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[99.254.144.39]) by smtp.gmail.com with ESMTPSA id cr14-20020ad456ee000000b0065aff6b49afsm3058368qvb.110.2023.10.23.11.37.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 Oct 2023 11:37:25 -0700 (PDT) Date: Mon, 23 Oct 2023 14:37:23 -0400 From: Peter Xu To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, viro@zeniv.linux.org.uk, brauner@kernel.org, shuah@kernel.org, aarcange@redhat.com, lokeshgidra@google.com, david@redhat.com, hughd@google.com, mhocko@suse.com, axelrasmussen@google.com, rppt@kernel.org, willy@infradead.org, Liam.Howlett@oracle.com, jannh@google.com, zhangpeng362@huawei.com, bgeffon@google.com, kaleshsingh@google.com, ngeoffray@google.com, jdduke@google.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v3 2/3] userfaultfd: UFFDIO_MOVE uABI Message-ID: References: <20231009064230.2952396-1-surenb@google.com> <20231009064230.2952396-3-surenb@google.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 7B4C8140017 X-Stat-Signature: bdd4cgjsika6u5jkwhn43c6d4fmca9bs X-HE-Tag: 1698086260-849254 X-HE-Meta: U2FsdGVkX1/tROVpYBJbzDXpf0H0n7yHBTpEAeG4NVrRMRgY/4raQo4lrMrvs15I6KL7QkYz9VLzPmIRe0J56UnIAAW5+6clE+RKbc72UqetnN+IL8P3JNs3f1nIwEI/qaSX1i3YlnnIG9CK2NRNTX1CgIHRLwM9RN1wCRxDlUiDouC7YLFPm+Wxv6Ap3SMznZLcA9Q8O+28ng/UTsLAbNrLayCvq0wPkaYspHj3HtR3lttq3XC6BS98zcwwptStv1aIJlHJEvkxbxHkhUB9vZv1V8U/cT6iMVEZVM+vilS0TA2DlAgmzSS+2ehuzyXl8Pa2NPFZZIlocqDLp5xrhzqyT7ixJ/izTcR8L6bGg2coSYsnrgvVRorgPoyyNQVPFWBdIE5TF5XSv9gSWUpFPFCYiLn9U/ao447NuoXIgO8jK2Kn6QfhaL0E/IR3Jbe3z7Arkihd75aNQA4/faYRmgpmFUedXM2FuaSse75zcI/o5zx1GQEzP+9fndc1w7ni7ufGLJBUWJzH4jZxDdmesoSw6MkwikqpMBtI1Rtkb81oG6CxFDj6vWi2zyJdwakRXUGuZAd87hdsElma8RoKNQBcdimu4SKpd9MZQC03/nXlDjIJb3O6DbpV8ob5Z/qpt/x3AkdHrWcSBhhR1bJks6uoO3d129Lv7441mHBgHPzG58RkRDnOnoHfdFdKo/u0Uh4dDUzRXvQSI0cKQa6AS5tRiSVRz9gg/hoxN2/VT+1+BLjHcRf7K0Tb4ElK1I8CNii/Puzc5OhE4Q8bVuKGNMaATLLEzU3wFT4ephBtU1OnI+ENsBd3gOKmoqxE7jva6RNy2G9aBG7F9xubTisl5Rdz4tKU98H2MiJTBwwyg46TCHnV6WLXSR87pLmL7y6FYEziOwtjgGgcme7Z1QdIai5PA7YxeQSTqjcmr0YYLnh1Om0QlHFaxaP4x/zfMtlHC1idMF5NyQPzINCY9Zx 7algEJGY 8YAC2dOmEN1+upT5RwbirL4lvVtIIKR7KzAY9oQXaRb2qqrbWaydbi86JPpQxdWJT41zW043TJSMmixKHpUorQrZtDCw0HVkIixBP/gCwD7JNP0jOPA2MUuv6Bk6A1yHwfKplXODNkf5C1/uzWKiXsB5+pbPsFS/AYtomTVA/iu7k8HvkQ46edVzSYoeHoLc54egUIHEpoIqz2zSIBZchTRcTPrVAO2qcNr8IUyYr90NTxKkRI0Ge8uWsP55zxA3hfH7lugFOyRv8rhGR3SlGgnvytr/PxDrmZos8LVyt7iQPWOf6MztLNP3bour8J5kj/wVZ3PtTPt/oMHruHYF0IqnAiqfXYkRkS7Kx1FkluAtm66MMVcISNKCNPXlj6nvg7/IMYJFi7oaSgL0g0qNelU/y8x+RL/P5AnEAhhk8QpGt3HmLzVVi9e1xYg== 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 Mon, Oct 23, 2023 at 10:43:49AM -0700, Suren Baghdasaryan wrote: > > Maybe we should follow what it does with mremap()? Then your current code > > is fine. Maybe that's the better start. > > I think that was the original intention, basically treating remapping > as a write operation. Maybe I should add a comment here to make it > more clear? Please avoid mention "emulate as a write" - this is not a write, e.g., we move a swap entry over without faulting in the page. We also keep the page states, e.g. on hotness. A write will change all of that. Now rethinking with the recently merged WP_ASYNC: we ignore uffd-wp, which means dirty from uffd-wp async tracking POV, that matches with soft-dirty always set. Looks all good. Perhaps something like "Follow mremap() behavior; ignore uffd-wp for now" should work? -- Peter Xu