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From: Jan Kara <jack@suse.cz>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: Jan Kara <jack@suse.cz>,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	Christoph Hellwig <hch@infradead.org>,
	Dave Chinner <david@fromorbit.com>,
	Miklos Szeredi <miklos@szeredi.hu>,
	linux-nvdimm <linux-nvdimm@lists.01.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	virtio-fs@redhat.com, Stefan Hajnoczi <stefanha@redhat.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH 01/19] dax: remove block device dependencies
Date: Wed, 15 Jan 2020 10:03:06 +0100
Message-ID: <20200115090306.GA31450@quack2.suse.cz> (raw)
In-Reply-To: <20200114212805.GB3145@redhat.com>

On Tue 14-01-20 16:28:05, Vivek Goyal wrote:
> On Tue, Jan 14, 2020 at 12:39:00PM -0800, Dan Williams wrote:
> > I think we should at least try to delete the partition support and see
> > if anyone screams. Have a module option to revert the behavior so
> > people are not stuck waiting for the revert to land, but if it stays
> > quiet then we're in a better place with that support pushed out of the
> > dax core.
> 
> Hi Dan,
> 
> So basically keep partition support code just that disable it by default
> and it is enabled by some knob say kernel command line option/module
> option.
> 
> At what point of time will we remove that code completely. I mean what
> if people scream after two kernel releases, after we have removed the
> code.
> 
> Also, from distribution's perspective, we might not hear from our
> customers for a very long time (till we backport that code in to
> existing releases or release this new code in next major release). From
> that view point I will not like to break existing user visible behavior.
> 
> How bad it is to keep partition support around. To me it feels reasonaly
> simple where we just have to store offset into dax device into another
> dax object and pass that object around (instead of dax_device). If that's
> the case, I am not sure why to even venture into a direction where some
> user's setup might be broken.
> 
> Also from an application perspective, /dev/pmem is a block device, so it
> should behave like a block device, (including kernel partition table support).
> From that view, dax looks like just an additional feature of that device
> which can be enabled by passing option "-o dax".

Well, not all block devices are partitionable. For example cdroms are
standard block devices but partitioning does not run for them. Similarly
device mapper devices are block devices but not partitioned. So there is
some precedens in not doing partitioning for some types of block devices.

For the rest I agree that kernels where pmem devices are partitionable have
shipped in enterprise distros and are going to be supported (and used) for
5-10 years before users decide to move on to something newer - at which
point we'll only find out whether someone used the feature or not. So
deprecation is going to be somewhat interesting. On the other hand clever
udev rule that detects partition table on pmem device and uses kpartx to
partition these devices (like what happens e.g. for dm-multipath devices)
could possibly be used as a replacement for kernel support so there's a way
out of this...

So I don't care too deeply about what the decision is going to be.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR
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  parent reply index

