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

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Date:	Thu, 7 Jul 2011 10:24:20 +0530
From:	Ankita Garg <ankita@...ibm.com>
To:	david@...g.hm
Cc:	Pekka Enberg <penberg@...nel.org>,
	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,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH 00/10] mm: Linux VM Infrastructure to support Memory
 Power Management

On Wed, Jul 06, 2011 at 01:20:55PM -0700, david@...g.hm wrote:
> On Wed, 6 Jul 2011, Pekka Enberg wrote:
> 
> >Why does the allocator need to know about address boundaries? Why
> >isn't it enough to make the page allocator and reclaim policies favor using
> >memory from lower addresses as aggressively as possible? That'd mean
> >we'd favor the first memory banks and could keep the remaining ones
> >powered off as much as possible.
> >
> >IOW, why do we need to support scenarios such as this:
> >
> >  bank 0     bank 1   bank 2    bank3
> >| online  | offline | online  | offline |
> 
> I believe that there are memory allocations that cannot be moved
> after they are made (think about regions allocated to DMA from
> hardware where the hardware has already been given the address space
> to DMA into)
>

Thats true. These are kernel allocations which are not movable. However,
the ZONE_MOVABLE would enable us to create complete movable zones and
the ones that have the kernel allocations could be flagged as kernelcore
zone.
 
> As a result, you may not be able to take bank 2 offline, so your
> option is to either leave banks 0-2 all online, or support emptying
> bank 1 and taking it offline.
> 

-- 
Regards,
Ankita Garg (ankita@...ibm.com)
Linux Technology Center
IBM India Systems & Technology Labs,
Bangalore, India
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