Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Fri, 7 Dec 2001 13:03:25 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 7 Dec 2001 13:03:15 -0500 Received: from stine.vestdata.no ([195.204.68.10]:28575 "EHLO stine.vestdata.no") by vger.kernel.org with ESMTP id ; Fri, 7 Dec 2001 13:03:08 -0500 Date: Fri, 7 Dec 2001 19:03:01 +0100 From: =?iso-8859-1?Q?Ragnar_Kj=F8rstad?= To: Daniel Phillips Cc: Hans Reiser , linux-kernel@vger.kernel.org, reiserfs-dev@namesys.com Subject: Re: [reiserfs-dev] Re: Ext2 directory index: ALS paper and benchmarks Message-ID: <20011207190301.C6640@vestdata.no> In-Reply-To:

<20011207174726.B6640@vestdata.no> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit User-Agent: Mutt/1.2.5i In-Reply-To: ; from phillips@bonn-fries.net on Fri, Dec 07, 2001 at 06:41:53PM +0100 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 07, 2001 at 06:41:53PM +0100, Daniel Phillips wrote: > I've observed disk cache effects with Ext2, the relevant relationship being > directory entry order vs inode order. Layout of the index itself doesn't > seem to matter much because of its small size, and 'popularity', which tends > to keep it in cache. Exactly. And if the files have data in them (all my tests were done with files with bodies) then there is a third data-type (the allocated blocks) whose order compared to the entry-order and the inode-order also matters. > With ReiserFS we see slowdown due to random access even with small > directories. I don't think this is a cache effect. I can't see why the benefit from read-ahead on the file-data should be affected by the directory-size? I forgot to mention another important effect of hash-ordering: If you mostly add new files to the directory it is far less work if you almost always can add the new entry at the end rather than insert it in the middle. Well, it depends on your implementation of course, but this effect is quite noticable on reiserfs. When untaring a big directory of maildir the performance difference between the tea hash and a special maildir hash was approxemately 20%. The choice of hash should not affect the performance on writing the data itself, so it has to be related to the cost of the insert operation. -- Ragnar Kj?rstad Big Storage - 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/