Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933481AbbFWTa4 (ORCPT ); Tue, 23 Jun 2015 15:30:56 -0400 Received: from mga11.intel.com ([192.55.52.93]:21109 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932810AbbFWTar (ORCPT ); Tue, 23 Jun 2015 15:30:47 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.13,667,1427785200"; d="scan'208";a="593428928" Date: Tue, 23 Jun 2015 15:30:43 -0400 From: Matthew Wilcox To: Christoph Hellwig Cc: Dan Williams , Jens Axboe , "linux-nvdimm@lists.01.org" , "linux-kernel@vger.kernel.org" , Linux ACPI , linux-fsdevel , Ingo Molnar Subject: Re: [PATCH 14/15] libnvdimm: support read-only btt backing devices Message-ID: <20150623193043.GE1971@linux.intel.com> References: <20150617235209.12943.24419.stgit@dwillia2-desk3.amr.corp.intel.com> <20150617235602.12943.24958.stgit@dwillia2-desk3.amr.corp.intel.com> <20150621101346.GF5915@lst.de> <20150621135406.GA9572@lst.de> <20150622063028.GA30434@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150622063028.GA30434@lst.de> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1108 Lines: 20 On Mon, Jun 22, 2015 at 08:30:28AM +0200, Christoph Hellwig wrote: > > Good to hear that we don't need BTT for XFS v5, can we make the > > guarantee for all filesystems that may want to support DAX? I still > > think stacking is a natural fit for this problem. > > I can't make any guarantees, especially not without verification. But > if correctly implemented any filesystems that does out of place metadata > writes (and that includes a traditional log) and uses checksum to ensure > the integrity of these updates it should be fine. You'd still have > the issue of sector atomicy of file I/O though. Is ext4 one of the filesystems that copes with torn updates to the log? I see there's a checksum in the tail of at least some blocks, but I'd like someone who understands ext4 to reassure me that it also doesn't need the ability to put its log on a BTT. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/