On Mon, Nov 28, 2016 at 03:21:54PM +0100, Michal Hocko wrote:
> On Tue 08-11-16 08:31:49, Naoya Horiguchi wrote:
> > Introduces CONFIG_ARCH_ENABLE_THP_MIGRATION to limit thp migration
> > functionality to x86_64, which should be safer at the first step.
>
> Please make sure to describe why this has to be arch specific and what
> are arches supposed to provide in order to enable this option.
OK, the below will be added in the future version:
Thp migration is an arch-specific feature because it depends on the
arch-dependent behavior of non-present format of page table entry.
What you need to enable this option in other archs are:
- to define arch-specific transformation functions like __pmd_to_swp_entry()
and __swp_entry_to_pmd(),
- to make sure that arch-specific page table walking code can properly handle
!pmd_present case (gup_pmd_range() is a good example),
- (if your archs enables CONFIG_HAVE_ARCH_SOFT_DIRTY,) to define soft dirty
routines like pmd_swp_mksoft_dirty.
Thanks,
Naoya Horiguchi
