Re: [PATCH 4/4] Memory controller soft limit reclaim on contention (v5)

[Balbir Singh <balbir@linux.vnet.ibm.com>]

* KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> [2009-03-13 15:54:03]:

> > > > My point is, contention case kswapd wakeup. and kswapd reclaim by
> > > > global lru order before soft limit shrinking.
> > > > Therefore, In typical usage, mem_cgroup_soft_limit_reclaim() almost
> > > > don't call properly.
> > > > 
> > > > soft limit shrinking should run before processing global reclaim.
> > > 
> > > Do you have the reason of disliking call from kswapd ?
> > >
> > 
> > Yes, I sent that reason out as comments to Kame's patches. kswapd or
> > balance_pgdat controls the zones, priority and in effect how many
> > pages we scan while doing reclaim. I did lots of experiments and found
> > that if soft limit reclaim occurred from kswapd, soft_limit_reclaim
> > would almost always fail and shrink_zone() would succeed, since it
> > looks at the whole zone and is always able to find some pages at all
> > priority levels. It also does not allow for targetted reclaim based on
> > how much we exceed the soft limit by. 
> 
> hm
> I read past discussion. so, I think we discuss many aspect at once.
> So, my current thinking is below, 
> 
> (1) if the group don't have any soft limit shrinking page, 
>     mem_cgroup_soft_limit_reclaim() spent time unnecessary.
>     -> right.

If the soft limit RB tree is empty, we don't spend any time at all.
Are you referring to something else? Am I missing something? The tree
will be empty if no group is over the soft limit.

>       actually, past global reclaim had similar problem.
>       then zone_is_all_unreclaimable() was introduced.
>       maybe we can use similar technique to memcg.
> 
> (2) mem_cgroup_soft_limit_reclaim() should be called from?
>     -> under discussion.
>        we should solve (1) at first for proper constructive
>        discussion.
> 
> (3) What's "fairness" of soft limit?
>     -> perfectly another aspect.
> 
> So, I'd like to discuss (1) at first.
> Although we don't kswapd shrinking, (1) is problem.
> 

-- 
	Balbir

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