Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759630AbZKYTwx (ORCPT ); Wed, 25 Nov 2009 14:52:53 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759614AbZKYTww (ORCPT ); Wed, 25 Nov 2009 14:52:52 -0500 Received: from palinux.external.hp.com ([192.25.206.14]:39956 "EHLO mail.parisc-linux.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759608AbZKYTwv (ORCPT ); Wed, 25 Nov 2009 14:52:51 -0500 Date: Wed, 25 Nov 2009 12:52:57 -0700 From: Matthew Wilcox To: J?r?my Cochoy Cc: Liuweni , linux-kernel , strongzgy , xgr178 , Liu Hui , viro , akpm , jack , npiggin , linux-fsdevel Subject: Re: [PATCH 1/3]fs/inode: iunique() Optimize Performance Message-ID: <20091125195256.GL9482@parisc-linux.org> References: <200911252209432039291@gmail.com> <20091125141505.GH9482@parisc-linux.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2176 Lines: 48 On Wed, Nov 25, 2009 at 08:20:02PM +0100, J?r?my Cochoy wrote: > Hello, > > There is something strange in iunique : what will happend if all inode > between max_reserved+1 and (unsinged in)(0-1) ? Will it make an > infinite loop or an interruption can happen and make an inode become > free? Another process can free an inode while this loop is executing. > In that case, it will be better to stop search when counter overflow, no? If you have all four billion inodes allocated, you have significantly bigger problems than this loop. For a start, at 600 bytes per inode, I'd like to see your machine with 2.4TB of memory. Then there's the size of your inode hash, and the depth of the chains within it. > Will it not be better to use a field max_ino_used (in superblock, for > exemple) where we store the last inode allocated with iunique and make > a search only if max_ino_used become to (unsigned)(-1) ? > > But, if iunique is here to provide a solution in order to generate > unused inode in filesystem which have various inode number, it's > better to use a list of used ino, in a short hash table which use the > first 8 bits of the inode, always use the same function to create a > new inode and look at the head if we can add a new inode with bigger > ino and still in the range. (But i think filesystems developper prefer > to write ther own functions in order to do that, no?) > > Well, if we want to stop in case of full inode filesystem, we can put > the first condition in the head and add change return as : > return inode->i_ino > max_reserved ? res : 0; // 0 might "i can't find > an inode after max_reserved" Gloves. http://thedailywtf.com/Articles/The_Complicator_0x27_s_Gloves.aspx -- Matthew Wilcox Intel Open Source Technology Centre "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step." -- 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/