From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DF883C433FF for ; Tue, 13 Aug 2019 05:31:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B490420651 for ; Tue, 13 Aug 2019 05:31:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725820AbfHMFb2 (ORCPT ); Tue, 13 Aug 2019 01:31:28 -0400 Received: from lgeamrelo11.lge.com ([156.147.23.51]:34352 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725786AbfHMFb2 (ORCPT ); Tue, 13 Aug 2019 01:31:28 -0400 Received: from unknown (HELO lgeamrelo04.lge.com) (156.147.1.127) by 156.147.23.51 with ESMTP; 13 Aug 2019 14:31:25 +0900 X-Original-SENDERIP: 156.147.1.127 X-Original-MAILFROM: byungchul.park@lge.com Received: from unknown (HELO X58A-UD3R) (10.177.222.33) by 156.147.1.127 with ESMTP; 13 Aug 2019 14:31:25 +0900 X-Original-SENDERIP: 10.177.222.33 X-Original-MAILFROM: byungchul.park@lge.com Date: Tue, 13 Aug 2019 14:29:54 +0900 From: Byungchul Park To: Joel Fernandes Cc: "Paul E. McKenney" , Byungchul Park , LKML , Rao Shoaib , kernel-team@android.com, kernel-team , Davidlohr Bueso , Josh Triplett , Lai Jiangshan , Mathieu Desnoyers , rcu , Steven Rostedt Subject: Re: [PATCH RFC v1 1/2] rcu/tree: Add basic support for kfree_rcu batching Message-ID: <20190813052954.GA18373@X58A-UD3R> References: <20190807175215.GE28441@linux.ibm.com> <20190808095232.GA30401@X58A-UD3R> <20190808125607.GB261256@google.com> <20190808180916.GP28441@linux.ibm.com> <20190811083626.GA9486@X58A-UD3R> <20190811084950.GB9486@X58A-UD3R> <20190811234939.GC28441@linux.ibm.com> <20190812101052.GA10478@X58A-UD3R> <20190812131234.GC27552@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190812131234.GC27552@google.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Mon, Aug 12, 2019 at 09:12:34AM -0400, Joel Fernandes wrote: > On Mon, Aug 12, 2019 at 07:10:52PM +0900, Byungchul Park wrote: > > On Sun, Aug 11, 2019 at 04:49:39PM -0700, Paul E. McKenney wrote: > > > Maybe. Note well that I said "potential issue". When I checked a few > > > years ago, none of the uses of rcu_barrier() cared about kfree_rcu(). > > > They cared instead about call_rcu() callbacks that accessed code or data > > > that was going to disappear soon, for example, due to module unload or > > > filesystem unmount. > > > > > > So it -might- be that rcu_barrier() can stay as it is, but with changes > > > as needed to documentation. > > Right, we should update the docs. Byungchul, do you mind sending a patch that > documents the rcu_barrier() behavior? Are you trying to give me the chance? I feel thankful. It doens't matter to try it at the moment though, I can't follow-up until September. I'd better do that in Septamber or give it up this time. Thanks, Byungchul > > > It also -might- be, maybe now or maybe some time in the future, that > > > there will need to be a kfree_rcu_barrier() or some such. But if so, > > > let's not create it until it is needed. For one thing, it is reasonably > > > likely that something other than a kfree_rcu_barrier() would really > > > be what was needed. After all, the main point would be to make sure > > > that the old memory really was freed before allocating new memory. > > > > Now I fully understand what you meant thanks to you. Thank you for > > explaining it in detail. > > > > > But if the system had ample memory, why wait? In that case you don't > > > really need to wait for all the old memory to be freed, but rather for > > > sufficient memory to be available for allocation. > > > > Agree. Totally make sense. > > Agreed, all makes sense. > > thanks, > > - Joel > > [snip]