From: Sarthak Kukreti <sarthakkukreti@chromium.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Mike Snitzer <snitzer@kernel.org>, Joe Thornber <ejt@redhat.com>,
Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, "Theodore Ts'o" <tytso@mit.edu>,
Stefan Hajnoczi <stefanha@redhat.com>,
"Michael S. Tsirkin" <mst@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>,
linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org,
Jason Wang <jasowang@redhat.com>,
Alasdair Kergon <agk@redhat.com>
Subject: Re: [PATCH v7 0/5] Introduce provisioning primitives
Date: Thu, 25 May 2023 19:35:14 -0700 [thread overview]
Message-ID: <CAG9=OMPxHOzYcy8TQRnvNfNvPvvU=A1pceyL72JfyQwJSKNjQQ@mail.gmail.com> (raw)
In-Reply-To: <ZHANCbnHuhnwCrGz@dread.disaster.area>
On Thu, May 25, 2023 at 6:36 PM Dave Chinner <david@fromorbit.com> wrote:
>
> On Thu, May 25, 2023 at 03:47:21PM -0700, Sarthak Kukreti wrote:
> > On Thu, May 25, 2023 at 9:00 AM Mike Snitzer <snitzer@kernel.org> wrote:
> > > On Thu, May 25 2023 at 7:39P -0400,
> > > Dave Chinner <david@fromorbit.com> wrote:
> > > > On Wed, May 24, 2023 at 04:02:49PM -0400, Mike Snitzer wrote:
> > > > > On Tue, May 23 2023 at 8:40P -0400,
> > > > > Dave Chinner <david@fromorbit.com> wrote:
> > > > > > It's worth noting that XFS already has a coarse-grained
> > > > > > implementation of preferred regions for metadata storage. It will
> > > > > > currently not use those metadata-preferred regions for user data
> > > > > > unless all the remaining user data space is full. Hence I'm pretty
> > > > > > sure that a pre-provisioning enhancment like this can be done
> > > > > > entirely in-memory without requiring any new on-disk state to be
> > > > > > added.
> > > > > >
> > > > > > Sure, if we crash and remount, then we might chose a different LBA
> > > > > > region for pre-provisioning. But that's not really a huge deal as we
> > > > > > could also run an internal background post-mount fstrim operation to
> > > > > > remove any unused pre-provisioning that was left over from when the
> > > > > > system went down.
> > > > >
> > > > > This would be the FITRIM with extension you mention below? Which is a
> > > > > filesystem interface detail?
> > > >
> > > > No. We might reuse some of the internal infrastructure we use to
> > > > implement FITRIM, but that's about it. It's just something kinda
> > > > like FITRIM but with different constraints determined by the
> > > > filesystem rather than the user...
> > > >
> > > > As it is, I'm not sure we'd even need it - a preiodic userspace
> > > > FITRIM would acheive the same result, so leaked provisioned spaces
> > > > would get cleaned up eventually without the filesystem having to do
> > > > anything specific...
> > > >
> > > > > So dm-thinp would _not_ need to have new
> > > > > state that tracks "provisioned but unused" block?
> > > >
> > > > No idea - that's your domain. :)
> > > >
> > > > dm-snapshot, for certain, will need to track provisioned regions
> > > > because it has to guarantee that overwrites to provisioned space in
> > > > the origin device will always succeed. Hence it needs to know how
> > > > much space breaking sharing in provisioned regions after a snapshot
> > > > has been taken with be required...
> > >
> > > dm-thinp offers its own much more scalable snapshot support (doesn't
> > > use old dm-snapshot N-way copyout target).
> > >
> > > dm-snapshot isn't going to be modified to support this level of
> > > hardening (dm-snapshot is basically in "maintenance only" now).
>
> Ah, of course. Sorry for the confusion, I was kinda using
> dm-snapshot as shorthand for "dm-thinp + snapshots".
>
> > > But I understand your meaning: what you said is 100% applicable to
> > > dm-thinp's snapshot implementation and needs to be accounted for in
> > > thinp's metadata (inherent 'provisioned' flag).
>
> *nod*
>
> > A bit orthogonal: would dm-thinp need to differentiate between
> > user-triggered provision requests (eg. from fallocate()) vs
> > fs-triggered requests?
>
> Why? How is the guarantee the block device has to provide to
> provisioned areas different for user vs filesystem internal
> provisioned space?
>
After thinking this through, I stand corrected. I was primarily
concerned with how this would balloon thin snapshot sizes if users
potentially provision a large chunk of the filesystem but that's
putting the cart way before the horse.
Best
Sarthak
> > I would lean towards user provisioned areas not
> > getting dedup'd on snapshot creation,
>
> <twitch>
>
> Snapshotting is a clone operation, not a dedupe operation.
>
> Yes, the end result of both is that you have a block shared between
> multiple indexes that needs COW on the next overwrite, but the two
> operations that get to that point are very different...
>
> </pedantic mode disegaged>
>
> > but that would entail tracking
> > the state of the original request and possibly a provision request
> > flag (REQ_PROVISION_DEDUP_ON_SNAPSHOT) or an inverse flag
> > (REQ_PROVISION_NODEDUP). Possibly too convoluted...
>
> Let's not try to add everyone's favourite pony to this interface
> before we've even got it off the ground.
>
> It's the simple precision of the API, the lack of cross-layer
> communication requirements and the ability to implement and optimise
> the independent layers independently that makes this a very
> appealing solution.
>
> We need to start with getting the simple stuff working and prove the
> concept. Then once we can observe the behaviour of a working system
> we can start working on optimising individual layers for efficiency
> and performance....
>
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@fromorbit.com
next prev parent reply other threads:[~2023-05-26 2:35 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 [this message]
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
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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