From: Dave Chinner <david@fromorbit.com>
To: Sarthak Kukreti <sarthakkukreti@chromium.org>
Cc: Mike Snitzer <snitzer@kernel.org>, Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, Joe Thornber <thornber@redhat.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
Jason Wang <jasowang@redhat.com>,
"Darrick J. Wong" <djwong@kernel.org>,
Brian Foster <bfoster@redhat.com>,
Bart Van Assche <bvanassche@google.com>,
linux-kernel@vger.kernel.org,
Christoph Hellwig <hch@infradead.org>,
dm-devel@redhat.com, Andreas Dilger <adilger.kernel@dilger.ca>,
Stefan Hajnoczi <stefanha@redhat.com>,
linux-fsdevel@vger.kernel.org, Theodore Ts'o <tytso@mit.edu>,
linux-ext4@vger.kernel.org, Joe Thornber <ejt@redhat.com>,
Alasdair Kergon <agk@redhat.com>
Subject: Re: [PATCH v7 0/5] Introduce provisioning primitives
Date: Wed, 7 Jun 2023 12:15:12 +1000 [thread overview]
Message-ID: <ZH/oMK7BoBo8a3Hu@dread.disaster.area> (raw)
In-Reply-To: <CAG9=OMNv80fOyVixEY01XESnOFzYyfj9j8etHMq_Ap52z4UWNQ@mail.gmail.com>
On Mon, Jun 05, 2023 at 02:14:44PM -0700, Sarthak Kukreti wrote:
> On Sat, Jun 3, 2023 at 8:57 AM Mike Snitzer <snitzer@kernel.org> wrote:
> > On Fri, Jun 02 2023 at 8:52P -0400,
> > Dave Chinner <david@fromorbit.com> wrote:
> > > On Fri, Jun 02, 2023 at 11:44:27AM -0700, Sarthak Kukreti wrote:
> > > > > The only way to distinquish the caller (between on-behalf of user data
> > > > > vs XFS metadata) would be REQ_META?
> > > > >
> > > > > So should dm-thinp have a REQ_META-based distinction? Or just treat
> > > > > all REQ_OP_PROVISION the same?
> > > > >
> > > > I'm in favor of a REQ_META-based distinction.
> > >
> > > Why? What *requirement* is driving the need for this distinction?
> >
> > Think I answered that above, XFS delalloc accounting parity on thinp.
> >
> I actually had a few different use-cases in mind (apart from the user
> data provisioning 'fear' that you pointed out): in essence, there are
> cases where userspace would benefit from having more control over how
> much space a snapshot takes:
>
> 1) In the original RFC patchset [1], I alluded to this being a
> mechanism for pre-allocating space for preserving space for thin
> logical volumes. The use-case I'd like to explore is delta updatable
> read-only filesystems similar to systemd system extensions [2]: In
> essence:
> a) Preserve space for a 'base' thin logical volume that will contain a
> read-only filesystem on over-the-air installation: for filesystems
> like squashfs and erofs, pretty much the entire image is a compressed
> file that I'd like to reserve space for before installation.
> b) Before update, create a thin snapshot and preserve enough space to
> ensure that a delta update will succeed (eg. block level diff of the
> base image). Then, the update is guaranteed to have disk space to
> succeed (similar to the A-B update guarantees on ChromeOS). On
> success, we merge the snapshot and reserve an update snapshot for the
> next possible update. On failure, we drop the snapshot.
Sounds very similar to the functionality blksnap is supposed to
provide....
https://lore.kernel.org/linux-fsdevel/20230404140835.25166-1-sergei.shtepa@veeam.com/
> 2) The other idea I wanted to explore was rollback protection for
> stateful filesystem features: in essence, if an update from kernel 4.x
> to 5.y failed very quickly (due to unrelated reasons) and we enabled
> some stateful filesystem features that are only supported on 5.y, we'd
> be able to rollback to 4.x if we used short-lived snapshots (in the
> ChromiumOS world, the lifetime of these snapshots would be < 10s per
> boot).
