Re: [RFC][PATCH 1/5] memcg: change for softlimit.

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

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-08-28 23:58:39]:

> Balbir Singh wrote:
> > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-08-28
> > 23:29:09]:
> >
> >> Balbir Singh wrote:
> >> > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-08-28
> >> > 16:35:23]:
> >> >
> >>
> >> >>
> >> >> Current soft-limit RB-tree will be easily broken i.e. not-sorted
> >> >> correctly
> >> >> if used under use_hierarchy=1.
> >> >>
> >> >
> >> > Not true, I think the sorted-ness is delayed and is seen when we pick
> >> > a tree for reclaim. Think of it as being lazy :)
> >> >
> >> plz explain how enexpectedly unsorted RB-tree can work sanely.
> >>
> >>
> >
> > There are two checks built-in
> >
> > 1. In the reclaim path (we see how much to reclaim, compared to the
> > soft limit)
> > 2. In the dequeue path where we check if we really are over soft limit
> >
> that's not a point.
> 
> > I did lot of testing with the time based approach and found no broken
> > cases, I;ve been testing it with the mmotm (event based approach and I
> > am yet to see a broken case so far).
> >
> I'm sorry if I don't understand RB-tree.
> I think RB-tree is a system which can sort inputs passed by caller
> one by one and will be in broken state if value of nodes changed
> while it's in tree. Wrong ?
> While a subtree is
>                7
>               / \
>              3   9
> And, by some magic, the value can be changed without extract
>                7
>               / \
>              13  9
> The biggest is 13. But the biggest number which will be selecte will be "9".
>

This cannot happen today, we keep the values the same till we update
the tree. I hope that clarifies. 

-- 
	Balbir

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