On Wed, Jul 06, 2011 at 01:20:55PM -0700, david@lang.hm wrote:

On Wed, 6 Jul 2011, Pekka Enberg wrote:

quoted

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

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