Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752296AbbFVGai (ORCPT ); Mon, 22 Jun 2015 02:30:38 -0400 Received: from verein.lst.de ([213.95.11.211]:40802 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932606AbbFVGab (ORCPT ); Mon, 22 Jun 2015 02:30:31 -0400 Date: Mon, 22 Jun 2015 08:30:28 +0200 From: Christoph Hellwig To: Dan Williams Cc: 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: <20150622063028.GA30434@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> 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: 1872 Lines: 37 On Sun, Jun 21, 2015 at 08:11:25AM -0700, Dan Williams wrote: > The labels only allow allocation of persistent media between pmem and > blk. For a given dimm you may access in either mode and the label > records the decision. We can have a btt on either the pmem or > blk-mode disk type, or partition thereof. Sounds like the spec should allow a btt type as well insteaad of requiring the OS to work around it, as that seems to be one of the few useful things to do with a run-time label. Either way, partitions are trivial things and we could add them to the nvdimm layer. > Yes, it's this hybrid thing that mostly fits into the existing block > device model save for two new block_device_operations > ->direct_access() and ->rw_bytes(). We then use property of a > block_device that allows it to be claimed for exclusive ownership by a > filesystem or another block_device to layer storage semantics on top > be it files+directories, raid, caching, or atomic sectors. NVDIMM > devices don't present the same complexity as MTD devices. The only > complexity they present is byte-address-ability, not erase-block-size, > wear-leveling, etc... I didn't say they show the same complexities, but the same layering. > 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in Please read the FAQ at http://www.tux.org/lkml/