Alistair Popple wrote:

On Mon, Jan 13, 2025 at 07:35:07PM -0800, Dan Williams wrote:

quoted

Alistair Popple wrote:

[...]

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...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/

quoted

-- 8< --
Subject: dcssblk: Mark DAX broken, remove FS_DAX_LIMITED support

From: Dan Williams <redacted>

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.