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Re: [PATCH v2 04/12] mm: thp: introduce CONFIG_ARCH_ENABLE_THP_MIGRATION

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  Re: [PATCH v2 04/12] mm: thp: introduce  CONFIG_ARCH_ENABLE_THP_MIGRATION Michal Hocko <mhocko@kernel.org> - 2016-11-28 15:30 +0100
    Re: [PATCH v2 04/12] mm: thp: introduce  CONFIG_ARCH_ENABLE_THP_MIGRATION Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> - 2016-11-29 09:00 +0100
      Re: [PATCH v2 04/12] mm: thp: introduce  CONFIG_ARCH_ENABLE_THP_MIGRATION Michal Hocko <mhocko@kernel.org> - 2016-11-29 09:50 +0100

#1531346 — Re: [PATCH v2 04/12] mm: thp: introduce CONFIG_ARCH_ENABLE_THP_MIGRATION

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.
-- 
Michal Hocko
SUSE Labs

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#1531979

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

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#1531997

On Tue 29-11-16 07:50:06, Naoya Horiguchi wrote:
> 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 this is _much_ better!
-- 
Michal Hocko
SUSE Labs

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