Date: Fri, 14 Apr 2017 06:39:51 -0700
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Eric Dumazet <edumazet@google.com>, Vlastimil Babka <vbabka@suse.cz>,
        LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@kernel.org>,
        jiangshanlai@gmail.com, dipankar@in.ibm.com,
        Andrew Morton <akpm@linux-foundation.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Josh Triplett <josh@joshtriplett.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Steven Rostedt <rostedt@goodmis.org>,
        David Howells <dhowells@redhat.com>,
        Frederic Weisbecker <fweisbec@gmail.com>, oleg@redhat.com,
        pranith kumar <bobby.prani@gmail.com>,
        Christoph Lameter <cl@linux.com>, Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>, linux-mm <linux-mm@kvack.org>
Subject: Re: [PATCH tip/core/rcu 01/13] mm: Rename SLAB_DESTROY_BY_RCU to
 SLAB_TYPESAFE_BY_RCU
Reply-To: paulmck@linux.vnet.ibm.com
References: <20170412165441.GA17149@linux.vnet.ibm.com>
 <1492016149-18834-1-git-send-email-paulmck@linux.vnet.ibm.com>
 <20170413091248.xnctlppstkrm6eq5@hirez.programming.kicks-ass.net>
 <50d59b9c-fa8e-1992-2613-e84774ec5428@suse.cz>
 <20170413161709.ej3qxuqitykhqtyf@hirez.programming.kicks-ass.net>
 <CANn89iLAG9COnimUgqKFipX1VOuXdVFS-jJ8yoVDHSCNu7f+6w@mail.gmail.com>
 <20170414084544.wgubp4ikqmohgn67@hirez.programming.kicks-ass.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20170414084544.wgubp4ikqmohgn67@hirez.programming.kicks-ass.net>
User-Agent: Mutt/1.5.21 (2010-09-15)
Message-Id: <20170414133951.GY3956@linux.vnet.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1362
Lines: 35

On Fri, Apr 14, 2017 at 10:45:44AM +0200, Peter Zijlstra wrote:
> On Thu, Apr 13, 2017 at 02:30:19PM -0700, Eric Dumazet wrote:
> > On Thu, Apr 13, 2017 at 9:17 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> > 
> > > git log -S SLAB_DESTROY_BY_RCU
> > 
> > Maybe, but "git log -S" is damn slow at least here.
> > 
> > While "git grep" is _very_ fast
> 
> All true. But in general we don't leave endless markers around like
> this.
> 
> For instance:
> 
>   /* the function formerly known as smp_mb__before_clear_bit() */
> 
> is not part of the kernel tree. People that used that thing out of tree
> get to deal with it in whatever way they see fit.

Sometimes we don't provide markers and sometimes we do:

$ git grep synchronize_kernel
Documentation/RCU/RTFP.txt:,Title="API change: synchronize_kernel() deprecated"
Documentation/RCU/RTFP.txt:     Jon Corbet describes deprecation of synchronize_kernel()
kernel/rcu/tree.c: * synchronize_kernel() API.  In contrast, synchronize_rcu() only

Given that it has been more than a decade, I could easily see my way to
removing this synchronize_kernel() tombstone in kernel/rcu/tree.c if
people are annoyed by it.  But thus far, no one has complained.

So how long should we wait to remove the SLAB_DESTROY_BY_RCU tombstone?
I can easily add an event to my calendar to remind me to remove it.

							Thanx, Paul