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

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Date:   Wed, 15 Sep 2021 13:48:48 -0500
From:   Eric Sandeen <sandeen@...deen.net>
To:     Dan Williams <dan.j.williams@...el.com>,
        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 9/15/21 1:35 PM, Dan Williams wrote:
> 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?

Thanks for that update, Dan. I'm wondering, even if we have renewed
hopes and dreams for dax+reflink, would it make sense to go ahead and
declare dax without reflink non-experimental, and tag dax+reflink as
a new "EXPERIMENTAL feature if and when it lands?

-Eric