From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755352AbcI2MCE (ORCPT ); Thu, 29 Sep 2016 08:02:04 -0400 Received: from szxga01-in.huawei.com ([58.251.152.64]:31687 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752818AbcI2MB4 (ORCPT ); Thu, 29 Sep 2016 08:01:56 -0400 Subject: Re: [PATCH 1/2] f2fs: use crc and cp version to determine roll-forward recovery To: Jaegeuk Kim , , , References: <20160920025504.72524-1-jaegeuk@kernel.org> From: Chao Yu Message-ID: <5b3d81fe-902e-5512-4766-30ad62390373@huawei.com> Date: Thu, 29 Sep 2016 20:01:32 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.0 MIME-Version: 1.0 In-Reply-To: <20160920025504.72524-1-jaegeuk@kernel.org> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.134.22.195] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2016/9/20 10:55, Jaegeuk Kim wrote: > Previously, we used cp_version only to detect recoverable dnodes. > In order to avoid same garbage cp_version, we needed to truncate the next > dnode during checkpoint, resulting in additional discard or data write. > If we can distinguish this by using crc in addition to cp_version, we can > remove this overhead. > > There is backward compatibility concern where it changes node_footer layout. > But, it only affects the direct nodes written after the last checkpoint. > We simply expect that user would change kernel versions back and forth after > stable checkpoint. Seems with new released v4.8 f2fs, old image with recoverable data could be mounted successfully, but meanwhile all fsynced data which needs to be recovered will be lost w/o any hints? Could we release a new version mkfs paired with new kernel module, so we can tag image as a new layout one, then new kernel module can recognize the image layout and adjust version suited comparing method with old or new image? Thanks,