linux-ext4 - Re: [PATCH 0/3 RFC] Remove DAX experimental warnings

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Date:   Wed, 15 Sep 2021 11:35:11 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Eric Sandeen <sandeen@...hat.com>
Cc:     linux-xfs <linux-xfs@...r.kernel.org>,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Shiyang Ruan <ruansy.fnst@...itsu.com>
Subject: Re: [PATCH 0/3 RFC] Remove DAX experimental warnings

On Wed, Sep 15, 2021 at 10:23 AM Eric Sandeen <sandeen@...hat.com> wrote:
>
> For six years now, when mounting xfs, ext4, or ext2 with dax, the drivers
> have logged "DAX enabled. Warning: EXPERIMENTAL, use at your own risk."
>
> IIRC, dchinner added this to the original XFS patchset, and Dan Williams
> followed suit for ext4 and ext2.
>
> After brief conversations with some ext4 and xfs developers and maintainers,
> it seems that it may be time to consider removing this warning.
>
> For XFS, we had been holding out for reflink+dax capability, but proposals
> which had seemed promising now appear to be indefinitely stalled, and
> I think we might want to consider that dax-without-reflink is no longer
> EXPERIMENTAL, while dax-with-reflink is simply an unimplemented future
> feature.

I do regret my gap in engagement since the last review as I got
distracted by CXL, but I've recently gotten my act together and picked
up the review again to help get Ruan's patches over the goal line [1].
I am currently awaiting Ruan's response to latest review feedback
(looks like a new posting this morning). During that review Christoph
identified some cleanups that would help Ruan's series, and those are
now merged upstream [2]. The last remaining stumbling block (further
block-device entanglements with dax-devices) I noted here [2]. The
proposal is to consider eliding device-mapper dax-reflink support for
now and proceed with just xfs-on-/dev/pmem until Mike, Jens, and
Christoph can chime in on the future of dax on block devices.

As far as I can see we have line of sight to land xfs-dax-reflink
support for v5.16, does anyone see that differently at this point?

[1]: https://lore.kernel.org/linux-xfs/CAPcyv4h0p+zD5tsT8HDUpNq_ZDCqo249KsmPLX-U8ia146r2Tg@mail.gmail.com/
[2]: https://lore.kernel.org/linux-xfs/CAPcyv4ic+LDagR8uF18tO3cCb6t=YTZNkAOK=vnsnERqY6Ze_g@mail.gmail.com/
[3]: https://lore.kernel.org/nvdimm/CAPcyv4hvzS1c01BweBkgDsjg=VGnaUUKi7b6j+1X=Rqzzm961Q@mail.gmail.com/