Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754095AbZLBJmq (ORCPT ); Wed, 2 Dec 2009 04:42:46 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753503AbZLBJmp (ORCPT ); Wed, 2 Dec 2009 04:42:45 -0500 Received: from cantor2.suse.de ([195.135.220.15]:51283 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751605AbZLBJmp (ORCPT ); Wed, 2 Dec 2009 04:42:45 -0500 Date: Wed, 2 Dec 2009 10:42:50 +0100 From: Nick Piggin To: Matthew Wilcox Cc: Liuweni , strongzgy , xgr178 , Liu Hui , viro , akpm , jack , linux-fsdevel , linux-kernel Subject: Re: Re: [PATCH 1/3]fs/inode: iunique() Optimize Performance Message-ID: <20091202094250.GB31517@wotan.suse.de> References: <20091201120337.GV9482@parisc-linux.org> <200912012115341872867@gmail.com> <20091201140041.GW9482@parisc-linux.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20091201140041.GW9482@parisc-linux.org> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1418 Lines: 30 On Tue, Dec 01, 2009 at 07:00:41AM -0700, Matthew Wilcox wrote: > On Tue, Dec 01, 2009 at 09:21:32PM +0800, Liuweni wrote: > > * BUGS: > > * With a large number of inodes live on the file system this function > > * currently becomes quite slow. > > > > I don't believe that comment is correct. In any case, your optimisation > wouldn't make a lick of difference to the speed; it's a single comparison > in a loop which also calculates a hash, makes a function call, and walks > the length of a hash chain. > > The old adage about debugging code, not comments applies here. Don't take > somebody else's word for it that there's a performance problem here. > Devise a test to demonstrate the performance problem. Otherwise, how > will you know if you solved it? Yeah I agree. And then we can debate the usefulness of that workload. iunique is not used in many filesystems. If performance really becomes a problem, then you most likely need another data structure. A per-sb ida or something would come to mind, but I expect any filesystem that cares already has a decent inode number allocation so iunique is just a simple hack for those that don't care so much. -- 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/