Re: memcg: softlimit on internal nodes

[Tejun Heo <tj@kernel.org>]

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
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

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