From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2683CC33CB3 for ; Tue, 14 Jan 2020 20:31:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E605624655 for ; Tue, 14 Jan 2020 20:31:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="aGNveF/y" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728808AbgANUbu (ORCPT ); Tue, 14 Jan 2020 15:31:50 -0500 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:38134 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727102AbgANUbu (ORCPT ); Tue, 14 Jan 2020 15:31:50 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579033908; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=wtpq5coZ2n/ZQ8jUD3c2zBl1PMy/gRfERqCXjCgcqe0=; b=aGNveF/y13pQdlpCrRHJjfk9+pVVd/SUw6ttc5hrkTGS5M8AQRVlR0Wm9wiay5zThIP3Hm sLzYtrKp8VyouXQLl7b4F0i1CaInHDOAX77rLNv12H8L7peA4vuxyQzi8ZM72D3I4/WbuP vZn01Pbf6O+PiLDpAfIOMg+n2Ifbem4= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-54-8W0FTxhgPbSbgnwHyRaNiQ-1; Tue, 14 Jan 2020 15:31:45 -0500 X-MC-Unique: 8W0FTxhgPbSbgnwHyRaNiQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id BA35EDB62; Tue, 14 Jan 2020 20:31:43 +0000 (UTC) Received: from horse.redhat.com (unknown [10.18.25.35]) by smtp.corp.redhat.com (Postfix) with ESMTP id D992760BE0; Tue, 14 Jan 2020 20:31:38 +0000 (UTC) Received: by horse.redhat.com (Postfix, from userid 10451) id 6B78F220A24; Tue, 14 Jan 2020 15:31:38 -0500 (EST) Date: Tue, 14 Jan 2020 15:31:38 -0500 From: Vivek Goyal To: Dan Williams Cc: Jan Kara , "Darrick J. Wong" , Christoph Hellwig , Dave Chinner , Miklos Szeredi , linux-nvdimm , Linux Kernel Mailing List , "Dr. David Alan Gilbert" , virtio-fs@redhat.com, Stefan Hajnoczi , linux-fsdevel Subject: Re: [PATCH 01/19] dax: remove block device dependencies Message-ID: <20200114203138.GA3145@redhat.com> References: <20200107125159.GA15745@infradead.org> <20200107170731.GA472641@magnolia> <20200107180101.GC15920@redhat.com> <20200107183307.GD15920@redhat.com> <20200109112447.GG27035@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Jan 09, 2020 at 12:03:01PM -0800, Dan Williams wrote: > On Thu, Jan 9, 2020 at 3:27 AM Jan Kara wrote: > > > > On Tue 07-01-20 10:49:55, Dan Williams wrote: > > > On Tue, Jan 7, 2020 at 10:33 AM Vivek Goyal wrote: > > > > W.r.t partitioning, bdev_dax_pgoff() seems to be the pain point where > > > > dax code refers back to block device to figure out partition offset in > > > > dax device. If we create a dax object corresponding to "struct block_device" > > > > and store sector offset in that, then we could pass that object to dax > > > > code and not worry about referring back to bdev. I have written some > > > > proof of concept code and called that object "dax_handle". I can post > > > > that code if there is interest. > > > > > > I don't think it's worth it in the end especially considering > > > filesystems are looking to operate on /dev/dax devices directly and > > > remove block entanglements entirely. > > > > > > > IMHO, it feels useful to be able to partition and use a dax capable > > > > block device in same way as non-dax block device. It will be really > > > > odd to think that if filesystem is on /dev/pmem0p1, then dax can't > > > > be enabled but if filesystem is on /dev/mapper/pmem0p1, then dax > > > > will work. > > > > > > That can already happen today. If you do not properly align the > > > partition then dax operations will be disabled. This proposal just > > > extends that existing failure domain to make all partitions fail to > > > support dax. > > > > Well, I have some sympathy with the sysadmin that has /dev/pmem0 device, > > decides to create partitions on it for whatever (possibly misguided) > > reason and then ponders why the hell DAX is not working? And PAGE_SIZE > > partition alignment is so obvious and widespread that I don't count it as a > > realistic error case sysadmins would be pondering about currently. > > > > So I'd find two options reasonably consistent: > > 1) Keep status quo where partitions are created and support DAX. > > 2) Stop partition creation altogether, if anyones wants to split pmem > > device further, he can use dm-linear for that (i.e., kpartx). > > > > But I'm not sure if the ship hasn't already sailed for option 2) to be > > feasible without angry users and Linus reverting the change. > > Christoph? I feel myself leaning more and more to the "keep pmem > partitions" camp. > > I don't see "drop partition support" effort ending well given the long > standing "ext4 fails to mount when dax is not available" precedent. > > I think the next least bad option is to have a dax_get_by_host() > variant that passes an offset and length pair rather than requiring a > later bdev_dax_pgoff() to recall the offset. This also prevents > needing to add another dax-device object representation. I am wondering what's the conclusion on this. I want to this to make progress in some direction so that I can make progress on virtiofs DAX support. Thanks Vivek