Received-SPF: pass (google.com: domain of linux-ext4-owner@vger.kernel.org designates 23.128.96.38 as permitted sender) client-ip=23.128.96.38;
MIME-Version: 1.0
References: <ZHFEfngPyUOqlthr@dread.disaster.area> <CAJ0trDZJQwvAzngZLBJ1hB0XkQ1HRHQOdNQNTw9nK-U5i-0bLA@mail.gmail.com>
 <ZHYB/6l5Wi+xwkbQ@redhat.com> <CAJ0trDaUOevfiEpXasOESrLHTCcr=oz28ywJU+s+YOiuh7iWow@mail.gmail.com>
 <ZHYWAGmKhwwmTjW/@redhat.com> <CAG9=OMMnDfN++-bJP3jLmUD6O=Q_ApV5Dr392_5GqsPAi_dDkg@mail.gmail.com>
 <ZHqOvq3ORETQB31m@dread.disaster.area> <ZHti/MLnX5xGw9b7@redhat.com>
 <CAG9=OMNv80fOyVixEY01XESnOFzYyfj9j8etHMq_Ap52z4UWNQ@mail.gmail.com>
 <ZIESXNF5anyvJEjm@redhat.com> <ZIOMLfMjugGf4C2T@redhat.com>
In-Reply-To: <ZIOMLfMjugGf4C2T@redhat.com>
From:   Sarthak Kukreti <sarthakkukreti@chromium.org>
Date:   Fri, 6 Oct 2023 18:30:22 -0700
Message-ID: <CAG9=OMPqGmX75ZmK=Fc7DNE7dcxS+t-UPkjtCVDF+dPN+xkrNg@mail.gmail.com>
Subject: Re: [PATCH v7 0/5] Introduce provisioning primitives
To:     Mike Snitzer <snitzer@redhat.com>
Cc:     Jens Axboe <axboe@kernel.dk>,
        Christoph Hellwig <hch@infradead.org>,
        Joe Thornber <thornber@redhat.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        "Darrick J. Wong" <djwong@kernel.org>,
        Jason Wang <jasowang@redhat.com>,
        Bart Van Assche <bvanassche@google.com>,
        Dave Chinner <david@fromorbit.com>,
        linux-kernel@vger.kernel.org, Joe Thornber <ejt@redhat.com>,
        linux-block@vger.kernel.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, Brian Foster <bfoster@redhat.com>,
        Alasdair Kergon <agk@redhat.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Fri, Jun 9, 2023 at 1:31=E2=80=AFPM Mike Snitzer <snitzer@redhat.com> wr=
ote:
>
> On Wed, Jun 07 2023 at  7:27P -0400,
> Mike Snitzer <snitzer@kernel.org> wrote:
>
> > On Mon, Jun 05 2023 at  5:14P -0400,
> > Sarthak Kukreti <sarthakkukreti@chromium.org> wrote:
> >
> > > On Sat, Jun 3, 2023 at 8:57=E2=80=AFAM Mike Snitzer <snitzer@kernel.o=
rg> wrote:
> > > >
> > > > We all just need to focus on your proposal and Joe's dm-thin
> > > > reservation design...
> > > >
> > > > [Sarthak: FYI, this implies that it doesn't really make sense to ad=
d
> > > > dm-thinp support before Joe's design is implemented.  Otherwise we'=
ll
> > > > have 2 different responses to REQ_OP_PROVISION.  The one that is
> > > > captured in your patchset isn't adequate to properly handle ensurin=
g
> > > > upper layer (like XFS) can depend on the space being available acro=
ss
> > > > snapshot boundaries.]
> > > >
> > > Ack. Would it be premature for the rest of the series to go through
> > > (REQ_OP_PROVISION + support for loop and non-dm-thinp device-mapper
> > > targets)? I'd like to start using this as a reference to suggest
> > > additions to the virtio-spec for virtio-blk support and start looking
> > > at what an ext4 implementation would look like.
> >
> > Please drop the dm-thin.c and dm-snap.c changes.  dm-snap.c would need
> > more work to provide the type of guarantee XFS requires across
> > snapshot boundaries. I'm inclined to _not_ add dm-snap.c support
> > because it is best to just use dm-thin.
> >
> > And FYI even your dm-thin patch will be the starting point for the
> > dm-thin support (we'll keep attribution to you for all the code in a
> > separate patch).
> >
> > > Fair points, I certainly don't want to derail this conversation; I'd
> > > be happy to see this work merged sooner rather than later.
> >
> > Once those dm target changes are dropped I think the rest of the
> > series is fine to go upstream now.  Feel free to post a v8.
>
> FYI, I've made my latest code available in this
> 'dm-6.5-provision-support' branch (based on 'dm-6.5'):
> https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.gi=
t/log/?h=3Ddm-6.5-provision-support
>
> It's what v8 should be plus the 2 dm-thin patches (that I don't think
> should go upstream yet, but are theoretically useful for Dave and
> Joe).
>
Cheers! Apologies for dropping the ball on this, I just sent out v8
with the dm-thin patches dropped.


- Sarthak

> The "dm thin: complete interface for REQ_OP_PROVISION support" commit
> establishes all the dm-thin interface I think is needed.  The FIXME in
> process_provision_bio() (and the patch header) cautions against upper
> layers like XFS using this dm-thinp support quite yet.
>
> Otherwise we'll have the issue where dm-thinp's REQ_OP_PROVISION
> support initially doesn't provide the guarantee that XFS needs across
> snapshots (which is: snapshots inherit all previous REQ_OP_PROVISION).
>
> Mike
>