Fwd: [PATCH] mm: add config option to select the initial overcommit mode

[Sebastian Frias]

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
> --- Begin Message ---
> 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@xxxxxxxxxxx>
> ---
>
> 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"
> +	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.
> +
> +	config OVERCOMMIT_ALWAYS
> +		bool "Always"
> +	help
> +	  Selecting this option forces the initial value of overcommit mode to
> +	  "Always" overcommit.
> +	  See Documentation/vm/overcommit-accounting for more information.
> +
> +	config OVERCOMMIT_NEVER
> +		bool "Never"
> +	help
> +	  Selecting this option forces the initial value of overcommit mode to
> +	  "Never" overcommit.
> +	  See Documentation/vm/overcommit-accounting for more information.
> +
> +endchoice
> +
>  #
>  # UP and nommu archs use km based percpu allocator
>  #
> diff --git a/mm/util.c b/mm/util.c
> index 917e0e3..fd098bb 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -418,7 +418,13 @@ int __page_mapcount(struct page *page)
>  }
>  EXPORT_SYMBOL_GPL(__page_mapcount);
>  
> -int sysctl_overcommit_memory __read_mostly = OVERCOMMIT_GUESS;
> +#if defined(CONFIG_OVERCOMMIT_NEVER)
> +int sysctl_overcommit_memory __read_mostly = OVERCOMMIT_NEVER;
> +#elif defined(CONFIG_OVERCOMMIT_ALWAYS)
> +int sysctl_overcommit_memory __read_mostly = OVERCOMMIT_ALWAYS;
> +#else
> +int sysctl_overcommit_memory __read_mostly = OVERCOMMIT_GUESS;
> +#endif
>  int sysctl_overcommit_ratio __read_mostly = 50;
>  unsigned long sysctl_overcommit_kbytes __read_mostly;
>  int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT;
> -- 
> 2.1.4
>
>
> --- End Message ---