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

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Message-ID: <20090828150723.GQ4889@balbir.in.ibm.com>
Date:	Fri, 28 Aug 2009 20:37:23 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>
Subject: Re: [RFC][PATCH 1/5] memcg: change for softlimit.

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

> Balbir Singh wrote:
> > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2009-08-28
> > 23:29:09]:
> >
> >> Balbir Singh wrote:
> >> > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@...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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