On Mon, Nov 28, 2016 at 03:21:54PM +0100, Michal Hocko wrote:

On Tue 08-11-16 08:31:49, Naoya Horiguchi wrote:

quoted

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
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