Re: [PATCH] memcg: Provide knob for force OOM into the memcg

[Chintan Pandya]

On 12/17/2014 04:03 AM, David Rientjes wrote:
> On Tue, 16 Dec 2014, Michal Hocko wrote:
>
> > > We may want to use memcg to limit the total memory
> > > footprint of all the processes within the one group.
> > > This may lead to a situation where any arbitrary
> > > process cannot get migrated to that one  memcg
> > > because its limits will be breached. Or, process can
> > > get migrated but even being most recently used
> > > process, it can get killed by in-cgroup OOM. To
> > > avoid such scenarios, provide a convenient knob
> > > by which we can forcefully trigger OOM and make
> > > a room for upcoming process.
> > >
> > > To trigger force OOM,
> > > $ echo 1>  /<memcg_path>/memory.force_oom
> >
> > What would prevent another task deplete that memory shortly after you
> > triggered OOM and end up in the same situation? E.g. while the moving
> > task is migrating its charges to the new group...

Idea was to trigger an OOM until we can migrate any particular process 
onto desired cgroup.

> > Why cannot you simply disable OOM killer in that memcg and handle it
> > from userspace properly?

Well, this can be done it seems. Let me explore around this. Thanks for 
this suggestion.

> It seems to be proposed as a shortcut so that the kernel will determine
> the best process to kill.  That information is available to userspace so
> it should be able to just SIGKILL the desired process (either in the
> destination memcg or in the source memcg to allow deletion), so this
> functionality isn't needed in the kernel.

Yes, this can be seen as a shortcut because we are off-loading some 
task-selection to be killed by OOM on kernel rather than userspace 
decides by itself.

--
Chintan Pandya

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