Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751918AbZL1IkG (ORCPT ); Mon, 28 Dec 2009 03:40:06 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751330AbZL1Ij7 (ORCPT ); Mon, 28 Dec 2009 03:39:59 -0500 Received: from bombadil.infradead.org ([18.85.46.34]:37952 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751643AbZL1Ij6 (ORCPT ); Mon, 28 Dec 2009 03:39:58 -0500 Subject: Re: [RFC PATCH] asynchronous page fault. From: Peter Zijlstra To: balbir@linux.vnet.ibm.com Cc: KAMEZAWA Hiroyuki , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "minchan.kim@gmail.com" , cl@linux-foundation.org In-Reply-To: <20091228005746.GE3601@balbir.in.ibm.com> References: <20091225105140.263180e8.kamezawa.hiroyu@jp.fujitsu.com> <1261912796.15854.25.camel@laptop> <20091228005746.GE3601@balbir.in.ibm.com> Content-Type: text/plain; charset="UTF-8" Date: Mon, 28 Dec 2009 09:32:53 +0100 Message-ID: <1261989173.7135.5.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1225 Lines: 29 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. You cannot make the assignment paths atomic (without locks) that's the whole problem. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/