linux-kernel - Re: [PATCH 2/4] Memory controller soft limit interface (v3)

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Message-ID: <20090302062951.GI11421@balbir.in.ibm.com>
Date:	Mon, 2 Mar 2009 11:59:51 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	linux-mm@...ck.org, Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
	YAMAMOTO Takashi <yamamoto@...inux.co.jp>,
	Bharata B Rao <bharata@...ibm.com>,
	Paul Menage <menage@...gle.com>, lizf@...fujitsu.com,
	linux-kernel@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Pavel Emelianov <xemul@...nvz.org>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/4] Memory controller soft limit interface (v3)

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2009-03-02 15:19:53]:

> On Mon, 2 Mar 2009 11:37:26 +0530
> Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> 
> > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2009-03-02 14:35:18]:
> > 
> > > On Mon, 2 Mar 2009 10:16:31 +0530
> > > Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> > > 
> > > > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2009-03-02 11:03:23]:
> > > > 
> > > > > On Sun, 01 Mar 2009 12:00:11 +0530
> > > > > Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> > > > > 
> > > > > > 
> > > > > > From: Balbir Singh <balbir@...ux.vnet.ibm.com>
> > > > > > 
> > > > > > Changelog v2...v1
> > > > > > 1. Add support for res_counter_check_soft_limit_locked. This is used
> > > > > >    by the hierarchy code.
> > > > > > 
> > > > > > Add an interface to allow get/set of soft limits. Soft limits for memory plus
> > > > > > swap controller (memsw) is currently not supported. Resource counters have
> > > > > > been enhanced to support soft limits and new type RES_SOFT_LIMIT has been
> > > > > > added. Unlike hard limits, soft limits can be directly set and do not
> > > > > > need any reclaim or checks before setting them to a newer value.
> > > > > > 
> > > > > > Kamezawa-San raised a question as to whether soft limit should belong
> > > > > > to res_counter. Since all resources understand the basic concepts of
> > > > > > hard and soft limits, it is justified to add soft limits here. Soft limits
> > > > > > are a generic resource usage feature, even file system quotas support
> > > > > > soft limits.
> > > > > > 
> > > > > I don't convice adding more logics to res_counter is a good to do, yet.
> > > > >
> > > > 
> > > > Even though it is extensible and you pay the cost only when soft
> > > > limits is turned on? Can you show me why you are not convinced?
> > > >  
> > > Inserting more codes (like "if") to res_counter itself is not welcome..
> > > I think res_counter is too complex as counter already.
> > >
> > 
> > Darn.. we better stop all code development!
> >  
> I don't say such a thing. My point is we have to keep res_counter as light-weight
> as possible. If there are alternatives, we should use that.
>

Any sort of new feature like this needs support from res_counters, we
need to extend them to remain consistent with out design and code.
Yes, if there are better alternatives, I would use them. BTW, I am
working on a newer scheme to change res_counter locking, but not sure
if that should come in the way of this development. 

-- 
	Balbir
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