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Tue, 3 Mar 2026 16:52:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772556736; bh=Qn6I79b9anQ0/JVDeoM+6n7E0s13tIg0fpBnemT2nlI=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=klr7DOX9CHzFzm6sWy1c0fxP6yxy6lrZYqHbKtF3f+fI+MGEtwe4cZKwqrR/95Ssl Aeua37APry0L/8w0eT88sD2fGPh/4VJH64DXNPH1NS855z51D11oYQRSugFIqIgO1d 4m7Neylvc6Tqbn2sY3axAaZTr+uJBW0Dj6jWGveoCzv4ZJu42evjOqA/KXV8C1FCm0 93GdR/i2wYBwLiZN6A43ZGrR9gTfLzcoTG6zxzxmN18c30/RGDtUCVBhV9u+s08KmI geGMBdGXOtGXllUkOqkQJ0zKjS7kPIMVmcnsUUQaVp5vA7+B4pX73hHI4vyWeKGOJO O1uScEXbqPl7A== Message-ID: Date: Tue, 3 Mar 2026 17:52:07 +0100 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 03/13] mm/migrate_device: Make migrate_device_{pfns,range}() take mpfns To: Jordan Niethe , linux-mm@kvack.org Cc: balbirs@nvidia.com, matthew.brost@intel.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, ziy@nvidia.com, apopple@nvidia.com, lorenzo.stoakes@oracle.com, lyude@redhat.com, dakr@kernel.org, airlied@gmail.com, simona@ffwll.ch, rcampbell@nvidia.com, mpenttil@redhat.com, jgg@nvidia.com, willy@infradead.org, linuxppc-dev@lists.ozlabs.org, intel-xe@lists.freedesktop.org, jgg@ziepe.ca, Felix.Kuehling@amd.com, jhubbard@nvidia.com, maddy@linux.ibm.com, mpe@ellerman.id.au, ying.huang@linux.alibaba.com References: <20260202113642.59295-1-jniethe@nvidia.com> <20260202113642.59295-4-jniethe@nvidia.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 2/2/26 12:36, Jordan Niethe wrote: > A future change will remove device private pages from the physical > address space. This will mean that device private pages no longer have a > pfn. > > This causes an issue for migrate_device_{pfns,range}() which take pfn > parameters. Depending on if the device is MEMORY_DEVICE_PRIVATE or > MEMORY_DEVICE_COHERENT will effect how that parameter should be > interpreted. > > A MIGRATE_PFN flag will be introduced that distinguishes between mpfns > that contain a pfn vs an offset into device private memory, we will take > advantage of that here. > > Update migrate_device_{pfns,range}() to take a mpfn instead of pfn. > > Update the users of migrate_device_{pfns,range}() to pass in an mpfn. > > To support this change, update > dpagemap_devmem_ops::populate_devmem_pfn() to instead return mpfns and > rename accordingly. > > Signed-off-by: Jordan Niethe > --- > v2: New to series > v3: No change > --- The fact that "migrate pfns" are just dressed as ordinary pfns is confusing and error prone, especially when we suddenly have to derive from the variable name whether something is a pfn or an mpfn ... Something to think about would be treating migrate pfns as opaque objects and move from misleading "unsigned long" to something like typedef struct migrate_pfn { unsigned long data; } migrate_pfn_t; And providing proper accessors. That would make it much clearer when passing these things around what they are ... and the compiler can easily catch bugs. -- Cheers, David