linux-kernel - Re: [PATCH tip/core/rcu 01/13] mm: Rename SLAB_DESTROY_BY_RCU to SLAB_TYPESAFE_BY

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Message-Id: <20170414133951.GY3956@linux.vnet.ibm.com>
Date:   Fri, 14 Apr 2017 06:39:51 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>, jiangshanlai@...il.com,
        dipankar@...ibm.com, Andrew Morton <akpm@...ux-foundation.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Triplett <josh@...htriplett.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        David Howells <dhowells@...hat.com>,
        Frederic Weisbecker <fweisbec@...il.com>, oleg@...hat.com,
        pranith kumar <bobby.prani@...il.com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH tip/core/rcu 01/13] mm: Rename SLAB_DESTROY_BY_RCU to
 SLAB_TYPESAFE_BY_RCU

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@...radead.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