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 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