[PATCH 2/2][v2] powerpc: Make the CMM memory hotplug aware

[Christoph Lameter]

On Thu, 15 Oct 2009, Gerald Schaefer wrote:

> > The pages allocated as __GFP_MOVABLE are used to store the list of pages
> > allocated by the balloon.  They reference virtual addresses and it would
> > be fine for the kernel to migrate the physical pages for those, the
> > balloon would not notice this.
>
> Does page migration really work for kernel pages that were allocated
> with __get_free_page()? I was wondering if we can do this on s390, where
> we have a 1:1 mapping of kernel virtual to physical addresses, but
> looking at migrate_pages() and friends, it seems that kernel pages
> w/o mapping and rmap should not be migrateable at all. Any thoughts from
> the memory migration experts?

page migration only works for pages where we have some way of accounting
for all the references to a page. This usually mean using reverse mappings
(anon list, radix trees and page tables).