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

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Message-ID: <20090828072007.GH4889@balbir.in.ibm.com>
Date:	Fri, 28 Aug 2009 12:50:08 +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 13:23:21]:

> This patch tries to modify softlimit handling in memcg/res_counter.
> There are 2 reasons in general.
> 
>  1. soft_limit can use only against sub-hierarchy root.
>     Because softlimit tree is sorted by usage, putting prural groups
>     under hierarchy (which shares usage) will just adds noise and unnecessary
>     mess. This patch limits softlimit feature only to hierarchy root.
>     This will make softlimit-tree maintainance better. 
> 
>  2. In these days, it's reported that res_counter can be bottleneck in
>     massively parallel enviroment. We need to reduce jobs under spinlock.
>     The reason we check softlimit at res_counter_charge() is that any member
>     in hierarchy can have softlimit.
>     But by chages in "1", only hierarchy root has soft_limit. We can omit
>     hierarchical check in res_counter.
> 
> After this patch, soft limit is avaliable only for root of sub-hierarchy.
> (Anyway, softlimit for hierarchy children just makes users confused, hard-to-use)
>


I need some time to digest this change, if the root is a hiearchy root
then only root can support soft limits? I think the change makes it
harder to use soft limits. Please help me understand better. 

-- 
	Balbir
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