linux-kernel - Re: [RFC][PATCH 0/4] Memory controller soft limit patches

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Message-ID: <20090108034634.GA7294@balbir.in.ibm.com>
Date:	Thu, 8 Jan 2009 09:16:35 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	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 0/4] Memory controller soft limit patches

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2009-01-08 09:37:00]:

> On Thu, 8 Jan 2009 00:26:27 +0530
> Dhaval Giani <dhaval@...ux.vnet.ibm.com> wrote:
> 
> > On Thu, Jan 08, 2009 at 12:11:10AM +0530, Balbir Singh wrote:
> > > 
> > > Here is v1 of the new soft limit implementation. Soft limits is a new feature
> > > for the memory resource controller, something similar has existed in the
> > > group scheduler in the form of shares. We'll compare shares and soft limits
> > > below. I've had soft limit implementations earlier, but I've discarded those
> > > approaches in favour of this one.
> > > 
> > > Soft limits are the most useful feature to have for environments where
> > > the administrator wants to overcommit the system, such that only on memory
> > > contention do the limits become active. The current soft limits implementation
> > > provides a soft_limit_in_bytes interface for the memory controller and not
> > > for memory+swap controller. The implementation maintains an RB-Tree of groups
> > > that exceed their soft limit and starts reclaiming from the group that
> > > exceeds this limit by the maximum amount.
> > > 
> > > This is an RFC implementation and is not meant for inclusion
> > > 
> > > TODOs
> > > 
> > > 1. The shares interface is not yet implemented, the current soft limit
> > >    implementation is not yet hierarchy aware. The end goal is to add
> > >    a shares interface on top of soft limits and to maintain shares in
> > >    a manner similar to the group scheduler
> > 
> > Just to clarify, when there is no contention, you want to share memory
> > proportionally?
> > 
> I don't like to add "share" as the kernel interface of memcg.
> We used "bytes" to do (hard) limit. Please just use "bytes".
>

Yes, we'll have soft limit in bytes, but for a hierarchical view,
shares do make a lot of sense. The user can use whichever interface
suits them the most.

-- 
	Balbir
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