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

From	Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2 04/12] mm: thp: introduce CONFIG_ARCH_ENABLE_THP_MIGRATION
Date	2016-11-29 09:00 +0100
Message-ID	<sILuy-5oV-23@gated-at.bofh.it> (permalink)
References	<sB1Ga-1xZ-7@gated-at.bofh.it> <sB1Ga-1xZ-19@gated-at.bofh.it> <sIv6p-3fu-15@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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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

Thread

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

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