linux-kernel - Re: [PATCH 00/10] mm: Linux VM Infrastructure to support Memory Power Management

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Message-ID: <20110610184738.GG2230@linux.vnet.ibm.com>
Date:	Fri, 10 Jun 2011 11:47:38 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Matthew Garrett <mjg59@...f.ucam.org>
Cc:	Kyungmin Park <kmpark@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ankita Garg <ankita@...ibm.com>,
	linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org,
	svaidy@...ux.vnet.ibm.com, thomas.abraham@...aro.org
Subject: Re: [PATCH 00/10] mm: Linux VM Infrastructure to support Memory
 Power Management

On Fri, Jun 10, 2011 at 07:08:07PM +0100, Matthew Garrett wrote:
> On Fri, Jun 10, 2011 at 10:52:48AM -0700, Paul E. McKenney wrote:
> > On Fri, Jun 10, 2011 at 06:23:07PM +0100, Matthew Garrett wrote:
> > > I haven't seen too many ARM servers with 256GB of RAM :) I'm mostly 
> > > looking at this from an x86 perspective.
> > 
> > But I have seen ARM embedded systems with CPU power consumption in
> > the milliwatt range, which greatly reduces the amount of RAM required
> > to get significant power savings from this approach.  Three orders
> > of magnitude less CPU power consumption translates (roughly) to three
> > orders of magnitude less memory required -- and embedded devices with
> > more than 256MB of memory are quite common.
> 
> I'm not saying that powering down memory isn't a win, just that in the 
> server market we're not even getting unused memory into self refresh at 
> the moment. If we can gain that hardware capability then sub-node zoning 
> means that we can look at allocating (and migrating?) RAM in such a way 
> as to get a lot of the win that we'd gain from actually cutting the 
> power, without the added overhead of actually shrinking our working set.

Agreed.

And if I understand you correctly, then the patches that Ankita posted
should help your self-refresh case, along with the originally intended
the power-down case and special-purpose use of memory case.

							Thanx, Paul
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