Thread overview: 76+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-21 17:57 [PATCH v3 00/19][RFC] virtio-fs: Enable DAX support Vivek Goyal
2019-08-21 17:57 ` [PATCH 01/19] dax: remove block device dependencies Vivek Goyal
2019-08-26 11:51   ` Christoph Hellwig
2019-08-27 16:38     ` Vivek Goyal
2019-08-28  6:58       ` Christoph Hellwig
2019-08-28 17:58         ` Vivek Goyal
2019-08-28 22:53           ` Dave Chinner
2019-08-29  0:04             ` Dan Williams
2019-08-29  9:32               ` Christoph Hellwig
2019-12-16 18:10               ` Vivek Goyal
2020-01-07 12:51                 ` Christoph Hellwig
2020-01-07 14:22                   ` Dan Williams
2020-01-07 17:07                     ` Darrick J. Wong
2020-01-07 17:29                       ` Dan Williams
2020-01-07 18:01                         ` Vivek Goyal
2020-01-07 18:07                           ` Dan Williams
2020-01-07 18:33                             ` Vivek Goyal
2020-01-07 18:49                               ` Dan Williams
2020-01-07 19:02                                 ` Darrick J. Wong
2020-01-07 19:46                                   ` Dan Williams
2020-01-07 23:38                                     ` Dan Williams
2020-01-09 11:24                                 ` Jan Kara
2020-01-09 20:03                                   ` Dan Williams
2020-01-10 12:36                                     ` Christoph Hellwig
2020-01-14 20:31                                     ` Vivek Goyal
2020-01-14 20:39                                       ` Dan Williams
2020-01-14 21:28                                         ` Vivek Goyal
2020-01-14 22:23                                           ` Dan Williams
2020-01-15 19:56                                             ` Vivek Goyal
2020-01-15 20:17                                               ` Dan Williams
2020-01-15 21:08                                                 ` Jeff Moyer
2020-01-16 18:09                                                   ` Dan Williams
2020-01-16 18:39                                                     ` Vivek Goyal
2020-01-16 19:09                                                       ` Dan Williams
2020-01-16 19:23                                                         ` Vivek Goyal
2020-01-15  9:03                                           ` Jan Kara [this message]
2019-08-21 17:57 ` [PATCH 02/19] dax: Pass dax_dev to dax_writeback_mapping_range() Vivek Goyal
2019-08-26 11:53   ` Christoph Hellwig
2019-08-26 20:33     ` Vivek Goyal
2019-08-26 20:58       ` Vivek Goyal
2019-08-26 21:33         ` Dan Williams
2019-08-28  6:58         ` Christoph Hellwig
2020-01-03 14:12         ` Vivek Goyal
2020-01-03 18:12           ` Dan Williams
2020-01-03 18:18             ` Dan Williams
2020-01-03 18:33               ` Vivek Goyal
2020-01-03 19:30                 ` Dan Williams
2020-01-03 18:43               ` Vivek Goyal
2019-08-27 13:45       ` Jan Kara
2019-08-21 17:57 ` [PATCH 03/19] virtio: Add get_shm_region method Vivek Goyal
2019-08-21 17:57 ` [PATCH 04/19] virtio: Implement get_shm_region for PCI transport Vivek Goyal
2019-08-26  1:43   ` [Virtio-fs] " piaojun
2019-08-26 13:06     ` Vivek Goyal
2019-08-27  9:41       ` piaojun
2019-08-27  8:34   ` Cornelia Huck
2019-08-27  8:46     ` Cornelia Huck
2019-08-27 11:53     ` Vivek Goyal
2019-08-21 17:57 ` [PATCH 05/19] virtio: Implement get_shm_region for MMIO transport Vivek Goyal
2019-08-27  8:39   ` Cornelia Huck
2019-08-27 11:54     ` Vivek Goyal
2019-08-21 17:57 ` [PATCH 06/19] fuse, dax: add fuse_conn->dax_dev field Vivek Goyal
2019-08-21 17:57 ` [PATCH 07/19] virtio_fs, dax: Set up virtio_fs dax_device Vivek Goyal
2019-08-21 17:57 ` [PATCH 08/19] fuse: Keep a list of free dax memory ranges Vivek Goyal
2019-08-21 17:57 ` [PATCH 09/19] fuse: implement FUSE_INIT map_alignment field Vivek Goyal
2019-08-21 17:57 ` [PATCH 10/19] fuse: Introduce setupmapping/removemapping commands Vivek Goyal
2019-08-21 17:57 ` [PATCH 11/19] fuse, dax: Implement dax read/write operations Vivek Goyal
2019-08-21 19:49   ` Liu Bo
2019-08-22 12:59     ` Vivek Goyal
2019-08-21 17:57 ` [PATCH 12/19] fuse, dax: add DAX mmap support Vivek Goyal
2019-08-21 17:57 ` [PATCH 13/19] fuse: Define dax address space operations Vivek Goyal
2019-08-21 17:57 ` [PATCH 14/19] fuse, dax: Take ->i_mmap_sem lock during dax page fault Vivek Goyal
2019-08-21 17:57 ` [PATCH 15/19] fuse: Maintain a list of busy elements Vivek Goyal
2019-08-21 17:57 ` [PATCH 16/19] dax: Create a range version of dax_layout_busy_page() Vivek Goyal
2019-08-21 17:57 ` [PATCH 17/19] fuse: Add logic to free up a memory range Vivek Goyal
2019-08-21 17:57 ` [PATCH 18/19] fuse: Release file in process context Vivek Goyal
2019-08-21 17:57 ` [PATCH 19/19] fuse: Take inode lock for dax inode truncation Vivek Goyal

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