linux-kernel - Re: Fwd: [PATCH] mm: add config option to select the initial overcommit mode

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Date:	Tue, 10 May 2016 13:39:41 +0100
From:	Andy Whitcroft <apw@...onical.com>
To:	Sebastian Frias <sf84@...oste.net>
Cc:	Joe Perches <joe@...ches.com>, mason <slash.tmp@...e.fr>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Fwd: [PATCH] mm: add config option to select the initial
 overcommit mode

On Tue, May 10, 2016 at 02:00:47PM +0200, Sebastian Frias wrote:
> Hi,
> 
> Using checkpatch.pl on the forwarded patch results in:
> 
> WARNING: please write a paragraph that describes the config symbol fully
> #57: FILE: mm/Kconfig:451:
> +       config OVERCOMMIT_GUESS
> 
> WARNING: please write a paragraph that describes the config symbol fully
> #64: FILE: mm/Kconfig:458:
> +       config OVERCOMMIT_ALWAYS
> 
> but there is a 'help' section for those 'config' sections.
> NOTE: I followed the same indentation than the code laying just above the place where I inserted mine.
> 
> I think it is a false positive, what do you think?
> 
> Best regards,
> 
> Sebastian

Well, I am expecting the issue to be that the per option help is not
indented within the option like I am expecting ...

> Date: Tue, 10 May 2016 13:56:30 +0200
> From: Sebastian Frias <sf84@...oste.net>
> To: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>, Michal
>  Hocko <mhocko@...e.com>, Linus Torvalds <torvalds@...ux-foundation.org>
> CC: LKML <linux-kernel@...r.kernel.org>, mason <slash.tmp@...e.fr>
> Subject: [PATCH] mm: add config option to select the initial overcommit mode
> User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101
>  Thunderbird/31.2.0
> 
> Currently the initial value of the overcommit mode is OVERCOMMIT_GUESS.
> However, on embedded systems it is usually better to disable overcommit
> to avoid waking up the OOM-killer and its well known undesirable
> side-effects.
> 
> This config option allows to setup the initial overcommit mode to any of
> the 3 available values, OVERCOMMIT_GUESS (which remains as default),
> OVERCOMMIT_ALWAYS and OVERCOMMIT_NEVER.
> The overcommit mode can still be changed thru sysctl after the system
> boots up.
> 
> This config option depends on CONFIG_EXPERT.
> This patch does not introduces functional changes.
> 
> Signed-off-by: Sebastian Frias <sf84@...oste.net>
> ---
> 
> NOTE: I understand that the overcommit mode can be changed dynamically thru
> sysctl, but on embedded systems, where we know in advance that overcommit
> will be disabled, there's no reason to postpone such setting.
> 
> I would also be interested in knowing if you guys think this option should
> disable sysctl access for overcommit mode, essentially hardcoding the
> overcommit mode when this option is used.
> 
> NOTE2: I tried to track down the history of overcommit but back then there
> were no single patches apparently and the patch that appears to have
> introduced the first overcommit mode (OVERCOMMIT_ALWAYS) is commit
> 9334eab8a36f ("Import 2.1.27"). OVERCOMMIT_NEVER was introduced with commit
> 502bff0685b2 ("[PATCH] strict overcommit").
> My understanding is that prior to commit 9334eab8a36f ("Import 2.1.27")
> there was no overcommit, is that correct?
> 
> NOTE3: checkpatch.pl is warning about missing description for the config
> symbols ("please write a paragraph that describes the config symbol fully")
> but my understanding is that that is a false positive (or the warning message
> not clear enough for me to understand it) considering that I have added
> 'help' sections for each 'config' section.
> ---
>  mm/Kconfig | 32 ++++++++++++++++++++++++++++++++
>  mm/util.c  |  8 +++++++-
>  2 files changed, 39 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/Kconfig b/mm/Kconfig
> index abb7dcf..6dad57d 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -439,6 +439,38 @@ choice
>  	  benefit.
>  endchoice
>  
> +choice
> +	prompt "Overcommit Mode"
> +	default OVERCOMMIT_GUESS
> +	depends on EXPERT
> +	help
> +	  Selects the initial value for Overcommit mode.
> +
> +	  NOTE: The overcommit mode can be changed dynamically through sysctl.
> +
> +	config OVERCOMMIT_GUESS
> +		bool "Guess"

I am expecting the help below to be indented at the same level as the
bool above.  As you have done with the help for the choice itself.  I am
pretty sure checkpatch is assuming the "contents" of the config item are
all intented more than it is.

> +	help
> +	  Selecting this option forces the initial value of overcommit mode to
> +	  "Guess" overcommits. This is the default value.
> +	  See Documentation/vm/overcommit-accounting for more information.
[...]

-apw