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 [off-list ref] wrote:

quoted

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 at in.ibm.com)
Linux Technology Center
IBM India Systems & Technology Labs,
Bangalore, India