From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with ESMTP id 8F96760021B for ; Tue, 29 Dec 2009 04:54:54 -0500 (EST) Received: from d23relay04.au.ibm.com (d23relay04.au.ibm.com [202.81.31.246]) by e23smtp09.au.ibm.com (8.14.3/8.13.1) with ESMTP id nBT9sl70017171 for ; Tue, 29 Dec 2009 20:54:47 +1100 Received: from d23av04.au.ibm.com (d23av04.au.ibm.com [9.190.235.139]) by d23relay04.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id nBT9oa1H1761338 for ; Tue, 29 Dec 2009 20:50:37 +1100 Received: from d23av04.au.ibm.com (loopback [127.0.0.1]) by d23av04.au.ibm.com (8.14.3/8.13.1/NCO v10.0 AVout) with ESMTP id nBT9skk3032241 for ; Tue, 29 Dec 2009 20:54:47 +1100 Date: Tue, 29 Dec 2009 15:24:41 +0530 From: Balbir Singh Subject: Re: [RFC PATCH] asynchronous page fault. Message-ID: <20091229095441.GP3601@balbir.in.ibm.com> Reply-To: balbir@linux.vnet.ibm.com References: <20091225105140.263180e8.kamezawa.hiroyu@jp.fujitsu.com> <1261912796.15854.25.camel@laptop> <20091228005746.GE3601@balbir.in.ibm.com> <1261989173.7135.5.camel@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <1261989173.7135.5.camel@laptop> Sender: owner-linux-mm@kvack.org To: Peter Zijlstra Cc: KAMEZAWA Hiroyuki , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "minchan.kim@gmail.com" , cl@linux-foundation.org List-ID: * Peter Zijlstra [2009-12-28 09:32:53]: > On Mon, 2009-12-28 at 06:27 +0530, Balbir Singh wrote: > > * Peter Zijlstra [2009-12-27 12:19:56]: > > > > > Your changelog states as much. > > > > > > "Even if RB-tree rotation occurs while we walk tree for look-up, we just > > > miss vma without oops." > > > > > > However, since this is the case, do we still need the > > > rcu_assign_pointer() conversion your patch does? All I can see it do is > > > slow down all RB-tree users, without any gain. > > > > Don't we need the rcu_assign_pointer() on the read side primarily to > > make sure the pointer is still valid and assignments (writes) are not > > re-ordered? Are you suggesting that the pointer assignment paths be > > completely atomic? > > rcu_assign_pointer() is the write side, but if you need a barrier, you > can make do with a single smp_wmb() after doing the rb-tree op. There is > no need to add multiple in the tree-ops themselves. > Yes, that makes sense. > You cannot make the assignment paths atomic (without locks) that's the > whole problem. > True, but pre-emption can be nasty in some cases. But I am no expert in the atomicity of operations like assignments across architectures. I assume all word, long assignments are. -- Balbir -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org