Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933718AbWK0ViD (ORCPT ); Mon, 27 Nov 2006 16:38:03 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S933744AbWK0ViD (ORCPT ); Mon, 27 Nov 2006 16:38:03 -0500 Received: from smtp.osdl.org ([65.172.181.25]:32713 "EHLO smtp.osdl.org") by vger.kernel.org with ESMTP id S933718AbWK0ViB (ORCPT ); Mon, 27 Nov 2006 16:38:01 -0500 Date: Mon, 27 Nov 2006 13:37:48 -0800 From: Andrew Morton To: Eric Dumazet Cc: linux-kernel , Daniel McNeil Subject: Re: [PATCH] fs : reorder some 'struct inode' fields to speedup i_size manipulations Message-Id: <20061127133748.4ebcd6b3.akpm@osdl.org> In-Reply-To: <200611231157.30056.dada1@cosmosbay.com> References: <20061120151700.4a4f9407@frecb000686> <20061123092805.1408b0c6@frecb000686> <20061123004053.76114a75.akpm@osdl.org> <200611231157.30056.dada1@cosmosbay.com> X-Mailer: Sylpheed version 2.2.7 (GTK+ 2.8.6; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1378 Lines: 36 On Thu, 23 Nov 2006 11:57:29 +0100 Eric Dumazet wrote: > On 32bits SMP platforms, 64bits i_size is protected by a seqcount > (i_size_seqcount). > > When i_size is read or written, i_size_seqcount is read/written as well, so it > make sense to group these two fields together in the same cache line. > > Before this patch, accessing i_size needed 3 cache lines (2 for i_size, one > for i_size_seqcount). After, only one cache line is needed/ (dirtied on a > i_size change). I didn't understand that paragraph at all, really, so I took it out. At present an i_size change will dirty one, two or three cachelines, most likely one or two. After your patch an i_size change will dirty one or two cachelines, most likely one. yes? > This patch moves i_size_seqcount next to i_size, and also moves i_version to > let offsetof(struct inode, i_size) being 0x40 instead of 0x3c (for 32bits > platforms). > > For 64 bits platforms, i_size_seqcount doesnt exist, and the move of a 'long > i_version' should not introduce a new hole because of padding. > > Signed-off-by: Eric Dumazet - 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/