From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933157Ab2IUWtR (ORCPT ); Fri, 21 Sep 2012 18:49:17 -0400 Received: from ipmail05.adl6.internode.on.net ([150.101.137.143]:51933 "EHLO ipmail05.adl6.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758330Ab2IUWtQ (ORCPT ); Fri, 21 Sep 2012 18:49:16 -0400 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AqUNACruXFB5LFPK/2dsb2JhbABFhSK3eAIBgQOBCYIgAQEFOhwjEAgDDgouFCUDIROIBLk0FIsIcYE4gx1gA5VjkCOCeQ Date: Sat, 22 Sep 2012 08:49:12 +1000 From: Dave Chinner To: Guo Chao Cc: viro@zeniv.linux.org.uk, dchinner@redhat.com, hch@infradead.org, jack@suse.cz, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC v4 Patch 0/4] fs/inode.c: optimization for inode lock usage Message-ID: <20120921224912.GA20960@dastard> References: <1348219866-1799-1-git-send-email-yan@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1348219866-1799-1-git-send-email-yan@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 21, 2012 at 05:31:02PM +0800, Guo Chao wrote: > This patchset optimizes several places which take the per inode spin lock. > They have not been fully tested yet, thus they are marked as RFC. Inodes are RCU freed. The i_lock spinlock on the i_state field forms part of the memory barrier that allows the RCU read side to correctly detect a freed inode during a RCU protected cache lookup (hash list traversal for the VFS, or a radix tree traversal for XFS). The i_lock usage around the hahs list operations ensures the hash list operations are atomic with state changes so that such changes are correctly detected during RCU-protected traversals... IOWs, removing the i_lock from around the i_state transitions and inode hash insert/remove/traversal operations will cause races in the RCU lookups and result in incorrectly using freed inodes instead of failing the lookup and creating a new one. So I don't think this is a good idea at all... Cheers, Dave. -- Dave Chinner david@fromorbit.com