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

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Date:	Fri, 28 Aug 2009 23:58:39 +0900 (JST)
From:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>,
	"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.

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".

Thanks,
-Kame







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