Re: memcg: softlimit on internal nodes

[Tejun Heo <tj@kernel.org>]

On Mon, Apr 22, 2013 at 08:57:03AM -0700, Tejun Heo wrote:
> On Mon, Apr 22, 2013 at 05:19:08PM +0200, Michal Hocko wrote:
> > We can try to be clever during the outside pressure and prefer
> > reclaiming over soft limit groups first. Which we used to do and will
> > do after rework as well. As a side effect of that a properly designed
> > hierachy with opt-in soft limited groups can actually accomplish some
> > isolation is a nice side effect but no _guarantee_.
> 
> Okay, so it *is* a soft limit.  Good.  If so, a subtree going over the
> limit of course forces reclaim on its children even though their
> individual configs aren't over limit.  It's exactly the same as
> hardlimit.  There doesn't need to be any difference and there's
> nothing questionable or interesting about it.
> 
> Also, then, a cgroup which has been configured explicitly shouldn't be
                                ^
				not

> disadvantaged compared to a cgroup with a limit configured.  ie. the
> current behavior of giving maximum to the knob on creation is the
> correct one.  The knob should create *extra* pressure.  It shouldn't
> lessen the pressure.  When populated weith other cgroups with limits
> configured, it would change the relative pressure felt by each but in
> general it's a limiting mechanism not an isolation one.  I think the
> bulk of confusion is coming from this, so please make that abundantly
> clear.
> 
> And, if people want a mechanism for isolation / lessening of pressure,
> which looks like a valid use case to me, add another knob for that
> which is prioritized under both hard and soft limits.  That is the
> only sensible way to do it.
> 
> Alright, no complaint anymore.  Thanks.
> 
> -- 
> tejun

-- 
tejun

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