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Tue, 8 Jul 2025 09:21:58 +0800 Message-ID: <94a3d35d-0872-5696-0333-7273f4a69979@huawei.com> Date: Tue, 8 Jul 2025 09:21:57 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.15.1 To: Andrew Morton , David Hildenbrand , , , Peter Xu , Zi Yan , , , , , , , CC: , Kefeng Wang , From: Jinjiang Tu Subject: [Question] get_vma_policy() isn't compatible with {pin, get}_user_pages_remote Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.179.13] X-ClientProxiedBy: kwepems500002.china.huawei.com (7.221.188.17) To kwepemo200002.china.huawei.com (7.202.195.209) X-Rspam-User: X-Rspamd-Queue-Id: B2F4DC0006 X-Rspamd-Server: rspam09 X-Stat-Signature: 3nrdoxyg9b76p55g7c4zfm9ufya3j49x X-HE-Tag: 1751937722-766784 X-HE-Meta: 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 T7Wym8pT fS/Zz 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: get_vma_policy() returns the mempolicy for the vma. If the vma has set mempolicy, the policy is returned. Otherwise, call get_task_policy(current) to get the mempolicy of current task. However, it isn't reasonable for pin_user_pages_remote() and get_user_pages_remote() cases. Assume task A calls pin_user_pages_remote() to pin user pages from task B. If the [start, start + nr_pages) isn't populated with pages, handle_mm_fault() will be called by task A. However, if the vma doesn't set memory policy, the mempolicy of task A instead of task B is used to allocate. It seems to be unreasonable. See dequeue_hugetlb_folio_vma()->huge_node(). We can only obtain mm in get_vma_policy(), but we couldn't get the task, since a mm can be associated with multiple tasks(threads) and the task mempolicy is at thread granularity. Is this situation reasonable? And if not, how could we fix it? Thanks.