linux-kernel - Re: [PATCH] srcu: Debloat the <linux/rcu

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Message-Id: <20170502125648.GA1286@linux.vnet.ibm.com>
Date:   Tue, 2 May 2017 05:56:48 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] srcu: Debloat the <linux/rcu_segcblist.h> header

On Tue, May 02, 2017 at 03:25:03AM -0700, Paul E. McKenney wrote:
> On Tue, May 02, 2017 at 10:31:18AM +0200, Ingo Molnar wrote:
> > 
> > * Ingo Molnar <mingo@...nel.org> wrote:
> > 
> > > > I will get rid of the unused rcu_segcblist_extract_all() function and create a 
> > > > kernel/rcu/segcblist.c for the functions that are either non-trivial or 
> > > > performance-insensitive.
> > > > 
> > > > Does that cover it, or am I missing something?
> > > 
> > > I'd also suggest moving as much of the RCU internal data types into kernel/rcu/ 
> > > as possible. It's not clear to me which part of it is supposed to be a public 
> > > API and which bits are internal. It might make sense to keep it internal for the 
> > > time being, and only export things once there are users.
> > > 
> > > I.e. a pretty good solution would be to move all of 
> > > include/linux/rcu_segcblist.h to kernel/rcu/rcu_segcblist.c or so - and do a 
> > > kernel/rcu/rcu_segcblist.h with the data types and function prototypes.
> > 
> > I.e. the attached patch as a first step.
> > 
> > Only minimally build tested, but it appears to be do the trick.
> > 
> > This changes the <linux/rcu_segcblist.h> header from ~700 lines to only 90 lines - 
> > 60% of which is comments.
> > 
> > The deinlining of the inline functions within kernel/rcu/ should also be done, as 
> > a separate patch on top of this.
> > 
> > What do you think?
> 
> Thank you very much!
> 
> I have pulled this in and started a short rcutorture run.  I will do
> de-inline and create a .c file on top of this and retest after the
> rcutorture has finished.

And I am applying the following fixlet for !SMP builds, which I am
retesting.  Other than that, initial rcutorture ran fine!

							Thanx, Paul

------------------------------------------------------------------------

diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index b8293527ee18..36e1f82faed1 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -30,6 +30,7 @@
 #include <linux/srcu.h>
 
 #include <linux/rcu_node_tree.h>
+#include "rcu_segcblist.h"
 #include "rcu.h"
 
 static int init_srcu_struct_fields(struct srcu_struct *sp)