Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751423AbZL1DQe (ORCPT ); Sun, 27 Dec 2009 22:16:34 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751056AbZL1DQe (ORCPT ); Sun, 27 Dec 2009 22:16:34 -0500 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:59499 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750823AbZL1DQd (ORCPT ); Sun, 27 Dec 2009 22:16:33 -0500 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 Date: Mon, 28 Dec 2009 12:13:18 +0900 From: KAMEZAWA Hiroyuki To: balbir@linux.vnet.ibm.com Cc: Peter Zijlstra , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "minchan.kim@gmail.com" , cl@linux-foundation.org Subject: Re: [RFC PATCH] asynchronous page fault. Message-Id: <20091228121318.780fd104.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20091228025839.GF3601@balbir.in.ibm.com> References: <20091225105140.263180e8.kamezawa.hiroyu@jp.fujitsu.com> <1261912796.15854.25.camel@laptop> <20091228005746.GE3601@balbir.in.ibm.com> <20091228100514.ec6f9949.kamezawa.hiroyu@jp.fujitsu.com> <20091228025839.GF3601@balbir.in.ibm.com> Organization: FUJITSU Co. LTD. X-Mailer: Sylpheed 2.7.1 (GTK+ 2.10.14; i686-pc-mingw32) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1596 Lines: 45 On Mon, 28 Dec 2009 08:28:39 +0530 Balbir Singh wrote: > * KAMEZAWA Hiroyuki [2009-12-28 10:05:14]: > > - rb-tree's rb_left and rb_right don't points to memory other than > > rb-tree. (or NULL) And vmas are not freed/reused while rcu_read_lock(). > > Then, we don't dive into unknown memory. > > - Then, we can skip rcu_assign_pointer(). > > > > We can, but the data being on read-side is going to be out-of-date > more than without the use of rcu_assign_pointer(). Do we need variants > like to rcu_rb_next() to avoid overheads for everyone? > I myself can't know how often out-of-date data can be seen (because I use x86). But, I feel that we don't see broken tree so often. Because... - Single-threaded apps never see broken tree. - Even if rb-tree modification frequently happens, tree rotation is not very often and sub-trees tend to be stable as a chunk. Hmm, adding barrier like this ? static inline void __vma_unlink(struct mm_struct *mm, struct vm_area_struct *vma, struct vm_area_struct *prev) { prev->vm_next = vma->vm_next; rb_erase(&vma->vm_rb, &mm->mm_rb); if (mm->mmap_cache == vma) mm->mmap_cache = prev; smp_wb(); <==============================================(new) } Regards, -Kame -- 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/