Re: [discuss][memcg] oom-kill extension

[Balbir Singh <balbir@linux.vnet.ibm.com>]

KAMEZAWA Hiroyuki wrote:
> Under memory resource controller(memcg), oom-killer can be invoked when it
> reaches limit and no memory can be reclaimed.
> 
> In general, not under memcg, oom-kill(or panic) is an only chance to recover
> the system because there is no available memory. But when oom occurs under
> memcg, it just reaches limit and it seems we can do something else.
> 
> Does anyone have plan to enhance oom-kill ?
> 
> What I can think of now is
>   - add an notifier to user-land.
>     - receiver of notify should work in another cgroup.

The discussion at the mini-summit was to notify a FIFO in the cgroup and any
application can listen in for events.

>     - automatically extend the limit as emergency

No.. I don't like this

>     - trigger fail-over process.

I had suggested memrlimits for the ability to fail application allocations, but
no-one liked the idea. We can still implement overcommit functionality if needed
and catch failures at allocation time.

>     - automatically create a precise report of OOM.
>       - record snapshot of 'ps -elf' and so on of memcg which triggers oom.
> 
>   - freeze processes under cgroup.
>     - maybe freezer cgroup should be mounted at the same time.
>     - can we add memcg-oom-freezing-point in somewhere we can sleep ?
>   
> Is there a chance to add oom_notifier to memcg ? (netlink ?)
> 

Yes, we should add the oom-notifier. We already have cgroupstats if you want to
make use of it.

> But the real problem is that what we can do in the kernel is limited
> and we need proper userland, anyway ;)
> 

Agreed.

-- 
	Balbir

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