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Date: Wed, 9 Dec 2020 16:39:22 -0800 From: "Paul E. McKenney" <paulmck@...nel.org> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Matthew Wilcox <willy@...radead.org>, Al Viro <viro@...iv.linux.org.uk>, "Eric W. Biederman" <ebiederm@...ssion.com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, Christian Brauner <christian.brauner@...ntu.com>, Oleg Nesterov <oleg@...hat.com>, Jann Horn <jann@...jh.net> Subject: Re: [PATCH] files: rcu free files_struct On Wed, Dec 09, 2020 at 03:29:09PM -0800, Linus Torvalds wrote: > On Wed, Dec 9, 2020 at 3:07 PM Matthew Wilcox <willy@...radead.org> wrote: > > > > #. It is not necessary to use rcu_assign_pointer() when creating > > linked structures that are to be published via a single external > > - pointer. The RCU_INIT_POINTER() macro is provided for this task > > - and also for assigning ``NULL`` pointers at runtime. > > + pointer. The RCU_INIT_POINTER() macro is provided for this task. > > + It used to be more efficient to use RCU_INIT_POINTER() to store a > > + ``NULL`` pointer, but rcu_assign_pointer() now optimises for a constant > > + ``NULL`` pointer itself. > > I would just remove the historical note about "It used to be more > efficient ..". It's not really helpful. > > If somebody wants to dig into the history, it's there in git. > > Maybe the note could be part of the commit message for the comment > update, explaining that it used to be more efficient but no longer is. > Because commit messages are about the explanation for the change. > > But I don't feel it makes any sense in the source code. Like this, then? Thanx, Paul #. It is not necessary to use rcu_assign_pointer() when creating linked structures that are to be published via a single external - pointer. The RCU_INIT_POINTER() macro is provided for this task - and also for assigning ``NULL`` pointers at runtime. + pointer. The RCU_INIT_POINTER() macro is provided for this task.
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