From: Eric Sandeen Subject: Re: delalloc is crippling fs_mark performance Date: Mon, 21 Jul 2008 11:22:39 -0500 Message-ID: <4884B7CF.7060800@redhat.com> References: <4880C0B2.9040706@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit To: ext4 development Return-path: Received: from mx1.redhat.com ([66.187.233.31]:59142 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751329AbYGUQWl (ORCPT ); Mon, 21 Jul 2008 12:22:41 -0400 Received: from int-mx1.corp.redhat.com (int-mx1.corp.redhat.com [172.16.52.254]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id m6LGMfYm010502 for ; Mon, 21 Jul 2008 12:22:41 -0400 Received: from pobox-2.corp.redhat.com (pobox-2.corp.redhat.com [10.11.255.15]) by int-mx1.corp.redhat.com (8.13.1/8.13.1) with ESMTP id m6LGMeX4006870 for ; Mon, 21 Jul 2008 12:22:40 -0400 Received: from Liberator.local (sebastian-int.corp.redhat.com [172.16.52.221]) by pobox-2.corp.redhat.com (8.13.1/8.13.1) with ESMTP id m6LGMdML018416 for ; Mon, 21 Jul 2008 12:22:40 -0400 In-Reply-To: <4880C0B2.9040706@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: Eric Sandeen wrote: > running fs_mark like this: > > fs_mark -d /mnt/test -D 256 -n 100000 -t 4 -s 20480 -F -S 0 > > (256 subdirs, 100000 files/iteration, 4 threads, 20k files, no sync) > > on a 1T fs, with and without delalloc (mount option), is pretty interesting: > > http://people.redhat.com/esandeen/ext4/fs_mark.png I've updated this graph with another run where the group_prealloc tuneable was set to a perfect multiple of the allocation size, or 500 blocks. This way the leftover 2-block preallocations don't wind up causing the list to grow with unuseable tiny leftover preallocations. After tuning this way, it does clearly seem to be the problem here. -Eric