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

From: Balbir Singh <balbir@linux.vnet.ibm.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: linux-mm@kvack.org, Sudhir Kumar <skumar@linux.vnet.ibm.com>,
	YAMAMOTO Takashi <yamamoto@valinux.co.jp>,
	Bharata B Rao <bharata@in.ibm.com>,
	Paul Menage <menage@google.com>,
	lizf@cn.fujitsu.com, linux-kernel@vger.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
	David Rientjes <rientjes@google.com>,
	Pavel Emelianov <xemul@openvz.org>,
	Dhaval Giani <dhaval@linux.vnet.ibm.com>,
	Rik van Riel <riel@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 2/4] Memory controller soft limit interface (v3)
Date: Mon, 2 Mar 2009 11:37:26 +0530	[thread overview]
Message-ID: <20090302060726.GH11421@balbir.in.ibm.com> (raw)
In-Reply-To: <20090302143518.43f5fcc2.kamezawa.hiroyu@jp.fujitsu.com>

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-03-02 14:35:18]:

> On Mon, 2 Mar 2009 10:16:31 +0530
> Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> 
> > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-03-02 11:03:23]:
> > 
> > > On Sun, 01 Mar 2009 12:00:11 +0530
> > > Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> > > 
> > > > 
> > > > From: Balbir Singh <balbir@linux.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'm now searching a way to reduce res_counter->lock ping-pong but have no
> good idea.
> 

I've been doing some detailed analysis on the memory controller
overhead. I have a set of patches that I am testing right now. I'll
share the details once I am done with them.

-- 
	Balbir