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

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Message-Id: <20170429001040.GH3956@linux.vnet.ibm.com>
Date:   Fri, 28 Apr 2017 17:10:40 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Nicolas Pitre <nicolas.pitre@...aro.org>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC tip/core/rcu] Make SRCU be once again optional

On Fri, Apr 28, 2017 at 05:51:15PM -0400, Nicolas Pitre wrote:
> 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.

I would feel better if it wasn't me who had added the 2K, but then
again, I do look forward to seeing a negative-sized kernel!  ;-)

> > ------------------------------------------------------------------------
> > 
> > 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>

Applied, thank you!

							Thanx, Paul

> > 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
> > 
> > 
>