Re: [PATCH -mm -v4 01/21] mm, THP, swap: Enable PMD swap operations for CONFIG_THP_SWAP

[Dan Williams]

On Thu, Jun 21, 2018 at 8:55 PM Huang, Ying <ying.huang@xxxxxxxxx> wrote:
>
> From: Huang Ying <ying.huang@xxxxxxxxx>
>
> Previously, the PMD swap operations are only enabled for
> CONFIG_ARCH_ENABLE_THP_MIGRATION.  Because they are only used by the
> THP migration support.  We will support PMD swap mapping to the huge
> swap cluster and swapin the THP as a whole.  That will be enabled via
> CONFIG_THP_SWAP and needs these PMD swap operations.  So enable the
> PMD swap operations for CONFIG_THP_SWAP too.
>
> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Shaohua Li <shli@xxxxxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> Cc: Zi Yan <zi.yan@xxxxxxxxxxxxxx>
> Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
> ---
>  arch/x86/include/asm/pgtable.h |  2 +-
>  include/asm-generic/pgtable.h  |  2 +-
>  include/linux/swapops.h        | 44 ++++++++++++++++++++++--------------------
>  3 files changed, 25 insertions(+), 23 deletions(-)
>
> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> index 99ecde23c3ec..13bf58838daf 100644
> --- a/arch/x86/include/asm/pgtable.h
> +++ b/arch/x86/include/asm/pgtable.h
> @@ -1224,7 +1224,7 @@ static inline pte_t pte_swp_clear_soft_dirty(pte_t pte)
>         return pte_clear_flags(pte, _PAGE_SWP_SOFT_DIRTY);
>  }
>
> -#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
> +#if defined(CONFIG_ARCH_ENABLE_THP_MIGRATION) || defined(CONFIG_THP_SWAP)

How about introducing a new config symbol representing the common
infrastructure between the two and have them select that symbol.

Would that also allow us to clean up the usage of
CONFIG_ARCH_ENABLE_THP_MIGRATION in fs/proc/task_mmu.c? In other
words, what's the point of having nice ifdef'd alternatives in header
files when ifdefs are still showing up in C files, all of it should be
optionally determined by header files.