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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 29658C433E0 for ; Wed, 10 Mar 2021 13:55:48 +0000 (UTC) Received: from ml01.01.org (ml01.01.org [198.145.21.10]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A7C3E64F53 for ; Wed, 10 Mar 2021 13:55:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A7C3E64F53 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-nvdimm-bounces@lists.01.org Received: from ml01.vlan13.01.org (localhost [IPv6:::1]) by ml01.01.org (Postfix) with ESMTP id 8113D100EB343; Wed, 10 Mar 2021 05:55:47 -0800 (PST) Received-SPF: None (mailfrom) identity=mailfrom; client-ip=2001:8b0:10b:1236::1; helo=casper.infradead.org; envelope-from=willy@infradead.org; receiver= Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)) (No client certificate requested) by ml01.01.org (Postfix) with ESMTPS id D2A83100EB335 for ; Wed, 10 Mar 2021 05:55:41 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=ASkeCYNO3dhrSyJuXDJUBfebpEQzrlHM2DpTFAkPLVI=; b=Tt7ayNXNWXK2bTVKrYTcEgnkh+ f1XcrJPHapkQa44CIKSbezQvxwWp57snh9ZQwPdTMAk8AB48/hoKyAYsV3ZU4LGI3DP+I6nECBWbe mY8h829FSnSMNv/PCAsrzVymOeG/qWx13tFKzswafFltkt9XHyX7vptRhmgxV+4sHHs8TT+u96GSL 4nlKgrcNvpOFZWyOF3okP7Uk5+XNkqMtBb7NgFccqDeLTOWWgoQL+VFa7b1Ix9secQvnL/Gs/rzb7 Aq26qRzbQFKc31DbCj6H7qdLZAgtko2Pd9+6RYYvXLu4N3eSeb9hz4Wf+6HZD9JmGcZZiCUZ26U0N zLJxPIow==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1lJzJD-003a9C-NN; Wed, 10 Mar 2021 13:55:32 +0000 Date: Wed, 10 Mar 2021 13:55:31 +0000 From: Matthew Wilcox To: Neal Gompa Subject: Re: [PATCH v2 00/10] fsdax,xfs: Add reflink&dedupe support for fsdax Message-ID: <20210310135531.GP3479805@casper.infradead.org> References: <20210226002030.653855-1-ruansy.fnst@fujitsu.com> <20210310130227.GN3479805@casper.infradead.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: Message-ID-Hash: J7FMDJBCSX5RQM7BNRZUKZPA6YNWRUSG X-Message-ID-Hash: J7FMDJBCSX5RQM7BNRZUKZPA6YNWRUSG X-MailFrom: willy@infradead.org X-Mailman-Rule-Hits: nonmember-moderation X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation CC: Shiyang Ruan , linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-nvdimm@lists.01.org, linux-fsdevel , darrick.wong@oracle.com, jack@suse.cz, viro@zeniv.linux.org.uk, Btrfs BTRFS , ocfs2-devel@oss.oracle.com, david@fromorbit.com, hch@lst.de, rgoldwyn@suse.de X-Mailman-Version: 3.1.1 Precedence: list List-Id: "Linux-nvdimm developer list." Archived-At: List-Archive: List-Help: List-Post: List-Subscribe: List-Unsubscribe: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Wed, Mar 10, 2021 at 08:36:06AM -0500, Neal Gompa wrote: > On Wed, Mar 10, 2021 at 8:02 AM Matthew Wilcox wrote: > > > > On Wed, Mar 10, 2021 at 07:30:41AM -0500, Neal Gompa wrote: > > > Forgive my ignorance, but is there a reason why this isn't wired up to > > > Btrfs at the same time? It seems weird to me that adding a feature > > > > btrfs doesn't support DAX. only ext2, ext4, XFS and FUSE have DAX support. > > > > If you think about it, btrfs and DAX are diametrically opposite things. > > DAX is about giving raw access to the hardware. btrfs is about offering > > extra value (RAID, checksums, ...), none of which can be done if the > > filesystem isn't in the read/write path. > > > > That's why there's no DAX support in btrfs. If you want DAX, you have > > to give up all the features you like in btrfs. So you may as well use > > a different filesystem. > > So does that mean that DAX is incompatible with those filesystems when > layered on DM (e.g. through LVM)? Yes. It might be possible to work through RAID-0 or read-only through RAID-1, but I'm not sure anybody's bothered to do that work. > Also, based on what you're saying, that means that DAX'd resources > would not be able to use reflinks on XFS, right? That'd put it in > similar territory as swap files on Btrfs, I would think. You can use DAX with reflinks because the CPU can do read-only mmaps. On a write fault, we break the reflink, copy the data and put in a writable PTE. _______________________________________________ Linux-nvdimm mailing list -- linux-nvdimm@lists.01.org To unsubscribe send an email to linux-nvdimm-leave@lists.01.org