Re: memcg: softlimit on internal nodes

[Tejun Heo <tj@kernel.org>]

Hey,

On Mon, Apr 22, 2013 at 05:54:54PM +0200, Michal Hocko wrote:
> > Oh, if so, I'm happy.  Sorry about being brash on the thread; however,
> > please talk with google memcg people.  They have very different
> > interpretation of what "softlimit" is and are using it according to
> > that interpretation.  If it *is* an actual soft limit, there is no
> > inherent isolation coming from it and that should be clear to
> > everyone.
> 
> We have discussed that for a long time. I will not speak for Greg & Ying
> but from my POV we have agreed that the current implementation will work
> for them with some (minor) changes in their layout.
> As I have said already with a careful configuration (e.i. setting the
> soft limit only where it matters - where it protects an important
> memory which is usually in the leaf nodes) you can actually achieve
> _high_ probability for not being reclaimed after the rework which was not
> possible before because of the implementation which was ugly and
> smelled.

I don't know.  I'm not sure this is a good idea.  It's still
encouraging abuse of the knob even if that's not the intention and
once the usage sticks you end up with something you can't revert
afterwards.  I think it'd be better to make it *very* clear that
"softlimit" can't be used for isolation in any reliable way.

Thanks.

-- 
tejun

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