Date:   Wed, 30 Nov 2022 15:08:39 -0800
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Shiyang Ruan <ruansy.fnst@...itsu.com>,
        linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        nvdimm@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
        david@...morbit.com
Subject: Re: [PATCH 0/2] fsdax,xfs: fix warning messages

On Wed, Nov 30, 2022 at 01:48:59PM -0800, Dan Williams wrote:
> Andrew Morton wrote:
> > On Tue, 29 Nov 2022 19:59:14 -0800 Dan Williams <dan.j.williams@...el.com> wrote:
> > 
> > > [ add Andrew ]
> > > 
> > > Shiyang Ruan wrote:
> > > > Many testcases failed in dax+reflink mode with warning message in dmesg.
> > > > This also effects dax+noreflink mode if we run the test after a
> > > > dax+reflink test.  So, the most urgent thing is solving the warning
> > > > messages.
> > > > 
> > > > Patch 1 fixes some mistakes and adds handling of CoW cases not
> > > > previously considered (srcmap is HOLE or UNWRITTEN).
> > > > Patch 2 adds the implementation of unshare for fsdax.
> > > > 
> > > > With these fixes, most warning messages in dax_associate_entry() are
> > > > gone.  But honestly, generic/388 will randomly failed with the warning.
> > > > The case shutdown the xfs when fsstress is running, and do it for many
> > > > times.  I think the reason is that dax pages in use are not able to be
> > > > invalidated in time when fs is shutdown.  The next time dax page to be
> > > > associated, it still remains the mapping value set last time.  I'll keep
> > > > on solving it.
> > > > 
> > > > The warning message in dax_writeback_one() can also be fixed because of
> > > > the dax unshare.
> > > 
> > > Thank you for digging in on this, I had been pinned down on CXL tasks
> > > and worried that we would need to mark FS_DAX broken for a cycle, so
> > > this is timely.
> > > 
> > > My only concern is that these patches look to have significant collisions with
> > > the fsdax page reference counting reworks pending in linux-next. Although,
> > > those are still sitting in mm-unstable:
> > > 
> > > http://lore.kernel.org/r/20221108162059.2ee440d5244657c4f16bdca0@linux-foundation.org
> > 
> > As far as I know, Dan's "Fix the DAX-gup mistake" series is somewhat
> > stuck.  Jan pointed out:
> > 
> > https://lore.kernel.org/all/20221109113849.p7pwob533ijgrytu@quack3/T/#u
> > 
> > or have Jason's issues since been addressed?
> 
> No, they have not. I do think the current series is a step forward, but
> given the urgency remains low for the time being (CXL hotplug use case
> further out, no known collisions with ongoing folio work, and no
> MEMORY_DEVICE_PRIVATE users looking to build any conversions on top for
> 6.2) I am ok to circle back for 6.3 for that follow on work to be
> integrated.
> 
> > > My preference would be to move ahead with both in which case I can help
> > > rebase these fixes on top. In that scenario everything would go through
> > > Andrew.
> > > 
> > > However, if we are getting too late in the cycle for that path I think
> > > these dax-fixes take precedence, and one more cycle to let the page
> > > reference count reworks sit is ok.
> > 
> > That sounds a decent approach.  So we go with this series ("fsdax,xfs:
> > fix warning messages") and aim at 6.3-rc1 with "Fix the DAX-gup
> > mistake"?
> > 
> 
> Yeah, that's the path of least hassle.

Sounds good.  I still want to see patch 1 of this series broken up into
smaller pieces though.  Once the series goes through review, do you want
me to push the fixes to Linus, seeing as xfs is the only user of this
functionality?

--D

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