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b=JV+htoEFB0wO2aziMKYdhq0dvY+C5OmmZw5YpFsknRRVCpqmW6JvCjDnS0gz6zY6P 5jDdjxYGB8V53GIu/3zWtFjDab+zbJlKJqlz5i/SvnKwVlkf8JgSx3In4EhCND6ZAT c4fwD8NFjUU9GSl8yL+3w4mCYGD3ACM0+L2CP2Yp1VU1eXg/w74xV6tEn6mRJK5EB1 0dZvMnKaKQxwYrMzV4yt7tVJ8TYXOk94DCBbHmF6KJalI2T7VYiL2OQzF/3RLMnayW 5k8sy46SJ2opItsi+qX9h+imOmMqpPVf3plrJBwb/Mx/OHG0gk/xJd0C5epIwvl5Wl rDC/A/c+btr1w== Message-ID: <4520e7b0-8218-404d-8ede-e62d95c50825@kernel.org> Date: Thu, 22 Jan 2026 23:41:24 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/8] mm/memory_hotplug: add APIs for explicit online type control To: Gregory Price Cc: linux-mm@kvack.org, linux-cxl@vger.kernel.org, nvdimm@lists.linux.dev, linux-kernel@vger.kernel.org, virtualization@lists.linux.dev, kernel-team@meta.com, dan.j.williams@intel.com, vishal.l.verma@intel.com, dave.jiang@intel.com, mst@redhat.com, jasowang@redhat.com, xuanzhuo@linux.alibaba.com, eperezma@redhat.com, osalvador@suse.de, akpm@linux-foundation.org References: <20260114085201.3222597-1-gourry@gourry.net> <20260114085201.3222597-4-gourry@gourry.net> From: "David Hildenbrand (Red Hat)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: E4C758000B X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: dmgku4gdd9p94mwd5bz4xrxostebsk5r X-HE-Tag: 1769121692-308753 X-HE-Meta: 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 IZHGHmwE faSvJd2ZTj9PKSigTPVw9k4nUiiK2iYpSmXHPFATrDPUwSE2shU8xzVssjAyKLT4vzI2JxLNq5fLIq7FHixSYWjvgUW8yYxKW4AG8UjxO4QI/gQkr5VpRz23SkDD+sCqoLGvmF3jzduaA/bGu9rxo8xMcul1qVLQUg5Qfba3zobuzcM/VFcmIk67rgqpHZBzg20+K3FQ3Sp/V5JP1Q6aG5Dok2C8NLbNuRWwDKNJ/WmQYHHCKBX3pe73coZA8/CRZ+nMl1FZjPQE+gLcU5vTtE48nrsIfxdhGBvFPTnKF6b3G2qrPRF7yC+KTjQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: >> For dax we know that user space will define the policy. >> > > Actually this may not always be true. A driver spawning a dax on probe > might also end up selecting the policy... eventually... maybe... I might > be planning to add that glue between CXL and DAX so I can add some > config similar to the system-default policy to avoid systems with > multiple memory-devices being forced into the same policy > > (e.g. CXL memory device can online auto in ZONE_MOVABLE, but the other > device can have its own policy). > > There's a weird corner case for CXL auto-regions (BIOS configured > everything but left the memory EFI_MEMORY_SP - so comes up as DAX). > I'm trying to keep those systems working the same as they have been > while the userland policy stuff catches up. Early CXL patterns are :[ Right, but I don't want any other OOT kernel module to be able to make use of add_memory_driver_managed() to do arbitrary things, because we don't know if it's really user space setting the policy for that memory then. So either restrict add_memory_driver_managed() to kmem+virtio_mem completely, or add another variant that will be kmem-only (or however that dax/cxl module is called). -- Cheers David