From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [RCU PATCH 06/14] net: sched: fw use RCU Date: Thu, 13 Mar 2014 14:15:09 -0700 Message-ID: <20140313211509.GP21124@linux.vnet.ibm.com> References: <20140310170008.3011.73599.stgit@nitbit.x32> <20140310170546.3011.82918.stgit@nitbit.x32> <1394473279.3607.46.camel@edumazet-glaptop2.roam.corp.google.com> <53208E3F.5090401@gmail.com> <1394643673.21721.48.camel@edumazet-glaptop2.roam.corp.google.com> <20140313202245.GK21124@linux.vnet.ibm.com> <1394744203.21721.53.camel@edumazet-glaptop2.roam.corp.google.com> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: John Fastabend , xiyou.wangcong@gmail.com, jhs@mojatatu.com, netdev@vger.kernel.org, davem@davemloft.net To: Eric Dumazet Return-path: Received: from e33.co.us.ibm.com ([32.97.110.151]:37507 "EHLO e33.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752254AbaCMVPO (ORCPT ); Thu, 13 Mar 2014 17:15:14 -0400 Received: from /spool/local by e33.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 13 Mar 2014 15:15:14 -0600 Received: from b03cxnp07029.gho.boulder.ibm.com (b03cxnp07029.gho.boulder.ibm.com [9.17.130.16]) by d03dlp02.boulder.ibm.com (Postfix) with ESMTP id 9E8323E40026 for ; Thu, 13 Mar 2014 15:15:10 -0600 (MDT) Received: from d03av06.boulder.ibm.com (d03av06.boulder.ibm.com [9.17.195.245]) by b03cxnp07029.gho.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id s2DJCMYS11993358 for ; Thu, 13 Mar 2014 20:12:22 +0100 Received: from d03av06.boulder.ibm.com (loopback [127.0.0.1]) by d03av06.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id s2DLIhdC027039 for ; Thu, 13 Mar 2014 15:18:43 -0600 Content-Disposition: inline In-Reply-To: <1394744203.21721.53.camel@edumazet-glaptop2.roam.corp.google.com> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, Mar 13, 2014 at 01:56:43PM -0700, Eric Dumazet wrote: > On Thu, 2014-03-13 at 13:22 -0700, Paul E. McKenney wrote: > > > Hmmm... You know, the offset that kfree uses is a byte offset. I see > > no reason why any of the rcu_head structures should be misaligned. If > > HTSIZE is too big by only a factor of four or smaller, would the following > > (untested) patch to RCU be appropriate? > > > > Thanx, Paul > > > > ------------------------------------------------------------------------ > > > > rcu: Increase kfree_rcu() offset range > > > > The kfree_rcu() function operates by placing an offset into the rcu_head > > structure in place of the function pointer that is normally there. > > This offset cannot exceed 4095, on the theory that no Linux kernel will > > ever have executable code in page zero. However, the rcu_head structure > > contains a pair of function pointers, and should never be misaligned. > > This commit therefore divides the offset by the size of a pointer when > > being placed into the rcu_head structure, and multiplies it by this > > same constant when pulling it out. > > > > Signed-off-by: Paul E. McKenney > > SGTM, thanks Paul. > > Reviewed-by: Eric Dumazet Very good, thank you! John, could you please give it a try with that rcu_head structure moved to the end and let me know how it goes? Thanx, Paul