linux-kernel - Re: [RFC][PATCH 3/4] Memory controller soft limit organize cgroups

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Message-ID: <20090108042558.GC7294@balbir.in.ibm.com>
Date:	Thu, 8 Jan 2009 09:55:58 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
	YAMAMOTO Takashi <yamamoto@...inux.co.jp>,
	Paul Menage <menage@...gle.com>, lizf@...fujitsu.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	David Rientjes <rientjes@...gle.com>,
	Pavel Emelianov <xemul@...nvz.org>
Subject: Re: [RFC][PATCH 3/4] Memory controller soft limit organize cgroups

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2009-01-08 10:11:48]:

> On Thu, 08 Jan 2009 00:11:28 +0530
> Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> 
> > From: Balbir Singh <balbir@...ux.vnet.ibm.com>
> > 
> > This patch introduces a RB-Tree for storing memory cgroups that are over their
> > soft limit. The overall goal is to
> > 
> > 1. Add a memory cgroup to the RB-Tree when the soft limit is exceeded.
> >    We are careful about updates, updates take place only after a particular
> >    time interval has passed
> > 2. We remove the node from the RB-Tree when the usage goes below the soft
> >    limit
> > 
> > The next set of patches will exploit the RB-Tree to get the group that is
> > over its soft limit by the largest amount and reclaim from it, when we
> > face memory contention.
> > 
> 
> Hmm,  Could you clarify following ?
>   
>   - Usage of memory at insertsion and usage of memory at reclaim is different.
>     So, this *sorted* order by RB-tree isn't the best order in general.

True, but we frequently update the tree at an interval of HZ/4.
Updating at every page fault sounded like an overkill and building the
entire tree at reclaim is an overkill too.

>     Why don't you sort this at memory-reclaim dynamically ?
>   - Considering above, the look of RB tree can be
> 
>                 +30M (an amount over soft limit is 30M)
>                 /  \
>              -15M   +60M

We don't have elements below their soft limit in the tree

>      ?
> 
>     At least, pleease remove the node at uncharge() when the usage goes down.
>

We do remove the tree if it goes under its soft limit at commit_charge,
I thought I had the same code in uncharge(), but clearly that is
missing. Thanks, I'll add it there.


> Thanks,
> -Kame

-- 
	Balbir
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