Re: [RFC] memory cgroup: my thoughts on memsw

[Kamezawa Hiroyuki]

(2014/09/10 21:01), Vladimir Davydov wrote:
> On Mon, Sep 08, 2014 at 10:53:48PM +0900, Kamezawa Hiroyuki wrote:
> > (2014/09/08 20:01), Vladimir Davydov wrote:
> > > On Sat, Sep 06, 2014 at 08:15:44AM +0900, Kamezawa Hiroyuki wrote:
> > > > As you noticed, hitting anon+swap limit just means oom-kill.
> > > > My point is that using oom-killer for "server management" just seems crazy.
> > > >
> > > > Let my clarify things. your proposal was.
> > > >   1. soft-limit will be a main feature for server management.
> > > >   2. Because of soft-limit, global memory reclaim runs.
> > > >   3. Using swap at global memory reclaim can cause poor performance.
> > > >   4. So, making use of OOM-Killer for avoiding swap.
> > > >
> > > > I can't agree "4". I think
> > > >
> > > >   - don't configure swap.
> > >
> > > Suppose there are two containers, each having soft limit set to 50% of
> > > total system RAM. One of the containers eats 90% of the system RAM by
> > > allocating anonymous pages. Another starts using file caches and wants
> > > more than 10% of RAM to work w/o issuing disk reads. So what should we
> > > do then?
> > > We won't be able to shrink the first container to its soft
> > > limit, because there's no swap. Leaving it as is would be unfair from
> > > the second container's point of view. Kill it? But the whole system is
> > > going OK, because the working set of the second container is easily
> > > shrinkable. Besides there may be some progress in shrinking file caches
> > >from the first container.
> > > >   - use zram
> > >
> > > In fact this isn't different from the previous proposal (working w/o
> > > swap). ZRAM only compresses data while still storing them in RAM so we
> > > eventually may get into a situation where almost all RAM is full of
> > > compressed anon pages.
> >
> > In above 2 cases, "vmpressure" works fine.
>
> What if a container allocates memory so fast that the userspace thread
> handling its threshold notifications won't have time to react before it
> eats all memory?

Softlimit is for avoiding such unfair memory scheduling, isn't it ?

Thanks,
-Kame





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