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[2003:cb:c70f:6900:6c56:80f8:c14:6d2a]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a073e5d479sm2116638f8f.92.2025.04.25.04.23.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 25 Apr 2025 04:23:27 -0700 (PDT) Message-ID: <96738f27-25bc-4d9e-9c4e-709e840563eb@redhat.com> Date: Fri, 25 Apr 2025 13:23:26 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/2] mm/huge_memory: Adjust try_to_migrate_one() and split_huge_pmd_locked() To: Zi Yan , Gavin Guo Cc: linux-mm@kvack.org, akpm@linux-foundation.org, gshan@redhat.com, willy@infradead.org, linmiaohe@huawei.com, hughd@google.com, revest@google.com, kernel-dev@igalia.com, linux-kernel@vger.kernel.org References: <20250425103859.825879-1-gavinguo@igalia.com> <20250425103859.825879-2-gavinguo@igalia.com> <40B90370-92E1-4E12-979D-7220887CB780@nvidia.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <40B90370-92E1-4E12-979D-7220887CB780@nvidia.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: EwRAKNbiCSWqAzBUbQsAckilhLrGAv30l_mEPFFs0G0_1745580208 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 4AC2B4000E X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: 3bfjppotuaxfmo6gbn4agduif7cx4gxj X-HE-Tag: 1745580211-860920 X-HE-Meta: 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 rF2MhvbF RGogi91NUl2yL3mZV9ijbBjp7lV4cwR4QMDVjmxGMQcoZUZx8jiffDUS9WP8shLNEBAcbTCRhyErQ0sB+KroUbVIvNH5R/1lddnvwnf/sRhP4G24kcrO4ocmNwa1rSMmCWqSh 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 25.04.25 13:10, Zi Yan wrote: > On 25 Apr 2025, at 6:38, Gavin Guo wrote: > >> The split_huge_pmd_locked function currently performs redundant checks >> for migration entries and folio validation that are already handled by >> the page_vma_mapped_walk mechanism in try_to_migrate_one. >> >> Specifically, page_vma_mapped_walk already ensures that: >> - The folio is properly mapped in the given VMA area >> - pmd_trans_huge, pmd_devmap, and migration entry validation are >> performed >> >> To leverage page_vma_mapped_walk's work, moving TTU_SPLIT_HUGE_PMD >> handling to the while loop checking and removing these duplicate checks >> from split_huge_pmd_locked. >> >> Suggested-by: David Hildenbrand >> Link: https://lore.kernel.org/all/98d1d195-7821-4627-b518-83103ade56c0@redhat.com/ >> Link: https://lore.kernel.org/all/91599a3c-e69e-4d79-bac5-5013c96203d7@redhat.com/ >> Signed-off-by: Gavin Guo >> Acked-by: David Hildenbrand >> --- > > I wonder if we need a WARN here to make sure when THP migration support is not > present all PMDs are split in try_to_migrate_one(). Can you elaborate on the condition you have in mind? If we have TTU_SPLIT_HUGE_PMD set, we'll never reach that point. Without CONFIG_ARCH_ENABLE_THP_MIGRATION, we should be running into the VM_BUG_ON_FOLIO(!pvmw.pte, folio); right? -- Cheers, David / dhildenb