From: Eric Sandeen Subject: Where all does preallocated/extra space hide? Date: Tue, 29 Sep 2009 11:47:19 -0500 Message-ID: <4AC23A17.5020100@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 ([209.132.183.28]:18148 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752562AbZI2QrR (ORCPT ); Tue, 29 Sep 2009 12:47:17 -0400 Received: from int-mx05.intmail.prod.int.phx2.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.18]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id n8TGlLVH018729 for ; Tue, 29 Sep 2009 12:47:21 -0400 Received: from neon.msp.redhat.com (neon.msp.redhat.com [10.15.80.10]) by int-mx05.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id n8TGlKR1020256 for ; Tue, 29 Sep 2009 12:47:20 -0400 Sender: linux-ext4-owner@vger.kernel.org List-ID: I was running some of the xfstests enospc tests on ext4, and they were failing; in one case, manymanymany small files are made to fill up a 100M filesystem. ext4 stops quite early with -ENOSPC, but after a bit, (or after a "sync") we get 40MB free again. So 40% of the fs space is hidden somewhere in preallocation... I tried calling out to discard group prealloc but that's only a few blocks. I'll go trace through the sync paths to see what all gets released, but if anyone knows offhand where the rest of that space is hiding, please give me a shout. :) Thanks, -Eric