Not sure that blksnap has a "roll origin back to read-only snapshot"
feature yet, but that's what you'd need for this. i.e. on success,
drop the snapshot. On failure, "roll origin back to snapshot and
reboot".
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2023-06-07 2:15 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-18 22:33 [PATCH v7 0/5] Introduce provisioning primitives Sarthak Kukreti
2023-05-18 22:33 ` [PATCH v7 1/5] block: Don't invalidate pagecache for invalid falloc modes Sarthak Kukreti
2023-05-19 4:09 ` Christoph Hellwig
2023-05-19 15:17 ` Darrick J. Wong
2023-05-18 22:33 ` [PATCH v7 2/5] block: Introduce provisioning primitives Sarthak Kukreti
2023-05-19 4:18 ` Christoph Hellwig
2023-06-09 20:00 ` Mike Snitzer
2023-05-18 22:33 ` [PATCH v7 3/5] dm: Add block provisioning support Sarthak Kukreti
2023-05-18 22:33 ` [PATCH v7 4/5] dm-thin: Add REQ_OP_PROVISION support Sarthak Kukreti
2023-05-19 15:23 ` Mike Snitzer
2023-06-08 21:24 ` Mike Snitzer
2023-06-09 0:28 ` Mike Snitzer
2023-05-18 22:33 ` [PATCH v7 5/5] loop: Add support for provision requests Sarthak Kukreti
2023-05-22 16:37 ` [dm-devel] " Darrick J. Wong
2023-05-22 22:09 ` Sarthak Kukreti
2023-05-23 1:22 ` Darrick J. Wong
2023-10-07 1:29 ` Sarthak Kukreti
2023-05-19 4:09 ` [PATCH v7 0/5] Introduce provisioning primitives Christoph Hellwig
2023-05-19 14:41 ` Mike Snitzer
2023-05-19 23:07 ` Dave Chinner
2023-05-22 18:27 ` Mike Snitzer
2023-05-23 14:05 ` Brian Foster
2023-05-23 15:26 ` Mike Snitzer
2023-05-24 0:40 ` Dave Chinner
2023-05-24 20:02 ` Mike Snitzer
2023-05-25 11:39 ` Dave Chinner
2023-05-25 16:00 ` Mike Snitzer
2023-05-25 22:47 ` Sarthak Kukreti
2023-05-26 1:36 ` Dave Chinner
2023-05-26 2:35 ` Sarthak Kukreti
2023-05-26 15:56 ` Brian Foster
2023-05-25 16:19 ` Brian Foster
2023-05-26 9:37 ` Dave Chinner
2023-05-26 15:47 ` Brian Foster
[not found] ` <CAJ0trDbspRaDKzTzTjFdPHdB9n0Q9unfu1cEk8giTWoNu3jP8g@mail.gmail.com>
2023-05-26 23:45 ` Dave Chinner
[not found] ` <CAJ0trDZJQwvAzngZLBJ1hB0XkQ1HRHQOdNQNTw9nK-U5i-0bLA@mail.gmail.com>
2023-05-30 14:02 ` Mike Snitzer
[not found] ` <CAJ0trDaUOevfiEpXasOESrLHTCcr=oz28ywJU+s+YOiuh7iWow@mail.gmail.com>
2023-05-30 15:28 ` Mike Snitzer
2023-06-02 18:44 ` Sarthak Kukreti
2023-06-02 21:50 ` Mike Snitzer
2023-06-03 0:52 ` Dave Chinner
2023-06-03 15:57 ` Mike Snitzer
2023-06-05 21:14 ` Sarthak Kukreti
2023-06-07 2:15 ` Dave Chinner [this message]
2023-06-07 23:27 ` Mike Snitzer
2023-06-09 20:31 ` Mike Snitzer
2023-06-09 21:54 ` Dave Chinner
2023-10-07 1:30 ` Sarthak Kukreti
2023-06-07 2:01 ` Dave Chinner
2023-06-07 23:50 ` Mike Snitzer
2023-06-09 3:32 ` Dave Chinner
2023-06-08 2:03 ` Martin K. Petersen
2023-06-09 0:10 ` Dave Chinner
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