From: Theodore Tso Subject: Re: [PATCH] fix bogus BUG_ONs in in mballoc code Date: Thu, 12 Mar 2009 20:38:55 -0400 Message-ID: <20090313003855.GM17104@mit.edu> References: <49B93E44.8070109@ph.tum.de> <49B958A1.6060805@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Thiemo Nagel , Ext4 Developers List To: Eric Sandeen Return-path: Received: from THUNK.ORG ([69.25.196.29]:42821 "EHLO thunker.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750752AbZCMAjE (ORCPT ); Thu, 12 Mar 2009 20:39:04 -0400 Content-Disposition: inline In-Reply-To: <49B958A1.6060805@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Thu, Mar 12, 2009 at 01:46:57PM -0500, Eric Sandeen wrote: > Thiemo Nagel reported that: > > # dd if=/dev/zero of=image.ext4 bs=1M count=2 > # mkfs.ext4 -v -F -b 1024 -m 0 -g 512 -G 4 -I 128 -N 1 \ > -O large_file,dir_index,flex_bg,extent,sparse_super image.ext4 > # mount -o loop image.ext4 mnt/ > # dd if=/dev/zero of=mnt/file > > oopsed, with a BUG_ON in ext4_mb_normalize_request because > size == EXT4_BLOCKS_PER_GROUP > > It appears to me (esp. after talking to Andreas) that the BUG_ON > is bogus; a request of exactly EXT4_BLOCKS_PER_GROUP should > be allowed, though larger sizes do indicate a problem. Clearly we should make this change to avoid the BUG_ON; but stupid question, why shouldn't we allow sizes larger than EXT4_BLOCKS_PER_GROUP? Especially with flex_bg, it is possible for an allocation size > EXT4_BLOCKS_PER_GROUP to be satisifed, especially if the filesystem isn't that full yet, and it might even make sense to request a larger allocation for video files that are getting preallocated, for example.... - Ted