Re: memcg: softlimit on internal nodes

[Michal Hocko <mhocko@suse.cz>]

On Tue 23-04-13 17:13:20, Glauber Costa wrote:
> On 04/23/2013 05:06 PM, Michal Hocko wrote:
> > On Tue 23-04-13 05:51:36, Michel Lespinasse wrote:
> > [...]
> >> The issue I see is that even when people configure soft limits B+C <
> >> A, your current proposal still doesn't "leave the other alone" as
> >> Glauber and I think we should.
> > 
> > If B+C < A then B resp. C get reclaimed only if A is over the limit
> > which means that it couldn't reclaimed enough to get bellow the limit
> > when we bang on it before B and C. We can update the implementation
> > later to be more clever in situations like this but this is not that
> > easy because once we get away from the round robin over the tree then we
> > might end up having other issues - like unfairness etc... That's why I
> > wanted to have this as simple as possible.
> > 
> Nobody is opposing this, Michal.
> 
> What people are opposing is you saying that the children should be
> reclaimed *regardless* of their softlimit when the parent is over their
> soft limit. Someone, specially you, saying this, highly threatens
> further development in this direction.

OK, I am feeling like repeating myself. Anyway once more. I am _all_ for
protecting children that are under their limit if that is _possible_[1].
We are not yet there though for generic configuration. That's why I was
so careful about the wording and careful configuration at this stage.
Is this sufficient for your concerns?

I do not see any giant obstacles in the current implementation to allow
this behavior. 

> It doesn't really matter if your current set is doing this, simply
> everybody already agreed that you are moving in a good direction.
> 
> If you believe that it is desired to protect the children from reclaim
> in situation in which the offender is only one of the children and that
> can be easily identified, please state that clearly.

Clearly yes.

---
[1] and to be even more clear there are cases where this will never be
possible. For an example:
	A (soft:0)
	|
	B (soft:MAX)

where B smart ass thinks that his group never gets reclaim although he
is the only source of the pressure. This is what I call untrusted
environment.
-- 
Michal Hocko
SUSE Labs

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