linux-kernel - Re: [PATCH] mm: kconfig: make Transparent Hugepage Support sysfs defaults to match the documentation

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Message-ID: <20191119104741.rtjc7awl4k57boyu@box>
Date:   Tue, 19 Nov 2019 13:47:41 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Rafael Aquini <aquini@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: kconfig: make Transparent Hugepage Support sysfs
 defaults to match the documentation

On Mon, Nov 18, 2019 at 10:01:02PM -0500, Rafael Aquini wrote:
> Documentation/admin-guide/mm/transhuge.rst (originally in Documentation/vm/transhuge.txt)
> states that TRANSPARENT_HUGEPAGE_MADVISE is the default option for THP config:
> 
> "
> madvise
>         will enter direct reclaim like ``always`` but only for regions
>         that are have used madvise(MADV_HUGEPAGE). This is the default
>         behaviour.
> "
> 
> This patch changes mm/Kconfig to reflect that fact, accordingly.

No. You've read it incorrectly.

The documentation describes default behaviour wrt defragmentaton ("defrag"
file), not page fault ("enabled" file). We don't have any Kconfig option
to set default behaviour for "defrag".

> Besides keeping consistency between documentation and the code behavior,
> other reasons to perform this minor adjustment are noted at:
> https://bugzilla.redhat.com/show_bug.cgi?id=1772133
> 
> Signed-off-by: Rafael Aquini <aquini@...hat.com>
> ---
>  mm/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/Kconfig b/mm/Kconfig
> index a5dae9a7eb51..c12a559aa1e5 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -385,7 +385,7 @@ config TRANSPARENT_HUGEPAGE
>  choice
>  	prompt "Transparent Hugepage Support sysfs defaults"
>  	depends on TRANSPARENT_HUGEPAGE
> -	default TRANSPARENT_HUGEPAGE_ALWAYS
> +	default TRANSPARENT_HUGEPAGE_MADVISE
>  	help
>  	  Selects the sysfs defaults for Transparent Hugepage Support.
>  
> -- 
> 2.17.2
> 
> 

-- 
 Kirill A. Shutemov