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[174.89.135.121]) by smtp.gmail.com with ESMTPSA id af79cd13be357-83631a7fc2fsm195959385a.54.2025.09.18.11.20.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 18 Sep 2025 11:20:53 -0700 (PDT) Date: Thu, 18 Sep 2025 14:20:51 -0400 From: Peter Xu To: David Hildenbrand Cc: Lorenzo Stoakes , Nikita Kalyazin , "Liam R. Howlett" , Mike Rapoport , Suren Baghdasaryan , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vlastimil Babka , Muchun Song , Hugh Dickins , Andrew Morton , James Houghton , Michal Hocko , Andrea Arcangeli , Oscar Salvador , Axel Rasmussen , Ujwal Kundur Subject: Re: [PATCH v2 1/4] mm: Introduce vm_uffd_ops API Message-ID: References: <930d8830-3d5d-496d-80d8-b716ea6446bb@amazon.com> <4czztpp7emy7gnigoa7aap2expmlnrpvhugko7q4ycfj2ikuck@v6aq7tzr6yeq> <7cccbceb-b833-4a21-bdc4-1ff9d1d6c14f@lucifer.local> <74b92ce3-9e0e-4361-8117-7abda27f2dd4@redhat.com> MIME-Version: 1.0 In-Reply-To: <74b92ce3-9e0e-4361-8117-7abda27f2dd4@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: IUQghZLpS6BCtdZz59UA2WlogXTYP08wUa5mo0-5gWw_1758219654 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Queue-Id: 0D3478000F X-Stat-Signature: qoxz3n77i161b87m8e7t7qidrex3qnye X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1758219656-528915 X-HE-Meta: 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 9+6T34bC fJjlMjmtd7LkHYcpB9/xweTbmn4ktR4CwLvsDpC8bOas1nHBJFwewmhb/hcFPE4NlA+jzYnOcGsocCrYClX2t3vYRqbjmiIzY3fiUmDlb7N8Z1dwAytGQX1dIJIa9I8KpePoVTiu3SD6+zob1p3blR7kzeybthgVcfwfoSuLr2HCAJ20lofb1OuxBp/nNpnHc9LaoK6Rfu2aofNMv85LIkKneAm+fyGva3WbcH+hY1xMlT5MzYfBJT8E0WMRdYMIL5H0f9suw8w+3FDPjGKctUt4jvcrqceFoGIZ4hehzsenncn2VHaeZ1WCMXZ0g2zYiULE7mNlJQdoCtXDpZwy3ZBib3Ule+FHANtB7dmPyFOZc4u1y7fWVSGeE4G7XfcbesXue9E0xdtdLJ85CC9fD6lTy868kxdqLW0Ki0b+CPpc1lveG1QU3ufC3hr9TPmN7uOakraByW5Q7+PA9uZRdJyzXNf2Ei271X/PfdUuXQOSJQFU= 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: On Thu, Sep 18, 2025 at 07:53:46PM +0200, David Hildenbrand wrote: > Re Nikita: If we could just reuse fault() for userfaultfd purposes, that > might actually be pretty nice. I commented on that. https://lore.kernel.org/all/aEiwHjl4tsUt98sh@x1.local/ That'll need to leak FAULT_FLAG_USERFAULT_CONTINUE which isn't necessary, make it extremely hard to know when to set the flag, and comlicates the fault path which isn't necessary. I think Mike's comment was spot on, that the new API is literally do_fault() for shmem, but only used in userfaultfd context so it's even an oneliner. I do not maintain mm, so above is only my two cents, so I don't make decisions. Personally I still prefer the current approach of keep the mm main fault path clean. Besides, this series also cleans up other places all over the places, the vm_uffd_ops is a most simplified version of description for a memory type. So IMHO it's beneficial in other aspects as well. If uffd_copy() is a concern, fine, we drop it. We don't plan to have more use of UFFDIO_COPY outside of the known three memory types after all. Thanks, -- Peter Xu