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

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Message-ID: <20110616042044.GA28563@in.ibm.com>
Date:	Thu, 16 Jun 2011 09:50:44 +0530
From:	Ankita Garg <ankita@...ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	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

Hi,

On Mon, Jun 13, 2011 at 01:47:01PM +0900, KAMEZAWA Hiroyuki wrote:
> On Fri, 27 May 2011 18:01:28 +0530
> Ankita Garg <ankita@...ibm.com> wrote:
> 
> > Hi,
> > 
> 
> I'm sorry if you've answered already.
> 
> Is memory hotplug is too bad and cannot be enhanced for this purpose ?
> 
> I wonder
>   - make section-size smaller (IIUC, IBM's system has 16MB section size)
> 
>   - add per section statistics
> 
>   - add a kind of balloon driver which does software memory offline
>     (which means making a contiguous chunk of free pages of section_size
>      by page migration) in background with regard to memory usage statistics.
>     If system says "need more memory!", balloon driver can online pages.
> 
> can work for your purpose. It can allow you page isolatation and
> controls in 16MB unit.  If you need whole rework of memory hotplug, I think
> it's better to rewrite memory hotplug, too.
>

Interesting idea, but a few issues -

- Correctly predicting memory pressure is difficult and thereby being
  able to online the required pages at the right time could be a
  challenge
- Memory hotplug is a heavy operation, so the overhead involved may be
  high
- Powering off memory is just one of the ways in which memory power could
  be saved. The platform can also dynamically transition areas of memory
  into a  content-preserving lower power state if it is not referenced
  for a pre-defined threshold of time. In such a case, we would need a
  mechanism to soft offline the pages - i.e, no new allocations to be
  directed to that memory

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