linux-kernel - Re: The performance and behaviour of the anti-fragmentation related patches

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Message-Id: <20070302100257.fd0d44a8.akpm@linux-foundation.org>
Date:	Fri, 2 Mar 2007 10:02:57 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	mgross@...ux.intel.com
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Balbir Singh <balbir@...ibm.com>, Mel Gorman <mel@...net.ie>,
	npiggin@...e.de, clameter@...r.sgi.com, mingo@...e.hu,
	jschopp@...tin.ibm.com, arjan@...radead.org, mbligh@...igh.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: The performance and behaviour of the anti-fragmentation related
 patches

On Fri, 2 Mar 2007 09:35:27 -0800
Mark Gross <mgross@...ux.intel.com> wrote:

> > 
> > Will it be possible to just power the DIMMs off?  I don't see much point in
> > some half-power non-destructive mode.
> 
> I think so, but need to double check with the HW folks.
> 
> Technically, the dims could be powered off, and put into 2 different low
> power non-destructive states.  (standby and suspend), but putting them
> in a low power non-destructive mode has much less latency and provides
> good bang for the buck or LOC change needed to make work.
> 
> Which lower power mode an application chooses will depend on latency
> tolerances of the app.  For the POC activities we are looking at we are
> targeting the lower latency option, but that doesn't lock out folks from
> trying to do something with the other options.
> 

If we don't evacuate all live data from all of the DIMM, we'll never be
able to power the thing down in many situations.

Given that we _have_ emptied the DIMM, we can just turn it off.  And
refilling it will be slow - often just disk speed.

So I don't see a useful use-case for non-destructive states.
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