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Wed, 10 Mar 2021 05:56:12 -0800 Received: from pps.filterd (aserp3020.oracle.com [127.0.0.1]) by aserp3020.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 12ADpXqu007173 for ; Wed, 10 Mar 2021 13:56:12 GMT Received: from userp2040.oracle.com (userp2040.oracle.com [156.151.31.90]) by aserp3020.oracle.com with ESMTP id 374kn0yrw9-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK) for ; Wed, 10 Mar 2021 13:56:12 +0000 Received: from pps.filterd (userp2040.oracle.com [127.0.0.1]) by userp2040.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 12ADsF2E048358 for ; Wed, 10 Mar 2021 13:56:11 GMT Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by userp2040.oracle.com with ESMTP id 3740bwnf7u-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO) for ; Wed, 10 Mar 2021 13:56:09 +0000 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 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: X-PDR: PASS X-Source-IP: 90.155.50.34 X-ServerName: casper.infradead.org X-Proofpoint-SPF-Result: None X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=9918 signatures=668683 X-Proofpoint-Spam-Details: rule=tap_notspam policy=tap score=0 malwarescore=0 phishscore=0 mlxscore=0 priorityscore=305 impostorscore=0 clxscore=297 bulkscore=0 lowpriorityscore=0 suspectscore=0 spamscore=0 mlxlogscore=812 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2103100068 X-Spam: Clean Cc: jack@suse.cz, linux-nvdimm@lists.01.org, darrick.wong@oracle.com, david@fromorbit.com, linux-kernel@vger.kernel.org, Shiyang Ruan , linux-xfs@vger.kernel.org, ocfs2-devel@oss.oracle.com, viro@zeniv.linux.org.uk, linux-fsdevel , dan.j.williams@intel.com, Btrfs BTRFS Subject: Re: [Ocfs2-devel] [PATCH v2 00/10] fsdax, xfs: Add reflink&dedupe support for fsdax X-BeenThere: ocfs2-devel@oss.oracle.com X-Mailman-Version: 2.1.9 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: ocfs2-devel-bounces@oss.oracle.com Errors-To: ocfs2-devel-bounces@oss.oracle.com X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=9918 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 phishscore=0 adultscore=0 malwarescore=0 bulkscore=0 suspectscore=0 mlxscore=0 mlxlogscore=999 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2103100068 X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=9918 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxscore=0 lowpriorityscore=0 impostorscore=0 mlxlogscore=999 malwarescore=0 suspectscore=0 adultscore=0 phishscore=0 spamscore=0 priorityscore=1501 bulkscore=0 clxscore=1034 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2103100068 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. _______________________________________________ Ocfs2-devel mailing list Ocfs2-devel@oss.oracle.com https://oss.oracle.com/mailman/listinfo/ocfs2-devel