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=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 24CA0C33CA2 for ; Thu, 9 Jan 2020 20:03:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ED2242072A for ; Thu, 9 Jan 2020 20:03:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=intel-com.20150623.gappssmtp.com header.i=@intel-com.20150623.gappssmtp.com header.b="tavN+wgv" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728243AbgAIUDN (ORCPT ); Thu, 9 Jan 2020 15:03:13 -0500 Received: from mail-oi1-f195.google.com ([209.85.167.195]:44079 "EHLO mail-oi1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725763AbgAIUDM (ORCPT ); Thu, 9 Jan 2020 15:03:12 -0500 Received: by mail-oi1-f195.google.com with SMTP id d62so6974900oia.11 for ; Thu, 09 Jan 2020 12:03:12 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=aEPP3QvZTscWYv3Miihx0fBYyJilXweNv6Guj9B9KD8=; b=tavN+wgvdGNcOGcjKHqkAn5BjiXAReV94+OSH9Ri1PEiPT4LHVwg6b1hXbJyjtNOio yt+3CISS4TMH86U9kKgU8YPArehaT0FusWvpSVefSqnA63GewXNc+iMnr6ZN89GHlxNa I9xtBLZtZiieLaHNV/YWCS5IF2kdx6cBLmi6/YRneC/5UTcL8YKTe0qVGWfehSZnrWv9 YsnAn85tdplqslZaJiAyOUvkKc3WlQ6ZG+UvCzJ00JIQxKAKUKINJoyIUTQOONSw3QOj 1W72+PiwSitSGIes31XNdQt0P0T6DKzDvCP6YPxL/5GB664MG6OsTA5BfZF4LBGWHzr7 Jvig== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=aEPP3QvZTscWYv3Miihx0fBYyJilXweNv6Guj9B9KD8=; b=hG2Py1k8v1gJPwyGkOlH0BOqNAou3gUZfkBLRkYr/FZEuMMoMISoTHuadigOd3+Jkk TxPyjRMXvOkteIWKsqYj0bcUe81MjKswJeDOYmWYsUmav7+o3Q9TDn3b7kzk5FTiFqjH XhcugbZXp967uoYaOM3zIyxi3y/37aYnuExtDdJJv1UHVWxfVXGLAMpnRjveaWmWA8T/ ZPQXuklsNIzi9MoZX0cX/+Njqr7NuuI6TqoDgLeAfoCtVSUkDaktm22pg+G+GwwPv4XV dZqUG19+cq4q8i7iBjZ6nRaycZzoMOIS+9Us9VBQeRSPrQDdax85Ip6BRen6XnYND1oc FziA== X-Gm-Message-State: APjAAAVOWrWHsYVkEuWvsyYsxc87RXl7NcRky3s+nkLErws1f5ifRpXX ff99P7As6YmS058EM15AlphpvzYnAMNihU/uGBX1ag== X-Google-Smtp-Source: APXvYqy8zIIpMCxwYPaK1lH7NGY047llhJ6X2TGv4+wlxidYTW8JIfkG1ylN1wkgzWx+t/HR+ipJvvJ3iI320Zd/2yQ= X-Received: by 2002:a05:6808:a83:: with SMTP id q3mr4809955oij.0.1578600191907; Thu, 09 Jan 2020 12:03:11 -0800 (PST) MIME-Version: 1.0 References: <20191216181014.GA30106@redhat.com> <20200107125159.GA15745@infradead.org> <20200107170731.GA472641@magnolia> <20200107180101.GC15920@redhat.com> <20200107183307.GD15920@redhat.com> <20200109112447.GG27035@quack2.suse.cz> In-Reply-To: <20200109112447.GG27035@quack2.suse.cz> From: Dan Williams Date: Thu, 9 Jan 2020 12:03:01 -0800 Message-ID: Subject: Re: [PATCH 01/19] dax: remove block device dependencies To: Jan Kara Cc: Vivek Goyal , "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 Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.