Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753157AbbFVPlF (ORCPT ); Mon, 22 Jun 2015 11:41:05 -0400 Received: from verein.lst.de ([213.95.11.211]:42686 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751987AbbFVPk7 (ORCPT ); Mon, 22 Jun 2015 11:40:59 -0400 Date: Mon, 22 Jun 2015 17:40:56 +0200 From: Christoph Hellwig To: Dan Williams Cc: Christoph Hellwig , Jens Axboe , "linux-nvdimm@lists.01.org" , Boaz Harrosh , "Kani, Toshimitsu" , "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: <20150622154056.GB7952@lst.de> 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> <20150622072844.GA31263@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1154 Lines: 22 On Mon, Jun 22, 2015 at 12:39:34AM -0700, Dan Williams wrote: > Now I'm confused, you *don't* want the raw device to be hidden *and* > you want to kill the stacking? Something got crossed. The current > implementation hides nothing, you get to see the entire stacked > composition. I'd much prefer to avoid hiding anything. You see it, but you can't actually use it. The proper way to expose it would be to the devices visible in the low-level bus sysfs enumeration logic but only one ULD attach to it. > The sinister aspect of sector tearing is that most applications don't > know they have this dependency. At least today's disk's rarely ever > tear sectors and if they do you almost certainly get a CRC error on > access. NVDIMMs will always tear and always silently. I think not > merging BTT at all to see what happens is simply wrong. So now you leave your users with a choice between a rock and a hard place, that is using BTT to introduce non-significant overhead and not supporting DAX or just use it as-is. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in Please read the FAQ at http://www.tux.org/lkml/