linux-kernel - Re: [PATCH v6 21/26] fs/dax: Properly refcount fs dax pages

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Message-ID: <67a59f0f7832c_2d1e294fa@dwillia2-xfh.jf.intel.com.notmuch>
Date: Thu, 6 Feb 2025 21:50:07 -0800
From: Dan Williams <dan.j.williams@...el.com>
To: Alistair Popple <apopple@...dia.com>, Dan Williams
	<dan.j.williams@...el.com>
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Subject: Re: [PATCH v6 21/26] fs/dax: Properly refcount fs dax pages

Alistair Popple wrote:
> On Mon, Jan 13, 2025 at 07:35:07PM -0800, Dan Williams wrote:
> > Alistair Popple wrote:
> 
> [...]
> 
> > ...and here is that aformentioned patch:
> 
> This patch is different from what you originally posted here:
> https://yhbt.net/lore/linux-s390/172721874675.497781.3277495908107141898.stgit@dwillia2-xfh.jf.intel.com/
> 
> > -- 8< --
> > Subject: dcssblk: Mark DAX broken, remove FS_DAX_LIMITED support
> > 
> > From: Dan Williams <dan.j.williams@...el.com>
> > 
> > The dcssblk driver has long needed special case supoprt to enable
> > limited dax operation, so called CONFIG_FS_DAX_LIMITED. This mode
> > works around the incomplete support for ZONE_DEVICE on s390 by forgoing
> > the ability of dax-mapped pages to support GUP.
> > 
> > Now, pending cleanups to fsdax that fix its reference counting [1] depend on
> > the ability of all dax drivers to supply ZONE_DEVICE pages.
> > 
> > To allow that work to move forward, dax support needs to be paused for
> > dcssblk until ZONE_DEVICE support arrives. That work has been known for
> > a few years [2], and the removal of "pte_devmap" requirements [3] makes the
> > conversion easier.
> > 
> > For now, place the support behind CONFIG_BROKEN, and remove PFN_SPECIAL
> > (dcssblk was the only user).
> 
> Specifically it no longer removes PFN_SPECIAL. Was this intentional? Or should I
> really have picked up the original patch from the mailing list?

I think this patch that only removes the dccsblk usage of PFN_SPECIAL is
sufficient. Leave the rest to the pfn_t cleanup.