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Thu, 9 Jul 2026 17:46:40 -0400 (EDT) Date: Thu, 09 Jul 2026 14:46:39 -0700 From: "Dan Williams (nvidia)" To: Gregory Price , linux-mm@kvack.org Cc: nvdimm@lists.linux.dev, linux-kernel@vger.kernel.org, linux-cxl@vger.kernel.org, driver-core@lists.linux.dev, linux-kselftest@vger.kernel.org, kernel-team@meta.com, david@kernel.org, osalvador@suse.de, gregkh@linuxfoundation.org, rafael@kernel.org, dakr@kernel.org, djbw@kernel.org, vishal.l.verma@intel.com, dave.jiang@intel.com, alison.schofield@intel.com, akpm@linux-foundation.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, shuah@kernel.org, gourry@gourry.net, iweiny@kernel.org, Smita.KoralahalliChannabasappa@amd.com, apopple@nvidia.com Message-ID: <6a5016bf71df4_3b7ee5100b3@djbw-dev.notmuch> In-Reply-To: <20260630211842.2252800-8-gourry@gourry.net> References: <20260630211842.2252800-1-gourry@gourry.net> <20260630211842.2252800-8-gourry@gourry.net> Subject: Re: [PATCH v6 07/10] dax: plumb hotplug online_type through dax Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 04CF6140006 X-Rspam-User: X-Stat-Signature: 8hpjc4domxx9sofr5scb5k8arofigo56 X-Rspamd-Server: rspam03 X-HE-Tag: 1783633603-971170 X-HE-Meta: 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 QJcRh5rm XB+MoSr6zfFbWYCZS91Cmp3BdGgWzTouspEy4lK3bxWbb9IZUJaBCE7A6xjWa4umbGRi29aaZy1PDS/himRzSNBL70ZhD8O6I2q5vUV17HMfStY1ihaS/H/Rdd9OYfBFwKiEEmKYNlQH/URjlT3hSIxd00ifNNT97xPluPWBR6Z+8sG8I59SQHgu+UMUfqjjIO88qYh1iijoaz7BVHiHCo1md601I5y3DdErETTbA3KrEDeDNjsuyfmsFUWkU3A1b771U04rseZLyfYaLe4w2cvePOXEolU7sGIrLLfukHIieIodK8bRGhbB00cxbu2St62KSFrPFafs/ZPjx/gtigrGwcByIMyvdSJHW6SHPqTYyfbCqrzN1+0gmDxrI2C27ftw90L0u/JuofYSzau76yj2z3OpC7XcA+xjP Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Gregory Price wrote: > There is no way for drivers leveraging dax_kmem to plumb through a > preferred auto-online policy - the system default policy is forced. > > Add 'enum mmop' field to DAX device creation path to allow drivers > to specify an auto-online policy when using the kmem driver. > > Capturing the system default would otherwise break the ABI, because > the system default can change - but we would be statically assigning > the value at device creation time. > > To resolve this we add DAX_ONLINE_DEFAULT, which defaults devices to > the current behavior, while providing a clean way to override it. > > No behavioural change for existing callers (still the system default). So I know you have some future usage for this ability, but it is not present in this set. The only piece that *is* used is that the online-type from the new sysfs interface gets plumbed through to __add_memory_driver_managed(). Are these touches: > drivers/dax/cxl.c | 1 + > drivers/dax/hmem/hmem.c | 1 + > drivers/dax/pmem.c | 1 + ...premature until the first user arrives that with the background story about how it knows to set the policy? If DAX_ONLINE_DEFAULT is a sentinel for "default" should DAX_KMEM_UNPLUGGED be a different sentinel than (-1)? Feel free to add: Reviewed-by: Dan Williams ...to this and the previous patches when that is fixed up.