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

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

> > > 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.
      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.



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