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Tue, 1 Oct 2024 10:29:27 +0000 (GMT) Date: Tue, 1 Oct 2024 12:29:25 +0200 From: Gerald Schaefer To: Dan Williams Cc: hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, Christian Borntraeger , Sven Schnelle , Jan Kara , Matthew Wilcox , Christoph Hellwig , Alistair Popple , linux-s390@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] dcssblk: Mark DAX broken Message-ID: <20241001122925.52558c08@thinkpad-T15> In-Reply-To: <172721874675.497781.3277495908107141898.stgit@dwillia2-xfh.jf.intel.com> References: <172721874675.497781.3277495908107141898.stgit@dwillia2-xfh.jf.intel.com> X-Mailer: Claws Mail 4.3.0 (GTK 3.24.43; x86_64-redhat-linux-gnu) Content-Type: text/plain; charset=US-ASCII X-TM-AS-GCONF: 00 X-Proofpoint-GUID: ruMcx1VKO3ZyLX4ztnq2rFmxFuw6PeE0 X-Proofpoint-ORIG-GUID: ruMcx1VKO3ZyLX4ztnq2rFmxFuw6PeE0 Content-Transfer-Encoding: 7bit X-Proofpoint-UnRewURL: 0 URL was un-rewritten Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1051,Hydra:6.0.680,FMLib:17.12.62.30 definitions=2024-10-01_07,2024-09-30_01,2024-09-30_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxscore=0 priorityscore=1501 clxscore=1011 lowpriorityscore=0 suspectscore=0 mlxlogscore=999 bulkscore=0 phishscore=0 spamscore=0 adultscore=0 impostorscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2408220000 definitions=main-2410010066 On Tue, 24 Sep 2024 15:59:08 -0700 Dan Williams wrote: > 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. Thanks, that's great news! Without requiring the extra PTE bit, it should now finally be possible to add struct pages and ZONE_DEVICE support for dcssblk. In the meantime, it is OK to pause the DAX support for dcssblk as you suggested, and finally remove that ugly CONFIG_FS_DAX_LIMITED. Thanks for bearing with us for so long! > > For now, place the support behind CONFIG_BROKEN, and remove PFN_SPECIAL > (dcssblk was the only user). Ok, I guess that PFN_SPECIAL was there because we had no struct pages for the DCSS memory. When we come back, with proper ZONE_DEVICE and struct pages, it should not be needed any more. And yes, the chance to completely remove pfn_t, after Alistair's series, is quite impressive and even more motivation than CONFIG_FS_DAX_LIMITED. > > Link: http://lore.kernel.org/cover.9f0e45d52f5cff58807831b6b867084d0b14b61c.1725941415.git-series.apopple@nvidia.com [1] > Link: http://lore.kernel.org/20210820210318.187742e8@thinkpad/ [2] > Link: http://lore.kernel.org/4511465a4f8429f45e2ac70d2e65dc5e1df1eb47.1725941415.git-series.apopple@nvidia.com [3] > Cc: Gerald Schaefer > Cc: Heiko Carstens > Cc: Vasily Gorbik > Cc: Alexander Gordeev > Cc: Christian Borntraeger > Cc: Sven Schnelle > Cc: Jan Kara > Cc: Matthew Wilcox > Cc: Christoph Hellwig > Cc: Alistair Popple > Signed-off-by: Dan Williams > --- > drivers/s390/block/Kconfig | 12 ++++++++++-- > drivers/s390/block/dcssblk.c | 26 +++++++++++++++++--------- > fs/Kconfig | 9 +-------- > fs/dax.c | 12 ------------ > include/linux/pfn_t.h | 15 --------------- > mm/memory.c | 2 -- > mm/memremap.c | 4 ---- > 7 files changed, 28 insertions(+), 52 deletions(-) When you also remove the now unused dax_dev definition at the top of dcssblk_add_store(), as noticed by kernel test robot: Reviewed-by: Gerald Schaefer