linux-kernel - Re: [PATCH RFC tip/core/rcu] Make SRCU be once again optional

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Date:   Fri, 28 Apr 2017 17:51:15 -0400 (EDT)
From:   Nicolas Pitre <nicolas.pitre@...aro.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC tip/core/rcu] Make SRCU be once again optional

On Fri, 28 Apr 2017, Paul E. McKenney wrote:

> Hello, Nicolas!
> 
> Saw the TTY write up LWN and figured I should send this your way.
> It should be worth about 2K compared to current -next, which gave
> up the 2K compared to v4.10.  So really getting things back to where
> they were.
> 
> My current plan is to push this into v4.13.

Excellent!

If every maintainer finds a way to (optionally) reduce the size of the 
code they maintain by 2K then we'll get a much smaller kernel pretty 
soon.

> 
> 							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> commit e01ef0529ed548c1b30206058c2b5eecbbc07998
> Author: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Date:   Fri Apr 28 13:53:04 2017 -0700
> 
>     srcu: Make SRCU be once again optional
>     
>     Commit d160a727c40e ("srcu: Make SRCU be built by default") in response
>     to build errors, which were caused by code that included srcu.h
>     despite !SRCU.  However, srcutiny.o is almost 2K of code, which is not
>     insignificant for those attempting to run the Linux kernel on IoT devices.
>     This commit therefore makes SRCU be once again optional, and adjusts
>     srcu.h to allow error-free inclusion in !SRCU kernel builds.
>     
>     Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
>     Cc: Nicolas Pitre <nicolas.pitre@...aro.org>

Acked-by: Nicolas Pitre <nico@...aro.org>


> 
> diff --git a/include/linux/srcu.h b/include/linux/srcu.h
> index 167ad8831aaf..c0143fe2e39d 100644
> --- a/include/linux/srcu.h
> +++ b/include/linux/srcu.h
> @@ -62,7 +62,7 @@ int init_srcu_struct(struct srcu_struct *sp);
>  #include <linux/srcutree.h>
>  #elif defined(CONFIG_CLASSIC_SRCU)
>  #include <linux/srcuclassic.h>
> -#else
> +#elif defined(CONFIG_SRCU)
>  #error "Unknown SRCU implementation specified to kernel configuration"
>  #endif
>  
> diff --git a/init/Kconfig b/init/Kconfig
> index 42a346b0df43..fe72c12e06a5 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -521,7 +521,6 @@ config RCU_EXPERT
>  
>  config SRCU
>  	bool
> -	default y
>  	help
>  	  This option selects the sleepable version of RCU. This version
>  	  permits arbitrary sleeping or blocking within RCU read-side critical
> 
>