From: Ted Ts'o Subject: Re: [PATCH] libext2fs: reserve exclude bitmap fields in group descriptor Date: Thu, 15 Sep 2011 17:57:59 -0400 Message-ID: <20110915215759.GG28181@thunk.org> References: <20110915131606.GG15782@thunk.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Amir Goldstein , "Darrick J. Wong" , Sunil Mushran , Andi Kleen , Mingming Cao , Joel Becker , linux-ext4@vger.kernel.org, Coly Li , Yongqiang Yang To: Andreas Dilger Return-path: Received: from li9-11.members.linode.com ([67.18.176.11]:41928 "EHLO test.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935187Ab1IOV6I (ORCPT ); Thu, 15 Sep 2011 17:58:08 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-ext4-owner@vger.kernel.org List-ID: On Thu, Sep 15, 2011 at 01:08:34PM -0600, Andreas Dilger wrote: > In that light, why not continue to use an inode to map the exclude bitmap > blocks, where the bitmap offset is (group * blocksize), instead of > explicitly listing all of the blocks in the group descriptor? This is > how the buddy bitmap works in memory only, but it could be done for the > exclude bitmap on disk. I seem to recall the use of an inode to map the exclude bitmap added a huge amount of complexity to the snapshot patches. Amir, am I remembering this correctly? - Ted